Articles de revues : « Density distortion »

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Wang, Q. C., Xiao Dong Hu, W. Li et Ju Long Yuan. « Numerical Simulation of Machining Distortion of Residually Stressed Aircraft Aluminum Components ». Key Engineering Materials 315-316 (juillet 2006) : 235–38. http://dx.doi.org/10.4028/www.scientific.net/kem.315-316.235.

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The presence of residual stress in aircraft aluminum components can give rise to distortion after machining. Excessive distortion may result in the rejection of a part or the need for costly and time-consuming rework prior to placement in service. The purpose of this research was to develop a methodology for the prediction of machining-induced distortions of residually stressed aircraft aluminum components. Numerical simulation results show that the magnitude of machining distortion is strongly related to the square root of Stain Energy Density W or Stress Range σ . The experimental results demonstrate good agreement with the predicted machining distortions of 7075T73 bulkheads. It included that the original residual stress in the blocks of aircraft aluminum component is one of key factors to cause machining distortion.

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Harvey, Pierre D., et Christian Reber. « Article ». Canadian Journal of Chemistry 77, n^o 1 (1 janvier 1999) : 16–23. http://dx.doi.org/10.1139/v98-212.

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Density functional theory is used to characterize the lowest energy excited spin triplet orbital configurations of square-planar halide complexes of palladium(II). Calculations for the eg –> b1g orbital excitation (D4h labels) predict a non-totally symmetric distortion along the b1g normal coordinate, leading to unequal bond lengths for perpendicular metal-ligand bonds (D2h symmetry). Calculated bond length changes are 0.15 Å (0.11 Å) and 0.05 Å (0.00 Å) for PdCl42- (PdBr42-). These values compare favorably to the emitting-state distortions of 0.12 Å and 0.09 Å for K2PdCl4 (0.12 Å, and 0.07 Å for K2PdBr4) determined from resolved single-crystal luminescence spectra. The calculations indicate that the non-totally symmetric distortion is an intrinsic molecular property of these complexes.Key words: palladium(II) complexes, excited state distortions, density functional theory.

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Wang, Kan, et Meng Wang. « Aero-optics of subsonic turbulent boundary layers ». Journal of Fluid Mechanics 696 (24 février 2012) : 122–51. http://dx.doi.org/10.1017/jfm.2012.11.

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AbstractCompressible large-eddy simulations are carried out to study the aero-optical distortions caused by Mach 0.5 flat-plate turbulent boundary layers at Reynolds numbers of ${\mathit{Re}}_{\theta } = 875$, 1770 and 3550, based on momentum thickness. The fluctuations of refractive index are calculated from the density field, and wavefront distortions of an optical beam traversing the boundary layer are computed based on geometric optics. The effects of aperture size, small-scale turbulence, different flow regions and beam elevation angle are examined and the underlying flow physics is analysed. It is found that the level of optical distortion decreases with increasing Reynolds number within the Reynolds-number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role, followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analysed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton’s linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.

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Luty, Tadeusz, et John C. Raich. « Molecular to atomic transformation in solid iodine under high pressure ». Canadian Journal of Chemistry 66, n^o 4 (1 avril 1988) : 812–18. http://dx.doi.org/10.1139/v88-141.

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Structural transformations in solid iodine under high pressure are analyzed from the point of view of symmetries of possible charge density distortions coupled to phonons. The transition from the high pressure atomic phase to the low pressure molecular phase is interpreted in terms of phonon softening and formation of molecular bonds and is seen as a condensation of a charge density distortion wave coupled to a phonon mode.

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Kaczmarek, Michał, et Ernest Stano. « Magnetic Flux Density under Single Harmonic Distortion ». Materials Science Forum 1034 (15 juin 2021) : 151–57. http://dx.doi.org/10.4028/www.scientific.net/msf.1034.151.

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In the paper the change of the magnetic flux density under single harmonic distortion is discussed. Presented results show the dependence of the value of the magnetic flux density in the toroidal magnetic core made from the Ni80Fe20 tape of the phase angle of higher harmonic in relation to the main harmonic of distorted magnetizing current. Moreover, the influence of higher harmonic depends from it frequency and it becomes undetectable above 15th higher harmonic, even if its level reaches 50% of the RMS value of the main harmonic of distorted magnetizing current. Laboratory tests were carried out for the magnetic toroidal core of iCT with a current ratio equal to 300 A / 5 A. The oscilloscope is used to measure waveforms of the excitation current and the secondary voltage through the voltage probes. Build in numerical integration is used to determine the magnetic flux density from secondary voltage. In the case of tested 5th higher harmonic the highest value of the magnetic flux density is obtained for phase angle equal to 90° between main and higher harmonics, while the lowest is obtained for 270°. This depends from the initial phase of the magnetic field strength and results from the integration of distorted secondary voltage with the particular content of higher harmonics.

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Park, Sang-Cheol, Hee-Seon Bang et Woo-Jae Seong. « Effects of Material Properties on Angular Distortion in Wire Arc Additive Manufacturing : Experimental and Computational Analyses ». Materials 13, n^o 6 (19 mars 2020) : 1399. http://dx.doi.org/10.3390/ma13061399.

