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Genç, Gençer, Semai Bek, Tayfun Kasikci, Umit Hidir Ulas, Seref Demirkaya, and Zeki Odabasi. "Strength-Duration Time Constant in Peripheral Nerve: No Abnormality in Multiple Sclerosis." Multiple Sclerosis International 2012 (2012): 1–6. http://dx.doi.org/10.1155/2012/390157.
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Fam, M. A., and M. B. Dusseault. "Effect of unloading duration on unconfined compressive strength." Canadian Geotechnical Journal 36, no. 1 (August 8, 1999): 166–72. http://dx.doi.org/10.1139/t98-074.
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This note examines the effect of unloading duration on unconfined compression test results. Artificial clayey specimens were prepared using the slurry consolidation technique. Extracted specimens were loaded vertically under K0 conditions, and the load was kept constant until the end of primary consolidation. Specimens were unloaded and unconfined compression tests were carried out at different times after unloading. It is observed that the longer the unloading duration, the lower the measured unconfined strength. This behavior is attributed to the presence of negative excess pore pressure that dissipates with time, reducing the strength. Using the measured coefficient of consolidation, the degree of excess pore pressure dissipation and therefore the average mean effective stress near the failure zone can be calculated at the time of failure. Mohr circles are drawn tangential to the total shear envelope, using the calculated mean effective stresses. Reasonable agreement between predicted and measured unconfined compressive strengths has been observed, suggesting that consolidation theory can be adopted to assess the effect of unloading duration on unconfined compressive strength. Finally, engineering applications using a similar concept are briefly discussed.Key words: clays, unloading, consolidation, unconfined compression tests, triaxial tests.
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Spencer, R. A., and Borg Madsen. "Duration of load tests for shear strength." Canadian Journal of Civil Engineering 13, no. 2 (April 1, 1986): 188–95. http://dx.doi.org/10.1139/l86-026.
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The strength of wood falls with time under load, and in current design codes the short-term strength of wood is reduced by about 40% to account for duration of load effects. This figure is based on tests made on small bending specimens. In this paper are described tests made on wooden torque tubes to investigate the effect of duration of load on shear strength. A control sample was tested to establish a curve for short-term strength, and four groups of 80 specimens each were then tested under various levels of constant long-term load. Stress ratio at failure was estimated by assuming that the short-term strength of each group could be represented by the control curve, and that under long-term loading specimens would fail in the order of their short-term strength. In each group the stress ratio at failure fell with time under load, and this reduction appears to be related to that predicted by a viscoelastic plastic model. It is concluded that the Madison curve presently used to predict duration of load effects may be conservative at normal levels of applied stress. Key words: wood, shear, long-term loading, duration of load.
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D’Ostilio, K., S. Goetz, M. Ciocca, R. Chieffo, J. C. A. Chen, A. V. Peterchev, and J. C. Rothwell. "P282: Effect of coil orientation on strength-duration time constant with controllable pulse parameter transcranial magnetic stimulation." Clinical Neurophysiology 125 (June 2014): S123. http://dx.doi.org/10.1016/s1388-2457(14)50400-2.
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Koyanagi, Jun, Hiroshi Hatta, Fumio Ogawa, and Hiroyuki Kawada. "Time-dependent Reduction of Tensile Strength Caused by Interfacial Degradation under Constant Strain Duration in UD-CFRP." Journal of Composite Materials 41, no. 25 (December 2007): 3007–26. http://dx.doi.org/10.1177/0021998307082175.
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François, R. J., and A. A. Van Haute. "The Role of Rapid Mixing Time on a Flocculation Process." Water Science and Technology 17, no. 6-7 (June 1, 1985): 1091–101. http://dx.doi.org/10.2166/wst.1985.0204.
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The influence of the duration of rapid mixing on a flocculation process is evaluated by investigating the characteristics of the hydroxide flocs formed under carefully controlled conditions. Two different methods are used for measuring floc dimensions and their distribution. From the experimental results other floc characteristics such as floc strength and size of the flocculi are deduced. Also the reaction constant, the destabilization factor and the growing constant of the coagulation and flocculation process are calculated. Using the influence of rapid mixing time on all floc characteristics and kinetic parameters minimum and maximum limits for the rapid mixing time are deduced.
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Zawadzki, Tadeusz. "Electrical properties of Lupinus angustifolius L. stem. III. RC model, time constant, latency and threshold charge." Acta Societatis Botanicorum Poloniae 48, no. 2 (2015): 305–15. http://dx.doi.org/10.5586/asbp.1979.025.
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The changes of potential in the stem of <i>Lupinus</i> were characterized on the basis of the strength-duration relation and of electrotonic potentials. It was found that the stimulated stem behaves like an electrical RC circuit. The time constants of electrotonic potential rise and decay were determined. A simple electrical model characterizing the passive electrical properties of the <i>Lupinus</i> stem is suggested. The values of resistance and capacitance of the <i>Lupinus</i> stem were determined on the basis of the RC circuit. The resistance-capacitance properties of the stem tissues serve as basis to gain a better knowledge of the parametres describing excitation, such as the strength-duration relation or latency. These properties in the stem of <i>Lupinus</i> are of the same nature as those in nerves or muscles. The values of the threshold charge of the order of 10-6 C were calculated. It is suggested that the regularities occurring here may be connected with accommodation and processes regulating the resting potential of cells.
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Catalin, B., A. M. Cobzaru, I. Codita, I. Popa, C. A. Panea, I. Mandruta, and M. Moldovan. "P777: Reduction in motor nerve strength-duration time constant during the anti-voltage-gated Na+ channel therapy in epilepsy." Clinical Neurophysiology 125 (June 2014): S250. http://dx.doi.org/10.1016/s1388-2457(14)50818-8.
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D’Ostilio, Kevin, Stefan M. Goetz, Ricci Hannah, Matteo Ciocca, Raffaella Chieffo, Jui-Cheng A. Chen, Angel V. Peterchev, and John C. Rothwell. "Effect of coil orientation on strength–duration time constant and I-wave activation with controllable pulse parameter transcranial magnetic stimulation." Clinical Neurophysiology 127, no. 1 (January 2016): 675–83. http://dx.doi.org/10.1016/j.clinph.2015.05.017.
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Tabary, Ariane, and Beate Rassler. "Increased breathing resistance compromises the time course of rhythmical forearm movements—a pilot study." Journal of Translational Internal Medicine 3, no. 4 (December 1, 2015): 161–66. http://dx.doi.org/10.1515/jtim-2015-0022.
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Abstract Background and Objectives: Skeletal muscle dysfunction is a major problem among the co-morbidities associated with chronic obstructive pulmonary disease (COPD). However, muscle weakness and increased fatigability are not the only limitations of skeletal muscle function. Motor–respiratory coordination (MRC) may occur even during movements at lowest workloads. MRC modifies the temporal pattern of motor actions, thus probably impairing motor performance and movement precision. Little attention has been paid to the question of whether motor functions may be compromised in COPD patients independent of workload and required muscle strength and endurance. The present pilot study was designed to investigate the effects of a simulated obstruction (SO) in healthy subjects on their breathing pattern and the timing of a rhythmical forearm movement. Methods: Twenty-one subjects performed flexion–extension movements with their right forearm at a self-chosen rate within a range between 0.2 and 0.4 Hz. After a control experiment with normal breathing, a plug with a narrow hole was inserted between face mask and pneumotachograph to simulate obstruction. Subjects were required to repeat the rhythmical forearm movement at the same rate as in the control experiment. Results: The condition of SO significantly prolonged breath duration but reduced tidal volume and ventilation. In addition, period duration of the forearm movement increased significantly under this condition while the movement-to-breathing frequency ratio remained almost constant. Increased breathing resistance was considered to cause prolonged breath duration accompanied by an increase in movement period duration. The constant near-integer ratio between movement and breathing rates indicates that the change in movement period duration resulted from MRC. Conclusions: The findings of this pilot study demonstrate that increased breathing resistance may compromise motor performance even at lower workloads. This means that in COPD patients, not only muscle strength and endurance are reduced but, moreover, fine motor skills may be impaired. This aspect has particular importance for many everyday activities as reduced fine motor performance substantially contributes to a progressive inability of the patients to manage their daily life.
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Boinagrov, David, Jim Loudin, and Daniel Palanker. "Strength–Duration Relationship for Extracellular Neural Stimulation: Numerical and Analytical Models." Journal of Neurophysiology 104, no. 4 (October 2010): 2236–48. http://dx.doi.org/10.1152/jn.00343.2010.
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The strength–duration relationship for extracellular stimulation is often assumed to be similar to the classical intracellular stimulation model, with a slope asymptotically approaching 1/τ at pulse durations shorter than chronaxy. We modeled extracellular neural stimulation numerically and analytically for several cell shapes and types of active membrane properties. The strength–duration relationship was found to differ significantly from classical intracellular models. At pulse durations between 4 μs and 5 ms stimulation is dominated by sodium channels, with a slope of −0.72 in log-log coordinates for the Hodgkin–Huxley ion channel model. At shorter durations potassium channels dominate and slope decreases to −0.13. Therefore the charge per phase is decreasing with decreasing stimulus duration. With pulses shorter than cell polarization time (∼0.1–1 μs), stimulation is dominated by polarization dynamics with a classical −1 slope and the charge per phase becomes constant. It is demonstrated that extracellular stimulation can have not only lower but also upper thresholds and may be impossible below certain pulse durations. In some regimes the extracellular current can hyperpolarize cells, suppressing rather than stimulating spiking behavior. Thresholds for burst stimuli can be either higher or lower than that of a single pulse, depending on pulse duration. The modeled thresholds were found to be comparable to published experimental data. Electroporation thresholds, which limit the range of safe stimulation, were found to exceed stimulation thresholds by about two orders of magnitude. These results provide a biophysical basis for understanding stimulation dynamics and guidance for optimizing the neural stimulation efficacy and safety.
