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 a...... number of layers. The effective parameters retrieval method based on the wave propagation simulation is proposed and compared with standard procedure. It is shown that standard restoration method while used for the S-parameters spectra calculations with pulse sources excitation can contain an error...
Nested structures approach for bulk 3D negative index materials
DEFF Research Database (Denmark)
Andryieuski, Andrei; Malureanu, Radu; Lavrinenko, Andrei
2009-01-01
We propose a generic conceptual idea to obtain bulk 3D negative index metamaterials, which exhibit isotropic properties. The design is based on the nested structures approach, when one element providing magnetic response is inserted into another design with negative dielectric constant. Both...
Nested structures approach in designing an isotropic negative-index material for infrared
DEFF Research Database (Denmark)
Andryieuski, Andrei; Malureanu, Radu; Lavrinenko, Andrei
2009-01-01
We propose a new generic approach for designing isotropic metamaterial with nested cubic structures. As an example, a three-dimensional isotropic unit cell design "Split Cube in Cage" (SCiC) is shown to exhibit an effective negative refractive index on infrared wavelengths. We report on the refra...... refractive index reaching -2.3 and the figure of merit as high as 2.7. The structure exhibits potential for application as a building block of isotropic negative-index materials....
A Three-Dimensionally Isotropic and Perfectly Vacuum-Impedance-Matched Negative-Index Material
Shen, Jian Qi
2014-12-01
A new scenario for realizing a gain left-handed atomic vapor medium based on both dressed-state mixed-parity transitions (for simultaneous electric- and magnetic-dipole resonance) and incoherently-pumped population transfer (for high gain amplification) in a four-level atomic system is suggested. Dressed-state assisted simultaneous electric- and magnetic-dipole allowed transitions in such a four-level atomic system (of, e.g., neutral alkali-metal atoms such as lithium and potassium atoms) are utilized for achieving negative refractive index with impedance perfectly matched to vacuum. The attractive features of the present scenario include: i) three-dimensionally isotropic negative indices; ii) incoherent-gain wave amplification; iii) perfect impedance matching to vacuum. All these important properties of the double-negative medium would have potential applications in designing some optical and photonic devices, including particularly subwavelength focusing system and negative-index superlens for perfect imaging.
International Nuclear Information System (INIS)
We investigate theoretically and numerically the photonic band structure in the optical domain of an array of core–shell metal-semiconductor nanowires. Corresponding negative-index photonic bands are calculated, showing isotropic equifrequency surfaces. The effective (negative) electric permittivity and magnetic permeability, retrieved from S-parameters, are used to compare the performance of such nanowire arrays with homogeneous media in canonical examples, such as refraction through a prism and flat-lens focusing. Very good agreement is found, confirming the effective medium behavior of the nanowire array as a low-loss, isotropic (2D) and bulk, optical negative index metamaterial. Indeed, disorder is introduced to further stress its robustness. (paper)
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...
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.
Chiral Negative-Index Metamaterials in Terahertz
Zhang, Shuang; Park, Yong-Shik; Li, Jensen; Lu, Xinchao; Zhang, Weili; Zhang, Xiang
2008-01-01
Negative index metamaterials (NIMs) give rise to unusual and intriguing properties and phenomena, which may lead to important applications such as superlens, subwavelength cavity and slow light devices. However, the negative refractive index in metamaterials normally requires a stringent condition of simultaneously negative permittivity and negative permeability. A new class of negative index metamaterials - chiral NIMs, have been recently proposed. In contrast to the conventional NIMs, chira...
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.
Chiral Negative-Index Metamaterials in Terahertz
Zhang, Shuang; Li, Jensen; Lu, Xinchao; Zhang, Weili; Zhang, Xiang
2008-01-01
Negative index metamaterials (NIMs) give rise to unusual and intriguing properties and phenomena, which may lead to important applications such as superlens, subwavelength cavity and slow light devices. However, the negative refractive index in metamaterials normally requires a stringent condition of simultaneously negative permittivity and negative permeability. A new class of negative index metamaterials - chiral NIMs, have been recently proposed. In contrast to the conventional NIMs, chiral NIMs do not require the above condition, thus presenting a very robust route toward negative refraction. Here we present the first experimental demonstration of a chiral metamaterial exhibiting negative refractive index down to n=-5 at terahertz frequencies, with only a single chiral resonance. The strong chirality present in the structure lifts the degeneracy for the two circularly polarized waves and relieves the double negativity requirement. Chiral NIM are predicted to possess intriguing electromagnetic properties t...
Controlling the second-harmonic in a phase matched negative-index metamaterial
Rose, Alec; Huang, Da; Smith, David R.
2011-01-01
Nonlinear metamaterials (NLMMs) have been predicted to support new and exciting domains in the manipulation of light, including novel phase matching schemes for wave mixing. Most notable is the so-called nonlinear-optical mirror, in which a nonlinear negative-index medium emits the generated frequency towards the source of the pump. For the first time, we experimentally demonstrate the nonlinear-optical mirror effect in a bulk negative-index NLMM, along with two other novel phase matching con...
Negative-Index Media for Matter Waves
Perales, F.; Bocvarski, V.; Baudon, J.; Hamamda, M.; Grucker, J.; Dutier, G.; Mainos, C.; Boustimi, M.; Ducloy, M.
2010-02-01
One reviews the recently introduced field of matter-wave "meta-optics", i.e. the extension of optical negative-index media (NIM) to atom optics. After emphasizing the differences with light meta-optics and particularly the necessary transient character of NIM's in atom optics, we present the way of generating matter-wave NIM's and their general properties: negative refraction, atom meta-lenses. Finally their specific features are reviewed: longitudinal wave packet narrowing associated to a time-reversal effect, transient revivals of evanescent matter waves and atom reflection echoes at a potential barrier.
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.
Structures with negative index of refraction
Soukoulis, Costas M.; Zhou, Jiangfeng; Koschny, Thomas; Zhang, Lei; Tuttle, Gary
2011-11-08
The invention provides simplified negative index materials (NIMs) using wire-pair structures, 4-gap single ring split-ring resonator (SRR), fishnet structures and overleaf capacitor SRR. In the wire-pair arrangement, a pair of short parallel wires and continuous wires are used. In the 4-gap single-ring SRR, the SRRs are centered on the faces of a cubic unit cell combined with a continuous wire type resonator. Combining both elements creates a frequency band where the metamaterial is transparent with simultaneously negative .di-elect cons. and .mu.. In the fishnet structure, a metallic mesh on both sides of the dielectric spacer is used. The overleaf capacitor SRR changes the gap capacities to small plate capacitors by making the sections of the SRR ring overlap at the gaps separated by a thin dielectric film. This technique is applicable to conventional SRR gaps but it best deploys for the 4-gap single-ring structures.
Modulation instability of structured-light beams in negative-index metamaterials
Silahli, Salih Z; Litchinitser, Natalia M
2016-01-01
One of the most fundamental properties of isotropic negative-index metamaterials, namely opposite directionality of the Poynting vector and the wavevector, enable many novel linear and nonlinear regimes of light-matter interactions. Here, we predict distinct characteristics of azimuthal modulation instability of optical vortices with different topological charges in negative-index metamaterials with Kerr-type and saturable nonlinearity. We derive an analytical expression for the spatial modulation-instability gain for the Kerr-nonlinearity case and show that a specific condition relating the diffraction and the nonlinear lengths must be fulfilled for the azimuthal modulation instability to occur. Finally, we investigate the rotation of the necklace beams due to the transfer of orbital angular momentum of the generating vortex onto the movement of solitary necklace beams. We show that the direction of rotation is opposite in the positive- and negative-index materials.
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...
Isotropic optical metamaterials
DEFF Research Database (Denmark)
Lederer, Falk; Rockstuhl, C.; Menzel, C.; Paul, T.; Andryieuski, Andrei; Malureanu, Radu; Lavrinenko, Andrei
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...
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.
International Nuclear Information System (INIS)
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)max increased from 65 to 120 kJ/m3 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
Modulation instability of structured-light beams in negative-index metamaterials
Silahli, Salih Z.; Walasik, Wiktor; Litchinitser, Natalia M.
2016-05-01
One of the most fundamental properties of isotropic negative-index metamaterials (NIMs), namely opposite directionality of the Poynting vector and the wavevector, enable many novel linear and nonlinear regimes of light–matter interactions. Here, we predict distinct characteristics of azimuthal modulation instability (MI) of optical vortices with different topological charges in NIMs with Kerr-type and saturable nonlinearity. We derive an analytical expression for the spatial modulation-instability gain for the Kerr-nonlinearity case and show that a specific condition relating the diffraction and the nonlinear lengths must be fulfilled for the azimuthal MI to occur. Finally, we investigate the rotation of the necklace beams due to the transfer of orbital angular momentum of the generating vortex on the movement of solitary necklace beams. We show that the direction of rotation is opposite in positive- and negative-index materials.
Subwavelength resolution with a negative-index metamaterial superlens
Aydin, Koray; Bulu, Irfan; Ozbay, Ekmel
2007-06-01
Negative-index metamaterials are candidates for imaging objects with sizes smaller than a half-wavelength. The authors report an impedance-matched, low loss negative-index metamaterial superlens that is capable of resolving subwavelength features of a point source with a 0.13λ resolution, which is the highest resolution achieved by a negative-index metamaterial. By separating two point sources with a distance of λ /8, they were able to detect two distinct peaks on the image plane. They also showed that the metamaterial based structure has a flat lens behavior.
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. PMID:21231386
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.
Numerical study of electromagnetic waves interacting with negative index materials.
Kolinko, Pavel; Smith, David
2003-04-01
We study numerically the electromagnetic scattering properties of structures with negative indices of refraction. To perform this analysis, we utilize a commercial finite-element based electromagnetic solver (HFSS, Ansoft), in which a negative index material can be formed from mesh elements whose permittivity and permeability are both negative. In particular, we investigate the expected transmission characteristics of a finite beam incident on negative index prisms and lenses. We also confirm numerically the predicted superlens effect of an image formed by a planar slab with index n=-1, using two subwavelength (ë/20) slits as objects. PMID:19461776
Dynamics of evanescent matter waves in negative-index media
Hamamda, M.; Bocvarski, V.; Perales, F.; Baudon, J.; Dutier, G.; Mainos, C.; Boustimi, M.; Ducloy, M.
2010-11-01
Semi-evanescent and evanescent matter waves produced by an atom wave packet impinging on a repulsive barrier can be back-refracted and reconstructed by the application of negative-index 'comoving' potential pulses. One shows that those collapses and revivals generate a matter wave confined on both sides of the barrier border ('surface matter wave') and should be observable via the retardation of atom reflection from the barrier interface. This property, joined to the possibility recently demonstrated of inducing negative refraction of atom waves, makes such potentials a matter-wave counterpart of negative-index materials or 'meta materials' well known in light optics.
Negative Index Materials and Plasmonic Antennas Based Nanocouplers
DEFF Research Database (Denmark)
Andryieuski, Andrei
This thesis describes the development, design and fabrication of the nanocoupler that is a device coupling light from conventional optical fiber to the nanosize plasmonic slot waveguide. This device can decrease the coupling region to several micrometers providing compact interface between 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...... geometrical parameters of the nanoantenna couplers are found out. The best performance is shown by the battle axe nanocoupler that has an antenna figure of merit equal to 1.8 μm2 for five antenna periods. That is 90 times larger than antenna figure of merit for the waveguide without nanocoupler (0.02 μm2...
Surface waves excited from negative-index materials
International Nuclear Information System (INIS)
Studies on electromagnetic surface waves along the surface of a finitely thick plate made from negative-index materials are presented in this paper. Through theoretical analysis we worked out requirements on permeability and permittivity for surface waves to exist. Comparing with the model of a plate with infinite thickness, the one of finite thickness shows released requirements, leading to potential applications in guiding wave and developing radiation sources. With the help of particle-in-cell simulations, we examined theoretical predictions and demonstrated field distributions of surface waves. - Highlights: • Surface modes along a finitely thick plate with/without PEC substrate are studied. • Both positive-index material and negative-index material models are investigated. • Requirements are obtained to make surface waves exist. • The requirements are released comparing with an infinitely thick model. • Higher frequency of some surface modes can be excited with thicker NIM plate
Self-assembled hexagonal double fishnets as negative index materials
Lodewijks, Kristof; Van Roy, Willem; Borghs, Gustaaf; Van Dorpe, Pol
2010-01-01
We show experimentally the successful use of colloidal lithography for the fabrication of negative index metamaterials in the near-infrared wavelength range. In particular, we investigated a specific implementation of the widely studied double fishnet metamaterials, consisting of a gold-silica-gold layer stack perforated by a hexagonal array of round holes. Tuning of the hole diameter allows us to tailor these self-assembled metamaterials both as single- ({\\epsilon} < 0) and double ({\\epsilon} < 0 and {\\mu} < 0) negative metamaterials.
Defect in photonic crystal with negative index material
Institute of Scientific and Technical Information of China (English)
TANG Kang-song; XIANG Yuan-jiang; WEN Shuang-chun
2006-01-01
The transmission property of the photonic crystal containing negative index material is analyzed by means of transfer matrix method.It is demonstrated that a defect mode appears in the conventional Bragg gap and the defect mode is sensitive to the position of the defect cell.For the first time to our knowledge we introduce two defects into such a structure and discuss the dependence of the transmission on the interval of the two defect cells.It is found that a wide degenerate defect mode appears in the Bragg gap,and this degenerate defect mode splits into two different defect modes when the two defect cells become closer.
Stability criterion for Gaussian pulse propagation through negative index materials
International Nuclear Information System (INIS)
We analyze the dynamics of propagation of a Gaussian light pulse through a medium having a negative index of refraction employing the recently reported projection operator technique. The governing modified nonlinear Schroedinger equation, obtained by taking into account the Drude dispersive model, is expressed in terms of the parameters of Gaussian pulse, called collective variables, such as width, amplitude, chirp, and phase. This approach yields a system of ordinary differential equations for the evolution of all the pulse parameters. We demonstrate the dependence of stability of the fixed-point solutions of these ordinary differential equations on the linear and nonlinear dispersion parameters. In addition, we validate the analytical approach numerically utilizing the method of split-step Fourier transform.
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.
Matzner, H; Matzner, Haim; Donald, Kirk T. Mc
2003-01-01
We give two examples of antennas with isotropic radiation patterns. Because these involve elliptically polarized radiation, they evade the "hairy-ball theorem" that suggests isotropic radiation would be impossible.
Low-loss negative index metamaterials for X, Ku, and K microwave bands
International Nuclear Information System (INIS)
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
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...
Focus modulation of cylindrical vector beams through negative-index grating lenses
Wang, Shengming; Xu, Ji; Zhong, Yi; Ren, Rong; Lu, Yunqing; Wan, Hongdan; Wang, Jin; Ding, Jianping
2016-08-01
A cylindrically symmetric negative-index grating lens composed of unitary material is proposed as an effective method to modulate the focusing of cylindrical vector beams (CVBs). The grating parameters are designed to obtain an appropriate negative index, and the lens profile is tailored to realize the constructive interference. The plano-concave lens is parameterized to achieve desired focal length and the plano-cone lens is proposed to obtain large depth of focus. An optical needle is generated with radially polarized incidence, and an optical tube is achieved with incidence of azimuthal polarization. Moreover, the presented modulation methods can be applied for any arbitrary polarized CVBs. This work offers a more flexible and effective approach to design negative-index lenses for subwavelength focusing of CVBs, which has potential application value in related areas, such as optical trapping, and other nano-optics fields.
Nanoengineering of a Negative-Index Binary-Staircase Lens for the Optics Regime
Casse, B D F; Lu, W T; Huang, Y J; Selvarasah, S; Dokmeci, M; Sridhar, S
2008-01-01
We show that a binary-staircase optical element can be engineered to exhibit an effective negative index of refraction, thereby expanding the range of optical properties theoretically available for future optoelectronic devices. The mechanism for achieving a negative-index lens is based on exploiting the periodicity of the surface corrugation. By designing and nanofabricating a plano-concave binary-staircase lens in the InP/InGaAsP platform, we have experimentally demonstrated at 1.55 microns that such negative-index concave lenses can focus plane waves. The beam propagation in the lens was studied experimentally and was in excellent agreement with the three-dimensional finite-difference time-domain numerical simulations.
Negative index of refraction, perfect lenses and transformation optics -- some words of caution
Bergamin, Luzi
2010-01-01
In this paper we show that a negative index of refraction is not a direct implication of transformation optics with orientation-reversing diffeomorphisms. Rather a negative index appears due to a specific choice of sign freedom. Furthermore, we point out that the transformation designed lens, which relies on the concept of spacetime folding, does not amplify evanescent modes, in contrast to the Pendry-Veselago lens. Instead, evanescent modes at the image point are produced by a duplicated source and thus no imaging of the near field (perfect lensing) takes place.
Specific absorption rate analysis of broadband mobile antenna with negative index metamaterial
Alam, Touhidul; Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul
2016-03-01
This paper presents a negative index metamaterial-inspired printed mobile wireless antenna that can support most mobile applications such as GSM, UMTS, Bluetooth and WLAN frequency bands. The antenna consists of a semi-circular patch, a 50Ω microstrip feed line and metamaterial ground plane. The antenna occupies a very small space of 37 × 47 × 0.508 mm3, making it suitable for mobile wireless application. The perceptible novelty shown in this proposed antenna is that reduction of specific absorption rate using the negative index metamaterial ground plane. The proposed antenna reduced 72.11 and 75.53 % of specific absorption rate at 1.8 and 2.4 GHz, respectively.
Flat lenses constructed by graded negative index-based photonic crystals with tuned configurations
International Nuclear Information System (INIS)
Flat lenses are designed by means of graded negative refractive index-based photonic crystals (PCs) constructed using air-holes tuned with different shapes. By gradually modifying the filling factor along the transverse direction, we obtain the graded negative index-based lenses for the purpose of focusing an incident plane wave. The finite-difference and time-domain (FDTD) algorithm is adopted for numerical calculation. Our calculation results indicate that these lenses can finely focus incident plane waves. Moreover, for the same size of air-holes, the focusing properties of the lens with rectangular air-holes are better than those with the other shaped air-holes. The graded negative index PCs lenses could possibly enable new applications in optoelectronic systems. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Creating double negative index materials using the Babinet principle with one metasurface
Zhang, Lei; Koschny, Thomas; Soukoulis, Costas 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 \\epsilon, with perpendicular direction. Here we propose a new design, etched in a metallic plate to provide negative magnetic permeability \\mu, with perpendicular direction. The co...
Strong effect of surfaces on resolution limit of negative-index "superlens"
Bratkovsky, A. M.; A. Cano; Levanyuk, A. P.
2004-01-01
We show that subwavelength imaging by negative index materials (NIM), related to their "soft" electromagnetic response, is very (and non trivially) sensitive to the surface properties. A minute deviation of dielectric permittivity epsilon or magnetic permeability mu from the ideal values epsilon = mu = -1 in thin surface layer(s) results in drastic reduction of the resolution limit of a NIM slab. There may be a gap in the polariton spectrum and this would allow establishment of a stationary r...
Measurements of Broadband Negative Index in Space-Coiling Acoustic Metamaterials
Xie, Yangbo; Popa, Bogdan-Ioan; Zigoneanu, Lucian; Cummer, Steven A.
2012-01-01
We report the experimental demonstration of 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 l...
Sharma, Vivek Kumar; Goyal, Amit
2016-05-01
We explore the modulational instability and existence of dark, bright solitary wave solutions in negative index-materials (NIMs) modeled by generalized nonlinear Schrödinger equation with competing cubic-quintic and higher-order nonlinearities with dispersive permittivity and permeability. Parameter domains are delineated in which these ultrashort pulses exist in NIMs. Unlike the ordinary materials, these novel excitations occur for different signs of dispersion, Kerr and non-Kerr nonlinearities.
Modulation instability in a triangular three-core coupler with a negative-index material channel
Shafeeque Ali, A. K.; Nithyanandan, K.; Porsezian, K.; Maimistov, Andrei I.
2016-03-01
A theoretical investigation of the modulation instability (MI) in the three core triangular oppositely directed coupler with negative index material channel is presented. This class of couplers have an effective feedback mechanism due to the opposite directionality of the phase velocities in the negative and positive index channels. It is found that the MI in the nonlinear three core triangular oppositely directed coupler is significantly influenced by the ratio of the forward- to backward-propagating wave power and nonlinearity. Also, in the case of the normal dispersion regime a threshold-like behavior is observed, whereas this behavior is not identified in the anomalous dispersion regime. For the asymmetric case (h\
A single-layer wide-angle negative-index metamaterial at visible freque
Energy Technology Data Exchange (ETDEWEB)
Burgos, Stanley P. [California Inst. of Technology (CalTech), Pasadena, CA (United States); de Waele, Rene [FOM Inst. AMOLF, Amersterdam (Netherlands); Polman, Albert [FOM Inst. AMOLF, Amersterdam (Netherlands); Atwater, Harry A. [California Inst. of Technology (CalTech), Pasadena, CA (United States)
2010-04-18
Metamaterials are materials with artificial electromagnetic properties defined by their sub-wavelength structure rather than their chemical composition. Negative-index materials (NIMs) are a special class of metamaterials characterized by an effective negative index that gives rise to such unusual wave behaviour as backwards phase propagation and negative refraction. These extraordinary properties lead to many interesting functions such as sub-diffraction imaging and invisibility cloaking. So far, NIMs have been realized through layering of resonant structures, such as split-ring resonators, and have been demonstrated at microwave to infrared frequencies over a narrow range of angles-of-incidence and polarization. However, resonant-element NIM designs suffer from the limitations of not being scalable to operate at visible frequencies because of intrinsic fabrication limitations, require multiple functional layers to achieve strong scattering and have refractive indices that are highly dependent on angle of incidence and polarization. Here we report a metamaterial composed of a single layer of coupled plasmonic coaxial waveguides that exhibits an effective refractive index of -2 in the blue spectral region with a figure-of-merit larger than 8. The resulting NIM refractive index is insensitive to both polarization and angle-of-incidence over a ±50° angular range, yielding a wide-angle NIM at visible frequencies.
Shafeeque Ali, A. K.; Nithyanandan, K.; Porsezian, K.; Maimistov, Andrei I.
2016-02-01
A theoretical investigation on the influence of birefringence in the modulational instability (MI) spectra of an oppositely directed coupler (ODC) with a negative index material (NIM) channel is presented. We study the effect of birefringence on MI in linear and circular birefringent ODCs for both normal and anomalous dispersion regimes. It is found that besides the instability band due to nonlinear positive index material (PIM) and negative index material (NIM) channels, new symmetric instability regions are observed as a result of birefringent effects. Also defocusing nonlinearity suppresses the NIM band in the normal dispersion regime, but in the anomalous dispersion regime the defocusing nonlinearity enhances the gain of the NIM band. In contrast to the case of linear birefringence, in terms of MI gain from circular birefringence, only two birefringent bands dominate: the inherently PIM and NIM bands. This preponderance is attributed to the fact that the cross-phase modulation effect for the case of circular birefringence is stronger, thus allowing a better coupling between the beams, which results in the enhancement of the gain. Therefore, the manipulation of MI and solitons in an ODC is better performed when the birefringence is circular rather than linear. Here we report how to generate and manipulate MI and solitons in birefringent ODCs with a particular emphasis on a NIM channel.
Reversal of wave momentum in isotropic left-handed media
International Nuclear Information System (INIS)
The electromagnetic wave momentum is derived for a Lorentz medium and applied to study the momentum transfer to stationary, isotropic left-handed materials. The model includes material dispersion and losses, which are necessary for a causal medium with negative index of refraction. The results provide a rigorous proof of the force on free currents in a lossy medium and a validation of the theoretical separation of force based on the real and imaginary parts of the permittivity and permeability. The resulting electromagnetic wave momentum conservation theorem proves that the momentum flux of a monochromatic wave in an isotropic left-handed material is opposite to the power flow direction. However, the momentum density in a lossy medium with a negative index of refraction may be parallel or antiparallel to the power flow. The results are applied to predict the reversal of radiation pressure on free currents in a material with a negative index of refraction. Furthermore, conservation of momentum at a material boundary states that the tangential component of the wave momentum is conserved. Thus there is no electromagnetic shear force at the boundary between isotropic media, regardless of the sign of the refractive index
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.
Krowne, Clifford M
2007-01-01
This book deals with the subject of optical and electronic negative refraction (NR) and negative index materials NIM). Diverse approaches for achieving NR and NIM are covered, such as using photonic crystals, phononic crystals, split-ring resonators (SRRs) and continuous media, focusing of waves, guided-wave behavior, and nonlinear effects. Specific topics treated are polariton theory for LHMs (left handed materials), focusing of waves, guided-wave behavior, nonlinear optical effects, magnetic LHM composites, SRR-rod realizations, low-loss guided-wave bands using SRR-rods unit cells as LHMs, NR of electromagnetic and electronic waves in uniform media, field distributions in LHM guided-wave structures, dielectric and ferroelectric NR bicrystal heterostructures, LH metamaterial photonic-crystal lenses, subwavelength focusing of LHM/NR photonic crystals, focusing of sound with NR and NIMs, and LHM quasi-crystal materials for focusing.
Minimization of losses in a structure having a negative index of refraction
International Nuclear Information System (INIS)
A structure consisting of an array of wires cladded with a nonmagnetic dielectric and embedded in a ferrimagnetic host has been calculated to have a negative index of refraction. The structure has moderate losses over a bandwidth of a few GHz. The calculation takes into account the skin effect within the wires and is valid provided the wavelength of electromagnetic waves in the structure is long compared to the radius of the cladded wires. The structure's electromagnetic response is accurately described by the ferrimagnet's permeability and a permittivity derived in the long wavelength limit. Losses can be minimized by choosing the pass band to be between 30 and 80% of the plasma frequency and by choosing wires to be of the highest possible conductivity and largest radius compatible with the required plasma frequency
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. PMID:23679743
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.
International Nuclear Information System (INIS)
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
Parazzoli, Claudio G.; Greegor, Robert B.; Tanielian, M. H.
Metamaterials are engineered ring and wire composites whose response to an incident electromagnetic wave can be described by an effective negative dielectric permittivity ɛ and magnetic permeability μ. Simultaneous negative ɛ and μ within a given frequency band of a metamaterial gives rise to a negative index of refraction n. This has been demonstrated via a Snell's law experiment. The electromagnetic properties of many metamaterial structures in the microwave region are investigated through numerical simulations and experiments. A negative index of refraction, n, allows lenses with reduced primary (Seidel) aberrations compared to equivalent positive index lens. This is demonstrated both for cylindrical lenses and spherical lenses, as well as for the gradient index lenses. Detailed field maps of the focal region of the metamaterials lenses are made and compared to a comparable positive index of refraction lens.
International Nuclear Information System (INIS)
Superlenses based on metamaterials are promising candidates for achieving subwavelength resolution. We report here our experimental studies on super-resolution imaging from one-dimensional (1D) negative index metamaterial superlenses at microwave frequencies. The metamaterial structure under investigation is shown to have a left-handed transmission band at frequencies where both effective permittivity and permeability are negative. The retrieved effective parameters are in good agreement with the measurements. We achieved a resolution of 0.2λ by imaging a single point source from a 1D superlens. Moreover, the effect of the superlens' thickness on the resolution is studied. A thicker superlens suffers from more losses, which in turn reduces the resolution. Two point sources that were separated by distances that were smaller than a half-wavelength were successfully resolved with the negative index superlens
Energy Technology Data Exchange (ETDEWEB)
Ozbay, Ekmel; Li, Zhaofeng; Aydin, Koray [Nanotechnology Research Center and Department of Physics, Bilkent University, Bilkent, 06800 Ankara (Turkey)], E-mail: ozbay@bilkent.edu.tr, E-mail: aydin@fen.bilkent.edu.tr
2008-07-30
Superlenses based on metamaterials are promising candidates for achieving subwavelength resolution. We report here our experimental studies on super-resolution imaging from one-dimensional (1D) negative index metamaterial superlenses at microwave frequencies. The metamaterial structure under investigation is shown to have a left-handed transmission band at frequencies where both effective permittivity and permeability are negative. The retrieved effective parameters are in good agreement with the measurements. We achieved a resolution of 0.2{lambda} by imaging a single point source from a 1D superlens. Moreover, the effect of the superlens' thickness on the resolution is studied. A thicker superlens suffers from more losses, which in turn reduces the resolution. Two point sources that were separated by distances that were smaller than a half-wavelength were successfully resolved with the negative index superlens.
Ozbay, Ekmel; Li, Zhaofeng; Aydin, Koray
2008-07-01
Superlenses based on metamaterials are promising candidates for achieving subwavelength resolution. We report here our experimental studies on super-resolution imaging from one-dimensional (1D) negative index metamaterial superlenses at microwave frequencies. The metamaterial structure under investigation is shown to have a left-handed transmission band at frequencies where both effective permittivity and permeability are negative. The retrieved effective parameters are in good agreement with the measurements. We achieved a resolution of 0.2λ by imaging a single point source from a 1D superlens. Moreover, the effect of the superlens' thickness on the resolution is studied. A thicker superlens suffers from more losses, which in turn reduces the resolution. Two point sources that were separated by distances that were smaller than a half-wavelength were successfully resolved with the negative index superlens.
International Nuclear Information System (INIS)
This research focuses on a coherently driven four-level atomic medium with the aim of inducing a negative index of refraction while taking into consideration local field corrections as well as magnetoelectric cross coupling (i.e.,chirality) within the material's response functions. Two control fields are used to render the medium transparent for a probe field which simultaneously couples to an electric and a magnetic dipole transition, thus allowing one to test the permittivity and permeability of the material at the same time. Numerical simulations show that a negative index of refraction with low absorption can be obtained for a range of probe detunings while depending on number density and the ratio between the intensities of the control fields.
Derek Michael Forrester; Valerie J. Pinfield
2015-01-01
Here we show that, for sub-wavelength particles in a fluid, viscous losses due to shear waves and their influence on neighbouring particles significantly modify the effective acoustic properties, and thereby the conditions at which negative acoustic refraction occurs. Building upon earlier single particle scattering work, we adopt a multiple scattering approach to derive the effective properties (density, bulk modulus, wavenumber). We show,through theoretical prediction, the implications for ...
Md. Moinul Islam; Mohammad Tariqul Islam; Md. Samsuzzaman; Mohammad Rashed Iqbal Faruque; Norbahiah Misran; Mohd Fais Mansor
2015-01-01
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 ...
Energy Technology Data Exchange (ETDEWEB)
Wang, Yuanyuan; Wei, Yanyu; Jiang, Xuebing; Tang, Xianfeng; Shi, Xianbao; Gong, Yubin [National Key Laboratory of Science and Technology on Vacuum Electronics, School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054 (China); Li, Dazhi [Institute for Laser Technology, Suita, Osaka 565-0781 (Japan); Takano, Keisuke; Nakajima, Makoto [Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0781 (Japan); Feng, Jinjun [Beijing Vacuum Electronics Research Institute, Beijing 100016 (China); Miyamoto, Shuji [Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Ako, Hyogo 678-1205 (Japan)
2015-08-15
We present an analysis of a Cherenkov free-electron laser based on a single slab made from negative-index materials. In this system, a flat electron beam with finite thickness travelling close to the surface of the slab interacts with the copropagating electromagnetic surface mode. The dispersion equation for a finitely thick slab is worked out and solved numerically to study the dispersion relation of surface modes supported by negative-index materials, and the calculations are in good agreement with the simulation results from a finite difference time domain code. We find that under suitable conditions there is inherent feedback in such a scheme due to the characteristics of negative-index materials, which means that the system can oscillate without external reflectors when the beam current exceeds a threshold value, i.e., start current. Using the hydrodynamic approach, we setup coupled equations for this system, and solve these equations analytically in the small signal regime to obtain formulas for the spatial growth rate and start current.
International Nuclear Information System (INIS)
We present an analysis of a Cherenkov free-electron laser based on a single slab made from negative-index materials. In this system, a flat electron beam with finite thickness travelling close to the surface of the slab interacts with the copropagating electromagnetic surface mode. The dispersion equation for a finitely thick slab is worked out and solved numerically to study the dispersion relation of surface modes supported by negative-index materials, and the calculations are in good agreement with the simulation results from a finite difference time domain code. We find that under suitable conditions there is inherent feedback in such a scheme due to the characteristics of negative-index materials, which means that the system can oscillate without external reflectors when the beam current exceeds a threshold value, i.e., start current. Using the hydrodynamic approach, we setup coupled equations for this system, and solve these equations analytically in the small signal regime to obtain formulas for the spatial growth rate and start current
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.
Forrester, Derek Michael; Pinfield, Valerie J.
2015-12-01
Here we show that, for sub-wavelength particles in a fluid, viscous losses due to shear waves and their influence on neighbouring particles significantly modify the effective acoustic properties, and thereby the conditions at which negative acoustic refraction occurs. Building upon earlier single particle scattering work, we adopt a multiple scattering approach to derive the effective properties (density, bulk modulus, wavenumber). We show,through theoretical prediction, the implications for the design of “soft” (ultrasonic) metamaterials based on locally-resonant sub-wavelength porous rubber particles, through selection of particle size and concentration, and demonstrate tunability of the negative speed zones by modifying the viscosity of the suspending medium. For these lossy materials with complex effective properties, we confirm the use of phase angles to define the backward propagation condition in preference to “single-” and “double-negative” designations.
Dorodnitsyn, V.; Van Damme, B.