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In wire arc additive manufacturing (AM), as in arc welding, arc heat thermally deforms substrates and articles. For industrial applications, deformation characteristics of various materials must be understood and appropriate materials and methods of reducing deformation must be devised. Therefore, angular distortions of different materials were investigated through bead-on-plate welding and finite element analysis. A model that simplifies temperature-dependent properties was developed to establish relationships between thermomechanical properties and angular distortion. A simplified model of temperature-dependent properties was used, and angular distortion characteristics were extensively investigated for different material properties and heat inputs. Coefficient of thermal expansion, density, and specific heat all notably affected angular distortion depending on heat input conditions. Results showed that during wire arc AM, flatness of both substrates and articles could vary depending on material properties, heat input, substrate thickness, and bead accumulation. Study findings can provide insight into deformation characteristics of new materials and how to mitigate thermal distortions.

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Hussein, Rageh K., Ibrahim I. Bashter, Mohamed El-Okr et Medhat Ahmed Ibrahim. « DFT Investigation of Structural and Electronic Properties of Modified PZT ». Acta Chemica Iasi 27, n^o 1 (1 juin 2019) : 15–30. http://dx.doi.org/10.2478/achi-2019-0002.

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Abstract Density of states and geometrical structures of modified Lead zirconate titanate are investigated using density functional theory within local density approximation. The electronic properties and bond length variation have been studied in terms of electronic structure and bonding mechanism principles respectively. Hybridization between Ti 3d - O 2p states and ferroelectric distortion have been addressed as a theoretical approach, to rule the improvement of ferroelectric properties of Lead zirconate titanate. The analysis of Ga, Tl modified Lead zirconate titanate were found to diminish the hybridization between Ti 3d - O 2p states, the relaxed behavior lead to the reversal of the known ferroelectric distortion. Y, Ho, Yb and Lu modified Lead zirconate titanate compounds have a tendency to intense the ferroelectric stability, its exhibit higher hybridization between Ti 3d - O 2p states than pure Lead zirconate titanate, also the arrangement of the ions distortions is strongly the same as the more favoured ferroelectric states of Lead zirconate titanate.

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Birkinshaw, Mark, Josie Rawes et Diana Worrall. « Extreme jet distortions in low-z radio galaxies ». Proceedings of the International Astronomical Union 14, A30 (août 2018) : 61–65. http://dx.doi.org/10.1017/s1743921319003466.

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AbstractJets often display bends and knots at which the flows change character. Extreme distortions have implications for the nature of jet flows and their interactions. We present the results of three radio mapping campaigns. The distortion of 3CRR radio galaxy NGC 7385 is caused by a collision with a foreground magnetised gas cloud which causes Faraday rotation and free-free absorption, and is triggered into star formation. For NGC 6109 the distortion is more extreme, creating a ring-shaped structure, but no deflector can be identified in cold or hot gas. Similar distortions in NGC 7016 are apparently associated with an X-ray gas cavity, and the adjacent NGC 7018 shows filaments drawn out beyond 100 kpc. Encounters with substructures in low-density, magnetised, intergalactic gas are likely causes of many of these features.

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Bakhtiyarov, Sayavur I. « Numerical Simulations and Experimental Study of Liquid Metal Flow Around Sand Core ». Journal of Fluids Engineering 128, n^o 3 (25 octobre 2005) : 541–47. http://dx.doi.org/10.1115/1.2175160.

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This paper presents the results of experimental and numerical studies of the hot distortion phenomenon in the phenolic urethane cold box systems used in metal casting. Dual Pushrod Dilatometry has been used to measure a thermal expansion/contraction of phenolic urethane cold box sand core specimens at temperatures ranging from 20°C to 600°C. High temperature tensile tests showed that the tensile strength of the phenolic urethane cold box sand cores is significantly affected by the bench life, temperature and binders level. High temperature hot distortion furnace tests on cylindrical cores showed that some coatings increase the temperature limit when distortion starts, but application of coating cannot prevent distortion. The hot distortion test during metal casting showed that regardless of the application of coating, the type of coating, and anti-veining additives, all cores with density greater than the density of the molten metal (magnesium alloy) were significantly distorted. Numerical simulations of the liquid metal flow around the cylindrical sand core and analysis of dynamic forces acting on the core during the fill process showed that a buoyancy force is the major contributor to the hot distortion. It is concluded that the one of the solutions in preventing the hot distortion of sand cores is optimizing their weight, which will balance the buoyancy force and will bring the resultant force to the minimum. The hot distortion test castings using optimized sand cores with density almost equal to the density of the molten magnesium proved our predictions, and hot distortion has been prevented.

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Bak, Peter, Matthias Schaefer, Andreas Stoffel, Daniel A. Keim et Itzhak Omer. « Density Equalizing Distortion of Large Geographic Point Sets ». Cartography and Geographic Information Science 36, n^o 3 (janvier 2009) : 237–50. http://dx.doi.org/10.1559/152304009788988288.

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Uejima, Motoyuki, Tohru Sato, Daisuke Yokoyama, Kazuyoshi Tanaka et Jong-Wook Park. « Quantum yield in blue-emitting anthracene derivatives : vibronic coupling density and transition dipole moment density ». Phys. Chem. Chem. Phys. 16, n^o 27 (2014) : 14244–56. http://dx.doi.org/10.1039/c4cp01428f.

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Huan, S. L., et A. R. Pater. « Analysis and prediction of geophone performance parameters ». GEOPHYSICS 50, n^o 8 (août 1985) : 1221–28. http://dx.doi.org/10.1190/1.1441994.