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Ciocanel, Constantin, Kevin Molyet, Hideki Yamamoto, Sheila L. Vieira, and Nagi G. Naganathan. "Magnetorheological Fluid Behavior Under Constant Shear Rates and High Magnetic Fields Over Long Time Periods." Journal of Engineering Materials and Technology 128, no. 2 (August 29, 2005): 163–68. http://dx.doi.org/10.1115/1.2172276.
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This paper presents a new magnetorheological (MR) cell design along with a study of the magnetic field, shear rate, and time/shear strain influences on the properties and behavior of a MR fluid tested for long periods of time. The MR cell was designed to adapt a commercially available rheometer to measure the rheological properties of the fluid. Overall characteristics of the designed MR cell output capability are provided. Constant shear rate tests, two hours in duration, have been performed at shear rates between 0.1l∕s and 200l∕s under magnetic field intensities up to 0.4T. The rheological measurements indicated that over time the fluid’s shear stress magnitude decreases until it reaches a steady state. The time required to reach the steady state depends on both the magnetic field strength and the shear rate. The higher the field and the smaller the shear rate the shorter the time for the steady state to be reached.
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Bekar, I., M. S. H. Fatt, and J. Padovan. "Deformation and Fracture of Rubber under Tensile Impact Loading." Tire Science and Technology 30, no. 1 (January 1, 2002): 45–58. http://dx.doi.org/10.2346/1.2135247.
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Abstract An impact experiment is designed to obtain the deformation and fracture characteristics of SBR specimens under tensile impact loading. The experimental apparatus is capable of achieving very large strains (about 300%) and high strain rates (between 10 and 1000 s−1) in the specimen. Dynamic stress-strain curves reveal that SBR goes through several phases of deformation and fracture as the strain rate increases in the specimen. In the first phase, the initial modulus, yield stress, tensile strength, and fracture strain increase, while the final modulus remains fairly constant with increasing strain rate. Increases in the initial modulus, tensile strength, and strain at fracture with increasing strain rate are due to a lack of stress relaxation in constituents that have longer relaxation times than the load duration. Local scale relaxation times are shorter than the load duration in this phase so that the final modulus is almost insensitive to strain rate. In the second phase, the initial modulus and the yield stress remain roughly constant while the final modulus increases with increasing strain rate. The tensile strength also increases, but the fracture strain decreases as the strain rate increases. Increases in the final modulus and tensile strength are due to a lack of relaxation on a local scale. The tensile fracture strain decreases because convolutions do not have sufficient time to slip completely. In the third phase, all stress-strain curves follow a master curve, but both the tensile strength and fracture strain decrease with increasing strain rate. The decrease in tensile strength as the strain rate increases could be due to stress concentration at the tip of microcracks within the SBR.
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Nieminen, Jaakko O., Jens Voigt, Stefan Hartwig, Hans Jürgen Scheer, Martin Burghoff, Lutz Trahms, and Risto J. Ilmoniemi. "Improved Contrast in Ultra-Low-Field MRI with Time-Dependent Bipolar Prepolarizing Fields: Theory and NMR Demonstrations." Metrology and Measurement Systems 20, no. 3 (September 1, 2013): 327–36. http://dx.doi.org/10.2478/mms-2013-0028.
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Abstract The spin-lattice (T1) relaxation rates of materials depend on the strength of the external magnetic field in which the relaxation occurs. This T1 dispersion has been suggested to offer a means to discriminate between healthy and cancerous tissue by performing magnetic resonance imaging (MRI) at low magnetic fields. In prepolarized ultra-low-field (ULF) MRI, spin precession is detected in fields of the order of 10-100 μT. To increase the signal strength, the sample is first magnetized with a relatively strong polarizing field. Typically, the polarizing field is kept constant during the polarization period. However, in ULF MRI, the polarizing-field strength can be easily varied to produce a desired time course. This paper describes how a novel variation of the polarizing-field strength and duration can optimize the contrast between two types of tissue having different T1 relaxation dispersions. In addition, NMR experiments showing that the principle works in practice are presented. The described procedure may become a key component for a promising new approach of MRI at ultra-low fields
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VASEGHI, B., G. REZAEI, and S. KHORSHIDIAN. "NONLINEAR EFFECTS ON THE ENTANGLEMENT BETWEEN QUANTIZED ELECTROMAGNETIC FIELDS AND 3-LEVEL ATOMS." International Journal of Quantum Information 09, no. 07n08 (October 2011): 1653–63. http://dx.doi.org/10.1142/s0219749911008295.
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In this paper, we study the entanglement dynamics, its measure, and mean photon number of the field in the interaction between a quantized electromagnetic field and a 3-level atom surrounded by a nonlinear Kerr-like medium. Using the density matrix approach, we have calculated the time evolution of the entanglement and its magnitude at an arbitrary time, for different nonlinear coupling constant. Moreover, to show the effects of nonlinearity on the atom–field interaction and its relation with the entanglement the mean photon number of the field is also presented as a function of nonlinear coupling strength, χ. The results show that, envelope of entanglement fluctuation, their duration and amplitude strongly depend on the nonlinear coupling strength. Since the entanglement decreases with increasing nonlinearity, the mean number of photons reaches a constant value as a result of absorption increment by the surrounding medium.
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Ferreira, Fernanda Bessa, Paulo M. Pereira, Castorina Silva Vieira, and Maria de Lurdes Lopes. "Time-Dependent Response of a Recycled C&D Material-Geotextile Interface under Direct Shear Mode." Materials 14, no. 11 (June 4, 2021): 3070. http://dx.doi.org/10.3390/ma14113070.
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Geosynthetic-reinforced soil structures have been used extensively in recent decades due to their significant advantages over more conventional earth retaining structures, including the cost-effectiveness, reduced construction time, and possibility of using locally-available lower quality soils and/or waste materials, such as recycled construction and demolition (C&D) wastes. The time-dependent shear behaviour at the interfaces between the geosynthetic and the backfill is an important factor affecting the overall long-term performance of such structures, and thereby should be properly understood. In this study, an innovative multistage direct shear test procedure is introduced to characterise the time-dependent response of the interface between a high-strength geotextile and a recycled C&D material. After a prescribed shear displacement is reached, the shear box is kept stationary for a specific period of time, after which the test proceeds again, at a constant displacement rate, until the peak and large-displacement shear strengths are mobilised. The shear stress-shear displacement curves from the proposed multistage tests exhibited a progressive decrease in shear stress with time (stress relaxation) during the period in which the shear box was restrained from any movement, which was more pronounced under lower normal stress values. Regardless of the prior interface shear displacement and duration of the stress relaxation stage, the peak and residual shear strength parameters of the C&D material-geotextile interface remained similar to those obtained from the conventional (benchmark) tests carried out under constant displacement rate.
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Asrofi, Mochamad, Hairul Abral, Anwar Kasim, Adjar Pratoto, Herwin Gevin, and Melbi Mahardika. "PENGARUH LAMA WAKTU PENGGETARAN ULTRASONIC BATH TERHADAP SIFAT MEKANIK DAN MORFOLOGI PATAHAN BIOKOMPOSIT PATI TAPIOKA/SERAT RAMI (BOEHMERIA NIVEA)." ROTOR 10, no. 2 (November 1, 2017): 23. http://dx.doi.org/10.19184/rotor.v10i2.5574.
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This study reported about mechanical properties and fracture surface of ramie fiber reinforced tapioca starch based biocomposites. The amount of fibers in matrix was kept constant at 10% from dry weight starch basis. Fabrication of biocomposites was solution casting. The effect of vibration duration from ultrasonic bath was 0, 15, 30, and 45 min. This treatment was applied to biocomposites while gelatinized. Tensile test was carried out to determine the mechanical properties of biocomposites. Fracture surface of biocomposites after tensile test was observed by using scanning electron microscopy (SEM). The result shows that, tensile strength increased when vibration time was added. The maximum tensile strength was obtained at 45 min vibration time with 2,84 MPa. This phenomenon was supported by SEM observation which indicate compact structure.
Keywords: Tapioca starch, ramie fiber, biocomposites, mechanical properties, SEM
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SHARIFI, HOSSEIN, MAHMOOD ALIOFKHAZRAEI, GHASEM BRATAI DARBAND, and SUMAN SHRESTHA. "A REVIEW ON ADHESION STRENGTH OF PEO COATINGS BY SCRATCH TEST METHOD." Surface Review and Letters 25, no. 03 (March 8, 2018): 1830004. http://dx.doi.org/10.1142/s0218625x18300046.
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Adhesion strength is one of the important properties that reflects the quality of a plasma electrolytic oxidation (PEO) coating. Scratch testing can be considered as an appropriate technique to evaluate the adhesion strength of PEO coatings on magnesium, titanium, and aluminum substrates. The scratch test is usually performed either under a constant or a progressively increasing normal load, where the critical load is used as a measure of adhesion strength of the coatings. In this review paper, the effect of different factors such as duration of coating processing, electrolyte composition, and processing current density, as well as different additives to the electrolyte bath, was studied on the adhesion strength of PEO coatings formed on magnesium, titanium, and aluminum substrates. It is understood that an optimum increase in process time and input energy leads to a corresponding increase in thickness of the PEO dense oxide layer and, consequently, an increase in critical load and adhesion strength. Moreover, the electrolyte composition and additives were found to affect the coating microstructure and composition and, subsequently, the coating adhesion strength.
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Sottek, Roland, and Thiago Lobato. "High-resolution spectral analysis (HSA) vs. discrete fourier transform (DFT)." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no. 4 (August 1, 2021): 2555–66. http://dx.doi.org/10.3397/in-2021-2172.
