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Journal articles on the topic 'Potential gradient'
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1
Parisis, K., F. Shuang, B. Wang, P. Hu, A. Giannakoudakis, and A. Konstantinidis. "From Gradient Elasticity to Gradient Interatomic Potentials: The Case-Study of Gradient London Potential." Journal of Applied Mathematics and Physics 8 (September 15, 2020): 1826–37. https://doi.org/10.4236/jamp.2020.89137.
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Motivated by the special theory of gradient elasticity (GradEla), a proposal is advanced for extending it to construct gradient models for interatomic potentials, commonly used in atomistic simulations. Our focus is on London’s quantum mechanical potential which is an analytical expression valid until a certain characteristic distance where “attractive” molecular interactions change character and become “repulsive” and cannot be described by the classical form of London’s potential. It turns out that the suggested internal length gradient (ILG) generalization of London’s potential generates both an “attractive” and a “repulsive” branch, and by adjusting the corresponding gradient parameters, the behavior of the empirical Lennard-Jones potentials is theoretically captured.
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Parisis, Kostas, Fei Shuang, Bo Wang, Pu Hu, Andreas Giannakoudakis, and Avraam Konstantinidis. "From Gradient Elasticity to Gradient Interatomic Potentials: The Case-Study of Gradient London Potential." Journal of Applied Mathematics and Physics 08, no. 09 (2020): 1826–37. http://dx.doi.org/10.4236/jamp.2020.89137.
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Martin, M. "Materials in thermodynamic potential gradients." Pure and Applied Chemistry 75, no. 7 (2003): 889–903. http://dx.doi.org/10.1351/pac200375070889.
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In materials that are exposed to thermodynamic potential gradients (i.e., gradients of chemical potentials, electrical potential, temperature, or pressure), transport processes of the mobile components occur. These transport processes and the coupling between different processes are not only of fundamental interest, but are also the origin of degradation processes, such as kinetic demixing and decomposition and changes in the morphology of the material, all of which are of great practical relevance.Two classes of materials will be considered: semi-and ion-conducting oxides and ion-conducting halides. In oxides, kinetic demixing of the cations in a multicomponent oxide and kinetic decomposition of the oxide under the influence of an applied thermodynamic potential gradient will be considered for homovalent oxide solid solutions and for heterovalently doped oxides. In ion-conducting halides, the morphological stability of solid/solid interfaces, which are driven by an external electrical potential gradient, is studied. Monte Carlo simulations show that the morphological stability of the interface is determined by the difference in the ionic conductivities of the two crystals.
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Bermúdez, Andrea N., Enrique M. Spinelli, and Carlos H. Muravchik. "Bio-potential amplifier for potential gradient measurements." Journal of Physics: Conference Series 90 (November 1, 2007): 012022. http://dx.doi.org/10.1088/1742-6596/90/1/012022.
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He, W. M., and R. M. Callaway. "The potential for misleading correlations in single-factor analysis of complex gradients." Web Ecology 9, no. 1 (2009): 77–81. http://dx.doi.org/10.5194/we-9-77-2009.
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Abstract. Gradient analysis is an important tool for describing patterns in ecology. Natural environmental gradients are complex combinations of factors, suggesting that gradientsshould, when possible, be analyzed in multi-factorial ways. We searched papers published in Ecology, Global Change Biology, Journal of Ecology, Oecologia, Oikos, and Journal of Vegetation Science from January 2001 to December 2005, and found 133 papers matching two keywords: “gradient analysis” and “environmental gradient”. Of these, 86 utilized single-factor correlation analyses between ecological entities and natural environmental gradients. Thus the use of single-factor correlations in studies of natural environmental gradients is widespread despite the potential of this approach to overemphasize the importance of the particular factor chosen. We reanalyzed a data set from the literature, provided a example of contrasting analyses, and analyzed our own data with both single- and multiple-factor analyses to demonstrate how single-factor correlation can result in correlations that provide incomplete analysis. Integrated multi-factor approaches to studying natural environmental gradients cannot solve all analytical problems when two or more important variables are correlated, but are likely to better test the relative importance of factors driving ecological patterns.
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Hamilton, Stewart M., and Keiko H. Hattori. "Spontaneous potential and redox responses over a forest ring." GEOPHYSICS 73, no. 3 (2008): B67—B75. http://dx.doi.org/10.1190/1.2890287.
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Forest rings are large, circular features in boreal forests that commonly exceed [Formula: see text] in diameter and are visible on aerial photographs. A detailed study of redox conditions and spontaneous potential (SP) was carried out over a forest ring that overlies an [Formula: see text] accumulation. Studies included drilling, monitoring well installation, and downhole SP using both polarizing and nonpolarizing electrodes. Also measured were redox potential of groundwater and soils, concentrations of sulfur species in groundwater, and headspace concentrations of redox-sensitive gases in monitoring wells. The results show positive SP anomalies in the shallow subsurface and near-horizontal, negative-inward redox gradients in the water-saturated overburden at theedges of the ring. SP anomalies are spatially correlated with redox gradients, suggesting that the two are related. The SP anomalies may be produced in response to redox gradients as redox-active ions and polar molecules spontaneously align with the negative poles toward the oxidizing end of the gradient, i.e., toward their more electronegative neighbors. This orientation of dipoles imparts a macroscopic electrical polarity to the redox gradient and results in the observed positive electrical anomaly inside the forest ring. Ongoing oxidation reactions occurring around the periphery of the forest ring maintain strong [Formula: see text] concentration gradients, which result in an outward steady-state diffusive flux of [Formula: see text]. Electromigration of redox-active ions in the redox-induced electrical field may also contribute to maintenance of the redox gradient.
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Freeman, Mark, and Wayne Hiebert. "Gradient force shows its potential." Nature Nanotechnology 4, no. 6 (2009): 344–45. http://dx.doi.org/10.1038/nnano.2009.132.
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Nizamuddin, Syed. "Orographic effect on potential gradient." Pure and Applied Geophysics PAGEOPH 122, no. 1 (1985): 86–88. http://dx.doi.org/10.1007/bf00879650.
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Ten Tusscher, K. H. W. J., and A. V. Panfilov. "Reentry in heterogeneous cardiac tissue described by the Luo-Rudy ventricular action potential model." American Journal of Physiology-Heart and Circulatory Physiology 284, no. 2 (2003): H542—H548. http://dx.doi.org/10.1152/ajpheart.00608.2002.
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Heterogeneity of cardiac tissue is an important factor determining the initiation and dynamics of cardiac arrhythmias. In this paper, we studied the effects of gradients of electrophysiological heterogeneity on reentrant excitation patterns using computer simulations. We investigated the dynamics of spiral waves in a two-dimensional sheet of cardiac tissue described by the Luo-Rudy phase 1 (LR1) ventricular action potential model. A gradient of action potential duration (APD) was imposed by gradually varying the local current density of K+ current or inward rectifying K+ current along one axis of the tissue sheet. We show that a gradient of APD resulted in spiral wave drift. This drift consisted of two components. The longitudinal (along the gradient) component was always directed toward regions of longer spiral wave period. The transverse (perpendicular to the gradient) component had a direction dependent on the direction of rotation of the spiral wave. We estimated the velocity of the drift as a function of the magnitude of the gradient and discuss its implications.