2016-04-01
A concept for acoustic metamaterials consisting of a cellular medium with fluid-filled cells is fabricated and studied experimentally. In such a system, the fluid and solid structure explicitly interact, and elastic wave propagation is coupled to both phases. Focusing here on shear wave behavior, we confirm previous numerical studies in three steps. We first measure the material deformations pertaining to three qualitatively different shear wave modes in the frequency range below 3.5 kHz. We then measure the group velocity and demonstrate that, within a certain frequency interval, the group and phase velocity have opposite signs. This shows that the system acts as a negative-index metamaterial. Finally, we confirm the presence of band gaps due to the locally resonant behavior of the cell walls. The demonstrated concept of a closed, fluid-filled cellular material as an acoustic metamaterial opens a wide space for applications.
Shen, Jian Qi
2014-03-01
Since previous negative-index atomic media based on quantum optical approaches are highly lossy, a proposal for realizing a three-dimensionally isotropic left-handed atomic vapor medium is suggested based on a mechanism of incoherent gain assisted atomic transitions. Two three-level atomic systems are utilized for producing simultaneously negative permittivity and negative permeability, respectively, in the same frequency band. We suggest that fine and hyperfine level transitions of atoms (e.g., a hyperfine level transition in a hydrogen atomic system and a fine level transition in an alkali-metal atomic system) would be applicable to realization of such a negatively refracting atomic vapor. The attractive features of the present scenario include: i) three-dimensionally isotropic negative indices; ii) incoherent gain wave amplification in the negative-index atomic vapor; iii) tunable negative indices depending upon external fields. Such a left-handed quantum optical medium can serve as a supporting substrate for lossy negative-index materials for loss compensation. It can also be used in designing new quantum optical and photonic devices (e.g., a subwavelength focusing system and a negative-index superlens for perfect imaging) because of its attractive properties of three-dimensional isotropy and high-gain wave amplification.
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 include......-layers-thick polymer woodpile photonic crystal. Characterization of such samples before and after metal deposition in the 700 nm 1700 nm range exposes some unpredictable features like an enhanced broadband transmission, which still waits to be explained.......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 isotropic radio background revisited
Fornengo, Nicolao; Regis, Marco; Taoso, Marco
2014-01-01
We present an extensive analysis on the determination of the isotropic radio background. We consider six different radio maps, ranging from 22 MHz to 2.3 GHz and covering a large fraction of the sky. The large scale emission is modeled as a linear combination of an isotropic component plus the Galactic synchrotron radiation and thermal bremsstrahlung. Point-like and extended sources are either masked or accounted for by means of a template. We find a robust estimate of the isotropic radio background, with limited scatter among different Galactic models. The level of the isotropic background lies significantly above the contribution obtained by integrating the number counts of observed extragalactic sources. Since the isotropic component dominates at high latitudes, thus making the profile of the total emission flat, a Galactic origin for such excess appears unlikely. We conclude that, unless a systematic offset is present in the maps, and provided that our current understanding of the Galactic synchrotron emi...
Depletion induced isotropic-isotropic phase separation in suspensions of rod-like colloids.
Jungblut, S; Tuinier, R; Binder, K; Schilling, T
2007-12-28
When non-adsorbing polymers are added to an isotropic suspension of rod-like colloids, the colloids effectively attract each other via depletion forces. We performed Monte Carlo simulations to study the phase diagram of such rod-polymer mixture. The colloidal rods were modeled as hard spherocylinders; the polymers were described as spheres of the same diameter as the rods. The polymers may overlap with no energy cost, while the overlap of polymers and rods is forbidden. Large amounts of depletant cause phase separation of the mixture. We estimated the phase boundaries of isotropic-isotropic coexistence both in the bulk and in confinement. To determine the phase boundaries we applied the grand canonical ensemble using successive umbrella sampling [J. Chem. Phys. 120, 10925 (2004)], and we performed a finite size scaling analysis to estimate the location of the critical point. The results are compared with predictions of the free volume theory developed by Lekkerkerker and Stroobants [Nuovo Cimento D 16, 949 (1994)]. We also give estimates for the interfacial tension between the coexisting isotropic phases and analyze its power-law behavior on the approach of the critical point. PMID:18163708
Islam, Mohammad Tariqul; Islam, Md Moinul; Samsuzzaman, Md; Faruque, Mohammad Rashed Iqbal; Misran, Norbahiah
2015-01-01
This paper presents a negative index metamaterial incorporated UWB antenna with an integration of complementary SRR (split-ring resonator) and CLS (capacitive loaded strip) unit cells for microwave imaging sensor applications. This metamaterial UWB antenna sensor consists of four unit cells along one axis, where each unit cell incorporates a complementary SRR and CLS pair. This integration enables a design layout that allows both a negative value of permittivity and a negative value of permeability simultaneous, resulting in a durable negative index to enhance the antenna sensor performance for microwave imaging sensor applications. The proposed MTM antenna sensor was designed and fabricated on an FR4 substrate having a thickness of 1.6 mm and a dielectric constant of 4.6. The electrical dimensions of this antenna sensor are 0.20 λ × 0.29 λ at a lower frequency of 3.1 GHz. This antenna sensor achieves a 131.5% bandwidth (VSWR sensors. PMID:26007721
Mohammad Tariqul Islam; Md. Moinul Islam; Md. Samsuzzaman; Mohammad Rashed Iqbal Faruque; Norbahiah Misran
2015-01-01
This paper presents a negative index metamaterial incorporated UWB antenna with an integration of complementary SRR (split-ring resonator) and CLS (capacitive loaded strip) unit cells for microwave imaging sensor applications. This metamaterial UWB antenna sensor consists of four unit cells along one axis, where each unit cell incorporates a complementary SRR and CLS pair. This integration enables a design layout that allows both a negative value of permittivity and a negative value of permea...
Isotropic radical CO{sub 2}{sup -} in biological apatites
Energy Technology Data Exchange (ETDEWEB)
Rudko, V.V. [Institute of Semiconductor Physics of National Academy of Sciences of Ukraine, 45, pr. Nauky, Kiev 03028 (Ukraine)], E-mail: vv_rudko@yahoo.com; Ishchenko, S.S.; Vorona, I.P.; Baran, N.P. [Institute of Semiconductor Physics of National Academy of Sciences of Ukraine, 45, pr. Nauky, Kiev 03028 (Ukraine)
2007-10-15
The isotropic CO{sub 2}{sup -} EPR spectrum at g{approx}2.0006 for {gamma}-irradiated powders of dental enamel annealed at different temperatures up to 320{sup 0}C is studied. The signal intensity is found to increase with the growth of annealing temperature up to 240{sup 0}C. This finding contradicts to the existing model of isotropic CO{sub 2}{sup -} radical in apatites. The possible models of the radical in biological apatite are analyzed and discussed. On the basis of the results obtained it is suggested that in tooth enamel apatite the isotropic CO{sub 2}{sup -} radical is the bulk radical localized in structural voids of hydroxyapatite lattice, which occur in the vicinity of a carbon radical in position B.
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 attainabl...... isotropic three-dimensional three-phase composites with cylindrical inclusions of arbitrary cross-sections (plane strain problem) or transversely isotropic thin plates (plane stress or bending of plates problems). (C) 2000 Elsevier Science Ltd. All rights reserved.......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...
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.
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.
International Nuclear Information System (INIS)
The present investigation is concerned with the study of pulsed second-harmonic generation under conditions of phase and group velocity mismatch, and generally low conversion efficiencies and pump intensities. In positive-index, nonmetallic materials, we generally find qualitative agreement with previous reports regarding the presence of a double-peaked second harmonic signal, which comprises a pulse that walks off and propagates at the nominal group velocity one expects at the second-harmonic frequency, and a second pulse that is 'captured' and propagates under the pump pulse. We find that the origin of the double-peaked structure resides in a phase-locking mechanism that characterizes not only second-harmonic generation, but also χ(3) processes and third-harmonic generation. The phase-locking mechanism that we describe occurs for arbitrarily small pump intensities, and so it is not a soliton effect, which usually relies on a threshold mechanism, although multicolor solitons display similar phase locking characteristics. Thus, in second harmonic generation a phase-matched component is always generated, even under conditions of material phase mismatch: This component is anomalous, because the material does not allow energy exchange between the pump and the second-harmonic beam. On the other hand, if the material is phase matched, phase locking and phase matching are indistinguishable, and the conversion process becomes efficient. We also report a similar phase-locking phenomenon in negative index materials. A spectral analysis of the pump and the generated signals reveals that the phase-locking phenomenon causes the forward moving, phase-locked second-harmonic pulse to experience the same negative index as the pump pulse, even though the index of refraction at the second-harmonic frequency is positive. Our analysis further shows that the reflected second-harmonic pulse generated at the interface and the forward-moving, phase-locked pulse appear to be part of the
Spherical cloaking with homogeneous isotropic multilayered structures.
Qiu, Cheng-Wei; Hu, Li; Xu, Xiaofei; Feng, Yijun
2009-04-01
We propose a practical realization of electromagnetic spherical cloaking by layered structure of homogeneous isotropic materials. By mimicking the classic anisotropic cloak by many alternating thin layers of isotropic dielectrics, the permittivity and permeability in each isotropic layer can be properly determined by effective medium theory in order to achieve invisibility. The model greatly facilitates modeling by Mie theory and realization by multilayer coating of dielectrics. Eigenmode analysis is also presented to provide insights of the discretization in multilayers. PMID:19518392
Isotropic light source for underwater applications
Brown, Robert A.; Honey, Richard C.; Maffione, Robert A.
1991-12-01
The design and construction of an isotropic light source is described. The instrument's design is well suited to underwater applications. Any combination of light sources (flashlamps, CW sources, or lasers) and spectral filters (absorption or interference) can be simultaneously incorporated to provide a single isotropic source with any desired temporal and spectral characteristics. This design was recently used in an underwater experiment that required a synchronously triggered isotropic flash to simultaneously measure absorption, scattering, and attenuation. The design of this particular isotropic source is presented along with data demonstrating the isotropy of the light field produced by the source.
Dayside isotropic precipitation of energetic protons
Directory of Open Access Journals (Sweden)
V. A. Sergeev
Full Text Available Recently it has been shown that isotropic precipitation of energetic protons on the nightside is caused by a non-adiabatic effect, namely pitch-angle scattering of protons in curved magnetic field lines of the tail current sheet. Here we address the origin of isotropic proton precipitation on the dayside. Computations of proton scattering regions in the magnetopheric models T87, T89 and T95 reveal two regions which contribute to the isotropic precipitation. The first is the region of weak magnetic field in the outer cusp which provides the 1–2° wide isotropic precipitation on closed field lines in a ~2–3 hour wide MLT sector centered on noon. A second zone is formed by the scattering on the closed field lines which cross the nightside equatorial region near the magnetopause which provides isotropic precipitation starting ≈ 1.5–2 h MLT from noon and which joins smoothly the precipitation coming from the tail current sheet. We also analyzed the isotropic proton precipitation using observations of NOAA low altitude polar spacecraft. We find that isotropic precipitation of >30 to >80 keV protons continues around noon forming the continuous oval-shaped region of isotropic precipitation. Part of this region lies on open field lines in the region of cusp-like or mantle precipitation, its equatorward part is observed on closed field lines. Near noon it extends ~1–2° below the sharp boundary of solar electron fluxes (proxy of the open/closed field line boundary and equatorward of the cusp-like auroral precipitation. The observed energy dispersion of its equatorward boundary (isotropic boundary agrees with model predictions of expected particle scattering in the regions of weak and highly curved magnetic field. We also found some disagreement with model computations. We did not observe the predicted split of the isotropic precipitation region into separate nightside and dayside isotropic zones. Also, the oval-like shape of the isotropic
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
Lindholm, Ulric S.; Chan, Kwai S.
1986-01-01
The objective of the program is to evaluate and develop existing constitutive models for use in finite-element structural analysis of turbine engine hot section components. The class of constitutive equation studied is considered unified in that all inelastic deformation including plasticity, creep, and stress relaxation are treated in a single term rather than a classical separation of plasticity (time independent) and creep (time dependent) behavior. The unified theories employed also do not utilize the classical yield surface or plastic potential concept. The models are constructed from an appropriate flow law, a scalar kinetic relation between strain rate, temperature and stress, and evolutionary equations for internal variables describing strain or work hardening, both isotropic and directional (kinematic). This and other studies have shown that the unified approach is particularly suited for determining the cyclic behavior of superalloy type blade and vane materials and is entirely compatible with three-dimensional inelastic finite-element formulations. The behavior was examined of a second nickel-base alloy, MAR-M247, and compared it with the Bodner-Partom model, further examined procedures for determining the material-specific constants in the models, and exercised the MARC code for a turbine blade under simulated flight spectrum loading. Results are summarized.
Kattamis, T. Z.
1984-01-01
Bulk undercooling methods and procedures will first be reviewed. Measurement of various parameters which are necessary to understand the solidification mechanism during and after recalescence will be discussed. During recalescence of levitated, glass-encased large droplets (5 to 8 mm diam) high speed temperature sensing devices coupled with a rapid response oscilloscope are now being used at MIT to measure local thermal behavior in hypoeutectic and eutectic binary Ni-Sn alloys. Dendrite tip velocities were measured by various investigators using thermal sensors or high speed cinematography. The confirmation of the validity of solidification models of bulk-undercooled melts is made difficult by the fineness of the final microstructure, the ultra-rapid evolution of the solidifying system which makes measurements very awkward, and the continuous modification of the microstructure which formed during recalescence because of precipitation, remelting and rapid coarsening.
Crossover from Isotropic to Directed Percolation
Frey, E.; Täuber, U. C.; Schwabl, F.
1994-01-01
Percolation clusters are probably the simplest example for scale--invariant structures which either are governed by isotropic scaling--laws (``self--similarity'') or --- as in the case of directed percolation --- may display anisotropic scaling behavior (``self--affinity''). Taking advantage of the fact that both isotropic and directed bond percolation (with one preferred direction) may be mapped onto corresponding variants of (Reggeon) field theory, we discuss the crossover between self--sim...
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.
Ahmadivand, Arash; Karabiyik, Mustafa; Pala, Nezih
2015-05-01
In this study, we investigated numerically the plasmon response of a dimer configuration composed of a couple of split and concentric Au nanoshells in a complex orientation. We showed that an isolated composition of two concentric split nanoshells could be tailored to support strong plasmon resonant modes in the visible wavelengths. After determining the accurate geometric dimensions for the presented antisymmetric nanostructure, we designed a dimer array that shows complex behavior during exposure to different incident polarizations. We verified that the examined dimer was able to support destructive interference between dark and bright plasmon modes, which resulted in a pronounced Fano-like dip. Observation of a Fano minimum in such a simple molecular orientation of subwavelength particles opens new avenues for employing this structure in designing various practical plasmonic devices. Depositing the final dimer in a strong coupling condition on a semiconductor metasurface and measuring the effective refractive index at certain wavelengths, we demonstrate that each one of dimer units can be considered a meta-atom due to the high aspect ratio in the geometric parameters. Using this method, by extending the number of dimers periodically and illuminating the structure, we examined the isotropic, polarization-dependent, and transmission behavior of the metamaterial configuration. Using numerical methods and calculating the effective refractive indices, we computed and sketched corresponding figure of merit over the transmission window, where the maximum value obtained was 42.3 for Si and 54.6 for gallium phosphide (GaP) substrates. PMID:25811974
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. PMID:27403842
Isotropic-nematic transition and dynamics of rigid charged molecules
Karatrantos, Argyrios
2016-03-01
Using molecular dynamics, an isotropic-nematic transition was found in bulk salt-free solutions of charged rods with their counterions in the semidilute regime. This phase transition is driven primarily by electrostatics, rather than by excluded volume. The counterion condensation effect, which is controlled by the Manning parameter, leads to liquid crystalline phases of rods. For elevated values of the Manning parameter, an attraction is obtained between the rods, and the nematic phase appears. For small values of the Manning parameter the counterions de-condense, and the nematic phase disappears. Instead, in a neutral system of rods and spheres there is no appearance of nematic phase. The diffusivity of both rods and counterions is reduced with the Manning parameter.
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; Liempi, Luis; Rodríguez, Pablo
2016-06-01
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 are no spherically symmetric traversable wormholes sustained by sources with a linear equation of state p = ωρ for the isotropic pressure, independently of the form of the redshift function ϕ (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.
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.
Stable Isotropic Cosmological Singularities in Quadratic Gravity
Barrow, J D; Barrow, John D.; Middleton, Jonathan
2007-01-01
We show that, in quadratic lagrangian theories of gravity, isotropic cosmological singularities are stable to the presence of small scalar, vector and tensor inhomogeneities. Unlike in general relativity, a particular exact isotropic solution is shown to be the stable attractor on approach to the initial cosmological singularity. This solution is also known to act as an attractor in Bianchi universes of types I, II and IX, and the results of this paper reinforce the hypothesis that small inhomogeneous and anisotropic perturbations of this attractor form part of the general cosmological solution to the field equations of quadratic gravity. Implications for the existence of a 'gravitational entropy' are also discussed.
Crossover from Isotropic to Directed Percolation
Frojdh, Per; Nijs, Marcel den
1996-01-01
Directed percolation is one of the generic universality classes for dynamic processes. We study the crossover from isotropic to directed percolation by representing the combined problem as a random cluster model, with a parameter $r$ controlling the spontaneous birth of new forest fires. We obtain the exact crossover exponent $y_{DP}=y_T-1$ at $r=1$ using Coulomb gas methods in 2D. Isotropic percolation is stable, as is confirmed by numerical finite-size scaling results. For $D \\geq 3$, the s...
Texture of low temperature isotropic pyrocarbons
International Nuclear Information System (INIS)
Isotropic pyrocarbon deposited on fuel particles was studied by transmission electron microscopy in order to determine its texture. The material consists of an agglomerate of spherical growth features similar to those of carbon black. The spherical growth features are formed from the cristallites of turbostratic carbon and the distribution gives an isotropic structure. Neutron irradiation modifies the morphology of the pyrocarbon. The spherical growth features are deformed and the coating becomes strongly anisotropic. The transformation leads to the rupture of the coating caused by strong irradiation doses
Subwavelength resolution with three-dimensional isotropic transmission-line lenses
Alitalo, Pekka; Tretyakov, Sergei
2007-01-01
Dispersion, impedance matching and resolution characteristics of an isotropic three-dimensional flat lens ("superlens") are studied. The lens is based on cubic meshes of interconnected transmission lines and bulk loads. We study a practical realization of the lens, based on the microstrip technology. The dispersion equations that have been previously derived, are verified with full-wave simulations. The isotropy of the structure is verified with analytical as well as simulation results. The r...
Decay and Eigenvalue Problems in Isotropic Turbulence
Ran, Zheng
2016-01-01
Based on the Karman-Howarth equation in 3D incompressible fluid, a new isotropic turbulence scale evolution equation and its related theory progress. The present results indicate that the energy cascading process has remarkable similarities with the determinisitic construction rules of the isotonic oscillators in quantum mechanics.
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.
Stable isotropic cosmological singularities in quadratic gravity
International Nuclear Information System (INIS)
We show that, in quadratic Lagrangian theories of gravity, isotropic cosmological singularities are stable to the presence of small scalar, vector, and tensor inhomogeneities. We study the effects of the quadratic Ricci term on the dynamics of the Universe at early times. Unlike in general relativity, a particular exact isotropic solution is shown to be the stable attractor on approach to the initial cosmological singularity. This solution is also known to act as an attractor in Bianchi universes of types I, II, and IX, and the results of this paper reinforce the hypothesis that small inhomogeneous and anisotropic perturbations of this attractor form part of the general cosmological solution to the field equations of quadratic gravity. Implications for the existence of a 'gravitational entropy' are also discussed
Radiation change of structural isotropic graphite properties
International Nuclear Information System (INIS)
Samples of three kinds of isotropic graphite properties by different density and grain size were irradiated to the neutron fluence (1.7 - 2.8) x 1026 m-2 (E > 0.18 MeV) at 360 - 400 Deg C at the BOR-60 reactor. Changing sizes, specific electric resistance, temperature coefficient of linear expansion, Young modulus were investigated following irradiation. It is established that the increase of density in the 1.67 - 1.76 g/cm3 range causes growth of maximum rate and deep of the volume shrinkage of the isotropic fine graphite. Equation approximating temperature dependence of the critical neutron fluence in the 380 - 780 Deg C range is suggested for the investigated graphite samples
Gravitational Wave Propagation in Isotropic Cosmologies
Hogan, P A
2002-01-01
We study the propagation of gravitational waves carrying arbitrary information through isotropic cosmologies. The waves are modelled as small perturbations of the background Robertson-Walker geometry. The perfect fluid matter distribution of the isotropic background is, in general, modified by small anisotropic stresses. For pure gravity waves, in which the perturbed Weyl tensor is radiative (i.e. type N in the Petrov classification), we construct explicit examples for which the presence of the anisotropic stress is shown to be essential and the histories of the wave-fronts in the background Robertson-Walker geometry are shear-free null hypersurfaces. The examples derived in this case are analogous to the Bateman waves of electromagnetic theory.
Killing Forms of Isotropic Lie Algebras
Malagon, Audrey
2010-01-01
This paper presents a method for computing the Killing form of an isotropic Lie algebra defined over an arbitrary field based on the Killing form of a subalgebra containing its anisotropic kernel. This approach allows for streamlined formulas for many Lie algebras of types E6 and E7 and yields a unified formula for all Lie algebras of inner type E6, including the anisotropic ones.
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.
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.
A Statistical Theory of Homogeneous Isotropic Turbulence
de Divitiis, Nicola
2009-01-01
The present work proposes a theory of isotropic and homogeneous turbulence for incompressible fluids, which assumes that the turbulence is due to the bifurcations associated to the velocity field. The theory is formulated using a representation of the fluid motion which is more general than the classical Navier-Stokes equations, where the fluid state variables are expressed in terms of the referential coordinates. The theory is developed according to the following four items: 1) Study of the ...
A Giambelli formula for isotropic Grassmannians
Buch, Anders S; Kresch, Andrew; Tamvakis, Harry
2008-01-01
Let X be a symplectic or odd orthogonal Grassmannian parametrizing isotropic subspaces in a vector space equipped with a nondegenerate (skew) symmetric form. We prove a Giambelli formula which expresses an arbitrary Schubert class in H^*(X,Z) as a polynomial in certain special Schubert classes. We study theta polynomials, a family of polynomials defined using raising operators whose algebra agrees with the Schubert calculus on X. Furthermore, we prove that theta polynomials are special cases ...
Depression of nonlinearity in decaying isotropic turbulence
International Nuclear Information System (INIS)
Simulations of decaying isotropic Navier--Stokes turbulence exhibit depression of the normalized mean-square nonlinear term to 57% of the value for a Gaussianly distributed velocity field with the same instantaneous velocity spectrum. Similar depression is found for dynamical models with random coupling coefficients (modified Betchov models). This suggests that the depression is dynamically generic rather than specifically driven by alignment of velocity and vorticity
Isotropic singularity in inhomogeneous brane cosmological models
International Nuclear Information System (INIS)
We discuss the asymptotic dynamical evolution of spatially inhomogeneous brane-world cosmological models close to the initial singularity. By introducing suitable scale-invariant dependent variables and a suitable gauge, we write the evolution equations of the spatially inhomogeneous G2 brane cosmological models with one spatial degree of freedom as a system of autonomous first-order partial differential equations. We study the system numerically, and we find that there always exists an initial singularity, which is characterized by the fact that spatial derivatives are dynamically negligible. More importantly, from the numerical analysis we conclude that there is an initial isotropic singularity in all these spatially inhomogeneous brane cosmologies for a range of parameter values which include the physically important cases of radiation and a scalar field source. The numerical results are supported by a qualitative dynamical analysis and a calculation of the past asymptotic decay rates. Although the analysis is local in nature, the numerics indicate that the singularity is isotropic for all relevant initial conditions. Therefore this analysis, and a preliminary investigation of general inhomogeneous (G0) models, indicates that it is plausible that the initial singularity is isotropic in spatially inhomogeneous brane-world cosmological models and consequently that brane cosmology naturally gives rise to a set of initial data that provide the conditions for inflation to subsequently take place
Expansions and contractions of isotropic stochastic flows of homeomorphisms
Piterbarg, Vladimir V.
1998-01-01
A sequence of piecewise constant approximations to rescaled isotropic homeomorphic stochastic flows is shown to converge weakly in Skorohod metric to the coalescing Brownian flow. Intermittent behavior of isotropic flows is exposed, and the clustering properties of isotropic flows are studied by the means of this convergence. We obtain qualitative and quantitative description of expansions and contractions of an arbitrary isotropic homeomorphic flow on large time-and space-s...
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
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.
Interbasis expansions for isotropic harmonic oscillator
International Nuclear Information System (INIS)
The exact solutions of the isotropic harmonic oscillator are reviewed in Cartesian, cylindrical polar and spherical coordinates. The problem of interbasis expansions of the eigenfunctions is solved completely. The explicit expansion coefficients of the basis for given coordinates in terms of other two coordinates are presented for lower excited states. Such a property is occurred only for those degenerated states for given principal quantum number n. -- Highlights: ► Exact solutions of harmonic oscillator are reviewed in three coordinates. ► Interbasis expansions of the eigenfunctions is solved completely. ► This is occurred only for those degenerated states for given quantum number n.
Isotropization of nematic liquid crystals by TMDSC
Energy Technology Data Exchange (ETDEWEB)
Chen, Wei; Dadmun, M.; Zhang, Ge; Boller, A.; Wunderlich, B. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry]|[Oak Ridge National Lab., TN (United States)
1997-12-01
Temperature-modulated differential scanning calorimetry (TMDSC) and traditional DSC are used to study the transition between the nematic liquid crystalline state and the isotropic liquid for two small molecules [4,4{prime}-azoxyanisole and N,N`-bis(4-n-octyloxybenzal)-1,4-phenylenediamine] and one macromolecule (4,4{prime}-dihydroxy-{alpha}-methylstilbene copolymerized with a 1:1 molar mixture of 1,7-dibromoheptane and 1,9-dibromononane). The DSC measurements with 4,4{prime}-azoxyanisole were used for temperature calibration with varying heating and cooling rates. Quasi-isothermal TMDSC with small temperature amplitude and standard TMDSC with underlying heating and cooling rates were utilized to analyze the breadth of the transitions. It could be verified that the isotropization transition of a nematic liquid crystal is, indeed, reversible for all three molecules. The nature of the transition changes, however, from relatively sharp, for small, rigid molecules, to about three kelvins wide for the small molecule with flexible ends, to as broad as 20 K for the macromolecule. It was also demonstrated that quantitative heats of fusion of sharp transitions can be extracted from TMDSC, but only from the time-domain heat-flow signal.
Can we remove the systematic error due to isotropic inhomogeneities?
Negishi, Hiroyuki
2016-01-01
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 the cosmological parameters. In particular, from only the distance-redshift relation, we can not 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(CMBR) and the scale of the baryon acoustic oscillation(BAO), and compare these observables in two universe models; One is the inhomogeneous isotropic universe model with the cosmological constant and the...
Multiscales and cascade in isotropic turbulence
Ran, Zheng
2010-01-01
The central problem of fully developed turbulence is the energy cascading process. It has revisited all attempts at a full physical understanding or mathematical formulation. The main reason for this failure are related to the large hierarchy of scales involved, the highly nonlinear character inherent in the Navier-Stokes equations, and the spatial intermittency of the dynamically active regions. Richardson has described the interplay between large and small scales and the phenomena so described are known as the Richardson cascade. This local interplay also forms the basis of a theory by Kolmogorov. In this letter, we use the explicit map method to analyze the nonlinear dynamical behavior for cascade in isotropic turbulence. This deductive scale analysis is shown to provide the first visual evidence of the celebrated Richardson cascade, and reveals in particular its multiscale character. The results also indicate that the energy cascading process has remarkable similarities with the deterministic construction...
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.
The homogeneous and isotropic Weyssenhoff fluid
Boehmer, C G; Boehmer, Christian G.; Bronowski, Piotr
2006-01-01
We consider a Weyssenhoff fluid assuming that the spacetime is homogeneous and isotropic, therefore being relevant for cosmological considerations of gravity theories with torsion. In this paper, it is explicitely shown that the Weyssenhoff fluids obeying the Frenkel condition or the Papapetrou-Corinaldesi condition are incompatible with the cosmological principle, which restricts the torsion tensor to have only a vector and an axial vector component. Moreover it turns out that the Weyssenhoff fluid obeying the Tulczyjew condition is also incompatible with the cosmological principle. Based on this result we propose to reconsider a number of previous works that analysed cosmological solutions of Einstein-Cartan theory, since their spin fluids usually did not obey the cosmological principle.
Elastic constants of layers in isotropic laminates.
Heyliger, Paul R; Ledbetter, Hassel; Kim, Sudook; Reimanis, Ivar
2003-11-01
The individual laminae elastic constants in multilayer laminates composed of dissimilar isotropic layers were determined using ultrasonic-resonance spectroscopy and the linear theory of elasticity. Ultrasonic resonance allows one to measure the free-vibration response spectrum of a traction-free solid under periodic vibration. These frequencies depend on pointwise density, laminate dimensions, layer thickness, and layer elastic constants. Given a material with known mass but unknown constitution, this method allows one to extract the elastic constants and density of the constituent layers. This is accomplished by measuring the frequencies and then minimizing the differences between these and those calculated using the theory of elasticity for layered media to select the constants that best replicate the frequency-response spectrum. This approach is applied to a three-layer, unsymmetric laminate of WpCu, and very good agreement is found with the elastic constants of the two constituent materials. PMID:14649998
Isotropic loop quantum cosmology with matter
International Nuclear Information System (INIS)
A free massless scalar field is coupled to homogeneous and isotropic loop quantum cosmology. The coupled model is investigated in the vicinity of the classical singularity, where discreteness is essential and where the quantum model is nonsingular, as well as in the regime of large volumes, where it displays the expected semiclassical features. The particular matter content (massless, free scalar) is chosen to illustrate how the discrete structure regulates pathological behavior caused by kinetic terms of matter Hamiltonians (which in standard quantum cosmology leads to wave functions with an infinite number of oscillations near the classical singularity). Because of this modification of the small volume behavior the dynamical initial conditions of loop quantum cosmology are seen to provide a meaningful generalization of DeWitt's initial condition
Lyapunov Analysis of Homogeneous Isotropic Turbulence
de Divitiis, Nicola
2009-01-01
The present work studies the isotropic and homogeneous turbulence for incompressible fluids, through an opportune Lyapunov analysis, assuming that the turbulence is due to the bifurcations associated to the velocity field. A particular representation of the fluid motion is adopted, where the fluid state variables are expressed in terms of the referential coordinates. The analysis is based on the Taylor and Kolmogorov scales and is developed according to the following four items: 1) Qualitative description of the route toward the turbulence through the bifurcations of the velocity field. 2) Referential description of the motion and calculation of the velocity fluctuation using the Lyapunov analysis of the local deformation. 3) Study of the mechanism of the energy cascade from large to small scales through the Lyapunov analysis of the relative kinematics equations of motion. 4) Determination of the statistics of the velocity difference with the Fourier analysis. %Each item contributes to the formulation of the ...
A Statistical Theory of Homogeneous Isotropic Turbulence
de Divitiis, Nicola
2009-01-01
The present work proposes a theory of isotropic and homogeneous turbulence for incompressible fluids, which assumes that the turbulence is due to the bifurcations associated to the velocity field. The theory is formulated using a representation of the fluid motion which is more general than the classical Navier-Stokes equations, where the fluid state variables are expressed in terms of the referential coordinates. The theory is developed according to the following four items: 1) Study of the route toward the turbulence through the bifurcations analysis of the kinematic equations. 2) Referential description of the motion and calculation of the velocity fluctuation using the Lyapunov analysis of the local deformation. 3) Study of the mechanism of the energy cascade from large to small scales through the Lyapunov analysis of the relative kinematics equations of motion. 4) Determination of the statistics of the velocity difference with the Fourier analysis. Each item contributes to the formulation of the theory. ...
Static Isotropic Spacetimes with Radially Imperfect Fluids
Konopka, Tomasz
2009-01-01
When solving the equations of General Relativity in a symmetric sector, it is natural to consider the same symmetry for the geometry and stress-energy. This implies that for static and isotropic spacetimes, the most general natural stress-energy tensor is a sum of a perfect fluid and a radial imperfect fluid component. In the special situations where the perfect fluid component vanishes or is a spacetime constant, the solutions to Einstein's equations can be thought of as modified Schwarzschild and Schwarzschild-de Sitter spaces. Exact solutions of this type are derived and it is shown that whereas deviations from the unmodified solutions can be made small, among the manifestations of the imperfect fluid component is a shift in angular momentum scaling for orbiting test-bodies at large radius. Based on this effect, the question of whether the imperfect fluid component can feasibly describe dark matter phenomenology is addressed.
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.
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...
On the algebraical structure of isotropic generalized elasticity theories
AUFFRAY, Nicolas
2013-01-01
International audience In this paper the algebraical 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 elem...
Subwavelength resolution with three-dimensional isotropic transmission-line lenses
Alitalo, P; Alitalo, Pekka; Tretyakov, Sergei
2007-01-01
Dispersion, impedance matching and resolution characteristics of an isotropic three-dimensional flat lens ("superlens") are studied. The lens is based on cubic meshes of interconnected transmission lines and bulk loads. We study a practical realization of the lens, based on the microstrip technology. The dispersion equations that have been previously derived, are verified with full-wave simulations. The isotropy of the structure is verified with analytical as well as simulation results. The resolution characteristics of a practically realizable, lossy lens are studied analytically.