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The Discrete Fourier Transform (DFT) is the standard technique for performing spectral analysis. It is used in the form of the well-known fast implementation (FFT) in almost all areas that deal with signal processing. However, the DFT algorithm has some limitations in terms of its resolution in time and frequency: the higher the time resolution, the lower the frequency resolution, and vice versa. The product of time (analysis duration) and analysis bandwidth (frequency resolution) is a constant. DFT results depend on the analysis window used (type and duration), although the physical signal properties do not change. The High-Resolution Spectral Analysis (HSA) method, published at the ASST '90, considers the window influence through spectral deconvolution and thus leads to a much lower time-bandwidth product, correlating better with human perception. Recently, variants of the HSA have been used for a psychoacoustic standard (roughness). Additionally, HSA is planned for a new model of fluctuation strength. This paper describes the improvements made to the HSA algorithm as well as its robustness against noise, and compares application results for both methods: HSA and DFT.
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Kruger, Deon, Neil Herbst, and Jannes Bester. "The Effect of Polymer Emulsion Addition on the Setting Time, Crack Formation and Strength of Cementitious Patch Repair Mortars." Advanced Materials Research 1129 (November 2015): 86–93. http://dx.doi.org/10.4028/www.scientific.net/amr.1129.86.
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With millions of square meters of ageing exposed concrete surfaces throughout the world, concrete patch repair is becoming a major component of the civil construction industry. To ensure effective and efficient repairs and rehabilitation of deteriorating concrete surfaces, patch materials with excellent workability during the repair phase and durability during its design life cycle are required. The addition of polymer emulsions to cementitious repair mortars increase the setting time, crack resistance while negatively affects the strength properties of the mortar. Polymer emulsions include natural rubber, polyacrylonitrile and polivinylacetate, to name just a few [1]. This paper focus on the effect of adding different polymer emulsions at varying dosages to cementitious repair mortars to obtain a better understanding of the influences on setting times, crack formation properties and curing regime requirements for optimal strength development. Ambient temperature and relative humidity were kept constant during the testing cycles. The results obtained indicated that the introduction of a polymer emulsion tend to reduce both the initial and final setting times of the repair mortars but that is extends the duration between initial and final set when compared to unmodified repair mortars. Compressive strength reductions were observed when adding polymer emulsions to the repair mortar but it was clear that crack formation was eliminated with the addition of the emulsions
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Liu, Jin, and Dongmin Wang. "The Role of Phosphorus Slag in Steam-Cured Concrete." Advances in Materials Science and Engineering 2017 (2017): 1–14. http://dx.doi.org/10.1155/2017/8392435.
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Steam curing is an effective method to increase the hydration degree of binder containing phosphorus slag. The role of phosphorus slag in steam-cured concrete was investigated by determining the hydration heat, hydration products, nonevaporable water content, pore structure of paste, and the compressive strength and chloride ion permeability of concrete. The results show that elevated steam curing temperature does not lead to new crystalline hydration products of the composite binder containing phosphorus slag. Elevating steam curing temperature enhances the early hydration heat and nonevaporable water content of the binder containing phosphorus slag more significantly than increasing steam curing time, and it also results in higher late-age hydration degree and finer pore structure. For steam-cured concrete containing phosphorus slag, elevating curing temperature from 60°C to 80°C tends to decrease the late-age strength and increase the chloride permeability. However, at constant curing temperature of 60°C, the steam-cured concrete containing phosphorus slag can achieve satisfied demoulding strength and late-age strength and chloride permeability by extending the steam curing duration.
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Bitterman, N., and Y. Grossman. "Increased axonal excitability during exposure to hyperbaric oxygen." Canadian Journal of Physiology and Pharmacology 65, no. 10 (October 1, 1987): 2044–47. http://dx.doi.org/10.1139/y87-319.
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The effect of high oxygen pressure on neural function was studied in the isolated nervous system of the cockroach. Intracellular and extracellular action potentials were recorded from single giant axons during exposure to 7 ATA (atmosphere absolute) (1 ATA = 0.1 MPa) of oxygen. Axonal excitability was measured as changes in stimulus strength–duration relationship. Initially, a transient increase in the rheobase current was observed followed by a significant decline to 75% of air control values. This decrease was accompanied by a parallel increase in the membrane time constant. The results demonstrate that hyperbaric oxygen increases axonal excitability. Such changes are consistent with the epileptogenic properties of high oxygen pressure.
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Delgado-Lezama, Rodolfo, Justo Aguilar, and Rafael Cueva-Rolón. "Synaptic Strength Between Motoneurons and Terminals of the Dorsolateral Funiculus Is Regulated by GABA Receptors in the Turtle Spinal Cord." Journal of Neurophysiology 91, no. 1 (January 2004): 40–47. http://dx.doi.org/10.1152/jn.00569.2003.
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The role of GABAA and GABAB receptors in modulation of excitatory synaptic transmission between motoneurons and terminals from dorsolateral funiculus (DLF) was studied in in vitro spinal cord slices of adult turtles. Muscimol—a GABAA receptor agonist— depressed the monosynaptic excitatory postsynaptic potential (EPSP) induced by stimulation of the DLF and shortened its duration. The input resistance and the membrane time constant also were strongly reduced. The input membrane resistance, the amplitude, and the half-width of the EPSP were reduced at the same rate in the presence of muscimol. Bicuculline—a GABAA receptor antagonist—increased the EPSPs amplitude and the input membrane resistance. The EPSP amplitude ratio elicited by a paired-pulse protocol did not change significantly. Our results suggest that muscimol acts mainly by activation of postsynaptic GABAA receptors located on the motoneuron and the synaptic strength on motoneurons may be modulated by tonic activation of postsynaptic GABAA receptors. Baclofen—a GABAB receptor agonist—also depressed DLF-motoneuron synaptic transmission. However, it did not affect the falling phase of the EPSPs or the motoneuron membrane time constant but induced a small decrement in input resistance. In the presence of baclofen, the amplitude ratio produced by a paired-pulse protocol increased significantly. This suggests that baclofen decreased the synaptic strength by inhibition of neurotransmitter release from the DLF terminals via activation of presynaptic GABAB receptors.
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Tian, W. M., A. J. Silva, G. E. Veyera, and M. H. Sadd. "Drained creep of undisturbed cohesive marine sediments." Canadian Geotechnical Journal 31, no. 6 (December 1, 1994): 841–55. http://dx.doi.org/10.1139/t94-101.
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Long-term, drained triaxial creep and direct simple shear creep tests were conducted on undisturbed marine specimens from the Gulf of Mexico and the north-central Pacific. Results indicated that time-dependent deformations can be represented by a power law equation, and the creep strain rate can be represented by an equation similar to that suggested earlier by other researchers. However, it was found that the m parameter suggested by these scientists was not a constant but dependent on stress level and sediment plasticity. Ageing effects were evidenced in triaxial specimens by the increase of shear strength with both test duration and stress level. The results provided a guide for the development of mathematical stress–strain–time relationships that will be developed in a separate paper. Key words : drained triaxial creep, simple shear creep, stress–strain–time behavior.
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Koroleva, Tatiana A., Lyubov A. Milovidova, and Andrey A. Dryakhlitsyn. "Production of High-Yield Hardwood Pulp by Bisulfite Minimizing the Chlorine Content Cooking." Lesnoy Zhurnal (Forestry Journal), no. 3 (May 20, 2021): 161–69. http://dx.doi.org/10.37482/0536-1036-2021-3-161-169.
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The article presents the results of the development of a technological mode for obtaining bisulfite hardwood pulp of high yield on a magnesium base for the production of various types of containerboard. The reliable and effective chemical and heat recovery technology implemented in the bisulfite method allows to use it in independent sulfite process. The effect of the duration of stay at the final temperature on the pulp yield and kappa number was studied when developing the technological mode of cooking. It was found that the increase in the duration of stay at the final temperature of 160 °C more than 40 min leads to violations of the selectivity of the cooking process. Increasing the duration of stay at the final temperature up to 70 min is accompanied by a decrease in pulp yield by 6 % at a constant value of the kappa number of the semi-finished product. Technological cooking mode: hydromodule 5, SO2 consumption 15.0 %, cooking solution pH 4.3–4.5, impregnation time at 120 °C – 35 min, cooking duration at 160 °C – 40 min. The mode allows to get a semi-finished product with a high yield of 60–65 % with a kappa number of 58–60 units without a hot grinding stage. An assessment of the mechanical strength characteristics of the laboratory samples of bisulfite pulp was carried out in accordance with the standards of the Russian Federation. The obtained values of bursting strength, resistance to flat compression, breaking strength, and breaking stress were comparable with the values of the industrial sample of hardwood neutral sulfite semi-chemical pulp with a semi-finished product yield of 75–78 %. It is shown that the presence of bark in the technological chips in the amount of 7.5 % is accompanied by a decrease in the yield of bisulfite hardwood pulp by 4.5 % and mechanical strength by 7.8 %. For citation: Koroleva T.A., Milovidova L.A., Dryakhlitsyn A.A. Production of High-Yield Hardwood Pulp by Bisulfite Cooking. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 3, pp. 161–169. DOI: 10.37482/0536-1036-2021-3-161-169
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Litvinov, Rustem I., Henry Shuman, John Weisel, and Joel S. Bennett. "Measurement of the Lifetime of Bonds Between αIIbβ3 and Fibrinogen Using Constant Unbinding Forces Generated by Optical Tweezers." Blood 112, no. 11 (November 16, 2008): 254. http://dx.doi.org/10.1182/blood.v112.11.254.254.
