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Journal articles on the topic 'Negative Curvature Parameters'
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Wang, Liming, and Thomas J. McCarthy. "Capillary-bridge–derived particles with negative Gaussian curvature." Proceedings of the National Academy of Sciences 112, no. 9 (February 17, 2015): 2664–69. http://dx.doi.org/10.1073/pnas.1424383112.
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We report the preparation of millimeter-scale particles by thermal polymerization of liquid monomer capillary bridges to form catenoid-shaped particles that exhibit negative Gaussian curvature. The shape of the capillary bridges and resulting particles can be finely tuned using several addressable parameters: (i) the shape, size, and orientation of lithographic pinning features on the spanned surfaces; (ii) the distance between opposing support surfaces; and (iii) the lateral displacement (shear) of opposing features. The catenoid-shaped particles exhibit controllable optical properties as a result of their concave menisci, the shape of which can be easily manipulated. The particles self assemble in the presence of a condensing liquid (water) to form reversible neck-to-neck pairs and less reversible end-to-end aggregates. We argue that this approach could be scaled down to micrometer dimensions by fabricating an array of micrometer-scale particles. We also argue, with a discussion of dynamic wetting, that these particles will exhibit interesting anisotropic adhesive properties.
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Fomin, Yu D., N. V. Gribova, and V. N. Ryzhov. "Complex Phase Behavior of Systems with Negative Curvature Potentials." Defect and Diffusion Forum 277 (April 2008): 155–60. http://dx.doi.org/10.4028/www.scientific.net/ddf.277.155.
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The comprehensive computer simulation study of the phase diagram of the repulsive step potential system in three dimensions is represented. We show that the system with a simple purely repulsive isotropic potential demonstrates a number of unusual features. The maxima and minima on the melting curve are found for some regions of potential parameters. It is shown that the phase diagram in ρ-T plane includes two isostructural crystalline parts separated by the disordered phase which is amorphous at low enough temperatures. Phase diagram in the (P-T) plane shows that the transition to the amorphous state occurs approximately along the extrapolated spinodals. Structural FCC-BCC phase transition is found at high densities.
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Alagashev, G. K., A. D. Pryamikov, A. F. Kosolapov, A. N. Kolyadin, A. Yu Lukovkin, and A. S. Biriukov. "Impact of geometrical parameters on the optical properties of negative curvature hollow-core fibers." Laser Physics 25, no. 5 (April 8, 2015): 055101. http://dx.doi.org/10.1088/1054-660x/25/5/055101.
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Junesch, Juliane, Gustav Emilsson, Kunli Xiong, Shailabh Kumar, Takumi Sannomiya, Hudson Pace, Janos Vörös, Sang-Hyun Oh, Marta Bally, and Andreas B. Dahlin. "Location-specific nanoplasmonic sensing of biomolecular binding to lipid membranes with negative curvature." Nanoscale 7, no. 37 (2015): 15080–85. http://dx.doi.org/10.1039/c5nr04208a.
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Беляева, Ирина Николаевна, Игорь Константинович Кириченко, Олег Дмитриевич Пташный, Наталья Николаевна Чеканова, and Татьяна Александровна Ярхо. "NORMALIZATION OF CLASSICAL HAMILTONIAN SYSTEMS WITH TWO DEGREES OF FREEDOM." Physical and Chemical Aspects of the Study of Clusters, Nanostructures and Nanomaterials, no. 12() (December 15, 2020): 348–55. http://dx.doi.org/10.26456/pcascnn/2020.12.348.
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В работе исследовано семейство гамильтоновых систем с двумя степенями свободы. Расчетами сечений Пуанкаре показано, что при произвольных значениях параметров функции Гамильтона система является неинтегрируемой и в ней реализуется динамический хаос. Найдено, что для трех наборов параметров рассматриваемая система является интегрируемой, однако в одном интегрируемом случае при этих же значениях параметров на поверхности потенциальной энергии имеется область с отрицательной гауссовой кривизной, в то же время в двух других случаях интегрируемости при соответствующих значениях параметров областей с отрицательной гауссовой кривизной не имеется. Таким образом, наличие областей с отрицательной гауссовой кривизной на поверхности потенциальной энергии не достаточно для развития в системе глобального хаоса. Получена классическая нормальная форма для произвольных значений параметров. The family of the Hamiltonian systems with two degrees of freedom was investigated. The calculations of the Poincaré sections show that with arbitrary values of the parameters of the Hamilton function, the system is non-integrable and dynamic chaos is realized in it. For the three parameter sets, the system in question was found to be integrable, but shows that in one integrable case on the potential energy surface (PES) there are regions with the negative Gaussian curvature. It was found that in one integrable case for the same values of the parameters, the potential energy surface has a region with the negative Gaussian curvature. At the same time, in the other two cases, the domains with negative Gaussian curvature are not integrable for the corresponding values of the parameters. Thus, the presence of regions with negative Gaussian curvature on the potential energy surface is not enough for the development of the global chaos in the system. The classical normal form for arbitrary parameter values is obtained.
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Xu, Jin, Kui Yang, YiMing Shao, and GongYuan Lu. "An Experimental Study on Lateral Acceleration of Cars in Different Environments in Sichuan, Southwest China." Discrete Dynamics in Nature and Society 2015 (2015): 1–16. http://dx.doi.org/10.1155/2015/494130.
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In view of the tremendous improvements in the dynamic performance of automobiles and changes in the composition of drivers over the past several decades, it is valuable to examine the distribution of automobile’s lateral acceleration in new environments. The lateral accelerations, speeds, and trajectory curvatures of a passenger car on twelve highways with different design speeds and topographies were obtained. By synchronizing, matching, and counting, the distribution of the lateral acceleration was obtained, and the level of driving comfort was estimated. The10th,15th,50th,85th, and90thpercentile values of the lateral acceleration on three road types (six-lane road, four-lane road, and two-lane road) were found. Combined with scatter diagrams of the lateral acceleration over the curvature, the negative correlation between the lateral acceleration and the curvature was analyzed and interpreted. In addition, regression models of the lateral acceleration with the curvature for the three kinds of roads were established. Based on scatter diagrams of the lateral acceleration over the speed, regression models of the averageaydepending on the speed and the85thpercentileaydepending on the speed of passenger cars and buses were established. The research provides calculation parameters and a control basis for operating speed prediction, pavement material design, and maximum and minimum limit value determination for the superelevation ratios and curve radii.
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CHERN, DE-CHING, JAMES M. NESTER, and HWEI-JANG YO. "POSITIVE ENERGY TEST OF POINCARÉ GAUGE THEORY." International Journal of Modern Physics A 07, no. 09 (April 10, 1992): 1993–2003. http://dx.doi.org/10.1142/s0217751x92000879.
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The positive total energy test is applied to the Poincaré Gauge Theory of gravity. Both the asymptotically flat and asymptotically constant negative curvature case are considered. The test shows that in either case, the theory with generic values for the parameters is not viable.
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Huisman, A. E., and D. J. Brown. "Genetic parameters for bodyweight, wool, and disease resistance and reproduction traits in Merino sheep. 4. Genetic relationships between and within wool traits." Animal Production Science 49, no. 4 (2009): 289. http://dx.doi.org/10.1071/ea08173.
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The aim of this paper was to describe the genetic relationship among expressions at different ages of seven wool traits: greasy and clean fleece weights, fibre diameter, coefficient of variation of fibre diameter, staple length and strength, and mean fibre curvature. Genetic correlations among measurements at different ages for the same trait were moderate to high, and ranged from ~0.6 for both fleece weights to 0.9 and higher for mean fibre diameter and curvature. Generally, low to moderate genetic correlations (0.3–0.4) were estimated between fleece weights and fibre diameter, clean fleece weight and staple length, and fibre diameter and staple strength. Small positive genetic correlations (0.2) were estimated between greasy and clean fleece weight with fibre diameter coefficient of variation, and between fibre diameter and staple length. Mean fibre curvature had a negative genetic correlation (approximately –0.4) with most other wool traits, the exceptions were staple strength (~0.0) and coefficient of variation of fibre diameter (approximately –0.1). Fibre diameter, staple length and staple strength had negative genetic correlations with coefficient of variation of fibre diameter (–0.15, –0.10, and –0.61, respectively). The results indicate that for most wool traits only one measurement across ages is required to make accurate selection decisions. The relationships between traits are generally moderate to low suggesting that simultaneous genetic improvement is possible.