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Chittur K, Subramaniam, Aishwarya Chandran, Ashwini Khandelwal, and Sivakumar A. "Energy Conversion using electrolytic concentration gradients." MRS Proceedings 1774 (2015): 51–62. http://dx.doi.org/10.1557/opl.2015.758.
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ABSTRACTSalinity gradient is an enormous source of clean energy. A process for potential generation from an ionic concentration gradient produced in single and multicell assembly is presented. The ionic gradient is created using a fuel cell type cell with a micro-porous ion exchange membrane, both anionic (AEM) and cationic (CEM). Various salinity gradients, Salt : Fresh, from 100 : 0 to 16000 : 0 was established using NaCl solution, in the electrode chambers. A potential of 20 mV/cm to 25 mV/cm can be realized at ambient temperatures and pressures for a bipolar AEM/CEM cell. The performance was optimized for various static and dynamic flow rates of the saline and fresh water. The cell performance can further be optimized for Membrane Electrode System (MES) morphology. A multicell unit was assembled and the results presented for various conditions like concentration gradients, flow rates and pressure. The thermodynamic and electrical efficiency needs to be evaluated for various gradients and flow rates. The relation with number of valance electrons/ ion and the potential generated changes for various dynamic condition of salinity. The higher the salinity gradient the larger is the potential generated. This is limited by the membrane characteristics. There exists a monotonic relation between the number of valence electron/ion/unit time and the potential generated up to about 16000 concentration. The membrane characteristics have been studied for optimal ion crossover for various gradients and flow. The graph between ln (gradient) versus Voltage provides insights into this process. This presents a very cost effective and clean process of energy conversion.
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Balasuriya, S. "Gradient evolution for potential vorticity flows." Nonlinear Processes in Geophysics 8, no. 4/5 (2001): 253–63. http://dx.doi.org/10.5194/npg-8-253-2001.
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Abstract. Two-dimensional unsteady incompressible flows in which the potential vorticity (PV) plays a key role are examined in this study, through the development of the evolution equation for the PV gradient. For the case where the PV is conserved, precise statements concerning topology-conservation are presented. While establishing some intuitively well-known results (the numbers of eddies and saddles is conserved), other less obvious consequences (PV patches cannot be generated, some types of Lagrangian and Eulerian entities are equivalent) are obtained. This approach enables an improvement on an integrability result for PV conserving flows (if there were no PV patches at time zero, the flow would be integrable). The evolution of the PV gradient is also determined for the nonconservative case, and a plausible experiment for estimating eddy diffusivity is suggested. The theory is applied to an analytical diffusive Rossby wave example.
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Alvarez-Silva, O. A., A. F. Osorio, and C. Winter. "Practical global salinity gradient energy potential." Renewable and Sustainable Energy Reviews 60 (July 2016): 1387–95. http://dx.doi.org/10.1016/j.rser.2016.03.021.
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Ruedenberg, Klaus, and Jun‐Qiang Sun. "Gradient fields of potential energy surfaces." Journal of Chemical Physics 100, no. 8 (1994): 5836–48. http://dx.doi.org/10.1063/1.467147.
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Chen, Xinquan, Junqi Gao, Biqing Qi, et al. "Fast and Slow Gradient Approximation for Binary Neural Network Optimization." Proceedings of the AAAI Conference on Artificial Intelligence 39, no. 25 (2025): 26913–21. https://doi.org/10.1609/aaai.v39i25.34896.
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Binary Neural Networks (BNNs) have garnered significant attention due to their immense potential for deployment on edge devices. However, the non-differentiability of the quantization function poses a challenge for the optimization of BNNs, as its derivative cannot be backpropagated. To address this issue, hypernetwork based methods, which utilize neural networks to learn the gradients of non-differentiable quantization functions, have emerged as a promising approach due to their adaptive learning capabilities to reduce estimation errors. However, existing hypernetwork based methods typically rely solely on current gradient information, neglecting the influence of historical gradients. This oversight can lead to accumulated gradient errors when calculating gradient momentum during optimization. To incorporate historical gradient information, we design a Historical Gradient Storage (HGS) module, which models the historical gradient sequence to generate the first-order momentum required for optimization. To further enhance gradient generation in hypernetworks, we propose a Fast and Slow Gradient Generation (FSG) method. Additionally, to produce more precise gradients, we introduce Layer Recognition Embeddings (LRE) into the hypernetwork, facilitating the generation of layer-specific fine gradients. Extensive comparative experiments on the CIFAR-10 and CIFAR-100 datasets demonstrate that our method achieves faster convergence and lower loss values, outperforming existing baselines.
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Sha, Lei, Gianrico Farrugia, W. Scott Harmsen, and Joseph H. Szurszewski. "Membrane potential gradient is carbon monoxide-dependent in mouse and human small intestine." American Journal of Physiology-Gastrointestinal and Liver Physiology 293, no. 2 (2007): G438—G445. http://dx.doi.org/10.1152/ajpgi.00037.2007.
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The aims of this study were to quantify the change in resting membrane potential (RMP) across the thickness of the circular muscle layer in the mouse and human small intestine and to determine whether the gradient in RMP is dependent on the endogenous production of carbon monoxide (CO). Conventional sharp glass microelectrodes were used to record the RMPs of circular smooth muscle cells at different depths in the human small intestine and in wild-type, HO2-KO, and W/WV mutant mouse small intestine. In the wild-type mouse and human intestine, the RMP of circular smooth muscle cells near the myenteric plexus was −65.3 ± 2 mV and −58.4 ± 2 mV, respectively, and −60.1 ± 2 mV and −49.1 ± 1 mV, respectively, in circular smooth muscle cells at the submucosal border. Oxyhemoglobin (20 μM), a trapping agent for CO, and chromium mesoporphyrin IX, an inhibitor of heme oxygenase, abolished the transwall gradient. The RMP gradients in mouse and human small intestine were not altered by NG-nitro-l-arginine (200 μM). No transwall RMP gradient was found in HO2-KO mice and W/WV mutant mice. TTX (1 μM) and 1H-[1,2,4-]oxadiazolo[4,3-a]quinoxalin-1-one (10 μM) had no effect on the RMP gradient. These data suggest that the gradient in RMP across the thickness of the circular muscle layer of mouse and human small intestine is CO dependent.
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Zhang, Yixin, Yang Liu, Junlei Mei, Chunxi Zhang, and Jinling Wang. "A Study on the Characteristics of the Ionospheric Gradient under Geomagnetic Perturbations." Sensors 20, no. 7 (2020): 1805. http://dx.doi.org/10.3390/s20071805.
