Bulk isotropic negative-index material design for infrared
DEFF Research Database (Denmark)
Andryieuski, Andrei; Malureanu, Radu; Lavrinenko, Andrei
Responding to the strong call for isotropic bulk negative index material we propose a Split Cube in Car-cass design. It shows negative refractive index -1.5, figure-of-merit 2 and transmittivity 30% for one layer at the telecommunication wavelength 1.6 μm. Effective parameters converge fast with ...
Optical isotropic negative index metamaterials
DEFF Research Database (Denmark)
Menzel, Christoph; Paul, Thomas; Rockstuhl, Carsten;
2010-01-01
Towards isotropic metamaterials, we analyze isofrequency surfaces of the dispersion relation of high symmetry metamaterials and show that they are optically not isotropic. We achieve instead isotropic metamaterials that consist of carefully designed multiple layers....
Paniagua-Dominguez, R; Sanchez-Gil, J A
2012-01-01
In the past few years, many of the fascinating and previously almost unconceivable properties predicted for those novel, artificial, man-made materials, so called metamaterials, were demonstrated to be not only a tangible reality, but a very useful one. However, plenty of the best achievements in that newly discovered field are far from having a direct translation to the, in many aspects more interesting, high frequency range, without being burdened not only by technological difficulties, but also conceptual ones. Of particular importance within the realm of optical metamaterials having a negative index of refraction, often designated negative-index metamaterials (NIM), is the issue of simultaneously achieving a strong response of the system and low associated losses. In the present work, we demonstrate the possibility to use hybrid metal-semiconductor nanowires to obtain an isotropic optical NIM, with very strong electric and magnetic responses, which exhibits extremely low losses (about two orders of magnit...
The split cube in a cage: bulk negative-index material for infrared applications
DEFF Research Database (Denmark)
Andryieuski, Andrei; Menzel, C.; Rockstuhl, C.
2009-01-01
We propose the split cube in a cage (SCiC) design for application in producing a bulk metamaterial. Applying realistic material data for thin silver films, we observe an immediate convergence of the effective parameters obtained with a number of layers towards the bulk properties. Results are obt...
Paniagua-Domínguez, R; Marqués, R
2011-01-01
We propose a fully 3D, isotropic metamaterial with strong electric and magnetic response in the optical regime, based on metal-dielectric core-shell nanospheres. The magnetic response stems from the lowest, magnetic-dipole resonance of the dielectric nanoshell with high refractive index. The magnetic resonance can be tuned to coincide with the plasmon resonance of the metal core, responsible for the electric response. Since the response does not stem from coupling between structures, no particular periodic arrangement needs to be imposed.
Negative Index Materials and Plasmonic Antennas Based Nanocouplers
DEFF Research Database (Denmark)
Andryieuski, Andrei
an optical fiber and future optical integrated circuit. Multiple nanocoupler possibilities are analyzed. Two realizations are investigated: negative index metamaterial and plasmonic nanoantenna based. The cubic symmetric negative index metamaterial Split cube in Cage and Split cube in Carcass designs...... for the telecom frequencies are proposed. It is shown that despite the exceptional bulkness (effective properties do not depend on the number of layers) and cubic symmetry the abovementioned designs exhibit strong spatial dispersion in the frequency range of interest. That prevents treating them as an isotropic...... negative index material. The wave propagation retrieval method for metamaterials with linear and circular eigenpolarizations and the field averaging of the restored Bloch mode method are proposed for metamaterials effective properties characterization. The methods are based on observation of the wave...
Tapping of Love waves in an isotropic surface waveguide by surface-to-bulk wave transduction.
Tuan, H.-S.; Chang, C.-P.
1972-01-01
A theoretical study of tapping a Love wave in an isotropic microacoustic surface waveguide is given. The surface Love wave is tapped by partial transduction into a bulk wave at a discontinuity. It is shown that, by careful design of the discontinuity, the converted bulk wave power and the radiation pattern may be controlled. General formulas are derived for the calculation of these important characteristics from a relatively general surface contour deformation.
Baena, J D; Marques, R
2007-01-01
In this paper a systematic approach to the design of bulk isotropic magnetic metamaterials is presented. The role of the symmetries of both the constitutive element and the lattice are analyzed. For this purpose it is assumed that the metamaterial is composed by cubic SRR resonators, arranged in a cubic lattice. The minimum symmetries needed to ensure an isotropic behavior are analyzed, and some particular configurations are proposed. Besides, an equivalent circuit model is proposed for the considered cubic SRR resonators. Experiments are carried out in order to validate the proposed theory. We hope that this analysis will pave the way to the design of bulk metamaterials with strong isotropic magnetic response, including negative permeability and left-handed metamaterials.
The role of bulk viscosity on the decay of compressible, homogeneous, isotropic turbulence
Johnsen, Eric; Pan, Shaowu
2016-11-01
The practice of neglecting bulk viscosity in studies of compressible turbulence is widespread. While exact for monatomic gases and unlikely to strongly affect the dynamics of fluids whose bulk-to-shear viscosity ratio is small and/or of weakly compressible turbulence, this assumption is not justifiable for compressible, turbulent flows of gases whose bulk viscosity is orders of magnitude larger than their shear viscosities (e.g., CO2). To understand the mechanisms by which bulk viscosity and the associated phenomena affect compressible turbulence, we conduct DNS of freely decaying compressible, homogeneous, isotropic turbulence for ratios of bulk-to-shear viscosity ranging from 0-1000. Our simulations demonstrate that bulk viscosity increases the decay rate of turbulent kinetic energy; while enstrophy exhibits little sensitivity to bulk viscosity, dilatation is reduced by an order of magnitude within the two eddy turnover time. Via a Helmholtz decomposition of the flow, we determined that bulk viscosity damps the dilatational velocity and reduces dilatational-solenoidal exchanges, as well as pressure-dilatation coupling. In short, bulk viscosity renders compressible turbulence incompressible by reducing energy transfer between translational and internal modes.
Energy flow in negative index materials
Institute of Scientific and Technical Information of China (English)
Lorenzo Bolla; Michele Midrio; Carlo G. Someda
2004-01-01
From Maxwell's equations, we compute the speed and the direction of propagation of active power refractedfrom air into a negative index material. We prove, both analytically and numerically that the power mayrefract positively even if phase fronts refract negatively. Considerations on the usage of ray optics inproblems involving negative index materials are drawn.
Institute of Scientific and Technical Information of China (English)
LI Tong-qi; HU Zi-jun; WANG Jun-shan; GUO Yu-ming; WANG Cheng-yang
2006-01-01
Mesocarbon microbeads (MCMB) and super fine mesophase powder (SFMP) were prepared firstly from a coal tar pitch and then hot-condensed into high-density isotropic carbon (HDIC) bulks under 160 Mpa and finally sintered at 1 000 ℃. By analyzing the thermogravimetric behavior of the MCMB and SFMP powders, their volume shrinkage and weight loss during sintering and the bulk density and flexural strengths of their sintered bulks, it was found that the smaller sizes and the richer β-resin contents of SFMP have facilitated formation of sintered bulks with more compact isotropic structure and higher flexural strengths than MCMB. Because of the filling and bonding effects of SFMP on MCMB bulks, addition of SFMP, albeit a little, can greatly increase the flexural strengths of sintered bulks of MCMB. However, adding MCMB, even a slight amount, into SFMP can severely impair the flexural strength of sintered bulks. This might be attributed to both the crack initiation along the boundaries between MCMB and SFMP and the formation of layered texture of MCMB sphere.
Śliwa, Izabela; Zakharov, A V
2017-01-01
Calculations of translational self-diffusion coefficient in free-standing smectic films during a series of layer-thinning transitions as the temperature is raised above the bulk smectic-A-isotropic transition have been carried out. A molecular model based upon the random walk theory is applied for calculating the translational diffusion coefficient (TDC) D_{∥} across the smectic film both in the bulk of the film, as well as in the vicinity of the bounding surfaces. Calculations of D_{∥} require the set of the orientational and translational order parameters (OPs) which have been obtained by using the extended McMillan approach with anisotropic forces. The effect of E on the orientational and translational OPs, as well as on the TDC of smectic films has been investigated. A reasonable agreement between the theoretically predicted and the experimentally obtained data on the TDC in the bulk of the partially fluorinated H10F5MOPP film has been obtained. We also found, in agreement with the experimentally observed behavior of D_{∥}(N)(N=25,13,11,10), that the translational diffusion coefficient in the bulk of the film gradually increases as the film thickness N is decreased.
Mak, M K; Harko, T
2001-01-01
We consider the evolution of a flat Friedmann-Robertson-Walker Universe, filled with a causal bulk viscous cosmological fluid, in the presence of variable gravitational and cosmological constants. The basic equation for the Hubble parameter, generalizing the evolution equation in the case of constant gravitational coupling and cosmological term, is derived, under the supplementary assumption that the total energy of the Universe is conserved. By assuming that the cosmological constant is proportional to the square of the Hubble parameter and a power law dependence of the bulk viscosity coefficient, temperature and relaxation time on the energy density of the cosmological fluid, two classes of exact solutions of the field equations are obtained. In the first class of solutions the Universe ends in an inflationary era, while in the second class of solutions the expansion of the Universe is non-inflationary for all times. In both models the cosmological "constant" is a decreasing function of time, while the grav...
Towards negative index self-assembled metamaterials
Fruhnert, Martin; Lederer, Falk; Rockstuhl, Carsten
2016-01-01
We investigate the magnetic response of meta-atoms that can be fabricated by a bottom-up technique. Usually such meta-atoms consist of a dielectric core surrounded by a large number of solid metallic nanoparticles. In contrast to those meta-atoms considered thus far, we study here for the first time hollow metallic nanoparticles (shells). In doing so we solve one of the most pertinent problems of current self-assembled metamaterials, namely implementing meta-atoms with sufficiently large resonance strength and small absorption. Both conditions have to be met for deep sub-wavelength meta-atoms to obtain effectively homogeneous metamaterials which may be meaningfully described by negative material parameters. Eventually we show that by using these findings self-assembled negative index materials come in reach.
Energy Technology Data Exchange (ETDEWEB)
Deng, Xiangxing [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Liu, Zhongwu, E-mail: zwliu@scut.edu.cn [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Yu, Hongya [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Xiao, Zhiyu [School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640 (China); Zhang, Guoqing [Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095 (China)
2015-09-15
NdFeB powders were consolidated into nanocrystalline bulk magnets by a near-net-shape process of high-velocity compaction (HVC) at room temperature with no binder employed. The nanostructure can be maintained after compaction. The compacted magnets with relatively high density can inherit the coercivity of the starting powders. The mechanical strength of the HVCed magnet after heat treatment is comparable to that of the conventional bonded NdFeB magnets. The anisotropic magnet has also been prepared by hot deformation using HVCed magnet as the precursor. The remanence value along the pressing direction increased from 0.64 to 0.95 T and maximum energy product (BH){sub max} increased from 65 to 120 kJ/m{sup 3} after hot deformation. The processing–structure–properties relationships for both isotropic and anisotropic magnets are discussed. - Highlights: • HVC is a feasible binder-free approach for preparing NdFeB magnets. • The compacted magnets can inherit the coercivity of the starting powders. • The magnets post heat treatment have compression strength higher than bonded magnets. • The approach of HVC is a potential pre-process for anisotropic NdFeB bulk magnets.
Isotropic optical metamaterials
DEFF Research Database (Denmark)
Lederer, Falk; Rockstuhl, C.; Menzel, C.;
2010-01-01
Metamaterial imaging applications require optical isotropy. We show that highly symmetric unit cells do not necessarily exhibit this property. We prove that the dispersion relation can be tailored using a supercell metama-terial. Such metamaterial exhibits an isotropic negative index close to -1...
High symmetry versus optical isotropy of a negative-index metamaterial
DEFF Research Database (Denmark)
Menzel, Christoph; Rockstuhl, Carsten; Lliew, Rumen;
2010-01-01
Optically isotropic metamaterials MMs are required for the implementation of subwavelength imaging systems. At first glance one would expect that their design should be based on unit cells exhibiting a cubic symmetry being the highest crystal symmetry. It is anticipated that this is a sufficient...... in carcass negative index MM. We show that this MM is basically optically isotropic but not in the spectral domain where it exhibits negative refraction. The primary goal of this contribution is to introduce a tool that allows to probe a MM against optical isotropy....
Verhagen, Ewold; L.,; Kuipers,; Polman, Albert
2010-01-01
We identify a route towards achieving a negative index of refraction at optical frequencies based on coupling between plasmonic waveguides that support backwards waves. We show how modal symmetry can be exploited in metal-dielectric waveguide pairs to achieve negative refraction of both phase and energy. By properly controlling coupling between adjacent waveguides, a metamaterial consisting of a one-dimensional multilayer stack exhibiting an isotropic index of -1 can be achieved at a free-space wavelength of 400 nm. The general concepts developed here may inspire new low-loss metamaterial designs operating close to the metal plasma frequency.
Verhagen, Ewold; de Waele, René; Kuipers, L.; Polman, Albert
2010-11-01
We identify a route towards achieving a negative index of refraction at optical frequencies based on coupling between plasmonic waveguides that support backwards waves. We show how modal symmetry can be exploited in metal-dielectric waveguide pairs to achieve negative refraction of both phase and energy. Control of waveguide coupling yields a metamaterial consisting of a one-dimensional multilayer stack that exhibits an isotropic index of -1 at a free-space wavelength of 400 nm. The concepts developed here may inspire new low-loss metamaterial designs operating close to the metal plasma frequency.
Verhagen, Ewold; de Waele, René; Kuipers, L; Polman, Albert
2010-11-26
We identify a route towards achieving a negative index of refraction at optical frequencies based on coupling between plasmonic waveguides that support backwards waves. We show how modal symmetry can be exploited in metal-dielectric waveguide pairs to achieve negative refraction of both phase and energy. Control of waveguide coupling yields a metamaterial consisting of a one-dimensional multilayer stack that exhibits an isotropic index of -1 at a free-space wavelength of 400 nm. The concepts developed here may inspire new low-loss metamaterial designs operating close to the metal plasma frequency.
Optical properties of multilayer optics including negative index materials
Lequime, Michel; Gralak, Boris; guenneau, sebastien; Zerrad, Myriam; Amra, Claude
2013-01-01
Negative indices are revisited through the thin-film admittance formalism. Effective indices and phase delay associated with wave propagation through negative index layers are carefully defined and computational rules easily implementable in standard thin-film software are derived from this approach. This admittance formalism is then used to recover the main features of the perfect lens and to highlight the benefit of such negative index materials to improve the performances of quarter-wavele...
Optical properties of multilayer optics including negative index materials
Lequime, Michel; Guenneau, Sebastien; Zerrad, Myriam; Amra, Claude
2013-01-01
Negative indices are revisited through the thin-film admittance formalism. Effective indices and phase delay associated with wave propagation through negative index layers are carefully defined and computational rules easily implementable in standard thin-film software are derived from this approach. This admittance formalism is then used to recover the main features of the perfect lens and to highlight the benefit of such negative index materials to improve the performances of quarter-wavelength Bragg mirrors and Fabry-Perot band-pass filters.
Radiation Pressure and Photon Momentum in Negative-Index Media
Mansuripur, Masud
2013-01-01
Radiation pressure and photon momentum in negative-index media are no different than their counterparts in ordinary (positive-index) materials. This is because the parameters responsible for these properties are the admittance, sqrt(epsilon/mu), and the group refractive index n_g of the material (both positive entities), and not the phase refractive index, n=sqrt(epsilon*mu), which is negative in negative-index media. One approach to investigating the exchange of momentum between electromagnetic waves and material media is via the Doppler shift phenomenon. In this paper we use the Doppler shift to arrive at an expression for the radiation pressure on a mirror submerged in a negative-index medium. In preparation for the analysis, we investigate the phenomenon of Doppler shift in various settings, and show the conditions under which a so-called "inverse" Doppler shift could occur. We also argue that a recent observation of the inverse Doppler shift upon reflection from a negative-index medium cannot be correct,...
Negative-index metamaterials: looking into the unit cell
Burresi, M.; Diessel, D.; van Oosten, D.; Linden, Stefan; Wegener, M.; Kuipers, L.
2010-01-01
With their potential for spectacular applications, like superlensing and cloaking, metamaterials are a powerful class of nanostructured materials. All these applications rely on the metamaterials acting as a homogeneous material. We investigate a negative index metamaterial with a phase-sensitive ne
Veum, M; Duelge, L; Droske, J; Nguyen, H T; Huang, C C; Mirantsev, L V
2009-09-01
Using differential scanning calorimetry, the transition enthalpies and temperatures for the bulk smectic-isotropic phase transition have been measured for a series of liquid-crystal compounds. For five compounds, those values were used as parameters in a microscopic mean-field model to predict the temperature dependence of the difference in free-energy density between a sample of material in a free-standing smectic film and that in the bulk. The model predicts a weak temperature dependence below the bulk clearing point and a pronounced monotonic increase with temperature above the transition temperature. The compounds used in this study were chosen specifically because they were also the subject of a previous independent experimental study [M. Veum, Phys. Rev. E 74, 011703 (2006)] that demonstrated a sudden monotonic increase in the free-standing film tension with temperature, which is qualitatively consistent with the predictions of the above-mentioned mean-field model. This study presents a direct and quantitative comparison between the predictions of the mean-field model and the results from previous tension experiments.
On the Fourier coefficients of negative index meromorphic Jacobi forms
Bringmann, Kathrin; Zwegers, Sander
2015-01-01
In this paper, we consider the Fourier coefficients of meromorphic Jacobi forms of negative index. This extends recent work of Creutzig and the first two authors for the special case of Kac-Wakimoto characters which occur naturally in Lie theory, and yields, as easy corollaries, many important PDEs arising in combinatorics such as the famous rank-crank PDE of Atkin and Garvan. Moreover, we discuss the relation of our results to partial theta functions and quantum modular forms as introducted by Zagier, which together with previous work on positive index meromorphic Jacobi forms illuminates the general structure of the Fourier coefficients of meromorphic Jacobi forms.
Merging Nonlinear Optics and Negative-Index Metamaterials
Popov, Alexander K
2011-01-01
The extraordinary properties of nonlinear optical propagation processes in double-domain positive/negative index metamaterials are reviewed. These processes include second harmonic generation, three- and four-wave frequency mixing, and optical parametric amplification. Striking contrasts with the properties of the counterparts in ordinary materials are shown. We also discuss the possibilities for compensating strong losses inherent to plasmonic metamaterials, which present a major obstacle in numerous exciting applications, and the possibilities for creation of unique ultracompact photonic devices such as data processing chips and nonlinear-optical sensors. Finally, we propose similar extraordinary three-wave mixing processes in crystals based on optical phonons with negative dispersion.
Electromagnetic field energy density in homogeneous negative index materials.
Shivanand; Webb, Kevin J
2012-05-07
An exact separation of both electric and magnetic energies into stored and lost energies is shown to be possible in the special case when the wave impedance is independent of frequency. A general expression for the electromagnetic energy density in such a dispersive medium having a negative refractive index is shown to be accurate in comparison with numerical results. Using an example metamaterial response that provides a negative refractive index, it is shown that negative time-averaged stored energy can occur. The physical meaning of this negative energy is explained as the energy temporarily borrowed by the field from the material. This observation for negative index materials is of interest when approaching properties for a perfect lens. In the broader context, the observation of negative stored energy is of consequence in the study of dispersive materials.
Optical Properties of Synthetic Cannabinoids with Negative Indexes
Shen, Yao
2016-01-01
Some kinds of psychoactive drugs have the structures which are called split-ring resonators (SRRs). SRRs might result in negative permittivity and permeability simultaneously in electromagnetic field. Simultaneous negative indexes can lead to the famous phenomenon of negative refraction. This optical property makes it possible to distinguish synthetic cannabinoids from other abusive psychoactive drugs in the UV-vis region. This optical method is non-damaged and superior in forensic science. In this paper, we use tight-binding model calculating the permittivity and permeability of the main ingredients of synthetic cannabinoids. At the same time, we give two more results of zolpidem and caffeine. Further we discuss the negative refraction of the category of zepam qualitatively.
Sub-picosecond optical switching with a negative index metamaterial
Energy Technology Data Exchange (ETDEWEB)
Dani, Keshav M [Los Alamos National Laboratory; Upadhya, Prashant C [Los Alamos National Laboratory; Zahyum, Ku [CHTM-UNM
2009-01-01
Development of all-optical signal processing, eliminating the performance and cost penalties of optical-electrical-optical conversion, is important for continu,ing advances in Terabits/sec (Tb/s) communications.' Optical nonlinearities are generally weak, traditionally requiring long-path, large-area devicesl,2 or very high-Q, narrow-band resonator structures.3 Optical metamaterials offer unique capabilities for optical-optical interactions. Here we report 600 femtosecond (fs) all-optical modulation using a fIShnet (2D-perforated metallamorphous-Si (a-Si)/metal film stack) negative-index meta material with a structurally tunable broad-band response near 1.2 {micro}m. Over 20% modulation (experimentally limited) is achieved in a path length of only 116 nm by photo-excitation of carriers in the a-Si layer. This has the potential for Tb/s aU-optical communication and will lead to other novel, compact, tunable sub-picosecond (ps) photonic devices.
Low-loss negative index metamaterials for X, Ku, and K microwave bands
Directory of Open Access Journals (Sweden)
David A. Lee
2015-04-01
Full Text Available Low-loss, negative-index of refraction metamaterials were designed and tested for X, Ku, and K microwave frequency bands. An S-shaped, split-ring resonator was used as a unit cell to design homogeneous slabs of negative-index metamaterials. Then, the slabs of metamaterials were cut unto prisms to measure experimentally the negative index of refraction of a plane electromagnetic wave. Theoretical simulations using High-Frequency Structural Simulator, a finite element equation solver, were in good agreement with experimental measurements. The negative index of refraction was retrieved from the angle- and frequency-dependence of the transmitted intensity of the microwave beam through the metamaterial prism and compared well to simulations; in addition, near-field electromagnetic intensity mapping was conducted with an infrared camera, and there was also a good match with the simulations for expected frequency ranges for the negative index of refraction.
Relationship between the Kramers-Kronig relations and negative index of refraction
Hickey, Mark C; Kussow, Adil-Gerai
2010-01-01
The condition for a negative index of refraction with respect to the vacuum index is established in terms of permittivity and permeability susceptibilities. It is found that the imposition of analyticity to satisfy the Kramers-Kronig relations is a sufficiently general criterion for a physical negative index. The satisfaction of the Kramers-Kronig relations is a manifestation of the principle of causality and the predicted frequency region of negative index agrees with the Depine-Lakhtakia condition for the phase velocity being anti-directed to the Poynting vector, although the conditions presented here do not assume {\\it a priori} a negative solution branch for n.
Plasmon-Enhanced Photonic Crystal Negative Index Materials for Superlensing Applications Project
National Aeronautics and Space Administration — Negative index materials (NIMs) offer tremendous potential for the formation of highly compact as well as large-area deployable thin-film optical components. Omega...
Relations between Multi-Poly-Bernoulli numbers and Poly-Bernoulli numbers of negative index
Komaki, Hiroyuki
2015-01-01
Poly-Bernoulli numbers $B_n^{(k)}\\in\\mathbb{Q}$\\,($n \\geq 0$,\\,$k \\in \\mathbb{Z}$) are defined by Kaneko in 1997. Multi-Poly-Bernoulli numbers\\,$B_n^{(k_1,k_2,\\ldots, k_r)}$, defined by using multiple polylogarithms, are generations of Kaneko's Poly-Bernoulli numbers\\,$B_n^{(k)}$. We researched relations between Multi-Poly-Bernoulli numbers and Poly-Bernoulli numbers of negative index in particular. In section 2, we introduce a identity for Multi-Poly-Bernoulli numbers of negative index which...
The use of a negative index planoconcave lens array for wide-viewing angle integral imaging.
Kim, Hwi; Hahn, Joonku; Lee, Byoungho
2008-12-22
Wide-viewing angle integral imaging by means of a negative refractive index planoconcave lens array is theoretically investigated. The optical properties of a negative refractive index lens are analyzed from the point of view of integral imaging. The effective focal length of a positive index planoconvex lens and a negative index planoconcave lens with the same surface spherical curvature R are approximated as fP,eff = 2R and fN,eff = 0.4 R, respectively. This short effective focal length of the negative index lens is advantageous for extending the viewing angle of the integral imaging. In addition, some other optical properties of a negative index lens are analyzed and compared for a positive index lens. Three-dimensional ray-tracing observation simulations of integral imaging systems with a negative index lens array and a positive index lens array are then performed, in a comparative study of the wide- ewing angle mode for integral imaging. A three-dimensional ray-tracing simulator for an integral imaging system is then developed. Some interesting issues that appear in the wide-viewing mode of integral imaging are discussed. The negative refractive index planoconcave lens was found to give a wider viewing angle of -60(deg.) approximately +60(deg.) and reduces aberration with only a single spherical planoconcave lens.
(Department of Science)On certain properties of poly-Bernoulli numbers with negative index
坂田, 実加; 大野, 泰生
2013-01-01
Poly-Bernoulli numbers were introduced and studied by M. Kaneko as a generalization of classical Bernoulli numbers. In this article, for any prime number ρ, certain congruence properties of poly-Bernoulli numbers with negative index modulo ρare given.
Negative-index gratings formed by femtosecond laser overexposure and thermal regeneration.
He, Jun; Wang, Yiping; Liao, Changrui; Wang, Chao; Liu, Shen; Yang, Kaiming; Wang, Ying; Yuan, Xiaocong; Wang, Guo Ping; Zhang, Wenjing
2016-03-16
We demonstrate a method for the preparation of negative-index fibre Bragg gratings (FBGs) using 800 nm femtosecond laser overexposure and thermal regeneration. A positive-index type I-IR FBG was first inscribed in H2-free single-mode fibre using a femtosecond laser directed through a phase mask, and then a highly polarization dependant phase-shifted FBG (P-PSFBG) was fabricated from the type I-IR FBG by overexposure to the femtosecond laser. Subsequently, the P-PSFBG was thermally annealed at 800 °C for 12 hours. Grating regeneration was observed during thermal annealing, and a negative-index FBG was finally obtained with a high reflectivity of 99.22%, an ultra-low insertion loss of 0.08 dB, a blueshift of 0.83 nm in the Bragg wavelength, and an operating temperature of up to 1000 °C for more than 10 hours. Further annealing tests showed that the thermal stability of the negative-index FBG was lower than that of a type II-IR FBG, but much higher than that of a type I-IR FBG. Moreover, the formation of such a negative-index grating may result from thermally regenerated type IIA photosensitivity.
Xiang, Yuanjiang; Dai, Xiaoyu; Wen, Shuangchun; Fan, Dianyuan
2007-11-01
We show that the frequency range of the zero averaged refractive index gap in a photonic heterostructure containing negative-index materials can be enlarged owing to the property that its lower and upper frequency edges depend on the thickness ratio of the positive- and negative-index materials. Compared to the zero averaged refractive index gap of a single photonic crystal, the frequency range of the zero averaged refractive index gaps in a photonic heterostructure can be notably enlarged. Moreover, it is shown that the band edge of the zero averaged refractive index gap is determined not only by the TM polarization but also by the TE polarization, which is obviously different from the omnidirectional band gaps in conventional photonic crystals, whose bandwidth is determined by the TM polarization.
Creating double negative index materials using the Babinet principle with one metasurface
Zhang, Lei; Koschny, Thomas; Soukoulis, C. M.
2013-01-01
Metamaterials are patterned metallic structures which permit access to a novel electromagnetic response, negative index of refraction, impossible to achieve with naturally occurring materials. Using the Babinet principle, the complementary split ring resonator (SRR) is etched in a metallic plate to provide negative ɛ, with perpendicular direction. Here we propose a new design, etched in a metallic plate to provide negative magnetic permeability μ, with perpendicular direction. The combined electromagnetic response of this planar metamaterial, where the negative μ comes from the aperture and the negative ɛ from the remainder of the continuous metallic plate, allows achievement of a double negative index metamaterial (NIM) with only one metasurface and strong transmission. These designs can be used to fabricate NIMs at microwave and optical wavelengths and three-dimensional metamaterials.
Observation of the inverse Doppler effect in negative-index materials at optical frequencies
Chen, Jiabi; Wang, Yan; Jia, Baohua; Geng, Tao; Li, Xiangping; Feng, Lie; Qian, Wei; Liang, Bingming; Zhang, Xuanxiong; Gu, Min; Zhuang, Songlin
2011-04-01
The Doppler effect is a fundamental frequency shift phenomenon that occurs whenever a wave source and an observer are moving with respect to one another. It has well-established applications in astrophotonics, biological diagnostics, weather and aircraft radar systems, velocimetry and vibrometry. The counterintuitive inverse Doppler effect was theoretically predicted in 1968 by Veselago in negative-index materials. However, because of the tremendous challenges of frequency shift measurements inside such materials, most investigations of the inverse Doppler effect have been limited to theoretical predictions and numerical simulations. Indirect experimental measurements have been conducted only in nonlinear transmission lines at ~1-2 GHz (ref. 8) and in acoustic media at 1-3 kHz (ref. 9). Here, we report the first experimental observation of the inverse Doppler shift at an optical frequency (λ = 10.6 µm) by refracting a laser beam in a photonic-crystal prism that has the properties of a negative-index material.
Influence of Filling Medium of Holes on the Negative-Index Response of Sandwiched Metamaterials
Institute of Scientific and Technical Information of China (English)
WANG Xu-Dong; YE Yong-Hong; MA Ji; JIANG Mei-Ping
2010-01-01
@@ We numerically study the negative index properties of sandwiched metamaterials,perforated with a square array of circle holes filled with different media.Transmission spectra indicate that the filling medium can effectively change the position of the localized resonant peak,while keeping the position of the other transmission peaks hardly changed.Reflection spectra and retrieved effective impedance verify that an appropriate choice of the filling medium can provide a perfect impedance match.Due to the perfect impedance match,the electromagnetic responses of the negative index band based on the internal surface plasmon polaritons change in many aspects,such as a stronger magnetic resonance,a higher figure of merit and a narrower negative refractive index band.
Low-loss multilayered metamaterial exhibiting a negative index of refraction at visible wavelengths
Garcia-Meca, Carlos
2012-02-01
Over the last decade, metamaterials have attracted a great interest thanks to their potential to expand the range of electromagnetic properties found in natural materials. In particular, the possibility of achieving negative refractive index media (NIM) enables us to implement superlenses and optical storing devices. Since the first experimental demonstration at microwave frequencies, much effort has been put in extending negative refraction to the visible spectrum, where we can take full advantage of NIM properties. For instance, the superior imaging ability of NIM would be essential for visible microscopy. The desired features for NIM are low loss and isotropy. This last property includes polarization independence and negative-index behavior in all spatial directions. None of these features have been attained in previous experiments. Thus, the current challenge is to improve such aspects in order to make NIM suitable for practical applications. In this work, we experimentally demonstrate a low-loss multilayer metamaterial exhibiting a double-negative index in the visible spectrum, while presenting polarization independence at normal incidence. This has been achieved by exploiting the properties of a second-order magnetic resonance of the so-called fishnet structure, in contrast to previous works that used first-order magnetic resonances, both related to gap surface plasmon polariton (SPP) modes. The low-loss nature of the employed magnetic resonance, together with the effect of the interacting adjacent layers, results in a figure of merit as high as 3.34. A wide spectral range of negative index is achieved, covering the wavelength region between 620 and 806 nm with only two different designs. The fabricated metamaterials are the first experimental multilayer NIM in the visible spectrum, which entails an important step towards homogeneous NIM in this range. Finally, we found that the SPP modes determining the permeability resonance display weak angular dispersion.
On metallic gratings coated conformally with isotropic negative-phase-velocity materials
Energy Technology Data Exchange (ETDEWEB)
Inchaussandague, Marina E. [GEA-Grupo de Electromagnetismo Aplicado, Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellon I, 1428 Buenos Aires (Argentina); CONICET-Consejo Nacional de Investigaciones Cientificas y Tecnicas, Rivadavia 1917, Buenos Aires (Argentina)], E-mail: mei@df.uba.ar; Lakhtakia, Akhlesh [CATMAS-Computational and Theoretical Materials Sciences Group, Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, PA 16802-6812 (United States)], E-mail: akhlesh@psu.edu; Depine, Ricardo A. [GEA-Grupo de Electromagnetismo Aplicado, Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellon I, 1428 Buenos Aires (Argentina); CONICET-Consejo Nacional de Investigaciones Cientificas y Tecnicas, Rivadavia 1917, Buenos Aires (Argentina)], E-mail: rdep@df.uba.ar
2008-03-31
Application of the differential method (also called the C method) to plane-wave diffraction by a perfectly conducting, sinusoidally corrugated metallic grating coated with a linear, homogeneous, isotropic, lossless dielectric-magnetic material shows that coating materials with negative index of refraction may deliver enhanced maximum nonspecular reflection efficiencies in comparison to coating materials with positive index of refraction.
Measurement of a broadband negative index with space-coiling acoustic metamaterials.
Xie, Yangbo; Popa, Bogdan-Ioan; Zigoneanu, Lucian; Cummer, Steven A
2013-04-26
We report the experimental demonstration of a broadband negative refractive index obtained in a labyrinthine acoustic metamaterial structure. Two different approaches were employed to prove the metamaterial negative index nature: one-dimensional extractions of effective parameters from reflection and transmission measurements and two-dimensional prism-based measurements that convincingly show the transmission angle corresponding to negative refraction. The transmission angles observed in the latter case also agree very well with the refractive index obtained in the one-dimensional measurements and numerical simulations. We expect this labyrinthine metamaterial to become the unit cell of choice for practical acoustic metamaterial devices that require broadband and significantly negative indices of refraction.
Measurement of a Broadband Negative Index with Space-Coiling Acoustic Metamaterials
Xie, Yangbo; Popa, Bogdan-Ioan; Zigoneanu, Lucian; Cummer, Steven A.
2013-04-01
We report the experimental demonstration of a broadband negative refractive index obtained in a labyrinthine acoustic metamaterial structure. Two different approaches were employed to prove the metamaterial negative index nature: one-dimensional extractions of effective parameters from reflection and transmission measurements and two-dimensional prism-based measurements that convincingly show the transmission angle corresponding to negative refraction. The transmission angles observed in the latter case also agree very well with the refractive index obtained in the one-dimensional measurements and numerical simulations. We expect this labyrinthine metamaterial to become the unit cell of choice for practical acoustic metamaterial devices that require broadband and significantly negative indices of refraction.
Institute of Scientific and Technical Information of China (English)
Dong Zheng-Gao; Zhu Shi-Ning; Liu Hui
2006-01-01
Negative-index refraction is demonstrated in a lamellar composite with epsilon-negative (ENG) and mu-negative (MNG) materials stacked alternatively. Based on the effective medium approximation, simultaneously negative effective permittivity and permeability of such a lamellar composite are obtained theoretically and further proven by full-wave simulations. Consequently, the renowned left-handed metamaterial comprising split ring resonators and wires is interpreted as an analogy of such ENG-MNG layers. In addition, beyond the effective medium approximation, the propagating field squeezed near the ENG/MNG interface is demonstrated to be left-handed surface waves with backward phase velocity.
Energy Technology Data Exchange (ETDEWEB)
Chen, Yihang, E-mail: kallenmail@sina.co [School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China)
2009-04-07
Multiple defect modes may generate in one-dimensional dual-defective photonic crystals containing negative-index materials. The interference between the two kinds of defect states of the proposed structure is avoided. Therefore, the frequency, frequency interval and number of the defect modes corresponding to different kinds of defects can be tuned independently as desired. These defect modes inside the zero n-bar gap are insensitive to the incident angle. It thus opens a promising way to fabricate omnidirectional multichannel filters with specific channels.
Institute of Scientific and Technical Information of China (English)
XIANG Yuan-jiang; DAI Xiao-yu; WEN Shuang-chun
2007-01-01
School of Computer and Communication, Hunan University, Changsha 410082, ChinaThe photonic band gap structure of 1D photonic crystal with a negative index medium defect layer is studied by using the transfer matrix method. Investigations show that the introdution of negative index medium defect layer and the increase of the negative index value will result in an extension of the band gap. Moreover, by increasing the negative index, the width of defect layer and the numbers of period photonic crystal, the width of defect modes will be narrowed, which is advantaged to obtain optical filters with narrow band. Finally, the effects of absorption on the properties of band gap and on defect modes have been discussed.
Antisymmetric PT-photonic structures with balanced positive and negative index materials
Ge, Li
2012-01-01
In this Letter we study a new class of synthetic materials in which the refractive index satisfies a special symmetry, n(-x)=-n^*(x), which we term antisymmetric parity-time (APT) systems. Unlike PT-symmetric systems which require balanced gain and loss, i.e. n(-x)=n^*(x), APT systems consist of balanced positive and negative index materials (NIMs). Despite the seemingly PT-symmetric optical potential $V(x)\\equiv n(x)^2\\omega^2/c^2$, such systems are not invariant under combined PT operation due to the discontinuity of the spatial derivative of the wavefunction. We show that APT systems display intriguing properties such as spontaneous phase transition of the scattering matrix, bidirectional invisibility, and a continuous lasing spectrum.
Creating wide-band negative-index-of-refraction metamaterials with fractal-based geometry
Penney, Keith
2009-11-01
A burgeoning topic of modern research in electrodynamics and antenna design is the design and fabrication of ``left-handed'' metamaterials. This ``left-handedness'' is often created through use of an array of conductive structures with geometry appropriate for coupling on the wavelength scale with incident radiation to produce a phase-shifted reflected wave that cancels out incoming radiation and prevents transmission. This property has been demonstrated in several papers published in the last decade. In every instance, though the ``left-handed'' response is only exhibited in a small bandwidth centered about a specific frequency (bandwidth typically less that 0.1 GHz). I will show that through use of tessellated, fractal-based structures, one can create a repeatable geometry that exhibits a negative index of refraction (NIR) for multiple frequency bands, limited only by fabrication precision, with the ultimate goal being a wide-band absorptive response.
Aberration-free two-thin-lens systems based on negative-index materials
Institute of Scientific and Technical Information of China (English)
Lin Zhi-Li; Ding Jie-Chen; Zhang Pu
2008-01-01
Since the complete correction of all five monochromatic Seidel aberrations for a singlet lens with random shape or a two-thin-lens system is unprocurable merely by using the conventional positive-index materials both in theory and practice, this paper proposes that when one or both of the two lenses is/are made from negative-index materials, an imaging system composed of a pair of spherical thin lenses is possible to form a real image, in air, free from all five monochromatic Seidel aberrations. The calculated numerical solutions to the structural parameters of such lens systems possessing superior performance are provided and examples of them are illustrated for the given combinations of the two lenses' refractive indices, including an ultimately-remote imaging system.
Backward phase-matching for nonlinear optical generation in negative-index materials
Lan, Shoufeng; Kang, Lei; Schoen, David T.; Rodrigues, Sean P.; Cui, Yonghao; Brongersma, Mark L.; Cai, Wenshan
2015-08-01
Metamaterials have enabled the realization of unconventional electromagnetic properties not found in nature, which provokes us to rethink the established rules of optics in both the linear and nonlinear regimes. One of the most intriguing phenomena in nonlinear metamaterials is `backward phase-matching', which describes counter-propagating fundamental and harmonic waves in a negative-index medium. Predicted nearly a decade ago, this process is still awaiting a definitive experimental confirmation at optical frequencies. Here, we report optical measurements showing backward phase-matching by exploiting two distinct modes in a nonlinear plasmonic waveguide, where the real parts of the mode refractive indices are 3.4 and -3.4 for the fundamental and the harmonic waves respectively. The observed peak conversion efficiency at the excitation wavelength of ~780 nm indicates the fulfilment of the phase-matching condition of k2ω = 2kω and n2ω = -nω, where the coherent harmonic wave emerges along a direction opposite to that of the incoming fundamental light.
Yuan, Xu-Jin
2012-09-01
In comparison with the phenomenon of negative index refraction observed in artificial meta-materials, it is interesting to ask if this type of behavior also exists or not in reaction-diffusion systems that support nonlinear chemical waves. Previous studies indicate that the negative index refraction could occur on a interface between a medium of a normal wave and a medium that supports anti-waves. Here we investigate the phenomenon in the complex Ginzburg—Landau equation (CGLE) in a close relationship with the quantitative model for the chloriteiodide-malonic acid (CIMA) reaction. The amplitude equation CGLE is deduced from the CIMA reaction, and simulations with mapped parameters from the reaction-diffusion equation reveal that the competition between normal waves and anti-waves on the interface determines whether the negative index refraction occurs or not.
The Universe With Bulk Viscosity
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Exact solutions for a model with variable G, A and bulk viscosity areobtained. Inflationary solutions with constant (de Sitter-type) and variable energydensity are found. An expanding anisotropic universe is found to isotropize duringits expansion but a static universe cannot isotropize. The gravitational constant isfound to increase with time and the cosmological constant decreases with time asAo∝t-2.
Isotropic Single Negative Metamaterials
Directory of Open Access Journals (Sweden)
P. Protiva
2008-09-01
Full Text Available This paper presents the application of simple, and therefore cheap, planar resonators for building 3D isotropic metamaterials. These resonators are: a broadside-coupled split ring resonator with a magnetic response providing negative permeability; an electric dipole terminated by a loop inductor together with a double H-shaped resonator with an electric response providing negative permittivity. Two kinds of 3D isotropic single negative metamaterials are reported. The first material consists of unit cells in the form of a cube bearing on its faces six equal planar resonators with tetrahedral symmetry. In the second material, the planar resonators boxed into spherical plastic shells and randomly distributed in a hosting material compose a real 3D volumetric metamaterial with an isotropic response. In both cases the metamaterial shows negative permittivity or permeability, according to the type of resonators that are used. The experiments prove the isotropic behavior of the cells and of the metamaterial specimens.
Energy, Momentum, and Force in Classical Electrodynamics: Application to Negative-index Media
Mansuripur, Masud; 10.1016/j.optcom.2010.06.101
2012-01-01
The classical theory of electromagnetism is based on Maxwell's macroscopic equations, an energy postulate, a momentum postulate, and a generalized form of the Lorentz law of force. These seven postulates constitute the foundation of a complete and consistent theory, thus eliminating the need for physical models of polarization P and magnetization M - these being the distinguishing features of Maxwell's macroscopic equations. In the proposed formulation, P(r,t) and M(r,t) are arbitrary functions of space and time, their physical properties being embedded in the seven postulates of the theory. The postulates are self-consistent, comply with special relativity, and satisfy the laws of conservation of energy, linear momentum, and angular momentum. The Abraham momentum density p_EM(r,t)= E(r,t)\\timesH(r,t)/c^2 emerges as the universal electromagnetic momentum that does not depend on whether the field is propagating or evanescent, and whether or not the host media are homogeneous, transparent, isotropic, linear, di...
Directory of Open Access Journals (Sweden)
Md. Moinul Islam
2015-01-01
Full Text Available A miniaturized antenna employing a negative index metamaterial with modified split-ring resonator (SRR and capacitance-loaded strip (CLS unit cells is presented for Ultra wideband (UWB microwave imaging applications. Four left-handed (LH metamaterial (MTM unit cells are located along one axis of the antenna as the radiating element. Each left-handed metamaterial unit cell combines a modified split-ring resonator (SRR with a capacitance-loaded strip (CLS to obtain a design architecture that simultaneously exhibits both negative permittivity and negative permeability, which ensures a stable negative refractive index to improve the antenna performance for microwave imaging. The antenna structure, with dimension of 16 × 21 × 1.6 mm3, is printed on a low dielectric FR4 material with a slotted ground plane and a microstrip feed. The measured reflection coefficient demonstrates that this antenna attains 114.5% bandwidth covering the frequency band of 3.4–12.5 GHz for a voltage standing wave ratio of less than 2 with a maximum gain of 5.16 dBi at 10.15 GHz. There is a stable harmony between the simulated and measured results that indicate improved nearly omni-directional radiation characteristics within the operational frequency band. The stable surface current distribution, negative refractive index characteristic, considerable gain and radiation properties make this proposed negative index metamaterial antenna optimal for UWB microwave imaging applications.
Aghajamali, Alireza; Barati, Mahmood; Wu, Chien-Jang
2014-01-01
In this paper the characteristic matrix method is used to study the propagation of electromagnetic waves through one-dimensional lossy photonic crystals composed of negative and positive refractive index material layers with symmetric and asymmetric geometric structures with a defect layer at the center of the structure. First, the positive index material defect layer is considered, and the effects of the polarization and the angle of incidence on the defect mode in the transmission spectra of the both structures are investigated. The results show that the number of the defect modes in the transmission spectra depends on the geometry (symmetric or asymmetric) of the structure. In addition, it is shown that the defect mode frequency increases as the angle of incidence increases. This property is independent of the geometry of the structure. Then, for normal incidence, the negative index material defect layer is considered, and the properties of defect modes for both structures are investigated. The results can...
Distributed chaos and isotropic turbulence
Bershadskii, A
2015-01-01
Power spectrum of the distributed chaos can be represented by a weighted superposition of the exponential functions which is converged to a stretched exponential $\\exp-(k/k_{\\beta})^{\\beta }$. An asymptotic theory has been developed in order to estimate the value of $\\beta$ for the isotropic turbulence. This value has been found to be $\\beta =3/4$. Excellent agreement has been established between this theory and the data of direct numerical simulations not only for the velocity field but also for the passive scalar and energy dissipation fields. One can conclude that the isotropic turbulence emerges from the distributed chaos.
Spherical 3D isotropic wavelets
Lanusse, F.; Rassat, A.; Starck, J.-L.
2012-04-01
Context. Future cosmological surveys will provide 3D large scale structure maps with large sky coverage, for which a 3D spherical Fourier-Bessel (SFB) analysis in spherical coordinates is natural. Wavelets are particularly well-suited to the analysis and denoising of cosmological data, but a spherical 3D isotropic wavelet transform does not currently exist to analyse spherical 3D data. Aims: The aim of this paper is to present a new formalism for a spherical 3D isotropic wavelet, i.e. one based on the SFB decomposition of a 3D field and accompany the formalism with a public code to perform wavelet transforms. Methods: We describe a new 3D isotropic spherical wavelet decomposition based on the undecimated wavelet transform (UWT) described in Starck et al. (2006). We also present a new fast discrete spherical Fourier-Bessel transform (DSFBT) based on both a discrete Bessel transform and the HEALPIX angular pixelisation scheme. We test the 3D wavelet transform and as a toy-application, apply a denoising algorithm in wavelet space to the Virgo large box cosmological simulations and find we can successfully remove noise without much loss to the large scale structure. Results: We have described a new spherical 3D isotropic wavelet transform, ideally suited to analyse and denoise future 3D spherical cosmological surveys, which uses a novel DSFBT. We illustrate its potential use for denoising using a toy model. All the algorithms presented in this paper are available for download as a public code called MRS3D at http://jstarck.free.fr/mrs3d.html
S-curvature of isotropic Berwald metrics
Institute of Scientific and Technical Information of China (English)
Akbar TAYEBI; Mehdi RAFIE-RAD
2008-01-01
Isotropic Berwald metrics are as a generalization of Berwald metrics. Shen proved that every Berwald metric is of vanishing S-curvature. In this paper, we generalize this fact and prove that every isotropic Berwald metric is of isotropic S-curvature. Let F = α + β be a Randers metric of isotropic Berwald curvature. Then it corresponds to a conformal vector field through navigation representation.
Spherical 3D Isotropic Wavelets
Lanusse, F; Starck, J -L
2011-01-01
Future cosmological surveys will provide 3D large scale structure maps with large sky coverage, for which a 3D Spherical Fourier-Bessel (SFB) analysis in is natural. Wavelets are particularly well-suited to the analysis and denoising of cosmological data, but a spherical 3D isotropic wavelet transform does not currently exist to analyse spherical 3D data. The aim of this paper is to present a new formalism for a spherical 3D isotropic wavelet, i.e. one based on the Fourier-Bessel decomposition of a 3D field and accompany the formalism with a public code to perform wavelet transforms. We describe a new 3D isotropic spherical wavelet decomposition based on the undecimated wavelet transform (UWT) described in Starck et al. 2006. We also present a new fast Discrete Spherical Fourier-Bessel Transform (DSFBT) based on both a discrete Bessel Transform and the HEALPIX angular pixelisation scheme. We test the 3D wavelet transform and as a toy-application, apply a denoising algorithm in wavelet space to the Virgo large...
Viscous dissipative Chaplygin gas dominated homogenous and isotropic cosmological models
Pun, C S J; Mak, M K; Kovács, Z; Szabó, G M; Harko, T
2008-01-01
The generalized Chaplygin gas, which interpolates between a high density relativistic era and a non-relativistic matter phase, is a popular dark energy candidate. We consider a generalization of the Chaplygin gas model, by assuming the presence of a bulk viscous type dissipative term in the effective thermodynamic pressure of the gas. The dissipative effects are described by using the truncated Israel-Stewart model, with the bulk viscosity coefficient and the relaxation time functions of the energy density only. The corresponding cosmological dynamics of the bulk viscous Chaplygin gas dominated universe is considered in detail for a flat homogeneous isotropic Friedmann-Robertson-Walker geometry. For different values of the model parameters we consider the evolution of the cosmological parameters (scale factor, energy density, Hubble function, deceleration parameter and luminosity distance, respectively), by using both analytical and numerical methods. In the large time limit the model describes an acceleratin...
Poromechanical behaviour of hardened cement paste under isotropic loading
Ghabezloo, Siavash; Guédon, Sylvine; Martineau, Francçois; Saint-Marc, Jérémie
2008-01-01
The poromechanical behaviour of hardened cement paste under isotropic loading is studied on the basis of an experimental testing program of drained, undrained and unjacketed compression tests. The macroscopic behaviour of the material is described in the framework of the mechanics of porous media. The poroelastic parameters of the material are determined and the effect of stress and pore pressure on them is evaluated. Appropriate effective stress laws which control the evolution of total volume, pore volume, solid volume, porosity and drained bulk modulus are discussed. A phenomenon of degradation of elastic properties is observed in the test results. The microscopic observations showed that this degradation is caused by the microcracking of the material under isotropic loading. The good compatibility and the consistency of the obtained poromechanical parameters demonstrate that the behaviour of the hardened cement paste can be indeed described within the framework of the theory of porous media.
How Isotropic is the Universe?
Saadeh, Daniela; Feeney, Stephen M; Pontzen, Andrew; Peiris, Hiranya V; McEwen, Jason D
2016-09-23
A fundamental assumption in the standard model of cosmology is that the Universe is isotropic on large scales. Breaking this assumption leads to a set of solutions to Einstein's field equations, known as Bianchi cosmologies, only a subset of which have ever been tested against data. For the first time, we consider all degrees of freedom in these solutions to conduct a general test of isotropy using cosmic microwave background temperature and polarization data from Planck. For the vector mode (associated with vorticity), we obtain a limit on the anisotropic expansion of (σ_{V}/H)_{0}Universe is strongly disfavored, with odds of 121 000:1 against.
Semiflexible particles in isotropic turbulence
Ali, Aamir; Plan, Emmanuel Lance Christopher Medillo, VI; Ray, Samriddhi Sankar; Vincenzi, Dario
2016-12-01
The Lagrangian dynamics of semiflexible particles in homogeneous and isotropic turbulent flows is studied by means of analytically solvable stochastic models and direct numerical simulations. The stationary statistics of the bending angle shows a strong dependence on the dimension of the flow. In two-dimensional turbulence, particles are found in either a fully extended or a fully folded configuration; in three dimensions, the predominant configuration is the fully extended one. Such a sensitivity of the bending statistics on the dimensionality of the flow is peculiar to fluctuating flows and is not observed in laminar stretching flows.
Isotropic Negative Thermal Expansion Metamaterials.