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In the past, designers relied greatly on simplified geophone models to describe the physical quantities of a geophone. Several iterations of fine tuning the geophone variables were required to achieve a desired geophone characteristic. Although many geophone prototypes were built before a geophone design was finalized, it was still impossible to assure an optimum geophone design. An easier, faster, and more accurate method of predicting geophone parameters is described and the method of computer‐aided geophone design is outlined. A description of a nonlinear geophone model is presented and a numerical method to compute the nonlinear magnetic flux density distribution is outlined. An integration algorithm is used to compute the geophone sensitivity and open‐circuit damping. The measurement of geophone distortion is described, and the harmonic distortion due to nonlinearity of sensitivity and damping is computed. The data of a geophone spring constant were obtained through a recent experiment, and the harmonic distortions caused by the nonlinearity of the spring are computed. Finally, the total harmonic distortion of a geophone is obtained. Programs developed to predict geophone sensitivity, damping, and distortion are described. It is shown that the method used to compute the nonlinear flux density distribution converges properly and the results obtained are meaningful. Three different types of geophones are analyzed and a comparison between the simulated and measured data is made. In all three cases, good correlation exists between the parameters predicted and the parameters actually measured. Information obtained by geophone parameter prediction can be very useful in the geophone design process, in optimizing geophones, and in achieving higher performance levels.

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Darcie, T. E., R. M. Jopson et R. W. Tkach. « Intermodulation distortion in optical amplifiers from carrier-density modulation ». Electronics Letters 23, n^o 25 (1987) : 1392. http://dx.doi.org/10.1049/el:19870961.

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Jingxian Wu et Ning Sun. « Optimum Sensor Density in Distortion-Tolerant Wireless Sensor Networks ». IEEE Transactions on Wireless Communications 11, n^o 6 (juin 2012) : 2056–64. http://dx.doi.org/10.1109/twc.2012.041612.110127.

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Nieznański, J. « Analytical establishment of the minimum-distortion pulse density modulation ». Electrical Engineering 80, n^o 4 (août 1997) : 251–58. http://dx.doi.org/10.1007/bf01232797.

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Pohl, Anna, Heiko Meider et Michael Springborg. « On the Peierls' distortion and the local-density approximation ». Journal of Molecular Structure : THEOCHEM 305 (mars 1994) : 165–73. http://dx.doi.org/10.1016/0166-1280(94)80151-7.

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Li, Chunlian, Guihua Bai, Shiaoman Chao et Zhonghua Wang. « A High-Density SNP and SSR Consensus Map Reveals Segregation Distortion Regions in Wheat ». BioMed Research International 2015 (2015) : 1–10. http://dx.doi.org/10.1155/2015/830618.

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Segregation distortion is a widespread phenomenon in plant and animal genomes and significantly affects linkage map construction and identification of quantitative trait loci (QTLs). To study segregation distortion in wheat, a high-density consensus map was constructed using single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) markers by merging two genetic maps developed from two recombinant-inbred line (RIL) populations, Ning7840 × Clark and Heyne × Lakin. Chromosome regions with obvious segregation distortion were identified in the map. A total of 3541 SNPs and 145 SSRs were mapped, and the map covered 3258.7 cM in genetic distance with an average interval of 0.88 cM. The number of markers that showed distorted segregation was 490 (18.5%) in the Ning7840 × Clark population and 225 (10.4%) in the Heyne × Lakin population. Most of the distorted markers (630) were mapped in the consensus map, which accounted for 17.1% of mapped markers. The majority of the distorted markers clustered in the segregation distortion regions (SDRs) on chromosomes 1B, 2A, 2B, 3A, 3B, 4B, 5A, 5B, 5D, 6B, 7A, and 7D. All of the markers in a given SDR skewed toward one of the parents, suggesting that gametophytic competition during zygote formation was most likely one of the causes for segregation distortion in the populations.

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Li, Y. Q., et X. L. Gao. « Constitutive Equations for Hyperelastic Materials Based on the Upper Triangular Decomposition of the Deformation Gradient ». Mathematics and Mechanics of Solids 24, n^o 6 (24 décembre 2018) : 1785–99. http://dx.doi.org/10.1177/1081286518806950.

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The upper triangular decomposition has recently been proposed to multiplicatively decompose the deformation gradient tensor into a product of a rotation tensor and an upper triangular tensor called the distortion tensor, whose six components can be directly related to pure stretch and simple shear deformations, which are physically measurable. In the current paper, constitutive equations for hyperelastic materials are derived using strain energy density functions in terms of the distortion tensor, which satisfy the principle of material frame indifference and the first and second laws of thermodynamics. Being expressed directly as derivatives of the strain energy density function with respect to the components of the distortion tensor, the Cauchy stress components have simpler expressions than those based on the invariants of the right Cauchy-Green deformation tensor. To illustrate the new constitutive equations, strain energy density functions in terms of the distortion tensor are provided for unconstrained and incompressible isotropic materials, incompressible transversely isotropic composite materials, and incompressible orthotropic composite materials with two families of fibers. For each type of material, example problems are solved using the newly proposed constitutive equations and strain energy density functions, both in terms of the distortion tensor. The solutions of these problems are found to be the same as those obtained by applying the polar decomposition-based invariants approach, thereby validating and supporting the newly developed, alternative method based on the upper triangular decomposition of the deformation gradient tensor.

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Beene, Daniel, Su Zhang, Christopher D. Lippitt et Susan M. Bogus. « Performance Evaluation of Multiple Pan-Sharpening Techniques on NDVI : A Statistical Framework ». Geographies 2, n^o 3 (13 juillet 2022) : 435–52. http://dx.doi.org/10.3390/geographies2030027.