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The Earth’s ionosphere is greatly influenced by geomagnetic activities, especially geomagnetic storms. During a geomagnetic storm, the ionosphere suffers many perturbations, leading to a spatial gradient that are neglected during geomagnetically quiet periods. An ionospheric gradient generates potential hazards for a ground-based argumentation system (GBAS) by enlarging the errors in the delay corrections between ground monitor stations and users. To address this problem, this work investigates the characteristics of the ionospheric gradient under geomagnetic storms. Global Navigation Satellite System (GNSS) observations from the continuously operating reference station (CORS) network were used to analyze the ionospheric gradients during the geomagnetic storm on 8 September 2017. The statistical behavior of the ionospheric gradient was further discussed. Experiments show that strong geomagnetic perturbations lead to large ionospheric gradients, and the gradients also vary with the geomagnetic location.
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Baysal, K., D. W. Jung, K. K. Gunter, T. E. Gunter, and G. P. Brierley. "Na(+)-dependent Ca2+ efflux mechanism of heart mitochondria is not a passive Ca2+/2Na+ exchanger." American Journal of Physiology-Cell Physiology 266, no. 3 (1994): C800—C808. http://dx.doi.org/10.1152/ajpcell.1994.266.3.c800.
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Net Ca2+ flux across the inner membrane of respiring heart mitochondria was evaluated under conditions in which virtually all Ca2+ movement can be attributed to the Na+/Ca2+ antiport. If this antiport promotes a passive electroneutral exchange of Ca2+ for 2Na+, the Ca2+ gradient should be equal to the square of the Na+ gradient at equilibrium. Because the mitochondrial Na+/H+ antiport equilibrates the Na+ and H+ gradients, the Ca2+ gradient should also equal the square of the H+ gradient. In a series of > 20 determinations at different matrix [Ca2+], different delta pH, and varying membrane potential, it was found that Ca2+ is transported out of the mitochondrion against gradients from 15- to 100-fold greater than the value predicted for passive electroneutral exchange. It is concluded that the observed gradients are too large to be sustained by passive Ca2+/2Na+ exchange. The observed gradients are compatible with an electrogenic Ca2+/3Na+ exchange. Alternatively another source of energy is available to support these gradients.
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AHEARN, GREGORY A., and LAUREL P. CLAY. "Membrane-Potential-Sensitive, Na+-Independent Lysine Transport by Lobster Hepatopancreatic Brush Border Membrane Vesicles." Journal of Experimental Biology 127, no. 1 (1987): 373–87. http://dx.doi.org/10.1242/jeb.127.1.373.
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Transport of l-[3H]lysine by epithelial brush border membrane vesicles (BBMV) of lobster hepatopancreas, formed by a magnesium precipitation technique, was insensitive to transmembrane gradients of Na+, K+, TMA+ or H+. Apparent initial lysine entry rates (15 s uptake) and extent of amino acid accumulation against a concentration gradient (overshoot) were both stimulated by transmembrane anion gradients according to the following sequence: SCN− > Cl− > gluconate−. The magnitude of this anion-gradient-dependent transport was significantly increased by bilateral acidic pH. Lysine transport at acidic pH strongly responded to transmembrane potential developed by addition of valinomycin to K+-loaded vesicles, or was markedly reduced if K+-equilibrated vesicles were incubated with the ionophore in the presence of an inwardly directed SCN− gradient. Lysine influx occurred by the combination of at least one carrier process and ‘apparent diffusion’. l-Arginine, l-alanine and l-leucine, added to the external medium, were all strong inhibitors of lysine influx. The first two were competitive inhibitors of lysine entry, while the latter was non-competitive in effect. These results suggest that lysine, arginine and alanine may share a common, Na+-independent, membrane-potential-sensitive transport mechanism in lobster BBMV. Leucine transport may occur in these membranes by a separate agency.
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Takano, Jun, and Tsutomu Sugiyama. "Genetic analysis of developmental mechanisms in hydra." Development 90, no. 1 (1985): 123–38. http://dx.doi.org/10.1242/dev.90.1.123.
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Effect of food was examined on the budding rate and the developmental gradients of a mutant hydra strain L4. This mutant strain has very high levels of head-inhibition potential gradient along its body axis (Takano & Sugiyama, 1983). It also has a reduced budding capacity when it is cultured using brine shrimp nauplii as food, but its budding capacity is significantly improved when a small amount of tubifex worm tissue is added to its diet of brine shrimp (Takano, 1984). To test whether or not this change of budding rate is correlated with the change in the levels of the head-activation or head-inhibition potential gradients, L4 animals were cultured on the diet of brine shrimp with or without addition of tubifex worm tissue and the budding rates and the gradient levels were examined in these animals. The results showed that food affected the budding rate in L4 without affecting its gradient levels. This suggests that the gradient levels and the budding rate in L4 are uncorrelated to each other, and that therefore the high levels of head-inhibition potential are not the cause for the low budding rate in this strain (cf., Takano & Sugiyama, 1983).
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Cooper, G. R. "Balancing images of potential-field data." GEOPHYSICS 74, no. 3 (2009): L17—L20. http://dx.doi.org/10.1190/1.3096615.
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Horizontal and vertical gradients, and filters based on them (such as the analytic signal), are used routinely to enhance detail in aeromagnetic data. However, when the data contain anomalies with a large range of amplitudes, the filtered data also will contain large and small amplitude responses, making the latter hard to see. This study suggests balancing the analytic signal amplitude (sometimes called the total gradient) by the use of its orthogonal Hilbert transforms, and shows that the balanced profile curvature can be an effective method of enhancing potential-field data. Source code is available from the author on request.
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Wróbel, Marek, and Andriy Burbelko. "A Diffusion Model of Binary Systems Controlled by Chemical Potential Gradient." Journal of Casting & Materials Engineering 6, no. 2 (2022): 39–44. http://dx.doi.org/10.7494/jcme.2022.6.2.39.
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The paper presents a model of diffusion in a single phase with chemical potential gradient as the driving force of the process. Fick’s laws are strictly empirical and the assumption that the concentration gradients are the driving forces of diffusion is far from precise. Instead, the gradient of chemical potential μi of component i is the real driving force. The matter of governing equations of models that incorporate this approach will be raised and discussed in this article. One of more important features is the ability to acquire results where diffusion against the concentration gradient may occur. The presented model uses the Finite Difference Method (FDM) and employs the CALPHAD method to obtain chemical potentials. The calculations of chemical potential are carried out for instant conditions – temperature and composition – in the entire task domain by Thermo-Calc via a TQ-Interface. Then the heterogeneity of chemical potentials is translated into mass transfer for each individual element. Calculations of two modelling tasks for one-dimension diffusion field were carried out. First: isothermal conditions with linear initial composition distribution and second: constant temperature gradient with uniform chemical composition in the specimen. Results for two binary solid solutions: Fe-C and Fe-Si, in the FCC phase for the given tasks will be presented. Modelling allows us to estimate the time needed to reach a desired state in a particular equilibrium or quasi-equilibrium state. It also shows the path of the composition change during the process. This can be used to determine whether the system at some point is getting close to the formation of another phase due to significant deviation from its initial conditions.