Wu, Lingling; Li, Bo; Zhou, Ji
2016-07-13
Negative thermal expansion materials are important and desirable in science and engineering applications. However, natural materials with isotropic negative thermal expansion are rare and usually unsatisfied in performance. Here, we propose a novel method to achieve two- and three-dimensional negative thermal expansion metamaterials via antichiral structures. The two-dimensional metamaterial is constructed with unit cells that combine bimaterial strips and antichiral structures, while the three-dimensional metamaterial is fabricated by a multimaterial 3D printing process. Both experimental and simulation results display isotropic negative thermal expansion property of the samples. The effective coefficient of negative thermal expansion of the proposed models is demonstrated to be dependent on the difference between the thermal expansion coefficient of the component materials, as well as on the circular node radius and the ligament length in the antichiral structures. The measured value of the linear negative thermal expansion coefficient of the three-dimensional sample is among the largest achieved in experiments to date. Our findings provide an easy and practical approach to obtaining materials with tunable negative thermal expansion on any scale.
Isotropic stars in general relativity
Mak, M K
2013-01-01
We present a general solution of the Einstein gravitational field equations for the static spherically symmetric gravitational interior spacetime of an isotropic fluid sphere. The solution is obtained by transforming the pressure isotropy condition, a second order ordinary differential equation, into a Riccati type first order differential equation, and using a general integrability condition for the Riccati equation. This allows us to obtain an exact non-singular solution of the interior field equations for a fluid sphere, expressed in the form of infinite power series. The physical features of the solution are studied in detail numerically by cutting the infinite series expansions, and restricting our numerical analysis by taking into account only $n=21$ terms in the power series representations of the relevant astrophysical parameters. In the present model all physical quantities (density, pressure, speed of sound etc.) are finite at the center of the sphere. The physical behavior of the solution essential...
Macroscopic simulation of isotropic permanent magnets
Bruckner, Florian; Abert, Claas; Vogler, Christoph; Heinrichs, Frank; Satz, Armin; Ausserlechner, Udo; Binder, Gernot; Koeck, Helmut; Suess, Dieter
2016-03-01
Accurate simulations of isotropic permanent magnets require to take the magnetization process into account and consider the anisotropic, nonlinear, and hysteretic material behaviour near the saturation configuration. An efficient method for the solution of the magnetostatic Maxwell equations including the description of isotropic permanent magnets is presented. The algorithm can easily be implemented on top of existing finite element methods and does not require a full characterization of the hysteresis of the magnetic material. Strayfield measurements of an isotropic permanent magnet and simulation results are in good agreement and highlight the importance of a proper description of the isotropic material.
Macroscopic Simulation of Isotropic Permanent Magnets
Bruckner, Florian; Vogler, Christoph; Heinrichs, Frank; Satz, Armin; Ausserlechner, Udo; Binder, Gernot; Koeck, Helmut; Suess, Dieter
2015-01-01
Accurate simulations of isotropic permanent magnets require to take the magnetization process into account and consider the anisotropic, nonlinear, and hysteretic material behaviour near the saturation configuration. An efficient method for the solution of the magnetostatic Maxwell equations including the description of isotropic permanent magnets is presented. The algorithm can easily be implemented on top of existing finite element methods and does not require a full characterization of the hysteresis of the magnetic material. Strayfield measurements of an isotropic permanent magnet and simulation results are in good agreement and highlight the importance of a proper description of the isotropic material.
Controlling elastic wave with isotropic transformation materials
Chang, Zheng; Hu, Gengkai; Tao, Ran; Wang, Yue
2010-01-01
There are great demands to design functional devices with isotropic materials, however the transformation method usually leads to anisotropic material parameters difficult to be realized in practice. In this letter, we derive the isotropic transformed material parameters in case of elastodynamic under local conformal transformation, they are subsequently used to design a beam bender, a four-beam antenna and an approximate carpet cloak for elastic wave with isotropic materials, the simulation results validate the derived transformed material parameters. The obtained materials are isotropic and greatly simplify subsequent experimental implementation.
Thick brane isotropization in the 5D anisotropic standing wave braneworld model
Gogberashvili, Merab; Malagon-Morejon, Dagoberto; Mora-Luna, Refugio Rigel; Nucamendi, Ulises
2014-01-01
We study a smooth cosmological solution of the 5D anisotropic standing wave braneworld model generated by gravity coupled to a phantom-like scalar field. In this model the brane emits anisotropic waves into the bulk with different amplitudes along different spatial dimensions. We found a natural mechanism which isotropizes the braneworld, rendering a 3-brane with de Sitter symmetry embedded in a 5D de Sitter space-time for a wide class of initial conditions. The resulting thick geometrical braneworld (a de Sitter 3-brane) possesses a series of remarkable features. By explicitly solving the bulk field equations we are able to give a physical interpretation of the anisotropic dissipation: as the anisotropic energy on the 3-brane rapidly leaks into the bulk, through the nontrivial Weyl tensor components, the bulk becomes less isotropic.
Multiphase composites with extremal bulk modulus
DEFF Research Database (Denmark)
Gibiansky, L. V.; Sigmund, Ole
2000-01-01
This paper is devoted to the analytical and numerical study of isotropic elastic composites made of three or more isotropic phases. The ranges of their effective bulk and shear moduli are restricted by the Hashin-Shtrikman-Walpole (HSW) bounds. For two-phase composites, these bounds are attainable......, that is, there exist composites with extreme bulk and shear moduli. For multiphase composites, they may or may not be attainable depending on phase moduli and volume fractions. Sufficient conditions of attainability of the bounds and various previously known and new types of optimal composites...... are described. Most of our new results are related to the two-dimensional problem. A numerical topology optimization procedure that solves the inverse homogenization problem is adopted and used to look for two-dimensional three-phase composites with a maximal effective bulk modulus. For the combination...
Isotropic bodies and Bourgain's problem
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
[1]Milman, V. D., Pajor, A., Isotropic position and inertia ellipsoid and zonoids of the unit ball of a normed ndimensional space, Geometric aspects of functional analysis (1987-1988), Lecture Notes in Math., 1989, 1376:64-104.[2]Blaschke, W., Uber affine Geometry ⅩⅣ: eine minimum Aufgabe fur Legendres tragheits Ellipsoid, Ber. verh.sachs. Akad. d. Wiss., 1918, 70: 72-75.[3]Blaschke, W., Uber affine Geometry Ⅺ: losing der "Vierpunkproblems" von Sylvester aus der Teorie der geometrischen Wahrsdeinlichkeiten, Leipziger Berichte, 1917, 69: 436-453.[4]John, F., Polar correspondence with respect to convex regions, Duke Math. J., 1937, 3(2): 355-369.[5]Lutwak, E., Yang, D., Zhang, G., A new ellipsoid associated with convex bodes, Duke. Math. J., 2000, 104:375-390.[6]Bourgain, J., On the distribution of polynomails on high dimensional convex sets, Geometric aspects of functional analysis (1989-1990), Lecture Notes in Math., 1991, 1469: 127-137.[7]Dar, S., Remarks on Bourgain's problem on slicing of convex bodies, Geomitric aspects of functional analysis,in Oper. Theory Adv. Appl., Vol, 77, Basel: Birkhauser, 1995, 61-66.[8]Ball, K., Normed spaces with a weak-Gordon-Lewis property, in: Proc. of Funct. Anal., University of Texas and Austin (1987-1989), Lecture Notes in Math., 1991, 1470: 36-47.[9]Schneider, R., Weil, W., Zonoids and related topics, in Convexity and Its Applications (eds. Gruber, P. M., Wills,J. M.), Basel: Birkhauser, 1983, 296-317.[10]Bourgain, J., Klartag, B., Milman, V., A reduction of the slicing problem to finite volume ratio bodies, Geometry/Functional Analysis, C. R. Acad. Sci. Paris, Ser. I, 2003, 336: 331-334.[11]Ren, D. L., An Introduction to Integral Geometry (in Chinese), Shanghai: Science and Technology Press, 1988.[12]Gardner, R. J., Geometric Tomography, Cambridge: Cambridge University Press, 1995.[13]Leichtweiβ, K., Affine Geometry of Convex Bodies, Heidelberg: J. A. Barth, 1998.[14]Schneider, R., Convex Bodies: The Brunn
How isotropic is the Universe?
Saadeh, Daniela; Pontzen, Andrew; Peiris, Hiranya V; McEwen, Jason D
2016-01-01
A fundamental assumption in the standard model of cosmology is that the Universe is isotropic on large scales. Breaking this assumption leads to a set of solutions to Einstein's field equations, known as Bianchi cosmologies, only a subset of which have ever been tested against data. For the first time, we consider all degrees of freedom in these solutions to conduct a general test of isotropy using cosmic microwave background temperature and polarization data from Planck. For the vector mode (associated with vorticity), we obtain a limit on the anisotropic expansion of $(\\sigma_V/H)_0 < 4.7 \\times 10^{-11}$ (95% CI), which is an order of magnitude tighter than previous Planck results that used CMB temperature only. We also place upper limits on other modes of anisotropic expansion, with the weakest limit arising from the regular tensor mode, $(\\sigma_{T,\\rm reg}/H)_0<1.0 \\times 10^{-6}$ (95% CI). Including all degrees of freedom simultaneously for the first time, anisotropic expansion of the Universe is...
Constitutive modeling for isotropic materials
Chan, K. S.; Lindholm, U. S.; Bodner, S. R.
1988-01-01
The third and fourth years of a 4-year research program, part of the NASA HOST Program, are described. The program goals were: (1) to develop and validate unified constitutive models for isotropic materials, and (2) to demonstrate their usefulness for structural analysis of hot section components of gas turbine engines. The unified models selected for development and evaluation were those of Bodner-Partom and of Walker. The unified approach for elastic-viscoplastic constitutive equations is a viable method for representing and predicting material response characteristics in the range where strain rate and temperature dependent inelastic deformations are experienced. This conclusion is reached by extensive comparison of model calculations against the experimental results of a test program of two high temperature Ni-base alloys, B1900+Hf and Mar-M247, over a wide temperature range for a variety of deformation and thermal histories including uniaxial, multiaxial, and thermomechanical loading paths. The applicability of the Bodner-Partom and the Walker models for structural applications has been demonstrated by implementing these models into the MARC finite element code and by performing a number of analyses including thermomechanical histories on components of hot sections of gas turbine engines and benchmark notch tensile specimens. The results of the 4-year program have been published in four annual reports. The results of the base program are summarized in this report. The tasks covered include: (1) development of material test procedures, (2) thermal history effects, and (3) verification of the constitutive model for an alternative material.
Empirical isotropic chemical shift surfaces
Energy Technology Data Exchange (ETDEWEB)
Czinki, Eszter; Csaszar, Attila G. [Eoetvoes University, Laboratory of Molecular Spectroscopy, Institute of Chemistry (Hungary)], E-mail: csaszar@chem.elte.hu
2007-08-15
A list of proteins is given for which spatial structures, with a resolution better than 2.5 A, are known from entries in the Protein Data Bank (PDB) and isotropic chemical shift (ICS) values are known from the RefDB database related to the Biological Magnetic Resonance Bank (BMRB) database. The structures chosen provide, with unknown uncertainties, dihedral angles {phi} and {psi} characterizing the backbone structure of the residues. The joint use of experimental ICSs of the same residues within the proteins, again with mostly unknown uncertainties, and ab initio ICS({phi},{psi}) surfaces obtained for the model peptides For-(l-Ala){sub n}-NH{sub 2}, with n = 1, 3, and 5, resulted in so-called empirical ICS({phi},{psi}) surfaces for all major nuclei of the 20 naturally occurring {alpha}-amino acids. Out of the many empirical surfaces determined, it is the 13C{sup {alpha}} ICS({phi},{psi}) surface which seems to be most promising for identifying major secondary structure types, {alpha}-helix, {beta}-strand, left-handed helix ({alpha}{sub D}), and polyproline-II. Detailed tests suggest that Ala is a good model for many naturally occurring {alpha}-amino acids. Two-dimensional empirical 13C{sup {alpha}}-{sup 1}H{sup {alpha}} ICS({phi},{psi}) correlation plots, obtained so far only from computations on small peptide models, suggest the utility of the experimental information contained therein and thus they should provide useful constraints for structure determinations of proteins.
A Relativistic Algorithm with Isotropic Coordinates
Directory of Open Access Journals (Sweden)
S. A. Ngubelanga
2013-01-01
Full Text Available We study spherically symmetric spacetimes for matter distributions with isotropic pressures. We generate new exact solutions to the Einstein field equations which also contain isotropic pressures. We develop an algorithm that produces a new solution if a particular solution is known. The algorithm leads to a nonlinear Bernoulli equation which can be integrated in terms of arbitrary functions. We use a conformally flat metric to show that the integrals may be expressed in terms of elementary functions. It is important to note that we utilise isotropic coordinates unlike other treatments.
Fabrication of Isotropic Pyrocarbon at 1400℃ by Thermal Gradient Chemical Vapor Deposition Apparatus
Institute of Scientific and Technical Information of China (English)
GUO Lingjun; ZHANG Dongsheng; LI Kezhi; LI Hejun
2009-01-01
An experiment was designed to prepare isotropic pyrocarbon by thermal gradient chemical vapor deposition apparatus.The deposition was performed under ambient atmosphere at 1400℃,with natural gas volume flow of 3.5 m~3/h for 80 h.The results show that the thickness and the bulk density of the deposit are about 1.95 g/cm~3 and 10 mm,respectively.The microstructure of the deposit was examined by polarized light microscopy and scanning electron microscopy,which shows that the deposit is constituted of sphere isotropic pyrocarbon,pebble pyrocarbon and laminar pyrocarbon.
Isotropic metal deposition technique for metamaterials fabrication
DEFF Research Database (Denmark)
Malureanu, Radu; Andryieuski, Andrei; Lavrinenko, Andrei
2009-01-01
In this work we will present the first steps taken towards isotropic deposition of thin metallic layers on dielectric substrates. The deposition takes place in aqueous environment thus making it both cheap and easy to be implemented....
Macroscopic Simulation of Isotropic Permanent Magnets
Bruckner, Florian; Abert, Claas; Vogler, Christoph; Heinrichs, Frank; Satz, Armin; Ausserlechner, Udo; Binder, Gernot; Koeck, Helmut; Suess, Dieter
2015-01-01
Accurate simulations of isotropic permanent magnets require to take the magnetization process into account and consider the anisotropic, nonlinear, and hysteretic material behaviour near the saturation configuration. An efficient method for the solution of the magnetostatic Maxwell equations including the description of isotropic permanent magnets is presented. The algorithm can easily be implemented on top of existing finite element methods and does not require a full characterization of the...
Effects of bulk viscosity on cosmological evolution
Pimentel, L O; Pimentel, L O; Diaz-Rivera, L M
1994-01-01
Abstract:The effect of bulk viscisity on the evolution of the homogeneous and isotropic cosmological models is considered. Solutions are found, with a barotropic equation of state, and a viscosity coefficient that is proportional to a power of the energy density of the universe. For flat space, power law expansions, related to extended inflation are found as well as exponential solutions, related to old inflation; also a solution with expansion that is an exponential of an exponential of the time is found.
Bulk metamaterials: Design, fabrication and characterization
DEFF Research Database (Denmark)
Andryieuski, Andrei; Malureanu, Radu; Alabastri, Alessandro
2009-01-01
Bulk metamaterials claim a lot of attention worldwide. We report about our activity and advances in design, fabrication and characterization of metal-dielectric composites with three-dimensional lattices. The nomenclature of designs exhibiting negative index behaviour in the near infrared includes...... the generic family of so-called nested structures. Such designs allow keeping the cubic symmetry of the unit cell along with the electric and magnetic responses showed by different parts in separate. For extraction of effective parameters we employ homemade wave propagation retrieving method free from...... ambiguity generic to the standard S-parameters retrieval method. Accurateness of the method is highlighted by a set of numerical checks. To fabricate smooth metal three-dimensional structures we develop an electroless chemical technique. We present the results of silver deposition on the surface of a 30...
Isotropic Growth of Graphene toward Smoothing Stitching.
Zeng, Mengqi; Tan, Lifang; Wang, Lingxiang; Mendes, Rafael G; Qin, Zhihui; Huang, Yaxin; Zhang, Tao; Fang, Liwen; Zhang, Yanfeng; Yue, Shuanglin; Rümmeli, Mark H; Peng, Lianmao; Liu, Zhongfan; Chen, Shengli; Fu, Lei
2016-07-26
The quality of graphene grown via chemical vapor deposition still has very great disparity with its theoretical property due to the inevitable formation of grain boundaries. The design of single-crystal substrate with an anisotropic twofold symmetry for the unidirectional alignment of graphene seeds would be a promising way for eliminating the grain boundaries at the wafer scale. However, such a delicate process will be easily terminated by the obstruction of defects or impurities. Here we investigated the isotropic growth behavior of graphene single crystals via melting the growth substrate to obtain an amorphous isotropic surface, which will not offer any specific grain orientation induction or preponderant growth rate toward a certain direction in the graphene growth process. The as-obtained graphene grains are isotropically round with mixed edges that exhibit high activity. The orientation of adjacent grains can be easily self-adjusted to smoothly match each other over a liquid catalyst with facile atom delocalization due to the low rotation steric hindrance of the isotropic grains, thus achieving the smoothing stitching of the adjacent graphene. Therefore, the adverse effects of grain boundaries will be eliminated and the excellent transport performance of graphene will be more guaranteed. What is more, such an isotropic growth mode can be extended to other types of layered nanomaterials such as hexagonal boron nitride and transition metal chalcogenides for obtaining large-size intrinsic film with low defect.
Derivatives on the isotropic tensor functions
Institute of Scientific and Technical Information of China (English)
DUI; Guansuo; WANG; Zhengdao; JIN; Ming
2006-01-01
The derivative of the isotropic tensor function plays an important part in continuum mechanics and computational mechanics, and also it is still an opening problem. By means of a scalar response function and solving a tensor equation, this problem is well studied. A compact explicit expression for the derivative of the isotropic tensor function is presented, which is valid for both distinct and repeated eigenvalue cases. Throughout the analysis, the formulation holds for general isotropic tensor functions without need to solve eigenvector problems or determine coefficients. On the theoretical side, a very simple solution of a tensor equation is obtained. As an application to continuum mechanics, a base-free expression for the Hill's strain rate is given, which is more compact than the existent results. Finally, with an example we compute the derivative of an exponent tensor function. And the efficiency of the present formulations is demonstrated.
Hypersurfaces with Isotropic Para-Blaschke Tensor
Institute of Scientific and Technical Information of China (English)
Jian Bo FANG; Kun ZHANG
2014-01-01
Let Mn be an n-dimensional submanifold without umbilical points in the (n+1)-dimen-sional unit sphere Sn+1. Four basic invariants of Mn under the Moebius transformation group of Sn+1 are a1-form Φ called moebius form, a symmetric (0, 2) tensor A called Blaschke tensor, a symmetric (0, 2) tensor B called Moebius second fundamental form and a positive definite (0, 2) tensor g called Moebius metric. A symmetric (0, 2) tensor D = A+μB called para-Blaschke tensor, where μ is constant, is also an Moebius invariant. We call the para-Blaschke tensor is isotropic if there exists a function λ such that D = λg. One of the basic questions in Moebius geometry is to classify the hypersurfaces with isotropic para-Blaschke tensor. When λ is not constant, all hypersurfaces with isotropic para-Blaschke tensor are explicitly expressed in this paper.
Static spherically symmetric wormholes with isotropic pressure
Cataldo, Mauricio; Rodríguez, Pablo
2016-01-01
In this paper we study static spherically symmetric wormhole solutions sustained by matter sources with isotropic pressure. We show that such spherical wormholes do not exist in the framework of zero-tidal-force wormholes. On the other hand, it is shown that for the often used power-law shape function there is no spherically symmetric traversable wormholes sustained by sources with a linear equation of state $p=\\omega \\rho$ for the isotropic pressure, independently of the form of the redshift function $\\phi(r)$. We consider a solution obtained by Tolman at 1939 for describing static spheres of isotropic fluids, and show that it also may describe wormhole spacetimes with a power-law redshift function, which leads to a polynomial shape function, generalizing a power-law shape function, and inducing a solid angle deficit.
Preferential sampling of helicity by isotropic helicoids
Gustavsson, Kristian
2016-01-01
We present a theoretical and numerical study on the motion of isotropic helicoids in complex flows. These are particles whose motion is invariant under rotations but not under mirror reflections of the particle. This is the simplest, yet unexplored, extension of the much studied case of small spherical particles. We show that heavy isotropic helicoids, due to the coupling between translational and rotational degrees of freedom, preferentially sample different helical regions in laminar or chaotic advecting flows. This opens the way to control and engineer particles able to track complex flow structures with potential applications to microfluidics and turbulence.
Approximating a harmonizable isotropic random field
Directory of Open Access Journals (Sweden)
Randall J. Swift
2001-01-01
Full Text Available The class of harmonizable fields is a natural extension of the class of stationary fields. This paper considers a stochastic series approximation of a harmonizable isotropic random field. This approximation is useful for numerical simulation of such a field.
Mapping of moveout in tilted transversely isotropic media
Stovas, A.
2013-09-09
The computation of traveltimes in a transverse isotropic medium with a tilted symmetry axis tilted transversely isotropic is very important both for modelling and inversion. We develop a simple analytical procedure to map the traveltime function from a transverse isotropic medium with a vertical symmetry axis (vertical transversely isotropic) to a tilted transversely isotropic medium by applying point-by-point mapping of the traveltime function. This approach can be used for kinematic modelling and inversion in layered tilted transversely isotropic media. © 2013 European Association of Geoscientists & Engineers.
Isotropic-planar illumination for PIV experiments
Atkins, Michael D.; Kim, Tongbeum
2015-03-01
A new method for laser illumination in particle image velocimetry (PIV) has been introduced: internal "isotropic-planar" illumination that provides laser light to regions of the flow field that were previously cast into shadow using the conventional external (laser light sheet) illumination method. To demonstrate the effectiveness of the isotropic-planar illumination method, a comparison of the measured velocity field around five side-by-side circular cylinders that are immersed in uniform flow is made against the conventional external illumination method. The new method is effective at eliminating the shadow region, allowing the velocity field of the upstream, gap and downstream regions around the five side-by-side circular cylinders to be measured simultaneously. These PIV measurements provide new insight into the behavior of the gap flow that passes between the cylinders.
ISOTROPIC TEXTURING OF POLYCRYSTALLINE SILICON WAFERS
Institute of Scientific and Technical Information of China (English)
L. Wang; H. Shen; Y.F. Hu
2005-01-01
An isotropic etching technique of texturing silicon solar cells has been applied to polycrystalline silicon wafers with different acid concentrations. Optimal etching conditions have been determined by etching rate calculation, scanning electron microscope (SEM) image and reflectance measurement. The surface morphology of the textured wafers varies in accordance with the different etchant concentration which in turn leads to the dissimilarity of etching speed. Textured polycrystalline silicon wafer surfaces display randomly located etched pits which can reduce the surface reflection and enhance the light absorption. The special relationship between reflectivity and etching rate was studied. Reflectance measurements show that isotropic texturing is one of the suitable techniques for texturing polycrystalline silicon wafers and benefits solar cells performances.
Taming electromagnetic metamaterials for isotropic perfect absorbers
Directory of Open Access Journals (Sweden)
Doan Tung Anh
2015-07-01
Full Text Available Conventional metamaterial absorbers, which consist of a dielectric spacer sandwiched between metamaterial resonators and a metallic ground plane, have been inherently anisotropic. In this paper, we present an alternative approach for isotropic perfect absorbers using symmetric metamaterial structures. We show that by systematically manipulating the electrically and magnetically induced losses, one can achieve a desired absorption without breaking the structural homogeneity. Finite integration simulations and standard retrieval method are performed to elaborate on our idea.
Fundamental solutions for transversely isotropic piezoelectric media
Institute of Scientific and Technical Information of China (English)
丁皓江; 梁剑; 陈波
1996-01-01
A general solution for the.equilibrium equations of pieajelectric media under body forces is obtained. With regard to the transversely isotropic piezoelectric material, closed forms for the displacements and electric potential function for an infinite solid loaded with point forces and point charge are then obtained by using the general solution together with potential theory and constructing a kind of harmonic functions. Thus, the fundamental solutions which are utilizable in boundary element method are obtained.
Infinite Products of Random Isotropically Distributed Matrices
Il'yn, A S; Zybin, K P
2016-01-01
Statistical properties of infinite products of random isotropically distributed matrices are investigated. Both for continuous processes with finite correlation time and discrete sequences of independent matrices, a formalism that allows to calculate easily the Lyapunov spectrum and generalized Lyapunov exponents is developed. This problem is of interest to probability theory, statistical characteristics of matrix T-exponentials are also needed for turbulent transport problems, dynamical chaos and other parts of statistical physics.
Isotropization of the quark gluon plasma
Energy Technology Data Exchange (ETDEWEB)
Epelbaum, T.; Gelis, F.
2014-06-15
We report here recent analytical and numerical work on the theoretical treatment of the early stages of heavy ion collisions, that amounts to solving the classical Yang–Mills equations with fluctuating initial conditions. Our numerical simulations suggest a fast isotropization of the pressure tensor of the system. This trend appears already for small values of the coupling constant α{sub s}. In addition, the system exhibits an anomalously small shear viscosity.
Infinite Products of Random Isotropically Distributed Matrices
Il'yn, A. S.; Sirota, V. A.; Zybin, K. P.
2017-01-01
Statistical properties of infinite products of random isotropically distributed matrices are investigated. Both for continuous processes with finite correlation time and discrete sequences of independent matrices, a formalism that allows to calculate easily the Lyapunov spectrum and generalized Lyapunov exponents is developed. This problem is of interest to probability theory, statistical characteristics of matrix T-exponentials are also needed for turbulent transport problems, dynamical chaos and other parts of statistical physics.
A New Type of Isotropic Cosmological Model
Naboulsi, R
2003-01-01
The Einstein equations with quantum one-loop contributions of conformally covariant matter fields in the poresence of frac{1}{t^2} decaying matter density and decaying cosmological constant is used to study an isotropic homogenous FRW space-time. We show that scale factor depends on the sums of contributions from quantum fields with different spin values. For some specific values of this later, the Universe could be in an accelerated regime.
Representation and prediction for locally harmonizable isotropic random fields
Directory of Open Access Journals (Sweden)
Randall J. Swift
1995-01-01
Full Text Available The class of harmonizable fields is a natural extension of the class of stationary fields. This paper considers fields whose increments are harmonizable and isotropic. Spectral representations are obtained for locally harmonizable isotropic fields. A linear least squares prediction for locally harmonizable isotropic fields is considered.
Prospects for Detecting a Cosmic Bulk Flow
Rose, Benjamin; Garnavich, Peter M.; Mathews, Grant James
2015-01-01
The ΛCDM model is based upon a homogeneous, isotropic space-time leading to uniform expansion with random peculiar velocities caused by local gravitation perturbations. The Cosmic Microwave Background (CMB) radiation evidences a significant dipole moment in the frame of the Local Group. This motion is usually explained with the Local Group's motion relative to the background Hubble expansion. An alternative explanation, however, is that the dipole moment is the result of horizon-scale curvature remaining from the birth of space-time, possibly a result of quantum entanglement with another universe. This would appear as a single velocity (a bulk flow) added to all points in space. These two explanations differ observationally on cosmic distance scales (z > 0.1). There have been many differing attempts to detect a bulk flow, many with no detectable bulk flow but some with a bulk flow velocity as large as 1000 km/s. Here we report on a technique based upon minimizing the scatter around the expected cosine distribution of the Hubble redshift residuals with respect to angular distance on the sky. That is, the algorithm searches for a directional dependence of Hubble residuals. We find results consistent with most other bulk flow detections at z Type Ia Supernovae to be ~0.01, whereas the current error (~0.2.) is more than an order of magnitude too large for the detection of bulk flow beyond z~0.05.
Institute of Scientific and Technical Information of China (English)
许森东; 徐弼军
2014-01-01
In order to study the propagation characteristics of Gaussian-Schell model(GSM) beams in negative index medium, the analytical expression was obtained for the cross-spectral density function of GSM beam passing through negative index medium based on the matrix optics theory , diffraction integral theory and unification theory of coherence and polarization .The spectral density and the spectral coherence degree of the beam passing through the negative index medium were obtained with the formula .Numerical examples show that both the spectral density and the coherence spectral degree of GSM beam can be modulated by the frequency of the negative index medium .The results provide a new modulation method for the beam propagation .%为了研究高斯-谢尔模型光束在负折射率介质中的传输特性，利用矩阵光学理论、衍射积分理论、相干偏振统一理论推导了高斯-谢尔模型光束通过负折射率介质中传输交叉谱密度方程的解析表达式，并利用该解析表达式得到了高斯-谢尔模型光束通过负折射率介质的谱密度和谱相干度。结果表明，高斯-谢尔模型光束的谱密度和谱相干度都可以通过负折射率介质的工作频率调控。此研究结果提供了一种新的调控光传输的方法和技术。
Topological optimization for the design of microstructures of isotropic cellular materials
Radman, A.; Huang, X.; Xie, Y. M.
2013-11-01
The aim of this study was to design isotropic periodic microstructures of cellular materials using the bidirectional evolutionary structural optimization (BESO) technique. The goal was to determine the optimal distribution of material phase within the periodic base cell. Maximizing bulk modulus or shear modulus was selected as the objective of the material design subject to an isotropy constraint and a volume constraint. The effective properties of the material were found using the homogenization method based on finite element analyses of the base cell. The proposed BESO procedure utilizes the gradient-based sensitivity method to impose the isotropy constraint and gradually evolve the microstructures of cellular materials to an optimum. Numerical examples show the computational efficiency of the approach. A series of new and interesting microstructures of isotropic cellular materials that maximize the bulk or shear modulus have been found and presented. The methodology can be extended to incorporate other material properties of interest such as designing isotropic cellular materials with negative Poisson's ratio.
An Improved Isotropic Periodic Sum Method That Uses Linear Combinations of Basis Potentials
Takahashi, Kazuaki Z.
2012-11-13
Isotropic periodic sum (IPS) is a technique that calculates long-range interactions differently than conventional lattice sum methods. The difference between IPS and lattice sum methods lies in the shape and distribution of remote images for long-range interaction calculations. The images used in lattice sum calculations are identical to those generated from periodic boundary conditions and are discretely positioned at lattice points in space. The images for IPS calculations are "imaginary", which means they do not explicitly exist in a simulation system and are distributed isotropically and periodically around each particle. Two different versions of the original IPS method exist. The IPSn method is applied to calculations for point charges, whereas the IPSp method calculates polar molecules. However, both IPSn and IPSp have their advantages and disadvantages in simulating bulk water or water-vapor interfacial systems. In bulk water systems, the cutoff radius effect of IPSn strongly affects the configuration, whereas IPSp does not provide adequate estimations of water-vapor interfacial systems unless very long cutoff radii are used. To extend the applicability of the IPS technique, an improved IPS method, which has better accuracy in both homogeneous and heterogeneous systems has been developed and named the linear-combination-based isotropic periodic sum (LIPS) method. This improved IPS method uses linear combinations of basis potentials. We performed molecular dynamics (MD) simulations of bulk water and water-vapor interfacial systems to evaluate the accuracy of the LIPS method. For bulk water systems, the LIPS method has better accuracy than IPSn in estimating thermodynamic and configurational properties without the countercharge assumption, which is used for IPSp. For water-vapor interfacial systems, LIPS has better accuracy than IPSp and properly estimates thermodynamic and configurational properties. In conclusion, the LIPS method can successfully estimate
Hubble Parameter in Bulk Viscous Cosmology
Tawfik, A; Wahba, M
2009-01-01
We discuss influences of bulk viscosity on the Early Universe, which is modeled by Friedmann-Robertson-Walker metric and Einstein field equations. We assume that the matter filling the isotropic and homogeneous background is relativistic viscous characterized by ultra-relativistic equations of state deduced from recent lattice QCD simulations. We obtain a set of complicated differential equations, for which we suggest approximate solutions for Hubble parameter $H$. We find that finite viscosity in Eckart and Israel-Stewart fluids would significantly modify our picture about the Early Universe.
Qualitative analysis of collapsing isotropic fluid spacetimes
Giambò, Roberto
2013-01-01
The structure of the Einstein field equations describing the gravitational collapse of spherically symmetric isotropic fluids is analyzed here for general equations of state. A suitable system of coordinates is constructed which allows us, under a hypothesis of Taylor-expandability with respect to one of the coordinates, to approach the problem of the nature of the final state without knowing explicitely the metric. The method is applied to investigate the singularities of linear barotropic perfect fluids solutions and to a family of accelerating fluids.
Incoherent subharmonic light scattering in isotropic media.
Feng, D H; Xu, Z Z; Feng, X L; Jia, T Q; Li, X X; Liu, J S
2005-02-01
Incoherent subharmonic light scattering in isotropic media is a new kind of nonlinear light scattering, which involves single input photon and multiple output photons of equal frequency. We investigate theoretically the dependence of the subharmonic scattering intensity on the hyperpolarizability of molecules and the incident intensity using nonlinear optics theory similar to that used for Hyper-Rayleigh scattering and degenerate optical parametric oscillators. It is derived that the subharmonic scattering intensities grow exponentially or superexponentially with the hyperpolarizability of molecules and the incident intensity.
Isotropic cosmological singularities other matter models
Tod, K P
2003-01-01
Isotropic cosmological singularities are singularities which can be removed by rescaling the metric. In some cases already studied (gr-qc/9903008, gr-qc/9903009, gr-qc/9903018) existence and uniqueness of cosmological models with data at the singularity has been established. These were cosmologies with, as source, either perfect fluids with linear equations of state or massless, collisionless particles. In this article we consider how to extend these results to a variety of other matter models. These are scalar fields, massive collisionless matter, the Yang-Mills plasma of Choquet-Bruhat, or matter satisfying the Einstein-Boltzmann equation.
Linearized Holographic Isotropization at Finite Coupling
Atashi, Mahdi; Jafari, Ghadir
2016-01-01
We study holographic isotropization of an anisotropic homogeneous non-Abelian strongly coupled in the presence of Gauss-Bonnet corrections. It was verified before that one can linearize Einstein's equations around the final black hole background and simplify the complicated setup. Using this approach, we study the expectation value of the boundary stress tensor. Although we consider small values of the Gauss-Bonnet coupling constant, it is found that increasing the Gauss-Bonnet coupling leads to significant increasing of the thermalization time. By including higher order corrections, we extend the results to study the effect of the Gauss-Bonnet coupling on the entropy production on the event horizon.
Isotropic Broadband E-Field Probe
Directory of Open Access Journals (Sweden)
Béla Szentpáli
2008-01-01
Full Text Available An E-field probe has been developed for EMC immunity tests performed in closed space. The leads are flexible resistive transmission lines. Their influence on the field distribution is negligible. The probe has an isotropic reception from 100 MHz to 18 GHz; the sensitivity is in the 3 V/m–10 V/m range. The device is an accessory of the EMC test chamber. The readout of the field magnitude is carried out by personal computer, which fulfils also the required corrections of the raw data.
ON NON-ISOTROPIC JACOBI PSEUDOSPECTRAL METHOD
Institute of Scientific and Technical Information of China (English)
Benyu Guo; Keji Zhang
2008-01-01
In this paper,a non-isotropic Jacobi pseudospectral method is proposed and its applications are considered.Some results on the multi-dimensional Jacobi-Gauss type interpolation and the related Bernstein-Jackson type inequalities are established,which play an important role in pseudospectral method.The pseudospectral method is applied to a twodimensional singular problem and a problem on axisymmetric domain.The convergence of proposed schemes is established.Numerical results demonstrate the efficiency of the proposed method.
Extensibility enables locomotion under isotropic drag
Pak, On Shun
2011-01-01
Anisotropic viscous drag is usually believed to be a requirement for the low Reynolds number locomotion of slender bodies such as flagella and cilia. Here we show that locomotion under isotropic drag is possible for extensible slender bodies. After general considerations, a two-ring swimmer and a model dinoflagellate flagellum are studied analytically to illustrate how extensibility can be exploited for self-propulsion without drag anisotropy. This new degree of freedom could be useful for some complex swimmer geometries and locomotion in complex fluid environments where drag anisotropy is weak or even absent.
Into the Bulk: A Covariant Approach
Engelhardt, Netta
2016-01-01
I propose a general, covariant way of defining when one region is "deeper in the bulk" than another. This definition is formulated outside of an event horizon (or in the absence thereof) in generic geometries; it may be applied to both points and surfaces, and may be used to compare the depth of bulk points or surfaces relative to a particular boundary subregion or relative to the entire boundary. Using the recently proposed "lightcone cut" formalism, the comparative depth between two bulk points can be determined from the singularity structure of Lorentzian correlators in the dual field theory. I prove that, by this definition, causal wedges of progressively larger regions probe monotonically deeper in the bulk. The definition furthermore matches expectations in pure AdS and in static AdS black holes with isotropic spatial slices, where a well-defined holographic coordinate exists. In terms of holographic RG flow, this new definition of bulk depth makes contact with coarse-graining over both large distances ...
Vector solitons in nonlinear isotropic chiral metamaterials
Tsitsas, N L; Frantzeskakis, D J
2011-01-01
Starting from the Maxwell equations, we used the reductive perturbation method to derive a system of two coupled nonlinear Schr\\"{o}dinger (NLS) equations for the two Beltrami components of the electromagnetic field propagating along a fixed direction in an isotropic nonlinear chiral metamaterial. With single-resonance Lorentz models for the permittivity and permeability and a Condon model for the chirality parameter, in certain spectral regimes, one of the two Beltrami components exhibits a negative real refractive index when nonlinearity is ignored and the chirality parameter is sufficiently large.We found that, inside such a spectral regime, there may exist a subregime wherein the system of the NLS equations can be approximated by the Manakov system. Bright-bright, dark-dark, and dark-bright vector solitons can be formed in that spectral subregime.
Kinematical uniqueness of homogeneous isotropic LQC
Engle, Jonathan; Hanusch, Maximilian
2017-01-01
In a paper by Ashtekar and Campiglia, invariance under volume preserving residual diffeomorphisms has been used to single out the standard representation of the reduced holonomy-flux algebra in homogeneous loop quantum cosmology (LQC). In this paper, we use invariance under all residual diffeomorphisms to single out the standard kinematical Hilbert space of homogeneous isotropic LQC for both the standard configuration space {{{R}}\\text{Bohr}} , as well as for the Fleischhack one {R}\\sqcup {{{R}}\\text{Bohr}} . We first determine the scale invariant Radon measures on these spaces, and then show that the Haar measure on {{{R}}\\text{Bohr}} is the only such measure for which the momentum operator is hermitian w.r.t. the corresponding inner product. In particular, the measure is forced to be identically zero on {R} in the Fleischhack case, so that for both approaches, the standard kinematical LQC-Hilbert space is singled out.
Vector solitons in nonlinear isotropic chiral metamaterials
Energy Technology Data Exchange (ETDEWEB)
Tsitsas, N L [School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Zografos, Athens 15773 (Greece); Lakhtakia, A [Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, PA 16802-6812 (United States); Frantzeskakis, D J, E-mail: dfrantz@phys.uoa.gr [Department of Physics, University of Athens, Panepistimiopolis, Zografos, Athens 15784 (Greece)
2011-10-28
Starting from the Maxwell equations, we used the reductive perturbation method to derive a system of two coupled nonlinear Schroedinger (NLS) equations for the two Beltrami components of the electromagnetic field propagating along a fixed direction in an isotropic nonlinear chiral metamaterial. With single-resonance Lorentz models for the permittivity and permeability and a Condon model for the chirality parameter, in certain spectral regimes, one of the two Beltrami components exhibits a negative-real refractive index when nonlinearity is ignored and the chirality parameter is sufficiently large. We found that, inside such a spectral regime, there may exist a subregime wherein the system of the NLS equations can be approximated by the Manakov system. Bright-bright, dark-dark, and dark-bright vector solitons can be formed in that spectral subregime. (paper)
An exhaustive list of isotropic apocalyptic scenarios
Parnovsky, S L
2016-01-01
We study the possible types of future singularities in the isotropic homogeneous cosmological models for the arbitrary equation of state of the contents of the Universe. We obtain all known types of these singularities as well as two new types using a simple approach. No additional singularity types are possible. We name the new singularities type "Big Squeeze" and "Little Freeze". The "Big Squeeze" is possible only in the flat Universe after a finite time interval. The density of the matter and dark energy tends to zero and its pressure to minus infinity. This requires the dark energy with a specific equation of state that has the same asymptotical behaviour at low densities as the generalised Chaplygin gas. The "Little Freeze" involves an eternal expansion of the Universe. Some solutions can mimic the $\\Lambda$CDM model.
Direct numerical simulation of compressible isotropic turbulence
Institute of Scientific and Technical Information of China (English)
LI; Xinliang(李新亮); FU; Dexun(傅德薰); MAYanwen(马延文)
2002-01-01
Direct numerical simulation (DNS) of decaying compressible isotropic turbulence at tur-bulence Mach numbers of Mt = 0.2-0.7 and Taylor Reynolds numbers of 72 and 153 is per-formed by using the 7th order upwind-biased difference and 8th order center difference schemes.Results show that proper upwind-biased difference schemes can release the limit of "start-up"problem to Mach numbers.Compressibility effects on the statistics of turbulent flow as well as the mechanics of shockletsin compressible turbulence are also studied, and the conclusion is drawn that high Mach numberleads to more dissipation. Scaling laws in compressible turbulence are also analyzed. Evidence isobtained that scaling laws and extended self similarity (ESS) hold in the compressible turbulentflow in spite of the presence of shocklets, and compressibility has little effect on scaling exponents.
A tilted transversely isotropic slowness surface approximation
Stovas, A.
2012-05-09
The relation between vertical and horizontal slownesses, better known as the dispersion relation, for transversely isotropic media with a tilted symmetry axis (TTI) requires solving a quartic polynomial equation, which does not admit a practical explicit solution to be used, for example, in downward continuation. Using a combination of the perturbation theory with respect to the anelliptic parameter and Shanks transform to improve the accuracy of the expansion, we develop an explicit formula for the vertical slowness that is highly accurate for all practical purposes. It also reveals some insights into the anisotropy parameter dependency of the dispersion relation including the low impact that the anelliptic parameter has on the vertical placement of reflectors for a small tilt in the symmetry angle. © 2012 European Association of Geoscientists & Engineers.
Kinematical uniqueness of homogeneous isotropic LQC
Engle, Jonathan
2016-01-01
In a paper by Ashtekar and Campiglia, invariance under volume preserving residual diffeomorphisms has been used to single out the standard representation of the reduced holonomy-flux algebra in homogeneous loop quantum cosmology (LQC). In this paper, we use invariance under all residual diffeomorphisms to single out the standard kinematical Hilbert space of homogeneous isotropic LQC for both the standard configuration space $\\mathbb{R}_{\\mathrm{Bohr}}$, as well as for the Fleischhack one $\\mathbb{R} \\sqcup \\mathbb{R}_{\\mathrm{Bohr}}$. We first determine the scale invariant Radon measures on these spaces, and then show that the Haar measure on $\\mathbb{R}_{\\mathrm{Bohr}}$ is the only such measure for which the momentum operator is hermitian w.r.t. the corresponding inner product. In particular, the measure is forced to be identically zero on $\\mathbb{R}$ in the Fleischhack case, so that for both approaches, the standard kinematical LQC-Hilbert space is singled out.
Can we remove the systematic error due to isotropic inhomogeneities?
Negishi, Hiroyuki; Nakao, Ken-ichi
2017-01-01
Usually, we assume that there is no inhomogeneity isotropic in terms of our location in our Universe. This assumption has not been observationally confirmed yet in sufficient accuracy, and we need to consider the possibility that there are non-negligible large-scale isotropic inhomogeneities in our Universe. The existence of large-scale isotropic inhomogeneities affects the determination of cosmological parameters. In particular, from only the distance-redshift relation, we cannot distinguish the inhomogeneous isotropic universe model from the homogeneous isotropic one, because of the ambiguity in the cosmological parameters. In this paper, in order to avoid such ambiguity, we consider three observables—the distance-redshift relation, the fluctuation spectrum of the cosmic microwave background radiation, and the scale of the baryon acoustic oscillation—and compare these observables in two universe models. One is the inhomogeneous isotropic universe model with the cosmological constant, and the other is the homogeneous isotropic universe model with dark energy other than the cosmological constant. We show that these two universe models cannot predict the same observational data of all three observables but the same ones of only two of three, as long as the perturbations are adiabatic. In principle, we can distinguish the inhomogeneous isotropic universe from the homogeneous isotropic one through the appropriate three observables, if the perturbations are adiabatic.
Viscous propulsion in active transversely isotropic media
Cupples, G.; Dyson, R. J.; Smith, D. J.
2017-02-01
Taylor's swimming sheet is a classical model of microscale propulsion and pumping. Many biological fluids and substances are fibrous, having a preferred direction in their microstructure; for example cervical mucus is formed of polymer molecules which create an oriented fibrous network. Moreover, suspensions of elongated motile cells produce a form of active oriented matter. To understand how these effects modify viscous propulsion, we extend Taylor's classical model of small-amplitude zero-Reynolds-number propulsion of a 'swimming sheet' via the transversely-isotropic fluid model of Ericksen, which is linear in strain rate and possesses a distinguished direction. The energetic costs of swimming are significantly altered by all rheological parameters and the initial fibre angle. Propulsion in a passive transversely-isotropic fluid produces an enhanced mean rate of working, independent of the initial fibre orientation, with an approximately linear dependence of energetic cost on the extensional and shear enhancements to the viscosity caused by fibres. In this regime the mean swimming velocity is unchanged from the Newtonian case. The effect of the constant term in Ericksen's model for the stress, which can be identified as a fibre tension or alternatively a stresslet characterising an active fluid, is also considered. This stress introduces an angular dependence and dramatically changes the streamlines and flow field; fibres aligned with the swimming direction increase the energetic demands of the sheet. The constant fibre stress may result in a reversal of the mean swimming velocity and a negative mean rate of working if sufficiently large relative to the other rheological parameters.
Contact mechanics and friction for transversely isotropic viscoelastic materials
Mokhtari, M.; Schipper, D.J.; Vleugels, N.; Noordermeer, J.W.M.; Yoshimoto, S.; Hashimoto, H.
2015-01-01
Transversely isotropic materials are an unique group of materials whose properties are the same along two of the principal axes of a Cartesian coordinate system. Various natural and artificial materials behave effectively as transversely isotropic elastic solids. Several materials can be classified
Practical improvements on photon diffusion theory : application to isotropic scattering
Graaff, R; Rinzema, K
2001-01-01
Based on the analysis of an isotropic point source in an infinite, isotropically scattering turbid medium, we suggest several modifications to the well-known diffusion theory. Compared with standard diffusion theory these modifications, which require very little extra mathematics, lead to a substant
On the decay of homogeneous isotropic turbulence
Skrbek, L.; Stalp, Steven R.
2000-08-01
Decaying homogeneous, isotropic turbulence is investigated using a phenomenological model based on the three-dimensional turbulent energy spectra. We generalize the approach first used by Comte-Bellot and Corrsin [J. Fluid Mech. 25, 657 (1966)] and revised by Saffman [J. Fluid Mech. 27, 581 (1967); Phys. Fluids 10, 1349 (1967)]. At small wave numbers we assume the spectral energy is proportional to the wave number to an arbitrary power. The specific case of power 2, which follows from the Saffman invariant, is discussed in detail and is later shown to best describe experimental data. For the spectral energy density in the inertial range we apply both the Kolmogorov -5/3 law, E(k)=Cɛ2/3k-5/3, and the refined Kolmogorov law by taking into account intermittency. We show that intermittency affects the energy decay mainly by shifting the position of the virtual origin rather than altering the power law of the energy decay. Additionally, the spectrum is naturally truncated due to the size of the wind tunnel test section, as eddies larger than the physical size of the system cannot exist. We discuss effects associated with the energy-containing length scale saturating at the size of the test section and predict a change in the power law decay of both energy and vorticity. To incorporate viscous corrections to the model, we truncate the spectrum at an effective Kolmogorov wave number kη=γ(ɛ/v3)1/4, where γ is a dimensionless parameter of order unity. We show that as the turbulence decays, viscous corrections gradually become more important and a simple power law can no longer describe the decay. We discuss the final period of decay within the framework of our model, and show that care must be taken to distinguish between the final period of decay and the change of the character of decay due to the saturation of the energy containing length scale. The model is applied to a number of experiments on decaying turbulence. These include the downstream decay of turbulence in
On the algebraic structure of isotropic generalized elasticity theories
Auffray, Nicolas
2013-01-01
In this paper the algebraic structure of the isotropic nth-order gradient elasticity is investigated. In the classical isotropic elasticity it is well-known that the constitutive relation can be broken down into two uncoupled relations between elementary part of the strain and the stress tensors (deviatoric and spherical). In this paper we demonstrate that this result can not be generalized and since 2nd-order isotropic elasticity there exist couplings between elementary parts of higher-order strain and stress tensors. Therefore, and in certain way, nth-order isotropic elasticity have the same kind of algebraic structure as anisotropic classical elasticity. This structure is investigated in the case of 2nd-order isotropic elasticity, and moduli characterizing the behavior are provided.
A modified failure criterion for transversely isotropic rocks
Institute of Scientific and Technical Information of China (English)
Omid Saeidi; Vamegh Rasouli; Rashid Geranmayeh Vaneghi; Raoof Gholami; Seyed Rahman Torabi
2014-01-01
A modified failure criterion is proposed to determine the strength of transversely isotropic rocks. Me-chanical properties of some metamorphic and sedimentary rocks including gneiss, slate, marble, schist, shale, sandstone and limestone, which show transversely isotropic behavior, were taken into consider-ation. Afterward, introduced triaxial rock strength criterion was modified for transversely isotropic rocks. Through modification process an index was obtained that can be considered as a strength reduction parameter due to rock strength anisotropy. Comparison of the parameter with previous anisotropy in-dexes in literature showed reasonable results for the studied rock samples. The modified criterion was compared to modified Hoek-Brown and Ramamurthy criteria for different transversely isotropic rocks. It can be concluded that the modified failure criterion proposed in this study can be used for predicting the strength of transversely isotropic rocks.
Nonlinear elastic inclusions in isotropic solids
Yavari, A.
2013-10-16
We introduce a geometric framework to calculate the residual stress fields and deformations of nonlinear solids with inclusions and eigenstrains. Inclusions are regions in a body with different reference configurations from the body itself and can be described by distributed eigenstrains. Geometrically, the eigenstrains define a Riemannian 3-manifold in which the body is stress-free by construction. The problem of residual stress calculation is then reduced to finding a mapping from the Riemannian material manifold to the ambient Euclidean space. Using this construction, we find the residual stress fields of three model systems with spherical and cylindrical symmetries in both incompressible and compressible isotropic elastic solids. In particular, we consider a finite spherical ball with a spherical inclusion with uniform pure dilatational eigenstrain and we show that the stress in the inclusion is uniform and hydrostatic. We also show how singularities in the stress distribution emerge as a consequence of a mismatch between radial and circumferential eigenstrains at the centre of a sphere or the axis of a cylinder.
Shocklet statistics in compressible isotropic turbulence
Wang, Jianchun; Gotoh, Toshiyuki; Watanabe, Takeshi
2017-02-01
Shocklet statistics in compressible isotropic turbulence are studied by using numerical simulations with solenoidal forcing, at the turbulent Mach number Mt ranging from 0.5 up to 1.0 and at the Taylor Reynolds number Reλ ranging from 110 to 250. A power-law region of the probability density function (PDF) of the shocklet strength Mn-1 (Mn is the normal shock Mach number) is observed. The magnitude of the power-law exponent is found to decrease with the increase of Mt. We show that the most probable shocklet strength is proportional to Mt3, and the shocklet thickness corresponding to the most probable shock Mach number is proportional to Mt-2 in our numerical simulations. The PDFs of the jumps of the velocity and thermodynamic variables across a shocklet exhibit a similar power-law scaling. The statistics of the jumps of the velocity and thermodynamic variables are further investigated by conditioned average. Nonlinear models for the conditional average of the jumps of the velocity and thermodynamic variables are developed and verified.