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Pan-sharpening is a pixel-level image fusion process whereby a lower-spatial-resolution multispectral image is merged with a higher-spatial-resolution panchromatic one. One of the drawbacks of this process is that it may introduce spectral or radiometric distortion. The degree to which distortion is introduced is dependent on the imaging sensor, the pan-sharpening algorithm employed, and the context of the scene analyzed. Studies that evaluate the quality of pan-sharpening algorithms often fail to account for changes in geographic context and are agnostic to any specific applications of an end user. This research proposes an evaluation framework to assess the effects of six widely used pan-sharpening algorithms on normalized difference vegetation index (NDVI) calculation in five contextually diverse geographic locations. Output image quality is assessed by comparing the empirical cumulative density function of NDVI values that are calculated by using pre-sharpened and sharpened imagery. The premise is that an effective algorithm will generate a sharpened multispectral image with a cumulative NDVI distribution that is similar to the pre-sharpened image. Research results revealed that, generally, the Gram–Schmidt algorithm introduces a significant degree of spectral distortion regardless of sensor and spatial context. In addition, higher-spatial-resolution imagery is more susceptible to spectral distortions upon pan-sharpening. Furthermore, variability in cumulative density of spectral information in fused images justifies the application of an analytical framework to assist users in selecting the most effective methods for their intended application.

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Tang, Fu Ling, F. C. Wan, X. Q. Dai et W. J. Lu. « Atomic Simulation for Lattice Structure of La/SrMnO₃ Superlattice ». Materials Science Forum 689 (juin 2011) : 49–57. http://dx.doi.org/10.4028/www.scientific.net/msf.689.49.

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We studied in detail the lattice transition and local lattice structure (including Jahn-Teller distortion) in LaMnO3/SrMnO3surperlattices by classical atomistic simulation. For a certain doping density, it is found that the superlattices with short modulation period have small lattice energies and larger differences among lattice parametersa,b/√2 andc. The average La-Mn (Mn3+-O) distance is larger than the average Sr-Mn (Mn4+-O) distance for all doping densities and superlattice configurations at certain doping density. The standard deviation of Mn-O bond lengths and Jahn-Teller distortion of MnO6octahedra have been calculated. Both the standard deviation and Jahn-Teller distortion of Mn3+O6octahedra in the superlattices are much smaller than those of Mn3+O6octahedra in LaMnO3, while Mn4+O6octahedra in the superlattices have the smallest lattice distortion, but larger than those in SrMnO3.

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Schoenberg, Sam E., David J. Green, Albert E. Segall, Gary L. Messing, Abraham S. Grader et Phillip M. Halleck. « Stresses and Distortion Due to Green Density Gradients During Densification ». Journal of the American Ceramic Society 89, n^o 10 (octobre 2006) : 3027–33. http://dx.doi.org/10.1111/j.1551-2916.2006.01182.x.

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Kalika, Douglass S., et Morton M. Denn. « Wall Slip and Extrudate Distortion in Linear Low‐Density Polyethylene ». Journal of Rheology 31, n^o 8 (novembre 1987) : 815–34. http://dx.doi.org/10.1122/1.549942.

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Kooi, Derk P., et Paola Gori-Giorgi. « A Variational Approach to London Dispersion Interactions without Density Distortion ». Journal of Physical Chemistry Letters 10, n^o 7 (13 mars 2019) : 1537–41. http://dx.doi.org/10.1021/acs.jpclett.9b00469.

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Zhang, Duan, Yecun Wu, Yu-Hsin Su, Ming-Chien Hsu, Cormac Ó Coileáin, Jiung Cho, Miri Choi et al. « Charge density waves and degenerate modes in exfoliated monolayer 2H-TaS2 ». IUCrJ 7, n^o 5 (25 août 2020) : 913–19. http://dx.doi.org/10.1107/s2052252520011021.

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Charge density waves spontaneously breaking lattice symmetry through periodic lattice distortion, and electron–electron and electron–phonon interactions, can lead to a new type of electronic band structure. Bulk 2H-TaS2 is an archetypal transition metal dichalcogenide supporting charge density waves with a phase transition at 75 K. Here, it is shown that charge density waves can exist in exfoliated monolayer 2H-TaS2 and the transition temperature can reach 140 K, which is much higher than that in the bulk. The degenerate breathing and wiggle modes of 2H-TaS2 originating from the periodic lattice distortion are probed by optical methods. The results open an avenue to investigating charge density wave phases in two-dimensional transition metal dichalcogenides and will be helpful for understanding and designing devices based on charge density waves.

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Isbister, D. J., et D. H. Chaplin. « The Influence of the Skin Effect on the Amplitude of Single Pulse Gamma Detected NMR on Oriented Nuclei Signals ». Zeitschrift für Naturforschung A 45, n^o 1 (1 janvier 1990) : 43–49. http://dx.doi.org/10.1515/zna-1990-0109.

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AbstractThe effects of skin depth on gamma detected single pulse Nuclear Magnetic Resonance on Oriented Nuclei (NMRON) signals are theoretically explored for narrow, intermediate and broad line metallic samples, using the density matrix approach describing a pure Zeeman system. It is shown that the skin effect distortion of the signal can dominate over intermediate to broadline distortions for that range of experimental conditions generally applicable to ferromagnetic hosts. In particular, the skin effect distortions of the first maximum, obtained when the excitation pulse width is lengthened, are significant and can determine the accuracy of calibration of the radiofrequency "(rf)" field amplitude at the resonating nuclei when assigning an average turn angle to this maximum.