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Legge, NJ. "Relating Water Potential Gradients in Mountain Ash (Eucalyptus regnans F. Muell.) To Transpiration Rate." Functional Plant Biology 12, no. 1 (1985): 89. http://dx.doi.org/10.1071/pp9850089.
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Osmotic tensiometers recording in situ stem water potential, Ψst, were implanted at two heights in the trunks of mountain ash (Eucalyptus regnans) in mature and 1939 regrowth forests. Measurements over one summer showed that Ψst gradients, obtained from the mean Ψst values at each height, reached over 50 kPa/m, with the diurnal maxima generally occurring between 1500 and 1600 h. When Ψst gradients were averaged over 24 h it was found that, unless temperatures were extremely high or the foliage was wet, the average diurnal gradient was linearly related to the average vapour pressure deficit. From this relationship the average diurnal gradient during two earlier summers was estimated to be 23 kPa/m. The forest transpiration rate during this time was estimated to be 4.1 mm/day and when these data, together with sapwood area data, were put into a simple tree transpiration model, the relative conductivity of the sapwood was found to be approximately 7.9 × 10-12 m2.
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Tuğba Küçükseyhan. "Optimal control of the gradient systems." GSC Advanced Research and Reviews 21, no. 2 (2024): 382–91. http://dx.doi.org/10.30574/gscarr.2024.21.2.0453.
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In this paper we consider the optimal control problems governed by the gradient systems for the Ginzburg-Landau free energy where denotes a potential function and ε is the diffusivity. One example of gradient systems are the Schlögl equation arising in chemical waves with a quartic potential function F(y). Gradient systems are characterized by energy decreasing property . Numerical integrators that preserve the energy decreasing property in the discrete setting are called energy or gradient stable. It is known that the implicit Euler method is first order unconditionally energy stable method. The only second order unconditionally energy stable method is the average vector field (AVF) method. We discretize the gradients systems by discontinuous Galerkin method in space and by AVF integrator in time. We solve optimal control problems for the Schlögl equation with traveling and spiraling waves using sparse and regularized controls .
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Shlyonsky, Vadim. "Ion permeability of artificial membranes evaluated by diffusion potential and electrical resistance measurements." Advances in Physiology Education 37, no. 4 (2013): 392–400. http://dx.doi.org/10.1152/advan.00068.2013.
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In the present article, a novel model of artificial membranes that provides efficient assistance in teaching the origins of diffusion potentials is proposed. These membranes are made of polycarbonate filters fixed to 12-mm plastic rings and then saturated with a mixture of creosol and n-decane. The electrical resistance and potential difference across these membranes can be easily measured using a low-cost volt-ohm meter and home-made Ag/AgCl electrodes. The advantage of the model is the lack of ionic selectivity of the membrane, which can be modified by the introduction of different ionophores to the organic liquid mixture. A membrane treated with the mixture containing valinomycin generates voltages from −53 to −25 mV in the presence of a 10-fold KCl gradient (in to out) and from −79 to −53 mV in the presence of a bi-ionic KCl/NaCl gradient (in to out). This latter bi-ionic gradient potential reverses to a value from +9 to +20 mV when monensin is present in the organic liquid mixture. Thus, the model can be build stepwise, i.e., all factors leading to the development of diffusion potentials can be introduced sequentially, helping students to understand the quantitative relationships of ionic gradients and differential membrane permeability in the generation of cell electrical signals.
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O’Brien, Enda. "Balancing the Potential Vorticity Seesaw: The Bare Essentials of Baroclinic Instability." Earth Systems and Environment 3, no. 3 (2019): 341–51. http://dx.doi.org/10.1007/s41748-019-00128-7.
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Abstract This paper bypasses the mathematical technicalities of baroclinic instability and tries to provide a more conceptual, mechanistic explanation for a phenomenon that is fundamentally important to the dynamics of the earth’s atmosphere and oceans. The standard conceptual picture of baroclinic instability is reviewed and stripped down to identify the most essential features. These are: (a) Regions with both positive and negative potential vorticity (PV) gradients, (b) separate Rossby wave perturbations in each region where PV gradients are of different signs, and (c) cooperative phase locking between Rossby waves in regions of opposite PV gradient, which renders them stationary, and allows them to amplify to reduce the background temperature gradient (or baroclinicity) while still conserving total PV. These three factors constitute the “counterpropagating Rossby wave” perspective, and suggest the heuristic picture of a “PV seesaw”, which remains balanced as the instabilities (i.e., the phase-locked PV wave perturbations) grow out along opposite limbs. After reviewing the key characteristics of PV and Rossby waves, the process is illustrated by the spontaneous onset of baroclinic instability during spin-up of the Held–Suarez dynamical core atmospheric model.
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Heinson, Graham, Antony White, David Robinson, and Nader Fathianpour. "Marine self-potential gradient exploration of the continental margin." GEOPHYSICS 70, no. 5 (2005): G109—G118. http://dx.doi.org/10.1190/1.2057981.
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The self-potential (SP) method for mineral exploration is seldom used on land, primarily because of electrode noise problems and nonunique interpretations. Marine measurements of the horizontal gradient of the SP field, on the other hand, are relatively simple to make with an array of electrodes towed behind a ship. With low ship speeds of 5 to 10 km/hour, dense spatial sampling (∼1 m) can be obtained with resolution of better than 1 μV/m. In this paper we report on gradient SP data recorded on the continental shelf of South Australia by a horizontal array of towed electrodes approximately 20 m above the seafloor. Ocean waves and swells with periods of 5 to 15 s yielded large amplitude signals ±20 μV/m, but subseafloor mineralization produced SP gradient anomalies of ±50 μV/m and widths of 2 km or more in a number of parallel traverses. Integrating the observed SP gradients along each line delineated SP anomalies of amplitude up to −100 mV. Self-potential and magnetic anomaly data show limited spatial correlation and have different wavelengths, suggesting that SP sources are probably nonferrous minerals, such as graphite, and are deeper than the magnetic sources. The source of the SP signal is probably reduction-oxidation (redox) potential ([Formula: see text]) variations across a conducting body below the seafloor. We approximate the source as being two dimensional and find the most probable locations of line sources by an image reconstruction method. Numerical finite-element modeling of more realistic source regions suggests shallow, easterly dipping (∼15°) conductors of 1 Ω.m in the uppermost 2 km.