Near isotropic behaviour of turbulent thermal convection
Nath, Dinesh; Kumar, Abhishek; Verma, Mahendra K
2016-01-01
We investigate the anisotropy in turbulent convection in a 3D box using direct numerical simulation. We compute the anisotropic parameter $A = u_\\perp^{2}/(2u_{\\parallel}^{2})$, where $u_{\\perp}$ and $u_{\\parallel}$ are the components of velocity perpendicular and parallel to the buoyancy direction, the shell and ring spectra, and shell-to-shell energy transfers. We observe that the flow is nearly isotropic for the Prandtl number $\\mathrm{Pr} \\approx 1$, but the anisotropy increases with the Prandtl number. For $\\mathrm{Pr}=\\infty$, $A \\approx 0.3$, thus anisotropy is not very significant even in extreme cases. We also observe that $u_{\\parallel}$ feeds energy to $u_{\\perp}$ via pressure. The computation of shell-to-shell energy transfers show that the energy transfer in turbulent convection is local and forward, similar to fluid turbulence. These results are consistent with the Kolmogorov's spectrum observed by Kumar et al.~[Phys. Rev. E {\\bf 90}, 023016 (2014)] for turbulent convection.
Design of a reaction field using a linear-combination-based isotropic periodic sum method.
Takahashi, Kazuaki Z
2014-04-30
In our previous study (Takahashi et al., J. Chem. Theory Comput. 2012, 8, 4503), we developed the linear-combination-based isotropic periodic sum (LIPS) method. The LIPS method is based on the extended isotropic periodic sum theory that produces a ubiquitous interaction potential function to estimate homogeneous and heterogeneous systems. The LIPS theory also provides the procedure to design a periodic reaction field. To demonstrate this, in the present work, a novel reaction field of the LIPS method was developed. The novel reaction field was labeled LIPS-SW, because it provides an interaction potential function with a shape that resembles that of the switch function method. To evaluate the ability of the LIPS-SW method to describe in homogeneous and heterogeneous systems, we carried out molecular dynamics (MD) simulations of bulk water and water-vapor interfacial systems using the LIPS-SW method. The results of these simulations show that the LIPS-SW method gives higher accuracy than the conventional interaction potential function of the LIPS method. The accuracy of simulating water-vapor interfacial systems was greatly improved, while that of bulk water systems was maintained using the LIPS-SW method. We conclude that the LIPS-SW method shows great potential for high-accuracy, high-performance computing to allow large scale MD simulations. © 2014 Wiley Periodicals, Inc.
Sudden relaminarisation and lifetimes in forced isotropic turbulence
Linkmann, Moritz
2015-01-01
We demonstrate an unexpected connection between isotropic turbulence and wall-bounded shear flows. We perform direct numerical simulations of isotropic turbulence forced at large scales at moderate Reynolds numbers and observe sudden transitions from chaotic dynamics to a spatially simple flow, analogous to the laminar state in wall-bounded shear flows. We find that the survival probabilities of turbulence are exponential and the typical lifetimes increase super-exponentially with the Reynolds number. Our results suggest that both isotropic turbulence and wall-bounded shear flows share the same phase-space dynamics.
Killing vector fields and a homogeneous isotropic universe
Katanaev, M O
2016-01-01
Some basic theorems on Killing vector fields are reviewed. In particular, the topic of a constant-curvature space is examined. A detailed proof is given for a theorem describing the most general form of the metric of a homogeneous isotropic space-time. Although this theorem can be considered to be commonly known, its complete proof is difficult to find in the literature. An example metric is presented such that all its spatial cross sections correspond to constant-curvature spaces, but it is not homogeneous and isotropic as a whole. An equivalent definition of a homogeneous and isotropic space-time in terms of embedded manifolds is also given.
Pseudo-Riemannian Universe from Euclidean bulk
Vasilić, Milovan
2015-01-01
I develop the idea that our world is a brane-like object embedded in Euclidean bulk. In its ground state, the brane constituent matter is assumed to be homogeneous and isotropic, and of negligible influence on the bulk geometry. No action functional is initially specified. Instead, the brane dynamics is derived from the universally valid stress-energy conservation equations. The present work studies the cosmology of a $3$-sphere in the $5$-dimensional Euclidean bulk. It is shown that the conventional equation of state $p=\\alpha\\rho$ is universal in the sector of small energy densities, and so is the resulting brane dynamics. The inequality $\\alpha<0$ is found to be a necessary condition for the existence of a stable ground state of the Universe. It is demonstrated that the generic braneworld physics rules out the Big Bang cosmology, and in that matter, any cosmology of finite lifetime. I also demonstrate that stable brane vibrations satisfy Klein-Gordon-like equation with an effective metric of Minkowski s...
Bulk viscous cosmology in early Universe
Indian Academy of Sciences (India)
C P Singh
2008-07-01
The effect of bulk viscosity on the early evolution of Universe for a spatially homogeneous and isotropic Robertson-Walker model is considered. Einstein's field equations are solved by using `gamma-law' equation of state = ( - 1)ρ, where the adiabatic parameter gamma () depends on the scale factor of the model. The `gamma' function is defined in such a way that it describes a unified solution of early evolution of the Universe for inflationary and radiation-dominated phases. The fluid has only bulk viscous term and the coefficient of bulk viscosity is taken to be proportional to some power function of the energy density. The complete general solutions have been given through three cases. For flat space, power-law as well as exponential solutions are found. The problem of how the introduction of viscosity affects the appearance of singularity, is briefly discussed in particular solutions. The deceleration parameter has a freedom to vary with the scale factor of the model, which describes the accelerating expansion of the Universe.
Large area bulk superconductors
Miller, Dean J.; Field, Michael B.
2002-01-01
A bulk superconductor having a thickness of not less than about 100 microns is carried by a polycrystalline textured substrate having misorientation angles at the surface thereof not greater than about 15.degree.; the bulk superconductor may have a thickness of not less than about 100 microns and a surface area of not less than about 50 cm.sup.2. The textured substrate may have a thickness not less than about 10 microns and misorientation angles at the surface thereof not greater than about 15.degree.. Also disclosed is a process of manufacturing the bulk superconductor and the polycrystalline biaxially textured substrate material.
Renormalization of Hierarchically Interacting Isotropic Diffusions
den Hollander, F.; Swart, J. M.
1998-10-01
We study a renormalization transformation arising in an infinite system of interacting diffusions. The components of the system are labeled by the N-dimensional hierarchical lattice ( N≥2) and take values in the closure of a compact convex set bar D subset {R}^d (d ≥slant 1). Each component starts at some θ ∈ D and is subject to two motions: (1) an isotropic diffusion according to a local diffusion rate g: bar D to [0,infty ] chosen from an appropriate class; (2) a linear drift toward an average of the surrounding components weighted according to their hierarchical distance. In the local mean-field limit N→∞, block averages of diffusions within a hierarchical distance k, on an appropriate time scale, are expected to perform a diffusion with local diffusion rate F ( k) g, where F^{(k)} g = (F_{c_k } circ ... circ F_{c_1 } ) g is the kth iterate of renormalization transformations F c ( c>0) applied to g. Here the c k measure the strength of the interaction at hierarchical distance k. We identify F c and study its orbit ( F ( k) g) k≥0. We show that there exists a "fixed shape" g* such that lim k→∞ σk F ( k) g = g* for all g, where the σ k are normalizing constants. In terms of the infinite system, this property means that there is complete universal behavior on large space-time scales. Our results extend earlier work for d = 1 and bar D = [0,1], resp. [0, ∞). The renormalization transformation F c is defined in terms of the ergodic measure of a d-dimensional diffusion. In d = 1 this diffusion allows a Yamada-Watanabe-type coupling, its ergodic measure is reversible, and the renormalization transformation F c is given by an explicit formula. All this breaks down in d≥2, which complicates the analysis considerably and forces us to new methods. Part of our results depend on a certain martingale problem being well-posed.
Constitutive modeling for isotropic materials (HOST)
Chan, Kwai S.; Lindholm, Ulric S.; Bodner, S. R.; Hill, Jeff T.; Weber, R. M.; Meyer, T. G.
1986-01-01
The results of the third year of work on a program which is part of the NASA Hot Section Technology program (HOST) are presented. The goals of this program are: (1) the development of unified constitutive models for rate dependent isotropic materials; and (2) the demonstration of the use of unified models in structural analyses of hot section components of gas turbine engines. The unified models selected for development and evaluation are those of Bodner-Partom and of Walker. A test procedure was developed for assisting the generation of a data base for the Bodner-Partom model using a relatively small number of specimens. This test procedure involved performing a tensile test at a temperature of interest that involves a succession of strain-rate changes. The results for B1900+Hf indicate that material constants related to hardening and thermal recovery can be obtained on the basis of such a procedure. Strain aging, thermal recovery, and unexpected material variations, however, preluded an accurate determination of the strain-rate sensitivity parameter is this exercise. The effects of casting grain size on the constitutive behavior of B1900+Hf were studied and no particular grain size effect was observed. A systematic procedure was also developed for determining the material constants in the Bodner-Partom model. Both the new test procedure and the method for determining material constants were applied to the alternate material, Mar-M247 . Test data including tensile, creep, cyclic and nonproportional biaxial (tension/torsion) loading were collected. Good correlations were obtained between the Bodner-Partom model and experiments. A literature survey was conducted to assess the effects of thermal history on the constitutive behavior of metals. Thermal history effects are expected to be present at temperature regimes where strain aging and change of microstructure are important. Possible modifications to the Bodner-Partom model to account for these effects are outlined
Negative Index of Refraction in Optical Metamaterials
Shalaev, V M; Chettiar, U; Yuan, H K; Sarychev, A K; Drachev, V P; Kildishev, A V; Shalaev, Vladimir M.; Cai, Wenshan; Chettiar, Uday; Yuan, Hsiao-Kuan; Sarychev, Andrey K.; Drachev, Vladimir P.; Kildishev, Alexander V.
2005-01-01
An array of pairs of parallel gold nanorods is shown to have a negative refractive index in the optical range, close to a wavelength of 1 micron. Such behavior results from the plasmon resonance in the pairs of nanorods for both the electric and magnetic components of light. The metal rods act as inductive elements whereas the dielectric gaps perform as capacitive elements, forming an optical LC-circuit. Our experiments and simulations demonstrate the resonant behavior for an index of refraction. Above the resonance, the refractive index becomes negative. Paired metal nanorods open new opportunities for developing negative-refraction materials in optics.
Characterizing error propagation in quantum circuits: the Isotropic Index
Fonseca de Oliveira, André L.; Buksman, Efrain; Cohn, Ilan; García López de Lacalle, Jesús
2017-02-01
This paper presents a novel index in order to characterize error propagation in quantum circuits by separating the resultant mixed error state in two components: an isotropic component that quantifies the lack of information, and a disalignment component that represents the shift between the current state and the original pure quantum state. The Isotropic Triangle, a graphical representation that fits naturally with the proposed index, is also introduced. Finally, some examples with the analysis of well-known quantum algorithms degradation are given.
A defect mediated lamellar to isotropic transition of amphiphile bilayers
Pal, Antara; Pabst, Georg; Raghunathan, V. A.
2011-01-01
We report the observation of a novel isotropic phase of amphiphile bilayers in a mixed system consisting of the ionic surfactant, sodium docecylsulphate (SDS), and the organic salt p-toludine hydrochloride (PTHC). This system forms a collapsed lamellar ($L_\\alpha$) phase over a wide range of water content, which transforms into an isotropic phase on heating. This transition is not observed in samples without excess water, where the $L_\\alpha$ phase is stable at higher temperatures. Our observ...
Some exact solutions in K-essence theory isotropic cosmology
Pimentel, Luis O
2016-01-01
We use a simple form of the K-essence theory and apply it to the classic isotropic cosmological model and seek exact solutions. The particular form of the kinetic term that we choose is $K \\left(\\phi, X \\right)= K_0(\\phi)X^m +K_1$. The resulting field equations in the homogeneous and isotropic cosmology (FRW)is considered. Several exact solutions are obtained.
Elasticity of transversely isotropic materials%"Elasticity of Transversely Isotropic Materials"一书评介
Institute of Scientific and Technical Information of China (English)
王敏中
2006-01-01
@@ 浙江大学土木系丁皓江教授和陈伟球教授及澳大利亚悉尼大学航空、机械与机电工程学院章亮炽教授的专著"Elasticity of Transversely Isotropic Materials"(ISBN:1-4020-4033-4),2006年由Springer公司出版,该书是加拿大著名力学家G.M.L.Gladwell 教授主编的丛书"Solid Mechanics and its Applications"的第126本,是我国大陆学者第一次在该丛书框架下出版专著.
Phantom dark energy as an effect of bulk viscosity
Velten, Hermano; Meng, Xinhe
2013-01-01
In a homogeneous and isotropic universe bulk viscosity is the unique viscous effect capable to modify the background dynamics. Effects like shear viscosity or heat conduction can only change the evolution of the perturbations. The existence of a bulk viscous pressure in a fluid, which in order to obey to the second law of thermodynamics is negative, reduces its effective pressure. We discuss in this study the degeneracy in bulk viscous cosmologies and address the possibility that phantom dark energy cosmology could be caused by the existence of non-equilibrium pressure in any cosmic component. We establish the conditions under which either matter or radiation viscous cosmologies can be mapped into the phantom dark energy scenario with constraints from multiple observational data-sets
Dynamic wetting model for the isotropic-to-nematic transition over a flat substrate.
Rey, Alejandro D; Herrera-Valencia, E E
2014-03-14
Phase ordering over solid substrates is a ubiquitous and important soft material transformation process whose description incorporates wetting, anchoring and phase transition kinetics. In this paper the kinetics of the isotropic-to-nematic isothermal phase transition over a flat solid surface in a growing spherical drop is analyzed based on the Landau-de Gennes Q-tensor order parameter equations. The model, based on a previously derived interface force balance and a newly derived contact line force balance, is shown to be consistent with the generic model of conservative interface and contact line motions. The advancing dynamic contact angle equation is extracted from kinematic compatibility between the moving isotropic-nematic interface and contact line. A tractable surface phase transition kinetic model obtained by focusing on the dominant phase transition and wetting driving forces yields: (i) the constant advancing dynamic contact angle θ, and (ii) the contact line speed as a function of undercooling ΔT. It is shown that as undercooling increases, the surface phase transition mode approaches the bulk phase transition mode, such that θ approaches π. The elastic and wetting parameters that control the phase transformation process are identified and experiments for their determination are defined. These dynamic wetting and surface phase transition results significantly expand existing characterization methods of LC-substrate interfaces based on static phase transition droplet methods.
Efficient anisotropic wavefield extrapolation using effective isotropic models
Alkhalifah, Tariq Ali
2013-06-10
Isotropic wavefield extrapolation is more efficient than anisotropic extrapolation, and this is especially true when the anisotropy of the medium is tilted (from the vertical). We use the kinematics of the wavefield, appropriately represented in the high-frequency asymptotic approximation by the eikonal equation, to develop effective isotropic models, which are used to efficiently and approximately extrapolate anisotropic wavefields using the isotropic, relatively cheaper, operators. These effective velocity models are source dependent and tend to embed the anisotropy in the inhomogeneity. Though this isotropically generated wavefield theoretically shares the same kinematic behavior as that of the first arrival anisotropic wavefield, it also has the ability to include all the arrivals resulting from a complex wavefield propagation. In fact, the effective models reduce to the original isotropic model in the limit of isotropy, and thus, the difference between the effective model and, for example, the vertical velocity depends on the strength of anisotropy. For reverse time migration (RTM), effective models are developed for the source and receiver fields by computing the traveltime for a plane wave source stretching along our source and receiver lines in a delayed shot migration implementation. Applications to the BP TTI model demonstrates the effectiveness of the approach.
Properties of elastic percolating networks in isotropic media with arbitrary elastic constants
Pla, O.; Garcia-Molina, R.; Guinea, F.; Louis, E.
1990-06-01
The properties of diluted elastic media in two dimensions are investigated in an isotropic system in which the ratio between the two Lamé coefficients can be varied. Changes in the ratio between the continuum elastic constants induce significant variations in the behavior of the system away from the threshold for percolation, but not in the properties near the percolation transition. We discuss the results in both cases and their relevance to the definition of the universal properties of diluted elastic networks. It is shown that many features of interest, like the bulk modulus at intermediate concentrations of voids and the backbone, are very dependent on the microscopic details of the model, and not only on its macroscopic behavior. Thus, elastic percolation does not seem to have the same degree of universality as scalar percolation.
Comparative analysis of isotropic diffusion weighted imaging sequences
Vellmer, Sebastian; Stirnberg, Rüdiger; Edelhoff, Daniel; Suter, Dieter; Stöcker, Tony; Maximov, Ivan I.
2017-02-01
Visualisation of living tissue structure and function is a challenging problem of modern imaging techniques. Diffusion MRI allows one to probe in vivo structures on a micrometer scale. However, conventional diffusion measurements are time-consuming procedures, because they require several measurements with different gradient directions. Considerable time savings are therefore possible by measurement schemes that generate an isotropic diffusion weighting in a single shot. Multiple approaches for generating isotropic diffusion weighting are known and have become very popular as useful tools in clinical research. Thus, there is a strong need for a comprehensive comparison of different isotropic weighting approaches. In the present work we introduce two new sequences based on simple (co)sine modulations and compare their performance to established q-space magic-angle spinning sequences and conventional DTI, using a diffusion phantom assembled from microcapillaries and in vivo experiments at 7 T. The advantages and disadvantages of all compared schemes are demonstrated and discussed.
The refined theory of transversely isotropic piezoelectric rectangular beams
Institute of Scientific and Technical Information of China (English)
GAO; Yang; WANG; Minzhong
2006-01-01
The problem of deducing one-dimensional theory from two-dimensional theory for a transversely isotropic piezoelectric rectangular beam is investigated. Based on the piezoelasticity theory, the refined theory of piezoelectric beams is derived by using the general solution of transversely isotropic piezoelasticity and Lur'e method without ad hoc assumptions. Based on the refined theory of piezoelectric beams, the exact equations for the beams without transverse surface loadings are derived, which consist of two governing differential equations: the fourth-order equation and the transcendental equation. The approximate equations for the beams under transverse loadings are derived directly from the refined beam theory. As a special case, the governing differential equations for transversely isotropic elastic beams are obtained from the corresponding equations of piezoelectric beams. To illustrate the application of the beam theory developed, a uniformly loaded and simply supported piezoelectric beam is examined.
Sudden relaminarisation and lifetimes in forced isotropic turbulence
Linkmann, Moritz; Morozov, Alexander
2015-11-01
We demonstrate an unexpected connection between isotropic turbulence and wall-bounded shear flows. We perform direct numerical simulations of isotropic turbulence forced at large scales at moderate Reynolds numbers and observe sudden transitions from chaotic dynamics to a spatially simple flow, analogous to the laminar state in wall bounded shear flows. We find that the survival probabilities of turbulence are exponential and the typical lifetimes increase super-exponentially with the Reynolds number, similar to results on relaminarisation of localised turbulence in pipe and plane Couette flow. Results from simulations subjecting the observed large-scale flow to random perturbations of variable amplitude demonstrate that it is a linearly stable simple exact solution that can be destabilised by a finite-amplitude perturbation, like the Hagen-Poiseuille profile in pipe flow. Our results suggest that both isotropic turbulence and wall-bounded shear flows qualitatively share the same phase-space dynamics.
Scaling of Lyapunov Exponents in Homogeneous, Isotropic DNS
Fitzsimmons, Nicholas; Malaya, Nicholas; Moser, Robert
2013-11-01
Lyapunov exponents measure the rate of separation of initially infinitesimally close trajectories in a chaotic system. Using the exponents, we are able to probe the chaotic nature of homogeneous isotropic turbulence and study the instabilities of the chaotic field. The exponents are measured by calculating the instantaneous growth rate of a linear disturbance, evolved with the linearized Navier-Stokes equation, at each time step. In this talk, we examine these exponents in the context of homogeneous isotropic turbulence with two goals: 1) to investigate the scaling of the exponents with respect to the parameters of forced homogeneous isotropic turbulence, and 2) to characterize the instabilities that lead to chaos in turbulence. Specifically, we explore the scaling of the Lyapunov exponents with respect to the Reynolds number and with respect to the ratio of the integral length scale and the computational domain size.
GENERAL EXPRESSIONS OF CONSTITUTIVE EQUATIONS FOR ISOTROPIC ELASTIC DAMAGED MATERIALS
Institute of Scientific and Technical Information of China (English)
唐雪松; 蒋持平; 郑健龙
2001-01-01
The general expressions of constitutive equations for isotropic elastic damaged materials were derived directly from the basic law of irreversible thermodynamics. The limitations of the classical damage constitutive equation based on the well-known strain equivalence hypothesis were overcome. The relationships between the two elastic isotropic damage models(i. e. single and double scalar damage models)were revealed. When a single scalar damage variable defined according to the microscopic geometry of a damaged material is used to describle the isotropic damage state, the constitutive equations contain two "damage effect functions", which describe the different influences of damage on the two independent elastic constants. The classical damage constitutive equation based on the strain equivalence hypothesis is only the first-order approximation of the general expression.It may be unduly simplified and may fail to describe satisfactorily the damage phenomena of practical materials.
Haveren, van J.; Scott, E.L.; Sanders, J.P.M.
2008-01-01
Given the current robust forces driving sustainable production, and available biomass conversion technologies, biomass-based routes are expected to make a significant impact on the production of bulk chemicals within 10 years, and a huge impact within 20-30 years. In the Port of Rotterdam there is a
Isotropic Scale-Invariant Dissipation of Solar Wind Turbulence
Kiyani, K H; Khotyaintsev, Yu V; Turner, A; Hnat, B; Sahraoui, F
2010-01-01
The anisotropic nature of solar wind magnetic fluctuations is investigated scale-by-scale using high cadence in-situ magnetic field measurements spanning five decades in scales from the inertial to dissipation ranges of plasma turbulence. We find an abrupt transition at ion kinetic scales to a single isotropic stochastic process that characterizes the dissipation range on all observable scales. In contrast to the inertial range, this is accompanied by a successive scale-invariant reduction in the ratio between parallel and transverse power. We suggest a possible phase space mechanism for this, based on nonlinear wave-particle interactions, operating in this scale-invariant isotropic manner.
Massive gravity: nonlinear instability of the homogeneous and isotropic universe
De Felice, Antonio; Mukohyama, Shinji
2012-01-01
We study the propagating modes for nonlinear massive gravity on a Bianchi type--I manifold. We analyze their kinetic terms and dispersion relations as the background manifold approaches the homogeneous and isotropic limit. We show that in this limit, at least one ghost always exists and that its frequency tends to vanish for large scales, meaning that it cannot be integrated out from the low energy effective theory. Since this ghost mode can be considered as a leading nonlinear perturbation around a homogeneous and isotropic background, we conclude that the universe in this theory must be either inhomogeneous or anisotropic.
Thermalization and isotropization in heavy-ion collisions
Indian Academy of Sciences (India)
Michael Strickland
2015-05-01
Our current understanding of the processes driving the thermalization and isotropization of the quark gluon plasma (QGP) created in ultrarelativistic heavy-ion collisions (URHICs) is reviewed. Initially, the phenomenological evidence in favour of the creation of a thermal but momentum–space anisotropic QGP in URHICs is discussed. Further, the degree of isotropization using viscous (dissipative) hydrodynamics, weak-coupling approaches to QGP dynamics, and strong-coupling approaches to QGP dynamics are discussed. Finally, recent progress in the area of real-time non-Abelian gauge field simulations and non-Abelian Boltzmann–Vlasov-based hard-loop simulations are reported.
The problem of isotropic rectangular plate with four clamped edges
Indian Academy of Sciences (India)
C Erdem İmrak; Ismail Gerdemeli
2007-06-01
The examination of the exact solution of the governing equation of the rectangular plate is important for many reasons. This report discusses in exact solution of the governing equation of an isotropic rectangular plate with four clamped edges. A numerical method for clamped isotropic rectangular plate under distributed loads and an exact solution of the governing equation in terms of trigonometric and hyperbolic function are given. Finally, an illustrative example is given and the results are compared with those reported earlier. This method is found to be easier and effective. The results show reasonable agreement with other available results, but with a simpler and practical approach.
Chen, X
2001-01-01
Viscous resistance to changes in the volume of a gas arises when different degrees of freedom have different relaxation times. Collisions tend to oppose the resulting departures from equilibrium and, in so doing, generate entropy. Even for a classical gas of hard spheres, when the mean free paths or mean flight times of constituent particles are long, we find a nonvanishing bulk viscosity. Here we apply a method recently used to uncover this result for a classical rarefied gas to radiative transfer theory and derive an expression for the radiative stress tensor for a gray medium with absorption and Thomson scattering. We determine the transport coefficients through the calculation of the comoving entropy generation. When scattering dominates absorption, the bulk viscosity becomes much larger than either the shear viscosity or the thermal conductivity.
Seeing is believing : communication performance under isotropic teleconferencing conditions
Werkhoven, P.J.; Schraagen, J.M.C.; Punte, P.A.J.
2001-01-01
The visual component of conversational media such as videoconferencing systems communicates important non-verbal information such as facial expressions, gestures, posture and gaze. Unlike the other cues, selective gaze depends critically on the configuration of cameras and monitors. Under isotropic
NON-ISOTROPIC JACOBI SPECTRAL METHODS FOR UNBOUNDED DOMAINS
Institute of Scientific and Technical Information of China (English)
王立联; 郭本瑜
2004-01-01
Some specific non-isotropic Jacobi approximations in multiple-dimensions are investigated, which are used for numerical solutions of differential equations on various unbounded domains. The convergence of proposed schemes are proved. Some efficient algorithms are provided. Numerical results are presented to illustrate the efficiency of this new approach.
Exact isotropic scalar field cosmologies in Einstein-Cartan theory
Energy Technology Data Exchange (ETDEWEB)
Galiakhmetov, A M, E-mail: agal17@mail.r [Department of Physics, Donetsk National Technical University, Kirova street 51, 84646, Gorlovka (Ukraine)
2010-03-07
Exact general solutions to the Einstein-Cartan equations are obtained for spatially flat isotropic and homogeneous cosmologies with a nonminimally coupled scalar field. It is shown that both singular and nonsingular models are possible. Exact general solutions of an analogous problem in the torsion-less case are derived. The role of torsion in the evolution of models is elucidated.
Simultaneous amplification and attenuation in isotropic chiral materials
Mackay, Tom G
2015-01-01
The electromagnetic field phasors in an isotropic chiral material (ICM) are superpositions of two Beltrami fields of different handedness. Application of the Bruggeman homogenization formalism to two-component composite materials delivers ICMs wherein Beltrami fields of one handedness attenuate whereas Beltrami waves of the other handedness amplify. One component material is a dissipative ICM, the other an active dielectric material.
A Simple Mechanical Model for the Isotropic Harmonic Oscillator
Nita, Gelu M.
2010-01-01
A constrained elastic pendulum is proposed as a simple mechanical model for the isotropic harmonic oscillator. The conceptual and mathematical simplicity of this model recommends it as an effective pedagogical tool in teaching basic physics concepts at advanced high school and introductory undergraduate course levels. (Contains 2 figures.)
Solitary plane waves in an isotropic hexagonal lattice
DEFF Research Database (Denmark)
Zolotaryuk, Yaroslav; Savin, A.V.; Christiansen, Peter Leth
1998-01-01
Solitary plane-wave solutions in a two-dimensional hexagonal lattice which can propagate in different directions on the plane are found by using the pseudospectral method. The main point of our studies is that the lattice model is isotropic and we show that the sound velocity is the same for diff...
Angular Momentum of Supersymmetric Non-isotropic Traps
Institute of Scientific and Technical Information of China (English)
XU Qiang
2001-01-01
A simple way to explain quantum behavior of supersymmetric non-isotropic traps is proposed in the framework of sermiunitary formulation of supersymmetric quantum mechanics. Using semiunitary formulation we can simultaneously supersymmetrize the complete set of observables, especially including angular moment.
Switch isotropic/anisotropic wettability via dual-scale rods
Directory of Open Access Journals (Sweden)
Yang He
2014-10-01
Full Text Available It is the first time to demonstrate the comparison of isotropic/anisotropic wettability between dual-scale micro-nano-rods and single-scale micro-rods. Inspired by the natural structures of rice leaf, a series of micro-nano-rods and micro-rods with different geometric parameters were fabricated using micro-fabrication technology. Experimental measured apparent contact angles and advancing and receding contact angles from orthogonal orientations were characterized. The difference of contact angles from orthogonal orientation on dual-scale rods was much smaller than those on single-scale rods in both static and dynamic situation. It indicated that the dual-scale micro-nano-rods showed isotropic wettability, while single-scale micro-rods showed anisotropic wettability. The switch of isotropic/anisotropic wettability could be illustrated by different wetting state and contact line moving. It offers a facial way to switch isotropic/anisotropic wettability of the surface via dual-scale or single-scale structure.
Coupling of Elastic Isotropic Medium Parameters in Iterative Linearized Inversion
Anikiev, D.V.; Kashtan, B.M.; Mulder, W.A.; Troyan, V.N.
2014-01-01
An elastic isotropic medium is described with three parameters. In seismic migration the perturbation of one elastic parameter affects the images of all the three, which means that these parameters are coupled. For an effective quantitative reconstruction of the true elastic medium reflectivity one
Switch isotropic/anisotropic wettability via dual-scale rods
He, Yang; Jiang, Chengyu; Wang, Shengkun; Ma, Zhibo; Yuan, Weizheng
2014-10-01
It is the first time to demonstrate the comparison of isotropic/anisotropic wettability between dual-scale micro-nano-rods and single-scale micro-rods. Inspired by the natural structures of rice leaf, a series of micro-nano-rods and micro-rods with different geometric parameters were fabricated using micro-fabrication technology. Experimental measured apparent contact angles and advancing and receding contact angles from orthogonal orientations were characterized. The difference of contact angles from orthogonal orientation on dual-scale rods was much smaller than those on single-scale rods in both static and dynamic situation. It indicated that the dual-scale micro-nano-rods showed isotropic wettability, while single-scale micro-rods showed anisotropic wettability. The switch of isotropic/anisotropic wettability could be illustrated by different wetting state and contact line moving. It offers a facial way to switch isotropic/anisotropic wettability of the surface via dual-scale or single-scale structure.
Guided waves in a fluid-loaded transversely isotropic plate
Directory of Open Access Journals (Sweden)
Ahmad F.
2002-01-01
Full Text Available Dispersion relations are obtained for the propagation of symmetric and antisymmetric modes in a free transversely isotropic plate. Dispersion curves are plotted for the first four symmetric modes for a magnesium plate immersed in water. The first mode is highly damped and switches over to the second mode when the normalized frequency exceeds 12.
Semiclassical States Associated with Isotropic Submanifolds of Phase Space
Guillemin, V.; Uribe, A.; Wang, Z.
2016-05-01
We define classes of quantum states associated with isotropic submanifolds of cotangent bundles. The classes are stable under the action of semiclassical pseudo-differential operators and covariant under the action of semiclassical Fourier integral operators. We develop a symbol calculus for them; the symbols are symplectic spinors. We outline various applications.
Thermoplastic Micro-Forming of Bulk Metallic Glasses: A Review
Li, Ning; Chen, Wen; Liu, Lin
2016-04-01
Bulk metallic glasses are a fascinating class of metallic alloys with an isotropic amorphous structure that is rapidly quenched from liquid melts. The absence of a crystalline micro-structure endows them with a portfolio of properties such as high strength, high elasticity, and excellent corrosion resistance. Whereas the limited plasticity and hence poor workability at ambient temperature impede the structural application of bulk metallic glasses, the unique superplasticity within the supercooled liquid region opens an alternative window of so-called thermoplastic forming, which allows precise and versatile net-shaping of complex geometries on length scales ranging from nanometers to centimeters that were previously unachievable with conventional crystalline metal processing. Thermoplastic forming not only breaks through the bottleneck of the manufacture of bulk metallic glasses at ambient temperature but also offers an alluring prospect in micro-engineering applications. This paper comprehensively reviews some pivotal aspects of bulk metallic glasses during thermoplastic micro-forming, including an in-depth understanding of the crystallization kinetics of bulk metallic glasses and the thermoplastic processing time window, the thermoplastic forming map that clarifies the relationship between the flow characteristics and the formability, the interfacial friction in micro-forming and novel forming methods to improve the formability, and the potential applications of the hot-embossed micro-patterns/components.
Hubble Parameter in QCD Universe for finite Bulk Viscosity
Tawfik, A; Mansour, H; Harko, T
2010-01-01
The influence of perturbative bulk viscosity on the evolution of Hubble parameter in the QCD era of the early Universe has been analyzed, where Friedmann-Robertson-Walker metric and Einstein field equations are utilized. Homogeneous and isotropic background matter is assumed to be characterized by barotropic equations of state deduced from recent lattice QCD simulations and heavy--ion collisions. Taking into account perturbative bulk viscosity coefficient, an estimation for the evolution of the Hubble parameter has been introduced and compared with its evolution in a non--viscous matter. A numerical solution for finite viscous Israel-Stewart background matter is also worked out. Both methods qualitatively agree in reproducing viscous Hubble parameter that turns to be slightly different from the non--viscous one. This treatment is strictly limited within a very narrow temperature-- or time--interval in QCD era, where the QGP matter is likely dominant.
Dissipative Processes in the Early Universe: Bulk Viscosity
Tawfik, A; Mansour, H; Wahba, M
2009-01-01
In this talk, we discuss one of the dissipative processes which likely take place in the Early Universe. We assume that the matter filling the isotropic and homogeneous background is to be described by a relativistic viscous fluid characterized by an ultra-relativistic equation of state and finite bulk viscosity deduced from recent lattice QCD calculations and heavy-ion collisions experiments. We concentrate our treatment to bulk viscosity as one of the essential dissipative processes in the rapidly expanding Early Universe and deduce the dependence of the scale factor and Hubble parameter on the comoving time $t$. We find that both scale factor and Hubble parameter are finite at $t=0$, revering to absence of singularity. We also find that their evolution apparently differs from the one resulting in when assuming that the background matter is an ideal and non-viscous fluid.
Bounding Isotropic Lorentz Violation Using Synchrotron Losses at LEP
Altschul, Brett
2009-01-01
Some deviations from special relativity--especially isotropic effects--are most efficiently constrained using particles with velocities very close to 1. While there are extremely tight bounds on some of the relevant parameters coming from astrophysical observations, many of these rely on our having an accurate understanding of the dynamics of high-energy sources. It is desirable to have reliable laboratory constraints on these same parameters. The fastest-moving particles in a laboratory were electrons and positrons at LEP. The energetics of the LEP beams were extremely well understood, and measurements of the synchrotron emission rate indicates that that any isotropic deviation of the speed of light from 1 must be smaller than 1.2 x 10^(-15).
Bounding isotropic Lorentz violation using synchrotron losses at LEP
Altschul, Brett
2009-11-01
Some deviations from special relativity—especially isotropic effects—are most efficiently constrained using particles with velocities very close to 1. While there are extremely tight bounds on some of the relevant parameters coming from astrophysical observations, many of these rely on our having an accurate understanding of the dynamics of these high-energy sources. It is desirable to have reliable laboratory constraints on these same parameters. The fastest-moving particles in a laboratory were electrons and positrons at LEP. The energetics of the LEP beams were extremely well understood, and measurements of the synchrotron emission rate indicate that the isotropic Lorentz violation coefficient |κ˜tr-(4)/(3)c00| must be smaller than 5×10-15.
Viscous propulsion in active transversely-isotropic media
Cupples, Gemma; Smith, David J
2016-01-01
Taylor's swimming sheet is a classical model of microscale propulsion and pumping. Many biological fluids and substances are fibrous, having a preferred direction in their microstructure; for example cervical mucus is formed of polymer molecules which create an oriented fibrous network. Moreover, suspensions of elongated motile cells produce a form of active oriented matter. To understand how these effects modify viscous propulsion, we extend Taylor's classical model of small-amplitude zero-Reynolds-number propulsion of a 'swimming sheet' via the transversely-isotropic fluid model of Ericksen, which is linear in strain rate and possesses a distinguished direction. The energetic costs of swimming are significantly altered by all rheological parameters and the initial fibre angle. Propulsion in a passive transversely-isotropic fluid produces an enhanced mean rate of working, independent of the initial fibre orientation, with an approximately linear dependence of energetic cost on the extensional and shear enhan...
Quasi-isotropic cascade in MHD turbulence with mean field
Grappin, Roland; Gürcan, Özgür
2012-01-01
We propose a phenomenological theory of incompressible magnetohydrodynamic turbulence in the presence of a strong large-scale magnetic field, which establishes a link between the known anisotropic models of strong and weak MHD turbulence We argue that the Iroshnikov-Kraichnan isotropic cascade develops naturally within the plane perpendicular to the mean field, while oblique-parallel cascades with weaker amplitudes can develop, triggered by the perpendicular cascade, with a reduced flux resulting from a quasi-resonance condition. The resulting energy spectrum $E(k_\\parallel,k_\\bot)$ has the same slope in all directions. The ratio between the extents of the inertial range in the parallel and perpendicular directions is equal to $b_{rms}/B_0$. These properties match those found in recent 3D MHD simulations with isotropic forcing reported in [R. Grappin and W.-C. M\\"uller, Phys. Rev. E \\textbf{82}, 26406 (2010)].
Gravitational Landau damping for an isotropic cluster of stars
Habib, Salman; Kandrup, Henry E.; Yip, Ping F.
1986-01-01
The problem of ascertaining the dynamical stability and the existence of Landau damping in static, isotropic 'collisionless' star clusters is addressed. The second-order formalism of Kandrup and Sygnet (1985) is applied to a homogeneous and isotropic plasma, demonstrating formally that the unperturbed configuration will always be stable and that the modes must be purely oscillatory. The form of these modes is explicitly examined, culminating in an analytic expression for the time evolution of the density induced by an initial perturbation. It is shown how these considerations can be adapted trivially to localized, nonradial disturbances of a self-gravitating system of stars. The possible existence of gravitational Landau damping for more generic perturbations is discussed.
A generalized plane strain theory for transversely isotropic piezoelectric plates
Institute of Scientific and Technical Information of China (English)
XU Si-peng; WANG Wei
2005-01-01
Study of generalized plane strain has so far been limited to elasticity. The present is aimed at parallel development of transversely isotropic piezoelasticity. By assuming that the along depth distribution of electric potential is linear, and that commonly used Kane-Mindlin kinematical assumption is valid, two dimensional solution systems were deduced, for which, explicit solutions of the out-of-plane constraint factor, as well as the stress resultant concentration factor around a circular hole in a transversely isotropic piezoelectric plate subjected to remote biaxial tension are obtained. Comparisons of these formulas with their counterparts for elastic case yielded suggestions that whether the piezoelectric effect exacerbates or mitigates the stress resultant concentration greatly depends on material properties, particularly, the piezoelectric coefficients;the effect of plate thickness was extensively investigated.
Dielectrophoretic manipulation of the mixture of isotropic and nematic liquid
Kim, Soo-Dong; Lee, Bomi; Kang, Shin-Woong; Song, Jang-Kun
2015-08-01
In various applications involving liquid crystals, the manipulation of the nanoscale molecular assembly and microscale director alignment is highly useful. Here we show that a nematic-isotropic mixture, a unique bi-liquid system, has potential for the fabrication of microstructures having an ordered phase within a disordered phase, or vice versa. The volume expansion and shrinkage, migration, splitting, mergence and elongation of one phase within the other are easily accomplished via thermal treatment and dielectrophoretic manipulation. This is particularly achievable when one phase is suspended in the middle. In that case, a highly biased ordered-phase preference of surfaces, that is, the nematic-philic nature of a polyimide layer and the nematic-phobic nature of a self-assembled monolayer of chlorosilane derivatives, is used. Further, by combining this approach with photopolymerization, the patterned microstructure is solidified as a patterned polymer film having both isotropic and anisotropic molecular arrangements simultaneously, or as a template with a morphological variation.
Systematic effects induced by a flat isotropic dielectric slab
Macculi, C; Cortiglioni, S; Peverini, O A; Tascone, R; Zannoni, M; Carretti, Ettore; Cortiglioni, Stefano; Macculi, Claudio; Peverini, Oscar Antonio; Tascone, Riccardo; Zannoni, Mario
2006-01-01
The instrumental polarization induced by a flat isotropic dielectric slab in microwave frequencies is faced. We find that, in spite of its isotropic nature, such a dielectric can produce spurious polarization either by transmitting incoming anisotropic diffuse radiation or emitting when it is thermally inhomogeneous. We present evaluations of instrumental polarization generated by materials usually adopted in Radioastronomy, by using the Mueller matrix formalism. As an application, results for different slabs in front of a 32 GHz receiver are discussed. Such results are based on measurements of their complex dielectric constant. We evaluate that a 0.33 cm thick Teflon slab introduces negligible spurious polarization ($< 2.6 \\times 10^{-5}$ in transmission and $< 6 \\times 10^{-7}$ in emission), even minimizing the leakage ($< 10^{-8}$ from $Q$ to $U$ Stokes parameters, and viceversa) and the depolarization ($\\sim 1.3 \\times 10^{-3}$).
3D geometrically isotropic metamaterial for telecom wavelengths
DEFF Research Database (Denmark)
Malureanu, Radu; Andryieuski, Andrei; Lavrinenko, Andrei
2009-01-01
We present a new design for a unit cell with the cubic symmetry and sizes less than one sixth of the vacuum wavelength possessing a negative refractive index in the IR region. The main challenges in designing and fabricating metamaterials nowadays are in obtaining isotropic electric and magnetic...... is obtained in a certain bandwidth. The proposed unit cell has the cubic point group of symmetry and being repeatedly placed in space can effectively reveal isotropic optical properties. We use the CST commercial software to characterise the “cube-in-cage” structure. Reflection and transmission spectra...... are shown in Fig.1a. The effective refractive index is retrieved accordingly to the standard algorithm [5] (see Fig.1b). After several cycles of naïve optimizations, the refractive index reaches -2.4 at 1.55μm (ca. 192.5THz). The maximum FOM in the band, where Re(n)
Reynolds number scaling of velocity increments in isotropic turbulence
Iyer, Kartik P.; Sreenivasan, Katepalli R.; Yeung, P. K.
2017-02-01
Using the largest database of isotropic turbulence available to date, generated by the direct numerical simulation (DNS) of the Navier-Stokes equations on an 81923 periodic box, we show that the longitudinal and transverse velocity increments scale identically in the inertial range. By examining the DNS data at several Reynolds numbers, we infer that the contradictory results of the past on the inertial-range universality are artifacts of low Reynolds number and residual anisotropy. We further show that both longitudinal and transverse velocity increments scale on locally averaged dissipation rate, just as postulated by Kolmogorov's refined similarity hypothesis, and that, in isotropic turbulence, a single independent scaling adequately describes fluid turbulence in the inertial range.
Isotropic Forms of Dynamics in the Relativistic Direct Interaction Theory
Duviryak, A A; Tretyak, V I
1998-01-01
The Lagrangian relativistic direct interaction theory in the various forms of dynamics is formulated and its connections with the Fokker-type action theory and with the constrained Hamiltonian mechanics are established. The motion of classical two-particle system with relativistic direct interaction is analysed within the framework of isotropic forms of dynamics in the two- and four-dimensional space-time. Some relativistic exactly solvable quantum-mechanical models are also discussed.
The universe as a black hole in isotropic coordinates
Poplawski, Nikodem J.
2009-01-01
We show that the radial geodesic motion of a particle inside a black hole in isotropic coordinates (the Einstein-Rosen bridge) is physically different from the radial motion inside a Schwarzschild black hole. A particle enters the interior region of an Einstein-Rosen black hole which is regular and physically equivalent to the asymptotically flat exterior of a white hole, and the particle's proper time extends to infinity. Because the motion across the Einstein-Rosen bridge is unidirectional,...
Gravitational radiation of a free isotropic plasma. I
Energy Technology Data Exchange (ETDEWEB)
Galtsov, D.V.; Grats, IU.V.; Melkumova, E.IU.
1985-06-01
The gravitational radiation of a free isotropic plasma is studied on the basis of kinetic theory. It is demonstrated that gravitational-wave effects are determined by the correlation function of the energy-momentum tensors of the particles and electromagnetic field. Finally, a formula is obtained which defines the total gravitational radiation of a nonrelativistic plasma, taking into account all possible radiation mechanisms. 10 references.
Plane Waves in a Transparent Isotropic Chiral Medium
Fisanov, V. V.
2015-04-01
A homogeneous isotropic transparent chiral medium supports two normal plane waves with left and right circular polarization and differently valued positive wave numbers. The presence or absence of forward and backward Beltrami waves and their helicity are regulated by the signs of the permittivity and permeability and the strength of the chirality. The ray refractive index is a universal parameter whose sign differentiates the forward and backward waves.
Negative refraction in (bi)-isotropic periodic arrangements of chiral SRRs
Jelinek, L; Mesa, F; Baena, J D
2007-01-01
Bi-isotropic and isotropic negative refractive index (NRI) 3D metamaterials made from periodic arrangements of chiral split ring resonators (SRRs) are proposed and demonstrated. An analytical theory for the characterization and design of these metamaterials is provided and validated by careful full-wave electromagnetic simulations. The reported results are expected to pave the way to the design of practical 3D bi-isotropic and isotropic NRI metamaterials made from a single kind of inclusions.
The Isotropic Radio Background and Annihilating Dark Matter
Energy Technology Data Exchange (ETDEWEB)
Hooper, Dan [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Belikov, Alexander V. [Institut d' Astrophysique (France); Jeltema, Tesla E. [Univ. of California, Santa Cruz, CA (United States); Linden, Tim [Univ. of California, Santa Cruz, CA (United States); Profumo, Stefano [Univ. of California, Santa Cruz, CA (United States); Slatyer, Tracy R. [Princeton Univ., Princeton, NJ (United States)
2012-11-01
Observations by ARCADE-2 and other telescopes sensitive to low frequency radiation have revealed the presence of an isotropic radio background with a hard spectral index. The intensity of this observed background is found to exceed the flux predicted from astrophysical sources by a factor of approximately 5-6. In this article, we consider the possibility that annihilating dark matter particles provide the primary contribution to the observed isotropic radio background through the emission of synchrotron radiation from electron and positron annihilation products. For reasonable estimates of the magnetic fields present in clusters and galaxies, we find that dark matter could potentially account for the observed radio excess, but only if it annihilates mostly to electrons and/or muons, and only if it possesses a mass in the range of approximately 5-50 GeV. For such models, the annihilation cross section required to normalize the synchrotron signal to the observed excess is sigma v ~ (0.4-30) x 10^-26 cm^3/s, similar to the value predicted for a simple thermal relic (sigma v ~ 3 x 10^-26 cm^3/s). We find that in any scenario in which dark matter annihilations are responsible for the observed excess radio emission, a significant fraction of the isotropic gamma ray background observed by Fermi must result from dark matter as well.
Isotropic Compression Behaviour of Fibre Reinforced Cemented Sand
Directory of Open Access Journals (Sweden)
Salahuddin
2013-07-01
Full Text Available Fibre-reinforced cemented sands have many applications in improving the response of soils. In this paper, an experimental investigation for the analysis of fiber-reinforced cemented sand in the framework of isotropic compression is presented. The experimental investigations were carried out using a high pressure triaxial apparatus having the capacity of 64 MPa of confining pressure. Tests have been conducted on Portaway sand specimens reinforced with randomly oriented discrete polypropylene fibers with different percentages of fiber and cement contents. Results are presented in the form of e-logp` curves as well as SEM (Scanning Electron Microscopy micrographs. The effects of the addition of fibre in sand and cemented sand for different initial void ratios were investigated. The results demonstrate that the influence of fibre is not significant in both cemented and uncemented sand during the isotropic compression stage. Moreover, from the SEM micrographs it could be seen that there is breakage of sand particles and cement bonds. The fiber threads were seen pinched and found rarely broken in the specimen exhumed after isotropic compression.
DEFF Research Database (Denmark)
Benetti, Ana Raquel; Havndrup-Pedersen, Cæcilie; Honoré, Daniel;
2015-01-01
the restorative procedure. The aim of this study, therefore, was to compare the depth of cure, polymerization contraction, and gap formation in bulk-fill resin composites with those of a conventional resin composite. To achieve this, the depth of cure was assessed in accordance with the International Organization...... for Standardization 4049 standard, and the polymerization contraction was determined using the bonded-disc method. The gap formation was measured at the dentin margin of Class II cavities. Five bulk-fill resin composites were investigated: two high-viscosity (Tetric EvoCeram Bulk Fill, SonicFill) and three low......-viscosity (x-tra base, Venus Bulk Fill, SDR) materials. Compared with the conventional resin composite, the high-viscosity bulk-fill materials exhibited only a small increase (but significant for Tetric EvoCeram Bulk Fill) in depth of cure and polymerization contraction, whereas the low-viscosity bulk...
Fukushima, Keita; Kumar, Jason; Sandick, Pearl; Yamamoto, Takahiro
2014-01-01
Recent experimental results from the LHC have placed strong constraints on the masses of colored superpartners. The MSSM parameter space is also constrained by the measurement of the Higgs boson mass, and the requirement that the relic density of lightest neutralinos be consistent with observations. Although large regions of the MSSM parameter space can be excluded by these combined bounds, leptophilic versions of the MSSM can survive these constraints. In this paper we consider a scenario in which the requirements of minimal flavor violation, vanishing $CP$-violation, and mass universality are relaxed, specifically focusing on scenarios with light sleptons. We find a large region of parameter space, analogous to the original bulk region, for which the lightest neutralino is a thermal relic with an abundance consistent with that of dark matter. We find that these leptophilic models are constrained by measurements of the magnetic and electric dipole moments of the electron and muon, and that these models have ...
Creating bulk nanocrystalline metal.
Energy Technology Data Exchange (ETDEWEB)
Fredenburg, D. Anthony (Georgia Institute of Technology, Atlanta, GA); Saldana, Christopher J. (Purdue University, West Lafayette, IN); Gill, David D.; Hall, Aaron Christopher; Roemer, Timothy John (Ktech Corporation, Albuquerque, NM); Vogler, Tracy John; Yang, Pin
2008-10-01
Nanocrystalline and nanostructured materials offer unique microstructure-dependent properties that are superior to coarse-grained materials. These materials have been shown to have very high hardness, strength, and wear resistance. However, most current methods of producing nanostructured materials in weapons-relevant materials create powdered metal that must be consolidated into bulk form to be useful. Conventional consolidation methods are not appropriate due to the need to maintain the nanocrystalline structure. This research investigated new ways of creating nanocrystalline material, new methods of consolidating nanocrystalline material, and an analysis of these different methods of creation and consolidation to evaluate their applicability to mesoscale weapons applications where part features are often under 100 {micro}m wide and the material's microstructure must be very small to give homogeneous properties across the feature.
Energy Technology Data Exchange (ETDEWEB)
Miller, Jacob Lee
2015-04-21
An explosive bulk charge, including: a first contact surface configured to be selectively disposed substantially adjacent to a structure or material; a second end surface configured to selectively receive a detonator; and a curvilinear side surface joining the first contact surface and the second end surface. The first contact surface, the second end surface, and the curvilinear side surface form a bi-truncated hemispherical structure. The first contact surface, the second end surface, and the curvilinear side surface are formed from an explosive material. Optionally, the first contact surface and the second end surface each have a substantially circular shape. Optionally, the first contact surface and the second end surface consist of planar structures that are aligned substantially parallel or slightly tilted with respect to one another. The curvilinear side surface has one of a smooth curved geometry, an elliptical geometry, and a parabolic geometry.
