A multidirectional cloak for visible light

NASA Astrophysics Data System (ADS)

Chen, Zhen Sheng; Lei Mei, Zhong; Jiang, Wei Xiang; Cui, Tie Jun

2018-04-01

A new macroscopic multidirectional cloak scheme for extraordinary rays is proposed by controlling the optical axes of uniaxial crystals. It eliminates the complicated material constraints and can also be utilized to design a cloaking device for ordinary rays or isotropic cloaks after simplification. Numerical ray tracing and full-wave simulation results validate our design. Moreover, if the uniaxial crystals are changed into other materials whose optical axes can be modulated, like liquid crystals, this scheme has the potential to fabricate direction-tunable cloaks.

Viewing zone duplication of multi-projection 3D display system using uniaxial crystal.

PubMed

Lee, Chang-Kun; Park, Soon-Gi; Moon, Seokil; Lee, Byoungho

2016-04-18

We propose a novel multiplexing technique for increasing the viewing zone of a multi-view based multi-projection 3D display system by employing double refraction in uniaxial crystal. When linearly polarized images from projector pass through the uniaxial crystal, two possible optical paths exist according to the polarization states of image. Therefore, the optical paths of the image could be changed, and the viewing zone is shifted in a lateral direction. The polarization modulation of the image from a single projection unit enables us to generate two viewing zones at different positions. For realizing full-color images at each viewing zone, a polarization-based temporal multiplexing technique is adopted with a conventional polarization switching device of liquid crystal (LC) display. Through experiments, a prototype of a ten-view multi-projection 3D display system presenting full-colored view images is implemented by combining five laser scanning projectors, an optically clear calcite (CaCO₃) crystal, and an LC polarization rotator. For each time sequence of temporal multiplexing, the luminance distribution of the proposed system is measured and analyzed.

Electronic excitations and chemistry in Nitromethane and HMX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reed, E J; Manaa, M R; Joannopoulos, J D

2001-06-19

The nature of electronic excitations in crystalline solid nitromethane under conditions of shock loading and static compression are examined. Density functional theory calculations are used to determine the crystal bandgap under hydrostatic stress, uniaxial strain, and shear strain. Bandgap lowering under uniaxial strain due to molecular defects and vacancies is considered. In all cases, the bandgap is not lowered enough to produce a significant population of excited states in the crystal. Preliminary simulations on the formation of detonation product molecules from HMX are discussed.

Modeling of yield surface evolution in uniaxial and biaxial loading conditions using a prestrained large scale specimen

NASA Astrophysics Data System (ADS)

Zaman, Shakil Bin; Barlat, Frédéric; Kim, Jin Hwan

2018-05-01

Large-scale advanced high strength steel (AHSS) sheet specimens were deformed in uniaxial tension, using a novel grip system mounted on a MTS universal tension machine. After pre-strain, they were used as a pre-strained material to examine the anisotropic response in the biaxial tension tests with various load ratios, and orthogonal tension tests at 45° and 90° from the pre-strain axis. The flow curve and the instantaneous r-value of the pre-strained steel in each of the aforementioned uniaxial testing conditions were also measured and compared with those of the undeformed steel. Furthermore, an exhaustive analysis of the yield surface was also conducted and the results, prior and post-prestrain were represented and compared. The homogeneous anisotropic hardening (HAH) model [1] was employed to predict the behavior of the pre-strained material. It was found that the HAH-predicted flow curves after non-linear strain path change and the yield loci after uniaxial pre-strain were in good agreement with the experiments, while the r-value evolution after strain path change was qualitatively well predicted.

Mechanochemical Synthesis of Carbon Nanothread Single Crystals.

PubMed

Li, Xiang; Baldini, Maria; Wang, Tao; Chen, Bo; Xu, En-Shi; Vermilyea, Brian; Crespi, Vincent H; Hoffmann, Roald; Molaison, Jamie J; Tulk, Christopher A; Guthrie, Malcolm; Sinogeikin, Stanislav; Badding, John V

2017-11-15

Synthesis of well-ordered reduced dimensional carbon solids with extended bonding remains a challenge. For example, few single-crystal organic monomers react under topochemical control to produce single-crystal extended solids. We report a mechanochemical synthesis in which slow compression at room temperature under uniaxial stress can convert polycrystalline or single-crystal benzene monomer into single-crystalline packings of carbon nanothreads, a one-dimensional sp 3 carbon nanomaterial. The long-range order over hundreds of microns of these crystals allows them to readily exfoliate into fibers. The mechanochemical reaction produces macroscopic single crystals despite large dimensional changes caused by the formation of multiple strong, covalent C-C bonds to each monomer and a lack of reactant single-crystal order. Therefore, it appears not to follow a topochemical pathway, but rather one guided by uniaxial stress, to which the nanothreads consistently align. Slow-compression room-temperature synthesis may allow diverse molecular monomers to form single-crystalline packings of polymers, threads, and higher dimensional carbon networks.

The role of biaxial stresses in discriminating between meaningful and illusory composite failure theories

NASA Technical Reports Server (NTRS)

Hart-Smith, L. J.

1992-01-01

The irrelevance of most composite failure criteria to conventional fiber-polymer composites is claimed to have remained undetected primarily because the experiments that can either validate or disprove them are difficult to perform. Uniaxial tests are considered inherently incapable of validating or refuting any composite failure theory because so much of the total load is carried by the fibers aligned in the direction of the load. The Ten-Percent Rule, a simple rule-of-mixtures analysis method, is said to work well only because of this phenomenon. It is stated that failure criteria can be verified for fibrous composites only by biaxial tests, with orthogonal in-plane stresses of the same as well as different signs, because these particular states of combined stress reveal substantial differences between the predictions of laminate strength made by various theories. Three scientifically plausible failure models for fibrous composites are compared, and it is shown that only the in-plane shear test (orthogonal tension and compression) is capable of distinguishing between them. This is because most theories are 'calibrated' against the measured uniaxial tension and compression tests and any cross-plied laminate tests dominated by those same states of stress must inevitably 'confirm' the theory.

Dynamical electron diffraction simulation for non-orthogonal crystal system by a revised real space method.

PubMed

Lv, C L; Liu, Q B; Cai, C Y; Huang, J; Zhou, G W; Wang, Y G

2015-01-01

In the transmission electron microscopy, a revised real space (RRS) method has been confirmed to be a more accurate dynamical electron diffraction simulation method for low-energy electron diffraction than the conventional multislice method (CMS). However, the RRS method can be only used to calculate the dynamical electron diffraction of orthogonal crystal system. In this work, the expression of the RRS method for non-orthogonal crystal system is derived. By taking Na2 Ti3 O7 and Si as examples, the correctness of the derived RRS formula for non-orthogonal crystal system is confirmed by testing the coincidence of numerical results of both sides of Schrödinger equation; moreover, the difference between the RRS method and the CMS for non-orthogonal crystal system is compared at the accelerating voltage range from 40 to 10 kV. Our results show that the CMS method is almost the same as the RRS method for the accelerating voltage above 40 kV. However, when the accelerating voltage is further lowered to 20 kV or below, the CMS method introduces significant errors, not only for the higher-order Laue zone diffractions, but also for zero-order Laue zone. These indicate that the RRS method for non-orthogonal crystal system is necessary to be used for more accurate dynamical simulation when the accelerating voltage is low. Furthermore, the reason for the increase of differences between those diffraction patterns calculated by the RRS method and the CMS method with the decrease of the accelerating voltage is discussed. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Substructure based modeling of nickel single crystals cycled at low plastic strain amplitudes

NASA Astrophysics Data System (ADS)

Zhou, Dong

In this dissertation a meso-scale, substructure-based, composite single crystal model is fully developed from the simple uniaxial model to the 3-D finite element method (FEM) model with explicit substructures and further with substructure evolution parameters, to simulate the completely reversed, strain controlled, low plastic strain amplitude cyclic deformation of nickel single crystals. Rate-dependent viscoplasticity and Armstrong-Frederick type kinematic hardening rules are applied to substructures on slip systems in the model to describe the kinematic hardening behavior of crystals. Three explicit substructure components are assumed in the composite single crystal model, namely "loop patches" and "channels" which are aligned in parallel in a "vein matrix," and persistent slip bands (PSBs) connected in series with the vein matrix. A magnetic domain rotation model is presented to describe the reverse magnetostriction of single crystal nickel. Kinematic hardening parameters are obtained by fitting responses to experimental data in the uniaxial model, and the validity of uniaxial assumption is verified in the 3-D FEM model with explicit substructures. With information gathered from experiments, all control parameters in the model including hardening parameters, volume fraction of loop patches and PSBs, and variation of Young's modulus etc. are correlated to cumulative plastic strain and/or plastic strain amplitude; and the whole cyclic deformation history of single crystal nickel at low plastic strain amplitudes is simulated in the uniaxial model. Then these parameters are implanted in the 3-D FEM model to simulate the formation of PSB bands. A resolved shear stress criterion is set to trigger the formation of PSBs, and stress perturbation in the specimen is obtained by several elements assigned with PSB material properties a priori. Displacement increment, plastic strain amplitude control and overall stress-strain monitor and output are carried out in the user subroutine DISP and URDFIL of ABAQUS, respectively, while constitutive formulations of the FEM model are coded and implemented in UMAT. The results of the simulations are compared to experiments. This model verified the validity of Winter's two-phase model and Taylor's uniform stress assumption, explored substructure evolution and "intrinsic" behavior in substructures and successfully simulated the process of PSB band formation and propagation.

Van der Waals interaction mediated by an optically uniaxial layer

NASA Astrophysics Data System (ADS)

Šarlah, A.; Žumer, S.

2001-11-01

We study the van der Waals interaction between macroscopic bodies separated by a thin anisotropic film with a uniaxial permittivity tensor. We describe the effect of anisotropy of the media on the magnitude and sign of the interaction. The resulting differences in the van der Waals interaction are especially important for the stability of strongly confined liquid crystals, and nanostructures characterized by highly uniaxial macroscopic molecular arrangement, such as in self-assemblies of long organic molecules forming films, membranes, colloids, etc. We introduce an improved expression for the Hamaker constant which takes into account the uniaxial symmetry of a medium. In special cases neglecting the optical anisotropy even leads to an incorrect sign of the interaction.

The rate of the exciton self-trapping in KI and RbI at different temperatures

NASA Astrophysics Data System (ADS)

Zhanturina, N.; Shunkeev, K.

2012-12-01

The article disclosed the theory of the kinetics of excitons self-trapping in alkali halide crystals. On the example of KI and RbI crystals the time of excitons self-trapping and the length of free path before self-trapping were calculated. Also, the theory of self-trapping rate was revealed. According to the Arrhenius law the dependence of excitons self-trapping rate on the temperature and the degree of depth and uniaxial compression was analyzed. The increase of the rate of excitons self-trapping by temperature increasing was shown; while increasing the degree of compression at the full rate of strain localization decreases under uniaxial - is increasing. These data are good agreed with the experimental fact of luminescencei increasing under uniaxial compression and allow to make a conclusion about weakening of the luminescence by applying hydrostatic pressure.

A polarization-independent liquid crystal phase modulation using polymer-network liquid crystal with orthogonal alignment layers

NASA Astrophysics Data System (ADS)

Chen, Ming-Syuan; Lin, Wei-Chih; Tsou, Yu-Shih; Lin, Yi-Hsin

2012-10-01

A polarization-independent liquid crystal (LC) phase modulation using polymer-network liquid crystals with orthogonal alignments layers (T-PNLC) is demonstrated. T-PNLC consists of three layers. LC directors in the two layers near glass substrates are orthogonal to each other. In the middle layer, LC directors are perpendicular to the glass substrate. The advantages of such T-PNLC include polarizer-free, larger phase shift (~0.4π rad) than the residual phase type (<0.05π rad), and low operating voltage (< 30Vrms). It does not require bias voltage for avoiding scattering because the refractive index of liquid crystals matches that of polymers. The phase shift of T-PNLC is affected by the cell gap and the curing voltages. The potential applications are laser beam steering, spatial light modulators and electrically tunable micro-lens arrays.

Synthesis of full Poincaré beams by means of uniaxial crystals

NASA Astrophysics Data System (ADS)

Piquero, G.; Monroy, L.; Santarsiero, M.; Alonzo, M.; de Sande, J. C. G.

2018-06-01

A simple optical system is proposed to generate full-Poincaré beams (FPBs), i.e. beams presenting all possible states of (total) polarization across their transverse section. The method consists in focusing a uniformly polarized laser beam onto a uniaxial crystal having its optic axis parallel to the propagation axis of the impinging beam. A simple approximated model is used to obtain the analytical expression of the beam polarization at the output of the crystal. The output beam is then proved to be a FPB. By changing the polarization state of the input field, full-Poincaré beams are still obtained, but presenting different distributions of the polarization state across the beam section. Experimental results are reported, showing an excellent agreement with the theoretical predictions.

Importance of uniaxial compression for the appearance of superconductivity in NdO1-xFxBiS2

NASA Astrophysics Data System (ADS)

A, Omachi; T, Hiroi; J, Kajitani; O, Miura; Y, Mizuguchi

2014-05-01

We have investigated the crystal structure and superconducting properties of the new layered superconductor NdO1-xFxBiS2. Bulk superconductivity with a Tc above 4.5 K was observed. It was found that the Tc depended on both F concentration and crystal structure. Uniaxial compression along the c axis upon F substitution seemed to be linked with the appearance of bulk superconductivity. Furthermore, we considered that a higher Tc can be achieved when the c/a parameter was optimized in the NdO1-xFxBiS2 system.

The behavior of single-crystal silicon to dynamic loading using in-situ X-ray diffraction and phase contrast imaging

NASA Astrophysics Data System (ADS)

Lee, Hae Ja; Xing, Zhou; Galtier, Eric; Arnold, Brice; Granados, Eduardo; Brown, Shaughnessy B.; Tavella, Franz; McBride, Emma; Fry, Alan; Nagler, Bob; Schropp, Andreas; Seiboth, Frank; Samberg, Dirk; Schroer, Christian; Gleason, Arianna E.; Higginbotham, Andrew

Hydrostatic and uniaxial compression studies have revealed that crystalline silicon undergoes phase transitions from a cubic diamond structure to a variety of phases including orthorhombic Imma phase, body-centered tetragonal phase, and a hexagonal primitive phase. The dynamic response of silicon at high pressure, however, is not well understood. Phase contrast imaging has proven to be a powerful tool for probing density changes caused by the shock propagation into a material. In order to characterize the elastic and phase transitions, we image shock waves in Si with high spatial resolution using the LCLS X-ray free electron laser and Matter in Extreme Conditions instrument. In this study, the long pulse optical laser with pseudo-flat top shape creates high pressures up to 60 GPa. We measure the crystal structure by observing X-ray diffraction orthogonal to the shock propagation direction over a range of pressures. We describe the capability of simultaneously performing phase contrast imaging and in situ X-ray diffraction during shock loading and discuss the dynamic response of Si in high-pressure phases Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The MEC instrument is supported by.

Structural phase transition of gold under uniaxial, tensile, and triaxial stresses: An ab initio study

NASA Astrophysics Data System (ADS)

Durandurdu, Murat

2007-07-01

The behavior of gold crystal under uniaxial, tensile, and three different triaxial stresses is studied using an ab initio constant pressure technique within a generalized gradient approximation. Gold undergoes a phase transformation from the face-centered-cubic structure (fcc) to a body-centered-tetragonal (bct) structure having the space group of I4/mmm with the application of uniaxial stress, while it transforms to a face-centered-tetragonal (fct) phase within I4/mmm symmetry under uniaxial tensile loading. Further uniaxial compression of the bct phase results in a symmetry change from I4/mmm to P1 at high stresses and ultimately structural failure around 200.0GPa . For the case of triaxial stresses, gold also converts into a bct state. The critical stress for the fcc-to-bct transformation increases as the ratio of the triaxial stress increases. Both fct and bct phases are elastically unstable.

Nonlinear modeling of crystal system transition of black phosphorus using continuum-DFT model.

PubMed

Setoodeh, A R; Farahmand, H

2018-01-24

In this paper, the nonlinear behavior of black phosphorus crystals is investigated in tandem with dispersion-corrected density functional theory (DFT-D) analysis under uniaxial loadings. From the identified anisotropic behavior of black phosphorus due to its morphological anisotropy, a hyperelastic anisotropic (HA) model named continuum-DFT is established to predict the nonlinear behavior of the material. In this respect, uniaxial Cauchy stresses are employed on both the DFT-D and HA models along the zig-zag and armchair directions. Simultaneously, the transition of the crystal system is recognized at about 4.5 GPa of the applied uniaxial tensile stress along the zig-zag direction on the DFT-D simulation in the nonlinear region. In order to develop the nonlinear continuum model, unknown constants are surveyed with the optimized least square technique. In this regard, the continuum model is obtained to reproduce the Cauchy stress-stretch and density of strain-stretch results of the DFT-D simulation. Consequently, the modified HA model is introduced to characterize the nonlinear behavior of black phosphorus along the zig-zag direction. More importantly, the specific transition of the crystal system is successfully predicted in the new modified continuum-DFT model. The results reveal that the multiscale continuum-DFT model is well defined to replicate the nonlinear behavior of black phosphorus along the zig-zag and armchair directions.

On real-space Density Functional Theory for non-orthogonal crystal systems: Kronecker product formulation of the kinetic energy operator

NASA Astrophysics Data System (ADS)

Sharma, Abhiraj; Suryanarayana, Phanish

2018-05-01

We present an accurate and efficient real-space Density Functional Theory (DFT) framework for the ab initio study of non-orthogonal crystal systems. Specifically, employing a local reformulation of the electrostatics, we develop a novel Kronecker product formulation of the real-space kinetic energy operator that significantly reduces the number of operations associated with the Laplacian-vector multiplication, the dominant cost in practical computations. In particular, we reduce the scaling with respect to finite-difference order from quadratic to linear, thereby significantly bridging the gap in computational cost between non-orthogonal and orthogonal systems. We verify the accuracy and efficiency of the proposed methodology through selected examples.

Negative refraction in molybdenum disulfide.

PubMed

Wang, Wenhui; Cui, Xudong; Yang, Erchan; Fan, Quanping; Xiang, Bin

2015-08-24

Recently, negative refractions have been demonstrated in uniaxial crystals with no necessary of negative permittivity and permeability. However, the small anisotropy parameterγin the uniaxial crystals limits the negative refraction occurrence only in a small range of the incident light angle, retarding its practical applications. In this paper, we report negative refraction induced by a pronounced anisotropic behavior in the bulk MoS(2). Using the first-principles, the dielectric function and refractive index calculations confirm a uniaxial trait of MoS(2) with a calculated anisotropy parameterγlarger than 2.5 in the entire range of visible wavelength. The critical incident angle to trigger a negative refraction in the bulk MoS(2) is calculated up to 90°. The finite-difference time-domain simulations prove that the incident light with a density of 59.5% can be negatively refracted in a MoS(2) slab with a thickness of 0.1 µm. Our results open up a new pathway for MoS(2)-like materials to a novel field of optical integration.

Van der Waals interaction in uniaxial anisotropic media.

PubMed

Kornilovitch, Pavel E

2013-01-23

Van der Waals interactions between flat surfaces in uniaxial anisotropic media are investigated in the nonretarded limit. The main focus is the effect of nonzero tilt between the optical axis and the surface normal on the strength of the van der Waals attraction. General expressions for the van der Waals free energy are derived using the surface mode method and the transfer-matrix formalism. To facilitate numerical calculations a temperature-dependent three-band parameterization of the dielectric tensor of the liquid crystal 5CB is developed. A solid slab immersed in a liquid crystal experiences a van der Waals torque that aligns the surface normal relative to the optical axis of the medium. The preferred orientation is different for different materials. Two solid slabs in close proximity experience a van der Waals attraction that is strongest for homeotropic alignment of the intervening liquid crystal for all the materials studied. The results have implications for the stability of plate-like colloids in liquid crystal hosts.

Uniaxial alignment of triisopropylsilylethynyl pentacene via zone-casting technique.

PubMed

Su, Yajun; Gao, Xiang; Liu, Jiangang; Xing, Rubo; Han, Yanchun

2013-09-14

Uniaxially aligned triisopropylsilylethynyl pentacene (TIPS-pentacene) crystals over a large area were fabricated using zone-casting technique. The array of TIPS-pentacene displayed a high orientation degree with a dichroic ratio (DR) of 0.80. The crystals were arranged with c axis perpendicular to the substrate and the long axis of the ribbon corresponded to the a axis of TIPS-pentacene. The properties of the solutions and the processing parameters were shown to influence the formation of the oriented TIPS-pentacene crystalline array. Solvent with a low boiling point (such as chloroform) favoured the orientation of the ribbon-like crystals. The concentration of the solution should be appropriate, ensuring the crystallization velocity of TIPS-pentacene matching with the receding of the meniscus. Besides, we proved that the casting speed should be large enough to induce a sufficient concentration gradient. The orientation mechanism of TIPS-pentacene was attributed to a synergy of the ordered nuclei and a match between the crystallization velocity and the casting speed. Field effect transistors (FETs) based on the oriented TIPS-pentacene crystalline array showed a mobility of 0.67 cm(2) V(-1) s(-1).

Radiation of X-Rays Using Uniaxially Polarized LiNbO3 Single Crystal

NASA Astrophysics Data System (ADS)

Fukao, Shinji; Nakanishi, Yoshikazu; Mizoguchi, Tadahiro; Ito, Yoshiaki; Nakamura, Toru; Yoshikado, Shinzo

2009-03-01

X-rays are radiated due to the bremsstrahlung caused by the collision of electrons with a metal target placed opposite the negative electric surface of a crystal by changing the temperature of a LiNbO3 single crystal uniaxially polarized in the c-axis direction. It is suggested that both electric field intensity and electron density determine the intensity of X-ray radiation. Electrons are supplied by the ionization of residual gas in space, field emission from a case inside which a crystal is located, considered to be due to the high electric-field intensity formed by the surface charges on the crystal, and an external electron source, such as a thermionic source. In a high vacuum, it was found that the electrons supplied by electric-field emission mainly contribute to the radiation of X-rays. It was found that the integrated intensity of X-rays can be maximized by supplying electrons both external and by electric-field emission. Furthermore, the integrated intensity of the X-rays is stable for many repeated temperature changes.

A simple X-ray source of two orthogonal beams for small samples imaging

NASA Astrophysics Data System (ADS)

Hrdý, J.

2018-04-01

A simple method for simultaneous imaging of small samples by two orthogonal beams is proposed. The method is based on one channel-cut crystal which is oriented such that the beam is diffracted on two crystallographic planes simultaneously. These planes are symmetrically inclined to the crystal surface. The beams are three times diffracted. After the first diffraction the beam is split. After the second diffraction the split beams become parallel. Finally, after the third diffraction the beams become convergent and may be used for imaging. The corresponding angular relations to obtain orthogonal beams are derived.

Integral imaging with multiple image planes using a uniaxial crystal plate.

PubMed

Park, Jae-Hyeung; Jung, Sungyong; Choi, Heejin; Lee, Byoungho

2003-08-11

Integral imaging has been attracting much attention recently for its several advantages such as full parallax, continuous view-points, and real-time full-color operation. However, the thickness of the displayed three-dimensional image is limited to relatively small value due to the degradation of the image resolution. In this paper, we propose a method to provide observers with enhanced perception of the depth without severe resolution degradation by the use of the birefringence of a uniaxial crystal plate. The proposed integral imaging system can display images integrated around three central depth planes by dynamically altering the polarization and controlling both elemental images and dynamic slit array mask accordingly. We explain the principle of the proposed method and verify it experimentally.

Uniaxial Pressure and High-Field Effects on Superconducting Single-Crystal CeCoIn5

NASA Astrophysics Data System (ADS)

Johnson, Scooter David

We have measured the a.c. susceptibility response of single-crystal CeCoIn 5 under uniaxial pressure up to 4.07 kbar and in d.c. field parallel to the c axis up to 5 T. From these measurements we report on several pressure and field characteristics of the superconducting state. The results are divided into 3 chapters: (1) We find a non-linear dependence of the superconducting transition temperature Tc on pressure, with a maximum close to 2 kbar. The transition also broadens significantly as pressure increases. We model the broadening as a product of non-uniform pressure and discuss its implications for the pressure dependence of the transition temperature. We relate our measurements to previous theoretical work. (2) We provided evidence and pressure dependence for the FFLO phase with field and pressure along the c axis. The FFLO phase boundary is temperature independent and tracks with the suppression to lower fields of the upper critical field with pressure. We also report the strengthening of the Pauli-limited field in this orientation by calculating the increase of the orbitally-limited field with uniaxial pressure. (3) We extract the critical current using the Bean critical state model and compare it to the expected Ginzberg-Landau behavior. We find that the exponent of the critical current depends on uniaxial pressure and d.c. field. Within a d.c. field the pressure dependence of the exponent may be obscured by the field effect. We have also measured resistivity, susceptibility, and specific heat of high-quality single-crystal YIn3 below 1 K and present a refinement of Tc from previous measurements. We make suggestions for experimental comparisons to the heavy fermion family CeXIn5, (X = Rh, Ir, Co) and the parent compound CeIn3.

Role of Molecular Structure on X-ray Diffraction in Thermotropic Uniaxial and Biaxial Nematic Liquid Crystal Phases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena

2009-08-27

X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution functionmore » is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.« less

Role of Molecular Structure on X-ray Diffraction in Uniaxial and Biaxial Phases of Thermotropic Liquid Crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena

2009-04-29

X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution functionmore » is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.« less

Light propagation in two-dimensional photonic crystals based on uniaxial polar materials: results on polaritonic spectrum

NASA Astrophysics Data System (ADS)

Gómez-Urrea, H. A.; Duque, C. A.; Pérez-Quintana, I. V.; Mora-Ramos, M. E.

2017-03-01

The dispersion relations of two-dimensional photonic crystals made of uniaxial polaritonic cylinders arranged in triangular lattice are calculated. The particular case of the transverse magnetic polarization is taken into account. Three different uniaxial materials showing transverse phonon-polariton excitations are considered: aluminum nitride, gallium nitride, and indium nitride. The study is carried out by means of the finite-difference time-domain technique for the solution of Maxwell equations, together with the method of the auxiliary differential equation. It is shown that changing the filling fraction can result in the modification of both the photonic and polaritonic bandgaps in the optical dispersion relations. Wider gaps appear for smaller filling fraction values, whereas a larger number of photonic bandgaps will occur within the frequency range considered when a larger filling fraction is used. The effect of including the distinct wurtzite III-V nitride semiconductors as core materials in the cylinders embedded in the air on the photonic properties is discussed as well, highlighting the effect of the dielectric anisotropy on the properties of the polaritonic part of the photonic spectrum.

Magnetostructural Properties of Colossal Magnetoresistance Manganites Under External Magnetic Fields and Uniaxial Pressure

NASA Astrophysics Data System (ADS)

Kaplan, Michael; Zimmerman, George

2002-03-01

In the colossal magnetoresistance manganites the transport and magnetostructural properties are tightly connected [1,2]. Many magnetic field induced structural phase transitions and anomalous magnetoacoustical properties continue to be discovered in various manganite derivatives. Nevertheless the mechanism of structural transitions and microscopic theory of corresponding anomalous properties are still to be completely understood. Here we present a microscopic model of magnetic field and uniaxial pressure induced structural phase transitions in lightly doped manganites. The model is based on the cooperative Jahn-Teller effect which takes into account the Mn3+-ground doublet and excited triplet electronic states. Numerous calculations for different orientation magnetic field suggest the explanations of the origin of the structural transitions and of the measured magnetostriction data. The calculations for the two-sublattice antiferrodistortive crystals under uniaxial pressure support the idea of metaelasticity - a property typical for Jahn-Teller antiferroelastics. 1.Y. Tokura, ed. Colossal Magnetoresistance Oxides. Gordon & Breach, London, 2000. 2.M. Kaplan, G. Zimmerman, eds. Vibronic Interactions: Jahn-Teller Effect in Crystal and Molecules. NATO Science Series, Dordrecht/Boston/London, 2001

100-Fold Enhancement of Charge Transport in Uniaxially Oriented Mesoporous Anatase TiO 2 Films

DOE PAGES

Li, Ke; Liu, Jie; Sheng, Xia; ...

2017-12-04

Mesoporous semiconductor films are of considerable interest for applications in photoelectrochemical devices, however, despite intensive research till now, their charge transport properties remain significantly lower than their single-crystal counterparts. Herein, we report a novel low-temperature template-free technique for growing high surface area mesoporous anatase TiO2 films with a preferred [001] crystalline-orientation on FTO-coated glass substrate. Compared to mesoporous films that comprised of randomly oriented crystallites, the uniaxial orientation enables a 100-fold increase in the rate of electron transport. The uniaxially oriented mesoporous anatase TiO2 films exhibit should greatly facilitate the development and application of photoelectrochemical and electrochemical devices.

Electric-regulated enhanced in-plane uniaxial anisotropy in FeGa/PMN-PT composite using oblique pulsed laser deposition

NASA Astrophysics Data System (ADS)

Zhang, Yi; Huang, Chaojuan; Turghun, Mutellip; Duan, Zhihua; Wang, Feifei; Shi, Wangzhou

2018-04-01

The FeGa film with in-plane uniaxial magnetic anisotropy was fabricated onto different oriented single-crystal lead magnesium niobate-lead titanate using oblique pulsed laser deposition. An enhanced in-plane uniaxial magnetic anisotropy field of FeGa film can be adjusted from 18 Oe to 275 Oe by tuning the oblique angle and polarizing voltage. The competitive relationship of shape anisotropy and strain anisotropy has been discussed, which was induced by oblique angle and polarizing voltage, respectively. The (100)-oriented and (110)-oriented PMN-PT show completely different characters on voltage-dependent magnetic properties, which could be attributed to various anisotropy directions depended on different strain directions.

Numerical method to determine mechanical parameters of engineering design in rock masses.

PubMed

Xue, Ting-He; Xiang, Yi-Qiang; Guo, Fa-Zhong

2004-07-01

This paper proposes a new continuity model for engineering in rock masses and a new schematic method for reporting the engineering of rock continuity. This method can be used to evaluate the mechanics of every kind of medium; and is a new way to determine the mechanical parameters used in engineering design in rock masses. In the numerical simulation, the experimental parameters of intact rock were combined with the structural properties of field rock. The experimental results for orthogonally-jointed rock are given. The results included the curves of the stress-strain relationship of some rock masses, the curve of the relationship between the dimension Delta and the uniaxial pressure-resistant strength sc of these rock masses, and pictures of the destructive procedure of some rock masses in uniaxial or triaxial tests, etc. Application of the method to engineering design in rock masses showed the potential of its application to engineering practice.

Nonlinear polarization rotation and orthogonal polarization generation experienced in a single-beam configuration

NASA Astrophysics Data System (ADS)

Minkovski, N.; Petrov, G. I.; Saltiel, S. M.; Albert, O.; Etchepare, J.

2004-09-01

Nonlinear polarization rotation and generation of a polarization component orthogonal to the input beam were observed along fourfold axes of YVO4 and BaF2 crystals. We demonstrate experimentally that in both crystals the angle of rotation is proportional, at low intensities, to the square of the product of the input intensity and the crystal length and is the result of simultaneous action of two third-order processes. This type of nonlinear polarization rotation is driven by the real part of the cubic susceptibility. The recorded energy exchange between the two orthogonal components can exceed 10%. It is to our knowledge the highest energy-conversion efficiency achieved in a single beam nonresonant χ(3) interaction. A simple theoretical model is elaborated to describe the dependence of nonlinear polarization rotation and orthogonal polarization generation on the intensity of the input beam at both low- and high-intensity levels. It reveals the potential contributions from the real and the imaginary parts of the susceptibility tensor. Moreover, this kind of measurement is designed to permit the determination of the magnitude and the sign of the anisotropy of the real part of third-order nonlinearity in crystals with cubic or tetragonal symmetry on the basis of polarization-rotation measurements. The χxxxx(3) component of the third-order susceptibility tensor and its anisotropy sign and amplitude value for BaF2 and YVO4 crystals are estimated and discussed.

Analysis of Electric Field Propagation in Anisotropically Absorbing and Reflecting Waveplates

NASA Astrophysics Data System (ADS)

Carnio, B. N.; Elezzabi, A. Y.

2018-04-01

Analytical expressions are derived for half-wave plates (HWPs) and quarter-wave plates (QWPs) based on uniaxial crystals. This general analysis describes the behavior of anisotropically absorbing and reflecting waveplates across the electromagnetic spectrum, which allows for correction to the commonly used equations determined assuming isotropic absorptions and reflections. This analysis is crucial to the design and implementation of HWPs and QWPs in the terahertz regime, where uniaxial crystals used for waveplates are highly birefringent and anisotropically absorbing. The derived HWP equations describe the rotation of linearly polarized light by an arbitrary angle, whereas the QWP analysis focuses on manipulating a linearly polarized electric field to obtain any ellipticity. The HWP and QWP losses are characterized by determining equations for the total electric field magnitude transmitted through these phase-retarding elements.

Ultrafast diffraction conoscopy of the structural phase transition in VO2: Evidence of two lattice distortions

NASA Astrophysics Data System (ADS)

Kumar, Nardeep; Rúa, Armando; Fernández, Félix E.; Lysenko, Sergiy

2017-06-01

Photoinduced phase transitions in complex correlated systems occur very rapidly and involve the interplay between various electronic and lattice degrees of freedom. For these materials to be considered for practical applications, it is important to discover how their phase transitions take place. Here we use a novel ultrafast diffraction conoscopy technique to study the evolution of vanadium dioxide (VO2) from biaxial to uniaxial symmetry. A key finding in this study is an additional relaxation process through which the phase transition takes place. Our results show that the biaxial monoclinic crystal initially, within the first 100-300 fs, transforms to a transient biaxial crystal, and within the next 300-400 fs converts into a uniaxial rutile crystal. The characteristic times for these transitions depend on film morphology and are presumably altered by misfit strain. We take advantage of Landau phenomenology to describe the complex dynamics of VO2 phase transition in the femtosecond regime.

Electronic excitations in shocked nitromethane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reed, Evan J.; Joannopoulos, J. D.; Fried, Laurence E.

2000-12-15

The nature of electronic excitations in crystalline solid nitromethane under conditions of shock loading and static compression are examined. Density-functional theory calculations are used to determine the crystal bandgap under hydrostatic stress, uniaxial strain, and shear strain. Bandgap lowering under uniaxial strain due to molecular defects and vacancies is considered. Ab initio molecular-dynamics simulations are done of all possible nearest-neighbor collisions at a shock front, and of crystal shearing along a sterically hindered slip plane. In all cases, the bandgap is not lowered enough to produce a significant population of excited states in the crystal. The nearly free rotation ofmore » the nitromethane methyl group and localized nature of the highest occupied molecular orbital and lowest unoccupied molecular orbital states play a role in this result. Dynamical effects have a more significant effect on the bandgap than static effects, but relative molecule velocities in excess of 6 km/s are required to produce a significant thermal population of excited states.« less

Dual-comb self-mode-locked monolithic Yb:KGW laser with orthogonal polarizations.

PubMed

Chang, M T; Liang, H C; Su, K W; Chen, Y F

2015-04-20

The dependence of lasing threshold on the output transmission is numerically analyzed to find the condition for the gain-to-loss balance for the orthogonal Np and Nm polarizations with a Ng-cut Yb:KGW laser crystal. With the numerical analysis, an orthogonally polarized dual-comb self-mode-locked operation is experimentally achieved with a coated Yb:KGW crystal to form a monolithic cavity. At a pump power of 5.2 W, the average output power, the pulse repetition rate, and the pulse duration are measured to be 0.24 (0.6) W, 25.8 (25.3) GHz, and 1.06 (1.12) ps for the output along the Np (Nm) polarization.

Low-stress pressure solution experiments on halite single-crystals

NASA Astrophysics Data System (ADS)

Martin, Brigitte; Röller, Klaus; Stöckhert, Bernhard

1999-07-01

Pressure solution experiments on halite single-crystals in saturated solution were carried out at atmospheric pressure under uniaxial stress ranging from 0.1 to 2.0 MPa and at temperatures of 303 and 323 K. The experiments were performed in ceramic loading rigs with damp-proofed sample chambers. The low uniaxial stress is applied by loading the piston with steel weights ranging from 0.5 to 5.0 kg. The position of the piston is measured by an electronic displacement transducer, connected to a data acquisition system. Deviations caused by fluctuations of temperature and output voltage of the power supply are corrected after data acquisition. The halite cubes {100} with edge dimensions of 3-9 mm are prepared by cleaving and placed with a (100) cleavage face on the (001) face of a muscovite single-crystal (10×10×0.1 mm), a polished quartz (0001) plate, or another halite crystal oriented to form a 45° twist boundary. The four free (100) faces of the halite cube are in contact with the surrounding NaCl solution. The initial displacement rate of the piston after flooding of the system and loading is up to 50.0 μm/day, attributed to smoothing of the halite face and elimination of point contacts with high stress concentration. Within 2 to 3 days this stage grades into steady-state displacement with rates of 0.1-2.0 μm/day. In some experiments stages of higher displacement rates (2.0-5.0 μm/day) lasting for 3-5 days are observed episodically, with intervals of 10-15 days. These cycles appear not to be triggered by external events. Experiments with a dry mica-halite interface, carried out for comparison at the same temperature and at an uniaxial stress of 2 MPa, result in a displacement rate below the limits of detection. This rules out a significant contribution of crystal plastic deformation in the wet experiments. The experimental results show no simple correlation between displacement rate and magnitude of uniaxial stress, crystal size, type of the interface, and temperature. At the given conditions, convergence at a single interface due to pressure solution is apparently not a steady-state process. The alternating stages of lower and higher displacement rates observed in many experiments suggest that the mechanisms of transport or dissolution may change spontaneously during the experiment. It is possible that the process itself leads to an unstable configuration causing episodic changes.

Review of the role of dielectric anisotropy in Dyakonov surface-wave propagation

NASA Astrophysics Data System (ADS)

Nelatury, Sudarshan R., II; Polo, John A., Jr.; Lakhtakia, Akhlesh

2008-08-01

Surface waves (SWs) are localized waves that travel along the planar interface between two different mediums when certain dispersion relations are satisfied. If both mediums have purely dielectric constitutive properties, the characteristics of SW propagation are determined by the anisotropy of both mediums. Surface waves are then called Dyakonov SWs (DSWs), after Dyakonov who theoretically established the possibility of SW propagation at the planar interface of an isotropic dielectric and a positive uniaxial dielectric. Since then, DSW propagation guided by interfaces between a variety of dielectrics has been studied. With an isotropic dielectric on one side, the dielectric on the other side of the interface can be not only positive uniaxial but also biaxial. DSW propagation can also occur along an interface between two uniaxial or biaxial dielectrics that are twisted about a common axis with respect to each other but are otherwise identical. Recently, DSW propagation has been studied taking (i) uniaxial dielectrics such as calomel and dioptase crystals; (ii) biaxial dielectrics such as hemimorphite, crocoite, tellurite, witherite, and cerussite; and (iii) electro-optic materials such as potassium niobate. With materials that are significantly anisotropic, the angular regime of directions for DSW propagation turns out to be narrow. In the case of naturally occurring crystals, one has to accept the narrow angular existence domain (AED). However, exploiting the Pockels effect not only facilitates dynamic electrical control of DSW propagation, but also widens the AED for DSW propagation.

Thickness dependence of voltage-driven magnetization switching in FeCo/PI/piezoelectric actuator heterostructures

NASA Astrophysics Data System (ADS)

Cui, B. S.; Guo, X. B.; Wu, K.; Li, D.; Zuo, Y. L.; Xi, L.

2016-03-01

Strain mediated magnetization switching of ferromagnetic/substrate/piezoelectric actuator heterostructures has become a hot issue due to the advantage of low-power consumption. In this work, Fe65Co35 thin films were deposited on a flexible polyamides (PI) substrate, which has quite low Young’s module (~4 GPa for PI as compared to ~180 GPa for Si) and benefits from complete transfer of the strain from the piezoelectric actuator to magnetic thin films. A complete 90° transition of the magnetic easy axis was realized in 50 nm thick FeCo films under the voltage of 70 V, while a less than 90° rotation angle of the magnetic easy axis direction was observed in other samples, which was ascribed to the distribution of the anisotropy field and/or the orthogonal misalignment between stress induced anisotropy and original uniaxial anisotropy. A model considering two uniaxial anisotropies with orthogonal arrangement was used to quantitatively understand the observed results and the linear-like voltage dependent anisotropy field, especially for 10 nm FeCo films, in which the switching mechanism along the easy axis direction can be explained by the domain wall depinning model. It indicates that the magnetic domain-wall movement velocity may be controlled by strain through tuning the energy barrier of the pinning in heterostructures. Moreover, voltage-driven 90° magnetization switching with low-power consumption was achieved in this work.

First order transitions by conduction calorimetry: Application to deuterated potassium dihydrogen phosphate ferroelastic crystal under uniaxial pressure

NASA Astrophysics Data System (ADS)

Gallardo, M. C.; Jiménez, J.; Koralewski, M.; del Cerro, J.

1997-03-01

The specific heat c and the heat power W exchanged by a Deuterated Potassium Dihydrogen Phosphate ferroelectric-ferroelastic crystal have been measured simultaneously for both decreasing and increasing temperature at a low constant rate (0.06 K/h) between 175 and 240 K. The measurements were carried out under controlled uniaxial stresses of 0.3 and 4.5±0.1 bar applied to face (110). At Tt=207.9 K, a first order transition is produced with anomalous specific heat behavior in the interval where the transition heat appears. This anomalous behavior is explained in terms of the temperature variation of the heat power during the transition. During cooling, the transition occurs with coexistence of phases, while during heating it seems that metastable states are reached. Excluding data affected by the transition heat, the specific heat behavior agrees with the predictions of a 2-4-6 Landau potential in the range of 4-15 K below Tt while logarithmic behavior is obtained in the range from Tt to 1 K below Tt. Data obtained under 0.3 and 4.5 bar uniaxial stresses exhibit the same behavior.

Apparatus for measurement of acoustic wave propagation under uniaxial loading with application to measurement of third-order elastic constants of piezoelectric single crystals.

PubMed

Zhang, Haifeng; Kosinski, J A; Karim, Md Afzalul

2013-05-01

We describe an apparatus for the measurement of acoustic wave propagation under uniaxial loading featuring a special mechanism designed to assure a uniform mechanical load on a cube-shaped sample of piezoelectric material. We demonstrate the utility of the apparatus by determining the effects of stresses on acoustic wave speed, which forms a foundation for the final determination of the third-order elastic constants of langasite and langatate single crystals. The transit time method is used to determine changes in acoustic wave velocity as the loading is varied. In order to minimize error and improve the accuracy of the wave speed measurements, the cross correlation method is used to determine the small changes in the time of flight. Typical experimental results are presented and discussed.

Strong anisotropy of electric field effects on uniaxial relaxor ferroelectric Sr0.75Ba0.25Nb2O6 crystals proved by acoustic emission

NASA Astrophysics Data System (ADS)

Dul'kin, E.; Kojima, S.; Roth, M.

2018-01-01

[001] oriented Sr0.75Ba0.25Nb2O6 uniaxial relaxor ferroelectric crystals have been studied by acoustic emission in the temperature range of 20÷200 °C and under an external electric field up to 1 kV/cm. Under the application of an electric field the temperature of a dielectric maximum exhibits a nontrivial behavior: it remains constant at first, secondly steep decreases down to some threshold field, and thirdly starts to increase as a field enhances, whereas the same temperature of a dielectric maximum under a bias electric field to [100] oriented Sr0.75Ba0.25Nb2O6 crystals exhibits a smoothed minimum before the start to increase as a field enhances (E. Dul'kin et al., J. Appl. Phys. 110, 044106 (2011)). Such a difference of electric field effects in c- and a-cut crystals is discussed from the viewpoint of random-bond-random-field model of relaxor ferroelectrics. By the comparison between experimental and theoretical data, a dipole moment of the PNR was estimated to be 0.1 (C cm).

Generalized Reliability Methodology Applied to Brittle Anisotropic Single Crystals. Degree awarded by Washington Univ., 1999

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.

2002-01-01

A generalized reliability model was developed for use in the design of structural components made from brittle, homogeneous anisotropic materials such as single crystals. The model is based on the Weibull distribution and incorporates a variable strength distribution and any equivalent stress failure criteria. In addition to the reliability model, an energy based failure criterion for elastically anisotropic materials was formulated. The model is different from typical Weibull-based models in that it accounts for strength anisotropy arising from fracture toughness anisotropy and thereby allows for strength and reliability predictions of brittle, anisotropic single crystals subjected to multiaxial stresses. The model is also applicable to elastically isotropic materials exhibiting strength anisotropy due to an anisotropic distribution of flaws. In order to develop and experimentally verify the model, the uniaxial and biaxial strengths of a single crystal nickel aluminide were measured. The uniaxial strengths of the <100> and <110> crystal directions were measured in three and four-point flexure. The biaxial strength was measured by subjecting <100> plates to a uniform pressure in a test apparatus that was developed and experimentally verified. The biaxial strengths of the single crystal plates were estimated by extending and verifying the displacement solution for a circular, anisotropic plate to the case of a variable radius and thickness. The best correlation between the experimental strength data and the model predictions occurred when an anisotropic stress analysis was combined with the normal stress criterion and the strength parameters associated with the <110> crystal direction.

An Investigation of Physico-Mechanical Properties of Ultrafine-Grained Magnesium Alloys Subjected to Severe Plastic Deformation

NASA Astrophysics Data System (ADS)

Kozulyn, A. A.; Skripnyak, V. A.; Krasnoveikin, V. A.; Skripnyak, V. V.; Karavatskii, A. K.

2015-01-01

The results of investigations of physico-mechanical properties of specimens made from the structural Mg-based alloy (Russian grade Ma2-1) in its coarse-grained and ultrafine-grained states after SPD processing are presented. To form the ultrafine-grained structure, use was made of the method of orthogonal equal-channel angular pressing. After four passes through the die, a simultaneous increase was achieved in microhardness, yield strength, ultimate tensile strength and elongation to failure under conditions of uniaxial tensile loading.

On the equivalence between Young's double-slit and crystal double-refraction interference experiments.

PubMed

Ossikovski, Razvigor; Arteaga, Oriol; Vizet, Jérémy; Garcia-Caurel, Enric

2017-08-01

We show, both analytically and experimentally, that under common experimental conditions the interference pattern produced in a classic Young's double-slit experiment is indistinguishable from that generated by means of a doubly refracting uniaxial crystal whose optic axis makes a skew angle with the light propagation direction. The equivalence between diffraction and crystal optics interference experiments, taken for granted by Arago and Fresnel in their pioneering research on the interference of polarized light beams, is thus rigorously proven.

Control of the formation of vortex Bessel beams in uniaxial crystals by varying the beam divergence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paranin, V D; Karpeev, S V; Khonina, S N

The transformation of zero-order Bessel beams into a second-order vortex Bessel beam in CaCO3 and LiNbO3 crystals is experimentally studied, and a possibility of controlling the beam transformation by changing the wavefront curvature of the illumi-nating beam is shown. A quasi-periodic nature of the Bessel beam transformation in a crystal while illuminating the diffraction axi-con by a convergent beam is observed (laser beams)

Passively Q-switched side pumped monolithic ring laser

NASA Technical Reports Server (NTRS)

Li, Steven X. (Inventor)

2012-01-01

Disclosed herein are systems and methods for generating a side-pumped passively Q-switched non-planar ring oscillator. The method introduces a laser into a cavity of a crystal, the cavity having a round-trip path formed by a reflection at a dielectrically coated front surface, a first internal reflection at a first side surface of the crystal at a non-orthogonal angle with the front, a second internal reflection at a top surface of the crystal, and a third internal reflection at a second side surface of the crystal at a non-orthogonal angle with the front. The method side pumps the laser at the top or bottom surface with a side pump diode array beam and generates an output laser emanating at a location on the front surface. The design can include additional internal reflections to increase interaction with the side pump. Waste heat may be removed by mounting the crystal to a heatsink.

High-Performance Digital Imaging System for Development and Characterization of Novel Materials and Processes

DTIC Science & Technology

2006-08-08

taking into account the effects of polycrystalline microstructures, elastic anisotropy of the crystals, and material damages due to microplasticity and...anisotropic crystal elasticity, intragranular microplasticity and intergranular microfracture have been developed and implemented into the ABAQUS codes...Zhang, K. S., Wu, M. S., and Feng, R. (2005). Simulation of microplasticity -induced deformation in uniaxially strained ceramics by 3-D Voronoi

Structure-phase state and mechanical properties of surface layers in titanium nikelide single crystals after shock mechanical treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Surikova, N., E-mail: surikova@ispms.tsc.ru; Panin, V., E-mail: paninve@ispms.tsc.ru; Vlasov, I.

2015-10-27

The influence of ultrasonic shock surface treatment (USST) on refine structure and mechanical characteristics of surface layers and deformation behaviour of volume samples of TiNi(Fe, Mo) shape memory effect alloy single crystals is studied using optical and transmission electron microscope, X-ray diffraction, nanoindentation, mechanical attrition testing and experiments on uniaxial tension.

Structure-phase state and mechanical properties of surface layers in titanium nikelide single crystals after shock mechanical treatment

NASA Astrophysics Data System (ADS)

Surikova, N.; Panin, V.; Vlasov, I.; Narkevich, N.; Surikov, N.; Tolmachev, A.

2015-10-01

The influence of ultrasonic shock surface treatment (USST) on refine structure and mechanical characteristics of surface layers and deformation behaviour of volume samples of TiNi(Fe, Mo) shape memory effect alloy single crystals is studied using optical and transmission electron microscope, X-ray diffraction, nanoindentation, mechanical attrition testing and experiments on uniaxial tension.

Pressure-induced Polarization Reversal in Z-type Hexaferrite Single Crystal

NASA Astrophysics Data System (ADS)

Jeon, Byung-Gu; Chun, Sae Hwan; Kim, Kee Hoon

2012-02-01

Multiferroic materials with a gigantic magnetoelectric (ME) coupling at room temperature have been searched for applications to novel devices. Recently, large direct and converse ME effects were realized at room temperature in the so-called Z-type hexaferrite (Ba,Sr)3Co2Fe24O41 single crystals [1,2]. To obtain a new control parameter for realizing a sensitive ME tuning, we studied ME properties of the crystals under uniaxial pressure. Upon applying a tiny uniaxial pressure of about 0.6 GPa, magnetic field-driven electric polarization reversal and anomaly in a M-H loop start to appear at 10 K and gradually disappear at higher temperature above 130 K. By comparing those results with longitudinal magnetostriction at ambient pressure, we propose the pressure-dependent variations of transverse conical spin configuration as well as its domain structure under small magnetic field bias, and point out the possibility of having two different physical origins of the ME coupling in this system. [1] Y. Kitagawa et al., Nat. Mater. 9, 797 (2010) [2] S. H. Chun et al., submitted.

Multi-scale Modeling of the Impact Response of a Strain Rate Sensitive High-Manganese Austenitic Steel

NASA Astrophysics Data System (ADS)

Önal, Orkun; Ozmenci, Cemre; Canadinc, Demircan

2014-09-01

A multi-scale modeling approach was applied to predict the impact response of a strain rate sensitive high-manganese austenitic steel. The roles of texture, geometry and strain rate sensitivity were successfully taken into account all at once by coupling crystal plasticity and finite element (FE) analysis. Specifically, crystal plasticity was utilized to obtain the multi-axial flow rule at different strain rates based on the experimental deformation response under uniaxial tensile loading. The equivalent stress - equivalent strain response was then incorporated into the FE model for the sake of a more representative hardening rule under impact loading. The current results demonstrate that reliable predictions can be obtained by proper coupling of crystal plasticity and FE analysis even if the experimental flow rule of the material is acquired under uniaxial loading and at moderate strain rates that are significantly slower than those attained during impact loading. Furthermore, the current findings also demonstrate the need for an experiment-based multi-scale modeling approach for the sake of reliable predictions of the impact response.

Hot Electron Injection into Uniaxially Strained Silicon

NASA Astrophysics Data System (ADS)

Kim, Hyun Soo

In semiconductor spintronics, silicon attracts great attention due to the long electron spin lifetime. Silicon is also one of the most commonly used semiconductor in microelectronics industry. The spin relaxation process of diamond crystal structure such as silicon is dominant by Elliot-Yafet mechanism. Yafet shows that intravalley scattering process is dominant. The conduction electron spin lifetime measured by electron spin resonance measurement and electronic measurement using ballistic hot electron method well agrees with Yafet's theory. However, the recent theory predicts a strong contribution of intervalley scattering process such as f-process in silicon. The conduction band minimum is close the Brillouin zone edge, X point which causes strong spin mixing at the conduction band. A recent experiment of electric field-induced hot electron spin relaxation also shows the strong effect of f-process in silicon. In uniaxially strained silicon along crystal axis [100], the suppression of f-process is predicted which leads to enhance electron spin lifetime. By inducing a change in crystal structure due to uniaxial strain, the six fold degeneracy becomes two fold degeneracy, which is valley splitting. As the valley splitting increases, intervalley scattering is reduced. A recent theory predicts 4 times longer electron spin lifetime in 0.5% uniaxially strained silicon. In this thesis, we demonstrate ballistic hot electron injection into silicon under various uniaxial strain. Spin polarized hot electron injection under strain is experimentally one of the most challenging part to measure conduction electron spin lifetime in silicon. Hot electron injection adopts tunnel junction which is a thin oxide layer between two conducting materials. Tunnel barrier, which is an oxide layer, is only 4 ˜ 5 nm thick. Also, two conducting materials are only tens of nanometer. Therefore, under high pressure to apply 0.5% strain on silicon, thin films on silicon substrate can be easily destroyed. In order to confirm the performance of tunnel junction, we use tunnel magnetoresistance(TMR). TMR consists of two kinds of ferromagnetic materials and an oxide layer as tunnel barrier in order to measure spin valve effect. Using silicon as a collector with Schottky barrier interface between metal and silicon, ballistic hot spin polarized electron injection into silicon is demonstrated. We also observed change of coercive field and magnetoresistance due to modification of local states in ferromagnetic materials and surface states at the interface between metal and silicon due to strain.

Rapid recovery of high content phytosterols from corn silk.

PubMed

Zhang, Haiyan; Cao, Xiaowan; Liu, Yong; Shang, Fude

2017-10-18

Phytosterols have important physiological and officinal function. An efficient ultrasonic assisted extraction, purification and crystallization procedure of phytosterols was established from corn silk for the first time. The orthogonal test was applied to optimize the process parameters and a maximum phytosterols recovery as high as 10.5886 mg/g was achieved by ultrasonic treatment for 55 min with liquid-solid ratio of 12:1 at 35 °C, 220 w. The ultrasonic extraction temperature (T, °C) has the most significant effect on extraction yield of phytosterols. An orthogonal crystallization test was performed and the optimal conditions [crystallization temperature of 8 °C, time of 12 h and solid-liquid ratio of 1:1 (g/ml)] afforded maximum phytosterols purity of 92.76 ± 0.43%. An efficient extraction and crystallization procedure was established.

Electrically switchable photonic liquid crystal devices for routing of a polarized light wave

NASA Astrophysics Data System (ADS)

Rushnova, Irina I.; Melnikova, Elena A.; Tolstik, Alexei L.; Muravsky, Alexander A.

2018-04-01

The new mode of LC alignment based on photoalignment AtA-2 azo dye where the refractive interface between orthogonal orientations of the LC director exists without voltage and disappeared or changed with critical voltage has been proposed. The technology to fabricate electrically controlled liquid crystal elements for spatial separation and switching of linearly polarized light beams on the basis of the total internal reflection effect has been significantly improved. Its distinctive feature is the application of a composite alignment material comprising two sublayers of Nylon-6 and AtA-2 photoalignment azo dye offering patterned liquid crystal director orientation with high alignment quality value q = 0 . 998. The fabricated electrically controlled spatially structured liquid crystal devices enable implementation of propagation directions separation for orthogonally polarized light beams and their switching with minimal crosstalk.

Transformation of a Plane Wavefront in Hemispherical Lenses Made of Leuco-Sapphire

NASA Astrophysics Data System (ADS)

Vetrov, V. N.; Ignatenkov, B. A.; Yakobson, V. E.

2018-01-01

An algorithm for wavefront calculation of ordinary and extraordinary waves after propagation through hemispherical components made of a uniaxial crystal is developed. The influence of frequency dispersion of n o and n e , as well as change in the direction of the optic axis of the crystal, on extraordinary wavefront in hemispheres made of from leuco-sapphire and a plastically deformed analog thereof is determined.

Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe2 -xTxAs2 (T =Co,Ni )

NASA Astrophysics Data System (ADS)

Tam, David W.; Song, Yu; Man, Haoran; Cheung, Sky C.; Yin, Zhiping; Lu, Xingye; Wang, Weiyi; Frandsen, Benjamin A.; Liu, Lian; Gong, Zizhou; Ito, Takashi U.; Cai, Yipeng; Wilson, Murray N.; Guo, Shengli; Koshiishi, Keisuke; Tian, Wei; Hitti, Bassam; Ivanov, Alexandre; Zhao, Yang; Lynn, Jeffrey W.; Luke, Graeme M.; Berlijn, Tom; Maier, Thomas A.; Uemura, Yasutomo J.; Dai, Pengcheng

2017-02-01

We use neutron diffraction and muon spin relaxation to study the effect of in-plane uniaxial pressure on the antiferromagnetic (AF) orthorhombic phase in BaFe2As2 and its Co- and Ni-substituted members near optimal superconductivity. In the low-temperature AF ordered state, uniaxial pressure necessary to detwin the orthorhombic crystals also increases the magnetic ordered moment, reaching an 11% increase under 40 MPa for BaFe1.9Co0.1As2 , and a 15% increase for BaFe1.915Ni0.085As2 . We also observe an increase of the AF ordering temperature (TN) of about 0.25 K/MPa in all compounds, consistent with density functional theory calculations that reveal better Fermi surface nesting for itinerant electrons under uniaxial pressure. The doping dependence of the magnetic ordered moment is captured by combining dynamical mean field theory with density functional theory, suggesting that the pressure-induced moment increase near optimal superconductivity is closely related to quantum fluctuations and the nearby electronic nematic phase.

Modeling the polydomain-monodomain transition of liquid crystal elastomers.

PubMed

Whitmer, Jonathan K; Roberts, Tyler F; Shekhar, Raj; Abbott, Nicholas L; de Pablo, Juan J

2013-02-01

We study the mechanism of the polydomain-monodomain transition in liquid crystalline elastomers at the molecular scale. A coarse-grained model is proposed in which mesogens are described as ellipsoidal particles. Molecular dynamics simulations are used to examine the transition from a polydomain state to a monodomain state in the presence of uniaxial strain. Our model demonstrates soft elasticity, similar to that exhibited by side-chain elastomers in the literature. By analyzing the growth dynamics of nematic domains during uniaxial extension, we provide direct evidence that at a molecular level the polydomain-monodomain transition proceeds through cluster rotation and domain growth.

Periodic surface instabilities in stressed polymer solids

NASA Astrophysics Data System (ADS)

Tsukruk, Vladimir V.; Reneker, Darrell H.

1995-03-01

The surface morphology of isothermally grown polymer single crystals of polypropylene is observed by atomic force microscopy. The distinguishing features of the polymer single crystals studied are periodic undulations and transverse fractures (cracks) across the single crystal laths. Up to 20 wrinkles are observed near the edges of the cracks. The periodicity of these surface perturbations is 400+/-100 nm and the amplitude is 6+/-3 nm. The formation of the periodic modulations and transverse fractures is attributed to surface stress relief caused by the uniaxial thermal contraction of polymer solids.

Phase-matching directions, refined Sellmeier equations, and second-order nonlinear coefficient of the infrared Langatate crystal La₃Ga(5.5)Ta(0.5)O₁₄.

PubMed

Boursier, Elodie; Segonds, Patricia; Boulanger, Benoit; Félix, Corinne; Debray, Jérôme; Jegouso, David; Ménaert, Bertrand; Roshchupkin, Dmitry; Shoji, Ichiro

2014-07-01

We directly measured phase-matching directions of second harmonic, sum, and difference frequency generations in the Langatate La₃Ga(5.5)Ta(0.5)O₁₄ (LGT) uniaxial crystal. The simultaneous fit of the data enabled us to refine the Sellmeier equations of the ordinary and extraordinary principal refractive indices over the entire transparency range of the crystal, and to calculate the phase-matching curves and efficiencies of LGT for infrared optical parametric generation.

Transverse shifts of a light beam reflected from a uniaxially anisotropic chiral slab

NASA Astrophysics Data System (ADS)

Xu, Guoding; Li, Jun; Xiao, Yuting; Mao, Hongmin; Sun, Jian; Pan, Tao

2015-01-01

We study for the first time the transverse shifts of a Gaussian beam reflected from a uniaxially anisotropic chiral (UAC) slab, where the chirality appears only in one direction and the host medium is a uniaxial crystal or an electric plasma. The results indicate that the transverse shifts are closely related to the propagation behaviors of the eigenwaves in the slab. Specifically, when one or both of the eigenwaves are totally reflected at the second interface of the slab, the spatial transverse shift becomes resonances but is not enhanced; when one eigenwave is totally reflected at the first interface and the other is transmitted at the second interface, the larger and negative transverse shifts can be obtained. The propagation behaviors of the eigenwaves in the UAC slab provide more abundant information about the transverse shifts than in a single interface structure.

Resistivity in the Vicinity of a van Hove Singularity: Sr2RuO4 under Uniaxial Pressure

NASA Astrophysics Data System (ADS)

Barber, M. E.; Gibbs, A. S.; Maeno, Y.; Mackenzie, A. P.; Hicks, C. W.

2018-02-01

We report the results of a combined study of the normal-state resistivity and superconducting transition temperature Tc of the unconventional superconductor Sr2 RuO4 under uniaxial pressure. There is strong evidence that, as well as driving Tc through a maximum at ˜3.5 K , compressive strains ɛ of nearly 1% along the crystallographic [100] axis drive the γ Fermi surface sheet through a van Hove singularity, changing the temperature dependence of the resistivity from T2 above, and below the transition region to T1.5 within it. This occurs in extremely pure single-crystals in which the impurity contribution to the resistivity is <100 n Ω cm , so our study also highlights the potential of uniaxial pressure as a more general probe of this class of physics in clean systems.

Polarization of the induced THz emission of donors in silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovalevsky, K. A., E-mail: atan4@yandex.ru; Zhukavin, R. Kh.; Tsyplenkov, V. V.

2016-12-15

The polarization of the terahertz (4.9–6.4 THz) stimulated emission of Group-V (Sb, P, As, Bi) donors in single-crystal silicon under pumping (photoionization) by a CO{sub 2} laser (photon energy 117 meV), depending on the uniaxial compressive deformation of the crystal along the [100] axis, is experimentally investigated. The influence of the field direction of the pump wave on its efficiency is discussed.

Point-Wise Phase Matching for Nonlinear Frequency Generation in Dielectric Resonators

NASA Technical Reports Server (NTRS)

Yu, Nan (Inventor); Strekalov, Dmitry V. (Inventor); Lin, Guoping (Inventor)

2016-01-01

An optical resonator fabricated from a uniaxial birefringent crystal, such as beta barium borate. The crystal is cut with the optical axis not perpendicular to a face of the cut crystal. In some cases the optical axis lies in the plane of the cut crystal face. An incident (input) electromagnetic signal (which can range from the infrared through the visible to the ultraviolet) is applied to the resonator. An output signal is recovered which has a frequency that is an integer multiple of the frequency of the input signal. In some cases a prism is used to evanescently couple the input and the output signals to the resonator.

Raman scattering in crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Edwards, D.F.