Cosmic no hair for braneworlds with a bulk dilaton field
Lidsey, James E.; Seery, David
2005-11-01
Braneworld cosmology supported by a bulk scalar field with an exponential potential is developed. A general class of separable backgrounds for both single and two-brane systems is derived, where the bulk metric components are given by products of world volume and bulk coordinates and the world-volumes represent any anisotropic and inhomogeneous solution to an effective four-dimensional Brans-Dicke theory of gravity. We deduce a cosmic no hair theorem for all ever-expanding, spatially homogeneous Bianchi world volumes and find that the spatially flat and isotropic inflationary scaling solution represents a late-time attractor when the bulk potential is sufficiently flat. The dependence of this result on the separable nature of the bulk metric is investigated by applying the techniques of Hamilton-Jacobi theory to five-dimensional Einstein gravity. We employ the spatial gradient expansion method to determine the asymptotic form of the bulk metric up to third-order in spatial gradients. It is found that the condition for the separable form of the metric to represent the attractor of the system is precisely the same as that for the four-dimensional world-volume to isotropize. We also derive the fourth-order contribution to the Hamilton-Jacobi generating functional. Finally, we conclude by placing our results within the context of the holographic approach to braneworld cosmology.
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
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.
Pair reversal in homogeneous isotropic turbulence
International Nuclear Information System (INIS)
We show that the separation of particle pairs in the inertial subrange of homogeneous isotropic turbulence is strongly influenced by the pairs that separate quasi-diffusively. We quantify the influence of the diffusive separators by considering the probability that a pair will 'reverse' direction across a given separation i.e. its separation will decrease (before eventually increasing) and derive an analytical expression for the expected number of reversals across this separation for a quasi-one-dimensional model of relative dispersion in the inertial subrange with Gaussian turbulence. We compare this theoretical result with three different Lagrangian stochastic models in which the influence of the diffusive and ballistic separators (the latter dominated by velocity memory) can be varied by means of the value of C0, the constant of proportionality in the Lagrangian velocity structure function, which appears explicitly in Lagrangian stochastic models. We also compare these results with data from a direct numerical simulation of turbulence. The results indicate the importance of the transverse relative velocity component (i.e. the ability of pairs to rotate), which is absent in Q1D models, in determining the correct quantitative relative dispersion statistics.
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.
Crossover from isotropic to directed percolation.
Zhou, Zongzheng; Yang, Ji; Ziff, Robert M; Deng, Youjin
2012-08-01
We generalize the directed percolation (DP) model by relaxing the strict directionality of DP such that propagation can occur in either direction but with anisotropic probabilities. We denote the probabilities as p(↓) = pp(d) and p(↑) = p(1-p(d)), with p representing the average occupation probability and p(d) controlling the anisotropy. The Leath-Alexandrowicz method is used to grow a cluster from an active seed site. We call this model with two main growth directions biased directed percolation (BDP). Standard isotropic percolation (IP) and DP are the two limiting cases of the BDP model, corresponding to p(d) =1/2 and p(d) = 0,1 respectively. In this work, besides IP and DP, we also consider the 1/2 percolation thresholds of the BDP model for p(d) = 0.6 and 0.8, and determine various critical exponents. These exponents are found to be consistent with those for standard DP. We also determine the renormalization exponent associated with the asymmetric perturbation due to p(d)-1/2 ≠ 0 near IP, and confirm that such an asymmetric scaling field is relevant at IP. PMID:23005718
On isotropic cylindrically symmetric stellar models
Nolan, B C
2004-01-01
We attempt to match the most general cylindrically symmetric vacuum space-time with a Robertson-Walker interior. The matching conditions show that the interior must be dust filled and that the boundary must be comoving. Further, we show that the vacuum region must be polarized. Imposing the condition that there are no trapped cylinders on an initial time slice, we can apply a result of Thorne's and show that trapped cylinders never evolve. This results in a simplified line element which we prove to be incompatible with the dust interior. This result demonstrates the impossibility of the existence of an isotropic cylindrically symmetric star (or even a star which has a cylindrically symmetric portion). We investigate the problem from a different perspective by looking at the expansion scalars of invariant null geodesic congruences and, applying to the cylindrical case, the result that the product of the signs of the expansion scalars must be continuous across the boundary. The result may also be understood in ...
International Nuclear Information System (INIS)
It is attempted to produce high density, high strength and isotropic carbon made from carbonaceous powder. The carbonaceous powder was prepared by carbonization of coal-tar pitch at a temperature of 440 - 5000C and subsequent distillation under reduced pressure. The distillation was performed at a temperature of 300 - 5000C below the carbonization temperature. In some cases additional quinoline extraction was carried out on the powder. Green carbon body was formed without binder pitch under isostatic pressure at room temperature. The body was heat-treated at a temperature of 1100 - 28000C. Bulk density, weight loss, shrinkage, strength, lattice parameter, crystallite size and BAF of the obtained carbon body were measured. It is confirmed that high density, high strength and isotropic carbon made from the carbonaceous powder and the following results were obtained. 1) BS (benzene soluble) fraction, β-resin (benzene insoluble and quinoline soluble) fraction and QI (quinoline insoluble) fraction were able to fractionate by distillation under reduced pressure. Concentration gradient of each fraction seems to exist in the carbonaceous powder. 2) Using the powder prepared by a lower temperature of the carbonization and/or the distillation, the carbon body had higher bulk density and higher strength. 3) The β-resin fraction had the effects of increasing the green density and enhancing the shrinkage of carbon body during the heat treatment. (author)
Process for the preparation of isotropic petroleum coke
International Nuclear Information System (INIS)
A description is given of a process for preparing isotropic coke from oil residue charge. It includes blowing air into the residue until it reaches a softening temperature of around 49 to 116 deg C, the deferred coking of the residue having undergone blowing at a temperature of around 247 to 640 deg C, at a pressure between around 1.38x105 and 1.72x106 Pa, and the recovery of isotropic coke with a thermal expansion coefficient ratio under 1.5 approximately. The isotropic coke is used for preparing hexagonal graphite bars for nuclear reactor moderators
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
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.
Metric tensors for homogeneous, isotropic, 5-dimensional pseudo riemannian models
Anchordoqui, Luis A.; Birman, Graciela S.
2012-01-01
In this paper westudy the metric tensor of a homogeneous, isotropic, 5-dimensional pseudo Riemannian space, solving the corresponding Einstein equations when the spatial component is flat, spherical or pseudo spherical
Capillary and anchoring effects in thin hybrid nematic films and connection with bulk behavior.
de las Heras, D; Mederos, Luis; Velasco, Enrique
2009-01-01
By means of a molecular model, we examine hybrid nematic films with antagonistic anchoring angles where one of the surfaces is in the strong anchoring regime. If anchoring at the other surface is weak, and in the absence of wetting by the isotropic phase, the anchoring transition may interact with the capillary isotropic-nematic transition. For general anchoring conditions on this surface we confirm the existence of the steplike biaxial phase and the associated transition to the linear constant-tilt-rotation, configuration. The steplike phase is connected with the bulk isotropic phase for increasing film thickness so that the latter transition is to be interpreted as the capillary isotropic-nematic transition in a hybrid film. PMID:19257057
Isotropic Spin Wave Theory of Short-Range Magnetic Order
Sokol, Alexander; Singh, Rajiv R. P.; Elstner, Norbert
1996-01-01
We present an isotropic spin wave (ISW) theory of short-range order in Heisenberg magnets, and apply it to square lattice S=1/2 and S=1 antiferromagnets. Our theory has three identical (isotropic) spin wave modes, whereas the conventional spin wave theory has two transverse and one longitudinal mode. We calculate temperature dependences of various thermodynamic observables analytically and find good (several per cent) agreement with independently obtained numerical results in a broad temperat...
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...
Neutrino emissivity and bulk viscosity of iso-CSL quark matter in neutron stars
Blaschke, D.; Berdermann, J.
2007-01-01
We present results for neutrino emissivities and bulk viscosities of a two-flavor color superconducting quark matter phase with isotropic color-spin-locked (iso-CSL) single-flavor pairing which fulfill the constraints on quark matter derived from cooling and rotational evolution of compact stars. We compare with results for the phenomenologically successful, but yet heuristic 2SC+X phase.
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.
Ab initio design of elastically isotropic TiZrNbMoVx high-entropy alloys
International Nuclear Information System (INIS)
Highlights: • The refractory high-entropy alloys are studied with ab initio theory. • We study the effect of alloying elements on the elastic parameters. • We propose an criterion of elastically isotropic refractory high-entropy alloys. - Abstract: The TiZrVNb and TiZrNbMoVx (x = 0–1.5) high-entropy alloys (HEAs) are single-phase solid solutions having the body centered cubic crystallographic structure. Here we use the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation to study the equilibrium bulk properties of the above refractory HEAs. We provide a detailed investigation of the effect of alloying elements on the electronic structure and elastic parameters. Our results indicate that vanadium enhances the anisotropy of TiZrNbMoVx. As an application of the present theoretical database, we verify the often quoted correlation between the valence electron concentration (VEC) and the micro-mechanical properties in the case of multi-component alloys. Furthermore, we predict that the present HEAs become elastically isotropic for VEC∼4.72
LORENTZ-FACTOR–ISOTROPIC-LUMINOSITY/ENERGY CORRELATIONS OF GAMMA-RAY BURSTS AND THEIR INTERPRETATION
International Nuclear Information System (INIS)
The bulk Lorentz factor of the gamma-ray burst (GRB) ejecta (Γ0) is a key parameter to understanding GRB physics. Liang et al. have discovered a correlation between Γ0 and isotropic γ-ray energy: Γ0∝E0.25γ,iso,52. By including more GRBs with updated data and more methods to derive Γ0, we confirm this correlation and obtain Γ0 ≅ 91E0.29γ,iso,52. Evaluating the mean isotropic γ-ray luminosities Lγ,iso of the GRBs in the same sample, we discover an even tighter correlation Γ0 ≅ 249L0.30γ,iso,52. We propose an interpretation to this later correlation. Invoking a neutrino-cooled hyperaccretion disk around a stellar mass black hole as the central engine of GRBs, we derive jet luminosity powered by neutrino annihilation and baryon loading from a neutrino-driven wind. Applying beaming correction, we finally derive Γ0∝L0.22γ,iso, which is consistent with the data. This suggests that the central engine of long GRBs is likely a stellar mass black hole surrounded by a hyper-accreting disk.
Peculiarities of Thermic Hysteresis by the Smectica A-Isotropic Liquid Phase Transition
International Nuclear Information System (INIS)
Dynamics of changes of the thermotropic and morphologic properties near the phase transition between smectic A mesophase and isotropic liquid have been investigated for two monomorphic smectogens. The thermic hysteresis and availability of the heterophase regions for the smectic A - isotropic liquid and isotropic liquid - smectic A phase transitions have been found. Key words: Smectics, Smectic A-Isotropic Liquid, Phase Transitions
Density-functional study of the nematic-isotropic interface of hard spherocylinders.
Velasco, E; Mederos, L; Sullivan, D E
2002-08-01
The Somoza-Tarazona density-functional theory is applied to the isotropic-nematic interface of hard spherocylinders with length (L)-to-diameter (D) ratios in the range L/D=5-20. Properties such as the density and orientational order-parameter profiles and the variation of interfacial tension with bulk nematic tilt angle agree qualitatively with results of previous studies at larger values of L/D using both computer simulation and the Onsager second-virial approximation. The minimum interfacial tension is obtained at a tilt angle of 90 degrees. For values of L/D approximately 5, it is found that the Onsager approximation predicts a spurious minimum in the interfacial tension at small tilt angles. PMID:12241197
Effective Ginzburg-Landau free energy functional for multi-band isotropic superconductors
Grigorishin, Konstantin V.
2016-04-01
It has been shown that interband mixing of gradients of two order parameters (drag effect) in an isotropic bulk two-band superconductor plays important role - such a quantity of the intergradients coupling exists that the two-band superconductor is characterized with a single coherence length and a single Ginzburg-Landau (GL) parameter. Other quantities or neglecting of the drag effect lead to existence of two coherence lengths and dynamical instability due to violation of the phase relations between the order parameters. Thus so-called type-1.5 superconductors are impossible. An approximate method for solving of set of GL equations for a multi-band superconductor has been developed: using the result about the drag effect it has been shown that the free-energy functional for a multi-band superconductor can be reduced to the GL functional for an effective single-band superconductor.
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.
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
Ferromagnetic bulk glassy alloys
International Nuclear Information System (INIS)
This paper deals with the review on the formation, thermal stability and magnetic properties of the Fe-based bulk glassy alloys in as-cast bulk and melt-spun ribbon forms. A large supercooled liquid region over 50 K before crystallization was obtained in Fe-(Al, Ga)-(P, C, B, Si), Fe-(Cr, Mo, Nb)-(Al, Ga)-(P, C, B) and (Fe, Co, Ni)-Zr-M-B (M=Ti, Hf, V, Nb, Ta, Cr, Mo and W) systems and bulk glassy alloys were produced in a thickness range below 2 mm for the Fe-(Al, Ga)-(P, C, B, Si) system and 6 mm for the Fe-Co-(Zr, Nb, Ta)-(Mo, W)-B system by copper-mold casting. The ring-shaped glassy Fe-(Al, Ga)-(P, C, B, Si) alloys exhibit much better soft magnetic properties as compared with the ring-shaped alloy made from the melt-spun ribbon because of the formation of the unique domain structure. The good combination of high glass-forming ability and good soft magnetic properties indicates the possibility of future development as a new bulk glassy magnetic material
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.
The texture of low-temperature isotropic pyrocarbon
International Nuclear Information System (INIS)
Isotropic pyrocarbon deposited on fuel particles from high temperature reactors is studied by transmission electron microscopy. The aim is to determine its texture and to come to a better understanding of its mode of fabrication. The material consists of an agglomerate of spherical growth features similar to those of carbon black. The spherical growth features are formed from cristallites of fluidized bed carbon, the distribution of which leads to an isotropic structure. Irradiation by neutrons gives a transformation in the morphology of the pyrocarbon. The spherical growth feature are deformed and the coating become strongly anisotropic. This transformation leads to the rupture of the coating caused by high radiation doses. (orig./IHOE)
Flow birefringence in lyotropic mixtures in the isotropic phase
International Nuclear Information System (INIS)
The flow-induced birefringence (δn) in lyotropic mixtures in the isotropic phase (ISO) was measured by means of optical techniques. As a function of temperature, the ISO is surrounded by two lamellar (LAM) phases. The shear flow produced by a perturbation in ISO induces a birefringent phase, which relaxes back to ISO with a typical relaxation time τ. τ increases near the transition to the more ordered LAM phases, and the behavior of τ versus temperature indicates the existence of a virtual nematic phase in the isotropic domain
Heat transport in bulk/nanoporous/bulk silicon devices
Energy Technology Data Exchange (ETDEWEB)
Criado-Sancho, M. [Departamento de Ciencias y Técnicas Físicoquimicas, Facultad de Ciencias, UNED, Senda del Rey 9, 20040 Madrid (Spain); Jou, D., E-mail: David.Jou@uab.cat [Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia (Spain); Institut d' Estudis Catalans, Carme 47, 08001 Barcelona, Catalonia (Spain)
2013-02-04
We study heat transport in bulk/nanoporous/bulk silicon devices; we show that, despite bulk/nanoporous devices may act as thermal rectifiers, the non-linear aspects of their joint thermal conductance are not strong enough to lead to a negative differential thermal resistance, necessary to allow bulk/nanoporous/bulk Si devices to act as thermal transistors. Furthermore, we explicitly study the effective thermal conductivity of the mentioned devices for several temperatures, geometries, porosities, and pore size.
Poisson Lie Group Symmetries for the Isotropic Rotator
Marmo, G; Stern, A
1995-01-01
We find a new Hamiltonian formulation of the classical isotropic rotator where left and right $SU(2)$ transformations are not canonical symmetries but rather Poisson Lie group symmetries. The system corresponds to the classical analog of a quantum mechanical rotator which possesses quantum group symmetries. We also examine systems of two classical interacting rotators having Poisson Lie group symmetries.
Implementing simulations of isotropic turbulence in highly parallel computers
International Nuclear Information System (INIS)
The first steps for the simulation of isotropic turbulence in Newtonian incompressible fluids are done in such a way to acquire a basic knowhow. Highly parallel hardware and techniques are used following previous published papers. An elementary stability analysis is provided. The preliminary tests are carried out and the results indicate that the implemented codes are operational
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 ...
General isotropic flags are general (for Grassmannian Schubert calculus)
Sottile, Frank
2008-01-01
We show that general isotropic flags for odd-orthogonal and symplectic groups are general for Schubert calculus on the classical Grassmannian in that Schubert cells defined by such flags meet transversally. This strengthens a result of Belkale and Kumar in arXiv:0708.0398.
On Randers Metrics with Isotropic S-Curvature
Institute of Scientific and Technical Information of China (English)
Zhong Min SHEN; Hao XING
2008-01-01
In this paper, we study a class of Finsler metrics defined by a vector field on a Riemannian space form. We give an explicit formula for those with isotropic S-curvature. This class contains all Randers metrics of constant flag curvature.
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.)
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
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.
Brocard angle of the standard triangle in an isotropic plane
Kolar-Begović, Zdenka; Kolar - Šuper, Ružica; Volenec, Vladimir
2009-01-01
The concept of Brocard angle of the standard triangle in an isotropic plane I2 is introduced. The relationships between Brocard angles of the allowable triangle and circum-Ceva’s triangle of its centroid and circum-Ceva’s triangle of its Feuerbach point are investigated.
Jordens, Sophia; Isa, Lucio; Usov, Ivan; Mezzenga, Raffaele
2013-05-01
Two-dimensional alignment of shape-anisotropic colloids is ubiquitous in nature, ranging from interfacial virus assembly to amyloid plaque formation. The principles governing two-dimensional self-assembly have therefore long been studied, both theoretically and experimentally, leading, however, to diverging fundamental interpretations on the nature of the two-dimensional isotropic-nematic phase transition. Here we employ single-molecule atomic force microscopy, cryogenic scanning electron microscopy and passive probe particle tracking to study the adsorption and liquid crystalline ordering of semiflexible β-lactoglobulin fibrils at liquid interfaces. Fibrillar rigidity changes on increasing interfacial density, with a maximum caused by alignment and a subsequent decrease stemming from crowding and domain bending. Coexistence of nematic and isotropic regions is resolved and quantified by a length scale-dependent order parameter S2D(d). The nematic surface fraction increases with interfacial fibril density, but depends, for a fixed interfacial density, on the initial bulk concentration, ascribing the observed two-dimensional isotropic-nematic coexistence to non-equilibrium phenomena.
Bulk materials handling review
Energy Technology Data Exchange (ETDEWEB)
NONE
2007-02-15
The paper provides details of some of the most important coal handling projects and technologies worldwide. It describes development by Aubema Crushing Technology GmbH, Bedeschi, Cimbria Moduflex, DBT, Dynamic Air Conveying Systems, E & F Services, InBulk Technologies, Nord-Sen Metal Industries Ltd., Pebco Inc, Primasonics International Ltd., R.J.S. Silo Clean (International) Ltd., Takraf GmbH, and The ACT Group. 17 photos.
Pettersen, Sigurd R.; Kristiansen, Helge; Nagao, Shijo; Helland, Susanne; Njagi, John; Suganuma, Katsuaki; Zhang, Zhiliang; He, Jianying
2016-04-01
Recently, there has been an increasing interest in silver thin film coated polymer spheres as conductive fillers in isotropic conductive adhesives (ICAs). Such ICAs yield resistivities similar to conventional silver flake based ICAs while requiring only a fraction of the silver content. In this work, effects of the nanostructure of silver thin films on inter-particle contact resistance were investigated. The electrical resistivity of ICAs with similar particle content was shown to decrease with increasing coating thickness. Scanning electron micrographs of ion milled cross-sections revealed that the silver coatings formed continuous metallurgical connections at the contacts between the filler particles after adhesive curing at 150°C. The electrical resistivity decreased for all samples after environmental treatment for 3 weeks at 85°C/85% relative humidity. It was concluded that after the metallurgical connections formed, the bulk resistance of these ICAs were no longer dominated by the contact resistance, but by the geometry and nanostructure of the silver coatings. A figure of merit (FoM) was defined based on the ratio between bulk silver resistivity and the ICA resistivity, and this showed that although the resistivity was lowest in the ICAs containing the most silver, the volume of silver was more effectively used in the ICAs with intermediate silver contents. This was attributed to a size effect due to smaller grains in the thickest coating.
Pettersen, Sigurd R.; Kristiansen, Helge; Nagao, Shijo; Helland, Susanne; Njagi, John; Suganuma, Katsuaki; Zhang, Zhiliang; He, Jianying
2016-07-01
Recently, there has been an increasing interest in silver thin film coated polymer spheres as conductive fillers in isotropic conductive adhesives (ICAs). Such ICAs yield resistivities similar to conventional silver flake based ICAs while requiring only a fraction of the silver content. In this work, effects of the nanostructure of silver thin films on inter-particle contact resistance were investigated. The electrical resistivity of ICAs with similar particle content was shown to decrease with increasing coating thickness. Scanning electron micrographs of ion milled cross-sections revealed that the silver coatings formed continuous metallurgical connections at the contacts between the filler particles after adhesive curing at 150°C. The electrical resistivity decreased for all samples after environmental treatment for 3 weeks at 85°C/85% relative humidity. It was concluded that after the metallurgical connections formed, the bulk resistance of these ICAs were no longer dominated by the contact resistance, but by the geometry and nanostructure of the silver coatings. A figure of merit (FoM) was defined based on the ratio between bulk silver resistivity and the ICA resistivity, and this showed that although the resistivity was lowest in the ICAs containing the most silver, the volume of silver was more effectively used in the ICAs with intermediate silver contents. This was attributed to a size effect due to smaller grains in the thickest coating.
Ductile damage prediction in sheet and bulk metal forming
Badreddine, Houssem; Labergère, Carl; Saanouni, Khemais
2016-04-01
This paper is dedicated to the presentation of an advanced 3D numerical methodology for virtual sheet and/or bulk metal forming simulation to predict the anisotropic ductile defects occurrence. First, the detailed formulation of thermodynamically-consistent fully coupled and fully anisotropic constitutive equations is given. The proposed constitutive equations account for the main material nonlinearities as the anisotropic plastic flow, the mixed isotropic and kinematic hardening and the anisotropic ductile damage under large inelastic strains. Second, the related numerical aspects required to solve the initial and boundary value problem (IBVP) are very briefly presented in the framework of the 3D finite element method. The global resolution schemes as well as the local integration schemes of the fully coupled constitutive equations are briefly discussed. Finally, some typical examples of sheet and bulk metal forming processes are numerically simulated using the proposed numerical methodology.
Analysis of ultrasonic wave propagation in transversely isotropic austenitic welds
International Nuclear Information System (INIS)
Ultrasonic testing of austenitic welds is widely known to be difficult mainly due to the anisotropy and inhomogeneity of their elastic properties. This study investigates the physical phenomena of ultrasonic wave propagation and scattering in austenitic welds, modeled as homogeneous and transversely isotropic. The velocity and slowness surfaces are obtained for the transversely isotropic plane of austenitic welds, using the elasticity analysis. Also, the phenomena of wave generation, propagation and scattering in the same medium are simulated using the mass-spring lattice model. The numerical results show good qualitative agreement with the analytical results, and various waves in the numerical results are identified by comparing with the analytical results. Further development of this work will provide useful and practical results for the field ultrasonic testing of austenitic welds.
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.
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.
An endochronic theory for transversely isotropic fibrous composites
Pindera, M. J.; Herakovich, C. T.
1981-01-01
A rational methodology of modelling both nonlinear and elastic dissipative response of transversely isotropic fibrous composites is developed and illustrated with the aid of the observed response of graphite-polyimide off-axis coupons. The methodology is based on the internal variable formalism employed within the text of classical irreversible thermodynamics and entails extension of Valanis' endochronic theory to transversely isotropic media. Applicability of the theory to prediction of various response characteristics of fibrous composites is illustrated by accurately modelling such often observed phenomena as: stiffening reversible behavior along fiber direction; dissipative response in shear and transverse tension characterized by power-laws with different hardening exponents; permanent strain accumulation; nonlinear unloading and reloading; and stress-interaction effects.
Hidden symmetries in the two-dimensional isotropic antiferromagnet
Leonel, S A; Oliveira, W; Silva, G L; Xavier, L M V
2013-01-01
We discuss the two-dimensional isotropic antiferromagnet in the framework of gauge invariance. Gauge invariance is one of the most subtle useful concepts in theoretical physics, since it allows one to describe the time evolution of complex physical systesm in arbitrary sequences of reference frames. All theories of the fundamental interactions rely on gauge invariance. In Dirac's approach, the two-dimensional isotropic antiferromagnet is subject to second class constraints, which are independent of the Hamiltonian symmetries and can be used to eliminate certain canonical variables from the theory. We have used the symplectic embedding formalism developed by a few of us to make the system under study gauge-invariant. After carrying out the embedding and Dirac analysis, we systematically show how second class constraints can generate hidden symmetries. We obtain the invariant second-order Lagrangian and the gauge-invariant model Hamiltonian. Finally, for a particular choice of factor ordering, we derive the fun...
Vertical vibration of a pile in transversely isotropic multilayered soils
Ai, Zhi Yong; Liu, Chun Lin
2015-11-01
A new method for the dynamic response of a vertically loaded single pile embedded in transversely isotropic multilayered soils is proposed in this paper. The dynamic response of the pile is governed by the one-dimensional (1D) vibration theory, and that of transversely isotropic multilayered soils is achieved by using an analytical layer-element method. Then, with the aid of the displacement compatibility and the contact forces equilibrium along the pile-soil contact surface, the dynamic pile-soil interaction problem is solved efficiently. The presented solution method is proved to be correct and efficient by comparing the obtained results with other existing solutions. Selected numerical results are presented to study the influence of mass density ratio, length-radius ratio, frequency of excitation, soil anisotropy and hard soil stratum on the pile vertical impedance.
Statistical theory of isotropic turbulence Part IV: multiscales and cascade
Ran, Zheng
2010-01-01
This paper is the forth part of our series of work, is devoted to the analysis on the multiscales and cascade aspects of the statistical theory of isotropic turbulence based on the new Sedov-type solution. In this paper, we use the explicit map method to analyse the nonlinear dynamical behaviour for cascade in isotorpic turbulence. This deductive scale analysis is shown to provide the first visual evidence of the celebrated Richardson cascade, and reveals in partcular its multiscale character. The results also indicate that the energy cascading process has remarkable similarities with the determinisitic construction rules of the logistic map. Cascade of period-doubling bifurcations have been seen in this isotropic turbuent systems that exhibit chaotic behaviour. The 'cascade' appears as an infinite sequence of period-doubling bifurcations.
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...
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 ($\\sim 1.3 \\times 10^{-3}$).
Emergence of Chirality from Isotropic Interactions of Three Length Scales
Mkhonta, S. K.; Elder, K. R.; Huang, Zhi-Feng
2016-05-01
Chirality is known to play a pivotal role in determining material properties and functionalities. However, it remains a great challenge to understand and control the emergence of chirality and the related enantioselective process particularly when the building components of the system are achiral. Here we explore the generic mechanisms driving the formation of two-dimensional chiral structures in systems characterized by isotropic interactions and three competing length scales. We demonstrate that starting from isotropic and rotationally invariant interactions, a variety of chiral ordered patterns and superlattices with anisotropic but achiral units can self-assemble. The mechanisms for selecting specific states are related to the length-scale coupling and the selection of resonant density wave vectors. Sample phase diagrams and chiral elastic properties are identified. These findings provide a viable route for predicting chiral phases and selecting the desired handedness.
Wormholes in Bulk Viscous Cosmology
Jamil, Mubasher
2008-01-01
We investigate the effects of the accretion of phantom energy with non-zero bulk viscosity onto a Morris-Thorne wormhole. We have found that if the bulk viscosity is large then the mass of wormhole increases rapidly as compared to small or zero bulk viscosity.
Strong Coupling Isotropization of Non-Abelian Plasmas Simplified
Heller, M.P.; Mateos, D.; van der Schee, W.; Trancanelli, D.
2012-01-01
We study the isotropization of a homogeneous, strongly coupled, non-Abelian plasma by means of its gravity dual. We compare the time evolution of a large number of initially anisotropic states as determined, on the one hand, by the full non-linear Einstein's equations and, on the other, by the Einstein's equations linearized around the final equilibrium state. The linear approximation works remarkably well even for states that exhibit large anisotropies. For example, it predicts with a 20% ac...
Dielectrophoretic manipulation of the mixture of isotropic and nematic liquid
Kim, Soo-Dong; Lee, Bomi; Kang, Shin-Woong; Song, Jang-Kun
2015-01-01
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 ...
Effective Thermal Conductivity of Tri-Isotropic (TRISO) Fuel Compacts
Folsom, Charles P.
2012-01-01
Thermal conductivity is an important thermophysical property needed for effectively predicting nuclear fuel performance. As part of the Next Generation Nuclear Plant (NGNP) program, the thermal conductivity of tri-isotropic (TRISO) fuel needs to be measured over a temperature range characteristic of its usage. The composite nature of TRISO fuel requires that measurement be performed over the entire length of the compact in a non-destructive manner. No existing measurement system is capable of...
Positive isotropic curvature and self-duality in dimension 4
Richard, Thomas; Seshadri, Harish
2013-01-01
We study a positivity condition for the curvature of oriented Riemannian 4-manifolds: The half-$PIC$ condition. It is a slight weakening of the positive isotropic curvature ($PIC$) condition introduced by M. Micallef and J. Moore. We observe that the half-$PIC$ condition is preserved by the Ricci flow and satisfies a maximality property among all Ricci flow invariant positivity conditions on the curvature of oriented 4-manifolds. We also study some geometric and topological aspects of half-$P...
Method of calculating densities for isotropic L\\'evy Walks
Magdziarz, Marcin; Zorawik, Tomasz
2016-01-01
We provide explicit formulas for asymptotic densities of $d$-dimensional isotropic L\\'evy walks, when $d>1$. The densities of multidimensional undershooting and overshooting L\\'evy walks are presented as well. Interestingly, when the number of dimensions is odd the densities of all these L\\'evy walks are given by elementary functions. When $d$ is even, we can express the densities as fractional derivatives of hypergeometric functions, which makes an efficient numerical evaluation possible.
Thermodynamic and transport anomalies near isotropic-nematic phase transition
Jose, Prasanth P.; Bagchi, Biman
2008-01-01
A theoretical study of the variation of thermodynamic and transport properties of calamitic liquid crystals across the isotropic-nematic phase transition is carried out by calculating the {\\it wavenumber (k) and time (t)} dependent intermediate scattering function of the liquid, via computer simulations of model nematogens. The objective is to understand the experimentally observed anomalies and sharp variation in many thermodynamic and transport properties, namely specific heat $C$, sound at...
Isotropic three-dimensional left-handed meta-materials
Koschny, Th.; Zhang, L; Soukoulis, C. M.
2005-01-01
We investigate three-dimensional left-handed and related meta-materials based on a fully symmetric multi-gap single-ring SRR design and crossing continuous wires. We demonstrate isotropic transmission properties of a SRR-only meta-material and the corresponding left-handed material which possesses a negative effective index of refraction due to simultaneously negative effective permeability and permittivity. Minor deviations from complete isotropy are due to the finite thickness of the meta-m...
Time Varying Isotropic Vector Random Fields on Spheres
Ma, Chunsheng
2016-01-01
For a vector random field that is isotropic and mean square continuous on a sphere and stationary on a temporal domain, this paper derives a general form of its covariance matrix function and provides a series representation for the random field, which involve the ultraspherical polynomials. The series representation is somehow an imitator of the covariance matrix function, but differs from the the spectral representation in terms of the ordinary spherical harmonics, and is useful for modelin...
The temperature spectrum generated by frictional heating in isotropic turbulence
Bos, Wouter
2014-01-01
In every turbulent flow with non-zero viscosity, heat is generated by viscous friction. This heat is then mixed by the velocity field. We consider how heat fluctuations generated this way are injected and distributed over length scales in isotropic turbulence. A triadic closure is derived and numerically integrated. It is shown how the heat fluctuation spectrum depends on the Reynolds and Prandtl numbers.
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.
3-D DYNAMIC RESPONSE OF TRANSVERSELY ISOTROPIC SATURATED SOILS
Institute of Scientific and Technical Information of China (English)
WANG Xiao-gang; HUANG Yi
2005-01-01
A study on dynamic response of transversely isotropic saturated poroelastic media under a circular non-axisymmetrical harmonic source has been presented by Huang Yi et al.using the technique of Fourier expansion and Hankel transform. However, the method may not always be valid. The work is extended to the general case being in the rectangular coordinate. The purpose is to study the 3-d dynamic response of transversely isotropic saturated soils under a general source distributing in arbitrary rectangular zoon on the medium surface. Based on Biot's theory for fluid-saturated porous media, the 3-d wave motion equations in rectangular coordinate for transversely isotropic saturated poroelastic media were transformed into the two uncoupling governing differential equations of 6-order and 2-order respectively by means of the displacement functions. Then, using the technique of double Fourier transform, the governing differential equations were easily solved. Integral solutions of soil skeleton displacements and pore pressure as well as the total stresses for poroelastic media were obtained. Furthermore, a systematic study on half-space problem in saturated soils was performed. Integral solutions for surface displacements under the general harmonic source distributing on arbitrary surface zone,considering both case of drained surface and undrained surface,were presented.
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.
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.
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 ...