Energy Technology Data Exchange (ETDEWEB)
Zakharov, A. V., E-mail: avz0911@yahoo.com [Saint Petersburg Institute for Machine Sciences, The Russian Academy of Sciences, Saint Petersburg 199178 (Russian Federation); Śliwa, Izabela, E-mail: izasliwa@ifmpan.poznan.pl [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan (Poland)
2014-03-28
We have carried out a numerical study of both the structural and thermodynamic properties of free-standing smectic films for the case of enhanced pair interaction in the bounding layers. Calculations, based upon the extended McMillan's mean-field theory with anisotropic forces, show that the layer-thinning transitions are characterized by abrupt drops to lower values, both for a disjoining pressure and a fluctuation-induced long-range interaction between the smectic film surfaces, and then continues to increase with a larger positive slope. Reasonable agreement between the theoretically predicted and the experimentally obtained data on the surface tension of the partially fluorinated 5-n-alkyl-2-(4-n-(perfluoroalkyl-metheleneoxy)phenyl) film has been obtained.
Sein, A; Engberts, JBFN
1996-01-01
The dynamics of the formation of a lyotropic lamellar arrangement. of surfactant molecules has been studied by means of a contact experiment. Technical grade dodecylbenzenesulfonic acid (HDoBS) was brought into contact with water or an aqueous solution containing sodium hydroxide or sodium hydroxide
Scanning anisotropy parameters in horizontal transversely isotropic media
Masmoudi, Nabil
2016-10-12
The horizontal transversely isotropic model, with arbitrary symmetry axis orientation, is the simplest effective representative that explains the azimuthal behaviour of seismic data. Estimating the anisotropy parameters of this model is important in reservoir characterisation, specifically in terms of fracture delineation. We propose a travel-time-based approach to estimate the anellipticity parameter η and the symmetry axis azimuth ϕ of a horizontal transversely isotropic medium, given an inhomogeneous elliptic background model (which might be obtained from velocity analysis and well velocities). This is accomplished through a Taylor\\'s series expansion of the travel-time solution (of the eikonal equation) as a function of parameter η and azimuth angle ϕ. The accuracy of the travel time expansion is enhanced by the use of Shanks transform. This results in an accurate approximation of the solution of the non-linear eikonal equation and provides a mechanism to scan simultaneously for the best fitting effective parameters η and ϕ, without the need for repetitive modelling of travel times. The analysis of the travel time sensitivity to parameters η and ϕ reveals that travel times are more sensitive to η than to the symmetry axis azimuth ϕ. Thus, η is better constrained from travel times than the azimuth. Moreover, the two-parameter scan in the homogeneous case shows that errors in the background model affect the estimation of η and ϕ differently. While a gradual increase in errors in the background model leads to increasing errors in η, inaccuracies in ϕ, on the other hand, depend on the background model errors. We also propose a layer-stripping method valid for a stack of arbitrary oriented symmetry axis horizontal transversely isotropic layers to convert the effective parameters to the interval layer values.
The thermoelectric magnetic field of isotropic inclusions in anisotropic metals
Faidi, W. I.; Nayfeh, A. H.
2006-02-01
In this paper we model the thermoelectric magnetic field around isotropic inclusions in anisotropic media. It is demonstrated that while the presence of the inclusion will be the dominant source of the thermoelectric signal, the anisotropy of the host material will affect the signal. Although such a phenomenon will occur for all shapes of inclusions, for simplicity we shall demonstrate our theoretical and numerical modeling on the more mathematically tractable case of a cylindrical inclusion aligned along an axis of symmetry of an anisotropic metal medium.
Rotation of slender swimmers in isotropic-drag media
Koens, Lyndon
2016-01-01
The drag anisotropy of slender filaments is a critical physical property allowing swimming in low-Reynolds number flows, and without it linear translation is impossible. Here we show that, in contrast, net rotation can occur under isotropic drag. We first demonstrate this result formally by considering the consequences of the force- and torque-free conditions on swimming bodies and we then illustrate it with two examples (a simple swimmers made of three rods and a model bacterium with two helical flagellar filaments). Our results highlight the different role of hydrodynamic forces in generating translational vs.~rotational propulsion.
Modelling of the decay of isotropic turbulence by the LES
Energy Technology Data Exchange (ETDEWEB)
Abdibekov, U S; Zhakebaev, D B, E-mail: uali1@mail.ru, E-mail: daurjaz@mail.ru [Al-Farabi Kazakh National University (Kazakhstan)
2011-12-22
This work deals with the modelling of degeneration of isotropic turbulence. To simulate the turbulent process the filtered three-dimensional nonstationary Navier-Stokes equation is used. The basic equation is closed with the dynamic model. The problem is solved numerically, and the equation of motion is solved by a modified method of fractional steps using compact schemes, the equation for pressure is solved by the Fourier method with a combination of matrix factorization. In the process of simulation changes of the kinetic energy of turbulence in the time, micro scale of turbulence and changes of inlongitudinal-transverse correlation functions are obtained, longitudinal and transverse one-dimensional spectra are defined.
Localization by Acoustic Emission in Transversely Isotropic Slate
Directory of Open Access Journals (Sweden)
Bjorn Debecker
2011-01-01
Full Text Available A method for localization by acoustic emission in transversely isotropic media is developed and validated. Velocities are experimentally measured and then used to calculate a database of theoretical arrival times for a large number of positions. During an actual test, positions are assigned by comparing measured arrival times with the database's arrival times. The method is applied during load tests on slate samples and compared with visual observations of fractures. The localization method allowed for a good identification of the regions of fracturing at different stages during the test.
Effective equations for isotropic quantum cosmology including matter
Bojowald, Martin; Skirzewski, Aureliano
2007-01-01
Effective equations often provide powerful tools to develop a systematic understanding of detailed properties of a quantum system. This is especially helpful in quantum cosmology where several conceptual and technical difficulties associated with the full quantum equations can be avoided in this way. Here, effective equations for Wheeler-DeWitt and loop quantizations of spatially flat, isotropic cosmological models sourced by a massive or interacting scalar are derived and studied. The resulting systems are remarkably different from that given for a free, massless scalar. This has implications for the coherence of evolving states and the realization of a bounce in loop quantum cosmology.
Elastic constants of Transversely Isotropically Porous (TIP) materials
Energy Technology Data Exchange (ETDEWEB)
Tuchinskii, L.I.; Kalimova, N.L. [Institute of Problems of Materials Science, Kiev (Ukraine)
1994-11-01
The authors derive formulas describing the dependence of the elastic characteristics of multicapillary materials on the capillary porosity. The investigated materials are classified as transversely isotropic, and the anisotropy in their properties is the result of the directionality of the capillary pores. Analysis of the dependences obtained has shown that the elasticity moduli of these materials may be calculated using formulas suggested for reinforced materials, in which the elastic constants of the fibers are assumed to be equal to zero. The authors derive a relation between the Poisson`s ratios and the capillary porosity.
P-wave seismic imaging through dipping transversely isotropic media
Leslie, Jennifer Meryl
2000-10-01
P-wave seismic anisotropy is of growing concern to the exploration industry. The transmissional effects through dipping anisotropic strata, such as shales, cause substantial depth and lateral positioning errors when imaging subsurface targets. Using anisotropic physical models the limitations of conventional isotropic migration routines were determined to be significant. In addition, these models were used to validate both anisotropic depth migration routines and an anisotropic, numerical raytracer. In order to include anisotropy in these processes, one must be able to quantify the anisotropy using two parameters, epsilon and delta. These parameters were determined from headwave velocity measurements on anisotropic strata, in the parallel-, perpendicular- and 45°-to-bedding directions. This new method was developed using refraction seismic techniques to measure the necessary velocities in the Wapiabi Formation shales, the Brazeau Group interbedded sandstones and shales, the Cardium Formation sandstones and the Palliser Formation limestones. The Wapiabi Formation and Brazeau Group rocks were determined to be anisotropic with epsilon = 0.23 +/- 0.05, delta = --0.05 +/- 0.07 and epsilon = 0.11 +/- 0.04, delta = 0.42 +/- 0.06, respectively. The sandstones and limestones of the Cardium and Palliser formations were both determined to be isotropic, in these studies. In a complementary experiment, a new procedure using vertical seismic profiling (VSP) techniques was developed to measure the anisotropic headwave velocities. Using a multi-offset source configuration on an appropriately dipping, uniform panel of anisotropic strata, the required velocities were measured directly and modelled. In this study, the geologic model was modelled using an anisotropic raytracer, developed for the experiment. The anisotropy was successfully modelled using anisotropic parameters based on the refraction seismic results. With a firm idea of the anisotropic parameters from the
The comparative study for the isotropic and orthotropic circular plates
Popa, C.; Tomescu, G.
2016-08-01
The aim of study is static bending analysis of an isotropic circular plate using analytical method i.e. Classical Plate Theory, Finite Element software ANSYS and experimental methods. The diameter of circular plate, material properties, like modulus of elasticity (E), poissons ratio (µ) and intensity of loading is assumed at the initial stage of research work. In comparison with this plane plate we analyze a plate of same dimensions and charge, but having ribs, to see the advantage of the rigidify. The two plates are fixed supported subjected to uniformly distributed load.
Thermo elastic waves with thermal relaxation in isotropic micropolar plate
Indian Academy of Sciences (India)
Soumen Shaw; Basudeb Mukhopadhyay
2011-04-01
In the present investigation, we have discussed about the features of waves in different modes of wave propagation in an inﬁnitely long thermoelastic, isotropic micropolar plate, when the generalized theory of Lord–Shulman (L–S) is considered. A more general dispersion equation is obtained. The different analytic expressions in symmetric and anti-symmetric vibration for short as well as long waves are obtained in different regions of phase velocities. It is found that results agree with that of the existing results predicted by Sharma and Eringen in the context of various theories of classical as well as micropolar thermoelasticity.
Assessment of the modulated gradient model in decaying isotropic turbulence
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
A recently introduced nonlinear model undergoes evaluations based on two isotropic turbulent cases:a University of Wiscosion-Madison case at a moderate Reynolds number and a Johns Hopkins University case at a high Reynolds number.The model uses an estimation of the subgrid-scale(SGS) kinetic energy to model the magnitude of the SGS stress tensor,and uses the normalized velocity gradient tensor to model the structure of the SGS stress tensor.Testing is performed for the first case through a comparison betwee...
Gravitational waves in a free isotropic plasma. II
Energy Technology Data Exchange (ETDEWEB)
Galtsov, D.V.; Grats, IU.V.; Melkumova, E.IU.
1985-07-01
The generation of gravitational waves in an isotropic homogeneous plasma is investigated theoretically, within the frame work of a recently developed formalism. The effectiveness of different mechanisms generating gravitational waves is considered. Attention is given to thermal gravitational radiation by a two-component plasma; the transformation of longitudinal plasma waves into gravitons due to current fluctuations; and the generation of gravitational waves due to Langmuir turbulence. It is shown that collective plasma effects play a critical role in the generation of gravitational waves.
New Sedov-Type Solution of Isotropic Turbulence
Institute of Scientific and Technical Information of China (English)
RAN Zheng
2008-01-01
@@ The starting point lies in the results obtained by Sedov (1944) for isotropic turbulence with a self-preserving hypothesis.A careful consideration of the mathematical structure of the Kaxman-Howaxth equation leads to an exact analysis of all cases possible and to all admissible solutions of the problem.I study this interesting problem from a new point of view.New solutions axe obtained.Based on these exact solutions, some physical significant consequences of recent advances in the theory of self-preserved homogeneous statistical solution of the Navier-Stokes equations axe presented.
Are EeV cosmic rays isotropic at intermediate scales?
Zotov, M Yu
2014-01-01
We study anisotropy of cosmic rays in the energy range 0.2-1.4 EeV at intermediate angular scales using the public data set of the Pierre Auger Observatory. At certain scales, the analysis reveals a number of deviations from the isotropic distribution with the statistical significance above three standard deviations. It also demonstrates that the anisotropy evolves with energy. If confirmed with the complete Auger or Telescope Array data sets, the result can shed new light on the structure of galactic magnetic fields and the problem of transition from galactic to extragalactic cosmic rays.
Isotropic Stars in Higher-Order Torsion Scalar Theories
Directory of Open Access Journals (Sweden)
Gamal G. L. Nashed
2016-01-01
Full Text Available Two different nondiagonal tetrad spaces reproducing spherically symmetric spacetime are applied to the field equations of higher-order torsion scalar theories. Assuming the existence of conformal Killing vector, two isotropic solutions are derived. We show that the first solution is not stable while the second one confirms a stable behavior. We also discuss the construction of the stellar model and show that one of our solutions is capable of such construction while the other is not. Finally, we discuss the generalized Tolman-Oppenheimer-Volkoff and show that one of our models has a tendency to equilibrium.
Isotropic stars in higher-order torsion scalar theories
Nashed, Gamal G L
2016-01-01
Two tetrad spaces reproducing spherically symmetric spacetime are applied to the equations of motion of higher-order torsion theories. Assuming the existence of conformal Killing vector, two isotropic solutions are derived. We show that the first solution is not stable while the second one confirms a stable behavior. We also discuss the construction of the stellar model and show that one of our solution capable of such construction while the other cannot. Finally, we discuss the generalized Tolman-Oppenheimer-Volkoff and show that one of our models has a tendency to equilibrium.
Isotropic 2D quadrangle meshing with size and orientation control
Pellenard, Bertrand
2011-12-01
We propose an approach for automatically generating isotropic 2D quadrangle meshes from arbitrary domains with a fine control over sizing and orientation of the elements. At the heart of our algorithm is an optimization procedure that, from a coarse initial tiling of the 2D domain, enforces each of the desirable mesh quality criteria (size, shape, orientation, degree, regularity) one at a time, in an order designed not to undo previous enhancements. Our experiments demonstrate how well our resulting quadrangle meshes conform to a wide range of input sizing and orientation fields.
A symplectic eigensolution method in transversely isotropic piezoelectric cylindrical media
Institute of Scientific and Technical Information of China (English)
XU Xin-sheng; GU Qian; LEUNG Andrew Y.T.; ZHENG Jian-jun
2005-01-01
This paper reports establishment ofa symplectic system and introduces a 3D sub-symplectic structure for transversely isotropic piezoelectric media. A complete space of eigensolutions is obtained directly. Thus all solutions of the problem are reduced to finding eigenvalues and eigensolutions, which include zero-eigenvalue solutions and all their Jordan normal form of the corresponding Hamiltonian matrix and non-zero-eigenvalue solutions. The classical solutions are described by zero-eigensolutions and non-zero-eigensolutions show localized solutions. Numerical results show some rules of non-zero-eigenvalue and their eigensolutions.
Cluster Monte Carlo simulations of the nematic-isotropic transition
Priezjev, N. V.; Pelcovits, Robert A.
2001-06-01
We report the results of simulations of the three-dimensional Lebwohl-Lasher model of the nematic-isotropic transition using a single cluster Monte Carlo algorithm. The algorithm, first introduced by Kunz and Zumbach to study two-dimensional nematics, is a modification of the Wolff algorithm for spin systems, and greatly reduces critical slowing down. We calculate the free energy in the neighborhood of the transition for systems up to linear size 70. We find a double well structure with a barrier that grows with increasing system size. We thus obtain an upper estimate of the value of the transition temperature in the thermodynamic limit.
Phenomenological Theory of Isotropic-Genesis Nematic Elastomers
Lu, Bing-Sui; Ye, Fangfu; Xing, Xiangjun; Goldbart, Paul M.
2012-06-01
We consider the impact of the elastomer network on the nematic structure and fluctuations in isotropic-genesis nematic elastomers, via a phenomenological model that underscores the role of network compliance. The model contains a network-mediated nonlocal interaction as well as a new kind of random field that reflects the memory of the nematic order present at network formation and also encodes local anisotropy due to localized nematogenic polymers. This model enables us to predict regimes of short-ranged oscillatory spatial correlations (thermal and glassy) in the nematic alignment.
RAYLEIGH LAMB WAVES IN MICROPOLAR ISOTROPIC ELASTIC PLATE
Institute of Scientific and Technical Information of China (English)
Rajneesh Kumar; Geeta Partap
2006-01-01
The propagation of waves in a homogeneous isotropic micropolar elastic cylindrical plate subjected to stress free conditions is investigated. The secular equations for symmetric and skew symmetric wave mode propagation are derived. At short wave limit,the secular equations for symmetric and skew symmetric waves in a stress free circular plate reduces to Rayleigh surface wave frequency equation. Thin plate results are also obtained. The amplitudes of displacements and microrotation components are obtained and depicted graphically. Some special cases are also deduced from the present investigations. The secular equations for symmetric and skew symmetric modes are also presented graphically.
Genericness of Big Bounce in isotropic loop quantum cosmology
Date, Ghanashyam; Hossain, Golam Mortuza
2004-01-01
The absence of isotropic singularity in loop quantum cosmology can be understood in an effective classical description as the universe exhibiting a Big Bounce. We show that with scalar matter field, the big bounce is generic in the sense that it is independent of quantization ambiguities and details of scalar field dynamics. The volume of the universe at the bounce point is parametrized by a single parameter. It provides a minimum length scale which serves as a cut-off for computations of den...
A fast algorithm for radiative transport in isotropic media
Ren, Kui; Zhong, Yimin
2016-01-01
We propose in this work a fast numerical algorithm for solving the equation of radiative transfer (ERT) in isotropic media. The algorithm has two steps. In the first step, we derive an integral equation for the angularly averaged ERT solution by taking advantage of the isotropy of the scattering kernel, and solve the integral equation with a fast multipole method (FMM). In the second step, we solve a scattering-free transport equation to recover the original ERT solution. Numerical simulations are presented to demonstrate the performance of the algorithm for both homogeneous and inhomogeneous media.
Can bulk viscosity drive inflation
Energy Technology Data Exchange (ETDEWEB)
Pacher, T.; Stein-Schabes, J.A.; Turner, M.S.
1987-09-15
Contrary to other claims, we argue that bulk viscosity associated with the interactions of non- relativistic particles with relativistic particles around the time of the grand unified theory (GUT) phase transition cannot lead to inflation. Simply put, the key ingredient for inflation, negative pressure, cannot arise due to the bulk-viscosity effects of a weakly interacting mixture of relativistic and nonrelativistic particles.
Brane Couplings from Bulk Loops
Georgi, Howard; Grant, Aaron K.; Hailu, Girma
2000-01-01
We compute loop corrections to the effective action of a field theory on a five-dimensional $S_1/Z_2$ orbifold. We find that the quantum loop effects of interactions in the bulk produce infinite contributions that require renormalization by four-dimensional couplings on the orbifold fixed planes. Thus bulk couplings give rise to renormalization group running of brane couplings.
The Isotropic Radio Background and Annihilating Dark Matter
Hooper, Dan; Jeltema, Tesla E; Linden, Tim; Profumo, Stefano; Slatyer, Tracy R
2012-01-01
Observations by ARCADE-2 and other telescopes sensitive to low frequency radiation have revealed the presence of an isotropic radio background with a hard spectral index. The intensity of this observed background is found to exceed the flux predicted from astrophysical sources by a factor of approximately 5-6. In this article, we consider the possibility that annihilating dark matter particles provide the primary contribution to the observed isotropic radio background through the emission of synchrotron radiation from electron and positron annihilation products. For reasonable estimates of the magnetic fields present in clusters and galaxies, we find that dark matter could potentially account for the observed radio excess, but only if it annihilates mostly to electrons and/or muons, and only if it possesses a mass in the range of approximately 5-50 GeV. For such models, the annihilation cross section required to normalize the synchrotron signal to the observed excess is sigma v ~ (0.4-30) x 10^-26 cm^3/s, sim...
Direction of unsaturated flow in a homogeneous and isotropic hillslope
Lu, Ning; Kaya, Basak Sener; Godt, Jonathan W.
2011-01-01
The distribution of soil moisture in a homogeneous and isotropic hillslope is a transient, variably saturated physical process controlled by rainfall characteristics, hillslope geometry, and the hydrological properties of the hillslope materials. The major driving mechanisms for moisture movement are gravity and gradients in matric potential. The latter is solely controlled by gradients of moisture content. In a homogeneous and isotropic saturated hillslope, absent a gradient in moisture content and under the driving force of gravity with a constant pressure boundary at the slope surface, flow is always in the lateral downslope direction, under either transient or steady state conditions. However, under variably saturated conditions, both gravity and moisture content gradients drive fluid motion, leading to complex flow patterns. In general, the flow field near the ground surface is variably saturated and transient, and the direction of flow could be laterally downslope, laterally upslope, or vertically downward. Previous work has suggested that prevailing rainfall conditions are sufficient to completely control these flow regimes. This work, however, shows that under time-varying rainfall conditions, vertical, downslope, and upslope lateral flow can concurrently occur at different depths and locations within the hillslope. More importantly, we show that the state of wetting or drying in a hillslope defines the temporal and spatial regimes of flow and when and where laterally downslope and/or laterally upslope flow occurs.
Large Deformation Constitutive Laws for Isotropic Thermoelastic Materials
Energy Technology Data Exchange (ETDEWEB)
Plohr, Bradley J. [Los Alamos National Laboratory; Plohr, Jeeyeon N. [Los Alamos National Laboratory
2012-07-25
We examine the approximations made in using Hooke's law as a constitutive relation for an isotropic thermoelastic material subjected to large deformation by calculating the stress evolution equation from the free energy. For a general thermoelastic material, we employ the volume-preserving part of the deformation gradient to facilitate volumetric/shear strain decompositions of the free energy, its first derivatives (the Cauchy stress and entropy), and its second derivatives (the specific heat, Grueneisen tensor, and elasticity tensor). Specializing to isotropic materials, we calculate these constitutive quantities more explicitly. For deformations with limited shear strain, but possibly large changes in volume, we show that the differential equations for the stress components involve new terms in addition to the traditional Hooke's law terms. These new terms are of the same order in the shear strain as the objective derivative terms needed for frame indifference; unless the latter terms are negligible, the former cannot be neglected. We also demonstrate that accounting for the new terms requires that the deformation gradient be included as a field variable
Fluctuational shift of nematic-isotropic phase transition temperature
Kats, E. I.
2017-02-01
In this work we discuss a macroscopic counterpart to the microscopic mechanism of the straightening dimer mesogens conformations, proposed recently by S.M. Saliti, M.G.Tamba, S.N. Sprunt, C.Welch, G.H.Mehl, A. Jakli, J.T. Gleeson (Phys. Rev. Lett. 116, 217801 (2016)) to explain their experimental observation of the unprecedentedly large shift of the nematic-isotropic transition temperature. Our interpretation is based on singular longitudinal fluctuations of the nematic order parameter. Since these fluctuations are governed by the Goldstone director fluctuations they exist only in the nematic state. External magnetic field suppresses the singular longitudinal fluctuations of the order parameter (similarly as it is the case for the transverse director fluctuations, although with a different scaling over the magnetic field). The reduction of the fluctuations changes the equilibrium value of the modulus of the order parameter in the nematic state. Therefore it leads to additional (with respect to the mean field contribution) fluctuational shift of the nematic-isotropic transition temperature. Our mechanism works for any nematic liquid crystals, however the magnitude of the fluctuational shift increases with decrease of the Frank elastic moduli. Since some of these moduli supposed to be anomalously small for so-called bent-core or dimer nematic liquid crystals, just these liquid crystals are promising candidates for the observation of the predicted fluctuational shift of the phase transition temperature.
Geometric Models for Isotropic Random Porous Media: A Review
Directory of Open Access Journals (Sweden)
Helmut Hermann
2014-01-01
Full Text Available Models for random porous media are considered. The models are isotropic both from the local and the macroscopic point of view; that is, the pores have spherical shape or their surface shows piecewise spherical curvature, and there is no macroscopic gradient of any geometrical feature. Both closed-pore and open-pore systems are discussed. The Poisson grain model, the model of hard spheres packing, and the penetrable sphere model are used; variable size distribution of the pores is included. A parameter is introduced which controls the degree of open-porosity. Besides systems built up by a single solid phase, models for porous media with the internal surface coated by a second phase are treated. Volume fraction, surface area, and correlation functions are given explicitly where applicable; otherwise numerical methods for determination are described. Effective medium theory is applied to calculate physical properties for the models such as isotropic elastic moduli, thermal and electrical conductivity, and static dielectric constant. The methods presented are exemplified by applications: small-angle scattering of systems showing fractal-like behavior in limited ranges of linear dimension, optimization of nanoporous insulating materials, and improvement of properties of open-pore systems by atomic layer deposition of a second phase on the internal surface.
PDF Modeling of Evaporating Droplets in Isotropic Turbulence.
Mashayek, F.; Pandya, R. V. R.
2000-11-01
We use a statistical closure scheme of Van Kampen [1] to obtain an approximate equation for probability density function p(τ_d, t) to predict the time (t) evolution of statistical properties related to particle time constant τd of collisionless evaporating droplets suspended in isothermal isotropic turbulent flows. The resulting Fokker-Planck equation for p(τ_d, t) has non-linear, time-dependent drift and diffusion coefficients that depend on the statistical properties of droplet's slip velocity. Approximate analytical expressions for these properties are derived and the equation is solved numerically after implementing a numerical method based on path-integral formalism. Time evolution of various droplet diameter related statistical properties are then calculated and are compared with the data available from the stochastic and direct numerical simulations (DNS) studies performed by Mashayek[2]. A good agreement for temporal evolution of mean and standard deviation of particle diameter is observed with DNS results. Reference [1] Van Kampen, N.G., Stochastic Processes in Physics and Chemistry, Elsevier Science Publishers, North Holland, Amsterdam, 1992. [2] Mashayek, F., Stochastic Simulations of Particle-Laden Isotropic Turbulent Flow, Int. J. Multiphase Flow, 25(8):1575-1599 (1999).
The universe as a black hole in isotropic coordinates
Poplawski, Nikodem J
2009-01-01
We show that the radial geodesic motion of a particle inside a black hole in isotropic coordinates (the Einstein-Rosen bridge) is physically different from the radial motion inside a Schwarzschild black hole. A particle enters the interior region of an Einstein-Rosen black hole which is regular and physically equivalent to the asymptotically flat exterior of a white hole, and the particle's proper time extends to infinity. Because the motion across the Einstein-Rosen bridge is unidirectional, and the surface of a black hole is the event horizon for distant observers, an Einstein-Rosen black hole is indistinguishable from a Schwarzschild black hole for such observers. Observers inside an Einstein-Rosen black hole perceive its interior as a closed universe that began when the black hole formed, with an initial radius equal to the Schwarzschild radius of the black hole $r_g$, and with an initial accelerated expansion. Therefore the model of a universe as a black hole in isotropic coordinates explains the origin ...
Isotropic extensions of the vacuum solutions in general relativity
Energy Technology Data Exchange (ETDEWEB)
Molina, C. [Universidade de Sao Paulo (USP), SP (Brazil); Martin-Moruno, Prado [Victoria University of Wellington (New Zealand); Gonzalez-Diaz, Pedro F. [Consejo Superior de Investigaciones Cientificas, Madrid (Spain)
2012-07-01
Full text: Spacetimes described by spherically symmetric solutions of Einstein's equations are of paramount importance both in astrophysical applications and theoretical considerations. And among those, black holes are highlighted. In vacuum, Birkhoff's theorem and its generalizations to non-asymptotically flat cases uniquely fix the metric as the Schwarzschild, Schwarzschild-de Sitter or Schwarzschild-anti-de Sitter geometries, the vacuum solutions of the usual general relativity with zero, positive or negative values for the cosmological constant, respectively. In this work we are mainly interested in black holes in a cosmological environment. Of the two main assumptions of the cosmological principle, homogeneity is lost when compact objects are considered. Nevertheless isotropy is still possible, and we enforce this condition. Within this context, we investigate spatially isotropic solutions close - continuously deformable - to the usual vacuum solutions. We obtain isotropic extensions of the usual spherically symmetric vacuum geometries in general relativity. Exact and perturbative solutions are derived. Maximal extensions are constructed and their causal structures are discussed. The classes of geometries obtained include black holes in compact and non-compact universes, wormholes in the interior region of cosmological horizons, and anti-de Sitter geometries with excess/deficit solid angle. The tools developed here are applicable in more general contexts, with extensions subjected to other constraints. (author)
Charged isotropic non-Abelian dyonic black branes
Directory of Open Access Journals (Sweden)
Yves Brihaye
2015-05-01
Full Text Available We construct black holes with a Ricci-flat horizon in Einstein–Yang–Mills theory with a negative cosmological constant, which approach asymptotically an AdSd spacetime background (with d≥4. These solutions are isotropic, i.e. all space directions in a hypersurface of constant radial and time coordinates are equivalent, and possess both electric and magnetic fields. We find that the basic properties of the non-Abelian solutions are similar to those of the dyonic isotropic branes in Einstein–Maxwell theory (which, however, exist in even spacetime dimensions only. These black branes possess a nonzero magnetic field strength on the flat boundary metric, which leads to a divergent mass of these solutions, as defined in the usual way. However, a different picture is found for odd spacetime dimensions, where a non-Abelian Chern–Simons term can be incorporated in the action. This allows for black brane solutions with a magnetic field which vanishes asymptotically.
An Areal Isotropic Spline Filter for Surface Metrology.
Zhang, Hao; Tong, Mingsi; Chu, Wei
2015-01-01
This paper deals with the application of the spline filter as an areal filter for surface metrology. A profile (2D) filter is often applied in orthogonal directions to yield an areal filter for a three-dimensional (3D) measurement. Unlike the Gaussian filter, the spline filter presents an anisotropic characteristic when used as an areal filter. This disadvantage hampers the wide application of spline filters for evaluation and analysis of areal surface topography. An approximation method is proposed in this paper to overcome the problem. In this method, a profile high-order spline filter serial is constructed to approximate the filtering characteristic of the Gaussian filter. Then an areal filter with isotropic characteristic is composed by implementing the profile spline filter in the orthogonal directions. It is demonstrated that the constructed areal filter has two important features for surface metrology: an isotropic amplitude characteristic and no end effects. Some examples of applying this method on simulated and practical surfaces are analyzed.
Even harmonic generation in isotropic media of dissociating homonuclear molecules
Silva, R E F; Morales, F; Smirnova, O; Ivanov, M; Martín, F
2016-01-01
Isotropic gases irradiated by long pulses of intense IR light can generate very high harmonics of the incident field. It is generally accepted that, due to the symmetry of the generating medium, be it an atomic or an isotropic molecular gas, only odd harmonics of the driving field can be produced. Here we show how the interplay of electronic and nuclear dynamics can lead to a marked breakdown of this standard picture: a substantial part of the harmonic spectrum can consist of even rather than odd harmonics. We demonstrate the effect using ab-initio solutions of the time-dependent Schr\\"odinger equation for $H$$_2$$^+$ and its isotopes in full dimensionality. By means of a simple analytical model, we identify its physical origin, which is the appearance of a permanent dipole moment in dissociating homonuclear molecules, caused by light-induced localization of the electric charge during dissociation. The effect arises for sufficiently long laser pulses and the region of the spectrum where even harmonics are pro...
Energy Technology Data Exchange (ETDEWEB)
Inampudi, Sandeep; Nazari, Mina; Forouzmand, Ali; Mosallaei, Hossein, E-mail: hosseinm@coe.neu.edu [Department of Electrical and Computer Engineering, Northeastern University, 360 Huntington Ave., Boston, Massachusetts 02115 (United States)
2016-01-14
We present a comprehensive analysis of surface plasmon polariton dispersion characteristics associated with isotropic and anisotropic two-dimensional atomically thin layered materials (2D sheets) coupled to h-BN heterostructures. A scattering matrix based approach is presented to compute the electromagnetic fields and related dispersion characteristics of stacked layered systems composed of anisotropic 2D sheets and uniaxial bulk materials. We analyze specifically the surface plasmon polariton (SPP) dispersion characteristics in case of isolated and coupled two-dimensional layers with isotropic and anisotropic conductivities. An analysis based on residue theorem is utilized to identify optimum optical parameters (surface conductivity) and geometrical parameters (separation between layers) to maximize the SPP field at a given position. The effect of type and degree of anisotropy on the shapes of iso-frequency curves and propagation characteristics is discussed in detail. The analysis presented in this paper gives an insight to identify optimum setup to enhance the SPP field at a given position and in a given direction on the surface of two-dimensional materials.
Homogeneous, isotropic turbulence phenomenology, renormalization, and statistical closures
McComb, W David
2014-01-01
Fluid turbulence is often referred to as 'the unsolved problem of classical physics'. Yet, paradoxically, its mathematical description resembles quantum field theory. The present book addresses the idealised problem posed by homogeneous, isotropic turbulence, in order to concentrate on the fundamental aspects of the general problem. It is written from the perspective of a theoretical physicist, but is designed to be accessible to all researchers in turbulence, both theoretical and experimental, and from all disciplines. The book is in three parts, and begins with a very simple overview of the basic statistical closure problem, along with a summary of current theoretical approaches. This is followed by a precise formulation of the statistical problem, along with a complete set of mathematical tools (as needed in the rest of the book), and a summary of the generally accepted phenomenology of the subject. Part 2 deals with current issues in phenomenology, including the role of Galilean invariance, the physics of...
Assessing the Structure of Isotropic and Anisotropic Turbulent Magnetic Fields
Fatuzzo, Marco; Holden, Lisa; Grayson, Lindsay; Wallace, Kirk
2016-10-01
Turbulent magnetic fields permeate our universe, impacting a wide range of astronomical phenomena across all cosmic scales. A clear example is the magnetic field that threads the interstellar medium (ISM), which impacts the motion of cosmic rays through that medium. Understanding the structure of magnetic turbulence within the ISM and how it relates to the physical quantities that characterize it can thus inform our analysis of particle transport within these regions. Toward that end, we probe the structure of magentic turbulence through the use of Lyapunov exponents for a suite of isotropic and nonisotropic Alfvénic turbulence profiles. Our results provide a means of calculating a “turbulence lengthscale” that can then be connected to how cosmic rays propagate through magentically turbulent environments, and we perform such an analysis for molecular cloud environments.
Helicity statistics in homogeneous and isotropic turbulence and turbulence models
Sahoo, Ganapati; De Pietro, Massimo; Biferale, Luca
2017-02-01
We study the statistical properties of helicity in direct numerical simulations of fully developed homogeneous and isotropic turbulence and in a class of turbulence shell models. We consider correlation functions based on combinations of vorticity and velocity increments that are not invariant under mirror symmetry. We also study the scaling properties of high-order structure functions based on the moments of the velocity increments projected on a subset of modes with either positive or negative helicity (chirality). We show that mirror symmetry is recovered at small scales, i.e., chiral terms are subleading and they are well captured by a dimensional argument plus anomalous corrections. These findings are also supported by a high Reynolds numbers study of helical shell models with the same chiral symmetry of Navier-Stokes equations.
Influence of stable stratification on three-dimensional isotropic turbulence
Metais, O.
The influence of a stable stratification on three-dimensional homogeneous turbulence is investigated by performing large eddy simulations with the subgrid scales procedure developed by Chollet and Lesieur for isotropic turbulence. Computational initial conditions close to those of the experiments performed by Itsweire, Helland and Van Atta allow the comparison of the experimental and numerical evolutions of density-stratified turbulent flows. Theoretical works by Riley, Metcalfe and Weisman and by Lilly suggest that low Froude number stably-stratified turbulence may be a nearly noninteracting superposition of wave and quasi-horizontal turbulent vortex motions. For our computations the stably-stratified turbulence seems to be a decaying three-dimensional turbulence pulsed by internal gravity waves. However some tendencies towards two-dimensional turbulence are observed.
Instability induced pressure isotropization in a longitudinally expanding system
Dusling, Kevin; Gelis, François; Venugopalan, Raju
2012-01-01
In two previous works [arXiv:1009.4363,arXiv:1107.0668], we studied the time evolution of a system of real scalar fields with quartic coupling which shares important features with the Color Glass Condensate description of heavy ion collisions. Our primary objective was to understand how such a system, when initialized with a non-perturbatively large classical field configuration, reaches thermal equilibrium. An essential goal of these works was to highlight the role played by the quantum fluctuations. However, these studies considered only a system confined within a box of fixed volume. In the present paper, we extend this work to a system that expands in the longitudinal direction thereby more closely mimicking a heavy ion collision. We conclude that the microscopic processes that drive the system towards equilibrium are able to keep up with the expansion of the system; the pressure tensor becomes isotropic despite the anisotropic expansion.
Rotations of small, inertialess triaxial ellipsoids in isotropic turbulence
Pujara, Nimish
2016-01-01
The statistics of rotational motion of small, inertialess triaxial ellipsoids are computed along Lagrangian trajectories extracted from direct numerical simulations of homogeneous isotropic turbulence. The particle angular velocity and its components along the three principal axes of the particle are considered, expanding on the results presented by \\citet{ChevillardMeneveau13}. The variance of the particle angular velocity, referred to as the particle enstrophy, is found to increase for particles with elongated shapes. This trend is explained by considering the contributions of vorticity and strain-rate to particle rotation. It is found that the majority of particle enstrophy is due to fluid vorticity. Strain-rate-induced rotations, which are sensitive to shape, are mostly cancelled by strain-vorticity interactions. The remainder of the strain-rate-induced rotations are responsible for weak variations in particle enstrophy. For particles of all shapes, the majority of the enstrophy is in rotations about the ...
The Characteristic of Thermoelastic Waves in Transversely Isotropic Finite Cylinders
Directory of Open Access Journals (Sweden)
Bai Hao
2017-01-01
Full Text Available A theoretical as well as a numerical investigation of the propagation of thermoelastic waves and vibration of transversely isotropic cylinders of finite length is discussed. Lord-Shulman theory is adopted here to model the thermoelastic deformation of cylinders. A semi analytical finite element (SAFE method is employed to study dispersion of thermoelastic waves and natural frequencies of vibration of finite cylinders with traction free curved surfaces having both ends insulated and constrained by frictionless rigid walls. Numerical results obtained by the SAFE method for the frequencies of vibration of a sapphire rod are found to be in excellent agreement with published results. Natural frequencies of vibration for first three axisymmetric and asymmetric modes are presented graphically for a silicon nitride thermoelastic cylinder. Also, numerical results showing dispersion of both propagating and evanescent circumferential waves in infinite and finite cylinders are presented also.
A spatially homogeneous and isotropic Einstein-Dirac cosmology
Finster, Felix; Hainzl, Christian
2011-04-01
We consider a spatially homogeneous and isotropic cosmological model where Dirac spinors are coupled to classical gravity. For the Dirac spinors we choose a Hartree-Fock ansatz where all one-particle wave functions are coherent and have the same momentum. If the scale function is large, the universe behaves like the classical Friedmann dust solution. If however the scale function is small, quantum effects lead to oscillations of the energy-momentum tensor. It is shown numerically and proven analytically that these quantum oscillations can prevent the formation of a big bang or big crunch singularity. The energy conditions are analyzed. We prove the existence of time-periodic solutions which go through an infinite number of expansion and contraction cycles.
A Spatially Homogeneous and Isotropic Einstein-Dirac Cosmology
Finster, Felix
2011-01-01
We consider a spatially homogeneous and isotropic cosmological model where Dirac spinors are coupled to classical gravity. For the Dirac spinors we choose a Hartree-Fock ansatz where all one-particle wave functions are coherent and have the same momentum. If the scale function is large, the universe behaves like the classical Friedmann dust solution. If however the scale function is small, quantum effects lead to oscillations of the energy-momentum tensor. It is shown numerically and proven analytically that these quantum oscillations can prevent the formation of a big bang or big crunch singularity. The energy conditions are analyzed. We prove the existence of time-periodic solutions which go through an infinite number of expansion and contraction cycles.
Determination of the decay exponent in mechanically stirred isotropic turbulence
Directory of Open Access Journals (Sweden)
J. Blair Perot
2011-06-01
Full Text Available Direct numerical simulation is used to investigate the decay exponent of isotropic homogeneous turbulence over a range of Reynolds numbers sufficient to display both high and low Re number decay behavior. The initial turbulence is generated by the stirring action of the flow past many small randomly placed cubes. Stirring occurs at 1/30th of the simulation domain size so that the low-wavenumber and large scale behavior of the turbulent spectrum is generated by the fluid and is not imposed. It is shown that the decay exponent in the resulting turbulence matches the theoretical predictions for a k2 low-wavenumber spectrum at both high and low Reynolds numbers. The transition from high Reynolds number behavior to low Reynolds number behavior occurs relatively abruptly at a turbulent Reynolds number of around 250 ( Re λ≈41.
Cosmological Simulations of Isotropic Conduction in Galaxy Clusters
Smith, Britton D; Voit, G Mark; Ventimiglia, David; Skillman, Samuel W
2013-01-01
Simulations of galaxy clusters have a difficult time reproducing the radial gas-property gradients and red central galaxies observed to exist in the cores of galaxy clusters. Thermal conduction has been suggested as a mechanism that can help bring simulations of cluster cores into better alignment with observations by stabilizing the feedback processes that regulate gas cooling, but this idea has not yet been well tested with cosmological numerical simulations. Here we present cosmological simulations of ten galaxy clusters performed with five different levels of isotropic Spitzer conduction, which alters both the cores and outskirts of clusters, but not dramatically. In the cores, conduction flattens central temperature gradients, making them nearly isothermal and slightly lowering the central density but failing to prevent a cooling catastrophe there. Conduction has little effect on temperature gradients outside of cluster cores because outward conductive heat flow tends to inflate the outer parts of the in...
Helicity statistics in homogeneous and isotropic turbulence and turbulence models
Sahoo, Ganapati; Biferale, Luca
2016-01-01
We study the statistical properties of helicity in direct numerical simulations of fully developed homogeneous and isotropic turbulence and in a class of turbulence shell models. We consider correlation functions based on combinations of vorticity and velocity increments that are not invariant under mirror symmetry. We also study the scaling properties of high-order structure functions based on the moments of the velocity increments projected on a subset of modes with either positive or negative helicity (chirality). We show that mirror symmetry is recovered at small-scales, i.e. chiral terms are always subleading and they are well captured by a dimensional argument plus a small anomalous correction. We confirm these findings with numerical study of helical shell models at high Reynolds numbers.
From Weakly to Strongly Magnetized Isotropic MHD Turbulence
Alexakis, Alexandros
2012-01-01
High Reynolds number isotropic magneto-hydro-dynamic turbulence in the presence of large scale magnetic fields is investigated as a function of the magnetic field strength. For a variety of flow configurations the energy dissipation rate \\epsilon, follows the Kolmogorov scaling \\epsilon ~ U^3/L even when the large scale magnetic field energy is twenty times larger than the kinetic. Further increase of the magnetic energy showed a transition to the \\epsilon ~ U^2 B / L scaling implying that magnetic shear becomes more efficient at this point at cascading the energy than the velocity fluctuations. Strongly helical configurations form helicity condensates that deviate from these scalings. Weak turbulence scaling was absent from the investigation. Finally, the magnetic energy spectra showed support for the Kolmogorov spectrum k^{-5/3} while kinetic energy spectra are closer to the Iroshnikov-Kraichnan spectrum k^{-3/2}.
Shape-dependence of particle rotation in isotropic turbulence
Byron, M; Gustavsson, K; Voth, G; Mehlig, B; Variano, E
2014-01-01
We consider the rotation of neutrally buoyant axisymmetric particles suspended in isotropic turbulence. Using laboratory experiments as well as numerical and analytical calculations, we explore how particle rotation depends upon particle shape. We find that shape strongly affects orientational trajectories, but that it has negligible effect on the variance of the particle angular velocity. Previous work has shown that shape significantly affects the variance of the tumbling rate of axisymmetric particles. It follows that shape affects the spinning rate in a way that is, on average, complementary to the shape-dependence of the tumbling rate. We confirm this relationship using direct numerical simulations, showing how tumbling rate and spinning rate variances show complementary trends for rod-shaped and disk-shaped particles. We also consider a random but non-turbulent flow. This allows us to explore which of the features observed for rotation in turbulent flow are due to the effects of particle alignment in vo...
A new approach to Lagrangian investigations of isotropic turbulence
Barjona, Manuel; B. da Silva, Carlos; Idmec Team
2016-11-01
A new numerical approach is used in conjunction with direct numerical simulations (DNS) of statistically stationary (forced) isotropic turbulence to investigate the high Reynolds number scaling properties of turbulence characteristics in a Lagrangian frame. The new method provides an alternative route to the determination of the classical Lagrangian turbulence quantities, such as the second order Lagrangian velocity structure function and two point particle separation, at a much higher Reynolds number than as obtained in previous numerical simulations, and displays excellent agreement with the classical theoretical predictions and existing numerical simulations and experimental data. The authors acknowledge the Laboratory for Advanced Computing at University of Coimbra for providing HPC, computing, consulting resources that have contributed to the research results reported within this paper. URL http://www.lca.uc.pt.
Coherent inelastic backscattering of laser light from three isotropic atoms
Ketterer, Andreas; Shatokhin, Vyacheslav N
2014-01-01
We study the impact of double and triple scattering contributions on coherent backscattering of laser light from saturated isotropic atoms, in the helicity preserving polarization channel. Using the recently proposed diagrammatic pump-probe approach, we analytically derive single-atom spectral responses to a classical polychromatic driving field, combine them self-consistently to double and triple scattering processes, and numerically deduce the corresponding elastic and inelastic spectra, as well as the total backscattered intensities. We find that account of the triple scattering contribution leads to a faster decay of phase-coherence with increasing saturation of the atomic transition as compared to double scattering alone, and to a better agreement with the experiment on strontium atoms.
The modified cumulant expansion for two-dimensional isotropic turbulence
Tatsumi, T.; Yanase, S.
1981-09-01
The two-dimensional isotropic turbulence in an incompressible fluid is investigated using the modified zero fourth-order cumulant approximation. The dynamical equation for the energy spectrum obtained under this approximation is solved numerically and the similarity laws governing the solution in the energy-containing and enstrophy-dissipation ranges are derived analytically. At large Reynolds numbers the numerical solutions yield the k to the -3rd power inertial subrange spectrum which was predicted by Kraichnan (1967), Leith (1968) and Batchelor (1969), assuming a finite enstrophy dissipation in the inviscid limit. The energy-containing range is found to satisfy an inviscid similarity while the enstrophy-dissipation range is governed by the quasi-equilibrium similarity with respect to the enstrophy dissipation as proposed by Batchelor (1969). There exists a critical time which separates the initial period and the similarity period in which the enstrophy dissipation vanishes and remains non-zero respectively in the inviscid limit.
Modes and frequencies of transversely isotropic slightly curved Timoshenko beams.
Rossettos, J. N.; Squires, D. C.
1973-01-01
An analysis of the vibration of transversely isotropic Timoshenko beams, which have small constant initial curvature, is presented, and a closed-form general solution to the governing equations is derived. Natural modes and frequencies are determined for both clamped and simply supported end conditions, and comparisons are made. The combined effects of initial curvature, transverse shear deformation, and boundary conditions are evaluated and discussed. Specifically, it is shown in what manner the clamped beam tends to be more sensitive to shear deformation than the simply supported beam, and how initial curvature reduces the difference. Calculations also show how, in cases where shear deformation becomes more important, the initial curvature has a correspondingly smaller influence on the results.
Component Separation of a Isotropic Gravitational Wave Background
Parida, Abhishek; Jhingan, Sanjay
2015-01-01
A Gravitational Wave Background (GWB) is expected in the universe from the superposition of a large number of unresolved astrophysical sources and phenomena in the early universe. Each component of the background (e.g., from primordial metric perturbations, binary neutron stars, milli-second pulsars etc.) has its own spectral shape. Many ongoing experiments aim to probe GWB at a variety of frequency bands. In the last two decades, using data from ground-based laser interferometric gravitational wave (GW) observatories, upper limits on GWB were placed in the frequency range of ~50-1000 Hz, considering one spectral shape at a time. However, one strong component can significantly enhance the estimated strength of another component. Hence, estimation of the amplitudes of the components with different spectral shapes should be done jointly. Here we propose a method for "component separation" of a statistically isotropic background, that can, for the first time, jointly estimate the amplitudes of many components an...
Directory of Open Access Journals (Sweden)
Sanjeev Sharma
2009-05-01
Full Text Available Elastic-plastic stresses for a transversely isotropic thick-walled rotating cylinder under internal pressure have been obtained by using Seth’s transition theory. It has been observed that a thick-walled circular cylinder made of isotropic material yields at the internal surface at a high pressure as compared to cylinder made of transversely isotropic material. With the increase in angular speed, much less pressure is required for initial yielding at the internal surface for transversely isotropic material as compared to isotropic material. For fullyplastic state, circumferential stress is maximum at the external surface. Thick-walled circular cylinder made of transversely isotropic material requires high percentage increase in pressure to become fully plastic as compared to isotropic cylinder. Therefore, circular cylinder made of transversely isotropic material is on the safer side of the design as compared to cylinder made of isotropic material.Defence Science Journal, 2009, 59(3, pp.260-264, DOI:http://dx.doi.org/10.14429/dsj.59.1519
Shrinking device realized by using layered structures of homogeneous isotropic materials
Institute of Scientific and Technical Information of China (English)
Guo Ya-Nan; Liu Shao-Bin; Zhao Xin; Wang Shen-Yun; Chen Chen
2012-01-01
We propose the practical realization of a shrinking device by using layered structures of homogeneous isotropic materials.By mimicking the shrinking device with concentric alternating thin layers of isotropic dielectrics,the permittivity and the permeability in each isotropic layer can be properly determined from the effective medium theory in order to achieve the shrinking effect.The device realized by multilayer coating with dielectrics is validated by TE wave simulation,and good shrinking performance is demonstrated with only a few layers of homogeneous isotropic materials.
The signature of initial production mechanisms in isotropic turbulence decay
Meldi, M.
2016-03-01
In the present work the quantification of the time-lasting effects of production mechanisms in homogeneous isotropic turbulence decay is addressed. The analysis is developed through the use of theoretical tools as well as numerical calculations based on the eddy damped quasinormal Markovian (EDQNM) model. In both cases a modified Lin equation is used, which accounts for production mechanisms as proposed by Meldi, Lejemble, and Sagaut ["On the emergence of non-classical decay regimes in multiscale/fractal generated isotropic turbulence," J. Fluid Mech. 756, 816-843 (2014)]. The approaches used show that an exponential decay law can be observed if the intensity of the forcing is strong enough to drive the turbulence dynamics, before a power-law decay is eventually attained. The EDQNM numerical results indicate that the exponential regime can persist for long evolution times, longer than the observation time in grid turbulence experiments. A rigorous investigation of the self-similar behavior of the pressure spectrum has been performed by a comprehensive comparison of EDQNM data with direct numerical simulation (DNS)/experiments in the literature. While DNS and free decay EDQNM simulations suggest the need of a very high Reλ threshold in order to observe a clear -7/3 slope of the pressure inertial range, experimental data and forced EDQNM calculations indicate a significantly lower value. This observation suggests that the time-lasting effects of production mechanisms, which cannot be excluded in experiments, play a role in the lack of general agreement with classical numerical approaches. These results reinforce the urge to evolve the numerical simulation state of the art towards the prediction of realistic physical states.
Mechanical metamaterials at the theoretical limit of isotropic elastic stiffness
Berger, J. B.; Wadley, H. N. G.; McMeeking, R. M.
2017-02-01
A wide variety of high-performance applications require materials for which shape control is maintained under substantial stress, and that have minimal density. Bio-inspired hexagonal and square honeycomb structures and lattice materials based on repeating unit cells composed of webs or trusses, when made from materials of high elastic stiffness and low density, represent some of the lightest, stiffest and strongest materials available today. Recent advances in 3D printing and automated assembly have enabled such complicated material geometries to be fabricated at low (and declining) cost. These mechanical metamaterials have properties that are a function of their mesoscale geometry as well as their constituents, leading to combinations of properties that are unobtainable in solid materials; however, a material geometry that achieves the theoretical upper bounds for isotropic elasticity and strain energy storage (the Hashin–Shtrikman upper bounds) has yet to be identified. Here we evaluate the manner in which strain energy distributes under load in a representative selection of material geometries, to identify the morphological features associated with high elastic performance. Using finite-element models, supported by analytical methods, and a heuristic optimization scheme, we identify a material geometry that achieves the Hashin–Shtrikman upper bounds on isotropic elastic stiffness. Previous work has focused on truss networks and anisotropic honeycombs, neither of which can achieve this theoretical limit. We find that stiff but well distributed networks of plates are required to transfer loads efficiently between neighbouring members. The resulting low-density mechanical metamaterials have many advantageous properties: their mesoscale geometry can facilitate large crushing strains with high energy absorption, optical bandgaps and mechanically tunable acoustic bandgaps, high thermal insulation, buoyancy, and fluid storage and transport. Our relatively simple
Can bulk viscosity drive inflation
Energy Technology Data Exchange (ETDEWEB)
Pacher, T.; Stein-Schabes, J.A.; Turner, M.S.