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Qiu, Dandan, Lei Luo, Songtao Wang, Bengt Ake Sunden, and Xinhong Zhang. "Analysis of heat transfer and fluid flow of a slot jet impinging on a confined concave surface with various curvature and small jet to target spacing." International Journal of Numerical Methods for Heat & Fluid Flow 29, no. 8 (August 5, 2019): 2885–910. http://dx.doi.org/10.1108/hff-07-2018-0354.
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Purpose This study aims to focus on the surface curvature, jet to target spacing and jet Reynolds number effects on the heat transfer and fluid flow characteristics of a slot jet impinging on a confined concave target surface at constant jet to target spacing. Design/methodology/approach Numerical simulations are used in this research. Jet to target spacing, H/B is varying from 1.0 to 2.2, B is the slot width. The jet Reynolds number, Rej, varies from 8,000 to 40,000, and the surface curvature, R2/B, varies from 4 to 20. Results of the target surface heat transfer, flow parameters and fluid flow in the concave channel are performed. Findings It is found that an obvious backflow occurs near the upper wall. Both the local and averaged Nusselt numbers considered in the defined region respond positively to the Rej. The surface curvature plays a positive role in increasing the averaged Nusselt number for smaller surface curvature (4-15) but affects little as the surface curvature is large enough (> 15). The thermal performance is larger for smaller surface curvature and changes little as the surface curvature is larger than 15. The jet to target spacing shows a negative effect in heat transfer enhancement and thermal performance. Originality/value The surface curvature effects are conducted by verifying the concave surface with constant jet size. The flow characteristics are first obtained for the confined impingement cases. Then confined and unconfined slot jet impingements are compared. An ineffective point for surface curvature effects on heat transfer and thermal performance is obtained.
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ITIN, YAKOV. "COFRAME TELEPARALLEL MODELS OF GRAVITY: EXACT SOLUTIONS." International Journal of Modern Physics D 10, no. 04 (August 2001): 547–73. http://dx.doi.org/10.1142/s0218271801001025.
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The superstring and superbrane theories include gravity as a necessary and fundamental part of a (future) unified field theory. Thus it is important to consider the alternative representations of general relativity as well as the alternative models of gravity.We study the coframe teleparallel theory of gravity with a most general quadratic Lagrangian. The coframe field on a differentiable manifold is a basic dynamical variable. A metric tensor as well as a metric compatible connection is generated by a coframe in a unique manner.The Lagrangian is a general linear combination of Weitzenböck's quadratic invariants with free dimensionless parameters ρ1, ρ2, ρ3. Every independent term of the Lagrangian is a global SO(1,3)-invariant 4-form. For a special choice of parameters which confirms with the local SO(1,3) invariance this theory gives an alternative description of Einsteinian gravity — teleparallel equivalent of GR.The field equations of the theory is studied by a "diagonal" coframe ansatz which is a subclass of a most general spherical-nsymmetric Einstein–Mayer ansatz. The restricted Lagrangian depends only on two free parameters ρ1, ρ3.We obtain a formula for scalar curvature of a pseudo-Riemannian manifold with a metric constructed from the static "diagonal" solution of the field equation. It is proved that the sign of the scalar curvature depends only on a relation between the parameters ρ1and ρ3. Thus by a specific choice of free parameters a manifold of positive or negative curvature can be obtained. The scalar curvature vanishes only for a subclass of models with ρ1=0. This subclass includes the teleparallel equivalent of GR.We obtain the explicit form of all spherically symmetric static solutions of the "diagonal" type to the field equations for an arbitrary choice of free parameters. We prove that the unique asymptotic-flat solution with Newtonian limit is the Schwarzschild solution that holds for a subclass of teleparallel models with ρ1=0. Thus the Yang–Mills-type term of the general quadratic coframe Lagrangian should be rejected.
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Seffen, K. A. "‘Morphing’ bistable orthotropic elliptical shallow shells." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, no. 2077 (August 2006): 67–83. http://dx.doi.org/10.1098/rspa.2006.1750.
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This study is concerned with the equilibrium shapes of orthotropic, elliptical plates and shells deforming elastically without initial stresses. The aim is to explore potential bistable configurations and their dependencies on material parameters and initial shape for elucidating novel morphing structures. A strain energy formulation gives way to a compact set of governing equations of deformation, which can be solved in closed form for some isotropic and orthotropic conditions. It is shown that bistability depends on the change in Gaussian curvature of the shell, in particular, for initially untwisted shells, isotropy precludes bistability, where there is negative initial Gaussian curvature, but orthotropic materials yield bistability irrespective of the sign of the initial Gaussian curvature. This improved range of performance stems from increasing the independent shear modulus, which imparts sufficient torsional rigidity to stabilize against perturbations in the deformed state. It is also shown that the range of bistable configurations for initially twisted shells generally diminishes as the degree of twist increases.
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Su, Xiu-Yun, Zhe Zhao, Jing-Xin Zhao, Li-Cheng Zhang, An-Hua Long, Li-Hai Zhang, and Pei-Fu Tang. "Three-Dimensional Analysis of the Curvature of the Femoral Canal in 426 Chinese Femurs." BioMed Research International 2015 (2015): 1–8. http://dx.doi.org/10.1155/2015/318391.
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Purpose. The human femur has long been considered to have an anatomical anterior curvature in the sagittal plane. We established a new method to evaluate the femoral curvature in three-dimensional (3D) space and reveal its influencing factors in Chinese population. Methods. 3D models of 426 femurs and the medullary canal were constructed using Mimics software. We standardized the positions of all femurs using 3ds Max software. After measuring the anatomical parameters, including the radius of femoral curvature (RFC) and banking angle, of the femurs using the established femur-specific coordinate system, we analyzed and determined the relationships between the anatomical parameters of the femur and the general characteristics of the population. Results. Pearson’s correlation analyses showed that there were positive correlations between the RFC and height (r=0.339, p<0.001) and the femoral length and RFC (r=0.369, p<0.001) and a negative correlation between the femoral length and banking angle (r=-0.223, p<0.001). Stepwise linear regression analyses showed that the most relevant factors for the RFC and banking angle were the femoral length and gender, respectively. Conclusions. This study concluded that the banking angle of the femur was significantly larger in female than in male.
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Dotera, Tomonari, Masakiyo Kimoto, and Junichi Matsuzawa. "Hard spheres on the gyroid surface." Interface Focus 2, no. 5 (January 18, 2012): 575–81. http://dx.doi.org/10.1098/rsfs.2011.0092.
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We find that 48/64 hard spheres per unit cell on the gyroid minimal surface are entropically self-organized. Striking evidence is obtained in terms of the acceptance ratio of Monte Carlo moves and order parameters. The regular tessellations of the spheres can be viewed as hyperbolic tilings on the Poincaré disc with a negative Gaussian curvature, one of which is, equivalently, the arrangement of angels and devils in Escher's Circle Limit IV .
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Xirouchakis, Paul C. "The Elastic-Softening Failure of Floating Beams." Journal of Ship Research 32, no. 01 (March 1, 1988): 37–43. http://dx.doi.org/10.5957/jsr.1988.32.1.37.
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The solution is presented for an infinite elastic-softening floating beam under a point load. The response depends on two nondimensional parameters: the negative stiffness coefficient that characterizes the descending part of the moment-curvature curve, and the nondimensional softening region half-length. The solution exhibits two important features that the elastic-perfectly plastic solution does not show. First, in certain ranges of parameters, the elastic-softening beam has a clearly defined maximum load carrying capacity. Second, in some other ranges of parameters, the elastic-softening beam has a minimum load or residual strength. The beam stiffens up upon further deformation due to the reactions of the water foundation. Critical softening parameters are calculated that separate stable from unstable behavior.
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Ameur, Houari. "Mixing of Shear Thinning Fluids in Cylindrical Tanks: Effect of the Impeller Blade Design and Operating Conditions." International Journal of Chemical Reactor Engineering 14, no. 5 (October 1, 2016): 1025–33. http://dx.doi.org/10.1515/ijcre-2015-0200.