1988-09-30

A tutorial presentation is given of Raman scattering in crystals. The physical concepts are emphasized rather than the detailed mathematical formalism. Starting with an introduction to the concepts of phonons and conservation laws, the effects of photon-phonon interactions are presented. This interaction concept is shown for a simple cubic crystal and is extended to a uniaxial crystal. The correlation table method is used for determining the number and symmetry of the Raman active modes. Finally, examples are given to illustrate the relative ease of using this group theoretical method and the predictions are compared with measured Raman spectra. 37 refs.,more » 17 figs., 6 tabs.« less

Structural modeling of carbonaceous mesophase amphotropic mixtures under uniaxial extensional flow.

PubMed

Golmohammadi, Mojdeh; Rey, Alejandro D

2010-07-21

The extended Maier-Saupe model for binary mixtures of model carbonaceous mesophases (uniaxial discotic nematogens) under externally imposed flow, formulated in previous studies [M. Golmohammadi and A. D. Rey, Liquid Crystals 36, 75 (2009); M. Golmohammadi and A. D. Rey, Entropy 10, 183 (2008)], is used to characterize the effect of uniaxial extensional flow and concentration on phase behavior and structure of these mesogenic blends. The generic thermorheological phase diagram of the single-phase binary mixture, given in terms of temperature (T) and Deborah (De) number, shows the existence of four T-De transition lines that define regions that correspond to the following quadrupolar tensor order parameter structures: (i) oblate (perpendicular, parallel), (ii) prolate (perpendicular, parallel), (iii) scalene O(perpendicular, parallel), and (iv) scalene P(perpendicular, parallel), where the symbols (perpendicular, parallel) indicate alignment of the tensor order ellipsoid with respect to the extension axis. It is found that with increasing T the dominant component of the mixture exhibits weak deviations from the well-known pure species response to uniaxial extensional flow (uniaxial perpendicular nematic-->biaxial nematic-->uniaxial parallel paranematic). In contrast, the slaved component shows a strong deviation from the pure species response. This deviation is dictated by the asymmetric viscoelastic coupling effects emanating from the dominant component. Changes in conformation (oblate <==> prolate) and orientation (perpendicular <==> parallel) are effected through changes in pairs of eigenvalues of the quadrupolar tensor order parameter. The complexity of the structural sensitivity to temperature and extensional flow is a reflection of the dual lyotropic/thermotropic nature (amphotropic nature) of the mixture and their cooperation/competition. The analysis demonstrates that the simple structures (biaxial nematic and uniaxial paranematic) observed in pure discotic mesogens under uniaxial extensional flow are significantly enriched by the interaction of the lyotropic/thermotropic competition with the binary molecular architectures and with the quadrupolar nature of the flow.

Uniaxial stress induced symmetry breaking for muon sites in Fe

NASA Technical Reports Server (NTRS)

Kossler, W. J.; Namkung, M.; Hitti, B.; Li, Y.; Kempton, J.; Stronach, C. E.; Goode, L. R., Jr.; Lankford, W. F.; Patterson, B. D.; Kuendig, W.

1984-01-01

Uniaxial stress was used on Fe single crystals to induce muon precession frequency shifts. The frequency shift for a nominally pure Fe sample at 302K was -0.34 + or - .023 MHz per 100 microstrain along the 100 magnetization axis. This corresponds to a change of magnetic field at the muon of 25.1 + to 1.6G/100 magnetic moment. For an Fe (3wt%Si) single crystal the shifts were -0.348 + or - .008 MHz/100 magnetic moment. The agreement between the shifts for Fe and Fe(3wt%Si) shows the effect to be intrinsic to iron and not strongly impurity sensitive. These shifts and their temperature dependence (1/T) are dominated by the effect of strain inducted population shifts between crystallographically equivalent, but mgnetically inequivalent sites. Their magnitudes are in good agreement ith previous theoretical predictions and by previous extrapolation from calculations on Nb and V especially if both 4T(0) and 1T sites contribute comparably.

Assessment of structural, thermal, and mechanical properties of portlandite through molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hajilar, Shahin, E-mail: shajilar@iastate.edu; Shafei, Behrouz, E-mail: shafei@iastate.edu

The structural, thermal, and mechanical properties of portlandite, the primary solid phase of ordinary hydrated cement paste, are investigated using the molecular dynamics method. To understand the effects of temperature on the structural properties of portlandite, the coefficients of thermal expansion of portlandite are determined in the current study and validated with what reported from the experimental tests. The atomic structure of portlandite equilibrated at various temperatures is then subjected to uniaxial tensile strains in the three orthogonal directions and the stress-strain curves are developed. Based on the obtained results, the effect of the direction of straining on the mechanicalmore » properties of portlandite is investigated in detail. Structural damage analysis is performed to reveal the failure mechanisms in different directions. The energies of the fractured surfaces are calculated in different directions and compared to those of the ideal surfaces available in the literature. The key mechanical properties, including tensile strength, Young's modulus, and fracture strain, are extracted from the stress-strain curves. The sensitivity of the obtained mechanical properties to temperature and strain rate is then explored in a systematic way. This leads to valuable information on how the structural and mechanical properties of portlandite are affected under various exposure conditions and loading rates. - Graphical abstract: Fracture mechanism of portlandite under uniaxial strain in the z-direction. - Highlights: • The structural, thermal, and mechanical properties of portlandite are investigated. • The coefficients of thermal expansion are determined. • The stress-strain relationships are studied in three orthogonal directions. • The effects of temperature and strain rate on mechanical properties are examined. • The plastic energy required for fracture in the crystalline structure is reported.« less

Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe 2 - x T x As 2 ( T = Co , Ni )

DOE PAGES

Tam, David W.; Song, Yu; Man, Haoran; ...

2017-02-17

In this paper, we use neutron diffraction and muon spin relaxation to study the effect of in-plane uniaxial pressure on the antiferromagnetic (AF) orthorhombic phase in BaFe 2As 2 and its Co- and Ni-substituted members near optimal superconductivity. In the low-temperature AF ordered state, uniaxial pressure necessary to detwin the orthorhombic crystals also increases the magnetic ordered moment, reaching an 11% increase under 40 MPa for BaFe 1.9Co 0.1As 2, and a 15% increase for BaFe 1.915Ni 0.085As 2. We also observe an increase of the AF ordering temperature (T N) of about 0.25 K/MPa in all compounds, consistent withmore » density functional theory calculations that reveal better Fermi surface nesting for itinerant electrons under uniaxial pressure. Finally, the doping dependence of the magnetic ordered moment is captured by combining dynamical mean field theory with density functional theory, suggesting that the pressure-induced moment increase near optimal superconductivity is closely related to quantum fluctuations and the nearby electronic nematic phase.« less

Method for solid state crystal growth

DOEpatents

Nolas, George S.; Beekman, Matthew K.

2013-04-09

A novel method for high quality crystal growth of intermetallic clathrates is presented. The synthesis of high quality pure phase crystals has been complicated by the simultaneous formation of both clathrate type-I and clathrate type-II structures. It was found that selective, phase pure, single-crystal growth of type-I and type-II clathrates can be achieved by maintaining sufficient partial pressure of a chemical constituent during slow, controlled deprivation of the chemical constituent from the primary reactant. The chemical constituent is slowly removed from the primary reactant by the reaction of the chemical constituent vapor with a secondary reactant, spatially separated from the primary reactant, in a closed volume under uniaxial pressure and heat to form the single phase pure crystals.

Realization of the revival of silenced echo (ROSE) quantum memory scheme in orthogonal geometry

NASA Astrophysics Data System (ADS)

Minnegaliev, M. M.; Gerasimov, K. I.; Urmancheev, R. V.; Moiseev, S. A.; Chanelière, T.; Louchet-Chauvet, A.

2018-02-01

We demonstrated quantum memory scheme on revival of silenced echo in orthogonal geometry in Tm3+: Y3Al5O12 crystal. The retrieval efficiency of ˜14% was demonstrated with the 36 µs storage time. In this scheme for the first time we also implemented a suppression of the revived echo signal by applying an external electric field and the echo signal has been recovered on demand if we then applied a second electric pulse with opposite polarity. This technique opens the possibilities for realizing addressing in multi-qubit quantum memory in Tm3+: Y3Al5O12 crystal.

Cavity enhanced interference of orthogonal modes in a birefringent medium

NASA Astrophysics Data System (ADS)

Kolluru, Kiran; Saha, Sudipta; Gupta, S. Dutta

2018-03-01

Interference of orthogonal modes in a birefringent crystal mediated by a rotator is known to lead to interesting physical effects (Solli et al., 2003). In this paper we show that additional feedback offered by a Fabry-Perot cavity (containing the birefringent crystal and the rotator) can lead to a novel strong interaction regime. Usual signatures of the strong interaction regime like the normal mode splitting and avoided crossings, sensitive to the rotator orientation, are reported. A high finesse cavity is shown to offer an optical setup for measuring small angles. The results are based on direct calculations of the cavity transmissions along with an analysis of its dispersion relation.

σ-Hole and π-Hole Synthon Mimicry in Third-Generation Crystal Engineering: Design of Elastic Crystals.

PubMed

Saha, Subhankar; Desiraju, Gautam R

2017-04-06

Designing elastic crystals is a difficult task and is of relevance in potential applications from materials to biology. Here, multi-step crystal engineering based on σ-hole and π-hole synthon mimicry is performed to obtain binary organic molecular crystals with a high degree of flexibility. A structural model is proposed based only on σ-hole-oriented type-II halogen bonds with their characteristic orthogonal geometry. These σ-hole contacts are then partly replaced by chemically and geometrically similar π-hole synthons to obtain new crystals in the second step. In the final step, all the σ-hole interactions are replaced with π-hole interactions and elastic crystals of non-halogenated compounds are obtained. All the crystals obtained according to our protocols are found to be elastic. When crystals that do not conform to the desired structure type appeared, they were found to be brittle. This underlines the role of orthogonal-type interactions, whether they are of the σ-hole or π-hole type, in achieving elasticity. This is the first report in which π-hole interactions are used for property engineering. This example may illustrate a new generation of crystal engineering in which a particular property is associated more with topological rather than chemical attributes, although the significance of the latter cannot be completely excluded. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bulk growth of <001> organic nonlinear optical (NLO) L-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP) single crystals by SR method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandian, Muthu Senthil, E-mail: senthilpandianm@ssn.edu.in; Sivasubramani, V.; Ramasamy, P.

2015-06-24

A transparent uniaxial L-arginine 4-nitrophenolate 4-nitrophenol dehydrate (LAPP) single crystal having dimension of 20 mm diameter and 45 mm length was grown by Sankaranarayanan-Ramasamy (SR) method with a growth rate of 1 mm per day. Using an identical solution the conventional crystal grown to a dimension of 8×5×5 mm{sup 3} was obtained over a period of 30 days. The crystal structure has been confirmed by single crystal X-ray diffraction measurement. The crystalline perfection of LAPP crystals grown by slow evaporation solution technique (SEST) and SR method were characterized using Vickers microhardness, UV-Vis NIR, chemical etching, dark and photo current measurements. The above study indicatesmore » that the crystal quality of the Sankaranarayanan-Ramasamy (SR) method grown LAPP is good compared to the conventional method grown crystal.« less

Fatigue Failure of Space Shuttle Main Engine Turbine Blades

NASA Technical Reports Server (NTRS)

Swanson, Gregrory R.; Arakere, Nagaraj K.

2000-01-01

Experimental validation of finite element modeling of single crystal turbine blades is presented. Experimental results from uniaxial high cycle fatigue (HCF) test specimens and full scale Space Shuttle Main Engine test firings with the High Pressure Fuel Turbopump Alternate Turbopump (HPFTP/AT) provide the data used for the validation. The conclusions show the significant contribution of the crystal orientation within the blade on the resulting life of the component, that the analysis can predict this variation, and that experimental testing demonstrates it.

Control of Grain Boundaries and Defects in Nano-Engineered Transparent Scintillator Ceramics

DTIC Science & Technology

2013-03-01

cost  materials   for   such  detector   systems   is  a   primary... costs  over  single  crystal  material.  This  study  has  also  shown  the  potential  for   using  hot  uniaxial...performance  compared  with  single  crystals   and   at   lower   cost .   In   addition   to   SrI2,   other  

Optical Anisotropy of Photonic Crystals of Cubic Symmetry Induced by Multiple Diffraction of Light

NASA Astrophysics Data System (ADS)

Ukleev, T. A.; Shevchenko, N. N.; Iurasova, D. I.; Sel'kin, A. V.

2018-05-01

The optical spectra of Bragg reflection from opal-like photonic crystals under conditions of the resonant enhancement of the multiple diffraction of light have been studied experimentally and theoretically using the photonic crystal structures prepared of monodisperse polystyrene globules. It is shown that the reflection signal registered in mutually orthogonal configurations of the polarizer and analyzer is related to the intrinsic optical anisotropy of the crystals and is a specific manifestation of the multiple Bragg diffraction in three-dimensional photonic crystals.

Heterojunction-induced magnetic anisotropy and magnetization reversal of Ni wires on LiNbO3 substrate

NASA Astrophysics Data System (ADS)

Yamaguchi, Akinobu; Ohkochi, Takuo; Yasui, Akira; Kinoshita, Toyohiko; Yamada, Keisuke

2018-05-01

We report magnetic domain formation control within micro-scale polycrystalline Ni wires on a single-crystal Y-cut 128° LiNbO3 substrate. X-ray magnetic circular dichroism photoemission electron microscopy (XCDM-PEEM), micromagnetic simulations, and magnetoresistance (MR) measurements allowed us to estimate the uniaxial magnetic anisotropy induced by the magnetoelastic effect that originated at the interface between each Ni layer and the LiNbO3 substrate. Comparison of the XMCD-PEEM and MR measurement results shows that the competition between the shape magnetic anisotropy and the uniaxial magnetic anisotropy parallel to the orientation flat (OF) direction of the substrate leads to variations in both the magnetization order and the magnetization reversal process. The uniaxial magnetic anisotropy is estimated to be approximately 3.3 kJ/m3. This heterojunction structure composed of ferromagnetic and ferroelectric layers thus offers alternative ways to produce artificial functional multiferroic materials and devices.

Hydrocode and Molecular Dynamics modelling of uniaxial shock wave experiments on Silicon

NASA Astrophysics Data System (ADS)

Stubley, Paul; McGonegle, David; Patel, Shamim; Suggit, Matthew; Wark, Justin; Higginbotham, Andrew; Comley, Andrew; Foster, John; Rothman, Steve; Eggert, Jon; Kalantar, Dan; Smith, Ray

2015-06-01

Recent experiments have provided further evidence that the response of silicon to shock compression has anomalous properties, not described by the usual two-wave elastic-plastic response. A recent experimental campaign on the Orion laser in particular has indicated a complex multi-wave response. While Molecular Dynamics (MD) simulations can offer a detailed insight into the response of crystals to uniaxial compression, they are extremely computationally expensive. For this reason, we are adapting a simple quasi-2D hydrodynamics code to capture phase change under uniaxial compression, and the intervening mixed phase region, keeping track of the stresses and strains in each of the phases. This strain information is of such importance because a large number of shock experiments use diffraction as a key diagnostic, and these diffraction patterns depend solely on the elastic strains in the sample. We present here a comparison of the new hydrodynamics code with MD simulations, and show that the simulated diffraction taken from the code agrees qualitatively with measured diffraction from our recent Orion campaign.

Molecular reorientation of a nematic liquid crystal by thermal expansion

PubMed Central

Kim, Young-Ki; Senyuk, Bohdan; Lavrentovich, Oleg D.

2012-01-01

A unique feature of nematic liquid crystals is orientational order of molecules that can be controlled by electromagnetic fields, surface modifications and pressure gradients. Here we demonstrate a new effect in which the orientation of nematic liquid crystal molecules is altered by thermal expansion. Thermal expansion (or contraction) causes the nematic liquid crystal to flow; the flow imposes a realigning torque on the nematic liquid crystal molecules and the optic axis. The optical and mechanical responses activated by a simple temperature change can be used in sensing, photonics, microfluidic, optofluidic and lab-on-a-chip applications as they do not require externally imposed gradients of temperature, pressure, surface realignment, nor electromagnetic fields. The effect has important ramifications for the current search of the biaxial nematic phase as the optical features of thermally induced structural changes in the uniaxial nematic liquid crystal mimic the features expected of the biaxial nematic liquid crystal. PMID:23072803

Multi-channel unidirectional transmission of phononic crystal heterojunctions

NASA Astrophysics Data System (ADS)

Xu, Zhenlong; Tong, Jie; Wu, Fugen

2018-02-01

Two square steel columns are arranged in air to form two-dimensional square lattice phononic crystals (PNCs). Two PNCs can be combined into a non-orthogonal 45∘ heterojunction when the difference in the directional band gaps of the two PNC types is utilized. The finite element method is used to calculate the acoustic band structure, the heterogeneous junction transmission characteristics, acoustic field distribution, and many others. Results show that a non-orthogonal PNC heterojunction can produce a multi-channel unidirectional transmission of acoustic waves. With the square scatterer rotated, the heterojunction can select a frequency band for unidirectional transmission performance. This capability is particularly useful for constructing acoustic diodes with wide-bands and high-efficiency unidirectional transmission characteristics.

Determination of piezo-optic coefficients of crystals by means of four-point bending.

PubMed

Krupych, Oleg; Savaryn, Viktoriya; Krupych, Andriy; Klymiv, Ivan; Vlokh, Rostyslav

2013-06-10

A technique developed recently for determining piezo-optic coefficients (POCs) of isotropic optical media, which represents a combination of digital imaging laser interferometry and a classical four-point bending method, is generalized and applied to a single-crystalline anisotropic material. The peculiarities of measuring procedures and data processing for the case of optically uniaxial crystals are described in detail. The capabilities of the technique are tested on the example of canonical nonlinear optical crystal LiNbO3. The high precision achieved in determination of the POCs for isotropic and anisotropic materials testifies that the technique should be both versatile and reliable.

Resonant stimulation of Raman scattering from single-crystal thiophene/phenylene co-oligomers

NASA Astrophysics Data System (ADS)

Yanagi, Hisao; Marutani, Yusuke; Matsuoka, Naoki; Hiramatsu, Toru; Ishizumi, Atsushi; Sasaki, Fumio; Hotta, Shu

2013-12-01

Amplified Raman scattering was observed from single crystals of thiophene/phenylene co-oligomers (TPCOs). Under ns-pulsed excitation, the TPCO crystals exhibited amplified spontaneous emission (ASE) at resonant absorption wavelengths. With increasing excitation wavelength to the 0-0 absorption edge, the stimulated resonant Raman peaks appeared both in the 0-1 and 0-2 ASE band regions. When the excitation wavelength coincided with the 0-1 ASE band energy, the Raman peaks selectively appeared in the 0-2 ASE band. Such unusual enhancement of the 0-2 Raman scattering was ascribed to resonant stimulation via vibronic coupling with electronic transitions in the uniaxially oriented TPCO molecules.

Exploiting pattern transformation to tune phononic band gaps in a two-dimensional granular crystal.

PubMed

Göncü, F; Luding, S; Bertoldi, K

2012-06-01

The band structure of a two-dimensional granular crystal composed of silicone rubber and polytetrafluoroethylene (PTFE) cylinders is investigated numerically. This system was previously shown to undergo a pattern transformation with uniaxial compression by Göncü et al. [Soft Matter 7, 2321 (2011)]. The dispersion relations of the crystal are computed at different levels of deformation to demonstrate the tunability of the band structure, which is strongly affected by the pattern transformation that induces new band gaps. Replacement of PTFE particles with rubber ones reveals that the change of the band structure is essentially governed by pattern transformation rather than particles' mechanical properties.

Generation of orthogonally polarized self-mode-locked Nd:YAG lasers with tunable beat frequencies from the thermally induced birefringence.

PubMed

Sung, C L; Cheng, H P; Lee, C Y; Cho, C Y; Liang, H C; Chen, Y F

2016-04-15

The simultaneous self-mode-locking of two orthogonally polarized states in a Nd:YAG laser is demonstrated by using a short linear cavity. A total output power of 3.8 W can be obtained at an incident pump power of 8.2 W. The beat frequency Δfc between two orthogonally polarized mode-locked components is observed and measured precisely. It is found that the beat frequency increases linearly with an increase in the absorbed pump power. The origin of the beat frequency can be utterly manifested by considering the thermally induced birefringence in the Nd:YAG crystal. The present result offers a promising approach to generate orthogonally polarized mode-locked lasers with tunable beat frequency.

Electro-optic high voltage sensor

DOEpatents

Davidson, James R.; Seifert, Gary D.

2003-09-16

A small sized electro-optic voltage sensor capable of accurate measurement of high voltages without contact with a conductor or voltage source is provided. When placed in the presence of an electric field, the sensor receives an input beam of electromagnetic radiation. A polarization beam displacer separates the input beam into two beams with orthogonal linear polarizations and causes one linearly polarized beam to impinge a crystal at a desired angle independent of temperature. The Pockels effect elliptically polarizes the beam as it travels through the crystal. A reflector redirects the beam back through the crystal and the beam displacer. On the return path, the polarization beam displacer separates the elliptically polarized beam into two output beams of orthogonal linear polarization. The system may include a detector for converting the output beams into electrical signals and a signal processor for determining the voltage based on an analysis of the output beams.

High-mobility strained organic semiconductors (Conference Presentation)

NASA Astrophysics Data System (ADS)

Takeya, Jun; Matsui, H.; Kubo, T.; Hausermann, Roger

2016-11-01

Small molecular organic semiconductor crystals form interesting electronic systems of periodically arranged "charge clouds" whose mutual electronic coupling determines whether or not electronic states can be coherent over fluctuating molecules. This presentation focuses on two methods to reduce molecular fluctuation, which strongly restricts mobility of highly mobile charge in single-crystal organic transistors. The first example is to apply external hydrostatic pressure. Using Hall-effect measurement for pentacene FETs, which tells us the extent of the electronic coherence, we found a crossover from hopping-like transport of nearly localized charge to band transport of delocalized charge with full coherence. As the result of temperature dependence measurement, it turned out that reduced molecular fluctuation is mainly responsible for the crossover. The second is to apply uniaxial strain to single-crystal organic FETs. We applied stain by bending thin films of newly synthesized decyldinaphthobenzodithiophene (C10-DNBDT) on plastic substrate so that 3% strain is uniaxially applied. As the result, the room-temperature mobility increased by the factor of 1.7. In-depth analysis using X-ray diffraction (XRD) measurements and density functional theory (DFT) calculations reveal the origin to be the suppression of the thermal fluctuation of the individual molecules, which is confirmed by temperature dependent measurements. Our findings show that compressing the crystal structure directly restricts the vibration of the molecules, thus suppressing dynamic disorder, a unique mechanism in organic semiconductors. Since strain can easily be induced during the fabrication process, these findings can directly be exploited to build high performance organic devices.

Propagation properties of chirped Airy vortex beams with x-polarization through uniaxial crystals

NASA Astrophysics Data System (ADS)

Wang, Linyi; Zhang, Jianbin; Feng, Liyan; Pang, Zihao; Zhong, Tianfen; Deng, Dongmei

2018-05-01

Not Available Project supported by the National Natural Science Foundation of China (Grant Nos. 11775083 and 11374108), the National Training Program of Innovation and Entrepreneurship for Undergraduates, China, and Special Funds for the Cultivation of Guangdong College Students’ Scientific and Technological Innovation, China (Grant No. pdjh2017b0137).

Modeling Finite Deformations in Trigonal Ceramic Crystals with Lattice Defects

DTIC Science & Technology

2010-02-08

International Journal of Plasticity 26 (2010) 1357–1386 1385Farber, Y.A., Yoon, S.Y., Lagerlof, K.P.D., Heuer, A.H., 1993. Microplasticity during high... microplasticity -induced deformation in uniaxially strained ceramics by 3-D Voronoi polycrystal modeling. Int. J. Plast. 21, 801–834. Zhang, C., Kalia, R.K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kasemer, Matthew; Quey, Romain; Dawson, Paul

Discussed is a computational study of the influence of the microstructure’s geometric morphology on the yield strength and ductility of Ti-6Al-4V. Uniaxial tension tests were conducted on physical specimens to determine the macroscopic yield strength and ductility of two microstructural variations (mill annealed and β annealed) to establish comparisons of macroscopic properties. A multi-experimental approach was utilized to gather two dimensional and three dimensional data, which were used to inform the construction of representative β annealed polycrystals. A highly parallelized crystal plasticity finite element framework was employed to model the deformation response of the generated polycrystals subjected to uniaxial tension.more » To gauge the macroscopic response’s sensitivity to the morphology of the geometry, the key geometrical features - namely the number of high temperature β phase grains, α phase colonies, and size of remnant secondary β phase lamellae - were altered systematically in a suite of simulations. Both single phase and dual phase aggregates were studied. Presented are the calculated yield strengths and ductilities, and the resulting trends as functions of geometric parameters are examined in light of the heterogeneity in deformation at the crystal scale.« less

Phase field crystal simulation of stress induced localized solid-state amorphization in nanocrystalline materials

NASA Astrophysics Data System (ADS)

Xi, Wen; Song, Xiaoqing; Hu, Shi; Chen, Zheng

2017-11-01

In this work, the phase field crystal (PFC) method is used to study the localized solid-state amorphization (SSA) and its dynamic transformation process in polycrystalline materials under the uniaxial tensile deformation with different factors. The impacts of these factors, including strain rates, temperatures and grain sizes, are analyzed. Kinetically, the ultra-high strain rate causes the lattice to be seriously distorted and the grain to gradually collapse, so the dislocation density rises remarkably. Therefore, localized SSA occurs. Thermodynamically, as high temperature increases the activation energy, the atoms are active and prefer to leave the original position, which induce atom rearrangement. Furthermore, small grain size increases the percentage of grain boundary and the interface free energy of the system. As a result, Helmholtz free energy increases. The dislocations and Helmholtz free energy act as the seed and driving force for the process of the localized SSA. Also, the critical diffusion-time step and the percentage of amorphous region areas are calculated. Through this work, the PFC method is proved to be an effective means to study localized SSA under uniaxial tensile deformation.

Different Variations of Néel Temperature TN and Kondo Temperature TK in the Alloy System Ce(Ru1-xOsx)2Al10 under Uniaxial Pressure

NASA Astrophysics Data System (ADS)

Takeuchi, Takashi; Hayashi, Kyosuke; Umeo, Kazunori; Takabatake, Toshiro

2018-05-01

We report magnetic, transport, and specific-heat measurements for single crystals of the antiferromagnetic (AFM) Kondo semiconductor alloy series Ce(Ru1-xOsx)2Al10 (0 ≤ x ≤ 1), which crystallize into an orthorhombic structure. The specific-heat and resistivity data show that the isoelectronic substitution does not damage the hybridization gap or the AFM transition. The Kondo temperature TK increases linearly with x, whereas the Néel temperature TN exhibits a maximum value of 29.2 K for x = 0.71. Under increasing uniaxial pressure P || a, TN increases for x = 0 but decreases for x = 1, while TK increases in the entire range of x. Under P || b, in contrast, TN increases steadily in the whole range of x while TK remains unchanged for each x. The strongly anisotropic change in TN indicates the presence of another mechanism to enhance TN in this system in addition to the anisotropic hybridization of the 4f state with conduction bands.

Phase field crystal simulation of stress induced localized solid-state amorphization in nanocrystalline materials.

PubMed

Xi, Wen; Song, Xiaoqing; Hu, Shi; Chen, Zheng

2017-11-29

In this work, the phase field crystal (PFC) method is used to study the localized solid-state amorphization (SSA) and its dynamic transformation process in polycrystalline materials under the uniaxial tensile deformation with different factors. The impacts of these factors, including strain rates, temperatures and grain sizes, are analyzed. Kinetically, the ultra-high strain rate causes the lattice to be seriously distorted and the grain to gradually collapse, so the dislocation density rises remarkably. Therefore, localized SSA occurs. Thermodynamically, as high temperature increases the activation energy, the atoms are active and prefer to leave the original position, which induce atom rearrangement. Furthermore, small grain size increases the percentage of grain boundary and the interface free energy of the system. As a result, Helmholtz free energy increases. The dislocations and Helmholtz free energy act as the seed and driving force for the process of the localized SSA. Also, the critical diffusion-time step and the percentage of amorphous region areas are calculated. Through this work, the PFC method is proved to be an effective means to study localized SSA under uniaxial tensile deformation.

Highly Polarized Fluorescent Illumination Using Liquid Crystal Phase.

PubMed

Gim, Min-Jun; Turlapati, Srikanth; Debnath, Somen; Rao, Nandiraju V S; Yoon, Dong Ki

2016-02-10

Liquid crystal (LC) materials are currently the dominant electronic materials in display technology because of the ease of control of molecular orientation using an electric field. However, this technology requires the fabrication of two polarizers to create operational displays, reducing light transmission efficiency below 10%. It is therefore desirable to develop new technologies to enhance the light efficiency while maintaining or improving other properties such as the modulation speed of the molecular orientation. Here we report a uniaxial-oriented B7 smectic liquid crystalline film, using fluorescent bent-core LC molecules, a chemically modified substrate, and an in-plane electric field. A LC droplet under homeotropic boundary conditions of air/LC as well as LC/substrate exhibits large focal conic like optical textures. The in-plane electric field induced uniaxial orientation of the LC molecules, in which molecular polar directors are aligned in the direction of the electric field. This highly oriented LC film exhibits linearly polarized luminescence and microsecond time-scale modulation characteristics. The resultant device is both cheap and easy to fabricate and thus has great potential for electro-optic applications, including LC displays, bioimaging systems, and optical communications.

Electrical resistivity of CeNiSn under uniaxial and hydrostatic pressures

NASA Astrophysics Data System (ADS)

Echizen, Y.; Umeo, K.; Igaue, T.; Takabatake, T.

2002-05-01

We present measurements of the electrical resistivity ρ(T) on high-quality single-crystalline CeNiSn under both hydrostatic pressure up to 1 GPa and uniaxial pressure up to 0.25 GPa. At ambient pressure, ρ(T) along the orthorhombic a-axis (b-axis) shows two maxima at TL = 12 K (14 K) and TH = 74 K (40 K), respectively, which arise from the Kondo scattering of conduction electrons by the crystal-field ground state and excited states. With increasing hydrostatic pressure, both TL and TH increase linearly, and for P≥0.8 GPa, the anisotropy in ρ(T) for I∥a and I∥b almost vanishes as a result of increased hybridization between the 4f electrons and the conduction electrons. Under P∥a, both TL and TH in ρ(I∥b) increase similarly to under hydrostatic pressure. Under P∥c, however, the depression of TL in ρ(I∥a) and ρ(I∥b) suggests that the c-f hybridization in the crystal-field ground state is weakened in the a-b plane of CeNiSn.

Uniaxial ferromagnetism of local uranium moments in hexagonal UBeGe

NASA Astrophysics Data System (ADS)

Gumeniuk, Roman; Yaresko, Alexander N.; Schnelle, Walter; Nicklas, Michael; Kvashnina, Kristina O.; Hennig, Christoph; Grin, Yuri; Leithe-Jasper, Andreas

2018-05-01

The new intermetallic uranium beryllium germanide UBeGe and its thorium analogon ThBeGe crystallize with the hexagonal ZrBeSi type of structure. Studies of magnetic, thermal, and transport properties were performed on polycrystalline samples between 1.8 and 750K. UBeGe is a uniaxial ferromagnet and there are indications for two magnetic transitions at TC(1 )≈160 K and TC(2 )≈150 K . The high paramagnetic effective moment μeff≈3.1 μB , x-ray absorption near-edge spectroscopy (XANES, 17-300 K), as well as theoretical DFT calculations indicate localized U 5 f2 states in UBeGe. ThBeGe is a diamagnetic metallic material with low density of states at the Fermi level.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Time-domain polarisation scrambler on one bulk LiNbO3 crystal with quadrupole electrodes

NASA Astrophysics Data System (ADS)

Davydov, B. L.; Mironov, V. Yu

2010-02-01

As distinct from the classic Billings depolariser, a simple time-domain polarisation scrambler can be made on one crystal possessing a threefold axis among its symmetry elements and displaying a linear electro-optical effect (Pockels effect). We demonstrate a polarisation scrambler on a LiNbO3 uniaxial crystal with two pairs of electrodes to which two harmonic voltages identical in amplitude and differing in phase by 90° are applied. The residual degree of polarisation of the depolarised light, quantified by the polarisation extinction ratio, is less than 0.1 dB. Tolerances on the crystal orientation and the phase difference between the control voltages are estimated. The quality of the crystal is shown to be critical to the performance of the scrambler.

Buckling-Induced Kirigami

NASA Astrophysics Data System (ADS)

Rafsanjani, Ahmad; Bertoldi, Katia

2017-02-01

We investigate the mechanical response of thin sheets perforated with a square array of mutually orthogonal cuts, which leaves a network of squares connected by small ligaments. Our combined analytical, experimental and numerical results indicate that under uniaxial tension the ligaments buckle out of plane, inducing the formation of 3D patterns whose morphology is controlled by the load direction. We also find that by largely stretching the buckled perforated sheets, plastic strains develop in the ligaments. This gives rise to the formation of kirigami sheets comprising periodic distribution of cuts and permanent folds. As such, the proposed buckling-induced pop-up strategy points to a simple route for manufacturing complex morphable structures out of flat perforated sheets.

A finite element beam propagation method for simulation of liquid crystal devices.

PubMed

Vanbrabant, Pieter J M; Beeckman, Jeroen; Neyts, Kristiaan; James, Richard; Fernandez, F Anibal

2009-06-22

An efficient full-vectorial finite element beam propagation method is presented that uses higher order vector elements to calculate the wide angle propagation of an optical field through inhomogeneous, anisotropic optical materials such as liquid crystals. The full dielectric permittivity tensor is considered in solving Maxwell's equations. The wide applicability of the method is illustrated with different examples: the propagation of a laser beam in a uniaxial medium, the tunability of a directional coupler based on liquid crystals and the near-field diffraction of a plane wave in a structure containing micrometer scale variations in the transverse refractive index, similar to the pixels of a spatial light modulator.

Influence of bending strains on radio frequency characteristics of flexible microwave switches using single-crystal silicon nanomembranes on plastic substrate

NASA Astrophysics Data System (ADS)

Qin, Guoxuan; Yuan, Hao-Chih; Celler, George K.; Ma, Jianguo; Ma, Zhenqiang

2011-10-01

This letter presents radio frequency (RF) characterization of flexible microwave switches using single-crystal silicon nanomembranes (SiNMs) on plastic substrate under various uniaxial mechanical tensile bending strains. The flexible switches shows significant/negligible performance enhancement on strains under on/off states from dc to 10 GHz. Furthermore, an RF/microwave strain equivalent circuit model is developed and reveals the most influential factors, and un-proportional device parameters change with bending strains. The study demonstrates that flexible microwave single-crystal SiNM switches, as a simple circuit example towards the goal of flexible monolithic microwave integrated circuits, can be properly operated and modeled under mechanical bending conditions.

Bessel beam transformation in c-cuts of uniaxial crystals by varying the source wavelength

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paranin, V. D.

Transformation of Bessel beam of a zero order to Bessel beam of the second order in c-cut of CaCO{sub 3} crystal is experimentally investigated. Possibility of output beam control at changing of wavelength and using of a diffraction axicon is shown. Full transformation of beams at changing of wavelength Δλ=1.5 nanometers is received at initial wavelength λ=637.5 nanometers for a crystal of CaCO{sub 3} with 15 mm long and a diffraction axicon with period of 2 microns. The theoretical value of necessary wavelength changing is Δλ=1.7 nanometers that is according with experimental results.

Parametric Raman anti-Stokes laser at 503 nm with phase-matched collinear beam interaction of orthogonally polarized Raman components in calcite under 532 nm 20 ps laser pumping

NASA Astrophysics Data System (ADS)

Smetanin, Sergei; Jelínek, Michal; Kubeček, Václav

2017-05-01

Lasers based on stimulated-Raman-scattering process can be used for the frequency-conversion to the wavelengths that are not readily available from solid-state lasers. Parametric Raman lasers allow generation of not only Stokes, but also anti-Stokes components. However, practically all the known crystalline parametric Raman anti-Stokes lasers have very low conversion efficiencies of about 1 % at theoretically predicted values of up to 40 % because of relatively narrow angular tolerance of phase matching in comparison with angular divergence of the interacting beams. In our investigation, to widen the angular tolerance of four-wave mixing and to obtain high conversion efficiency into the antiStokes wave we propose and study a new scheme of the parametric Raman anti-Stokes laser at 503 nm with phasematched collinear beam interaction of orthogonally polarized Raman components in calcite under 532 nm 20 ps laser pumping. We use only one 532-nm laser source to pump the Raman-active calcite crystal oriented at the phase matched angle for orthogonally polarized Raman components four-wave mixing. Additionally, we split the 532-nm laser radiation into the orthogonally polarized components entering to the Raman-active calcite crystal at the certain incidence angles to fulfill the tangential phase matching compensating walk-off of extraordinary waves for collinear beam interaction in the crystal with the widest angular tolerance of four-wave mixing. For the first time the highest 503-nm anti-Stokes conversion efficiency of 30 % close to the theoretical limit of about 40 % at overall optical efficiency of the parametric Raman anti-Stokes generation of up to 3.5 % in calcite is obtained due to realization of tangential phase matching insensitive to the angular mismatch.

Tunable electronic lens using a gradient polymer network liquid crystal

NASA Astrophysics Data System (ADS)

Ren, Hongwen; Wu, Shin-Tson

2003-01-01

Tunable electronic lenses using gradient polymer network liquid crystal (PNLC) cells were demonstrated. By changing the photomask pattern, both positive and negative lenses were fabricated. The advantages of such a PNLC lens are low operation voltage, large aperture size, and simple electrode design. To overcome the polarization dependence, stacking two orthogonal homogeneous PNLC cells is considered.

Dynamic cholesteric liquid crystal superstructures photoaligned by one-step polarization holography

NASA Astrophysics Data System (ADS)

Li, Sen-Sen; Shen, Yuan; Chang, Zhen-Ni; Li, Wen-Song; Xu, Yan-Chao; Fan, Xing-Yu; Chen, Lu-Jian

2017-12-01

A convenient approach to modulate the fingerprint textures of methyl red (MR) doped cholesteric liquid crystals by asymmetric photoalignment in the green-light waveband is presented, resulting in the generation of voltage-controllable helical superstructures. The interaction between the MR molecules and the incident light polarization determines the initial twisted planar geometry, providing a multivariant control over the stripe directions of fingerprint textures by applying a proper electric field. The key factors for precise manipulation of fingerprint stripes in a predictable and rewritable manner are analyzed theoretically and investigated experimentally, which involves the alignment asymmetry, the ratio of cell gap to natural pitch length, and the chirality of chiral dopant. Dynamic periodic fingerprint textures in shapes of dashed curve and dashed line are further demonstrated by utilizing a facile one-step polarization holography process using two beams with orthogonal circular and orthogonal linear polarizations, respectively. It is believed that the practical approach described in this study would enrich the research contents of self-assembled hierarchical superstructures using soft liquid crystal building blocks.

Optical switch based on the electrically controlled liquid crystal interface.

PubMed

Komar, Andrei A; Tolstik, Alexei L; Melnikova, Elena A; Muravsky, Alexander A

2015-06-01

The peculiarities of the linearly polarized light beam reflection at the interface within the bulk of a nematic liquid crystal (NLC) cell with different orientations of the director are analyzed. Two methods to create the interface are considered. Combination of the planar and homeotropic orientations of the NLC director is realized by means of a spatially structured electrode under the applied voltage. In-plane patterned azimuthal alignment of the NLC director is created by the patterned rubbing alignment technique. All possible orthogonal orientations of the LC director are considered; the configurations for realization of total internal reflection are determined. The revealed relationship between the propagation of optical beams in a liquid crystal material and polarization of laser radiation has enabled realization of the spatial separation for the orthogonally polarized light beams at the interface between two regions of NLC with different director orientations (domains). Owing to variations in the applied voltage and, hence, in the refractive index gradient, the light beam propagation directions may be controlled electrically.

Polymer blend effect on molecular alignment induced by contact freezing of mesogenic phthalocyanine

NASA Astrophysics Data System (ADS)

Kitagawa, Takahiro; Fiderana Ramananarivo, Mihary; Fujii, Akihiko; Ozaki, Masanori

2018-04-01

The polymer blend effect in the fabrication of uniaxially oriented thin films of a mesogenic phthalocyanine, 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH2), by contact freezing was studied. Contact freezing was induced by thermal stimulation to a supercooled liquid crystal state of the mixture of C6PcH2 and poly(3-hexylthiophene) (P3HT). With the blending of P3HT with C6PcH2 at an appropriate blend ratio, the cracks observed in a pure C6PcH2 film disappeared while maintaining the uniaxial alignment of C6PcH2. The polymer blend effect was discussed by taking the anisotropic optical absorption and molecular stacking structure in the thin films into consideration.

FAST TRACK COMMUNICATION: High pressure study of BaFe2As2—the role of hydrostaticity and uniaxial stress

NASA Astrophysics Data System (ADS)

Duncan, W. J.; Welzel, O. P.; Harrison, C.; Wang, X. F.; Chen, X. H.; Grosche, F. M.; Niklowitz, P. G.

2010-02-01

We investigate the evolution of the electrical resistivity of BaFe2As2 single crystals with pressure. The samples used were from the same batch, grown using a self-flux method, and showed properties that were highly reproducible. Samples were pressurized using three different pressure media: pentane-isopentane (in a piston-cylinder cell), Daphne oil (in an alumina anvil cell) and steatite (in a Bridgman cell). Each pressure medium has its own intrinsic level of hydrostaticity, which dramatically affects the phase diagram. An increasing uniaxial pressure component in this system quickly reduces the spin density wave order and favours the appearance of superconductivity, which is similar to what is seen in SrFe2As2.

Evidence for Spin Singlet Pairing with Strong Uniaxial Anisotropy in URu2Si2 Using Nuclear Magnetic Resonance

NASA Astrophysics Data System (ADS)

Hattori, T.; Sakai, H.; Tokunaga, Y.; Kambe, S.; Matsuda, T. D.; Haga, Y.

2018-01-01

In order to identify the spin contribution to superconducting pairing compatible with the so-called "hidden order", Si 29 nuclear magnetic resonance measurements have been performed using a high-quality single crystal of URu2 Si2 . A clear reduction of the Si 29 Knight shift in the superconducting state has been observed under a magnetic field applied along the crystalline c axis, corresponding to the magnetic easy axis. These results provide direct evidence for the formation of spin-singlet Cooper pairs. Consequently, results indicating a very tiny change of the in-plane Knight shift reported previously demonstrate extreme uniaxial anisotropy for the spin susceptibility in the hidden order state.

Eigenmode multiplexing with SLM for volume holographic data storage

NASA Astrophysics Data System (ADS)

Chen, Guanghao; Miller, Bo E.; Takashima, Yuzuru

2017-08-01

The cavity supports the orthogonal reference beam families as its eigenmodes while enhancing the reference beam power. Such orthogonal eigenmodes are used as additional degree of freedom to multiplex data pages, consequently increase storage densities for volume Holographic Data Storage Systems (HDSS) when the maximum number of multiplexed data page is limited by geometrical factor. Image bearing holograms are multiplexed by orthogonal phase code multiplexing via Hermite-Gaussian eigenmodes in a Fe:LiNbO3 medium with a 532 nm laser at multiple Bragg angles by using Liquid Crystal on Silicon (LCOS) spatial light modulators (SLMs) in reference arms. Total of nine holograms are recorded with three angular and three eigenmode.

USSR and Eastern Europe Scientific Abstracts Physics and Mathematics No. 35

DTIC Science & Technology

1977-06-15

depends on the film thickness, on the conditions of demagnetization , and on the constant of uniaxial magnetic anisotropy. The distribution of...Acoustics 2 Crystals and Semiconductors.. .*. 16 Electricity and Magnetism 51 Fluid Dynamics 64 Lasers and Masers 88 Magnetohydrodynamics 110...Molecular Physics 132 Nuclear Physics 133 Optics and Spectroscopy 158 Stress, Strain and Deformation 165 Superconductivity 170 Theoretical

Summer research fellowship program

NASA Technical Reports Server (NTRS)

Darden, G. C. (Compiler)

1979-01-01

Significant accomplishments reported include uniaxial compression tests of high strength graphite-epoxy laminates. The results show that Young's modulus and fracture stress depend upon the specimen's dimensions. Also presented are: an investigation of robot vision; estimation of spectral signatures of algae from the airborne lidar oceanographic probing equipment; impact tests on polymeric compounds; calibration of quartz crystal microbalance; and a profile of naturally occurring hydrocarbons.

In-situ neutron diffraction of LaCoO3 perovskite under uniaxial compression. I. Crystal structure analysis and texture development

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aman, Amjad; Chen, Yan; Lugovy, Mykola

2014-01-01

The dynamics of texture formation, changes in crystal structure and stress accommodation mechanisms are studied in R3c rhombohedral LaCoO3 perovskite during in-situ uniaxial compression experiment by neutron diffraction. The neutron diffraction revealed the complex crystallographic changes causing the texture formation and significant straining along certain crystallographic directions during in-situ compression, which are responsible for the appearance of hysteresis and non-linear ferroelastic deformation in LaCoO3 perovskite. The irreversible strain after the first loading was connected with the appearance of non-recoverable changes in the intensity ratio of certain crystallographic peaks, causing non-reversible texture formation. However in the second loading/unloading cycle the hysteresismore » loop was closed and no irreversible strain appears after deformation. The significant texture formation is responsible for increase in the Young s modulus of LaCoO3 at high compressive loads, where the reported values of Young s modulus increase from 76 GPa measured at the very beginning of the loading to 194 GPa at 900 MPa applied compressive stress measured at the beginning of the unloading curve.« less

Unconventional Superconductivity in Luttinger Semimetals: Theory of Complex Tensor Order and the Emergence of the Uniaxial Nematic State

NASA Astrophysics Data System (ADS)

Boettcher, Igor; Herbut, Igor F.

2018-02-01

We investigate unconventional superconductivity in three-dimensional electronic systems with the chemical potential close to a quadratic band touching point in the band dispersion. Short-range interactions can lead to d -wave superconductivity, described by a complex tensor order parameter. We elucidate the general structure of the corresponding Ginzburg-Landau free energy and apply these concepts to the case of an isotropic band touching point. For a vanishing chemical potential, the ground state of the system is given by the superconductor analogue of the uniaxial nematic state, which features line nodes in the excitation spectrum of quasiparticles. In contrast to the theory of real tensor order in liquid crystals, however, the ground state is selected here by the sextic terms in the free energy. At a finite chemical potential, the nematic state has an additional instability at weak coupling and low temperatures. In particular, the one-loop coefficients in the free energy indicate that at weak coupling genuinely complex orders, which break time-reversal symmetry, are energetically favored. We relate our analysis to recent measurements in the half-Heusler compound YPtBi and discuss the role of cubic crystal symmetry.

A coupled ductile fracture phase-field model for crystal plasticity

NASA Astrophysics Data System (ADS)

Hernandez Padilla, Carlos Alberto; Markert, Bernd

2017-07-01

Nowadays crack initiation and evolution play a key role in the design of mechanical components. In the past few decades, several numerical approaches have been developed with the objective to predict these phenomena. The objective of this work is to present a simplified, nonetheless representative phenomenological model to predict the crack evolution of ductile fracture in single crystals. The proposed numerical approach is carried out by merging a conventional elasto-plastic crystal plasticity model and a phase-field model modified to predict ductile fracture. A two-dimensional initial boundary value problem of ductile fracture is introduced considering a single-crystal setup and Nickel-base superalloy material properties. The model is implemented into the finite element context subjected to a quasi-static uniaxial tension test. The results are then qualitatively analyzed and briefly compared to current benchmark results in the literature.

Intrinsic Polarization and Tunable Color of Electroluminescence from Organic Single Crystal-based Light-Emitting Devices

PubMed Central

Ding, Ran; Feng, Jing; Zhou, Wei; Zhang, Xu-Lin; Fang, Hong-Hua; Yang, Tong; Wang, Hai-Yu; Hotta, Shu; Sun, Hong-Bo

2015-01-01

A single crystal-based organic light-emitting device (OLED) with intrinsically polarized and color-tunable electroluminescence (EL) has been demonstrated without any subsequent treatment. The polarization ratio of 5:1 for the transversal-electric (TE) and transversal-magnetic (TM) polarization at the emission peak of 575 nm, and 4.7:1 for the TM to TE polarization at the emission peak of 635 nm, respectively, have been obtained. The emitting color is tunable between yellow, yellow-green and orange by changing the polarization angle. The polarized EL and the polarization-induced color tunability can be attributed to the anisotropic microcavity formed by the BP3T crystal with uniaxial alignment of the molecules. PMID:26207723

Diode-pumped SrMoO4:Tm3+ crystal lasing near 1500 nm

NASA Astrophysics Data System (ADS)

Doroshenko, M. E.; Sulc, J.; Jelinkova, H.; Nemec, M.; Ivleva, L. I.; Dunaeva, E. E.

2018-04-01

Diode-pumped lasing of Tm3+ ions in SrMoO4 crystal at wavelength near 1500 nm was obtained for the first time to our best knowledge. Two laser lines with orthogonal polarizations were observed at 1452 and 1492 nm. The laser pulse was self-terminated about 500 µs after the pump start.

Interplay between spin-orbit coupling and crystal-field effect in topological insulators

NASA Astrophysics Data System (ADS)

Lee, Hyungjun; Yazyev, Oleg V.

2015-07-01

Band inversion, one of the key signatures of time-reversal invariant topological insulators (TIs), arises mostly due to the spin-orbit (SO) coupling. Here, based on ab initio density-functional calculations, we report a theoretical investigation of the SO-driven band inversion in isostructural bismuth and antimony chalcogenide TIs from the viewpoint of its interplay with the crystal-field effect. We calculate the SO-induced energy shift of states in the top valence and bottom conduction manifolds and reproduce this behavior using a simple one-atom model adjusted to incorporate the crystal-field effect. The crystal-field splitting is shown to compete with the SO coupling, that is, stronger crystal-field splitting leads to weaker SO band shift. We further show how both these effects can be controlled by changing the chemical composition, whereas the crystal-field splitting can be tuned by means of uniaxial strain. These results provide a practical guidance to the rational design of novel TIs as well as to controlling the properties of existing materials.

Three-dimensional spin mapping of antiferromagnetic nanopyramids having spatially alternating surface anisotropy at room temperature.

PubMed

Wang, Kangkang; Smith, Arthur R

2012-11-14

Antiferromagnets play a key role in modern spintronic devices owing to their ability to modify the switching behavior of adjacent ferromagnets via the exchange bias effect. Consequently, detailed measurements of the spin structure at antiferromagnetic interfaces and surfaces are highly desirable, not only for advancing technologies but also for enabling new insights into the underlying physics. Here using spin-polarized scanning tunneling microscopy at room-temperature, we reveal in three-dimensions an orthogonal spin structure on antiferromagnetic compound nanopyramids. Contrary to expected uniaxial anisotropy based on bulk properties, the atomic terraces are found to have alternating in-plane and out-of-plane magnetic anisotropies. The observed layer-wise alternation in anisotropy could have strong influences on future nanoscale spintronic applications.

New Mechanism for Toughening Ceramic Materials

DTIC Science & Technology

1994-02-01

Ferroelastic toughening, twinning, domain switching 1 17. 340.TY Q .Al MD0 .I SOWL&Nrv CLO.ASS1RC M SIS . W CASSWCAMlS 9: j"hTAfCm Of AMTLACT OF AD...crystal (Cubefaces orthogonal to (IM()) on the basis of the pseudocubic si mmetry X-ray diffraction traces using CuKa radiation were obtained show ing...Metastable Te- observed on ground or fracture surfaces of single crystals an- tragonal Zirconia Crystals." J. MAter Si . 18. 2619-28 (1983) ’T. C. Yuan

Vibrational properties of Ni-Mn-Ga shape memory alloy in the martensite phases

NASA Astrophysics Data System (ADS)

Ener, Semih; Mehaddene, Tarik; Pedersen, Björn; Leitner, Michael; Neuhaus, Jürgen; Petry, Winfried

2013-12-01

Studying the phonon dispersion of the ferromagnetic shape memory alloy system Ni-Mn-Ga gives insight into the mechanism of the martensite transition and the forces driving the transition. Transformation of austenite single crystals under uniaxial stress results in the coexistence of two martensitic variants with perpendicular modulation vector. Here we report on inelastic neutron scattering studies of martensite crystals with off-stoichiometric compositions, varying from non-modulated (NM) to five- (5M) and seven- (7M) layer modulated martensite phases. Both the 5M and 7M crystals show fully commensurate satellite peaks along [\\xi \\bar {\\xi } 0], corresponding to the five- and seven-layer modulation. These superstructure peaks become Γ-points of the modulated structure. Due to the coexistence of two variants within the (001) plane, both new acoustic phonons reflecting the modulation vector [\\xi \\bar {\\xi } 0] and acoustic TA2[ξξ0] phonons corresponding to the non-modulated direction are observed. The latter display a pronounced softening around ξ = 0.2-0.4 when approaching the martensite-austenite transition from above and below, i.e. this soft mode has lowest frequency at the transition temperature. Overall the phonon dispersion of the austenite and martensite phase resemble each other very much. The coexistence of two martensitic variants after uniaxial transformation explains the particular behaviour of the low-energy excitations, in contrast to previous interpretations involving charge-density waves and associated phason modes.

A two degrees-of-freedom piezoelectric single-crystal micromotor

NASA Astrophysics Data System (ADS)

Chen, Zhijiang; Li, Xiaotian; Liu, Guoxi; Dong, Shuxiang

2014-12-01

A two degrees-of-freedom (DOF) ultrasonic micromotor made of piezoelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystal square-bar (dimensions 2 × 2 × 9 mm3) was developed. The PIN-PMN-PT square-bar stator can generate standing wave elliptical motions in two orthogonal vertical planes by combining the first longitudinal and second bending vibration modes, enabling it to drive a slider in two orthogonal directions. The relatively large driving forces of 0.25 N and motion speed of 35 mm/s were obtained under a voltage of 80 Vpp at its resonance frequency of 87.5 kHz. The proposed micromotor has potential for applications in micro robots, cell manipulators, and digital cameras as a two-DOF actuator.

Dynamics of uniaxially oriented elastomers using dielectric spectroscopy

NASA Astrophysics Data System (ADS)

Lee, Hyungki; Fragiadakis, Daniel; Martin, Darren; Runt, James

2009-03-01

We summarize our initial dielectric spectroscopy investigation of the dynamics of oriented segmented polyurethanes and crosslinked polyisoprene elastomers. A specially designed uniaxial stretching rig is used to control the draw ratio, and the electric field is applied normal to the draw direction. For the segmented PUs, we observe a dramatic reduction in relaxation strength of the soft phase segmental process with increasing extension ratio, accompanied by a modest decrease in relaxation frequency. Crosslinking of the polyisoprene was accomplished with dicumyl peroxide and the dynamics of uncrosslinked and crosslinked versions are investigated in the undrawn state and at different extension ratios. Complimentary analysis of the crosslinked PI is conducted with wide angle X- ray diffraction to examine possible strain-induced crystallization, DSC, and swelling experiments. Quantitative analysis of relaxation strengths and shapes as a function of draw ratio will be discussed.

Theoretical and experimental evaluation of piezo-optic parameters and photoelastic constant in tetragonal PWO.

PubMed

Natali, Pier Paolo; Montalto, Luigi; Daví, Fabrizio; Mengucci, Paolo; Ciriaco, Andrea; Paone, Nicola; Rinaldi, Daniele

2018-02-01

The tetragonal PbWO 4 (PWO) is one of the most important scintillating crystals, being used both in the Compact Muon Solenoid (CMS) experiment at the European Organization for Nuclear Research (CERN) and in the PANDA project at the Facility for Antiproton and Ion Research (FAIR). Light yield and other relevant scintillation properties depend, among many factors, also on the crystal mechanical quality. Accordingly, a detailed knowledge of crystal piezo-optic properties is a mandatory step toward understanding elasto-optic behavior and performing crystal quality control. In this paper, we evaluate for the first time, to the best of our knowledge, by means of both photoelastic and x-ray measurements, some components of the piezo-optic tensor; moreover, when the crystal is acted upon by a uniaxial stress, we obtain an evaluation for the rotation angle of the optic plane under stress as well as the photoelastic constant. These parameters are necessary to detect the residual stresses within the crystal, if any, and to give an overall quality measure. Such a methodology is in general suitable for any tetragonal crystals.

Magnetic properties of ultrathin tetragonal Heusler D022-Mn3Ge perpendicular-magnetized films

NASA Astrophysics Data System (ADS)

Sugihara, A.; Suzuki, K. Z.; Miyazaki, T.; Mizukami, S.

2015-05-01

We investigated the crystal structure and magnetic properties of Manganese-germanium (Mn3Ge) films having the tetragonal D022 structure, with varied thicknesses (5-130 nm) prepared on chromium (Cr)-buffered single crystal MgO(001) substrates. A crystal lattice elongation in the in-plane direction, induced by the lattice mismatch between the D022-Mn3Ge and the Cr buffer layer, increased with decreasing thickness of the D022-Mn3Ge layer. The films exhibited clear magnetic hysteresis loops with a squareness ratio close to unity, and a step-like magnetization reversal even at a 5-nm thickness under an external field perpendicular to the film's plane. The uniaxial magnetic anisotropy constant of the films showed a reduction to less than 10 Merg/cm3 in the small thickness range (≤20 nm), likely due to the crystal lattice elongation in the in-plane direction.

The Multiphase Rheology of Monte Nuovo's Eruption (Campi Flegrei, Italy)

NASA Astrophysics Data System (ADS)

Vona, A.; Romano, C.; Giordano, D.; Russell, K.

2011-12-01

We present a study of high-temperature, uniaxial deformation experiments of natural, partially crystallized samples from the Monte Nuovo (1538 AD) trachytic eruption. The experiments were performed at dry atmospheric conditions and controlled deformation rate using a high-temperature uniaxial Geocomp LoadTrac II press. Experiments were performed isothermally by deforming cores of the natural (i.e., crystal- and vesicle-bearing) samples at constant displacement rates (CDR) corresponding to constant strain rates between 10-7 and 10-4 s-1. The measurements were all performed in the viscous-flow regime and showed non-Newtonian shear thinning behavior. Measured viscosities vary between 1010 and 1013 Pa s. As no yield stress was detected, the flow behavior of the investigated specimens could be described with a simplified Herschel-Bulkley equation in terms of consistency K and flow index n. As the pure liquid and the liquid+crystal rheology of these samples were already measured in previous studies, we were able to estimate the net effects of crystals and vesicles on the rheology of the multiphase suspensions. The results revealed that the presence of vesicles has a major impact on the rheological response of magmas leading to a marked decrease of their viscosity, which partially balances the increase of viscosity due to the presence of crystals. At the same time, the presence of bubbles leads to a strong decrease in the shear strength of the magma inducing local and temporal variation in the deformation regimes (viscous vs. brittle). Brittle and ductile failure were in fact observed at T=600°C and strain rates of 10-5 s-1 and at T=800°C for the higher applied strain rate (10-4 s-1), respectively. During lava flow emplacement, this may explain the origin of the flow banding textures frequently observed in many silicic obsidian lava flows.

Effects of local field and inherent strain in reflectance anisotropy spectra of A{sup III}B{sup V} semiconductors with naturally oxidized surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berkovits, V. L.; Kosobukin, V. A.; Gordeeva, A. B.

2015-12-28

Reflectance anisotropy (RA) spectra of naturally oxidized (001) surfaces of GaAs and InAs crystals are measured for photon energies from 1.5 up to 5.5 eV. The differential high-accuracy RA spectra reveal features substantially different from those caused by either a reconstruction of clean surface or a built-in near-surface electric field. Models of atomic structure with anisotropic transition layers of excess arsenic atoms specific for GaAs(001)/oxide and InAs(001)/oxide interfaces are proposed. In conformity with these models, a general theory of reflectance anisotropy is developed for semiconductor/oxide interfaces within the Green's function technique. The theory takes into account the combined effect of localmore » field due to interface dipoles and of intrinsic near-surface strain of the crystal. Measured RA spectra are analyzed in the model of valence-bond dipoles occupying a rectangular lattice in a multilayer medium. Comparing the measured and calculated spectra, we conclude that RA spectra of oxidized GaAs(001) and InAs(001) surfaces are simultaneously influenced by interface and near-surface anisotropies. The former is responsible for the broad-band spectral features which are associated with polarizability of the valence bonds attached to As atoms at the crystal/oxide interface. The near-surface anisotropy is due to inherent uniaxial straining the near-surface region of crystal. The effect of strain on RA spectra is experimentally and theoretically substantiated for GaAs crystal wafers undergone a uniaxial applied stress. Basically, this work results in the following. It establishes the physical nature of different levels of RA spectra observed in a majority of papers, but never analyzed. It demonstrates how the studied features of RA spectra could be applied for optical characterization of strained interfaces and atomic layers.« less

Effects of local field and inherent strain in reflectance anisotropy spectra of AIIIBV semiconductors with naturally oxidized surfaces

NASA Astrophysics Data System (ADS)

Berkovits, V. L.; Kosobukin, V. A.; Gordeeva, A. B.

2015-12-01

Reflectance anisotropy (RA) spectra of naturally oxidized (001) surfaces of GaAs and InAs crystals are measured for photon energies from 1.5 up to 5.5 eV. The differential high-accuracy RA spectra reveal features substantially different from those caused by either a reconstruction of clean surface or a built-in near-surface electric field. Models of atomic structure with anisotropic transition layers of excess arsenic atoms specific for GaAs(001)/oxide and InAs(001)/oxide interfaces are proposed. In conformity with these models, a general theory of reflectance anisotropy is developed for semiconductor/oxide interfaces within the Green's function technique. The theory takes into account the combined effect of local field due to interface dipoles and of intrinsic near-surface strain of the crystal. Measured RA spectra are analyzed in the model of valence-bond dipoles occupying a rectangular lattice in a multilayer medium. Comparing the measured and calculated spectra, we conclude that RA spectra of oxidized GaAs(001) and InAs(001) surfaces are simultaneously influenced by interface and near-surface anisotropies. The former is responsible for the broad-band spectral features which are associated with polarizability of the valence bonds attached to As atoms at the crystal/oxide interface. The near-surface anisotropy is due to inherent uniaxial straining the near-surface region of crystal. The effect of strain on RA spectra is experimentally and theoretically substantiated for GaAs crystal wafers undergone a uniaxial applied stress. Basically, this work results in the following. It establishes the physical nature of different levels of RA spectra observed in a majority of papers, but never analyzed. It demonstrates how the studied features of RA spectra could be applied for optical characterization of strained interfaces and atomic layers.

Diamond anvil cells using boron-doped diamond electrodes covered with undoped diamond insulating layer

NASA Astrophysics Data System (ADS)

Matsumoto, Ryo; Yamashita, Aichi; Hara, Hiroshi; Irifune, Tetsuo; Adachi, Shintaro; Takeya, Hiroyuki; Takano, Yoshihiko

2018-05-01

Diamond anvil cells using boron-doped metallic diamond electrodes covered with undoped diamond insulating layers have been developed for electrical transport measurements under high pressure. These designed diamonds were grown on a bottom diamond anvil via a nanofabrication process combining microwave plasma-assisted chemical vapor deposition and electron beam lithography. The resistance measurements of a high-quality FeSe superconducting single crystal under high pressure were successfully demonstrated by just putting the sample and gasket on the bottom diamond anvil directly. The superconducting transition temperature of the FeSe single crystal was increased to up to 43 K by applying uniaxial-like pressure.