1987-04-01
Contrary to other claims, we argue that, bulk viscosity associated with the interactions of nonrelativistic particles with relativistic particles around the time of the grand unified theory (GUT) phase transition cannot lead to inflation. Simply put, the key ingredient for inflation, negative pressure, cannot arise due to the bulk viscosity effects of a weakly-interacting mixture of relativistic and nonrelativistic particles. 13 refs., 1 fig.
Busselez, Rémi; Cerclier, Carole V; Ndao, Makha; Ghoufi, Aziz; Lefort, Ronan; Morineau, Denis
2014-10-07
A prototypical Gay Berne discotic liquid crystal was studied by means of molecular dynamics simulations both in the bulk state and under confinement in a nanoporous channel. The phase behavior of the confined system strongly differs from its bulk counterpart: the bulk isotropic-to-columnar transition is replaced by a continuous ordering from a paranematic to a columnar phase. Moreover, a new transition is observed at a lower temperature in the confined state, which corresponds to a reorganization of the intercolumnar order. It reflects the competing effects of pore surface interaction and genuine hexagonal packing of the columns. The translational molecular dynamics in the different phases has been thoroughly studied and discussed in terms of collective relaxation modes, non-Gaussian behavior, and hopping processes.
Two-dimensional isotropic damage elastoplastic model for quasi-brittle material
Beneš, P. (Pavel); Vavřík, D. (Daniel)
2014-01-01
Micro-mechanical model for isotropic damage of quasi-brittle material including frictionis presented. Damage is assumed to be isotropic and scalar damage variable is employed . Operatorsplitting method is applied. The article contains derived expressions for derivations necessary forcomputation of coefficients in two dimensions for strain and damage normality rules.
Observation of dynamical precursors of the isotropic-nematic transition by computer simulation
Allen, M.P.; Frenkel, D.
1987-01-01
We present the results of the first molecular-dynamics simulations of a molecular liquid, namely a system of prolate hard ellipsoids of revolution, near the isotropic-nematic liquid-crystal phase transition. Collective rotational motion in the isotropic phase slows down on approach to the transition
Institute of Scientific and Technical Information of China (English)
CHEN CHANG-YUAN
2000-01-01
In this paper, the general formulas and the recurrence formulas for radial matrix elements of N-dimensional isotropic harmonic oscillator are obtained. The relevant results of 2- dimensional and 3- dimensiona] isotropic harmonic oscillators reported in the reference papers are contained in a more general equations derived in this paper as special cases.
Modification of homogeneous and isotropic turbulence by solid particles
Hwang, Wontae
2005-12-01
Particle-laden flows are prevalent in natural and industrial environments. Dilute loadings of small, heavy particles have been observed to attenuate the turbulence levels of the carrier-phase flow, up to 80% in some cases. We attempt to increase the physical understanding of this complex phenomenon by studying the interaction of solid particles with the most fundamental type of turbulence, which is homogeneous and isotropic with no mean flow. A flow facility was developed that could create air turbulence in a nearly-spherical chamber by means of synthetic jet actuators mounted on the corners. Loudspeakers were used as the actuators. Stationary turbulence and natural decaying turbulence were investigated using two-dimensional particle image velocimetry for the base flow qualification. Results indicated that the turbulence was fairly homogeneous throughout the measurement domain and very isotropic, with small mean flow. The particle-laden flow experiments were conducted in two different environments, the lab and in micro-gravity, to examine the effects of particle wakes and flow structure distortion caused by settling particles. The laboratory experiments showed that glass particles with diameters on the order of the turbulence Kolmogorov length scale attenuated the fluid turbulent kinetic energy (TKE) and dissipation rate with increasing particle mass loadings. The main source of fluid TKE production in the chamber was the speakers, but the loss of potential energy of the settling particles also resulted in a significant amount of production of extra TKE. The sink of TKE in the chamber was due to the ordinary fluid viscous dissipation and extra dissipation caused by particles. This extra dissipation could be divided into "unresolved" dissipation caused by local velocity disturbances in the vicinity of the small particles and dissipation caused by large-scale flow distortions from particle wakes and particle clusters. The micro-gravity experiments in NASA's KC-135
Isotropic three-dimensional MRI-Fricke-infused gel dosimetry
Energy Technology Data Exchange (ETDEWEB)
Cho, Nai-Yu; Chu, Woei-Chyn [Institute of Biomedical Engineering, National Yang-Ming University, Taipei 11221, Taiwan (China); Huang, Sung-Cheng [Department of Molecular and Medical Pharmacology, UCLA David Geffen School of Medicine, Los Angeles, California 90095 (United States); Chung, Wen-Yuh [Neurological Institute, Taipei Veterans General Hospital, Taipei 11217, Taiwan (China); Guo, Wan-Yuo [Department of Radiology, Taipei Veterans General Hospital, Taipei 11217, Taiwan (China)
2013-05-15
Purpose: Fricke-infused gel has been shown to be a simple and attainable method for the conformal measurement of absorbed radiation dose. Nevertheless, its accuracy is seriously hindered by the irreversible ferric ion diffusion during magnetic resonance imaging, particularly when three-dimensional (3D) dose measurement in radiosurgery is considered. In this study, the authors developed a fast three-dimensional spin-echo based Fricke gel dosimetry technique to reduce the adverse effects of ferric ion diffusion and to obtain an accurate isotropic 3D dose measurement. Methods: A skull shaped phantom containing Fricke-infused gel was irradiated using Leksell Gamma Knife. The rapid image-based dosimetry technique was applied with the use of a 3D fast spin-echo magnetic resonance imaging sequence. The authors mathematically derived and experimentally validated the correlations between dose-response characteristics and parameters of the 3D fast spin-echo MR imaging sequence. Absorbed dose profiles were assessed and compared to the calculated profiles given by the Gamma Knife treatment planning system. Coefficient of variance (CV%) and coefficient of determination (R{sup 2}) were used to evaluate the precision of dose-response curve estimation. The agreement between the measured and the planned 3D dose distributions was quantified by gamma-index analysis of two acceptance criteria. Results: Proper magnetic resonance imaging parameters were explored to render an accurate three-dimensional absorbed dose mapping with a 1 mm{sup 3} isotropic image resolution. The efficacy of the dose-response estimation was approved by an R{sup 2} > 0.99 and an average CV% of 1.6%. Average gamma pass-rate between the experimentally measured and GammaPlan calculated dose distributions were 83.8% and 99.7% for 2%/2 and 3%/3 mm criteria, respectively. Conclusions: With the designed MR imaging sequence and parameters, total 3D MR acquisition time was confined to within 20 min postirradiation
Tang, Jianxin
1995-01-01
Isotropic to liquid crystalline phase transition for a lyotropic suspension of geometrically asymmetric macromolecules occurs to a wild class of synthetic polymers and biopolymers. Although in decades statistical mechanical theories have been developed to predict the thermodynamic conditions and the properties of such transition, quantitative comparison with theory has been compounded with complications such as charge, shape, polydispersity in size, and additional interactions with the solvent and among the macromolecules themselves. We chose the aqueous suspension of the filamentous bacteriophage fd as a model system to study the isotropic to liquid crystalline transition. The co-existence concentrations, as a function of ionic strength, were measured directly by spectrophotometry. Our data confirm quantitatively the predictions of a statistical mechanic treatment first described by Onsager, modified to include the effects of charge and flexibility of rodlike particles. We have also extended a previous study of the pretransitional angular correlations in the isotropic solutions of fd through the measurement of the magnetic-field-induced birefringence, i.e. the measurement of the Cotton-Mouton constant. At several ionic strengths the magnetic-field-induced birefringence, which is proportional to the number of particles in a correlation volume N_{rm corr}, was measured for fd concentrations spanning the entire isotropic region. From this data the limiting concentration of stability (spinodal) of the isotropic phase is obtained. A theoretical expression for the magnetic birefringence of persistent polymers was derived and agreed well with the data with the exception that N_{rm corr} at the isotropic to liquid crystal transition was smaller than predicted. In the proximity of the highest possible isotropic concentration, that is the isotropic in co-existence with anisotropic, we studied the effect of a high magnetic field. A first order field-induced isotropic
Maldacena, Juan; Zhiboedov, Alexander
2015-01-01
We consider Lorentzian correlators of local operators. In perturbation theory, singularities occur when we can draw a position-space Landau diagram with null lines. In theories with gravity duals, we can also draw Landau diagrams in the bulk. We argue that certain singularities can arise only from bulk diagrams, not from boundary diagrams. As has been previously observed, these singularities are a clear diagnostic of bulk locality. We analyze some properties of these perturbative singularities and discuss their relation to the OPE and the dimensions of double-trace operators. In the exact nonperturbative theory, we expect no singularity at these locations. We prove this statement in 1+1 dimensions by CFT methods.
Kim, Seulong
2016-01-01
Bi-isotropic media, which include isotropic chiral media and Tellegen media as special cases, are the most general form of linear isotropic media where the electric displacement and the magnetic induction are related to both the electric field and the magnetic intensity. In inhomogeneous bi-isotropic media, electromagnetic waves of two different polarizations are coupled to each other. In this paper, we develop a generalized version of the invariant imbedding method for the study of wave propagation in arbitrarily-inhomogeneous stratified bi-isotropic media, which can be used to solve the coupled wave propagation problem accurately and efficiently. We verify the validity and usefulness of the method by applying it to several examples, including the wave propagation in a uniform chiral slab, the surface wave excitation in a bilayer system made of a layer of Tellegen medium and a metal layer, and the mode conversion of transverse electromagnetic waves into longitudinal plasma oscillations in inhomogeneous Telle...
Critical buckling strain in high strength steel pipes using isotropic kinematic hardening
Energy Technology Data Exchange (ETDEWEB)
Fathi, A.; Roger Cheng, J. J.; Adeeb, Samer [Department of Civil and Environmental Engineering, University of Alberta (Canada); Zhou, Joe [TransCanada Pipelines Ltd. (Canada)
2010-07-01
In the natural gas sector, the use of high strength steel pipelines (HSSP) to transport huge volumes over long distances is increasing as it yields important savings in both capital and operational expenditures. In order to design HSSP, the critical buckling strain as to be taken into consideration but the models so far developed have been for isotropic materials while important material anisotropy is observed on HSSP due to their manufacturing process. The paper presents a model to assess the critical buckling strain of HSSP. An isotropic-kinematic hardening material model was developed and isotropic and anisotropic models were used to simulate pressurized and non-pressurized HSSP and were compared to test results. Results showed that the isotropic model is not suitable for predicting the buckling strain of HSSP but that the isotropic-kinematic hardening material model is. A model to better predict the buckling strain of HSSP was developed and successfully tested herein.
Cutoff radius effect of the isotropic periodic sum method in homogeneous system. II. Water.
Takahashi, Kazuaki; Narumi, Tetsu; Yasuoka, Kenji
2010-07-07
Molecular dynamics simulation has been applied for water to compare the isotropic periodic sum (IPS) method [X. Wu and B. R. Brooks, J. Chem. Phys. 122, 044107 (2005)] with the Ewald sum based on the diffusion coefficient and liquid structure. The IPS method gives a good estimation for the self-diffusion coefficient at a cutoff radius, r(c), greater than 2.2 nm; however, the radial distribution function g(r) has a notable deviation. The peak of this deviation appears at specific intermolecular distances which are near each cutoff radius and decrease in proportion to the inverse of the cube of r(c). Thus the deviation becomes insignificant (less than 1%) at r(c) greater than 2.2 nm. The distance dependent Kirkwood factor G(k)(r) was also calculated, and since the truncation of a long-range interaction of the cutofflike method (such as cutoff with or without the switch function and the reaction field) shows serious shortcomings for dipole-dipole correlations in bulk water systems, this was observed by comparing the shape to that of the Ewald sum [Y. Yonetani, J. Chem. Phys. 124, 204501 (2006); D. van der Spoel and P. J. van Maaren, J. Chem. Theory Comput. 2, 1 (2006)]. The G(k)(r) of cutofflike method greatly deviate from that of the Ewald sum. However, the discrepancy of G(k)(r) for the IPS method was found to be much less than that of other typical cutofflike methods. In conclusion, the IPS method is an adequately accurate technique for estimating transport coefficients and the liquid structure of water in a homogeneous system at long cutoff distances.
T.-S. Chin; Lin, C. Y.; Lee, M.C.; R.T. Huang; S. M. Huang
2009-01-01
Bulk metallic glasses (BMGs) Fe–B–Y–Nb–Cu, 2 mm in diameter, were successfully annealed to become bulk nano-crystalline alloys (BNCAs) with α-Fe crystallite 11–13 nm in size. A ‘crystallization-and-stop’ model was proposed to explain this behavior. Following this model, alloy-design criteria were elucidated and confirmed successful on another Fe-based BMG Fe–B–Si–Nb–Cu, 1 mm in diameter, with crystallite sizes 10–40 nm. It was concluded that BNCAs can be designed in general by the proposed cr...
Analysis of the Taylor dissipation surrogate in forced isotropic turbulence
McComb, W David; Yoffe, Samuel R
2013-01-01
From the energy balance in wavenumber space expressed by the Lin equation, we derive a new form for the local Karman-Howarth equation for forced isotropic turbulence in real space. This equation is then cast into a dimensionless form, from which a combined analytical and numerical study leads us to deduce a new model for the scale-independent nondimensional dissipation rate $\\Ceps$, which takes the form $\\Ceps = \\Cinf + C_L/R_L$, where the asymptotic value $\\Cinf$ can be evaluated from the third-order structure function. This is found to fit the numerical data with $\\Cinf = 0.47 \\pm 0.01$ and $C_L= 18.5 \\pm 1.3$. By considering $\\Ceps - \\Cinf$ on logarithmic scales, we show that $R_L^{-1}$ is indeed the correct Reynolds number behaviour. The model is compared to previous attempts in the literature, with encouraging agreement. The effects of the scale-dependence of the inertial and viscous terms due to finite forcing are then considered and shown to compensate one another, such that the model equation is appli...
Calculation of Theoretical Isotropic Compton Profile for Many Particle Systems
Alzubadi, Ali A.; Albayati, Khalil H.
Theoretical isotropic (spherically symmetric) Compton profiles (ICP) have been calculated for many particle systems' He, Li, Be and B atoms in their ground states. Our calculations were performed using Roothan-Hartree-Fock (RHF) wave function, HF wave function of Thakkar and re-optimized HF wave function of Clementi-Roetti, taking into account the impulse approximation. The theoretical analysis included a decomposition of the various intra and inter shells and their contributions in the total ICP. A high momentum region of up to 4 a.u. was investigated and a non-negligible tail was observed in all ICP curves. The existence of a high momentum tail was mainly due to the electron-electron interaction. The ICP for the He atom has been compared with the available experimental data and it is found that the ICP values agree very well with them. A few low order radial momentum expectation values and the total energy for these atomic systems have also been calculated and compared with their counterparts' wave functions.
Nonlinear optical spectroscopy of isotropic and anisotropic metallic nanocomposites
Energy Technology Data Exchange (ETDEWEB)
Fernandez-Hernandez, R C; Gleason-Villagran, R; Cheang-Wong, J C; Crespo-Sosa, A; Rodriguez-Fernandez, L; Lopez-Suarez, A; Oliver, A; Reyes-Esqueda, J A [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Mexico, D. F. 04510 (Mexico); Torres-Torres, C [Seccion de Estudios de Posgrado e Investigacion, ESIME-Zacatenco, Instituto Politecnico Nacional, Mexico, D. F. 07338 (Mexico); Rangel-Rojo, R, E-mail: reyes@fisica.unam.mx [CICESE/Depto. de Optica, A.P. 360, Ensenada, B. C. 22860 (Mexico)
2011-01-01
In this work, we studied the nonlinear absorption and refraction of isotropic and anisotropic metallic nanocomposites, which consist of Au and Ag nanoparticles (NPs) embedded in matrices of SiO{sub 2}. We performed this study at different wavelengths using the Z-scan technique in the picosecond regime. The wavelengths were selected accordingly to the absorption spectra of the nanocomposites, choosing wavelengths into the inter- and intra-band transitions regions, including the surface plasmon (SP) resonance, as well as in the transparent region. For the anisotropic nanocomposites, the polarization and the incident angle were varied in order to evaluate the different components of the third order susceptibility tensor, {chi}{sup (3)}. We observed dramatic changes of sign for both, nonlinear refraction and absorption, when passing from Au to Ag and/or varying the wave length. The results accentuate the importance of the hot-electrons contribution to the nonlinear optical response at this temporal regime, when compared to inter-band and intra-band transitions contributions.
A multiaxial theory of viscoplasticity for isotropic materials
Robinson, D. N.; Ellis, J. R.
1986-01-01
Many viscoplastic constitutive models for high temperature structural alloys are based exclusively on uniaxial test data. Generalization to multiaxial states of stress is made by assuming the stress dependence to be on the second principal invariant (J sub 2) of the deviatoric stress, frequently called the effective stress. If such a J sub 2 theory, based on uniaxial testing, is called upon to predict behavior under conditions other than uniaxial, e.g., pure shear, and it does so poorly, nothing is left to adjust in the theory. For a fully isotropic material whose inelastic deformation behavior is relatively independent of hydrostatic stress, the most general stress dependence is on the two (non-zero) principal invariants of the deviatoric stress, J sub 2 and J sub 3. These invariants constitute what is known as an integrity basis for the material. A time dependent constitutive theory with stress dependence on J sub 2 and J sub 3 is presented, that reduces to a known J sub 2 theory as a special case.
Wave Propagation in Isotropic Media with Two Orthogonal Fracture Sets
Shao, S.; Pyrak-Nolte, L. J.
2016-10-01
Orthogonal intersecting fracture sets form fracture networks that affect the hydraulic and mechanical integrity of a rock mass. Interpretation of elastic waves propagated through orthogonal fracture networks is complicated by guided modes that propagate along and between fractures, by multiple internal reflections, as well as by scattering from fracture intersections. The existence of some or all of these potentially overlapping modes depends on local stress fields that can preferentially close or open either one or both sets of fractures. In this study, an acoustic wave front imaging system was used to examine the effect of bi-axial loading conditions on acoustic wave propagation in isotropic media containing two orthogonal fracture sets. From the experimental data, orthogonal intersecting fracture sets support guided waves that depend on fracture spacing and fracture-specific stiffnesses. In addition, fracture intersections have stronger effects on propagating wave fronts than merely the superposition of the effects of two independent fractures because of energy partitioning among transmitted/reflected waves, scattered waves and guided modes. Interpretation of the properties of fractures or fracture sets from seismic measurements must consider non-uniform fracture stiffnesses within and among fracture sets, as well as considering the striking effects of fracture intersections on wave propagation.
Spark ignition of aviation fuel in isotropic turbulence
Krisman, Alex; Lu, Tianfeng; Borghesi, Giulio; Chen, Jacqueline
2016-11-01
Turbulent spark ignition occurs in combustion engines where the spark must establish a viable flame kernel that leads to stable combustion. A competition exists between kernel growth, due to flame propagation, and kernel attenuation, due to flame stretch and turbulence. This competition can be measured by the Karlovitz number, Ka, and kernel viability decreases rapidly for Ka >> 1 . In this study, the evolution of an initially spherical flame kernel in a turbulent field is investigated at two cases: Ka- (Ka = 25) and Ka+ (Ka = 125) using direct numerical simulation (DNS). A detailed chemical mechanism for jet fuel (Jet-A) is used, which is relevant for many practical conditions, and the mechanism includes a pyrolysis sub-model which is important for the ignition of large hydrocarbon fuels. An auxiliary non-reacting DNS generates the initial field of isotropic turbulence with a turbulent Reynolds number of 500 (Ka-) and 1,500 (Ka+). The kernel is then imposed at the center of the domain and the reacting DNS is performed. The Ka- case survives and the Ka+ case is extinguished. An analysis of the turbulence chemistry interactions is performed and the process of extinction is described. Department of Energy - Office of Basic Energy Science under Award No. DE-SC0001198.
Preferential Rotation of Chiral Dipoles in Isotropic Turbulence
Kramel, Stefan; Voth, Greg A.; Tympel, Saskia; Toschi, Federico
2016-10-01
We introduce a new particle shape which shows preferential rotation in three dimensional homogeneous isotropic turbulence. We call these particles chiral dipoles because they consist of a rod with two helices of opposite handedness, one at each end. 3D printing is used to fabricate these particles with a length in the inertial range and their rotations are tracked in a turbulent flow between oscillating grids. High aspect ratio chiral dipoles preferentially align with their long axis along the extensional eigenvectors of the strain rate tensor, and the helical ends respond to the extensional strain rate with a mean spinning rate that is nonzero. We use Stokesian dynamics simulations of chiral dipoles in pure strain flow to quantify the dependence of spinning on particle shape. Based on the known response to pure strain, we build a model that gives the spinning rate of small chiral dipoles using velocity gradients along Lagrangian trajectories from high resolution direct numerical simulations. The statistics of chiral dipole spinning determined with this model show surprisingly good agreement with the measured spinning of much larger chiral dipoles in the experiments.
Preferential rotation of chiral dipoles in isotropic turbulence
Kramel, Stefan; Toschi, Federico; Voth, Greg A
2016-01-01
Particles in the shape of chiral dipoles show a preferential rotation in three dimensional homogeneous isotropic turbulence. A chiral dipole consists of a rod with two helices of opposite handedness, one at each end. We can use 3d printing to fabricate these particles with length in the inertial range and track their rotations in a turbulent flow between oscillating grids. High aspect ratio chiral dipoles will align with the extensional eigenvectors of the strain rate tensor and the helical ends will respond to the strain field by spinning around its long axis. The mean of the measured spinning rate is non-zero and reflects the average stretching the particles experience. We use Stokesian dynamics simulations of chiral dipoles in pure strain flow to quantify the dependence of spinning on particle shape. Based on the known response to pure strain, we build a model that gives the spinning rate of small chiral dipoles using Lagrangian velocity gradients from high resolution direct numerical simulations. The stat...
Simulations of (an)isotropic diffusion on curved biological surfaces.
Sbalzarini, Ivo F; Hayer, Arnold; Helenius, Ari; Koumoutsakos, Petros
2006-02-01
We present a computational particle method for the simulation of isotropic and anisotropic diffusion on curved biological surfaces that have been reconstructed from image data. The method is capable of handling surfaces of high curvature and complex shape, which are often encountered in biology. The method is validated on simple benchmark problems and is shown to be second-order accurate in space and time and of high parallel efficiency. It is applied to simulations of diffusion on the membrane of endoplasmic reticula (ER) in live cells. Diffusion simulations are conducted on geometries reconstructed from real ER samples and are compared to fluorescence recovery after photobleaching experiments in the same ER samples using the transmembrane protein tsO45-VSV-G, C-terminally tagged with green fluorescent protein. Such comparisons allow derivation of geometry-corrected molecular diffusion constants for membrane components from fluorescence recovery after photobleaching data. The results of the simulations indicate that the diffusion behavior of molecules in the ER membrane differs significantly from the volumetric diffusion of soluble molecules in the lumen of the same ER. The apparent speed of recovery differs by a factor of approximately 4, even when the molecular diffusion constants of the two molecules are identical. In addition, the specific shape of the membrane affects the recovery half-time, which is found to vary by a factor of approximately 2 in different ER samples.
Density functional theory predictions of isotropic hyperfine coupling constants.
Hermosilla, L; Calle, P; García de la Vega, J M; Sieiro, C
2005-02-17
The reliability of density functional theory (DFT) in the determination of the isotropic hyperfine coupling constants (hfccs) of the ground electronic states of organic and inorganic radicals is examined. Predictions using several DFT methods and 6-31G, TZVP, EPR-III and cc-pVQZ basis sets are made and compared to experimental values. The set of 75 radicals here studied was selected using a wide range of criteria. The systems studied are neutral, cationic, anionic; doublet, triplet, quartet; localized, and conjugated radicals, containing 1H, 9Be, 11B, 13C, 14N, 17O, 19F, 23Na, 25Mg, 27Al, 29Si, 31P, 33S, and 35Cl nuclei. The considered radicals provide 241 theoretical hfcc values, which are compared with 174 available experimental ones. The geometries of the studied systems are obtained by theoretical optimization using the same functional and basis set with which the hfccs were calculated. Regression analysis is used as a basic and appropriate methodology for this kind of comparative study. From this analysis, we conclude that DFT predictions of the hfccs are reliable for B3LYP/TZVP and B3LYP/EPR-III combinations. Both functional/basis set scheme are the more useful theoretical tools for predicting hfccs if compared to other much more expensive methods.
Three-dimensional magnetospheric equilibrium with isotropic pressure
Energy Technology Data Exchange (ETDEWEB)
Cheng, C.Z.
1995-05-01
In the absence of the toroidal flux, two coupled quasi two-dimensional elliptic equilibrium equations have been derived to describe self-consistent three-dimensional static magnetospheric equilibria with isotropic pressure in an optimal ({Psi},{alpha},{chi}) flux coordinate system, where {Psi} is the magnetic flux function, {chi} is a generalized poloidal angle, {alpha} is the toroidal angle, {alpha} = {phi} {minus} {delta}({Psi},{phi},{chi}) is the toroidal angle, {delta}({Psi},{phi},{chi}) is periodic in {phi}, and the magnetic field is represented as {rvec B} = {del}{Psi} {times} {del}{alpha}. A three-dimensional magnetospheric equilibrium code, the MAG-3D code, has been developed by employing an iterative metric method. The main difference between the three-dimensional and the two-dimensional axisymmetric solutions is that the field-aligned current and the toroidal magnetic field are finite for the three-dimensional case, but vanish for the two-dimensional axisymmetric case. With the same boundary flux surface shape, the two-dimensional axisymmetric results are similar to the three-dimensional magnetosphere at each local time cross section.
Magnetic resonance investigations of lipid motion in isotropic bicelles.
Andersson, August; Mäler, Lena
2005-08-16
The dynamics of DMPC in different isotropic bicelles have been investigated by NMR and EPR methods. The local dynamics were obtained by interpretation of 13C NMR relaxation measurements of DMPC in the bicelles, and these results were compared to EPR spectra of spin-labeled lipids. The overall size of the bicelles was investigated by PFG NMR translational diffusion measurements. The dynamics and relative sizes were compared among three different bicelles: [DMPC]/[DHPC] = 0.25, [DMPC]/[DHPC] = 0.5, and [DMPC]/[CHAPS] = 0.5. The local motion is found to depend much more strongly on the choice of the detergent, rather than the overall size of the bicelle. The results provide an explanation for differences in apparent dynamics for different peptides, which are bound to bicelles. This in turn determines under what conditions reasonable NMR spectra can be observed. A model is presented in which extensive local motion, in conjunction with the overall size, affects the spectral properties. An analytical expression for the size dependence of the bicelles, relating the radius of the bilayer region with physical properties of the detergent and the lipid, is also presented.
DLVO interactions of carbon nanotubes with isotropic planar surfaces.
Wu, Lei; Gao, Bin; Tian, Yuan; Muñoz-Carpena, Rafael; Zigler, Kirk J
2013-03-26
Knowledge of the interaction between carbon nanotubes (CNTs) and planar surfaces is essential to optimizing CNT applications as well as reducing their environmental impact. In this work, the surface element integration (SEI) technique was coupled with the DLVO theory to determine the orientation-dependent interaction energy between a single-walled carbon nanotube (SWNT) and an infinite isotropic planar surface. For the first time, an analytical formula was developed to describe accurately the interaction between not only pristine but also surface-charged CNTs and planar surfaces with arbitrary rotational angles. Compared to other methods, the new analytical formulas were either more convenient or more accurate in describing the interaction between CNTs and planar surfaces, especially with respect to arbitrary angles. The results revealed the complex dependences of both force and torque between SWNTs and planar surfaces on the separation distances and rotational angles. With minor modifications, the analytical formulas derived for SWNTs can also be applied to multiwalled carbon nanotubes (MWNTs). The new analytical expressions presented in this work can be used as a robust tool to describe the DLVO interaction between CNTs and planar surfaces under various conditions and thus to assist in the design and application of CNT-based products.
Clustering of vertically constrained passive particles in homogeneous isotropic turbulence
De Pietro, Massimo; van Hinsberg, Michel A. T.; Biferale, Luca; Clercx, Herman J. H.; Perlekar, Prasad; Toschi, Federico
2015-05-01
We analyze the dynamics of small particles vertically confined, by means of a linear restoring force, to move within a horizontal fluid slab in a three-dimensional (3D) homogeneous isotropic turbulent velocity field. The model that we introduce and study is possibly the simplest description for the dynamics of small aquatic organisms that, due to swimming, active regulation of their buoyancy, or any other mechanism, maintain themselves in a shallow horizontal layer below the free surface of oceans or lakes. By varying the strength of the restoring force, we are able to control the thickness of the fluid slab in which the particles can move. This allows us to analyze the statistical features of the system over a wide range of conditions going from a fully 3D incompressible flow (corresponding to the case of no confinement) to the extremely confined case corresponding to a two-dimensional slice. The background 3D turbulent velocity field is evolved by means of fully resolved direct numerical simulations. Whenever some level of vertical confinement is present, the particle trajectories deviate from that of fluid tracers and the particles experience an effectively compressible velocity field. Here, we have quantified the compressibility, the preferential concentration of the particles, and the correlation dimension by changing the strength of the restoring force. The main result is that there exists a particular value of the force constant, corresponding to a mean slab depth approximately equal to a few times the Kolmogorov length scale η , that maximizes the clustering of the particles.
A Comprehensive Theory of Yielding and Failure for Isotropic Materials
Energy Technology Data Exchange (ETDEWEB)
Christensen, R M
2006-08-10
A theory of yielding and failure for homogeneous and isotropic materials is given. The theory is calibrated by two independent, measurable properties and from those it predicts possible failure for any given state of stress. It also differentiates between ductile yielding and brittle failure. The explicit ductile-brittle criterion depends not only upon the material specification through the two properties, but also and equally importantly depends upon the type of imposed stress state. The Mises criterion is a special (limiting) case of the present theory. A close examination of this case shows that the Mises material idealization does not necessarily imply ductile behavior under all conditions, only under most conditions. When the first invariant of the yield/failure stress state is sufficiently large relative to the distortional part, brittle failure will be expected to occur. For general material types, it is shown that it is possible to have a state of spreading plastic flow, but as the elastic-plastic boundary advances, the conditions for yielding on it can change over to conditions for brittle failure because of the evolving stress state. The general theory is of a three dimensional form and it applies to full density materials for which the yield/failure strength in uniaxial tension is less than or at most equal to the magnitude of that in uniaxial compression.
Hubble parameter in QCD Universe for finite bulk viscosity
Energy Technology Data Exchange (ETDEWEB)
Tawfik, A.; Wahba, M. [Egyptian Center for Theoretical Physics (ECTP), MTI University, Al Mukattam, Cairo 11212 (Egypt); Mansour, H. [Department of Physics, Cairo University, Giza (Egypt); Harko, T. [Department of Physics and Center for Theoretical and Computational Physics, The University of Hong Kong, Pok Fu Lam Road, Hong Kong (China)
2010-12-01
We consider the influence of the perturbative bulk viscosity on the evolution of the Hubble parameter in the QCD era of the early Universe. For the geometry of the Universe we assume the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker metric, while the background matter is assumed to be characterized by barotropic equations of state, obtained from recent lattice QCD simulations, and heavy-ion collisions, respectively. Taking into account a perturbative form for the bulk viscosity coefficient, we obtain the evolution of the Hubble parameter, and we compare it with its evolution for an ideal (non-viscous) cosmological matter. A numerical solution for the viscous QCD plasma in the framework of the causal Israel-Stewart thermodynamics is also obtained. Both the perturbative approach and the numerical solution qualitatively agree in reproducing the viscous corrections to the Hubble parameter, which in the viscous case turns out to be slightly different as compared to the non-viscous case. Our results are strictly limited within a very narrow temperature- or time-interval in the QCD era, where the quark-gluon plasma is likely dominant. (Copyright copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Longitudinal bulk acoustic mass sensor
DEFF Research Database (Denmark)
Hales, Jan Harry; Teva, Jordi; Boisen, Anja
2009-01-01
A polycrystalline silicon longitudinal bulk acoustic cantilever is fabricated and operated in air at 51 MHz. A mass sensitivity of 100 Hz/fg (1 fg=10(-15) g) is obtained from the preliminary experiments where a minute mass is deposited on the device by means of focused ion beam. The total noise i...
Bulk and surface electromagnetic response of metallic metamaterials to convection electrons
So, Jin-Kyu; Jang, Kyu-Ha; Park, Gun-Sik; Garcia-Vidal, F. J.
2011-08-01
The electromagnetic response of three-dimensional metallic metamaterials with isotropic effective index of refraction to fast-moving electrons is studied by numerical simulations. The considered metamaterials can support Cerenkov radiation [P. A. Cherenkov, Dokl. Akad. Nauk SSSR 2, 451 (1934)], and their effective dielectric behavior is confirmed by the detailed angular dependence of the generated radiation cone on the kinetic energy of electrons. Moreover, in addition to the predicted bulk modes, surface electromagnetic excitation is observed in a specific type of metamaterials and its dispersion is sensitive to the thickness of the subwavelength rods.
Traveltime approximations for transversely isotropic media with an inhomogeneous background
Alkhalifah, Tariq
2011-05-01
A transversely isotropic (TI) model with a tilted symmetry axis is regarded as one of the most effective approximations to the Earth subsurface, especially for imaging purposes. However, we commonly utilize this model by setting the axis of symmetry normal to the reflector. This assumption may be accurate in many places, but deviations from this assumption will cause errors in the wavefield description. Using perturbation theory and Taylor\\'s series, I expand the solutions of the eikonal equation for 2D TI media with respect to the independent parameter θ, the angle the tilt of the axis of symmetry makes with the vertical, in a generally inhomogeneous TI background with a vertical axis of symmetry. I do an additional expansion in terms of the independent (anellipticity) parameter in a generally inhomogeneous elliptically anisotropic background medium. These new TI traveltime solutions are given by expansions in and θ with coefficients extracted from solving linear first-order partial differential equations. Pade approximations are used to enhance the accuracy of the representation by predicting the behavior of the higher-order terms of the expansion. A simplification of the expansion for homogenous media provides nonhyperbolic moveout descriptions of the traveltime for TI models that are more accurate than other recently derived approximations. In addition, for 3D media, I develop traveltime approximations using Taylor\\'s series type of expansions in the azimuth of the axis of symmetry. The coefficients of all these expansions can also provide us with the medium sensitivity gradients (Jacobian) for nonlinear tomographic-based inversion for the tilt in the symmetry axis. © 2011 Society of Exploration Geophysicists.
Large-deviation statistics of vorticity stretching in isotropic turbulence.
Johnson, Perry L; Meneveau, Charles
2016-03-01
A key feature of three-dimensional fluid turbulence is the stretching and realignment of vorticity by the action of the strain rate. It is shown in this paper, using the cumulant-generating function, that the cumulative vorticity stretching along a Lagrangian path in isotropic turbulence obeys a large deviation principle. As a result, the relevant statistics can be described by the vorticity stretching Cramér function. This function is computed from a direct numerical simulation data set at a Taylor-scale Reynolds number of Re(λ)=433 and compared to those of the finite-time Lyapunov exponents (FTLE) for material deformation. As expected, the mean cumulative vorticity stretching is slightly less than that of the most-stretched material line (largest FTLE), due to the vorticity's preferential alignment with the second-largest eigenvalue of strain rate and the material line's preferential alignment with the largest eigenvalue. However, the vorticity stretching tends to be significantly larger than the second-largest FTLE, and the Cramér functions reveal that the statistics of vorticity stretching fluctuations are more similar to those of the largest FTLE. In an attempt to relate the vorticity stretching statistics to the vorticity magnitude probability density function in statistically stationary conditions, a model Kramers-Moyal equation is constructed using the statistics encoded in the Cramér function. The model predicts a stretched-exponential tail for the vorticity magnitude probability density function, with good agreement for the exponent but significant difference (35%) in the prefactor.
Joint Statistics of Finite Time Lyapunov Exponents in Isotropic Turbulence
Johnson, Perry; Meneveau, Charles
2014-11-01
Recently, the notion of Lagrangian Coherent Structures (LCS) has gained attention as a tool for qualitative visualization of flow features. LCS visualize repelling and attracting manifolds marked by local ridges in the field of maximal and minimal finite-time Lyapunov exponents (FTLE), respectively. To provide a quantitative characterization of FTLEs, the statistical theory of large deviations can be used based on the so-called Cramér function. To obtain the Cramér function from data, we use both the method based on measuring moments and measuring histograms (with finite-size correction). We generalize the formalism to characterize the joint distributions of the two independent FTLEs in 3D. The ``joint Cramér function of turbulence'' is measured from the Johns Hopkins Turbulence Databases (JHTDB) isotropic simulation at Reλ = 433 and results are compared with those computed using only the symmetric part of the velocity gradient tensor, as well as with those of instantaneous strain-rate eigenvalues. We also extend the large-deviation theory to study the statistics of the ratio of FTLEs. When using only the strain contribution of the velocity gradient, the maximal FTLE nearly doubles in magnitude and the most likely ratio of FTLEs changes from 4:1:-5 to 8:3:-11, highlighting the role of rotation in de-correlating the fluid deformations along particle paths. Supported by NSF Graduate Fellowship (DGE-1232825), a JHU graduate Fellowship, and NSF Grant CMMI-0941530. CM thanks Prof. Luca Biferale for useful discussions on the subject.
A Transversely Isotropic Thermo-mechanical Framework for Oil Shale
Semnani, S. J.; White, J. A.; Borja, R. I.
2014-12-01
The present study provides a thermo-mechanical framework for modeling the temperature dependent behavior of oil shale. As a result of heating, oil shale undergoes phase transformations, during which organic matter is converted to petroleum products, e.g. light oil, heavy oil, bitumen, and coke. The change in the constituents and microstructure of shale at high temperatures dramatically alters its mechanical behavior e.g. plastic deformations and strength, as demonstrated by triaxial tests conducted at multiple temperatures [1,2]. Accordingly, the present model formulates the effects of changes in the chemical constituents due to thermal loading. It is well known that due to the layered structure of shale its mechanical properties in the direction parallel to the bedding planes is significantly different from its properties in the perpendicular direction. Although isotropic models simplify the modeling process, they fail to accurately describe the mechanical behavior of these rocks. Therefore, many researchers have studied the anisotropic behavior of rocks, including shale [3]. The current study presents a framework to incorporate the effects of transverse isotropy within a thermo-mechanical formulation. The proposed constitutive model can be readily applied to existing finite element codes to predict the behavior of oil shale in applications such as in-situ retorting process and stability assessment in petroleum reservoirs. [1] Masri, M. et al."Experimental Study of the Thermomechanical Behavior of the Petroleum Reservoir." SPE Eastern Regional/AAPG Eastern Section Joint Meeting. Society of Petroleum Engineers, 2008. [2] Xu, B. et al. "Thermal impact on shale deformation/failure behaviors---laboratory studies." 45th US Rock Mechanics/Geomechanics Symposium. American Rock Mechanics Association, 2011. [3] Crook, AJL et al. "Development of an orthotropic 3D elastoplastic material model for shale." SPE/ISRM Rock Mechanics Conference. Society of Petroleum Engineers
Cosmological simulations of isotropic conduction in galaxy clusters
Energy Technology Data Exchange (ETDEWEB)
Smith, Britton; O' Shea, Brian W.; Voit, G. Mark; Ventimiglia, David [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Skillman, Samuel W., E-mail: smit1685@msu.edu [Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Science, University of Colorado, Boulder, CO 80309 (United States)
2013-12-01
Simulations of galaxy clusters have a difficult time reproducing the radial gas-property gradients and red central galaxies observed to exist in the cores of galaxy clusters. Thermal conduction has been suggested as a mechanism that can help bring simulations of cluster cores into better alignment with observations by stabilizing the feedback processes that regulate gas cooling, but this idea has not yet been well tested with cosmological numerical simulations. Here we present cosmological simulations of 10 galaxy clusters performed with five different levels of isotropic Spitzer conduction, which alters both the cores and outskirts of clusters, though not dramatically. In the cores, conduction flattens central temperature gradients, making them nearly isothermal and slightly lowering the central density, but failing to prevent a cooling catastrophe there. Conduction has little effect on temperature gradients outside of cluster cores because outward conductive heat flow tends to inflate the outer parts of the intracluster medium (ICM), instead of raising its temperature. In general, conduction tends reduce temperature inhomogeneity in the ICM, but our simulations indicate that those homogenizing effects would be extremely difficult to observe in ∼5 keV clusters. Outside the virial radius, our conduction implementation lowers the gas densities and temperatures because it reduces the Mach numbers of accretion shocks. We conclude that, despite the numerous small ways in which conduction alters the structure of galaxy clusters, none of these effects are significant enough to make the efficiency of conduction easily measurable, unless its effects are more pronounced in clusters hotter than those we have simulated.
Isotropic copper-invar alloys for microelectronics packaging
Cottle, Rand Duprez
The recent trend in microelectronics packaging toward surface mounted devices (SMD) has created a need for new types of materials that possess low thermal expansion and high electrical and thermal conductivity. Laminates that combine the high thermal and electrical conductivity of copper with the low thermal expansion of Invar, know as CuInvarCu or CIC, are widely use as core constraining materials in printed wire boards where SMDs are to be employed. CIC is highly anisotropic, and there are potential problems resulting from its anisotropy. An isotropic CuInvar alloy would be of great interest for a variety of applications. In suitable Cu-Fe-Ni alloys, a copper-rich solid solution equilibrates with an Invar-rich solid solution; casting such alloys invariably produces Invar-rich dendrites in a copper-rich solid solution. Casting followed by suitable heat treatments can produce two-phase alloys that combine the properties of copper and Invar. The overall composition controls the relative fractions of Invar and copper and the resulting trade-off between low thermal expansivity and electrical conductivity. Measured thermal expansivities (CTE) of CuInvar alloys follow very closely a linear rule of mixing. Electrical conductivities of as-cast specimens are quite poor due to iron and nickel contamination. Theoretical phase diagrams indicate that nearly pure copper equilibrates with an Invar-rich phase at temperatures below, roughly, 500°C. However, equilibrium compositions have been shown to take extremely, long to form, due to the very sluggish kinetics in the system. Long-term annealing was shown to improve conductivity significantly, but much greater improvements are needed to make CuInvar viable as an electrical conductive material.
Energy transfer and constrained simulations in isotropic turbulence
Jimenez, Javier
1993-01-01
The defining characteristic of turbulent flows is their ability to dissipate energy, even in the limit of zero viscosity. The Euler equations, if constrained in such a way that the velocity derivatives remain bounded, conserve energy. But when they arise as the limit of the Navier-Stokes (NS) equations, when the Reynolds number goes to infinity, there is persuasive empirical evidence that the gradients become singular as just the right function of Re for the dissipation to remain non-zero and to approach a well defined limit. It is generally believed that this limiting value of the dissipation is a property of the Euler equations themselves, independent of the particular dissipative mechanism involved, and that it can be normalized with the large scale properties of the turbulent flow (e.g. the kinetic energy per unit volume u'(exp 2)/2, and the integral scale L) without reference to the Reynolds number or to other dissipative quantities. This is usually taken to imply that the low wave number end of the energy spectrum, far from the dissipative range, is also independent of the particular mechanism chosen to dispose of the energy transfer. In the following sections, we present some numerical experiments on the effect of substituting different dissipation models into the truncated Euler equations. We will see that the effect is mainly felt in the 'near dissipation' range of the energy spectrum, but that this range can be quite wide in some cases, contaminating a substantial range of wave numbers. In the process, we will develop a 'practical' approximation to the subgrid energy transfer in isotropic turbulence, and we will gain insight into the structure of the nonlinear interactions among turbulent scales of comparable size, and into the nature of energy backscatter. Some considerations on future research directions are offered at the end.
On Isotropic Sets of Points in the Plane. Application to the Design of Robot Archirectures
Angeles, Jorge
2000-01-01
Various performance indices are used for the design of serial manipulators. One method of optimization relies on the condition number of the Jacobian matrix. The minimization of the condition number leads, under certain conditions, to isotropic configurations, for which the roundoff-error amplification is lowest. In this paper, the isotropy conditions, introduced elsewhere, are the motivation behind the introduction of isotropic sets of points. By connecting together these points, we define families of isotropic manipulators. This paper is devoted to planar manipulators, the concepts being currently extended to their spatial counterparts. Furthermore, only manipulators with revolute joints are considered here.
KINETICS OF TRANSITION FROM ISOTROPIC TO CHOLESTERIC PHASE FOR A THERMOTROPIC CELLULOSE DERIVATIVE
Institute of Scientific and Technical Information of China (English)
CHEN Shouxi; SUN Zheng; SONG Wenhui; JIN Yongze; HUANG Yong
1996-01-01
The kinetics of mesophase formation of a thermotropic hydroxyethyl cellulose acetate from isotropic phase to cholesteric mesophase has been studied by means of depolarizing transmittance method. Avrami type analysis of the data gives an exponent n close to 1, which suggests the nucleation followed by rod-like growth. It means that the kinetic behavior of phase transition from isotropic to cholesteric mesophase is very similar to that of the mesophase formation from isotropic to nematic mesophase.This work was supported by the National Basic Research Project-Macromolecular Condensed State.
Vasiliev, A. S.; Volkov, S. S.; Aizikovich, S. M.; Mitrin, B. I.
2017-02-01
Plane contact problem of the theory of elasticity on indentation of a non-deformable punch with a flat base into an elastic transversely-isotropic half-plane with a transversely-isotropic functionally graded coating is considered. Elastic moduli of the coating vary with depth according to arbitrary functions. An approximated analytical solution effective for a whole range of geometrical parameter (relative layer thickness) of the problem is constructed. Some properties of the contact normal pressure under the punch are obtained analytically and illustrated by the numerical examples for a transversely-isotropic homogeneous and functionally graded coatings with different types of variation of elastic moduli with depth. The distinctions in distribution of contact normal pressure for homogeneous and functionally graded materials, coated and non-coated bodies are studied analytically and numerically.
Bulk Superconductors in Mobile Application
Werfel, F. N.; Delor, U. Floegel-; Rothfeld, R.; Riedel, T.; Wippich, D.; Goebel, B.; Schirrmeister, P.
We investigate and review concepts of multi - seeded REBCO bulk superconductors in mobile application. ATZ's compact HTS bulk magnets can trap routinely 1 T@77 K. Except of magnetization, flux creep and hysteresis, industrial - like properties as compactness, power density, and robustness are of major device interest if mobility and light-weight construction is in focus. For mobile application in levitated trains or demonstrator magnets we examine the performance of on-board cryogenics either by LN2 or cryo-cooler application. The mechanical, electric and thermodynamical requirements of compact vacuum cryostats for Maglev train operation were studied systematically. More than 30 units are manufactured and tested. The attractive load to weight ratio is more than 10 and favours group module device constructions up to 5 t load on permanent magnet (PM) track. A transportable and compact YBCO bulk magnet cooled with in-situ 4 Watt Stirling cryo-cooler for 50 - 80 K operation is investigated. Low cooling power and effective HTS cold mass drives the system construction to a minimum - thermal loss and light-weight design.
Exploring the bulk in AdS /CFT : A covariant approach
Engelhardt, Netta
2017-03-01
I propose a general, covariant way of defining when one region is "deeper in the bulk" than another. This definition is formulated outside of an event horizon (or in the absence thereof) in generic geometries; it may be applied to both points and surfaces, and it may be used to compare the depth of bulk points or surfaces relative to a particular boundary subregion or relative to the entire boundary. Using the recently proposed "light-cone cut" formalism, the comparative depth between two bulk points can be determined from the singularity structure of Lorentzian correlators in the dual field theory. I prove that, by this definition, causal wedges of progressively larger regions probe monotonically deeper in the bulk. The definition furthermore matches expectations in pure AdS and in static AdS black holes with isotropic spatial slices, where a well-defined holographic coordinate exists. In terms of holographic renormalization group flow, this new definition of bulk depth makes contact with coarse graining over both large distances and long time scales.
Preferential concentration of heavy particles in compressible isotropic turbulence
Zhang, Qingqing; Liu, Han; Ma, Zongqiang; Xiao, Zuoli
2016-05-01
Numerical simulations of particle-laden compressible isotropic turbulence with Taylor Reynolds number Reλ ˜ 100 are conducted by using a high-order turbulence solver, which is based on high-order compact finite difference method in the whole flow domain and localized artificial diffusivities for discontinuities. For simplicity, only one-way coupling (i.e., the influence of fluid on particles) between the carrier flow and particles is considered. The focus is on the study of the preferential concentration of heavy particles in dissipative scale of turbulence and the underlying mechanisms. Firstly, the effect of Stokes number (St) on the particle distribution in flow of Mach 1.01 (referred to as high-Mach-number case in this study) is investigated as a necessary supplementation for the previous studies in incompressible and weakly compressible flows. It turns out that heavy particles with Stokes number close to unity exhibit the strongest preferential concentration, which is in agreement with the observation in incompressible flow. All types of heavy particles have a tendency to accumulate in high-density regions of the background flow. While all kinds of particles dominantly collect in low-vorticity regions, intermediate and large particles (St = 1 and St = 5) are also found to collect in high-vorticity regions behind the randomly formed shocklets. Secondly, the impact of turbulent Mach number (Mt) (or the compressibility) of the carrier flow on the spatial distribution of the particles with St = 1 is discussed using the simulated compressible flows with Mt being 0.22, 0.68, and 1.01, respectively. In low-Mach-number flow, particles tend to concentrate in regions of low vorticity due to the centrifuge effect of vortices and particle concentration decreases monotonically with the increasing vorticity magnitude. As Mach number increases, the degree of particle clustering is slightly weakened in low-vorticity regions but is enhanced in high-vorticity regions, which
Institute of Scientific and Technical Information of China (English)
CHEN Jiang-ying; CHEN Wei-qiu
2007-01-01
The analytical solution for an annular plate rotating at a constant angular velocity is derived by means of direct displacement method from the elasticity equations for axisymmetric problems of functionally graded transversely isotropic media.The displacement components are assumed as a linear combination of certain explicit functions of the radial coordinate, with seven undetermined coefficients being functions of the axial coordinate z. Seven equations governing these z-dependent functions are derived and solved by a progressive integrating scheme. The present solution can be degenerated into the solution of a rotating isotropic functionally graded annular plate. The solution also can be degenerated into that for transversely isotropic or isotropic homogeneous materials. Finally, a special case is considered and the effect of the material gradient index on the elastic field is illustrated numerically.
STUDY ON THE TENSILE FATIGUE DAMAGE OF QUASI-ISOTROPIC COMPOSITE LAMINATES
Institute of Scientific and Technical Information of China (English)
I.G.Kim; I.S.Kim; O.S.Kim; Yaragarra K.D.V. Prasad4
2003-01-01
Quasi-isotropic laminates have isotropic elastic properties in all in-plane directions.Therefore, this kind of laminate is widely used for structural elements. The simpleststacking sequence of quasi-isotropic laminates is [0/-60/60]s. When the direction ofapplied axial load to [0/-60/60]s laminate is inclined at a 30-degree angle, we havethe other quasi-isotropic laminate [30/-30/90]s under axial load. The failure mecha-nisms of these two laminates are, however, entirely different from each other becausethese two laminates have different distribution of the interlaminar stresses. It wasconfirmed by tensile fatigue tests that the [0/-60/60]s laminate does not show any vis-ible fatigue damage, but the [30/-30/90]s laminate develops edge-delamination duringcyclic loading. The analytical results were in good agreement with the experimental results.