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Baggett, Cory, and Sukyoung Lee. "Arctic Warming Induced by Tropically Forced Tapping of Available Potential Energy and the Role of the Planetary-Scale Waves." Journal of the Atmospheric Sciences 72, no. 4 (2015): 1562–68. http://dx.doi.org/10.1175/jas-d-14-0334.1.
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Abstract One of the challenging tasks in climate science is to understand the equator-to-pole temperature gradient. The poleward heat flux generated by baroclinic waves is known to be central in reducing the equator-to-pole temperature gradient from a state of radiative–convective equilibrium. However, invoking this relationship to explain the wide range of equator-to-pole temperature gradients observed in past climates is challenging because baroclinic waves tend to follow the flux–gradient relationship such that their poleward heat flux is proportional to the equator-to-pole temperature gradient and zonal available potential energy (ZAPE). With reanalysis data, the authors show the existence of poleward heat transport by planetary-scale waves that are independent of the flux–gradient relationship and baroclinic instability. This process arises from a forced tapping of atmospheric ZAPE by planetary-scale waves that are triggered by enhanced tropical convection over the Pacific warm pool region. The Rossby waves excited by this tropical convection propagate northeastward over the Pacific Ocean and constructively interfere with the climatological stationary waves at higher latitudes. During polar night, when the current warming is most rapid, the forced tapping of ZAPE by planetary-scale waves produces a substantially greater warming than that by the synoptic-scale eddy fluxes that presumably arise from baroclinic instability.
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Iguchi, Yoshiaki, Hirofumi Yamanami, and Jiro Hirao. "Reduction of Wustite in Oxygen-Potential Gradient." Journal of the Japan Institute of Metals 49, no. 5 (1985): 351–56. http://dx.doi.org/10.2320/jinstmet1952.49.5_351.
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Martin, Manfred. "Oxygen Potential Gradient Induced Degradation of Oxides." Journal of the Korean Ceramic Society 49, no. 1 (2012): 29–36. http://dx.doi.org/10.4191/kcers.2012.49.1.029.
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Chen, Kangkang, Xingjian Dong, Zhike Peng, and Guang Meng. "Reconfigurable topological gradient metamaterials and potential applications." Thin-Walled Structures 205 (December 2024): 112572. http://dx.doi.org/10.1016/j.tws.2024.112572.
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Xiong, Qi, and Zhenqiu Zhang. "Gradient potential estimates for elliptic obstacle problems." Journal of Mathematical Analysis and Applications 495, no. 1 (2021): 124698. http://dx.doi.org/10.1016/j.jmaa.2020.124698.
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Jiang, Longfei, Xiangxiang Zhu, Pengze Li, Binye Chen, Shaoyu Zhang, and Xufei Zhu. "Study on potential gradient in Ti anodization." Electrochemistry Communications 154 (September 2023): 107546. http://dx.doi.org/10.1016/j.elecom.2023.107546.
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Rajendran, V. M., J. M. Harig, and K. Ramaswamy. "Characteristics of glycyl-L-proline transport in intestinal brush-border membrane vesicles." American Journal of Physiology-Gastrointestinal and Liver Physiology 252, no. 2 (1987): G281—G286. http://dx.doi.org/10.1152/ajpgi.1987.252.2.g281.
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A proton-peptide symport mechanism has been postulated for transport of dipeptides in rabbit intestinal and renal brush-border membrane vesicles (BBMV). We have investigated the effects of a transmembrane potential (in mouse) and an inwardly directed proton gradient (in mouse, rabbit, and human) on the transport of glycyl-L-proline in intestinal BBMV. Membrane potential alterations, induced by permeant anions or generated by a K+-diffusion potential in the presence of valinomycin, did not accelerate the uptake of glycyl-L-proline. In contrast, in parallel experiments the uptake of D-glucose, whose cotransport system is electrogenic, was markedly increased by an interior negative membrane potential. Thus the transport of glycyl-L-proline in mouse intestinal BBMV is not electrogenic. Further studies on the effect of a proton gradient (extravesicular pH 5.5; intravesicular pH 7.5) on transport of glycyl-L-proline revealed an absence of stimulation of glycyl-L-proline transport and lower uptake rates in the presence of a proton gradient. The simultaneous presence of an interior negative membrane potential and an inwardly directed proton gradient did not accelerate the transport of glycyl-L-proline. These results demonstrate that the transport of glycyl-L-proline in mouse intestinal BBMV is neither electrogenic nor energized by an inwardly directed proton gradient. Likewise, pH gradients do not stimulate glycyl-L-proline uptake in either rabbit or human BBMV.
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Diening, Lars, та Franz Gmeineder. "Continuity Points Via Riesz Potentials for ℂ-Elliptic Operators". Quarterly Journal of Mathematics 71, № 4 (2020): 1201–18. http://dx.doi.org/10.1093/qmathj/haaa027.
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Abstract We establish a Riesz potential criterion for Lebesgue continuity points of functions of bounded $\mathbb{A}$-variation, where $\mathbb{A}$ is a $\mathbb{C}$-elliptic differential operator of arbitrary order. This result generalizes a potential criterion that is known for full gradients to the case where full gradient estimates are not available by virtue of Ornstein’s non-inequality.
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Hennig, Theresa, and Michael Kühn. "Potential Uranium Migration within the Geochemical Gradient of the Opalinus Clay System at the Mont Terri." Minerals 11, no. 10 (2021): 1087. http://dx.doi.org/10.3390/min11101087.
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Transport properties of potential host rocks for nuclear waste disposal are typically determined in laboratory or in-situ experiments under geochemically controlled and constant conditions. Such a homogeneous assumption is no longer applicable on the host rock scale as can be seen from the pore water profiles of the potential host rock Opalinus Clay at Mont Terri (Switzerland). The embedding aquifers are the hydro-geological boundaries, that established gradients in the 210 m thick low permeable section through diffusive exchange over millions of years. Present-day pore water profiles were confirmed by a data-driven as well as by a conceptual scenario. Based on the modelled profiles, the influence of the geochemical gradient on uranium migration was quantified by comparing the distances after one million years with results of common homogeneous models. Considering the heterogeneous system, uranium migrated up to 24 m farther through the formation depending on the source term position within the gradient and on the partial pressure of carbon dioxide pCO2 of the system. Migration lengths were almost equal for single- and multicomponent diffusion. Differences can predominantly be attributed to changes in the sorption capacity, whereby pCO2 governs how strong uranium migration is affected by the geochemical gradient. Thus, the governing parameters for uranium migration in the Opalinus Clay can be ordered in descending priority: pCO2, geochemical gradients, mineralogical heterogeneity.
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Laakso, H., T. L. Aggson, and R. F. Pfaff. "Plasma gradient effects on double-probe measurements in the magnetosphere." Annales Geophysicae 13, no. 2 (1995): 130–46. http://dx.doi.org/10.1007/s00585-995-0130-z.