Liyanage, Chamari R D G; Kodali, Venkata
2014-01-01
The accessibility and usage of body building supplements is on the rise with stronger internet marketing strategies by the industry. The dangers posed by the ingredients in them are underestimated. A healthy young man came to the emergency room with palpitations and feeling unwell. Initial history and clinical examination were non-contributory to find the cause. ECG showed atrial fibrillation. A detailed history for any over the counter or herbal medicine use confirmed that he was taking supplements to bulk muscle. One of the components in these supplements is yohimbine; the onset of symptoms coincided with the ingestion of this product and the patient is symptom free after stopping it. This report highlights the dangers to the public of consuming over the counter products with unknown ingredients and the consequential detrimental impact on health. PMID:25326558
International Nuclear Information System (INIS)
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
Bamba, Kazuharu
2015-01-01
We explore the perfect fluid description of the inflationary universe. In particular, we investigate a fluid model with the bulk-viscosity term. We find that the three observables of inflationary cosmology: the spectral index of the curvature perturbations, the tensor-to-scalar ratio of the density perturbations, and the running of the spectral index, can be consistent with the recent Planck results. We also reconstruct the explicit equation of state (EoS) of the viscous fluid from the spectral index of the curvature perturbations compatible with the Planck analysis. In the reconstructed models of the viscous fluid, the tensor-to-scalar ratio of the density perturbations can satisfy the constraints obtained from the Planck satellite. The running of the spectral index can explain the Planck data. In addition, it is demonstrated that in the reconstructed models of the viscous fluid, the graceful exit from inflation can be realized. Furthermore, we show that the singular inflation can occur in the viscous fluid ...
DEFF Research Database (Denmark)
Benetti, Ana Raquel; Havndrup-Pedersen, Cæcilie; Honoré, Daniel;
2015-01-01
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...
Characterization of Small Isotropic Bicelles with Various Compositions.
Mineev, K S; Nadezhdin, K D; Goncharuk, S A; Arseniev, A S
2016-07-01
Structural studies of membrane proteins are of great importance and interest, with solution and solid state NMR spectroscopy being very promising tools for that task. However, such investigations are hindered by a number of obstacles, and in the first place by the fact that membrane proteins need an adequate environment that models the cell membrane. One of the most widely used and prospective membrane mimetics is isotropic bicelles. While large anisotropic bicelles are well-studied, the field of small bicelles contains a lot of "white spots". The present work reports the radii of particles and concentration of the detergents in the monomeric state in solutions of isotropic bicelles, formed by 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC), 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate (CHAPSO), and sodium cholate, as a function of lipid/detergent ratio and temperature. These parameters were measured using (1)H NMR diffusion spectroscopy for the bicelles composed of lipids with saturated fatty chains of different length and lipids, containing unsaturated fatty acid residue. The influence of a model transmembrane protein (membrane domain of rat TrkA) on the properties of bicelles and the effect of the bicelle size and composition on the properties of the transmembrane protein were investigated with heteronuclear NMR and nuclear Overhauser effect spectroscopy. We show that isotropic bicelles that are applicable for solution NMR spectroscopy behave as predicted by the theoretical models and are likely to be bicelles rather than mixed micelles. Using the obtained data, we propose a simple approach to control the size of bicelles at low concentrations. On the basis of our results, we compared different rim-forming agents and selected CHAPS as a detergent of choice for structural studies in bicelles, if the deuteration of the detergent is not required. PMID:27285636
Subdiffusive dynamics of a liquid crystal in the isotropic phase
De Gaetani, Luca; Prampolini, Giacomo; Tani, Alessandro
2008-05-01
The isotropic phase dynamics of a system of 4-n-hexyl-4'-cyano-biphenyl (6CB) molecules has been studied by molecular dynamics computer simulations. We have explored the range of 275-330K keeping the system isotropic, although supercooled under its nematic transition temperature. The weak rototranslational coupling allowed us to separately evaluate translational (TDOF) and orientational degrees of freedom (ODOF). Evidences of subdiffusive dynamics, more apparent at the lowest temperatures, are found in translational and orientational dynamics. Mean square displacement as well as self-intermediate center of mass and rotational scattering functions show a plateau, also visible in the orientational correlation function. According to the mode coupling theory (MCT), this plateau is the signature of the β-relaxation regime. Three-time intermediate scattering functions reveal that the plateau is related to a homogeneous dynamics, more extended in time for the orientational degrees of freedom (up to 1ns). The time-temperature superposition principle and the factorization property predicted by the idealized version of MCT hold, again for both kinds of dynamics. The temperature dependence of diffusion coefficient and orientational relaxation time is well described by a power law. Critical temperatures Tc are 244±6 and 258±6K, respectively, the latter is some 10K below the corresponding experimental values. The different values of Tc we obtained indicate that ODOF freezes earlier than TDOF. This appears due to the strongly anisotropic environment that surrounds a 6CB molecule, even in the isotropic phase. The lifetime of these "cages," estimated by time dependent conditional probability functions, is strongly temperature dependent, ranging from some hundreds of picoseconds at 320K to a few nanoseconds at 275K.
Identifying Isotropic Events Using a Regional Moment Tensor Inversion
Energy Technology Data Exchange (ETDEWEB)
Ford, S R; Dreger, D S; Walter, W R
2008-11-04
We calculate the deviatoric and isotropic source components for 17 explosions at the Nevada Test Site, as well as 12 earthquakes and 3 collapses in the surrounding region of the western US, using a regional time-domain full waveform inversion for the complete moment tensor. The events separate into specific populations according to their deviation from a pure double-couple and ratio of isotropic to deviatoric energy. The separation allows for anomalous event identification and discrimination between explosions, earthquakes, and collapses. Confidence regions of the model parameters are estimated from the data misfit by assuming normally distributed parameter values. We investigate the sensitivity of the resolved parameters of an explosion to imperfect Earth models, inaccurate event depths, and data with low signal-to-noise ratio (SNR) assuming a reasonable azimuthal distribution of stations. In the band of interest (0.02-0.10 Hz) the source-type calculated from complete moment tensor inversion is insensitive to velocity models perturbations that cause less than a half-cycle shift (<5 sec) in arrival time error if shifting of the waveforms is allowed. The explosion source-type is insensitive to an incorrect depth assumption (for a true depth of 1 km), and the goodness-of-fit of the inversion result cannot be used to resolve the true depth of the explosion. Noise degrades the explosive character of the result, and a good fit and accurate result are obtained when the signal-to-noise ratio (SNR) is greater than 5. We assess the depth and frequency dependence upon the resolved explosive moment. As the depth decreases from 1 km to 200 m, the isotropic moment is no longer accurately resolved and is in error between 50-200%. However, even at the most shallow depth the resultant moment tensor is dominated by the explosive component when the data have a good SNR.
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...
Isotropic Negatively-Refracting Atomic-Vapor Medium
Shen, Jian Qi
A new scenario to realize negative refraction with a photonic-resonant vapor material that can exhibit both electric and magnetic responses via multilevel quantum coherence is suggested. Compared with the previous method of artificial composite metamaterial, where the mechanism was considered by means of classical electromagnetic theory and the materials produced have anisotropic millimetre-scale composite structures, the present scheme suggested within the framework of quantum optics can be used to design and fabricate isotropic negatively-refracting materials with atomic-scale microscopic structure units. Such an advantage may lead to a potentially important application in the techniques of superlens and perfect imaging.
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.
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.
Identifying Isotropic Events Using a Regional Moment Tensor Inversion
Energy Technology Data Exchange (ETDEWEB)
Dreger, D S; Ford, S R; Walter, W R
2009-08-03
In our previous work the deviatoric and isotropic source components for 17 explosions at the Nevada Test Site, as well as 12 earthquakes and 4 collapses in the surrounding region of the western US, were calculated using a regional time-domain full waveform inversion for the complete moment tensor (Dreger et al., 2008; Ford et al., 2008; Ford et al., 2009a). The events separate into specific populations according to their deviation from a pure double-couple and ratio of isotropic to deviatoric energy. The separation allows for anomalous event identification and discrimination between explosions, earthquakes, and collapses. Confidence regions of the model parameters are estimated from the data misfit by assuming normally distributed parameter values. We developed a new Network Sensitivity Solution (NSS) in which the fit of sources distributed over a source-type plot (Hudson et al., 1989) show the resolution of the source parameters. The NSS takes into account the unique station distribution, frequency band, and signal-to-noise ratio of a given event scenario. The NSS compares both a hypothetical pure source (for example an explosion or an earthquake) and the actual data with several thousand sets of synthetic data from a uniform distribution of all possible sources. The comparison with a hypothetical pure source provides the theoretically best-constrained source-type region for a given set of stations, and with it one can determine whether further analysis with the data is warranted. We apply the NSS to a NTS nuclear explosion, and earthquake, as well as the 2006 North Korean explosion, and a nearby earthquake. The results show that explosions and earthquakes are distinguishable, however the solution space depends strongly on the station coverage. Finally, on May 25, 2009 a second North Korean test took place. Our preliminary results show that the explosive nature of the event may be determined using the regional distance moment tensor method. Results indicate that
Modelling of the decay of isotropic turbulence by the LES
International Nuclear Information System (INIS)
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.
Two-dimensional, homogeneous, isotropic fluid turbulence with polymer additives
Gupta, Anupam; Pandit, Rahul
2012-01-01
We present the most extensive direct numerical simulations, attempted so far, of statistically steady, homogeneous, isotropic turbulence in two-dimensional fluid films with air-drag-induced friction and with polymer additives. Our study reveals that the polymers (a) reduce the total fluid energy, enstrophy, and palinstrophy, (b) modify the fluid energy spectrum both in inverse- and forward-cascade regimes, (c) reduce small-scale intermittency, (d) suppress regions of large vorticity and strain rate, and (e) stretch in strain-dominated regions. We compare our results with earlier experimental studies; and we propose new experiments.
Hysteresis modeling of anisotropic and isotropic nanocrystalline hard magnetic films
Cornejo, D. R.; Azevedo, A.; Rezende, S. M.
2003-05-01
In the Hauser model, the magnetic state of a system is obtained by minimizing the so-called total energy function for a statistical set of magnetic domains. In this article, this energetic model of ferromagnetic materials is used in order to calculate hysteresis loops of isotropic and anisotropic nanocrystalline SmCo films at room temperature. A qualitative very good agreement between the calculated and experimental curves is obtained, mainly in the anisotropic case. Also, it has been verified that, under suitable approximations, the free parameters of the model can tie with intrinsic characteristics of the reversal magnetization process.
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.
Simultaneous amplification and attenuation in isotropic chiral materials
Mackay, Tom G.; Lakhtakia, Akhlesh
2016-05-01
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 fields of the other handedness amplify. One component material is a dissipative ICM, the other an active dielectric material. The range of the volume fraction of the active component material for which simultaneous amplification and attenuation is exhibited decreases—but does not vanish—as the ICM component becomes more dissipative and as its chirality parameter reduces in magnitude.
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.
Quantum gravitational effects in an isotropic universe with torsion
International Nuclear Information System (INIS)
In the framework of the quasiclassical self-consistent approach they consider a non-minimally coupled scalar field which serves as a source of torsion in an isotropic homogeneous Universe. They obtain a local asymptotic expansion for the propagator of the scalar field and the effective action, taking into account the effects of vacuum polarization and interaction of scalar particles with the self-consistent gravitational field. The leading polarization contributions can be represented in general-covarient form. A simplified cosmological model is constructed which takes into account the interaction
Particle creation and vacuum polarisation in isotropic universe
International Nuclear Information System (INIS)
The particle interpretation of quantised fields in homogeneous isotropic space-time is given which is based on the diagonalisation of the Hamiltonian constructed via the metrical stress-energy tensor (SET). This interpretation and the regularisation procedure of Zeldovich and Starobinsky (ZhETF: 61, 2161 (1971)) allows the total renormalised vacuum expectation values of SET to be obtained which include both vacuum polarisation and non-local terms describing the creation of particles. The case of the explicitly soluble cosmological model with initial singularity which is asymptotically static in the future is considered. The results of the calculation of the total SET in realistic Friedman cosmological models are presented. (author)
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
Simple theory of transitions between smectic, nematic, and isotropic phases
Emelyanenko, A. V.; Khokhlov, A. R.
2015-05-01
The transitions between smectic, nematic, and isotropic phases are investigated in the framework of a unified molecular-statistical approach. The new translational order parameter is different from the one introduced in K. Kobayashi [Phys. Lett. A 31, 125 (1970)] and W. L. McMillan [Phys. Rev. A 4, 1238 (1971)]. The variance of the square sine of intermolecular shift angle along the director is introduced to take self-consistently into account the most probable location of the molecules with respect to each other, which is unique for every liquid crystal (LC) material and is mainly responsible for the order parameters and phase sequences. The mean molecular field was treated in terms of only two parameters specific to any intermolecular potential of elongated molecules: (1) its global minimum position with respect to the shift of two interacting molecules along the director and (2) its inhomogeneity/anisotropy ratio. A simple molecular model is also introduced, where the global minimum position is determined by the linking groups elongation Δ/d, while the inhomogeneity/anisotropy ratio Gβ/Gγ is determined by the ratio of electrostatic and dispersion contributions. All possible phase sequences, including abrupt/continuous transformation between the smectic and nematic states and the direct smectic-isotropic phase transition, are predicted. The theoretical prediction is in a good agreement with experimental data for some simple materials correlating with our molecular model, but it is expected to be valid for any LC material.
Interacting Generalized Ghost Dark Energy in Non-isotropic Background
Barati, F.
2016-04-01
In this work, the generalized Quantum Chromodynamics (QCD) ghost model of dark energy in the framework of Einstein gravity is investigated. At first, the non-interacting generalized ghost dark energy in a Bianchi type I (BI) background is discussed. Then the equation of state parameter, ω D = p D / ρ D , the deceleration parameter, and the evolution equation of the generalized ghost dark energy are obtained. It was found that, in this case, ω D cannot cross the phantom line (ω D >-1) and eventually the universe approaches a de-Sitter phase of expansion (ω D →-1). Then, this investigation was extended to the interacting ghost dark energy in a non-isotropic universe. It was found that the equation of state parameter of the interacting generalized ghost dark energy can cross the phantom line (ω D Einstein cosmology, another density parameter, Ω σ , is expected by the anisotropy. The anisotropy of the universe decreases and the universe transits to an isotropic flat FRW universe accommodating the present acceleration.
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.
Isotropic beam bouquets for shaped beam linear accelerator radiosurgery
Wagner, Thomas H.; Meeks, Sanford L.; Bova, Frank J.; Friedman, William A.; Buatti, John M.; Bouchet, Lionel G.
2001-10-01
In stereotactic radiosurgery and radiotherapy treatment planning, the steepest dose gradient is obtained by using beam arrangements with maximal beam separation. We propose a treatment plan optimization method that optimizes beam directions from the starting point of a set of isotropically convergent beams, as suggested by Webb. The optimization process then individually steers each beam to the best position, based on beam's-eye-view (BEV) critical structure overlaps with the target projection and the target's projected cross sectional area at each beam position. This final optimized beam arrangement maintains a large angular separation between adjacent beams while conformally avoiding critical structures. As shown by a radiosurgery plan, this optimization method improves the critical structure sparing properties of an unoptimized isotropic beam bouquet, while maintaining the same degree of dose conformity and dose gradient. This method provides a simple means of designing static beam radiosurgery plans with conformality indices that are within established guidelines for radiosurgery planning, and with dose gradients that approach those achieved in conventional radiosurgery planning.
Phase matching using an isotropic nonlinear optical material
Fiore, A.; Berger, V.; Rosencher, E.; Bravetti, P.; Nagle, J.
1998-01-01
Frequency conversion in nonlinear optical crystals, is an effective means of generating coherent light at frequencies where lasers perform poorly or are unavailable. For efficient conversion, it is necessary to compensate for optical dispersion, which results in different phase velocities for light of different frequencies. In anisotropic birefringent crystals such as LiNbO3 or KH2PO4 (`KDP'), phase matching can be achieved between electromagnetic waves having different polarizations. But this is not possible for optically isotropic materials, and as a result, cubic materials such as GaAs (which otherwise have attractive nonlinear optical properties) have been little exploited for frequency conversion applications. Quasi-phase-matching schemes,, which have achieved considerable success in LiNbO3 (ref. 4), provide a route to circumventing this problem,, but the difficulty of producing the required pattern of nonlinear properties in isotropic materials, particularly semiconductors, has limited the practical utility of such approaches. Here we demonstrate a different route to phase matching - based on a concept proposed by Van der Ziel 22 years ago - which exploits the artificial birefringence of multilayer composites of GaAs and oxidised AlAs. As GaAs is the material of choice for semiconductor lasers, such optical sources could be integrated in the core of frequency converters based on these composite structures.
Isotropic beam bouquets for shaped beam linear accelerator radiosurgery
International Nuclear Information System (INIS)
In stereotactic radiosurgery and radiotherapy treatment planning, the steepest dose gradient is obtained by using beam arrangements with maximal beam separation. We propose a treatment plan optimization method that optimizes beam directions from the starting point of a set of isotropically convergent beams, as suggested by Webb. The optimization process then individually steers each beam to the best position, based on beam's-eye-view (BEV) critical structure overlaps with the target projection and the target's projected cross sectional area at each beam position. This final optimized beam arrangement maintains a large angular separation between adjacent beams while conformally avoiding critical structures. As shown by a radiosurgery plan, this optimization method improves the critical structure sparing properties of an unoptimized isotropic beam bouquet, while maintaining the same degree of dose conformity and dose gradient. This method provides a simple means of designing static beam radiosurgery plans with conformality indices that are within established guidelines for radiosurgery planning, and with dose gradients that approach those achieved in conventional radiosurgery planning. (author)
Measuring and quantifying scatter from non-isotropic sources
Stover, John C.
2015-08-01
The usual definition for BRDF assumes that the illuminated surface is isotropic. This is why when the primary source of scatter is a surface pit or particle the differential scattering cross-section is used to quantify scatter. In these cases the DSC is independent of changes in illumination spot size and thus is a more meaningful characterization than the measured BRDF. The same thing is true for other situations. These include scatter from isolated scratches, non-isotropic roughness (such as a rolled surface) and scatter from the edge or corner of a surface. In these situations the measurements may be done differently and the quantified scatter often has different units - such as area/sr or 1/deg instead of the common 1/sr associated with BRDF. If the data is being taken for use in one of the stray radiation codes this can cause problems because those codes require BRDF as an input. This paper reviews these situations for both measurement and analysis issues.
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.
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...
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)
Polarization independent electro-optical waveguides with liquid crystals in isotropic phase
Costache, Florenta; Blasl, Martin; Bornhorst, Kirstin
2015-02-01
Electro-optically induced waveguides can be used in fiber optic networks for optical power control and the distribution of optical signals transmitted over optical fibers. Reliable operation is ensured with this type of waveguides due to their non-mechanical principle of operation. Their polarization dependent behavior caused by field-induced birefringence effects may limit however their practical applications. We report on a method to reduce the polarization dependent loss in electro-optically induced waveguides with a core made of liquid crystals in isotropic phase. The concept design enables a controlled adjustment of the electric field distribution, which is responsible for inducing and shaping the optical mode, by employing an optimized electrode arrangement. In this new waveguide structure, the TM and TE modes coexist spatially and are guided in a similar way. In order to demonstrate this concept, straight and bending waveguides in 1×1 and 1×2 light input to output configurations have been designed and fabricated. The electrode arrangement and single mode waveguide geometry were optimized using FEM simulations. Bulk silicon micromachining was used to fabricate these waveguides. In particular, the manufactured device consisted of two processed silicon substrates with a liquid crystal layer enclosed in between. Devices tested with varying driving voltage have revealed comparable transmitted power for both TE and TM modes. Very low polarization dependent losses over a more than 20 dB wide dynamic attenuation range have been obtained.
High-Q/V Monolithic Diamond Microdisks Fabricated with Quasi-isotropic Etching.
Khanaliloo, Behzad; Mitchell, Matthew; Hryciw, Aaron C; Barclay, Paul E
2015-08-12
Optical microcavities enhance light-matter interactions and are essential for many experiments in solid state quantum optics, optomechanics, and nonlinear optics. Single crystal diamond microcavities are particularly sought after for applications involving diamond quantum emitters, such as nitrogen vacancy centers, and for experiments that benefit from diamond's excellent optical and mechanical properties. Light-matter coupling rates in experiments involving microcavities typically scale with Q/V, where Q and V are the microcavity quality-factor and mode-volume, respectively. Here we demonstrate that microdisk whispering gallery mode cavities with high Q/V can be fabricated directly from bulk single crystal diamond. By using a quasi-isotropic oxygen plasma to etch along diamond crystal planes and undercut passivated diamond structures, we create monolithic diamond microdisks. Fiber taper based measurements show that these devices support TE- and TM-like optical modes with Q > 1.1 × 10(5) and V < 11(λ/n) (3) at a wavelength of 1.5 μm. PMID:26134379
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.
International Nuclear Information System (INIS)
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
Ab initio design of elastically isotropic TiZrNbMoV{sub x} high-entropy alloys
Energy Technology Data Exchange (ETDEWEB)
Tian, Fuyang, E-mail: fuytian@gmail.com [Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm SE-100 44 (Sweden); Institute for Applied Physics, University of Science and Technology Beijing, Beijing 100083 (China); Varga, Lajos Karoly [Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Chen, Nanxian [Institute for Applied Physics, University of Science and Technology Beijing, Beijing 100083 (China); Department of Physics, Tsinghua University, Beijing 100084 (China); Shen, Jiang [Institute for Applied Physics, University of Science and Technology Beijing, Beijing 100083 (China); Vitos, Levente [Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm SE-100 44 (Sweden); Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary); Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Box 516, SE-751210 Uppsala (Sweden)
2014-06-25
Highlights: • The refractory high-entropy alloys are studied with ab initio theory. • We study the effect of alloying elements on the elastic parameters. • We propose an criterion of elastically isotropic refractory high-entropy alloys. - Abstract: The TiZrVNb and TiZrNbMoV{sub x} (x = 0–1.5) high-entropy alloys (HEAs) are single-phase solid solutions having the body centered cubic crystallographic structure. Here we use the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation to study the equilibrium bulk properties of the above refractory HEAs. We provide a detailed investigation of the effect of alloying elements on the electronic structure and elastic parameters. Our results indicate that vanadium enhances the anisotropy of TiZrNbMoV{sub x}. As an application of the present theoretical database, we verify the often quoted correlation between the valence electron concentration (VEC) and the micro-mechanical properties in the case of multi-component alloys. Furthermore, we predict that the present HEAs become elastically isotropic for VEC∼4.72.
Asgari, Shadnaz; Ali, Andreas M.; Collier, Travis C.; Yao, Yuan; Hudson, Ralph E.; Yao, Kung; Taylor, Charles E.
2007-09-01
The focus of most direction-of-arrival (DOA) estimation problems has been based mainly on a two-dimensional (2D) scenario where we only need to estimate the azimuth angle. But in various practical situations we have to deal with a three-dimensional scenario. The importance of being able to estimate both azimuth and elevation angles with high accuracy and low complexity is of interest. We present the theoretical and the practical issues of DOA estimation using the Approximate-Maximum-Likelihood (AML) algorithm in a 3D scenario. We show that the performance of the proposed 3D AML algorithm converges to the Cramer-Rao Bound. We use the concept of an isotropic array to reduce the complexity of the proposed algorithm by advocating a decoupled 3D version. We also explore a modified version of the decoupled 3D AML algorithm which can be used for DOA estimation with non-isotropic arrays. Various numerical results are presented. We use two acoustic arrays each consisting of 8 microphones to do some field measurements. The processing of the measured data from the acoustic arrays for different azimuth and elevation angles confirms the effectiveness of the proposed methods.
Optical Third Harmonic Generation from Isotropic Multilayer Media.
Kaatz, Philip Gerald
Optical third harmonic generation, THG, has been used to characterize the nonlinear optical response in several types of isotropic multilayer media at fundamental wavelengths of 1064, 1542, and 1907 nm. The boundary conditions and the interaction of the optical waves produced by intense electromagnetic fields are presented and solved for the case of an isotropic slab, a polymeric film deposited onto an optical flat, and an optical glass cuvette filled with an organic liquid. The third harmonic from fused silica and BK7 optical glasses has been measured on optically flat samples of these glasses. The relative nonlinear susceptibility, chi^{(3)} , of BK7 optical glass to fused silica as measured by the intensity of the THG interference pattern and known refractive index data for these glasses varies from 1.28 at 1907 nm to 1.33 at 1542 nm and 1.42 at 1064 nm. The nonlinear wave interactions in bilayer media were analyzed and characterized for two polymeric materials deposited by spin casting from solutions onto fused silica optical flats. Poly(methylmethacrylate), PMMA films were used for the THG measurement. Refractive indices were measured by quasiwaveguiding onto PMMA films deposited onto heavy flint glass prisms for the visible wavelengths and by UV-VIS-NIR spectroscopy in the infrared. Poly(di-n-hexylsilylene) films of thicknesses ranging from.37 to 1.44 mu were also characterized by the preceding methods. These films exhibit a reversible thermochromism at 42^circ C, where the wavelength at the absorption maximum increases by ~60 nm to 374 nm below the thermochromic transition temperature. The third order nonlinear susceptibility, chi^{(3) }, relative to fused silica ranges from ~11 at 50^circC to ~55 below the thermochromic transition at 23^circC. An empirical relationship for chi^{(3) } as a function of the wavelength at maximum absorption was proposed and applied to polymeric media. The nonlinear optical response of several organic liquids was characterized
Identifying isotropic events using a regional moment tensor inversion
Energy Technology Data Exchange (ETDEWEB)
Ford, S R; Dreger, D S; Walter, W R
2008-07-16
The deviatoric and isotropic source components for 17 explosions at the Nevada Test Site, as well as 12 earthquakes and 3 collapses in the surrounding region of the western US, are calculated using a regional time-domain full waveform inversion for the complete moment tensor. The events separate into specific populations according to their deviation from a pure double-couple and ratio of isotropic to deviatoric energy. The separation allows for anomalous event identification and discrimination between explosions, earthquakes, and collapses. Confidence regions of the model parameters are estimated from the data misfit by assuming normally distributed parameter values. We investigate the sensitivity of the resolved parameters of an explosion to imperfect Earth models, inaccurate event depths, and data with a low signal-to-noise ratio (SNR) assuming a reasonable azimuthal distribution of stations. In the band of interest (0.02-0.10 Hz) the source-type calculated from complete moment tensor inversion is insensitive to velocity models perturbations that cause less than a half-cycle shift (<5 sec) in arrival time error if shifting of the waveforms is allowed. The explosion source-type is insensitive to an incorrect depth assumption (for a true depth of 1 km), but the goodness-of-fit of the inversion result cannot be used to resolve the true depth of the explosion. Noise degrades the explosive character of the result, and a good fit and accurate result are obtained when the signal-to-noise ratio (SNR) is greater than 5. We assess the depth and frequency dependence upon the resolved explosive moment. As the depth decreases from 1 km to 200 m, the isotropic moment is no longer accurately resolved and is in error between 50-200%. However, even at the most shallow depth the resultant moment tensor is dominated by the explosive component when the data has a good SNR. The sensitivity investigation is extended via the introduction of the network sensitivity solution, which takes
Graphene as a Tunable Anisotropic or Isotropic Plasmonic Metasurface.
Huidobro, Paloma A; Kraft, Matthias; Maier, Stefan A; Pendry, John B
2016-05-24
We demonstrate a tunable plasmonic metasurface by considering a graphene sheet subject to a periodically patterned doping level. The unique optical properties of graphene result in electrically tunable plasmons that allow for extreme confinement of electromagnetic energy in the technologically significant regime of THz frequencies. Here, we add an extra degree of freedom by using graphene as a metasurface, proposing to dope it with an electrical gate patterned in the micron or submicron scale. By extracting the effective conductivity of the sheet, we characterize metasurfaces periodically modulated along one or two directions. In the first case, and making use of the analytical insight provided by transformation optics, we show an efficient control of THz radiation for one polarization. In the second case, we demonstrate a metasurface with an isotropic response that is independent of wave polarization and orientation. PMID:27092391
Isotropic evolution of a JBD anisotropic Bianchi universe
Núñez-Yépez, H N
2001-01-01
I study the dynamical effects due to the Brans-Dicke scalar $\\phi$-field at the early stages of a supposedly anisotropic Universe expansion in the scalar-tensor cosmology of Jordan-Brans-Dicke. This is done considering the behaviour of the general solutions for the homogeneous model of Bianchi type VII in the vacuum case. I conclude that the Bianchi-VII$_0$ model shows an isotropic expansion and that its only physical solution is equivalent to a Friedman-Robertson-Walker spacetime whose evolution can, depending on the value of the JBD coupling constant, begin in a singularity and, after expanding (inflating, if $\\omega>0$), shrink to another, or starting in a non-singular state, collapse to a singularity. I also conclude that the general Bianchi-VII$_h$ (with $h\
Plane wave propagation in transversely isotropic laser-excited solids
International Nuclear Information System (INIS)
This paper concentrates on the study of body harmonic wave propagation in an anisotropic laser-excited solid in the context of the model based on coupled equations for the displacement and atomic defect concentration fields. The complex secular equations for transversely isotropic solids are derived and discussed. It is found, in general, four types of dispersive waves, namely a quasi-longitudinal (QL), two quasi-transverse (QT) and a quasi-defect wave (N-mode) can propagate in these types of crystals. The different characteristics of waves like phase velocity, attenuation coefficient are obtained and presented graphically. It is demonstrated that there is an appreciable variation in case of the QL mode as compared with QT and N-modes. Some particular cases have also been discussed
Generalized Hooke's law for isotropic second gradient materials
dell'Isola, F; Vidoli, S
2010-01-01
In the spirit of Germain the most general objective stored elastic energy for a second gradient material is deduced using a literature result of Fortun\\'e & Vall\\'ee. Linear isotropic constitutive relations for stress and hyperstress in terms of strain and strain-gradient are then obtained proving that these materials are characterized by seven elastic moduli and generalizing previous studies by Toupin, Mindlin and Sokolowski. Using a suitable decomposition of the strain-gradient, it is found a necessary and sufficient condition, to be verified by the elastic moduli, assuring positive definiteness of the stored elastic energy. The problem of warping in linear torsion of a prismatic second gradient cylinder is formulated, thus obtaining a possible measurement procedure for one of the second gradient elastic moduli.
Charged Particle Diffusion in Isotropic Random Static Magnetic Fields
Subedi, P.; Sonsrettee, W.; Matthaeus, W. H.; Ruffolo, D. J.; Wan, M.; Montgomery, D.
2013-12-01
Study of the transport and diffusion of charged particles in a turbulent magnetic field remains a subject of considerable interest. Research has most frequently concentrated on determining the diffusion coefficient in the presence of a mean magnetic field. Here we consider Diffusion of charged particles in fully three dimensional statistically isotropic magnetic field turbulence with no mean field which is pertinent to many astrophysical situations. We classify different regions of particle energy depending upon the ratio of Larmor radius of the charged particle to the characteristic outer length scale of turbulence. We propose three different theoretical models to calculate the diffusion coefficient each applicable to a distinct range of particle energies. The theoretical results are compared with those from computer simulations, showing very good agreement.
Waterlike glass polyamorphism in a monoatomic isotropic Jagla model.
Xu, Limei; Giovambattista, Nicolas; Buldyrev, Sergey V; Debenedetti, Pablo G; Stanley, H Eugene
2011-02-14
We perform discrete-event molecular dynamics simulations of a system of particles interacting with a spherically-symmetric (isotropic) two-scale Jagla pair potential characterized by a hard inner core, a linear repulsion at intermediate separations, and a weak attractive interaction at larger separations. This model system has been extensively studied due to its ability to reproduce many thermodynamic, dynamic, and structural anomalies of liquid water. The model is also interesting because: (i) it is very simple, being composed of isotropically interacting particles, (ii) it exhibits polyamorphism in the liquid phase, and (iii) its slow crystallization kinetics facilitate the study of glassy states. There is interest in the degree to which the known polyamorphism in glassy water may have parallels in liquid water. Motivated by parallels between the properties of the Jagla potential and those of water in the liquid state, we study the metastable phase diagram in the glass state. Specifically, we perform the computational analog of the protocols followed in the experimental studies of glassy water. We find that the Jagla potential calculations reproduce three key experimental features of glassy water: (i) the crystal-to-high-density amorphous solid (HDA) transformation upon isothermal compression, (ii) the low-density amorphous solid (LDA)-to-HDA transformation upon isothermal compression, and (iii) the HDA-to-very-high-density amorphous solid (VHDA) transformation upon isobaric annealing at high pressure. In addition, the HDA-to-LDA transformation upon isobaric heating, observed in water experiments, can only be reproduced in the Jagla model if a free surface is introduced in the simulation box. The HDA configurations obtained in cases (i) and (ii) are structurally indistinguishable, suggesting that both processes result in the same glass. With the present parametrization, the evolution of density with pressure or temperature is remarkably similar to the
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.
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...
Vertex corrections and 'optimal' subgrid models for homogeneous isotropic turbulence
International Nuclear Information System (INIS)
If the Fourier modes in a DNS of homogeneous isotropic turbulence are separated into 'resolved' (k c) and 'unresolved' (k > kc) modes by introducing a partition wavevector kc, projection of the part of the nonlinear interaction containing unresolved modes onto the resolved velocity gives a numerical eddy viscosity that models the effect of the unresolved interactions on the resolved velocity field. Evaluation of this eddy viscosity by DIA gives a result in fair overall agreement with numerical data. We consider the extension of this formalism to projection of the unresolved nonlinearity onto quadratic products of the resolved velocity. We evaluate this projection by perturbation theory, and attempt to relate the result to the vertex corrections predicted by Martin-Siggia-Rose theory. Non-Gaussian properties of turbulence prove to have a crucial role. We discuss the constraints imposed by Galilean invariance on this type of computation.