C-Axis-Oriented Hydroxyapatite Film Grown Using ZnO Buffer Layer

NASA Astrophysics Data System (ADS)

Sakoishi, Yasuhiro; Iguchi, Ryo; Nishikawa, Hiroaki; Hontsu, Shigeki; Hayami, Takashi; Kusunoki, Masanobu

2013-11-01

A method of fabricating c-axis-oriented hydroxyapatite film on a quartz crystal microbalance (QCM) sensor was investigated. ZnO was used as a template to obtain a hexagonal hydroxyapatite crystal of uniaxial orientation. The ZnO was grown as a c-axis film on a Au/quartz with the surface structure of a QCM sensor. Under optimized conditions, hydroxyapatite was deposited by pulsed laser deposition. X-ray diffraction showed the hydroxyapatite film to be oriented along the c-axis. Because Au and ZnO are applied to many devices, the anisotropic properties of hydroxyapatite may be incorporated into these devices as well as QCM sensors.

Effect of Crystal Orientation on Analysis of Single-Crystal, Nickel-Based Turbine Blade Superalloys

NASA Technical Reports Server (NTRS)

Swanson, G. R.; Arakere, N. K.

2000-01-01

High-cycle fatigue-induced failures in turbine and turbopump blades is a pervasive problem. Single-crystal nickel turbine blades are used because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities. Single-crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant and complicating factor. A fatigue failure criterion based on the maximum shear stress amplitude on the 24 octahedral and 6 cube slip systems is presented for single-crystal nickel superalloys (FCC crystal). This criterion greatly reduces the scatter in uniaxial fatigue data for PWA 1493 at 1,200 F in air. Additionally, single-crystal turbine blades used in the Space Shuttle main engine high pressure fuel turbopump/alternate turbopump are modeled using a three-dimensional finite element (FE) model. This model accounts for material orthotrophy and crystal orientation. Fatigue life of the blade tip is computed using FE stress results and the failure criterion that was developed. Stress analysis results in the blade attachment region are also presented. Results demonstrate that control of crystallographic orientation has the potential to significantly increase a component's resistance to fatigue crack growth without adding additional weight or cost.

Embedded Coplanar Strips Traveling-Wave Photomixers

NASA Technical Reports Server (NTRS)

Wyss, R. A.; Lee, T.; Pearson, J. C.; Matsuura, S.; Blake, G. A.; Kadow, C.; Gossard, A. C.

2001-01-01

The electric field distribution in photomixers with electrodes deposited on the surface has already been calculated. It was shown that the strength of the electric field diminishes rapidly with depth. It was argued that the resulting reduction of the effective interaction volume of the device lowers the optical-to-heterodyne conversion. In this paper, we will present the results of our investigation on the influence of the electrode placement on the performance of photomixers. We have fabricated and measured traveling-wave photomixer devices which have both embedded and surface electrodes - the nominal spacing between the electrodes was 2 micrometers. Devices were made using either low-temperature-grown (LTG)-GaAs or ErAs:GaAs as the photoconductive material. The dark current, photocurrent, and radio frequency (RF) emission were measured at nominally 1 THz. The experimental data show a surprising difference in the behavior of ErAs:GaAs devices when the electrodes are embedded. A factor of two increase in RF radiation is observed for electric fields < 20 kV/cm. No such improvement was observed for the LTG-GaAs devices. We argue that the distinctive behavior of the two photoconductive materials is due to differences in the crystal structure - LTG-GaAs is isotropic, while ErAs:GaAs is uniaxial. We find that the carrier mobility in-plane (parallel) to the ErAs layers in the ErAs:GaAs superlattice is larger than orthogonal to these layers. The data indicate that carrier velocity overshoot is responsible for the excess radiation produced for the embedded electrode ErAs:GaAs devices.

Optical harmonic generator

DOEpatents

Summers, M.A.; Eimerl, D.; Boyd, R.D.

1982-06-10

A pair of uniaxial birefringent crystal elements are fixed together to form a serially arranged, integral assembly which, alternatively, provides either a linearly or elliptically polarized second-harmonic output wave or a linearly polarized third-harmonic output wave. The extraordinary or e directions of the crystal elements are oriented in the integral assembly to be in quadrature (90/sup 0/). For a second-harmonic generation in the Type-II-Type-II angle tuned case, the input fundamental wave has equal amplitude o and e components. For a third-harmonic generation, the input fundamental wave has o and e components whose amplitudes are in a ratio of 2:1 (o:e reference first crystal). In the typical case of a linearly polarized input fundamental wave this can be accomplished by simply rotating the crystal assembly about the input beam direction by 10/sup 0/. For both second and third harmonic generation input precise phase-matching is achieved by tilting the crystal assembly about its two sensitive axeses (o).

Optical harmonic generator

DOEpatents

Summers, Mark A.; Eimerl, David; Boyd, Robert D.

1985-01-01

A pair of uniaxial birefringent crystal elements are fixed together to form a serially arranged, integral assembly which, alternatively, provides either a linearly or elliptically polarized second-harmonic output wave or a linearly polarized third-harmonic output wave. The "extraordinary" or "e" directions of the crystal elements are oriented in the integral assembly to be in quadrature (90.degree.). For a second-harmonic generation in the Type-II-Type-II angle tuned case, the input fundamental wave has equal amplitude "o" and "e" components. For a third-harmonic generation, the input fundamental wave has "o" and "e" components whose amplitudes are in a ratio of 2:1 ("o":"e" reference first crystal). In the typical case of a linearly polarized input fundamental wave this can be accomplished by simply rotating the crystal assembly about the input beam direction by 10.degree.. For both second and third harmonic generation input precise phase-matching is achieved by tilting the crystal assembly about its two sensitive axes ("o").

Spatial Instability of the Linearly Polarized Plane Wave in a Cubic Crystal

NASA Astrophysics Data System (ADS)

Kuz'mina, M. S.; Khazanov, E. A.

2016-12-01

We study theoretically the development of a small-scale spatial instability of a plane wave in a cubic crystal with [111], [001] and [101] orientations. It is shown that in the [111] oriented crystals the instability develops at lower intensities than in the [001] and [101] oriented crystals. In the latter two crystals, the instability can significantly be suppressed by choosing the optimal radiation polarization. It is found that in the case of a small B integral, the method of temporal contrast enhancement of laser pulses by generating an orthogonal polarization achieves the largest efficiency with the [101] orientation, while the [001] orientation is more preferable for B > 3.

Spatially orthogonal chemical functionalization of a hierarchical pore network for catalytic cascade reactions

NASA Astrophysics Data System (ADS)

Parlett, Christopher M. A.; Isaacs, Mark A.; Beaumont, Simon K.; Bingham, Laura M.; Hondow, Nicole S.; Wilson, Karen; Lee, Adam F.

2016-02-01

The chemical functionality within porous architectures dictates their performance as heterogeneous catalysts; however, synthetic routes to control the spatial distribution of individual functions within porous solids are limited. Here we report the fabrication of spatially orthogonal bifunctional porous catalysts, through the stepwise template removal and chemical functionalization of an interconnected silica framework. Selective removal of polystyrene nanosphere templates from a lyotropic liquid crystal-templated silica sol-gel matrix, followed by extraction of the liquid crystal template, affords a hierarchical macroporous-mesoporous architecture. Decoupling of the individual template extractions allows independent functionalization of macropore and mesopore networks on the basis of chemical and/or size specificity. Spatial compartmentalization of, and directed molecular transport between, chemical functionalities affords control over the reaction sequence in catalytic cascades; herein illustrated by the Pd/Pt-catalysed oxidation of cinnamyl alcohol to cinnamic acid. We anticipate that our methodology will prompt further design of multifunctional materials comprising spatially compartmentalized functions.

Transition from two-dimensional photonic crystals to dielectric metasurfaces in the optical diffraction with a fine structure

PubMed Central

Rybin, Mikhail V.; Samusev, Kirill B.; Lukashenko, Stanislav Yu.; Kivshar, Yuri S.; Limonov, Mikhail F.

2016-01-01

We study experimentally a fine structure of the optical Laue diffraction from two-dimensional periodic photonic lattices. The periodic photonic lattices with the C4v square symmetry, orthogonal C2v symmetry, and hexagonal C6v symmetry are composed of submicron dielectric elements fabricated by the direct laser writing technique. We observe surprisingly strong optical diffraction from a finite number of elements that provides an excellent tool to determine not only the symmetry but also exact number of particles in the finite-length structure and the sample shape. Using different samples with orthogonal C2v symmetry and varying the lattice spacing, we observe experimentally a transition between the regime of multi-order diffraction, being typical for photonic crystals to the regime where only the zero-order diffraction can be observed, being is a clear fingerprint of dielectric metasurfaces characterized by effective parameters. PMID:27491952

Strain transfer across grain boundaries in MoS2 monolayers grown by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Niehues, Iris; Blob, Anna; Stiehm, Torsten; Schmidt, Robert; Jadriško, Valentino; Radatović, Borna; Čapeta, Davor; Kralj, Marko; Michaelis de Vasconcellos, Steffen; Bratschitsch, Rudolf

2018-07-01

Monolayers of transition metal dichalcogenides (TMDC) mechanically exfoliated from bulk crystals have exceptional mechanical and optical properties. They are extremely flexible, sustaining mechanical strain of about 10% without breaking. Their optical properties dramatically change with applied strain. However, the fabrication of a large number of mechanical devices is tedious due to the micromechanical exfoliation process. Alternatively, monolayers can be grown by chemical vapor deposition (CVD) on the wafer scale, with the drawback of cracks and grain boundaries in the material. Therefore, it is important to investigate the mechanical properties of CVD-grown material and its potential as a material for mass production of nanomechanical devices. Here, we measure the optical absorption of CVD-grown MoS2 monolayers with applied uniaxial tensile strain. We derive a strain-dependent shift for the A exciton of  ‑42 meV/%. This value is identical to MoS2 monolayers, which are mechanically exfoliated from natural molybdenite crystals. Using angle-resolved second-harmonic generation spectroscopy, we find that the applied uniaxial tensile strain is fully transferred across grain boundaries of the CVD-grown monolayer. Our work demonstrates that large-area artificially grown MoS2 monolayers are promising for mass-produced nanomechanical devices.

Analytical studies on the crystal melt interface shape in the Czochralski process for oxide single crystals

NASA Astrophysics Data System (ADS)

Jeong, Ja Hoon; Kang, In Seok

2000-09-01

Effects of the operating conditions on the crystal-melt interface shape are analytically investigated for the Czochralski process of the oxide single crystals. The ideas, which were used for the silicon single-crystal growth by Jeong et al. (J. Crystal Growth 177 (1997) 157), are extended to the oxide single-crystal growth problem by considering the internal radiation in the crystal phase and the melt phase heat transfer with the high Prandtl number. The interface shape is approximated in the simplest form as a quadratic function of radial position and an expression for the deviation from the flat interface shape is derived as a function of operating conditions. The radiative heat transfer rate between the interface and the ambient is computed by calculating the view factors for the curved interface shape with the assumption that the crystal phase is completely transparent. For the melt phase, the well-known results from the thermal boundary layer analysis are applied for the asymptotic case of high Prandtl number based on the idea that the flow field near the crystal-melt interface can be modeled as either a uniaxial or a biaxial flow. Through this work, essential information on the interface shape deformation and the effects of operating conditions are brought out for the oxide single-crystal growth.

Structural and magnetic properties of new uniaxial nanocrystalline Pr5Co19 compound

NASA Astrophysics Data System (ADS)

Bouzidi, W.; Mliki, N.; Bessais, L.

2017-11-01

Highly-coercive nanocrystalline Pr5Co19 powders have been synthesized by mechanical milling for the first time. The structural properties are studied by X-ray diffraction and refined with Rietveld method. This analysis revealed that whatever annealing temperature, samples crystallize in the rhombohedral (3R) of Ce5Co19-type structure (space group R 3 bar m). The magnetization curve as a function of temperature shows a magnetic transition state at the Curie temperature TC = 690 K. The optimum hard magnetic properties have been obtained for Pr5Co19 milled for 5 h and annealed at 1048 K for 30 min. These alloys exhibit a coercivity of 15 kOe at room temperature. This high coercivity is attributed to the high uniaxial magnetocrystalline anisotropy, nanoscale grain size, and to the homogeneous nanostructure developed by mechanical milling process and subsequent annealing.

Field dependent magnetic anisotropy of Ga0.2Fe0.8 thin films

NASA Astrophysics Data System (ADS)

Resnick, Damon A.; McClure, A.; Kuster, C. M.; Rugheimer, P.; Idzerda, Y. U.

2011-04-01

Using longitudinal MOKE in combination with a variable strength rotating magnetic field, called the rotational MOKE (ROTMOKE) method, we show that the magnetic anisotropy for a Ga0.2Fe0.8 single crystal film with a thickness of 17 nm, grown on GaAs (001) with a thick ZnSe buffer layer, depends linearly on the strength of the applied magnetic field. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial, cubic, or fourfold anisotropy, as well as additional terms with a linear dependence on the applied magnetic field. The uniaxial and cubic anisotropy fields, taken from both the hard and the easy axis scans, are seen to remain field independent. The field dependent terms are evidence of a large affect of the magnetostriction and its contribution to the effective magnetic anisotropy in GaxFe1-x thin films.

Uniaxial stress control of skyrmion phase

PubMed Central

Nii, Y.; Nakajima, T.; Kikkawa, A.; Yamasaki, Y.; Ohishi, K.; Suzuki, J.; Taguchi, Y.; Arima, T.; Tokura, Y.; Iwasa, Y.

2015-01-01

Magnetic skyrmions, swirling nanometric spin textures, have been attracting increasing attention by virtue of their potential applications for future memory technology and their emergent electromagnetism. Despite a variety of theoretical proposals oriented towards skyrmion-based electronics (that is, skyrmionics), few experiments have succeeded in creating, deleting and transferring skyrmions, and the manipulation methodologies have thus far remained limited to electric, magnetic and thermal stimuli. Here, we demonstrate a new approach for skyrmion phase control based on a mechanical stress. By continuously scanning uniaxial stress at low temperatures, we can create and annihilate a skyrmion crystal in a prototypical chiral magnet MnSi. The critical stress is merely several tens of MPa, which is easily accessible using the tip of a conventional cantilever. The present results offer a new guideline even for single skyrmion control that requires neither electric nor magnetic biases and consumes extremely little energy. PMID:26460119

Uniaxial stress control of skyrmion phase.

PubMed

Nii, Y; Nakajima, T; Kikkawa, A; Yamasaki, Y; Ohishi, K; Suzuki, J; Taguchi, Y; Arima, T; Tokura, Y; Iwasa, Y

2015-10-13

Magnetic skyrmions, swirling nanometric spin textures, have been attracting increasing attention by virtue of their potential applications for future memory technology and their emergent electromagnetism. Despite a variety of theoretical proposals oriented towards skyrmion-based electronics (that is, skyrmionics), few experiments have succeeded in creating, deleting and transferring skyrmions, and the manipulation methodologies have thus far remained limited to electric, magnetic and thermal stimuli. Here, we demonstrate a new approach for skyrmion phase control based on a mechanical stress. By continuously scanning uniaxial stress at low temperatures, we can create and annihilate a skyrmion crystal in a prototypical chiral magnet MnSi. The critical stress is merely several tens of MPa, which is easily accessible using the tip of a conventional cantilever. The present results offer a new guideline even for single skyrmion control that requires neither electric nor magnetic biases and consumes extremely little energy.

Density functional theory for hard uniaxial particles: Complex ordering of pear-shaped and spheroidal particles near a substrate

NASA Astrophysics Data System (ADS)

Schönhöfer, Philipp W. A.; Schröder-Turk, Gerd E.; Marechal, Matthieu

2018-03-01

We develop a density functional for hard particles with a smooth uniaxial shape (including non-inversion-symmetric particles) within the framework of fundamental measure theory. By applying it to a system of tapered, aspherical liquid-crystal formers, reminiscent of pears, we analyse their behaviour near a hard substrate. The theory predicts a complex orientational ordering close to the substrate, which can be directly related to the particle shape, in good agreement with our simulation results. Furthermore, the lack of particle inversion-symmetry implies the possibility of alternating orientations in subsequent layers as found in a smectic/lamellar phase of such particles. Both theory and Monte Carlo simulations confirm that such ordering occurs in our system. Our results are relevant for adsorption processes of asymmetric colloidal particles and molecules at hard interfaces and show once again that tapering strongly affects the properties of orientationally ordered phases.

Self-Phase-Matched Second-Harmonic and White-Light Generation in a Biaxial Zinc Tungstate Single Crystal

PubMed Central

Osewski, Pawel; Belardini, Alessandro; Petronijevic, Emilija; Centini, Marco; Leahu, Grigore; Diduszko, Ryszard; Pawlak, Dorota A.; Sibilia, Concita

2017-01-01

Second-order nonlinear optical materials are used to generate new frequencies by exploiting second-harmonic generation (SHG), a phenomenon where a nonlinear material generates light at double the optical frequency of the input beam. Maximum SHG is achieved when the pump and the generated waves are in phase, for example through birefringence in uniaxial crystals. However, applying these materials usually requires a complicated cutting procedure to yield a crystal with a particular orientation. Here we demonstrate the first example of phase matching under the normal incidence of SHG in a biaxial monoclinic single crystal of zinc tungstate. The crystal was grown by the micro-pulling-down method with the (102) plane perpendicular to the growth direction. Additionally, at the same time white light was generated as a result of stimulated Raman scattering and multiphoton luminescence induced by higher-order effects such as three-photon luminescence enhanced by cascaded third-harmonic generation. The annealed crystal offers SHG intensities approximately four times larger than the as grown one; optimized growth and annealing conditions may lead to much higher SHG intensities. PMID:28338074

Self-Phase-Matched Second-Harmonic and White-Light Generation in a Biaxial Zinc Tungstate Single Crystal

NASA Astrophysics Data System (ADS)

Osewski, Pawel; Belardini, Alessandro; Petronijevic, Emilija; Centini, Marco; Leahu, Grigore; Diduszko, Ryszard; Pawlak, Dorota A.; Sibilia, Concita

2017-03-01

Second-order nonlinear optical materials are used to generate new frequencies by exploiting second-harmonic generation (SHG), a phenomenon where a nonlinear material generates light at double the optical frequency of the input beam. Maximum SHG is achieved when the pump and the generated waves are in phase, for example through birefringence in uniaxial crystals. However, applying these materials usually requires a complicated cutting procedure to yield a crystal with a particular orientation. Here we demonstrate the first example of phase matching under the normal incidence of SHG in a biaxial monoclinic single crystal of zinc tungstate. The crystal was grown by the micro-pulling-down method with the (102) plane perpendicular to the growth direction. Additionally, at the same time white light was generated as a result of stimulated Raman scattering and multiphoton luminescence induced by higher-order effects such as three-photon luminescence enhanced by cascaded third-harmonic generation. The annealed crystal offers SHG intensities approximately four times larger than the as grown one; optimized growth and annealing conditions may lead to much higher SHG intensities.

Correlation between swift effects and tension-compression asymmetry in various polycrystalline materials

NASA Astrophysics Data System (ADS)

Revil-Baudard, Benoit; Chandola, Nitin; Cazacu, Oana; Barlat, Frédéric

2014-10-01

The Swift phenomenon, which refers to the occurrence of permanent axial deformation during monotonic free-end torsion, has been known for a very long time. While plastic anisotropy is considered to be its main cause, there is no explanation as to why in certain materials irreversible elongation occurs while in others permanent shortening is observed. In this paper, a correlation between Swift effects and the stress-strain behavior in uniaxial tension and compression is established. It is based on an elastic-plastic model that accounts for the combined influence of anisotropy and tension-compression asymmetry. It is shown that, if for a given orientation the uniaxial yield stress in tension is larger than that in compression, the specimen will shorten when twisted about that direction; however, if the yield stress in uniaxial compression is larger than that in uniaxial tension, axial elongation will occur. Furthermore, it is shown that on the basis of a few simple mechanical tests it is possible to predict the particularities of the plastic response in torsion for both isotropic and initially anisotropic materials. Unlike other previous interpretations of the Swift effects, which were mainly based on crystal plasticity and/or texture evolution, it is explained the occurrence of Swift effects at small to moderate plastic strains. In particular, the very good quantitative agreement between model and data for a strongly anisotropic AZ31-Mg alloy confirm the correlation established in this work between tension-compression asymmetry and Swift effects. Furthermore, it is explained why the sign of the axial plastic strains that develop depends on the twisting direction.

Phonons in a magnetized Coulomb crystal of ions with polarizable electron background

NASA Astrophysics Data System (ADS)

Baiko, D. A.; Kozhberov, A. A.

2017-11-01

We have studied phonon modes of a body-centered cubic (bcc) Coulomb crystal of ions in the presence of a uniform magnetic field B taking into account the polarizability of the electron background (electron screening) described by the Thomas-Fermi formalism. For k ≫κTF (k and κTF are the phonon wavevector and Thomas-Fermi wavenumber, respectively), electron polarizability is not important. At k ≪κTF , the electron response results in a pronounced effect. One of the three available modes is acoustic. For orthogonal propagation ( k ⊥B ), its frequency Ω is independent of B and κTF . For k ∥B , Ω∝1 /κTF and is independent of B. Another mode is quadratic. Its frequency is ∝1 /(B κTF) for orthogonal propagation and ∝1 /B and independent of κTF for the parallel case. The third mode is optic with Ω≈ωB ( ωB is the ion cyclotron frequency). A general expression is derived for the dynamic matrix of a Coulomb crystal with a polarizable background and more than one ion in the primitive cell. It is employed for a study of a magnetized hexagonal close-packed Coulomb crystal. We have also presented an analysis of phonon polarization vectors in a magnetized bcc crystal with or without screening. The results obtained can be used for realistic calculations of electron-phonon scattering rates and electron thermal and electrical conductivities in neutron star crusts.

Linear dichroism of DNA: Characterization of the orientation distribution function caused by hydrodynamic shear.

PubMed

Sutherland, John C

2017-04-15

Linear dichroism provides information on the orientation of chromophores part of, or bound to, an orientable molecule such as DNA. For molecular alignment induced by hydrodynamic shear, the principal axes orthogonal to the direction of alignment are not equivalent. Thus, the magnitude of the flow-induced change in absorption for light polarized parallel to the direction of flow can be more than a factor of two greater than the corresponding change for light polarized perpendicular to both that direction and the shear axis. The ratio of the two flow-induced changes in absorption, the dichroic increment ratio, is characterized using the orthogonal orientation model, which assumes that each absorbing unit is aligned parallel to one of the principal axes of the apparatus. The absorption of the alienable molecules is characterized by components parallel and perpendicular to the orientable axis of the molecule. The dichroic increment ratio indicates that for the alignment of DNA in rectangular flow cells, average alignment is not uniaxial, but for higher shear, as produced in a Couette cell, it can be. The results from the simple model are identical to tensor models for typical experimental configurations. Approaches for measuring the dichroic increment ratio with modern dichrometers are discussed. Copyright © 2017. Published by Elsevier Inc.

The determination of the direction of the optic axis of uniaxial crystalline materials

NASA Technical Reports Server (NTRS)

Lock, J. A.; Schock, H. J.; Regan, C. A.

1986-01-01

The birefringence of crystalline substances in general, and of sapphire in particular, is described. A test is described whose purpose is to determine the direction of the optic axis of a cylindrically machined single crystal of sapphire. This test was performed on the NASA Lewis sapphire cylinder and it was found that the optic axis made an angle of 18 deg with the axis of symmetry of the cylinder.

Effect of crystal habits on the surface energy and cohesion of crystalline powders.

PubMed

Shah, Umang V; Olusanmi, Dolapo; Narang, Ajit S; Hussain, Munir A; Gamble, John F; Tobyn, Michael J; Heng, Jerry Y Y

2014-09-10

The role of surface properties, influenced by particle processing, in particle-particle interactions (powder cohesion) is investigated in this study. Wetting behaviour of mefenamic acid was found to be anisotropic by sessile drop contact angle measurements on macroscopic (>1cm) single crystals, with variations in contact angle of water from 56.3° to 92.0°. This is attributed to variations in surface chemical functionality at specific facets, and confirmed using X-ray photoelectron spectroscopy (XPS). Using a finite dilution inverse gas chromatography (FD-IGC) approach, the surface energy heterogeneity of powders was determined. The surface energy profile of different mefenamic acid crystal habits was directly related to the relative exposure of different crystal facets. Cohesion, determined by a uniaxial compression test, was also found to relate to surface energy of the powders. By employing a surface modification (silanisation) approach, the contribution from crystal shape from surface area and surface energy was decoupled. By "normalising" contribution from surface energy and surface area, needle shaped crystals were found to be ∼2.5× more cohesive compared to elongated plates or hexagonal cuboid shapes crystals. Copyright © 2014. Published by Elsevier B.V.

A methodology to determine the elastic moduli of crystals by matching experimental and simulated lattice strain pole figures using discrete harmonics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wielewski, Euan; Boyce, Donald E.; Park, Jun-Sang

Determining reliable single crystal material parameters for complex polycrystalline materials is a significant challenge for the materials community. In this work, a novel methodology for determining those parameters is outlined and successfully applied to the titanium alloy, Ti-6Al-4V. Utilizing the results from a lattice strain pole figure experiment conducted at the Cornell High Energy Synchrotron Source, an iterative approach is used to optimize the single crystal elastic moduli by comparing experimental and simulated lattice strain pole figures at discrete load steps during a uniaxial tensile test. Due to the large number of unique measurements taken during the experiments, comparisons weremore » made by using the discrete spherical harmonic modes of both the experimental and simulated lattice strain pole figures, allowing the complete pole figures to be used to determine the single crystal elastic moduli. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.« less

Suppressing molecular vibrations in organic semiconductors by inducing strain

PubMed Central

Kubo, Takayoshi; Häusermann, Roger; Tsurumi, Junto; Soeda, Junshi; Okada, Yugo; Yamashita, Yu; Akamatsu, Norihisa; Shishido, Atsushi; Mitsui, Chikahiko; Okamoto, Toshihiro; Yanagisawa, Susumu; Matsui, Hiroyuki; Takeya, Jun

2016-01-01

Organic molecular semiconductors are solution processable, enabling the growth of large-area single-crystal semiconductors. Improving the performance of organic semiconductor devices by increasing the charge mobility is an ongoing quest, which calls for novel molecular and material design, and improved processing conditions. Here we show a method to increase the charge mobility in organic single-crystal field-effect transistors, by taking advantage of the inherent softness of organic semiconductors. We compress the crystal lattice uniaxially by bending the flexible devices, leading to an improved charge transport. The mobility increases from 9.7 to 16.5 cm2 V−1 s−1 by 70% under 3% strain. In-depth analysis indicates that compressing the crystal structure directly restricts the vibration of the molecules, thus suppresses dynamic disorder, a unique mechanism in organic semiconductors. Since strain can be easily induced during the fabrication process, we expect our method to be exploited to build high-performance organic devices. PMID:27040501

Suppressing molecular vibrations in organic semiconductors by inducing strain.

PubMed

Kubo, Takayoshi; Häusermann, Roger; Tsurumi, Junto; Soeda, Junshi; Okada, Yugo; Yamashita, Yu; Akamatsu, Norihisa; Shishido, Atsushi; Mitsui, Chikahiko; Okamoto, Toshihiro; Yanagisawa, Susumu; Matsui, Hiroyuki; Takeya, Jun

2016-04-04

Organic molecular semiconductors are solution processable, enabling the growth of large-area single-crystal semiconductors. Improving the performance of organic semiconductor devices by increasing the charge mobility is an ongoing quest, which calls for novel molecular and material design, and improved processing conditions. Here we show a method to increase the charge mobility in organic single-crystal field-effect transistors, by taking advantage of the inherent softness of organic semiconductors. We compress the crystal lattice uniaxially by bending the flexible devices, leading to an improved charge transport. The mobility increases from 9.7 to 16.5 cm(2) V(-1) s(-1) by 70% under 3% strain. In-depth analysis indicates that compressing the crystal structure directly restricts the vibration of the molecules, thus suppresses dynamic disorder, a unique mechanism in organic semiconductors. Since strain can be easily induced during the fabrication process, we expect our method to be exploited to build high-performance organic devices.

Tuning the ground state of the Kondo lattice in UT Bi2 (T = Ag, Au) single crystals

NASA Astrophysics Data System (ADS)

Rosa, Priscila; Luo, Yongkang; Pagliuso, Pascoal; Bauer, Eric; Thompson, Joe; Fisk, Zachary

2015-03-01

Motivated by the interesting magnetic anisotropy found in the Ce-based heavy fermion family Ce TX2 (T = transition metal, X = pnictogen), here we study the novel U-based parent compounds U TBi2 (T = Ag, Au) by combining magnetization, electrical resistivity, and heat-capacity measurements. The single crystals, synthesized by the self-flux method, also crystallize in the tetragonal HfCuSi2-type structure (space group P4/nmm). Interestingly, although UAgBi2 is a low- γ antiferromagnet below TN = 181 K, UAuBi2 is a moderately heavy uniaxial ferromagnet below Tc = 22 K. Nevertheless, both compounds display the easy-magnetization direction along the c-axis and a large magnetocrystalline anisotropy. Our results point out to an incoherent Kondo behaviour in the paramagnetic state and an intricate competition between crystal field effects and two anisotropic exchange interactions, which lead to the remarkable difference in the observed ground states.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukao, Shinji; Nakanishi, Yoshikazu; Mizoguchi, Tadahiro

X-rays are radiated due to the bremsstrahlung caused by the collision of electrons with a metal target placed opposite the negative electric surface of a crystal by changing the temperature of a LiNbO{sub 3} single crystal uniaxially polarized in the c-axis direction. It is suggested that both electric field intensity and electron density determine the intensity of X-ray radiation. Electrons are supplied by the ionization of residual gas in space, field emission from a case inside which a crystal is located, considered to be due to the high electric-field intensity formed by the surface charges on the crystal, and anmore » external electron source, such as a thermionic source. In a high vacuum, it was found that the electrons supplied by electric-field emission mainly contribute to the radiation of X-rays. It was found that the integrated intensity of X-rays can be maximized by supplying electrons both external and by electric-field emission. Furthermore, the integrated intensity of the X-rays is stable for many repeated temperature changes.« less

Third harmonic frequency generation by type-I critically phase-matched LiB3O5 crystal by means of optically active quartz crystal.

PubMed

Gapontsev, Valentin P; Tyrtyshnyy, Valentin A; Vershinin, Oleg I; Davydov, Boris L; Oulianov, Dmitri A

2013-02-11

We present a method of third harmonic generation at 355 nm by frequency mixing of fundamental and second harmonic radiation of an ytterbium nanosecond pulsed all-fiber laser in a type-I phase-matched LiB(3)O(5) (LBO) crystal where originally orthogonal polarization planes of the fundamental and second harmonic beams are aligned by an optically active quartz crystal. 8 W of ultraviolet light at 355 nm were achieved with 40% conversion efficiency from 1064 nm radiation. The conversion efficiency obtained in a type-I phase-matched LBO THG crystal was 1.6 times higher than the one achieved in a type-II LBO crystal at similar experimental conditions. In comparison to half-wave plates traditionally used for polarization alignment the optically active quartz crystal has much lower temperature dependence and requires simpler optical alignment.

Controlling Crystal Microstructure to Minimize Loss in Polymer Dielectrics

NASA Astrophysics Data System (ADS)

Miranda, Daniel; Iacob, Ciprian; Zhang, Shihai; Runt, James

Polymer dielectric films are of great importance for high performance capacitors. For these films it is critical to reduce dielectric loss, as it diminishes efficiency and contributes to waste heat generation during device operation. Here, a model semi-crystalline polymer, poly(ethylene naphthalate) (PEN), was used to examine how morphological factors inhibit chain relaxations responsible for loss. This was achieved by manipulating the extent of crystallization and the crystalline microstructure through a combination of annealing and uniaxial drawing, and investigating their effects on dielectric performance. Varying crystallization conditions influenced the dynamic Tg and extent of rigid amorphous fraction formation, but had a limited effect on loss magnitude. Film orientation however greatly reduced loss, through strain-induced crystallization and development of oriented amorphous mesophasic regions. Post-drawing annealing conditions were capable of further refining the crystal microstructure and, in turn, the dielectric properties. These findings demonstrate that semi-crystalline polymer morphology has a very strong influence on amorphous chain relaxations, and understanding how processing conditions affect morphology is critical to the rational design of polymer dielectrics. Office of Naval Research.

Voltage sensing systems and methods for passive compensation of temperature related intrinsic phase shift

DOEpatents

Davidson, James R.; Lassahn, Gordon D.

2001-01-01

A small sized electro-optic voltage sensor capable of accurate measurement of high levels of voltages without contact with a conductor or voltage source is provided. When placed in the presence of an electric field, the sensor receives an input beam of electromagnetic radiation into the sensor. A polarization beam displacer serves as a filter to separate the input beam into two beams with orthogonal linear polarizations. The beam displacer is oriented in such a way as to rotate the linearly polarized beams such that they enter a Pockels crystal at a preferred angle of 45 degrees. The beam displacer is therefore capable of causing a linearly polarized beam to impinge a crystal at a desired angle independent of temperature. The Pockels electro-optic effect induces a differential phase shift on the major and minor axes of the input beam as it travels through the Pockels crystal, which causes the input beam to be elliptically polarized. A reflecting prism redirects the beam back through the crystal and the beam displacer. On the return path, the polarization beam displacer separates the elliptically polarized beam into two output beams of orthogonal linear polarization representing the major and minor axes. In crystals that introduce a phase differential attributable to temperature, a compensating crystal is provided to cancel the effect of temperature on the phase differential of the input beam. The system may include a detector for converting the output beams into electrical signals, and a signal processor for determining the voltage based on an analysis of the output beams. The output beams are amplitude modulated by the frequency of the electric field and the amplitude of the output beams is proportional to the magnitude of the electric field, which is related to the voltage being measured.

A Program of Research on Microfabrication Techniques for VLSI Magnetic Devices.

DTIC Science & Technology

1982-10-01

contribution to the implantation- induced uniaxial anisotropy field change. BACKGROUND Magnetic garnet films are grown by liquid phase epitaxy ( LPE ) on non...a single crystal, non-magnetic garnet substrate by the liquid phase epitaxy ( LPE ) method. These thin films , usually one to three microns in thickness...microscopy. Experimental Procedures Films of (SmYGdTm)3Ca0a.Fe4.6012 garnet were grown by liquid phase epitaxy ( LPE ) on gadolinium-gallium garnet (GGG

Low temperature anomalous field effect in SrxBa1-xNb2O6 uniaxial relaxor ferroelectric seen via acoustic emission

NASA Astrophysics Data System (ADS)

Dul'kin, E.; Kojima, S.; Roth, M.

2012-04-01

Sr0.75Ba0.25Nb2O6 [100]-oriented uniaxial tungsten bronze relaxor crystals have been studied by means of dedicated acoustic emission during their thermal cycling in 150-300 K temperature range under dc electric field (E). A 1st order transition in a modulated incommensurate tetragonal phase has been successfully detected at Tmi = 198 K on heating and Tmi = 184 K on cooling, respectively. As field E enhances, a thermal hysteresis gradually narrows and vanishes in the critical point at Eth = 0.31 kV/cm, above which a phase transition becomes to 2nd order. The Tmi(E) dependence looks as a V-shape dip, not similar that previously has been looked as a smeared minimum between both the two polar and nonpolar tetragonal phases near Tm = 220 ÷ 230 K in the same crystals (Dul'kin et al., J Appl. Phys. 110, 044106 (2011)). Due to such a V-shape dip is characteristic for Pb-based multiaxial perovskite relaxor, a rhombohedral phase is waited to be induced by a field E in the critical point temperature range. The emergence of this rhombohedral phase as a crucial evidence of an orthorhombic phase presumably existing within the modulated incommensurate tetragonal phase in tungsten bronze SrxBa1-xNb2O6 relaxor is discussed.

In situ grain fracture mechanics during uniaxial compaction of granular solids

NASA Astrophysics Data System (ADS)

Hurley, R. C.; Lind, J.; Pagan, D. C.; Akin, M. C.; Herbold, E. B.

2018-03-01

Grain fracture and crushing are known to influence the macroscopic mechanical behavior of granular materials and be influenced by factors such as grain composition, morphology, and microstructure. In this paper, we investigate grain fracture and crushing by combining synchrotron x-ray computed tomography and three-dimensional x-ray diffraction to study two granular samples undergoing uniaxial compaction. Our measurements provide details of grain kinematics, contacts, average intra-granular stresses, inter-particle forces, and intra-grain crystal and fracture plane orientations. Our analyses elucidate the complex nature of fracture and crushing, showing that: (1) the average stress states of grains prior to fracture vary widely in their relation to global and local trends; (2) fractured grains experience inter-particle forces and stored energies that are statistically higher than intact grains prior to fracture; (3) fracture plane orientations are primarily controlled by average intra-granular stress and contact fabric rather than the orientation of the crystal lattice; (4) the creation of new surfaces during fracture accounts for a very small portion of the energy dissipated during compaction; (5) mixing brittle and ductile grain materials alters the grain-scale fracture response. The results highlight an application of combined x-ray measurements for non-destructive in situ analysis of granular solids and provide details about grain fracture that have important implications for theory and modeling.

Dependence of Sum Frequency Generation (SFG) Spectral Features on the Mesoscale Arrangement of SFG-Active Crystalline Domains Interspersed in SFG-Inactive Matrix: A Case Study with Cellulose in Uniaxially Aligned Control Samples and Alkali-Treated Secondary Cell Walls of Plants

DOE PAGES

Makarem, Mohamadamin; Sawada, Daisuke; O'Neill, Hugh M.; ...

2017-04-21

Vibrational sum frequency generation (SFG) spectroscopy can selectively detect not only molecules at two-dimensional (2D) interfaces but also noncentrosymmetric domains interspersed in amorphous three-dimensional (3D) matrixes. However, the SFG analysis of 3D systems is more complicated than 2D systems because more variables are involved. One such variable is the distance between SFG-active domains in SFG-inactive matrixes. In this study, we fabricated control samples in which SFG-active cellulose crystals were uniaxially aligned in an amorphous matrix. Assuming uniform separation distances between cellulose crystals, the relative intensities of alkyl (CH) and hydroxyl (OH) SFG peaks of cellulose could be related to themore » intercrystallite distance. The experimentally measured CH/OH intensity ratio as a function of the intercrystallite distance could be explained reasonably well with a model constructed using the theoretically calculated hyperpolarizabilities of cellulose and the symmetry cancellation principle of dipoles antiparallel to each other. In conclusion, this comparison revealed physical insights into the intercrystallite distance dependence of the CH/OH SFG intensity ratio of cellulose, which can be used to interpret the SFG spectral features of plant cell walls in terms of mesoscale packing of cellulose microfibrils.« less

Theory of third-order spectroscopic methods to extract detailed molecular orientational dynamics for planar surfaces and other uniaxial systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishida, Jun; Fayer, Michael D., E-mail: fayer@stanford.edu

Functionalized organic monolayers deposited on planar two-dimensional surfaces are important systems for studying ultrafast orientational motions and structures of interfacial molecules. Several studies have successfully observed the orientational relaxation of functionalized monolayers by fluorescence depolarization experiments and recently by polarization-resolved heterodyne detected vibrational transient grating (HDTG) experiments. In this article we provide a model-independent theory to extract orientational correlation functions unique to interfacial molecules and other uniaxial systems based on polarization-resolved resonant third-order spectroscopies, such as pump-probe spectroscopy, HDTG spectroscopy, and fluorescence depolarization experiment. It will be shown (in the small beam-crossing angle limit) that five measurements are necessary tomore » completely characterize the monolayer's motions: I{sub ∥}(t) and I{sub ⊥}(t) with the incident beams normal to the surface, I{sub ∥}(t) and I{sub ⊥}(t) with a non-zero incident angle, and a time averaged linear dichroism measurement. Once these measurements are performed, two orientational correlation functions corresponding to in-plane and out-of-plane motions are obtained. The procedure is applicable not only for monolayers on flat surfaces, but any samples with uniaxial symmetry such as uniaxial liquid crystals and aligned planar bilayers. The theory is valid regardless of the nature of the actual molecular motions on interface. We then apply the general results to wobbling-in-a-cone model, in which molecular motions are restricted to a limited range of angles. Within the context of the model, the cone angle, the tilt of the cone relative to the surface normal, and the orientational diffusion constant can be determined. The results are extended to describe analysis of experiments where the beams are not crossing in the small angle limit.« less

Ab initio elastic properties and tensile strength of crystalline hydroxyapatite.

PubMed

Ching, W Y; Rulis, Paul; Misra, A

2009-10-01

We report elastic constant calculation and a "theoretical" tensile experiment on stoichiometric hydroxyapatite (HAP) crystal using an ab initio technique. These results compare favorably with a variety of measured data. Theoretical tensile experiments are performed on the orthorhombic cell of HAP for both uniaxial and biaxial loading. The results show considerable anisotropy in the stress-strain behavior. It is shown that the failure behavior of the perfect HAP crystal is brittle for tension along the z-axis with a maximum stress of 9.6 GPa at 10% strain. Biaxial failure envelopes from six "theoretical" loading tests show a highly anisotropic pattern. Structural analysis of the crystal under various stages of tensile strain reveals that the deformation behavior manifests itself mainly in the rotation of the PO(4) tetrahedron with concomitant movements of both the columnar and axial Ca ions. These results are discussed in the context of mechanical properties of bioceramic composites relevant to mineralized tissues.

Polymer lattices as mechanically tunable 3-dimensional photonic crystals operating in the infrared

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chernow, V. F., E-mail: vchernow@caltech.edu; Alaeian, H.; Department of Materials Science and Engineering, Stanford University, Stanford, California 94305

2015-09-07

Broadly tunable photonic crystals in the near- to mid-infrared region could find use in spectroscopy, non-invasive medical diagnosis, chemical and biological sensing, and military applications, but so far have not been widely realized. We report the fabrication and characterization of three-dimensional tunable photonic crystals composed of polymer nanolattices with an octahedron unit-cell geometry. These photonic crystals exhibit a strong peak in reflection in the mid-infrared that shifts substantially and reversibly with application of compressive uniaxial strain. A strain of ∼40% results in a 2.2 μm wavelength shift in the pseudo-stop band, from 7.3 μm for the as-fabricated nanolattice to 5.1 μm when strained.more » We found a linear relationship between the overall compressive strain in the photonic crystal and the resulting stopband shift, with a ∼50 nm blueshift in the reflection peak position per percent increase in strain. These results suggest that architected nanolattices can serve as efficient three-dimensional mechanically tunable photonic crystals, providing a foundation for new opto-mechanical components and devices across infrared and possibly visible frequencies.« less

Relationship between crystal structure and thermo-mechanical properties of kaolinite clay: Beyond standard density functional theory

DOE PAGES

Weck, Philippe F.; Kim, Eunja; Jove-Colon, Carlos F.

2015-03-04

In this study, the structural, mechanical and thermodynamic properties of 1 : 1 layered dioctahedral kaolinite clay, with ideal Al 2Si 2O 5(OH) 4 stoichiometry, were investigated using density functional theory corrected for dispersion interactions (DFT-D2). The bulk moduli of 56.2 and 56.0 GPa predicted at 298 K using the Vinet and Birch–Murnaghan equations of state, respectively, are in good agreement with the recent experimental value of 59.7 GPa reported for well-crystallized samples. The isobaric heat capacity computed for uniaxial deformation of kaolinite along the stacking direction reproduces calorimetric data within 0.7–3.0% from room temperature up to its thermal stabilitymore » limit.« less

Ising-like spin anisotropy and competing antiferromagnetic-ferromagnetic orders in GdBaCo2O5.5 single crystals.

PubMed

Taskin, A A; Lavrov, A N; Ando, Yoichi

2003-06-06

In RBaCo2O5+x compounds (R is rare earth), a ferromagnetic-antiferromagnetic competition is accompanied by a giant magnetoresistance. We study the magnetization of detwinned GdBaCo2O5.5 single crystals and find a remarkable uniaxial anisotropy of Co3+ spins which is tightly linked with the chain oxygen ordering in GdO0.5 planes. Reflecting the underlying oxygen order, CoO2 planes also develop a spin-state order consisting of Co3+ ions in alternating rows of S=1 and S=0 states. The magnetic structure appears to be composed of weakly coupled ferromagnetic ladders with Ising-like moments, which gives a simple picture for magnetotransport phenomena.

The Oseen-Frank Limit of Onsager's Molecular Theory for Liquid Crystals

NASA Astrophysics Data System (ADS)

Liu, Yuning; Wang, Wei

2018-03-01

We study the relationship between Onsager's molecular theory, which involves the effects of nonlocal molecular interactions and the Oseen-Frank theory for nematic liquid crystals. Under the molecular setting, we prove the existence of global minimizers for the generalized Onsager's free energy, subject to a nonlocal boundary condition which prescribes the second moment of the number density function near the boundary. Moreover, when the re-scaled interaction distance tends to zero, the global minimizers will converge to a uniaxial distribution predicted by a minimizing harmonic map. This is achieved through the investigations of the compactness property and the boundary behaviors of the corresponding second moments. A similar result is established for critical points of the free energy that fulfill a natural energy bound.

In situ ultra-small-angle X-ray scattering study under uniaxial stretching of colloidal crystals prepared by silica nanoparticles bearing hydrogen-bonding polymer grafts

DOE PAGES

Ishige, Ryohei; Williams, Gregory A.; Higaki, Yuji; ...

2016-04-19

A molded film of single-component polymer-grafted nanoparticles (SPNP), consisting of a spherical silica core and densely grafted polymer chains bearing hydrogen-bonding side groups capable of physical crosslinking, was investigated byin situultra-small-angle X-ray scattering (USAXS) measurement during a uniaxial stretching process. Static USAXS revealed that the molded SPNP formed a highly oriented twinned face-centered cubic (f.c.c.) lattice structure with the [11-1] plane aligned nearly parallel to the film surface in the initial state. Structural analysis ofin situUSAXS using a model of uniaxial deformation induced by rearrangement of the nanoparticles revealed that the f.c.c. lattice was distorted in the stretching direction inmore » proportion to the macroscopic strain until the strain reached 35%, and subsequently changed into other f.c.c. lattices with different orientations. The lattice distortion and structural transition behavior corresponded well to the elastic and plastic deformation regimes, respectively, observed in the stress–strain curve. The attractive interaction of the hydrogen bond is considered to form only at the top surface of the shell and then plays an effective role in cross-linking between nanoparticles. The rearrangement mechanism of the nanoparticles is well accounted for by a strong repulsive interaction between the densely grafted polymer shells of neighboring particles.« less

300% Enhancement of Carrier Mobility in Uniaxial-Oriented Perovskite Films Formed by Topotactic-Oriented Attachment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Dong Hoe; Park, Jaehong; Li, Zhen

Organic-inorganic perovskites with intriguing optical and electrical properties have attracted significant research interests due to their excellent performance in optoelectronic devices. Recent efforts on preparing uniform and large-grain polycrystalline perovskite films have led to enhanced carrier lifetime up to several microseconds. However, the mobility and trap densities of polycrystalline perovskite films are still significantly behind their single-crystal counterparts. Here, a facile topotactic-oriented attachment (TOA) process to grow highly oriented perovskite films, featuring strong uniaxial-crystallographic texture, micrometer-grain morphology, high crystallinity, low trap density (≈4 x 10 14 cm -3), and unprecedented 9 GHz charge-carrier mobility (71 cm 2 V -1 smore » -1), is demonstrated. TOA-perovskite-based n-i-p planar solar cells show minimal discrepancies between stabilized efficiency (19.0%) and reverse-scan efficiency (19.7%). In conclusion, the TOA process is also applicable for growing other state-of-the-art perovskite alloys, including triple-cation and mixed-halide perovskites.« less

A comparison of different powder compaction processes adopted for synthesis of lead-free piezoelectric ceramics

NASA Astrophysics Data System (ADS)

Mahesh, M. L. V.; Bhanu Prasad, V. V.; James, A. R.

2016-04-01

Barium zirconium titanate, Ba(Zr0.15Ti0.85)O3 nano-crystalline powders were synthesized using high energy ball milling. The calcined powders were compacted adopting two different approaches viz. the conventional uniaxial pressing and cold-isostatic pressing (CIP) and the compacts were sintered at 1350 °C. A single phase perovskite structure was observed in both cases. BZT ceramics compacted using CIP technique exhibited enhanced dielectric and ferroelectric properties compared to ceramics compacted by uniaxial pressing. The polarization current peaks have been used in this paper as an experimental evidence to prove the existence of ferroelectricity in the BZT ceramics under study. The peak polarization current was found to be ~700% higher in case of cold iso-statically compacted ceramics. Similarly electric field induces strain showed a maximum strain ( S max) of 0.08% at an electric field of 28 kV/cm. The dielectric and ferroelectric properties observed are comparable to single crystals of the same material.

300% Enhancement of Carrier Mobility in Uniaxial-Oriented Perovskite Films Formed by Topotactic-Oriented Attachment

DOE PAGES

Kim, Dong Hoe; Park, Jaehong; Li, Zhen; ...

2017-04-18

Organic-inorganic perovskites with intriguing optical and electrical properties have attracted significant research interests due to their excellent performance in optoelectronic devices. Recent efforts on preparing uniform and large-grain polycrystalline perovskite films have led to enhanced carrier lifetime up to several microseconds. However, the mobility and trap densities of polycrystalline perovskite films are still significantly behind their single-crystal counterparts. Here, a facile topotactic-oriented attachment (TOA) process to grow highly oriented perovskite films, featuring strong uniaxial-crystallographic texture, micrometer-grain morphology, high crystallinity, low trap density (≈4 x 10 14 cm -3), and unprecedented 9 GHz charge-carrier mobility (71 cm 2 V -1 smore » -1), is demonstrated. TOA-perovskite-based n-i-p planar solar cells show minimal discrepancies between stabilized efficiency (19.0%) and reverse-scan efficiency (19.7%). In conclusion, the TOA process is also applicable for growing other state-of-the-art perovskite alloys, including triple-cation and mixed-halide perovskites.« less

Structural investigation of the C-O complex in GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alt, H. Ch.; Kersch, A.; Wagner, H. E.

A carbon-oxygen complex occurring in gallium arsenide crystals after annealing at around 700 °C is studied. Fourier transform infrared absorption measurements on the associated vibrational band at 2060 cm-1 under uniaxial stress reveal that the center has tetragonal symmetry. From the intensity of the {sup 18}O-related satellite band it is concluded that four oxygen atoms are involved. Ab initio local density calculations show that a tetragonal CO{sub 4} molecule forms a stable entity in the gallium arsenide lattice.

Luminescent hyperbolic metasurfaces

NASA Astrophysics Data System (ADS)

Smalley, J. S. T.; Vallini, F.; Montoya, S. A.; Ferrari, L.; Shahin, S.; Riley, C. T.; Kanté, B.; Fullerton, E. E.; Liu, Z.; Fainman, Y.

2017-01-01

When engineered on scales much smaller than the operating wavelength, metal-semiconductor nanostructures exhibit properties unobtainable in nature. Namely, a uniaxial optical metamaterial described by a hyperbolic dispersion relation can simultaneously behave as a reflective metal and an absorptive or emissive semiconductor for electromagnetic waves with orthogonal linear polarization states. Using an unconventional multilayer architecture, we demonstrate luminescent hyperbolic metasurfaces, wherein distributed semiconducting quantum wells display extreme absorption and emission polarization anisotropy. Through normally incident micro-photoluminescence measurements, we observe absorption anisotropies greater than a factor of 10 and degree-of-linear polarization of emission >0.9. We observe the modification of emission spectra and, by incorporating wavelength-scale gratings, show a controlled reduction of polarization anisotropy. We verify hyperbolic dispersion with numerical simulations that model the metasurface as a composite nanoscale structure and according to the effective medium approximation. Finally, we experimentally demonstrate >350% emission intensity enhancement relative to the bare semiconducting quantum wells.

The mechanical response of woven Kevlar fabric

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warren, W.E.

1991-01-01

Woven Kevlar fabrics exhibit a number of beneficial mechanical properties which include strength, flexibility, and relatively low density. The desire to engineer or design Kevlar fabrics for specific applications has stimulated interest in the development of theoretical models which relate their effective mechanical properties to specific aspects of the fabric morphology and microstructure. In this work the author provides a theoretical investigation of the large deformation elastic response of a plane woven Kevlar fabric and compares these theoretical results with experimental data obtained from uniaxially loaded Kevlar fabrics. The theoretical analysis assumes the woven fabric to be a regular networkmore » of orthogonal interlaced yarns and the individual yarns are modeled as extensible elastica, thus coupling stretching and bending effects at the outset. This comparison of experiment with theory indicates that the deformation of woven fabric can be quite accurately predicted by modeling the individual yarns as extensible elastica. 2 refs., 1 fig.« less

Investigation about relationships between the symmetries of ferroelectric crystal Ca0.28Ba0.72Nb2O6 and second-harmonic patterns

NASA Astrophysics Data System (ADS)

Xu, Tianxiang; Yu, Haohai; Zhang, Huaijin; Wang, Jiyang

2015-08-01

The broadband quasi-phase matching (QPM) process in a uniaxial ferroelectric crystal Ca0.28Ba0.72Nb2O6 (CBN-28) was demonstrated with the second-harmonic wavelength range from 450 nm to 650 nm, and the relationship between the symmetries of CBN-28 and the second-harmonic patterns was experimentally and theoretically investigated based on the random anti-parallel domains in the crystal and QPM conditions. The dependences of frequency-doubled patterns on the wavelength and anisotropy of the nonlinear crystal were also studied, and the frequency-doubled photons were found to be trapped on circles. By analyzing the light-matter interacting Hamiltonians, the trapping force for second-harmonic photons was found to be centripetal and tunable by the fundamental lasers, and the variation tendencies of the rotational velocity of second-harmonic generation photons could also be predicated. The results indicate that the CBN-28 ferroelectric crystal is a promising nonlinear optical material for the generation of broadband frequency-doubled waves, and the analysis on centripetal force based on the interaction Hamiltonians may provide a novel recognition for the investigation of QPM process to be further studied.

Fluorescence X-ray absorption spectroscopy using a Ge pixel array detector: application to high-temperature superconducting thin-film single crystals.

PubMed

Oyanagi, H; Tsukada, A; Naito, M; Saini, N L; Lampert, M O; Gutknecht, D; Dressler, P; Ogawa, S; Kasai, K; Mohamed, S; Fukano, A

2006-07-01

A Ge pixel array detector with 100 segments was applied to fluorescence X-ray absorption spectroscopy, probing the local structure of high-temperature superconducting thin-film single crystals (100 nm in thickness). Independent monitoring of pixel signals allows real-time inspection of artifacts owing to substrate diffractions. By optimizing the grazing-incidence angle theta and adjusting the azimuthal angle phi, smooth extended X-ray absorption fine structure (EXAFS) oscillations were obtained for strained (La,Sr)2CuO4 thin-film single crystals grown by molecular beam epitaxy. The results of EXAFS data analysis show that the local structure (CuO6 octahedron) in (La,Sr)2CuO4 thin films grown on LaSrAlO4 and SrTiO3 substrates is uniaxially distorted changing the tetragonality by approximately 5 x 10(-3) in accordance with the crystallographic lattice mismatch. It is demonstrated that the local structure of thin-film single crystals can be probed with high accuracy at low temperature without interference from substrates.

Theoretical studies of the electronic properties of ceramic materials

NASA Astrophysics Data System (ADS)

Ching, W. Y.

1990-11-01

The first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method for electronic structure studies has been applied to a variety of complex inorganic crystals. The theory and the practice of the OLCAO method in the local density approximation are discussed in detail. Recent progress in the study of electronic and optical properties of a large list of ceramic systems are summarized. Eight selected topics on different ceramic crystals focusing on specific points of interest are presented as examples. The materials discussed are AlN, Cu2O, beta-Si3N4, Y2O3, LiB3O5, ferroelectric crystals, Fe-B compounds, and the YBa2Cu3O7 superconductor.

One-dimensional spatial dark soliton-induced channel waveguides in lithium niobate crystal.

PubMed

Zhang, Peng; Ma, Yanghua; Zhao, Jianlin; Yang, Dexing; Xu, Honglai

2006-04-01

The anisotropic dependence of the formation of one-dimensional (1-D) spatial dark solitons on the orientation of intensity gradients in lithium niobate crystal is numerically specified. Based on this, we propose an approach to fabricate channel waveguides by employing 1-D spatial dark solitons. By exposure of two 1-D dark solitons with different orientations, channel waveguides can be created. The structures of the channel waveguides can be tuned by adjustment of the widths of the solitons and/or the angles between the two exposures. A square channel waveguide is experimentally demonstrated in an iron-doped lithium niobate crystal by exposure of two orthogonal 1-D dark solitons in sequence.

Anisotropic planar Heisenberg model of the quantum heterobimetallic zigzag chains with bridged ReIV-CuII magnetic complexes

NASA Astrophysics Data System (ADS)

Sobczak, P.; Barasiński, A.; Kamieniarz, G.; Drzewiński, A.

2011-12-01

An anisotropic quantum planar Heisenberg model is proposed and thoroughly analyzed within the numerical density-matrix renormalization group approach. The model takes into account the site-dependent alternating directions of the local coordination system for the ReIV ions and both the axial and the rhombic single-ion anisotropy terms. Thermodynamic properties of a simpler collinear model without the rhombic term and its Ising counterpart as well as some previous approximations for ReIV-ion-containing compounds are discussed to point out the importance of quantum effects and deficiencies of classical approaches. For the noncollinear model with the alternating uniaxial local z axis tilted by the angle θ from the global chain axis formed by copper ions, some symmetries for the single-crystal susceptibilities are found. In the strong-anisotropy limit some striking maxima in the corresponding single-crystal χT products are revealed and their relation to the experimental determination of the anisotropy parameters is emphasized. Some cases to which the collinear model for zigzag chains is fully applicable are indicated. Finally, fitting the reference experimental data for a powder sample of given chloro- and cyanobridged zigzag chains, the weaker magnetic coupling and the uniaxial single-ion anisotropy term parameters have been found. The corrected value of the ferromagnetic interaction parameter implies that for the cyanobridge compound the record of the highest superexchange through cyanide has not been beaten.

Crystallographic and magnetic structure of the novel compound ErGe 1.83

NASA Astrophysics Data System (ADS)

Oleksyn, O.; Schobinger-Papamantellos, P.; Ritter, C.; de Groot, C. H.; Buschow, K. H. J.

1997-02-01

The crystal structure and the magnetic ordering of the novel orthorhombic compound ErGe 2-x has been studied by neutron powder diffraction and magnetic measurements. The crystal structure belongs to the DyGe 1.85-type (space group Cmc2 1)·ErGe 2-x ( x = 0.17 (2)) orders antiferromagnetically below TN = 6 K and displays a metamagnetic behaviour. The magnetic cell has the same size as the chemical unit cell ( q = 0 ). The magnetic space group is Cmc2 1 (Sh 36173). At T = 1.5 K the magnetic moments of the two erbium sites have the same ordered magnetic moment values of 7.63 (6) μB/Er and are antiferromagnetically coupled leading to an uniaxial structure along the a direction.

[Study on spectral gain characterization of FWM processes with multi-frequency pumps in photonic crystal fiber].

PubMed

Hui, Zhan-Qiang

2011-10-01

Spectral gain induced by four-wave-mixing with multi-frequency pump was investigated by exploiting the data signal and continue lights co-propagation in dispersion flattened high nonlinear photonic crystal fiber (PCF). The effects of wavelength drift of pump lights, polarization state of orthogonal or parallel of pump lights, polarization mismatch of signal light versus orthogonal pump lights, total power of signal and probe light on the spectrum gain were analyzed. The results show that good FWM gain effects with multi-frequency pump can be obtained in 36.4 nm wavelength range when power ratio of pump to probe light is appropriate and with identical polarization. Furthermore, the gain of FWM with multi-frequency pump is very sensitive to polarization fluctuation and the different idle waves obtain different gain with the variation in signal polarization state. Moreover, the impact of pump numbers was investigated. The obtained results would be helpful for further research on ultrahigh-speed all optical signal processing devices exploiting the FWM with multi-frequency pump in PCF for future photonics network.

In Situ Imaging during Compression of Plastic Bonded Explosives for Damage Modeling

NASA Astrophysics Data System (ADS)

Yeager, John; Manner, Virginia; Patterson, Brian; Walters, David; Cordes, Nikolaus; Henderson, Kevin; Tappan, Bryce; Luscher, Darby

2017-06-01

The microstructure of plastic bonded explosives (PBXs) is known to influence behavior during insults such as deformation, heating or initiation to detonation. Obtaining three-dimensional microstructural data can be difficult due in part to fragility of the material and small feature size. X-ray computed tomography (CT) is an ideal characterization technique but the explosive crystals and binder in formulations such as PBX 9501 do not have sufficient x-ray contrast to differentiate between the components. Here, we have formulated several PBXs using octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine (HMX) crystals and low-density binder systems. The full three-dimensional microstructure of these samples has been characterized using microscale CT during uniaxial mechanical compression in an interrupted in situ modality. The rigidity of the binder was observed to significantly influence fracture, crystal-binder delamination, and material flow. Additionally, the segmented, 3D images were meshed for finite element simulation. Initial results of the mesoscale modeling exhibit qualitatively similar delamination. Los Alamos National Laboratory - LDRD.

Neutron diffraction study of antiferromagnetic ErNi3Ga9 in magnetic fields

NASA Astrophysics Data System (ADS)

Ninomiya, Hiroki; Sato, Takaaki; Matsumoto, Yuji; Moyoshi, Taketo; Nakao, Akiko; Ohishi, Kazuki; Kousaka, Yusuke; Akimitsu, Jun; Inoue, Katsuya; Ohara, Shigeo

2018-05-01

We report specific heat, magnetization, magnetoresistance, and neutron diffraction measurements of single crystals of ErNi3Ga9. This compound crystalizes in a chiral structure with space group R 32 . The erbium ions form a two-dimensional honeycomb structure. ErNi3Ga9 displays antiferromagnetic order below 6.4 K. We determined that the magnetic structure is slightly amplitude-modulated as well as antiferromagnetic with q = (0 , 0 , 0.5) . The magnetic properties are described by an Ising-like model in which the magnetic moment is always along the c-axis owing to the large uniaxial anisotropy caused by the crystalline electric field effect in the low temperature region. When the magnetic field is applied along the c-axis, a metamagnetic transition is observed around 12 kOe at 2 K. ErNi3Ga9 possesses crystal chirality, but the antisymmetric magnetic interaction, the so-called Dzyaloshinskii-Moriya (DM) interaction, does not contribute to the magnetic structure, because the magnetic moments are parallel to the DM-vector.

Analytical saturated domain orientation textures and electromechanical properties of ferroelectric ceramics due to electric/mechanical poling

NASA Astrophysics Data System (ADS)

Li, F. X.; Rajapakse, R. K. N. D.

2007-03-01

Saturated domain orientation textures of three types of pseudocubic (tetragonal, rhombohedral, and orthorhombic) ferroelectric ceramics after complete electric and uniaxial tension (compression) poling is studied analytically in this paper. A one-dimensional orientation distribution function (ODF) of the domain polar vectors is explicitly derived from the uniform inverse pole figures of the poling field axes on a stereographic projection with respect to the fixed crystallite coordinates. The analytical ODF is used to obtain the analytical solutions of saturated polarization and strain after electric/mechanical poling. Based on the closed form solution of the saturated domain orientation textures, the resultant intrinsic electromechanical properties of ferroelectric ceramics, which depend only on the ODF and properties of the corresponding single crystals, are obtained. The results show how the macroscopic symmetries of ferroelectric crystals change from 4mm (tetragonal), 3m (rhombohedral), and mm2 (orthorhombic) single crystals to a ∞mm (transversely isotropic) completely poled ceramic.