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Zlatar, Matija, Carl-Wilhelm Schläpfer, Emmanuel Penka Fowe et Claude A. Daul. « Density functional theory study of the Jahn-Teller effect in cobaltocene ». Pure and Applied Chemistry 81, n^o 8 (31 juillet 2009) : 1397–411. http://dx.doi.org/10.1351/pac-con-08-06-04.

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A detailed discussion of the potential energy surface of bis(cyclopentadienyl)cobalt(II), cobaltocene, is given. Vibronic coupling coefficients are calculated using density functional theory (DFT). Results are in good agreement with experimental findings. On the basis of our calculation there is no second-order Jahn–Teller (JT) effect as predicted by group theory. The JT distortion can be expressed as a linear combination of all totally symmetric normal modes of the low-symmetry, minimum-energy conformation. The out-of-plane ring deformation is the most important mode. The JT distortion is analyzed by seeking the path of minimal energy of the adiabatic potential energy surface.

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Coelho-Silva, Fernanda, Luciano Augusto Cano Martins, Daniela Azeredo Braga, Eliana Zandonade, Francisco Haiter-Neto et Sergio Lins de-Azevedo-Vaz. « Influence of windowing and metal artefact reduction algorithms on the volumetric dimensions of five different high-density materials : a cone-beam CT study ». Dentomaxillofacial Radiology 49, n^o 8 (1 décembre 2020) : 20200039. http://dx.doi.org/10.1259/dmfr.20200039.

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Objective: To assess the influence of windowing and metal artefact reduction (MAR) algorithms on the volumetric dimensions of high-density materials using two CBCT systems. Methods: Four cylinders of amalgam, cobalt-chromium, gutta-percha, titanium and zirconium, were manufactured and their physical volumes (PV) were measured. A polymethyl methacrylate phantom containing the cylinders was submitted to CBCT acquisitions with Picasso Trio and OP300 units with their MAR enabled and disabled. The tomographic volume (TV) of all the cylinders was obtained by semi-automatic segmentation using two windowing adjustments: W1—large window width and upper window level; W2—narrow window width and low window level. Volumetric distortion was expressed as the difference between TV and PV. Statistics comprised intraclass correlation coefficient (ICC) and analysis of variance (ANOVA) for repeated measures with Tukey post hoc test (α = 5%). Results: The ICC values indicated excellent reproducibility of TV. Gutta-percha and titanium resulted in the smallest volumetric distortion. Using W1 provided less volumetric distortion for almost all experimental conditions (p < 0.05). Activating MAR algorithm of Picasso Trio underestimated gutta-percha and titanium TV (p < 0.05) and was inefficient in significantly reducing the volumetric distortion of the other materials (p > 0.05). Disabling MAR algorithm of OP300 resulted in smaller volumetric distortion for almost all experimental conditions (p < 0.05). Conclusions: The TV of gutta-percha and titanium were closer to the PV. In general, the MAR algorithms of both systems were inefficient in significantly reducing the volumetric distortion of high-density materials. We encourage the use of large window width and upper window level to evaluate high-density materials.

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Ignatjev V. K., Lebedev N. G. et Stankevich D. A. « The effect of the spin polarization control of conduction electrons through the deformation of a ferromagnet ». Technical Physics Letters 48, n^o 12 (2022) : 25. http://dx.doi.org/10.21883/tpl.2022.12.54941.19363.

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A model of the exchange interaction of collectivized conduction electrons with magnetization electrons in a deformed ferromagnet with taking into account spin-orbit corrections is proposed. Under the conditions of inhomogeneous torsion distortion, the conduction electron spin in the domain is oriented along the exchange interaction vector. If the conduction current density vector is orthogonal to the torsion axis, then the average conduction electron spin will be oriented predominantly along the current density vector. Keywords: spin-orbit interaction, transition metals, Wannier functions, torsion distortion.

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Jung, Haeyoon, Jiyeon Kim et Sooran Kim. « Phonon study of Jahn–Teller distortion and phase stability in NaMnO₂ for sodium-ion batteries ». Journal of Applied Physics 132, n^o 5 (7 août 2022) : 055101. http://dx.doi.org/10.1063/5.0086903.

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Cathode materials undergo various phase transitions during the charge/discharge process, and the structural transitions significantly affect the battery performance. Although phonon properties can provide a direct clue for structural stability and transitions, it has been less explored in sodium cathode materials. Here, using the first-principles calculations, we investigate phonon and electronic properties of various layered NaMnO2 materials, especially focusing on the dependency of the Jahn–Teller distortion of Mn3+. The phonon dispersion curves show that the O′3 and P′2 structures with the Jahn–Teller distortion are dynamically stable in contrast to undistorted O3 and P2 structures. The structural instability of O3 and P2 structures is directly observed from the imaginary phonon frequencies, as so-called phonon soft modes, whose corresponding displacements are from O atoms distorting along the local Mn–O bond direction in the MnO6 octahedra. This is consistent with the experimental stability and a structural transition with the Jahn–Teller distortion at the high Na concentration. The orbital-decomposed density of states presents the orbital redistribution by the Jahn–Teller distortion, such as eg-band splitting in both O′3 and P′2 system, and the stability of O′3 and P′2 is not sensitive to the electron–electron correlation. Our results demonstrate the importance of phonon analysis to further understand the structural stability and phase transitions in cathode materials.