DNS of evaporating droplets in decaying isotropic turbulence
Dodd, Michael; Ferrante, Antonino
2015-11-01
We have performed direct numerical simulation (DNS) of decaying isotropic turbulence laden with thousands of evaporating droplets of Taylor lengthscale size. The objective of this study is to explain the physical mechanisms occurring in evaporating droplet-laden homogeneous turbulence. To this end, we fully resolve the process of momentum, heat, and mass transfer between the droplets and the carrier fluid. The simulations are performed on a 10243 grid to resolve each droplet by 32 grids points per diameter with initial Taylor length-scale Reynolds number Reλ = 83 . We show the effects of varying the Weber number on the mean Nusselt number and Sherwood number of the droplets, and on the turbulence kinetic energy budget of the carrier fluid. This work was supported by the National Science Foundation CAREER Award, Grant No. OCI-1054591.
Static Isotropic Space-Times with Radially Imperfect Fluids
Konopka, Tomasz
When one is solving the equations of general relativity in a symmetric sector, it is natural to consider the same symmetry for the geometry and stress-energy. This implies that for static and isotropic space-times, the most general natural stress-energy tensor is a sum of a perfect fluid and a radially imperfect fluid component. In the special situations where the perfect fluid component vanishes or is a space-time constant, the solutions to Einstein's equations can be thought of as modified Schwarzschild and Schwarzschild-de Sitter spaces. Exact solutions of this type are derived and it is shown that whereas deviations from the unmodified solutions can be made small, among the manifestations of the imperfect fluid component is a shift in angular momentum scaling for orbiting test bodies at large radius. Based on this effect, the question of whether the imperfect fluid component can feasibly describe dark matter phenomenology is addressed.
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.
Rotation Rate of Particle Pairs in Homogeneous Isotropic Turbulence
Daddi-Moussa-Ider, Abdallah
2015-01-01
Understanding the dynamics of particles in turbulent flow is important in many environmental and industrial applications. In this paper, the statistics of particle pair orientation is numerically studied in homogeneous isotropic turbulent flow, with Taylor microscale Rynolds number of 300. It is shown that the Kolmogorov scaling fails to predict the observed probability density functions (PDFs) of the pair rotation rate and the higher order moments accurately. Therefore, a multifractal formalism is derived in order to include the intermittent behavior that is neglected in the Kolmogorov picture. The PDFs of finding the pairs at a given angular velocity for small relative separations, reveals extreme events with stretched tails and high kurtosis values. Additionally, The PDFs are found to be less intermittent and follow a complementary error function distribution for larger separations.
Isotropic-nematic phase transition in aqueous sepiolite suspensions.
Woolston, Phillip; van Duijneveldt, Jeroen S
2015-01-01
Aqueous suspensions of sepiolite clay rods in water tend to form gels on increase of concentration. Here it is shown how addition of a small amount (0.1% of the clay mass) of a common stabiliser for clay suspensions, sodium polyacrylate, can allow the observation of an isotropic-nematic liquid crystal phase transition. This transition was found to move to higher clay concentrations upon adding NaCl, with samples containing 10(-3) M salt or above only displaying a gel phase. Even samples that initially formed liquid crystals had a tendency to form gels after several weeks, possibly due to Mg(2+) ions leaching from the clay mineral. PMID:25313468
Uhlmann's geometric phase in presence of isotropic decoherence
Tidström, J; Tidstr\\"{o}m, Jonas; Sj\\"{o}qvist, Erik
2003-01-01
Uhlmann's mixed state geometric phase [Rep. Math. Phys. {\\bf 24}, 229 (1986)] is analyzed in the case of a qubit affected by isotropic decoherence treated in the Markovian approximation. It is demonstrated that this phase decreases rapidly with increasing decoherence rate and that it is most fragile to weak decoherence for pure or nearly pure initial states. In the unitary case, we compare Uhlmann's geometric phase for mixed states with that occurring in standard Mach-Zehnder interferometry [Phys. Rev. Lett. {\\bf 85}, 2845 (2000)] and show that the latter is more robust to reduction in the length of the Bloch vector. We also describe how Uhlmann's geometric phase in the present case could in principle be realized experimentally.
Uniqueness of the Representation in Homogeneous Isotropic LQC
Engle, Jonathan; Thiemann, Thomas
2016-01-01
We show that the standard representation of homogeneous isotropic loop quantum cosmology (LQC) is the GNS-representation that corresponds to the unique state on the reduced quantum holonomy-flux $^*$-algebra that is invariant under residual diffeomorphisms --- \\textit{both} when the standard algebra is used as well as when one uses the extended algebra proposed by Fleischhack. More precisely, we find that in both situations the GNS-Hilbert spaces coincide, and that in the Fleischhack case the additional algebra elements are just mapped to zero operators. In order for the residual diffeomorphisms to have a well-defined action on the quantum algebra, we have let them act on the fiducial cell as well as on the dynamical variables, thereby recovering covariance.
Calibration of quasi-isotropic parallel kinematic Machines: Orthoglide
Pashkevich, Anatoly; Wenger, Philippe; Chablat, Damien
2007-01-01
The paper proposes a novel approach for the geometrical model calibration of quasi-isotropic parallel kinematic mechanisms of the Orthoglide family. It is based on the observations of the manipulator leg parallelism during motions between the specific test postures and employs a low-cost measuring system composed of standard comparator indicators attached to the universal magnetic stands. They are sequentially used for measuring the deviation of the relevant leg location while the manipulator moves the TCP along the Cartesian axes. Using the measured differences, the developed algorithm estimates the joint offsets and the leg lengths that are treated as the most essential parameters. Validity of the proposed calibration technique is confirmed by the experimental results.
Circular random motion in diatom gliding under isotropic conditions
International Nuclear Information System (INIS)
How cells migrate has been investigated primarily for the case of trajectories composed by joined straight segments. In contrast, little is known when cellular motion follows intrinsically curved paths. Here, we use time-lapse optical microscopy and automated trajectory tracking to investigate how individual cells of the diatom Nitzschia communis glide across surfaces under isotropic environmental conditions. We find a distinct kind of random motion, where trajectories are formed by circular arcs traveled at constant speed, alternated with random stoppages, direction reversals and changes in the orientation of the arcs. Analysis of experimental and computer-simulated trajectories show that the circular random motion of diatom gliding is not optimized for long-distance travel but rather for recurrent coverage of limited surface area. These results suggest that one main biological role for this type of diatom motility is to efficiently build the foundation of algal biofilms. (paper)
Fundamental solutions for isotropic size-dependent couple stress elasticity
Hadjesfandiari, Ali R
2011-01-01
Fundamental solutions for two- and three-dimensional linear isotropic size-dependent couple stress elasticity are derived, based upon the decomposition of displacement fields into dilatational and solenoidal components. While several fundamental solutions have appeared previously in the literature, the present version is for the newly developed fully determinate couple stress theory. Within this theory, the couple stress tensor is skewsymmetrical and thus possesses vectorial character. The present derivation provides solutions for infinite domains of elastic materials under the influence of unit concentrated forces and couples. Unlike all previous work, unique solutions for displacements, rotations, force-stresses and couple-stresses are established, along with the corresponding force-tractions and couple-tractions. These fundamental solutions are central in analysis methods based on Green's functions for infinite domains and are required as kernels in the corresponding boundary integral formulations for size...
Renormalization Group Running of Newton's G: The Static Isotropic Case
Hamber, H W; Hamber, Herbert W.; Williams, Ruth M.
2007-01-01
Corrections are computed to the classical static isotropic solution of general relativity, arising from non-perturbative quantum gravity effects. A slow rise of the effective gravitational coupling with distance is shown to involve a genuinely non-perturbative scale, closely connected with the gravitational vacuum condensate, and thereby, it is argued, related to the observed effective cosmological constant. Several analogies between the proposed vacuum condensate picture of quantum gravitation, and non-perturbative aspects of vacuum condensation in strongly coupled non-abelian gauge theories are developed. In contrast to phenomenological approaches, the underlying functional integral formulation of the theory severely constrains possible scenarios for the renormalization group evolution of couplings. The expected running of Newton's constant $G$ is compared to known vacuum polarization induced effects in QED and QCD. The general analysis is then extended to a set of covariant non-local effective field equati...
A Avazpour; S M Hekmatzadeh
2014-01-01
Density functional approach was used to study the isotropic- nematic (I-N) transition and calculate the values of freezing parameters of the Gay- Berne liquid crystal model. New direct and pair correlation functions of a molecular fluid with Gay- Berne pair potential were used. These new functions were used in density functional theory as input to calculate the isotropic- nematic transition densities for elongation at various reduced temperatures. It was observed that the isotropic- nematic...
Quantitative analysis of pulmonary emphysema using isotropic Gaussian Markov random fields
Dharmagunawardhana, Chathurika; Mahmoodi, Sasan; Bennett, Michael; Niranjan, Mahesan
2014-01-01
A novel texture feature based on isotropic Gaussian Markov random fields is proposed for diagnosis and quantification of emphysema and its subtypes. Spatially varying parameters of isotropic Gaussian Markov random fields are estimated and their local distributions constructed using normalized histograms are used as effective texture features. These features integrate the essence of both statistical and structural properties of the texture. Isotropic Gaussian Markov Random Field parameter esti...
Mining the bulk positron lifetime
Energy Technology Data Exchange (ETDEWEB)
Aourag, H.; Guittom, A. [Centre de Recherche Nucleaire d' Alger (CRNA), Alger Gare - Algiers (Algeria)
2009-02-15
We introduce a new approach to investigate the bulk positron lifetimes of new systems based on data-mining techniques. Through data mining of bulk positron lifetimes, we demonstrate the ability to predict the positron lifetimes of new semiconductors on the basis of available semiconductor data already studied. Informatics techniques have been applied to bulk positron lifetimes for different tetrahedrally bounded semiconductors in order to discover computational design rules. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Mining the bulk positron lifetime
International Nuclear Information System (INIS)
We introduce a new approach to investigate the bulk positron lifetimes of new systems based on data-mining techniques. Through data mining of bulk positron lifetimes, we demonstrate the ability to predict the positron lifetimes of new semiconductors on the basis of available semiconductor data already studied. Informatics techniques have been applied to bulk positron lifetimes for different tetrahedrally bounded semiconductors in order to discover computational design rules. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Advances in bulk port development
Energy Technology Data Exchange (ETDEWEB)
Soros, P. (Soros Associates Consulting Engineers, New York, NY (USA))
1991-03-01
The article features several recently developed bulk ports which illustrate aspects of new technology or concepts in maritime transport. Low handling capacity bulk terminals at Ponta da Madeira, Brazil and Kooragang Island, Australia and the low-cost bulk port at Port of Corpus Christi, Texas are described. Operations at the ports of Pecket and Tocopilla in Chile, which had special technical problems, are mentioned. Coal terminals at Port Kembla, Australia and St. Johns River in Florid Jacksonville, Florida are featured as examples of terminals which had to be designed to meet high environmental standards. 13 refs., 2 figs., 14 photos.
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.
Shrinking device realized by using layered structures of homogeneous isotropic materials
International Nuclear Information System (INIS)
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. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Bulk Nuclear Properties from Reactions
Danielewicz, P.
2002-01-01
Extraction of bulk nuclear properties by comparing reaction observables to results from semiclassical transport-model simulations is discussed. Specific properties include the nuclear viscosity, incompressibility and constraints on the nuclear pressure at supranormal densities.
Bulk charges in eleven dimensions
Hawking, Stephen William
1998-01-01
Eleven dimensional supergravity has electric type currents arising from the Chern-Simon and anomaly terms in the action. However the bulk charge integrates to zero for asymptotically flat solutions with topological trivial spatial sections. We show that by relaxing the boundary conditions to generalisations of the ALE and ALF boundary conditions in four dimensions one can obtain static solutions with a bulk charge preserving between 1/16 and 1/4 of the supersymmetries. One can introduce membranes with the same sign of charge into these backgrounds. This raises the possibility that these generalized membranes might decay quantum mechanically to leave just a bulk distribution of charge. Alternatively and more probably, a bulk distribution of charge can decay into a collection of singlely charged membranes. Dimensional reductions of these solutions lead to novel representations of extreme black holes in four dimensions with up to four charges. We discuss how the eleven-dimensional Kaluza-Klein monopole wrapped a...
International Nuclear Information System (INIS)
The procedure of calculation of the line form and aperture ratio developed for a spectrometer based on cylindrical curved multilayer mirror is presented. This approach is applicable for account of aperture ratio and line form for a bulk isotropic X-ray source. The calculation results for several geometries measurements are represented
Negative-Index Media for Matter-Wave Optics
Baudon, J.; Hamamda, M.; Grucker, J.; Boustimi, M.; Perales, F.; Dutier, G.; Ducloy, M.
2009-04-01
We consider the extension of optical metamaterials to matter waves and then the down scaling of metaoptics to nanometric wavelengths. We show that the generic property of pulsed comoving magnetic fields allows us to fashion the wave-number dependence of the atomic phase shift. It can be used to produce a transient negative group velocity of an atomic wave packet, which results into a negative refraction of the matter wave. Application to slow metastable argon atoms Ar*(P23) shows that the device is able to operate either as an efficient beam splitter or an atomic metalens.
Soft 3D acoustic metamaterial with negative index.
Brunet, Thomas; Merlin, Aurore; Mascaro, Benoit; Zimny, Kevin; Leng, Jacques; Poncelet, Olivier; Aristégui, Christophe; Mondain-Monval, Olivier
2015-04-01
Many efforts have been devoted to the design and achievement of negative-refractive-index metamaterials since the 2000s. One of the challenges at present is to extend that field beyond electromagnetism by realizing three-dimensional (3D) media with negative acoustic indices. We report a new class of locally resonant ultrasonic metafluids consisting of a concentrated suspension of macroporous microbeads engineered using soft-matter techniques. The propagation of Gaussian pulses within these random distributions of 'ultra-slow' Mie resonators is investigated through in situ ultrasonic experiments. The real part of the acoustic index is shown to be negative (up to almost - 1) over broad frequency bandwidths, depending on the volume fraction of the microbeads as predicted by multiple-scattering calculations. These soft 3D acoustic metamaterials open the way for key applications such as sub-wavelength imaging and transformation acoustics, which require the production of acoustic devices with negative or zero-valued indices. PMID:25502100
Soft 3D acoustic metamaterial with negative index
Brunet, Thomas; Merlin, Aurore; Mascaro, Benoit; Zimny, Kevin; Leng, Jacques; Poncelet, Olivier; Aristégui, Christophe; Mondain-Monval, Olivier
2015-04-01
Many efforts have been devoted to the design and achievement of negative-refractive-index metamaterials since the 2000s. One of the challenges at present is to extend that field beyond electromagnetism by realizing three-dimensional (3D) media with negative acoustic indices. We report a new class of locally resonant ultrasonic metafluids consisting of a concentrated suspension of macroporous microbeads engineered using soft-matter techniques. The propagation of Gaussian pulses within these random distributions of ‘ultra-slow’ Mie resonators is investigated through in situ ultrasonic experiments. The real part of the acoustic index is shown to be negative (up to almost - 1) over broad frequency bandwidths, depending on the volume fraction of the microbeads as predicted by multiple-scattering calculations. These soft 3D acoustic metamaterials open the way for key applications such as sub-wavelength imaging and transformation acoustics, which require the production of acoustic devices with negative or zero-valued indices.
Negative-Index Media for Matter-Wave Optics
International Nuclear Information System (INIS)
We consider the extension of optical metamaterials to matter waves and then the down scaling of metaoptics to nanometric wavelengths. We show that the generic property of pulsed comoving magnetic fields allows us to fashion the wave-number dependence of the atomic phase shift. It can be used to produce a transient negative group velocity of an atomic wave packet, which results into a negative refraction of the matter wave. Application to slow metastable argon atoms Ar*(3P2) shows that the device is able to operate either as an efficient beam splitter or an atomic metalens
Comment about quasi-isotropic solution of Einstein equations near cosmological singularity
Khalatnikov, I. M.; Kamenshchik, A. Yu.; Starobinsky, A. A.
2002-01-01
We generalize for the case of arbitrary hydrodynamical matter the quasi-isotropic solution of Einstein equations near cosmological singularity, found by Lifshitz and Khalatnikov in 1960 for the case of radiation-dominated universe. It is shown that this solution always exists, but dependence of terms in the quasi-isotropic expansion acquires a more complicated form.
Comment about quasi-isotropic solution of Einstein equations near the cosmological singularity
International Nuclear Information System (INIS)
For the case of arbitrary hydrodynamical matter, we generalize the quasi-isotropic solution of Einstein equations near the cosmological singularity, found by Lifshitz and Khalatnikov in 1960 for the case of the radiation-dominated universe. It is shown that this solution always exists, but dependence of terms in the quasi-isotropic expansion acquires a more complicated form
Isotropization of Bianchi type models and a new FRW solution in Brans-Dicke theory
Cervantes-Cota, J L; Cervantes-Cota, Jorge L.; Nahmad, Marcos
2001-01-01
Using scaled variables we are able to integrate an equation valid for isotropic and anisotropic Bianchi type I, V, IX models in Brans-Dicke (BD) theory. We analyze known and new solutions for these models in relation with the possibility that anisotropic models asymptotically isotropize, and/or possess inflationary properties. In particular, a new solution of curve ($k\
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.
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...
Three-dimensional magnetospheric equilibrium with isotropic pressure
International Nuclear Information System (INIS)
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 (Ψ,α,χ) flux coordinate system, where Ψ is the magnetic flux function, χ is a generalized poloidal angle, α is the toroidal angle, α = φ - δ(Ψ,φ,χ) is the toroidal angle, δ(Ψ,φ,χ) is periodic in φ, and the magnetic field is represented as rvec B = ∇Ψ x ∇α. 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
The Isotropic Semicircle Law and Deformation of Wigner Matrices
Knowles, Antti
2011-01-01
We analyse the spectrum of additive finite-rank deformations of $N \\times N$ Wigner matrices $H$. The spectrum of the deformed matrix undergoes a transition, associated with the creation or annihilation of an outlier, when an eigenvalue $d_i$ of the deformation crosses a critical value $\\pm 1$. This transition happens on the scale $|d_i| - 1 \\sim N^{-1/3}$. We allow the eigenvalues $d_i$ of the deformation to depend on $N$ under the condition $|\\abs{d_i} - 1| \\geq (\\log N)^{C \\log \\log N} N^{-1/3}$. We make no assumptions on the eigenvectors of the deformation. In the limit $N \\to \\infty$, we identify the law of the outliers and prove that the non-outliers close to the spectral edge have a universal distribution coinciding with that of the extremal eigenvalues of a Gaussian matrix ensemble. A key ingredient in our proof is the \\emph{isotropic local semicircle law}, which establishes optimal high-probability bounds on the quantity $$, where $m(z)$ is the Stieltjes transform of Wigner's semicircle law and $v, w...
The isotropic XY model on the inhomogeneous periodic chain
International Nuclear Information System (INIS)
The static and dynamic properties of the isotropic XY-model (s=12) on the inhomogeneous periodic chain, composed of N segments with n different exchange interactions and magnetic moments, in a transverse field h, are obtained exactly at arbitrary temperatures. The properties are determined by introducing the generalized Jordan-Wigner transformation and by reducing the problem to a diagonalization of a finite matrix of nth order. The diagonalization procedure is discussed in detail and the critical behaviour induced by the transverse field, at T=0, is presented. The quantum transitions are determined by analyzing the behaviour of the induced magnetization, defined as (1/n)-bar m=1nμmj,mz> where μm is the magnetic moment at site m within the segment j, as a function of the field, and the critical fields determined exactly. The dynamic correlations, j,mz(t)Sj',m'z(0)>, and the dynamic susceptibility χqzz(ω) are also obtained at arbitrary temperatures. Explicit results are presented in the limit T=0, where the critical behaviour occurs, for the static susceptibility χqzz(0) as a function of the transverse field h, and for the frequency dependency of dynamic susceptibility χqzz(ω). Also in this limit, the transverse time-correlation j,mx(t)Sj',m'x(0)> and the dynamic and isothermal susceptibilities, χqxx(ω) and χTxx, are obtained for the transverse field greater or equal than the saturation field
Scalar Statistics along Inertial Particle Trajectory in Isotropic Turbulence
International Nuclear Information System (INIS)
The statistics of a passive scalar along inertial particle trajectory in homogeneous isotropic turbulence with a mean scalar gradient is investigated by using direct numerical simulation. We are interested in the influence of particle inertia on such statistics, which is crucial for further understanding and development of models in non-isothermal gas-particle flows. The results show that the scalar variance along particle trajectory decreases with the increasing particle inertia firstly; when the particle's Stokes number St is less than 1.0, it reaches the minimal value when St is around 1.0, then it increases if St increases further. However, the scalar dissipation rate along the particle trajectory shows completely contrasting behavior in comparison with the scalar variance. The mechanical-to-thermal time scale ratios averaged along particle, p, are approximately two times smaller than that computed in the Eulerian frame r, and stay at nearly 1.77 with a weak dependence on particle inertia. In addition, the correlations between scalar dissipation and now structure characteristics along particle trajectories, such as strain and vorticity, are also computed, and they reach their maximum and minimum, 0.31 and 0.25, respectively, when St is around 1.0. (fundamental areas of phenomenology (including applications))
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...
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...
Isotropically sensitive optical filter employing atomic resonance transitions
International Nuclear Information System (INIS)
An ultra-high Q isotropically sensitive optical filter or optical detector employing atomic resonance transitions is described. More specifically, atomic resonance transitions utilized in conjunction with two optical bandpass filters provide an optical detector having a wide field of view (*2 pi steradians) and very narrow acceptance bandwidth approaching 0.01 A. A light signal to be detected is transmitted through an outer bandpass filter into a resonantly absorbing atomic vapor, the excited atomic vapor then providing a fluorescence signal at a different wavelength which is transmitted through an inner bandpass filter. The outer and inner bandpass filters have no common transmission band, thereby resulting in complete blockage of all optical signals that are not resonantly shifted in wavelength by the intervening atomic vapor. Two embodiments are disclosed, one in which the light signal raises atoms contained in the atomic vapor from the ground state to an excited state from which fluorescence occurs, and the other in which a pump laser is used to raise the atoms in the ground state to a first excited state from which the light signal then is resonantly absorbed, thereby raising the atoms to a second excited state from which fluorescence occurs. A specific application is described in which an optical detector according to the present invention can be used as an underwater detector for light from an optical transmitter which could be located in an orbiting satellite
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.
Gamma probe dry bulk densities
International Nuclear Information System (INIS)
The gamma density probe is a useful instrument for measuring water content in small volumes of soil. Essentially, the gamma probe measures the density of the soil and water between a source and a detector. To transpose the gamma densities into water content, the dry bulk density of the soil is needed. A nondestructive method for estimating dry bulk densities for use with the gamma probe is proposed. The procedure is based on the assumption that water content values in a field dry condition were more stable than the dry bulk density values and could be transferred from one point to another. The procedure was successfully used on three areas in Reynolds Creek Experimental Watershed in southwest Idaho. (U.S.)
Preoteasa, Eugen A.; Apostol, Marian V.
2008-01-01
In the frame of collective dynamics in water, models built on elementary excitations and long-range electromagnetic interactions in the cell and bulk liquid are presented. Making use of the low effective mass of water coherence domains (CDs), we examined the relevance of simple quantum models to cellular characteristics. A hypothesis of CDs Bose-type condensation, and models of CD in spherical wells with impenetrable and semipenetrable walls, and of an isotropic oscillator consisting of two i...
Bulk Viscosity of Interacting Hadrons
Wiranata, A.; M. Prakash
2009-01-01
We show that first approximations to the bulk viscosity $\\eta_v$ are expressible in terms of factors that depend on the sound speed $v_s$, the enthalpy, and the interaction (elastic and inelastic) cross section. The explicit dependence of $\\eta_v$ on the factor $(\\frac 13 - v_s^2)$ is demonstrated in the Chapman-Enskog approximation as well as the variational and relaxation time approaches. The interesting feature of bulk viscosity is that the dominant contributions at a given temperature ari...
Bulk Viscosity of Interacting Hadrons
Wiranata, A
2009-01-01
We show that first approximations to the bulk viscosity $\\eta_v$ are expressible in terms of factors that depend on the sound speed $v_s$, the enthalpy, and the interaction (elastic and inelastic) cross section. The explicit dependence of $\\eta_v$ on the factor $(\\frac 13 - v_s^2)$ is demonstrated in the Chapman-Enskog approximation as well as the variational and relaxation time approaches. The interesting feature of bulk viscosity is that the dominant contributions at a given temperature arise from particles which are neither extremely nonrelativistic nor extremely relativistic. Numerical results for a model binary mixture are reported.
Bulk charges in eleven dimensions
Hawking, S. W.; Taylor-Robinson, M. M.
1998-07-01
Eleven dimensional supergravity has electric type currents arising from the Chern-Simon and anomaly terms in the action. However the bulk charge integrates to zero for asymptotically flat solutions with topological trivial spatial sections. We show that by relaxing the boundary conditions to generalisations of the ALE and ALF boundary conditions in four dimensions one can obtain static solutions with a bulk charge. Solutions involving anomaly terms preserve between 1/16 and 1/4 of the supersymmetries but Chern-Simons fluxes generally break all of the remaining supersymmetry. One can introduce membranes with the same sign of charge into these backgrounds. This raises the possibility that these generalized membranes might decay quantum mechanically to leave just a bulk distribution of charge. Alternatively and more probably, a bulk distribution of charge can decay into a collection of singly charged membranes. Dimensional reductions of these solutions lead to novel representations of extreme black holes in four dimensions with up to four charges. We discuss how the eleven-dimensional Kaluza-Klein monopole wrapped around a space with non-zero first Pontryagin class picks up an electric charge proportional to the Pontryagin number.
Bulk viscosity and deflationary universes
Lima, J A S; Waga, I
2007-01-01
We analyze the conditions that make possible the description of entropy generation in the new inflationary model by means of a nearequilibrium process. We show that there are situations in which the bulk viscosity cannot describe particle production during the coherent field oscillations phase.
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...
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
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.
Kim, Seulong; Kim, Kihong
2016-06-01
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 Tellegen media. In contrast to the case of ordinary isotropic media, we find that the surface wave excitation and the mode conversion occur for both s and p waves in bi-isotropic media.
International Nuclear Information System (INIS)
The linear Boltzmann equation for the transport of neutral particles is investigated with the objective of generating benchmark-quality evaluations of solutions for homogeneous infinite media. In all cases, the problems are stationary, of one energy group, and the scattering is isotropic. The solutions are generally obtained through the use of Fourier transform methods with the numerical inversions constructed from standard numerical techniques such as Gauss-Legendre quadrature, summation of infinite series, and convergence acceleration. Consideration of the suite of benchmarks in infinite homogeneous media begins with the standard one-dimensional problems: an isotropic point source, an isotropic planar source, and an isotropic infinite line source. The physical and mathematical relationships between these source configurations are investigated. The progression of complexity then leads to multidimensional problems with source configurations that also emit particles isotropically: the finite line source, the disk source, and the rectangular source. The scalar flux from the finite isotropic line and disk sources will have a two-dimensional spatial variation, whereas a finite rectangular source will have a three-dimensional variation in the scalar flux. Next, sources emitting particles anisotropically are considered. The most basic such source is the point beam giving rise to the Green's function, which is physically the most fundamental transport problem, yet may be constructed from the isotropic point source solution. Finally, the anisotropic plane and anisotropically emitting infinite line sources are considered. Thus, a firm theoretical and numerical base is established for the most fundamental neutral particle benchmarks in infinite homogeneous media
Polymerisationseigenschaften von Bulk-Fill Kompositen
Maier, Eva
2015-01-01
Hintergrund und Ziele: Untersuchung der Polymerisationseigenschaften von Bulk-Fill Kompositen bzgl. Konversionsrate (degree of conversion = DC), Vickers-Härte (HV), Polymerisationsschrumpfungsstress (PSS) und Polymerisationsvolumenschrumpfung (PVS) im Vergleich zu konventionellen Kompositen. Material und Methode: Untersucht wurden die Bulk-Fill Komposite Filtek Bulk Fill Flowable (FBF, 3M ESPE, Seefeld), Surefil Smart Dentin Replacement (SDR, Dentsply, Konstanz), Tetric EvoCeram Bulk Fill...
muSR linewidth and isotropic pairing in superconducting PrOs4Sb12
MacLaughlin, D.E.; J. E. Sonier; Heffner, R. H.; Bernal, O. O.; Young, B. -L.; Rose, M S; Morris, G. D.; BAUER E.d.; Lo, T. D.; M.B. Maple
2002-01-01
Transverse-field muon spin rotation measurements in the vortex-lattice mixed state of the heavy-fermion (HF) superconductor PrOs4Sb12 yield a temperature dependence of the penetration depth indicative of an isotropic or nearly isotropic energy gap. This is not seen to date in any other HF superconductor and is a signature of isotropic pairing symmetry, possibly related to a novel nonmagnetic "quadrupolar Kondo" HF mechanism in PrOs4Sb12. The T = 0 relaxation rate \\sigma_s(0) = 0.91(1) \\mu s^-...
Spectral shifts in the properties of a periodic multilayered stack due to isotropic chiral layers
Ramakrishna, S Anantha
2009-01-01
Investigating the canonical problem of a periodic multilayered stack containing isotropic chiral layers, we homogenized it as a uniaxial bianisotropic medium and derived its effective constitutive parameters. The stack shows a resonant behavior, when its unit cell consists of a metallic layer and an isotropic chiral layer. The presence of isotropic chirality can result in small shifts of the resonance frequency for reasonably large values of the chirality parameter, implying that the sign of an effective permittivity can be switched. Such spectral shifts in the dielectric properties can be potentially useful for spectroscopic purposes.
Surface and bulk scattering by magnetic and dielectric inhomogeneities: a first-order method
International Nuclear Information System (INIS)
The scattering of a magneto-dielectric multilayer has been studied by a first-order method. The model reported in this manuscript relies on the equivalence between heterogeneities of the medium and fictitious electric and magnetic sources. Types of inhomogeneities considered are roughness and bulk inhomogeneities and concern both permittivity and permeability. The numerical results are compared to those given in previous papers for optical scattering. It is shown in the microwave spectra that angle-resolved scattering allows identification of the scattering origins (permittivity or permeability spectra). The cases of isotropic films and meta-materials are presented and discussed. (authors)
Surface and bulk scattering by magnetic and dielectric inhomogeneities: a first-order method.
Dieudonné, É; Malléjac, N; Amra, C; Enoch, S
2013-09-01
The scattering of a magnetodielectric multilayer has been studied by a first-order method. The model reported in this manuscript relies on the equivalence between heterogeneities of the medium and fictitious electric and magnetic sources. Types of inhomogeneities considered are roughness and bulk inhomogeneities and concern both permittivity and permeability. The numerical results are compared to those given in previous papers for optical scattering. It is shown in the microwave spectra that angle-resolved scattering allows identification of the scattering origins (permittivity or permeability spectra). The cases of isotropic films and metamaterials are presented and discussed. PMID:24323258
Experimental Evidence of s-Wave Superconductivity in Bulk CaC6
Lamura, G.; Aurino, M.; Cifariello, G.; di Gennaro, E.; Andreone, A.; Emery, N.; Hérold, C.; Marêché, J.-F.; Lagrange, P.
2006-03-01
The temperature dependence of the in-plane magnetic penetration depth, λab(T), has been measured in a c-axis oriented polycrystalline CaC6 bulk sample using a high-resolution mutual inductance technique. A clear exponential behavior of λab(T) has been observed at low temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the standard BCS theory yields λab(0)=(720±80)Å and Δ(0)=(1.79±0.08)meV. The ratio 2Δ(0)/kBTc=(3.6±0.2) gives indication for a weakly coupled superconductor.
Bulk waves excited by a laser line pulse in a bi-layer cylinder
Pan, Y.; Chigarev, N.; Audoin, B.
2010-03-01
In this paper, the transient displacement excited by a laser line source is calculated for a bi-layer cylinder made of homogeneous and isotropic materials. A sample made by welding tin in a copper tube and a sample of cooper rod are considered. Experimental displacements are observed by the laser ultrasonic technique, and corresponding theoretical waveforms are calculated. Good agreement is found in the arrival time, shape and relative amplitude of various longitudinal and shear bulk waves propagating through the sample or reflected by the interface.
Coulombic Fluids Bulk and Interfaces
Freyland, Werner
2011-01-01
Ionic liquids have attracted considerable interest in recent years. In this book the bulk and interfacial physico-chemical characteristics of various fluid systems dominated by Coulomb interactions are treated which includes molten salts, ionic liquids as well as metal-molten salt mixtures and expanded fluid metals. Of particular interest is the comparison of the different systems. Topics in the bulk phase concern the microscopic structure, the phase behaviour and critical phenomena, and the metal-nonmetal transition. Interfacial phenomena include wetting transitions, electrowetting, surface freezing, and the electrified ionic liquid/ electrode interface. With regard to the latter 2D and 3D electrochemical phase formation of metals and semi-conductors on the nanometer scale is described for a number of selected examples. The basic concepts and various experimental methods are introduced making the book suitable for both graduate students and researchers interested in Coulombic fluids.