Temperature and baric dependence of nuclear quadruple resonance spectra in indium and gallium monoselenides

NASA Astrophysics Data System (ADS)

Khandozhko, Victor; Raranskii, Nikolai; Balazjuk, Vitaly; Samila, Andriy; Kovalyuk, Zahar

2013-12-01

Pulsed radiospectroscopy method has been used to study nuclear quadruple resonance (NQR) spectra of 69Ga and 115In isotopes in the layered semiconductors GaSe and InSe. It has been found that in GaSe and InSe there is a considerable temperature dependence of NQR frequency which in the temperature range of 250 to 390 K is practically linear with conversion slope 1.54 kHz/degree for 69Ga and 2.35 kHz/degree for 115In. In the same crystals the effect of uniaxial pressure on NQR spectra applied along the optical axis с up to the values of 500 kg/сm2 has been studied. A strong attenuation of NQR spectra intensity with increase in pressure on layered crystal package has been established. The unvaried multiplicity of resonance spectra indicates the absence of structural transformations in these layered crystals over the investigated range of temperatures and pressures.

Macroscopic inhomogeneous deformation behavior arising in single crystal Ni-Mn-Ga foils under tensile loading

NASA Astrophysics Data System (ADS)

Murasawa, Go; Yeduru, Srinivasa R.; Kohl, Manfred

2016-12-01

This study investigated macroscopic inhomogeneous deformation occurring in single-crystal Ni-Mn-Ga foils under uniaxial tensile loading. Two types of single-crystal Ni-Mn-Ga foil samples were examined as-received and after thermo-mechanical training. Local strain and the strain field were measured under tensile loading using laser speckle and digital image correlation. The as-received sample showed a strongly inhomogeneous strain field with intermittence under progressive deformation, but the trained sample result showed strain field homogeneity throughout the specimen surface. The as-received sample is a mainly polycrystalline-like state composed of the domain structure. The sample contains many domain boundaries and large domain structures in the body. Its structure would cause large local strain band nucleation with intermittence. However, the trained one is an ideal single-crystalline state with a transformation preferential orientation of variants after almost all domain boundary and large domain structures vanish during thermo-mechanical training. As a result, macroscopic homogeneous deformation occurs on the trained sample surface during deformation.

The fractography of casting alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Powell, G.W.

1994-10-01

Several types of casting alloys were fractured using various loading modes (uniaxial tension, bending, impact, and torsion, and cyclic stressing), and the corresponding mechanical properties were determined. The unetched and etched fracture surfaces and the microstructures were examined using conventional techniques. The types of casting alloys that were the subjects f these investigations include gray iron, ductile iron, cast steel, and aluminum-base alloys (A380, A356, and 319). The fractographic studies have yielded these generalizations regarding the topography of the fracture surfaces. In the case of low-ductility alloys such as gray iron and the aluminum-base alloys, the tensile edge of amore » fracture surface produced by a stress system with a strong bending-moment component has a highly irregular contour, whereas the compressive edge of the fracture surface is quite straight and parallel to the bend axis. On the other hand, the periphery of a fracture surface produced by uniaxial tension has a completely irregular contour. The fracture surface produced by cyclic loading of a gray iron does not display any macroscopic evidence (such as a thumb nail) of the loading mode. However, the fracture surface of each of the other casting alloys displays clear, macroscopic evidence of failure induced by fatigue. The aluminum-base alloys fracture completely within the interdendritic region of the microstructure when subjected to monotonic loading by uniaxial tension or bending, whereas a fatigue crack propagates predominantly through the primary crystals of the microstructure.« less

Electro-optic high voltage sensor

DOEpatents

Davidson, James R.; Seifert, Gary D.

2002-01-01

A small sized electro-optic voltage sensor capable of accurate measurement of high levels of voltages without contact with a conductor or voltage source is provided. When placed in the presence of an electric field, the sensor receives an input beam of electromagnetic radiation into the sensor. A polarization beam displacer serves as a filter to separate the input beam into two beams with orthogonal linear polarizations. The beam displacer is oriented in such a way as to rotate the linearly polarized beams such that they enter a Pockels crystal having at a preferred angle of 45 degrees. The beam displacer is therefore capable of causing a linearly polarized beam to impinge a crystal at a desired angle independent of temperature. The Pockels electro-optic effect induces a differential phase shift on the major and minor axes of the input beam as it travels through the Pockels crystal, which causes the input beam to be elliptically polarized. A reflecting prism redirects the beam back through the crystal and the beam displacer. On the return path, the polarization beam displacer separates the elliptically polarized beam into two output beams of orthogonal linear polarization representing the major and minor axes. The system may include a detector for converting the output beams into electrical signals, and a signal processor for determining the voltage based on an analysis of the output beams. The output beams are amplitude modulated by the frequency of the electric field and the amplitude of the output beams is proportional to the magnitude of the electric field, which is related to the voltage being measured.

Three-dimensional imaging through turbid media based on polarization-difference liquid-crystal microlens array

NASA Astrophysics Data System (ADS)

Xin, Zhaowei; Wei, Dong; Li, Dapeng; Xie, Xingwang; Chen, Mingce; Zhang, Xinyu; Wang, Haiwei; Xie, Changsheng

2018-02-01

In this paper, a polarization difference liquid-crystal microlens array (PD-LCMLA) for three dimensional imaging application through turbid media is fabricated and demonstrated. This device is composed of a twisted nematic liquidcrystal cell (TNLCC), a polarizer and a liquid-crystal microlens array. The polarizer is sandwiched between the TNLCC and LCMLA to help the polarization difference system achieving the orthogonal polarization raw images. The prototyped camera for polarization difference imaging has been constructed by integrating the PD-LCMLA with an image sensor. The orthogonally polarized light-field images are recorded by switching the working state of the TNLCC. Here, by using a special microstructure in conjunction with the polarization-difference algorithm, we demonstrate that the three-dimensional information in the scattering media can be retrieved from the polarization-difference imaging system with an electrically tunable PD-LCMLA. We further investigate the system's potential function based on the flexible microstructure. The microstructure provides a wide operation range in the manipulation of incident beams and also emerges multiple operation modes for imaging applications, such as conventional planar imaging, polarization imaging mode, and polarization-difference imaging mode. Since the PD-LCMLA demonstrates a very low power consumption, multiple imaging modes and simple manufacturing, this kind of device presents a potential to be used in many other optical and electro-optical systems.

Research into material behaviour of the polymeric samples obtained after 3D-printing and subjected to compression test

NASA Astrophysics Data System (ADS)

Petrov, Mikhail A.; Kosatchyov, Nikolay V.; Petrov, Pavel A.

2016-10-01

The paper represents the results of the study concerning the investigation of the influence of the filling grade (material density) on the force characteristic during the uniaxial compression test of the cylindrical polymer probes produced by additive technology based on FDM. The authors have shown that increasing of the filling grate follows to the increase of the deformation forces. However, the dependency is not a linear function and characterized by soft-elastic model of material behaviour, which is typical for polymers partly crystallized structure.

Near-Infrared Chromophore Functionalized Soft Actuator with Ultrafast Photoresponsive Speed and Superior Mechanical Property.

PubMed

Liu, Li; Liu, Mei-Hua; Deng, Lin-Lin; Lin, Bao-Ping; Yang, Hong

2017-08-23

In this Communication, we develop a two-step acyclic diene metathesis in situ polymerization/cross-linking method to synthesize uniaxially aligned main-chain liquid crystal elastomers with chemically bonded near-infrared absorbing four-alkenyl-tailed croconaine-core cross-linkers. Because of the extraordinary photothermal conversion property, such a soft actuator material can raise its local temperature from 18 to 260 °C in 8 s, and lift up burdens 5600 times heavier than its own weight, under 808 nm near-infrared irradiation.

Multiscale crystal defect dynamics: A coarse-grained lattice defect model based on crystal microstructure

NASA Astrophysics Data System (ADS)

Lyu, Dandan; Li, Shaofan

2017-10-01

Crystal defects have microstructure, and this microstructure should be related to the microstructure of the original crystal. Hence each type of crystals may have similar defects due to the same failure mechanism originated from the same microstructure, if they are under the same loading conditions. In this work, we propose a multiscale crystal defect dynamics (MCDD) model that models defects by considering its intrinsic microstructure derived from the microstructure or material genome of the original perfect crystal. The main novelties of present work are: (1) the discrete exterior calculus and algebraic topology theory are used to construct a scale-up (coarse-grained) dual lattice model for crystal defects, which may represent all possible defect modes inside a crystal; (2) a higher order Cauchy-Born rule (up to the fourth order) is adopted to construct atomistic-informed constitutive relations for various defect process zones, and (3) an hierarchical strain gradient theory based finite element formulation is developed to support an hierarchical multiscale cohesive (process) zone model for various defects in a unified formulation. The efficiency of MCDD computational algorithm allows us to simulate dynamic defect evolution at large scale while taking into account atomistic interaction. The MCDD model has been validated by comparing of the results of MCDD simulations with that of molecular dynamics (MD) in the cases of nanoindentation and uniaxial tension. Numerical simulations have shown that MCDD model can predict dislocation nucleation induced instability and inelastic deformation, and thus it may provide an alternative solution to study crystal plasticity.

A finite-strain homogenization model for viscoplastic porous single crystals: II - Applications

NASA Astrophysics Data System (ADS)

Song, Dawei; Ponte Castañeda, P.

2017-10-01

In part I of this work (Song and Ponte Castañeda, 2017a), a new homogenization-based constitutive model was developed for the finite-strain, macroscopic response of porous viscoplastic single crystals. In this second part, the new model is first used to investigate the instantaneous response and the evolution of the microstructure for porous FCC single crystals for a wide range of loading conditions. The loading orientation, Lode angle and stress triaxiality are found to have significant effects on the evolution of porosity and average void shape, which play crucial roles in determining the overall hardening/softening behavior of porous single crystals. The predictions of the model are found to be in fairly good agreement with numerical simulations available from the literature for all loadings considered, especially for low triaxiality conditions. The model is then used to investigate the strong effect of crystal anisotropy on the instantaneous response and the evolution of the microstructure for porous HCP single crystals. For uniaxial tension and compression, the overall hardening/softening behavior of porous HCP crystals is found to be controlled mostly by the evolution of void shape, and not so much by the evolution of porosity. In particular, porous HCP crystals exhibit overall hardening behavior with increasing porosity, while they exhibit overall softening behavior with decreasing porosity. This interesting behavior is consistent with corresponding results for porous FCC crystals, but is found to be more significant for porous HCP crystals with large anisotropy, such as porous ice, where the non-basal slip systems are much harder than the basal systems.

Stress-dislocation interaction mechanism in low-temperature thermo-compression sintering of Ag NPs

NASA Astrophysics Data System (ADS)

Wang, Fuliang; Tang, Zikai; He, Hu

2018-04-01

The sintering of metal nanoparticles (NPs) has been widely studied in the field of nanotechnology, and low-temperature sintering has become the industry standard. In this study, a molecular dynamics (MD) model was established to study the sintering behaviour of silver NPs during low-temperature thermo-compression. Primarily, we studied the sintering process, in which the ratio of neck radius to particle radius (x/r) changes. Under a uniaxial pressure, the maximum ratio in the temperature range 420-425 K was 1. According to the change of x/r, the process can be broken down into three stages: the neck-formation stage, neck-growth stage, and neck-stability stage. In addition, the relationship between potential energy, internal stress, and dislocation density during sintering is discussed. The results showed that cycling internal stress played an important role in sintering. Under the uniaxial pressure, the stress-dislocation interaction was found to be the major mechanism for thermo-compression sintering because the plastic deformation product dislocation intensified the diffusion of atoms. Also, the displacement vector, the mean square displacement, and the changing crystal structure during sintering were studied.

Morphology study of peroxide-induced dynamically vulcanized polypropylene/ethylene-propylene-diene monomer/zinc dimethacrylate blends during tensile deformation.

PubMed

Chen, Yukun; Xu, Chuanhui; Cao, Liming; Wang, Yanpeng; Fang, Liming

2013-06-27

Polypropylene (PP)/ethylene-propylene-diene monomer (EPDM)/zinc dimethacrylate (ZDMA) blend (EPDM/PP ratio of 30/70) with remarkable extensibility was successfully prepared via peroxide dynamic vulcanization. The uniaxial tensile properties, crystallization behavior, structure, and morphology during stretching were investigated. The tensile process study showed that the PP/EPDM/ZDMA blend exhibited the rubbery-like behavior with an elongation beyond 600%. The ZDMA graft-product domain increased the compatibility and interfacial adhesion between rubber and PP phases, while it reduced the crystallinity of the PP phase. On the basis of TEM and SEM analyses, we found that the cross-linked rubber particles could be elongated and oriented along the tensile direction, whereas the ZDMA graft-product domain "encapsulated" rubber phase together, acting as a "bridge" between elongated rubber phases and the PP phase during uniaxial stretching. The stress could be effectively transferred from the PP phase to the numerous elongated rubber phases due to the excellent compatibility and interfacial adhesion between rubber and PP phases, resulting in the rubbery-like behavior.

Phonon dispersion evolution in uniaxially strained aluminum crystal

NASA Astrophysics Data System (ADS)

Parthasarathy, Ranganathan; Misra, Anil; Aryal, Sitaram; Ouyang, Lizhi

2018-04-01

The influence of loading upon the phonon dispersion of crystalline materials could be highly nonlinear with certain particular trends that depend upon the loading path. In this paper, we have calculated the influence of [100] uniaxial strain on the phonon dispersion and group velocities in fcc aluminum using second moments of position obtained from molecular dynamics (MD) simulation at 300 K. In contrast to nonlinear monotonic variation of both longitudinal and transverse phonon frequencies along the Δ , Λ and Σ lines of the first Brillouin zone under tension, transverse phonon branches along the Λ line show inflection at specific wavevectors when the compressive strain exceeds 5%. Further, the longitudinal group velocities along the high-symmetry Δ line vary non-monotonically with strain, reaching a minimum at 5% compressive strain. Throughout the strain range studied, the equilibrium positions of atoms displace in an affine manner preserving certain static structural symmetry. We attribute the anomalies in the phonon dispersion to the non-affine evolution of second moments of atomic position, and the associated plateauing of force constants under the applied strain path.

Fluoropolymer Microstructure and Dynamics: Influence of Molecular Orientation Induced by Uniaxial Drawing

NASA Astrophysics Data System (ADS)

Miranda, Daniel; Yin, Chaoqing; Runt, James

Fluorinated semi-crystalline polymer films are attractive for dielectric film applications due to their chemical inertness, heat resistance, and high thermal stability. In the present investigation we explore the influence of orientation induced by uniaxial drawing on the crystalline microstructure and relaxation processes of poly(ethylene-tetrafluoroethylene) (ETFE), in order to ascertain how morphological control can benefit polymer dielectric design. When drawn below or near the Tg, the crystallinity of the drawn films is unchanged, and oriented amorphous structures and crystalline microfibrils form at high draw ratios. This orientation slows segmental relaxation, reflected by an increase in the dynamic Tg, and also delays the transition to the high temperature crystalline form of ETFE. When drawing above the Tg, the films undergo strain-induced crystallization at high draw ratios. For these films an increase in the dynamic Tg is also observed, in addition to a second segmental relaxation process, appearing as a shoulder on the primary process. We propose that this represents a contribution from a rigid amorphous fraction, having slowed chain dynamics. Supported by Office of Naval Research.

Scattering and propagation of a Laguerre-Gaussian vortex beam by uniaxial anisotropic bispheres

NASA Astrophysics Data System (ADS)

Qu, Tan; Wu, Zhensen; Shang, Qingchao; Li, Zhengjun; Wu, Jiaji; Li, Haiying

2018-04-01

Within the framework of the generalized multi-particle Mie (GMM) theory, analytical solution to electromagnetic scattering of two interacting homogeneous uniaxial anisotropic spheres by a Laguerre-Gaussian (LG) vortex beam is investigated. The particles with different size and dielectric parameter tensor elements are arbitrarily configured. Based on the continuous boundary conditions at each sphere surface, the interactive scattering coefficients are derived. The internal and near-surface field is investigated to describe the propagation of LG vortex beam through the NaCl crystal. In addition, the far fields of some typical anisotropic medium such as LiNbO3, TiO2 bispheres illuminated by an LG vortex beam are numerically presented in detail to analyze the influence of the anisotropic parameters, sphere positions, separation distance and topological charge etc. The results show that LG vortex beam has a better recovery after interacting with a spherical particle compared with Gaussian beam. The study in the paper are useful for the further research on the scattering and propagation characteristics of arbitrary vortex beam in anisotropic chains and periodic structure.

Mechanochemical formation of heterogeneous diamond structures during rapid uniaxial compression in graphite

NASA Astrophysics Data System (ADS)

Kroonblawd, Matthew P.; Goldman, Nir

2018-05-01

We predict mechanochemical formation of heterogeneous diamond structures from rapid uniaxial compression in graphite using quantum molecular dynamics simulations. Ensembles of simulations reveal the formation of different diamondlike products starting from thermal graphite crystal configurations. We identify distinct classes of final products with characteristic probabilities of formation, stress states, and electrical properties and show through simulations of rapid quenching that these products are nominally stable and can be recovered at room temperature and pressure. Some of the diamond products exhibit significant disorder and partial closure of the energy gap between the highest-occupied and lowest-unoccupied molecular orbitals (i.e., the HOMO-LUMO gap). Seeding atomic vacancies in graphite significantly biases toward forming products with small HOMO-LUMO gap. We show that a strong correlation between the HOMO-LUMO gap and disorder in tetrahedral bonding configurations informs which kinds of structural defects are associated with gap closure. The rapid diffusionless transformation of graphite is found to lock vacancy defects into the final diamond structure, resulting in configurations that prevent s p3 bonding and lead to localized HOMO and LUMO states with a small gap.

Resonant x-ray diffraction revealing chemical disorder in sputtered L10 FeNi on Si(0 0 1)

NASA Astrophysics Data System (ADS)

Frisk, Andreas; Lindgren, Bengt; Pappas, Spiridon D.; Johansson, Erik; Andersson, Gabriella

2016-10-01

In the search for new rare earth free permanent magnetic materials, FeNi with a L10 structure is a possible candidate. We have synthesized the phase in the thin film form by sputtering onto HF-etched Si(0 0 1) substrates. Monatomic layers of Fe and Ni were alternately deposited on a Cu buffer layer, all of which grew epitaxially on the Si substrates. A good crystal structure and epitaxial relationship was confirmed by in-house x-ray diffraction (XRD). The chemical order, which to some part is the origin of an uniaxial magnetic anisotropy, was measured by resonant XRD. The 0 0 1 superlattice reflection was split in two symmetrically spaced peaks due to a composition modulation of the Fe and Ni layers. Furthermore the influence of roughness induced chemical anti-phase domains on the RXRD pattern is exemplified. A smaller than expected magnetic uniaxial anisotropy energy was obtained, which is partly due to the composition modulations, but the major reason is concluded to be the Cu buffer surface roughness.

Resonant x-ray diffraction revealing chemical disorder in sputtered L10 FeNi on Si(0 0 1).

PubMed

Frisk, Andreas; Lindgren, Bengt; Pappas, Spiridon D; Johansson, Erik; Andersson, Gabriella

2016-10-12

In the search for new rare earth free permanent magnetic materials, FeNi with a L10 structure is a possible candidate. We have synthesized the phase in the thin film form by sputtering onto HF-etched Si(0 0 1) substrates. Monatomic layers of Fe and Ni were alternately deposited on a Cu buffer layer, all of which grew epitaxially on the Si substrates. A good crystal structure and epitaxial relationship was confirmed by in-house x-ray diffraction (XRD). The chemical order, which to some part is the origin of an uniaxial magnetic anisotropy, was measured by resonant XRD. The 0 0 1 superlattice reflection was split in two symmetrically spaced peaks due to a composition modulation of the Fe and Ni layers. Furthermore the influence of roughness induced chemical anti-phase domains on the RXRD pattern is exemplified. A smaller than expected magnetic uniaxial anisotropy energy was obtained, which is partly due to the composition modulations, but the major reason is concluded to be the Cu buffer surface roughness.

Uniaxial Strain Redistribution in Corrugated Graphene: Clamping, Sliding, Friction, and 2D Band Splitting.

PubMed

Wang, Xuanye; Tantiwanichapan, Khwanchai; Christopher, Jason W; Paiella, Roberto; Swan, Anna K

2015-09-09

Graphene is a promising material for strain engineering based on its excellent flexibility and elastic properties, coupled with very high electrical mobility. In order to implement strain devices, it is important to understand and control the clamping of graphene to its support. Here, we investigate the limits of the strong van der Waals interaction on friction clamping. We find that the friction of graphene on a SiO2 substrate can support a maximum local strain gradient and that higher strain gradients result in sliding and strain redistribution. Furthermore, the friction decreases with increasing strain. The system used is graphene placed over a nanoscale SiO2 grating, causing strain and local strain variations. We use a combination of atomic force microscopy and Raman scattering to determine the friction coefficient, after accounting for compression and accidental charge doping, and model the local strain variation within the laser spot size. By using uniaxial strain aligned to a high crystal symmetry direction, we also determine the 2D Raman Grüneisen parameter and deformation potential in the zigzag direction.

Method and apparatus for second-rank tensor generation

NASA Technical Reports Server (NTRS)

Liu, Hua-Kuang (Inventor)

1991-01-01

A method and apparatus are disclosed for generation of second-rank tensors using a photorefractive crystal to perform the outer-product between two vectors via four-wave mixing, thereby taking 2n input data to a control n squared output data points. Two orthogonal amplitude modulated coherent vector beams x and y are expanded and then parallel sides of the photorefractive crystal in exact opposition. A beamsplitter is used to direct a coherent pumping beam onto the crystal at an appropriate angle so as to produce a conjugate beam that is the matrix product of the vector beam that propagates in the exact opposite direction from the pumping beam. The conjugate beam thus separated is the tensor output xy (sup T).

Acoustic band gaps of the woodpile sonic crystal with the simple cubic lattice

NASA Astrophysics Data System (ADS)

Wu, Liang-Yu; Chen, Lien-Wen

2011-02-01

This study theoretically and experimentally investigates the acoustic band gap of a three-dimensional woodpile sonic crystal. Such crystals are built by blocks or rods that are orthogonally stacked together. The adjacent layers are perpendicular to each other. The woodpile structure is embedded in air background. Their band structures and transmission spectra are calculated using the finite element method with a periodic boundary condition. The dependence of the band gap on the width of the stacked rods is discussed. The deaf bands in the band structure are observed by comparing with the calculated transmission spectra. The experimental transmission spectra for the Γ-X and Γ-X' directions are also presented. The calculated results are compared with the experimental results.

Tensile strength of Iß crystalline cellulose predicted by molecular dynamics simulation

Treesearch

Xiawa Wu; Robert J. Moon; Ashlie Martini

2014-01-01

The mechanical properties of Iß crystalline cellulose are studied using molecular dynamics simulation. A model Iß crystal is deformed in the three orthogonal directions at three different strain rates. The stress-strain behaviors for each case are analyzed and then used to calculate mechanical properties. The results show that the elastic modulus, Poisson's ratio...

Investigation of Strain Aging in the Ordered Intermetallic Compound beta-NiAl. Ph.D. Thesis Final Contractor Report

NASA Technical Reports Server (NTRS)

Weaver, Mark Lovell

1995-01-01

The phenomenon of strain aging has been investigated in polycrystalline and single crystal NiAl alloys at temperatures between 300 and 1200 K. Static strain aging studies revealed that after annealing at 1100 K for 7200 s (i.e., 2h) followed by furnace cooling, high purity, nitrogen-doped and titanium-doped polycrystalline alloys exhibited continuous yielding, while conventional-purity and carbon-doped alloys exhibited distinct yield points and Luders strains. Prestraining by hydrostatic pressurization removed the yield points, but they could be reintroduced by further annealing treatments. Yield points could be reintroduced more rapidly if the specimens were prestrained uniaxially rather than hydrostatically, owing to the arrangement of dislocations into cell structures during uniaxial deformation. The time dependence of the strain aging events followed at t(exp 2/3) relationship suggesting that the yield points observed in polycrystalline NiAl were the result of the pinning of mobile dislocations by interstitials, specifically carbon. Between 700 and 800 K, yield stress plateaus, yield stress transients upon a ten-fold increase in strain rate, work hardening peaks, and dips in the strain rate sensitivity (SRS) have been observed in conventional-purity and carbon-doped polycrystals. In single crystals, similar behavior was observed; in conventional-purity single crystals, however, the strain rate sensitivity became negative resulting in serrated yielding, whereas, the strain rate sensitivity stayed positive in high purity and in molybdenum-doped NiAl. These observations are indicative of dynamic strain aging (DSA) and are discussed in terms of conventional strain aging theories. The impact of these phenomena on the composition-structure-property relations are discerned. Finally, a good correlation has been demonstrated between the properties of NiAl alloys and a recently developed model for strain aging in metals and alloys developed by Reed-Hill et al.

Computer simulation of thermal conductivity in vulcanized polyisoprene at variable strain and temperature

NASA Astrophysics Data System (ADS)

Engelmann, Sven; Meyer, Jan; Hentschke, Reinhard

2017-08-01

We study the thermal conductivity tensor in an atomistic model of vulcanized cis-1,4-polyisoprene (PI) rubber via molecular dynamics simulations. Our polymer force field is based on V. A. Harmandaris et al. [J. Chem. Phys. 116, 436 (2002), 10.1063/1.1416872], whereas the polymerization algorithm follows the description in J. Hager et al. [Macromolecules 48, 9039 (2015), 10.1021/acs.macromol.5b01864]. The polymer chains are chemically cross linked via sulfur bridges of adjustable cross-link density. A volume-conserving uniaxial strain of up to 200% is applied to the systems. The widely used GROMACS simulation package is adapted to allow using the Green-Kubo approach to calculate the thermal conductivity tensor components. Our analysis of the heat flux autocorrelation functions leads to the conclusion that the thermal conductivity in PI is governed by short-lived phonon modes at low wave numbers due to deformation of the monomers along the polymer backbone. Applying uniaxial strain causes increased orientation of monomers along the strain direction, which enhances the attendant thermal conductivity component. We find an exponential increase of the conductivity in stretch direction in terms of an attendant orientation order parameter. This is accompanied by a simultaneous decline of thermal conductivity in the orthogonal directions. Increase of the cross-link density only has a weak effect on thermal conductivity in the unstrained system, even at high cross-link density. In the strained system we do observed a rising thermal conductivity in the limit of high stress. This increase is attributed to enhanced coupling between chains rather than to their orientation.

Ordonezite from the Theodoso Soto Mine, Sapioris, Durango, Mexico: new data and structure refinement

USGS Publications Warehouse

Ercit, T.S.; Foord, E.E.; Fitzpatrick, J.J.

2002-01-01

A new occurrence of the rare mineral species ordonezite has been found at the Theodoso Soto tin mine, near Sapioris, Durango, Mexico. The average composition of the samples is (Zn0.98Fe0.02)Σ1.00Sb2.00O6; the core of the crystals is slightly richer in Fe than the rim. The mineral is uniaxial (+), with all n greater than 2.30 (ncalc is 2.38 at 589 nm); Dobs 6.66 g/cm3, Dcalc 6.67 g/cm3. It is isostructural with ferrotapiolite, with a 4.668(2), c 9.269(6) A (from powder-diffraction data), space group P42/mnm, and is twinned on {103}. Its crystal structure, refined to R=4.1, wR=4.3% using 163 observed reflections, is fully cation-ordered.

Subdiffractional focusing and guiding of polaritonic rays in a natural hyperbolic material

PubMed Central

Dai, S.; Ma, Q.; Andersen, T.; Mcleod, A. S.; Fei, Z.; Liu, M. K.; Wagner, M.; Watanabe, K.; Taniguchi, T.; Thiemens, M.; Keilmann, F.; Jarillo-Herrero, P.; Fogler, M. M.; Basov, D. N.

2015-01-01

Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. In such materials, light propagation is unusual leading to novel and often non-intuitive optical phenomena. Here we report infrared nano-imaging experiments demonstrating that crystals of hexagonal boron nitride, a natural mid-infrared hyperbolic material, can act as a ‘hyper-focusing lens' and as a multi-mode waveguide. The lensing is manifested by subdiffractional focusing of phonon–polaritons launched by metallic disks underneath the hexagonal boron nitride crystal. The waveguiding is revealed through the modal analysis of the periodic patterns observed around such launchers and near the sample edges. Our work opens new opportunities for anisotropic layered insulators in infrared nanophotonics complementing and potentially surpassing concurrent artificial hyperbolic materials with lower losses and higher optical localization. PMID:25902364

Magnetic measurements of superconducting LiFeAs single crystals under high pressure

NASA Astrophysics Data System (ADS)

Miyoshi, Kiyotaka; Otsuka, Keisuke; Ogawa, Saki; Takeuchi, Jun

2018-05-01

Measurements of DC magnetization for single crystal specimens of LiFeAs have been performed under pressure using liquid argon and NaCl as pressure transmitting media (PTM) to generate hydrostatic and nearly uniaxial pressure along c-axis, respectively. It has been found that Tc linearly decreases under pressure with pressure coefficient dTc / dP ∼ - 1.6 - 1.7 K/GPa, and then shows a pressure independent behavior with Tc ∼ 8 K above 5 GPa. These behaviors are observed independently of whether we select liquid argon or NaCl as PTM. This suggests that c-axis lattice constant is not an important factor to determine Tc in LiFeAs, in contrast to KxFe2-ySe2 and (NH3)yAxFe2Se2 (A=alkali metal).

Device for magneto-optic signal detection with a small crystal prism.

PubMed

Saito, K; Sato, S; Shino, K; Taniguchi, T

2000-03-10

A device made of a birefringent crystal for signal detection of magneto-optic (MO) disks is presented. The light beam from a MO disk is separated into two orthogonally polarized components at the surface of a birefringent prism. After these two components are reflected by the top and the bottom surfaces of the prism inside, at the detector they become sufficiently separated from each other for discrete detection, even though the prism is small. A method for calculating the light intensities and the positions of focused beams in a birefringent prism and the results of a fundamental experiment are presented.

Circularly polarized vacuum field in three-dimensional chiral photonic crystals probed by quantum dot emission

NASA Astrophysics Data System (ADS)

Takahashi, S.; Ota, Y.; Tajiri, T.; Tatebayashi, J.; Iwamoto, S.; Arakawa, Y.

2017-11-01

The modification of a circularly polarized vacuum field in three-dimensional chiral photonic crystals was measured by spontaneous emission from quantum dots in the structures. Due to the circularly polarized eigenmodes along the helical axis in the GaAs-based mirror-asymmetric structures we studied, we observed highly circularly polarized emission from the quantum dots. Both spectroscopic and time-resolved measurements confirmed that the obtained circularly polarized light was influenced by a large difference in the photonic density of states between the orthogonal components of the circular polarization in the vacuum field.

Reconstructing three-dimensional protein crystal intensities from sparse unoriented two-axis X-ray diffraction patterns

PubMed Central

Lan, Ti-Yen; Wierman, Jennifer L.; Tate, Mark W.; Philipp, Hugh T.; Elser, Veit

2017-01-01

Recently, there has been a growing interest in adapting serial microcrystallography (SMX) experiments to existing storage ring (SR) sources. For very small crystals, however, radiation damage occurs before sufficient numbers of photons are diffracted to determine the orientation of the crystal. The challenge is to merge data from a large number of such ‘sparse’ frames in order to measure the full reciprocal space intensity. To simulate sparse frames, a dataset was collected from a large lysozyme crystal illuminated by a dim X-ray source. The crystal was continuously rotated about two orthogonal axes to sample a subset of the rotation space. With the EMC algorithm [expand–maximize–compress; Loh & Elser (2009). Phys. Rev. E, 80, 026705], it is shown that the diffracted intensity of the crystal can still be reconstructed even without knowledge of the orientation of the crystal in any sparse frame. Moreover, parallel computation implementations were designed to considerably improve the time and memory scaling of the algorithm. The results show that EMC-based SMX experiments should be feasible at SR sources. PMID:28808431

Investigation about relationships between the symmetries of ferroelectric crystal Ca{sub 0.28}Ba{sub 0.72}Nb{sub 2}O{sub 6} and second-harmonic patterns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Tianxiang; Yu, Haohai, E-mail: haohaiyu@sdu.edu.cn; Zhang, Huaijin, E-mail: huaijinzhang@sdu.edu.cn

2015-08-07

The broadband quasi-phase matching (QPM) process in a uniaxial ferroelectric crystal Ca{sub 0.28}Ba{sub 0.72}Nb{sub 2}O{sub 6} (CBN-28) was demonstrated with the second-harmonic wavelength range from 450 nm to 650 nm, and the relationship between the symmetries of CBN-28 and the second-harmonic patterns was experimentally and theoretically investigated based on the random anti-parallel domains in the crystal and QPM conditions. The dependences of frequency-doubled patterns on the wavelength and anisotropy of the nonlinear crystal were also studied, and the frequency-doubled photons were found to be trapped on circles. By analyzing the light-matter interacting Hamiltonians, the trapping force for second-harmonic photons was found tomore » be centripetal and tunable by the fundamental lasers, and the variation tendencies of the rotational velocity of second-harmonic generation photons could also be predicated. The results indicate that the CBN-28 ferroelectric crystal is a promising nonlinear optical material for the generation of broadband frequency-doubled waves, and the analysis on centripetal force based on the interaction Hamiltonians may provide a novel recognition for the investigation of QPM process to be further studied.« less

Compensation for Phase Anisotropy of a Metal Reflector

NASA Technical Reports Server (NTRS)

Hong, John

2007-01-01

A method of compensation for the polarization- dependent phase anisotropy of a metal reflector has been proposed. The essence of the method is to coat the reflector with multiple thin alternating layers of two dielectrics that have different indices of refraction, so as to introduce an opposing polarization-dependent phase anisotropy. The anisotropy in question is a phenomenon that occurs in reflection of light at other than normal incidence: For a given plane wave having components polarized parallel (p) and perpendicular (s) to the plane of incidence, the phase of s-polarized reflected light differs from the phase p-polarized light by an amount that depends on the angle of incidence and the complex index of refraction of the metal. The magnitude of the phase difference is zero at zero angle of incidence (normal incidence) and increases with the angle of incidence. This anisotropy is analogous to a phase anisotropy that occurs in propagation of light through a uniaxial dielectric crystal. In such a case, another uniaxial crystal that has the same orientation but opposite birefringence can be used to cancel the phase anisotropy. Although it would be difficult to prepare a birefringent material in a form suitable for application to the curved surface of a typical metal reflector in an optical instrument, it should be possible to effect the desired cancellation of phase anisotropy by exploiting the form birefringence of multiple thin dielectric layers. (The term "form birefringence" can be defined loosely as birefringence arising, in part, from a regular array of alternating subwavelength regions having different indices of refraction.)

Ferroelectric materials for applications in sensor protection

NASA Astrophysics Data System (ADS)

Bhalla, Amar S.; Cross, L. Eric

1995-07-01

The focus of this program has been upon producing and characterizing new functional materials whose properties can be fine tuned to provide eye sensor protection against laser threats and to suit a range of optoelectronic device applications. Material systems that maximize orientational anisotropy (for use in scattering mode systems) and systems that minimize orientational anisotropy (for use in high field modulators and field induced photorefractive applications) were both approached. Relaxor ferroelectric tungsten bronze single crystals (Sr,Ba)Nb2O6 and (Pb,Ba)Nb2O6 solid solution families and relaxor ferroelectric perovskite (1-x)Pb(Mg(1/3)Nb(2/3))O(3-x)PbTiO3 (PMN-PT) families, were studied extensively. The unique capabilities of a laser heated pedestal growth (LHPG) system were utilized for growth of new materials in single crystal fiber form that produces crystals of long interaction length for optical wave in the crystal and high crystal perfection with maximized properties along chosen directions. Hot uniaxial pressing, hot forging, or appropriate solid state reaction processing methods were used to produce transparent polycrystalline ceramics to provide low scattering, high anisotropy ceramics or high scattering, high anisotropy ceramics. This final report summarizes significant results produced from this program through combination of experimental and crystal chemistry approaches in this field, delineates conclusions drawn from the research, and provides recommendations for future research.

Life prediction and constitutive models for engine hot section anisotropic materials program

NASA Technical Reports Server (NTRS)

Nissley, D. M.; Meyer, T. G.

1992-01-01

This report presents the results from a 35 month period of a program designed to develop generic constitutive and life prediction approaches and models for nickel-based single crystal gas turbine airfoils. The program is composed of a base program and an optional program. The base program addresses the high temperature coated single crystal regime above the airfoil root platform. The optional program investigates the low temperature uncoated single crystal regime below the airfoil root platform including the notched conditions of the airfoil attachment. Both base and option programs involve experimental and analytical efforts. Results from uniaxial constitutive and fatigue life experiments of coated and uncoated PWA 1480 single crystal material form the basis for the analytical modeling effort. Four single crystal primary orientations were used in the experiments: (001), (011), (111), and (213). Specific secondary orientations were also selected for the notched experiments in the optional program. Constitutive models for an overlay coating and PWA 1480 single crystal material were developed based on isothermal hysteresis loop data and verified using thermomechanical (TMF) hysteresis loop data. A fatigue life approach and life models were selected for TMF crack initiation of coated PWA 1480. An initial life model used to correlate smooth and notched fatigue data obtained in the option program shows promise. Computer software incorporating the overlay coating and PWA 1480 constitutive models was developed.

Hydrogen-Bonding Network and OH Stretch Vibration of Cellulose: Comparison of Computational Modeling with Polarized IR and SFG Spectra.

PubMed

Lee, Christopher M; Kubicki, James D; Fan, Bingxin; Zhong, Linghao; Jarvis, Michael C; Kim, Seong H

2015-12-10

Hydrogen bonds play critical roles in noncovalent directional interactions determining the crystal structure of cellulose. Although diffraction studies accurately determined the coordinates of carbon and oxygen atoms in crystalline cellulose, the structural information on hydrogen atoms involved in hydrogen-bonding is still elusive. This could be complemented by vibrational spectroscopy; but the assignment of the OH stretch peaks has been controversial. In this study, we performed calculations using density functional theory with dispersion corrections (DFT-D2) for the cellulose Iβ crystal lattices with the experimentally determined carbon and oxygen coordinates. DFT-D2 calculations revealed that the OH stretch vibrations of cellulose are highly coupled and delocalized through intra- and interchain hydrogen bonds involving all OH groups in the crystal. Additionally, molecular dynamics (MD) simulations of a single cellulose microfibril showed that the conformations of OH groups exposed at the microfibril surface are not well-defined. Comparison of the computation results with the experimentally determined IR dichroism of uniaxially aligned cellulose microfibrils and the peak positions of various cellulose crystals allowed unambiguous identification of OH stretch modes observed in the vibrational spectra of cellulose.

Crystallization and properties of Sr-Ba aluminosilicate glass-ceramic matrices

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Hyatt, Mark J.; Drummond, Charles H., III

1991-01-01

Powders of roller quenched (Sr,Ba)O-Al2O3-2SiO2 glasses of various compositions were uniaxially pressed into bars and hot isostatically pressed at 1350 C for 4 hours or cold isostatically pressed and sintered at different temperatures between 800 to 1500 C for 10 or 20 hours. Densities, flexural strengths, and linear thermal expansion were measured for three compositions. The glass transition and crystallization temperatures were determined by Differential Scanning Calorimetry (DSC). The liquidus and crystallization temperature from the melt were measured using high temperature Differential Thermal Analysis (DTA). Crystalline phases formed on heat treatment of the glasses were identified by powder X ray diffraction. In Sr containing glasses, the monoclinic celsian phase always crystallized at temperatures above 1000 C. At lower temperatures, the hexagonal analog formed. The temperature for orthorhombic to hexagonal structural transformation increased monotonically with SrO content, from 327 C for BaO-Al2O3-2SiO2 to 758 C for SrO-Al2O3-2SiO2. These glass powders can be sintered to almost full densities and monoclinic celsian phase at a relatively low temperature of 1100 C.

Crystallization and properties of Sr-Ba aluminosilicate glass-ceramic matrices

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Hyatt, Mark J.; Drummond, Charles H., III

1991-01-01

Powders of roller quenched (Sr,Ba)O-Al2O3-2SiO2 glasses of various compositions were uniaxially pressed into bars and hot isostatically pressed at 1350 C for 4 hours or cold isostatically pressed and sintered at different temperatures between 800 to 1500 C for 10 or 20 hours. Densities, flexural strengths, and linear thermal expansion were measured for three compositions. The glasss transition and crystallization temperatures were determined by Differential Scanning Calorimetry (DSC). The liquidus and crystallization temperature from the melt were measured using high temperature Differential Thermal Analysis (DTA). Crystalline phases formed on heat treatment of the glasses were identified by powder x ray diffraction. In Sr containing glasses, the monoclinic celsian phase always crystallized at temperatures above 1000 C. At lower temperatures, the hexagonal analog formed. The temperature for orthorhombic to hexagonal structure transformation increased monotonically with SrO content, from 327 C for BaO-Al2O3-2SiO2 to 758 C for SrO-Al2O3-2SiO2. These glass powders can be sintered to almost full densities and monoclinic celsian phase at a relatively low temperature of 1100 C.

Common-path conoscopic interferometry for enhanced picosecond ultrasound detection

NASA Astrophysics Data System (ADS)

Liu, Liwang; Guillet, Yannick; Audoin, Bertrand

2018-05-01

We report on a common-path implementation of conoscopic interferometry in picosecond pump-probe reflectometry for simple and efficient detection of picosecond ultrasounds. The interferometric configuration proposed here is greatly simplified, involving only the insertion of a birefringent crystal in a standard reflectometry setup. Our approach is demonstrated by the optical detection of coherent acoustic phonons propagating through thin metal films under two representative geometries, one a particular case where the crystal slab is part of a sample as substrate of a metal film, and the other a more general case where the crystal slab is independent of the sample as part of the detection system. We first illustrate the former with a 300 nm thin film of polycrystalline titanium, deposited by physical vapor deposition on top of a 1 mm-thick uniaxial (0001) sapphire crystal. A signal-to-noise ratio (SNR) enhancement of more than 15 dB is achieved compared to conventional reflectometry. Next, the general case is demonstrated with a 900 nm-tungsten film sputtered on a silicon wafer substrate. More echoes can be discriminated by using the reported approach compared to standard reflectometry, which confirms the improvement in SNR and suggests broad applications for the reported method.

Molecular dynamics simulations of shock waves in oriented nitromethane single crystals: plane-specific effects.

PubMed

He, Lan; Sewell, Thomas D; Thompson, Donald L

2012-01-21

Molecular dynamics simulations of supported shock waves (shock pressure P(s) ∼ 15 GPa) propagating along the [110], [011], [101], and [111] directions in crystalline nitromethane initially at T = 200 K were performed using the nonreactive Sorescu-Rice-Thompson force field [D. C. Sorescu, B. M. Rice, and D. L. Thompson, J. Phys. Chem. B 104, 8406 (2000)]. These simulations, combined with those from a preceding study of shocks propagating along [100], [010], and [001] directions in nitromethane for similar conditions of temperature and shock pressure [L. He, T. D. Sewell, and D. L. Thompson, J. Chem. Phys. 134, 124506 (2011)], have been used to study the post-shock relaxation phenomena. Shocks along [010] and [101] lead to a crystal-crystal structure transformation. Shocks propagating along [011], [110], [111], [100], and [001] exhibit plane-specific disordering, which was characterized by calculating as functions of time the 1D mean square displacement (MSD), 2D radial distribution function (RDF), and 2D orientation order parameter P(2)(θ) in orthogonal planes mutually perpendicular to the shock plane; and by calculating as functions of distance behind the shock front the Cartesian components of intermolecular, intramolecular, and total kinetic energies. The 2D RDF results show that the structural disordering for shocks along [100], [110], and [111] is strongly plane-specific; whereas for shocks along [001] and [011], the loss of crystal structural order is almost equivalent in the orthogonal planes perpendicular to the shock plane. Based on the entire set of simulations, there is a trend for the most extensive disordering to occur in the (010) and (110) planes, less extensive disordering to occur in the (100) plane, and essentially no disordering to occur in the (001) plane. The 2D P(2)(θ) and 1D MSD profiles show, respectively, that the orientational and translational disordering is plane-specific, which results in the plane-specific structural disordering observed in the 2D RDF. By contrast, the kinetic energy partitioning and redistribution do not exhibit plane specificity, as shown by the similarity of spatial profiles of the Cartesian components of the intermolecular, intramolecular, and total kinetic energies in orthogonal planes perpendicular to the shock plane. © 2012 American Institute of Physics

Voltage‐Controlled Switching of Strong Light–Matter Interactions using Liquid Crystals

PubMed Central

Hertzog, Manuel; Rudquist, Per; Hutchison, James A.; George, Jino; Ebbesen, Thomas W.

2017-01-01

Abstract We experimentally demonstrate a fine control over the coupling strength of vibrational light–matter hybrid states by controlling the orientation of a nematic liquid crystal. Through an external voltage, the liquid crystal is seamlessly switched between two orthogonal directions. Using these features, for the first time, we demonstrate electrical switching and increased Rabi splitting through transition dipole moment alignment. The C−Nstr vibration on the liquid crystal molecule is coupled to a cavity mode, and FT‐IR is used to probe the formed vibropolaritonic states. A switching ratio of the Rabi splitting of 1.78 is demonstrated between the parallel and the perpendicular orientation. Furthermore, the orientational order increases the Rabi splitting by 41 % as compared to an isotropic liquid. Finally, by examining the influence of molecular alignment on the Rabi splitting, the scalar product used in theoretical modeling between light and matter in the strong coupling regime is verified. PMID:29155469

Handheld dual thermal neutron detector and gamma-ray spectrometer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stowe, Ashley C.; Burger, Arnold; Bhattacharya, Pijush

2017-05-02

A combined thermal neutron detector and gamma-ray spectrometer system, including: a first detection medium including a lithium chalcopyrite crystal operable for detecting neutrons; a gamma ray shielding material disposed adjacent to the first detection medium; a second detection medium including one of a doped metal halide, an elpasolite, and a high Z semiconductor scintillator crystal operable for detecting gamma rays; a neutron shielding material disposed adjacent to the second detection medium; and a photodetector coupled to the second detection medium also operable for detecting the gamma rays; wherein the first detection medium and the second detection medium do not overlapmore » in an orthogonal plane to a radiation flux. Optionally, the first detection medium includes a .sup.6LiInSe.sub.2 crystal. Optionally, the second detection medium includes a SrI.sub.2(Eu) scintillation crystal.« less

Low-Temperature Crystal Structures of the Hard Core Square Shoulder Model.

PubMed

Gabriëlse, Alexander; Löwen, Hartmut; Smallenburg, Frank

2017-11-07

In many cases, the stability of complex structures in colloidal systems is enhanced by a competition between different length scales. Inspired by recent experiments on nanoparticles coated with polymers, we use Monte Carlo simulations to explore the types of crystal structures that can form in a simple hard-core square shoulder model that explicitly incorporates two favored distances between the particles. To this end, we combine Monte Carlo-based crystal structure finding algorithms with free energies obtained using a mean-field cell theory approach, and draw phase diagrams for two different values of the square shoulder width as a function of the density and temperature. Moreover, we map out the zero-temperature phase diagram for a broad range of shoulder widths. Our results show the stability of a rich variety of crystal phases, such as body-centered orthogonal (BCO) lattices not previously considered for the square shoulder model.

[Preparation of ibuprofen/EC-PVP sustained-release composite particles by supercritical CO2 anti-solvent technology].

PubMed

Cai, Jin-Yuan; Huang, De-Chun; Wang, Zhi-Xiang; Dang, Bei-Lei; Wang, Qiu-Ling; Su, Xin-Guang

2012-06-01

Ibuprofen/ethyl-cellulose (EC)-polyvinylpyrrolidone (PVP) sustained-release composite particles were prepared by using supercritical CO2 anti-solvent technology. With drug loading as the main evaluation index, orthogonal experimental design was used to optimize the preparation process of EC-PVP/ibuprofen composite particles. The experiments such as encapsulation efficiency, particle size distribution, electron microscope analysis, infrared spectrum (IR), differential scanning calorimetry (DSC) and in vitro dissolution were used to analyze the optimal process combination. The orthogonal experimental optimization process conditions were set as follows: crystallization temperature 40 degrees C, crystallization pressure 12 MPa, PVP concentration 4 mgmL(-1), and CO2 velocity 3.5 Lmin(-1). Under the optimal conditions, the drug loading and encapsulation efficiency of ibuprofen/EC-PVP composite particles were 12.14% and 52.21%, and the average particle size of the particles was 27.621 microm. IR and DSC analysis showed that PVP might complex with EC. The experiments of in vitro dissolution showed that ibuprofen/EC-PVP composite particles had good sustained-release effect. Experiment results showed that, ibuprofen/EC-PVP sustained-release composite particles can be prepared by supercritical CO2 anti-solvent technology.

Exploring Orthogonal Hydrogen Bonding towards Designing Organic-Salt-Based Supramolecular Gelators: Synthesis, Structures, and Anticancer Properties.

PubMed

Chakraborty, Poulami; Dastidar, Parthasarathi

2018-05-18

A series of primary ammonium monocarboxylate (PAM) salts derived from β-alanine derivatives of pyrene and naphthalene acetic acid, along with the parent acids, were explored to probe the plausible role of orthogonal hydrogen bonding resulting from amide⋅⋅⋅amide and PAM synthons on gelation. Single-crystal X-ray diffraction (SXRD) studies were performed on two parent acids and five PAM salts in the series. The data revealed that orthogonal hydrogen bonding played an important role in gelation. Structure-property correlation based on SXRD and powder X-ray diffraction data also supported the working hypothesis upon which these gelators were designed. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and cell migration assay on a highly aggressive human breast cancer cell line, MDA-MB-231, revealed that one of the PAM salts in the series, namely, PAA.B2, displayed anticancer properties, and internalization of the gelator salt in the same cell line was confirmed by cell imaging. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evidence for gap anisotropy in SmB6

NASA Astrophysics Data System (ADS)

Derr, J.; Knebel, G.; Lapertot, G.; Salce, B.; Kunii, S.; Flouquet, J.

2007-03-01

Resistivity measurements under uniaxial stress have been performed on the intermediate valence compound SmB6 for various directions of the crystal. The experimental technique allows us to explore a limited pressure area (basically 0-3 kbar). Nevertheless, the results clearly show an anisotropy; indeed, the effect of the stress in the decrease of the residual resistivity is much higher in the <1 1 1> direction than in the <1 0 0> and the <1 1 0> orientations. This change is witness to the gap anisotropy which must be linked to the theory of excitonic semiconductors.

Three holes bound to a double acceptor - Be(+) in germanium

NASA Technical Reports Server (NTRS)

Haller, E. E.; Mcmurray, R. E., Jr.; Falicov, L. M.; Haegel, N. M.; Hansen, W. L.

1983-01-01

A double acceptor binding three holes has been observed for the first time with photoconductive far-infrared spectroscopy in beryllium-doped germanium single crystals. This new center, Be(+), has a hole binding energy of about 5 meV and is only present when free holes are generated by ionization of either neutral shallow acceptors or neutral Be double acceptors. The Be(+) center thermally ionizes above 4 K. It disappears at a uniaxial stress higher than about a billion dyn/sq cm parallel to (111) as a result of the lifting of the valence-band degeneracy.

Entropy-driven crystal formation on highly strained substrates

PubMed Central

Savage, John R.; Hopp, Stefan F.; Ganapathy, Rajesh; Gerbode, Sharon J.; Heuer, Andreas; Cohen, Itai

2013-01-01

In heteroepitaxy, lattice mismatch between the deposited material and the underlying surface strongly affects nucleation and growth processes. The effect of mismatch is well studied in atoms with growth kinetics typically dominated by bond formation with interaction lengths on the order of one lattice spacing. In contrast, less is understood about how mismatch affects crystallization of larger particles, such as globular proteins and nanoparticles, where interparticle interaction energies are often comparable to thermal fluctuations and are short ranged, extending only a fraction of the particle size. Here, using colloidal experiments and simulations, we find particles with short-range attractive interactions form crystals on isotropically strained lattices with spacings significantly larger than the interaction length scale. By measuring the free-energy cost of dimer formation on monolayers of increasing uniaxial strain, we show the underlying mismatched substrate mediates an entropy-driven attractive interaction extending well beyond the interaction length scale. Remarkably, because this interaction arises from thermal fluctuations, lowering temperature causes such substrate-mediated attractive crystals to dissolve. Such counterintuitive results underscore the crucial role of entropy in heteroepitaxy in this technologically important regime. Ultimately, this entropic component of lattice mismatched crystal growth could be used to develop unique methods for heterogeneous nucleation and growth of single crystals for applications ranging from protein crystallization to controlling the assembly of nanoparticles into ordered, functional superstructures. In particular, the construction of substrates with spatially modulated strain profiles would exploit this effect to direct self-assembly, whereby nucleation sites and resulting crystal morphology can be controlled directly through modifications of the substrate. PMID:23690613

Synthesis of an un-supported, high-flow ZSM-22 zeolite membrane

DOEpatents

Thoma, Steven G [Albuquerque, NM; Nenoff, Tina M [Albuquerque, NM

2006-10-10

Novel methods for synthesizing wholly un-supported, high-flow catalytic membranes consisting of 100% crystalline ZSM-22 crystals with no binder phase, having sufficient porosity to allow high Weight Hourly Space Velocities of feedstock to pass through without generating back pressure. The ZSM-22 membranes perform favorably to existing bulk ZSM-22 catalysts (e.g., via 1-butene conversion and selectivity). The method of membrane synthesis, based on Vapor Phase Transport, allows free-standing, binder-less membranes to be fabricated in varied geometries and sizes so that membranes can be tailor-made for particular geometries applications. The ZSM-22 precursor gel may be consolidated into a semi-cohesive body prior to vapor phase crystallization, for example, by uniaxial pressing. These crystalline membranes may be modified by ion exchange, pore ion exchange, framework exchange, synthesis modification techniques to incorporate other elements into the framework, such as K, H, Mg, Zn, V, Ga, and Pt.

Changes in magnetic domain structure during twin boundary motion in single crystal Ni-Mn-Ga exhibiting magnetic shape memory effect

NASA Astrophysics Data System (ADS)

Kopecký, V.; Fekete, L.; Perevertov, O.; Heczko, O.

2016-05-01

The complexity of Ni-Mn-Ga single crystal originates from the interplay between ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure in the vicinity of single twin boundary was studied using magneto-optical indicator film and magnetic force microscopy technique. The single twin boundary of Type I was formed mechanically and an initial magnetization state in both variants were restored by local application of magnetic field (≈40 kA/m). The differently oriented variants exhibited either stripe or labyrinth magnetic domain pattern in agreement with the uniaxial magnetocrystalline anisotropy of the martensite. The twin boundary was then moved by compressive or tensile stress. The passage of the boundary resulted in the formation of granular or rake domains, respectively. Additionally, the specific magnetic domains pattern projected by twin boundary gradually vanished during twin boundary motion.

Non-covalent synthesis of supermicelles with complex architectures using spatially confined hydrogen-bonding interactions

PubMed Central

Li, Xiaoyu; Gao, Yang; Boott, Charlotte E.; Winnik, Mitchell A.; Manners, Ian

2015-01-01

Nature uses orthogonal interactions over different length scales to construct structures with hierarchical levels of order and provides an important source of inspiration for the creation of synthetic functional materials. Here, we report the programmed assembly of monodisperse cylindrical block comicelle building blocks with crystalline cores to create supermicelles using spatially confined hydrogen-bonding interactions. We also demonstrate that it is possible to further program the self-assembly of these synthetic building blocks into structures of increased complexity by combining hydrogen-bonding interactions with segment solvophobicity. The overall approach offers an efficient, non-covalent synthesis method for the solution-phase fabrication of a range of complex and potentially functional supermicelle architectures in which the crystallization, hydrogen-bonding and solvophobic interactions are combined in an orthogonal manner. PMID:26337527

Digital Beam Steering Device Based on Decoupled Birefringent Prism Deflector and Polarization Rotator

NASA Technical Reports Server (NTRS)

Pishnyak, Oleg; Kreminska, Lyubov; Laventovich, Oleg D.; Pouch, John J.; Miranda, Felix A.; Winker, Bruce K.

2004-01-01

We describe digital beam deflectors (DBDs) based on liquid crystals. Each stage of the device comprises a polarization rotator and a birefringent prism deflector. The birefringent prism deflects the beam by an angle that depends on polarization of the incident beam. The prism can be made of the uniaxial smectic A (SmA) liquid crystal (LC) or a solid crystal such as yttrium orthovanadate (YVO4). SmA prisms have high birefringence and can be constructed in a variety of shapes, including single prisms and prismatic blazed gratings of different angles and profiles. We address the challenges of uniform alignment of SmA, such as elimination of focal conic domains. Rotation of linear polarization is achieved by an electrically switched twisted nematic (TN) cell. A DBD composed of N rotator-deflector pairs steers the beam into 2(sup N) directions. As an example, we describe a four-stage DBD deflecting normally incident laser beam within the range of +/- 56 mrad with 8 mrad steps. Redirection of the beam is achieved by switching the TN cells.

Revisiting polarimetry near the isotropic point of an optically active, non-enantiomorphous, molecular crystal.

PubMed

Martin, Alexander T; Tan, Melissa; Nichols, Shane M; Timothy, Emily; Kahr, Bart

2018-07-01

Accurate polarimetric measurements of the optical activity of crystals along low symmetry directions are facilitated by isotropic points, frequencies where dispersion curves of eigenrays cross and the linear birefringence disappears. We report here the optical properties and structure of achiral, uniaxial (point group D 2d ) potassium trihydrogen di-(cis-4-cyclohexene-1,2-dicarboxylate) dihydrate, whose isotropic point was previously detected (S. A. Kim, C. Grieswatch, H. Küppers, Zeit. Krist. 1993; 208:219-222) and exploited for a singular measurement of optical activity normal to the optic axis. The crystal structure associated with the aforementioned study was never published. We report it here, confirming the space group assignment I 4¯c2, along with the frequency dependence of the fundamental optical properties and the constitutive tensors by fitting optical dispersion relations to measured Mueller matrix spectra. k-Space maps of circular birefringence and of the Mueller matrix near the isotropic wavelength are measured and simulated. The signs of optical rotation are correlated with the absolute crystallographic directions. © 2018 Wiley Periodicals, Inc.

Local structure in anisotropic systems determined by molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Komolkin, Andrei V.; Maliniak, Arnold

In the present communication we describe the investigation of local structure using a new visualization technique. The approach is based on two-dimensional pair correlation functions derived from a molecular dynamics computer simulation. We have used this method to analyse a trajectory produced in a simulation of a nematic liquid crystal of 4-n-pentyl-4'-cyanobiphenyl (5CB) (Komolkin et al., 1994, J. chem. Phys., 101, 4103). The molecule is assumed to have cylindrical symmetry, and the liquid crystalline phase is treated as uniaxial. The pair correlation functions or cylindrical distribution functions (CDFs) are calculated in the molecular (m) and laboratory (l) frames, gm2(z1 2, d1 2) and g12(Z1 2, D1 2). Anisotropic molecular organization in the liquid crystal is reflected in laboratory frame CDFs. The molecular excluded volume is determined and the effect of the fast motion in the alkyl chain is observed. The intramolecular distributions are included in the CDFs and indicate the size of the motional amplitude in the chain. Absence of long range order was confirmed, a feature typical for a nematic liquid crystal.

The fatigue damage behavior of a single crystal superalloy

NASA Technical Reports Server (NTRS)

Mcgaw, Michael A.

1988-01-01

The uniaxial fatigue behavior of a single crystal superalloy, PWA 1480, is described. Both monotonic tensile and constant amplitude fatigue tests were conducted at room temperature, in an effort to assess the applicability of polycrystalline-based fatigue life prediction methods to a single crystal superalloy. The observed constant amplitude behavior correlated best using a stress-based life criterion. Nearly all specimens failed at surface or slightly subsurface microporosity; this is thought to be responsible for the unusually large amount of scatter in the test results. An additional term is developed in the stress-life equation for the purpose of accounting for the effect of microporosity on fatigue life. The form chosen is a function of the effective area of the failure-producing microporosity projected on a plane perpendicular to the loading axis, as well as the applied stress. This additional term correlated the data to within factors of two on life. Although speculative, extrapolation of the microporosity relation to zero micropore area indicates that approximately an order of magnitude improvement in fatigue life should result.

On the use of SEM correlative tools for in situ mechanical tests.

PubMed

Shi, Qiwei; Roux, Stéphane; Latourte, Félix; Hild, François; Loisnard, Dominique; Brynaert, Nicolas

2018-01-01

In situ SEM mechanical tests are key to study crystal plasticity. In particular, imaging and diffraction (EBSD) allow microstructure and surface kinematics to be monitored all along the test. However, to get a full benefit from different modalities, it is necessary to register all images and crystallographic orientation maps from EBSD into the same frame. Different correlative approaches tracking either Pt surface markings, crystal orientations or grain boundaries, allow such registrations to be performed and displacement as well as rotation fields to be measured, a primary information for crystal plasticity identification. However, the different contrasts that are captured in different modalities and unavoidable stage motions also give rise to artifacts that are to be corrected to register the different information onto the same material points. The same image correlation tools reveal very powerful to correct such artifacts. Illustrated by an in situ uniaxial tensile test performed on a bainitic-ferritic steel sample, recent advances in image correlation techniques are reviewed and shown to provide a comprehensive picture of local strain and rotation maps. Copyright © 2017 Elsevier B.V. All rights reserved.

An experimental system for high temperature X-ray diffraction studies with in situ mechanical loading

PubMed Central

Oswald, Benjamin B.; Schuren, Jay C.; Pagan, Darren C.; Miller, Matthew P.

2013-01-01

An experimental system with in situ thermomechanical loading has been developed to enable high energy synchrotron x-ray diffraction studies of crystalline materials. The system applies and maintains loads of up to 2250 N in uniaxial tension or compression at a frequency of up to 100 Hz. The furnace heats the specimen uniformly up to a maximum temperature of 1200 °C in a variety of atmospheres (oxidizing, inert, reducing) that, combined with in situ mechanical loading, can be used to mimic processing and operating conditions of engineering components. The loaded specimen is reoriented with respect to the incident beam of x-rays using two rotational axes to increase the number of crystal orientations interrogated. The system was used at the Cornell High Energy Synchrotron Source to conduct experiments on single crystal silicon and polycrystalline Low Solvus High Refractory nickel-based superalloy. The data from these experiments provide new insights into how stresses evolve at the crystal scale during thermomechanical loading and complement the development of high-fidelity material models. PMID:23556825

Vortex Airy beams directly generated via liquid crystal q-Airy-plates

NASA Astrophysics Data System (ADS)

Wei, Bing-Yan; Liu, Sheng; Chen, Peng; Qi, Shu-Xia; Zhang, Yi; Hu, Wei; Lu, Yan-Qing; Zhao, Jian-Lin

2018-03-01

Liquid crystal q-Airy-plates with director distributions integrated by q-plates and polarization Airy masks are proposed and demonstrated via the photoalignment technique. Single/dual vortex Airy beams of opposite topological charges and orthogonal circular polarizations are directly generated with polarization-controllable characteristic. The singular phase of the vortex part is verified by both astigmatic transformation and digital holography. The trajectory of vortex Airy beams is investigated, manifesting separate propagation dynamics of optical vortices and Airy beams. Meanwhile, Airy beams still keep their intrinsic transverse acceleration, self-healing, and nondiffraction features. This work provides a versatile candidate for generating high-quality vortex Airy beams.

Observation of band gaps in the gigahertz range and deaf bands in a hypersonic aluminum nitride phononic crystal slab

NASA Astrophysics Data System (ADS)

Gorisse, M.; Benchabane, S.; Teissier, G.; Billard, C.; Reinhardt, A.; Laude, V.; Defaÿ, E.; Aïd, M.