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Min, Taewon, Wooseon Choi, Jinsol Seo, Gyeongtak Han, Kyung Song, Sangwoo Ryu, Hyungwoo Lee et al. « Cooperative evolution of polar distortion and nonpolar rotation of oxygen octahedra in oxide heterostructures ». Science Advances 7, n^o 17 (avril 2021) : eabe9053. http://dx.doi.org/10.1126/sciadv.abe9053.

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Polarity discontinuity across LaAlO3/SrTiO3 (LAO/STO) heterostructures induces electronic reconstruction involving the formation of two-dimensional electron gas (2DEG) and structural distortions characterized by antiferrodistortive (AFD) rotation and ferroelectric (FE) distortion. We show that AFD and FE modes are cooperatively coupled in LAO/STO (111) heterostructures; they coexist below the critical thickness (tc) and disappear simultaneously above tc with the formation of 2DEG. Electron energy-loss spectroscopy and density functional theory (DFT) calculations provide direct evidence of oxygen vacancy (VO) formation at the LAO (111) surface, which acts as the source of 2DEG. Tracing the AFD rotation and FE distortion of LAO reveals that their evolution is strongly correlated with VO distribution. The present study demonstrates that AFD and FE modes in oxide heterostructures emerge as a consequence of interplay between misfit strain and polar field, and further that their combination can be tuned to competitive or cooperative coupling by changing the interface orientation.

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Leinhos, Dirk C., Norbert R. Schmid et Leonhard Fottner. « The Influence of Transient Inlet Distortions on the Instability Inception of a Low-Pressure Compressor in a Turbofan Engine ». Journal of Turbomachinery 123, n^o 1 (1 février 2000) : 1–8. http://dx.doi.org/10.1115/1.1330271.

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While studies on compressor flow instabilities under the presence of inlet distortions have been carried out with steady distortions in the past, the investigation presented here focuses on the influence of transient inlet distortions as generated by variable geometry engine intakes of super- and hypersonic aircraft on the characteristic and the nature of the instability inception of a LPC. The flow patterns (total pressure distortion with a superimposed co- or counterrotating swirl) of the distortions are adopted from a hypersonic concept aircraft. A LARZAC 04 twin-spool turbofan was operated with transient inlet distortions, generated by a moving delta wing, and steady total pressure distortions starting close to the LPC’s stability limit until it stalled. High-frequency pressure signals are recorded at different engine power settings. Instabilities are investigated with regard to the inception process and the early detection of stall precursors for providing data for a future stability control device. It turned out that the transient distortion does not have an influence on the surge margin of the LPC compared to the steady distortion, but that it changes the nature of stall inception. The pressure traces are analyzed in the time and frequency domain and also with tools like Spatial FFT, Power Spectral Density, and Traveling Wave Energy. A Wavelet Transformation algorithm is applied as well. While in the case of clean inlet flow, the compressor exhibits different types of stall inception depending on the engine speed, stall is always initiated by spike-type disturbances under the presence of steady or transient distortions. Modal disturbances are present in the mid-speed range that do not grow into stall, but rather interact with the inlet flow and produce short length scale disturbances. The obtained early warning times prior to stall are adversely affected by transient distortions in some cases. The problem of appropriate thresholding becomes evident. The best warning times have been acquired using a statistical evaluation of the Wavelet coefficients, which might be promising to apply in a staged active control system. This system could include different phases of detection and actuation depending on the current precursor.

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Tang, Jingfan, Meijia Zhou, Pengfei Li, Min Zhang et Ming Jiang. « Crowd Counting Based on Multiresolution Density Map and Parallel Dilated Convolution ». Scientific Programming 2021 (20 janvier 2021) : 1–10. http://dx.doi.org/10.1155/2021/8831458.

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The current crowd counting tasks rely on a fully convolutional network to generate a density map that can achieve good performance. However, due to the crowd occlusion and perspective distortion in the image, the directly generated density map usually neglects the scale information and spatial contact information. To solve it, we proposed MDPDNet (Multiresolution Density maps and Parallel Dilated convolutions’ Network) to reduce the influence of occlusion and distortion on crowd estimation. This network is composed of two modules: (1) the parallel dilated convolution module (PDM) that combines three dilated convolutions in parallel to obtain the deep features on the larger receptive field with fewer parameters while reducing the loss of multiscale information; (2) the multiresolution density map module (MDM) that contains three-branch networks for extracting spatial contact information on three different low-resolution density maps as the feature input of the final crowd density map. Experiments show that MDPDNet achieved excellent results on three mainstream datasets (ShanghaiTech, UCF_CC_50, and UCF-QNRF).

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Yoshinaka, Akio, Serge Desgreniers et Anguang Hu. « Nitroethane at high density : an experimental and computational vibrational study ». Physical Chemistry Chemical Physics 23, n^o 15 (2021) : 9325–36. http://dx.doi.org/10.1039/d0cp06557a.

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Raman and IR vibrational spectra confirm two molecular units associated with the monoclinic unit cell of nitroethane under high pressure. Raman spectra are extremely sensitive to predicted effects of unit cell distortion due to changes in H-bonding.

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Ikeda, Tatsuhiko, Hirokazu Tsunetsugu et Kenji Yonemitsu. « Photoinduced Dynamics of Commensurate Charge Density Wave in 1T-TaS2 Based on Three-Orbital Hubbard Model ». Applied Sciences 9, n^o 1 (25 décembre 2018) : 70. http://dx.doi.org/10.3390/app9010070.