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
International Nuclear Information System (INIS)
A stationary Green function is calculated for the Schroedinger Hamiltonian of the multidimensional isotropic harmonic oscillator and for physical systems, which may, somehow, have their Hamiltonian reduced to one in the form of a harmonic oscillator, for any dimension
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...
Directory of Open Access Journals (Sweden)
A Avazpour
2014-12-01
Full Text Available Density functional approach was used to study the isotropic- nematic (I-N transition and calculate the values of freezing parameters of the Gay- Berne liquid crystal model. New direct and pair correlation functions of a molecular fluid with Gay- Berne pair potential were used. These new functions were used in density functional theory as input to calculate the isotropic- nematic transition densities for elongation at various reduced temperatures. It was observed that the isotropic- nematic transition densities increase as the temperature increases. It was found that the new direct correlation function is suitable to study the isotropic- nematic transition of Gay- Berne liquids. Comparison to other works showed qualitative agreement
In-plane Isotropic Microwave Performance of CoZr Trilayer in GHz Range
Pan, Lulu; Wang, Fenglong; Wang, Wenfeng; Chai, Guozhi; Xue, Desheng
2016-02-01
In this paper, we investigate the high frequency performance of Co90Zr10/SiO2/Co90Zr10 trilayers. It is demonstrated that the in-plane isotropic microwave performance is theoretically derived from the solution of the Landau-Lifshitz-Gilbert equation and experimentally achieved in that sandwich structured film. The valuable isotropic behavior comes from the superposition of two uncouple ferromagnetic layers in which the uniaxial magnetic anisotropic fields are equivalent but mutually orthogonal. Moreover, the isotropic microwave performance can be tuned to higher resonance frequency up to 5.3 GHz by employing the oblique deposition technique. It offers a convenient and effective way to achieve an unusual in-plane isotropic microwave performance with high permeability in GHz, holding promising applications for the magnetic devices in the high frequency information technology.
Structure of the isotropic transport operators in three independent space variables
Abu-Shumays, I. K.; Bareiss, E. H.
1969-01-01
Based on the idea of separation of variables, a spectral theory for the three-dimensional, stationary, isotropic transport operator in a vector space of complex-valued Borel functions results in continuous sets of regular and generalized eigenfunctions.
International Nuclear Information System (INIS)
Typical half-space problems in two-group neutron transport theory are solved numerically using the singular-eigenfunction-expansion technique, considering isotropic-and linearly anisotropic scattering. Numerical results are reported for the Albedo, Milne and Constant-Source problems in a half-space pure light-water medium using isotropic scattering data set of Metacalf and Zweifel and considering various degrees of anisotropy
Response of Isotropic and Laminated Plates to Close Proximity Blast Loads
Coggin, John Moore
2000-01-01
Response of Isotropic and Laminated Plates to Close Proximity Blast Loads By John M. Coggin Rakesh K. Kapania, Chairman Eric R. Johnson, Co-Chairman (ABSTRACT) The transient response of various plate structures subject to blast loads is analyzed. In particular, simply supported isotropic and laminated composite plates are modeled using the commercial finite element code NASTRAN and the method of modal superposition. Both analysis procedures are used to quantify the li...
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.
On velocity structure functions and the spherical vortex model for isotropic turbulence
Aivazis, Keri A.; Pullin, D. I.
2001-01-01
We investigate a stochastic model for homogeneous, isotropic turbulence based on Hill's spherical vortex. This is an extension of the method of Synge and Lin [Trans. R. Soc. Can. 37, 45 (1943)], to the calculation of higher even-order velocity structure functions. Isotropic turbulence is represented by a homogeneous distribution of eddies, each modeled by a spherical vortex. The cascade process of eddy breakdown is incorporated into the statistical model through an average over an assumed log...
Isotropic-nematic phase separation in suspensions of polydisperse colloidal platelets
Kooij, F.M. van der; Beek, David van der; Lekkerkerker, H.N.W.
2001-01-01
We are studying the phase behavior of a suspension of platelike colloids which has a very broad size distribution, particularly in thickness. This suspension exhibits an isotropic-nematic phase separation over a notably wide range of particle concentrations, displaying a remarkable phenomenon. In part of the coexistence region, phase separation yields a nematic upper phase in coexistence with an isotropic bottom phase. If the nematic phase is isolated and diluted, the reverse situation is obs...
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....
Experimental Test of the validity of "Isotropic" Approximation for the Mechanical Behaviour of Clay
Evesque, P.; Hattab, M
2005-01-01
Experimental data from axially symmetric compression test at constant mean pressure p on kaolinite clay are used to study the validity of an "isotropic" modelling as a function of the overconsolidation ratio (OCR).The isotropic assumption is found to be quite good for 210), anisotropic response is observed at few percents of axial deformation. Relation with anisotropic distribution of local forces is made. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn
Bulk metallic glass tube casting
International Nuclear Information System (INIS)
Research highlights: → Tubular specimens of Zr55Cu30Al10Ni5 cast in custom arc-melting furnace. → Tilt casting supplemented by suction casting. → Bulk metallic glass formed only with optimized processing parameters. → Fully amorphous tubes with 1.8 mm wall thickness and 25 mm diameter. - Abstract: Tubular bulk metallic glass specimens were produced, using a custom-built combined arc-melting tilt-casting furnace. Zr55Cu30Al10Ni5 tubes with outer diameter of 25 mm and 0.8-3 mm wall thicknesses were cast, with both tilt and suction casting to ensure mold filling. Tilt casting was found to fill one side of the tube mold first, with the rest of the tube circumference filled subsequently by suction casting. Optimized casting parameters were required to fully fill the mold and ensure glass formation. Too small melt mass and too low arc power filled the mold only partially. However, too large melt mass and higher arc power which lead to the best mold filling also lead to partial crystallization. Variations in processing parameters were explored, until a glassy ring with 1.8 mm thickness was produced. Different sections of the as-cast ring were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and instrumented indentation to ensure amorphous microstructure. Atomic force microscopy (AFM) was used to compare the surface qualities of the first- and last-filled sections. These measurements confirmed the glassy structure of the cast ring, and that, the tilt cast tube section consistently showed better surface quality than the suction cast section. Optimized casting parameters are required to fully realize the potential of directly manufacturing complex shapes out of high-purity bulk metallic glasses by tilt casting.
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.
Gold based bulk metallic glass
Schroers, Jan; Lohwongwatana, Boonrat; Johnson, William L.; Peker, Atakan
2005-01-01
Gold-based bulk metallic glass alloys based on Au-Cu-Si are introduced. The alloys exhibit a gold content comparable to 18-karat gold. They show very low liquidus temperature, large supercooled liquid region, and good processibility. The maximum casting thickness exceeds 5 mm in the best glassformer. Au49Ag5.5Pd2.3Cu26.9Si16.3 has a liquidus temperature of 644 K, a glass transition temperature of 401 K, and a supercooled liquid region of 58 K. The Vickers hardness of the alloys in this system...
Iron - based bulk amorphous alloys
Directory of Open Access Journals (Sweden)
R. Babilas
2010-07-01
Full Text Available Purpose: The paper presents a structure characterization, thermal and soft magnetic properties analysis of Fe-based bulk amorphous materials in as-cast state and after crystallization process. In addition, the paper gives some brief review about achieving, formation and structure of bulk metallic glasses as a special group of amorphous materials.Design/methodology/approach: The studies were performed on Fe72B20Si4Nb4 metallic glass in form of ribbons and rods. The amorphous structure of tested samples was examined by X-ray diffraction (XRD, transmission electron microscopy (TEM and scanning electron microscopy (SEM methods. The thermal properties of the glassy samples were measured using differential thermal analysis (DTA and differential scanning calorimetry (DSC. The magnetic properties contained initial and maximum magnetic permeability, coercive force and magnetic after-effects measurements were determined by the Maxwell-Wien bridge and VSM methods.Findings: The X-ray diffraction and transmission electron microscopy investigations revealed that the studied as-cast bulk metallic glasses in form of ribbons and rods were amorphous. Two stage crystallization process was observed for studied bulk amorphous alloy. The differences of crystallization temperature between ribbons and rods with chosen thickness are probably caused by different amorphous structures as a result of the different cooling rates in casting process. The SEM images showed that studied fractures could be classified as mixed fractures with indicated two zones contained “river” and “smooth” areas. The changing of chosen soft magnetic properties (μr, Bs, Hc obtained for samples with different thickness is a result of the non-homogenous amorphous structure of tested metallic glasses. The annealing process in temperature range from 373 to 773 K causes structural relaxation of tested amorphous materials, which leads to changes in their physical properties. The qualitative
Enhanced Methanol Diffusion in Homogeneous Isotropic and Anisotropic Silica Aerogels
Lee, Jeongseop; Mounce, A. M.; Oh, Sangwon; Zimmerman, A. M.; Halperin, W. P.
2014-03-01
It has recently been shown that chiral superfluid 3He states can be stabilized using stretched, anisotropic, high porosity silica aerogel.[2] We present a novel approach to characterize the aerogel structure using nuclear magnetic resonance measurement of the enhanced diffusion of methanol vapor, similar to previous reports of diffusion of water in partially filled porous glass.[3] The diffusion coefficient is determined by the molecular motion in the vapor phase in fast exchange with adsorbed phase. Consequently, the diffusion is enhanced by two orders of magnitude beyond that of the bulk fluid but is limited by the elastic mean free path λ for ballistic molecular motion in the aerogel. The mean free paths in the presence of global anisotropy in a stretched (radially shrunken) aerogel, were found to be larger in the direction of strain by an amount consistent with the strain amplitude measured independently. This work was supported by the DOE BES under grants No. DE-FG02-05ER46248.
Bulk dynamics for interfacial growth models
López, Cristóbal; Santos, Fernando; Garrido, P. L.
2000-01-01
We study the influence of the bulk dynamics of a growing cluster of particles on the properties of its interface. First, we define a general bulk growth model by means of a continuum Master equation for the evolution of the bulk density field. This general model just considers an arbitrary addition of particles (though it can be easily generalized to consider subtraction) with no other physical restriction. The corresponding Langevin equation for this bulk density field is derived where the i...
Schmidt, Marcus; Olsson, Mattias; Maurer, Frans H. J.
2000-06-01
We made a series of isotropic pressure-densified (0-200 MPa) amorphous homopolymer [atactic polystyrene (a-PS)] and copolymer [poly(styrene-co-acrylonitrile) (SAN) and poly(styreneco-maleic anhydride) (SMA)] glasses and studied their macroscopic pressure-volume-temperature (PVT) properties vs their free-volume characteristics from the Simha-Somcynsky equation-of-state (EOS) theory and from positron annihilation lifetime spectroscopy (PALS). The glass densities lie in the range of 1.0403-1.0535 g/cm3 (PS), 1.0573-1.0759 g/cm3 (SAN), and 1.0989-1.1196 g/cm3 (SMA). With increasing formation pressure, all pressure-densified glasses exhibit decreasing volume and free-volume characteristics such that the changes in specific volume (1.26%-1.85%) are thermal expansivity α0 remains constant. There is a one-to-one correlation of τ3 and of I3 when calculated from POSITRONFIT and the maximum entropy lifetime (MELT) program. The full width at half maximum of free-volume distributions determined from PALS data and MELT does not change with formation pressure within established limits of uncertainty. Neither h vs V(τ3) nor h vs bulk modulus K, calculated from the Tait EOS of the glasses, show unique relations that are common to all the studied glasses. On the other hand, K vs V(τ3) gives a universal curve for all pressure-densified glasses from this study and from our previous study on PMMA: K=8.190-4.479×10-2V(τ3) (r2=0.92). Moreover, three more polymers from the literature are well described by this curve. The bulk moduli increase by up to 11.5% (PMMA), 7.6% (PS), 11.2% (SAN), and 10.2% (SMA) and they follow the order PS
Kalakonda, Parvathalu; Iannacchione, Germano S.
2013-03-01
Modulated Differential Scanning Calorimetry (MDSC) is used to investigate the weakly first-order isotropic to nematic (I- N) and the continuous nemat to smectic- A (N-Sm A) phase transitions of the liquid crystal octylcyanobiphenyl (8CB) doped with well-dispersed quantum dots (QdS) as a function of Qd concentrations. Thermal scans were performed for all samples having Qd (CdS) weight percent from ϕw = 0.3 to 3 wt % first on cooling and then heating under near-equilibrium conditions. The I-N transitions heat capacity peak first glows then decreases in magnitude with increasing ϕw leaving a maximum at ϕw = 0.3 %. The N-SmA heat capacity peak remains bulk-like for all samples. Both transitions temperatures shift lower monotonically by 3 K for ϕw = 0.3 %. The enthalpy of both transitions evolve in a nontrival way, generally decreasing with increasing ϕw. These results are discussed in terms of the predominate disordering effects of the Qds.
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
Galactic Winds Driven by Isotropic and Anisotropic Cosmic-Ray Diffusion in Disk Galaxies
Pakmor, R.; Pfrommer, C.; Simpson, C. M.; Springel, V.
2016-06-01
The physics of cosmic rays (CRs) 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 1011 M ⊙ halo with the moving-mesh code 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 the simulation with anisotropic diffusion, most CRs remain in the disk once the magnetic field becomes dominated by its azimuthal component, which occurs after ∼300 Myr. This has important consequences for the gas dynamics in the disk. In particular, we show that isotropic diffusion strongly suppresses the amplification of the magnetic field in the disk compared to anisotropic or no diffusion models. We therefore conclude that reliable simulations which include CR transport inevitably need to account for anisotropic diffusion.
Stability of an isotropic cosmological singularity in higher-order gravity
International Nuclear Information System (INIS)
We study the stability of the isotropic vacuum Friedmann universe in gravity theories with higher-order curvature terms of the form (RabRab)n added to the Einstein-Hilbert Lagrangian of general relativity on approach to an initial cosmological singularity. Earlier, we had shown that, when n=1, a special isotropic vacuum solution exists which behaves like the radiation-dominated Friedmann universe and is stable to anisotropic and small inhomogeneous perturbations of scalar, vector, and tensor type. This is completely different to the situation that holds in general relativity, where an isotropic initial cosmological singularity is unstable in vacuum and under a wide range of nonvacuum conditions. We show that when n≠1, although a special isotropic vacuum solution found by Clifton and Barrow always exists, it is no longer stable when the initial singularity is approached. We find the particular stability conditions under the influence of tensor, vector, and scalar perturbations for general n for both solution branches. On approach to the initial singularity, the isotropic vacuum solution with scale factor a(t)=tP-/3 is found to be stable to tensor perturbations for 0.5P+/3 is not relevant to the case of an initial singularity for n>1 and is unstable as t 0 for all n for each type of perturbation
The evolution of a spatially homogeneous and isotropic universe filled with a collisionless gas
International Nuclear Information System (INIS)
We review the evolution of a spatially homogeneous and isotropic universe described by a Friedmann-Robertson-Walker spacetime filled with a collisionless, neutral, simple, massive gas. The gas is described by a one-particle distribution function which satisfies the Liouville equation and is assumed to be homogeneous and isotropic. Making use of the isometries of the spacetime, we define precisely the homogeneity and isotropicity property of the distribution function, and based on this definition we give a concise derivation of the most general family of such distribution functions. For this family, we construct the particle current density and the stress-energy tensor and consider the coupled Einstein-Liouville system of equations. We find that as long as the distribution function is collisionless, homogenous and isotropic, the evolution of a Friedmann-Robertson-Walker universe exhibits a singular origin. Its future development depends upon the curvature of the spatial sections: spatially flat or hyperboloid universes expand forever and this expansion dilutes the energy density and pressure of the gas, while a universe with compact spherical sections reaches a maximal expansion, after which it reverses its motion and recollapses to a final crunch singularity where the energy density and isotropic pressure diverge. Finally, we analyze the evolution of the universe filled with the collisionless gas once a cosmological constant is included
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.
Gold based bulk metallic glass
Schroers, Jan; Lohwongwatana, Boonrat; Johnson, William L.; Peker, Atakan
2005-08-01
Gold-based bulk metallic glass alloys based on Au-Cu-Si are introduced. The alloys exhibit a gold content comparable to 18-karat gold. They show very low liquidus temperature, large supercooled liquid region, and good processibility. The maximum casting thickness exceeds 5mm in the best glassformer. Au49Ag5.5Pd2.3Cu26.9Si16.3 has a liquidus temperature of 644K, a glass transition temperature of 401K, and a supercooled liquid region of 58K. The Vickers hardness of the alloys in this system is ˜350Hv, twice that of conventional 18-karat crystalline gold alloys. This combination of properties makes the alloys attractive for many applications including electronic, medical, dental, surface coating, and jewelry.
Gold based bulk metallic glass
International Nuclear Information System (INIS)
Gold-based bulk metallic glass alloys based on Au-Cu-Si are introduced. The alloys exhibit a gold content comparable to 18-karat gold. They show very low liquidus temperature, large supercooled liquid region, and good processibility. The maximum casting thickness exceeds 5 mm in the best glassformer. Au49Ag5.5Pd2.3Cu26.9Si16.3 has a liquidus temperature of 644 K, a glass transition temperature of 401 K, and a supercooled liquid region of 58 K. The Vickers hardness of the alloys in this system is ∼350 Hv, twice that of conventional 18-karat crystalline gold alloys. This combination of properties makes the alloys attractive for many applications including electronic, medical, dental, surface coating, and jewelry
Bulk analysis using nuclear techniques
International Nuclear Information System (INIS)
Bulk analysis techniques developed for the mining industry are reviewed. Using penetrating neutron and #betta#-radiations, measurements are obtained directly from a large volume of sample (3-30 kg) #betta#-techniques were used to determine the grade of iron ore and to detect shale on conveyor belts. Thermal neutron irradiation was developed for the simultaneous determination of iron and aluminium in iron ore on a conveyor belt. Thermal-neutron activation analysis includes the determination of alumina in bauxite, and manganese and alumina in manganese ore. Fast neutron activation analysis is used to determine silicon in iron ores, and alumina and silica in bauxite. Fast and thermal neutron activation has been used to determine the soil in shredded sugar cane. (U.K.)
Isotopic signatures by bulk analyses
International Nuclear Information System (INIS)
Los Alamos National Laboratory has developed a series of measurement techniques for identification of nuclear signatures by analyzing bulk samples. Two specific applications for isotopic fingerprinting to identify the origin of anthropogenic radioactivity in bulk samples are presented. The first example is the analyses of environmental samples collected in the US Arctic to determine the impact of dumping of radionuclides in this polar region. Analyses of sediment and biota samples indicate that for the areas sampled the anthropogenic radionuclide content of sediments was predominantly the result of the deposition of global fallout. The anthropogenic radionuclide concentrations in fish, birds and mammals were very low. It can be surmised that marine food chains are presently not significantly affected. The second example is isotopic fingerprinting of water and sediment samples from the Rocky Flats Facility (RFP). The largest source of anthropogenic radioactivity presently affecting surface-waters at RFP is the sediments that are currently residing in the holding ponds. One gram of sediment from a holding pond contains approximately 50 times more plutonium than 1 liter of water from the pond. Essentially 100% of the uranium in Ponds A-1 and A-2 originated as depleted uranium. The largest source of radioactivity in the terminal Ponds A-4, B-5 and C-2 was naturally occurring uranium and its decay product radium. The uranium concentrations in the waters collected from the terminal ponds contained 0.05% or less of the interim standard calculated derived concentration guide for uranium in waters available to the public. All of the radioactivity observed in soil, sediment and water samples collected at RFP was naturally occurring, the result of processes at RFP or the result of global fallout. No extraneous anthropogenic alpha, beta or gamma activities were detected. The plutonium concentrations in Pond C-2 appear to vary seasonally
Guidelines for Measuring Bulk Density of Soil
International Nuclear Information System (INIS)
Bulk density is defined as the dry weight of soil per unit volume of undisturbed soil. • Bulk density can be used to give an indication of the porosity and structure of the soil influencing O2 and H2O movement in the soil. • Soils with a bulk density higher than 1.6 g/cm3 may restrict root development. • Bulk density is also a measurement of the degree of compaction of the soil. • Bulk density increases with compaction and tends to increase with soil depth. • Sandy soils tend to have higher bulk density (1.4-1.5 g/cm3) than clay soils (1.2-1/3g/cm3). The measurement of soil bulk density is carried out by collecting undisturbed soil samples through inserting metal rings (with a known volume) into the soil, and determining the weight of the collected soil after drying
Superfluid density of bulk CaC 6
Lamura, G.; Aurino, M.; Cifariello, G.; Di Gennaro, E.; Andreone, A.; Emery, N.; Hérold, C.; Marêché, J.-F.; Lagrange, P.
2007-09-01
The recent discovery of superconductivity at 11.5 K in the graphite intercalation compound (GIC) CaC6 has opened new perspectives in the physics of graphite. One of the main open questions for superconducting GICs is related to the nature of the pairing mechanism, since the possibility of an unconventional, excitonic or plasmonic, origin of superconductivity has also been invoked as an alternative to a simple electron-phonon interaction. To better understand the origin of pairing mechanism in these compounds, a first step is to determine the symmetry of the superconducting gap function and the nature of the elementary excitations. To this aim, we have performed the first high-resolution measurement of the in-plane magnetic penetration depth, λab(T), in a c-axis oriented polycrystalline CaC6 bulk sample using a high-resolution mutual inductance technique. A clear exponential behavior of λab(T) has been observed at low temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the standard BCS theory yields λab(0) = (720 ± 80) Å and Δ(0) = (1.79 ± 0.08) meV. The ratio 2Δ(0)/kBTC = (3.6 ± 0.2) gives therefore indication for a conventional weakly coupled superconductor. By using these results as fixed parameters, a BCS calculation on the superfluid density in the overall temperature range shows that the sample under test lies in the local dirty limit.
Ghoufi, Aziz; Morineau, Denis; Lefort, Ronan; Malfreyt, Patrice
2011-01-01
Molecular simulations in the isothermal statistical ensembles require that the macroscopic thermal and mechanical equilibriums are respected and that the local values of these properties are constant at every point in the system. The thermal equilibrium in Monte Carlo simulations can be checked through the calculation of the configurational temperature, {k_BT_{conf}={}/{}}, where nabla _r is the nabla operator of position vector r. As far as we know, T_{conf} was never calculated with the anisotropic Gay-Berne potential, whereas the calculation of T_{conf} is much more widespread with more common potentials (Lennard Jones, electrostatic, …). We establish here an operational expression of the macroscopic and local configurational temperatures, and we investigate locally the isotropic liquid phase, the liquid / vapor interface, and the isotropic-nematic transition by Monte Carlo simulations.
Fast switching from isotropic liquids to nematic liquid crystals: rotaxanes as smart fluids.
He, Hao; Sevick, Edith M; Williams, David R M
2015-11-28
We examine a solution of rod-like piston-rotaxanes, which can switch their length by external excitation (for example optically) from a short state of length L to a long state of length qL. We show that this solution can exhibit a number of different behaviours. In particular it can rapidly switch from an isotropic to a nematic liquid crystalline state. There is a minimum ratio q* = 1.13 for which transitions from a pure isotropic state to a pure nematic state are possible. We present a phase-switching diagram, which gives the six possible behaviours for this system. It turns out that a large fraction of the phase switching diagram is occupied by the transition from a pure isotropic to a pure nematic state. PMID:26419821
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.
International Nuclear Information System (INIS)
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. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
The Stability of an Isotropic Cosmological Singularity in Higher-Order Gravity
Middleton, Jonathan
2008-01-01
We study the stability of the isotropic vacuum Friedmann universe in gravity theories with higher-order curvature terms of the form $(R_{ab}R^{ab})^{n}$ added to the Einstein-Hilbert Lagrangian of general relativity on approach to an initial cosmological singularity. Earlier, we had shown that, when $% n=1$, a special isotropic vacuum solution exists which behaves like the radiation-dominated Friedmann universe and is stable to anisotropic and small inhomogeneous perturbations of scalar, vector and tensor type. This is completely different to the situation that holds in general relativity, where an isotropic initial cosmological singularity is unstable in vacuum and under a wide range of non-vacuum conditions. We show that when $n\
Streamlines in stationary homogeneous isotropic turbulence and fractal-generated turbulence
Boschung, J.; Peters, N.; Laizet, S.; Vassilicos, J. C.
2016-04-01
We compare streamline statistics in stationary homogeneous isotropic turbulence and in turbulence generated by a fractal square grid. We examine streamline segments characterised by the velocity difference {{Δ }}u and the distance l between extremum points. We find close agreement between the stationary homogeneous isotropic turbulence and the decay region of the fractal-generated turbulence as well as the production region of the fractal flow for small segments. The statistics of larger segments are very similar for the isotropic turbulence and the decay region, but differ for the production region. Specifically, we examine the first, second and third conditional mean . Noticeably, non-vanishing for n=1,3 are due to an asymmetry of positive and negative segments, i.e. those for which {{Δ }}u\\gt 0 and {{Δ }}u\\lt 0, respectively. This asymmetry is not only kinematic, but is also due to dissipative effects and therefore contains cascade information.
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.
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 ...
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 ...
Influence of particle shape on the nematic—isotropic transition of colloidal platelet systems
Bates, Martin A.
1999-07-01
We study the nematic-isotropic transition in model colloidal systems composed of platelets of various shapes using grand canonical simulations. This is of relevance for recently synthesized hard platelet systems, since the platelets in such systems are found to be not circular but irregular hexagons, and so cannot be described by the simulation data currently available. We show that the coexistence densities scale with an effective volume related to the isotropic orientation-averaged excluded volume of a pair of platelets. This excluded volume can be obtained from the perimeter of the face of the particles and so can be easily calculated for both regular and irregular particle shapes.
Chen, Ming-Ji; Pei, Yong-Mao; Fang, Dai-Ning
2010-03-01
The classic anisotropic spherical cloak can be mimicked by many alternating thin layers of isotropic metamaterials [Qiu et al. Phys. Rev. E 79 (2009) 047602]. We propose an improved method of designing permittivity and permeability in each isotropic layer, which eliminates the jumping of the refractive index at the interface. Multilayered spherical cloaks designed by the present method perform much better than those by Qiu et al., especially for forward scattering. It is found that the ratio of layer thickness to the operating wavelength plays an important role in achieving invisibility. The presented cloak should be discretized to at least 40 layers to meet the thickness threshold corresponding to 10% scattering.
Damage spreading in 2-dimensional isotropic and anisotropic Bak-Sneppen models
Bakar, B.; Tirnakli, U.
2008-03-01
We implement the damage spreading technique on 2-dimensional isotropic and anisotropic Bak-Sneppen models. Our extensive numerical simulations show that there exists a power-law sensitivity to the initial conditions at the statistically stationary state (self-organized critical state). Corresponding growth exponent α for the Hamming distance and the dynamical exponent z are calculated. These values allow us to observe a clear data collapse of the finite size scaling for both versions of the Bak-Sneppen model. Moreover, it is shown that the growth exponent of the distance in the isotropic and anisotropic Bak-Sneppen models is strongly affected by the choice of the transient time.
Hydromagnetic waves in a plasma of isotropic thermal and anisotropic suprathermal components
International Nuclear Information System (INIS)
Low frequency plane waves supported by a medium containing a thermal plasma of isotropic pressure and a suprathermal collisionless plasma having anisotropic pressure are investigated. The usual Alfvacute en, slow and fast modes of isotropic pressure magnetohydrodynamics persist. In addition, a suprathermal mode appears which displays a rich variety of behavior due to an additional degree of freedom compared to the analogous mode when both the plasma components are described by collision-dominated magnetohydrodynamics. Since these modes are significant in a number of situations, they are extensively investigated by computing their phase speeds for wide-ranging numerical parameters. copyright 1996 American Institute of Physics
Hydromagnetic waves in a plasma of isotropic thermal and anisotropic suprathermal components
Energy Technology Data Exchange (ETDEWEB)
Kalra, G.L.; Ghildyal, V. [Department of Physics and Astrophysics, University of Delhi, Delhi 110 007 (India)
1996-10-01
Low frequency plane waves supported by a medium containing a thermal plasma of isotropic pressure and a suprathermal collisionless plasma having anisotropic pressure are investigated. The usual Alfv{acute e}n, slow and fast modes of isotropic pressure magnetohydrodynamics persist. In addition, a suprathermal mode appears which displays a rich variety of behavior due to an additional degree of freedom compared to the analogous mode when both the plasma components are described by collision-dominated magnetohydrodynamics. Since these modes are significant in a number of situations, they are extensively investigated by computing their phase speeds for wide-ranging numerical parameters. {copyright} {ital 1996 American Institute of Physics.}
Optically isotropic liquid crystal composite incorporating in-plane electric field geometry
International Nuclear Information System (INIS)
We demonstrate an intriguing liquid crystal display (LCD) mode that comprises an optically isotropic LC composite incorporating in-plane electric field geometry. No surface treatment, such as rubbing, is required to fabricate the LCD mode because it is based on an isotropic state. The measured response time is of submillisecond order. This rapid response originates from the local reorientation of molecules in small LC clusters as well as from strong polymer stabilization. The LCD mode has several unique features such as fast response, continuous greyscale capability and a high contrast ratio. (fast track communication)
About zone structure of a stack of a cholesteric liquid crystal and isotropic medium layers
International Nuclear Information System (INIS)
The optical properties of a stack of metamaterial-based cholesteric liquid crystal (CLC) layers and isotropic medium layers are investigated. CLCs with two types of chiral nihility are defined. The peculiarities of the reflection spectra of this system are investigated and it is shown that the reflection spectra of the stacks of CLC layers of these two types differ from each other. The influence of: the CLC sublayer thicknesses; incidence angle; local dielectric (magnetic) anisotropy of the CLC layers; refraction indices and thicknesses of the isotropic media layers on the reflection spectra and other optical characteristics of the system is investigated.
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.
International Nuclear Information System (INIS)
The electronic structures and optical properties of N-doped ZnO bulks and nanotubes are investigated using the first-principles density functional method. The calculated results show that the main optical parameters of ZnO bulks are isotropic (especially in the high frequency region), while ZnO nanotubes exhibit anisotropic optical properties. N doping results show that ZnO bulks and nanotubes present more obvious anisotropies in the low-frequency region. Thereinto, the optical parameters of N-doped ZnO bulks along the [100] direction are greater than those along the [001] direction, while for N-doped nanotubes, the variable quantities of optical parameters along the [100] direction are less than those along the [001] direction. In addition, refractive indexes, electrical conductivities, dielectric constants, and absorption coefficients of ZnO bulks and nanotubes each contain an obvious spectral band in the deep ultraviolet (UV) (100 nm ∼ 300 nm). For each of N-doped ZnO bulks and nanotubes, a spectral peak appears in the UV and visible light region, showing that N doping can broaden the application scope of the optical properties of ZnO. (condensed matter: structural, mechanical, and thermal properties)
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.
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.
Coupling brane fields to bulk supergravity
International Nuclear Information System (INIS)
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.)
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.)
Bulk scalar field in DGP braneworld cosmology
Ansari, Rizwan ul Haq
2007-01-01
We investigated the effects of bulk scalar field in the braneworld cosmological scenario. The Friedmann equations and acceleration condition in presence of the bulk scalar field for a zero tension brane and cosmological constant are studied. In DGP model the effective Einstein equation on the brane is obtained with bulk scalar field. The rescaled bulk scalar field on the brane in the DGP model behaves as an effective four dimensional field, thus standard type cosmology is recovered. In present study of the DGP model, the late-time accelerating phase of the universe can be explained .
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.
International Nuclear Information System (INIS)
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)
The radiance from an isotropic point source in a multiple scattering medium
International Nuclear Information System (INIS)
Starting from the general solution of the equation of radiative transfer in the small-angle scattering approximation expressions are derived for the radiance and irradiance from an isotropically radiating point source in a multiple scattering medium. These expressions are exact and comparatively simple to evaluate numerically. Comparisons are made with the corresponding results obtained with an approximate theory. (author)
Approximate conditions for the all-axis triplication in transversely isotropic media
Czech Academy of Sciences Publication Activity Database
Vavryčuk, Václav
Prague : Charles University, 2003, s. 91-105 R&D Projects: GA AV ČR IAA3012309 Institutional research plan: CEZ:AV0Z3012916 Keywords : mechanical waves * elastic waves * isotropic media Subject RIV: DC - Siesmology, Volcanology, Earth Structure
A congruence modulo four in real Schubert calculus with isotropic flags
Hein, Nickolas; Sottile, Frank; Zelenko, Igor
2014-01-01
We previously obtained a congruence modulo four for the number of real solutions to many Schubert problems on a square Grassmannian given by osculating flags. Here, we consider Schubert problems given by more general isotropic flags, and prove this congruence modulo four for the largest class of Schubert problems that could be expected to exhibit this congruence.
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.
Study of magnetic properties for isotropic nanostructured iron-rich Fe-Pt films
International Nuclear Information System (INIS)
The isotropic nanostructured iron-rich Fe-Pt films with XFe=50-73 at% were prepared by annealing DC sputtered Fe/Pt multilayer films. Studies showed that coercivity of these films is mainly controlled by pinning mechanism and magnetization of all films is dominated by ferromagnetic exchange coupling between neighboring grains
Reconstruction of the material parameters of the homogenous isotropic or orthotropic 2D continuum
Šika Z.; Valášek M.; Vampola T.
2007-01-01
The paper describes the way how to find the material parameters of the homogenous isotropic or orthotropic 2D continuum from measurements of deformation of selected nodes. The FE method is used for reconstruction of the stiffness matrix. The developed method enables to determine the angle between the material axes of the continuum and the local coordinate system of the used elements.