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Abstract We have shown that the distribution of rupture forces between individual αIIbβ3 and fibrinogen molecules displays at least two components that differ in kinetics, loading rate dependence, and susceptibility to activation and inhibition of the integrin. This suggests that the binding and unbinding of αIIbβ3 and fibrinogen is a complex multistep process that depends on the conformational state of both αIIbβ3 and fibrinogen, the duration of their interaction, and environmental factors such as externally-applied shear force. To directly test these possibilities, we quantified the lifetime of bonds stabilizing individual αIIbβ3-fibrinogen complexes with a novel nanoscale laser tweezers-based system that uses an optical trap to apply a constant unbinding force to single-molecule protein-protein interactions. When a ligand-coated bead is brought into repeated contact with a receptor-coated silica pedestal using an optical trap, the signal parameters that are measured correspond to both compressive and rupture forces. To measure bond lifetimes, the amplitude of the generated tensile force signal must remain constant throughout the lifetime of the bond. This can be accomplished by incorporating an analog feedback circuit within the optical system. The system also enables us to control the time of contact between interacting surfaces, the magnitude of compressive force during contact, the magnitude of the tensile force, and the time of protein-protein separation when binding occurs. To quantify the forced unbinding of fibrinogen molecules covalently bound to latex beads and αIIbβ3 molecules covalently attached to silica microspheres, we measured the distribution of bond lifetimes obtained under constant tensile force, mimicking the effect of hydrodynamic blood flow on an adherent platelet. We found that the separation times of the αIIbβ3- and fibrinogen-coated surfaces varied, indicating that the interactions occurring at the interface had heterogeneous kinetic and thermodynamic properties. Discrimination of specific αIIbβ3-fibrinogen binding events versus non-specific interactions was based on comparison of bond lifetime distributions in the absence and presence of abciximab or eptifibatide, specific inhibitors of fibrinogen binding to activated αIIbβ3. We found that the separation times of the αIIbβ3- and fibrinogen-coated surfaces were bimodal, with specific integrin-fibrinogen interactions lasting more than 2s under a constant tensile force of 50 pN. Varying the time of contact between αIIbβ3 and fibrinogen from 0.1s to 2.0s at the same unbinding force revealed that the bond lifetimes increased as the duration of contact between that interacting surfaces increased, suggesting that stability of αIIbβ3-fibrinogen interactions is time-dependent. Because these measurements mimic the binding/unbinding parameters and the time course of the αIIbβ3-fibrinogen interactions under conditions of shear, they are relevant to physiological processes of fibrinogen-mediated platelet adhesion and platelet aggregation. Taken together, our data suggest a model for fibrinogen binding to αIIbβ3 in which the initial interaction is followed by reorganization of the binding interface, thereby enhancing the strength and stability of fibrinogen binding.
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Memon, R. P., A. R. M. Sam, A. Z. Awang, and U. I. Memon. "Effect of Improper Curing on the Properties of Normal Strength Concrete." Engineering, Technology & Applied Science Research 8, no. 6 (December 22, 2018): 3536–40. http://dx.doi.org/10.48084/etasr.2376.
Full textAbstract:
In real applications, 28 days are regarded as proper curing time for concrete. There is a self-evident need to minimize the duration of curing days. For this purpose, this research investigates 1 to 7 days of curing and compares it with concrete cured for 28 days. Three grades of normal concrete strength grade 30, grade 35 and grade 40 were made. After curing, two exposure conditions were applied to the concrete, inside laboratory-controlled environment and outside environment. Results indicate that slump increases with cement content in DOE method at constant water content. The concrete density in all grades reduces when the concrete is subject to inside exposure in comparison with outside exposure. Water loss from concrete reduces with increase in curing days in all concrete grades. Compression strength of all concrete grades increases with increase in curing days. For the uniformity of concrete, ultrasonic pulse velocity indicated that with an increase in curing days, concrete becomes denser and a bit void. Results showed that an increase in curing days also improves the surface quality of concrete. The significance point noticed is that there was not much difference in the concrete properties between 7 days of curing and 28 days of curing in all grades.
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Atia, Mostafa K. S., and Mukesh K. Jain. "A novel approach to hot die-less clinching process for high strength AA7075-T6 sheets." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 234, no. 19 (April 7, 2020): 3809–25. http://dx.doi.org/10.1177/0954406220917406.
Full textAbstract:
High strength AA7075-T6 aluminum sheets were joined by hot die-less clinching by locally heating the clinching region with an electrical resistance heating method. This method applied a large amount of current in the range 7.5–15 kA over a time period of 2–3 s to enhance the local ductility of AA7075-T6 sheets. A modified die-less clinching tool was developed to carry current from the blank holder to the anvil through a pair of AA7075-T6 sheets to be clinched. The above range of applied current and time duration led to an increase in sheet metal temperature in the range 175–260 ℃ leading to material softening and a consequent reduction in the clinch forming force as well as improved material flow. The clinched joints produced with constant forming force of 60 kN resulted in an increase in lap shear joint strength up to 41% with an applied current of 15 kA. Microstructure examination of the clinched region for a range of electrical resistance heating conditions revealed sound joints with previously reported forming and force locking mechanisms as well as recently identified elevated temperature material locking mechanism in the literature. The geometric interlock resulted in nonlinear increase in force with displacement in the lap shear test as well as instantaneous drop in the force due to failure of material locking.
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Cureton, Kirk J., Phillip D. Tomporowski, Arpit Singhal, Jeffrey D. Pasley, Kevin A. Bigelman, Kathleen Lambourne, Jennifer L. Trilk, Kevin K. McCully, Maurice J. Arnaud, and Qun Zhao. "Dietary quercetin supplementation is not ergogenic in untrained men." Journal of Applied Physiology 107, no. 4 (October 2009): 1095–104. http://dx.doi.org/10.1152/japplphysiol.00234.2009.
Full textAbstract:
Quercetin supplementation increases muscle oxidative capacity and endurance in mice, but its ergogenic effect in humans has not been established. Our study investigates the effects of short-duration chronic quercetin supplementation on muscle oxidative capacity; metabolic, perceptual, and neuromuscular determinants of performance in prolonged exercise; and cycling performance in untrained men. Using a double-blind, pretest-posttest control group design, 30 recreationally active, but not endurance-trained, young men were randomly assigned to quercetin and placebo groups. A noninvasive measure of muscle oxidative capacity (phosphocreatine recovery rate using magnetic resonance spectroscopy), peak oxygen uptake (V̇o2peak), metabolic and perceptual responses to submaximal exercise, work performed on a 10-min maximal-effort cycling test following the submaximal cycling, and voluntary and electrically evoked strength loss following cycling were measured before and after 7–16 days of supplementation with 1 g/day of quercetin in a sports hydration beverage or a placebo beverage. Pretreatment-to-posttreatment changes in phosphocreatine recovery time constant, V̇o2peak, substrate utilization, and perception of effort during submaximal exercise, total work done during the 10-min maximal effort cycling trial, and voluntary and electrically evoked strength loss were not significantly different ( P > 0.05) in the quercetin and placebo groups. Short duration, chronic dietary quercetin supplementation in untrained men does not improve muscle oxidative capacity; metabolic, neuromuscular and perceptual determinants of performance in prolonged exercise; or cycling performance. The null findings indicate that metabolic and physical performance consequences of quercetin supplementation observed in mice should not be generalized to humans.
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Yang, Aiwu, Shaokun Yang, Guofang Xu, and Wei Zhang. "Study of the Long-Term Deformation Characteristics of Municipal Sludge Solidified Soil under the Coupling Action of Dry-Wet Cycles and Initial Static Deviatoric Stress." Advances in Civil Engineering 2020 (November 10, 2020): 1–15. http://dx.doi.org/10.1155/2020/8824414.
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A self-developed curing agent is used to solidify the municipal sludge taken from Tianjin. Then, the long-term deformation characteristics of the sludge solidified soil are investigated by means of unconsolidated undrained creep tests with different dry-wet cycles for considering the influence of climate. The experimental results show that the attenuation rate of the shear peak strength of municipal sludge solidified soil decreases gradually with the increase of the number of dry-wet cycles, and the strength remains unchanged when the number of dry-wet cycles is greater than 10. The variation laws under different initial static deviatoric stresses are basically identical. When the applied stress is less than the yield stress of the sludge solidified soil, the duration curves of creep show only attenuated stage, i.e., with very small deformation, and the deformation reaches a constant in a short period of time. When the deviatoric stress reaches the long-term strength of the soil, the instantaneous deformation of the sludge solidified soil becomes large and damage occurs quickly. Under the same deviatoric stress, the creep deformation increases with the increase of the number of dry-wet cycles. When the load applied in each step is of the same magnitude, the higher the initial static deviatoric stress is, the larger the deformation of sludge solidified soil will be. It is found that the stress-strain relationship and the relationship between creep strain and time can be well described by an exponential function and a hyperbolic function, respectively. On this basis, a creep model is proposed for the long-term deformation considering the effect of dry-wet cycle times and initial static deviatoric stress. The model is further validated by comparing the predictions with the test results under different deviatoric stresses; the good agreement between which shows the potential application of the model to relevant practical engineering.
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Kamid, Tri Siswanto, I. D. G. Ary Subagia, and I. Ketut Gede Wirawan. "Karakteristik Komposit Hibrida Serat Basalt – Karbon Epoksi Resin pada Perendaman Air Laut." Jurnal METTEK 5, no. 1 (April 30, 2019): 57. http://dx.doi.org/10.24843/mettek.2019.v05.i01.p08.