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We study the coupled charge-lattice dynamics in the commensurate charge density wave (CDW) phase of the layered compound 1T-TaS 2 driven by an ultrashort laser pulse. For describing its electronic structure, we employ a tight-binding model of previous studies including the effects of lattice distortion associated with the CDW order. We further add on-site Coulomb interactions and reproduce an energy gap at the Fermi level within a mean-field analysis. On the basis of coupled equations of motion for electrons and the lattice distortion, we numerically study their dynamics driven by an ultrashort laser pulse. We find that the CDW order decreases and even disappears during the laser irradiation while the lattice distortion is almost frozen. We also find that the lattice motion sets in on a longer time scale and causes a further decrease in the CDW order even after the laser irradiation.

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Hori, Akira, Takeo Hondoh, Mitsugu Oguro et Vladimir Ya Lipenkov. « Ice-lattice distortion along the deepest section of the Vostok core from X-ray diffraction measurements ». Annals of Glaciology 39 (2004) : 501–4. http://dx.doi.org/10.3189/172756404781814528.

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AbstractWe performed X-ray diffraction measurements on eight ice samples taken between 3200 and 3611 m depth of the Vostok (Antarctica) ice core to observe lattice distortions of ice crystals. Selected samples represent three distinct sections of the core: (i) glacier (meteoric) ice with well-preserved climatic record (down to 3310 m), (ii) ‘shear zone’ at the base of the glacier ice (3450– 3537 m) within which the climatic record is disturbed by ice deformation, and (iii) accretion ice formed by freezing of subglacial Vostok lake waters at the base of the ice sheet (from about 3537 m depth to the bottom of the core). The dislocation density decreases from 1012 to 108m–2 with increasing depth. In the accretion ice, lattice distortion tends to decrease with depth. However, the dislocation density does not reach a level typical for laboratory-grown columnar ice even at 3610 m. This reflects plastic deformation which accretion ice has undergone after its formation.

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Liu, Jin, Lyudmyla Adamska, Stephen K. Doorn et Sergei Tretiak. « Singlet and triplet excitons and charge polarons in cycloparaphenylenes : a density functional theory study ». Physical Chemistry Chemical Physics 17, n^o 22 (2015) : 14613–22. http://dx.doi.org/10.1039/c5cp01782c.

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Zhao, Shengyang, et Zhibo Chen. « Various density light field image coding based on distortion minimization interpolation ». Journal of Visual Communication and Image Representation 75 (février 2021) : 103036. http://dx.doi.org/10.1016/j.jvcir.2021.103036.

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Yu, Mujian, Xiaolin Yin, Wanteng Liu et Wei Lu. « Secure halftone image steganography based on density preserving and distortion fusion ». Signal Processing 188 (novembre 2021) : 108227. http://dx.doi.org/10.1016/j.sigpro.2021.108227.

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Schultz, R. W., et M. E. Karabin. « Characterization of Machining Distortion by Strain Energy Density and Stress Range ». Materials Science Forum 404-407 (août 2002) : 61–68. http://dx.doi.org/10.4028/www.scientific.net/msf.404-407.61.

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Jopson, R. M., T. E. Darcie, K. T. Gayliard, R. T. Ku, R. E. Tench, T. C. Rice et N. A. Olsson. « Measurement of carrier-density mediated intermodulation distortion in an optical amplifier ». Electronics Letters 23, n^o 25 (1987) : 1394. http://dx.doi.org/10.1049/el:19870962.

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Sun, Zhibin, Mingkai Shao, Jun Chen, Kon Wong et Xiaolin Wu. « Achieving the rate-distortion bound with low-density generator matrix codes ». IEEE Transactions on Communications 58, n^o 6 (juin 2010) : 1643–53. http://dx.doi.org/10.1109/tcomm.2010.06.090203.

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Jo, Takeo, et Kunitomo Hirai. « Lattice Distortion and Multiple Spin Density Wave State in γMn Alloys ». Journal of the Physical Society of Japan 55, n^o 6 (15 juin 1986) : 2017–23. http://dx.doi.org/10.1143/jpsj.55.2017.

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Sakita, B., et K. Shizuya. « Moving charge density waves without peierls distortion in one-dimensional conductors ». Physics Letters A 145, n^o 4 (avril 1990) : 209–13. http://dx.doi.org/10.1016/0375-9601(90)90683-f.

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GANGADHAR REDDY, G., T. VENKATAPPA RAO, A. RAMAKANTH, S. K. GHATAK et S. N. BEHERA. « REENTRANT-LIKE BAND JAHN–TELLER EFFECT AND ITS FIELD DEPENDENCE ». International Journal of Modern Physics B 22, n^o 04 (10 février 2008) : 423–34. http://dx.doi.org/10.1142/s0217979208038612.

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In the presence of the electron–lattice interaction where the lattice strain is coupled to the difference in orbital occupancy, the metallic system whose Fermi level lies in an orbitally degenerate eg band undergoes a structural transition to a lower symmetric state with distortion. The distortion is the consequence of the band Jahn–Teller (J–T) effect, and results from the gain of the electronic energy against the increase in the elastic energy. The extent of distortion depends on the nature of the density of states (DOS) and carrier concentration. These effects are examined for a system described by a different model DOS, and an orbitally degenerate eg band with the J–T interaction. In a certain region of parameter space, the temperature dependence of distortion exhibits a reentrant-like behavior, and the magnetic field augments the distortion in this region. In the parameter space where there is no reentrant-like behavior, the field suppresses the distortion, and the normalized distortion becomes a universal function of the normalized field. A phase diagram is obtained in the magnetic field–temperature plane.