Gerritsen, W.J.; de Kruijff, B.; Verkleij, A.J.; Gier, J.; Van Deenen, L. L. M.
1980-01-01
Ca2+ induces a structural change in phosphatidylcholine-cardiolipin bilayers, which is visualised by freeze-fracturing as lipidic particles associated with the bilayer and is detected by 31P-NMR as isotropic motion of the phospholipids. In this structure a rapid transbilayer movement of phosphatidylcholine and a highly increased permeability towards Mn2+ are observed.
Corrsin's Hypothesis and Two-Particle Dispersion in Isotropic, Stationary Turbulence
DEFF Research Database (Denmark)
Kristensen, Leif; Kirkegaard, Peter
On the basis of Corrsin’s independence hypothesis, in conjunction with specific assumptions about the form of the distance-neighbour function, an equation is derived for twoparticle dispersion in isotropic turbulence with no mean motion. It is formulated in terms of the mean-square difference...
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. ...
International Nuclear Information System (INIS)
For any planar motion a constant of the motion called generalized Laplace-Runge-Lenz vector is defined with the matrix representation. Taking the tensor product of the generalized vector with itself, the conserved symmetric tensor corresponding to the Hamiltonian of a two-dimensional isotropic harmonic oscillator is simply constructed
International Nuclear Information System (INIS)
A physical interpretation of the early detected ambiguity of the electrodynamic material equations of isotropic, inertially moving media which mathematically manifests itself through complementarity of the equations invariant under the Galileo group in some cases and in other ones - under the Lorentz group that can be experimentally discovered in the aberration phenomenon and Doppler effect
Gill, Michelle L.; Palmer, Arthur G.
2014-01-01
The present work demonstrates that NMR spin relaxation rate constants for molecules interconverting between states with different diffusion tensors can be modeled theoretically by combining orientational correlation functions for exchanging spherical molecules with locally isotropic approximations for the diffusion anisotropic tensors. The resulting expressions are validated by comparison with correlation functions obtained by Monte Carlo simulations and are accurate for moderate degrees of d...
Characteristics of dissimilar laser-brazed joints of isotropic graphite to WC–Co alloy
International Nuclear Information System (INIS)
Highlights: ► Ti was required in the filler metal for brazing graphite to WC–Co alloy. ► The shear strength of the joint increased with Ti content up to 1.7 mass%. ► Ti concentrated at the interface of graphite/filler metal. ► 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.
Maximum likelihood based multi-channel isotropic reverberation reduction for hearing aids
DEFF Research Database (Denmark)
Kuklasiński, Adam; Doclo, Simon; Jensen, Søren Holdt; Jensen, Jesper
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...
Henein, Simon; Vardi, Ilan; Rubbert, Lennart
2015-01-01
The mechanical isotropic harmonic oscillator comprises at least a two degrees of freedom linkage supporting an orbiting mass with respect to a fixed base with springs having isotropic and linear restoring force properties wherein the mass has a tilting motion. The oscillator may be used in a timekeeper, such a watch.
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...
Bulk equations of motion from CFT correlators
Kabat, Daniel
2015-01-01
To O(1/N) we derive, purely from CFT data, the bulk equations of motion for interacting scalar fields and for scalars coupled to gauge fields and gravity. We first uplift CFT operators to mimic local AdS fields by imposing bulk microcausality. This requires adding an infinite tower of smeared higher-dimension double-trace operators to the CFT definition of a bulk field, with coefficients that we explicitly compute. By summing the contribution of the higher-dimension operators we derive the equations of motion satisfied by these uplifted CFT operators and show that we precisely recover the expected bulk equations of motion. We exhibit the freedom in the CFT construction which corresponds to bulk field redefinitions.
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.
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.
Chiadini, Francesco; Fiumara, Vincenzo; 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, and 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 composition of the PMLID material. Some of these are p-polarized, the others are s-polarized. All of them differ in phase speed, attenuation rate, and field profile, even though all are excitable at the same frequency. The multiplicity and dependence of the number of compound SPP waves on the relative permittivity of the HID material when the metal layer is thin could be useful for optical sensing applications and intrachip plasmonic optical communication.
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...
International Nuclear Information System (INIS)
Aim: To compare the diagnostic accuracies of three-dimensional (3D) isotropic magnetic resonance arthrography (MRA) using fat-suppressed proton density (PD) or volume interpolated breath-hold examination (VIBE) sequences with that of conventional MRA for the diagnosis of rotator cuff and labral lesions. Materials and methods: Eighty-six patients who underwent arthroscopic surgery were included. 3D isotropic sequences were performed in the axial plane using fat-suppressed PD (group A) in 53 patients and using VIBE (group B) in 33 patients. Reformatted images were obtained corresponding to conventional images, and evaluated for the presence of labral and rotator cuff lesions using conventional and 3D isotropic sequences. The diagnostic performances of each sequence were determined using arthroscopic findings as the standard. Results: Good to excellent interobserver agreements were obtained for both 3D isotropic sequences for the evaluation of rotator cuff and labral lesions. Excellent agreement was found between two-dimensional (2D) and 3D isotropic MRA, except for supraspinatus tendon (SST) tears by both readers and for subscapularis tendon (SCT) tears by reader 2 in group B. 2D MRA and 3D isotropic sequences had high diagnostic performances for rotator and labral tears, and the difference between the two imaging methods was insignificant. Conclusions: The diagnostic performances of 3D isotropic VIBE and PD sequences were similar to those of 2D MRA
Superfluid density of bulk CaC{sub 6}
Energy Technology Data Exchange (ETDEWEB)
Lamura, G. [CNR-INFM Coherentia and Department of Physics, University of Naples ' Federico II' , 80125 Naples (Italy)], E-mail: lamura@na.infn.it; Aurino, M.; Cifariello, G.; Di Gennaro, E.; Andreone, A. [CNISM and Department of Physics, University of Naples ' Federico II' , 80125 Naples (Italy); Emery, N.; Herold, C.; Mareche, J.-F.; Lagrange, P. [Laboratoire de Chimie du Solide Mineral-UMR 7555, Universite Henri Poincare Nancy I, B.P. 239, 54506 Vandoeuvre-les-Nancy Cedex (France)
2007-09-01
The recent discovery of superconductivity at 11.5 K in the graphite intercalation compound (GIC) CaC{sub 6} has opened new perspectives in the physics of graphite. One of the main open questions for superconducting GICs is related to the nature of the pairing mechanism, since the possibility of an unconventional, excitonic or plasmonic, origin of superconductivity has also been invoked as an alternative to a simple electron-phonon interaction. To better understand the origin of pairing mechanism in these compounds, a first step is to determine the symmetry of the superconducting gap function and the nature of the elementary excitations. To this aim, we have performed the first high-resolution measurement of the in-plane magnetic penetration depth, {lambda}{sub ab}(T), in a c-axis oriented polycrystalline CaC{sub 6} bulk sample using a high-resolution mutual inductance technique. A clear exponential behavior of {lambda}{sub ab}(T) has been observed at low temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the standard BCS theory yields {lambda}{sub ab}(0) = (720 {+-} 80) A and {delta}(0) = (1.79 {+-} 0.08) meV. The ratio 2{delta}(0)/k{sub B}T{sub C} = (3.6 {+-} 0.2) gives therefore indication for a conventional weakly coupled superconductor. By using these results as fixed parameters, a BCS calculation on the superfluid density in the overall temperature range shows that the sample under test lies in the local dirty limit.
Bulk Viscosity in Holographic Lifshitz Hydrodynamics
Hoyos, Carlos; Oz, Yaron
2013-01-01
We compute the bulk viscosity in holographic models dual to theories with Lifshitz scaling and/or hyperscaling violation, using a generalization of the bulk viscosity formula derived in arXiv:1103.1657 from the null focusing equation. We find that only a class of models with massive vector fields are truly Lifshitz scale invariant, and have a vanishing bulk viscosity. For other holographic models with scalars and/or massless vector fields we find a universal formula in terms of the dynamical exponent and the hyperscaling violation exponent.
Bulk viscosity in holographic Lifshitz hydrodynamics
Carlos Hoyos; Bom Soo Kim; Yaron Oz
2014-01-01
We compute the bulk viscosity in holographic models dual to theories with Lifshitz scaling and/or hyperscaling violation, using a generalization of the bulk viscosity formula derived in arXiv:1103.1657 from the null focusing equation. We find that only a class of models with massive vector fields are truly Lifshitz scale invariant, and have a vanishing bulk viscosity. For other holographic models with scalars and/or massless vector fields we find a universal formula in terms of the dynamical ...
Bulk viscosity in holographic Lifshitz hydrodynamics
International Nuclear Information System (INIS)
We compute the bulk viscosity in holographic models dual to theories with Lifshitz scaling and/or hyperscaling violation, using a generalization of the bulk viscosity formula derived in arXiv:1103.1657 from the null focusing equation. We find that only a class of models with massive vector fields are truly Lifshitz scale invariant, and have a vanishing bulk viscosity. For other holographic models with scalars and/or massless vector fields we find a universal formula in terms of the dynamical exponent and the hyperscaling violation exponent
Bulk viscosity of hot and dense hadrons
International Nuclear Information System (INIS)
The bulk viscosity of hot and dense hadrons has been estimated within the framework of hadronic resonance gas model. We observe that the bulk viscosity to entropy ratio increases faster with temperature for higher μB. The magnitude of ζ is more at high μB. This results will have crucial importance for fire-ball produced at low energy nuclear collisions (FAIR, NICA). We note that the bulk to shear viscosity ratio remains above the bound set by AdS/CFT
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)
Bulk waves excited by a laser line pulse in a two-layered cylinder
Pan, Y.; Chigarev, N.; Audoin, B.
2010-01-01
The acoustic displacements excited by a laser line source under either the ablation or thermoelastic regime are calculated for a two-layered cylinder made of homogeneous and isotropic materials. Two samples made by welding tin in two different copper tubes are considered. Experimental displacements are observed by the laser ultrasonic technique, and corresponding theoretical waveforms are calculated. Good agreement is found in the arrival time, shape, and relative amplitude of various longitudinal and shear bulk waves propagating in the two-layered cylinders, and the waves reflected by the interface are further identified by the ray trajectory analysis. The longitudinal wave reflected at the interface may be used for the nondestructive evaluation of the interface quality.
International Nuclear Information System (INIS)
The jumps of the strain and stress tensors on the surface of elastic homogeneous or inhomogeneous ellipsoidal inclusions embedded in an elastic matrix are obtained from results reported in the literature. They are used to derive closed-form expressions for the thermodynamic force in such matrix-inclusion systems that are subjected to a generally defined homogeneous transformation eigenstrain. A detailed study is presented for an isotropic spheroidal inclusion in an isotropic matrix in which the most important parameters are the inclusion's aspect ratio α and an eigenstrain triaxiality parameter d-bar. The fluctuations of the thermodynamic force are investigated for a set of specific transformation eigenstrain tensors and are presented for inclusion shapes ranging from disk-like to fiber-like spheroids
JKR adhesive contact for a transversely isotropic layer of finite thickness
International Nuclear Information System (INIS)
A frictionless contact interaction with a circular area of contact between an arbitrary axisymmetric rigid probe and a transversely isotopic elastic layer deposited on a substrate is studied in the framework of the JKR (Johnson, Kendall, and Roberts) adhesion theory. Under the assumption that the diameter of the contact area is less than the thickness of the elastic layer, the forth-order asymptotic model is explicitly written out. The effect of the layer thickness and the material anisotropy is taken into account via the asymptotic coefficients, which are integral characteristics of the elastic layer and also depend on the boundary conditions at the layer/substrate interface. A special case of an isotropic elastic layer bonded to an isotropic elastic half-space is considered in detail. (paper)
Microscopic domain structures in unidirectional and isotropic exchange-coupled NiO/NiFe bilayers
International Nuclear Information System (INIS)
The dependence on nickel oxide thickness in unidirectional and isotropic exchange-coupled NiO/NiFe bilayer films was investigated by magnetic force microscopy to better understand exchange biasing at microscopic length scales. As the NiO thickness increased, the domain structure of unidirectional biased films formed smaller and more complex in-plane domains. By contrast, for the isotropically coupled films, large domains generally formed with increasing NiO thickness including a new cross type domain with out-of-plane magnetization orientation. The density of the cross domain is proportional to exchange biasing field, and the fact that the domain mainly originated from the strongest exchange coupled region was confirmed by imaging in an applied external field during a magnetization cycle
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.
Self-organization at low Reynolds numbers in randomly forced isotropic fluid motion
McComb, W D; Berera, A; Yoffe, S R; Jankauskas, B
2014-01-01
We observe the formation at long times of a self-organized state in direct numerical simulation (DNS) of the Navier-Stokes equation with random, isotropic forcing. In this state the kinetic energy is contained only in modes at the lowest resolved wavenumber, the skewness vanishes, and visualization of the flows shows a lack of small-scale structure. Accordingly we conclude that the state is not turbulent. Furthermore, we observe that this state is maximally helical. That is, the velocity field is an eigenfunction of the curl operator and is thus a Beltrami field. We put forward numerical evidence suggesting the presence of critical behavior, and outline arguments to support the existence of an upper Reynolds number bound for the occurrence of such self-organized states in forced isotropic fluid motion.
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...
A geometric approach to self-propelled motion in isotropic and anisotropic environments
Großmann, Robert; Bär, Markus
2015-01-01
We propose a geometric perspective to describe the motion of self-propelled particles moving at constant speed in d dimensions. We exploit the fact that the vector that conveys the direction of motion of the particle performs a random walk on a $(d-1)$-dimensional manifold. We show that the particle performs isotropic diffusion in d-dimensions if the manifold corresponds to a hypersphere. In contrast, we find that the self-propelled particle exhibits anisotropic diffusion if this manifold corresponds to a deformed hypersphere (e.g. an ellipsoid). This simple approach provides an unified framework to deal with isotropic as well as anisotropic diffusion of particles moving at constant speed in any dimension.
Bar, Doron E.; Nepomnyashchy, Alexander A.
1999-08-01
We consider spontaneous generation of long waves in the presence of a conservation law in both cases of isotropic systems (e.g., Bénard-Marangoni waves) and anisotropic systems (e.g., waves in a film on an inclined plane). We found that near the instability threshold the problem is governed by the dissipation-modified Kadomtsev-Petviashvili equation in the former case and by the anisotropic dissipation-modified Korteweg-de Vries equation in the latter case. In frames of the derived 2+1-dimensional amplitude equations, we investigate the stability of one-dimensional waves. In isotropic systems the one-dimensional waves turned out to be always unstable with respect to a long-wave transverse modulation of the front. In anisotropic systems, only the one-dimensional periodic waves moving in the most preferred direction are found to be stable. Any deviation from this direction leads to instability of such an oblique wave.
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.
Yu, Huidan
2009-01-01
We study Lagrangian statistics of the magnitudes of velocity and pressure gradients in isotropic turbulence by quantifying their correlation functions and their characteristic time scales. It has been found that the Lagrangian time-correlations of the velocity and pressure gradient tensor and vector elements scale with the locally-defined Kolmogorov time scale, defined from the box-averaged dissipation-rate and viscosity. In this work, we study the Lagrangian time-correlations of the absolute values of velocity and pressure gradients. We explore the appropriate temporal scales with the aim to achieve collapse of the correlation functions. The data used in this study are sampled from the web-services accessible public turbulence database(http://turbulence.pha.jhu.edu). The database archives a pseudo-spectral direct numerical simulation of forced isotropic turbulence with Taylor-scale Reynolds number 433, and supports spatial differentiation and spatial/temporal interpolation inside the database. The analysis s...
Isotropic properties of the photonic band gap in quasicrystals with low-index contrast
Priya Rose, T.; di Gennaro, E.; Abbate, G.; Andreone, A.
2011-09-01
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 were 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∘ to 30∘ were used 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.
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.
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.
International Nuclear Information System (INIS)
The purpose of this work was to construct a Brownian motion with values in simplicial complexes with piecewise differential structure. After a martingale theory attempt, we constructed a family of continuous Markov processes with values in an admissible complex; we named every process of this family, isotropic transport process. We showed that the family of the isotropic processes contains a subsequence, which converged weakly to a measure; we named it the Wiener measure. Then, we constructed, thanks to the finite dimensional distributions of the Wiener measure a new continuous Markov process with values in an admissible complex: the Brownian motion. We finished with a geometric analysis of this Brownian motion, to determinate, under hypothesis on the complex, the recurrent or transient behavior of such process. (author)
How to estimate isotropic distributions and mean values in crystalline solids
International Nuclear Information System (INIS)
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. (paper)
Optical properties of a stack of cholesteric liquid crystal and isotropic medium layers
Energy Technology Data Exchange (ETDEWEB)
Gevorgyan, A. H., E-mail: agevorgyan@ysu.am [Yerevan State University (Armenia)
2015-12-15
Some new optical properties of a stack consisting of cholesteric liquid crystal (CLC) and isotropic medium layers are studied. The problem is solved by the modified Ambartsumyan method for the summation of layers. Bragg conditions for the photonic band gaps of the proposed system are presented. It is shown that the choice of proper sublayer parameters can be used to control the band structure of the system. In the general case, the effect of full suppression of absorption, which is observed in a finite homogeneous CLC layer, is not detected in the presence of anisotropic absorption in CLC sublayers. It is shown that this effect can be generated in the system under study if certain conditions are imposed on the isotropic sublayer thickness. Under these conditions, the maximum photonic density of states (PDS) increases significantly at the boundaries of the corresponding band. The influence of a change in the CLC sublayer thickness and the system thickness on PDS is investigated.
CONTACT STRESSES IN A TRANSVERSELY ISOTROPIC SOLID CYLINDER LATERALLY COMPRESSED BY AN INDENTER
Directory of Open Access Journals (Sweden)
Ahmet YAPICI
2004-03-01
Full Text Available In this study, an elastostatic contact problem for a laterally compressed transversely isotropic cylinder subjected to radial compression through a circumferential rigid indenter is considered. The extent of the contact region and the stress distribution are sought. It is assumed that the contact between the cylinder and the rigid indenter is frictionless and only compressive normal tractions can be transmitted through the interface. Due to the geometry of the configuration, Fourier transform techniques are chosen. The problem is reduced to a singular integral equation. It is reduced to linear algebraic equation system by using Gauss Chebyshev Integration Formulae and is solved by using Gauss Elimination method. E glass and barium titanate are used as a transversely isotropic materials. The stress analysis is performed for different contact area, punch radiuses and cylinder radiuses. The obtained results are shown in figures.
Flow of anisotropic and isotropic objects in quasi-twodimensional fluids
Stannarius, Ralf; Eremin, Alexey; Dölle, Sarah; Harth, Kirsten; Klopp, Christoph
We study the motion of microscopic objects in very thin freely suspended smectic liquid-crystal films. The aspect ratios of these films are of the order of 1:106. Hydrodynamic motion is restricted to the film plane. Thus such films represent quasi-twodimensional fluids. Not only do they provide the opportunity to test theoretical models on mobilities in thin membranes, they also allow access to viscosity parameters of in-plane isotropic (smectic A) and anisotropic (smectic C) fluids. Combinations of these environments with isotropic and anisotropic geometries of inclusions provide rich information about interactions of rotational and translational particle motions, the anchoring-induced and flow-induced alignments of the embedding fluid, and interactions of particles via flow and director fields. Thermal diffusion in horizontal films as well as controlled effective gravity in tilted films are explored. Funding by DLR with Grant 50WM1430 and by DFG with Grant STA 425/28 is acknowledged.
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...
Dual-channel near-field control by polarizations using isotropic and inhomogeneous metasurface
Xiang Wan; Ben Geng Cai; Yun Bo Li; Tie Jun Cui
2015-01-01
We propose a method for dual-channel near-field manipulations by designing isotropic but inhomogeneous metasurfaces. As example, we present a dual-channel near-field focusing metasurface device. When the device is driven by surface waves from different channels on the metasurface, the near fields will be focused at the same spatial point with different polarizations. Conversely, if a linearly polarized source is radiated at the spatial focal point, different channels will be evoked on the met...
THE NON-AXISYMMETRICAL DYNAMIC RESPONSE OF TRANSVERSELY ISOTROPIC SATURATED POROELASTIC MEDIA
Institute of Scientific and Technical Information of China (English)
张引科; 黄义
2001-01-01
The Biot' s wave equations of transversely isotropic saturated poroelastic media excited by non- axisymmetrical harmonic source were solved by means of Fourier expansion and Hankel transform. Then the components of total stress in porous media are expressed with the solutions of Biot's wave equations. The method of research on non-axisymmetrical dynamic response of saturated porous media is discussed, and a numerical result is presented.
Einstein-Maxwell Field Equation in Isotropic Coordinates: An Application to Modeling Superdense Star
Pant, Neeraj; Ahmad, Mohammad; Pradhan, N.
2016-03-01
We present a charged analogue of Pant et al. (2010, Astrophys. Space Sci., 330, 353) solution of the general relativistic field equations in isotropic coordinates by using simple form of electric intensity E that involve charge parameter K. Our solution is well behaved in all respects for all values of X lying in the range 0 work might have astrophysical significance in the study of more realistic internal structures of compact stars.
Zito, Gianluigi; Rusciano, Giulia; Pesce, Giuseppe; Dochshanov, Alden; Sasso, Antonio
2015-04-01
Label-free chemical imaging of live cell membranes can shed light on the molecular basis of cell membrane functionalities and their alterations under membrane-related diseases. In principle, this can be done by surface-enhanced Raman scattering (SERS) in confocal microscopy, but requires engineering plasmonic architectures with a spatially invariant SERS enhancement factor G(x, y) = G. To this end, we exploit a self-assembled isotropic nanostructure with characteristics of homogeneity typical of the so-called near-hyperuniform disorder. The resulting highly dense, homogeneous and isotropic random pattern consists of clusters of silver nanoparticles with limited size dispersion. This nanostructure brings together several advantages: very large hot spot density (~104 μm-2), superior spatial reproducibility (SD molecular basis of cell membrane functionalities and their alterations under membrane-related diseases. In principle, this can be done by surface-enhanced Raman scattering (SERS) in confocal microscopy, but requires engineering plasmonic architectures with a spatially invariant SERS enhancement factor G(x, y) = G. To this end, we exploit a self-assembled isotropic nanostructure with characteristics of homogeneity typical of the so-called near-hyperuniform disorder. The resulting highly dense, homogeneous and isotropic random pattern consists of clusters of silver nanoparticles with limited size dispersion. This nanostructure brings together several advantages: very large hot spot density (~104 μm-2), superior spatial reproducibility (SD Electronic supplementary information (ESI) available: Additional details of the methods, further experimental data and data analysis, Raman assignment with additional references. Further sections: Basis Analysis (for two-analyte statistics), substrate oxidation, long-term stability and nanotoxicity issues. See DOI: 10.1039/c5nr01341k
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 spin...
Approximate conditions for the off-axis triplication in transversely isotropic media
Czech Academy of Sciences Publication Activity Database
Vavryčuk, Václav
2004-01-01
Roč. 48, č. 1 (2004), s. 187-198. ISSN 0039-3169 R&D Projects: GA AV ČR IAA3012309; GA AV ČR KSK3012103 Institutional research plan: CEZ:AV0Z3012916 Keywords : seismic waves * off-axis triplication * tranversely isotropic media Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.447, year: 2004
Audus, Debra J.; Starr, Francis W.; Douglas, Jack F.
2016-02-01
The interactions of molecules and particles in solution often involve an interplay between isotropic and highly directional interactions that lead to a mutual coupling of phase separation and self-assembly. This situation arises, for example, in proteins interacting through hydrophobic and charged patch regions on their surface and in nanoparticles with grafted polymer chains, such as DNA. As a minimal model of complex fluids exhibiting this interaction coupling, we investigate spherical particles having an isotropic interaction and a constellation of five attractive patches on the particle's surface. Monte Carlo simulations and mean-field calculations of the phase boundaries of this model depend strongly on the relative strength of the isotropic and patch potentials, where we surprisingly find that analytic mean-field predictions become increasingly accurate as the directional interactions become increasingly predominant. We quantitatively account for this effect by noting that the effective interaction range increases with increasing relative directional to isotropic interaction strength. We also identify thermodynamic transition lines associated with self-assembly, extract the entropy and energy of association, and characterize the resulting cluster properties obtained from simulations using percolation scaling theory and Flory-Stockmayer mean-field theory. We find that the fractal dimension and cluster size distribution are consistent with those of lattice animals, i.e., randomly branched polymers swollen by excluded volume interactions. We also identify a universal functional form for the average molecular weight and a nearly universal functional form for a scaling parameter characterizing the cluster size distribution. Since the formation of branched clusters at equilibrium is a common phenomenon in nature, we detail how our analysis can be used in experimental characterization of such associating fluids.
Influence of damping on the vanishing of the electro-optic effect in chiral isotropic media
Agarwal, G. S.; Boyd, Robert W.
2002-01-01
Using first principles, it is demonstrated that radiative damping alone cannot lead to a nonvanishing electro-optic effect in a chiral isotropic medium. This conclusion is in contrast with that obtained by a calculation in which damping effects are included using the standard phenomenological model. We show that these predictions differ because the phenomenological damping equations are valid only in regions where the frequencies of the applied electromagnetic fields are nearly resonant with ...
Analytical reconstruction of isotropic turbulence spectra based on the Gaussian transform
Wohlbrandt, Attila; Hu, Nan; Guerin, Sebastien; Ewert, Roland
2015-01-01
The Random Particle Mesh (RPM) method used to simulate turbulence-induced broadband noise in several aeroacoustic applications is extended to realise isotropic turbulence spectra. With this method turbulent fluctuations are synthesised by filtering white noise with a Gaussian filter kernel that in turn gives a Gaussian spectrum. The Gaussian function is smooth and its derivatives and integrals are again Gaussian functions. The Gaussian filter is efficient and finds wide-spread applications in...
Physical modeling and analysis of P-wave attenuation anisotropy in transversely isotropic media
Digital Repository Service at National Institute of Oceanography (India)
Zhu, Y.; Tsvankin, I.; Dewangan, P.; Van Wijk, K.
and analysis of P-wave attenuation anisotropy in transversely isotropic media Yaping Zhu1, Ilya Tsvankin2, Pawan Dewangan3, and Kasper van Wijk4 ABSTRACT Anisotropic attenuation can provide sensitive attributes for fracture detection and lithology...-preserving migration, and seismic fracture detec- tion. INTRODUCTION Most existing publications on seismic anisotropy are devoted to the influence of angular velocity variation in purely elastic media on the traveltimes and amplitudes of seismic waves. It is likely...
Universality Classes in Isotropic, Abelian and non-Abelian, Sandpile Models
Milshtein, E.; Biham, O.; Solomon, S.
1998-01-01
Universality in isotropic, abelian and non-abelian, sandpile models is examined using extensive numerical simulations. To characterize the critical behavior we employ an extended set of critical exponents, geometric features of the avalanches, as well as scaling functions describing the time evolution of average quantities such as the area and size during the avalanche. Comparing between the abelian Bak-Tang-Wiesenfeld model [P. Bak, C. Tang and K. Wiensenfeld, Phys. Rev. Lett. 59, 381 (1987)...
Spin nematic state for a spin S=3/2 isotropic non-Heisenberg magnet
Fridman, Yu. A.; Kosmachev, O. A.; Ivanov, B. A.
2009-01-01
$S=3/2$ system with general isotropic nearest-neighbor exchange within a mean-field approximation possesses a magnetically ordered ferromagnetic state and antiferromagnetic state, and two different spin nematic states, with zero spin expectation values. Both spin nematic phases display complicated symmetry break, including standard rotational break described by the vector-director $\\vec {u}$ and specific symmetry break with respect to the time reversal. The break of time reversal is determine...
Convergence dynamics of 2-dimensional isotropic and anisotropic Bak-Sneppen models
Bakar, Burhan; Tirnakli, Ugur
2008-01-01
The conventional Hamming distance measurement captures only the short-time dynamics of the displacement between the uncorrelated random configurations. The minimum difference technique introduced by Tirnakli and Lyra [Int. J. Mod. Phys. C 14, 805 (2003)] is used to study the short-time and long-time dynamics of the two distinct random configurations of the isotropic and anisotropic Bak-Sneppen models on a square lattice. Similar to 1-dimensional case, the time evolution of the displacement is...
Damage spreading in 2-dimensional isotropic and anisotropic Bak-Sneppen models
Bakar, Burhan; Tirnakli, Ugur
2007-01-01
We implement the damage spreading technique on 2-dimensional isotropic and anisotropic Bak-Sneppen models. Our extensive numerical simulations show that there exists a power-law sensitivity to the initial conditions at the statistically stationary state (self-organized critical state). Corresponding growth exponent $\\alpha$ for the Hamming distance and the dynamical exponent $z$ are calculated. These values allow us to observe a clear data collapse of the finite size scaling for both versions...
Fundamental connections between models of active suspensions and transversely-isotropic fluids
Holloway, Craig R.; Cupples, Gemma; Smith, David J.; Green, J. Edward F.; Clarke, Richard J.; Dyson, Rosemary J.
2016-01-01
Suspensions of self-motile, elongated particles are a topic of significant current interest, exemplifying a form of 'active matter'. Examples include self-propelling bacteria, algae and sperm, and artificial swimmers. Ericksen's model of a transversely-isotropic fluid [J. L. Ericksen, Colloid Polym. Sci. 173(2):117-122 (1960)] treats suspensions of non-motile particles as a continuum with an evolving preferred direction; this model describes fibrous materials as diverse as extracellular matri...
Relativistic Drag and Emission Radiation Pressures in an Isotropic Photonic Gas
Lee, Jeff S.; Cleaver, Gerald B.
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...
One-dimensional energy spectra in three-dimensional incompressible homogeneous isotropic turbulence
Zheng, Ran; Xing-jie, Yuan
2013-01-01
The paper investigates the detailed features of one-dimensional energy spectra in three-dimensional isotropic turbulence, based on the exact solution of Karman-Howarth equation. Particular interest will be paid on the degree to which spectral scaling can lead the spectral data to be collapsed. The theory appears to be consistent with the wealth of experimental data (G.Comte-Bellot and S. Corrsin, 1971) at least in low Taylor microscale Reynolds number.
Allen Phillip A.; Wilson, Christopher D.
2003-01-01
The development of a pressure-dependent constitutive model with combined multilinear kinematic and isotropic hardening is presented. The constitutive model is developed using the ABAQUS user material subroutine (UMAT). First the pressure-dependent plasticity model is derived. Following this, the combined bilinear and combined multilinear hardening equations are developed for von Mises plasticity theory. The hardening rule equations are then modified to include pressure dependency. The method for implementing the new constitutive model into ABAQUS is given.
Bars, Itzhak; Chen, Shih-Hung; Steinhardt, Paul J.; Turok, Neil
2012-01-01
We study a model of a scalar field minimally coupled to gravity, with a specific potential energy for the scalar field, and include curvature and radiation as two additional parameters. Our goal is to obtain analytically the complete set of configurations of a homogeneous and isotropic universe as a function of time. This leads to a geodesically complete description of the universe, including the passage through the cosmological singularities, at the classical level. We give all the solutions...
On eigenvalue problems of the one-speed neutron transport equation for isotropic scattering
International Nuclear Information System (INIS)
Highlights: • We consider isoperimetric inequalities for the one-speed neutron transport equation. • A ball will be a minimizer domain of the first eigenvalue. • We prove the Rayleigh–Faber–Krahn inequality for the neutron transport equation. - Abstract: In this paper, we consider eigenvalue problems of the one-speed neutron transport equation with isotropic scattering in a steady state and prove the Rayleigh–Faber–Krahn type inequality for the first eigenvalue
Mode locking of Yb:GdYAG ceramic lasers with an isotropic cavity
International Nuclear Information System (INIS)
We report on the passive mode locking of a diode pumped Yb:GdYAG ceramic laser with a near isotropic cavity. It is found that the laser could simultaneously mode lock in the two orthogonal principal polarization directions of the cavity, and the mode locked pulses of the two polarizations have identical features and are temporally perfectly synchronized. However, their pulse energy varies out-of-phase periodically, manifesting the antiphase dynamics of mode locked lasers. (letter)
Development of an isotropic optical light source for testing nuclear instruments
Yokley, Zachary W; Vogelaar, R Bruce
2015-01-01
Nuclear instruments that require precise characterization and calibration of their optical components need well-characterized optical light sources with the desired wavelength, intensity, and directivity. This paper presents a novel technique for determining the performance of optical components by producing an isotropic-like source with a robotically positioned LED. The theory of operation for this light source, results of Monte Carlo validation studies, and experimental results are presented.
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.
How isotropic are turbulent flows generated by using periodic conditions in a cube?
Qin, Z. C.; Fang, L.; Fang, J.
2016-03-01
In numerical simulations, "isotropic" turbulent flows are always generated by using periodic conditions. We show that these periodic conditions mathematically lead to large-scale anisotropy which can be about 10% of the mean values, and thus prevent existing post-processing results from being accurate. A decomposition method by employing spherical harmonics is then proposed to distinguish this scale-dependent anisotropy effect from others and to minimize the related post-processing error.
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.
Isotropic Quenched Disorder Triggers a Robust Nematic State in Electron-Doped Pnictides
Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio
2015-01-01
The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic quenched disorder strength by means of computational techniques applied to a three-orbital ($xz$, $yz$, $xy$) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to addres...
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.