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Material komposit dengan laminasi serat penguat karbon dan basalt telah diproduksi melalui proses cetakan injeksi. Tujuan penelitian adalah menganalisa laju korosi material komposit oleh air laut. Perendaman komposit hibrida untuk masing-masing variasi dilakukan pada air laut dengan durasi waktu perendaman selama 2 minggu, 4 minggu, dan 6 minggu. Hasil uji menunjukkan seluruh variasi komposit hibrida mengalami penyerapan dibuktikan dengan meningkatnya massa benda uji dari setiap durasi waktu perendaman. Peningkatan massa untuk masing-masing komposit hibrida sangat besar terjadi pada minggu ke-2 (dua) yaitu 3,9% untuk CFRP, 1,4% untuk B2C3B2C3, 1,3% untuk B4C6, 1,3% untuk C2B2C2B2C2, dan 1,5% untuk BFRP. Kemudian untuk durasi perendaman selanjutnya relatif tetap (constant). Dari hasil tersebut disimpulkan bahwa perendaman komposit hibrida dengan serat basalt/carbon/epoxy sangat rendah dari minggu ke minggu. Analisa SEM menunjukkan pada setiap komposit hibrida teramati terjadi korosi disebabkan karena serat basalt memiliki kandungan besi (Fe), tetapi laju korosi sangat rendah (< 0,5%). Efek korosi ditunjukkan dengan adanya zona delaminasi yang dapat menurunkan kekuatan dan keuletan dari komposit hibrida.
Composite materials with carbon fiber and basalt fiber laminates have been produced through the injection molding process. The aim is to analyze the corrosion rate of composite materials by sea water. Immersion of hybrid composites for each variation was carried out on sea water with a duration of immersion time of 2 weeks, 4 weeks and 6 weeks. The test results showed that all variations of hybrid composites experienced absorption as evidenced by the increase in the mass of the specimen from each duration of immersion time. The mass increase for each hybrid composite was very large at the second week is 3.9% for CFRP, 1.4% for B2C3B2C3, 1.3% for B4C6, 1.3% for C2B2C2B2C2, and 1,5% for BFRP. Then for the duration of subsequent immersion it is relatively constant. From these results it was concluded that immersion of hybrid composites with basalt / carbon / epoxy fibers was very low from week to week. SEM analysis showed that each hybrid composite observed corrosion due to basalt fibers having iron (Fe) content, but the corrosion rate was very low (<0.5%). Corrosion effects are indicated by a delamination zone which can reduce the strength and ductile of hybrid composites.
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Maex, Reinoud, and Boris Gutkin. "Temporal integration and 1/f power scaling in a circuit model of cerebellar interneurons." Journal of Neurophysiology 118, no. 1 (July 1, 2017): 471–85. http://dx.doi.org/10.1152/jn.00789.2016.
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Inhibitory interneurons interconnected via electrical and chemical (GABAA receptor) synapses form extensive circuits in several brain regions. They are thought to be involved in timing and synchronization through fast feedforward control of principal neurons. Theoretical studies have shown, however, that whereas self-inhibition does indeed reduce response duration, lateral inhibition, in contrast, may generate slow response components through a process of gradual disinhibition. Here we simulated a circuit of interneurons (stellate and basket cells) of the molecular layer of the cerebellar cortex and observed circuit time constants that could rise, depending on parameter values, to >1 s. The integration time scaled both with the strength of inhibition, vanishing completely when inhibition was blocked, and with the average connection distance, which determined the balance between lateral and self-inhibition. Electrical synapses could further enhance the integration time by limiting heterogeneity among the interneurons and by introducing a slow capacitive current. The model can explain several observations, such as the slow time course of OFF-beam inhibition, the phase lag of interneurons during vestibular rotation, or the phase lead of Purkinje cells. Interestingly, the interneuron spike trains displayed power that scaled approximately as 1/ f at low frequencies. In conclusion, stellate and basket cells in cerebellar cortex, and interneuron circuits in general, may not only provide fast inhibition to principal cells but also act as temporal integrators that build a very short-term memory. NEW & NOTEWORTHY The most common function attributed to inhibitory interneurons is feedforward control of principal neurons. In many brain regions, however, the interneurons are densely interconnected via both chemical and electrical synapses but the function of this coupling is largely unknown. Based on large-scale simulations of an interneuron circuit of cerebellar cortex, we propose that this coupling enhances the integration time constant, and hence the memory trace, of the circuit.
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Volkov, Grigory, Andrey Logachev, Nikolai Granichin, Ya-Pu Zhao, Yin Zhang, and Yuri Petrov. "The Influence of Background Ultrasonic Field on the Strength of Adhesive Zones under Dynamic Impact Loads." Materials 14, no. 12 (June 9, 2021): 3188. http://dx.doi.org/10.3390/ma14123188.
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The influence of background ultrasonic field on the ultimate dynamic strength of adhesive joints is studied using fracture mechanics analysis. Winkler foundation-type models are applied to describe the cohesion zone, and the incubation time fracture criterion is used. The challenging task is to study whether relatively weak ultrasound is able to decrease the threshold values of the external impact load depending on a joint model, such as an “elastic membrane” or “beam” approximation, and various boundary conditions at the ends. The specific task was to investigate the case of short pulse loading through application of time-dependent fracture criterion instead of the conventional principle of critical stress. Three different load cases, namely, step constant force, dynamic pulse, and their combination with ultrasonic vibrations, were also studied. The analytical solution to the problem demonstrates that background vibrations at certain frequencies can significantly decrease threshold values of fracture impact load. Specific calculations indicate that even a weak background sonic field is enough to cause a significant reduction in the threshold amplitude of a dynamic short pulse load. Additionally, non-monotonic dependency of threshold amplitude on pulse duration for weak background field was observed, which demonstrates the existence of optimal regimes of impact energy input. Moreover, this phenomenon does not depend on the way in which the beam edges mount, whether they are clamped or hinged, and it could be applied for micro-electro-mechanical switch design processes as an additional tool to control operational regimes.
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Tuncer, Seçkin, Tülay Tuncer Peker, İlksen Burat, Erhan Kiziltan, Barkin İlhan, and Nizamettin Dalkiliç. "Axonal excitability and conduction alterations caused by levobupivacaine in rat." Acta Pharmaceutica 67, no. 3 (September 1, 2017): 293–307. http://dx.doi.org/10.1515/acph-2017-0025.
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Abstract In this study, effects of the long-acting amide-type local anesthetic levobupivacaine on axonal conduction and excitability parameters of the rat sciatic nerve were thoroughly examined both in vitro and in vivo. In order to deduce its effects on isolated nerve conduction, compound nerve action potential (CNAP) recordings were performed using the suction method over sciatic nerves of Wistar rats before and after administration of 0.05 % (1.7 mmol L−1) levobupivacaine. Levobupivacaine caused complete CNAP area and amplitude depression by blocking conduction in a time-dependent manner. To assess the influence of levobupivacaine on in vivo excitability properties, threshold-tracking (TT) protocols were performed at sciatic nerves of rats injected with perineural 0.05 % (1.7 mmol L−1) levobupivacaine or vehicle alone. Charge-duration TT results revealed that levobupivacaine increases the rheobase and decreases the strength-duration time constant, suggesting interference of the anesthetic with the opening of Na+ channels. Twenty and 40 % threshold electrotonus curves were found for both groups to follow the same paths, suggesting no significant effect of levobupivacaine on K+ channels for either the fastest or relatively slow conducting fibers. Current-threshold relationship results revealed no significant effect on axonal rectifying channels. However, according to the results of the recovery cycle protocol yielding the pattern of excitability changes following the impulse, potential deviation was found in the recovery characteristics of Na+ channels from the absolute refractory period. Consequently, conduction blockage caused by levobupivacaine may not be due to the passive (capacitive) properties of axon or the conductance of potassium channels but to the decrease in sodium channel conductance.
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Lindenfeld, Avishay, and Yehuda Partom. "Improving data interpretation from SHTB tests on ductile metals." EPJ Web of Conferences 183 (2018): 01006. http://dx.doi.org/10.1051/epjconf/201818301006.
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This work presents a methodology to calibrate a strength model for ductile metals, based on dynamic tension tests of relatively long Dog-Bone specimens conducted on a Split Hopkinson Tension Bar (SHTB). We address the main difficulties involved in conducting and interpreting such tests, namely the duration of the loading pulse needed to deform long specimens and the non-uniform stress and strain distributions along the specimen due to neck formation. The first issue is addressed by using the waves‘ reflections within the output bar, as explained below. When the first loading (tension) wave does not cause failure of the specimen, a reflected compression wave travels from the specimen‘s bar end to the free bar‘s end. Upon reaching the free end this latter compression wave is reflected again as a second tension wave, which travels back along the bar until it reaches the specimen and loads it the second time. This enables further deformation of the specimen, practically doubling the loading pulse duration without changing the striker‘s length. The second issue is addresses by using full numerical simulations of the experimental setup, including the striker, the bars and the specimen. This way, the full dynamic behaviour of the specimen is taken into account, eliminating the need to consider specimen equilibrium and taking into account the current strain rate in the specimen as it deforms. Hence, model calibration can be done from the very start of plastic deformation and without the need to keep the strain rate constant during deformation. As a result, it is possible to reliably calibrate the strength model considering necking and neck location, as well as plastic heating which is a significant factor in the plastic deformation of ductile metals.
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Nozari Nezhad, Masume, Alireza Kolahi, Mahmood Kazemzad, and Maryam Saiedifar. "Electrolytic Coloring of Anodized Aluminum by Copper." Advanced Materials Research 829 (November 2013): 381–85. http://dx.doi.org/10.4028/www.scientific.net/amr.829.381.
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It is important to generate aluminum oxide layer on the surface of aluminum in order to enhance the adhesion of the dye molecules in coloring aluminum industry. One of the major advantages of aluminum is the formation of a resistant oxide layer naturally, but the thickness of this layer is not high enough and it should be damaged due to lack of mechanical strength. However, the thickness of oxide layer can be increased through anodizing; this process improves its abrasion and corrosion resistance as well as its mechanical properties. In the present study, specimens of pure aluminum were anodized under galvanostatic condition in sulfuric acid electrolyte and porous nanostructured aluminum oxide layer was formed. Porosity of the anodized layer was controlled by optimizing the working conditions such as electrolyte concentration, anodizing time and current density. Finally, the specimens were electrolytically colored by applying alternating current to copper (Cu) solutions. Colored coatings were created at constant voltage and different coloring duration. The results indicated that the shade of different metal ions can be optimized by controlling the coloring parameters, the longer time of coloring results in the darker colors. The samples were examined by X-Ray Diffraction (XRD) spectroscopy and Scanning Electron Microscopy (SEM) and electrochemical test.