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Kooi, Derk Pieter, et Paola Gori-Giorgi. « London dispersion forces without density distortion : a path to first principles inclusion in density functional theory ». Faraday Discussions 224 (2020) : 145–65. http://dx.doi.org/10.1039/d0fd00056f.

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We analyse a path to construct density functionals for the dispersion interaction energy from an expression in terms of the ground state densities and exchange–correlation holes of the isolated fragments.

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Bougrab, H., K. Inal, H. Sabar et M. Berveiller. « Periodic dislocation configuration analysis by lattice distortion evaluation : micromechanical approach and X-ray diffraction line broadening ». Journal of Applied Crystallography 37, n^o 2 (17 mars 2004) : 270–78. http://dx.doi.org/10.1107/s0021889804001748.

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This work concerns dislocation microstructure analysis in order to assess stored elastic energy using Fourier coefficients of diffraction lines. These coefficients are related to the lattice distortion heterogeneity evaluated using a micromechanical approach. The lattice distortion formulation is based on dislocation density and Green's function tensors. The first tensor, which is a state quantity, characterizes the distortion incompatibility, while the second one characterizes the interaction phenomena between spatial positions. The proposed approach considers a given dislocation configuration in order to calculate the exact associated fields in a deterministic way. Periodic dislocation distributions were examined and the lattice distortion was calculated as a function of the distanceHbetween two successive dislocations (dislocation density). A short-range interaction effect was found for two values:H= 50 and 100 Å. Then Fourier coefficients of {h00}, {hhh} and {hkl} diffraction lines were estimated. It was observed that the sensitivity of the Fourier coefficients toHdepends strongly on the choice of the diffraction vector. Since the dislocation configurations were crystallographically defined, the contrast factor is included directly in our approach. For the considered slip system, it is shown that the screw periodical distribution has a higher Fourier coefficient variation than the periodical edge dislocations.

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Vassilikou-Dova, A. B., et G. Lehmann. « Superposition Model Analysis of NMR Data for TlPbI3 ». Zeitschrift für Naturforschung A 43, n^o 12 (1 décembre 1988) : 1072–74. http://dx.doi.org/10.1515/zna-1988-1210.

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Chemical shift anisotropies of 205Tl and 207Pb in TlPbI3 from the literature are shown to be determined by the distortions of the MIn coordination polyhedra. Application of the superposition model results in very good agreement with the patterns calculated from crystal structure data with an exponent t = 24 for the dependence on bond distance and intrinsic shift parameters of - 83.5 and -600 ppm distortion for 205Tl and 207Pb resp., larger than the value for 29Si in Mg2SiO4. The high value for the exponent suggests that mechanisms proportional to a higher power of overlap of electron density dominate whereas purely electrostatic mechanisms are of minor importance.

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Kohonen, Teuvo. « Comparison of SOM Point Densities Based on Different Criteria ». Neural Computation 11, n^o 8 (1 novembre 1999) : 2081–95. http://dx.doi.org/10.1162/089976699300016098.

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Point densities of model (codebook) vectors in self-organizing maps (SOMs) are evaluated in this article. For a few one-dimensional SOMs with finite grid lengths and a given probability density function of the input, the numerically exact point densities have been computed. The point density derived from the SOM algorithm turned out to be different from that minimizing the SOM distortion measure, showing that the model vectors produced by the basic SOM algorithm in general do not exactly coincide with the optimum of the distortion measure. A new computing technique based on the calculus of variations has been introduced. It was applied to the computation of point densities derived from the distortion measure for both the classical vector quantization and the SOM with general but equal dimensionality of the input vectors and the grid, respectively. The power laws in the continuum limit obtained in these cases were found to be identical.

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Fu, Liangwei, Meijie Yin, Di Wu, Wei Li, Dan Feng, Li Huang et Jiaqing He. « Large enhancement of thermoelectric properties in n-type PbTe via dual-site point defects ». Energy & ; Environmental Science 10, n^o 9 (2017) : 2030–40. http://dx.doi.org/10.1039/c7ee01871a.

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Thangavel, Arumugam, Marika Wieliczko, Christopher Scarborough, Birger Dittrich et John Bacsa. « An investigation of the electron density of a Jahn–Teller-distorted CrIIcation : the crystal structure and charge density of hexakis(acetonitrile-κN)chromium(II) bis(tetraphenylborate) acetonitrile disolvate ». Acta Crystallographica Section C Structural Chemistry 71, n^o 11 (13 octobre 2015) : 936–43. http://dx.doi.org/10.1107/s2053229615015739.

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In the crystal structure of the title homoleptic CrIIcomplex, [Cr(CH3CN)6](C24H20B)2·CH3CN, the [Cr(CH3CN)6]2+cation is a high-spind4complex with strong static, rather than dynamic, Jahn–Teller distortion. The electron density of the cation was determined by single-crystal X-ray refinements using aspherical structure factors from wavefunction calculations. The detailed picture of the electronic density allowed us to assess the extent and directionality of the Jahn–Teller distortion of the CrIIcation away from idealized octahedral symmetry. The topological analysis of the asphericald-electron density about the CrIIcation showed that there are significant valence charge concentrations along the axial Cr—N axes. Likewise, there were significant valence charge depletions about the CrIIcation along the equatorial Cr—N bonds. These charge concentrations are in accordance with a Jahn–Teller-distorted six-coordinate complex.

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