2011-06-01

We report on the observation of elastic waves propagating in a two-dimensional phononic crystal composed of air holes drilled in an aluminum nitride membrane. The theoretical band structure indicates the existence of an acoustic band gap centered around 800 MHz with a relative bandwidth of 6.5% that is confirmed by gigahertz optical images of the surface displacement. Further electrical measurements and computation of the transmission reveal a much wider attenuation band that is explained by the deaf character of certain bands resulting from the orthogonality of their polarization with that of the source.

Flow-induced birefringence measurement system using dual-crystal transverse electro-optic modulator for microgravity fluid physics applications

NASA Technical Reports Server (NTRS)

Mackey, Jeffrey R.

1999-01-01

We have developed a new instrument that can measure fast transient birefringence and polymer chain orientation angle in complex fluids. The instrument uses a dual-crystal transverse electro-optic modulator with the second crystal's modulation voltage applied 180 deg out of phase from that of the first crystal. In this manner, the second crystal compensates for the intrinsic static birefringence of the first crystal, and it doubles the modulation depth. By incorporating a transverse electro-optic modulator with two lithium-niobate (LiNbO3) crystals oriented orthogonal to each other with a custom-designed optical system, we have produced a very small robust instrument capable of fast transient retardation measurements. By measuring the sample thickness or optical path length through the sample, we can calculate the transient birefringence. This system can also measure dichroism. We have compared the calibration results and retardation and orientation angle measurements of this instrument with those of a photoelastic modulator (PEM) based system using a quarter wave plate and a high-precision 1/16-wave plate to simulate a birefringent sample. Transient birefringence measurements on the order of 10(exp -9) can be measured using either modulator.

Spectral and Polarimetric Analysis of Hyperspectral Data Collected by an Acousto-Optic Tunable Filter System

DTIC Science & Technology

1993-09-23

dioxide ( TeO2 ) crystal which splits a beam of light entering the sensor into a set of two narrow band, orthogonally polarized images for each...See Figure 3) These laws hold true for Light ry V m .Li t ray , &o r air RefairRefractive lade: a, )’i i .- t 1 V Refractive inaex n’ Glass or

Orthogonal time-of-flight mass spectrometry of an ion beam with a broad kinetic energy profile.

PubMed

Miller, S W; Prince, B D; Bemish, R J

2017-10-01

A combined experimental and modeling effort is undertaken to assess a detection system composed of an orthogonal extraction time-of-flight (TOF) mass spectrometer coupled to a continuous ion source emitting an ion beam with kinetic energy of several hundred eV. The continuous ion source comprises an electrospray capillary system employing an undiluted ionic liquid emitting directly into vacuum. The resulting ion beam consists of ions with kinetic energy distributions of width greater than a hundred of eV and mass-to-charge (m/q) ratios ranging from 111 to 500 000 amu/q. In particular, the investigation aims to demonstrate the kinetic energy resolution along the ion beam axis (axial) of orthogonally extracted ions in measurements of the axial kinetic energy-specific mass spectrum, mass flow rate, and total ion current. The described instrument is capable of simultaneous measurement of a broad m/q range in a single acquisition cycle with approximately 25 eV/q axial kinetic energy resolution. Mass resolutions of ∼340 (M/ΔM, FWHM) were obtained for ions at m/q = 1974. Comparison of the orthogonally extracted TOF mass spectrum to mass flow and ion current measurements obtained with a quartz-crystal microbalance and Faraday cup, respectively, shows reasonable numeric agreement and qualitative agreement in the trend as a function of energy defect.

Durability of building stones against artificial salt crystallization

NASA Astrophysics Data System (ADS)

Min, K.; Park, J.; Han, D.

2005-12-01

Salts have been known as the most powerful weathering agents, especially when combined with frost action. Salt crystallization test along with freezing-thawing test and acid immersion test was carried out to assess the durability of building stones against weathering. Granite, limestone, marble and basalt were sampled from different quarries in south Korea for this study. One cycle of artificial salt crystallization test was composed of immersion of cored rock specimens in oversaturated solutions of CaCl2, KCl, NaCl and Na2SO4, respectively for 15 hours and successive drying in an oven of 105°C for 3 hours and cooling at room temperature. Tests were performed up to 30 cycles, and specific gravity and ultrasonic velocity were measured after experiencing every 10 cycles and uniaxial compressive strength was measured only after 30 cycles. During the repeated Na2SO4 salt crystallization, some rock samples were gradually deformed excessively and burst after 20 to 30 cycles of test. The variation patterns of physical properties during the salt crystallization tests are too variable to generalize the effect of salt weathering on physical properties but limestone, marble and basalt samples showed relatively greater change of physical properties than granite samples. The recrystallized salts were well observed in the cracks of rock samples through the scanning electron microscope. In the all salt crystallization tests, apparent specific gravities for all tested samples increased generally but not so significantly due to recrystallization of salts. It can be inferred that filling the pores with salt crystals cause the increase of ultrasonic velocity during the early stage of salt crystallization and then in later stages the repeated cycles of salt crystallization result in development of cracks leading decrease of ultrasonic velocity for some rock samples.

Preparation of a Non-Polar ZnO Film on a Single-Crystal NdGaO3 Substrate by the RF Sputtering Method

NASA Astrophysics Data System (ADS)

Kashiwaba, Y.; Tanaka, Y.; Sakuma, M.; Abe, T.; Imai, Y.; Kawasaki, K.; Nakagawa, A.; Niikura, I.; Kashiwaba, Y.; Osada, H.

2018-04-01

Preparation of non-polar ZnO ( 11\\overline{2} 0 ) films on single-crystal NdGaO3 (NGO) (001) substrates was successfully achieved by the radio frequency (RF) sputtering method. Orientation, deposition rate, and surface roughness of ZnO films strongly depend on the working pressure. Characteristics of ZnO films deposited on single-crystal NGO (001) substrates were compared with those of ZnO films deposited on single-crystal sapphire ( 01\\overline{1} 2 ) substrates. An x-ray diffraction peak of the ZnO ( 11\\overline{2} 0 ) plane was observed on ZnO films deposited on single-crystal NGO (001) substrates under working pressure of less than 0.5 Pa. On the other hand, uniaxially oriented ZnO ( 11\\overline{2} 0 ) films on single-crystal sapphire ( 01\\overline{1} 2 ) substrates were observed under working pressure of 0.1 Pa. The mechanism by which the diffraction angle of the ZnO ( 11\\overline{2} 0 ) plane on single-crystal NGO (001) substrates was shifted is discussed on the basis of anisotropic stress of lattice mismatch. The deposition rate of ZnO films decreased with an increase in working pressure, and the deposition rate on single-crystal NGO (001) substrates was larger than that on single-crystal sapphire ( 01\\overline{1} 2 ) substrates. Root mean square (RMS) roughness of ZnO films increased with an increase in working pressure, and RMS roughness of ZnO films on single-crystal NGO (001) substrates was smaller than that of ZnO films on single-crystal sapphire ( 01\\overline{1} 2 ) substrates even though the film thickness on single-crystal NGO (001) substrates was greater than that on sapphire substrates. It is thought that a single-crystal NGO (001) substrate is useful for deposition of non-polar ZnO ( 11\\overline{2} 0 ) films.

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response

PubMed Central

Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-01-01

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process. PMID:29027925

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response.

PubMed

Hu, Li; Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-10-13

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process.

Ultrafast shock-induced orientation of polycrystalline films: Applications to high explosives

NASA Astrophysics Data System (ADS)

Franken, Jens; Hambir, Selezion A.; Dlott, Dana D.

1999-02-01

Tiny laser-driven shock waves of ˜5 GPa pressure (nanoshocks) are used to study fast mechanical processes occurring in a thin layer of polycrystalline insensitive energetic material, (3-nitro-1,2,4-triazol-5-one) (NTO). Ultrafast coherent Raman spectroscopy of shocked NTO shows the existence of three distinct mechanical processes. Very fast (˜600 ps) changes in intensity and the appearance of new transitions are associated with the uniaxial nature of compression by the shock front. Frequency shifting and broadening processes which track the ˜2 ns duration nanoshock are associated with transient changes in density and temperature. A novel slower process (5-10 ns) starts as the shock begins to unload, and continues for several nanoseconds after the shock is over, resulting in changes of widths and intensities of several vibrational transitions. By comparing ultrafast spectra to static Raman spectra of single NTO crystals in various orientations, it is concluded that this process involves shock-induced partial orientation of the crystals in the NTO layer. The NTO crystals are oriented faster than the time scale for initiating chemical reactions. The sensitivity of explosive crystals to shock initiation may depend dramatically on the orientation of the crystal relative to the direction of shock propagation, so the implications of fast shock-induced orientation for energetic materials initiation are discussed briefly.

In-situ neutron diffraction and crystal plasticity finite element modeling to study the kinematic stability of retained austenite in bearing steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voothaluru, Rohit; Bedekar, Vikram; Xie, Qingge

This work integrates in-situ neutron diffraction and crystal plasticity finite element modeling to study the kinematic stability of retained austenite in high carbon bearing steels. The presence of a kinematically metastable retained austenite in bearing steels can significantly affect the macro-mechanical and micro-mechanical material response. Mechanical characterization of metastable austenite is a critical component in accurately capturing the micro-mechanical behavior under typical application loads. Traditional mechanical characterization techniques are unable to discretely quantify the micro-mechanical response of the austenite, and as a result, the computational predictions rely heavily on trial and error or qualitative descriptions of the austenite phase. Inmore » order to overcome this, in the present work, we use in-situ neutron diffraction of a uniaxial tension test of an A485 Grade 1 bearing steel specimen. The mechanical response determined from the neutron diffraction analysis was incorporated into a hybrid crystal plasticity finite element model that accounts for the martensite's crystal plasticity and the stress-assisted transformation from austenite to martensite in bearing steels. Here, the modeling response was used to estimate the single crystal elastic constants of the austenite and martensite phases. Finally, the results show that using in-situ neutron diffraction, coupled with a crystal plasticity model, can successfully predict both the micro-mechanical and macro-mechanical responses of bearing steels while accounting for the martensitic transformation of the retained austenite.« less

In-situ neutron diffraction and crystal plasticity finite element modeling to study the kinematic stability of retained austenite in bearing steels

DOE PAGES

Voothaluru, Rohit; Bedekar, Vikram; Xie, Qingge; ...

2018-11-21

This work integrates in-situ neutron diffraction and crystal plasticity finite element modeling to study the kinematic stability of retained austenite in high carbon bearing steels. The presence of a kinematically metastable retained austenite in bearing steels can significantly affect the macro-mechanical and micro-mechanical material response. Mechanical characterization of metastable austenite is a critical component in accurately capturing the micro-mechanical behavior under typical application loads. Traditional mechanical characterization techniques are unable to discretely quantify the micro-mechanical response of the austenite, and as a result, the computational predictions rely heavily on trial and error or qualitative descriptions of the austenite phase. Inmore » order to overcome this, in the present work, we use in-situ neutron diffraction of a uniaxial tension test of an A485 Grade 1 bearing steel specimen. The mechanical response determined from the neutron diffraction analysis was incorporated into a hybrid crystal plasticity finite element model that accounts for the martensite's crystal plasticity and the stress-assisted transformation from austenite to martensite in bearing steels. Here, the modeling response was used to estimate the single crystal elastic constants of the austenite and martensite phases. Finally, the results show that using in-situ neutron diffraction, coupled with a crystal plasticity model, can successfully predict both the micro-mechanical and macro-mechanical responses of bearing steels while accounting for the martensitic transformation of the retained austenite.« less

Life prediction and constitutive models for engine hot section anisotropic materials program

NASA Technical Reports Server (NTRS)

Nissley, D. M.; Meyer, T. G.; Walker, K. P.

1992-01-01

This report presents a summary of results from a 7 year program designed to develop generic constitutive and life prediction approaches and models for nickel-based single crystal gas turbine airfoils. The program was composed of a base program and an optional program. The base program addressed the high temperature coated single crystal regime above the airfoil root platform. The optional program investigated the low temperature uncoated single crystal regime below the airfoil root platform including the notched conditions of the airfoil attachment. Both base and option programs involved experimental and analytical efforts. Results from uniaxial constitutive and fatigue life experiments of coated and uncoated PWA 1480 single crystal material formed the basis for the analytical modeling effort. Four single crystal primary orientations were used in the experiments: group of zone axes (001), group of zone axes (011), group of zone axes (111), and group of zone axes (213). Specific secondary orientations were also selected for the notched experiments in the optional program. Constitutive models for an overlay coating and PWA 1480 single crystal materials were developed based on isothermal hysteresis loop data and verified using thermomechanical (TMF) hysteresis loop data. A fatigue life approach and life models were developed for TMF crack initiation of coated PWA 1480. A life model was developed for smooth and notched fatigue in the option program. Finally, computer software incorporating the overlay coating and PWA 1480 constitutive and life models was developed.

A micromechanical constitutive model for anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals

NASA Astrophysics Data System (ADS)

Yu, Chao; Kang, Guozheng; Kan, Qianhua

2015-09-01

Based on the experimental observations on the anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals done by Gall and Maier (2002), a crystal plasticity based micromechanical constitutive model is constructed to describe such anisotropic cyclic deformation. To model the internal stress caused by the unmatched inelastic deformation between the austenite and martensite phases on the plastic deformation of austenite phase, 24 induced martensite variants are assumed to be ellipsoidal inclusions with anisotropic elasticity and embedded in the austenite matrix. The homogeneous stress fields in the austenite matrix and each induced martensite variant are obtained by using the Mori-Tanaka homogenization method. Two different inelastic mechanisms, i.e., martensite transformation and transformation-induced plasticity, and their interactions are considered in the proposed model. Following the assumption of instantaneous domain growth (Cherkaoui et al., 1998), the Helmholtz free energy of a representative volume element of a NiTi shape memory single crystal is established and the thermodynamic driving forces of the internal variables are obtained from the dissipative inequalities. The capability of the proposed model to describe the anisotropic cyclic deformation of super-elastic NiTi single crystals is first verified by comparing the predicted results with the experimental ones. It is concluded that the proposed model can capture the main quantitative features observed in the experiments. And then, the proposed model is further used to predict the uniaxial and multiaxial transformation ratchetting of a NiTi single crystal.

Biaxial potential of surface-stabilized ferroelectric liquid crystals

NASA Astrophysics Data System (ADS)

Kaznacheev, Anatoly; Pozhidaev, Evgeny; Rudyak, Vladimir; Emelyanenko, Alexander V.; Khokhlov, Alexei

2018-04-01

A biaxial surface potential Φs of smectic-C* surface-stabilized ferroelectric liquid crystals (SSFLCs) is introduced in this paper to explain the experimentally observed electric-field dependence of polarization P˜cell(E ) , in particular the shape of the static hysteresis loops. Our potential consists of three independent parts. The first nonpolar part Φn describes the deviation of the prime director n (which is the most probable orientation of the long molecular axes) from the easy alignment axis R , which is located in the boundary surface plane. It is introduced in the same manner as the uniaxial Rapini potential. The second part Φp of the potential is a polar term associated with the presence of the polar axis in a FLC. The third part Φm relates to the inherent FLC biaxiality, which has not been taken into consideration previously. The Φm part takes into account the deviations of the secondary director m (which is the most probable orientation of the short molecular axes) from the normal to the boundary surface. The overall surface potential Φs, which is a sum of Φn,Φp , and Φm, allows one to model the conditions when either one, two, or three minima of the SSFLC cell free energy are realized depending on the biaxiality extent. A monodomain or polydomain structure, as well as the bistability or monostability of SSFLC cells, depends on the number of free-energy minima, as confirmed experimentally. In this paper, we analyze the biaxiality impact on the FLC alignment. We also answer the question of whether the bistable or monostable structure can be formed in an SSFLC cell. Our approach is essentially based on a consideration of the biaxial surface potential, while the uniaxial surface potential cannot adequately describe the experimental observations in the FLC.

Nanosecond electric modification of order parameters

NASA Astrophysics Data System (ADS)

Borshch, Volodymyr

In this Dissertation, we study a nanosecond electro-optic response of a nematic liquid crystal in a geometry where an applied electric field E modifies the tensor order parameter but does not change the orientation of the optic axis (director N̂). We use nematics with negative dielectric anisotropy with the electric field applied perpendicularly to N̂. The field changes the dielectric tensor at optical frequencies (optic tensor), due to the following mechanisms: (a) nanosecond creation of biaxial orientational order; (b) uniaxial modification of the orientational order that occurs over the timescales of tens of nanoseconds, and (c) quenching of director fluctuations with a wide range of characteristic times up to milliseconds. We develop a model to describe the dynamics of all three mechanisms. We design the experimental conditions to selectively suppress the contributions from the quenching of director fluctuations (c) and from the biaxial order effect (a) and thus, separate the contributions of the three mechanisms in the electro-optic response. As a result, the experimental data can be well fitted with the model parameters. The analysis provides a rather detailed physical picture of how the liquid crystal responds to a strong electric field, E ˜ 108 V/m, on a timescale of nanoseconds. This work provides a useful guide in the current search of the biaxial nematic phase. Namely, the temperature dependence of the biaxial susceptibility allows one to estimate the temperature of the potential uniaxial-to-biaxial phase transition. An analysis of the quenching of director fluctuations indicates that on a timescale of nanoseconds, the classic model with constant viscoelastic material parameters might reach its limit of validity. The effect of nanosecond electric modification of the order parameter (NEMOP) can be used in applications in which one needs to achieve ultrafast (nanosecond) changes of optical characteristics, such as birefringence.

Nonlinear geometries in liquid crystals and liquid crystalline polymers

NASA Astrophysics Data System (ADS)

Dingemans, Theo Jacobus

The thermodynamic properties of thermotropic liquid crystals (LCs), and polymeric LCs are strongly dependent on mesogenic shape and in order to explore the relationships between shape and physical properties new, nonlinear geometries were examined. Symmetric oxadiazole based model compounds were synthesized and despite an internal exocyclic bond angle of 134sp° the model compounds exhibit a variety of mesophases. Conoscopic studies on bis(p-hexyloxyphenyl) 4,4sp'- (1,3,4-oxadiazole-2,5-diyl) dicarboxylate in its phase Ssb{A} phase are not consistent with the uniaxial Ssb{A} phase, but rather a biaxial Ssb{CM} phase. Uniaxial and biaxial mesogenic monomers were incorporated in main-chain polyesters. Transition temperatures of the interfacially prepared polymers were higher than materials that were melt polymerized. sp{13}C NMR showed that all polymers prepared by melt condensation have random monomer sequence distributions at the diad level. Thiophene and 1,3-phenylene modified p-quinquephenyls were synthesized in order to investigate the effects of mesogen nonlinearity and dipole direction on the LC thermodynamic properties. Results indicate that shape asymmetry favors mesophase formation and stability; the thiophene dipole moment appears to have no effect. The 120sp° exocyclic bond angle disrupts liquid crystallinity in 1,3-phenylene derivatives. Additionally the placement of 2,5-thiophene in "p-quinquephenyls" affects a red shift in its UV absorption. This was exploited in single layer light emitting diodes (LEDs) to tune the electroluminescence emission. In double layer LEDs these compounds function as efficient hole transport materials with high light outputs. Ferroelectric LCs derived from isoleucine were synthesized and shown to have spontaneous polarizations that are a strong function of halogen size (F > Cl > Br).

Complex free-energy landscapes in biaxial nematic liquid crystals and the role of repulsive interactions: A Wang-Landau study

NASA Astrophysics Data System (ADS)

Kamala Latha, B.; Murthy, K. P. N.; Sastry, V. S. S.

2017-09-01

General quadratic Hamiltonian models, describing the interaction between liquid-crystal molecules (typically with D2 h symmetry), take into account couplings between their uniaxial and biaxial tensors. While the attractive contributions arising from interactions between similar tensors of the participating molecules provide for eventual condensation of the respective orders at suitably low temperatures, the role of cross coupling between unlike tensors is not fully appreciated. Our recent study with an advanced Monte Carlo technique (entropic sampling) showed clearly the increasing relevance of this cross term in determining the phase diagram (contravening in some regions of model parameter space), the predictions of mean-field theory, and standard Monte Carlo simulation results. In this context, we investigated the phase diagrams and the nature of the phases therein on two trajectories in the parameter space: one is a line in the interior region of biaxial stability believed to be representative of the real systems, and the second is the extensively investigated parabolic path resulting from the London dispersion approximation. In both cases, we find the destabilizing effect of increased cross-coupling interactions, which invariably result in the formation of local biaxial organizations inhomogeneously distributed. This manifests as a small, but unmistakable, contribution of biaxial order in the uniaxial phase. The free-energy profiles computed in the present study as a function of the two dominant order parameters indicate complex landscapes. On the one hand, these profiles account for the unusual thermal behavior of the biaxial order parameter under significant destabilizing influence from the cross terms. On the other, they also allude to the possibility that in real systems, these complexities might indeed be inhibiting the formation of a low-temperature biaxial order itself—perhaps reflecting the difficulties in their ready realization in the laboratory.

High Temperature Fatigue Properties Research of GH4169 under Multiaxial Cyclic Loading

NASA Astrophysics Data System (ADS)

Ma, Shaojun; Tong, Dihua; Li, Liyun; Cheng, Yangyang; Hu, Benrun; Chen, Bo

2018-03-01

The high temperature (550°C and 650°C) fatigue properties of GH4169 for thin-wall tube specimen are investigated under uniaxial tension, uniaxial torsion, proportional tension-torsion and nonproportional tension-torsion. All tests are strain-controlled. The results indicate that the shape of the hysteresis loops of uniaxial tension, uniaxial torsion and proportional tension-torsion are similar, but hysteresis loop of non-proportional tension-torsion has distortion; the cyclic softening behavior is shown for GH4169 under uniaxial tension, uniaxial torsion and proportional tension-torsion, but the cyclic hardening behavior is shown for the first several cycles of nonproportional tension-torsion.

Electronic localization in an extreme 1-D conductor: the organic salt (TTDM-TTF) [Au(mnt)

NASA Astrophysics Data System (ADS)

Lopes, E. B.; Alves, H.; Ribera, E.; Mas-Torrent, M.; Auban-Senzier, P.; Canadell, E.; Henriques, R. T.; Almeida, M.; Molins, E.; Veciana, J.; Rovira, C.; Jérome, D.

2002-09-01

This article reports the investigation of a new low-dimensional organic salt, (TTDM-TTF)2 [ Au(mnt)2] , by single crystal X-ray diffraction, static magnetic susceptibility, EPR, thermopower, electrical resistivity measurements under pressure up to 25 kbar and band structure calculations. The crystal structure consists in a dimerized head to tail stacking of TTDM-TTF molecules separated by layers of orthogonal Au(mnt)2 anions. The absence of overlap between neighboring chains coming from this particular crystal structure leads to an extreme one-dimensionality (1-D) for which the carriers of the half-filled conduction band become strongly localized in a Mott-Hubbard insulating state. This material is the first 1-D conductor in which the Mott-Hubbard insulating character cannot be suppressed under pressure.

Topologically protected bound states in photonic parity-time-symmetric crystals.

PubMed

Weimann, S; Kremer, M; Plotnik, Y; Lumer, Y; Nolte, S; Makris, K G; Segev, M; Rechtsman, M C; Szameit, A

2017-04-01

Parity-time (PT)-symmetric crystals are a class of non-Hermitian systems that allow, for example, the existence of modes with real propagation constants, for self-orthogonality of propagating modes, and for uni-directional invisibility at defects. Photonic PT-symmetric systems that also support topological states could be useful for shaping and routing light waves. However, it is currently debated whether topological interface states can exist at all in PT-symmetric systems. Here, we show theoretically and demonstrate experimentally the existence of such states: states that are localized at the interface between two topologically distinct PT-symmetric photonic lattices. We find analytical closed form solutions of topological PT-symmetric interface states, and observe them through fluorescence microscopy in a passive PT-symmetric dimerized photonic lattice. Our results are relevant towards approaches to localize light on the interface between non-Hermitian crystals.

Effects of flow on the dynamics of a ferromagnetic nematic liquid crystal

NASA Astrophysics Data System (ADS)

Potisk, Tilen; Pleiner, Harald; Svenšek, Daniel; Brand, Helmut R.

2018-04-01

We investigate the effects of flow on the dynamics of ferromagnetic nematic liquid crystals. As a model, we study the coupled dynamics of the magnetization, M , the director field, n , associated with the liquid crystalline orientational order, and the velocity field, v . We evaluate how simple shear flow in a ferromagnetic nematic is modified in the presence of small external magnetic fields, and we make experimentally testable predictions for the resulting effective shear viscosity: an increase by a factor of 2 in a magnetic field of about 20 mT. Flow alignment, a characteristic feature of classical uniaxial nematic liquid crystals, is analyzed for ferromagnetic nematics for the two cases of magnetization in or perpendicular to the shear plane. In the former case, we find that small in-plane magnetic fields are sufficient to suppress tumbling and thus that the boundary between flow alignment and tumbling can be controlled easily. In the latter case, we furthermore find a possibility of flow alignment in a regime for which one obtains tumbling for the pure nematic component. We derive the analogs of the three Miesowicz viscosities well-known from usual nematic liquid crystals, corresponding to nine different configurations. Combinations of these can be used to determine several dynamic coefficients experimentally.

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites.

PubMed

Kim, Hojin; Zhu, Bohan; Chen, Huiying; Adetiba, Oluwatomiyin; Agrawal, Aditya; Ajayan, Pulickel; Jacot, Jeffrey G; Verduzco, Rafael

2016-02-06

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and as soft robots. Here, we demonstrate the preparation of shape-responsive liquid crystal elastomers (LCEs) and LCE nanocomposites along with characterization of their shape-responsiveness, mechanical properties, and microstructure. Two types of LCEs - polysiloxane-based and epoxy-based - are synthesized, aligned, and characterized. Polysiloxane-based LCEs are prepared through two crosslinking steps, the second under an applied load, resulting in monodomain LCEs. Polysiloxane LCE nanocomposites are prepared through the addition of conductive carbon black nanoparticles, both throughout the bulk of the LCE and to the LCE surface. Epoxy-based LCEs are prepared through a reversible esterification reaction. Epoxy-based LCEs are aligned through the application of a uniaxial load at elevated (160 °C) temperatures. Aligned LCEs and LCE nanocomposites are characterized with respect to reversible strain, mechanical stiffness, and liquid crystal ordering using a combination of imaging, two-dimensional X-ray diffraction measurements, differential scanning calorimetry, and dynamic mechanical analysis. LCEs and LCE nanocomposites can be stimulated with heat and/or electrical potential to controllably generate strains in cell culture media, and we demonstrate the application of LCEs as shape-responsive substrates for cell culture using a custom-made apparatus.

Cells Recognize and Prefer Bone-like Hydroxyapatite: Biochemical Understanding of Ultrathin Mineral Platelets in Bone.

PubMed

Liu, Cuilian; Zhai, Halei; Zhang, Zhisen; Li, Yaling; Xu, Xurong; Tang, Ruikang

2016-11-09

Hydroxyapatite (HAP) nanocrystallites in all types of bones are distinguished by their ultrathin characteristics, which are uniaxially oriented with fibrillar collagen to uniquely expose the (100) faces. We speculate that living organisms prefer the specific crystal morphology and orientation of HAP because of the interactions between cells and crystals at the mineral-cell interface. Here, bone-like platy HAP (p-HAP) and two different rod-like HAPs were synthesized to investigate the ultrathin mineral modulating effect on cell bioactivity and bone generation. Cell viability and osteogenic differentiation of mesenchymal stem cells (MSCs) were significantly promoted by the platy HAP with (100) faces compared to rod-like HAPs with (001) faces as the dominant crystal orientation, which indicated that MSCs can recognize the crystal face and prefer the (100) HAP faces. This face-specific preference is dependent on the selective adsorption of fibronectin (FN), a plasma protein that plays a central role in cell adhesion, on the HAP surface. This selective adsorption is further confirmed by molecule dynamics (MD) simulation. Our results demonstrate that it is an intelligent choice for cells to use ultrathin HAP with a large (100) face as a basic building block in the hierarchical structure of bone, which is crucial to the promotion of MSCs osteoinductions during bone formation.

Highly anisotropic exchange interactions of j eff = 1 2 iridium moments on the fcc lattice in La 2 B IrO 6   ( B = Mg , Zn )

DOE PAGES

Aczel, A. A.; Cook, A. M.; Williams, T. J.; ...

2016-06-20

Here we have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites Lamore » $$_2$$ZnIrO$$_6$$ and La$$_2$$MgIrO$$_6$$, which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated $$j_{\\rm eff}=1/2$$ Mott insulators provide clear evidence for gapped spin wave excitations with very weak dispersion. The INS results and thermodynamic data on these materials can be reproduced by conventional Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only arise from the weak crystal distortions away from the ideal fcc limit. This may suggest that even weak distortions in $$j_{\\rm eff}=1/2$$ Mott insulators might lead to strong exchange anisotropies. More tantalizingly, however, we find an alternative viable explanation of the INS results in terms of spin models with a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the highly-directional Kitaev interaction is a type of exchange anisotropy which is symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev couplings generated by the symmetry-lowering due to lattice distortions can pin the order and enhance the magnon gap. In conclusion, our findings highlight how even conventional magnetic orders in heavy transition metal oxides may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling.« less

A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell

NASA Astrophysics Data System (ADS)

Lin, Yi-Hsin; Chen, Ming-Syuan; Lin, Wei-Chih; Tsou, Yu-Shih

2012-07-01

A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell (T-PNLC) is demonstrated. T-PNLC consists of three layers. Liquid crystal (LC) directors in the two layers near glass substrates are orthogonal to each other and those two layers modulate two eigen-polarizations of an incident light. As a result, two eigen-polarizations of an incident light experience the same phase shift. In the middle layer, LC directors are perpendicular to the glass substrate and contribute no phase shift. The phase shift of T-PNLC is electrically tunable and polarization-independent. T-PNLC does not require any bias voltage for operation. The phase shift is 0.28 π rad for the voltage of 30 Vrms. By measuring and analyzing the optical phase shift of T-PNLC at the oblique incidence of transverse magnetic wave, the pretilt angle of LC directors and the effective thickness of three layers are obtained and discussed. The potential applications are spatial light modulators, laser beam steering, and micro-lens arrays.

Absence of internal conical refraction with the spatially dispersive index surface of fluorine; discussion of the orthogonality of the Poynting vector to the index surface.

PubMed

Dettwiller, Luc

2006-04-17

Since 2001 the intrinsic birefringence of fluorine has been accessible to experiment. It is known that its intrinsic anisotropy is entirely due to spatial dispersion, and that the index surface of fluorine and crystals with the same symmetry has seven optical axes, four of them intersecting this surface at pairs of conical points. I point out the fact that there is no internal conical refraction, but only simple refraction (and without walkoff), with these conical points. I also explain why the rays are not a priori normal to the index surface in the case of fluorine because of its spatial dispersion; and I discuss two particular cases of spatial dispersion where the Poynting vector remains orthogonal to the index surface.

Involvement of conformational isomerism in the complexity of the crystal network of 1-(4-nitrophenyl)-1H-1,3-benzimidazole derivatives driven by C-H...A (A = NO2, Npy and π) and orthogonal Npy...NO2 and ONO...Csp2 interactions.

PubMed

García-Aranda, Mónica I; Gómez-Castro, Carlos Z; García-Báez, Efrén V; Gómez, Yolanda Gómez Y; Castrejón-Flores, José L; Padilla-Martínez, Itzia I

2018-04-01

A detailed structural analysis of the benzimidazole nitroarenes 1-(4-nitrophenyl)-1H-1,3-benzimidazole, C 13 H 9 N 3 O 2 , (I), 1-(4-nitrophenyl)-2-phenyl-1H-1,3-benzimidazole, C 19 H 13 N 3 O 2 , (II), and 2-(3-methylphenyl)-1-(4-nitrophenyl)-1H-1,3-benzimidazole, C 20 H 15 N 3 O 2 , (III), has been performed. They are nonplanar structures whose crystal arrangement is governed by Csp 2 -H...A (A = NO 2 , N py and π) hydrogen bonding. The inherent complexity of the supramolecular arrangements of compounds (I) (Z' = 2) and (II) (Z' = 4) into tapes, helices and sheets is the result of the additional participation of π-π NO2 and n-π* (n = O and N py ; π* = Csp 2 and N NO2 ) interactions that contribute to the stabilization of the equi-energetic conformations adopted by each of the independent molecules in the asymmetric unit. In contrast, compound (III) (Z' = 1) is self-paired, probably due to the effect of the steric demand of the methyl group on the crystal packing. Theoretical ab initio calculations confirmed that the presence of the arene ring at the benzimidazole 2-position increases the rotational barrier of the nitrobenzene ring and also supports the electrostatic nature of the orthogonal ONO...Csp 2 and N py ...NO 2 interactions.

Capsize of polarization in dilute photonic crystals.

PubMed

Gevorkian, Zhyrair; Hakhoumian, Arsen; Gasparian, Vladimir; Cuevas, Emilio

2017-11-29

We investigate, experimentally and theoretically, polarization rotation effects in dilute photonic crystals with transverse permittivity inhomogeneity perpendicular to the traveling direction of waves. A capsize, namely a drastic change of polarization to the perpendicular direction is observed in a one-dimensional photonic crystal in the frequency range 10 ÷ 140 GHz. To gain more insights into the rotational mechanism, we have developed a theoretical model of dilute photonic crystal, based on Maxwell's equations with a spatially dependent two dimensional inhomogeneous dielectric permittivity. We show that the polarization's rotation can be explained by an optical splitting parameter appearing naturally in Maxwell's equations for magnetic or electric fields components. This parameter is an optical analogous of Rashba like spin-orbit interaction parameter present in quantum waves, introduces a correction to the band structure of the two-dimensional Bloch states, creates the dynamical phase shift between the waves propagating in the orthogonal directions and finally leads to capsizing of the initial polarization. Excellent agreement between theory and experiment is found.

Anisotropies in the linear polarization of vacancy photoluminescence in diamond induced by crystal rotations and strong magnetic fields

NASA Astrophysics Data System (ADS)

Braukmann, D.; Popov, V. P.; Glaser, E. R.; Kennedy, T. A.; Bayer, M.; Debus, J.

2018-03-01

We study the linear polarization properties of the photoluminescence of ensembles of neutral and negatively charged nitrogen vacancies and neutral vacancies in diamond crystals as a function of their symmetry and their response to strong external magnetic fields. The linear polarization degree, which exceeds 10% at room temperature, and rotation of the polarization plane of their zero-phonon lines significantly depend on the crystal rotation around specific axes demonstrating anisotropic angular evolutions. The sign of the polarization plane rotation is changed periodically through the crystal rotation, which indicates a switching between electron excited states of orthogonal linear polarizations. At external magnetic fields of up to 10 T, the angular dependencies of the linear polarization degree experience a remarkable phase shift. Moreover, the rotation of the linear polarization plane increases linearly with rising magnetic field at 6 K and room temperature, for the negatively charged nitrogen vacancies, which is attributed to magneto-optical Faraday rotation.

Effects of uniaxial strain on electron effective mass and tunneling capability of direct gap Ge{sub 1−x}Sn{sub x} alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Lei; Liang, Renrong, E-mail: liangrr@tsinghua.edu.cn; Wang, Jing

2016-01-15

Direct gap Ge{sub 1−x}Sn{sub x} alloys under [100] and [110] uniaxial strain are comprehensively investigated by theoretical calculations using the nonlocal empirical pseudopotential method (EPM). It is shown that [100] uniaxial tensile strain aids indirect-to-direct gap transition in Ge{sub 1−x}Sn{sub x} alloys. The Γ electron effective mass along the optimal direction under [110] uniaxial strain is smaller than those under [100] uniaxial strain and (001) biaxial strain. Additionally, the direct tunneling gap is smallest along the strain-perpendicular direction under [110] uniaxial tensile strain, resulting in a maximum direct band-to-band tunneling generation rate. An optimal [110] uniaxial tensile strain is favorablemore » for high-performance direct gap Ge{sub 1−x}Sn{sub x} electronic devices.« less

[Preparation of curcumin-EC sustained-release composite particles by supercritical CO2 anti-solvent technology].

PubMed

Bai, Wei-li; Yan, Ting-yuan; Wang, Zhi-xiang; Huang, De-chun; Yan, Ting-xuan; Li, Ping

2015-01-01

Curcumin-ethyl-cellulose (EC) sustained-release composite particles were prepared by using supercritical CO2 anti-solvent technology. With drug loading and yield of inclusion complex as evaluation indexes, on the basis of single factor tests, orthogonal experimental design was used to optimize the preparation process of curcumin-EC sustained-release composite particles. The experiments such as drug loading, yield, particle size distribution, electron microscope analysis (SEM) , infrared spectrum (IR), differential scanning calorimetry (DSC) and in vitro dissolution were used to analyze the optimal process combination. The orthogonal experimental optimization process conditions were set as follows: crystallization temperature 45 degrees C, crystallization pressure 10 MPa, curcumin concentration 8 g x L(-1), solvent flow rate 0.9 mL x min(-1), and CO2 velocity 4 L x min(-1). Under the optimal conditions, the average drug loading and yield of curcumin-EC sustained-release composite particles were 33.01% and 83.97%, and the average particle size of the particles was 20.632 μm. IR and DSC analysis showed that curcumin might complex with EC. The experiments of in vitro dissolution showed that curcumin-EC composite particles had good sustained-release effect. Curcumin-EC sustained-release composite particles can be prepared by supercritical CO2 anti-solvent technology.

Crystal structure of 2-benzoyl­amino-N′-(4-hy­droxy­benzyl­idene)-3-(thio­phen-2-yl)prop-2-eno­hydrazide

PubMed Central

Subbulakshmi, Karanth N.; Narayana, Badiadka; Yathirajan, Hemmige S.; Jasinski, Jerry P.; Rathore, Ravindranath S.; Glidewell, Christopher

2016-01-01

In the title compound, C21H17N3O3S, the non-H atoms, apart from those in the benzoyl group, are almost coplanar (r.m.s. deviation = 0.049 Å) and the benzoyl group is almost orthogonal to the plane of the rest of the mol­ecule [dihedral angle = 80.34 (6)°]. In the crystal, a combination of N—H⋯O and asymmetric bifurcated O—H⋯(N,O) hydrogen bonds link the mol­ecules into a three-dimensional network. Weak C—H⋯O inter­actions are also observed. PMID:27536390

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate—Part I: Cu(II)—a case of orthorhombic symmetry

NASA Astrophysics Data System (ADS)

Sambasiva Rao, P.; Rajendiran, T. M.; Venkatesan, R.; Madhu, N.; Chandrasekhar, A. V.; Reddy, B. J.; Reddy, Y. P.; Ravikumar, R. V. S. S. N.

2001-12-01

Single crystal electron paramagnetic resonance (EPR) studies on Cu(II) doped zinc potassium phosphate hexahydrate (ZPPH) were carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice substitutionally in place of Zn(II) and the spin Hamiltonian parameters calculated from these spectra are gxx=2.188, gyy=2.032, gzz=2.373, Axx=50 G, Ayy=65.0 G and Azz=80 G. The g and A tensors were coincident and these values matched fairly well with the values obtained from powder spectrum. The bonding parameters have also been calculated.

3-Nitro-phenol-1,3,5-triazine-2,4,6-tri-amine (2/1).

PubMed

Sangeetha, V; Kanagathara, N; Chakkaravarthi, G; Marchewka, M K; Anbalagan, G

2013-06-01

The asymmetric unit of the title compound, C3H6N6·2C6H5NO3, contains one melamine and two 3-nitro-phenol mol-ecules. The mean planes of the 3-nitro-phenol mol-ecules are almost orthogonal to the plane of melamine, making dihedral angles of 82.77 (4) and 88.36 (5)°. In the crystal, mol-ecules are linked via O-H⋯N, N-H⋯N and N-H⋯O hydrogen bonds, forming a three-dimensional network. The crystal also features weak C-H⋯π and π-π inter-actions [centroid-centroid distance = 3.9823 (9) Å].

The Multiphase Rheology of Andesitic Magmas from the 1.9ka Eruption of Turrialba Volcano (Costa Rica)

NASA Astrophysics Data System (ADS)

Vona, A.; Di Piazza, A.; Romano, C.; De Astis, G.; Soto, G. J.

2014-12-01

We present a study of high-temperature, uniaxial deformation experiments of natural magma from an andesitic eruption of Turrialba volcano (1.9ka Plinian eruption). The aim of this work is to investigate the multiphase rheology (liquid+vesicles+crystals) of natural samples and the effect of vesicles and crystals on the magma viscosity. The experiments were performed using a high-temperature uniaxial Geocomp LoadTrac II press at dry atmospheric conditions and controlled deformation rates. Cores of natural sample (with Φcrys=0.20-0.30 and Φves=0.41-0.58) were deformed isothermally (790-870°C) at variable strain rates (VSR, from 10-6 to 10-4 s-1) and constant strain rate (CSR, 10-5 s-1). VSR were performed at low total amount of strain (e<0.10) to parameterize the flow behavior of these complex natural materials. The stress-strain rate relationships under flow conditions showed a linear trend between the applied stress and strain rate in the temperature interval investigated. All the samples display a steep linear trend, typical of Newtonian fluids (n index ~ 1), with a very small shear thinning behavior. CSR tests were performed at different total amount of strain (e=0.15-0.25-0.35). Strain hardening was observed with increasing deformation, resulting in an increase of apparent viscosity (up to 100.5 Pa s). This increase is related to the loss of total porosity (up to ΔΦves=0.15) due to compaction of the sample as indicated by post-run analyses . The measured multiphase rheology of Turrialba magmas was compared with literature models for both crystal- and bubble-bearing suspension. We calculate a difference of ~101 Pa s in magma apparent viscosity between high and low density samples, that coupled with a lateral temperature gradient inside the conduit of the volcano, could increase up to ~103 Pa s. The large difference in viscosity could be responsible of significant rheological contrasts, possibly resulting in strain localization and brittle fragmentation of magma.

Angular dispersion of oblique phonon modes in BiFeO3 from micro-Raman scattering

NASA Astrophysics Data System (ADS)

Hlinka, J.; Pokorny, J.; Karimi, S.; Reaney, I. M.

2011-01-01

The angular dispersion of oblique phonon modes in a multiferroic BiFeO3 has been obtained from a micro-Raman spectroscopic investigation of a coarse grain ceramic sample. Continuity of the measured angular dispersion curves allows conclusive identification of all pure zone-center polar modes. The method employed here to reconstruct the anisotropic crystal property from a large set of independent local measurements on a macroscopically isotropic ceramic sample profits from the considerable dispersion of the oblique modes in ferroelectric perovskites and it can be in principle conveniently applied to any other optically uniaxial ferroelectric material.

A numerical investigation of the crystallographic texture effect on the surface roughening in aluminum polycrystals

NASA Astrophysics Data System (ADS)

Romanova, V.; Balokhonov, R.; Batukhtina, E.; Zinovieva, O.; Bezmozgiy, I.

2015-10-01

The results of a numerical analysis of the mesoscale surface roughening in a polycrystalline aluminum alloy exposed to uniaxial tension are presented. A 3D finite-element model taking an explicit account of grain structure is developed. The model describes a constitutive behavior of the material on the grain scale, using anisotropic elasticity and crystal plasticity theory. The effects of the grain shape and texture on the deformation-induced roughening are investigated. Calculation results have shown that surface roughness is much higher and develops at the highest rate in a polycrystal with equiaxed grains where both the micro- and mesoscale surface displacements are observed.

Bragg-Berry mirrors: reflective broadband q-plates.

PubMed

Rafayelyan, Mushegh; Brasselet, Etienne

2016-09-01

We report on the experimental realization of flat mirrors enabling the broadband generation of optical vortices upon reflection. The effect is based on the geometric Berry phase associated with the circular Bragg reflection phenomenon from chiral uniaxial media. We show the reflective optical vortex generation from both diffractive and nondiffractive paraxial light beams using spatially patterned chiral liquid crystal films. The intrinsic spectrally broadband character of spin-orbit generation of optical phase singularities is demonstrated over the full visible domain. Our results do not rely on any birefringent retardation requirement and, consequently, foster the development of a novel generation of robust optical elements for spin-orbit photonic technologies.

Structure of deformed silicon and implications for low cost solar cells

NASA Technical Reports Server (NTRS)

Mardesich, N.; Leipold, M. H.; Turner, G. B.; Digges, T. G., Jr.

1978-01-01

The microstructure and minority carrier lifetime of silicon were investigated in uniaxially compressed silicon samples. The objective of the investigation was to determine if it is feasible to produce silicon solar cells from sheet formed by high temperature rolling. The initial structure of the silicon samples ranged from single crystal to fine-grained polycrystals. The samples had been deformed at strain rates of 0.1 to 8.5/sec and temperatures of 1270-1380 C with subsequent annealing at 1270-1380 C. The results suggest that high temperature rolling of silicon to produce sheet for cells of high efficiency is not practical.

Abnormal arrangement of a collagen/apatite extracellular matrix orthogonal to osteoblast alignment is constructed by a nanoscale periodic surface structure.

PubMed

Matsugaki, Aira; Aramoto, Gento; Ninomiya, Takafumi; Sawada, Hiroshi; Hata, Satoshi; Nakano, Takayoshi

2015-01-01

Morphological and directional alteration of cells is essential for structurally appropriate construction of tissues and organs. In particular, osteoblast alignment is crucial for the realization of anisotropic bone tissue microstructure. In this article, the orientation of a collagen/apatite extracellular matrix (ECM) was established by controlling osteoblast alignment using a surface geometry with nanometer-sized periodicity induced by laser ablation. Laser irradiation induced self-organized periodic structures (laser-induced periodic surface structures; LIPSS) with a spatial period equal to the wavelength of the incident laser on the surface of biomedical alloys of Ti-6Al-4V and Co-Cr-Mo. Osteoblast orientation was successfully induced parallel to the grating structure. Notably, both the fibrous orientation of the secreted collagen matrix and the c-axis of the produced apatite crystals were orientated orthogonal to the cell direction. To the best of our knowledge, this is the first report demonstrating that bone tissue anisotropy is controllable, including the characteristic organization of a collagen/apatite composite orthogonal to the osteoblast orientation, by controlling the cell alignment using periodic surface geometry. Copyright © 2014 Elsevier Ltd. All rights reserved.

Superconductivity under uniaxial compression in β-(BDA-TTP) salts

NASA Astrophysics Data System (ADS)

Suzuki, T.; Onari, S.; Ito, H.; Tanaka, Y.

2009-10-01

In order to clarify the mechanism of organic superconductor β-(BDA-TTP) salts. We study the superconductivity under uniaxial compression with non-dimerized two-band Hubbard model. We have calculated the uniaxial compression dependence of T c by solving the Eliashberg’s equation using the fluctuation exchange (FLEX) approximation. The transfer integral under the uniaxial compression was estimated by the extended Huckel method. We have found that non-monotonic behaviors of T c in experimental results under uniaxial compression are understood taking the spin frustration and spin fluctuation into account.

A study of Channeling, Volume Reflection and Volume Capture of 3.35 - 14.0 GeV Electrons in a bent Silicon Crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wistisen, T. N.; Uggerhoj, U. I.; Wienands, U.

2015-12-03

We present the experimental data and analysis of experiments conducted at SLAC National Accelerator Laboratory investigating the processes of channeling, volume-reflection and volume-capture along the (111) plane in a strongly bent quasi-mosaic silicon crystal. Additionally, these phenomena were investigated at 5 energies: 3.35, 4.2, 6.3, 10.5 and 14.0 GeV with a crystal with bending radius of 0.15m, corresponding to curvatures of 0.070, 0.088, 0.13, 0.22 and 0.29 times the critical curvature respectively. We have extracted important parameters describing the channeling process such as the dechanneling length, the angle of volume reflection, the surface transmission and the widths of the distributionmore » of channeled particles parallel and orthogonal to the plane.« less

On the Landau-de Gennes Elastic Energy of a Q-Tensor Model for Soft Biaxial Nematics

NASA Astrophysics Data System (ADS)

Mucci, Domenico; Nicolodi, Lorenzo

2017-12-01

In the Landau-de Gennes theory of liquid crystals, the propensities for alignments of molecules are represented at each point of the fluid by an element Q of the vector space S_0 of 3× 3 real symmetric traceless matrices, or Q-tensors. According to Longa and Trebin (1989), a biaxial nematic system is called soft biaxial if the tensor order parameter Q satisfies the constraint tr(Q^2) = {const}. After the introduction of a Q-tensor model for soft biaxial nematic systems and the description of its geometric structure, we address the question of coercivity for the most common four-elastic-constant form of the Landau-de Gennes elastic free-energy (Iyer et al. 2015) in this model. For a soft biaxial nematic system, the tensor field Q takes values in a four-dimensional sphere S^4_ρ of radius ρ ≤ √{2/3} in the five-dimensional space S_0 with inner product < Q, P > = tr(QP). The rotation group it{SO}(3) acts orthogonally on S_0 by conjugation and hence induces an action on S^4_ρ \\subset {S}_0. This action has generic orbits of codimension one that are diffeomorphic to an eightfold quotient S^3/H of the unit three-sphere S^3, where H={± 1, ± i, ± j, ± k} is the quaternion group, and has two degenerate orbits of codimension two that are diffeomorphic to the projective plane RP^2. Each generic orbit can be interpreted as the order parameter space of a constrained biaxial nematic system and each singular orbit as the order parameter space of a constrained uniaxial nematic system. It turns out that S^4_ρ is a cohomogeneity one manifold, i.e., a manifold with a group action whose orbit space is one-dimensional. Another important geometric feature of the model is that the set Σ _ρ of diagonal Q-tensors of fixed norm ρ is a (geodesic) great circle in S^4_ρ which meets every orbit of S^4_ρ orthogonally and is then a section for S^4_ρ in the sense of the general theory of canonical forms. We compute necessary and sufficient coercivity conditions for the elastic energy by exploiting the it{SO}(3)-invariance of the elastic energy (frame-indifference), the existence of the section Σ _ρ for S^4_ρ , and the geometry of the model, which allow us to reduce to a suitable invariant problem on (an arc of) Σ _ρ . Our approach can ultimately be seen as an application of the general method of reduction of variables, or cohomogeneity method.

X-ray diffraction, crystal structure, and spectral features of the optical susceptibilities of single crystals of the ternary borate oxide lead bismuth tetraoxide, PbBiBO4.

PubMed

Reshak, Ali Hussain; Kityk, I V; Auluck, S; Chen, Xuean

2009-05-14

The all-electron full-potential linearized augmented plane-wave method has been used for an ab initio theoretical study of the band structure, the spectral features of the optical susceptibilities, the density of states, and the electron charge density for PbBiBO4. Our calculations show that the valence-band maximum (VBM) and conduction-band minimum (CBM) are located at the center of the Brillouin zone, resulting in a direct energy gap of about 3.2 eV. We have synthesized the PbBiBO4 crystal by employing a conventional solid-state reaction method. The theoretical calculations in this work are based on the structure built from our measured atomic parameters. We should emphasize that the observed experimental X-ray diffraction (XRD) pattern is in good agreement with the theoretical one, confirming that our structural model is valid. Our calculated bond lengths show excellent agreement with the experimental data. This agreement is attributed to our use of full-potential calculations. The spectral features of the optical susceptibilities show a small positive uniaxial anisotropy.

Investigation of tunable terahertz metamaterial perfect absorber with anisotropic dielectric liquid crystal

NASA Astrophysics Data System (ADS)

Hokmabadi, Mohammad P.; Tareki, Abubaker; Rivera, Elmer; Kung, Patrick; Lindquist, Robert G.; Kim, Seongsin M.

2017-01-01

In this letter, we report the unique design, simulation and experimental verification of an electrically tunable THz metamaterial perfect absorber consisting of complementary split ring resonator (CSRR) arrays integrated with liquid crystal as the subwavelength spacer in between. We observe a shift in resonance frequency of about 5.0 GHz at 0.567 THz with a 5 V bias voltage at 1KHz between the CSRR and the metal backplane, while the absorbance and full width at half maximum bandwidth are maintained at 90% and 0.025 THz, respectively. Simulated absorption spectrum by using a uniaxial model of LC matches perfectly the experiment data and demonstrates that the effective refractive index of LC changes between 1.5 and 1.7 by sweeping a 1 kHz bias voltage from 0 V to 5 V. By matching simulation and experiment for different bias voltages, we also estimate the angle of LC molecules versus the bias voltage. Additionally, we study the created THz fields inside the spacer to gain a better insight of the characteristics of tunable response of this device. This structure and associated study can support the design of liquid crystal based tunable terahertz detectors and sensors for various applications.

Optic properties of bile liquid crystals in human body

PubMed Central

Yang, Hai Ming; Wu, Jie; Li, Jin Yi; Zhou, Jian Li; He, Li Jun; Xu, Xian Fang

2000-01-01

AIM: To further study the properties of bile liquid crystals, and probe into the relationship between bile liquid crystals and gallbladder stone formation, and provide evidence for the prevention and treatment of cholecystolithiasis. METHODS: The optic properties of bile liquid crystals in human body were determined by the method of crystal optics under polarizing microscope with plane polarized light and perpendicular polarized light. RESULTS: Under a polarizing microscope with plane polarized light, bile liquid crystals scattered in bile appeared round, oval or irregularly round. The color of bile liquid crystals was a little lighter than that of the bile around. When the stage was turned round, the color of bile liquid crystals or the darkness and lightness of the color did not change obviously. On the border between bile liquid crystals and the bile around, brighter Becke-Line could be observed. When the microscope tube is lifted, Becke-Line moved inward, and when lowered, Becke-Line moved outward. Under a perpendicular polarized light, bile liquid crystals showd some special interference patterns, called Malta cross. When the stage was turning round at an angle of 360°, the Malta cross showed four times of extinction. In the vibrating direction of 45° angle of relative to upper and lower polarizing plate, gypsum test-board with optical path difference of 530 nm was inserted, the first and the third quadrants of Malt a cross appeared to be blue, and the second and the fourth quadrants appeared orange. When mica test-board with optical path difference of 147 nm was inserted, the first and the third quadrants of Malta cross appeared yellow, and the second and the fourth quadrants appeared dark grey. CONCLUSION: The bile liquid crystals were distributed in bile in the form of global grains. Their polychroism and absorption were slight, but the edge and Becke*Line were very clear. Its refractive index was larger than that of the bile. These liquid crystals were uniaxial positive crystals. The interference colors were the first order grey-white. The double refractive index of the liquid crystals was Δn = 0.011-0.015. PMID:11819567

Simulation of Texture Evolution during Uniaxial Deformation of Commercially Pure Titanium

NASA Astrophysics Data System (ADS)

Bishoyi, B.; Debta, M. K.; Yadav, S. K.; Sabat, R. K.; Sahoo, S. K.

2018-03-01

The evolution of texture in commercially pure (CP) titanium during uniaxial tension and compression through VPSC (Visco-plastic self-consistent) simulation is reported in the present study. CP-titanium was subjected to both uniaxial tension and compression upto 35% deformation. During uniaxial tension, tensile twin of \\{10\\bar{1}2\\}\\unicode{x003C;}\\bar{1}011\\unicode{x003E;} type and compressive twin of \\{11\\bar{2}2\\}\\unicode{x003C;}11\\bar{2}\\bar{3}\\unicode{x003E;} type were observed in the samples. However, only tensile twin of \\{10\\bar{1}2\\}\\unicode{x003C;}\\bar{1}011\\unicode{x003E;} type and compressive twin of type was observed in the samples during uniaxial compression. Volume fractions of the twins were increased linearly as a function of percentage deformation during uniaxial tension. Whereas, during uniaxial compression the twinning volume fraction was increased up to 20% deformation and then decreased rapidly on further increasing the percentage deformation. During uniaxial tension, the general t-type textures were observed in the samples irrespective of the percentage deformation. The initial non-basal texture was oriented to split basal texture during uniaxial compression of the sample. VPSC formulation was used for simulating the texture development in the material. Different hardening parameters were estimated through correlating the simulated stress-strain curve with the experimental stress-strain data. It was observed that, prismatic slip \\{10\\bar{1}0\\}\\unicode{x003C;}11\\bar{2}0\\unicode{x003E;} operated as the primary deformation mode during uniaxial tension whereas basal slip \\{0001\\}\\unicode{x003C;}11\\bar{2}0\\unicode{x003E;} acquired the leading role during deformation through uniaxial compression. It was also revealed that active deformation modes were fully depending on percentage deformation, loading direction, and orientation of grains.

Modeling dislocation generation in high pressure Czochralski growth of indium phosphide single crystals

NASA Astrophysics Data System (ADS)

Pendurti, Srinivas

InP is an important material for opto-electronic and high speed electronics applications. Its main use today is as the substrate material for epitaxy to produce GaInAsP lasers. The present technology for growing bulk InP is the high pressure Czochralski process. Bulk InP grown through this technique suffers from presence of a high density of line defects or dislocations, which are produced by thermal stresses the material goes through during its growth in the high temperature furnace. Modeling of these thermal stresses and the resulting plastic deformation, giving rise to dislocation densities, entails simulation of the entire thermal history of the crystal during its growth in the furnace, and studying the deformation of the crystal through suitable visco-plastic constitutive equations. Accordingly, a suitable visco-plastic model for deformation of InP was constructed, integrated with the ABAQUS finite element code, and verified through experimental data for uniaxial constant strain rate deformation tests available in literature. This was then coupled with a computation fluid dynamics model, predicting the entire temperature history in the furnace during crystal growth, to study the plastic deformation and dislocation density evolution in the crystal during growth. Growth in a variety of conditions was simulated and those conditions that generate minimum dislocation density identified. Macroscopic controllable parameters that affect the dislocation densities the most, have also been delineated. It was found that the strength of gas convection in the Czochralski furnace has the strongest effect on the dislocation densities in the fully grown crystal. Comparison of the simulated dislocation densities on wafers, with experimentally recorded etch pit profiles on as-grown crystals was reasonable. Finally some limitations in the work are discussed and avenues for future work identified.

Study on the Coupling Mechanism of the Orthogonal Dipoles with Surface Plasmon in Green LED by Cathodoluminescence.

PubMed

Feng, Yulong; Chen, Zhizhong; Jiang, Shuang; Li, Chengcheng; Chen, Yifan; Zhan, Jinglin; Chen, Yiyong; Nie, Jingxin; Jiao, Fei; Kang, Xiangning; Li, Shunfeng; Yu, Tongjun; Zhang, Guoyi; Shen, Bo

2018-04-16

We analyzed the coupling behavior between the localized surface plasmon (LSP) and quantum wells (QWs) using cathodoluminescence (CL) in a green light-emitting diodes (LED) with Ag nanoparticles (NPs) filled in photonic crystal (PhC) holes. Photoluminescence (PL) suppression and CL enhancement were obtained for the same green LED sample with the Ag NP array. Time-resolved PL (TRPL) results indicate strong coupling between the LSP and the QWs. Three-dimensional (3D) finite difference time domain (FDTD) simulation was performed using a three-body model consisting of two orthogonal dipoles and a single Ag NP. The LSP–QWs coupling effect was separated from the electron-beam (e-beam)–LSP–QW system by linear approximation. The energy dissipation was significantly reduced by the z-dipole introduction under the e-beam excitation. In this paper, the coupling mechanism is discussed and a novel emission structure is proposed.

Single-longitudinal mode Nd:YVO4 microchip laser with orthogonal-polarization bidirectional traveling-waves mode.

PubMed

Ma, Yingjun; Wu, Li; Wu, Hehui; Chen, Weimin; Wang, Yanli; Gu, Shijie

2008-11-10

We present a single longitudinal mode, diode pumped Nd:YVO(4) microchip laser where a pair of quarter-wave plates (QWPs) sandwich Nd:YVO(4) and the principle axes of QWPs are oriented at 45 degrees to the c-axis of Nd:YVO(4). Three pieces of crystals were optically bonded together as a microchip without adhesive. Owing to large birefringence of Nd:YVO(4), two standing waves with orthogonal polarizations compensate their hole-burning effects with each other, which diminish total spatial hole-burning effects in Nd:YVO(4). The maximum pump power of greater than 25 times the threshold for single longitudinal mode operation has been theoretically shown and experimentally demonstrated. The power of output, slope efficiencies and temperature range of single longitudinal mode operation are greater than 730 mw (at 1.25 W pump), 60% and 30 degrees C, respectively.

Transient electromagnetic scattering by a radially uniaxial dielectric sphere: Debye series, Mie series and ray tracing methods

NASA Astrophysics Data System (ADS)

Yazdani, Mohsen

Transient electromagnetic scattering by a radially uniaxial dielectric sphere is explored using three well-known methods: Debye series, Mie series, and ray tracing theory. In the first approach, the general solutions for the impulse and step responses of a uniaxial sphere are evaluated using the inverse Laplace transformation of the generalized Mie series solution. Following high frequency scattering solution of a large uniaxial sphere, the Mie series summation is split into the high frequency (HF) and low frequency terms where the HF term is replaced by its asymptotic expression allowing a significant reduction in computation time of the numerical Bromwich integral. In the second approach, the generalized Debye series for a radially uniaxial dielectric sphere is introduced and the Mie series coefficients are replaced by their equivalent Debye series formulations. The results are then applied to examine the transient response of each individual Debye term allowing the identification of impulse returns in the transient response of the uniaxial sphere. In the third approach, the ray tracing theory in a uniaxial sphere is investigated to evaluate the propagation path as well as the arrival time of the ordinary and extraordinary returns in the transient response of the uniaxial sphere. This is achieved by extracting the reflection and transmission angles of a plane wave obliquely incident on the radially oriented air-uniaxial and uniaxial-air boundaries, and expressing the phase velocities as well as the refractive indices of the ordinary and extraordinary waves in terms of the incident angle, optic axis and propagation direction. The results indicate a satisfactory agreement between Debye series, Mie series and ray tracing methods.

Constitutive Law and Flow Mechanism in Diamond Deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong

2012-11-19

Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. In this paper, we report, for the first time, the strain-stress constitutive relations and experimental demonstration of deformation mechanisms under confined high pressure. The deformation at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significantmore » ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. Finally, at high temperature the plastic deformation and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.« less

High-magnification super-resolution FINCH microscopy using birefringent crystal lens interferometers

NASA Astrophysics Data System (ADS)

Siegel, Nisan; Lupashin, Vladimir; Storrie, Brian; Brooker, Gary

2016-12-01

Fresnel incoherent correlation holography (FINCH) microscopy is a promising approach for high-resolution biological imaging but has so far been limited to use with low-magnification, low-numerical-aperture configurations. We report the use of in-line incoherent interferometers made from uniaxial birefringent α-barium borate (α-BBO) or calcite crystals that overcome the aberrations and distortions present with previous implementations that employed spatial light modulators or gradient refractive index lenses. FINCH microscopy incorporating these birefringent elements and high-numerical-aperture oil immersion objectives could outperform standard wide-field fluorescence microscopy, with, for example, a 149 nm lateral point spread function at a wavelength of 590 nm. Enhanced resolution was confirmed with sub-resolution fluorescent beads. Taking the Golgi apparatus as a biological example, three different proteins labelled with GFP and two other fluorescent dyes in HeLa cells were resolved with an image quality that is comparable to similar samples captured by structured illumination microscopy.