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Röken, Christian, Florian Schuppan, Katharina Proksch, and Sebastian Schöneberg. "Flaring of blazars from an analytical, time-dependent model for combined synchrotron and synchrotron self-Compton radiative losses of multiple ultrarelativistic electron populations." Astronomy & Astrophysics 616 (August 2018): A172. http://dx.doi.org/10.1051/0004-6361/201730622.
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We present a fully analytical, time-dependent leptonic one-zone model that describes a simplified radiation process of multiple interacting ultrarelativistic electron populations and accounts for the flaring of GeV blazars. In this model, several mono-energetic, ultrarelativistic electron populations are successively and instantaneously injected into the emission region, that is, a magnetized plasmoid propagating along the blazar jet, and subjected to linear, time-independent synchrotron radiative losses, which are caused by a constant magnetic field, and nonlinear, time-dependent synchrotron self-Compton radiative losses in the Thomson limit. Considering a general (time-dependent) multiple-injection scenario is, from a physical point of view, more realistic than the usual (time-independent) single-injection scenario invoked in common blazar models, as blazar jets may extend over tens of kiloparsecs and thus most likely pick up several particle populations from intermediate clouds. We analytically compute the electron number density by solving a kinetic equation using Laplace transformations and the method of matched asymptotic expansions. Moreover, we explicitly calculate the optically thin synchrotron intensity, the synchrotron self-Compton intensity in the Thomson limit, as well as the associated total fluences. In order to mimic injections of finite duration times and radiative transport, we model flares by sequences of these instantaneous injections, suitably distributed over the entire emission region. Finally, we present a parameter study for the total synchrotron and synchrotron self-Compton fluence spectral energy distributions for a generic three-injection scenario, varying the magnetic field strength, the Doppler factor, and the initial electron energy of the first injection in realistic parameter domains, demonstrating that our model can reproduce the typical broadband behavior seen in observational data.
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Rimmer, Katrina, and Alexander A. Harper. "Developmental Changes in Electrophysiological Properties and Synaptic Transmission in Rat Intracardiac Ganglion Neurons." Journal of Neurophysiology 95, no. 6 (June 2006): 3543–52. http://dx.doi.org/10.1152/jn.01220.2005.
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We charted postnatal changes in the intrinsic electrophysiological properties and synaptic responses of rat intrinsic cardiac ganglion (ICG) neurons. We developed a whole-mount ganglion preparation of the excised right atrial ganglion plexus. Using intracellular recordings and nerve stimulation we tested the hypothesis that substantial transformations in the intrinsic electrical characteristics and synaptic transmission accompany postnatal development. Membrane potential ( Em) did not change but time constant (τ) and cell capacitance increased with postnatal development. Accordingly, input resistance ( Rin) decreased but specific membrane resistance ( Rm) increased postnatally. Comparison of the somatic active membrane properties revealed significant changes in electrical phenotype. All neonatal neurons had somatic action potentials (APs) with small overshoots and small afterhyperpolarizations (AHPs). Adult neurons had somatic APs with large overshoots and large AHP amplitudes. The range of AHP duration was larger in adults than in neonates. The AP characteristics of juvenile neurons resembled those of adults, with the exception of AHP duration, which fell midway between neonate and adult values. Phasic, multiply adapting, and tonic evoked discharge activities were recorded from ICG neurons. Most neurons displayed phasic discharge at each developmental stage. All neurons received excitatory synaptic inputs from the vagus or interganglionic nerve trunk(s), the strength of which did not change significantly with postnatal age. The changes in the electrophysiological properties of the postganglionic neuron suggest that increased complexity of parasympathetic regulation of cardiac function accompanies postnatal development.
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Stoffels, Anouk A. F., Bram van den Borst, Jeannette B. Peters, Mariska P. M. Klaassen, Hanneke A. C. van Helvoort, Roy Meys, Peter Klijn, et al. "Correlates of variability in endurance shuttle walk test time in patients with chronic obstructive pulmonary disease." PLOS ONE 16, no. 4 (April 21, 2021): e0249786. http://dx.doi.org/10.1371/journal.pone.0249786.
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Background The endurance shuttle walk test (ESWT) is used to evaluate exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). The recommended pre-intervention tolerated duration (Tlim) is between 3–8 minutes for optimal interpretation of treatment effects. However, this window may be exceeded and factors determining ESWT Tlim are not completely understood. Therefore, we aimed to determine whether pulmonary function, physical and incremental shuttle walk test (ISWT) performance measures are associated with ESWT Tlim in COPD patients. Methods Assessment data from patients eligible for pulmonary rehabilitation was retrospectively analyzed. Inclusion criteria were: diagnosis of COPD and complete data availability regarding ESWT and ISWT. Patients performed an ESWT at 85% of ISWT speed and were divided into three groups (ESWT Tlim: <3 minutes, 3–8 minutes, >8 minutes). Subject characteristics, severity of complaints, pulmonary function, physical capacity and activity, exercise tolerance and quadriceps muscle strength were evaluated. Results 245 COPD patients (FEV1 38 (29–52)% predicted) were included. Median ESWT Tlim was 6.0 (3.7–10.3) minutes, 41 (17%) patients walked <3 minutes and 80 (33%) patients walked >8 minutes. Body mass index, maximal oxygen consumption, Tlim on constant work rate cycle test, physical activity level, maximal ISWT speed, dyspnoea Borg score at rest and increase of leg fatigue Borg score during ISWT independently predicted Tlim in multivariate regression analysis (R2 = 0.297, p<0.001). Conclusion This study reported a large variability in ESWT Tlim in COPD patients. Secondly, these results demonstrated that next to maximal ISWT speed, other ISWT performance measures as well as clinical measures of pulmonary function, physical capacity and physical activity were independent determinants of ESWT Tlim. Nevertheless, as these determinants only explained ~30% of the variability, future studies are needed to establish whether additional factors can be used to better adjust individual ESWT pace in order to reduce ESWT Tlim variability.
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Feng, Zhibin, and Jinxin Gong. "Study on normalization of residual displacements for single-degree-of-freedom systems." Earthquake Spectra 37, no. 3 (January 25, 2021): 1758–84. http://dx.doi.org/10.1177/8755293020988014.
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Residual displacement spectrum is one of the most important means to predict the permanent deformation of structures after the earthquake, and various normalizations of residual displacements have generally been used for construction of the spectrum. However, the issue regarding the merits and drawbacks of each normalization has not yet been investigated thoroughly. A comparison between two normalizations that relate the residual displacements to the elastic and inelastic displacements is made in terms of the effect of ground motion and structural characteristics by means of the results of nonlinear time history analysis. The statistical results reveal that the residual-to-peak-inelastic displacement ratios have the advantages of small dispersion, samples without any outliers, and relatively symmetric distribution, which benefits from the strong correlation between residual and peak inelastic displacements. Moreover, the residual-to-peak-inelastic displacement ratios are almost independent of site conditions, significant duration, and natural periods. Consequently, the peak inelastic displacements are superior to the elastic ones as an intermediate step for residual displacements estimation, provided that the peak inelastic displacements are estimated with a low uncertainty. For providing alternatives to estimate residual displacement demands, the constant-strength residual displacement spectra are developed for both normalizations.
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Sleutjes, Boudewijn T. H. M., Maria O. Kovalchuk, Naric Durmus, Jan R. Buitenweg, Michel J. A. M. van Putten, Leonard H. van den Berg, and Hessel Franssen. "Simulating perinodal changes observed in immune-mediated neuropathies: impact on conduction in a model of myelinated motor and sensory axons." Journal of Neurophysiology 122, no. 3 (September 1, 2019): 1036–49. http://dx.doi.org/10.1152/jn.00326.2019.
Full textAbstract:
Immune-mediated neuropathies affect myelinated axons, resulting in conduction slowing or block that may affect motor and sensory axons differently. The underlying mechanisms of these neuropathies are not well understood. Using a myelinated axon model, we studied the impact of perinodal changes on conduction. We extended a longitudinal axon model (41 nodes of Ranvier) with biophysical properties unique to human myelinated motor and sensory axons. We simulated effects of temperature and axonal diameter on conduction and strength-duration properties. We then studied effects of impaired nodal sodium channel conductance and paranodal myelin detachment by reducing periaxonal resistance, as well as their interaction, on conduction in the 9 middle nodes and enclosed paranodes. Finally, we assessed the impact of reducing the affected region (5 nodes) and adding nodal widening. Physiological motor and sensory conduction velocities and changes to axonal diameter and temperature were observed. The sensory axon had a longer strength-duration time constant. Reducing sodium channel conductance and paranodal periaxonal resistance induced progressive conduction slowing. In motor axons, conduction block occurred with a 4-fold drop in sodium channel conductance or a 7.7-fold drop in periaxonal resistance. In sensory axons, block arose with a 4.8-fold drop in sodium channel conductance or a 9-fold drop in periaxonal resistance. This indicated that motor axons are more vulnerable to developing block. A boundary of block emerged when the two mechanisms interacted. This boundary shifted in opposite directions for a smaller affected region and nodal widening. These differences may contribute to the predominance of motor deficits observed in some immune-mediated neuropathies. NEW & NOTEWORTHY Immune-mediated neuropathies may affect myelinated motor and sensory axons differently. By the development of a computational model, we quantitatively studied the impact of perinodal changes on conduction in motor and sensory axons. Simulations of increasing nodal sodium channel dysfunction and paranodal myelin detachment induced progressive conduction slowing. Sensory axons were more resistant to block than motor axons. This could explain the greater predisposition of motor axons to functional deficits observed in some immune-mediated neuropathies.