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Abstract. The effects on double-probe electric field measurements induced by electron density and temperature gradients are investigated. We show that on some occasions such gradients may lead to marked spurious electric fields if the probes are assumed to lie at the same probe potential with respect to the plasma. The use of a proper bias current will decrease the magnitude of such an error. When the probes are near the plasma potential, the magnitude of these error signals, ∆E, can vary as ∆E ~ Te(∆ne/ne)+0.5∆Te, where Te is the electron temperature, ∆ne/ne the relative electron density variation between the two sensors, and ∆Te the electron temperature difference between the two sensors. This not only implies that the error signals will increase linearly with the density variations but also that such signatures grow with Te, i.e., such effects are 10 times larger in a 10-eV plasma than in a 1-eV plasma. This type of error is independent of the probe separation distance provided the gradient scale length is much larger than this distance. The largest errors occur when the probes are near to the plasma potential. At larger positive probe potentials with respect to the plasma potential, the error becomes smaller if the probes are biased, as is usually the case with spherical double-probe experiments in the tenuous magnetospheric plasmas. The crossing of a plasma boundary (like the plasmapause or magnetopause) yields an error signal of a single peak. During the crossing of a small structure (e.g., a double layer) the error signal appears as a bipolar signature. Our analysis shows that errors in double-probe measurements caused by plasma gradients are not significant at large scale (»1 km) plasma boundaries, and may only be important in cases where small-scale (<1 km), internal gradient structures exist. Bias currents tailored for each plasma parameter regime (i.e., variable bias current) would o1q1improve the double-probe response to gradient effects considerably.
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Bachman, Scott D. "A Geometric Perspective on the Modulation of Potential Energy Release by a Lateral Potential Vorticity Gradient." Fluids 5, no. 3 (2020): 142. http://dx.doi.org/10.3390/fluids5030142.
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The release of available potential energy by growing baroclinic instability requires the slope of the eddy fluxes to be shallower than that of mean density surfaces, where the amount of energy released depends on both the flux angle and the distance of fluid parcel excursions against the background density gradient. The presence of a lateral potential vorticity (PV) gradient is known to affect the growth rate and energy release by baroclinic instability, but often makes the mathematics of formal linear stability analysis intractable. Here the effects of a lateral PV gradient on baroclinic growth are examined by considering its effects on the slope of the eddy fluxes. It is shown that the PV gradient systematically shifts the unstable modes toward higher wavenumbers and creates a cutoff to the instability at large scales, both of which steepen the eddy flux angle and limit the amount of energy released. This effect may contribute to the severe inhibition of baroclinic turbulence in systems dominated by barotropic jets, making them less likely to transition to turbulence-dominated flow regimes.
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Kamalova, N. S., N. N. Matveev, N. Yu Evsikova, and V. I. Lisitsyn. "Dynamics of potential difference changes in a biocomposite microsection for different temperature gradients." Известия Российской академии наук. Серия физическая 87, no. 9 (2023): 1322–26. http://dx.doi.org/10.31857/s0367676523702320.
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The method of formalized modeling revealed the complex nature of the dependence of the parameters of the process of rearrangement of the biocomposite microstructure on the temperature gradient. Based on the analysis of the dynamics of changes in the potential difference formed along the thickness of the birch wood microcut, the parameters of the biocomposite polarization process for various temperature gradients have determined.
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Lind, Kara R., Oskar Siemianowski, Bin Yuan, et al. "Evidence for root adaptation to a spatially discontinuous water availability in the absence of external water potential gradients." Proceedings of the National Academy of Sciences 118, no. 1 (2020): e2012892118. http://dx.doi.org/10.1073/pnas.2012892118.
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We hereby show that root systems adapt to a spatially discontinuous pattern of water availability even when the gradients of water potential across them are vanishingly small. A paper microfluidic approach allowed us to expose the entire root system ofBrassica rapaplants to a square array of water sources, separated by dry areas. Gradients in the concentration of water vapor across the root system were as small as 10−4⋅mM⋅m−1(∼4 orders of magnitude smaller than in conventional hydrotropism assays). Despite such minuscule gradients (which greatly limit the possible influence of the well-understood gradient-driven hydrotropic response), our results show that 1) individual roots as well as the root system as a whole adapt to the pattern of water availability to maximize access to water, and that 2) this adaptation increases as water sources become more rare. These results suggest that either plant roots are more sensitive to water gradients than humanmade water sensors by 3–5 orders of magnitude, or they might have developed, like other organisms, mechanisms for water foraging that allow them to find water in the absence of an external gradient in water potential.
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Gibson, A. C., H. W. Calkin, D. O. Raphael, and P. S. Nobel. "Water relations and xylem anatomy of ferns." Proceedings of the Royal Society of Edinburgh. Section B. Biological Sciences 86 (1985): 81–92. http://dx.doi.org/10.1017/s0269727000007995.
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SynopsisThe entire soil-plant-atmosphere continuum must be analysed to elucidate how xylem anatomy relates to water flow in plants. Measurements of water potential gradients and volume of water flow per unit time are needed to obtain values of hydraulic conductance per unit length. By comparing values of hydraulic conductance per unit length along the plant, the regions where xylem structure restricts water flow can be determined. Previous studies of fern water relations demonstrated that very large water potential gradients occurring in stipes of certain ferns were closely correlated with reduced conducting area of stipe xylem. A new study on Cyrtomium falcatum showed that the water potential gradient was relatively small and constant along the stipe and rachis; however, a much larger gradient occurred from the rachies into the pinnae. Hydraulic conductance per unit length varied with the leaf area to be supplied, leading to the fairly constant water potential gradient along the rachis.. The measured hydraulic conductance per unit length was only half the value predicted from the Hagen-Poiseuille equation. Although the Hagen-Poiseuille equation overestimated the measured value by a factor of 2, it did support the assumption that conduit number and lumen diameter are the principal determinants of water conductance in the xylem.
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Nakamura, Noboru, and Da Zhu. "Formation of Jets through Mixing and Forcing of Potential Vorticity: Analysis and Parameterization of Beta-Plane Turbulence." Journal of the Atmospheric Sciences 67, no. 9 (2010): 2717–33. http://dx.doi.org/10.1175/2009jas3159.1.