A strong law of large numbers for harmonizable isotropic random fields
Directory of Open Access Journals (Sweden)
Randall J. Swift
1997-01-01
Full Text Available The class of harmonizable fields is a natural extension of the class of stationary fields. This paper considers a strong law of large numbers for the spherical average of a harmonizable isotropic random field.
Isotropic blackbody cosmic microwave background radiation as evidence for a homogeneous universe.
Clifton, Timothy; Clarkson, Chris; Bull, Philip
2012-08-03
The question of whether the Universe is spatially homogeneous and isotropic on the largest scales is of fundamental importance to cosmology but has not yet been answered decisively. Surprisingly, neither an isotropic primary cosmic microwave background (CMB) nor combined observations of luminosity distances and galaxy number counts are sufficient to establish such a result. The inclusion of the Sunyaev-Zel'dovich effect in CMB observations, however, dramatically improves this situation. We show that even a solitary observer who sees an isotropic blackbody CMB can conclude that the Universe is homogeneous and isotropic in their causal past when the Sunyaev-Zel'dovich effect is present. Critically, however, the CMB must either be viewed for an extended period of time, or CMB photons that have scattered more than once must be detected. This result provides a theoretical underpinning for testing the cosmological principle with observations of the CMB alone.
Temperature Isotropization in Solar Flare Plasmas due to the Electron Firehose Instability
Messmer, P
2002-01-01
The isotropization process of a collisionless plasma with an electron temperature anisotropy along an external magnetic field ($T_\\| ^e\\gg T_\\perp^e$, $\\|$ and $\\perp$ with respect to the background magnetic field) and isotropic protons is investigated using a particle-in-cell(PIC) code. Restricting wave growth mainly parallel to the external magnetic field, the isotropization mechanism is identified to be the Electron Firehose Instability (EFI). The free energy in the electrons is first transformed into left-hand circularly polarized transverse low-frequency waves by a non-resonant interaction. Fast electrons can then be scattered towards higher perpendicular velocities by gyroresonance, leading finally to a complete isotropization of the velocity distribution. During this phase of the instability, Langmuir waves are generated which may lead to the emission of radio waves. A large fraction of the protons is resonant with the left-hand polarized electromagnetic waves, creating a proton temperature anisotropy ...
Entanglement of Formation for Werner States and Isotropic States via Logical Gates
Bertini, Cesarino; Chiara, Maria Luisa Dalla; Leporini, Roberto
To what extent is a logical characterization of entanglement possible? We investigate some correlations that hold between the concept of entanglement of formation for Werner states and for isotropic states and the probabilistic behavior of some quantum logical gates.
Supersymmetry and the constants of motion of the two-dimensional isotropic harmonic oscillator
Energy Technology Data Exchange (ETDEWEB)
Torres del Castillo, G.F. [Departamento de Fisica Matematica, Instituto de Ciencias, Universidad Autonoma de Puebla, 72570 Puebla (Mexico); Tepper G, T. [Escuela de Ciencias, Departamento de Fisica y Matematicas, Universidad de Las Americas-Puebla, Santa Catarina Martir, 72820 Cholula, Puebla (Mexico)
2002-07-01
It is shown that the constants of motion of the two-dimensional isotropic harmonic oscillator not related to the rotational invariance of the Hamiltonian can be derived using the ideas of supersymmetric quantum mechanics. (Author)
Carroll, Jonathan J; Blackman, Eric G
2010-01-01
Feedback from protostellar outflows can influence the nature of turbulence in star forming regions even if they are not the primary source of velocity dispersion for all scales of molecular clouds. For the rate and power expected in star forming regions, we previously (Carroll et al. 2009) demonstrated that outflows could drive supersonic turbulence at levels consistent with the scaling relations from Matzner 2007 although with a steeper velocity power spectrum than expected for an isotropically driven supersonic turbulent cascade. Here we perform higher resolution simulations and combine simulations of outflow driven turbulence with those of isotropically forced turbulence. We find that the presence of outflows within an ambient isotropically driven turbulent environment produces a knee in the velocity power spectrum at the outflow scale and a steeper slope at sub-outflow scales than for a purely isotropically forced case. We also find that the presence of outflows flattens the density spectrum at large scal...
Galactic winds driven by isotropic and anisotropic cosmic ray diffusion in disk galaxies
Pakmor, Ruediger; Simpson, Christine M; Springel, Volker
2016-01-01
The physics of cosmic rays (CR) is a promising candidate for explaining the driving of galactic winds and outflows. Recent galaxy formation simulations have demonstrated the need for active CR transport either in the form of diffusion or streaming to successfully launch winds in galaxies. However, due to computational limitations, most previous simulations have modeled CR transport isotropically. Here, we discuss high resolution simulations of isolated disk galaxies in a $10^{11}\\rm{M_\\odot}$ halo with the moving mesh code {\\sc Arepo} that include injection of CRs from supernovae, advective transport, CR cooling, and CR transport through isotropic or anisotropic diffusion. We show that either mode of diffusion leads to the formation of strong bipolar outflows. However, they develop significantly later in the simulation with anisotropic diffusion compared to the simulation with isotropic diffusion. Moreover, we find that isotropic diffusion allows most of the CRs to quickly diffuse out of the disk, while in th...
Isotropic Super-symmetric Descartes Tensor%各向同性超对称Descartes张量
Institute of Scientific and Technical Information of China (English)
秦清锋; 吴伟; 尹红然
2011-01-01
Isotropic tensor plays an extremely role in constructing elastic solid constitutive equations. Based on the expression of isotropic Descartes tensor and the proposition of super-symmetric tensor, the scalars of isotropic Descartes tensor are discussed. Then it comes to the representations of isotropic super-symmetric Descartes tensor from two order to six order.%各向同性张量在构造各向同性弹性固体的本构方程时有着极其重要的作用.基于各向同性Descartes张量的表达式并结合超对称张量的性质,探讨了各向同性Descartes张量各标量之间的关系,进而得出了二到六阶各向同性超对称Descartes 张量的一般表达式.
GENERAL SOLUTION FOR THE COUPLED EQUATIONS OF TRANSVERSELY ISOTROPIC MAGNETOELECTROELASTIC SOLIDS
Institute of Scientific and Technical Information of China (English)
刘金喜; 王祥琴; 王彪
2003-01-01
The coupling feature of transversely isotropic magnetoelectroelastic solids aregoverned by a system of five partial differential equations with respect to the elasticdisplacerments, the electric potential and the magnetic potential. Based on the potentialtheory, the coupled equations are reduced to the five uncoupled generalized Laplaceequations with respect to five potential functions. Further, the elastic fields andelectromagnetic fields are expressed in terms of the potential functions. These expressionsconstruct the general solution of transversely isotropic magnetoelectroelastic media.
Buranasiri, Prathan
2005-04-01
Using barium titanate as the photorefractive material, we demonstrate phase conjugation, beam coupling, higher diffraction order generation. At small incident angles less than 0.015 radian, both codirectional isotropic self-diffraction (CODIS) and contradirectional isotropic self-diffraction (CONDIS) are generated simultaneously. At bigger incident angles approximately more than 0.2094 radian, only codirectional anisotropic-self diffraction (CODAS) are generated. On going imaging correlation is also showing.
High-throughput in-volume processing in glass with isotropic spatial resolutions in three dimensions
Tan, Yuanxin; Chu, Wei; Liao, Yang; Qiao, Lingling; Cheng, Ya
2016-01-01
We report on fabrication of three dimensional (3D) microstructures in glass with isotropic spatial resolutions. To achieve high throughput fabrication, we expand the focal spot size with a low-numerical-aperture lens, which naturally results in a degraded axial resolution. We solve the problem with simultaneous spatial temporal focusing which leads to an isotropic laser-affected volume with a spatial resolution of ~100 micron.
Institute of Scientific and Technical Information of China (English)
WANG Xiao-Ou; GONG Li-Jing; LI Chun-Fei
2008-01-01
@@ Optical rectification (OR) effect in the isotropic thin film consisting of chiral molecules with a tripod-like structure is investigated.The expressions of static-electric polarization in the isotropic chiral thin films and the relations between the OR and microscopic parameters of chiral medium are obtaineel by theoretical derivation,Furthermore,the relations of static electric polarization with the wavelength of incident light and parameters of chiral molecules are simulated numerically.
A new approach to design of quasi-isotropic antenna systems for satellite applications
DEFF Research Database (Denmark)
Schjær-Jacobsen, Hans; Hansen, J.E.
1976-01-01
The new approach considered takes into account the maximum error of the quasi-isotropic radiation pattern relative to the ideal pattern. A design example involving a spherical satellite with quarter wave monopoles is used to demonstrate the effectiveness of the new approach. An investigation...... is conducted concerning the minimax optimization of power radiation patterns. It is shown that the minimax objective represents a useful alternative to the isotropy concept in the design of quasi-isotropic antenna systems for satellite applications....
A new isotropic cell for studying the thermo-mechanical behavior of unsaturated expansive clays
Tang, Anh-Minh; Barnel, Nathalie
2007-01-01
This paper presents a new suction-temperature controlled isotropic cell that can be used to study the thermo-mechanical behavior of unsaturated expansive clays. The vapor equilibrium technique is used to control the soil suction; the temperature of the cell is controlled using a thermostat bath. The isotropic pressure is applied using a volume/pressure controller that is also used to monitor the volume change of soil specimen. Preliminary experimental results showed good performance of the cell.
Bianchi Type-Ⅴ Bulk Viscous Barotropic Fluid Cosmological Model with Variable G and A
Institute of Scientific and Technical Information of China (English)
Raj Bali; Seema Tinker
2008-01-01
@@ We investigate the Bianehi type-Ⅴ bulk viscous barotropic fluid cosmological model with variable gravitational constant G and the cosmological constant A, assuming the condition on metric potential as A/A=B/B=C/C=m/ln, where A, B, and C are functions of time t, while m and n are constants. To obtain the deterministic model, we also assume the relations P= p-3ηH, p =γρ, η = ηoρs, where p is the isotropic pressure, η the bulk viscosity, 0 ≤γ≤1, H the Hubble constant, ηo and s are constants. Various physical aspects of the model are discussed. The case of n = 1 is also discussed to compare the results with the actual universe.
Bulk Moisture and Salinity Sensor
Nurge, Mark; Monje, Oscar; Prenger, Jessica; Catechis, John
2013-01-01
Measurement and feedback control of nutrient solutions in plant root zones is critical to the development of healthy plants in both terrestrial and reduced-gravity environments. In addition to the water content, the amount of fertilizer in the nutrient solution is important to plant health. This typically requires a separate set of sensors to accomplish. A combination bulk moisture and salinity sensor has been designed, built, and tested with different nutrient solutions in several substrates. The substrates include glass beads, a clay-like substrate, and a nutrient-enriched substrate with the presence of plant roots. By measuring two key parameters, the sensor is able to monitor both the volumetric water content and salinity of the nutrient solution in bulk media. Many commercially available moisture sensors are point sensors, making localized measurements over a small volume at the point of insertion. Consequently, they are more prone to suffer from interferences with air bubbles, contact area of media, and root growth. This makes it difficult to get an accurate representation of true moisture content and distribution in the bulk media. Additionally, a network of point sensors is required, increasing the cabling, data acquisition, and calibration requirements. measure the dielectric properties of a material in the annular space of the vessel. Because the pore water in the media often has high salinity, a method to measure the media moisture content and salinity simultaneously was devised. Characterization of the frequency response for capacitance and conductance across the electrodes was completed for 2-mm glass bead media, 1- to 2-mm Turface (a clay like media), and 1- to 2-mm fertilized Turface with the presence of root mass. These measurements were then used to find empirical relationships among capacitance (C), the dissipation factor (D), the volumetric water content, and the pore water salinity.
Toughness of Bulk Metallic Glasses
Directory of Open Access Journals (Sweden)
Shantanu V. Madge
2015-07-01
Full Text Available Bulk metallic glasses (BMGs have desirable properties like high strength and low modulus, but their toughness can show much variation, depending on the kind of test as well as alloy chemistry. This article reviews the type of toughness tests commonly performed and the factors influencing the data obtained. It appears that even the less-tough metallic glasses are tougher than oxide glasses. The current theories describing the links between toughness and material parameters, including elastic constants and alloy chemistry (ordering in the glass, are discussed. Based on the current literature, a few important issues for further work are identified.
Generalized Analytical Solutions for Nonlinear Positive-Negative Index Couplers
Directory of Open Access Journals (Sweden)
Zh. Kudyshev
2012-01-01
Full Text Available We find and analyze a generalized analytical solution for nonlinear wave propagation in waveguide couplers with opposite signs of the linear refractive index, nonzero phase mismatch between the channels, and arbitrary nonlinear coefficients.
Three-Dimensional Approaches to Assembling Negative Index Metamedia
2012-04-02
California, the IPO Distinguished Inventor (1998), the 1998 Thomas Alva Edison Award for innovation in emerging technology, the 1999 Materials Research...Near-field focusing plates and their design,” IEEE Trans. Antennas Propag. 56. 3159-3165 (2008). [5] A. Grbic, R. Merlin, E. M. Thomas and M. F...assembled InAs quantum dots on GaAs," Appl. Phys. Lett. 98, 021903 (2011). 72. A. Grbic, R. Merlin, E. M. Thomas and M. F. Imani, "Near-Field Plates
Self-Assembled Soft Optical Negative Index Materials
2008-08-05
Nanorods by Lyotropic Chromonic Materials’, Langmuir, 24 (2008), 13833-37. [15]. A. B. Golovin , and O. D. Lavrentovich, ’Electrically...Reconfigurable Optical Metamaterial Based on Colloidal Dispersion of Metal Nanorods in Dielectric Fluid’, Applied Physics Letters, 95 (2009) [16]. A. B. Golovin ...of Metal Nano-Rods in Dielectric Fluids’, Liquid Crystals Xiv, 7775 (2010) [17]. A. B. Golovin , J. Xiang, H. S. Park, L. Tortora, Y. A. Nastishin
Compact wavelength demultiplexing using focusing negative index photonic crystal superprisms.
Momeni, Babak; Huang, Jiandong; Soltani, Mohammad; Askari, Murtaza; Mohammadi, Saeed; Rakhshandehroo, Mohammad; Adibi, Ali
2006-03-20
Here, we demonstrate a compact photonic crystal wavelength demultiplexing device based on a diffraction compensation scheme with two orders of magnitude performance improvement over the conventional superprism structures reported to date. We show that the main problems of the conventional superprism-based wavelength demultiplexing devices can be overcome by combining the superprism effect with two other main properties of photonic crystals, i.e., negative diffraction and negative refraction. Here, a 4-channel optical demultiplexer with a channel spacing of 8 nm and cross-talk level of better than -6.5 dB is experimentally demonstrated using a 4500 microm(2) photonic crystal region.
Handling of bulk solids theory and practice
Shamlou, P A
1990-01-01
Handling of Bulk Solids provides a comprehensive discussion of the field of solids flow and handling in the process industries. Presentation of the subject follows classical lines of separate discussions for each topic, so each chapter is self-contained and can be read on its own. Topics discussed include bulk solids flow and handling properties; pressure profiles in bulk solids storage vessels; the design of storage silos for reliable discharge of bulk materials; gravity flow of particulate materials from storage vessels; pneumatic transportation of bulk solids; and the hazards of solid-mater
Energy Technology Data Exchange (ETDEWEB)
Lee, Yoon Hee; Cho, Bum Hee; Cho, Nam Zin [Dept. of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)
2016-06-15
As a type of accident-tolerant fuel, fully ceramic microencapsulated (FCM) fuel was proposed after the Fukushima accident in Japan. The FCM fuel consists of tristructural isotropic particles randomly dispersed in a silicon carbide (SiC) matrix. For a fuel element with such high heterogeneity, we have proposed a two-temperature homogenized model using the particle transport Monte Carlo method for the heat conduction problem. This model distinguishes between fuel-kernel and SiC matrix temperatures. Moreover, the obtained temperature profiles are more realistic than those of other models. In Part I of the paper, homogenized parameters for the FCM fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure are obtained by (1) matching steady-state analytic solutions of the model with the results of particle transport Monte Carlo method for heat conduction problems, and (2) preserving total enthalpies in fuel kernels and SiC matrix. The homogenized parameters have two desirable properties: (1) they are insensitive to boundary conditions such as coolant bulk temperatures and thickness of cladding, and (2) they are independent of operating power density. By performing the Monte Carlo calculations with the temperature-dependent thermal properties of the constituent materials of the FCM fuel, temperature-dependent homogenized parameters are obtained.
Probing bulk flow with nearby SNe Ia data
Appleby, Stephen; Johnson, Andrew
2014-01-01
We test the isotropy of the local Universe using low redshift Supernova data from various catalogs and the non-parametric method of smoothed residuals. Using a recently developed catalog which combines Supernova data from various surveys, we show that the isotropic hypothesis of a Universe with zero velocity perturbation can be rejected with moderate significance, with $p$-value $\\sim 0.07$ out to redshift $z < 0.045$. We estimate the direction of maximal anisotropy on the sky for various pre-existing catalogs and show that it remains relatively unaffected by the light curve fitting procedure. However the recovered direction is biased by the underlying distribution of data points on the sky. We estimate both the uncertainty and bias in the direction by creating mock data containing a randomly oriented bulk flow and using our method to reconstruct its direction. We conclude that the inhomogeneous nature of the data introduces a directional bias in galactic latitude of approximately $|\\Delta b_{\\rm max}| \\si...
Nanofluidics, from bulk to interfaces.
Bocquet, Lydéric; Charlaix, Elisabeth
2010-03-01
Nanofluidics has emerged recently in the footsteps of microfluidics, following the quest for scale reduction inherent to nanotechnologies. By definition, nanofluidics explores transport phenomena of fluids at nanometer scales. Why is the nanometer scale specific? What fluid properties are probed at nanometric scales? In other words, why does 'nanofluidics' deserve its own brand name? In this critical review, we will explore the vast manifold of length scales emerging for fluid behavior at the nanoscale, as well as the associated mechanisms and corresponding applications. We will in particular explore the interplay between bulk and interface phenomena. The limit of validity of the continuum approaches will be discussed, as well as the numerous surface induced effects occurring at these scales, from hydrodynamic slippage to the various electro-kinetic phenomena originating from the couplings between hydrodynamics and electrostatics. An enlightening analogy between ion transport in nanochannels and transport in doped semi-conductors will be discussed (156 references).
de Brito, K P S
2016-01-01
Spinor fields on 5-dimensional Lorentzian manifolds are classified, according to the geometric Fierz identities that involve their bilinear covariants. Based upon this classification that generalises the celebrated 4-dimensional Lounesto classification of spinor fields, new non-trivial classes of 5-dimensional spinor fields are, hence, found, with important potential applications regarding bulk fermions and their subsequent localisation on brane-worlds. In addition, quaternionic bilinear covariants are used to derive the quaternionic spin density, through the truncated exterior bundle. In order to accomplish a realisation of these new spinors, a Killing vector field is constructed on the horizon of 5-dimensional Kerr black holes. This Killing vector field is shown to reach the time-like Killing vector field at the spatial infinity, through a current 1-form density, constructed with the derived new spinor fields. The current density is, moreover, expressed as the f\\"unfbein components, assuming a condensed for...
de Brito, K. P. S.; da Rocha, Roldão
2016-10-01
The spinor fields on 5-dimensional Lorentzian manifolds are classified according to the geometric Fierz identities, which involve their bilinear covariants. Based upon this classification, which generalises the celebrated 4-dimensional Lounesto classification of spinor fields, new non-trivial classes of 5-dimensional spinor fields are hence found, with important potential applications regarding bulk fermions and their subsequent localisation on brane-worlds. In addition, quaternionic bilinear covariants are used to derive the quaternionic spin density through the truncated exterior bundle. In order to accomplish the realisation of these new spinors, a Killing vector field is constructed on the horizon of a 5-dimensional Kerr black hole. This Killing vector field is shown to reach the time-like Killing vector field at spatial infinity through a current 1-form density, constructed with the new derived spinor fields. The current density is, moreover, expressed as the fünfbein component, assuming a condensed form.
Carroll, Jonathan J.; Frank, Adam; Blackman, Eric G.
2010-10-01
Feedback from protostellar outflows can influence the nature of turbulence in star-forming regions even if they are not the primary source of velocity dispersion for all scales of molecular clouds. For the rate and power expected in star-forming regions, we previously (Carroll et al.) demonstrated that outflows could drive supersonic turbulence at levels consistent with the scaling relations from Matzner although with a steeper velocity power spectrum than expected for an isotropically driven supersonic turbulent cascade. Here, we perform higher resolution simulations and combine simulations of outflow driven turbulence with those of isotropically forced turbulence. We find that the presence of outflows within an ambient isotropically driven turbulent environment produces a knee in the velocity power spectrum at the outflow scale and a steeper slope at sub-outflow scales than for a purely isotropically forced case. We also find that the presence of outflows flattens the density spectrum at large scales effectively reducing the formation of large-scale turbulent density structures. These effects are qualitatively independent of resolution. We have also carried out Principal Component Analysis (PCA) for synthetic data from our simulations. We find that PCA as a tool for identifying the driving scale of turbulence has a misleading bias toward low amplitude large-scale velocity structures even when they are not necessarily the dominant energy containing scales. This bias is absent for isotropically forced turbulence but manifests strongly for collimated outflow driven turbulence.
High-Oriented Thermoelectric Nano-Bulk Fabricated from Thermoelectric Ink
Koyano, M.; Mizutani, S.; Hayashi, Y.; Nishino, S.; Miyata, M.; Tanaka, T.; Fukuda, K.
2016-10-01
Printing technology is expected to provide innovative and environmentally friendly processes for thermoelectric (TE) module fabrication. As described in this paper, we propose an orientation control process using plastic deformation at high temperatures and present high-oriented TE nano-bulks fabricated from bismuth telluride (Bi-Te) TE inks using this process. In the case of n-type Bi-Te, surface x-ray diffraction reveals that crystalline grains in the plastic-deformed nano-bulk demonstrate a c-plane orientation parallel to the pressed face. According to the high orientation, electrical resistivity ρ, thermal conductivity κ, and figure of merit ZT show anisotropic behavior. It is noteworthy that (ZT)// almost reaches unity (ZT)// ˜1 at 340 K, even at low temperatures of the plastic deformation process. In contrast, the ZT of plastic-deformed p-type nano-bulk indicates isotropic behavior. The difference in the process temperature dependence of ZT suggests that n-type and p-type nano-bulk orientation mechanisms mutually differ.
Excitation of surface waves on the interfaces of general bi-isotropic media
Kim, Seulong
2016-01-01
We study theoretically the characteristics of surface waves excited at the interface between a metal and a general bi-isotropic medium, which includes isotropic chiral media and Tellegen media as special cases. We derive an analytical dispersion relation for surface waves, using which we calculate the effective index and the propagation length numerically. We also calculate the absorptance, the cross-polarized reflectance and the spatial distribution of the electromagnetic fields for plane waves incident on a bilayer system consisting of a metal layer and a bi-isotropic layer in the Kretschmann configuration, using the invariant imbedding method. The results obtained using the invariant imbedding method agree with those obtained from the dispersion relation perfectly. In the case of chiral media, the effective index is an increasing function of the chirality index, whereas in Tellegen media, it is a decreasing function of the Tellegen parameter. The propagation length for surface waves in both cases increase ...
Buckling analysis of thick isotropic plates by using exponential shear deformation theory
Directory of Open Access Journals (Sweden)
Sayyad A. S.
2012-12-01
Full Text Available In this paper, an exponential shear deformation theory is presented for the buckling analysis of thick isotropic plates subjected to uniaxial and biaxial in-plane forces. The theory accounts for a parabolic distribution of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. Governing equations and associated boundary conditions of the theory are obtained using the principle of virtual work. The simply supported thick isotropic square plates are considered for the detailed numerical studies. A closed form solutions for buckling analysis of square plates are obtained. Comparison studies are performed to verify the validity of the present results. The effects of aspect ratio on the critical buckling load of isotropic plates is investigated and discussed.
Institute of Scientific and Technical Information of China (English)
LI Xiang-yu; DING Hao-jiang; CHEN Wei-qiu
2006-01-01
This paper considers the pure bending problem of simply supported transversely isotropic circular plates with elastic compliance coefficients being arbitrary functions of the thickness coordinate. First, the partial differential equation, which is satisfied by the stress functions for the axisymmetric deformation problem is derived. Then, stress functions are obtained by proper manipulation. The analytical expressions of axial force, bending moment and displacements are then deduced through integration.And then, stress functions are employed to solve problems of transversely isotropic functionally graded circular plate, with the integral constants completely determined from boundary conditions. An elasticity solution for pure bending problem, which coincides with the available solution when degenerated into the elasticity solutions for homogenous circular plate, is thus obtained.A numerical example is finally presented to show the effect of material inhomogeneity on the elastic field in a simply supported circular plate of transversely isotropic functionally graded material (FGM).
Isotropic negative permeability composite based on Mie resonance of the BST-MgO dielectric medium
Institute of Scientific and Technical Information of China (English)
ZHAO Qian; KANG Lei; DU Bo; ZHAO HongJie; XIE Qin; LI Bo; ZHOU Ji; LI LongTu; MENG YongGang
2008-01-01
Isotropic negative permeability composite, composed of BST-MgO dielectric cubes with high permit-tivity dispersed in the Teflon substrate with low permittivity, was designed and fabricated based on Mie resonance and the effective medium theory. Measurements and simulations showed that the dielectric composite exhibited a strong sub-wavelength magnetic resonance at the first Mie resonance and possessed isotropic negative permeability, which resulted from the displacement current excited in the cubes. The dielectric particle was equivalent to a magnetic dipole at the magnetic resonance, which could be adjusted by the size and permitllvity of the particles. It may provide a convenient method to design isotropic metamaterials and invisible cloak at infrared and visible frequencies.
TORSIONAL VIBRATIONS OF RIGID CIRCULAR PLATE ON TRANSVERSELY ISOTROPIC SATURATED SOIL
Institute of Scientific and Technical Information of China (English)
WU Da-zhi; CAI Yuan-qiang; XU Chang-jie; ZHAN Hong
2006-01-01
An analytical method was presented for the torsional vibrations of a rigid disk resting on transversely isotropic saturated soil. By Hankel transform, the dynamic governing differential equations for transversely isotropic saturated poroelastic medium were solved. Considering the mixed boundary-value conditions, the dual integral equations of torsional vibrations of a rigid circular plate resting on transversely isotropic saturated soil were established. By appropriate transform, the dual integral equations were converted into a Fredholm integral equation of the second kind. Subsequently, the dynamic compliance coefficient, the torsional angular amplitude of the foundation and the contact shear stress were expressed explicitly. Selected examples were presented to analyse the influence of saturated soil's anisotropy on the foundation's vibrations.
Institute of Scientific and Technical Information of China (English)
WUGang; TANGYouxi; LIShaoqian
2004-01-01
A novel deterministic model for downlink Multiple-input multiple-output (MIMO) channel with nonisotropic scattering around Mobile station (MS) is presented. For both Space-time codes (STC) scenario and Downlink beam-forming (DBF) scenario, statistical fading characteristics, including level-crossing rate, average duration of fades, and envelope cross-correlation are investigated in frequency-selective fast fading channels. The impact of non-isotropic scattering on capacity of MIMO channel is also studied. Numerical results show that loss of ergodic capacity caused by non-isotropic scattering almost reach 1bit/Hz/s for a 2×2 MIMO channel and maximum achievable capacity will be degraded mainly by transmit correlation rather than non-isotropic scattering.
Ni, Jincheng; Zhang, Chenchu; Hu, Yanlei; Yang, Liang; Lao, Zhaoxin; Xu, Bing; Li, Jiawen; Wu, Dong; Chu, Jiaru
2016-01-01
Optical vortices, as a kind of structured beam with helical phase wavefronts and doughnut shape intensity distribution, have been used for fabricating chiral structures in metal and spiral patterns in anisotropic polarization-dependent azobenzene polymer. However, in isotropic polymer, the fabricated microstructures are typically confined to non-chiral cylindrical geometry due to two-dimensional doughnut intensity profile of optical vortices. Here we develop a powerful strategy for realizing chiral microstructures in isotropic material by coaxial interference of a vortex beam and a plane wave, which produces three-dimensional (3D) spiral optical fields. This coaxial interference beams are creatively produced by designing the contrivable holograms consisting of azimuthal phase and equiphase loaded on liquid-crystal spatial light modulator. Then, in isotropic polymer, 3D chiral microstructures are achieved under illumination of the coaxial interference femtosecond laser beams with their chirality controlled by ...
Torsional vibration of a pipe pile in transversely isotropic saturated soil
Zheng, Changjie; Hua, Jianmin; Ding, Xuanming
2016-09-01
This study considers the torsional vibration of a pipe pile in a transversely isotropic saturated soil layer. Based on Biot's poroelastic theory and the constitutive relations of the transversely isotropic medium, the dynamic governing equations of the outer and inner transversely isotropic saturated soil layers are derived. The Laplace transform is used to solve the governing equations of the outer and inner soil layers. The dynamic torsional response of the pipe pile in the frequency domain is derived utilizing 1D elastic theory and the continuous conditions at the interfaces between the pipe pile and the soils. The time domain solution is obtained by Fourier inverse transform. A parametric study is conducted to demonstrate the influence of the anisotropies of the outer and inner soil on the torsional dynamic response of the pipe pile.
Institute of Scientific and Technical Information of China (English)
Ren Chun-Yu; Xiang Zhi-Hai; Cen Zhang-Zhi
2011-01-01
We present a method for designing an open acoustic cloak that can conceal a perturbation on flat ground and simultaneously meet the requirement of communication and matter interchange between the inside and the outside of the cloak.This cloak can be constructed with a multilayered structure and each layer is an isotropic and homogeneous medium.The design scheme consists of two steps:firstly,we apply a conformal coordinate transformation to obtain a quasi-perfect cloak with heterogeneous isotropic material; then,according to the profile of the material distribution,we degenerate this cloak into a multilayered-homogeneous isotropic cloak,which has two open windows with negligible disturbance on its invisibility performance.This may greatly facilitate the fabrication and enhance the applicability of such a carpet-type cloak.
Neff, Patrizio; Ghiba, Ionel-Dumitrel
2016-03-01
We investigate an immediate application in finite strain multiplicative plasticity of the family of isotropic volumetric-isochoric decoupled strain energies F mapsto W_eH(F):= widehat{W}_eH(U) := μ/k e^{k | dev_n log {U}|^2}+κ/2 {widehat{k}} e^{widehat{k} [ tr(log U)]^2}&quad if& det F > 0, + ∞ & quad if & det F ≤ 0, based on the Hencky-logarithmic (true, natural) strain tensor {log U} . Here, {μ > 0} is the infinitesimal shear modulus, {κ=2 μ+3λ/3 > 0} is the infinitesimal bulk modulus with λ the first Lamé constant, {k,widehat{k}} are additional dimensionless material parameters, {F=nabla \\varphi} is the gradient of deformation, {U=√{F^T F}} is the right stretch tensor, and dev n {log {U} =log {U}-1/n tr(log {U})\\cdot{1}} is the deviatoric part of the strain tensor {log U} . Based on the multiplicative decomposition {F=F_e F_p} , we couple these energies with some isotropic elasto-plastic flow rules {F_p {dt}/[F_p^{-1}]in-partial χ(dev_3 Σe)} defined in the plastic distortion F p , where {partial χ} is the subdifferential of the indicator function {χ} of the convex elastic domain {E_e({Σe},1/3{σ}_{y}^2)} in the mixed-variant {Σe} -stress space, {Σe=F_e^T D_{F_e}W_iso(F_e)} , and {W_iso(F_e)} represents the isochoric part of the energy. While {W_eH} may loose ellipticity, we show that loss of ellipticity is effectively prevented by the coupling with plasticity, since the ellipticity domain of {W_eH} on the one hand and the elastic domain in {Σe} -stress space on the other hand are closely related. Thus, the new formulation remains elliptic in elastic unloading at any given plastic predeformation. In addition, in this domain, the true stress-true strain relation remains monotone, as observed in experiments.
Preparation and investigation of bulk and thin film samples of strontium ferrite
Directory of Open Access Journals (Sweden)
A Poorbafrani
2008-07-01
Full Text Available In this article, bulk and thin film samples of strontium ferrite have been studied. Due to the high electrical resistivity in strontium ferrite, energy loss due to eddy currents reduces and because of this, it can be used in high frequency magnetic circuits. On the other hand, strontium ferrite has attracted much attention as a permanent magnet. At first, we study the preparation process of bulk samples of strontium ferrite by a solid state reaction technique. In preparation of samples, to optimize the magnetic properties, we have used the stoichiometry factor (n = Fe2O3 / SrO of 5.25. In addition, we have used additives such as CaO and SiO2 to control grain growth. The samples have been prepared in two series: Isotropic and Anisotropic. For preparation of anisotropic samples, the magnetic field of 1T has been used for orientation of the grains during the press. Then, X-ray diffraction, Scanning Electron Microscopy (SEM, EDAX analysis and Magnetometer, was used for analyzing and comparing of structural and magnetic properties of isotropic and anisotropic samples. The results indicate that, due to the applied magnetic field, the structural and Magnetic properties of anisotropic samples improved efficiently because of the orientation of the grains during the press. In the next stage, we used bulk samples to prepare strontium ferrite thin films by Pulsed Laser Deposition technique (PLD. The Si (111 substrate has been used to prepare the thin films. Then we have studied the microstructure of thin films by X-ray diffraction, SEM and EDAX analysis. These studies on different samples show that for the preparation of crystalline phase of strontium ferrite thin films, the substrate temperature must be higher than 800˚C. The optimum conditions for preparation of strontium, ferrite thin films have been achieved on the substrate temperature of 840˚C and oxygen pressure of 75 mtorr.
Completeness of General Solutions to Axisymmetric Problems of Transversely Isotropic Body
Institute of Scientific and Technical Information of China (English)
王炜; 徐新生; 王敏中
1994-01-01
In this paper a kind of problems,which are a little wider than the axisymmetric problems of a transversely isotropic elastic body,are considered in a rectangular coordinates system.Two new general solutions of the axisymmetric problems of a transversely isotropic body are concisely obtained in a cylindrical coordinates system.Their completeness is also proved.It is worth while pointing out thai whether the meridional half-section is simply connected or multiply connected,both the new general solutions are single-valued.Using these results eight special general solutions are derived,including some known famous solutions.
Isotropic proton-detected local-field nuclear magnetic resonancein solids
Energy Technology Data Exchange (ETDEWEB)
Havlin, Robert H.; Walls, Jamie D.; Pines, Alexander
2004-08-04
A new nuclear magnetic resonance (NMR) method is presented which produces linear, isotropic proton-detected local-field spectra for InS spin systems in powdered samples. The method, HETeronuclear Isotropic Evolution (HETIE), refocuses the anisotropic portion of the heteronuclear dipolar coupling frequencies by evolving the system under a series of specially designed Hamiltonians and evolution pathways. The theory behind HETIE is represented along with experimental studies conducted on a powdered sample of ferrocene, demonstrating the methodology outlined in this paper. Applications of HETIE for structural determination in solid-state NMR are discussed.
CIRCULAR CRACK IN A TRANSVERSELY ISOTROPIC PIEZOELECTRIC SPACE UNDER POINT FORCES AND POINT CHARGES
Institute of Scientific and Technical Information of China (English)
侯鹏飞; 丁皓江; 关富玲
2002-01-01
In this paper, two kinds of circular crack including external circular crack and penny-shaped crack in a transversely isotropic piezoelectric space are considered. Firstly, we obtain the solution to the problem of an external circular crack in a transversely isotropic piezoelectric space subjected to antisymmetric normal point forces and point charges. Based on this, the solution of one-sided loading of an external circular crack is constructed. Secondly, the real shape of an external circular crack and the opening displacement of a penny-shaped crack under an arbitrary point force and point charge are further obtained. At last, the results are presented in a graphical form.
Magnetic field sensor for isotropically sensing an incident magnetic field in a sensor plane
Pant, Bharat B. (Inventor); Wan, Hong (Inventor)
2001-01-01
A magnetic field sensor that isotropically senses an incident magnetic field. This is preferably accomplished by providing a magnetic field sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magnetic field. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magnetic field sensor device provides an output that is relatively independent of the direction of the incident magnetic field in the sensor plane.
How to estimate isotropic distributions and mean values in crystalline solids
Kontrym-Sznajd, G.; Dugdale, S. B.
2015-11-01
The concept of special directions in the Brillouin zone and the applicability of Houston’s formula (or its extended versions) to both theoretical and experimental investigations are discussed. We propose some expressions to describe the isotropic component in systems having both cubic and non-cubic symmetry. The results presented have implications for both experimentalists who want to obtain average properties from a small number of measurements on single crystals, and for theoretical calculations which are to be compared with isotropic experimental measurements, for example coming from investigations of polycrystalline or powder samples. As George Orwell might have put it: all directions are equal, but some directions are more equal than others.
Institute of Scientific and Technical Information of China (English)
刘颖; 刘凯欣
2004-01-01
According to generalized characteristic theory,a characteristic analysis for stress wave propagation in transversely isotropic fluid-saturated porous media was performed.The characteristic differential equations and compatibility relations along bicharacteristics were deduced and the analytical expressions for wave surfaces were obtained.The characteristic and shapes of the velocity surfaces and wave surfaces in the transversely isotropic fluid-saturated porous media were discussed in detail.The results also show that the characteristic equations for stress waves in pure solids are particular cases of the characteristic equations for fluid-saturated porous media.
A Simple Free Energy for the Isotropic-Nematic Phase Transition of Rods
Directory of Open Access Journals (Sweden)
Remco Tuinier
2016-01-01
Full Text Available A free energy expression is proposed that describes the isotropic-nematic binodal concentrations of hard rods. A simple analytical form for this free energy was yet only available using a Gaussian trial function for the orientation distribution function (ODF, leading, however, to a significant deviation of the predicted binodals. The new free energy proposed here is based upon a rationalized correction to the orientational and packing entropies when using the Gaussian ODF. In combination with Parsons-Lee theory or scaled particle theory, it enables describing the isotropic-nematic phase coexistence concentrations of rods accurately using the simple Gaussian ODF for a wide range of aspect ratios.
How to estimate isotropic distributions and mean values in crystalline solids.
Kontrym-Sznajd, G; Dugdale, S B
2015-11-04
The concept of special directions in the Brillouin zone and the applicability of Houston's formula (or its extended versions) to both theoretical and experimental investigations are discussed. We propose some expressions to describe the isotropic component in systems having both cubic and non-cubic symmetry. The results presented have implications for both experimentalists who want to obtain average properties from a small number of measurements on single crystals, and for theoretical calculations which are to be compared with isotropic experimental measurements, for example coming from investigations of polycrystalline or powder samples. As George Orwell might have put it: all directions are equal, but some directions are more equal than others.
Zhang, Zhizeng; Zhao, Zhao; Li, Yongtao
2016-06-01
This paper attempts to verify the correctness of the analytical displacement solution in transversely isotropic rock mass, and to determine the scope of its application. The analytical displacement solution of a circular tunnel in transversely isotropic rock mass was derived firstly. The analytical solution was compared with the numerical solution, which was carried out by FLAC3D software. The results show that the expression of the analytical displacement solution is correct, and the allowable engineering range is that the dip angle is less than 15 degrees.
Coupling brane fields to bulk supergravity
Energy Technology Data Exchange (ETDEWEB)
Parameswaran, Susha L. [Uppsala Univ. (Sweden). Theoretical Physics; Schmidt, Jonas [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2010-12-15
In this note we present a simple, general prescription for coupling brane localized fields to bulk supergravity. We illustrate the procedure by considering 6D N=2 bulk supergravity on a 2D orbifold, with brane fields localized at the fixed points. The resulting action enjoys the full 6D N=2 symmetries in the bulk, and those of 4D N=1 supergravity at the brane positions. (orig.)
Relative entropy equals bulk relative entropy
Jafferis, Daniel L; Maldacena, Juan; Suh, S Josephine
2015-01-01
We consider the gravity dual of the modular Hamiltonian associated to a general subregion of a boundary theory. We use it to argue that the relative entropy of nearby states is given by the relative entropy in the bulk, to leading order in the bulk gravitational coupling. We also argue that the boundary modular flow is dual to the bulk modular flow in the entanglement wedge, with implications for entanglement wedge reconstruction.
33 CFR 127.313 - Bulk storage.
2010-07-01
...) WATERFRONT FACILITIES WATERFRONT FACILITIES HANDLING LIQUEFIED NATURAL GAS AND LIQUEFIED HAZARDOUS GAS Waterfront Facilities Handling Liquefied Natural Gas Operations § 127.313 Bulk storage. (a) The...
Applications of bulk high-temperature superconductors
Hull, J. R.
The development of high-temperature superconductors (HTS's) can be broadly generalized into thin-film electronics, wire applications, and bulk applications. We consider bulk HTS's to include sintered or crystallized forms that do not take the geometry of filaments or tapes, and we discuss major applications for these materials. For the most part applications may be realized with the HTS's cooled to 77 K, and the properties of the bulk HTS's are often already sufficient for commercial use. A non-exhaustive list of applications for bulk HTS's includes trapped field magnets, hysteresis motors, magnetic shielding, current leads, and magnetic bearings. These applications are briefly discussed in this paper.
Fresnel Coefficients of Forward and Backward Waves Refracting at the Interface of Isotropic Media
Fisanov, V. V.
2017-01-01
The Fresnel coefficients are derived for cross- and co-polarization states of plane electromagnetic wave incident at the interface between two isotropic media. The media can support forward or backward normal waves. Based on introduction of wave type identifiers, without application of the notion of the negative refractive index, phenomena of positive and negative refractions are considered in the general case.
Bringmann, T.; Calore, F.; Di Mauro, M.; Donato, F.
2014-01-01
The nature of the isotropic γ-ray background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi γ-ray space telescope (Fermi) remains partially unexplained. Non-negligible contributions may originate from extragalactic populations of unresolved sources such as blazars, star-forming galax
Quasilocal Conserved Operators in the Isotropic Heisenberg Spin-1/2 Chain.
Ilievski, Enej; Medenjak, Marko; Prosen, Tomaž
2015-09-18
Composing higher auxiliary-spin transfer matrices and their derivatives, we construct a family of quasilocal conserved operators of isotropic Heisenberg spin-1/2 chain and rigorously establish their linear independence from the well-known set of local conserved charges.
Quasilocal Conserved Operators in the Isotropic Heisenberg Spin-1/2 Chain
Ilievski, E.; Medenjak, M.; Prosen, T.
2015-01-01
Composing higher auxiliary-spin transfer matrices and their derivatives, we construct a family of quasilocal conserved operators of isotropic Heisenberg spin-1/2 chain and rigorously establish their linear independence from the well-known set of local conserved charges.
The 3-D non-axisymmetrical Lamb's problem in transversely isotropic saturated poroelastic media
Institute of Scientific and Technical Information of China (English)
HUANG; Yi; WANG; Xiaogang
2004-01-01
Based on Biot's theory on fluid-saturated porous media, the displacement functions are adopted to convert the 3-D Biot's wave equations in the cylindrical coordinate for transversely isotropic saturated poroelastic media into two--one 6-order and one 2-order--uncoupling differential governing equations. Then, the differential equations are solved by the Fourier expanding and Hankel integral transform method.Integral solutions of soil skeleton displacements and pore pressure as well as the total stresses for poroelastic media are obtained. Furthermore, the systematic study on Lamb's problems for the transversely isotropic saturated poroelastic media is performed. Integral solutions for surface radial, vertical and circumferential displacements are obtained in both cases of drained surface and undrained surface under the vertical and horizontal harmonic excitation force. In the end of this paper, the numerical examples are presented.The calculation results indicate that the difference between the model of isotropic saturated poroelastic media and that of transversely isotropic saturated poroelastic media is obvious.
LOCALIZED BUCKLING OF THE SEMI-INFINITE ISOTROPIC PLATE NEAR ELASTICALLY FASTENED EDGE
Directory of Open Access Journals (Sweden)
Sharifian R.
2012-06-01
Full Text Available Localized buckling of a semi-infinite isotropic plate near elastically fastened edge has been investigated. Mathematical model is of structure is provided and characteristic equation of the problem is derived. The existence conditions of localized buckling are derived analytically. For the cases when localized buckling exists numerical solutions and plots for the critical loads are provided.
Multiaxial yield surface of transversely isotropic foams: Part I-Modeling
Ayyagari, Ravi Sastri; Vural, Murat
2015-01-01
A new yield criterion is proposed for transversely isotropic solid foams. Its derivation is based on the hypothesis that the yielding in foams is driven by the total strain energy density, rather than a completely phenomenological approach. This allows defining the yield surface with minimal number of parameters and does not require complex experiments. The general framework used leads to the introduction of new scalar measures of stress and strain (characteristic stress and strain) for transversely isotropic foams. Furthermore, the central hypothesis that the total strain energy density drives yielding in foams ascribes to the characteristic stress an analogous role of von Mises stress in metal plasticity. Unlike the overwhelming majority of yield models in literature the proposed model recognizes the tension-compression difference in yield behavior of foams through a linear mean stress term. Predictions of the proposed yield model are in excellent agreement with the results of uniaxial, biaxial and triaxial FE analyses implemented on both isotropic and transversely isotropic Kelvin foam models.
Isotropic averaging for cell-dynamical-system simulation of spinodal decomposition
Indian Academy of Sciences (India)
Anand Kumar
2003-07-01
Formulae have been developed for the isotropic averagings in two and three dimensions. Averagings are employed in the cell-dynamical-system simulation of spinodal decomposition for inter-cell coupling. The averagings used in earlier works on spinodal decomposition have been discussed.
European Pulsar Timing Array limits on an isotropic stochastic gravitational-wave background
Lentati, L.; Taylor, S.R.; Mingarelli, C.M.F.; Sesana, A.; Sanidas, S.A.; Vecchio, A.; Caballero, R.N.; Lee, K.J.; van Haasteren, R.; Babak, S.; Bassa, C.G.; Brem, P.; Burgay, M.; Champion, D.J.; Cognard, I.; Desvignes, G.; Gair, J.R.; Guillemot, L.; Hessels, J.W.T.; Janssen, G.H.; Karuppusamy, R.; Kramer, M.; Lassus, A.; Lazarus, P.; Liu, K.; Osłowski, S.; Perrodin, D.; Petiteau, A.; Possenti, A.; Purver, M.B.; Rosado, P.A.; Smits, R.; Stappers, B.; Theureau, G.; Tiburzi, C.; Verbiest, J.P.W.
2015-01-01
We present new limits on an isotropic stochastic gravitational-wave background (GWB) using a six pulsar data set spanning 18 yr of observations from the 2015 European Pulsar Timing Array data release. Performing a Bayesian analysis, we fit simultaneously for the intrinsic noise parameters for each p
Dielectric spectroscopy of isotropic liquids and liquid crystal phases with dispersed graphene oxide
Al-Zangana, Shakhawan; Iliut, Maria; Boran, Gökçen; Turner, Michael; Vijayaraghavan, Aravind; Dierking, Ingo
2016-08-01
Graphene oxide (GO) flakes of different sizes were prepared and dispersed in isotropic and nematic (anisotropic) fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature (25-60 oC) and frequency range (100 Hz-2 MHz). The mixtures containing GO flakes exhibited varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. Relaxation frequencies of the GO doped isotropic media, such as isopropanol IPA, were observed to be much lower than the GO doped thermotropic nematic medium 5CB. It is anticipated that the slow relaxation frequencies (~10 kHz) could be resulting from the relaxation modes of the GO flakes while the fast relaxation frequencies (~100 kHz) could indicate strongly slowed down molecular modes of the nematogenic molecules, which are anchored to the GO flakes via dispersion interactions. The relaxation frequencies decreased as the size of the GO flakes in the isotropic solvent was increased. Polarizing microscopy showed that GO flakes with a mean diameter of 10 μm, dispersed in water, formed a lyotropic nematic liquid crystal phase. This lyotropic nematic exhibited the slowest dielectric relaxation process, with relaxation frequencies in the order of 2 kHz, as compared to the GO-isotropic suspension and the GO-doped 5CB.
A new isotropic vector Preisach-type model of hysteresis and its identification
Energy Technology Data Exchange (ETDEWEB)
Mayergoyz, I.D.; Adly, A.A. (Univ. of Maryland, College Park, MD (United States))
1993-11-01
A new vector isotropic Preisach-type model of hysteresis is introduced and the identification problem for this model is posed. A mathematical machinery for the solution of the identification problem by using ''scalar'' and ''rotational'' experimental data is presented.
Limit on an Isotropic Diffuse Gamma-Ray Population with HAWC
,
2015-01-01
Data from 105 days from the High Altitude Water Cherenkov Observatory (HAWC) have been used to place a new limit on an isotropic diffuse gamma-ray population above 10 TeV. High- energy isotropic diffuse gamma-ray emission is produced by unresolved extragalactic objects such as active galactic nuclei, with potential contributions from interactions of high-energy cosmic rays with the inter-Galactic medium, or dark matter annihilation. Isotropic diffuse gamma-ray emission has been observed up to nearly 1 TeV. Above this energy, only upper limits have been reported. Observations or limits of the isotropic photon population above these energies are very sensitive to local astrophysical particle production. Of particular note, we expect a photon population to accompany the TeV-PeV astrophysical neutrino detection seen in the IceCube instrument. Observations or limits of a photon population above this energy can point to the origin of these neutrinos, indicating whether they are within the gamma-ray horizon or not. ...
Energy Technology Data Exchange (ETDEWEB)
Wilczek, M; Friedrich, R [Institute for Theoretical Physics, University of Muenster, Wilhelm-Klemm-Str. 9, 48149 Muenster (Germany); Kadoch, B [Aix-Marseille Universite and M2P2-CNRS Ecole Centrale de Marseille, 38 Rue Joliot-Curie, 13451 Marseille Cedex 20 (France); Schneider, K [M2P2-CNRS and CMI, Universite de Provence, 39 Rue Joliot-Curie, 13453 Marseille Cedex 13 (France); Farge, M, E-mail: mwilczek@uni-muenster.de [LMD-CNRS, Ecole Normale Superieure, 24 Rue Lhomond, 75231 Paris Cedex 5 (France)
2011-12-22
We study the conditional balance of vortex stretching and vorticity diffusion of fully developed three-dimensional homogeneous isotropic turbulence with respect to coherent and incoherent flow contributions. This decomposition is achieved by the Coherent Vorticity Extraction based on orthogonal wavelets applied to DNS data, which yields insights into the influence of the different contributions as well as their interaction.
Sridhar, A.; Perinchery, S.M.; Smits, E.C.P.; Mandamparambil, R.; Brand, J. van den
2015-01-01
The reliability of a commercially available isotropic conductive adhesive (ICA) deposited via laser induced forward transfer (LIFT) printing is reported. ICAs are particularly important for surfacemount device (SMD) integration onto low-cost, large-area system-in-foil (SiF) applications such as radi
Multiscale modeling of residual stresses in isotropic conductive adhesives with nano particles
Erinc, M.; Dijk, M. van; Kouznetsova, V.H.
2012-01-01
Isotropic Conductive Adhesives (ICAs) are promising candidates for low temperature joining technologies in microelectronics, enabling ultra-fine pitch sizes. Especially in solar and automotive applications, long-term reliability is a prerequisite in new generation electronics. It is essential that r
The isotropic-nematic phase transition of tangent hard-sphere chain fluids—Pure components
Van Westen, T.; Oyarzun, B.; Vlugt, T.J.H.; Gross, J.
2013-01-01
An extension of Onsager's second virial theory is developed to describe the isotropic-nematic phase transition of tangent hard-sphere chain fluids. Flexibility is introduced by the rod-coil model. The effect of chain-flexibility on the second virial coefficient is described using an accurate, analyt
Energy Technology Data Exchange (ETDEWEB)
Mota, R.D. [Unidad Profesional Interdisciplinaria de Ingenieria y Tecnologias Avanzadas, Mexico DF (Mexico)]. E-mail: mota@gina.esfm.ipn.mx; ravelo@esfm.ipn.mx; Granados, V.D.; Queijeiro, A.; Garcia, J. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, Mexico DF (Mexico)
2002-03-29
For the quantum two-dimensional isotropic harmonic oscillator we show that the Infeld-Hull radial operators, as well as those of the supersymmetric approach for the radial equation, are contained in the constants of motion of the problem. (author)
Monte Carlo study of the isotropic-nematic transition in a fluid of thin hard disk
Frenkel, D.; Eppenga, R.