Effect of Molecular Flexibility on the Nematic-to-Isotropic Phase Transition for Highly Biaxial Molecular Non-Symmetric Liquid Crystal Dimers

PubMed Central

Sebastián, Nerea; López, David Orencio; Diez-Berart, Sergio; de la Fuente, María Rosario; Salud, Josep; Pérez-Jubindo, Miguel Angel; Ros, María Blanca

2011-01-01

In this work, a study of the nematic (N)–isotropic (I) phase transition has been made in a series of odd non-symmetric liquid crystal dimers, the α-(4-cyanobiphenyl-4’-yloxy)-ω-(1-pyrenimine-benzylidene-4’-oxy) alkanes, by means of accurate calorimetric and dielectric measurements. These materials are potential candidates to present the elusive biaxial nematic (NB) phase, as they exhibit both molecular biaxiality and flexibility. According to the theory, the uniaxial nematic (NU)–isotropic (I) phase transition is first-order in nature, whereas the NB–I phase transition is second-order. Thus, a fine analysis of the critical behavior of the N–I phase transition would allow us to determine the presence or not of the biaxial nematic phase and understand how the molecular biaxiality and flexibility of these compounds influences the critical behavior of the N–I phase transition. PMID:28824100

Compression deformation of WC: atomistic description of hard ceramic material

NASA Astrophysics Data System (ADS)

Feng, Qing; Song, Xiaoyan; Liu, Xuemei; Liang, Shuhua; Wang, Haibin; Nie, Zuoren

2017-11-01

The deformation characteristics of WC, as a typical hard ceramic material, were studied on the nanoscale using atomistic simulations for both the single-crystal and polycrystalline forms under uniaxial compression. In particular, the effects of crystallographic orientation, grain boundary coordination and grain size on the origin of deformation were investigated. The deformation behavior of the single-crystal and polycrystalline WC both depend strongly on the orientation towards the loading direction. The grain boundaries play a significant role in the deformation coordination and the potential high fracture toughness of the nanocrystalline WC. In contrast to conventional knowledge of ceramics, maximum strength was obtained at a critical grain size corresponding to the turning point from a Hall-Petch to an inverse Hall-Petch relationship. For this the mechanism of the combined effect of dislocation motion within grains and the coordination of stress concentration at the grain boundaries were proposed. The present work has moved forward our understanding of plastic deformability and the possibility of achieving a high strength of nanocrystalline ceramic materials.

Compression deformation of WC: atomistic description of hard ceramic material.

PubMed

Feng, Qing; Song, Xiaoyan; Liu, Xuemei; Liang, Shuhua; Wang, Haibin; Nie, Zuoren

2017-11-24

The deformation characteristics of WC, as a typical hard ceramic material, were studied on the nanoscale using atomistic simulations for both the single-crystal and polycrystalline forms under uniaxial compression. In particular, the effects of crystallographic orientation, grain boundary coordination and grain size on the origin of deformation were investigated. The deformation behavior of the single-crystal and polycrystalline WC both depend strongly on the orientation towards the loading direction. The grain boundaries play a significant role in the deformation coordination and the potential high fracture toughness of the nanocrystalline WC. In contrast to conventional knowledge of ceramics, maximum strength was obtained at a critical grain size corresponding to the turning point from a Hall-Petch to an inverse Hall-Petch relationship. For this the mechanism of the combined effect of dislocation motion within grains and the coordination of stress concentration at the grain boundaries were proposed. The present work has moved forward our understanding of plastic deformability and the possibility of achieving a high strength of nanocrystalline ceramic materials.

Hardening mechanisms in olivine single crystal deformed at 1090 °C: an electron tomography study

NASA Astrophysics Data System (ADS)

Mussi, Alexandre; Cordier, Patrick; Demouchy, Sylvie; Hue, Benoit

2017-11-01

The dislocation microstructures in a single crystal of olivine deformed experimentally in uniaxial compression at 1090 °C and under a confining pressure of 300 MPa, have been investigated by transmission electron tomography in order to better understand deformation mechanisms at the microscale relevant for lithospheric mantle deformations. Investigation by electron tomography reveals microstructures, which are more complex than previously described, composed of ? and ? dislocations commonly exhibiting 3D configurations. Numerous mechanisms such as climb, cross-slip, double cross-slip as well as interactions like junction formations and collinear annihilations are the source of this complexity. The diversity observed advocates for microscale deformation of olivine significantly less simple than classic dislocation creep reported in metals or ice close to melting temperature. Deciphering mechanism of hardening in olivine at temperatures where ionic diffusion is slow and is then expected to play very little role is crucial to better understand and thus model deformation at larger scale and at temperatures (900-1100 °C) highly relevant for the lithospheric mantle.

Highly transparent ceramics with disordered crystal structure

NASA Astrophysics Data System (ADS)

Osipov, V. V.; Khasanov, O. L.; Solomonov, V. I.; Shitov, V. A.; Orlov, A. N.; Platonov, V. V.; Spirina, A. V.; Luk'yashin, K. E.; Dvilis, E. S.

2010-08-01

A highly transparent ceramic has been synthesized from Nd3+:Y2O3 to which 6 mol. % ZrO2 and 25 mol. % Sc2O3 or Lu2O3 were added for disordering the crystal structure. Nanopowders with an average particle size of 10-15 nm served as an initial material. They were compacted by the method of uniaxial static pressing combined with ultrasonic action on nanoparticles. The compacting pressure was 200 MPa; the power of the ultrasonic generator was 1.5 kW. It has been shown that the replacement of Y by isovalent Sc and Lu ions and by heterovalent Zr ions reduces the content of pores and the sizes of crystallites. The transparency of the Nd3+:Y2O3 ceramic with these additives reaches a maximum of 82.2%, and the 40% intensity level spectral band corresponding to the 4F3/2 → 4I11/2 transition widens from 11.4 to 40 nm.

Complex magnetic order in the kagome ferromagnet Pr3Ru4Al12

NASA Astrophysics Data System (ADS)

Henriques, M. S.; Gorbunov, D. I.; Andreev, A. V.; Fabrèges, X.; Gukasov, A.; Uhlarz, M.; Petříček, V.; Ouladdiaf, B.; Wosnitza, J.

2018-01-01

In the hexagonal crystal structure of Pr3Ru4Al12 , the Pr atoms form a distorted kagome lattice, and their magnetic moments, are subject to competing exchange and anisotropy interactions. We performed magnetization, magnetic-susceptibility, specific-heat, electrical-resistivity, and neutron-scattering measurements. Pr3Ru4Al12 is a uniaxial ferromagnet with TC=39 K that displays a collinear magnetic structure (in the high-temperature range of the magnetically ordered state) for which the only crystallographic position of Pr is split into two sites carrying different magnetic moments. A spin-reorientation phase transition is found at 7 K. Below this temperature, part of the Pr moments rotate towards the basal plane, resulting in a noncollinear magnetic state with a lower magnetic symmetry. We argue that unequal RKKY exchange interactions competing with the crystal electric field lead to a moment instability and qualitatively explain the observed magnetic phases in Pr3Ru4Al12 .

One-dimensional ferromagnetic array compound [Co3(SBA)2(OH)2(H2O)2]n, (SBA = 4-sulfobenzoate)

NASA Astrophysics Data System (ADS)

Honda, Zentaro; Nomoto, Naoyuki; Fujihara, Takashi; Hagiwara, Masayuki; Kida, Takanori; Sawada, Yuya; Fukuda, Takeshi; Kamata, Norihiko

2018-06-01

We report on the syntheses, crystal structure, and magnetic properties of the transition metal coordination polymer [Co3(SBA)2(OH)2(H2O)2]n, (SBA = 4-sulfobenzoate) in which CoO6 octahedra are linked through their edges, forming one-dimensional (1D) Co(II) arrays running along the crystal a-axis. These arrays are further perpendicularly bridged by SBA ligand to construct a three-dimensional framework. Its magnetic properties have been investigated, and ferromagnetic interactions within the arrays have been found. From heat capacity measurements, we have found that this compound exhibits a three-dimensional ferromagnetic phase transition at TC = 1.54 K, and the specific heat just above TC shows a Schottky anomaly which originates from an energy gap caused by uniaxial magnetic anisotropy. These results suggest that [Co3(SBA)2(OH)2(H2O)2]n consists of weakly coupled 1D ferromagnetic Ising arrays.

A Crystal Field Approach to Orbitally Degenerate SMMs: Beyond the Spin-Only Hamiltonian

NASA Astrophysics Data System (ADS)

Bhaskaran, Lakshmi; Marriott, Katie; Murrie, Mark; Hill, Stephen

Single-Molecule Magnets (SMMs) with large magnetization reversal barriers are promising candidates for high-density information storage. Recently, a large uniaxial magnetic anisotropy was observed for a mononuclear trigonal bipyramidal (TBP) [NiIICl3(Me-abco)2] SMM. High-field EPR studies analyzed on the basis of a spin-only Hamiltonian give ¦D¦>400 cm-1, which is close to the spin-orbit coupling parameter λ = 668 cm-1 for NiII, suggesting an orbitally degenerate ground state. The spin-only description is ineffective in this limit, necessitating the development of a model that includes the orbital moment. Here we describe a phenomenological approach that takes into account a full description of crystal field, electron-electron repulsion and spin-orbit coupling effects on the ground state of a NiII ion in a TBP coordination geometry. The model is in good agreement with the high-field EPR experiments, validating its use for spectroscopic studies of orbitally degenerate molecular nanomagnets. This work was supported by the NSF (DMR-1309463).

Transition-metal alloying of γ'-Ni3Al : Effects on the ideal uniaxial compressive strength from first-principles calculations

NASA Astrophysics Data System (ADS)

Wen, Minru; Wang, Chong-Yu

2018-01-01

The addition of transition-metal (TM) elements into the γ' precipitate phase of a Ni-based single-crystal superalloy can significantly affect its mechanical properties, including the intrinsic mechanical property of compressive strength. Using first-principles density functional calculations, the effects of 3 d (Sc-Zn), 4 d (Y-Cd), and 5 d (Hf-Au) TM alloying elements on the ideal uniaxial compressive strength of γ'-Ni3Al were investigated. The stress-strain relationships of pure Ni3Al under [100], [110], and [111] compressive loads and the site occupancy behavior of TM elements in Ni3Al were previously studied using a total-energy method based on density functional theory. Our results showed that the capacity of TM elements for strengthening the ideal compressive strength was associated with the d -electron number. The alloying elements with half-filled d bands (i.e., Cr, Mo, W, Tc, and Re) manifested the greatest efficacy for improving the ideal strength of Ni3Al under a deformation along the weakest compressive direction. Furthermore, the charge redistribution of Ni3Al doped with 5 d elements were also analyzed to understand the strengthening mechanisms of TM elements in the γ'-Ni3Al phase.

Valley magnetoelectricity in single-layer MoS2

NASA Astrophysics Data System (ADS)

Lee, Jieun; Wang, Zefang; Xie, Hongchao; Mak, Kin Fai; Shan, Jie

2017-09-01

The magnetoelectric (ME) effect, the phenomenon of inducing magnetization by application of an electric field or vice versa, holds great promise for magnetic sensing and switching applications. Studies of the ME effect have so far focused on the control of the electron spin degree of freedom (DOF) in materials such as multiferroics and conventional semiconductors. Here, we report a new form of the ME effect based on the valley DOF in two-dimensional Dirac materials. By breaking the three-fold rotational symmetry in single-layer MoS 2 via a uniaxial stress, we have demonstrated the pure electrical generation of valley magnetization in this material, and its direct imaging by Kerr rotation microscopy. The observed out-of-plane magnetization is independent of in-plane magnetic field, linearly proportional to the in-plane current density, and optimized when the current is orthogonal to the strain-induced piezoelectric field. These results are fully consistent with a theoretical model of valley magnetoelectricity driven by Berry curvature effects. Furthermore, the effect persists at room temperature, opening possibilities for practical valleytronic devices.

Valley magnetoelectricity in single-layer MoS2.

PubMed

Lee, Jieun; Wang, Zefang; Xie, Hongchao; Mak, Kin Fai; Shan, Jie

2017-09-01

The magnetoelectric (ME) effect, the phenomenon of inducing magnetization by application of an electric field or vice versa, holds great promise for magnetic sensing and switching applications. Studies of the ME effect have so far focused on the control of the electron spin degree of freedom (DOF) in materials such as multiferroics and conventional semiconductors. Here, we report a new form of the ME effect based on the valley DOF in two-dimensional Dirac materials. By breaking the three-fold rotational symmetry in single-layer MoS 2 via a uniaxial stress, we have demonstrated the pure electrical generation of valley magnetization in this material, and its direct imaging by Kerr rotation microscopy. The observed out-of-plane magnetization is independent of in-plane magnetic field, linearly proportional to the in-plane current density, and optimized when the current is orthogonal to the strain-induced piezoelectric field. These results are fully consistent with a theoretical model of valley magnetoelectricity driven by Berry curvature effects. Furthermore, the effect persists at room temperature, opening possibilities for practical valleytronic devices.

Optoelectronic associative memory

NASA Technical Reports Server (NTRS)

Chao, Tien-Hsin (Inventor)

1993-01-01

An associative optical memory including an input spatial light modulator (SLM) in the form of an edge enhanced liquid crystal light valve (LCLV) and a pair of memory SLM's in the form of liquid crystal televisions (LCTV's) forms a matrix array of an input image which is cross correlated with a matrix array of stored images. The correlation product is detected and nonlinearly amplified to illuminate a replica of the stored image array to select the stored image correlating with the input image. The LCLV is edge enhanced by reducing the bias frequency and voltage and rotating its orientation. The edge enhancement and nonlinearity of the photodetection improves the orthogonality of the stored image. The illumination of the replicate stored image provides a clean stored image, uncontaminated by the image comparison process.

Real-Time Fluorescence Detection in Aqueous Systems by Combined and Enhanced Photonic and Surface Effects in Patterned Hollow Sphere Colloidal Photonic Crystals.

PubMed

Zhong, Kuo; Wang, Ling; Li, Jiaqi; Van Cleuvenbergen, Stijn; Bartic, Carmen; Song, Kai; Clays, Koen

2017-05-16

Hollow sphere colloidal photonic crystals (HSCPCs) exhibit the ability to maintain a high refractive index contrast after infiltration of water, leading to extremely high-quality photonic band gap effects, even in an aqueous (physiological) environment. Superhydrophilic pinning centers in a superhydrophobic environment can be used to strongly confine and concentrate water-soluble analytes. We report a strategy to realize real-time ultrasensitive fluorescence detection in patterned HSCPCs based on strongly enhanced fluorescence due to the photonic band-edge effect combined with wettability differentiation in the superhydrophobic/superhydrophilic pattern. The orthogonal nature of the two strategies allows for a multiplicative effect, resulting in an increase of two orders of magnitude in fluorescence.

A high throughput liquid crystal light shutter for unpolarized light using polymer polarization gratings

NASA Astrophysics Data System (ADS)

Komanduri, Ravi K.; Lawler, Kris F.; Escuti, Michael J.

2011-05-01

We report on a broadband, diffractive, light shutter with the ability to modulate unpolarized light. This polarizer-free approach employs a conventional liquid crystal (LC) switch, combined with broadband Polarization Gratings (PGs) formed with polymer LC materials. The thin-film PGs act as diffractive polarizing beam-splitters, while the LC switch operates on both orthogonal polarization states simultaneously. As an initial experimental proof-of- concept for unpolarized light with +/-7° aperture, we utilize a commercial twisted-nematic LC switch and our own polymer PGs to achieve a peak transmittance of 80% and peak contrast ratio of 230:1. We characterize the optoelectronic performance, discuss the limitations, and evaluate its use in potential nonmechanical shutter applications (imaging and non-imaging).

Single crystal EPR and optical studies of paramagnetic ions doped zinc potassium phosphate hexahydrate--part I: Cu(II)--a case of orthorhombic symmetry.

PubMed

Sambasiva Rao, P; Rajendiran, T M; Venkatesan, R; Madhu, N; Chandrasekhar, A V; Reddy, B J; Reddy, Y P; Ravikumar, R V

2001-12-01

Single crystal electron paramagnetic resonance (EPR) studies on Cu(II) doped zinc potassium phosphate hexahydrate (ZPPH) were carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice substitutionally in place of Zn(II) and the spin Hamiltonian parameters calculated from these spectra are g(xx) = 2.188, g(yy) = 2.032, g(zz) = 2.373, Axx = 50 G, Ayy = 65.0 G and Azz = 80 G. The g and A tensors were coincident and these values matched fairly well with the values obtained from powder spectrum. The bonding parameters have also been calculated.

Solvent minimization induces preferential orientation and crystal clustering in serial micro-crystallography on micro-meshes, in situ plates and on a movable crystal conveyor belt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soares, Alexei S.; Mullen, Jeffrey D.; Parekh, Ruchi M.

X-ray diffraction data were obtained at the National Synchrotron Light Source from insulin and lysozyme crystals that were densely deposited on three types of surfaces suitable for serial micro-crystallography: MiTeGen MicroMeshes™, Greiner Bio-One Ltdin situmicro-plates, and a moving kapton crystal conveyor belt that is used to deliver crystals directly into the X-ray beam. 6° wedges of data were taken from ~100 crystals mounted on each material, and these individual data sets were merged to form nine complete data sets (six from insulin crystals and three from lysozyme crystals). Insulin crystals have a parallelepiped habit with an extended flat face thatmore » preferentially aligned with the mounting surfaces, impacting the data collection strategy and the design of the serial crystallography apparatus. Lysozyme crystals had a cuboidal habit and showed no preferential orientation. Preferential orientation occluded regions of reciprocal space when the X-ray beam was incident normal to the data-collection medium surface, requiring a second pass of data collection with the apparatus inclined away from the orthogonal. In addition, crystals measuring less than 20 µm were observed to clump together into clusters of crystals. Clustering required that the X-ray beam be adjusted to match the crystal size to prevent overlapping diffraction patterns. No additional problems were encountered with the serial crystallography strategy of combining small randomly oriented wedges of data from a large number of specimens. Lastly, high-quality data able to support a realistic molecular replacement solution were readily obtained from both crystal types using all three serial crystallography strategies.« less

Solvent minimization induces preferential orientation and crystal clustering in serial micro-crystallography on micro-meshes, in situ plates and on a movable crystal conveyor belt.

PubMed

Soares, Alexei S; Mullen, Jeffrey D; Parekh, Ruchi M; McCarthy, Grace S; Roessler, Christian G; Jackimowicz, Rick; Skinner, John M; Orville, Allen M; Allaire, Marc; Sweet, Robert M

2014-11-01

X-ray diffraction data were obtained at the National Synchrotron Light Source from insulin and lysozyme crystals that were densely deposited on three types of surfaces suitable for serial micro-crystallography: MiTeGen MicroMeshes™, Greiner Bio-One Ltd in situ micro-plates, and a moving kapton crystal conveyor belt that is used to deliver crystals directly into the X-ray beam. 6° wedges of data were taken from ∼100 crystals mounted on each material, and these individual data sets were merged to form nine complete data sets (six from insulin crystals and three from lysozyme crystals). Insulin crystals have a parallelepiped habit with an extended flat face that preferentially aligned with the mounting surfaces, impacting the data collection strategy and the design of the serial crystallography apparatus. Lysozyme crystals had a cuboidal habit and showed no preferential orientation. Preferential orientation occluded regions of reciprocal space when the X-ray beam was incident normal to the data-collection medium surface, requiring a second pass of data collection with the apparatus inclined away from the orthogonal. In addition, crystals measuring less than 20 µm were observed to clump together into clusters of crystals. Clustering required that the X-ray beam be adjusted to match the crystal size to prevent overlapping diffraction patterns. No additional problems were encountered with the serial crystallography strategy of combining small randomly oriented wedges of data from a large number of specimens. High-quality data able to support a realistic molecular replacement solution were readily obtained from both crystal types using all three serial crystallography strategies.

Solvent minimization induces preferential orientation and crystal clustering in serial micro-crystallography on micro-meshes, in situ plates and on a movable crystal conveyor belt

DOE PAGES

Soares, Alexei S.; Mullen, Jeffrey D.; Parekh, Ruchi M.; ...

2014-10-09

X-ray diffraction data were obtained at the National Synchrotron Light Source from insulin and lysozyme crystals that were densely deposited on three types of surfaces suitable for serial micro-crystallography: MiTeGen MicroMeshes™, Greiner Bio-One Ltdin situmicro-plates, and a moving kapton crystal conveyor belt that is used to deliver crystals directly into the X-ray beam. 6° wedges of data were taken from ~100 crystals mounted on each material, and these individual data sets were merged to form nine complete data sets (six from insulin crystals and three from lysozyme crystals). Insulin crystals have a parallelepiped habit with an extended flat face thatmore » preferentially aligned with the mounting surfaces, impacting the data collection strategy and the design of the serial crystallography apparatus. Lysozyme crystals had a cuboidal habit and showed no preferential orientation. Preferential orientation occluded regions of reciprocal space when the X-ray beam was incident normal to the data-collection medium surface, requiring a second pass of data collection with the apparatus inclined away from the orthogonal. In addition, crystals measuring less than 20 µm were observed to clump together into clusters of crystals. Clustering required that the X-ray beam be adjusted to match the crystal size to prevent overlapping diffraction patterns. No additional problems were encountered with the serial crystallography strategy of combining small randomly oriented wedges of data from a large number of specimens. Lastly, high-quality data able to support a realistic molecular replacement solution were readily obtained from both crystal types using all three serial crystallography strategies.« less

Solvent minimization induces preferential orientation and crystal clustering in serial micro-crystallography on micro-meshes, in situ plates and on a movable crystal conveyor belt

PubMed Central

Soares, Alexei S.; Mullen, Jeffrey D.; Parekh, Ruchi M.; McCarthy, Grace S.; Roessler, Christian G.; Jackimowicz, Rick; Skinner, John M.; Orville, Allen M.; Allaire, Marc; Sweet, Robert M.

2014-01-01

X-ray diffraction data were obtained at the National Synchrotron Light Source from insulin and lysozyme crystals that were densely deposited on three types of surfaces suitable for serial micro-crystallography: MiTeGen MicroMeshes™, Greiner Bio-One Ltd in situ micro-plates, and a moving kapton crystal conveyor belt that is used to deliver crystals directly into the X-ray beam. 6° wedges of data were taken from ∼100 crystals mounted on each material, and these individual data sets were merged to form nine complete data sets (six from insulin crystals and three from lysozyme crystals). Insulin crystals have a parallelepiped habit with an extended flat face that preferentially aligned with the mounting surfaces, impacting the data collection strategy and the design of the serial crystallography apparatus. Lysozyme crystals had a cuboidal habit and showed no preferential orientation. Preferential orientation occluded regions of reciprocal space when the X-ray beam was incident normal to the data-collection medium surface, requiring a second pass of data collection with the apparatus inclined away from the orthogonal. In addition, crystals measuring less than 20 µm were observed to clump together into clusters of crystals. Clustering required that the X-ray beam be adjusted to match the crystal size to prevent overlapping diffraction patterns. No additional problems were encountered with the serial crystallography strategy of combining small randomly oriented wedges of data from a large number of specimens. High-quality data able to support a realistic molecular replacement solution were readily obtained from both crystal types using all three serial crystallography strategies. PMID:25343789

Spin-polarized Second Harmonic Generation from the Antiferromagnetic CaCoSO Single Crystal

NASA Astrophysics Data System (ADS)

Reshak, A. H.

2017-04-01

The spin-polarized second harmonic generation (SHG) of the recently synthesized CaCoSO single crystal is performed based on the calculated electronic band structure. The calculation reveals that the spin-up (↑) channel of CaCoSO possesses a direct energy gap (Γv-Γc) of about 2.187 eV, 1.187 eV (Kv-Kc) for the spin-down (↓) channel and an indirect gap (Γv-Kc) of about 0.4 eV for the spin-polarized CaCoSO single crystal. The linear optical properties obtained reveal that the recently synthesized crystal exhibits considerable anisotropy with negative uniaxial anisotropy and birefringence favor to enhance the SHG. We have calculated the three non-zero tensor components of the SHG and found the is the dominat component, one with a large SHG of about (d33 = 6.936 pm/V at λ = 1064 nm), the half value of KTiOPO4 (KTP). As the values of (↑) < (↓) < spin-polarized are related to the values of the energy gap of (↑) 2.187 eV> (↓) 1.187 eV> spin-polarized gap 0.4 eV therefore, a smaller energy gap gives better SHG performance. Furthermore, the microscopic first hyperpolarizability, βijk, is calculated.

First observation of a negative elastic constant in intermediate valent TmSe

NASA Astrophysics Data System (ADS)

Boppart, H.; Treindl, A.; Wachter, P.; Roth, S.

1980-08-01

The sound velocities v L, v T 1 and v T 2 have been measured at 15 MHz on Tm 3+0.87Se and Tm 2.8+0.99Se between 300 K and 4.2 K and the elastic constants c ij have been derived. In intermediate valent Tm 2.8+0.99Se c 12 turned out to be negative. This sign is interpreted as being typical for intermediate valent compounds. Also for the first time experimental evidence is given for crystal field effects in Tm 3+0.87Se. Strong elastic nonlinearities are observed in intermediate valent Tm 2.8+0.99Se with uniaxial pressure.

Micropore Geometry Manipulation by Macroscopic Deformation Based on Shape Memory Effect in Porous PLLA Membrane and its Enhanced Separation Performance.

PubMed

Zhao, Jingxin; Yang, Qiucheng; Wang, Tao; Wang, Lian; You, Jichun; Li, Yongjin

2017-12-20

An effective strategy to tailor the microporous structures has been developed based on the shape memory effect in porous poly(l-lactic acid) membranes in which tiny crystals and amorphous matrix play the roles of shape-fixed phase and reversible-phase, respectively. Our results indicate that not only PLLA membranes but micropores exhibit shape memory properties. The proportional deformations on two scales have been achieved by uniaxial or biaxial tension, providing a facile way to manipulate continuously the size and the orientation degree of pores on microscale. The enhanced separation performance has been validated by taking polystyrene colloids with varying diameters as an example.

Simulation of uniaxial deformation of hexagonal crystals (Mg, Be)

NASA Astrophysics Data System (ADS)

Vlasova, A. M.; Kesarev, A. G.

2017-12-01

Molecular dynamics (MD) simulations were performed for the nanocompression loading of nanocrystalline magnesium and beryllium modeled by an interatomic potential of the embedded atom method (EAM). It is shown that the main deformation modes are prismatic slip and twinning for magnesium, and only prismatic slip for beryllium. The formation of stable configurations of dislocation grids in magnesium and beryllium was observed. Dislocation networks are formed in the habit plane of the twin in a magnesium nanocrystall. Some dislocation reactions are suggested to explain the appearance of such networks. Shockley partial dislocations in a beryllium nanocrystall form grids in the slip plane. A strong anisotropy between slip systems was observed, which is in agreement with experimental data.

The Microstructural Response of Granular Soil Under Uniaxial Strain

DTIC Science & Technology

1993-10-01

under uniaxial strains of up to 10 percent. The material tested was a poorly graded ottowa sand with specimens consisting of either 0.5- or 0.75-mm...microstructural effects in granular material under uniaxial strain of up to 10.0 percent. The relative influence of several microstructural effects (such as...uniaxial strain. The confinement vessel consisted of a base plate, four walls, and a loading cap. The sidewalls extended up beyond the specimen and served

Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys

NASA Technical Reports Server (NTRS)

Arakere, N. K.; Swanson, G.

2002-01-01

High cycle fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Single crystal nickel turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493, PWA 1484, RENE' N-5 and CMSX-4. These alloys play an important role in commercial, military and space propulsion systems. Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades are complicated to predict due to the material orthotropy and variations in crystal orientations. Fatigue life estimation of single crystal turbine blades represents an important aspect of durability assessment. It is therefore of practical interest to develop effective fatigue failure criteria for single crystal nickel alloys and to investigate the effects of variation of primary and secondary crystal orientation on fatigue life. A fatigue failure criterion based on the maximum shear stress amplitude /Delta(sub tau)(sub max))] on the 24 octahedral and 6 cube slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criterion reduces the scatter in uniaxial LCF test data considerably for PWA 1493 at 1200 F in air. Additionally, single crystal turbine blades used in the alternate advanced high-pressure fuel turbopump (AHPFTP/AT) are modeled using a large-scale three-dimensional finite element model. This finite element model is capable of accounting for material orthotrophy and variation in primary and secondary crystal orientation. Effects of variation in crystal orientation on blade stress response are studied based on 297 finite element model runs. Fatigue lives at critical points in the blade are computed using finite element stress results and the failure criterion developed. Stress analysis results in the blade attachment region are also presented. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to significantly increase a component S resistance to fatigue crack growth with- out adding additional weight or cost. [DOI: 10.1115/1.1413767

Induced Anisotropy in FeCo-Based Nanocrystalline Ferromagnetic Alloys (HITPERM) by Very High Field Annealing

NASA Technical Reports Server (NTRS)

Johnson, F.; Garmestani, H.; Chu, S.-Y.; McHenry, M. E.; Laughlin, D. E.

2004-01-01

Very high magnetic field annealing is shown to affect the magnetic anisotropy in FeCo-base nanocrystalline soft ferromagnetic alloys. Alloys of composition Fe(44.5)Co(44.5)Zr(7)B(4) were prepared by melt spinning into amorphous ribbons, then wound to form toroidal bobbin cores. One set of cores was crystallized in a zero field at 600 deg. C for 1 h, then, field annealed at 17 tesla (T) at 480 deg. C for 1 h. Another set was crystallized in a 17-T field at 480 deg. C for 1 h. Field orientation was transverse to the magnetic path of the toroidal cores. An induced anisotropy is indicated by a sheared hysteresis loop. Sensitive torque magnetometry measurements with a Si cantilever sensor indicated a strong, uniaxial, longitudinal easy axis in the zero-field-crystallized sample. The source is most likely magnetoelastic anisotropy, caused by the residual stress from nanocrystallization and the nonzero magnetostriction coefficient for this material. The magnetostrictive coefficient lambda(5) is measured to be 36 ppm by a strain gage technique. Field annealing reduces the magnitude of the induced anisotropy. Core loss measurements were made in the zero-field-crystallized, zero-field-crystallized- than-field-annealed, and field-crystallized states. Core loss is reduced 30%-50% (depending on frequency) by field annealing. X-ray diffraction reveals no evidence of crystalline texture or orientation that would cause the induced anisotropy. Diffusional pair ordering is thought to be the cause of the induced anisotropy. However, reannealing the samples in the absence of a magnetic field at 480 deg. C does not completely remove the induced anisotropy.

Accurate determination of chemical shift tensor orientations of single-crystals by solid-state magic angle spinning NMR

NASA Astrophysics Data System (ADS)

Avadhut, Yamini S.; Weber, Johannes; Schmedt auf der Günne, Jörn

2017-09-01

An improved implementation of single-crystal magic-angle-spinning (MAS) NMR is presented which gives access to chemical shift tensors both in orientation (relative to the crystal axis system) and principal axis values. For mounting arbitrary crystals inside ordinary MAS rotors, a mounting tool is described which allows to relate the crystal orientation determined by diffraction techniques to the rotor coordinate system. The crystal is finally mounted into a MAS rotor equipped with a special insert which allows a defined reorientation of the single-crystal by 90°. The approach is based on the idea that the dispersive spectra, which are obtained when applying read-pulses at specific rotor-phases, not only yield the size of the eigenvalues but also encode the orientation of the different chemical shift (rank-2) tensors. For this purpose two 2D-data sets with orthogonal crystal orientation are fitted simultaneously. The presented analysis for chemical shift tensors is supported by an analytical formula which allows fast calculation of phase and amplitude of individual spinning side-bands and by a protocol which solves the problem of finding the correct reference phase of the spectrum. Different rotor-synchronized pulse-sequences are introduced for the same reason. Experiments are performed on L-alanine and O-phosphorylethanolamine and the observed errors are analyzed in detail. The experimental data are opposed to DFT-computed chemical shift tensors which have been obtained by the extended embedded ion method.

7-Chloro-4-[(7-chloro­quinolin-4-yl)sulfan­yl]quinoline dihydrate

PubMed Central

Wardell, James L.; Tiekink, Edward R. T.

2012-01-01

In the title thio­ether dihydrate, C18H10Cl2N2S·2H2O, the S-bound quinolinyl residues are almost orthogonal, forming a dihedral angle of 72.36 (4)°. In the crystal, the four water mol­ecules are connected via an eight-membered {⋯OH}4 synthon with each of the four pendent water H atoms hydrogen bonded to a pyridine N atom to stabilize a three-dimensional architecture. PMID:22589973

Polarization-phase diagnostics of latent course of cholelithiasis in patients with chronic cholecystitis combined with diabetes mellitus type 2

NASA Astrophysics Data System (ADS)

Fediv, O. I.; Ivashchuk, O. I.; Marchuk, Yu. F.; Andriychuk, D. R.

2011-09-01

The principles of optical model of human bile polycrystalline structure are described. The three optical levels - isotropic, liquid-crystal and solid-crystal have been proposed. It has been introduced and proposed the scenarios of phase distribution formation in the boundary field of laser radiation, transformed by bile layers. The experimental scheme of direct measurement of coordinate phase distributions has been presented. The results of investigating the interrelation between the values of correlation and fractal parameters are presented. They characterize the coordinate distributions of phase shifts between the orthogonal components of the amplitude in the points of laser images of bile smears of cholelithiasis patients in combination with other pathologies. The diagnostic criteria of the cholelithiasis nascency and its severity degree differentiation are determined.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Generation of terahertz radiation upon filtration of a supercontinuum produced during the propagation of a femtosecond laser pulse in a GaAs crystal

NASA Astrophysics Data System (ADS)

Vardanyan, Aleksandr O.; Oganesyan, David L.

2008-11-01

The results of a theoretical study of the formation of a supercontinuum produced due to the interaction of femtosecond laser pulses with an isotropic nonlinear medium are presented. The system of nonlinear Maxwell's equations was numerically integrated in time by the finite-difference method. The interaction of mutually orthogonal linearly-polarised 1.98-μm, 30-fs, 30-nJ pulses propagating along the normal to the 110 plane in a 1-mm-long GaAs crystal was considered. In the nonlinear part of the polarisation medium, the inertialless second-order nonlinear susceptibility was taken into account. The formation process of a terahertz pulse obtained due to the supercontinuum filtration was studied.

Fabrication of double-sided thallium bromide strip detectors

NASA Astrophysics Data System (ADS)

Hitomi, Keitaro; Nagano, Nobumichi; Onodera, Toshiyuki; Kim, Seong-Yun; Ito, Tatsuya; Ishii, Keizo

2016-07-01

Double-sided strip detectors were fabricated from thallium bromide (TlBr) crystals grown by the traveling-molten zone method using zone-purified materials. The detectors had three 3.4-mm-long strips with 1-mm widths and a surrounding electrode placed orthogonally on opposite surfaces of the crystals at approximately 6.5×6.5 mm2 in area and 5 mm in thickness. Excellent charge transport properties for both electrons and holes were observed from the TlBr crystals. The mobility-lifetime products for electrons and holes in the detector were measured to be ~3×10-3 cm2/V and ~1×10-3 cm2/V, respectively. The 137Cs spectra corresponding to the gamma-ray interaction position were obtained from the detector. An energy resolution of 3.4% of full width at half maximum for 662-keV gamma rays was obtained from one "pixel" (an intersection of the strips) of the detector at room temperature.

Probing crystal structure and mesoscale assembly of cellulose microfibrils in plant cell walls, tunicate tests, and bacterial films using vibrational sum frequency generation (SFG) spectroscopy.

PubMed

Lee, Christopher M; Kafle, Kabindra; Park, Yong Bum; Kim, Seong H

2014-06-14

This study reports that the noncentrosymmetry and phase synchronization requirements of the sum frequency generation (SFG) process can be used to distinguish the three-dimensional organization of crystalline cellulose distributed in amorphous matrices. Crystalline cellulose is produced as microfibrils with a few nanometer diameters by plants, tunicates, and bacteria. Crystalline cellulose microfibrils are embedded in wall matrix polymers and assembled into hierarchical structures that are precisely designed for specific biological and mechanical functions. The cellulose microfibril assemblies inside cell walls are extremely difficult to probe. The comparison of vibrational SFG spectra of uniaxially-aligned and disordered films of cellulose Iβ nanocrystals revealed that the spectral features cannot be fully explained with the crystallographic unit structure of cellulose. The overall SFG intensity, the alkyl peak shape, and the alkyl/hydroxyl intensity ratio are sensitive to the lateral packing and net directionality of the cellulose microfibrils within the SFG coherence length scale. It was also found that the OH SFG stretch peaks could be deconvoluted to find the polymorphic crystal structures of cellulose (Iα and Iβ). These findings were used to investigate the cellulose crystal structure and mesoscale cellulose microfibril packing in intact plant cell walls, tunicate tests, and bacterial films.

Modulus and yield stress of drawn LDPE

NASA Astrophysics Data System (ADS)

Thavarungkul, Nandh

Modulus and yield stress were investigated in drawn low density polyethylene (LDPE) film. Uniaxially drawn polymeric films usually show high values of modulus and yield stress, however, studies have normally only been conducted to identify the structural features that determine modulus. In this study small-angle x-ray scattering (SAXS), thermal shrinkage, birefringence, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA) were used to examine, directly and indirectly, the structural features that determine both modulus and yield stress, which are often closely related in undrawn materials. Shish-kebab structures are proposed to account for the mechanical properties in drawn LDPE. The validity of this molecular/morphological model was tested using relationships between static mechanical data and structural and physical parameters. In addition, dynamic mechanical results are also in line with static data in supporting the model. In the machine direction (MD), "shish" and taut tie molecules (TTM) anchored in the crystalline phase account for E; whereas crystal lamellae with contributions from "shish" and TTM determine yield stress. In the transverse direction (TD), the crystalline phase plays an important roll in both modulus and yield stress. Modulus is determined by crystal lamellae functioning as platelet reinforcing elements in the amorphous matrix with an additional contributions from TTM and yield stress is determined by the crystal lamellae's resistance to deformation.

Generalized Finsler geometric continuum physics with applications in fracture and phase transformations

NASA Astrophysics Data System (ADS)

Clayton, J. D.

2017-02-01

A theory of deformation of continuous media based on concepts from Finsler differential geometry is presented. The general theory accounts for finite deformations, nonlinear elasticity, and changes in internal state of the material, the latter represented by elements of a state vector of generalized Finsler space whose entries consist of one or more order parameter(s). Two descriptive representations of the deformation gradient are considered. The first invokes an additive decomposition and is applied to problems involving localized inelastic deformation mechanisms such as fracture. The second invokes a multiplicative decomposition and is applied to problems involving distributed deformation mechanisms such as phase transformations or twinning. Appropriate free energy functions are posited for each case, and Euler-Lagrange equations of equilibrium are derived. Solutions are obtained for specific problems of tensile fracture of an elastic cylinder and for amorphization of a crystal under spherical and uniaxial compression. The Finsler-based approach is demonstrated to be more general and potentially more physically descriptive than existing hyperelasticity models couched in Riemannian geometry or Euclidean space, without incorporation of supplementary ad hoc equations or spurious fitting parameters. Predictions for single crystals of boron carbide ceramic agree qualitatively, and in many instances quantitatively, with results from physical experiments and atomic simulations involving structural collapse and failure of the crystal along its c-axis.

Thermoelectric anisotropy in the iron-based superconductor Ba (Fe1-xCox) 2As2

NASA Astrophysics Data System (ADS)

Matusiak, Marcin; Rogacki, Krzysztof; Wolf, Thomas

2018-06-01

We report on the in-plane anisotropy of the Seebeck and Nernst coefficients as well as of the electrical resistivity determined for a series of strain-detwinned single crystals of Ba (Fe1-xC ox) 2A s2 . Two underdoped samples (x =0.024 , 0.045) exhibiting a transition from the tetragonal paramagnetic phase to the orthorhombic spin density wave (SDW) phase (at Ttr=100 and 60 K, respectively) show an onset of Nernst anisotropy at temperatures above 200 K, which is significantly higher than Ttr. In the optimally doped sample (x =0.06 ) the transport properties also appear to be in-plane anisotropic below T ≈120 K, despite the fact that this particular composition does not show any evidence of long-range magnetic order. However, the anisotropy observed in the optimally doped crystal is rather small, and for the Seebeck and Nernst coefficients the difference between values measured along and across the uniaxial strain has an opposite sign to those observed for underdoped crystals with x =0.024 and 0.045. For these two samples, the insensitivity of the Nernst anisotropy to the SDW transition suggests that the origin of nematicity might be something other than magnetic.

A Geometric Interpretation of the Effective Uniaxial Anisotropy Field in Magnetic Films

NASA Astrophysics Data System (ADS)

Kozlov, V. I.

2018-01-01

It is shown that the effective uniaxial anisotropy field that is usually applied in thin magnetic films (TMFs), which is noncollinear to the magnetization vector, is insufficient for deeper understanding of these processes, although it explains many physical processes in films. The analysis of the magnetization discontinuity in films under certain conditions yields the component of the effective uniaxial anisotropy field collinear to the magnetization vector. This component explains the magnetization discontinuity and allows one to speak of the total effective uniaxial anisotropy field in TMFs.

Petrology and geochemistry of the orbicular granitoid of Caldera, northern Chile. Models and hypotheses on the formation of radial orbicular textures

NASA Astrophysics Data System (ADS)

Díaz-Alvarado, Juan; Rodríguez, Natalia; Rodríguez, Carmen; Fernández, Carlos; Constanzo, Ítalo

2017-07-01

The orbicular granitoid of Caldera, located at the northern part of the Chilean Coastal Range, is a spectacular example of radial textures in orbicular structures. The orbicular body crops out as a 375 m2 tabular to lensoidal intrusive sheet emplaced in the Lower Jurassic Relincho pluton. The orbicular structures are 3-7 cm in diameter ellipsoids hosted in a porphyritic matrix. The orbicules are comprised by a Qtz-dioritic core (3-5 cm in diameter) composed by Pl + Hbl + Qtz + Bt ± Kfs with equiaxial textures and a gabbroic shell (2-3 cm in diameter) characterized by feathery and radiate textures with a plagioclase + hornblende paragenesis. The radial shell crystals are rooted and orthogonally disposed in the irregular contact with the core. The radial shell, called here inner shell, is in contact with the granodioritic equiaxial interorbicular matrix through a 2-3 mm wide poikilitic band around the orbicule (outer shell). The outer shell and the matrix surrounding the orbicules are characterized by the presence of large hornblende and biotite oikocrystals that include fine-grained rounded plagioclase and magnetite. The oikocrystals of both the outer shell and the matrix have a circumferential arrangement around the orbicule, i.e. orthogonal to the radial inner shell. The coarse-grained granodioritic interorbicular matrix present pegmatitic domains with large acicular hornblende and K-feldspar megacrysts. This work presents a review of the textural characteristics of the orbicules and a complete new mineral and whole-rock geochemical study of the different parts of the orbicular granitoid, together with thermobarometric and crystallographic data, and theoretical modeling of the crystallization and element partitioning processes. We propose a model for the formation of the orbicular radial textures consisting of several processes that are suggested to occur fast and consecutively: superheating, volatile exsolution, undercooling, geochemical fractionation and columnar and equiaxial crystallization. According to the obtained results, the formation of the orbicular granitoid of Caldera may have initiated 1) during the generation of a magmatic fracture in the crystallization front of the Relincho pluton, where the water released by the host crystal mush was dissolved in the new batch of dioritic magma. 2) The high influx of water-rich liquids induced superheating conditions in the newly intruding magma that became a depolymerized liquid, where the only solid particules were the small irregular fragments of the host mush dragged from the fracture walls. 3) Volatile exsolution promoted crystallization under undercooling conditions. 4) Undercooling and nucleation around the core (cold germs) involved the physical and geochemical fractionation between two sub-systems: a gabbroic sub-system that comprises the solid paragénesis with a residual water-rich liquid and a granodioritic sub-system. 5) The orbicules, including core and inner shell, behaved as viscous bodies (crystals + residual liquid) floating in the granodioritic magma. 6) Higher undercooling rates occurred at the starting stage, close to the liquidus, promoting columnar crystallization around the cores and formation of the shells. Conversely, in the granodioritic matrix sub-system, equiaxial crystallization was promoted by low relative crystallization rates. 7) The rest of the crystallization process evolved later in the outer shell and the matrix, as suggested by the poikilitic textures observed in both sides of the orbicule contact, and under conditions close to the solidus of both sub-systems (shell and matrix). The water-rich residual liquid expelled during the orbicular shell crystallization was mingled with the partially crystallized matrix magma, generating the pegmatitic domains with large Kfs megacrysts.

Polarized emission from light-emitting electrochemical cells using uniaxially oriented polymer thin films of poly(9,9-dioctylfluorene-co-bithiophene)

NASA Astrophysics Data System (ADS)

Miyazaki, Masumi; Sakanoue, Tomo; Takenobu, Taishi

2018-03-01

Uniaxially oriented poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) films were prepared on rubbed polyimide substrates and applied to emitting layers of light-emitting electrochemical cells (LECs). The layered structure of the uniaxially oriented F8T2 film and ionic liquid electrolytes enabled us to demonstrate LEC operations with high anisotropic characteristics both in emission and charge transport. Polarized electroluminescence (EL) from electrochemically induced p-n junctions in the uniaxially oriented F8T2 was obtained. The dichroic ratios of EL were the same as those of photoluminescence, suggesting that the doping process into the oriented F8T2 did not interrupt the polymer ordering. This indicates the usefulness of the layered structure of the polymer/electrolyte for the fabrication of LECs based on highly oriented polymer films. In addition, uniaxially oriented F8T2 was found to show reduced threshold energy in optically pumped amplified spontaneous emission. These demonstrations suggest the advantage of uniaxially oriented polymer-based LECs for potential application in future electrically pumped lasers.

Amelogenin in Enamel Tissue Engineering.

PubMed

Uskoković, Vuk

2015-01-01

In this chapter the basic premises, the recent findings and the future challenges in the use of amelogenin for enamel tissue engineering are being discoursed on. Results emerging from the experiments performed to assess the fundamental physicochemical mechanisms of the interaction of amelogenin, the main protein of the enamel matrix, and the growing crystals of apatite, are mentioned, alongside a moderately comprehensive literature review of the subject at hand. The clinical importance of understanding this protein/mineral interaction at the nanoscale are highlighted as well as the potential for tooth enamel to act as an excellent model system for studying some of the essential aspects of biomineralization processes in general. The dominant paradigm stating that amelogenin directs the uniaxial growth of apatite crystals in enamel by slowing down the growth of (hk0) faces on which it adheres is being questioned based on the results demonstrating the ability of amelogenin to promote the nucleation and crystal growth of apatite under constant titration conditions designed to mimic those present in the developing enamel matrix. The role of numerous minor components of the enamel matrix is being highlighted as essential and impossible to compensate for by utilizing its more abundant ingredients only. It is concluded that the three major aspects of amelogenesis outlined hereby--(1) the assembly of amelogenin and other enamel matrix proteins, (2) the proteolytic activity, and (3) crystallization--need to be in precise synergy with each other in order for the grounds for the proper imitation of amelogenesis in the lab to be created.

Anisotropy-Induced Quantum Interference and Population Trapping between Orthogonal Quantum Dot Exciton States in Semiconductor Cavity Systems

NASA Astrophysics Data System (ADS)

Hughes, Stephen; Agarwal, Girish S.

2017-02-01

We describe how quantum dot semiconductor cavity systems can be engineered to realize anisotropy-induced dipole-dipole coupling between orthogonal dipole states in a single quantum dot. Quantum dots in single-mode cavity structures as well as photonic crystal waveguides coupled to spin states or linearly polarized excitons are considered. We demonstrate how the dipole-dipole coupling can control the radiative decay rate of excitons and form pure entangled states in the long time limit. We investigate both field-free entanglement evolution and coherently pumped exciton regimes, and show how a double-field pumping scenario can completely eliminate the decay of coherent Rabi oscillations and lead to population trapping. In the Mollow triplet regime, we explore the emitted spectra from the driven dipoles and show how a nonpumped dipole can take on the form of a spectral triplet, quintuplet, or a singlet, which has applications for producing subnatural linewidth single photons and more easily accessing regimes of high-field quantum optics and cavity-QED.

Quasi two-dimensional astigmatic solitons in soft chiral metastructures

NASA Astrophysics Data System (ADS)

Laudyn, Urszula A.; Jung, Paweł S.; Karpierz, Mirosław A.; Assanto, Gaetano

2016-03-01

We investigate a non-homogeneous layered structure encompassing dual spatial dispersion: continuous diffraction in one transverse dimension and discrete diffraction in the orthogonal one. Such dual diffraction can be balanced out by one and the same nonlinear response, giving rise to light self-confinement into astigmatic spatial solitons: self-focusing can compensate for the spreading of a bell-shaped beam, leading to quasi-2D solitary wavepackets which result from 1D transverse self-localization combined with a discrete soliton. We demonstrate such intensity-dependent beam trapping in chiral soft matter, exhibiting one-dimensional discrete diffraction along the helical axis and one-dimensional continuous diffraction in the orthogonal plane. In nematic liquid crystals with suitable birefringence and chiral arrangement, the reorientational nonlinearity is shown to support bell-shaped solitary waves with simple astigmatism dependent on the medium birefringence as well as on the dual diffraction of the input wavepacket. The observations are in agreement with a nonlinear nonlocal model for the all-optical response.

Anisotropy-Induced Quantum Interference and Population Trapping between Orthogonal Quantum Dot Exciton States in Semiconductor Cavity Systems.

PubMed

Hughes, Stephen; Agarwal, Girish S

2017-02-10

We describe how quantum dot semiconductor cavity systems can be engineered to realize anisotropy-induced dipole-dipole coupling between orthogonal dipole states in a single quantum dot. Quantum dots in single-mode cavity structures as well as photonic crystal waveguides coupled to spin states or linearly polarized excitons are considered. We demonstrate how the dipole-dipole coupling can control the radiative decay rate of excitons and form pure entangled states in the long time limit. We investigate both field-free entanglement evolution and coherently pumped exciton regimes, and show how a double-field pumping scenario can completely eliminate the decay of coherent Rabi oscillations and lead to population trapping. In the Mollow triplet regime, we explore the emitted spectra from the driven dipoles and show how a nonpumped dipole can take on the form of a spectral triplet, quintuplet, or a singlet, which has applications for producing subnatural linewidth single photons and more easily accessing regimes of high-field quantum optics and cavity-QED.

Dynamics of the magnetization of single domain particles having triaxial anisotropy subjected to a uniform dc magnetic field

NASA Astrophysics Data System (ADS)

Ouari, Bachir; Kalmykov, Yury P.

2006-12-01

Thermally induced relaxation of the magnetization of single domain ferromagnetic particles with triaxial (orthorhombic) anisotropy in the presence of a uniform external magnetic field H0 is considered in the context of Brown's continuous diffusion model. Simple analytic equations, which allow one to describe qualitatively the field effects in the relaxation behavior of the system for wide ranges of the field strength and damping parameters are derived. It is shown that these formulas are in complete agreement with the exact matrix continued fraction solution of the infinite hierarchy of linear differential-recurrence equations for the statistical moments, which governs the magnetization dynamics of an individual particle (this hierarchy is derived by averaging the underlying stochastic Landau-Lifshitz-Gilbert equation over its realizations). It is also demonstrated that in strong fields the longitudinal relaxation of the magnetization is essentially modified by the contribution of the high-frequency "intrawell" modes to the relaxation process. This effect discovered for uniaxial particles by Coffey et al. [Phys. Rev. B 51, 15947 (1995)] is the natural consequence of the depletion of population of the shallow potential well. However, in contrast to uniaxial anisotropy, for orthorhombic crystals there is an inherent geometric dependence of the complex magnetic susceptibility and the relaxation time on the damping parameter α arising from the coupling of longitudinal and transverse relaxation modes.

Localized and delocalized motion of colloidal particles on a magnetic bubble lattice.

PubMed

Tierno, Pietro; Johansen, Tom H; Fischer, Thomas M

2007-07-20

We study the motion of paramagnetic colloidal particles placed above magnetic bubble domains of a uniaxial garnet film and driven through the lattice by external magnetic field modulation. An external tunable precessing field propels the particles either in localized orbits around the bubbles or in superdiffusive or ballistic motion through the bubble array. This motion results from the interplay between the driving rotating signal, the viscous drag force and the periodic magnetic energy landscape. We explain the transition in terms of the incommensurability between the transit frequency of the particle through a unit cell and the modulation frequency. Ballistic motion dynamically breaks the symmetry of the array and the phase locked particles follow one of the six crystal directions.

Versatile module for experiments with focussing neutron guides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, T.; Pfleiderer, C.; Böni, P.

2014-09-22

We report the development of a versatile module that permits fast and reliable use of focussing neutron guides under varying scattering angles. A simple procedure for setting up the module and neutron guides is illustrated by typical intensity patterns to highlight operational aspects as well as typical parasitic artefacts. Combining a high-precision alignment table with separate housings for the neutron guides on kinematic mounts, the change-over between neutron guides with different focussing characteristics requires no readjustments of the experimental setup. Exploiting substantial gain factors, we demonstrate the performance of this versatile neutron scattering module in a study of the effectsmore » of uniaxial stress on the domain populations in the transverse spin density wave phase of single crystal Cr.« less

Muon spin rotation studies

NASA Technical Reports Server (NTRS)

1984-01-01

The bulk of the muon spin rotation research work centered around the development of the muon spin rotation facility at the Alternating Gradient Synchrotron (AGS) of Brookhaven National Laboratory (BNL). The collimation system was both designed and fabricated at Virginia State University. This improved collimation system, plus improvements in detectors and electronics enabled the acquisition of spectra free of background out to 15 microseconds. There were two runs at Brookhaven in 1984, one run was devoted primarily to beam development and the other run allowed several successful experiments to be performed. The effect of uniaxial strain on an Fe(Si) crystal at elevated temperature (360K) was measured and the results are incorporated herein. A complete analysis of Fe pulling data taken earlier is included.

Ising versus XY anisotropy in frustrated R(2)Ti(2)O(7) compounds as "Seen" by Polarized Neutrons.

PubMed

Cao, H; Gukasov, A; Mirebeau, I; Bonville, P; Decorse, C; Dhalenne, G

2009-07-31

We studied the field induced magnetic order in R(2)Ti(2)O(7) pyrochlore compounds with either uniaxial (R=Ho, Tb) or planar (R=Er, Yb) anisotropy, by polarized neutron diffraction. The determination of the local susceptibility tensor {chi(parallel to),chi(perpendicular)} provides a universal description of the field induced structures in the paramagnetic phase (2-270 K), whatever the field value (1-7 T) and direction. Comparison of the thermal variations of chi(parallel to) and chi(perpendicular) with calculations using the rare earth crystal field shows that exchange and dipolar interactions must be taken into account. We determine the molecular field tensor in each case and show that it can be strongly anisotropic.

Atomistic study of nanoprecipitates influence on plasticity and fracture of crystalline metals

NASA Astrophysics Data System (ADS)

Stegailov, Vladimir; Kuksin, Alexey; Norman, Genri; Yanilkin, Alexey

2007-06-01

The recent experimental results [G.I.Kanel et al., 2006] show the essential influence of the nanoprecipitates on spall strength of copper single crystals. In this work we address this issue by the molecular dynamics study. The models under consideration are the EAM systems of Al nanoclusters in the Cu matrix and Cu clusters in the Al matrix. We consider these two cases as the representative examples of nanocluster-matrix difference in shear strength. Three ways of the high strain rate deformation modeling are studied: hydrostatic and uniaxial strain and shock wave loading in the impactor-target model. The preexisting edge dislocation interaction with the precipitate under shear deformation is addressed. The effect of the precipitate size is considered.

Experimental study of uniaxial stress effects on Coulomb-limited mobility in p-type metal-oxide-semiconductor field-effect transistors

NASA Astrophysics Data System (ADS)

Kobayashi, Shigeki; Saitoh, Masumi; Nakabayashi, Yukio; Uchida, Ken

2007-11-01

Uniaxial stress effects on Coulomb-limited mobility (μCoulomb) in Si metal-oxide-semiconductor field-effect transistors (MOSFETs) are investigated experimentally. By using the four-point bending method, uniaxial stress corresponding to 0.1% strain is applied to MOSFETs along the channel direction. It is found that μCoulomb in p-type MOSFETs is enhanced greatly by uniaxial stress; μCoulomb is as sensitive as phonon-limited mobility. The high sensitivity of μCoulomb in p-type MOSFETs to stress arises from the stress-induced change of hole effective mass.

Experimentally quantifying critical stresses associated with basal slip and twinning in magnesium using micro-pillars

DOE PAGES

Liu, Yue; Li, Nan; Mariyappan, Arul Kumar; ...

2017-06-07

Basal slip and {01more » $$\\bar{1}$$2} twinning are two major plastic deformation mechanisms in hexagonal closed-packed magnesium. Here in this paper, we quantify the critical stresses associated with basal slip and twinning in single-crystal and bi-crystal magnesium samples by performing in situ compression of micropillars with different diameters in a scanning electron microscope. The micropillars are designed to favor either slip or twinning under uniaxial compression. Compression tests imply a negligible size effect related to basal slip and twinning as pillar diameter is greater than 10 μm. The critical resolved shear stresses are deduced to be 29 MPa for twinning and 6 MPa for basal slip from a series of micropillar compression tests. Employing full-field elasto-visco-plastic simulations, we further interpret the experimental observations in terms of the local stress distribution associated with multiple twinning, twin nucleation, and twin growth. Our simulation results suggest that the twinning features being studied should not be close to the top surface of the micropillar because of local stress perturbations induced by the hard indenter.« less

A programmable nanoreplica molding for the fabrication of nanophotonic devices.

PubMed

Liu, Longju; Zhang, Jingxiang; Badshah, Mohsin Ali; Dong, Liang; Li, Jingjing; Kim, Seok-min; Lu, Meng

2016-03-01

The ability to fabricate periodic structures with sub-wavelength features has a great potential for impact on integrated optics, optical sensors, and photovoltaic devices. Here, we report a programmable nanoreplica molding process to fabricate a variety of sub-micrometer periodic patterns using a single mold. The process utilizes a stretchable mold to produce the desired periodic structure in a photopolymer on glass or plastic substrates. During the replica molding process, a uniaxial force is applied to the mold and results in changes of the periodic structure, which resides on the surface of the mold. Direction and magnitude of the force determine the array geometry, including the lattice constant and arrangement. By stretching the mold, 2D arrays with square, rectangular, and triangular lattice structures can be fabricated. As one example, we present a plasmonic crystal device with surface plasmon resonances determined by the force applied during molding. In addition, photonic crystal slabs with different array patterns are fabricated and characterized. This unique process offers the capability of generating various periodic nanostructures rapidly and inexpensively.

A programmable nanoreplica molding for the fabrication of nanophotonic devices

PubMed Central

Liu, Longju; Zhang, Jingxiang; Badshah, Mohsin Ali; Dong, Liang; Li, Jingjing; Kim, Seok-min; Lu, Meng

2016-01-01

The ability to fabricate periodic structures with sub-wavelength features has a great potential for impact on integrated optics, optical sensors, and photovoltaic devices. Here, we report a programmable nanoreplica molding process to fabricate a variety of sub-micrometer periodic patterns using a single mold. The process utilizes a stretchable mold to produce the desired periodic structure in a photopolymer on glass or plastic substrates. During the replica molding process, a uniaxial force is applied to the mold and results in changes of the periodic structure, which resides on the surface of the mold. Direction and magnitude of the force determine the array geometry, including the lattice constant and arrangement. By stretching the mold, 2D arrays with square, rectangular, and triangular lattice structures can be fabricated. As one example, we present a plasmonic crystal device with surface plasmon resonances determined by the force applied during molding. In addition, photonic crystal slabs with different array patterns are fabricated and characterized. This unique process offers the capability of generating various periodic nanostructures rapidly and inexpensively. PMID:26925828

Strength statistics of single crystals and metallic glasses under small stressed volumes

DOE PAGES

Gao, Yanfei; Bei, Hongbin

2016-05-13

It has been well documented that plastic deformation of crystalline and amorphous metals/alloys shows a general trend of “smaller is stronger”. The majority of the experimental and modeling studies along this line have been focused on finding and reasoning the scaling slope or exponent in the logarithmic plot of strength versus size. In contrast to this view, here we show that the universal picture should be the thermally activated nucleation mechanisms in small stressed volume, the stochastic behavior as to find the weakest links in intermediate sizes of the stressed volume, and the convolution of these two mechanisms with respectmore » to variables such as indenter radius in nanoindentation pop-in, crystallographic orientation, pre-strain level, sample length as in uniaxial tests, and others. Furthermore, experiments that cover the entire spectrum of length scales and a unified model that treats both thermal activation and spatial stochasticity have discovered new perspectives in understanding and correlating the strength statistics in a vast of observations in nanoindentation, micro-pillar compression, and fiber/whisker tension tests of single crystals and metallic glasses.« less

Primary combination of phase-field and discrete dislocation dynamics methods for investigating athermal plastic deformation in various realistic Ni-base single crystal superalloy microstructures

NASA Astrophysics Data System (ADS)

Gao, Siwen; Rajendran, Mohan Kumar; Fivel, Marc; Ma, Anxin; Shchyglo, Oleg; Hartmaier, Alexander; Steinbach, Ingo

2015-10-01

Three-dimensional discrete dislocation dynamics (DDD) simulations in combination with the phase-field method are performed to investigate the influence of different realistic Ni-base single crystal superalloy microstructures with the same volume fraction of {γ\\prime} precipitates on plastic deformation at room temperature. The phase-field method is used to generate realistic microstructures as the boundary conditions for DDD simulations in which a constant high uniaxial tensile load is applied along different crystallographic directions. In addition, the lattice mismatch between the γ and {γ\\prime} phases is taken into account as a source of internal stresses. Due to the high antiphase boundary energy and the rare formation of superdislocations, precipitate cutting is not observed in the present simulations. Therefore, the plastic deformation is mainly caused by dislocation motion in γ matrix channels. From a comparison of the macroscopic mechanical response and the dislocation evolution for different microstructures in each loading direction, we found that, for a given {γ\\prime} phase volume fraction, the optimal microstructure should possess narrow and homogeneous γ matrix channels.

Deformation of periodic nanovoid structures in Mg single crystals

NASA Astrophysics Data System (ADS)

Xu, Shuozhi; Su, Yanqing; Zare Chavoshi, Saeed

2018-01-01

Large scale molecular dynamics (MD) simulations in Mg single crystal containing periodic cylindrical voids subject to uniaxial tension along the z direction are carried out. Models with different initial void sizes and crystallographic orientations are explored using two interatomic potentials. It is found that (i) a larger initial void always leads to a lower yield stress, in agreement with an analytic prediction; (ii) in the model with x[\\bar{1}100]-y[0001]-z[11\\bar{2}0] orientations, the two potentials predict different types of tension twins and phase transformation; (iii) in the model with x[0001]-y[11\\bar{2}0]-z[\\bar{1}100] orientations, the two potentials identically predict the nucleation of edge dislocations on the prismatic plane, which then glide away from the void, resulting in extrusions at the void surface; in the case of the smallest initial void, these surface extrusions pinch the void into two voids. Besides bringing new physical understanding of the nanovoid structures, our work highlights the variability and uncertainty in MD simulations arising from the interatomic potential, an issue relatively lightly addressed in the literature to date.

Investigation of Three-Dimensional Stress Fields and Slip Systems for FCC Single Crystal Superalloy Notched Specimens

NASA Technical Reports Server (NTRS)

Arakere, Nagaraj K.; Magnan, Shannon; Ebrahimi, Fereshteh; Ferroro, Luis

2004-01-01

Metals and their alloys, except for a few intermetallics, are inherently ductile, i.e. plastic deformation precedes fracture in these materials. Therefore, resistance to fracture is directly related to the development of the plastic zone at the crack tip. Recent studies indicate that the fracture toughness of single crystals depends on the crystallographic orientation of the notch as well as the loading direction. In general, the dependence of crack propagation resistance on crystallographic orientation arises from the anisotropy of (i) elastic constants, (ii) plastic deformation (or slip), and (iii) the weakest fracture planes (e.g. cleavage planes). Because of the triaxial stress state at the notch tips, many slip systems that otherwise would not be activated during uniaxial testing, become operational. The plastic zone formation in single crystals has been tackled theoretically by Rice and his co-workers and only limited experimental work has been conducted in this area. The study of the stresses and strains in the vicinity of a FCC single crystal notch tip is of relatively recent origin. We present experimental and numerical investigation of 3D stress fields and evolution of slip sector boundaries near notches in FCC single crystal tension test specimens, and demonstrate that a 3D linear elastic finite element model that includes the effect of material anisotropy is shown to predict active slip planes and sectors accurately. The slip sector boundaries are shown to have complex curved shapes with several slip systems active simultaneously near the notch. Results are presented for surface and mid-plane of the specimens. The results demonstrate that accounting for 3D elastic anisotropy is very important for accurate prediction of slip activation near FCC single crystal notches loaded in tension. Results from the study will help establish guidelines for fatigue damage near single crystal notches.