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Abstract The 3D flow fields and power consumption within a cylindrical vessel stirred by a rotating turbine are numerically studied. Simulations are performed to determine the impact of changes in operating parameters on the mixing characteristics. Investigations are focused on effects of the impeller blade curvature, shaft speed and impeller rotational direction. The fluid simulated has a shear thinning behavior. Designing the blade in retreat shape seems very promising in term of power consumption since a reduction of Np is obtained with increasing blade curvature. In the positive rotational direction, the retreat bladed impeller yields highly radial flows with less power consumption than the straight bladed impeller. The 45° retreat blade gave an increase in the radial velocity by 39 %, compared with the straight blade. But, a better axial circulation is obtained with the straight blade. The comparison between the positive rotational direction (+w) and the negative rotational direction (–w) cases revealed that, a reduced mixing time can be obtained with a retreat bladed impeller operating in the negative rotational direction (–w), but with further power consumption.
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BAOWAN, D., B. J. COX, and J. M. HILL. "DETERMINATION OF JOIN REGIONS BETWEEN CARBON NANOSTRUCTURES USING VARIATIONAL CALCULUS." ANZIAM Journal 54, no. 4 (April 2013): 221–47. http://dx.doi.org/10.1017/s1446181113000217.
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AbstractWe review the work of the present authors to employ variational calculus to formulate continuous models for the connections between various carbon nanostructures. In formulating such a variational principle, there is some evidence that carbon nanotubes deform as in perfect elasticity, and rather like the elastica, and therefore we seek to minimize the elastic energy. The calculus of variations is utilized to minimize the curvature subject to a length constraint, to obtain an Euler–Lagrange equation, which determines the connection between two carbon nanostructures. Moreover, a numerical solution is proposed to determine the geometric parameters for the connected structures. Throughout this review, we assume that the defects on the nanostructures are axially symmetric and that the into-the-plane curvature is small in comparison to that in the two-dimensional plane, so that the problems can be considered in the two-dimensional plane. Since the curvature can be both positive and negative, depending on the gap between the two nanostructures, two distinct cases are examined, which are subsequently shown to smoothly connect to each other.
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Chirkov, Dmitry, and Sergey A. Pavluchenko. "Some aspects of the cosmological dynamics in Einstein–Gauss–Bonnet gravity." Modern Physics Letters A 36, no. 13 (April 13, 2021): 2150092. http://dx.doi.org/10.1142/s0217732321500929.
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We study some aspects of dynamical compactification scenario where stabilization of extra dimensions occurs due to the presence of Gauss–Bonnet term and nonzero spatial curvature. In the framework of the model under consideration, there exists two-stages scenario of evolution of a Universe: in the first stage, the space evolves from a totally anisotropic state to the state with three-dimensional (corresponding to our “real” world) expanding and [Formula: see text]-dimensional contracting isotropic subspaces; on the second stage, constant curvature of extra dimensions begins to play role and provide compactification of extra dimensions. It is already known that such a scenario is realizable when constant curvature of extra dimensions is negative. Here we show that a range of coupling constants for which exponential solutions with three-dimensional expanding and [Formula: see text]-dimensional contracting isotropic subspaces are stable is located in a zone where compactification solutions with positively curved extra space are unstable, so that two-stage scenario analogous to the one described above is not realizable. Also we study “nearly-Friedmann” regime for the case of arbitrary constant curvature of extra dimensions and describe new parametrization of the general solution for the model under consideration which provide elegant way of describing areas of existence over parameters space.
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Sadegh Amiri, Iraj, and Ahmed Nabih Zaki Rashed. "Simulative Study of Simple Ring Resonator Based Brewster Plate for Power System operation Stability." Indonesian Journal of Electrical Engineering and Computer Science 16, no. 2 (November 1, 2019): 1070. http://dx.doi.org/10.11591/ijeecs.v16.i2.pp1070-1076.
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<span>This study has outlined the simulative study of simple ring resonator based Brewster plate in the air. The obtained results are achieved with the variations of space length, curvature radius and phase angle of the </span><span>spherical mirror</span><span>. Beam radius criterion and stability parameters are measured with the variations of </span><span>refractive index</span><span> and thickness of Brewster plate in the air. The negative and positive effects of increasing operating parameters are observed on the performance of ring resonator system efficiency. </span>
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Liu, Dejun, Wei Li, Qiang Wu, Haoyu Zhao, Fengzi Ling, Ke Tian, Changyu Shen, et al. "Negative Curvature Hollow Core Fiber Based All-Fiber Interferometer and Its Sensing Applications to Temperature and Strain." Sensors 20, no. 17 (August 23, 2020): 4763. http://dx.doi.org/10.3390/s20174763.
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Negative curvature hollow core fiber (NCHCF) is a promising candidate for sensing applications; however, research on NCHCF based fiber sensors starts only in the recent two years. In this work, an all-fiber interferometer based on an NCHCF structure is proposed for the first time. The interferometer was fabricated by simple fusion splicing of a short section of an NCHCF between two singlemode fibers (SMFs). Both simulation and experimental results show that multiple modes and modal interferences are excited within the NCHCF structure. Periodic transmission dips with high spectral extinction ratio (up to 30 dB) and wide free spectral range (FSR) are produced, which is mainly introduced by the modes coupling between HE11 and HE12. A small portion of light guiding by means of Anti-resonant reflecting optical waveguide (ARROW) mechanism is also observed. The transmission dips, resulting from multimode interferences (MMI) and ARROW effect have a big difference in sensitivities to strain and temperature, thus making it possible to monitor these two parameters with a single sensor head by using a characteristic matrix approach. In addition, the proposed sensor structure is experimentally proven to have a good reproducibility.
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GURZADYAN, V. G., and A. A. KOCHARYAN. "A NEW VIEW ON THE PROBLEM OF ANISOTROPY OF THE COSMIC BACKGROUND RADIATION." International Journal of Modern Physics D 02, no. 01 (March 1993): 97–104. http://dx.doi.org/10.1142/s0218271893000088.
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The anisotropy properties of the Cosmic Microwave Background Radiation (CMB) are considered within the framework of the photon beam mixing effect developed earlier. The existence of an observable characteristic of the CMB is shown, namely the geometrical shape of anisotropy spots and their degree of complexity, which can contain unique information on cosmological parameters and the life history of the Universe. If future experiments (COBE and others) indicate such features of anisotropy maps, then one can have serious evidence for the negative curvature of the Universe.
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Liew, K. M., and C. W. Lim. "A Higher-Order Theory for Vibration Analysis of Curvilinear Thick Shallow Shells with Constrained Boundaries." Journal of Vibration and Control 1, no. 1 (January 1995): 15–39. http://dx.doi.org/10.1177/107754639500100103.
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This article presents the vibration analysis of thick doubly curved shallow shells having curvilinear planform. The Gaussian curvature of shell varies from positive (such as spherical) to negative (such as hyperbolic paraboloidal). The boundaries are constrained with either soft-simply supported or fully clamped edges. A higher-order shear deformation theory, which includes transverse shear strain and rotary inertia, is developed to model the vibration characteristics of the shell. The inclusion of Lamé parameters in the present formulation accounts for the presence of shell curvature and yields cubic transverse shear strain distribution in contrast with the existing quadratic expressions. A set of versatile, globally continuous shape functions is adopted in the Ritz numerical procedure to approximate the displacement and rotation fields. A set of new results for a wide range of shell configurations is presented with some selected contour and three-dimensional displacement mode shapes.
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Parmeggiani, Claudio. "Quantum fields and gravity: Expanding space-times." International Journal of Modern Physics A 35, no. 02n03 (January 30, 2020): 2040039. http://dx.doi.org/10.1142/s0217751x20400394.
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We discuss a proposal for a somewhat new formulation of quantum field theory (set in a four-dimensional manifold, the space-time) that includes an analysis of its implications for the evolution of Einstein-Friedmann cosmological models. The proposed theory displays two peculiar features: (i) a local Hilbert-Fock space is associated with each space-time point: we are dealing with a vector bundle whose fibers are Hilbert spaces; the operator-valued sections of the bundle are the quantum fields; (ii) the vacuum energy density is finite, being regularized in a space-time curvature dependent way, independently at each point. In fact everything is finite: self-masses, self-charges, quantum fluctuations: they depend on the space-time curvature and diverge only for a flat metric. In an Einstein-Friedmann model the vacuum (zero-point) energy density is consequently time-dependent and in general not negligible. Then it is shown that, for some choices of the parameters of the theory, the big-bang singularity is resolved and replaced by a bounce driven by the vacuum energy density, which becomes (very) large and negative near the bounce (negative by the contribution of the Fermi fields). But for large times (now, say) the Bose fields’ positive vacuum energy eventually overcomes the negative one and we are finally left with the present vacuum energy: positive and reasonably small.