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Horne, R. S., N. D. De Preu, P. J. Berger, and A. M. Walker. "Arousal responses to hypertension in lambs: effect of sinoaortic denervation." American Journal of Physiology-Heart and Circulatory Physiology 260, no. 4 (April 1, 1991): H1283—H1289. http://dx.doi.org/10.1152/ajpheart.1991.260.4.h1283.
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Newborn lambs were subjected to hypertensive stimuli of 1-min duration to examine features of hypertension-induced arousal from sleep. Reflex mechanisms involved were studied by performing the same tests after sinoaortic denervation (SAD). In intact lambs, hypertension increased the probability of arousal from both quiet sleep (QS) and rapid-eye-movement (REM) sleep. Hypertension resulted in arousal in 51% (QS) and 50% (REM) of tests. Arousal time was significantly longer in REM (29.3 +/- 0.9 s, mean +/- SE) than in QS (22.6 +/- 0.6 s, P less than 0.01). Arterial oxygen saturation (So2) and partial pressure of oxygen (Po2) measured at the point of arousal, or after 60 s if arousal failed to occur, were unchanged from control values. After SAD hypertension did not increase the probability of arousal. Arousals significantly decreased (P less than 0.001) to 31% (QS) and 10% (REM). These findings indicate that acute hypertension, mediated via arterial baroreceptors, is a potent stimulus for arousal. In intact lambs, the arousal probability increased and arousal time decreased with increasing stimulus strength (1-30 mmHg), but the arousal time difference between QS and REM remained constant. Consideration of these findings in terms of a simple baroreflex threshold model suggests that the slower response in REM sleep is explained by slower neural processes after the achievement of a critical arousal input rather than by a higher threshold for baroreceptor input in this state.
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PAIREAU, O., P. TABELING, and B. LEGRAS. "A vortex subjected to a shear: an experimental study." Journal of Fluid Mechanics 351 (November 25, 1997): 1–16. http://dx.doi.org/10.1017/s0022112097006915.
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The two-dimensional erosion of a vortex subjected to an external, adverse shear is studied experimentally. The flow takes place in a thin stratified layer; the vortex is produced by electromagnetic forcing, whereas the shear is driven mechanically. The system thus allows the vortex strength and the external shear to be controlled independently. We observe the so-called ‘erosion’ process, i.e. the progressive decrease of the vortex area, leaving the vortex core unaffected. This process is controlled by the ratio γ=S/ωmax, where ωmax and S are respectively the maximum vorticity of the vortex and the external shear. At small γ, the erosion is weak and the vortex survives over the duration of the experiment. At large γ, the vortex is first eroded, and then, after a critical time, becomes stretched and eventually breaks up into filaments. During the first period of time, the compensated maximum vorticity (with friction decay removed) is constant and the vortex area decreases, while beyond the critical time, both quantities decrease with time. A critical value for γ, defining the transition between these two regimes, is determined experimentally: γc=0.051±0.017. The breaking process itself, during which the vorticity of the vortex core decreases, is investigated. All the qualitative aspects of the erosion process, the onset of breaking and the breaking process itself are found to be in excellent agreement with the theoretical and numerical description. The experimental value of γc and the properties of the filamentation process are consistent with the numerical estimates.
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Huang, Shengfang, Zhibo Zhang, Huimin Song, Yun Wu, Zhengzhong Sun, and Yinghong Li. "Analytic Model and the Influence of Actuator Number on the Performance of Plasma Synthetic Jet Actuator Array." Applied Sciences 8, no. 9 (September 1, 2018): 1534. http://dx.doi.org/10.3390/app8091534.
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Coupled with the multichannel discharge model and plasma synthetic jet actuator (PSJA) aerodynamic model, an analytical model to predict the performance of the PSJA array is put forward. The multichannel discharge model takes these factors into consideration, the delay time in the breakdown process, the electrical transformation of the discharge channel from a capacitor to a resistor induced by the air breakdown, and the varying plasma resistance in the discharge process. The PSJA aerodynamic model is developed based on the conservation equations of mass, momentum, energy, and the lumped capacitance method. The multichannel discharge model can simulate the multichannel discharge process and give the discharge energy in the plasma channel. With a constant heating efficiency, the time-independent heating energy deposition power in a discharge channel is obtained. Importing the heating energy, the PSJA aerodynamic model presents the evolution process of the jet. Simulation results show that the jet strength induced by a single actuator decreases with the number of actuators in the PSJA array. When the actuator number increases from 1 to 20, the weakening extent of mass ejected, peak jet velocity, and jet duration time is 62%, 54%, and 33%, respectively. The discharge efficiency increases with the actuator number, while the thermodynamic efficiency decreases with the actuator number. As a result, the total energy efficiency doesn’t always increase with an increase in the number of actuators. When the discharge efficiency of a conventional one channel discharge has been a relatively large value, the total energy efficiency actually decreases with the growth of actuator number.
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Litvinov, Rustem I., Valeri Barsegov, Andrey Mekler, John W. Weisel, and Joel S. Bennett. "The PLATELET INTEGRIN αIIbβ3 CHANGES FROM A LOWER- to A Higher-AFFINITY STATE DURING INTERACTION with FIBRINOGEN." Blood 118, no. 21 (November 18, 2011): 1130. http://dx.doi.org/10.1182/blood.v118.21.1130.1130.
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Abstract Abstract 1130 The integrin αIIbβ3 (GPIIb-IIIa) plays an essential role in platelet adhesion and cohesion by binding to a number of adhesive ligands including fibrinogen, von Willebrand factor, fibronectin, and vitronectin. Following ligand binding, αIIbβ3-mediated intracellular signaling is thought to stabilize platelet adhesive interactions, cause platelet spreading, and initiate clot retraction. Here we investigated the time course of interactions between purified αIIbβ3 and its major ligand fibrinogen when both were firmly attached to apposed surfaces, mimicking αIIbβ3-mediated platelet adhesive interactions. To measure the mechanical resistance of individual αIIbβ3-fibrinogen complexes under a constant tensile force, we used a previously described optical trap force clamp system (Litvinov et al., Biophys. J., 2011, 100, 165). Briefly, we trapped a fibrinogen-coated microscopic bead in a focused laser beam and intermittently brought it into contact with an αIIbβ3-coated silica pedestal. Repeated touching and separation of the bead and pedestal occurred with a compressive force of 20 pN and a constant pulling force of 50 pN. When the duration of contact between interacting molecules on the bead and pedestal was varied from 0.1s to 2s, the probability of αIIbβ3-fibrinogen interaction was time-dependent. This enabled us to extract two-dimensional kinetic parameters, i.e., how fast the αIIbβ3-fibrinogen complex forms and dissociates at the interface without the application of an external tensile force (zero-force kinetics). To convert the kinetic parameters to absolute values, we determined the density of αIIbβ3 molecules on the pedestal surface capable of binding 125I-fibrinogen to be ≈3,000 molecules per μm2. We found that the reactive αIIbβ3 exists in at least two states that differ significantly in their on-rates (kon1 =8×10−5 and kon2 =5.6×10−4 μm2/s), off-rates (koff1 =1.56 and koff2 =1.70 1/s) and affinities (Kd1 =2×104 and Kd2 =3×103 1/μm2) for fibrinogen. In the absence of αIIbβ3 activators, the interacting molecules reached a stable equilibrium in which 85% of the complexes were in the lower affinity form. In the presence of the activator Mn2+, the proportion of lower affinity forms decreased to 60%. Mn2+ also changed the on-rates (kon1 =3.38×10−5 and kon2 =9.9×10−4 μm2/s), off-rates (koff1 =2.99 and koff2 =4.82 1/s) and affinities (Kd1 =9×104 and Kd2 =5×103 1/μm2). We then tested whether the ratio between the two integrin activation states and the mechanical stability of the αIIbβ3-fibrinogen complex depends on the duration of contact between the interacting surfaces. As the contact duration was prolonged from 0.1s to 2s, the αIIbβ3-fibrinogen bond lifetime increased from shorter lifetimes (<2s) corresponding to the low-affinity state to longer lifetimes (up to 50s) corresponding to the high-affinity state. Moreover, the rate of transition from low- to high-affinity increased ∼3-fold, whereas the reverse rate decreased 1.5–2-fold, resulting in an overall 6-fold increase in the equilibrium rate constant. This means that reversible conformational transitions of αIIbβ3 from low- to high affinity states occur during its interaction with fibrinogen with the equilibrium gradually shifting toward the higher affinity state as contact duration increases. Thus, the strength of αIIbβ3-fibrinogen interactions is time-dependent due to a progressive increase in the affinity of the αIIbβ3-fibrinogen complex during the course of the interaction. These results provide kinetic and thermodynamic characteristics of the adhesive interaction between αIIbβ3 and fibrinogen at the single-molecule level and provide evidence for a direct fibrinogen-induced change in αIIbβ3 conformation as a potential mechanism for the initiation of αIIbβ3-mediated outside-in signaling in platelets. Disclosures: No relevant conflicts of interest to declare.
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Xiong, Zuqiang, Changsheng Song, Chengdong Su, Xiaolei Wang, Cheng Wang, and Yu Hao. "Uniaxial Compression Creep Relaxation and Grading of Coal Samples via Tests on the Progressive Failure Characteristics." Geofluids 2019 (February 7, 2019): 1–13. http://dx.doi.org/10.1155/2019/9069546.