Quantitative analysis of H-species in anisotropic minerals by polarized infrared spectroscopy along three orthogonal directions

NASA Astrophysics Data System (ADS)

Shuai, Kang; Yang, Xiaozhi

2017-03-01

Infrared spectroscopy is a powerful technique for probing H-species in nominally anhydrous minerals, and a particular goal of considerable efforts has been providing a simple yet accurate method for the quantification. The available methods, with either polarized or unpolarized analyses, are usually time-consuming or, in some cases, subjected to larger uncertainty than theoretically expected. It is shown here that an empirical approach for measuring the concentration, by determining three polarized infrared spectra along any three mutually perpendicular directions, is theoretically and in particular experimentally correct. The theoretical background is established by considering the integrated absorbance, and the experimental measurements are based on a careful evaluation of the species and content of H in a series of gem-quality orthogonal, monoclinic and triclinic crystals, including olivine, orthopyroxene, clinopyroxene, orthoclase and albite (natural and H-annealed). The results demonstrate that the sum of the integrated absorbance from two polarized spectra along two perpendicular directions in any given plane is a constant, and that the sum of the integrated absorbance from three polarized spectra along any three orthogonal directions is of essentially the same accuracy as that along the principal axes. It is also shown that this method works well, with a relative accuracy within 10%, even at some extreme cases where the sample absorption bands are both intense and strongly anisotropic.

Study of Experiment on Rock-like Material Consist of fly-ash, Cement and Mortar

NASA Astrophysics Data System (ADS)

Nan, Qin; Hongwei, Wang; Yongyan, Wang

2018-03-01

Study the uniaxial compression test of rock-like material consist of coal ash, cement and mortar by changing the sand cement ratio, replace of fine coal, grain diameter, water-binder ratio and height-diameter ratio. We get the law of four factors above to rock-like material’s uniaxial compression characteristics and the quantitative relation. The effect law can be sum up as below: sample’s uniaxial compressive strength and elasticity modulus tend to decrease with the increase of sand cement ratio, replace of fine coal and water-binder ratio, and it satisfies with power function relation. With high ratio increases gradually, the uniaxial compressive strength and elastic modulus is lower, and presents the inverse function curve; Specimen tensile strength decreases gradually with the increase of fly ash. By contrast, uniaxial compression failure phenomenon is consistent with the real rock common failure pattern.

Beam shaping with vortex beam generated by liquid crystal spatial light modulator

NASA Astrophysics Data System (ADS)

Gao, Yue; Liu, Ke; Sun, Zeng-yu; Guo, Lei; Gan, Yu

2015-02-01

An optical vortex is a beam of light with phase varying in a corkscrew-like manner along its direction of propagation and so has a helical wavefront. When such a vectorial vortex beam and the Gaussian beam with orthogonal polarization are focused by low NA lens, the Gaussian component causes a focal intensity distribution with a solid center and the vortex component causes a donut distribution with hollow dark center. The shape of the focus can be continuously varied by continuously adjusting the relative weight of the two components. Flat top focusing can be obtained under appropriate conditions. It is demonstrated through experiments with a liquid crystal spatial light modulator in such a beam, that flattop focus can be obtained by vectorial vortex beams with topological charge of +1 to achieve beam shaping vortex.

Crystal structure of quinolinium 2-carboxy-6-nitro-benzoate monohydrate.

PubMed

Mohana, J; Divya Bharathi, M; Ahila, G; Chakkaravarthi, G; Anbalagan, G

2015-05-01

In the anion of the title hydrated mol-ecular salt, C9H8N(+)·C8H4NO6 (-)·H2O, the protonated carboxyl and nitro groups makes dihedral angles of 27.56 (5) and 6.86 (8)°, respectively, with the attached benzene ring, whereas the deprotonated carb-oxy group is almost orthogonal to it with a dihedral angle of 80.21 (1)°. In the crystal, the components are linked by O-H⋯O and N-H⋯O hydrogen bonds, generating [001] chains. The packing is consolidated by weak C-H⋯N and C-H⋯O inter-actions as well as aromatic π-π stacking [centroid-to-centroid distances: 3.7023 (8) & 3.6590 (9)Å] inter-actions, resulting in a three-dimensional network.

Quantitative performance of a polarization diffraction grating polarimeter encoded onto two liquid-crystal-on-silicon displays

NASA Astrophysics Data System (ADS)

Cofré, Aarón; Vargas, Asticio; Torres-Ruiz, Fabián A.; Campos, Juan; Lizana, Angel; del Mar Sánchez-López, María; Moreno, Ignacio

2017-11-01

We present a quantitative analysis of the performance of a complete snapshot polarimeter based on a polarization diffraction grating (PDGr). The PDGr is generated in a common path polarization interferometer with a Z optical architecture that uses two liquid-crystal on silicon (LCoS) displays to imprint two different phase-only diffraction gratings onto two orthogonal linear states of polarization. As a result, we obtain a programmable PDGr capable to act as a simultaneous polarization state generator (PSG), yielding diffraction orders with different states of polarization. The same system is also shown to operate as a polarization state analyzer (PSA), therefore useful for the realization of a snapshot polarimeter. We analyze its performance using quantitative metrics such as the conditional number, and verify its reliability for the detection of states of polarization.

The microscopic protein structure of the lens with a theory for cataract formation as determined by Raman spectroscopy of intact bovine lenses.

PubMed

Schachar, R A; Solin, S A

1975-05-01

Intact bovine lenses have been studied using the polarized Raman spectroscopic technique. A brief theoretical and experimental review of Raman spectroscopy is presented. From the dependence of the Raman depolarization ratio on the propagation direction of the incident radiation we have determined that the uniaxial qualities of the lens result from microscopic anisotropy and have established the quantitative positional correlation of specific chemical bonds with respect to the lens optic axis. In particular, the hydrogen bonded linear CONH groups of the antiparallel beta-pleated sheet are preferentially oriented in directions orthogonal to the lens optic axis. The Raman spectra of intact lenses do not exhibit bands at positions characteristic of either the alpha-helix or the random coil protein structure. The antiparallel beta-pleated sheet protein microstructure and the lens fiber cross-sectional macrostructure exhibit a remarkable similarity. This similarity may be causal and is consistent with the protein concentration of the lens, the birefringent properties observed by both Lenhard and Brewster, the CONH bond angle distribution with respect to the optic axis, and the lens anatomy. It is suggested that cortical cataracts are caused by fluctuations in protein orientational order.

Strain distribution and failure mode of polymer separators for Li-ion batteries under biaxial loading

NASA Astrophysics Data System (ADS)

Kalnaus, Sergiy; Kumar, Abhishek; Wang, Yanli; Li, Jianlin; Simunovic, Srdjan; Turner, John A.; Gorney, Phillip

2018-02-01

Deformation of polymer separators for Li-ion batteries has been studied under biaxial tension by using a dome test setup. This deformation mode provides characterization of separator strength under more complex loading conditions, closer representing deformation of an electric vehicle battery during crash event, compared to uniaxial tension or compression. Two polymer separators, Celgard 2325 and Celgard 2075 were investigated by deformation with spheres of three different diameters. Strains in separators were measured in situ by using Digital Image Correlation (DIC) technique. The results show consistent rupture of separators along the machine direction coinciding with areas of high strain accumulation. The critical first principal strain for failure was independent of the sphere diameter and was determined to be approximately 34% and 43% for Celgard 2325 and Celgard 2075 respectively. These values can be taken as a criterion for internal short circuit in a battery following an out-of-plane impact. A Finite Element (FE) model was built with the anisotropic description of separator behavior, derived from tensile tests in orthogonal directions. The results of simulations predicted the response of separator rather well when compared to experimental results for various sizes of rigid sphere.

Strain distribution and failure mode of polymer separators for Li-ion batteries under biaxial loading

DOE PAGES

Kalnaus, Sergiy; Kumar, Abhishek; Wang, Yanli; ...

2017-12-16

Deformation of polymer separators for Li-ion batteries has been studied under biaxial tension by using a dome test setup. This deformation mode provides characterization of separator strength under more complex loading conditions, closer representing deformation of an electric vehicle battery during crash event, compared to uniaxial tension or compression. Two polymer separators, Celgard 2325 and Celgard 2075 were investigated by deformation with spheres of three different diameters. Strains in separators were measured in situ by using Digital Image Correlation (DIC) technique. The results show consistent rupture of separators along the machine direction coinciding with areas of high strain accumulation. Themore » critical first principal strain for failure was independent of the sphere diameter and was determined to be approximately 34% and 43% for Celgard 2325 and Celgard 2075 respectively. These values can be taken as a criterion for internal short circuit in a battery following an out-of-plane impact. A Finite Element (FE) model was built with the anisotropic description of separator behavior, derived from tensile tests in orthogonal directions. In conclusion, the results of simulations predicted the response of separator rather well when compared to experimental results for various sizes of rigid sphere.« less

Quantum dot-like emitters formed due to alloy fluctuations in GaNAs-based nanowires.

NASA Astrophysics Data System (ADS)

Buyanova, Irina; Jansson, M.; Filippov, S.; Stehr, J.; Palisaitis, J.; Persson, P.; Ishikawa, F.; Chen, Weimin

Group III-V semiconductor nanowires with embedded quantum dots (QDs) are currently attracting increasing attention as a highly attractive platform for a variety of advanced applications ranging from third generation photovoltaics to quantum information technologies. In this work, we show that local fluctuations in N composition inside coaxial GaAs/GaNAs nanowires induces three-dimensional confining potentials equivalent to that for QDs thus forming optically active and highly localized states inside the GaNAs shell. Principal quantization axis of these states is concluded to mainly coincide with the nanowire axis, based on the strong polarization of the detected emission orthogonal to the nanowire axis revealed from polarization-resolved micro-photoluminescence studies. This is partly attributed to a predominantly uniaxial tensile strain field in the GaNAs shell caused by lattice mismatch with the GaAs core. GaNAs alloys can, therefore, be used as an active material in hybrid QD-NW structures utilized for fabrication of nanoscale polarized-light sources that are efficient within the near-infrared spectral range. Financial support by the Swedish Energy Agency (Grant # P40119-1) and the Swedish Research Council (Grant # 2015-05532) is greatly appreciated.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalnaus, Sergiy; Kumar, Abhishek; Wang, Yanli

Deformation of polymer separators for Li-ion batteries has been studied under biaxial tension by using a dome test setup. This deformation mode provides characterization of separator strength under more complex loading conditions, closer representing deformation of an electric vehicle battery during crash event, compared to uniaxial tension or compression. Two polymer separators, Celgard 2325 and Celgard 2075 were investigated by deformation with spheres of three different diameters. Strains in separators were measured in situ by using Digital Image Correlation (DIC) technique. The results show consistent rupture of separators along the machine direction coinciding with areas of high strain accumulation. Themore » critical first principal strain for failure was independent of the sphere diameter and was determined to be approximately 34% and 43% for Celgard 2325 and Celgard 2075 respectively. These values can be taken as a criterion for internal short circuit in a battery following an out-of-plane impact. A Finite Element (FE) model was built with the anisotropic description of separator behavior, derived from tensile tests in orthogonal directions. In conclusion, the results of simulations predicted the response of separator rather well when compared to experimental results for various sizes of rigid sphere.« less

Pairing states of superfluid 3He in uniaxially anisotropic aerogel

NASA Astrophysics Data System (ADS)

Aoyama, Kazushi; Ikeda, Ryusuke

2006-02-01

Stable pairing states of superfluid 3He in aerogel are examined in the case with a global uniaxial anisotropy which may be created by applying a uniaxial stress to the aerogel. Due to such a global anisotropy, the stability region of an Anderson-Brinkman-Morel (ABM) pairing state becomes wider. In a uniaxially stretched aerogel, the pure polar pairing state with a horizontal line node is predicted to occur, as a three-dimensional superfluid phase, over a measurable width just below the superfluid transition at Tc (P) . A possible relevance of the present results to the case with no global anisotropy is also discussed.

A theoretical approach to quantify the effect of random cracks on rock deformation in uniaxial compression

NASA Astrophysics Data System (ADS)

Zhou, Shuwei; Xia, Caichu; Zhou, Yu

2018-06-01

Cracks have a significant effect on the uniaxial compression of rocks. Thus, a theoretically analytical approach was proposed to assess the effects of randomly distributed cracks on the effective Young’s modulus during the uniaxial compression of rocks. Each stage of the rock failure during uniaxial compression was analyzed and classified. The analytical approach for the effective Young’s modulus of a rock with only a single crack was derived while considering the three crack states under stress, namely, opening, closure-sliding, and closure-nonsliding. The rock was then assumed to have many cracks with randomly distributed direction, and the effect of crack shape and number during each stage of the uniaxial compression on the effective Young’s modulus was considered. Thus, the approach for the effective Young’s modulus was used to obtain the whole stress-strain process of uniaxial compression. Afterward, the proposed approach was employed to analyze the effects of related parameters on the whole stress-stain curve. The proposed approach was eventually compared with some existing rock tests to validate its applicability and feasibility. The proposed approach has clear physical meaning and shows favorable agreement with the rock test results.

Uniaxial and Multiaxial Fatigue Life Prediction of the Trabecular Bone Based on Physiological Loading: A Comparative Study.

PubMed

Fatihhi, S J; Harun, M N; Abdul Kadir, Mohammed Rafiq; Abdullah, Jaafar; Kamarul, T; Öchsner, Andreas; Syahrom, Ardiyansyah

2015-10-01

Fatigue assessment of the trabecular bone has been developed to give a better understanding of bone properties. While most fatigue studies are relying on uniaxial compressive load as the method of assessment, in various cases details are missing, or the uniaxial results are not very realistic. In this paper, the effect of three different load histories from physiological loading applied on the trabecular bone were studied in order to predict the first failure surface and the fatigue lifetime. The fatigue behaviour of the trabecular bone under uniaxial load was compared to that of multiaxial load using a finite element simulation. The plastic strain was found localized at the trabecular structure under multiaxial load. On average, applying multiaxial loads reduced more than five times the fatigue life of the trabecular bone. The results provide evidence that multiaxial loading is dominated in the low cycle fatigue in contrast to the uniaxial one. Both bone volume fraction and structural model index were best predictors of failure (p < 0.05) in fatigue for both types of loading, whilst uniaxial loading has indicated better values in most cases.

Electronic and Thermal Properties of Puckered Orthorhombic Materials

NASA Astrophysics Data System (ADS)

Fei, Ruixiang

Puckered orthorhombic crystals, such as black phosphorus and group IV monochalcogenides, are attracting tremendous attention because of their new exotic properties, which are of great interests for fundamental science and novel applications. Unlike those well studied layered hexagonal materials such as graphene and transition metal dichalcogenides, the puckered orthorhombic crystals possess highly asymmetrical in-plane crystal structures. Understanding the unique properties emerginge from their low symmetries is an intriguing and useful process, which gives insight into experimental observation and sheds light on manipulating their properties. In this thesis, we study and predict various properties of orthorhombic materials by using appropriate theoretical techniques such as first-principles calculations, Monte-Carlo simulations, and k · p models. In the first part of the thesis, we deal with the anisotropic electric and thermal properties of a typical puckered orthorhombic crystal, black phosphorus. We first study the electric properties in monolayer and few-layer black phosphorus, where the unique, anisotropic electrical conductance is founded. Furthermore, we find that the anisotropy of the electrical conductance can be rotated by 90° through applying appropriate uniaxial or biaxial strain. Beyond electrical conductance, we, for the first time, predict that the thermal conductance of black phosphorus is also anisotropic and, particularly, the preferred conducting direction is perpendicular to the preferred electrical conducting direction. Within the reasonable estimation regime, the thermoelectric figure of merit (ZT) ultimately reaches 1 at room temperature using only moderate doping. The second part of this thesis focuses on the electronic polarization of non-centrosymmetric puckered materials-group IV monochalcogenide. We propose that monolayer group IV monochalcogenides are a new class of two-dimensional (2D) ferroelectric materials with spontaneous in-plane polarization. We have developed an effective mean-field method for Monte Carlo simulations to calculate the phase transition of ferroelectricity. Moreover, we point out that the piezoelectric effect of these monolayer materials is dramatically enhanced, and the piezoelectric coefficient is about two orders of magnitude larger than that of other 2D and bulk materials. In the last part of thesis, we study the topological phase transition in compressed black phosphorus. In this study, we use the k · p model to figure out the quantum phase transition of black phosphorus from a normal insulator to a Dirac nodal line semimetal. Via the low-energy effective Hamiltonian, a novel "pseudo-spin-orbit" coupling mechanism is proposed to explain such a phase transition in this material with the mirror symmetry. By first principles simulations, we predict that applying a moderate uniaxial or hydrostatic pressure (>0.6 GPa) on bulk or multilayer black phosphorus can diminish its bandgap and produce two-dimensional Dirac cones, which has been confirmed by recent experiments.

Advection of nematic liquid crystals by chaotic flow

NASA Astrophysics Data System (ADS)

O'Náraigh, Lennon

2017-04-01

Consideration is given to the effects of inhomogeneous shear flow (both regular and chaotic) on nematic liquid crystals in a planar geometry. The Landau-de Gennes equation coupled to an externally prescribed flow field is the basis for the study: this is solved numerically in a periodic spatial domain. The focus is on a limiting case where the advection is passive, such that variations in the liquid-crystal properties do not feed back into the equation for the fluid velocity. The main tool for analyzing the results (both with and without flow) is the identification of the fixed points of the dynamical equations without flow, which are relevant (to varying degrees) when flow is introduced. The fixed points are classified as stable/unstable and further as either uniaxial or biaxial. Various models of passive shear flow are investigated. When tumbling is present, the flow is shown to have a strong effect on the liquid-crystal morphology; however, the main focus herein is on the case without tumbling. Accordingly, the main result of the work is that only the biaxial fixed point survives as a solution of the Q-tensor dynamics under the imposition of a general flow field. This is because the Q-tensor experiences not only transport due to advection but also co-rotation relative to the local vorticity field. A second result is that all families of fixed points survive for certain specific velocity fields, which we classify. We single out for close study those velocity fields for which the influence of co-rotation effectively vanishes along the Lagrangian trajectories of the imposed velocity field. In this scenario, the system exhibits coarsening arrest, whereby the liquid-crystal domains are "frozen in" to the flow structures, and the growth in their size is thus limited.

High Strain Rate and Shock-Induced Deformation in Metals

NASA Astrophysics Data System (ADS)

Ravelo, Ramon

2012-02-01

Large-scale non-equilibrium molecular Dynamics (MD) simulations are now commonly used to study material deformation at high strain rates (10^9-10^12 s-1). They can provide detailed information-- such as defect morphology, dislocation densities, and temperature and stress profiles, unavailable or hard to measure experimentally. Computational studies of shock-induced plasticity and melting in fcc and bcc single, mono-crystal metals, exhibit generic characteristics: high elastic limits, large directional anisotropies in the yield stress and pre-melting much below the equilibrium melt temperature for shock wave propagation along specific crystallographic directions. These generic features in the response of single crystals subjected to high strain rates of deformation can be explained from the changes in the energy landscape of the uniaxially compressed crystal lattice. For time scales relevant to dynamic shock loading, the directional-dependence of the yield strength in single crystals is shown to be due to the onset of instabilities in elastic-wave propagation velocities. The elastic-plastic transition threshold can accurately be predicted by a wave-propagation stability analysis. These strain-induced instabilities create incipient defect structures, which can be quite different from the ones, which characterize the long-time, asymptotic state of the compressed solid. With increase compression and strain rate, plastic deformation via extended defects gives way to amorphization associated with the loss in shear rigidity along specific deformation paths. The hot amorphous or (super-cooled liquid) metal re-crystallizes at rates, which depend on the temperature difference between the amorphous solid and the equilibrium melt line. This plastic-amorphous transition threshold can be computed from shear-waves stability analyses. Examples from selected fcc and bcc metals will be presented employing semi-empirical potentials of the embedded atom method (EAM) type as well as results from density functional theory calculations.

A Model for Predicting Thermomechanical Response of Large Space Structures.

DTIC Science & Technology

1985-06-01

Field in a Thermomechanically Heated Viscoplastic ....... Space Truss Structure 6.5 Analysis of a Thermoviscoplastic Uniaxial " Bar Under Prescribed...Stress Part I - Theoretical Development . -- 6.6 Analysis of a Thermoviscoplastic Uniaxial codes Bar Under Prescribed Stress Part II - or Boundary Layer...and Asymptotic Analysis 6.7 Analysis of a Thermoviscoplastic Uniaxial Bar Under Prescribed Stress Part III - Numerical Results for a Bar with Radiative

On the identifiability of the Hill-1948 model with one uniaxial tensile test

NASA Astrophysics Data System (ADS)

Bertin, Morgan; Hild, François; Roux, Stéphane

2017-06-01

A uniaxial experiment is performed on an ultra-thin specimen made of 17-7 precipitation hardened stainless steel. An anti-wrinkling setup allows for the characterization of the mechanical behavior with Integrated Digital Image Correlation (IDIC). The result shows that a single uniaxial experiment investigated via IDIC possesses enough data (and even more) to characterize a complete anisotropic elastoplastic model.

Multiple film plane diagnostic for shocked lattice measurements (invited)

NASA Astrophysics Data System (ADS)

Kalantar, Daniel H.; Bringa, E.; Caturla, M.; Colvin, J.; Lorenz, K. T.; Kumar, M.; Stölken, J.; Allen, A. M.; Rosolankova, K.; Wark, J. S.; Meyers, M. A.; Schneider, M.; Boehly, T. R.

2003-03-01

Laser-based shock experiments have been conducted in thin Si and Cu crystals at pressures above the Hugoniot elastic limit. In these experiments, static film and x-ray streak cameras recorded x rays diffracted from lattice planes both parallel and perpendicular to the shock direction. These data showed uniaxial compression of Si(100) along the shock direction and three-dimensional compression of Cu(100). In the case of the Si diffraction, there was a multiple wave structure observed, which may be due to a one-dimensional phase transition or a time variation in the shock pressure. A new film-based detector has been developed for these in situ dynamic diffraction experiments. This large-angle detector consists of three film cassettes that are positioned to record x rays diffracted from a shocked crystal anywhere within a full π steradian. It records x rays that are diffracted from multiple lattice planes both parallel and at oblique angles with respect to the shock direction. It is a time-integrating measurement, but time-resolved data may be recorded using a short duration laser pulse to create the diffraction source x rays. This new instrument has been fielded at the OMEGA and Janus lasers to study single-crystal materials shock compressed by direct laser irradiation. In these experiments, a multiple wave structure was observed on many different lattice planes in Si. These data provide information on the structure under compression.

Analyzing shear band formation with high resolution X-ray diffraction

DOE PAGES

Pagan, Darren C.; Obstalecki, Mark; Park, Jun-Sang; ...

2018-01-10

Localization of crystallographic slip into shear bands during uniaxial compression of a copper single crystal is studied using very far-field high-energy diffraction microscopy (vff-HEDM). Diffracted intensity was collected in-situ as the crystal deformed using a unique mobile detector stage that provided access to multiple diffraction peaks with high-angular resolution. From the diffraction data, single crystal orientation pole figures (SCPFs) were generated and are used to track the evolution of the distribution of lattice orientation that develops as slip localizes. To aid the identification of ‘signatures’ of shear band formation and analyze the SCPF data, a model of slip-driven lattice reorientationmore » within shear bands is introduced. Confidence is built in conclusions drawn from the SCPF data about the character of internal slip localization through comparisons with strain fields on the sample surface measured simultaneously using digital image correlation. From the diffraction data, we find that the active slip direction and slip plane are not directly aligned with the orientation of the shear bands that formed. In fact, by extracting the underlying slip system activity from the SCPF data, we show that intersecting shear bands measured on the surface of the sample arise from slip primarily on the same underlying single slip system. These new vff-HEDM results raise significant questions on the use of surface measurements for slip system activity estimation.« less

Statistical study of ductility-dip cracking induced plastic deformation in polycrystalline laser 3D printed Ni-based superalloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qian, Dan; Xue, Jiawei; Zhang, Anfeng

Ductility-dip cracking in Ni-based superalloy, resulting from heat treatment, is known to cause disastrous failure, but its mechanism is still not completely clear. A statistical study of the cracking behavior as a function of crystal orientation in a laser 3D-printed DL125L Ni-based superalloy polycrystal is investigated here using the synchrotron X-ray microdiffraction. The dislocation slip system in each of the forty crystal grains adjacent to the 300 μm long crack has been analyzed through Laue diffraction peak shapes. In all these grains, edge-type geometrically necessary dislocations (GNDs) dominate, and their dislocation line directions are almost parallel to the crack plane.more » Based on Schmid's law, the equivalent uniaxial tensile force direction is revealed normal to the trace of the crack. A qualitative mechanism is thus proposed. Thermal tensile stress perpendicular to the laser scanning direction is elevated due to a significant temperature gradient, and thus locations in the materials where the thermal stress exceeds the yield stress undergo plastic deformation mediated by GND activations. As the dislocations slip inside the crystal grains and pile up at the grain boundaries, local strain/stress keeps increasing, until the materials in these regions fail to sustain further deformation, leading to voids formation and cracks propagation.« less

Statistical study of ductility-dip cracking induced plastic deformation in polycrystalline laser 3D printed Ni-based superalloy

DOE PAGES

Qian, Dan; Xue, Jiawei; Zhang, Anfeng; ...

2017-06-06

Ductility-dip cracking in Ni-based superalloy, resulting from heat treatment, is known to cause disastrous failure, but its mechanism is still not completely clear. A statistical study of the cracking behavior as a function of crystal orientation in a laser 3D-printed DL125L Ni-based superalloy polycrystal is investigated here using the synchrotron X-ray microdiffraction. The dislocation slip system in each of the forty crystal grains adjacent to the 300 μm long crack has been analyzed through Laue diffraction peak shapes. In all these grains, edge-type geometrically necessary dislocations (GNDs) dominate, and their dislocation line directions are almost parallel to the crack plane.more » Based on Schmid's law, the equivalent uniaxial tensile force direction is revealed normal to the trace of the crack. A qualitative mechanism is thus proposed. Thermal tensile stress perpendicular to the laser scanning direction is elevated due to a significant temperature gradient, and thus locations in the materials where the thermal stress exceeds the yield stress undergo plastic deformation mediated by GND activations. As the dislocations slip inside the crystal grains and pile up at the grain boundaries, local strain/stress keeps increasing, until the materials in these regions fail to sustain further deformation, leading to voids formation and cracks propagation.« less

Analysis of electromagnetic scattering by uniaxial anisotropic bispheres.

PubMed

Li, Zheng-Jun; Wu, Zhen-Sen; Li, Hai-Ying

2011-02-01

Based on the generalized multiparticle Mie theory and the Fourier transformation approach, electromagnetic (EM) scattering of two interacting homogeneous uniaxial anisotropic spheres with parallel primary optical axes is investigated. By introducing the Fourier transformation, the EM fields in the uniaxial anisotropic spheres are expanded in terms of the spherical vector wave functions. The interactive scattering coefficients and the expansion coefficients of the internal fields are derived through the continuous boundary conditions on which the interaction of the bispheres is considered. Some selected calculations on the effects of the size parameter, the uniaxial anisotropic absorbing dielectric, and the sphere separation distance are described. The backward radar cross section of two uniaxial anisotropic spheres with a complex permittivity tensor changing with the sphere separation distance is numerically studied. The authors are hopeful that the work in this paper will help provide an effective calibration for further research on the scattering characteristic of an aggregate of anisotropic spheres or other shaped anisotropic particles.

Global architecture of the F-actin cytoskeleton regulates cell shape-dependent endothelial mechanotransduction.

PubMed

Shao, Yue; Mann, Jennifer M; Chen, Weiqiang; Fu, Jianping

2014-03-01

Uniaxial stretch is an important biophysical regulator of cell morphology (or shape) and functions of vascular endothelial cells (ECs). However, it is unclear whether and how cell shape can independently regulate EC mechanotransductive properties under uniaxial stretch. Herein, utilizing a novel uniaxial cell-stretching device integrated with micropost force sensors, we reported the first experimental evidence showing cell shape-dependent EC mechanotransduction via cytoskeleton (CSK) contractile forces in response to uniaxial stretch. Combining experiments and theoretical modeling from first principles, we showed that it was the global architecture of the F-actin CSK that instructed the cell shape-dependent EC mechanotransductive process. Furthermore, a cell shape-dependent nature was relayed in EC mechanotransduction via dynamic focal adhesion (FA) assembly. Our results suggested a novel mechanotransductive process in ECs wherein the global architecture of the F-actin CSK, governed by cell shape, controls mechanotransduction via CSK contractile forces and force-dependent FA assembly under uniaxial stretch.

Synchronous dual-wavelength pulse generation in coaxial pumping scheme and its application in terahertz difference frequency generation

NASA Astrophysics Data System (ADS)

Liu, Yang; Zhong, Kai; Mei, Jialin; Jin, Shuo; Ge, Meng; Xu, Degang; Yao, Jianquan

2018-02-01

A compact and flexible dual-wavelength laser with combined two laser crystals (a-cut and c-cut Nd:YLF) as the gain media under coaxially laser-diode (LD) end-pumping configuration was demonstrated and μW-level THz wave was generated based on difference frequency generation (DFG) in a GaSe crystal. The dynamics of coaxial pumping dualwavelength laser was theoretically investigated, showing that the power ratio and pulse interval for both wavelengths could be tuned by balancing the gains at both wavelengths via tuning pump focal position. Synchronized orthogonal 1047/1053 nm laser pulses were obtained and optimal power ratio was realized with the total output power of 2.92W at 5 kHz pumped by 10-W LD power. With an 8-mm-long GaSe crystal, 0.93 μW THz wave at 1.64 THz (182 μm) was generated. Such coaxially LD end-pumped lasers can be extended to various combinations of neodymium doped laser media to produce different THz wavelengths for costless and portable applications.

Squirming motion of baby skyrmions in nematic fluids.

PubMed

Ackerman, Paul J; Boyle, Timothy; Smalyukh, Ivan I

2017-09-22

Skyrmions are topologically protected continuous field configurations that cannot be smoothly transformed to a uniform state. They behave like particles and give origins to the field of skyrmionics that promises racetrack memory and other technological applications. Unraveling the non-equilibrium behavior of such topological solitons is a challenge. We realize skyrmions in a chiral liquid crystal and, using numerical modeling and polarized video microscopy, demonstrate electrically driven squirming motion. We reveal the intricate details of non-equilibrium topology-preserving textural changes driving this behavior. Direction of the skyrmion's motion is robustly controlled in a plane orthogonal to the applied field and can be reversed by varying frequency. Our findings may spur a paradigm of soliton dynamics in soft matter, with a rich interplay between topology, chirality, and orientational viscoelasticity.A skyrmion is a topological object originally introduced to model elementary particles and a baby skyrmion is its two-dimensional counterpart which can be realized as a defect in liquid crystals. Here the authors show that an electric field can drive uniform motion of baby skyrmions in liquid crystals.

A investigation on unixial and quasi-biaxial tensile mechanical properties of aging HTPB propellant under dynamic loading at low temperature

NASA Astrophysics Data System (ADS)

Duan, Leiguang; Wang, Guang; Zhang, Guoxing; Sun, Xinya; Shang, Hehao

2018-06-01

In order to study the uniaxial and quasi-biaxial mechanical properties of aging solid propellants under low temperature and high strain rate, stress-strain curves and tensile fracture surfaces of HTPB propellant were obtained in a wide range of temperature (-30,25 °C) and strain rates (0.4,4.0 and 14.29 s-1), respectively, by means of uniaxial and biaxial tensile tests and electron microscopy scanning on the fracture cross section. The results indicate that the quasi-biaxial tensile mechanical properties of aging HTPB propellant is same as the uniaxial tensile mechanical properties influenced distinctly by temperature and strain rate. With decreasing temperature and increasing strain rate, the mechanical properties gradually strengthen. The damage for HTPB propellant changes from "dehumidification" to grain fracture. The initial elastic modulus E and maximum tensile stress σ of the uniaxial and biaxial tensile increase gradually with decreasing temperature and increasing strain rate, and well present linear-log function relation with strain rate. The ratio of quasi-biaxial and uniaxial stretching under different loading conditions was obtained so that the researchers could predict the quasi-biaxial tensile mechanical properties of the propellant based on the uniaxial test data.

Polarization-dependent optics using gauge-field metamaterials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Fu; Xiao, Shiyi; Li, Jensen, E-mail: j.li@bham.ac.uk

2015-12-14

We show that effective gauge field for photons with polarization-split dispersion surfaces, being realized using uniaxial metamaterials, can be used for polarization control with unique opportunities. The metamaterials with the proposed gauge field correspond to a special choice of eigenpolarizations on the Poincaré sphere as pseudo-spins, in contrary to those from either conventional birefringent crystals or optical active media. It gives rise to all-angle polarization control and a generic route to manipulate photon trajectories or polarizations in the pseudo-spin domain. As demonstrations, we show beam splitting (birefringent polarizer), all-angle polarization control, unidirectional polarization filter, and interferometer as various polarization controlmore » devices in the pseudo-spin domain. We expect that more polarization-dependent devices can be designed under the same framework.« less

X-ray diffraction from shock-loaded polycrystals.

PubMed

Swift, Damian C

2008-01-01

X-ray diffraction was demonstrated from shock-compressed polycrystalline metals on nanosecond time scales. Laser ablation was used to induce shock waves in polycrystalline foils of Be, 25-125 microm thick. A second laser pulse was used to generate a plasma x-ray source by irradiation of a Ti foil. The x-ray source was collimated to produce a beam of controllable diameter, which was directed at the Be sample. X-rays were diffracted from the sample, and detected using films and x-ray streak cameras. The diffraction angle was observed to change with shock pressure. The diffraction angles were consistent with the uniaxial (elastic) and isotropic (plastic) compressions expected for the loading conditions used. Polycrystalline diffraction will be used to measure the response of the crystal lattice to high shock pressures and through phase changes.

Optical band gap in a cholesteric elastomer doped by metallic nanospheres

NASA Astrophysics Data System (ADS)

Hernández, Julio C.; Reyes, J. Adrián

2017-12-01

We analyzed the optical band gaps for axially propagating electromagnetic waves throughout a metallic doped cholesteric elastomer. The composed medium is made of metallic nanospheres (silver) randomly dispersed in a cholesteric elastomer liquid crystal whose dielectric properties can be represented by a resonant effective uniaxial tensor. We found that the band gap properties of the periodic system greatly depend on the volume fraction of nanoparticles in the cholesteric elastomer. In particular, we observed a displacement of the reflection band for quite small fraction volumes whereas for larger values of this fraction there appears a secondary band in the higher frequency region. We also have calculated the transmittance and reflectance spectra for our system. These calculations verify the mentioned band structure and provide additional information about the polarization features of the radiation.

Electronic transport on the Shastry-Sutherland lattice in Ising-type rare-earth tetraborides

NASA Astrophysics Data System (ADS)

Ye, Linda; Suzuki, Takehito; Checkelsky, Joseph G.

2017-05-01

In the presence of a magnetic field frustrated spin systems may exhibit plateaus at fractional values of saturation magnetization. Such plateau states are stabilized by classical and quantum mechanisms including order by disorder, triplon crystallization, and various competing order effects. In the case of electrically conducting systems, free electrons represent an incisive probe for the plateau states. Here we study the electrical transport of Ising-type rare-earth tetraborides R B4 (R =Er , Tm), a metallic Shastry-Sutherland lattice showing magnetization plateaus. We find that the longitudinal and transverse resistivities reflect scattering with both the static and the dynamic plateau structure. We model these results consistently with the expected strong uniaxial anisotropy on a quantitative level, providing a framework for the study of plateau states in metallic frustrated systems.

Field dependent magnetic anisotropy of Fe1-xZnx thin films

NASA Astrophysics Data System (ADS)

Resnick, Damon A.; McClure, A.; Kuster, C. M.; Rugheimer, P.; Idzerda, Y. U.

2013-05-01

Using longitudinal magneto-optical Kerr effect in combination with a variable strength rotating magnetic field, called the Rotational Magneto-Optic Kerr Effect (ROTMOKE) method, we show that the magnetic anisotropy for thin Fe82Zn18 single crystal films, grown on MgO(001) substrates, depends linearly on the strength of the applied magnetic field at low fields but is constant (saturates) at fields greater than 350 Oe. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial and cubic anisotropy with the addition of a cubic anisotropy that depends linearly on the applied magnetic field. The field dependent term is evidence of a large effect on the effective magnetic anisotropy in Fe1-xZnx thin films by the magnetostriction.

Optical behaviors of flexible photonic films via the developed multiple UV-exposed fabrications.

PubMed

Chien, Chih-Chieh; Liu, Jui-Hsiang

2014-07-01

Recently, extensive investigations are carried out on design of highly controlled architecture and morphology by polymerizing the monomers doped in well-defined liquid crystalline materials, followed by removal of the template liquid crystal molecules. In this communication, a photonic structure used as a new photonic bandgap (PBG) material is developed by imprinting helical structures on polymer matrices through multiple photocrosslinking processes in an induced chiral nematic mesophase using flexible polyethylene terephthalate (PET) films as substrates. The tuning properties of the reflection band of the imprinted cell are achieved using an uniaxial thermo-stretching equipment. Furthermore, refilling of isotropic materials into the imprinted cells tune the reflection light wavelength leads to the change of color. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High Strength Phosphogypsum and Its Use as a Building Material

NASA Astrophysics Data System (ADS)

Kanno, Wellington Massayuki; Rossetto, Hebert Luis; de Souza, Milton Ferreira; Máduar, Marcelo Francis; de Campos, Marcia Pires; Mazzilli, Barbara Paci

2008-08-01

A new process (patent applied) that works equally well with both plaster of mineral gypsum and phosphogypsum for the preparation of gypsum components, UCOS, has been developed. The process consists of the following steps: humidification of plaster by fine water droplets, uni-axial compression, hydration reaction and drying. Strong hydrogen bonds develop among the crystals together with adhesion provided by confined water that accounts for nearly 70% of the adhesion forces. By reducing the plaster to water ratio to close the minimum necessary, new features are generated. An experimental house has been constructed, in which walls and ceilings have been built of gypsum and phosphogypsum. Since phosphogypsum potentially contain radioactive elements, the application of an activity concentration index to the phosphogypsum employed in the building was carried out.

Intergranular Strain Evolution During Biaxial Loading: A Multiscale FE-FFT Approach

NASA Astrophysics Data System (ADS)

Upadhyay, M. V.; Capek, J.; Van Petegem, S.; Lebensohn, R. A.; Van Swygenhoven, H.

2017-05-01

Predicting the macroscopic and microscopic mechanical response of metals and alloys subjected to complex loading conditions necessarily requires a synergistic combination of multiscale material models and characterization techniques. This article focuses on the use of a multiscale approach to study the difference between intergranular lattice strain evolution for various grain families measured during in situ neutron diffraction on dog bone and cruciform 316L samples. At the macroscale, finite element simulations capture the complex coupling between applied forces and gauge stresses in cruciform geometries. The predicted gauge stresses are used as macroscopic boundary conditions to drive a mesoscale full-field elasto-viscoplastic fast Fourier transform crystal plasticity model. The results highlight the role of grain neighborhood on the intergranular strain evolution under uniaxial and equibiaxial loading.

Effect of uniaxial stress on electroluminescence, valence band modification, optical gain, and polarization modes in tensile strained p-AlGaAs/GaAsP/n-AlGaAs laser diode structures: Numerical calculations and experimental results

NASA Astrophysics Data System (ADS)

Bogdanov, E. V.; Minina, N. Ya.; Tomm, J. W.; Kissel, H.

2012-11-01

The effects of uniaxial compression in [110] direction on energy-band structures, heavy and light hole mixing, optical matrix elements, and gain in laser diodes with "light hole up" configuration of valence band levels in GaAsP quantum wells with different widths and phosphorus contents are numerically calculated. The development of light and heavy hole mixing caused by symmetry lowering and converging behavior of light and heavy hole levels in such quantum wells under uniaxial compression is displayed. The light or heavy hole nature of each level is established for all considered values of uniaxial stress. The results of optical gain calculations for TM and TE polarization modes show that uniaxial compression leads to a significant increase of the TE mode and a minor decrease of the TM mode. Electroluminescence experiments were performed under uniaxial compression up to 5 kbar at 77 K on a model laser diode structure (p-AlxGa1-xAs/GaAs1-yPy/n-AlxGa1-xAs) with y = 0.16 and a quantum well width of 14 nm. They reveal a maximum blue shift of 27 meV of the electroluminescence spectra that is well described by the calculated change of the optical gap and the increase of the intensity being referred to a TE mode enhancement. Numerical calculations and electroluminescence data indicate that uniaxial compression may be used for a moderate wavelength and TM/TE intensity ratio tuning.

A Multiscale Computational Model Combining a Single Crystal Plasticity Constitutive Model with the Generalized Method of Cells (GMC) for Metallic Polycrystals.

PubMed

Ghorbani Moghaddam, Masoud; Achuthan, Ajit; Bednarcyk, Brett A; Arnold, Steven M; Pineda, Evan J

2016-05-04

A multiscale computational model is developed for determining the elasto-plastic behavior of polycrystal metals by employing a single crystal plasticity constitutive model that can capture the microstructural scale stress field on a finite element analysis (FEA) framework. The generalized method of cells (GMC) micromechanics model is used for homogenizing the local field quantities. At first, the stand-alone GMC is applied for studying simple material microstructures such as a repeating unit cell (RUC) containing single grain or two grains under uniaxial loading conditions. For verification, the results obtained by the stand-alone GMC are compared to those from an analogous FEA model incorporating the same single crystal plasticity constitutive model. This verification is then extended to samples containing tens to hundreds of grains. The results demonstrate that the GMC homogenization combined with the crystal plasticity constitutive framework is a promising approach for failure analysis of structures as it allows for properly predicting the von Mises stress in the entire RUC, in an average sense, as well as in the local microstructural level, i.e. , each individual grain. Two-three orders of saving in computational cost, at the expense of some accuracy in prediction, especially in the prediction of the components of local tensor field quantities and the quantities near the grain boundaries, was obtained with GMC. Finally, the capability of the developed multiscale model linking FEA and GMC to solve real-life-sized structures is demonstrated by successfully analyzing an engine disc component and determining the microstructural scale details of the field quantities.

A Multiscale Computational Model Combining a Single Crystal Plasticity Constitutive Model with the Generalized Method of Cells (GMC) for Metallic Polycrystals

PubMed Central

Ghorbani Moghaddam, Masoud; Achuthan, Ajit; Bednarcyk, Brett A.; Arnold, Steven M.; Pineda, Evan J.

2016-01-01

A multiscale computational model is developed for determining the elasto-plastic behavior of polycrystal metals by employing a single crystal plasticity constitutive model that can capture the microstructural scale stress field on a finite element analysis (FEA) framework. The generalized method of cells (GMC) micromechanics model is used for homogenizing the local field quantities. At first, the stand-alone GMC is applied for studying simple material microstructures such as a repeating unit cell (RUC) containing single grain or two grains under uniaxial loading conditions. For verification, the results obtained by the stand-alone GMC are compared to those from an analogous FEA model incorporating the same single crystal plasticity constitutive model. This verification is then extended to samples containing tens to hundreds of grains. The results demonstrate that the GMC homogenization combined with the crystal plasticity constitutive framework is a promising approach for failure analysis of structures as it allows for properly predicting the von Mises stress in the entire RUC, in an average sense, as well as in the local microstructural level, i.e., each individual grain. Two–three orders of saving in computational cost, at the expense of some accuracy in prediction, especially in the prediction of the components of local tensor field quantities and the quantities near the grain boundaries, was obtained with GMC. Finally, the capability of the developed multiscale model linking FEA and GMC to solve real-life-sized structures is demonstrated by successfully analyzing an engine disc component and determining the microstructural scale details of the field quantities. PMID:28773458

Complexly zoned Ti-rich melanite-schorlomite garnets from Ambadungar carbonatite-alkalic complex, Deccan Igneous Province, Gujarat State, Western India

NASA Astrophysics Data System (ADS)

Gwalani, L. G.; Rock, N. M. S.; Ramasamy, R.; Griffin, B. J.; Mulai, B. P.

2000-04-01

Ti-rich garnet phenocrysts from a tephrite ('nephelinite') plug in the Ambadungar complex situated in the Chhota Udaipur alkalic subprovince show concentric zoning. Based on paired orthogonal traverses across three selected crystals (total 81 step-scan point analyses), andradite content ranges from 55 to 86 mol% (the remainder being almost entirely schorlomite), corresponding to the following wt% oxide variations: TiO 2 5.5-15.8, CaO 29.6-32.5, MgO 0.3-1.6, Fe 2O 3 20-26, Al 2O 3 0.7-3.5%; MnO, V 2O 3, Na 2O and ZrO 2 each rarely exceeds 0.5%. Zoning patterns in individual grains from this one rock differ considerably in several ways: (1) there may be 2-5 alternating pale and dark zones, the pale generally being more andradite-rich enriched in Ti, Mg and usually Zr but impoverished in Al; (2) the two orthogonal traverse may or may not be mirror images; (3) monotonic trends (decreasing Ca, Al, increasing Mg, Zr from core to rim) may or may not be present; (4) oscillatory zoning varies in amplitude; and (5) apparent substitutions differ, although all crystals clearly show the Si-Ti substitution inferred for Ti-rich garnets elsewhere. An idealized case is developed from an observed complexly zoned phenocryst population to piece together a history of the alkaline host magma that experienced several events such as polybaric differentiation, magma-mixing, and kinetic effects.

Dynamic evolution of light-induced orientation of dye-doped liquid crystals in liquid phase studied by time-resolved optically heterodyned optical Kerr effect technique.

PubMed

Yang, Pei; Liu, Liying; Xu, Lei

2008-02-28

Transient evolution of light-induced molecular reorientation both in 1-amino-anthraquinone (1AAQ) dye and azobenzene doped isotropic liquid crystals (LCs) were studied by time-resolved optically heterodyned optical Kerr effect method. The results give clear direct experimental proof that under short pulse (30 ps) excitation, LC molecules orientate toward the excitation light polarization direction in the 1AAQ/LC system. However, LC molecular orientation becomes orthogonal to the light polarization in azobenzene/LC system. Time-resolved excited-state absorption of 1AAQ and wavelength dependent excited-state absorption of azobenzene were also observed and their contributions to the early dynamics of the third order optical responses of the two systems were confirmed. A simplified two-level mean-field theory was derived to reveal the intensity dependence of orientation enhancement factor in azobenzene/LC system considering the photoisomerization process.

Hydrostatic Pressure Sensing with High Birefringence Photonic Crystal Fibers

PubMed Central

Fávero, Fernando C.; Quintero, Sully M. M.; Martelli, Cicero; Braga, Arthur M.B.; Silva, Vinícius V.; Carvalho, Isabel C. S.; Llerena, Roberth W. A.; Valente, Luiz C. G.

2010-01-01

The effect of hydrostatic pressure on the waveguiding properties of high birefringence photonic crystal fibers (HiBi PCF) is evaluated both numerically and experimentally. A fiber design presenting form birefringence induced by two enlarged holes in the innermost ring defining the fiber core is investigated. Numerical results show that modal sensitivity to the applied pressure depends on the diameters of the holes, and can be tailored by independently varying the sizes of the large or small holes. Numerical and experimental results are compared showing excellent agreement. A hydrostatic pressure sensor is proposed and demonstrated using an in-fiber modal interferometer where the two orthogonally polarized modes of a HiBi PCF generate fringes over the optical spectrum of a broad band source. From the analysis of experimental results, it is concluded that, in principle, an operating limit of 92 MPa in pressure could be achieved with 0.0003% of full scale resolution. PMID:22163435

Crystal structure of quinolinium 2-carboxy-6-nitro­benzoate monohydrate

PubMed Central

Mohana, J.; Divya Bharathi, M.; Ahila, G.; Chakkaravarthi, G.; Anbalagan, G.

2015-01-01

In the anion of the title hydrated mol­ecular salt, C9H8N+·C8H4NO6 −·H2O, the protonated carboxyl and nitro groups makes dihedral angles of 27.56 (5) and 6.86 (8)°, respectively, with the attached benzene ring, whereas the deprotonated carb­oxy group is almost orthogonal to it with a dihedral angle of 80.21 (1)°. In the crystal, the components are linked by O—H⋯O and N—H⋯O hydrogen bonds, generating [001] chains. The packing is consolidated by weak C—H⋯N and C—H⋯O inter­actions as well as aromatic π–π stacking [centroid-to-centroid distances: 3.7023 (8) & 3.6590 (9)Å] inter­actions, resulting in a three-dimensional network. PMID:25995899

Multibeam Interferometer Using a Photonic Crystal Fiber with Two Asymmetric Cores for Torsion, Strain and Temperature Sensing

PubMed Central

Naeem, Khurram; Kwon, Il-Bum; Chung, Youngjoo

2017-01-01

We present a fiber-optic multibeam Mach-Zehnder interferometer (m-MZI) for simultaneous multi-parameter measurement. The m-MZI is comprised of a section of photonic crystal fiber integrated with two independent cores of distinct construction and birefringence properties characterized for torsion, strain and temperature sensing. Due to the presence of small core geometry and use of a short fiber length, the sensing device demonstrates inter-modal interference in the small core alongside the dominant inter-core interference between the cores for each of the orthogonal polarizations. The output spectrum of the device is characterized by the three-beam interference model and is polarization-dependent. The two types of interferometers present in the fiber m-MZI exhibit distinct sensitivities to torsion, strain and temperature for different polarizations, and matrix coefficients allowing simultaneous measurement of the three sensing parameters are proposed in experiment. PMID:28085046

Pentacoordinate and Hexacoordinate Mn(III) Complexes of Tetradentate Schiff-Base Ligands Containing Tetracyanidoplatinate(II) Bridges and Revealing Uniaxial Magnetic Anisotropy.

PubMed

Nemec, Ivan; Herchel, Radovan; Trávníček, Zdeněk

2016-12-08

Crystal structures and magnetic properties of polymeric and trinuclear heterobimetallic Mn III ···Pt II ···Mn III coordination compounds, prepared from the Ba[Pt(CN)₄] and [Mn(L4A/B)(Cl)] ( 1a / b ) precursor complexes, are reported. The polymeric complex [{Mn(L4A)}₂{μ⁴-Pt(CN)₄}] n ( 2a ), where H₂L4A = N , N '-ethylene-bis(salicylideneiminate), comprises the {Mn(L4A)} moieties covalently connected through the [Pt(CN)₄] 2- bridges, thus forming a square-grid polymeric structure with the hexacoordinate Mn III atoms. The trinuclear complex [{Mn(L4B)}₂{μ-Pt(CN)₄}] ( 2b ), where H₂L4B = N , N '-benzene-bis(4-aminodiethylene-salicylideneiminate), consists of two [{Mn(L4B)} moieties, involving pentacoordinate Mn III atoms, bridged through the tetracyanidoplatinate (II) bridges to which they are coordinated in a trans fashion. Both complexes possess uniaxial type of magnetic anisotropy, with D (the axial parameter of zero-field splitting) = -3.7(1) in 2a and -2.2(1) cm -1 in 2b . Furthermore, the parameters of magnetic anisotropy 2a and 2b were also thoroughly studied by theoretical complete active space self-consistent field (CASSCF) methods, which revealed that the former is much more sensitive to the ligand field strength of the axial ligands.

Analytic derivative couplings and first-principles exciton/phonon coupling constants for an ab initio Frenkel-Davydov exciton model: Theory, implementation, and application to compute triplet exciton mobility parameters for crystalline tetracene.

PubMed

Morrison, Adrian F; Herbert, John M

2017-06-14

Recently, we introduced an ab initio version of the Frenkel-Davydov exciton model for computing excited-state properties of molecular crystals and aggregates. Within this model, supersystem excited states are approximated as linear combinations of excitations localized on molecular sites, and the electronic Hamiltonian is constructed and diagonalized in a direct-product basis of non-orthogonal configuration state functions computed for isolated fragments. Here, we derive and implement analytic derivative couplings for this model, including nuclear derivatives of the natural transition orbital and symmetric orthogonalization transformations that are part of the approximation. Nuclear derivatives of the exciton Hamiltonian's matrix elements, required in order to compute the nonadiabatic couplings, are equivalent to the "Holstein" and "Peierls" exciton/phonon couplings that are widely discussed in the context of model Hamiltonians for energy and charge transport in organic photovoltaics. As an example, we compute the couplings that modulate triplet exciton transport in crystalline tetracene, which is relevant in the context of carrier diffusion following singlet exciton fission.

An optical and magnetic resonance study of point defects in silicon, diamond, and aluminum nitride

NASA Astrophysics Data System (ADS)

Mason, Philip Wayne

1998-12-01

Optical and magnetic resonance studies of point defects in silicon, diamond, and aluminum nitride semiconducting crystals are described in this dissertation. In silicon, an optically detected magnetic resonance (ODMR) study of a sulfur-related defect with two stable configurations, Ssb{A} and Ssb{B}, each with its own photoluminescence (PL) band and associated ODMR spectrum, is discussed. Through ODMR and related linear polarization studies, the Ssb{A} configuration is conclusively determined to have Csb1 (triclinic) symmetry (which is also the tentative finding for Ssb{B}), a controversial issue in the literature. A conversion study comparing the PL and PLODMR shows a one-to-one conversion between the two configurations for each type of signal. Related findings also tentatively suggest that the Ssb{B} configuration is metastable in both the neutral and single positive charge states of the defect. In addition, an independent analysis presented of uniaxial stress data obtained at King's College, London, shows evidence that an inverted energy-level ordering of the excited electronic effective mass states (Asb1 above E) explains the data better than the opposite ordering which is usually observed for effective mass systems. The mechanism responsible for inversion is currently not known. In diamond, a 1.4 eV Ni-related band with very sharp zero-phonon lines is studied using magnetic circular dichroism in absorption (MCDA). A tunable laser was used to directly measure circular polarization properties of transitions between individual Zeeman-split spin states. The Zeeman study also provided a determination of their associated g-values. A comparison with a theoretical model involving intra-d-shell transitions of Ni indicates that a transition from a ground state of Gammasb{5,6}(sp2E) symmetry to a Gammasb4(sp2Asb1) excited state explains the experimental MCDA findings and agrees with results from a previous uniaxial stress polarization study of luminescence associated with the same transition. Finally, a PLODMR study of several aluminum nitride crystals is also presented. The crystals were observed to emit a broad PL band comprised of numerous overlapping bands, each with its own signature ODMR signal. These new spectra include four effective spin S = 1 centers and a pair of S = 1/2 centers exhibiting characteristics expected for distant-pair recombinations. Two recombination models, either of which may explain a pair of S = 1 centers that appear to be related, are discussed.

Edge effects on band gap energy in bilayer 2H-MoS{sub 2} under uniaxial strain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Liang; Wang, Jin; Dongare, Avinash M., E-mail: dongare@uconn.edu

2015-06-28

The potential of ultrathin MoS{sub 2} nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS{sub 2} film. In this study, a bilayer MoS{sub 2} supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS{sub 2} film under uniaxial mechanical deformations. The supercell contains an MoS{sub 2} bottom layer andmore » a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS{sub 2} flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS{sub 2} films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.« less

Molecular simulation of flow-enhanced nucleation in n-eicosane melts under steady shear and uniaxial extension.

PubMed

Nicholson, David A; Rutledge, Gregory C

2016-12-28

Non-equilibrium molecular dynamics is used to study crystal nucleation of n-eicosane under planar shear and, for the first time, uniaxial extension. A method of analysis based on the mean first-passage time is applied to the simulation results in order to determine the effect of the applied flow field type and strain rate on the steady-state nucleation rate and a characteristic growth rate, as well as the effects on kinetic parameters associated with nucleation: the free energy barrier, critical nucleus size, and monomer attachment pre-factor. The onset of flow-enhanced nucleation (FEN) occurs at a smaller critical strain rate in extension as compared to shear. For strain rates larger than the critical rate, a rapid increase in the nucleation rate is accompanied by decreases in the free energy barrier and critical nucleus size, as well as an increase in chain extension. These observations accord with a mechanism in which FEN is caused by an increase in the driving force for crystallization due to flow-induced entropy reduction. At high applied strain rates, the free energy barrier, critical nucleus size, and degree of stretching saturate, while the monomer attachment pre-factor and degree of orientational order increase steadily. This trend is indicative of a significant diffusive contribution to the nucleation rate under intense flows that is correlated with the degree of global orientational order in a nucleating system. Both flow fields give similar results for all kinetic quantities with respect to the reduced strain rate, which we define as the ratio of the applied strain rate to the critical rate. The characteristic growth rate increases with increasing strain rate, and shows a correspondence with the nucleation rate that does not depend on the type of flow field applied. Additionally, a structural analysis of the crystalline clusters indicates that the flow field suppresses the compaction and crystalline ordering of clusters, leading to the formation of large articulated clusters under strong flow fields, and compact well-ordered clusters under weak flow fields.

X-ray study of mesomorphism of bent-core and chromonic mesogens

NASA Astrophysics Data System (ADS)

Joshi, Leela Pradhan

The discovery of thermotropic biaxial nematic phase in bent-core mesogens, have engendered interest in these systems. Also, it undergoes optical switching about 100 times faster than conventional uniaxial nematic liquid crystal. Azo-substituted bent-core compounds, A131 and A103, were investigated as both offer an opportunity to observe their structures and phase transitions from the uniaxial nematic (Nu) to biaxial nematic (Nb) phase and from Nb to the underlying smectic-C (SmC) phase. Plank-like molecular systems are also expected to form Nb phase. Chromonic liquid crystals formed by aqueous solutions of plank-like dye molecules are interesting for their unique self-assembly and structural evolution. They have applications in optical element, coloring in food and textiles, and etc. Both systems were investigated with synchrotron x-ray scattering, polarizing optical microscopy, and differential scanning calorimetry. Temperature dependence of d-spacing and positional order correlations along the director clearly mark the phase boundaries where Nu-Nb transition was approximately 27° below the clearing point. Positional order correlation length of A131 increased from 1.5 in Nu to 3.3 molecular lengths in Nb phase, before it jumps by a factor of at least 5 in SmC phase. The lack of large discontinuous changes in the structural parameters and the subtle signatures in heat capacity establish the second order nature of Nu-Nb and Nb-SmC phase transitions. The chromonic system investigation results provide quantitative information of structural properties in nematic and columnar mesophases. We studied water solutions of (achiral) sunset yellow dye and (chiral and achiral) dihydrochloride salts of perylenebis-dicarboxydiimide. Positional order correlation lengths measurements, parallel and perpendicular to the aggregate axis, revealed that they increase with concentration and decrease with temperature. Temperature dependence of correlation lengths yielded the scission energy to be 1.8 (+/-0.1) x10-20J and 1.5 (+/-0.08) x10-20J in the nematic and columnar phases. The aggregates' small aspect ratio (2.5) is inconsistent with the Onsager model for the formation of an orientationally ordered phase, which strongly suggests more complicated aggregate-shape than simple cylindrical objects as postulated by Laventovich, et al.

Piezoelectric and Electrostrictive Materials for Transducer Applications.

DTIC Science & Technology

1988-01-01

No. 8, 9, 1986. 18. Y. Sun, L.E. Cross. "Investigations of Electrostriction Effects in Glass by Uniaxial Stress Compressometer." 19. Wuyi Pan, E...15. Y. Sun, L.E. Cross. "Investigations of Electrostrictive Effects in Glass by Uniaxial Stress Compressometer." A 16. M.J. Haun, T.R. Halemane, R.E...Points," Ind. Symp. Appl. Ferroelectrics (1986). 60. Y. Sun, L.E. Cross. "Investigations of Electrostrictive Effects in Glass by Uniaxial Stress

Energy dependence of the spin excitation anisotropy in uniaxial-strained BaFe 1.9Ni 0.1As 2

DOE PAGES

Song, Yu; Lu, Xingye; Abernathy, Douglas L.; ...

2015-11-06

In this study, we use inelastic neutron scattering to study the temperature and energy dependence of the spin excitation anisotropy in uniaxial-strained electron-doped iron pnictide BaFe 1.9Ni 0.1As 2 near optimal superconductivity (T c = 20K). Our work has been motivated by the observation of in-plane resistivity anisotropy in the paramagnetic tetragonal phase of electron-underdoped iron pnictides under uniaxial pressure, which has been attributed to a spin-driven Ising-nematic state or orbital ordering. Here we show that the spin excitation anisotropy, a signature of the spin-driven Ising-nematic phase, exists for energies below 60 meV in uniaxial-strained BaFe 1.9Ni 0.1As 2. Sincemore » this energy scale is considerably larger than the energy splitting of the d xz and d yz bands of uniaxial-strained Ba(Fe 1–xCox) 2As 2 near optimal superconductivity, spin Ising-nematic correlations are likely the driving force for the resistivity anisotropy and associated electronic nematic correlations.« less

Fatigue effect in ferroelectric crystals: Growth of the frozen domains

NASA Astrophysics Data System (ADS)

Shur, V. Ya.; Akhmatkhanov, A. R.; Baturin, I. S.

2012-06-01

The model of the fatigue effect during cyclic switching caused by growth of the frozen domain area with charged domain walls has been proposed. It was claimed on the basis of the previous experimental results that for switching in increasing field the frozen domain area started to grow at the given sub-threshold field value and stopped at the threshold field. The influence of the shape and frequency of the field pulses used for cyclic switching has been considered. The uniaxial ferroelectric stoichiometric lithium tantalate single crystals produced by vapor transport equilibration with record low value of coercive field have been chosen as a model material for experimental verification of the model. The formation of the charged domain walls as a result of cyclic switching has been revealed by analysis of the domain images obtained by optical and Raman confocal microscopy. It has been shown that the fatigue degree is equal to the fraction of the frozen domain area. The experimental dependence of the switched charge on the cycle number has been successfully fitted by modified Kolmogorov-Avrami formula. The experimentally observed frequency independence of fatigue profile for rectangular pulses and frequency dependence for triangular pulses has been explained by proposed model.

Crystal structure and partial Ising-like magnetic ordering of orthorhombic D y 2 Ti O 5

DOE PAGES

Shamblin, Jacob; Calder, Stuart; Dun, Zhiling; ...