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SOHBATZADEH, F., and S. P. HOSSEINI. "CONTROLLING THE REMOTE IONIZATION DISTANCE BY A LINEARLY CHIRPED FEMTOSECOND LASER PULSE IN AIR." Journal of Nonlinear Optical Physics & Materials 21, no. 04 (December 2012): 1250046. http://dx.doi.org/10.1142/s0218863512500464.
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In this paper, propagation of a linearly chirped laser pulse in air was investigated to control the remote ionization distance, numerically. Laser spot size and pulse length will be obtained versus effective initial parameters such as positive and negative initial chirp. It is seen that the initial chirp parameter and primary curvature of wave front have important role in focal distance variation and remote ionization. It was also shown that the group velocity dispersion (GVD) could alter and split the positively chirped laser pulse profile after nonlinear self-focusing.
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Ebadi, Zahra, and Behrouz Mirza. "Entanglement generation due to the background electric field and curvature of space–time." International Journal of Modern Physics A 30, no. 07 (March 5, 2015): 1550031. http://dx.doi.org/10.1142/s0217751x15500311.
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In Schwinger effect, quantum vacuum instability under the influence of an electric field leads to decay of vacuum into pairs of charged particles. We consider the entanglement of pair produced particles. We will show that the measure of entanglement depends on the geometry of space–time. Using the Schwinger pair production in curved space–time, dS2 and AdS2, we propose and demonstrate that the electric field can generate entanglement. In dS2 space–time, we study entanglement for scalar particles with zero spin in the absence and presence of a constant electric field. We show that the entanglement entropy depends on the choice of the α-vacua. But, for some values of the related parameters (mass, charge, scalar curvature, electric field), the entanglement entropy is independent of α. Also, we consider the generation of entanglement in the presence of a constant electric field for anti-de Sitter space–time. We will show that the positive (negative) curvature of space–time upgrades (degrades) the generated entanglement.
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Utaal, Shubhneek Kaur Dhillon, Rupali Chopra, and Nitin Batra. "Association of ocular biometric parameters with diabetic retinopathy." International Journal of Research in Medical Sciences 8, no. 10 (September 24, 2020): 3624. http://dx.doi.org/10.18203/2320-6012.ijrms20204240.
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Background: To study the association of ocular biometric parameters {Spherical equivalent (SE), Axial length (AL), Anterior chamber depth (ACD) and Corneal curvature (CC)} with diabetic retinopathy (DR) in subjects with Type 2 diabetes mellitus (DM).Methods: This prospective observational study was conducted in the Outpatient Department of Ophthalmology of a tertiary care teaching hospital in North India. The study included 100 subjects having various grades of DR as cases and 100 diabetics without DR as controls. The SE was assessed using objective autorefraction, while AL, CC and ACD were measured using the NIDEK AL SCAN. International Clinical Diabetic Retinopathy Disease Severity Scale was used for grading of DR.Results: A total of 181 eyes in the study group and 200 eyes in the control group were analysed. Progressive decrease in the mean AL was observed with the increasing severity of DR (p=0.017). Deeper ACD had a negative correlation with severity of DR (p=0.037). No statistically significant difference was observed for AL and ACD with the incidence of DR (p=0.147 and p=0.091 respectively). Likewise, there was no significant relation of DR with SE or CC.Conclusions: Longer AL and deep ACD were protective against progression to the severe forms of DR. However, there was no correlation of AL and ACD with the incidence of DR. The SE and CC were not found to be significant determinants for either development or severity of DR.
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Bolormaa, S., M. Olayemi, J. H. J. van der Werf, N. Baillie, F. Le Jambre, A. Ruvinsky, and S. W. Walkden-Brown. "Estimates of genetic and phenotypic parameters for production, haematological and gastrointestinal nematode-associated traits in Australian Angora goats." Animal Production Science 50, no. 1 (2010): 25. http://dx.doi.org/10.1071/an09035.
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Genetic parameters for liveweight (LWT), greasy fleece weight (GFW), mean fibre diameter (MFD), standard deviation of MFD (MFD-s.d.), mean fibre curvature (CURVE) percentage of medullated (%MED) and kemp (%KEMP) fibres, faecal worm egg count (WEC), packed cell volume (PCV), mean corpuscular volume (MCV) mean corpuscular haemoglobin content (MCHC), circulating anti-nematode IgG (IgG) and counts of circulating eosinophils (EOS), lymphocytes (LYM), neutrophils (NEU), basophils (BASO) and monocytes (MONO) up to 18 months of age were estimated in Australian Angora goats (608 animals, 14 sires 3 years of birth). Measurements were made during a period of natural parasite challenge up to 5 months of age, or following artificial challenge with 10 000 infective larvae of Trichostrongylus colubriformis at 5.25 months of age. Year of birth had a significant impact on production and parasite-associated traits at all ages studied. Sex had a marked effect on production and erythrocyte traits. Birth type had no effect on any traits in animals older than 6 months. Maternal effects were not significant except for LWT at 3, 5 and 6 months and for IgG at 3 months. Most production traits were highly (LWT, GFW, MFD, %MED) or moderately (CURVE, MFD-s.d.) heritable (range 0.17–0.59) with only %KEMP having a low heritability (0.02–0.14). The heritability estimates (±s.e.) for CURVE are novel for goats and ranged from 0.18 ± 0.09 at first shearing to 0.44 ± 0.14 at third shearing. Heritability estimates were low for WEC (0.02–0.16) and for specific IgG during natural infection (0.14–0.15) but higher for IgG following artificial challenge with T. colubriformis (0.42 ± 0.13). Of the haematological variables NEU and all red cell traits were highly heritable (0.45–0.71), LYM and MONO were moderately to highly heritable (0.31–0.55), and EOS was weakly to moderately heritable (0.06–0.28). Strong phenotypic correlations existed between production traits. MFD was positively correlated with GFW and negatively correlated with CURVE, indicating that finer fibres have a higher crimp or wave count. WEC had consistent negative phenotypic correlations with PCV, LYM and EOS, and positive correlations with NEU. Correlations with IgG were positive up to 5 months and negative thereafter. Phenotypic correlations between WEC and LWT as well as with GFW and MFD were negative. Heritability estimates for production traits were generally consistent with other studies. Haematological and fibre curvature findings are completely novel for Angora goats. Estimates of heritability for WEC fell in mid range of published findings for other goat breeds, and these results suggest that there is some scope for breeding for worm resistance in Angoras but the response is likely to be slow.
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Andriichuk, О. V., and S. O. Uzhehov. "THE FRACTURE TOUGHNESS OF THIN-WALLED COVER SHELLS HYPERBOLIC PARABOLOID SHAPED OF FERROCEMENT AND STEEL FIBER CONCRETE UNDER THE ACTION OF OPERATING LOADS." Ресурсоекономні матеріали, конструкції, будівлі та споруди, no. 37 (January 30, 2020): 89–96. http://dx.doi.org/10.31713/budres.v0i37.334.
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Experimental research of new materials and structures with improved parameters of strength, fracture toughness, bearing capacity and their lifetime in comparison with typical elements is an actual problem of building science.Nowadays there is a trend to design and use for buildings covering the new design solutions as the thin shells. One of the types of thin shells are Gaussian shells with negative curvature. It’s worth to note that in the last decade, a considerable number of researches of thin-walled structures made of steel fiber reinforced concrete were conducted, which confirmed the efficiency of its use to enhance their hardness, fracture toughness and thus longer life.The article presents the results of the authors’ experimental studies of fracture toughness of thin-walled cover structures with Gaussian negative curvature in the shape of hyperbolic paraboloid made of ferrocement and steel fiber reinforced concrete under the action of the operating load.The load application was carried out for ten steps, after each step the pause was for 15...20 min, during which the data of the strain-gauge station VNP-8 was recorded, using a microscope were measured and recorded the width of the cracks, deflections of the structure were measured etc.The external force was evenly-distributed to its applications and the impact was simulated according to the real conditions of construction use.The experimental part of the research was conducted at the laboratory of building materials and structures of Lutsk National Technical University. In scientific work carried out mapping and comparison of the obtained experimental results, carried out processing and analysis, presents the conclusions.During the researches it was found that the fracture toughness of thin-walled shell cover with Gaussian negative curvature in the shape of a hyperbolic paraboloid with dispersed reinforcement (steel fiber reinforced concrete) is higher than in the shell made of ferrocement. Accordingly, it can be argued about the increasing of the lifetime of steel fiber reinforced concrete shell covering in comparison with the ferrocement shell.