The Inversion of Terrestrial Water Storage Changes by Non-isotropic Combination Filter
CHAO Nengfang; Wang, Zhengtao; Sun, Jian
2015-01-01
The inversion of variations of terrestrial water storage by the earth time-variable gravity filed model makes a great contribution to global climate change, however, the spherical harmonics of time-variable gravity field have correlation problem and significant errors in high orders and degrees, and so optimal filtering method is needed to solve this problem. In this article, a new filter was devised named‘non-isotropic combination filter’, and showed a better performance. The basic idea of t...
Isotropic-nematic phase separation in asymmetrical rod-plate mixtures
Wensink, H.H.; Vroege, G. J.; Lekkerkerker, H. N. W.
2001-01-01
Recent experiments on mixtures of rodlike and platelike colloidal particles have uncovered the phase behavior of strongly asymmetrical rod-plate mixtures. In these mixtures, in which the excluded volume of the platelets is much larger than that of the rods, an extended isotropic (I)–plate-rich nematic (N-)–rod-rich nematic (N+) triphasic equilibrium was found. In this paper, we present a theoretical underpinning for the observed phase behavior starting from the Onsager theory in which higher ...
Uyaner, Mesut; Ahmet AKDEMİR; ERİM, Seçil; Avci, Ahmet
1999-01-01
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 ...
CONTACT STRESSES IN A TRANSVERSELY ISOTROPIC SOLID CYLINDER LATERALLY COMPRESSED BY AN INDENTER
YAPICI, Ahmet; Avci, Ahmet; Uyaner, Mesut
2004-01-01
In this study, an elastostatic contact problem for a laterally compressed transversely isotropic cylinder subjected to radial compression through a circumferential rigid indenter is considered. The extent of the contact region and the stress distribution are sought. It is assumed that the contact between the cylinder and the rigid indenter is frictionless and only compressive normal tractions can be transmitted through the interface. Due to the geometry of the configuration, Fourier transform...
Technical specifications for the bulk shielding reactor
International Nuclear Information System (INIS)
This report provides information concerning the technical specifications for the Bulk Shielding Reactor. Areas covered include: safety limits and limiting safety settings; limiting conditions for operation; surveillance requirements; design features; administrative controls; and monitoring of airborne effluents. 10 refs
The bulk radio expansion of Cassiopeia A
International Nuclear Information System (INIS)
Comparison, in the visibility plane, or radio observations of Cassiopeia A made at 151 MHz over a 2.3 yr interval indicates that the bulk of the radio emitting material has not been decelerated strongly
Faecal bulking efficacy of Australasian breakfast cereals.
Monro, John A
2002-01-01
Faecal bulk may play an important role in preventing a range of disorders of the large bowel, but as yet there is little information available on the relative faecal bulking capacities of various foods. Breakfast cereals are often promoted as a good source of potential bulk for 'inner health' because they provide dietary fibre, but their relative abilities to provide faecal bulk per se have not been described. The faecal bulking efficacy of 28 representative Australasian breakfast cereals was therefore measured. A rat model developed for the purpose, and shown to give similar responses as humans to cereal fibres, was used to measure faecal bulking efficacy as increases in fully hydrated faecal weight/100 g diet, based on precise measurements of food intake, faecal dry matter output and faecal water-holding capacity (g water held without stress/g faecal dry matter). Compared to a baseline diet containing 50% sucrose, increments in hydrated faecal weight due to 50% breakfast cereal ranged from slightly negative (Cornflakes, -2 g/100 g diet) to about 80 g/100 g diet (San Bran). Most breakfast cereals increased hydrated faecal weight by between 10 and 20 g/100 g diet from a baseline of 21 +/- 1.5 g/100 g diet, but four products containing high levels of wheat bran had an exceptionally large impact on hydrated faecal weight (increment > 20 g/100 g diet), and the changes resulted more from relative changes in dry matter output than in faecal water retention/gram. However, as faecal water retention was about 2.5 g water/g faecal dry matter on average, increases in dry matter represented large increases in faecal water load. Faecal bulking indices (FBI) for most of the breakfast cereals were less than 20 (wheat bran = 100). The content of wheat bran equivalents for faecal bulk (WBE(fb)) in the breakfast cereals was calculated from FBI. Most breakfast cereals contributed, per serve, less than 10% of a theoretical daily reference value for faecal bulk (DRV(fb) = 63 WBE
Institute of Scientific and Technical Information of China (English)
HUANG Yi; WANG Xiao-gang
2005-01-01
A study of the dynamic interaction between foundation and the underlying soil has been presented in a recent paper based on the assumption of saturated ground and elastic circular plate excited by the axisymmetrical harmonic source. However, the assumption may not always be valid. The work is extended to the case of a circular plate resting on transversely isotropic saturated soil and subjected to a non-axisymmetrical harmonic force. The analysis is based on the theory of elastic wave in transversely isotropic saturated poroelastic media established. By the technique of Fourier expansion and Hankel transform, the governing difference equations for transversely isotropic saturated soil are easily solved and the cooresponding Hankel transformed stress and displacement solutions are obtained. Then, under the contact conditions, the problem leads to a pair of dual integral equations which describe the mixed boundary-value problem. Furthermore, the dual integral equations can be reduced to the Fredholm integral equations of the second kind solved by numerical procedure. At the end, a numerical result is presented which indicates that on a certain frequency range, the displacement amplitude of the surface of the foundation increases with the increase of the frequency of the exciting force, and decreases in vibration form with the increase of the distance.
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)). PMID:26072250
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.
Isotropic realizability of a strain field for the two‑dimensional incompressible elasticity system
Briane, M.
2016-06-01
In the paper we study the problem of the isotropic realizability in {{{R}}}2 of a regular strain field e(U)=\\tfrac{1}{2}({DU}+{{DU}}T) for the incompressible elasticity system, namely the existence of a positive shear modulus μ \\gt 0 solving the elasticity system in {{{R}}}2 with the prescribed field e(U). We show that if e(U) does not vanish at some point, then the isotropic realizability holds in the neighborhood of that point. The global realizability in {{{R}}}2 or in the torus is much more delicate, since it involves the global existence of a regular solution to a semilinear wave equation, the coefficients of which depend on the derivatives of U. Using this semilinear wave equation we prove a small perturbation result: if DU is periodic and close enough to its average value for the C 4‑norm, then the associated strain field is isotropically realizable in a given disk centered at the origin. On the other hand, a counterexample shows that the global realizability in {{{R}}}2 may hold without the realizability in the torus, and it is discussed in connection with the associated semilinear wave equation. The case where the strain field vanishes is illustrated by an example. The singular case of a rank-one laminate field is also investigated.
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.
Energy Technology Data Exchange (ETDEWEB)
Hasheminejad, Seyyed M.; Maleki, M. [Iran University of Science and Technology, Acoustics Research Laboratory, Department of Mechanical Engineering, Narmak, Tehran (Iran)
2009-02-15
An exact analysis is carried out to study interaction of a time-harmonic plane-progressive sound field with a multi-layered elastic hollow sphere made of spherically isotropic materials with interlaminar bonding imperfections. A modal state equation with variable coefficients is set up in terms of appropriate displacement and stress functions and their spherical harmonics, ultimately leading to calculation of a global transfer matrix. A linear spring model is adopted to describe the interlaminar adhesive bonding whose effects are incorporated into the global transfer matrix by introduction of proper interfacial transfer matrices. The solution is first used to correlate the perturbation in the material elastic constants of an evacuated and water submerged steel (isotropic) spherical shell to the sensitivity of resonances appearing in the backscattered amplitude spectrum. The backscattering form function, in addition to the acoustic radiation force acting on selected transversely isotropic spherical shells with distinct degrees of material anisotropy, is subsequently calculated and discussed. An illustrative numerical example is given for a multi-layered hollow sphere with two distinct interlaminar interface conditions (i.e., perfectly and imperfectly bonded layers). Limiting cases are considered and fair agreements with solutions available in the literature are established. (orig.)
Effect of compressive prestress on the Young's modulus and strength of isotropic graphite
International Nuclear Information System (INIS)
It is well known that properties, such as Young's modulus, strength and so on, change when compressive or tensile prestresses are applied to graphite materials at room temperature. It is important from the designer's standpoint in the sense that it should be taken into consideration for the structural design of the graphite components if there is an effect of prestresses at high temperature on the mechanical properties. In this study compressive prestresses were applied to an isotropic fine-grained graphite at room temperature (RT) and high temperature (2010 deg. C). As a result decrease in Young's modulus due to high temperature prestressing was 56% which was much larger than the 6.4% that was due to RT prestressing. This finding was considered to be due primarily to difference in degree of preferred orientation of crystallites in the graphite on the basis of Bacon anisotropy factor (BAF) from X-ray diffraction measurement of the prestressed specimens. Furthermore, high temperature compressive prestressing produced an increase in the strength of the isotropic graphite, although room temperature prestressing produced no such effect. The results obtained here suggest that isotropic graphite which is subjected to high-temperature compressive stress becomes anisotropic. It is concluded that it should be considered in the design stage of the reactors that the anisotropy may change after long term operation of high temperature gas-cooled reactors. (author). 6 refs, 8 figs, 3 tabs
PHONON ECHOES IN BULK AND POWDERED MATERIALS
Kajimura, K.
1981-01-01
Experimental and theoretical studies of phonon echoes in bulk and powdered materials are reviewed. Phonon echoes have been observed in many materials such as bulk piezoelectric crystals, paramagnets, glasses, doped semiconductors, and piezoelectric, magnetic, and metallic powders, etc. The echoes arise from a time reversal of the phase, like spin echoes, of a primary pulsed acoustic excitation due to a second acoustic or rf pulse. The phase reversal occurs through the nonlinear interactions o...
Orbital magnetization in insulators: Bulk versus surface
Bianco, Raffaello; Resta, Raffaele
2016-05-01
The orbital magnetic moment of a finite piece of matter is expressed in terms of the one-body density matrix as a simple trace. We address a macroscopic system, insulating in the bulk, and we show that its orbital moment is the sum of a bulk term and a surface term, both extensive. The latter only occurs when the transverse conductivity is nonzero and it is due to conducting surface states. Simulations on a model Hamiltonian validate our theory.
An intrinsic mobility ceiling of Si bulk
Garcia-Castello, Nuria; Prades, Joan Daniel; Cirera, Albert
2011-01-01
We compute by Density Functional Theory-Non Equilibrium Green Functions Formalism (DFT-NEGFF) the conductance of bulk Si along different crystallographic directions. We find a ceiling value for the intrinsic mobility of bulk silicon of $8.4\\cdot10^6 cm^2/V\\cdot s$. We suggest that this result is related to the lowest effective mass of the $$ direction.
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
Hanukah, Eli
2013-01-01
We develop a new higher order closed-form model for the dynamics of a hyperelastic isotropic 3D cylindrical body. We derive, for the first time, a simple explicit expression for the fundamental frequency.
Directory of Open Access Journals (Sweden)
Eloyan A. V.
2013-12-01
Full Text Available The problem of determining the optimal location of the supports along the length of the elastic, isotropic rectangular plate in the case of simultaneous action of transverse load and temperature field.
International Nuclear Information System (INIS)
We have used the density-functional theory to study the effect of varying temperature on the isotropic-nematic transition of a fluid of molecules interacting via the Gay-Berne intermolecular potential. The nematic phase is found to be stable with respect to isotropic phase in the temperature range 0.80≤T*≤1.25. Pair correlation functions needed as input information in density-functional theory is calculated using the Percus-Yevick integral equation theory. We find that the density-functional theory is good for studying the isotropic-nematic transition in molecular fluids if the values of the pair-correlation functions in the isotropic phase are known accurately. We have also compared our results with computer simulation results wherever they are available
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.
Module 13: Bulk Packaging Shipments by Highway
International Nuclear Information System (INIS)
The Hazardous Materials Modular Training Program provides participating United States Department of Energy (DOE) sites with a basic, yet comprehensive, hazardous materials transportation training program for use onsite. This program may be used to assist individual program entities to satisfy the general awareness, safety training, and function specific training requirements addressed in Code of Federal Regulation (CFR), Title 49, Part 172, Subpart H -- ''Training.'' Module 13 -- Bulk Packaging Shipments by Highway is a supplement to the Basic Hazardous Materials Workshop. Module 13 -- Bulk Packaging Shipments by Highway focuses on bulk shipments of hazardous materials by highway mode, which have additional or unique requirements beyond those addressed in the ten module core program. Attendance in this course of instruction should be limited to those individuals with work experience in transporting hazardous materials utilizing bulk packagings and who have completed the Basic Hazardous Materials Workshop or an equivalent. Participants will become familiar with the rules and regulations governing the transportation by highway of hazardous materials in bulk packagings and will demonstrate the application of these requirements through work projects and examination
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.
The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV
Ackermann, Markus; Ajello, M.; Bissaldi, E.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J H.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Blandford, R. D.; Rainò, S.
2014-01-01
The {\\\\gamma}-ray sky can be decomposed into individually detected sources, diffuse emission attributed to the interactions of Galactic cosmic rays with gas and radiation fields, and a residual all-sky emission component commonly called the isotropic diffuse {\\\\gamma}-ray background (IGRB). The IGRB comprises all extragalactic emissions too faint or too diffuse to be resolved in a given survey, as well as any residual Galactic foregrounds that are approximately isotropic. The first IGRB measu...
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.
Micro benchtop optics by bulk silicon micromachining
Lee, Abraham P.; Pocha, Michael D.; McConaghy, Charles F.; Deri, Robert J.
2000-01-01
Micromachining of bulk silicon utilizing the parallel etching characteristics of bulk silicon and integrating the parallel etch planes of silicon with silicon wafer bonding and impurity doping, enables the fabrication of on-chip optics with in situ aligned etched grooves for optical fibers, micro-lenses, photodiodes, and laser diodes. Other optical components that can be microfabricated and integrated include semi-transparent beam splitters, micro-optical scanners, pinholes, optical gratings, micro-optical filters, etc. Micromachining of bulk silicon utilizing the parallel etching characteristics thereof can be utilized to develop miniaturization of bio-instrumentation such as wavelength monitoring by fluorescence spectrometers, and other miniaturized optical systems such as Fabry-Perot interferometry for filtering of wavelengths, tunable cavity lasers, micro-holography modules, and wavelength splitters for optical communication systems.
Bulk amorphous Mg-based alloys
DEFF Research Database (Denmark)
Pryds, Nini
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 a...... low glass transition temperature. The alloys were prepared by using a relatively simple technique, i.e. rapid cooling of the melt in a copper wedge mould. The essential structural changes that are achieved by going from the amorphous to the crystalline state through the supercooled liquid state are...... discussed in this paper. On the basis of these measurements phase diagrams of the different systems were constructed. Finally, it is demonstrated that when pressing the bulk amorphous alloy onto a metallic dies at temperatures within the supercooled liquid region, the alloy faithfully replicates the surface...
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.
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...
Flexural stiffnesses of and dimensional stability in circular quasi-isotropic laminate mirrors
Kim, Kyung-Pyo
Composite fiber reinforced plastics are being given favorable consideration for emerging applications in large aperture telescopes, such as the Hubble telescope or communication dishes. Many lightweight mirror fabrication concepts are currently being pursued. Presently, the technology is limited because it has an incomplete understanding of the mechanics associated with quasi-isotropic laminates for diffraction-limited displacement constraints, and lack of understanding for effects of resin buffer layers on composite mirrors for high surface smoothness. In this dissertation document, radial stiffness associated with stacking sequence effects in quasi-isotropic laminates (pi/n, where n=3, 4, and 6) and dimensional stability in the composite laminates are investigated numerically. The numerical results show that directional dependency of flexural stiffness in the laminates, which is strongly associated with stacking sequences, is a significant factor causing unfavorable sinusoidal surface waviness. The maximum radial flexural stiffness variation is found as +/-12.85% in pi/3 laminate while a minimum of +/-5.63% is found in pi/4 laminate. Mechanics of maximum asymmetry by +/-2º misorientation based on ideal pi/n laminate lay-ups are evaluated and the results are compared with ideal lay-up sequence cases. The calculated extensional and flexural stiffness values from the maximum asymmetric cases are within less than 0.05%. As such, the radial flexural stiffness variations in quasi-isotropic laminates are shown to be more problematic than asymmetry caused by common manufacturing variance. The types of surface deformations in quasi-isotropic laminates associated with directional dependency of flexural stiffness are evaluated using finite element analyses. Also, fiber print-through in replicated composite mirrors and the effects of the resin buffer layer present in the mirrors for mitigation of the fiber print-through are investigated and discussed. Numerical results
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.
Thermal relics in cosmology with bulk viscosity
International Nuclear Information System (INIS)
In this paper we discuss some consequences of cosmological models in which the primordial cosmic matter is described by a relativistic imperfect fluid. The latter takes into account the dissipative effects (bulk viscosity) arising from different cooling rates of the fluid components in the expanding Universe. We discuss, in particular, the effects of the bulk viscosity on Big Bang Nucleosynthesis and on the thermal relic abundance of particles, looking at recent results of PAMELA experiment. The latter has determined an anomalous excess of positron events, which cannot be explained by conventional cosmology and particle physics. (orig.)
Remedial investigations for quarry bulk wastes
International Nuclear Information System (INIS)
The US Department of Energy proposes, as a separate operable unit of the Weldon Spring Site Remedial Action Project, to remove contaminated bulk wastes from the Weldon Spring quarry and transport them approximately four miles to the chemical plant portion of the raffinate pits and chemical plant area. The wastes will be held in temporary storage prior to the record of decision for the overall remedial action. The decision on the ultimate disposal of these bulk wastes will be included as part of the decision for management of the waste materials resulting from remedial action activities at the raffinate pits and chemical plant area. 86 refs., 71 figs., 83 tabs
Radiation-hardened bulk CMOS technology
International Nuclear Information System (INIS)
The evolutionary development of a radiation-hardened bulk CMOS technology is reviewed. The metal gate hardened CMOS status is summarized, including both radiation and reliability data. The development of a radiation-hardened bulk silicon gate process which was successfully implemented to a commercial microprocessor family and applied to a new, radiation-hardened, LSI standard cell family is also discussed. The cell family is reviewed and preliminary characterization data is presented. Finally, a brief comparison of the various radiation-hardened technologies with regard to performance, reliability, and availability is made
Thermal relics in cosmology with bulk viscosity
Energy Technology Data Exchange (ETDEWEB)
Iorio, A. [Charles University in Prague, Faculty of Mathematics and Physics, Prague (Czech Republic); Lambiase, G. [Universita di Salerno, Dipartimento di Fisica E.R. Caianiello, Fisciano (Italy); INFN, Gruppo Collegato di Salerno, Fisciano (Italy)
2015-03-01
In this paper we discuss some consequences of cosmological models in which the primordial cosmic matter is described by a relativistic imperfect fluid. The latter takes into account the dissipative effects (bulk viscosity) arising from different cooling rates of the fluid components in the expanding Universe. We discuss, in particular, the effects of the bulk viscosity on Big Bang Nucleosynthesis and on the thermal relic abundance of particles, looking at recent results of PAMELA experiment. The latter has determined an anomalous excess of positron events, which cannot be explained by conventional cosmology and particle physics. (orig.)
Bulk Entropy in Loop Quantum Gravity
Livine, Etera R; Terno, Daniel R.
2007-01-01
In the framework of loop quantum gravity (LQG), having quantum black holes in mind, we generalize the previous boundary state counting (gr-qc/0508085) to a full bulk state counting. After a suitable gauge fixing we are able to compute the bulk entropy of a bounded region (the "black hole") with fixed boundary. This allows us to study the relationship between the entropy and the boundary area in details and we identify a holographic regime of LQG where the leading order of the entropy scales w...
Bulk Entropy in Loop Quantum Gravity
Livine, Etera R
2007-01-01
In the framework of loop quantum gravity (LQG), having quantum black holes in mind, we generalize the previous boundary state counting (gr-qc/0508085) to a full bulk state counting. After a suitable gauge fixing we are able to compute the bulk entropy of a bounded region (the "black hole") with fixed boundary. This allows us to study the relationship between the entropy and the boundary area in details and we identify a holographic regime of LQG where the leading order of the entropy scales with the area. We show that in this regime we can fine tune the factor between entropy and area without changing the Immirzi parameter.
ELBA, Bremsstrahlung Dose from Isotropic Electron Flux on Plane Al Shield
International Nuclear Information System (INIS)
1 - Description of problem or function: ELBA takes an incident isotropic electron flux with a given differential energy spectrum and calculates the dose rate received from Bremsstrahlung produced in a plane aluminium shield placed in front of the receiver. There is an option to also calculate the electron dose rate from the same source. 2 - Method of solution: The electron differential spectrum as a function of depth is inferred by assuming that electrons travel straight ahead and that distance travelled and energy are related by a range-energy relationship. The electron dose rate at a given depth is calculated by integrating, over energy and direction, the product of the electron flux, the stopping power, and the appropriate flux- to-dose rate conversion factor. The Bremsstrahlung source is assumed to be plane and isotropic at a given depth. This source is defined as the integral over energy and direction of the product of photon energy, the differential Bremsstrahlung spectrum from electrons of a given energy, and the electron flux differential spectrum. The differential Bremsstrahlung spectrum is derived from the Born approximation cross section multiplied by a correction factor. The Bremsstrahlung dose rate is obtained by integrating, over photon energy and slab volume, the product of the Bremsstrahlung source, photon energy flux-to-dose rate conversion factor, buildup factor, and attenuation kernel. The buildup factor assumed is a plane isotropic buildup factor generate by Monte Carlo calculations. The integrations are performed by evaluating the integrand at the midpoint of each integration step, multiplying by the step width, and summing the result. The incident electron spectrum, dose rate conversion factors, and range formula coefficients are input by the user. The buildup factor information is contained in three Data statements in subroutine BURP. 3 - Restrictions on the complexity of the problem: There are limitations on the dimensions of certain arrays
3-D Isotropic and Anisotropic S-velocity Structure in the North American Upper Mantle
Yuan, H.; Marone, F.; Romanowicz, B.; Abt, D.; Fischer, K.
2008-12-01
The tectonic diversity of the North American continent has led to a number of geological, tectonic and geodynamical models, many of which can be better tested with high resolution 3-d tomographic models of the isotropic and anisotropic mantle structure of the continent. In the framework of non-linear asymptotic coupling theory (NACT), we recently developed tools to invert long period seismic waveforms combined with SKS splitting data, for both isotropic and radial and azimuthal anisotropic S-wave velocity structure in the upper mantle at the continental scale (Marone et al., 2007; Marone and Romanowicz, 2007). Striking differences in both isotropic and anisotropic velocity structure were observed: beneath the high velocity stable cratonic region a distinct two-layer anisotropic domain is present, with the bottom layer fast axis direction aligned with the absolute plate motion, and a shallower lithospheric layer with north pointing fast axis most likely showing records of past tectonic history; under the active western US the direction of tomographically inferred anisotropy is stable with depth and compatible with the absolute plate motion direction. Here we present an updated model which includes nearly five more years of data, including data from newly operative USArray stations, and a somewhat more extended frequency band. Our new model confirms our previous results, and reveals greater yet complex details of the anisotropic velocity structure beneath the western U.S.. We also show initial results of incorporating constraints on the depth to the lithosphere-asthenosphere boundary (LAB) using teleseismic receiver functions. We discuss the different anisotropic domains resolved both laterally and in depth, in the context of tectonic history of the north American continent.
Design and characterization of an isotropic reconstituted wood for energy absorbers
International Nuclear Information System (INIS)
Wood has been used for years in the making of containers for transport of nuclear materials because of the good compromise offered by wood between resistance to impact and fire resistance. However wood is an anisotropic material especially when compressive strength is considered, parallel or perpendicular to the grain. The arrangement of wood inside the containers has to take into account different types of impact, especially oblique ones for which the choice of the orientation of wood elements is very difficult; for cylindrical containers with plane covers, corner zones are weak because the out of axis mechanical performances of wood is not good enough to insure a good behaviour during strong oblique shocks. In our Laboratory of Wood Rheology we decided, in co-operation with CEA/CESTA, to design an isotropic wood based material to be especially used in the corner zones of containers; on the other hand such an isotropic material is represented by very simpler constitute laws for computer modelling of crash-tests. This material was named IWOC for Isotropic Wood Composite. IWOC was studied, in connection with its elaboration process, for quasi-static simple or multiaxial compression in the elastic-plastic domain, even with high compression ratios, then for dynamic compression tests with impact speed up to 10 ms-1, with a falling mass system. These tests show that IWOC has good properties for energy absorption, especially when it is confined by metallic or fiber casings; its static or dynamic performances are not scattered at all; its sensitivity to deformation rate, in the range which was analyzed, can be correlated to the sensitivity of the different elements of this wooden composite material. (authors)
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.
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.
The problem of stability for the homogeneous and isotropic Universe in RTG
International Nuclear Information System (INIS)
The question of stability of homogeneous and isotropic Universe relative to small fluctuations of gravitational field and matter characteristics has been investigated in the framework of RTG. The equations for small perturbations of metric tensor gμν, energy density ρ and pressure p are obtained in linear approximation. The solutions of these equations are found provided the perturbations depending on time only. The analysis of physical nature of derived solutions is carried out. The comparison with the results of GR leads to the conclusion that all the distinctions are caused by the mass of graviton
Statistical Properties of the T-Exponential of Isotropically Distributed Random Matrices
Il'yn, A. S.; Sirota, V. A.; Zybin, K. P.
2016-05-01
A functional method for calculating averages of the time-ordered exponential of a continuous isotropic random N× N matrix process is presented. The process is not assumed to be Gaussian. In particular, the Lyapunov exponents and higher correlation functions of the T-exponent are derived from the statistical properties of the process. The approach may be of use in a wide range of physical problems. For example, in theory of turbulence the account of non-gaussian statistics is very important since the non-Gaussian behavior is responsible for the time asymmetry of the energy flow.
International Nuclear Information System (INIS)
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
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.
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./.
Are the ACAR spectra for positrons trapped at Al surface isotropic?
International Nuclear Information System (INIS)
Electronic properties of Al surface are computed within model of jellium. The positron annihilation characteristics are calculated for a correlated electron-positron system using the Kahana - type momentum -dependent enhancement factors in a local way. For the first time in the literature the change of the anisotropy direction in the shape of theoretical angular correlation of annihilation radiation spectra for positrons trapped at Al surface is obtained. The resulting momentum distributions is almost isotropic, in agreement with experimental data. 11 refs., 2 figs. (author)
Wilczek, Michael; Schneider, Kai; Friedrich, Rudolf; Farge, Marie; 10.1063/1.3694807
2012-01-01
We investigate the conditional vorticity budget of fully developed three-dimensional homogeneous isotropic turbulence with respect to coherent and incoherent flow contributions. The Coherent Vorticity Extraction based on orthogonal wavelets allows to decompose the vorticity field into coherent and incoherent contributions, of which the latter are noise-like. The impact of the vortex structures observed in fully developed turbulence on statistical balance equations is quantified considering the conditional vorticity budget. The connection between the basic structures present in the flow and their statistical implications is thereby assessed. The results are compared to those obtained for large- and small-scale contributions using a Fourier decomposition, which reveals pronounced differences.
Bieg, Bohdan; Chrzanowski, Janusz; Kravtsov, Yury A.; Orsitto, Francesco
Basic principles and recent findings of quasi-isotropic approximation (QIA) of a geometrical optics method are presented in a compact manner. QIA was developed in 1969 to describe electromagnetic waves in weakly anisotropic media. QIA represents the wave field as a power series in two small parameters, one of which is a traditional geometrical optics parameter, equal to wavelength ratio to plasma characteristic scale, and the other one is the largest component of anisotropy tensor. As a result, "" QIA ideally suits to tokamak polarimetry/interferometry systems in submillimeter range, where plasma manifests properties of weakly anisotropic medium.
Photonic density of states of a stack of cholesteric liquid crystal and isotropic medium layers
International Nuclear Information System (INIS)
We calculated the photonic density of states (PDS) of the eigen polarizations in the system composed of a stack of layers of a cholesteric liquid crystal and an isotropic medium. The reflection spectra and PDS peculiarities, as well as the peculiarities of absorption and emittance were investigated. We obtained the dependences of the PDS as a function of parameters characterizing absorption and gain. It was shown that the subject system can be used in lasers for obtaining low threshold lasers with the emittance wavelength tunable in wide ranges. The system also can work as a multi-position trigger.
First experimental demonstration of an isotropic electromagnetic cloak with strict conformal mapping
Ma, Yungui; Lan, Lu; Wu, Tiantian; Jiang, Wei; Ong, C K; He, Sailing
2013-01-01
In the past years quasi-conformal mapping has been typically used to design broadband electromagnetic cloaks. However, this technique has some inherit practical limitations such as the lateral beam shift, rendering the device visible or difficult to hide a large object. In this work we circumvent these issues by using strict conformal mapping to build the first isotropic cloak. Microwave near-field measurement shows that our device (with dielectric constant larger than unity everywhere) has a very good cloaking performance and a broad frequency response. The present dielectric approach could be technically extended to the fabrication of other conformal devices at higher frequencies.
Transverse susceptibility of the 1D isotropic XY-model at zero temperature
International Nuclear Information System (INIS)
An exact expression is obtained for the dynamic transverse susceptibility Xxx (w,i,j) of the one-dimensional isotropic XY-model both on an open and on a closed chain with arbitrary number of sites at zero temperature, when the transverse field is greater than the absolute value of the exchange constant. The dynamic transverse wave-vector-dependent susceptibility for the closed infinite chain is also determined, and it is shown that in all cases the isothermal susceptibility is identical to the static susceptibility. (Author)
Dynamic properties of the dimerized spin-1/2 isotropic XY chain in a transverse field
International Nuclear Information System (INIS)
The zz and xx(yy) dynamic structure factors of the dimerized spin-1/2 isotropic XY chain in a transverse (z) field are calculated for arbitrary temperatures. The zz structure factor can be given in analytical terms, involving a single integration, whereas the xx dynamic structure factor can be evaluated completely numerically for very long chains. We compare the two structure factors and discuss in some detail how a dimerization manifests itself in the dynamic structure factors at different external fields and temperatures. We compare our results to corresponding results for the dimerized Heisenberg chain obtained by approximate techniques. (author)
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...
Stability of isotropic self-similar dynamics for scalar-wave collapse
International Nuclear Information System (INIS)
The scalar model for collapse of Langmuir waves in plasmas is studied numerically in two and three dimensions, for both radially symmetric and anisotropic initial conditions. Using a dynamic rescaling method, singular solutions are shown to become isotropic and self-similar near collapse. In two dimensions, the self-similar profile is not universal. In the limit where the mass of the wave tends to its minimal value for collapse, the solution approaches a subsonic regime different from the generic singularity of the nonlinear Schroedinger equation
Energy Technology Data Exchange (ETDEWEB)
Milewski, J., E-mail: jsmilew@wp.pl [Institute of Mathematics, Poznań University of Technology, Piotrowo 3A, 60-965 Poznań (Poland); Lulek, B., E-mail: barlulek@amu.edu.pl [East European State Higher School, ul. Tymona Terleckiego 6, 37-700 Przemyśl (Poland); Lulek, T., E-mail: tadlulek@prz.edu.pl [Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań (Poland); East European State Higher School, ul. Tymona Terleckiego 6, 37-700 Przemyśl (Poland); Łabuz, M., E-mail: labuz@univ.rzeszow.pl [University of Rzeszow, Institute of Physics, Rejtana 16a, 35-959 Rzeszów (Poland); Stagraczyński, R., E-mail: rstag@prz.edu.pl [Rzeszow University of Technology, The Faculty of Mathematics and Applied Physics, Powstańców Warszawy 6, 35-959 Rzeszów (Poland)
2014-02-01
The exact Bethe eigenfunctions for the heptagonal ring within the isotropic XXX model exhibit a doubly degenerated energy level in the three-deviation sector at the centre of the Brillouin zone. We demonstrate an explicit construction of these eigenfunctions by use of algebraic Bethe Ansatz, and point out a relation of degeneracy to parity conservation, applied to the configuration of strings for these eigenfunctions. Namely, the internal structure of the eigenfunctions (the 2-string and the 1-string, with opposite quasimomenta) admits generation of two mutually orthogonal eigenfunctions due to the fact that the strings which differ by their length are distinguishable objects.
International Nuclear Information System (INIS)
This work investigates the isotropic etching properties in inductively coupled plasma (ICP) etcher for microneedle arrays fabrication. The effects of process variables including powers, gas and pressure on needle structure generation are characterized by factorial design of experiment (DOE). The experimental responses of vertical etching depth, lateral etching length, ratio of vertical etching depth to lateral etching length and photoresist etching rate are reported. The relevance of the etching variables is also presented. The obtained etching behaviours for microneedle structure generation will be applied to develop recipes to fabricate microneedles in designed dimensions
Study of the roughness in a photoresist masked, isotropic, SF6-based ICP silicon etch
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 pr...
Optimized cylindrical invisibility cloak with minimum layers of non-magnetic isotropic materials
International Nuclear Information System (INIS)
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.
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.
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.
Interbasis expansions for the isotropic 3D harmonic oscillator and bivariate Krawtchouk polynomials
International Nuclear Information System (INIS)
An explicit expression for the general bivariate Krawtchouk polynomials is obtained in terms of the standard Krawtchouk and dual Hahn polynomials. The bivariate Krawtchouk polynomials occur as matrix elements of the unitary reducible representations of SO(3) on the energy eigenspaces of the three-dimensional isotropic harmonic oscillator and the explicit formula is obtained from the decomposition of these representations into their irreducible components. The decomposition entails expanding the Cartesian basis states in the spherical bases that span irreducible SO(3) representations. The overlap coefficients are obtained from the Clebsch–Gordan problem for the su(1,1) Lie algebra. (paper)
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.