1982-01-01
The first numerical determination of the thermodynamic isotropic-nematic transition in a simple three-dimensional model fluid, viz., a system of infinitely thin hard platelets, is reported. Thermodynamic properties were studied with use of the constant-pressure Monte Carlo method; Widom's particle-i
Translation surfaces in the three-dimensional simply isotropic space 𝕀31
Karacan, Murat Kemal; Yoon, Dae Won; Bukcu, Bahaddin
2016-05-01
In this paper, we classify translation surfaces in the three-dimensional simply isotropic space 𝕀31 under the condition Δix i = λixi where Δ is the Laplace operator with respect to the first and second fundamental forms and λ is a real number. We also give explicit forms of these surfaces.
Weighted Multi-Parameter Non-Isotropic Flag Triebel-Lizorkin and Besov Spaces
Liao, F; Liu, Z.
2014-01-01
In this paper, the authors use the discrete Littlewood-Paley-Stein theory to introduce weighted multi-parameter Triebel-Lizorkin and Besov spaces associated with non-isotropic flag singular integrals under a rather weak weight condition $(w\\in A_\\infty)$. They also obtain the boundedness of flag singular integrals on these spaces.
Oude Nijhuis, A.C.P.; Krasnov, O.K.; Unal, C.M.H.; Russchenberg, H.W.J.; Yarovoy, A.
2015-01-01
Homogeneous isotropic turbulence (HIT) models are compared, with respect to optimization of turbulence remote sensing. HIT models have different applications such as load calculation for wind turbines (Mann, 1998) or droplet track modelling (Pinsky and Khain, 2006). Details of vortices seem of less
Bulk amorphous Mg-based alloys
DEFF Research Database (Denmark)
Pryds, Nini
2004-01-01
The present paper describes the preparation and properties of bulk amorphous quarternary Mg-based alloys and the influence of additional elements on the ability of the alloy to form bulk amorphous. The main goal is to find a Mg-based alloy system which shows both high strength to weight ratio and...
27 CFR 20.191 - Bulk articles.
2010-04-01
... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Bulk articles. 20.191... Users of Specially Denatured Spirits Operations by Users § 20.191 Bulk articles. Users who convey articles in containers exceeding one gallon may provide the recipient with a photocopy of subpart G of...
Ghosh, G.
2015-08-01
A comprehensive computational study of elastic properties of cementite (Fe3C) and its alloyed counterparts (M3C (M = Al, Co, Cr, Cu, Fe, Hf, Mn, Mo, Nb, Ni, Si, Ta, Ti, V, W, Zr, Cr2FeC and CrFe2C) having the crystal structure of Fe3C is carried out employing electronic density-functional theory (DFT), all-electron PAW pseudopotentials and the generalized gradient approximation for the exchange-correlation energy (GGA). Specifically, as a part of our systematic study of cohesive properties of solids and in the spirit of materials genome, following properties are calculated: (i) single-crystal elastic constants, Cij, of above M3Cs; (ii) anisotropies of bulk, Young's and shear moduli, and Poisson's ratio based on calculated Cijs, demonstrating their extreme anisotropies; (iii) isotropic (polycrystalline) elastic moduli (bulk, shear, Young's moduli and Poisson's ratio) of M3Cs by homogenization of calculated Cijs; and (iv) acoustic Debye temperature, θD, of M3Cs based on calculated Cijs. We provide a critical appraisal of available data of polycrystalline elastic properties of alloyed cementite. Calculated single crystal properties may be incorporated in anisotropic constitutive models to develop and test microstructure-processing-property-performance links in multi-phase materials where cementite is a constituent phase.
Directory of Open Access Journals (Sweden)
G. Ghosh
2015-08-01
Full Text Available A comprehensive computational study of elastic properties of cementite (Fe3C and its alloyed counterparts (M3C (M = Al, Co, Cr, Cu, Fe, Hf, Mn, Mo, Nb, Ni, Si, Ta, Ti, V, W, Zr, Cr2FeC and CrFe2C having the crystal structure of Fe3C is carried out employing electronic density-functional theory (DFT, all-electron PAW pseudopotentials and the generalized gradient approximation for the exchange-correlation energy (GGA. Specifically, as a part of our systematic study of cohesive properties of solids and in the spirit of materials genome, following properties are calculated: (i single-crystal elastic constants, Cij, of above M3Cs; (ii anisotropies of bulk, Young’s and shear moduli, and Poisson’s ratio based on calculated Cijs, demonstrating their extreme anisotropies; (iii isotropic (polycrystalline elastic moduli (bulk, shear, Young’s moduli and Poisson’s ratio of M3Cs by homogenization of calculated Cijs; and (iv acoustic Debye temperature, θD, of M3Cs based on calculated Cijs. We provide a critical appraisal of available data of polycrystalline elastic properties of alloyed cementite. Calculated single crystal properties may be incorporated in anisotropic constitutive models to develop and test microstructure-processing-property-performance links in multi-phase materials where cementite is a constituent phase.
Chiadini, Francesco; Scaglione, Antonio; Lakhtakia, Akhlesh
2015-01-01
Multiple p- and s-polarized compound surface plasmon-polariton (SPP) waves at a fixed frequency can be guided by a structure consisting of a metal layer sandwiched between a homogeneous isotropic dielectric (HID) material and a periodic multilayered isotropic dielectric (PMLID) material. For any thickness of the metal layer, at least one compound SPP wave must exist. It possesses the p-polarization state, is strongly bound to the metal/HID interface when the metal thickness is large but to both metal/dielectric interfaces when the metal thickness is small. When the metal layer vanishes, this compound SPP wave transmutes into a Tamm wave. Additional compound SPP waves exist, depending on the thickness of the metal layer, the relative permittivity of the HID material, and the period and the composition of the PMLID material. Some of these are p polarized, the others being s polarized. All of them differ in phase speed, attenuation rate, and field profile, even though all are excitable at the same frequency. The...
Pandey, Manoj Kumar; Yarava, Jayasubba Reddy; Zhang, Rongchun; Ramamoorthy, Ayyalusamy; Nishiyama, Yusuke
2016-01-01
Chemical shift anisotropy (CSA) tensors offer a wealth of information for structural and dynamics studies of a variety of chemical and biological systems. In particular, CSA of amide protons can provide piercing insights into hydrogen-bonding interactions that vary with the backbone conformation of a protein and dynamics. However, the narrow span of amide proton resonances makes it very difficult to measure (1)H CSAs of proteins even by using the recently proposed 2D (1)H/(1)H anisotropic/isotropic chemical shift (CSA/CS) correlation technique. Such difficulties due to overlapping proton resonances can in general be overcome by utilizing the broad span of isotropic chemical shifts of low-gamma nuclei like (15)N. In this context, we demonstrate a proton-detected 3D (15)N/(1)H/(1)H CS/CSA/CS correlation experiment at fast MAS frequency (70kHz) to measure (1)H CSA values of unresolved amide protons of N-acetyl-(15)N-l-valyl-(15)N-l-leucine (NAVL).
The bulk, surface and corner free energies of the square lattice Ising model
Baxter, R. J.
2017-01-01
We use Kaufman’s spinor method to calculate the bulk, surface and corner free energies {f}{{b}},{f}{{s}},{f}{{s}}\\prime ,{f}{{c}} of the anisotropic square lattice zero-field Ising model for the ordered ferromagnetic case. For {f}{{b}},{f}{{s}},{f}{{s}}\\prime our results of course agree with the early work of Onsager, McCoy and Wu. We also find agreement with the conjectures made by Vernier and Jacobsen (VJ) for the isotropic case. We note that the corner free energy f c depends only on the elliptic modulus k that enters the working, and not on the argument v, which means that VJ’s conjecture applies for the full anisotropic model. The only aspect of this paper that is new is the actual derivation of f c, but by reporting all four free energies together we can see interesting structures linking them.
Multifragmentation of a very heavy nuclear system (II): bulk properties and spinodal decomposition
Energy Technology Data Exchange (ETDEWEB)
Frankland, J.D.; Rivet, M.F.; Borderie, B. [Paris-11 Univ., Inst. de Physique Nucleaire, 91 - Orsay (France)] [and others
2000-07-01
The properties of fragments and light charged particles emitted in multifragmentation of single sources formed in central 36 A.MeV Gd+U collisions are reviewed. Most of the products are isotropically distributed in the reaction c.m. Fragment kinetic energies reveal the onset of radial collective energy. A bulk effect is experimentally evidenced from the similarity of the charge distribution with that from the lighter 32 A.MeV Xe+Sn system. Spinodal decomposition of finite nuclear matter exhibits the same property in simulated central collisions for the two systems, and appears therefore as a possible mechanism at the origin of multifragmentation in this incident energy domain. (authors)
Neutrino emissivities and bulk viscosity in neutral two-flavor quark matter
Berdermann, J.; Blaschke, D.; Fischer, T.; Kachanovich, A.
2016-12-01
We study thermodynamic and transport properties for the isotropic color-spin-locking (iso-CSL) phase of two-flavor superconducting quark matter under compact star constraints within a Nambu-Jona-Lasinio-type chiral quark model. Chiral symmetry breaking and the phase transition to superconducting quark matter leads to a density dependent change of quark masses, chemical potentials, and diquark gap. A self-consistent treatment of these physical quantities influences the microscopic calculations of transport properties. We present results for the iso-CSL direct URCA emissivities and bulk viscosities, which fulfil the constraints on quark matter derived from cooling and rotational evolution of compact stars. We compare our results with the phenomenologically successful, but yet heuristic 2 SC +X phase. We show that the microscopically founded iso-CSL phase can replace the purely phenomenological 2 SC +X phase in modern simulations of the cooling evolution for compact stars with color-superconducting quark matter interior.
Neutrino emissivities and bulk viscosity in neutral two flavor quark matter
Berdermann, J; Fischer, T; Kachanovich, A
2016-01-01
We study thermodynamic and transport properties for the isotropic color-spin-locking (iso-CSL) phase of two-flavor superconducting quark matter under compact star constraints within a NJL-type chiral quark model. Chiral symmetry breaking and the phase transition to superconducting quark matter leads to a density dependent change of quark masses, chemical potentials and diquark gap. A self-consistent treatment of these physical quantities influences on the microscopic calculations of transport properties. We present results for the iso-CSL direct URCA emissivities and bulk viscosities, which fulfill the constraints on quark matter derived from cooling and rotational evolution of compact stars. We compare our results with the phenomenologically successful, but yet heuristic 2SC+X phase. We show that the microscopically founded iso-CSL phase can replace the purely phenomenological 2SC+X phase in modern simulations of the cooling evolution for compact stars with color superconducting quark matter interior.
Blake, O. O.; Faulkner, D. R.
2016-04-01
Elastic properties are key parameters during the deformation of rocks. They can be measured statically or dynamically, but the two measurements are often different. In this study, the static and dynamic bulk moduli (Kstatic and Kdynamic) were measured at varying effective stress for dry and fluid-saturated Westerly granite with controlled fracture densities under isotropic and differential stress states. Isotropic fracturing of different densities was induced in samples by thermal treatment to 250, 450, 650, and 850°C. Results show that fluid saturation does not greatly affect static moduli but increases dynamic moduli. Under isotropic loading, high fracture density and/or low effective pressure results in a low Kstatic/Kdynamic ratio. For dry conditions Kstatic/Kdynamic approaches 1 at low fracture densities when the effective pressure is high, consistent with previous studies. Stress-induced anisotropy exists under differential stress state that greatly affects Kstatic compared to Kdynamic. As a result, the Kstatic/Kdynamic ratio is higher than that for the isotropic stress state and approaches 1 with increasing axial loading. The effect of stress-induced anisotropy increases with increasing fracture density. A key omission in previous studies comparing static and dynamic properties is that anisotropy has not been considered. The standard methods for measuring static elastic properties, such as Poisson's ratio, Young's and shear modulus, involve subjecting the sample to a differential stress state that promotes anisotropy. Our results show that stress-induced anisotropy resulting from differential stress state is a major contributor to the difference between static and dynamic elasticity and is dominant with high fracture density.
Superconducting bulk magnets for magnetic levitation systems
Fujimoto, H.; Kamijo, H.
2000-06-01
The major applications of high-temperature superconductors have mostly been confined to products in the form of wires and thin films. However, recent developments show that rare-earth REBa 2Cu 3O 7- x and light rare-earth LREBa 2Cu 3O 7- x superconductors prepared by melt processes have a high critical-current density at 77 K and high magnetic fields. These superconductors will promote the application of bulk high-temperature superconductors in high magnetic fields; the superconducting bulk magnet for the Maglev train is one possible application. We investigated the possibility of using bulk magnets in the Maglev system, and examined flux-trapping characteristics of multi-superconducting bulks arranged in array.
Goos-Hänchen Lateral Displacements at the Interface between Isotropic and Gyroelectric Media
Directory of Open Access Journals (Sweden)
Jinbao Wang
2013-01-01
Full Text Available A detailed study on Goos-Hänchen (GH lateral displacements of the reflected and transmitted waves propagating at the interface between an isotropic medium and a gyroelectric medium in Voigt configuration is presented. After the reflection coefficient and transmission coefficient are derived, based on the stationary phase approach, GH lateral displacements are obtained analytically. The numerical results for a specific gyroelectric medium are also given. It shows that with the existence of an applied magnetic field, the GH effect occurs not only during total reflection but also during nontotal reflection, which is not true for isotropic media. Moreover, due to the nonreciprocal property of the gyroelectric medium, the sign of the incident angle also influences the displacements. Finite-element method simulations have verified the theoretical results.
Determining Loading Field based on Required Deformation for Isotropic Hardening Material
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Eringen's and Trusedell's polar decomposition are formulated by explicit formulation of displacement field, based on Chen's additive decomposition of deformation gradient. Then the strain introduced by the multiplicative decomposition and the strain introduced by the additive decomposition are formulated explicitly with displacement gradient. This formulation clears the intrinsic contents of strains defined by taking the Eringen's and Trusedell's polar decomposition. After that, Chen's strain definition was introduced to show that the plastic deformation can be understood as the irreversible local average rotation. For initial isotropic simple elastic material, the research shows that path-dependent feature of classical plasticity theory is naturally expressed in Chen's strain definition. For rate-independent plasticity, the related deformation stress was discussed. The research shows that for isotropic hardening material the relation equation between the required geometric configuration and the corresponding loading field is explicitly formulated. Hence, for metal forming, this paper explicitly formulates the related fields by displacement field and invariant elastic constants.
General thermo-elastic solution of radially heterogeneous, spherically isotropic rotating sphere
Energy Technology Data Exchange (ETDEWEB)
Bayat, Yahya; EkhteraeiToussi, THamid [Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)
2015-06-15
A thick walled rotating spherical object made of transversely isotropic functionally graded materials (FGMs) with general types of thermo-mechanical boundary conditions is studied. The thermo-mechanical governing equations consisting of decoupled thermal and mechanical equations are represented. The centrifugal body forces of the rotation are considered in the modeling phase. The unsymmetrical thermo-mechanical boundary conditions and rotational body forces are expressed in terms of the Legendre series. The series method is also implemented in the solution of the resulting equations. The solutions are checked with the known literature and FEM based solutions of ABAQUS software. The effects of anisotropy and heterogeneity are studied through the case studies and the results are represented in different figures. The newly developed series form solution is applicable to the rotating FGM spherical transversely isotropic vessels having nonsymmetrical thermo-mechanical boundary condition.
Multiaxial yield surface of transversely isotropic foams: Part II—Experimental
Shafiq, Muhammad; Ayyagari, Ravi Sastri; Ehaab, Mohammad; Vural, Murat
2015-03-01
A robust understanding and modeling of the yield behavior in solid foams under complex stress states is essential to design and analysis of optimal structures using these lightweight materials. In pursuit of this objective a new custom-built Multi-Axial Testing Apparatus (MATA) is developed to probe the yield surface of transversely isotropic Divinycell H-100 PVC foam under a multitude of uniaxial, biaxial and triaxial strain paths. Experimental yield data produced constitutes the most comprehensive data set ever produced for any foam as it covers the entire spectrum of stress paths from hydrostatic compression to hydrostatic tension. Experimental results reveal that yielding in foams exhibits not only a quadratic pressure dependence, which is widely recognized in literature, but also a significant linear pressure dependence, which has been largely overlooked in previous studies. A new energy-based yield criterion developed for transversely isotropic foams is also validated using the experimental yield data.
Institute of Scientific and Technical Information of China (English)
Jiayong Tian; Zhoumin Xie
2008-01-01
Dynamic contact stiffness at the interface between a vibrating rigid sphere and a semi-infinite transversely isotropic viscoelastic solid is investigated. An oscillating force superimposed onto a static compressive force in the vertical direction excites the vibration of a rigid sphere, which causes variable contact radius and contact pressure distribution in the contact region. The assumption of a sufficiently small oscillating force yields a dynamic contact-pressure distribution of a constant contact radius, which gives dynamic contact stiffness at the interface between the rigid sphere and the semi-infinite solid. Numerical calculations show the influence of vibration frequency of the sphere, and elastic constants of the transversely isotropic solid on dynamic contact stiffness, which benefits quantitative evaluation of elastic constants and orientation of single hexagonal grains by resonance-frequency shifts of the oscillator in resonance ultrasound microscopy.
Optimized analysis of isotropic high-nuclearity spin clusters with GPU acceleration
Lamas Daviña, A.; Ramos, E.; Roman, J. E.
2016-12-01
The numerical simulation of molecular clusters formed by a finite number of exchange-coupled paramagnetic centers is very relevant for many applications, modeling systems between molecules and extended solids. In the context of realistic scenarios, many centers need to be considered, and thus the required computational effort grows very fast. In a previous work (Ramos et al., 2010), a set of parallel programs were presented with standard message-passing parallelization (MPI) for both anisotropic and isotropic systems. In this work, we have further developed the code for isotropic models. On one hand, the computational cost has been significantly reduced by avoiding some of the matrix diagonalizations, corresponding to blocks with negligible contribution for the particular configuration. On the other hand, we have extended the parallelization in order to exploit available graphics processing units (GPUs). The new MPI-GPU paradigm reduces the computational time by at least one additional order of magnitude and enables the resolution of larger problems.
Lee, Hee Jung; Cho, Yea Jin; Cho, Won; Oh, Moonhyun
2013-01-22
The ability to fabricate multicompositional hybrid materials in a precise and controlled manner is one of the primary goals of modern materials science research. In addition, an understanding of the phenomena associated with the systematic growth of one material on another can facilitate the evolution of multifunctional hybrid materials. Here, we demonstrate precise manipulation of the isotropic and/or anisotropic nanoscale growth of various coordination polymers (CPs) to obtain heterocompositional hybrid coordination polymer particles. Chemical composition analyses conducted at every growth step reveal the formation of accurately assembled hybrid nanoscale CPs, and microscopy images are used to examine the morphology of the particles and visualize the hybrid structures. The dissimilar growth behavior, that is, growth in an isotropic or anisotropic fashion, is found to be dependent on the size of the metal ions involved within the CPs.
Zonal disintegration mechanism of isotropic rock masses around a deep spherical tunnel
Institute of Scientific and Technical Information of China (English)
谷新保; 毕靖; 许明
2015-01-01
In order to investigate zonal disintegration mechanism of isotropic rock masses around a deep spherical tunnel, a new mechanical model subjected to dynamic unloading under hydrostatic pressure condition is proposed. The total elastic stress-field distributions is determined using the elastodynamic equation. The effects of unloading rate and dynamic mechanical parameters of isotropic deep rock masses on the zonal disintegration phenomenon of the surrounding rock masses around a deep spherical tunnel as well as the total elastic stress field distributions are considered. The number and size of fractured and non-fractured zones are determined by using the Hoek-Brown criterion. Numerical computation is carried out. It is found from numerical results that the number of fractured zones increases with increasing the disturbance coefficient, in-situ stress, unloading time and unloading rate, and it decreases with increasing parameter geological strength index, the strength parameter and the uniaxial compressive strength of intact rock.
Oscillating test of the isotropic shift of the speed of light.
Baynes, Fred N; Tobar, Michael E; Luiten, Andre N
2012-06-29
In this Letter, we present an improved constraint on possible isotropic variations of the speed of light. Within the framework of the standard model extension, we provide a limit on the isotropic, scalar parameter κ̃(tr) of 3±11×10({-10), an improvement by a factor of 6 over previous constraints. This was primarily achieved by modulating the orientation of the experimental apparatus with respect to the velocity of Earth. This orientation modulation shifts the signal for Lorentz invariance to higher frequencies, and we have taken advantage of the higher stability of the resonator at shorter time scales, together with better rejection of systematic effects, to provide a new constraint.
On the consistency of complex moduli for transversely-isotropic viscoelastic materials
Lesieutre, George A.
The ability of advanced composite materials and structures to damp vibration is important in many applications. Use of the complex modulus approach to represent the dissipative properties of transversely-isotropic materials, such as unidirectional fiber-reinforced composites, requires the definition of a set of 5 (imaginary) loss moduli in addition to the 5 (real) storage moduli needed to describe the elastic behavior. In practice, designers of composite materials rarely have experimental data for all 5 loss moduli, and must assume values for the remaining moduli in their analyses. If values for these unknown loss moduli are specified arbitrarily, physically unreasonable behavior can result. This paper develops the conditions necessary for physical consistency of the complex moduli of transversely isotropic materials.
Directory of Open Access Journals (Sweden)
Gupta R.R.
2014-02-01
Full Text Available The present investigation deals with the propagation of waves in a micropolar transversely isotropic half space with an overlying inviscid fluid layer. Effects of fluid loading and anisotropy on the phase velocity, attenuation coefficient, specific loss and relative frequency shift. Finally, a numerical solution was carried out for aluminium epoxy material and the computer simulated results for the phase velocity, attenuation coefficient, specific loss and relative frequency shift are presented graphically. A particular case for the propagation of Rayleigh waves in a micropolar transversely isotropic half-space is deduced and dispersion curves are plotted for the same as functions of the wave number. An amplitude of displacements and microrotation together with the path of surface particles are also calculated for the propagation of Rayleigh waves in the latter case
Isotropic properties of the photonic band gap in quasicrystals with low-index contrast
Rose, Priya; Abbate, G; Andreone, A
2011-01-01
We report on the formation and development of the photonic band gap in two-dimensional 8-, 10- and 12-fold symmetry quasicrystalline lattices of low index contrast. Finite size structures made of dielectric cylindrical rods were studied and measured in the microwave region, and their properties compared with a conventional hexagonal crystal. Band gap characteristics were investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0 \\degree to 30\\degree were used in order to investigate the isotropic nature of the band gap. The arbitrarily high rotational symmetry of aperiodically ordered structures could be practically exploited to manufacture isotropic band gap materials, which are perfectly suitable for hosting waveguides or cavities.
Time delay anisotropy in photoelectron emission from the isotropic ground state of helium
Heuser, Sebastian; Cirelli, Claudio; Sabbar, Mazyar; Boge, Robert; Lucchini, Matteo; Gallmann, Lukas; Ivanov, Igor; Kheifets, Anatoli S; Dahlström, J Marcus; Lindroth, Eva; Argenti, Luca; Martín, Fernando; Keller, Ursula
2015-01-01
Time delays of electrons emitted from an isotropic initial state and leaving behind an isotropic ion are assumed to be angle-independent. Using an interferometric method involving XUV attosecond pulse trains and an IR probe field in combination with a detection scheme, which allows for full 3D momentum resolution, we show that time delays between electrons liberated from the $1s^{2}$ spherically symmetric ground state of He depend on the emission direction of the electrons with respect to the linear polarization axis of the ionizing XUV light. Such time delays can exhibit values as large as 60 attoseconds. With the help of refined theoretical models we can attribute the observed anisotropy to the interplay between different final quantum states, which arise naturally when two photons are involved in the photoionization process. Since most measurement techniques tracing attosecond electron dynamics have involved at least two photons so far, this is a general, significant, and initially unexpected effect that m...
On the effects of isotropic turbulence on the evaporation rate of a liquid droplet
Dodd, Michael; Ferrante, Antonino
2016-11-01
Our objective is to explain the effects of isotropic turbulence on the vaporization rate of a liquid droplet in conditions that are relevant to spray combustion applications. To this end, we have performed direct numerical simulation (DNS) of a single droplet in homogeneous isotropic turbulence using the volume-of-fluid method for resolving fully the process of momentum, heat, and mass transfer between the liquid droplet and the gas. The simulations were performed using 10243 grid points. The effect of turbulence on the droplet vaporization rate is investigated by varying the gas-phase Reynolds number based on the Taylor microscale, Reλ. Reλ is increased from 0 to 75 by increasing the r.m.s. velocity of the gas phase while keeping all other physical properties constant. We will present the droplet evaporation rate as a function of turbulence Reynolds number and investigate the physical mechanisms.
Design of 3D isotropic metamaterial device using smart transformation optics.
Shin, Dongheok; Kim, Junhyun; Yoo, Do-Sik; Kim, Kyoungsik
2015-08-24
We report here a design method for a 3 dimensional (3D) isotropic transformation optical device using smart transformation optics. Inspired by solid mechanics, smart transformation optics regards a transformation optical medium as an elastic solid and deformations as coordinate transformations. Further developing from our previous work on 2D smart transformation optics, we introduce a method of 3D smart transformation optics to design 3D transformation optical devices by maintaining isotropic materials properties for all types of polarizations imposing free or nearly free boundary conditions. Due to the material isotropy, it is possible to fabricate such devices with structural metamaterials made purely of common dielectric materials. In conclusion, the practical importance of the method reported here lies in the fact that it enables us to fabricate, without difficulty, arbitrarily shaped 3D devices with existing 3D printing technology.
Tanaka, Kento; Watanabe, Tomoaki; Nagata, Koji; Sasoh, Akihiro; Sakai, Yasuhiko; Hayase, Toshiyuki; Nagoya Univ Collaboration
2016-11-01
The interaction between homogeneous isotropic turbulence and normal shock wave is investigated by direct numerical simulations (DNSs). In the DNSs, a normal shock wave with a shock Mach number 1.1 passes through homogeneous isotropic turbulence with a low turbulent Mach number and a moderate turbulent Reynolds number. The statistics are calculated conditioned on the distance from the shock wave. The results showed that the shock wave makes length scales related to turbulence small. This effect is significant for the Taylor microscale defined with the velocity derivative orthogonal to the shock wave. The decrease in the Kolmogorov scale is also found. Statistics of velocity derivative are found to be changed by the shock wave propagation. The shock wave causes enstrophy amplification due to the dilatation/vorticity interaction. By this interaction, the vorticity components parallel to the shock wave is more amplified than the normal component. The strain rate is also amplified by the shock wave.
Lamb waves in a thin isotropic layer between two anisotropic layers
Institute of Scientific and Technical Information of China (English)
ZHANG Haiyan; ZHOU Quan; L(U) Donghui
2004-01-01
Attenuative Lamb wave propagation in adhesively bonded anisotropic composite plates is introduced. The isotropic adhesive exhibits viscous behavior to stimulate the poor curing of the middle layer. Viscosity is assumed to vary linearly with frequency, implying that attenuation per wavelength is constant. Attenuation can be implemented in the analysis through modification of elastic properties of isotropic adhesive. The new properties become complex, but cause no further complications in the analysis. The characteristic equation is the same as that used for the elastic plate case, except that both real and imaginary parts of the wave number (i.e., the attenuation) must be computed. Based on the Lowe's solution in finding the complex roots of characteristic equation, the effect of longitudinal and shear attenuation coefficients of the middle adhesive layer on phase velocity dispersion curves and attenuation dispersion curves of Lamb waves propagating in bonded anisotropic composites is visualized numerically.
Measuring Bulk Flows in Large Scale Surveys
Feldman, H A; Feldman, Hume A.; Watkins, Richard
1993-01-01
We follow a formalism presented by Kaiser to calculate the variance of bulk flows in large scale surveys. We apply the formalism to a mock survey of Abell clusters \\'a la Lauer \\& Postman and find the variance in the expected bulk velocities in a universe with CDM, MDM and IRAS--QDOT power spectra. We calculate the velocity variance as a function of the 1--D velocity dispersion of the clusters and the size of the survey.
Characteristics of dissimilar laser-brazed joints of isotropic graphite to WC-Co alloy
Energy Technology Data Exchange (ETDEWEB)
Nagatsuka, Kimiaki, E-mail: nagatuka@jwri.osaka-u.ac.jp [Graduate School of Engineering, Osaka University, Joining and Welding Research Institute, 11-1, Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Sechi, Yoshihisa, E-mail: sechi@kagoshima-it.go.jp [Kagoshima Prefectural Institute of Industrial Technology, 1445-1 Oda, Hayato-cho, Kirishima, Kagoshima 899-5105 (Japan); Miyamoto, Yoshinari, E-mail: y_miyamoto@toyotanso.co.jp [Toyo Tanso Co., Ltd., 5-7-12 Takeshima, Nishiyodgawa-ku, Osaka 555-0011 (Japan); Nakata, Kazuhiro, E-mail: nakata@jwri.osaka-u.ac.jp [Joining and Welding Research Institute, Osaka University, 11-1, Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)
2012-04-25
Highlights: Black-Right-Pointing-Pointer Ti was required in the filler metal for brazing graphite to WC-Co alloy. Black-Right-Pointing-Pointer The shear strength of the joint increased with Ti content up to 1.7 mass%. Black-Right-Pointing-Pointer Ti concentrated at the interface of graphite/filler metal. Black-Right-Pointing-Pointer TiC was formed at the interface of graphite/filler metal. - Abstract: The effect of Ti serving as an activator in a eutectic Ag-Cu alloy filler metal in dissimilar laser-brazed joints of isotropic graphite and a WC-Co alloy on the joint strength and the interface structure of the joint is investigated in this study. To evaluate the joint characteristics, the Ti content in the filler metal was increased from 0 to 2.8 mass%. The laser brazing was carried out by irradiating a laser beam selectively on the WC-Co alloy plate in Ar atmosphere. The threshold content of Ti required to join isotropic graphite to WC-Co alloy was 0.4 mass%. The shear strength at the brazed joint increased rapidly with increasing Ti content up to 1.7 mass%, and a higher Ti content was found to be likely to saturate the shear strength to a constant value of about 14 MPa. The isotropic graphite blocks also fractured at this content. The concentration of Ti observed at the interface between isotropic graphite and the filler metal indicates the formation of an intermetallic layer of TiC.
2014-01-09
nanoparticles (NPs) were added to luminescent porous silicon by drop casting. These NPs interact with this system by modifying its optical properties ...response by Au NPs in sapphire: Nonlinear optical response of Au metallic NPs, synthesized and embedded in sapphire by using ion implantation, as a...Linear and nonlinear plasmonics from isotropic and anisotropic integrated nanocomposites for quantum information applications. Jorge-Alejandro Reyes
Jinxia Liu; Zhiwen Cui; Zhengliang Cao; Kexie Wang
2014-01-01
Stoneley wave in a fluid-filled pressurized borehole surrounded by a transversely isotropic elastic solid with nine independent third-order elastic constants in presence of biaxial stresses are studied. A simplified acoustoelastic formulation of Stoneley wave is presented for the parallelism of the borehole axis and the formation axis of symmetry. Sensitivity coefficients and velocity dispersions for Stoneley wave due to the presence of stresses are numerically investigated, respectively. The...
Energy landscapes of ion clusters in isotropic quadrupolar and octupolar traps
Yurtsever, Ersin; Calvo, F.; Wales, D.C.
2012-01-01
THE JOURNAL OF CHEMICAL PHYSICS 136, 024303 (2012) Energy landscapes of ion clusters in isotropic quadrupolar and octupolar traps F. Calvo,1,a) E. Yurtsever,2 and D. J. Wales3 1LASIM, Université Claude Bernard Lyon 1 and CNRS UMR 5579, 43 Bd du 11 Novembre 1918, F69622 Villeurbanne Cedex, France 2Koç University, Rumelifeneriyolu, Sariyer, Istanbul 34450, Turkey 3University Chemical Laboratories, Lensfield Road, Cambridge CB2 1EW, United Kingdom (Received 4 November 201...
On the Ricci Curvature of a Randers Metric of Isotropic S-curvature
Institute of Scientific and Technical Information of China (English)
Xiao Huan MO; Chang Tao YU
2008-01-01
We derive the integral inequality of a Randers metric with isotropic S-curvature in terms of its navigation representation. Using the obtained inequality we give some rigidity results under the condition of Ricci curvature. In particular, we show the following result: Assume that an n-dimensional compact Randers manifold (M, F)hasconstantS-curvature c.Then(M, F) must be Riemannian ifits Ricci curvature satisfies that Ric < - (n - 1)c2.
Magnetic Field Line Random Walk in Isotropic Turbulence with Varying Mean Field
Sonsrettee, W.; Subedi, P.; Ruffolo, D.; Matthaeus, W. H.; Snodin, A. P.; Wongpan, P.; Chuychai, P.; Rowlands, G.; Vyas, S.
2016-08-01
In astrophysical plasmas, the magnetic field line random walk (FLRW) plays an important role in guiding particle transport. The FLRW behavior is scaled by the Kubo number R=(b/{B}0)({{\\ell }}\\parallel /{{\\ell }}\\perp ) for rms magnetic fluctuation b, large-scale mean field {{\\boldsymbol{B}}}0, and coherence scales parallel ({{\\ell }}\\parallel ) and perpendicular ({{\\ell }}\\perp ) to {{\\boldsymbol{B}}}0. Here we use a nonperturbative analytic framework based on Corrsin’s hypothesis, together with direct computer simulations, to examine the R-scaling of the FLRW for varying B 0 with finite b and isotropic fluctuations with {{\\ell }}\\parallel /{{\\ell }}\\perp =1, instead of the well-studied route of varying {{\\ell }}\\parallel /{{\\ell }}\\perp for b \\ll {B}0. The FLRW for isotropic magnetic fluctuations is also of astrophysical interest regarding transport processes in the interstellar medium. With a mean field, fluctuations may have variance anisotropy, so we consider limiting cases of isotropic variance and transverse variance (with b z = 0). We obtain analytic theories, and closed-form solutions for extreme cases. Padé approximants are provided to interpolate all versions of theory and simulations to any B 0. We demonstrate that, for isotropic turbulence, Corrsin-based theories generally work well, and with increasing R there is a transition from quasilinear to Bohm diffusion. This holds even with b z = 0, when different routes to R\\to ∞ are mathematically equivalent; in contrast with previous studies, we find that a Corrsin-based theory with random ballistic decorrelation works well even up to R = 400, where the effects of trapping are barely perceptible in simulation results.
Stress concentration in a transversely isotropic spherical shell with two circular rigid inclusions
Chekhov, V. N.; Zakora, S. V.
2011-10-01
The refined Timoshenko-type theory that takes into account the transverse shear strains is used to find an analytic solution for the stress state of transversely isotropic shallow spherical shell with two circular rigid inclusions. The case of a shell with closely spaced rigid inclusions of unequal radii under internal pressure is analyzed numerically. The stresses in the shell increase considerably with decrease in the distance between the inclusions and increase in the transverse shear parameter
Time Decay Rates of the Isotropic Non-Newtonian Flows in Rn
Institute of Scientific and Technical Information of China (English)
Bo-Qing Dong
2007-01-01
This paper is concerned with time decay rates for weak solutions to a class system of isotropic incompressible non-Newtonian fluid motion in Rn. With the use of the spectral decomposition methods of Stokes operator, the optimal decay estimates of weak solutions in L2 norm are derived under the different conditions on the initial velocity. Moreover, the error estimates of the difference between non-Newtonian flow and Navier-Stokes flow are also investigated.
DYNAMICAL FORMATION OF CAVITY IN TRANSVERSELY ISOTROPIC HYPER-ELASTIC SPHERES
Institute of Scientific and Technical Information of China (English)
任九生; 程昌钧
2003-01-01
The cavity formation in a radial transversely isotropic hyper-elastic sphere of an incompressible Ogden material, subjected to a suddenly applied uniform radial tensile boundary deadload, is studied following the theory of finite deformation dynamics. A cavity forms at the center of the sphere when the tensile load is greater than its critical value. It is proved that the evolution of the cavity radius with time follows that of nonlinear periodic oscillations.
Simplified P$_N$ Equations for Nonclassical Transport with Isotropic Scattering
Vasques, R
2016-01-01
A nonclassical diffusion approximation has been previously derived for the the one-speed nonclassical transport equation with isotropic scattering. In this paper we use an asymptotic analysis to derive more accurate diffusion approximations to the nonclassical transport equation. If the free-path distribution is given by an exponential (classical transport), these approximations reduce to the simplified P$_N$ (SP$_N$) equations; therefore, they are labeled nonclassical SP$_N$ equations.
High-dimensional Gaussian fields with isotropic increments seen through spin glasses
Klimovsky, Anton
2011-01-01
We study the free energy of a particle in (arbitrary) high-dimensional Gaussian random potentials with isotropic increments. We prove a computable saddle-point variational representation in terms of a Parisi-type functional for the free energy in the infinite-dimensional limit. The proofs are based on the techniques developed in the course of the rigorous analysis of the Sherrington-Kirkpatrick model with vector spins.
Chang, Hing-Chiu; Sundman, Mark; Petit, Laurent; Guhaniyogi, Shayan; Chu, Mei-Lan; Petty, Christopher; Song, Allen W; Chen, Nan-kuei
2015-09-01
The advantages of high-resolution diffusion tensor imaging (DTI) have been demonstrated in a recent post-mortem human brain study (Miller et al., NeuroImage 2011;57(1):167-181), showing that white matter fiber tracts can be much more accurately detected in data at a submillimeter isotropic resolution. To our knowledge, in vivo human brain DTI at a submillimeter isotropic resolution has not been routinely achieved yet because of the difficulty in simultaneously achieving high resolution and high signal-to-noise ratio (SNR) in DTI scans. Here we report a 3D multi-slab interleaved EPI acquisition integrated with multiplexed sensitivity encoded (MUSE) reconstruction, to achieve high-quality, high-SNR and submillimeter isotropic resolution (0.85×0.85×0.85mm(3)) in vivo human brain DTI on a 3Tesla clinical MRI scanner. In agreement with the previously reported post-mortem human brain DTI study, our in vivo data show that the structural connectivity networks of human brains can be mapped more accurately and completely with high-resolution DTI as compared with conventional DTI (e.g., 2×2×2mm(3)).
Whole-animal functional and developmental imaging with isotropic spatial resolution.
Chhetri, Raghav K; Amat, Fernando; Wan, Yinan; Höckendorf, Burkhard; Lemon, William C; Keller, Philipp J
2015-12-01
Imaging fast cellular dynamics across large specimens requires high resolution in all dimensions, high imaging speeds, good physical coverage and low photo-damage. To meet these requirements, we developed isotropic multiview (IsoView) light-sheet microscopy, which rapidly images large specimens via simultaneous light-sheet illumination and fluorescence detection along four orthogonal directions. Combining these four views by means of high-throughput multiview deconvolution yields images with high resolution in all three dimensions. We demonstrate whole-animal functional imaging of Drosophila larvae at a spatial resolution of 1.1-2.5 μm and temporal resolution of 2 Hz for several hours. We also present spatially isotropic whole-brain functional imaging in Danio rerio larvae and spatially isotropic multicolor imaging of fast cellular dynamics across gastrulating Drosophila embryos. Compared with conventional light-sheet microscopy, IsoView microscopy improves spatial resolution at least sevenfold and decreases resolution anisotropy at least threefold. Compared with existing high-resolution light-sheet techniques, IsoView microscopy effectively doubles the penetration depth and provides subsecond temporal resolution for specimens 400-fold larger than could previously be imaged.
An Isotropic SPPP Mo del for Femto cells Networks with Outage Probability Constraints
Institute of Scientific and Technical Information of China (English)
ZHANG Jun; TIAN Hui
2015-01-01
Femtocells have been considered as a cost-eff ective solution to unload traffic from already overbur-dened macrocell networks in 4G cellular networks. The severe interference in spectrum-sharing macro and femto networks may cause User-equipment (UE) to experience outage. We derive an utmost isotropic Spatial Poisson point process (SPPP) density for Femtocell access points (FAPs) under the UEs’ outage constraints. Based on the derived isotropic SPPP density, we propose a distributed transmit probability self-regulation scheme for an FAP to adapt its transmit probability per Transmission time in-terval (TTI). The scheme adjusts the homogeneous dis-tributed FAPs in practice deployment to the proposed isotropic one. Simulation results show that the derived den-sity can fulfill the outage probability constraints of UEs while accommodating the maximum femtocells. The self-regulation scheme can adapt the femtocell transmit prob-abilities to provide reliable downlink service, for even a large number of femtocells per cell site.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The non-axisymmetrical vibration of elastic circular plate resting on a layered transversely isotropic saturated ground was studied. First, the 3-d dynamic equations in cylindrical coordinate for transversely isotropic saturated soils were transformed into a group of governing differential equations with 1-order by the technique of Fourier expanding with respect to azimuth, and the state equation is established by Hankel integral transform method, furthermore the transfer matrixes within layered media are derived based on the solutions of the state equation. Secondly, by the transfer matrixes, the general solutions of dynamic response for layered transversely isotropic saturated ground excited by an arbitrary harmonic force were established under the boundary conditions,drainage conditions on the surface of ground as well as the contact conditions. Thirdly, the problem was led to a pair of dual integral equations describing the mixed boundaryvalue problem which can be reduced to the Fredholm integral equations of the second kind solved by numerical procedure easily. At the end of this paper, a numerical result concerning vertical and radical displacements both the surface of saturated ground and plate is evaluated.
Diffraction of SH-waves by topographic features in a layered transversely isotropic half-space
Ba, Zhenning; Liang, Jianwen; Zhang, Yanju
2017-01-01
The scattering of plane SH-waves by topographic features in a layered transversely isotropic (TI) half-space is investigated by using an indirect boundary element method (IBEM). Firstly, the anti-plane dynamic stiffness matrix of the layered TI half-space is established and the free fields are solved by using the direct stiffness method. Then, Green's functions are derived for uniformly distributed loads acting on an inclined line in a layered TI half-space and the scattered fields are constructed with the deduced Green's functions. Finally, the free fields are added to the scattered ones to obtain the global dynamic responses. The method is verified by comparing results with the published isotropic ones. Both the steady-state and transient dynamic responses are evaluated and discussed. Numerical results in the frequency domain show that surface motions for the TI media can be significantly different from those for the isotropic case, which are strongly dependent on the anisotropy property, incident angle and incident frequency. Results in the time domain show that the material anisotropy has important effects on the maximum duration and maximum amplitudes of the time histories.
Directory of Open Access Journals (Sweden)
Anna I Sulatskaya
Full Text Available In this work, the fluorescence of thioflavin T (ThT was studied in a wide range of viscosity and temperature. It was shown that ThT fluorescence quantum yield varies from 0.0001 in water at room temperature to 0.28 in rigid isotropic solution (T/η→0. The deviation of the fluorescence quantum yield from unity in rigid isotropic solution suggests that fluorescence quantum yield depends not only on the ultra-fast oscillation of ThT fragments relative to each other in an excited state as was suggested earlier, but also depends on the molecular configuration in the ground state. This means that the fluorescence quantum yield of the dye incorporated into amyloid fibrils must depend on its conformation, which, in turn, depends on the ThT environment. Therefore, the fluorescence quantum yield of ThT incorporated into amyloid fibrils can differ from that in the rigid isotropic solution. In particular, the fluorescence quantum yield of ThT incorporated into insulin fibrils was determined to be 0.43. Consequently, the ThT fluorescence quantum yield could be used to characterize the peculiarities of the fibrillar structure, which opens some new possibilities in the ThT use for structural characterization of the amyloid fibrils.
Vertical Dynamic Response of Pile Embedded in Layered Transversely Isotropic Soil
Directory of Open Access Journals (Sweden)
Wenbing Wu
2014-01-01
Full Text Available The dynamic response of pile embedded in layered transversely isotropic soil and subjected to arbitrary vertical harmonic force is investigated. Based on the viscoelastic constitutive relations for a transversely isotropic medium, the dynamic governing equation of the transversely isotropic soil is obtained in cylindrical coordinates. By introducing the fictitious soil pile model and the distributed Voigt model, the governing equations of soil-pile system are also derived. Firstly, the vertical response of the soil layer is solved by using the Laplace transform technique and the separation of variables technique. Secondly, the analytical solution of velocity response in the frequency domain and its corresponding semianalytical solution of velocity response in the time domain are derived by means of inverse Fourier transform and convolution theorem. Finally, based on the obtained solutions, a parametric study has been conducted to investigate the influence of the soil anisotropy on the vertical dynamic response of pile. It can be seen that the influence of the shear modulus of soil in the vertical plane on the dynamic response of pile is more notable than the influence of the shear modulus of soil in the horizontal plane on the dynamic response of pile.
Buranasiri, Prathan; Banerjee, Partha P.; Polejaev, Vladimir; Sun, Ching-Cherng
2003-10-01
Using two beam coupling geometry, high order copropagating and contrapropagating isotropic and copropagating anisotropic self-diffraction are demonstrated using photorefractive cerium doped barium titanate. At small incident angles, typically less than 0.015 radians, both codirectional isotropic self-diffraction (CODIS) and contradirectional isotropic self-diffraction (CONDIS) orders are generated simultaneously. At larger incident angles, typically approximately more than 0.2094 radians, only codirectional anisotropic-self diffraction (CODAS) orders are generated. Ongoing work on image auto/cross correlation results are also shown.
Bianchi Type Ⅲ Bulk Viscous Barotropic Fluid Cosmological Models with Variable G and A
Institute of Scientific and Technical Information of China (English)
Raj Ba-li; Seema Tinker
2009-01-01
Bianchi type-Ⅲ bulk viscous barotropic fluid cosmological model with variables G and A is investigated. To obtainthe realistic model, we assume the conditions between the metric potentials A, B, C as A/A = B/B = m1/tnand C/C = m2/tn, P = p - 3ηH, η= ηops, p =γp, 0 γ 1, where p is isotropic pressure, η the coefficient of bulk viscosity, ηo and S the constants, H the Hubble constant, m1= 2m2 where m1 0, m2 0. The solutions obtained lead to inflationary phase and the results obtained match with the observations. The case n = 1 for S = 1 is also discussed, relating the results with the observations.PACS: 98. 80. Hω, 04.50. +h, 98.80. CqSpatially homogeneous and anisotropic cosmologi-cal models play a significant role in description of the large scale behaviour of the universe. The choice of anisotropic model in the Einstein system of field equa-tions permits us to obtain cosmological model more general than the Robertson-Walker model. Tikekar and Patel[1] have investigated some exact solutions of massive string for Bianchi type-Ⅲ spacetime in the presence and absence of magnetic field. They have also discussed the behaviour of the model in the ab-sence of magnetic field. Bali and Dave[2] investigated the Bianchi type-Ⅲ string cosmological model with bulk viscosity. Recently Bali and Pradhan[3] investi-gated the Bianchi type-Ⅲ string cosmological models with time-dependent bulk viscosity.
2010-10-19
... nonsubstantive changes, however, to correct grammar, internal paragraph references, and a temperature conversion... means the English version of the ``International Maritime Solid Bulk Cargoes Code'' published by...
Hydrophobic matrix-free graphene-oxide composites with isotropic and nematic states
Wåhlander, Martin; Nilsson, Fritjof; Carlmark, Anna; Gedde, Ulf W.; Edmondson, Steve; Malmström, Eva
2016-08-01
We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been immobilised on anionic GO and subsequently grafted with hydrophobic polymer grafts. Dense grafts of PBA, PBMA and PMMA with a wide range of average graft lengths (MW: 1-440 kDa) were polymerised by surface-initiated controlled radical precipitation polymerisation from the statistical MI. The surface modification is designed similarly to bimodal graft systems, where the cationic MI generates nanoparticle repulsion, similar to dense short grafts, while the long grafts offer miscibility in non-polar environments and cohesion. The state-of-the-art dispersions of grafted GO were in the isotropic state. Transparent and translucent matrix-free GO-composites could be melt-processed directly using only grafted GO. After processing, birefringence due to nematic alignment of grafted GO was observed as a single giant Maltese cross, 3.4 cm across. Permeability models for composites containing aligned 2D-fillers were developed, which were compared with the experimental oxygen permeability data and found to be consistent with isotropic or nematic states. The storage modulus of the matrix-free GO-composites increased with GO content (50% increase at 0.67 wt%), while the significant increases in the thermal stability (up to 130 °C) and the glass transition temperature (up to 17 °C) were dependent on graft length. The tuneable matrix-free GO-composites with rapid thermo-responsive shape-memory effects are promising candidates for a vast range of applications, especially selective membranes and sensors.We demonstrate a novel route to synthesise hydrophobic matrix-free composites of polymer-grafted graphene oxide (GO) showing isotropic or nematic alignment and shape-memory effects. For the first time, a cationic macroinitiator (MI) has been
Ricci Flow of Warped Product Metrics with Positive Isotropic Curvature on $S^{p+1}× S^1$
Indian Academy of Sciences (India)
H A Gururaja
2012-11-01
We study the asymptotic behaviour of the ODE associated to the evolution of curvature operator in the Ricci flow of a doubly warped product metric on $S^{p+1}× S^1$ with positive isotropic curvature.
Tichit, Paul-Henri; Burokur, Shah Nawaz; Qiu, Cheng-Wei; de Lustrac, André
2013-09-01
It has long been conjectured that isotropic radiation by a simple coherent source is impossible due to changes in polarization. Though hypothetical, the isotropic source is usually taken as the reference for determining a radiator’s gain and directivity. Here, we demonstrate both theoretically and experimentally that an isotropic radiator can be made of a simple and finite source surrounded by electric-field-driven LC resonator metamaterials designed by space manipulation. As a proof-of-concept demonstration, we show the first isotropic source with omnidirectional radiation from a dipole source (applicable to all distributed sources), which can open up several possibilities in axion electrodynamics, optical illusion, novel transformation-optic devices, wireless communication, and antenna engineering. Owing to the electric- field-driven LC resonator realization scheme, this principle can be readily applied to higher frequency regimes where magnetism is usually not present.
Development of superconductor bulk for superconductor bearing
Energy Technology Data Exchange (ETDEWEB)
Kim, Chan Joong; Jun, Byung Hyuk; Park, Soon Dong (and others)
2008-08-15
Current carrying capacity is one of the most important issues in the consideration of superconductor bulk materials for engineering applications. There are numerous applications of Y-Ba-Cu-O (YBCO) bulk superconductors e.g. magnetic levitation train, flywheel energy storage system, levitation transportation, lunar telescope, centrifugal device, magnetic shielding materials, bulk magnets etc. Accordingly, to obtain YBCO materials in the form of large, single crystals without weak-link problem is necessary. A top seeded melt growth (TSMG) process was used to fabricate single crystal YBCO bulk superconductors. The seeded and infiltration growth (IG) technique was also very promising method for the synthesis of large, single-grain YBCO bulk superconductors with good superconducting properties. 5 wt.% Ag doped Y211 green compacts were sintered at 900 .deg. C {approx} 1200 .deg.C and then a single crystal YBCO was fabricated by an infiltration method. A refinement and uniform distribution of the Y211 particles in the Y123 matrix were achieved by sintering the Ag-doped samples. This enhancement of the critical current density was ascribable to a fine dispersion of the Y211 particles, a low porosity and the presence of Ag particles. In addition, we have designed and manufactured large YBCO single domain with levitation force of 10-13 kg/cm{sup 2} using TSMG processing technique.
Institute of Scientific and Technical Information of China (English)
WEI Gao-Feng; LONG Chao-Yun; LONG Zheng-Wen; QIN Shui-Jie
2008-01-01
In this paper,the isotropic charged harmonic oscillator in uniform magnetic field is researched in the non-commutative phase space;the corresponding exact energy is obtained,and the analytic eigenfunction is presented in terms of the confluent hypergeometric function.It is shown that in the non-commutative space,the isotropic charged harmonic oscillator in uniform magnetic field has the similar behaviors to the Landau problem.