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Qiu, Shi, Jinhui Yuan, Xian Zhou, Feng Li, Qiwei Wang, Yuwei Qu, Binbin Yan, et al. "Hollow-Core Negative Curvature Fiber with High Birefringence for Low Refractive Index Sensing Based on Surface Plasmon Resonance Effect." Sensors 20, no. 22 (November 16, 2020): 6539. http://dx.doi.org/10.3390/s20226539.
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In this paper, a hollow-core negative curvature fiber (HC-NCF) with high birefringence is proposed for low refractive index (RI) sensing based on surface plasmon resonance effect. In the design, the cladding region of the HC-NCF is composed of only one ring of eight silica tubes, and two of them are selectively filled with the gold wires. The influences of the gold wires-filled HC-NCF structure parameters on the propagation characteristic are investigated by the finite element method. Moreover, the sensing performances in the low RI range of 1.20–1.34 are evaluated by the traditional confinement loss method and novel birefringence analysis method, respectively. The simulation results show that for the confinement loss method, the obtained maximum sensitivity, resolution, and figure of merit of the gold wires-filled HC-NCF-based sensor are −5700 nm/RIU, 2.63 × 10−5 RIU, and 317 RIU−1, respectively. For the birefringence analysis method, the obtained maximum sensitivity, resolution, and birefringence of the gold wires-filled HC-NCF-based sensor are −6100 nm/RIU, 2.56 × 10−5 RIU, and 1.72 × 10−3, respectively. It is believed that the proposed gold wires-filled HC-NCF-based low RI sensor has important applications in the fields of biochemistry and medicine.
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Mavromatis, Stergios, Nikiforos Stamatiadis, Basil Psarianos, and George Yannis. "Controlling Crest Vertical Curvature Rates Based on Variable Grade Stopping Sight Distance Calculation." Transportation Research Record: Journal of the Transportation Research Board 2521, no. 1 (January 2015): 31–44. http://dx.doi.org/10.3141/2521-04.
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Stopping sight distance (SSD) is a key control element that directly affects the suggested values of crucial road design parameters. Although there is a significant difference in SSD values between upgrades and downgrades, many design policies ignore the grade effect during vehicle braking on variable grades. Such a case occurs during the determination of crest vertical curvature rates in which the relevant SSD values are extracted assuming leveled road geometry. This paper investigates a possible deficiency of such an approach with regard to cases in which the length of the vertical curve exceeds the control SSD values. SSD calculation on variable grades during the braking process was addressed through a recently developed process that related the point mass model and the laws of mechanics. For a wide range of design speed values, charts illustrating the required SSDs were drawn as a function of negative ending grade values related to the control crest vertical curve rates adopted by AASHTO. The process revealed numerous SSD shortage areas for which revised crest vertical curvature rates were provided to grant SSD adequacy throughout the vehicles' braking process. This paper also aimed to provide designers with ready-to-use vertical design tools associated with amended vertical curvature rates to AASHTO's road functional classification as a function of the crest vertical curve's exit grade value.
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COLISTETE, R., J. C. FABRIS, S. V. B. GONÇALVES, and P. E. DE SOUZA. "BAYESIAN ANALYSIS OF THE CHAPLYGIN GAS AND COSMOLOGICAL CONSTANT MODELS USING THE SNe Ia DATA." International Journal of Modern Physics D 13, no. 04 (April 2004): 669–93. http://dx.doi.org/10.1142/s0218271804004852.
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The type Ia supernovae observational data are used to estimate the parameters of a cosmological model with cold dark matter and the Chaplygin gas. This exotic gas, which is characterized by a negative pressure varying with the inverse of density, represents in this model the dark energy responsible for the acceleration of the Universe. The Chaplygin gas model depends essentially on four parameters: the Hubble constant, the velocity of the sound of the Chaplygin gas, the curvature of the Universe and the fraction density of the Chaplygin gas and the cold dark matter. The Bayesian parameter estimation yields [Formula: see text] and [Formula: see text]. These and other results indicate that a Universe completely dominated by the Chaplygin gas is favoured, what reinforces the idea that the Chaplygin gas may unify the description for dark matter and dark energy, at least as the type Ia supernovae data are concerned. A closed and accelerating Universe is also favoured. The Bayesian statistics indicates that the Chaplygin gas model is more likely than the standard cosmological constant (ΛCDM) model at 55.3% confidence level when an integration on all free parameters is performed. Assuming the spatially flat curvature, this percentage mounts to 65.3%. On the other hand, if the density of dark matter is fixed at zero value, the Chaplygin gas model becomes more preferred than the ΛCDM model at 91.8% confidence level. Finally, the hypothesis of flat Universe and baryonic matter (Ωb0=0.04) implies a Chaplygin gas model preferred over the ΛCDM at a confidence level of 99.4%.
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Sadegh Amiri, Iraj, and Ahmed Nabih Zaki Rashed. "Numerical investigation of V shaped three elements resonator for optical closed loop system." Indonesian Journal of Electrical Engineering and Computer Science 16, no. 3 (December 1, 2019): 1392. http://dx.doi.org/10.11591/ijeecs.v16.i3.pp1392-1397.
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<span>This study have outlined numerical investigation of V shaped three element resonator. The stability parameter is measured against </span><span>back mirror curvature radius</span><span>, </span><span>back mirror phase angle</span><span>, </span><span>focusing length</span><span>, </span><span>focusing mirror phase angle</span><span>, </span><span>folding range</span><span> in both S plane and T plane. The stability parameter is changed in positive and negative trend under the operating system parameters. The stability parameter should be optimized in order to achieve high performance efficiency of resonator system. Beam radius variations are also measured versus </span><span>focusing range</span><span>, folding range, and back mirror phase angle. It is clear that the negative effects of increasing system parameters on beam radius variation in both S plane and T plane. </span>
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Wang, Ce, Shuo Li, and Jie Shan. "Non-Stationary Modeling of Microlevel Road-Curve Crash Frequency with Geographically Weighted Regression." ISPRS International Journal of Geo-Information 10, no. 5 (April 30, 2021): 286. http://dx.doi.org/10.3390/ijgi10050286.
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Vehicle crashes on roads are caused by many factors. However, the influence of these factors is not necessarily homogenous across locations, which is a challenge for non-stationary modeling approaches. To address this problem, this paper adopts two types of methods allowing parameters to fluctuate among observations, that is, the random parameter approach and the geographically weighted regression (GWR) approach. With road curvature, curve length, pavement friction, and traffic volume as independent variables, vehicle crash frequencies are modeled by two non-spatial methods, including the negative binomial (NB) model and random parameter negative binomial (RPNB), as well as three spatial methods (GWR approach). These models are calibrated in microlevel using a dataset of 9415 horizontal curve segments with a total length of 1545 kilometers for a period of three years (2016–2018) over the State of Indiana. The results revealed that the GWR approach can capture spatial heterogeneity and therefore significantly outperforms the conventional non-spatial approach. Based on the Akaike Information Criterion (AICc), geographically weighted negative binomial regression (GWNBR) was proved to be a superior approach for statewide microlevel crash analysis.
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Huisman, A. E., and D. J. Brown. "Genetic parameters for bodyweight, wool, and disease resistance and reproduction traits in Merino sheep. 3. Genetic relationships between ultrasound scan traits and other traits." Animal Production Science 49, no. 4 (2009): 283. http://dx.doi.org/10.1071/ea08172.
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The Australian Merino is the predominant genetic resource for both the lamb and sheep meat industries of Australia. There are very few studies that provide information on the relationships between wool and non-wool traits. This paper describes the genetic relationships between ultrasound scan traits and wool, disease resistance and reproduction traits in Merino sheep. Fleece weight and fibre diameter coefficient of variation were negatively correlated with ultrasound scanned fat and eye muscle depth (–0.10). Staple length, fibre curvature, and scrotal circumference were not correlated with scanned fat or eye muscle depth. Staple strength, number of lambs born and number of lambs weaned had a positive genetic correlation with fat and eye muscle depth (0.20–0.30). Faecal egg count had a negative genetic correlation with scanned fat (–0.10) and scanned eye muscle depth (–0.20). Results indicate that the combined improvement of carcass and wool characteristics in Merino sheep is possible.