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Abstract Formation of multiple jets in forced beta-plane turbulence is studied from the perspective of nonuniform nonconservative arrangement of potential vorticity (PV). Numerical simulations are analyzed to show that mixing and forcing reinforce jets by concentrating PV gradients at the axes of prograde jets. Based on the formalism developed in the companion paper, the nonconservative driving of jets is diagnosed and parameterized through the diffusive flux of PV and the source of wave activity. It is found that the two terms nearly balance on a long time scale, and they are both strongly anticorrelated with the PV gradient, which suggests that PV controls the nonconservative processes and that these processes could be parameterized as functions of the PV gradient. The flux is modeled using the effective diffusivity formula recently obtained by Ferrari and Nikurashin. Consistent with the PV barrier concept, the nonlinear diffusivity is a decreasing function of the squared PV gradient and agrees well with the diffusivity diagnosed from the numerical simulation. The source term is assumed to be inversely proportional to the PV gradient. The parameterization gives rise to a nonlinear partial differential equation (PDE) for the mean flow. A finite-difference model of the PDE predicts formation of a piecewise linear PV (staircase) and piecewise parabolic jets from a near-uniform initial condition when anisotropy and mixing of the flow are sufficiently strong. The origin of the discontinuities is antidiffusive instability of PV gradients, and although nonlinearity allows the discrete model to integrate stably, the solution is sensitive to the initial condition and resolution. The emerging jets in the 1D model have similar characteristics to those in the numerical simulation, but the details of the transient behavior are distinct. Similar discrete models of ill-posed PDEs in which discontinuities form also appear in image processing and granular matter dynamics.
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Martin, M., and S. Dorris. "Impurity Diffusion in a Chemical Potential Gradient (II): Iron Tracer Diffusion in Cobalt Oxide in an Oxygen Potential Gradient." Berichte der Bunsengesellschaft für physikalische Chemie 91, no. 8 (1987): 779–85. http://dx.doi.org/10.1002/bbpc.19870910804.
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Luo, Dehai, Xiaodan Chen, James Overland, Ian Simmonds, Yutian Wu, and Pengfei Zhang. "Weakened Potential Vorticity Barrier Linked to Recent Winter Arctic Sea Ice Loss and Midlatitude Cold Extremes." Journal of Climate 32, no. 14 (2019): 4235–61. http://dx.doi.org/10.1175/jcli-d-18-0449.1.
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Abstract A winter Eurasian cooling trend and a large decline of winter sea ice concentration (SIC) in the Barents–Kara Seas (BKS) are striking features of recent climate changes. The question arises as to what extent these phenomena are related. A mechanism is presented that establishes a link between recent winter SIC decline and midlatitude cold extremes. Such potential weather linkages are mediated by whether there is a weak north–south gradient of background tropospheric potential vorticity (PV). A strong background PV gradient, which usually occurs in North Atlantic and Pacific Ocean midlatitudes, acts as a barrier that inhibits atmospheric blocking and southward cold air intrusion. Conversely, atmospheric blocking is more persistent in weakened PV gradient regions over Eurasia, Greenland, and northwestern North America because of weakened energy dispersion and intensified nonlinearity. The small climatological PV gradients over mid- to high-latitude Eurasia have become weaker in recent decades as BKS air temperatures show positive trends due to SIC loss, and this has led to more persistent high-latitude Ural-region blocking. These factors contribute to increased cold winter trend in East Asia. It is found, however, that in years when the winter PV gradient is small the East Asian cold extremes can even occur in the absence of large negative SIC anomalies. Thus, the magnitude of background PV gradient is an important controller of Arctic–midlatitude weather linkages, but it plays no role if Ural blocking is not present. Thus, the “PV barrier” concept presents a critical insight into the mechanism producing cold Eurasian extremes and is hypothesized to set up such Arctic–midlatitude linkages in other locations.
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Calonge, M. L., A. Ilundain, and J. Bolufer. "Glycyl-L-sarcosine transport by ATP-depleted isolated enterocytes from chicks." American Journal of Physiology-Gastrointestinal and Liver Physiology 259, no. 5 (1990): G775—G780. http://dx.doi.org/10.1152/ajpgi.1990.259.5.g775.
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Normally energized and ATP-depleted isolated chicken enterocytes have been used to investigate the energetics of intestinal glycyl-L-sarcosine (Gly-Sar) transport, and the results were compared with those obtained for 3-O-methyl-D-glucose (3-OMG) active transport, which is known to be energized by the electrochemical Na+ gradient. The results show that even though Gly-Sar had no effect on Na+ efflux from labeled (22Na) enterocytes, 20 mM L-leucine and 20 mM 3-OMG increased the rate constant of Na+ efflux by 34 and 76%, respectively. In ATP-depleted cells 3-OMG was accumulated in response to experimentally imposed inward Na+ gradients; however, Gly-Sar was not accumulated. In the absence of Na+, an inward proton gradient slightly increased Gly-Sar uptake, although no transient accumulation was observed. An increase in membrane potential by replacement of Cl- by NO3- or by imposition of an outward K+ gradient in the presence of valinomycin stimulated both 3-OMG and Gly-Sar uptake, even in the absence of either H+ or Na+ gradient. When in addition to a K+ diffusion potential, a Na+ gradient was present, 3-OMG transient accumulation was further increased (approximately 2-fold over equilibrium value), and Gly-Sar uptake showed the same pattern as that observed when only membrane potential was present. However, in the presence of an outward K+ diffusion potential and an inward H+ gradient Gly-Sar was stimulated approximately threefold, clearly showing a significant overshoot, whereas 3-OMG was not transiently accumulated.
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Yuval, Janni, and Yohai Kaspi. "The Effect of Vertical Baroclinicity Concentration on Atmospheric Macroturbulence Scaling Relations." Journal of the Atmospheric Sciences 74, no. 5 (2017): 1651–67. http://dx.doi.org/10.1175/jas-d-16-0277.1.
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Abstract Motivated by the expectation that under global warming upper-level meridional temperature gradients will increase while lower-level temperature gradients will decrease, the relations between the vertical structure of baroclinicity and eddy fields are investigated. The sensitivity of eddies and the relation between the mean available potential energy and eddy quantities are studied for cases where the vertical structure of the lapse rate and meridional temperature gradient are modified. To investigate this systematically, an idealized general circulation model with a Newtonian cooling scheme that has a very short relaxation time for the mean state and a long relaxation time for eddies is used. This scheme allows for any chosen zonally mean state to be obtained with good precision. The results indicate that for similar change in the lapse rate or meridional temperature gradient, eddies are more sensitive to changes in baroclinicity where it is already large. Furthermore, when the vertical structure of the lapse rate or the meridional temperature gradient is modified, there is no universal linear relation between the mean available potential energy and eddy quantities.
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Reenstra, W. W., and J. G. Forte. "Characterization of K+ and Cl- conductances in apical membrane vesicles from stimulated rabbit oxyntic cells." American Journal of Physiology-Gastrointestinal and Liver Physiology 259, no. 5 (1990): G850—G858. http://dx.doi.org/10.1152/ajpgi.1990.259.5.g850.