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An RMT-150B electrohydraulic servo testing system was used to perform uniaxial compression and uniaxial grading relaxation (creep) tests. The deformation, strength, and failure characteristics of the progressive failure process of coal samples under three loading modes were analyzed. The analysis results show that the prepeak stress-strain curve of the coal samples and the load relationships are not clear and that the whole compression process of coal still showed compression, elastic, yielding, and failure stages. The local stress drop characteristics during our relaxation creep grading tests showed no clear peak value and showed a yield curve with the shape of a conventional single plateau. The values of the mechanical parameters of axial compression were significantly higher than those obtained in the grade relaxation (creep) tests, which showed the mechanical parameters of coal samples with aging characteristics. In the relaxation (creep) tests, when the stress ratio was less than 70%, the relaxation (creep) characteristics of the sample were not clear. When the ratio of stress relaxation (creep) was more than 70% in the relaxation (creep) tests during displacement (stress) with a constant relaxation (creep) over the duration of the test, the evolution, development, and convergence of microcracks in the coal samples were observed. Relaxation (creep) stress was higher, failure duration was shorter, and the duration of failure was longer. For fully mechanized coal faces, increasing the support resistance and timely moving the support after coal cutting may prevent rib spalling accidents by reducing coal stress and exposure time in the front of the working face. Additionally, routine uniaxial compressive failures showed a simple form, having a clear tension-shear dual rupture surface. The staged relaxation creep failure testing of coal is more complex. The entire coal samples were divided into many thin-sheet debris via gradual collapse and shedding, and the number of cracks increased significantly, showing evident lateral expansion characteristics that are similar to the rib spalling characteristics in high coal mining working faces.
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Langer, Daniel, Casey Ciavaglia, Azmy Faisal, Katherine A. Webb, J. Alberto Neder, Rik Gosselink, Sauwaluk Dacha, Marko Topalovic, Anna Ivanova, and Denis E. O’Donnell. "Inspiratory muscle training reduces diaphragm activation and dyspnea during exercise in COPD." Journal of Applied Physiology 125, no. 2 (August 1, 2018): 381–92. http://dx.doi.org/10.1152/japplphysiol.01078.2017.
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Among patients with chronic obstructive pulmonary disease (COPD), those with the lowest maximal inspiratory pressures experience greater breathing discomfort (dyspnea) during exercise. In such individuals, inspiratory muscle training (IMT) may be associated with improvement of dyspnea, but the mechanisms for this are poorly understood. Therefore, we aimed to identify physiological mechanisms of improvement in dyspnea and exercise endurance following inspiratory muscle training (IMT) in patients with COPD and low maximal inspiratory pressure (Pimax). The effects of 8 wk of controlled IMT on respiratory muscle function, dyspnea, respiratory mechanics, and diaphragm electromyography (EMGdi) during constant work rate cycle exercise were evaluated in patients with activity-related dyspnea (baseline dyspnea index <9). Subjects were randomized to either IMT or a sham training control group ( n = 10 each). Twenty subjects (FEV1 = 47 ± 19% predicted; Pimax = −59 ± 14 cmH2O; cycle ergometer peak work rate = 47 ± 21% predicted) completed the study; groups had comparable baseline lung function, respiratory muscle strength, activity-related dyspnea, and exercise capacity. IMT, compared with control, was associated with greater increases in inspiratory muscle strength and endurance, with attendant improvements in exertional dyspnea and exercise endurance time (all P < 0.05). After IMT, EMGdi expressed relative to its maximum (EMGdi/EMGdimax) decreased ( P < 0.05) with no significant change in ventilation, tidal inspiratory pressures, breathing pattern, or operating lung volumes during exercise. In conclusion, IMT improved inspiratory muscle strength and endurance in mechanically compromised patients with COPD and low Pimax. The attendant reduction in EMGdi/EMGdimax helped explain the decrease in perceived respiratory discomfort despite sustained high ventilation and intrinsic mechanical loading over a longer exercise duration. NEW & NOTEWORTHY In patients with COPD and low maximal inspiratory pressures, inspiratory muscle training (IMT) may be associated with improvement of dyspnea, but the mechanisms for this are poorly understood. This study showed that 8 wk of home-based, partially supervised IMT improved respiratory muscle strength and endurance, dyspnea, and exercise endurance. Dyspnea relief occurred in conjunction with a reduced activation of the diaphragm relative to maximum in the absence of significant changes in ventilation, breathing pattern, and operating lung volumes.
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Kavousi, Ayoub, and Valiallah Saba. "GENERATION OF RECTANGULAR BIPHASIC WAVEFORM TO DECREASE DEFIBRILLATION THRESHOLD FOR EXTERNAL DEFIBRILLATOR." Biomedical Engineering: Applications, Basis and Communications 24, no. 05 (October 2012): 395–401. http://dx.doi.org/10.4015/s1016237212500354.
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Studies have shown that defibrillation threshold for current amplitude of biphasic truncated exponential (BTE) waveform has a hyperbolic strength–duration relationship. Theoretical and experimental results have shown that decreasing the tilt of BTE waveforms decreases the defibrillation threshold. On the other hand, low peak current waveform reduces probability of myocardium damage and burn. Therefore, achieving a waveform with low tilt and low peak current is desired. All DC defibrillators use a capacitor to store and deliver required energy. Because of capacitor discharging nature, the tilt of waveforms is high. In rectilinear biphasic waveform (RBW), which was generated by ZOLL M-series defibrillator, the tilt of the first phase was decreased using an adjustable resistor connected in series with current path. But the defibrillator cannot keep the current constant in the second phase and in the both phases for high transthoracic impedances (TTI) either. In this paper, for solving these problems, a circuit that generates rectangular biphasic waveform is designed. In this circuit, five resistors are used and connected in series. Then an IGBT switch is connected to each resistor in parallel. Also, control of minimum current ripple is applied in order to decide which resistors should be worked in each time. The circuit is simulated in MATLAB/Simulink and a prototype model is constructed. Results demonstrate that the tilt of the waveform is notably reduced to a value less than 10%.
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Grzywacz, N. M., and F. R. Amthor. "Facilitation in ON-OFF directionally selective ganglion cells of the rabbit retina." Journal of Neurophysiology 69, no. 6 (June 1, 1993): 2188–99. http://dx.doi.org/10.1152/jn.1993.69.6.2188.
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1. We have investigated the facilitation of extracellularly recorded responses of ON-OFF directionally selective (DS) ganglion cells of the rabbit retina to two-slit preferred-direction apparent motion produced by both prolonged light steps, which simulate movement of an edge past two apertures, and light flashes, which simulate movement of a spot or slit. 2. Within the excitatory receptive-field center of DS ganglion cells, apparent motion with prolonged light steps elicits preferred-direction facilitation whose rise time (220 +/- 150 ms, average rise to 90% of maximum for 6 cells) is typically longer than the rise time of the excitatory response elicited by each slit. The decay time to baseline of facilitation during prolonged light steps is generally longer than 500 ms and hence greatly exceeds the typical duration of the excitatory response elicited by the slits. 3. Prolonged light steps are generally effective for facilitating any given excitatory receptive-field locus from a roughly ovoid area that typically extends on the order of 100-200 microns in the preferred direction, which is less than one-half the size of the excitatory receptive-field center. Within 100 microns, facilitation can occur for motion diagonal to the preferred-null axis as long as the projection of the motion on the preferred-null axis points in the preferred direction. 4. The time course of preferred-direction facilitation between two slits does not appear to have a strong systematical dependence on the interslit distance over the range in which facilitation is effective. 5. Short light flashes are ineffective for eliciting facilitation and, at sufficiently long interslit delays, elicit inhibition all around the test slit. This inhibition may be due to the antagonistic surround mechanism within the receptive-field center, which is effectively elicited by short-duration stimuli. 6. The effect of preferred-direction facilitation is addition-like, rather than multiplication-like. That is, the facilitatory effect of the first slit appears as the addition of a fixed value to the response-versus-contrast curve of the second slit, rather than a multiplication of the curve by a constant factor. The functional relationship between strength of facilitation and contrast of the first slit is sigmoidal, however, and thus nonlinear. 7. Experiments with long light steps show that the interaction between excitation and preferred-direction facilitation is largely segregated between the ON and OFF pathways.(ABSTRACT TRUNCATED AT 400 WORDS)
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Young, Laurence R., Charles M. Oman, Daniel Merfeld, Douglas Watt, Serge Roy, Carlo DeLuca, David Balkwill, et al. "Spatial Orientation and Posture During and Following Weightlessness: Human Experiments on Spacelab Life Sciences 1." Journal of Vestibular Research 3, no. 3 (September 1, 1993): 231–39. http://dx.doi.org/10.3233/ves-1993-3304.
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The 4 payload crew members of the Spacelab Life Sciences 9-day space flight in 1991 were subjected to limited vestibular testing in flight as well as pre and post flight. Major differences in individual “perceptual style” appeared in their reaction to the visual-vestibular stimuli in the rotating dome experiment, and especially in the extent to which nondirectional tactile cues served to anchor the subjective vertical and body postural reactions. The ability of subjects to point to remembered target positions was degraded in space, which produced a tendency to point low in some subjects in flight. The eye movements and subjective response to sudden stops and head pitching following continuous spinning (dumping) were measured both in space and on the ground. Although subjective duration of inflight rotation for the dumping tests was shorter than that for the preflight tests, the postrotatory nystagmus, with or without head pitch, was lengthened in time constant relative to preflight. Ground tests, in addition to the flight experiments, investigated the changes following in subjective and oculomotor reactions to whole body tilt, the ability to balance with eyes open and closed; leg muscle strength and stamina as related to posture; visual field dependence; and the perceptual and oculomotor reactions to horizontal linear acceleration. Several of these tests, as well as postflight measures of motion sickness susceptibility, revealed subtle evidence of neurovestibular alterations that lasted a week or more following the 10-day orbital exposure.