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GUMRUKCUOGLU, A. E., C. LIN, and S. MUKOHYAMA. "SELF-ACCELERATING UNIVERSE IN NONLINEAR MASSIVE GRAVITY." Modern Physics Letters A 28, no. 03 (January 23, 2013): 1340016. http://dx.doi.org/10.1142/s0217732313400166.
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We discuss the self-accelerating universe solutions in the framework of the potentially ghost-free, nonlinear massive gravity theory recently proposed by de Rham–Gabadadze–Tolley. The theory allows general Friedmann–Robertson–Walker solutions with negative curvature. The contribution of the mass terms at the background level is an effective cosmological constant term depending on the parameters of the theory. We also discuss the cosmological perturbations in these backgrounds, as well as similar solutions of the extended versions of the theory; the actions of the scalar and vector degrees do not undergo a modification with respect to general relativity, while the two polarizations of gravity waves acquire a time-dependent effective mass term. This may lead to a modification of the stochastic gravitational wave spectrum.
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Huisman, A. E., and D. J. Brown. "Genetic parameters for bodyweight, wool, and disease resistance and reproduction traits in Merino sheep. 2. Genetic relationships between bodyweight traits and other traits." Australian Journal of Experimental Agriculture 48, no. 9 (2008): 1186. http://dx.doi.org/10.1071/ea08120.
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The Australian Merino is the predominant genetic resource for both the prime lamb and sheep meat industries of Australia. There are very few studies that provide good information on the relationships between wool and non-wool traits. The objective of this paper was to describe genetic relationships within bodyweight traits and between bodyweight and other traits recorded in Merino sheep. The genetic correlation between bodyweight, fleece weight and fibre diameter was positive (0.1 to 0.2). While fibre diameter coefficient of variation, staple length, staple strength, mean fibre curvature, and faecal egg count were not correlated with bodyweight. Scrotal circumference (0.4), number of lambs born (0.1), and number of lambs weaned (0.1) were positively correlated with bodyweight. Results indicate that selection for an increase in bodyweight will have a positive effect on eye muscle depth, fleece weight, and reproduction traits, while selection for an increase in bodyweight will have a negative effect on fibre diameter and fibre diameter coefficient of variation.
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Jin, Long, Zhiqiang Yang, and Qiang Zhang. "Properties of Gaussian Beam Propagating in Ring Resonator Sensor." International Journal of Optics 2019 (March 3, 2019): 1–10. http://dx.doi.org/10.1155/2019/3573976.
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In this paper, we deduce the paraxial analytical expression for the Gaussian beam propagating in the sandwich slab system which contained double negative material based on light transfer matrix and generalized Huygens-Fresnel integral equation; the evolution properties of emerging Gaussian beam contour graph intensity distribution on the receiver plane, the relation between beam spot size and negative refractive index coefficient, and beam side transmission view in slab system changed with three negative refractive index parameters are illustrated through numerical examples. What is more, we propose a ring resonator sensor to measure the concentration of NaCl solution on the basis of above theory, of which the operating principle is deliberatively analyzed, the influence of the concave mirror curvature radius on the emerging beam evolution is acquired, the functional relation between the normalized central intensity of the emerging beam, the beam spot size, and NaCl solution concentration is further developed by fit linear method, and the mathematical statistics results reach high precision and linearity. It is expected that the proposed ring resonator sensor and the corresponding conclusions can be useful for precise optical measurement, especially for food safety inspection and medical services of health care.
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Johnson, R. A., and D. J. Oh. "Analytic embedded atom method model for bcc metals." Journal of Materials Research 4, no. 5 (October 1989): 1195–201. http://dx.doi.org/10.1557/jmr.1989.1195.
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The requirements for fitting bcc metals within the EAM format are discussed and, for comparative purposes, the EAM format is cast in a normalized form. A general embedding function is defined and an analytic first- and second-neighbor model is presented. The parameters in the model are determined from the cohesive energy, the equilibrium lattice constant, the three elastic constants, and the unrelaxed vacancy formation energy. Increasing the elastic constants, increasing the elastic anisotropy ratio, and decreasing the unrelaxed vacancy formation energy favor stability of a close-packed lattice over bcc. A stable bcc lattice relative to close packing is found for nine bcc metals, but this scheme cannot generate a model for Cr because the elastic constants of Cr require a negative curvature of the embedding function.
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Shojaie, H., and M. Farhoudi. "A varying-c cosmology." Canadian Journal of Physics 85, no. 12 (December 1, 2007): 1395–408. http://dx.doi.org/10.1139/p07-132.
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We develop a new model for the Universe based on two key assumptions: first, the inertial energy of the Universe is a constant, and second, the total energy of a particle, the inertial plus the gravitational potential energy produced by the other mass in the Universe, is zero. This model allows the speed of light and the total mass of the Universe to vary as functions of cosmological time, where we assume the gravitational constant to be a constant. By means of these assumptions, the relations between the scale factor and the other parameters are derived. The Einstein equation, by making it compatible with varying-c, is used and the Friedmann equations in this model are obtained. Assuming the matter content of the Universe to be perfect fluids, the model fixes γ to be 2/3. That is, the whole Universe always exhibits a negative pressure. Moreover, the behaviour of the scale factor is the same for any value of the curvature. It is also shown that the Universe began from a big bang with zero initial mass and expands forever even with positive curvature, but it is always decelerating. At the end, solutions to some famous problems, mainly of the standard big bang model, and an explanation for the observational data about the accelerating Universe are provided. PACS Nos.: 98.80.Bp, 98.80.Jk
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Wilkening, Jon. "Traveling-Standing Water Waves." Fluids 6, no. 5 (May 14, 2021): 187. http://dx.doi.org/10.3390/fluids6050187.
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We propose a new two-parameter family of hybrid traveling-standing (TS) water waves in infinite depth that evolve to a spatial translation of their initial condition at a later time. We use the square root of the energy as an amplitude parameter and introduce a traveling parameter that naturally interpolates between pure traveling waves moving in either direction and pure standing waves in one of four natural phase configurations. The problem is formulated as a two-point boundary value problem and a quasi-periodic torus representation is presented that exhibits TS-waves as nonlinear superpositions of counter-propagating traveling waves. We use an overdetermined shooting method to compute nearly 50,000 TS-wave solutions and explore their properties. Examples of waves that periodically form sharp crests with high curvature or dimpled crests with negative curvature are presented. We find that pure traveling waves maximize the magnitude of the horizontal momentum among TS-waves of a given energy. Numerical evidence suggests that the two-parameter family of TS-waves contains many gaps and disconnections where solutions with the given parameters do not exist. Some of these gaps are shown to persist to zero-amplitude in a fourth-order perturbation expansion of the solutions in powers of the amplitude parameter. Analytic formulas for the coefficients of this perturbation expansion are identified using Chebyshev interpolation of solutions computed in quadruple-precision.
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Lopes, Bernardo, Isaac C. Ramos, Bruno F. Valbon, Marcella Q. Salomao, Frederico P. Guerra, Livia F. Jordao, Ana Laura C. Canedo, and Rosane Correa. "Accuracy of Topometric Indices for Distinguishing between Keratoconic and Normal Corneas." International Journal of Keratoconus and Ectatic Corneal Diseases 2, no. 3 (2013): 108–12. http://dx.doi.org/10.5005/jp-journals-10025-1062.