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K+ and Cl- conductance pathways in apical membrane vesicles (SA vesicles) of stimulated oxyntic cells have been characterized. SA vesicles were prepared from rabbit fundic mucosa after stimulation of acid secretion with histamine. Conductive K+ and Cl- fluxes were assayed by several methods: by their effects on pH gradient formation by endogenous H(+)-K(+)-ATPase, by the protonophore-induced dissipation of preformed pH gradients, and by the effects of channel blockers. pH gradient formation by H(+)-K(+)-ATPase required K+ and was greatly reduced when the permeant anion chloride was replaced by gluconate or sulfate. In the presence of 75 mM K+, 1 mM Cl- was sufficient for generation of near maximal pH gradients, as was 5 mM K+ in the presence of 75 mM Cl-. At all K+ and Cl- concentrations tested, the ATP-generated formation of pH gradients was inhibited and the dissipation of these pH gradients stimulated by the protonophore tetrachlorosalicylanilide (TCS). Similar effects of TCS were also seen when Cl- was replaced by impermeant anions. Both processes were blocked by the K+ channel inhibitor Ba2+. The Ki for Ba2+ inhibition of pH gradient formation was 1.5 microM at 5 mM K+ and was proportional to the 3rd power of the K+ concentration. At 75 mM K+ the Cl- channel blocker diphenylamine-2-carboxylate inhibited ATP-dependent pH gradient formation when the Cl- concentration was 1 mM; however, when the Cl- concentration was greater than 5 mM no inhibition was observed. The membrane potential-sensitive dye DISC (5) was used to measure membrane potential generated by K+ gradients.(ABSTRACT TRUNCATED AT 250 WORDS)
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Khakdaman, Hamidreza, Yves Bourgault, and Marten Ternan. "A Mathematical Model of a Direct Propane Fuel Cell." Journal of Chemistry 2015 (2015): 1–13. http://dx.doi.org/10.1155/2015/102313.
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A rigorous mathematical model for direct propane fuel cells (DPFCs) was developed. Compared to previous models, it provides better values for the current density and the propane concentration at the exit from the anode. This is the first DPFC model to correctly account for proton transport based on the combination of the chemical potential gradient and the electrical potential gradient. The force per unit charge from the chemical potential gradient (concentration gradient) that pushes protons from the anode to the cathode is greater than that from the electrical potential gradient that pushes them in the opposite direction. By including the chemical potential gradient, we learn that the proton concentration gradient is really much different than that predicted using the previous models that neglected the chemical potential gradient. Also inclusion of the chemical potential gradient made this model the first one having an overpotential gradient (calculated from the electrical potential gradient) with the correct slope. That is important because the overpotential is exponentially related to the reaction rate (current density). The model described here provides a relationship between the conditions inside the fuel cell (proton concentration, overpotential) and its performance as measured externally by current density and propane concentration.
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Cardoso, A. F. S., O. Cavichia, M. Mollá, and L. Sánchez-Menguiano. "Analysis of the Internal Radial Gradient of Chemical Abundances in Spiral Galaxies from CALIFA." Astrophysical Journal 980, no. 1 (2025): 45. https://doi.org/10.3847/1538-4357/ad9eab.
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Abstract The study of chemical evolution is of paramount importance for understanding the evolution of galaxies. Models and observations propose an inside-out mechanism in the formation of spiral galaxy disks, implying a negative radial gradient of elemental abundances when represented on a logarithmic scale. However, in some instances, the observed chemical abundance gradients deviate from a single negative straight line, revealing inner drops or outer flattenings, particularly in more massive galaxies. This study analyzes oxygen abundance gradients in spiral galaxies based on observations from the Calar Alto Legacy Integral Field Area survey. Our focus is specifically on examining oxygen abundance gradient profiles, as obtained with data from H ii regions, with a special emphasis on the inner radial gradient. We employ an automated fitting procedure to establish correlations between the physical properties of galaxies and bulges and the presence of these inner drops, seeking potential explanations for these variations in gradient. We find that the different criteria used in the literature to distinguish H ii regions from other ionization sources in the galaxies, such as active galactic nuclei, significantly impact the results, potentially altering abundance gradient profiles and uncovering galaxies with distinct inner drops. Additionally, we analyze the abundance radial gradients to investigate the impact of diffuse ionized gas (DIG) decontamination on oxygen abundances over these inner drops. We observe that DIG, concentrated mainly in the central regions of galaxies, can modify oxygen abundance gradient profiles if left unaddressed.
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Mercier, Bertrand, Lionel Thomas, Benoit Tremblais, and Laurent David. "A Particle Based Approach For Improved Resolution PIV And TOMO-PIV Based On The Coherent Point Drift And The Affine Least-Squares Transformation." Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (July 8, 2024): 1–13. http://dx.doi.org/10.55037/lxlaser.21st.29.
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Particle Image Velocimetry (PIV) is a widely used method for flow diagnostics, but there is still potential for improvement, particularly in terms of velocity gradient estimation and computational cost when considering three-dimensional problems. This paper presents a framework that combines a Particle Tracking Velocity (PTV) approach with local gradient-based Eulerian reconstruction to improve PIV performance. The approach uses the Coherent Point Drift (CPD) method for particle pairing and introduces the Affine Least-Squares Transformation (ALST) for local deformation gradient estimation. The CPD method consists of pairing particles whose positions at two successive instants have been obtained from the images. The ALST estimates local deformation gradients, allowing the Eularian reconstruction of the velocity field. The effectiveness of the proposed method compared to traditional PIV algorithms is demonstrated by synthetic test cases in both 2D and 3D configurations. In 2D cases, the CPD+ALST approach outperforms standard PIV methods, especially in capturing local velocity gradients. In 3D cases, comparisons with TOMO-PIV show the improved performance of CPD+ALST in the context of locally large velocity gradients. However, the linear nature of ALST makes it less efficient than quadratic binning techniques. The study demonstrates the potential of CPD+ALST to improve velocity field reconstruction in complex flows.
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Allen, Robert B., and Robert K. Peet. "Gradient analysis of forests of the Sangre de Cristo Range, Colorado." Canadian Journal of Botany 68, no. 1 (1990): 193–201. http://dx.doi.org/10.1139/b90-026.
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Interrelationships between dominant compositional and environmental gradients were studied using 186 forest stands sampled on the east slope of the Sangre de Cristo Range, Colorado. Detrended correspondence analysis and detrended canonical correspondence analysis were used to analyze indirect and direct gradients, respectively. The dominant compositional gradient was strongly correlated with elevation. Increasing elevation was associated with decreasing soil pH and percent base saturation, and increasing total soil N. Ordination of stands stratified by elevation showed the major compositional gradient within each elevation class was strongly correlated with a topographic moisture index. Most soil variables correlated with this gradient in low and high elevation classes. In mid-elevation forests, a third compositional gradient correlated with soil pH, percent base saturation, and potential solar radiation. In these forests, Pinus contorta and Pseudotsuga menziesii were associated with acidic soils on north-facing slopes, whereas Populus tremuloides and Abies concolor were associated with base-rich soils on south-facing slopes. Ordination axes accounted for least variation in comparatively young mid-elevation forests. A plausible explanation is that the mid-elevation forests represent an unpredictable stage in forest development where competition has not yet had sufficient time to sort species along environmental gradients.