Directory of Open Access Journals (Sweden)
Y Yousefi
2012-09-01
Full Text Available In this paper, a system with spin S=3/2 with general isotropic nearest neighbor exchange within a mean field approximation possess is discnssed. We derive equations describing non-Heisenberg isotropic model using coherent states of SU(4 group in real parameters and then obtain dispersion equations of spin wave of dipole and quadrupole branches for a small linear excitation from the ground state.
Bulk fields from the boundary OPE
Guica, Monica
2016-01-01
Previous work has established an equality between the geodesic integral of a free bulk field in AdS and the contribution of the conformal descendants of its dual CFT primary operator to the OPE of two other operators inserted at the endpoints of the geodesic. Working in the context of AdS$_3$/CFT$_2$, we extend this relation to include all $1/N$ corrections to the bulk field obtained by dressing it with i) a $U(1)$ current and ii) the CFT stress tensor, and argue it equals the contribution of the Ka\\v{c}-Moody/the Virasoro block to the respective boundary OPE. This equality holds for a particular framing of the bulk field to the boundary that involves a split Wilson line.
A Diphoton Resonance from Bulk RS
Csaki, Csaba
2016-01-01
Recent LHC data hints at a 750 GeV mass resonance that decays into two photons. A significant feature of this resonance is that its decays to Higges and to any other Standard Model particles are so far too low to be detected. Such a state has a compelling explanation in terms of a scalar or a pseudoscalar that is strongly coupled to vector states charged under the Standard Model gauge groups. We argue that if the state is a scalar, some form of sequestering is likely to be necessary to naturally explain the suppressed scalar-Higgs interactions. Such a scenario is readily accommodated in bulk RS with a scalar localized in the bulk away from the Higgs. Turning this around, we argue that a good way to find the elusive bulk RS model might be the search for a resonance with prominent couplings to gauge bosons.
Bulk Comptonization by Turbulence in Accretion Disks
Kaufman, J
2016-01-01
Radiation pressure dominated accretion discs around compact objects may have turbulent velocities that greatly exceed the electron thermal velocities within the disc. Bulk Comptonization by the turbulence may therefore dominate over thermal Comptonization in determining the emergent spectrum. Bulk Comptonization by divergenceless turbulence is due to radiation viscous dissipation only. It can be treated as thermal Comptonization by solving the Kompaneets equation with an equivalent "wave" temperature, which is a weighted sum over the power present at each scale in the turbulent cascade. Bulk Comptonization by turbulence with non-zero divergence is due to both pressure work and radiation viscous dissipation. Pressure work has negligible effect on photon spectra in the limit of optically thin turbulence, and in this limit radiation viscous dissipation alone can be treated as thermal Comptonization with a temperature equivalent to the full turbulent power. In the limit of extremely optically thick turbulence, ra...
A diphoton resonance from bulk RS
Csáki, Csaba; Randall, Lisa
2016-07-01
Recent LHC data hinted at a 750 GeV mass resonance that decays into two photons. A significant feature of this resonance is that its decays to any other Standard Model particles would be too low to be detected so far. Such a state has a compelling explanation in terms of a scalar or a pseudoscalar that is strongly coupled to vector states charged under the Standard Model gauge groups. Such a scenario is readily accommodated in bulk RS with a scalar localized in the bulk away from but close to the Higgs. Turning this around, we argue that a good way to find the elusive bulk RS model might be the search for a resonance with prominent couplings to gauge bosons.
Orchestrating Bulk Data Movement in Grid Environments
Energy Technology Data Exchange (ETDEWEB)
Vazhkudai, SS
2005-01-25
Data Grids provide a convenient environment for researchers to manage and access massively distributed bulk data by addressing several system and transfer challenges inherent to these environments. This work addresses issues involved in the efficient selection and access of replicated data in Grid environments in the context of the Globus Toolkit{trademark}, building middleware that (1) selects datasets in highly replicated environments, enabling efficient scheduling of data transfer requests; (2) predicts transfer times of bulk wide-area data transfers using extensive statistical analysis; and (3) co-allocates bulk data transfer requests, enabling parallel downloads from mirrored sites. These efforts have demonstrated a decentralized data scheduling architecture, a set of forecasting tools that predict bandwidth availability within 15% error and co-allocation architecture, and heuristics that expedites data downloads by up to 2 times.
A stereoscopic look into the bulk
Czech, Bartlomiej; Lamprou, Lampros; McCandlish, Samuel; Mosk, Benjamin; Sully, James
2016-07-01
We present the foundation for a holographic dictionary with depth perception. The dictionary consists of natural CFT operators whose duals are simple, diffeomorphisminvariant bulk operators. The CFT operators of interest are the "OPE blocks," contributions to the OPE from a single conformal family. In holographic theories, we show that the OPE blocks are dual at leading order in 1 /N to integrals of effective bulk fields along geodesics or homogeneous minimal surfaces in anti-de Sitter space. One widely studied example of an OPE block is the modular Hamiltonian, which is dual to the fluctuation in the area of a minimal surface. Thus, our operators pave the way for generalizing the Ryu-Takayanagi relation to other bulk fields.
Spherically symmetric brane spacetime with bulk gravity
Chakraborty, Sumanta; SenGupta, Soumitra
2015-01-01
Introducing term in the five-dimensional bulk action we derive effective Einstein's equation on the brane using Gauss-Codazzi equation. This effective equation is then solved for different conditions on dark radiation and dark pressure to obtain various spherically symmetric solutions. Some of these static spherically symmetric solutions correspond to black hole solutions, with parameters induced from the bulk. Specially, the dark pressure and dark radiation terms (electric part of Weyl curvature) affect the brane spherically symmetric solutions significantly. We have solved for one parameter group of conformal motions where the dark radiation and dark pressure terms are exactly obtained exploiting the corresponding Lie symmetry. Various thermodynamic features of these spherically symmetric space-times are studied, showing existence of second order phase transition. This phenomenon has its origin in the higher curvature term with gravity in the bulk.
Making bulk-conductive glass microchannel plates
Yi, Jay J. L.; Niu, Lihong
2008-02-01
The fabrication of microchannel plate (MCP) with bulk-conductive characteristics has been studied. Semiconducting clad glass and leachable core glass were used for drawing fibers and making MCP. Co-axial single fiber was drawn from a platinum double-crucible in an automatic fiberizing system, and the fibers were stacked and redrawn into multifiber by a special gripping mechanism. The multifibers were stacked again and the boule was made and sliced into discs. New MCPs were made after chemically leaching process without the traditional hydrogen firing. It was shown that bulk-conductive glass MCP can operate at higher voltage with lower noise.
Synthesis of Bulk Superconducting Magnesium Diboride
Directory of Open Access Journals (Sweden)
Margie Olbinado
2002-06-01
Full Text Available Bulk polycrystalline superconducting magnesium diboride, MgB2, samples were successfully prepared via a one-step sintering program at 750°C, in pre Argon with a pressure of 1atm. Both electrical resistivity and magnetic susceptibility measurements confirmed the superconductivity of the material at 39K, with a transition width of 5K. The polycrystalline nature, granular morphology, and composition of the sintered bulk material were confirmed using X-ray diffractometry (XRD, scanning electron microscopy (SEM, and energy dispersive X-ray analysis (EDX.
Towards a Reconstruction of General Bulk Metrics
Engelhardt, Netta
2016-01-01
We prove that the metric of a general holographic spacetime can be reconstructed (up to an overall conformal factor) from distinguished spatial slices - "light-cone cuts" - of the conformal boundary. Our prescription is covariant and applies to bulk points in causal contact with the boundary. Furthermore, we describe a procedure for determining the light-cone cuts corresponding to bulk points in the causal wedge of the boundary in terms of the divergences of correlators in the dual field theory. Possible extensions for determining the conformal factor and including the cuts of points outside of the causal wedge are discussed. We also comment on implications for subregion/subregion duality.
The relationship between the adiabatic bulk modulus and enthalpy for mantle-related minerals
Anderson, Orson L.
1989-07-01
It is found that the adiabatic bulk modulus, KS, is linear with enthalpy over a wide temperature range: up to at least 1825 K, the present limit of the measurement of the bulk modulus. This correlation is shown to hold for Al2O3, MgO, and Mg2SiO4. Since the enthalpy is listed in thermodynamic tables up to 3000 K, one can reasonably safely extrapolate KS up to lower mantle temperatures using this correlation. This correlation was anticipated in a theoretical 1966 paper, where the definition of the anharmonic parameter δ S was made in terms of properties which vary with temperature, δ _s = - left( {1/{α K_S }} right)left( {{δ K}/{δ T}} right)_{P'} where α is the volume coefficient of thermal expansion. The correlation was first confirmed for polycrystalline oxides in an experimental 1966 paper. Since the isotropic shear modulus, G, is linear with T, it is possible to estimate the sound velocities in the temperature regime just below the melting point.
Waheed, Umair bin
2013-09-01
On several simple models of isotropic and anisotropic media, we have studied the accuracy of the two-point paraxial traveltime formula designed for the approximate calculation of the traveltime between points S\\' and R\\' located in the vicinity of points S and R on a reference ray. The reference ray may be situated in a 3D inhomogeneous isotropic or anisotropic medium with or without smooth curved interfaces. The twopoint paraxial traveltime formula has the form of the Taylor expansion of the two-point traveltime with respect to spatial Cartesian coordinates up to quadratic terms at points S and R on the reference ray. The constant term and the coefficients of the linear and quadratic terms are determined from quantities obtained from ray tracing and linear dynamic ray tracing along the reference ray. The use of linear dynamic ray tracing allows the evaluation of the quadratic terms in arbitrarily inhomogeneous media and, as shown by examples, it extends the region of accurate results around the reference ray between S and R (and even outside this interval) obtained with the linear terms only. Although the formula may be used for very general 3D models, we concentrated on simple 2D models of smoothly inhomogeneous isotropic and anisotropic (~8% and ~20% anisotropy) media only. On tests, in which we estimated twopoint traveltimes between a shifted source and a system of shifted receivers, we found that the formula may yield more accurate results than the numerical solution of an eikonal-based differential equation. The tests also indicated that the accuracy of the formula depends primarily on the length and the curvature of the reference ray and only weakly depends on anisotropy. The greater is the curvature of the reference ray, the narrower its vicinity, in which the formula yields accurate results.
The thermalization of soft modes in non-expanding isotropic quark gluon plasmas
Blaizot, Jean-Paul; Mehtar-Tani, Yacine
2016-01-01
We discuss the role of elastic and inelastic collisions and their interplay in the thermalization of the quark-gluon plasma. We consider a simplified situation of a static plasma, spatially uniform and isotropic in momentum space. We focus on the small momentum region, which equilibrates first, and on a short time scale. We obtain a simple kinetic equation that allows for an analytic description of the most important regimes. The present analysis suggests that the formation of a Bose condensate, expected when only elastic collisions are present, is strongly hindered by the inelastic, radiative, processes.
Bottom-up metamaterials with an isotropic magnetic response in the visible
Mühlig, Stefan; Dintinger, José; Cunningham, Alastair; Scharf, Toralf; Bürgi, Thomas; Rockstuhl, Carsten; Lederer, Falk
A theoretical framework to analyze the optical properties of amorphous metamaterials made from meta-atoms which are amenable for a fabrication with bottom-up technologies is introduced. The achievement of an isotropic magnetic resonance in the visible is investigated by suggesting suitable designs for the meta-atoms. Furthermore, two meta-atoms are discussed in detail that were fabricated by self-assembling plasmonic nanoparticles using techniques from the field of colloidal nanochemistry. The metamaterials are experimentally characterized by spectroscopic means and the excitation of the magnetic dipole moment is clearly revealed. Advantages and disadvantages of metamaterials made from such meta-atoms are discussed.
Propagation of waves in the layer of a thermo-viscoelastic transversely isotropic medium
Directory of Open Access Journals (Sweden)
Gupta R.R.
2016-02-01
Full Text Available The article is presented to enhance our knowledge about the propagation of Lamb waves in the layer of a viscoelastic transversely isotropic medium in the context of thermoelasticity with GN theory of type-II and III. Secular equations for symmetric and skew-symmetric modes of wave propagation in completely separate terms are derived. The amplitudes of displacements and temperature distribution were also obtained. Finally, the numerical solution was carried out for cobalt and the dispersion curves, amplitudes of displacements and temperature distribution for symmetric and skew-symmetric wave modes are presented to evince the effect of anisotropy. Some particular cases are also deduced.
Study on isotropic Heisenberg interaction for the realization of SWAP {sup ±α} gates
Energy Technology Data Exchange (ETDEWEB)
Muthuganesan, R.; Sankaranarayanan, R., E-mail: sankar@nitt.edu [Department of Physics, National Institute of Technology, Tiruchirappalli, Tamilnadu– 620015 (India); Balakrishnan, S. [Materials Physics Division, School of Advanced Sciences, VIT University, Vellore– 632014 (India)
2015-06-24
It is known that nonlocal two-qubit gates are geometrically represented by tetrahedron called as Weyl chamber. Two edges of the Weyl chamber are formed by SWAP{sup ±α} family gates with 0 ≤ α ≤ 1. In this work SWAP{sup ±α} are being realized as two spin system with isotropic Heisenberg exchange interaction. The real parameter α is shown to be the function of duration and strength of interaction. Entanglement of the states generated by these two families of gates is studied with concurrence. Significance of time scale in realizing CNOT using SWAP{sup ±1/2} is highlighted.
Relativistic drag and emission radiation pressures in an isotropic photonic gas
Lee, Jeffrey S.; Cleaver, Gerald B.
2016-06-01
By invoking the relativistic spectral radiance, as derived by Lee and Cleaver,1 the drag radiation pressure of a relativistic planar surface moving through an isotropic radiation field, with which it is in thermal equilibrium, is determined in inertial and non-inertial frames. The forward- and backward-directed emission radiation pressures are also derived and compared. A fleeting (inertial frames) or ongoing (some non-inertial frames) Carnot cycle is shown to exist as a result of an intra-surfaces temperature gradient. The drag radiation pressure on an object with an arbitrary frontal geometry is also described.
Fast IIR isotropic 2-D complex Gabor filters with boundary initialization.
Bernardino, Alexandre; Santos-Victor, José
2006-11-01
Gabor filters are widely applied in image analysis and computer vision applications. This paper describes a fast algorithm for isotropic complex Gabor filtering that outperforms existing implementations. The main computational improvement arises from the decomposition of Gabor filtering into more efficient Gaussian filtering and sinusoidal modulations. Appropriate filter initial conditions are derived to avoid boundary transients, without requiring explicit image border extension. Our proposal reduces up to 39% the number of required operations with respect to state-of-the-art approaches. A full C++ implementation of the method is publicly available.
Fang, L.; Zhang, Y. J.; Fang, J.; Zhu, Y.
2016-08-01
We show by direct numerical simulations (DNSs) that in different types of isotropic turbulence, the fourth-order statistical invariants have approximately a linear relation, which can be represented by a straight line in the phase plane, passing two extreme states: the Gaussian state and the restricted Euler state. Also, each DNS case corresponds to an equilibrium region that is roughly Reynolds-dependent. In addition, both the time reversal and the compressibility effect lead to nonequilibrium transition processes in this phase plane. This observation adds a new restriction on the mean-field theory.
Wei, Lei; Bhattacharya, Nandini; Urbach, H Paul
2016-01-01
A high index dielectric nano-sphere can be excited and yet remain radiationless. A method to excite the non-radiating anapole mode of a high index isotropic dielectric nanosphere is presented. With tightly focused radially polarized beam illumination, the main-contributing electric dipole mode and magnetic modes can be zero with only a weak electric quadruple contributing to the total scattering. Further, with a standing wave illumination formed by two counter-propagating focused radially polarized beam under $4\\pi$ configuration, the ideal radiationless ananpole can be excited.
Design of a New Model of Multiband Miniature Antenna Near Isotropic
Directory of Open Access Journals (Sweden)
Abdellatif Berkat
2011-11-01
Full Text Available In this paper, we propose a new slotted multiband antennas simulated at different frequencies. The insertion of slots in the patch gives a good adapting frequency with various forms on the radiation pattern. The main feature of the proposed antenna is the capability to generate a near isotropic radiation pattern in different frequencies .The design details of the conceived antenna are presented and discussed. Simulations of the different reflection coefficient and radiation pattern are presented. These were carried out using CST Microwave Studio. This model has got numerous applications in network sensors, field measurements and electromagnetic compatibility.
Directory of Open Access Journals (Sweden)
Mesut UYANER
1999-02-01
Full Text Available In this study, the problem of a ring shaped-crack contained in an infinitely long solid cylinder of elastic perfectly-plastic material is considered. The problem is formulated for a transversely isotropic material by using integral transform technique under uniform load. Due to the geometry of the configuration, Hankel and Fourier integral transform techniques are chosen and the problem is reduced to a singular integral equation. This integral equation is solved numerically by using Gaussian Quadrature Formulae and the values are evaluated for discrete points. The plastic zone lengths are obtained by using the plastic strip model.
Institute of Scientific and Technical Information of China (English)
HOU Peng-fei; DING Hao-jiang; Leung Andraw-YT
2006-01-01
Exact solutions in form of elementary functions were derived for the stress and electric displacement intensity factors of a circular crack in a transversely isotropic piezoelectric space interacting with various stress and charge sources: force dipoles, electric dipoles, moments, force dilatation and rotation. The circular crack includes penny-shaped crack and external circular crack and the locations and orientations of these resultant sources with respect to the crack are arbitrary. Such stress and charge sources may model defects like vacancies, foreign particles, and dislocations. Numerical results are presented at last.
Study of the roughness in a photoresist masked, isotropic, SF6-based ICP silicon etch
DEFF Research Database (Denmark)
Larsen, Kristian Pontoppidan; Petersen, Dirch Hjorth; Hansen, Ole
2006-01-01
In this paper we study the etching behavior and the resulting roughness in photoresist-masked isotropic silicon plasma etch performed in an inductively coupled plasma (ICP) etcher using SF6. We report detailed observations of the resulting roughness for various etching parameters, covering......: pressure from 2.5 to 70 mTorr, SF6 flow rate from 50 to 300 sccm, platen power from 0 to 16 W, and ICP power from 1000 to 3000 W. Etch processes with a normalized roughness below 0.005 were found at low pressure, p = 10 mTorr, while larger normalized roughness, above 0.02, occurred at higher pressures, p...
Generalization of strain-gradient theory to finite elastic deformation for isotropic materials
Beheshti, Alireza
2017-03-01
This paper concerns finite deformation in the strain-gradient continuum. In order to take account of the geometric nonlinearity, the original strain-gradient theory which is based on the infinitesimal strain tensor is rewritten given the Green-Lagrange strain tensor. Following introducing the generalized isotropic Saint Venant-Kirchhoff material model for the strain-gradient elasticity, the boundary value problem is investigated in not only the material configuration but also the spatial configuration building upon the principle of virtual work for a three-dimensional solid. By presenting one example, the convergence of the strain-gradient and classical theories is studied.
Near-affine-invariant texture learning for lung tissue analysis using isotropic wavelet frames.
Depeursinge, Adrien; Van de Ville, Dimitri; Platon, Alexandra; Geissbuhler, Antoine; Poletti, Pierre-Alexandre; Müller, Henning
2012-07-01
We propose near-affine-invariant texture descriptors derived from isotropic wavelet frames for the characterization of lung tissue patterns in high-resolution computed tomography (HRCT) imaging. Affine invariance is desirable to enable learning of nondeterministic textures without a priori localizations, orientations, or sizes. When combined with complementary gray-level histograms, the proposed method allows a global classification accuracy of 76.9% with balanced precision among five classes of lung tissue using a leave-one-patient-out cross validation, in accordance with clinical practice.
Perlekar, Prasad; Pandit, Rahul
2010-01-01
We carry out a direct numerical simulation (DNS) study that reveals the effects of polymers on statistically steady, forced, homogeneous, isotropic fluid turbulence. We find clear manifestations of dissipation-reduction phenomena: On the addition of polymers to the turbulent fluid, we obtain a reduction in the energy dissipation rate, a significant modification of the fluid energy spectrum, especially in the deep-dissipation range, a suppression of small-scale intermittency, and a decrease in small-scale vorticity filaments. We also compare our results with recent experiments and earlier DNS studies of decaying fluid turbulence with polymer additives.
Directory of Open Access Journals (Sweden)
Hilmi Volkan Demir
2009-11-01
Full Text Available We present circular architecture bioimplant strain sensors that facilitate a strong resonance frequency shift with mechanical deformation. The clinical application area of these sensors is for in vivo assessment of bone fractures. Using a rectangular geometry, we obtain a resonance shift of 330 MHz for a single device and 170 MHz for its triplet configuration (with three side-by-side resonators on chip under an applied load of 3,920 N. Using the same device parameters with a circular isotropic architecture, we achieve a resonance frequency shift of 500 MHz for the single device and 260 MHz for its triplet configuration, demonstrating substantially increased sensitivity.
Relativistic Drag and Emission Radiation Pressures in an Isotropic Photonic Gas
Lee, Jeff S
2015-01-01
By invoking the relativistic spectral radiance, as derived by Lee and Cleaver [1], the drag radiation pressure of a relativistic planar surface moving through an isotropic radiation field, with which it is in thermal equilibrium, is determined in inertial and non-inertial frames. The forward- and rearward-directed emission radiation pressures are also derived and compared. A fleeting (inertial frames) or ongoing (some non-inertial frames) Carnot cycle is shown to exist as a result of an intra-surfaces temperature gradient. The drag radiation pressure on an object with an arbitrary frontal geometry is also described.
Wave beam propagation in a weakly inhomogeneous isotropic medium: paraxial approximation and beyond
Energy Technology Data Exchange (ETDEWEB)
Bornatici, M [INFM, Physics Department ' A. Volta' , University of Pavia, I-27100 Pavia (Italy); Maj, O [INFM, Physics Department, University of Milan, I-20133 Milan (Italy)
2003-05-01
The various methods put forward for the description of paraxial wave beams propagating in weakly inhomogeneous media are shown to be equivalent to each other. This issue is discussed in terms of a comparative analysis with respect to the complex eikonal-based solution relevant to the propagation of a Gaussian wave beam in a lens-like isotropic medium (such a solution being readily extendible to the propagation in a plasma slab). The accuracy of the paraxial solution thus considered is assessed numerically in comparison with the corresponding exact solution of the Helmholtz equation.
Quantitative modelling of viscoelasticity of isotropic fibrous composites with viscoelastic matrices
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
Despite the wide usage of isotropic fibrous composites with a viscoelastic polymer matrix,no analytic model for their mechanical behaviour is known.This paper develops such a model for time-dependent Young's modulus,showing that for typical constituents the time constants of composites are up to about 6% greater than the matrix shear time constant.Viscoelasticity is strongly suppressed for stiff fibres even at modest fibre volume fractions.Comparison with known results for particle and oriented fibre compos...
A hidden non-Abelian monopole in a 16-dimensional isotropic harmonic oscillator
Energy Technology Data Exchange (ETDEWEB)
Le, Van-Hoang; Nguyen, Thanh-Son; Phan, Ngoc-Hung [Department of Physics, HCMC University of Pedagogy, 280 An Duong Vuong, Ward 10, Dist. 5, Ho Chi Minh City (Viet Nam)
2009-05-01
We suggest one variant of generalization of the Hurwitz transformation by adding seven extra variables that allow an inverse transformation to be obtained. Using this generalized transformation we establish the connection between the Schroedinger equation of a 16-dimensional isotropic harmonic oscillator and that of a nine-dimensional hydrogen-like atom in the field of a monopole described by a septet of potential vectors in a non-Abelian model of 28 operators. The explicit form of the potential vectors and all the commutation relations of the algebra are given./.
Self-diffusion of a Rodlike Virus in the Isotropic Phase
Cush, Randy; Russo, Paul
2003-03-01
The optical tracer self diffusion of tobacco mosaic virus (TMV) was measured as a function of concentration in the isotropic phase. Diffusion decreases almost exponentially to about 40to the semidilute behavior of the semiflexible polymer, poly(benzylglutamate), diffusion-reducing interactions begin at lower reduced concentrations for TMV but are ultimately not as severe. The diffusion decreases about three times faster than expected from the Brownian dynamics simulations of thin rods by Doi, Yamamoto and Kano (J. Phys. Soc. Japan, 1984, 53, 3000-3003).
Maximum likelihood based multi-channel isotropic reverberation reduction for hearing aids
DEFF Research Database (Denmark)
Kuklasiński, Adam; Doclo, Simon; Jensen, Søren Holdt;
2014-01-01
We propose a multi-channel Wiener filter for speech dereverberation in hearing aids. The proposed algorithm uses joint maximum likelihood estimation of the speech and late reverberation spectral variances, under the assumption that the late reverberant sound field is cylindrically isotropic....... The dereverberation performance of the algorithm is evaluated using computer simulations with realistic hearing aid microphone signals including head-related effects. The algorithm is shown to work well with signals reverberated both by synthetic and by measured room impulse responses, achieving improvements...
Dynamic stability of fcc crystals under isotropic loading from first principles.
Rehák, Petr; Cerný, Miroslav; Pokluda, Jaroslav
2012-05-30
Lattice dynamics and stability of four fcc crystals (Al, Ir, Pt and Au) under isotropic (hydrostatic) tensile loading are studied from first principles using the linear response method and the harmonic approximation. The results reveal that, contrary to former expectations, strengths of all the studied crystals are limited by instabilities related to soft phonons with finite or vanishing wavevectors. The critical strains associated with such instabilities are remarkably lower than those related to the volumetric instability. On the other hand, the corresponding reduction of the tensile strength is by 20% at the most. An analysis of elastic stability conditions is also performed and the results obtained by means of both approaches are compared.
Energy Technology Data Exchange (ETDEWEB)
Mota, R D [Departamento de Matematicas, Centro de Investigacion y de Estudios Avenzados del IPN, 07000, Mexico DF (Mexico); Granados, V D [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, Ed. 9, Unidad Profesional Adolfo Lopez Mateos, 07738 Mexico DF (Mexico); Queijeiro, A [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, Ed. 9, Unidad Profesional Adolfo Lopez Mateos, 07738 Mexico DF (Mexico); Garcia, J [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, Ed. 9, Unidad Profesional Adolfo Lopez Mateos, 07738 Mexico DF (Mexico); Guzman, L [Unidad Profesional Interdisciplinaria en Ingenieria y Tecnologias Avanzadas, IPN Av. Instituto Politecnico Nacional No 2580, Col. La Laguna Ticoman, Delegacion Gustavo A Madero, CP 07340 Mexico DF (Mexico)
2003-05-02
We show that the supersymmetric radial ladder operators of the three-dimensional isotropic harmonic oscillator are contained in the spherical components of the creation and annihilation operators of the system. Also, we show that the constants of motion of the problem, written in terms of these spherical components, lead us to second-order radial operators. Further, we show that these operators change the orbital angular momentum quantum number by two units and are equal to those obtained by the Infeld-Hull factorization method.
Optimized cylindrical invisibility cloak with minimum layers of non-magnetic isotropic materials
Energy Technology Data Exchange (ETDEWEB)
Yu Zhenzhong; Feng Yijun; Xu Xiaofei; Zhao Junming; Jiang Tian, E-mail: yjfeng@nju.edu.cn [Department of Electronic Engineering, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093 (China)
2011-05-11
We present optimized design of cylindrical invisibility cloak with minimum layers of non-magnetic isotropic materials. Through an optimization procedure based on genetic algorithm, simpler cloak structure and more realizable material parameters can be achieved with better cloak performance than that of an ideal non-magnetic cloak with a reduced set of parameters. We demonstrate that a cloak shell with only five layers of two normal materials can result in an average 20 dB reduction in the scattering width for all directions when covering the inner conducting cylinder with the cloak. The optimized design can substantially simplify the realization of the invisibility cloak, especially in the optical range.
Simulation of propagation along an isolated skeletal muscle fiber in an isotropic volume conductor
DEFF Research Database (Denmark)
Henneberg, Kaj-åge; F.A., Roberge
1997-01-01
three-dimensional isotropic volume conductor. The current through the T system outlets at the sarcolemmal surface is comparable in magnitude to the sarcolemmal current density, but is of opposite polarity. When it is added to the sarcolemmal current, the resulting triphasic waveform has a 100% increase...... of the extracellular potential. Compared to an isolated fiber in a large volume of Ringer's solution, uniform propagation within a 2-mu m-thick volume conductor annulus is slowed down from 1.92 to 0.72 m/s, and the extracellular potential is increased from 1 to 108 mV peak to peak, in agreement with published...
A new high strength stainless maraging spring steel with isotropic shaping capability
Energy Technology Data Exchange (ETDEWEB)
Weber, H.R. [VACUUMSCHMELZE GmbH+Co. KG, Hanau (Germany)
2001-09-01
The production of complex shapes coupled with the demand for maximum final strength is called for by many design engineers in the fields of components, springs or elements for control technology, pneumatics, and hydraulics in order to meet the increasing trend to miniaturization and reducing the number of parts. A new FeNiCoMo-based maraging steel succeeds in combining the maximum strengths and isotropic shaping capability of non-stainless maraging steels with the anti-corrosive properties of austenitic CrNi steels. (orig.)
Irreducible decomposition of strain gradient tensor in isotropic strain gradient elasticity
Lazar, Markus
2016-01-01
In isotropic strain gradient elasticity, we decompose the strain gradient tensor into its irreducible pieces under the n-dimensional orthogonal group O(n). Using the Young tableau method for traceless tensors, four irreducible pieces (n>2), which are canonical, are obtained. In three dimensions, the strain gradient tensor can be decomposed into four irreducible pieces with 7+5+3+3 independent components whereas in two dimensions, the strain gradient tensor can be decomposed into three irreducible pieces with 2+2+2 independent components. The knowledge of these irreducible pieces is extremely useful when setting up constitutive relations and strain energy.
Basis-free expressions for derivatives of a subclass of nonsymmetric isotropic tensor functions
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The present paper generalizes the method for solving the derivatives of symmetric isotropic tensor-valued functions proposed by Dui and Chen (2004) to a subclass of nonsymmetric tensor functions satisfying the commutative condition.This subclass of tensor functions is more general than those investigated by the existing methods.In the case of three distinct eigenvalues, the commutativity makes it possible to introduce two scalar functions, which will be used to construct the general nonsymmetric tensor functions and their derivatives.In the cases of repeated eigenvalues, the results are acquired by taking limits.
Lorentz-violating neutral-pion decays in isotropic modified Maxwell theory
Klinkhamer, F R
2016-01-01
We consider an extension of the Standard Model with isotropic nonbirefringent Lorentz violation in the photon sector and specialize to the case of a "fast" photon with a phase velocity larger than the maximum attainable velocity of the fermions. With our conventions, this case corresponds to a negative Lorentz-violating parameter $\\kappa$ in the action. The decay rate of a neutral pion into two photons is calculated as a function of the 3-momentum of the initial pion and the negative Lorentz-violating parameter $\\kappa$ of the final photons.
LDEF (Prelaunch), AO187-02 : Chemical and Isotropic Measurements of Micrometeoroids by Secondary Ion
1984-01-01
LDEF (Prelaunch), AO187-02 : Chemical and Isotropic Measurements of Micrometeoroids by Secondary Ion Mass Spectrometry, Tray E08 The prelaunch photograph shows one hundred twenty (120) experiment capture cells installed on six support panels that are mounted in LDEF provided experiment trays. A capture cell consist of four polished high purity germanium plates covered with a 2.5um thick Mylar foil coated with 1300 angstroms of tantalum vapor deposited on the backside and 100 angstroms of gold-palladium vapor deposited on the front side. The capture cells are mounted within an aluminum frame on each panel. The fasteners are nonmagnetic stainless steel.
A variation iteration method for isotropic velocity-dependent potentials: Scattering case
Energy Technology Data Exchange (ETDEWEB)
Eed, H. [Applied Science Private University, Basic Science Department, Amman (Jordan)
2014-12-01
We propose a new approximation scheme to obtain analytic expressions for the Schroedinger equation with isotropic velocity-dependent potential to determine the scattering phase shift. In order to test the validity of our approach, we applied it to an exactly solvable model for nucleon-nucleon scattering. The results of the variation iteration method (VIM) formalism compare quite well with those of the exactly solvable model. The developed formalism can be applied in problems concerning pion-nucleon, nucleon-nucleon, and electron-atom scattering. (orig.)
Short-time evolution of Lagrangian velocity gradient correlations in isotropic turbulence
Fang, Le; Jin, G D
2015-01-01
We show by direct numerical simulation (DNS) that the Lagrangian cross correlation of velocity gradients in homogeneous isotropic turbulence increases at short times, whereas its auto-correlation decreases. Kinematic considerations allow to show that two invariants of the turbulent velocity field determine the short-time velocity gradient correlations. In order to get a more intuitive understanding of the dynamics for longer times, heuristic models are proposed involving the combined action of local shear and rotation. These models quantitatively reproduce the effects and disentangle the different physical mechanisms leading to the observations in the DNS.
Large-eddy simulations of viscoelastic isotropic turbulence with the FENE-P fluid
Pinho, Fernando T.; Ferreira, Pedro O.; B. da Silva, Carlos; Idmec/Feup Collaboration
2016-11-01
A new subgrid-scale (SGS) model developed for large-eddy simulations (LES) of dilute polymer solutions described by the Finitely Extensible Nonlinear Elastic constitutive equation closed with the Peterlin approximation (FENE-P), is presented. The filtered conformation tensor evolution equation uses the self-similarity of the polymer stretching terms, and the global equilibrium of the trace of the conformation tensor, while the SGS stresses are modelled with the classical Smagorinsky model. The new closure is assessed in direct numerical simulations (DNS) of forced isotropic turbulence using classical a-priori tests, and in a-posteriori (LES) showing excellent agreement with all the exact (filtered DNS) results.
Gao, Zhiwen; Zhou, Youhe
2015-04-01
Real fundamental solution for fracture problem of transversely isotropic high temperature superconductor (HTS) strip is obtained. The superconductor E-J constitutive law is characterized by the Bean model where the critical current density is independent of the flux density. Fracture analysis is performed by the methods of singular integral equations which are solved numerically by Gauss-Lobatto-Chybeshev (GSL) collocation method. To guarantee a satisfactory accuracy, the convergence behavior of the kernel function is investigated. Numerical results of fracture parameters are obtained and the effects of the geometric characteristics, applied magnetic field and critical current density on the stress intensity factors (SIF) are discussed.
Indian Academy of Sciences (India)
Baljeet Singh; Anand Kumar Yadav
2013-08-01
Reflection of plane waves is studied at a free surface of a perfectly conducting transversely isotropic elastic solid half-space with initial stress. The governing equations are solved to obtain the velocity equation which indicates the existence of two quasi planar waves in the medium. Reflection coefficients and energy ratios for reflected qP and qSV waves are derived and computed numerically for a particular material. Effects of the initial stress and magnetic field are shown graphically on these reflection coefficients and energy ratios.
Nonlinear Spinor field in isotropic space-time and dark energy models
Saha, Bijan
2016-01-01
Within the scope of isotropic FRW cosmological model the role of nonlinear spinor field in the evolution of the Universe is studied. It is found that unlike in anisotropic cosmological models in the present case the spinor field does not possess nontrivial non-diagonal components of energy-momentum tensor. The spinor description of different matter was given and evolution of the Universe corresponding to these source is illustrated. In the framework of a three fluid system the utility of spinor description of matter is established.
THE OPTIMIZATION OF PLUSH YARNS BULKING PROCESS
Directory of Open Access Journals (Sweden)
VINEREANU Adam
2014-05-01
Full Text Available This paper presents the experiments that were conducted on the installation of continuous bulking and thermofixing “SUPERBA” type TVP-2S for optimization of the plush yarns bulking process. There were considered plush yarns Nm 6.5/2, made of the fibrous blend of 50% indigenous wool sort 41 and 50% PES. In the first stage, it performs a thermal treatment with a turboprevaporizer at a temperature lower than thermofixing temperature, at atmospheric pressure, such that the plush yarns - deposed in a freely state on a belt conveyor - are uniformly bulking and contracting. It was followed the mathematical modeling procedure, working with a factorial program, rotatable central composite type, and two independent variables. After analyzing the parameters that have a direct influence on the bulking degree, there were selected the pre-vaporization temperature (coded x1,oC and the velocity of belt inside pre-vaporizer (coded x 2, m/min. As for the dependent variable, it was chosen the plush yarn diameter (coded y, mm. There were found the coordinates of the optimal point, and then this pair of values was verified in practice. These coordinates are: x1optim= 90oC and x 2optim= 6.5 m/min. The conclusion is that the goal was accomplished: it was obtained a good cover degree f or double-plush carpets by reducing the number of tufts per unit surface.
The Bulk Multicore Architecture for Improved Programmability
2009-12-01
dependences bundled together. In the Bulk Multi- core, the log must store only the total order of chunk commits, an approach we call DeLorean .13 The...ACM Press, New York, 2007, 69–80. 13. Montesinos, P., Ceze, L., and Torrellas, J. DeLorean : Recording and deterministically replaying shared
Failure by fracture in bulk metal forming
DEFF Research Database (Denmark)
Silva, C.M.A.; Alves, Luis M.; Nielsen, Chris Valentin
2015-01-01
This paper revisits formability in bulk metal forming in the light of fundamental concepts of plasticity,ductile damage and crack opening modes. It proposes a new test to appraise the accuracy, reliability and validity of fracture loci associated with crack opening by tension and out-of-plane she...
Bulk viscosity effects on ultrasonic thermoacoustic instability
Lin, Jeffrey; Scalo, Carlo; Hesselink, Lambertus
2016-11-01
We have carried out unstructured fully-compressible Navier-Stokes simulations of a minimal-unit traveling-wave ultrasonic thermoacoustic device in looped configuration. The model comprises a thermoacoustic stack with 85% porosity and a tapered area change to suppress the fundamental standing-wave mode. A bulk viscosity model, which accounts for vibrational and rotational molecular relaxation effects, is derived and implemented via direct modification of the viscous stress tensor, τij ≡ 2 μSij +λ/2 μ ∂uk/∂xk δij , where the bulk viscosity is defined by μb ≡ λ +2/3 μ . The effective bulk viscosity coefficient accurately captures acoustic absorption from low to high ultrasonic frequencies and matches experimental wave attenuation rates across five decades. Using pressure-based similitude, the model was downscaled from total length L = 2 . 58 m to 0 . 0258 m, corresponding to the frequency range f = 242 - 24200 Hz, revealing the effects of bulk viscosity and direct modification of the thermodynamic pressure. Simulations are carried out to limit cycle and exhibit growth rates consistent with linear stability analyses, based on Rott's theory.
Forming of bulk metallic glass microcomponents
DEFF Research Database (Denmark)
Wert, John A.; Thomsen, Christian; Jensen, Rune Debel
2009-01-01
The present article considers forward extrusion, closed-die forging and backward extrusion processes for fabrication of individual microcomponents from two bulk metallic glass (BMG) compositions: Mg60Cu30Y10 and Zr44Cu40Ag8Al8. Two types of tooling were used in the present work: relatively massive...
Polymer-fullerene bulk heterojunction solar cells
Janssen, RAJ; Hummelen, JC; Saricifti, NS
2005-01-01
Nanostructured phase-separated blends, or bulk heterojunctions, of conjugated Polymers and fullerene derivatives form a very attractive approach to large-area, solid-state organic solar cells.The key feature of these cells is that they combine easy, processing from solution on a variety of substrate
Fluctuating brane in a dilatonic bulk
Brax, P; Rodríguez-Martinez, M; Brax, Philippe; Langlois, David; Rodriguez-Martinez, Maria
2003-01-01
We consider a cosmological brane moving in a static five-dimensional bulk spacetime endowed with a scalar field whose potential is exponential. After studying various cosmological behaviours for the homogeneous background, we investigate the fluctuations of the brane that leave spacetime unaffected. A single mode embodies these fluctuations and obeys a wave equation which we study for bouncing and ever-expanding branes.
Longitudinal bulk a coustic mass sensor
DEFF Research Database (Denmark)
Hales, Jan Harry; Teva, Jordi; Boisen, Anja;
2009-01-01
Design, fabrication and characterization, in terms of mass sensitivity, is presented for a polycrystalline silicon longitudinal bulk acoustic cantilever. The device is operated in air at 51 MHz, resulting in a mass sensitivity of 100 HZ/fg (1 fg = 10{su−15 g). The initial characterization...
A Stereoscopic Look into the Bulk
Czech, Bartlomiej; McCandlish, Samuel; Mosk, Benjamin; Sully, James
2016-01-01
We present the foundation for a holographic dictionary with depth perception. The dictionary consists of natural CFT operators whose duals are simple, diffeomorphism-invariant bulk operators. The CFT operators of interest are the "OPE blocks," contributions to the OPE from a single conformal family. In holographic theories, we show that the OPE blocks are dual at leading order in 1/N to integrals of effective bulk fields along geodesics or homogeneous minimal surfaces in anti-de Sitter space. One widely studied example of an OPE block is the modular Hamiltonian, which is dual to the fluctuation in the area of a minimal surface. Thus, our operators pave the way for generalizing the Ryu-Takayanagi relation to other bulk fields. Although the OPE blocks are non-local operators in the CFT, they admit a simple geometric description as fields in kinematic space--the space of pairs of CFT points. We develop the tools for constructing local bulk operators in terms of these non-local objects. The OPE blocks also allow ...
Energy Technology Data Exchange (ETDEWEB)
Ghosh, G., E-mail: g-ghosh@northwestern.edu [Department of Materials Science and Engineering, Robert R. McCormick School of Engineering and Applied Science, Northwestern University, 2220 Campus Drive, Evanston, IL 60208-3108 (United States)
2015-08-15
A comprehensive computational study of elastic properties of cementite (Fe{sub 3}C) and its alloyed counterparts (M{sub 3}C (M = Al, Co, Cr, Cu, Fe, Hf, Mn, Mo, Nb, Ni, Si, Ta, Ti, V, W, Zr, Cr{sub 2}FeC and CrFe{sub 2}C) having the crystal structure of Fe{sub 3}C is carried out employing electronic density-functional theory (DFT), all-electron PAW pseudopotentials and the generalized gradient approximation for the exchange-correlation energy (GGA). Specifically, as a part of our systematic study of cohesive properties of solids and in the spirit of materials genome, following properties are calculated: (i) single-crystal elastic constants, C{sub ij}, of above M{sub 3}Cs; (ii) anisotropies of bulk, Young’s and shear moduli, and Poisson’s ratio based on calculated C{sub ij}s, demonstrating their extreme anisotropies; (iii) isotropic (polycrystalline) elastic moduli (bulk, shear, Young’s moduli and Poisson’s ratio) of M{sub 3}Cs by homogenization of calculated C{sub ij}s; and (iv) acoustic Debye temperature, θ{sub D}, of M{sub 3}Cs based on calculated C{sub ij}s. We provide a critical appraisal of available data of polycrystalline elastic properties of alloyed cementite. Calculated single crystal properties may be incorporated in anisotropic constitutive models to develop and test microstructure-processing-property-performance links in multi-phase materials where cementite is a constituent phase.
Integration of bulk piezoelectric materials into microsystems
Aktakka, Ethem Erkan
Bulk piezoelectric ceramics, compared to deposited piezoelectric thin-films, provide greater electromechanical coupling and charge capacity, which are highly desirable in many MEMS applications. In this thesis, a technology platform is developed for wafer-level integration of bulk piezoelectric substrates on silicon, with a final film thickness of 5-100microm. The characterized processes include reliable low-temperature (200°C) AuIn diffusion bonding and parylene bonding of bulk-PZT on silicon, wafer-level lapping of bulk-PZT with high-uniformity (+/-0.5microm), and low-damage micro-machining of PZT films via dicing-saw patterning, laser ablation, and wet-etching. Preservation of ferroelectric and piezoelectric properties is confirmed with hysteresis and piezo-response measurements. The introduced technology offers higher material quality and unique advantages in fabrication flexibility over existing piezoelectric film deposition methods. In order to confirm the preserved bulk properties in the final film, diaphragm and cantilever beam actuators operating in the transverse-mode are designed, fabricated and tested. The diaphragm structure and electrode shapes/sizes are optimized for maximum deflection through finite-element simulations. During tests of fabricated devices, greater than 12microm PP displacement is obtained by actuation of a 1mm2 diaphragm at 111kHz with management IC, which incorporates a supply-independent bias circuitry, an active diode for low-dropout rectification, a bias-flip system for higher efficiency, and a trickle battery charger. The overall system does not require a pre-charged battery, and has power consumption of sleep-mode (simulated). Under lg vibration at 155Hz, a 70mF ultra-capacitor is charged from OV to 1.85V in 50 minutes.
46 CFR 148.04-23 - Unslaked lime in bulk.
2010-10-01
... 46 Shipping 5 2010-10-01 2010-10-01 false Unslaked lime in bulk. 148.04-23 Section 148.04-23... HAZARDOUS MATERIALS IN BULK Special Additional Requirements for Certain Material § 148.04-23 Unslaked lime in bulk. (a) Unslaked lime in bulk must be transported in unmanned, all steel, double-hulled...
Institute of Scientific and Technical Information of China (English)
钱祖文
1994-01-01
In the case of SV- or SH-wave oblique incidence,the reflection and refraction of the second-order bulk waves resulting from a plane boundary between two solid media are investigated and the mathematical expressions of them are given.It is shown that an SH-wave incidence is absolutely necessary to an overall knowledge of the relationship between the TOEs for isotropic solid.The importance of both contributions of the nonaccumulation waves and the effects of the boundary surface are indicated by numerical computation.
An equation of state for granular media at the limit state of isotropic compression
Oquendo, W. F.; Muñoz, J. D.; Radjai, F.
2016-04-01
It is well believed that the volumetric entropy of Edwards captures part of the physics of granular media, but it is still unclear whether it can be applied to granular systems under mechanical stress. By working out a recent proposal by Aste, Di Matteo et al. to measure Edwards' compactivity from the volume distribution of Voronoï or Delaunay tessellations (Phys. Rev. E, 77 (2008) 021309), and assuming that the total volume divides into elementary cells of fixed minimal volume, we derive an equation of state relating the compactivity to the packing fraction, and we show by extensive molecular-dynamics simulations that this equation and its underlying assumption describe well the volumetric aspects of both the limit state of isotropic compression and the limit state of shear (also called critical state in soil mechanics) for three-dimensional ensembles of mono-disperse spheres, for a broad range of the sliding and rolling friction coefficients. In addition, by using the limit state of isotropic compression as testing ground, we find that the compactivity, the entropy per elementary cell and the number of elementary cells per grain computed by this method are the same within statistical precision, either by using Voronoï, Delaunay, or centroidal Voronoï tessellations, allowing thus for an objective definition. This means that not only Aste's cell method is robust and suitable to measure Edwards' compactivity of granular systems under mechanical stress but also the actual nature of the elementary cells might be unimportant.
Growth-induced axial buckling of a slender elastic filament embedded in an isotropic elastic matrix
O'Keeffe, Stephen G.
2013-11-01
We investigate the problem of an axially loaded, isotropic, slender cylinder embedded in a soft, isotropic, outer elastic matrix. The cylinder undergoes uniform axial growth, whilst both the cylinder and the surrounding elastic matrix are confined between two rigid plates, so that this growth results in axial compression of the cylinder. We use two different modelling approaches to estimate the critical axial growth (that is, the amount of axial growth the cylinder is able to sustain before it buckles) and buckling wavelength of the cylinder. The first approach treats the filament and surrounding matrix as a single 3-dimensional elastic body undergoing large deformations, whilst the second approach treats the filament as a planar, elastic rod embedded in an infinite elastic foundation. By comparing the results of these two approaches, we obtain an estimate of the foundation modulus parameter, which characterises the strength of the foundation, in terms of the geometric and material properties of the system. © 2013 Elsevier Ltd. All rights reserved.
On the Schrodinger equations with isotropic and anisotropic fourth-order dispersion
Directory of Open Access Journals (Sweden)
Elder J. Villamizar-Roa
2016-01-01
Full Text Available This article concerns the Cauchy problem associated with the nonlinear fourth-order Schrodinger equation with isotropic and anisotropic mixed dispersion. This model is given by the equation $$ i\\partial_tu+\\epsilon \\Delta u+\\delta A u+\\lambda|u|^\\alpha u=0,\\quad x\\in\\mathbb{R}^{n},\\; t\\in \\mathbb{R}, $$ where A is either the operator $\\Delta^2$ (isotropic dispersion or $\\sum_{i=1}^d\\partial_{x_ix_ix_ix_i}$, $1\\leq d
Energy Technology Data Exchange (ETDEWEB)
Bruhns, O.T.; Xiao, H.; Meyers, A. [Bochum Univ. (Germany). Inst. fuer Mechanik
2001-07-01
Recently, a new Eulerian rate-type isotropic-hardening elastoplasticity model has been established by utilizing the newly discovered logarithmic rate. It has been proved that this model is unique among all isotropic hardening elastoplastic models with all possible objective corotational stress rates and other known objective stress rates by virtue of the self-consistency criterion: the hypoelastic formulation intended for elastic behaviour must be exactly integrable to deliver a hyperelastic relation. The simple shear response of this model has been studied and shown to be reasonable for both the shear and normal stress components. The objective of this work is to further study the large deformation response of this model, in particular, the second-order effects, including the well-known Swift effect, in torsion of thin-walled cylindrical tubes with free ends. An analytical perturbation solution is derived, and numerical results are presented by means of the Runge-Kutta method. It is shown that the prediction of this model for the shear stress is in good accord with experimental data, but the predicted axial length change is negligibly small and much less than experimental data. This suggests that the strain-induced anisotropy may be the main cause of the Swift effect. (orig.)
Alkhalifah, Tariq Ali
2012-04-30
Traveltime information is crucial for parameter estimation, especially if the medium is described by a set of anisotropy parameters. We can efficiently estimate these parameters if we are able to relate them analytically to traveltimes, which is generally hard to do in inhomogeneous media. I develop traveltime approximations for transversely isotropic media with a horizontal symmetry axis (HTI) as simplified and even linear functions of the anisotropy parameters. This is accomplished by perturbing the solution of the HTI eikonal equation with respect to the anellipticity parameter, η and the azimuth of the symmetry axis (typically associated with the fracture direction) from a generally inhomogeneous, elliptically anisotropic background medium. Such a perturbation is convenient since the elliptically anisotropic information might be obtained from well velocities in HTI media. Thus, we scan for only η and the symmetry-axis azimuth. The resulting approximations can provide a reasonably accurate analytical description of the traveltime in a homogenous background compared to other published moveout equations. They also help extend the inhomogenous background isotropic or elliptically anisotropic models to an HTI one with a smoothly variable η and symmetry-axis azimuth. © 2012 European Association of Geoscientists & Engineers.
Decoupled equations for reverse time migration in tilted transversely isotropic media
Zhan, Ge
2012-03-01
Conventional modeling and migration for tilted transversely isotropic (TTI) media may suffer from numerical instabilities and shear wave artifacts due to the coupling of the P-wave and SV-wave modes in the TTI coupled equations. Starting with the separated P- and SV-phase velocity expressions for vertical transversely isotropic (VTI) media, we extend these decoupled equations for modeling and reverse time migration (RTM) in acoustic TTI media. Compared with the TTI coupled equations published in the geophysical literature, the new TTI decoupled equations provide a more stable solution due to the complete separation of the P-wave and SV-wave modes. The pseudospectral method is the most convenient method to implement these equations due to the form of wavenumber expressions and has the added benefit of being highly accurate and thus avoiding numerical dispersion. The rapid expansion method (REM) in time is employed to produce a broad band numerically stable time evolution of the wavefields. Synthetic results validate the proposed TTI decoupled equations and show that modeling and RTM in TTI media with the decoupled equations remain numerically stable even for models with strong anisotropy and sharp contrasts. © 2012 Society of Exploration Geophysicists.