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ABSTRACT Purpose To evaluate the sensitivity and specificity of the Pentacam topometric indices derived from the corneal surface curvature to distinguish between normal and keratoconic corneas. Methods The study consisted of 226 normal corneas from 113 patients and 88 keratoconic eyes from 44 patients. Eyes were defined as keratoconus based on comprehensive ocular examination, including Placido-disk-based corneal topography (Atlas Corneal Topography System; Humphrey, San Leandro, California) and rotating Scheimpflug corneal tomography (Pentacam HR; Oculus, Wetzlar, Germany). Corneal Topometric indices ISV, IVA, KI, CKI, IHA and IHD, along with the TKC (Topometric Keratoconus Classification) score were calculated from the Pentacam HR exam. Statistical analysis were accomplished using BioEstat 5.0 (Instituto Mamiraua, Amazonas, Brazil) and MedCalc 12.0 (MedCalc Software, Mariakerke, Belgium) using unpaired nonparametric Mann Whitney test (Wilcoxon ranked-sum). ROC curves were calculated for each topometric parameter to determine the best cut off values from the significantly different parameters. A logistic regression analysis was performed to provide a combined parameter for optimizing accuracy. Results Statistical significant differences were found between keratoconic and normal corneas for all topometric indices (Mann Whitney, p < 0.05). There were four false negative cases among the keratoconic cases on the TKC classification (4.54%) and 16 false positive cases among normal (7.08%), so that the sensitivity and specificity of the TKC were 95.54 and 92.92% respectively. The areas under the ROC curves (AUC) for the individual topometric indices varied from 0.843 (CKI) and 0.992 (ISV). The sensitivity and specificity of the most accurate ISV were 97.7 and 96.5% respectively. The calculated parameter from logistic regression had AUC of 0.996, with sensitivity of 97.7% and specificity of 98.7%. Conclusion Pentacam topometric indices were useful for distinguishing between normal and keratoconic corneas. The TKC classification should be expected to have false positives and negatives and should not be considered alone. TKC had more false positives and false negatives than some individual topometric parameters. A novel combined parameter based on logistic regression analysis may improve accuracy for the diagnosis of keratoconus. Further studies are necessary to evaluate if adding other curvature derived indices is beneficial for the regression analysis, as well as for testing the sensitivity of such parameters for the diagnosis of milder forms of ectasia and for testing correlations with severity of the disease. How to cite this article Salomao MQ, Guerra FP, Ramos IC, Jordao LF, Canedo ALC, Valbon BF, Luz A, Correa R, Lopes B, Ambrósio Jr R. Accuracy of Topometric Indices for Distinguishing between Keratoconic and Normal Corneas. J Kerat Ect Cor Dis 2013;2(3):108-112.
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Bataille, Laurent, Ainhoa Molina-Martín, and David P. Piñero. "Relationship between Axial Length and Corneo-Scleral Topography: A Preliminary Study." Diagnostics 11, no. 3 (March 18, 2021): 542. http://dx.doi.org/10.3390/diagnostics11030542.
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The main objective of the current study was to investigate further the relationship of the overall length of the eye with a great variety of anterior segment parameters, including scleral geometry. A total of 64 eyes of 32 participants with ages from 12 to 52 years were included in this prospective non-randomized single-center study. All participants underwent a complete eye examination, including an analysis of corneo-scleral shape with a Fourier-domain profilometer. A strong negative correlation was found between axial length and temporal-nasal ocular sagittal height difference for different chord lengths. For the right eye, a consistent and stable linear model was obtained to predict the axial length from the spherical equivalent, the corneal diameter, the high-order aberrations root mean square, and the minimum sagittal height for 13- and 14-mm chord. For the left eye, a model was obtained to predict the axial length from the spherical equivalent and the mean corneal curvature, including other parameters such as corneal diameter or high-order aberrations, depending on the chord length, considered for estimating the sagittal height values. More studies with larger samples are needed to confirm these preliminary outcomes.
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Prajapati, Deepak K., and Mayank Tiwari. "The correlation between friction coefficient and areal topography parameters for AISI 304 steel sliding against AISI 52100 steel." Friction 9, no. 1 (July 29, 2020): 41–60. http://dx.doi.org/10.1007/s40544-019-0323-1.
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Abstract Dry wear experiments provide an insight detail on how severely contacting surfaces change under unlubricated sliding condition. The theory of dry sliding wear is used for understanding mixed-lubrication regime in which asperity interactions play a significant role in controlling of the friction coefficient (f). The purpose of this work is to study the tribological behavior of AISI 304 steel in contact with AISI 52100 steel during wear. Both materials are used in rolling element bearings commanly. Experiments are carried out using a pin-on-disc tribometer under dry friction condition. The areal (three dimensional, 3D) topography parameters are measured using a 3D white light interferometer (WLI) with a 10× objective. After wear tests, wear mechanisms are analyzed utilizing scanning electron microscope (SEM). Factorial design with custom response surface design (C-RSD) is used to study the mutual effect of load and speed on response variables such as f and topography parameters. It is observed that the root mean square roughness (Sq) decreases with an increase in sliding time. Within the range of sliding time, Sq decreases with an increase in the normal load. Within the range of sliding speed and normal load, it is found that Sq, mean summit curvature (Ssc), and root mean square slope (Sdq) are positively correlated with f. Whereas, negative correlation is found between f and correlation length (Sal), mean summit radius (R), and core roughness depth (Sk).
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COLISTETE, R., J. C. FABRIS, and S. V. B. GONÇALVES. "BAYESIAN STATISTICS AND PARAMETER CONSTRAINTS ON THE GENERALIZED CHAPLYGIN GAS MODEL USING SNeIa DATA." International Journal of Modern Physics D 14, no. 05 (May 2005): 775–96. http://dx.doi.org/10.1142/s0218271805006729.
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The type Ia supernovae ( SNe Ia ) observational data are used to estimate the parameters of a cosmological model with cold dark matter and the generalized Chaplygin gas model (GCGM). The GCGM depends essentially on five parameters: the Hubble constant, the parameter [Formula: see text] related to the velocity of the sound, the equation of state parameter α, the curvature of the Universe and the fraction density of the generalized Chaplygin gas (or the cold dark matter). The parameter α is allowed to take negative values and to be greater than one. The Bayesian parameter estimation yields [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], where t0 is the age of the Universe and q0 is the value of the deceleration parameter today. Our results indicate that a Universe completely dominated by the generalized Chaplygin gas is favored, which reinforces the idea that the this gas may unify the description for dark matter and dark energy, at least as far as the SNe Ia data is concerned. A closed and accelerating Universe is also favored. The traditional Chaplygin gas model (CGM), α = 1 is not ruled out, even if it does not give the best-fitting. Particular cases with four or three independent free parameters are also analyzed.
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Arcus, Vickery L., and Adrian J. Mulholland. "Temperature, Dynamics, and Enzyme-Catalyzed Reaction Rates." Annual Review of Biophysics 49, no. 1 (May 6, 2020): 163–80. http://dx.doi.org/10.1146/annurev-biophys-121219-081520.
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We review the adaptations of enzyme activity to different temperatures. Psychrophilic (cold-adapted) enzymes show significantly different activation parameters (lower activation enthalpies and entropies) from their mesophilic counterparts. Furthermore, there is increasing evidence that the temperature dependence of many enzyme-catalyzed reactions is more complex than is widely believed. Many enzymes show curvature in plots of activity versus temperature that is not accounted for by denaturation or unfolding. This is explained by macromolecular rate theory: A negative activation heat capacity for the rate-limiting chemical step leads directly to predictions of temperature optima; both entropy and enthalpy are temperature dependent. Fluctuations in the transition state ensemble are reduced compared to the ground state. We show how investigations combining experiment with molecular simulation are revealing fundamental details of enzyme thermoadaptation that are relevant for understanding aspects of enzyme evolution. Simulations can calculate relevant thermodynamic properties (such as activation enthalpies, entropies, and heat capacities) and reveal the molecular mechanisms underlying experimentally observed behavior.
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Warminski, J., M. P. Cartmell, A. Mitura, and M. Bochenski. "Active Vibration Control of a Nonlinear Beam with Self- and External Excitations." Shock and Vibration 20, no. 6 (2013): 1033–47. http://dx.doi.org/10.1155/2013/792795.
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An application of the nonlinear saturation control (NSC) algorithm for a self-excited strongly nonlinear beam structure driven by an external force is presented in the paper. The mathematical model accounts for an Euler-Bernoulli beam with nonlinear curvature, reduced to first mode oscillations. It is assumed that the beam vibrates in the presence of a harmonic excitation close to the first natural frequency of the beam, and additionally the beam is self-excited by fluid flow, which is modelled by a nonlinear Rayleigh term for self-excitation. The self- and externally excited vibrations have been reduced by the application of an active, saturation-based controller. The approximate analytical solutions for a full structure have been found by the multiple time scales method, up to the first-order approximation. The analytical solutions have been compared with numerical results obtained from direct integration of the ordinary differential equations of motion. Finally, the influence of a negative damping term and the controller's parameters for effective vibrations suppression are presented.
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Jamali, Alireza, Taghi Naghdi, Mohsen Hosseini Abardeh, Mojgan Jamalzehi, Maedeh Khalajzadeh, Moslem Kamangar, Niloofar Tehranchi, and Payam Nabovati. "Ocular biometry characteristics in cataract surgery candidates: A cross-sectional study." Medical Hypothesis, Discovery & Innovation in Ophthalmology 10, no. 1 (May 31, 2021): 11–17. http://dx.doi.org/10.51329/mehdiophthal1416.
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Background: This study was conducted to investigate ocular biometry parameters in cataract surgery candidates in northern Tehran, Iran using OA-2000 biometry device.
Methods: In this cross-sectional study, values of ocular biometry parameters, including axial length (AL), anterior chamber depth (ACD), mean corneal curvature (mean K), lens thickness (LT), corneal astigmatism (CA), and white-to-white (WTW) of 818 eyes with cataracts, were measured using the OA-2000 biometry device (Tomey, Nagoya, Japan). The participants were divided into six age subgroups, in 10-year intervals. Finally, the values of the biometry parameters were calculated, and the trend of changes was examined for both age and sex subgroups.
Results: The mean ± standard deviation (SD) of age of the participants was 63.82 ± 13.25 years. Mean ± SD of biometry parameters were as follows: AL, 23.36 ± 1.55 mm; ACD, 3.09 ± 0.40 mm; LT, 4.45 ± 0.55 mm; mean K, 44.51 ± 1.72 D; CA, 1.06 ± 0.94 D; and WTW, 11.81 ± 0.45 mm. Most of the parameters showed significant age-related changes in the total population. There was an increase in LT (P < 0.001) and mean K (P = 0.001), as well as a decrease in AL (P < 0.001) and ACD (P < 0.001) with age. Moreover, AL had a negative negligible correlation with LT (r = -0.24, P < 0.001) and mean K (r = -026, P < 0.001), as well as a weak positive correlation with ACD (r = 0.44, P < 0.001).
Conclusions: Our study revealed that the mean values of most biometric parameters varied across age and sex subgroups. Moreover, most of the parameters showed significant age-related changes in the total population.
Keywords: ocular biometry, cataract, axial length, anterior chamber depth, keratometry, lens thickness, corneal astigmatism, white to white
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Wu, Yanan, and Yan Wang. "Detailed Distribution of Corneal Epithelial Thickness and Correlated Characteristics Measured with SD-OCT in Myopic Eyes." Journal of Ophthalmology 2017 (2017): 1–8. http://dx.doi.org/10.1155/2017/1018321.
Full textAbstract:
Purpose.To investigate the detailed distribution of corneal epithelial thickness in single sectors and its correlated characteristics in myopic eyes.Methods.SD-OCT was used to measure the corneal epithelial thickness distribution profile. Differences of corneal epithelial thickness between different parameters and some correlations of characteristics were calculated.Results.The thickest and thinnest part of epithelium were found at the nasal-inferior sector (P<0.05) and at the superior side (P<0.05), respectively. Subjects in the low and moderate myopia groups have thicker epithelial thickness than those in the high myopia group (P<0.05). Epithelial thickness was 1.39 μm thicker in male subjects than in female subjects (P<0.001). There was a slight negative correlation between corneal epithelial thickness and age (r=−0.13,P=0.042). Weak positive correlations were found between corneal epithelial thickness and corneal thickness (r=0.148,P=0.031). No correlations were found between corneal epithelial thickness, astigmatism axis, corneal front curvature, and IOP.Conclusions.The epithelial thickness is not evenly distributed across the cornea. The thickest location of the corneal epithelium is at the nasal-inferior sector. People with high myopia tend to have thinner corneal epithelium than low–moderate myopic patients. The corneal epithelial thickness is likely to be affected by some parameters, such as age, gender, and corneal thickness.
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Zhang, Cheng, Victor F. Tarasenko, Tao Shao, Dmitry V. Beloplotov, Mikhail I. Lomaev, Dmitry A. Sorokin, and Ping Yan. "Generation of super-short avalanche electron beams in SF6." Laser and Particle Beams 32, no. 2 (April 17, 2014): 331–41. http://dx.doi.org/10.1017/s0263034614000147.
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AbstractIn this work, the generation of a super-short avalanche electron beam (SAEB) in SF6 in an inhomogeneous electric field is studied on two generators with pulse rise times of 0.5 and 2 ns, respectively. The SAEB parameters in SF6 are compared with those obtained in other gases (air, nitrogen, argon, and krypton). It is shown that the SAEB amplitude in SF6 at pressures ranging from 0.05 to 0.2 MPa is commensurable with that in krypton and is much lower than that in air and nitrogen. It is also found that in SF6, SF6 mixture with 2.5% of nitrogen, and other gases, a diffuse discharge is ignited not only at negative polarity but also at positive polarity of the electrode with small curvature radius. Furthermore, the velocity of the ionization wave front in SF6 in an inhomogeneous electric field is studied. Experimental results show that the velocity of the ionization wave front in SF6 is lower than that in air and nitrogen as well as such velocity decreases when the pressure increases from 0.05 to 0.3 MPa in all gases.
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Abu El-Maaty, Ahmed Ebrahim, Ghada Mousa Hekal, and Eman Muhammed Salah El-Din. "Modeling of Dowel Jointed Rigid Airfield Pavement under Thermal Gradients and Dynamic Loads." Civil Engineering Journal 2, no. 2 (February 1, 2016): 38–51. http://dx.doi.org/10.28991/cej-2016-00000011.
Full textAbstract:
Concrete pavements have been widely used for constructing runways, taxiways, and apron areas at airports. The aviation industry has responded to increased demand for air travel by developing longer, wider, and heavier aircraft with increasing numbers of wheels to support the aircraft while in ground operation. Many researchers developed their models based on the finite element method (FEM) for the analysis of jointed concrete pavement. Despite the notable improvement, important considerations were overlooked. These simplifications may affect the results of the developed models and make them unrealistic. Sensitivity studies were conducted in this study to investigate the effect of the loading parameters on the load transfer efficiency (LTE) indictors where concept of LTE is fundamental in airfield design procedures. The effect of main gear loading magnitudes in different wheel configurations combined with positive and negative thermal gradients was investigated. The verification process was presented to increases the confidence in the model results. Understanding the response of rigid airfield pavement under such circumstances is important developing a new pavement design procedure, as well as implementing a suitable remedial measure for existing pavements. The results obtained that utilizing a dynamic load allows studying the fatigue cycles that pavement can be subjected under different wheel configurations. Moreover, the change in the thermal gradient from positive to negative significantly changed the slab curvature shape.
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Schönhöfer, Philipp W. A., Laurence J. Ellison, Matthieu Marechal, Douglas J. Cleaver, and Gerd E. Schröder-Turk. "Purely entropic self-assembly of the bicontinuous Ia 3 d gyroid phase in equilibrium hard-pear systems." Interface Focus 7, no. 4 (June 16, 2017): 20160161. http://dx.doi.org/10.1098/rsfs.2016.0161.
Full textAbstract:
We investigate a model of hard pear-shaped particles which forms the bicontinuous Ia d structure by entropic self-assembly, extending the previous observations of Barmes et al. (2003 Phys. Rev. E 68 , 021708. ( doi:10.1103/PhysRevE.68.021708 )) and Ellison et al. (2006 Phys. Rev. Lett. 97 , 237801. ( doi:10.1103/PhysRevLett.97.237801 )). We specifically provide the complete phase diagram of this system, with global density and particle shape as the two variable parameters, incorporating the gyroid phase as well as disordered isotropic, smectic and nematic phases. The phase diagram is obtained by two methods, one being a compression–decompression study and the other being a continuous change of the particle shape parameter at constant density. Additionally, we probe the mechanism by which interdigitating sheets of pears in these systems create surfaces with negative Gauss curvature, which is needed to form the gyroid minimal surface. This is achieved by the use of Voronoi tessellation, whereby both the shape and volume of Voronoi cells can be assessed in regard to the local Gauss curvature of the gyroid minimal surface. Through this, we show that the mechanisms prevalent in this entropy-driven system differ from those found in systems which form gyroid structures in nature (lipid bilayers) and from synthesized materials (di-block copolymers) and where the formation of the gyroid is enthalpically driven. We further argue that the gyroid phase formed in these systems is a realization of a modulated splay-bend phase in which the conventional nematic has been predicted to be destabilized at the mesoscale due to molecular-scale coupling of polar and orientational degrees of freedom.