2016-07-12

The structure and magnetic properties of orthorhombic Dy 2TiO 5 have been investigated using x-ray diffraction, neutron diffraction, and alternating current (ac)/direct current (dc) magnetic susceptibility measurements. In this paper, we report a continuous structural distortion below 100 K characterized by negative thermal expansion in the [0 1 0] direction. Neutron diffraction and magnetic susceptibility measurements revealed that two-dimensional (2D) magnetic ordering begins at 3.1 K, which is followed by a three-dimensional magnetic transition at 1.7 K. The magnetic structure has been solved through a representational analysis approach and can be indexed with the propagation vector k = [0 1/2more » 0]. The spin structure corresponds to a coplanar model of interwoven 2D “sheets” extending in the [0 1 0] direction. The local crystal field is different for each Dy 3+ ion (Dy1 and Dy2), one of which possesses strong uniaxial symmetry indicative of Ising-like magnetic ordering. In conclusion, consequently, two succeeding transitions under magnetic field are observed in the ac susceptibility, which are associated with flipping each Dy 3+ spin independently.« less

Ferroelectric order in liquid crystal phases of polar disk-shaped ellipsoids

NASA Astrophysics Data System (ADS)

Bose, Tushar Kanti; Saha, Jayashree

2014-05-01

The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absence of any long range positional order is considered an outstanding problem of both fundamental and technological interest. Recently, we reported that a system of polar achiral disklike ellipsoids can spontaneously exhibit a long searched ferroelectric nematic phase and a ferroelectric columnar phase with strong axial polarization. The major role is played by the dipolar interactions. The model system of interest consists of attractive-repulsive Gay-Berne oblate ellipsoids embedded with two parallel point dipoles positioned symmetrically on the equatorial plane of the ellipsoids. In the present work, we investigate in detail the profound effects of changing the separation between the two symmetrically placed dipoles and the strength of the dipoles upon the existence of different ferroelectric discotic liquid crystal phases via extensive off-lattice N-P-T Monte Carlo simulations. Ferroelectric biaxial phases are exhibited in addition to the uniaxial ferroelectric fluids where the phase biaxiality results from the dipolar interactions. The structures of all the ferroelectric configurations of interest are presented in detail. Simple phase diagrams are determined which include different polar and apolar discotic fluids generated by the system.

Preparation of ordered mesoporous alumina-doped titania films with high thermal stability and their application to high-speed passive-matrix electrochromic displays.

PubMed

Jiang, Xiangfen; Bastakoti, Bishnu Prasad; Weng, Wu; Higuchi, Tetsuya; Oveisi, Hamid; Suzuki, Norihiro; Chen, Wei-Jung; Huang, Yu-Tzu; Yamauchi, Yusuke

2013-08-12

Ordered mesoporous alumina-doped titania thin films with anatase crystalline structure were prepared by using triblock copolymer Pluronic P123 as structure-directing agent. Uniform Al doping was realized by using aluminum isopropoxide as a dopant source which can be hydrolyzed together with titanium tetraisopropoxide. Aluminum doping into the titania framework can prevent rapid crystallization to the anatase phase, thereby drastically increasing thermal stability. With increasing Al content, the crystallization temperatures tend to increase gradually. Even when the Al content doped into the framework was increased to 15 mol %, a well-ordered mesoporous structure was obtained, and the mesostructural ordering was still maintained after calcination at 550 °C. During the calcination process, large uniaxial shrinkage occurred along the direction perpendicular to the substrate with retention of the horizontal mesoscale periodicity, whereby vertically oriented nanopillars were formed in the film. The resulting vertical porosity was successfully exploited to fabricate a high-speed and high-quality passive-matrix electrochromic display by using a leuco dye. The vertical nanospace in the films can effectively prevent drifting of the leuco dye. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen defects in α-Al2O3 and water weakening of sapphire and alumina ceramics between 600°C and 1000°C: II. Mechanical properties

USGS Publications Warehouse

Castaing, J.; Kronenberg, A.K.; Kirby, S.H.; Mitchell, T.E.

2000-01-01

Hydrogen impurities in alumina have been introduced by hydrothermal annealing (see part I). In this paper, we report on reductions in the flow strength of α-Al2O3 single crystals and polycrystals associated with hydrogen incorporation. Prior to deformation, α-Al2O3 single crystal and ceramic specimens were annealed in the presence of supercritical water at 850° or 900°C, under 1500 MPa pressure. Sapphire and alumina ceramics were plastically deformed between 600° and 1000°C under 1500 MPa pressure, by the addition of a uniaxial stress. Flow stresses are reduced by a factor of two, due to the presence of water, for sapphire and large grain (30–50 μm) polycrystals, as a result of enhanced dislocation mobility. Flow stresses of fine-grained (3–5 μm) polycrystals are reduced by water by a factor of six. This large reduction in strength is attributed to a change in mechanism from dislocation glide under dry conditions to grain boundary sliding under hydrothermal conditions.

Electronic, optical, infrared, and elastic properties of KCdCO3F from first principles

NASA Astrophysics Data System (ADS)

Huang, Xue-Qian; Xue, Han-Yu; Zhang, Can; Pang, Dong-Dong; Lv, Zhen-Long; Duan, Man-Yi

2018-05-01

KCdCO3F is a newly synthesized promising ultraviolet nonlinear optical crystal, but its structure is disputed and its fundamental properties have not been well studied. Here our first-principles study indicates that the structure with the space group P 6 bar c2 is energetically more stable than the P 6 bar m2 phase. We systematically investigated its electronic, optical, vibrational, infrared, and elastic properties. The results reveal that KCdCO3F is a direct-band-gap insulator with rather flat bands below the Fermi level. Analyses of its partial density of states revealed that the top (bottom) of its valence (conduction) band is formed by the O 2p (Cd 5s) orbital. It is a negative uniaxial crystal with ionic-covalent nature. Both infrared-active and Raman-active modes exist at its Brillouin zone center, and ions contribute more to its static dielectric constants. Its optical spectra in the visual and infrared ranges were studied, and their origins were revealed. Calculations indicate that KCdCO3F is mechanically stable but anisotropic since it is more vulnerable to shear stress and is easy to cleave along the c axis.

Investigation of the mechanical properties of organoplastic under shock wave loading conditions

NASA Astrophysics Data System (ADS)

Bragov, A. M.; Igumnov, L. A.; Konstantinov, A. Yu; Lomunov, A. K.

2018-04-01

The paper presents results of dynamic tests of a typical representative of new composite and damping materials: organoplastics. Compression testing was performed using the traditional Kolsky method and its original modification. The strength and deformation properties of organoplastics under conditions of uniaxial stress and uniaxial deformation were studied. When the organoplastic is compressed transversely to the Kevlar fabric layers under conditions of a uniaxial stress state, the material begins to break down (to lose the layer cohesion) at a stress of about 200 MPa, while under the conditions of uniaxial strain, it retains its apparent integrity at stresses up to 500 MPa. The small value of the lateral thrust factor indicates a large internal strength of the material in tension in the radial direction.

Creep Laboratory manual

NASA Astrophysics Data System (ADS)

Osgerby, S.; Loveday, M. S.

1992-06-01

A manual for the NPL Creep Laboratory, a collective name given to two testing laboratories, the Uniaxial Creep Laboratory and the Advanced High Temperature Mechanical Testing Laboratory, is presented. The first laboratory is devoted to uniaxial creep testing and houses approximately 50 high sensitivity creep machines including 10 constant stress cam lever machines. The second laboratory houses a low cycle fatigue testing machine of 100 kN capacity driven by a servo-electric actuator, five machines for uniaxial tensile creep testing of engineering ceramics at temperatures up to 1600C, and an electronic creep machine. Details of the operational procedures for carrying out uniaxial creep testing are given. Calibration procedures to be followed in order to comply with the specifications laid down by British standards, and to provide traceability back to the primary standards are described.

Elastic properties of uniaxial-fiber reinforced composites - General features

NASA Astrophysics Data System (ADS)

Datta, Subhendu; Ledbetter, Hassel; Lei, Ming

The salient features of the elastic properties of uniaxial-fiber-reinforced composites are examined by considering the complete set of elastic constants of composites comprising isotropic uniaxial fibers in an isotropic matrix. Such materials exhibit transverse-isotropic symmetry and five independent elastic constants in Voigt notation: C(11), C(33), C(44), C(66), and C(13). These C(ij) constants are calculated over the entire fiber-volume-fraction range 0.0-1.0, using a scattered-plane-wave ensemple-average model. Some practical elastic constants such as the principal Young moduli and the principal Poisson ratios are considered, and the behavior of these constants is discussed. Also presented are the results for the four principal sound velocities used to study uniaxial-fiber-reinforced composites: v(11), v(33), v(12), and v(13).

Tight-Binding study of Boron structures

NASA Astrophysics Data System (ADS)

McGrady, Joseph W.; Papaconstantopoulos, Dimitrios A.; Mehl, Michael J.

2014-10-01

We have performed Linearized Augmented Plane Wave (LAPW) calculations for five crystal structures (alpha, dhcp, sc, fcc, bcc) of Boron which we then fitted to a non-orthogonal tight-binding model following the Naval Research Laboratory Tight-Binding (NRL-TB) method. The predictions of the NRL-TB approach for complicated Boron structures such as R105 (or β-rhombohedral) and T190 are in agreement with recent first-principles calculations. Fully utilizing the computational speed of the NRL-TB method we calculated the energy differences of various structures, including those containing vacancies using supercells with up to 5000 atoms.

Fundamental studies of MALDI with an orthogonal TOF mass spectrometer

NASA Astrophysics Data System (ADS)

Qiao, Hui

The interaction between the matrix and analyte molecules are studied with a high resolution MALDI imaging technique in an orthogonal-injection time of flight (TOF) mass spectrometer. The analyte incorporation and distribution patterns have been clearly demonstrated. Purified protein analytes were found to be homogeneously incorporated in large single crystals of DHB and sinapinic acid matrices, with no evidence for preferred crystal faces. Segregation of some species was observed and appeared to correlate with analyte hydrophobicity, and to a lesser extent analyte mass or mobility. Similar segregation phenomena were observed with confocal laser scanning microscopy of the same analytes labeled with fluorescent dyes in 2,5-DHB single crystals. The above investigations may shed some light on optimizing sample preparation with different matrices. The influence of incident laser parameters on sensitivity in MALDI has been investigated using orthogonal-injection TOF instruments. A qualitative comparison was first made between the beam profiles obtained with a N 2 laser and a Nd:YAG laser using 2-m long optical fibers. The N 2 laser gives better sensitivity, consistent with a more uniform fluence distribution and therefore better coverage of the N2 laser profile. Most of the difference disappears when a 30-m long fiber is used or when the fibers are twisted during irradiation to smooth out the fluence distribution. In more systematic measurements, the total integrated ion yield from a single spot (a measure of sensitivity) was found to increase rapidly with fluence to a maximum, and then saturate or decrease slightly. Thus, the optimum sensitivity is achieved at high fluence. For a fluence near threshold, the integrated yield has a steep (cubic) dependence on the spot size, but the yield saturates at higher fluence for smaller spots. The area dependence is much weaker (close to linear) for fluence values above saturation, with the result that the highest integrated yields per unit area are obtained with the smallest spot sizes. The results have particular relevance for imaging MALDI, where sensitivity and spatial resolution are important figures of merit. Finally the detection properties of the MCP detector were studied with a hybrid MCP and CuBe venetian blind converter detector. The measurements show that the detection efficiency of the MCP drops with the increasing of ion mass and the decreasing of the ion energy. For transferrin (79,500 Da), the relative detection efficiency of the MCP is about 40% at 10.6 keV and it decreases to about 5% at 4.6 keV. The secondary electron emission coefficient of the MCP shows a linear dependence on mass and a power law dependence on velocity (˜3.2). No clear velocity threshold is observed for secondary electron emission.

Understanding the rheology of two and three-phase magmas

NASA Astrophysics Data System (ADS)

Coats, R.; Cai, B.; Kendrick, J. E.; Wallace, P. A.; Hornby, A. J.; Miwa, T.; von Aulock, F. W.; Ashworth, J. D.; Godinho, J.; Atwood, R. C.; Lee, P. D.; Lavallée, Y.

2017-12-01

The rheology of magma plays a fundamental role in determining the style of a volcanic eruption, be it explosive or effusive. Understanding how magmas respond to changes in stress/ strain conditions may help to enhance eruption forecast models. The presence of crystals and bubbles in magmas alter the viscosity of suspensions and favor a non-Newtonian response. Thus, with the aim of grasping the rheological behavior of volcanic materials, uniaxial compressive tests were performed on natural and synthetic samples. A suite of variably porous (10-32 vol.%), highly crystalline ( 50 vol.%) dacite from the 1991-95 eruption of Mt Unzen, Japan, was selected as the natural material, while synthetic samples were sintered with desired porosities (<3, 20 and 30 vol.%) and TiO2 particles (0-50 vol.%). Tests were carried out at both room temperature and above the glass transition temperature (Tg) of the different materials to cover the entirety of the extrusion process. Room temperature tests were performed at constant strain rates of 10-1, 10-3, and 10-5 s-1. The response was brittle and peak stresses reached were positively correlated to strain rate and negatively correlated to porosity. At temperatures above Tg, strain rates of 10-3, 10-4, and 10-5 s-1 were imposed resulting in dominantly brittle, transitional and dominantly viscous responses, respectively. Samples with a brittle response reached higher peak stresses, and strain-to-failure values, at high temperature than at room temperature. In both materials, non-Newtonian, shear-thinning behavior was observed and while synthetic samples showed an expected increase in apparent viscosity with increasing crystal content, surprisingly natural samples did not show a correlation between apparent viscosity and porosity. We hypothesise this is due to crystal content being the governing factor for the volume fractions explored. In situ, high temperature synchrotron X-ray tomography was performed on selected crystal/pore volume fractions at Diamond Light Source. Unexpectedly, these observations suggest that fractures nucleate in crystals due to crystal interactions, before propagating through the interstitial melt. This ongoing study promises to uncover the way crystal-bearing magmas flow or fail, necessary to constrain magmatic processes and volcanic hazards.

Effects of pressure and temperature on sintering of Cr-doped Al2O3 by pulsed electric current sintering process

NASA Astrophysics Data System (ADS)

Dang, K. Q.; Nanko, M.

2011-03-01

The aluminium oxide crystal, Al2O3, which contains a small amount of chromium, Cr, is called ruby. Pulsed electric current sintering (PECS) was applied to sinter ruby polycrystals. Cr2O3-Al2O3 powder mixture prepared by drying an aqueous slurry containing amounts of Al2O3 and Cr(NO3)3 was consolidated by PECS process. The PECS process was performed in vacuum at sintering temperature raging from 1100 to 1300°C with heating rate of 2 K/min under applied uniaxial pressure varied from 40 to 100 MPa. This study found that highly densified and transparent Cr-doped Al2O3 can be obtained by the PECS process with the high applied pressure at sintering temperature of 1200°C.

DOE Office of Scientific and Technical Information (OSTI.GOV)

X Li; Y Mao; H Ma

An ionic liquid (IL) 1-docosanyl-3-methylimidazolium bromide was incorporated into ultra-high molecular weight polyethylene (UHMWPE) and formed IL/UHMWPE blends by solution mixing. The structure evolution of these blends during uniaxial stretching was followed by in-situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. During deformation at room temperature, deformation-induced phase transformation from orthorhombic to monoclinic phase was observed in both IL/UHMWPE blends and neat UHMWPE. The elongation-to-break ratios of IL/UHMWPE blends were found to increase by 2-3 times compared with that of pure UHMWPE, while the tensile strength remained about the same. In contrast, during deformation at highmore » temperature (120 C), no phase transformation was observed. However, the blend samples showed much better toughness, higher crystal orientation and higher tilting extent of lamellar structure at high strains.« less

Effect of orientation on electrically conducting thermoplastic composite properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Genetti, W.B.; Grady, B.P.

1996-10-01

Properties of electrically conducting composites made from low density polyethylene (LDPE), high density polyethylene (HDPE), and polypropylene (PP) filled with nickel flake are being studied as a function of nickel concentration and draw ratio. The effect on electrical conduction, crystallinity, melt temperature, tensile modulus, and elongation at break are being tested. The melt temperature increases with increasing nickel concentration. The electrical conduction increases slowly with increased nickel concentration to the percolation volume fraction, then increases sharply. Orientation by uniaxial stretching of the films should allow conductive pathways to form throughout the polymer more easily by forcing particles closer together, thusmore » reducing the percolation volume fraction. This process could be caused by both alignment of the polymer chains and by stress induced crystallization that forces the particles into smaller amorphous regions.« less

Determination of magnetic anisotropy constants in Fe ultrathin film on vicinal Si(111) by anisotropic magnetoresistance

PubMed Central

Ye, Jun; He, Wei; Wu, Qiong; Liu, Hao-Liang; Zhang, Xiang-Qun; Chen, Zi-Yu; Cheng, Zhao-Hua

2013-01-01

The epitaxial growth of ultrathin Fe film on Si(111) surface provides an excellent opportunity to investigate the contribution of magnetic anisotropy to magnetic behavior. Here, we present the anisotropic magnetoresistance (AMR) effect of Fe single crystal film on vicinal Si(111) substrate with atomically flat ultrathin p(2 × 2) iron silicide as buffer layer. Owing to the tiny misorientation from Fe(111) plane, the symmetry of magnetocrystalline anisotropy energy changes from the six-fold to a superposition of six-fold, four-fold and a weakly uniaxial contribution. Furthermore, the magnitudes of various magnetic anisotropy constants were derived from torque curves on the basis of AMR results. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of various magnetic anisotropy constants. PMID:23828508

Effects of stress fiber contractility on uniaxial stretch guiding mitosis orientation and stress fiber alignment.

PubMed

Zhao, Lei; Sang, Chen; Yang, Chun; Zhuang, Fengyuan

2011-09-02

It has been documented that mitosis orientation (MO) is guided by stress fibers (SFs), which are perpendicular to exogenous cyclic uniaxial stretch. However, the effect of mechanical forces on MO and the mechanism of stretch-induced SFs reorientation are not well elucidated to date. In the present study, we used murine 3T3 fibroblasts as a model, to investigate the effects of uniaxial stretch on SFO and MO utilizing custom-made stretch device. We found that cyclic uniaxial stretch induced both SFs and mitosis directions orienting perpendicularly to the stretch direction. The F-actin and myosin II blockages, which resulted in disoriented SFs and mitosis directions under uniaxial stretch, suggested a high correlation between SFO and MO. Y27632 (10 μM), ML7 (50 μM, or 75 μM), and blebbistatin (50 μM, or 75 μM) treatments resulted in SFO parallel to the principle stretch direction. Upon stimulating and inhibiting the phosphorylation of myosin light chain (p-MLC), we observed a monotonic proportion of SFO to the level of p-MLC. These results suggested that the level of cell contraction is crucial to the response of SFs, either perpendicular or parallel, to the external stretch. Showing the possible role of cell contractility in tuning SFO under external stretch, our experimental data are valuable to understand the predominant factor controlling SFO response to exogenous uniaxial stretch, and thus helpful for improving mechanical models. Copyright © 2011 Elsevier Ltd. All rights reserved.

Ion beam modification of single crystalline BiVO4

NASA Astrophysics Data System (ADS)

Wendler, Elke; Bischoff, Marie; Schmidt, Emanuel; Schrempel, F.; Ellmer, Klaus; Kanis, Michael; van de Krol, Roel

2017-10-01

A single crystalline BiVO4 sample was investigated. Angular resolved Rutherford backscattering spectrometry (arRBS) was performed as a function of two orthogonal angles perpendicular to the surface. The crystal planes appearing in the angular charts are compared with the crystal structure of monoclinic BiVO4. By this comparison the crystal axis being almost normal to the surface was identified to be 〈0 0 1〉. These measurements support the control of orientation and quality of the grown BiVO4 crystal. Additionally it is found that during prolonged analysis the He ions produce a considerable amount of damage. As the nuclear energy loss of the He ions is negligibly low within the corresponding depth region, the damage is mainly caused by the electronic energy loss of the ions. For studying radiation resistance and damage formation, the BiVO4 single crystal was implanted with 200 keV Ar ions. The damage production in the Bi sublattice was analysed by RBS applying 1.8 MeV He ions in channelling configuration. The damage profiles determined from the channelling RBS spectra can be well represented by the electronic energy loss of the implanted Ar ions. From this it is concluded that, in agreement with the finding mentioned above, this energy mainly triggers damage formation in ion irradiated BiVO4. The energy for producing one displaced Bi atom as seen by RBS decreases with increasing damage concentration and varies between 33 and 3.4 eV.

Linear dichroism of DNA: Characterization of the orientation distribution function caused by hydrodynamic shear

DOE PAGES

Sutherland, John C.

2017-04-15

Linear dichroism provides information on the orientation of chromophores part of, or bound to, an orientable molecule such as DNA. For molecular alignment induced by hydrodynamic shear, the principal axes orthogonal to the direction of alignment are not equivalent. Thus, the magnitude of the flow-induced change in absorption for light polarized parallel to the direction of flow can be more than a factor of two greater than the corresponding change for light polarized perpendicular to both that direction and the shear axis. The ratio of the two flow-induced changes in absorption, the dichroic increment ratio, is characterized using the orthogonalmore » orientation model, which assumes that each absorbing unit is aligned parallel to one of the principal axes of the apparatus. The absorption of the alienable molecules is characterized by components parallel and perpendicular to the orientable axis of the molecule. The dichroic increment ratio indicates that for the alignment of DNA in rectangular flow cells, average alignment is not uniaxial, but for higher shear, as produced in a Couette cell, it can be. The results from the simple model are identical to tensor models for typical experimental configuration. Approaches for measuring the dichroic increment ratio with modern dichrometers are further discussed.« less

A DMAP Program for the Selection of Accelerometer Locations in MSC/NASTRAN

NASA Technical Reports Server (NTRS)

Peck, Jeff; Torres, Isaias

2004-01-01

A new program for selecting sensor locations has been written in the DMAP (Direct Matrix Abstraction Program) language of MSC/NASTRAN. The program implements the method of Effective Independence for selecting sensor locations, and is executed within a single NASTRAN analysis as a "rigid format alter" to the normal modes solution sequence (SOL 103). The user of the program is able to choose among various analysis options using Case Control and Bulk Data entries. Algorithms tailored for the placement of both uni-axial and tri- axial accelerometers are available, as well as several options for including the model s mass distribution into the calculations. Target modes for the Effective Independence analysis are selected from the MSC/NASTRAN ASET modes calculated by the "SOL 103" solution sequence. The initial candidate sensor set is also under user control, and is selected from the ASET degrees of freedom. Analysis results are printed to the MSCINASTRAN output file (*.f06), and may include the current candidate sensors set, and their associated Effective Independence distribution, at user specified iteration intervals. At the conclusion of the analysis, the model is reduced to the final sensor set, and frequencies and orthogonality checks are printed. Example results are given for a pre-test analysis of NASA s five-segment solid rocket booster modal test.

Linear dichroism of DNA: Characterization of the orientation distribution function caused by hydrodynamic shear

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sutherland, John C.

Linear dichroism provides information on the orientation of chromophores part of, or bound to, an orientable molecule such as DNA. For molecular alignment induced by hydrodynamic shear, the principal axes orthogonal to the direction of alignment are not equivalent. Thus, the magnitude of the flow-induced change in absorption for light polarized parallel to the direction of flow can be more than a factor of two greater than the corresponding change for light polarized perpendicular to both that direction and the shear axis. The ratio of the two flow-induced changes in absorption, the dichroic increment ratio, is characterized using the orthogonalmore » orientation model, which assumes that each absorbing unit is aligned parallel to one of the principal axes of the apparatus. The absorption of the alienable molecules is characterized by components parallel and perpendicular to the orientable axis of the molecule. The dichroic increment ratio indicates that for the alignment of DNA in rectangular flow cells, average alignment is not uniaxial, but for higher shear, as produced in a Couette cell, it can be. The results from the simple model are identical to tensor models for typical experimental configuration. Approaches for measuring the dichroic increment ratio with modern dichrometers are further discussed.« less

Permeability of compacting porous lavas

NASA Astrophysics Data System (ADS)

Ashwell, P. A.; Kendrick, J. E.; Lavallée, Y.; Kennedy, B. M.; Hess, K.-U.; von Aulock, F. W.; Wadsworth, F. B.; Vasseur, J.; Dingwell, D. B.

2015-03-01

The highly transient nature of outgassing commonly observed at volcanoes is in part controlled by the permeability of lava domes and shallow conduits. Lava domes generally consist of a porous outer carapace surrounding a denser lava core with internal shear zones of variable porosity. Here we examine densification using uniaxial compression experiments on variably crystalline and porous rhyolitic dome lavas from the Taupo Volcanic Zone. Experiments were conducted at 900°C and an applied stress of 3 MPa to 60% strain, while monitoring acoustic emissions to track cracking. The evolution of the porous network was assessed via X-ray computed tomography, He-pycnometry, and relative gas permeability. High starting connected porosities led to low apparent viscosities and high strain rates, initially accompanied by abundant acoustic emissions. As compaction ensued, the lavas evolved; apparent viscosity increased and strain rate decreased due to strain hardening of the suspensions. Permeability fluctuations resulted from the interplay between viscous flow and brittle failure. Where phenocrysts were abundant, cracks had limited spatial extent, and pore closure decreased axial and radial permeability proportionally, maintaining the initial anisotropy. In crystal-poor lavas, axial cracks had a more profound effect, and permeability anisotropy switched to favor axial flow. Irrespective of porosity, both crystalline samples compacted to a threshold minimum porosity of 17-19%, whereas the crystal-poor sample did not achieve its compaction limit. This indicates that unconfined loading of porous dome lavas does not necessarily form an impermeable plug and may be hindered, in part by the presence of crystals.

Analyzing shear band formation with high resolution X-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pagan, Darren C.; Obstalecki, Mark; Park, Jun-Sang

Localization of crystallographic slip into shear bands during uniaxial compression of a copper single crystal is studied using very far-field high-energy diffraction microscopy (vff-HEDM). Diffracted intensity was collected in-situ as the crystal deformed using a unique mobile detector stage that provided access to multiple diffraction peaks with high-angular resolution. From the diffraction data, single crystal orientation pole figures (SCPFs) were generated and are used to track the evolution of the distribution of lattice orientation that develops as slip localizes. To aid the identification of 'signatures' of shear band formation and analyze the SCPF data, a model of slip-driven lattice reorientationmore » within shear bands is introduced. Confidence is built in conclusions drawn from the SCPF data about the character of internal slip localization through comparisons with strain fields on the sample surface measured simultaneously using digital image correlation. From the diffraction data, we find that the active slip direction and slip plane are not directly aligned with the orientation of the shear bands that formed. In fact, by extracting the underlying slip system activity from the SCPF data, we show that intersecting shear bands measured on the surface of the sample arise from slip primarily on the same underlying single slip system. These new vff-HEDM results raise significant questions on the use of surface measurements for slip system activity estimation. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.« less

Correlations Between Structural and Magnetic Properties of Co2 FeSi Heusler-Alloy Thin Films

NASA Astrophysics Data System (ADS)

Zhu, Weihua; Wu, Di; Zhao, Bingcheng; Zhu, Zhendong; Yang, Xiaodi; Zhang, Zongzhi; Jin, Q. Y.

2017-09-01

The structural and magnetic properties are the most important parameters for practical applications of Co-based Heusler alloys. The correlations between the crystallization degree, chemical order, magnetic coercivity, saturation magnetization (MS ), and in-plane magnetic anisotropies are systematically investigated for Co2FeSi (CFS) films fabricated at different temperatures (TS ). XRD shows that the CFS layer changes progressively from a disordered crystal structure into a chemically disordered A 2 structure and further into a chemically ordered B 2 and even L 21 structures when increasing TS up to 480 °C . Meanwhile, the static angular remanence magnetization curves show a clear transition of magnetic anisotropy from twofold to fourfold symmetry, due to the competition effect between the uniaxial anisotropy field HU and biaxial anisotropy field HB . The HU value is found to be weakly dependent on TS , while HB shows a continuous enhancement at TS>300 °C , implying that the enhancement of the L 21 ordering degree would not weaken the biaxial anisotropy. The varying trend of HB is similar to MS , which can be respectively attributed to the improved crystal structure and chemical order. The anisotropic fields and their variation behaviors determined by a vibrating sample magnetometer are highly consistent with the results by a time-resolved magneto-optical Kerr effect study. Our findings provide a better understanding of the structural ordering and magnetic anisotropy, which will be helpful for designing advanced spintronic devices.

Load relaxation of olivine single crystals

NASA Astrophysics Data System (ADS)

Cooper, Reid F.; Stone, Donald S.; Plookphol, Thawatchai

2016-10-01

Single crystals of ferromagnesian olivine (San Carlos, AZ, peridot; Fo88-90) have been deformed in both uniaxial creep and load relaxation under conditions of ambient pressure, T = 1500°C and pO2 = 10-10 atm; creep stresses were in the range 40 ≤ σ1 (MPa) ≤ 220. The crystals were oriented such that the applied stress was parallel to [011]c, which promotes single slip on the slowest slip system in olivine, (010)[001]. The creep rates at steady state match well the results of earlier investigators, as does the stress sensitivity (a power law exponent of n = 3.6). Dislocation microstructures, including spatial distribution of low-angle (subgrain) boundaries, additionally confirm previous investigations. Inverted primary creep (an accelerating strain rate with an increase in stress) was observed. Load relaxation, however, produced a singular response—a single hardness curve—regardless of the magnitude of creep stress or total accumulated strain preceding relaxation. The log stress versus log strain rate data from load-relaxation and creep experiments overlap to within experimental error. The load-relaxation behavior is distinctly different than that described for other crystalline solids, where the flow stress is affected strongly by work hardening such that a family of distinct hardness curves is generated, which are related by a scaling function. The response of olivine for the conditions studied, we argue, indicates flow that is rate limited by dislocation glide, reflecting specifically a high intrinsic lattice resistance (Peierls stress).

Load Relaxation of Olivine Single Crystals

NASA Astrophysics Data System (ADS)

Cooper, R. F.; Stone, D. S.; Plookphol, T.

2016-12-01

Single crystals of ferromagnesian olivine (San Carlos, AZ, peridot; Fo90-92) have been deformed in both uniaxial creep and load relaxation under conditions of ambient pressure, T = 1500ºC and pO2 = 10-10 atm; creep stresses were in the range 40 ≤ σ1 (MPa) ≤ 220. The crystals were oriented such that the applied stress was parallel to [011]c, which promotes single slip on the slowest slip system in olivine, (010)[001]. The creep rates at steady state match well the results of earlier investigators, as does the stress sensitivity (a power-law exponent of n = 3.6). Dislocation microstructures, including spatial distribution of low-angle (subgrain) boundaries, additionally confirm previous investigations. Inverted primary creep (an accelerating strain rate with an increase in stress) was observed. Load-relaxation, however, produced a singular response—a single hardness curve—regardless of the magnitude of creep stress or total accumulated strain preceding relaxation. The log-stress v. log-strain rate data from load-relaxation and creep experiments overlap to within experimental error. The load-relaxation behavior is distinctly different that that described for other crystalline solids, where the flow stress is affected strongly by work hardening such that a family of distinct hardness curves is generated, which are related by a scaling function. The response of olivine for the conditions studied, thus, indicates flow that is rate-limited by dislocation glide, reflecting specifically a high intrinsic lattice resistance (Peierls stress).

Electrically tunable terahertz polarization converter based on overcoupled metal-isolator-metal metamaterials infiltrated with liquid crystals

NASA Astrophysics Data System (ADS)

Vasić, Borislav; Zografopoulos, Dimitrios C.; Isić, Goran; Beccherelli, Romeo; Gajić, Radoš

2017-03-01

Large birefringence and its electrical modulation by means of Fréedericksz transition makes nematic liquid crystals (LCs) a promising platform for tunable terahertz (THz) devices. The thickness of standard LC cells is in the order of the wavelength, requiring high driving voltages and allowing only a very slow modulation at THz frequencies. Here, we first present the concept of overcoupled metal-isolator-metal (MIM) cavities that allow for achieving simultaneously both very high phase difference between orthogonal electric field components and large reflectance. We then apply this concept to LC-infiltrated MIM-based metamaterials aiming at the design of electrically tunable THz polarization converters. The optimal operation in the overcoupled regime is provided by properly selecting the thickness of the LC cell. Instead of the LC natural birefringence, the polarization-dependent functionality stems from the optical anisotropy of ultrathin and deeply subwavelength MIM structures. The dynamic electro-optic control of the LC refractive index enables the spectral shift of the resonant mode and, consequently, the tuning of the phase difference between the two orthogonal field components. This tunability is further enhanced by the large confinement of the resonant electromagnetic fields within the MIM cavity. We show that for an appropriately chosen linearly polarized incident field, the polarization state of the reflected field at the target operation frequency can be continuously swept between the north and south pole of the Poincaré sphere. Using a rigorous Q-tensor model to simulate the LC electro-optic switching, we demonstrate that the enhanced light-matter interaction in the MIM resonant cavity allows the polarization converter to operate at driving voltages below 10 Volt and with millisecond switching times.

Electrically tunable terahertz polarization converter based on overcoupled metal-isolator-metal metamaterials infiltrated with liquid crystals.

PubMed

Vasić, Borislav; Zografopoulos, Dimitrios C; Isić, Goran; Beccherelli, Romeo; Gajić, Radoš

2017-03-24

Large birefringence and its electrical modulation by means of Fréedericksz transition makes nematic liquid crystals (LCs) a promising platform for tunable terahertz (THz) devices. The thickness of standard LC cells is in the order of the wavelength, requiring high driving voltages and allowing only a very slow modulation at THz frequencies. Here, we first present the concept of overcoupled metal-isolator-metal (MIM) cavities that allow for achieving simultaneously both very high phase difference between orthogonal electric field components and large reflectance. We then apply this concept to LC-infiltrated MIM-based metamaterials aiming at the design of electrically tunable THz polarization converters. The optimal operation in the overcoupled regime is provided by properly selecting the thickness of the LC cell. Instead of the LC natural birefringence, the polarization-dependent functionality stems from the optical anisotropy of ultrathin and deeply subwavelength MIM structures. The dynamic electro-optic control of the LC refractive index enables the spectral shift of the resonant mode and, consequently, the tuning of the phase difference between the two orthogonal field components. This tunability is further enhanced by the large confinement of the resonant electromagnetic fields within the MIM cavity. We show that for an appropriately chosen linearly polarized incident field, the polarization state of the reflected field at the target operation frequency can be continuously swept between the north and south pole of the Poincaré sphere. Using a rigorous Q-tensor model to simulate the LC electro-optic switching, we demonstrate that the enhanced light-matter interaction in the MIM resonant cavity allows the polarization converter to operate at driving voltages below 10 Volt and with millisecond switching times.

2.3 Å X-ray Structure of the Heme-Bound GAF Domain of Sensory Histidine Kinase DosT of Mycobacterium tuberculosis†

PubMed Central

Podust, Larissa M.; Ioanoviciu, Alexandra; Ortiz de Montellano, Paul R.

2009-01-01

Mycobacterium tuberculosis responds to the changes in environmental conditions through a two-component signaling system that detects reduced O2 tension and NO and CO exposures via the heme-binding GAF domains of two sensory histidine kinases, DosT and DevS, and the transcriptional regulator DosR. We report the first x-ray structure of the DosT heme-bound GAF domain (GAFDosT) in both oxy and deoxy forms determined to a resolution of 2.3 Å. In GAFDosT, heme binds in an orientation orthogonal to that in the PAS domains via a highly conserved motif including invariant H147 as a proximal heme axial ligand. On the distal side, invariant Y169 is in stacking interactions with the heme with its long axis parallel and the plane of the ring orthogonal to the heme plane. In one of the two protein monomers in an asymmetric unit, O2 binds as a second axial ligand to the heme iron, and is stabilized via an H-bond to the OH-group of Y169. The structure reveals two small tunnel-connected cavities and a pore on the protein surface that suggest a potential route for O2 access to the sensing pocket. The limited conformational differences observed between differently heme iron-ligated GAFDosT monomers in the asymmetric unit may result from crystal lattice limitations since atmospheric oxygen binding likely occurs in the crystal as a result of x-ray induced Fe3+ photoreduction during diffraction data collection. Determination of the GAFDosT structure sets up a framework in which to address ligand-recognition, discrimination, and signal propagation schemes in the heme-based GAF domains of biological sensors. PMID:18980385

Ethyl 2-(4-meth-oxy-phen-yl)-6-oxa-3-aza-bicyclo[3.1.0]hexane-3-carboxyl-ate: crystal structure and Hirshfeld analysis.

PubMed

Zukerman-Schpector, Julio; Sugiyama, Fabricia H; Garcia, Ariel L L; Correia, Carlos Roque D; Jotani, Mukesh M; Tiekink, Edward R T

2017-07-01

The title compound, C 14 H 17 NO 4 , features an epoxide-O atom fused to a pyrrolidyl ring, the latter having an envelope conformation with the N atom being the flap. The 4-meth-oxy-phenyl group is orthogonal to [dihedral angle = 85.02 (6)°] and lies to the opposite side of the five-membered ring to the epoxide O atom, while the N-bound ethyl ester group (r.m.s. deviation of the five fitted atoms = 0.0187 Å) is twisted with respect to the ring [dihedral angle = 17.23 (9)°]. The most prominent inter-actions in the crystal are of the type methine-C-H⋯O(carbon-yl) and these lead to the formation of linear supra-molecular chains along the c axis; weak benzene-C-H⋯O(epoxide) and methine-C-H⋯O(meth-oxy) inter-actions connect these into a three-dimensional architecture. The analysis of the Hirshfeld surface confirms the presence of C-H⋯O inter-actions in the crystal, but also the dominance of H⋯H dispersion contacts.

Shape transition of endotaxial islands growth from kinetically constrained to equilibrium regimes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhi-Peng, E-mail: LI.Zhipeng@nims.go.jp; Global Research Center for Environment and Energy based on Nanomaterials Science, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044; Tok, Engsoon

2013-09-01

Graphical abstract: - Highlights: • All Fe{sub 13}Ge{sub 8} islands will grow into Ge(0 0 1) substrate at temperatures from 350 to 675 °C. • Shape transition occurred from kinetically constrained to equilibrium regime. • All endotaxial islands can be clarified into two types. • The mechanisms of endotaxial growth and shape transition have been rationalized. - Abstract: A comprehensive study of Fe grown on Ge(0 0 1) substrates has been conducted at elevated temperatures, ranging from 350 to 675 °C. All iron germinide islands, with the same Fe{sub 13}Ge{sub 8} phase, grow into the Ge substrate with the samemore » epitaxial relationship. Shape transition occurs from small square islands (low temperatures), to elongated orthogonal islands or orthogonal nanowires (intermediate temperatures), and then finally to large square orthogonal islands (high temperatures). According to both transmission electron microscopy (TEM) and atomic force microscopy (AFM) investigations, all islands can be defined as either type-I or type-II. Type-I islands usually form at kinetically constrained growth regimes, like truncated pyramids. Type-II islands usually appear at equilibrium growth regimes forming a dome-like shape. Based on a simple semi-quantitative model, type-II islands have a lower total energy per volume than type-I, which is considered as the dominant mechanism for this type of shape transition. Moreover, this study not only elucidates details of endotaxial growth in the Fe–Ge system, but also suggests the possibility of controlled fabrication of temperature-dependent nanostructures, especially in materials with dissimilar crystal structures.« less

Preparation of uniaxially aligned TiO2 ultrafine fibers by electrospinning.

PubMed

Nien, Yu-Hsun; Tsai, Yan-Sheng; Wang, Jia-Yi; Syu, Shu-Ping

2012-11-01

TiO2 nanofibers are often produced by electrospinning using a collector consisting of two parallel electrodes. In this work, a high speed rotating drum was used as a collector to produce uniaxially aligned TiO2 ultrafine fibers. The apparatus to manufacture uniaxially aligned TiO2 ultrafine fiber consisted of a high-speed roller, a high-voltage power supply, a controllable syringe pump and a syringe. Titanium (IV) isopropoxide and polyvinylpyrrolidone were used as precursor and auxiliary, respectively. Titanium (IV) isopropoxide and polyvinylpyrrolidone were well mixed with other essential reagents to form the polymer solution. The polymer solution was poured into the syringe and pumped at various flow rates. The electrospun ultrafine fibers collected on the roller were heat treated up to 600 degrees C and the uniaxially aligned TiO2 ultrafine fibers were formed and characterized using scanning electron microscope and X-ray diffraction.

Synthesis and re-investigation of the elastic properties of single-crystal magnesium silicate perovskite

NASA Astrophysics Data System (ADS)

Yeganeh-Haeri, Amir

1994-12-01

Single crystals of MgSiO3 in the perovskite structure have been grown at a peak pressure of 26 GPa and temperature of approximately 1600 K using a 2000 ton uniaxial split-sphere high-pressure apparatus (USSA-2000). The specimens were subsequently utilized to re-investigate the single-crystal elastic properties of this phase at ambient conditions using laser Brillouin spectroscopy. The nine adiabatic single-crystal elastic stiffness coefficients, in units of GPa, are: C11 = 482, C22 = 537, C33 = 485, C44 = 204, C55 = 186, C66 = 147, C12 = 144, C13 = 147, C23 = 146. The resulting estimated Voigt-Reuss-Hill (VRH) aggregate isotropic elastic moduli are: K=264.0 and mu = 177.3 GPa, respectively. The single-crystal elastic moduli of MgSiO3 perovskite display a pattern that is elastically somewhat anisotropic. The maximum shear and compressional velocities are 18% and 7% greater than the minimum. The (010) crystallographic direction contains both the fastest and the slowest shear wave velocities. If, under lower mantle conditions, magnesium silicate perovskite grains were to become preferentially oriented, a shear wave propagating in the Earth's lower mantle could become polarized with two distinct velocities. The observed density and seismic parameter of the lower mantle over the depth range of 1000-2700 km are compared with the calculated profiles for a model mantle consisting of pure perovskite (Mg(0.89)Fe(0.11))SiO3 and for a mixture composed of silicate perovskite and magnesiowuestite using our new elasticity results. At present, literature values of thermoelastic properties for silicate perovskite, in particular, the coefficient of thermal expansion and the temperature derivative of the isothermal bulk modulus, vary widely. Because of this disparity, we find that mantle models ranging from pure perovskite to 'pyrolitic'-type compositions provide acceptable fits to the seismically observed density and velocity profiles of the Earth's lower mantle.

Disentangled solid state and metastable polymer melt; a solvent free route to high-modulus high-strength tapes and films of UHMWPE

NASA Astrophysics Data System (ADS)

Rastogi, Sanjay

2013-03-01

Ultra High Molecular Weight Polyethylene (UHMWPE) having average molar mass greater than a million g/mol is an engineering polymer. Due to its light-weight, high abrasion resistance and biocompatibility it is used for demanding applications such as body armour, prostheses etc. At present, because of its high melt viscosity to achieve the uniaxial/biaxial properties in the form of fibers/films the polymer is processed via solution route where nearly 95wt% of the solvent is used to process 5wt% of the polymer. In past several attempts have been made to process the polymer without using any solvent. However, compared to the solvent processing route the achieved mechanical properties were rather poor. Here we show that by controlled synthesis it is feasible to obtain UHMWPE that could be processed free of solvent to make uniaxial tapes and biaxial films, having unprecedented mechanical properties, exceeding that of the solution spun fibers. We address some of the fundamental aspects of chemistry, physics, rheology and processing for the development of desired morphological features to achieve the ultimate mechanical properties in tapes and films. The paper will also address the metastable melt state obtained on melting of the disentangled crystals and its implication on rheology in linear and nonlinear viscoelastic region. Solid state NMR studies will be applied to establish disentangled state in solid state to the polymerisation conditions. References: Macromolecules 2011, 44(14), 5558-5568; Nature Materials 2005, 4, 635-641; Phys Rev Lett 2006, 96(21), 218303-218205. The authors acknowledge financial support by the Dutch Polymer Institute.

Unexpected Magnetic Domain Behavior in LTP-MnBi

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, PK; Jin, S; Berkowitz, AE

2013-07-01

Low-temperature-phase MnBi (LTP-MnBi) has attracted much interest as a potential rare-earth-free permanent magnet material because of its high uniaxial magnetocrystalline anisotropy at room temperature, K approximate to 10(7) ergs/cc, and the unusual increase of anisotropy with increasing temperature, with an accompanying increasing coercive force (H-C) with temperature. However, due to the complex Mn-Bi phase diagram, bulk samples of LTP-MnBi with the optimum saturation moment, similar to 75-76 emu/g have been achieved only with zone-refined single crystals. We have prepared polycrystalline samples of LTP-MnBi by induction melting and annealing at 300 degrees C. The moment in 70 kOe is 73.5 emu/g,more » but H-C is only 50 Oe. This is quite surprising-the high saturation moment indicates the dominating presence of LTP-MnBi. Therefore, an H-C c of some significant fraction of 2K/M-S approximate to 30 kOe would seem reasonable in this polycrystalline sample. By examining "Bitter" patterns, we show that the sample is composed of similar to 50 - 100 mu m crystallites. The randomly oriented crystallites exhibit the variety of magnetic domain structures and orientations expected from the hexagonal-structured MnBi with its strong uniaxial anisotropy. Clearly, the reversal of magnetization in the sample proceeds by the low-field nucleation of reversed magnetization in each crystallite, rather than by a wall-pinning mechanism. When the annealed sample was milled into fine particles, H-C increased by several orders of magnitude, as expected.« less

Simulations of in situ x-ray diffraction from uniaxially compressed highly textured polycrystalline targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGonegle, David, E-mail: d.mcgonegle1@physics.ox.ac.uk; Wark, Justin S.; Higginbotham, Andrew

2015-08-14

A growing number of shock compression experiments, especially those involving laser compression, are taking advantage of in situ x-ray diffraction as a tool to interrogate structure and microstructure evolution. Although these experiments are becoming increasingly sophisticated, there has been little work on exploiting the textured nature of polycrystalline targets to gain information on sample response. Here, we describe how to generate simulated x-ray diffraction patterns from materials with an arbitrary texture function subject to a general deformation gradient. We will present simulations of Debye-Scherrer x-ray diffraction from highly textured polycrystalline targets that have been subjected to uniaxial compression, as maymore » occur under planar shock conditions. In particular, we study samples with a fibre texture, and find that the azimuthal dependence of the diffraction patterns contains information that, in principle, affords discrimination between a number of similar shock-deformation mechanisms. For certain cases, we compare our method with results obtained by taking the Fourier transform of the atomic positions calculated by classical molecular dynamics simulations. Illustrative results are presented for the shock-induced α–ϵ phase transition in iron, the α–ω transition in titanium and deformation due to twinning in tantalum that is initially preferentially textured along [001] and [011]. The simulations are relevant to experiments that can now be performed using 4th generation light sources, where single-shot x-ray diffraction patterns from crystals compressed via laser-ablation can be obtained on timescales shorter than a phonon period.« less

Simulations of in situ x-ray diffraction from uniaxially compressed highly textured polycrystalline targets

DOE PAGES

McGonegle, David; Milathianaki, Despina; Remington, Bruce A.; ...

2015-08-11

A growing number of shock compression experiments, especially those involving laser compression, are taking advantage of in situ x-ray diffraction as a tool to interrogate structure and microstructure evolution. Although these experiments are becoming increasingly sophisticated, there has been little work on exploiting the textured nature of polycrystalline targets to gain information on sample response. Here, we describe how to generate simulated x-ray diffraction patterns from materials with an arbitrary texture function subject to a general deformation gradient. We will present simulations of Debye-Scherrer x-ray diffraction from highly textured polycrystalline targets that have been subjected to uniaxial compression, as maymore » occur under planar shock conditions. In particular, we study samples with a fibre texture, and find that the azimuthal dependence of the diffraction patterns contains information that, in principle, affords discrimination between a number of similar shock-deformation mechanisms. For certain cases, we compare our method with results obtained by taking the Fourier transform of the atomic positions calculated by classical molecular dynamics simulations. Illustrative results are presented for the shock-induced α–ϵ phase transition in iron, the α–ω transition in titanium and deformation due to twinning in tantalum that is initially preferentially textured along [001] and [011]. In conclusion, the simulations are relevant to experiments that can now be performed using 4th generation light sources, where single-shot x-ray diffraction patterns from crystals compressed via laser-ablation can be obtained on timescales shorter than a phonon period.« less

Evidence for several dipolar quasi-invariants in liquid crystals

NASA Astrophysics Data System (ADS)

Bonin, C. J.; González, C. E.; Segnorile, H. H.; Zamar, R. C.

2013-10-01

The quasi-equilibrium states of an observed quantum system involve as many constants of motion as the dimension of the operator basis which spans the blocks of all the degenerate eigenvalues of the Hamiltonian that drives the system dynamics, however, the possibility of observing such quasi-invariants in solid-like spin systems in Nuclear Magnetic Resonance (NMR) is not a strictly exact prediction. The aim of this work is to provide experimental evidence of several quasi-invariants, in the proton NMR of small spin clusters, like nematic liquid crystal molecules, in which the use of thermodynamic arguments is not justified. We explore the spin states prepared with the Jeener-Broekaert pulse sequence by analyzing the time-domain signals yielded by this sequence as a function of the preparation times, in a variety of dipolar networks, solids, and liquid crystals. We observe that the signals can be explained with two dipolar quasi-invariants only within a range of short preparation times, however at longer times liquid crystal signals show an echo-like behaviour whose description requires assuming more quasi-invariants. We study the multiple quantum coherence content of such signals on a basis orthogonal to the z-basis and see that such states involve a significant number of correlated spins. Therefore, we show that the NMR signals within the whole preparation time-scale can only be reconstructed by assuming the occurrence of multiple quasi-invariants which we experimentally isolate.

Dual-polarized light-field imaging micro-system via a liquid-crystal microlens array for direct three-dimensional observation.

PubMed

Xin, Zhaowei; Wei, Dong; Xie, Xingwang; Chen, Mingce; Zhang, Xinyu; Liao, Jing; Wang, Haiwei; Xie, Changsheng

2018-02-19

Light-field imaging is a crucial and straightforward way of measuring and analyzing surrounding light worlds. In this paper, a dual-polarized light-field imaging micro-system based on a twisted nematic liquid-crystal microlens array (TN-LCMLA) for direct three-dimensional (3D) observation is fabricated and demonstrated. The prototyped camera has been constructed by integrating a TN-LCMLA with a common CMOS sensor array. By switching the working state of the TN-LCMLA, two orthogonally polarized light-field images can be remapped through the functioned imaging sensors. The imaging micro-system in conjunction with the electric-optical microstructure can be used to perform polarization and light-field imaging, simultaneously. Compared with conventional plenoptic cameras using liquid-crystal microlens array, the polarization-independent light-field images with a high image quality can be obtained in the arbitrary polarization state selected. We experimentally demonstrate characters including a relatively wide operation range in the manipulation of incident beams and the multiple imaging modes, such as conventional two-dimensional imaging, light-field imaging, and polarization imaging. Considering the obvious features of the TN-LCMLA, such as very low power consumption, providing multiple imaging modes mentioned, simple and low-cost manufacturing, the imaging micro-system integrated with this kind of liquid-crystal microstructure driven electrically presents the potential capability of directly observing a 3D object in typical scattering media.

Rheology of Pure Glasses and Crystal Bearing Melts: from the Newtonian Field to the Brittle Onset

NASA Astrophysics Data System (ADS)

Cordonnier, B.; Caricchi, L.; Pistone, M.; Castro, J. M.; Hess, K.; Dingwell, D. B.

2010-12-01

The brittle-ductile transition remains a central question of modern geology. If rocks can be perceived as a granular flow on geological time-scale, their behavior is brittle in dynamic areas. Understanding rock failure conditions is the main parameter in mitigating geological risks, more specifically the eruptive style transitions from effusive to explosive. If numerical simulations are the only way to fully understanding the physical processes involved, we are in a strong need of an experimental validation of the proposed models. here we present results obtained under torsion and uni-axial compression on both pure glasses and crystal bearing melts. We characterized the brittle onset of two phases magmas from 0 to 65% crystals. The strain-rates span a 5 orders magnitude range, from the Newtonian flow to the Brittle field (10-5 - 100 s-1). We particularly emphasize the time dependency of the measured rheology. The materials tested are a borosilicate glass from the National Bureau of Standards, a natural sample from Mt Unzen volcano and a synthetic sample. The lattest is an HPG8 melt with 7% sodium mole excess. The particles are quasi-isometric corundum crystalschosen for their shape and integrity under the stress range investigated. The crystal fraction ranges from 0 to 0.65. Concerning pure magmas, we recently demonstrated that the material passes from a Newtonian to a non-Nemtonian behavior with increasing strain-rate. This onset can mostly be explained by viscous-heating effects. However, for even greater strain-rates, the material cracks and finally fail. The brittle onset is here explained with the visco-elastic theory and corresponds to a Deborah number greater than 10-2. Concerning crystal bearing melts the departure from the Newtonian state is characterized by two effects: a shear-thinning and a time weakening effect. The first one is instantaneous and loading-unloading cyclic tests suggest an elastic contribution of the crystal network. The second one reflects a structural modification of the material (e.g. crystal reorganization, crystal failure, micro-cracking). In the special case presented here, the time weakening effect is the translation of plagioclase breaking during the magma flow. About the ultimate failure of the sample, crystal bearing melts appear to follow the general visco -elastic theory. However a crystal contribution has been here detected and corelate with smaller Deborah numbers before failure. Our observation offer a new vision on volcanic transition and an implication on the 90-95 eruptive crisis of Mt Unzen volcano is presented here.

Beam shaping with vectorial vortex beams under low numerical aperture illumination condition

NASA Astrophysics Data System (ADS)

Dai, Jianning; Zhan, Qiwen

2008-08-01

In this paper we propose and demonstrate a novel beam shaping method using vectorial vortex beam. A vectorial vortex beam is laser beam with polarization singularity in the beam cross section. This type of beams can be decomposed into two orthogonally polarized components. Each of the polarized components could have different vortex characteristics, and consequently, different intensity distribution when focused by lens. Beam shaping in the far field can be achieved by adjusting the relative weighing of these two components. As one example, we study the vectorial vortex that consists of a linearly polarized Gaussian component and a vortex component polarized orthogonally. When such a vectorial vortex beam is focus by low NA lens, the Gaussian component gives rise to a focal intensity distribution with a solid centre while the vortex component gives rise to a donut distribution with hollow dark center. The shape of the focus can be continuously varied by continuously adjusting the relative weight of the two components. Under appropriate conditions, flat top focusing can be obtained. We experimentally demonstrate the creation of such beams with a liquid crystal spatial light modulator. Flattop focus obtained by vectorial vortex beams with topological charge of +1 has been obtained.

Tunable Fano resonance using weak-value amplification with asymmetric spectral response as a natural pointer

NASA Astrophysics Data System (ADS)

Singh, Ankit K.; Ray, Subir K.; Chandel, Shubham; Pal, Semanti; Gupta, Angad; Mitra, P.; Ghosh, N.

2018-05-01

Weak measurement enables faithful amplification and high-precision measurement of small physical parameters and is under intensive investigation as an effective tool in metrology and for addressing foundational questions in quantum mechanics. Here we demonstrate weak-value amplification using the asymmetric spectral response of Fano resonance as the pointer arising naturally in precisely designed metamaterials, namely, waveguided plasmonic crystals. The weak coupling between the polarization degree of freedom and the spectral response of Fano resonance arises due to a tiny shift in the asymmetric spectral response between two orthogonal linear polarizations. By choosing the preselected and postselected polarization states to be nearly mutually orthogonal, we observe both real and imaginary weak-value amplifications manifested as a spectacular shift of the Fano-resonance peak and narrowing (or broadening) of the resonance linewidth, respectively. The remarkable control and tunability of Fano resonance in a single device enabled by weak-value amplification may enhance active Fano-resonance-based applications in the nano-optical domain. In general, weak measurements using Fano-type spectral response broadens the domain of applicability of weak measurements using natural spectral line shapes as a pointer in a wide range of physical systems.

Hyperspectral retrieval of surface reflectances: A new scheme

NASA Astrophysics Data System (ADS)

Thelen, Jean-Claude; Havemann, Stephan

2013-05-01

Here, we present a new prototype algorithm for the simultaneous retrieval of the atmospheric profiles (temperature, humidity, ozone and aerosol) and the surface reflectance from hyperspectral radiance measurements obtained from air/space borne, hyperspectral imagers. The new scheme, proposed here, consists of a fast radiative transfer code, based on empirical orthogonal functions (EOFs), in conjunction with a 1D-Var retrieval scheme. The inclusion of an 'exact' scattering code based on spherical harmonics, allows for an accurate treatment of Rayleigh scattering and scattering by aerosols, water droplets and ice-crystals, thus making it possible to also retrieve cloud and aerosol optical properties, although here we will concentrate on non-cloudy scenes.

Broadband spectral shaping in regenerative amplifier based on modified polarization-encoded chirped pulse amplification

NASA Astrophysics Data System (ADS)

Wang, Xinliang; Lu, Xiaoming; Liu, Yanqi; Xu, Yi; Wang, Cheng; Li, Shuai; Yu, Linpeng; Liu, Xingyan; Liu, Keyang; Xu, Rongjie; Leng, Yuxin

2018-06-01

We present an intra-cavity spectral shaping method to suppress the spectral narrowing in a Ti:sapphire (Ti:Sa) regenerative amplifier. The spectral shaping is realized by manipulating the stored energies of two Ti:Sa crystals with orthogonal c-axes, changing the length of a quartz plate, and rotating a broadband achromatic half-wave plate. Using this method, in our proof-of-concept experiment, an 84-nm-(FWHM)-broadband amplified pulse with an energy gain larger than 106 is obtained, which supports a 17.8 fs Fourier-transform-limited pulse duration. The pulse is compressed to 18.9 fs.

Einstein-Podolsky-Rosen-Bohm experiment and Bell inequality violation using Type 2 parametric down conversion

NASA Technical Reports Server (NTRS)

Kiess, Thomas E.; Shih, Yan-Hua; Sergienko, A. V.; Alley, Carroll O.

1994-01-01

We report a new two-photon polarization correlation experiment for realizing the Einstein-Podolsky-Rosen-Bohm (EPRB) state and for testing Bell-type inequalities. We use the pair of orthogonally-polarized light quanta generated in Type 2 parametric down conversion. Using 1 nm interference filters in front of our detectors, we observe from the output of a 0.5mm beta - BaB2O4 (BBO) crystal the EPRB correlations in coincidence counts, and measure an associated Bell inequality violation of 22 standard deviations. The quantum state of the photon pair is a polarization analog of the spin-1/2 singlet state.

A π-gel scaffold for assembling fullerene to photoconducting supramolecular rods

PubMed Central

Nair, Vishnu Sukumaran; Mukhopadhyay, Rahul Dev; Saeki, Akinori; Seki, Shu; Ajayaghosh, Ayyappanpillai

2016-01-01

Nonequilibrium self-assembly of molecules holds a huge prospect as a tool for obtaining new-generation materials for future applications. Crystallization of neutral molecules within a supramolecular gel matrix is one example in which two nonequilibrium processes occur orthogonal to each other. On the other hand, electronically interacting donor-acceptor two-component systems are expected to form phase-miscible hybrid systems. Contrary to the expectation, we report the behavior of a π-gel, derived from oligo(p-phenylenevinylene), OPVA, as a scaffold for the phase separation and crystallization of fullerene (C60) to supramolecular rods with increased transient photoconductivity (φƩμmax = 2.4 × 10−4 cm2 V−1 s−1). The C60 supramolecular rods in the π-gel medium exhibited high photocurrent in comparison to C60 loaded in a non–π-gel medium. This finding provides an opportunity for large-scale preparation of micrometer-sized photoconducting rods of fullerenes for device application. PMID:27679815

Redox potential trend with transition metal elements in lithium-ion battery cathode materials

NASA Astrophysics Data System (ADS)

Chen, Zhenlian; Li, Jun

2013-03-01

First-principles calculations are performed to investigate the relationship between the intrinsic voltage and element-lattice for the popular transition metal oxides and polyoxyanionic compounds as cathode materials for lithium-ion batteries. A V-shape redox potential in olivine phosphates LiMPO4 and orthogonal silicates Li2MSiO4 (M =Mn, Fe, Co, Ni), and an N-shape one in layered oxides LiMO2 (M =Mn, Fe, Co, Ni, Cu) relative to transition metal M elements are found to be inversely characteristic of electronic energy contribution, which costs energy in the lithiation process and is defined as electron affinity. The maxima of electron affinity, locating at different elements for different types of crystal lattices are determined by delectronic configurations that cross the turning point of a full occupancy of electronic bands, which is determined by the cooperative effect of crystal field splitting and intraionic exchange interactions. The Ningbo Key Innovation Team, National Natural Science Foundation of China, Postdoctoral Foundation of China

Experimental characterization of composites. [load test methods

NASA Technical Reports Server (NTRS)

Bert, C. W.

1975-01-01

The experimental characterization for composite materials is generally more complicated than for ordinary homogeneous, isotropic materials because composites behave in a much more complex fashion, due to macroscopic anisotropic effects and lamination effects. Problems concerning the static uniaxial tension test for composite materials are considered along with approaches for conducting static uniaxial compression tests and static uniaxial bending tests. Studies of static shear properties are discussed, taking into account in-plane shear, twisting shear, and thickness shear. Attention is given to static multiaxial loading, systematized experimental programs for the complete characterization of static properties, and dynamic properties.

Experimental investigation of cyclic thermomechanical deformation in torsion

NASA Technical Reports Server (NTRS)

Ellis, John R.; Castelli, Michael G.; Bakis, Charles E.

1992-01-01

An investigation of thermomechanical testing and deformation behavior of tubular specimens under torsional loading is described. Experimental issues concerning test accuracy and control specific to thermomechanical loadings under a torsional regime are discussed. A series of shear strain-controlled tests involving the nickel-base superalloy Hastelloy X were performed with various temperature excursions and compared to similar thermomechanical uniaxial tests. The concept and use of second invariants of the deviatoric stress and strain tensors as a means of comparing uniaxial and torsional specimens is also briefly presented and discussed in light of previous thermomechanical tests conducted under uniaxial conditions.

Electromagnetic emission memory phenomena related to LiF ionic crystal deformation

NASA Astrophysics Data System (ADS)

Mavromatou, C.; Tombras, G. S.; Ninos, D.; Hadjicontis, V.

2008-04-01

During the uniaxial compression of LiF ionic monocrystals, acoustic and electromagnetic emissions (EME) are detected. We observed that when the compression is performed in successive loading, unloading cycles and these emissions are being monitored, no new emissions will occur unless the maximum stress of the previous cycle is exceeded, meaning that the material presents memory characteristics. This is observed not only for the acoustic emission (AE), which is the well known Kaiser effect, but for the EME as well. In other words, the material appears to memorize and reveal the previously maximum stress it suffered while being deformed. The importance of an electromagnetic memory feature of a material can be related to various applications in material science, especially when the detection of AE is not feasible or gives false alert. Such cases may very well be earthquakes' predictive indications, monitoring of mines' stability, imminent landslides, etc.

Grain-scale investigations of deformation heterogeneities in aluminum alloys

NASA Astrophysics Data System (ADS)

Güler, Baran; Şimşek, Ülke; Yalçınkaya, Tuncay; Efe, Mert

2018-05-01

The anisotropic deformation of Aluminum alloys at micron scale exhibits localized deformation, which has negative implications on the macroscale mechanical and forming behavior. The scope of this work is twofold. Firstly, micro-scale deformation heterogeneities affecting forming behavior of aluminum alloys is investigated through experimental microstructure analysis at large strains and various strain paths. The effects of initial texture, local grain misorientation, and strain paths on the strain localizations are established. In addition to uniaxial tension condition, deformation heterogeneities are also investigated under equibiaxial tension condition to determine the strain path effects on the localization behavior. Secondly, the morphology and the crystallographic data obtained from the experiments is transferred to Abaqus software, in order to predict both macroscopic response and the microstructure evolution though crystal plasticity finite element simulations. The model parameters are identified through the comparison with experiments and the capability of the model to capture real material response is discussed as well.

Spin angular momentum induced by optical quasi-phonons activated in birefringent uniaxial crystals

NASA Astrophysics Data System (ADS)

Mohamadou, B.; Maïmounatou, B.; Erasmus, R. M.

2017-09-01

The present report formally establishes the expression of the angular momentum of the quasi-phonons induced by linearly polarized light. The transferred mechanical torque due to phonons is then determined from the spin angular momentum and is shown to be measurable from Raman scattering experiments. To investigate this, the electric field due the excited dipoles and the associated macroscopic dielectric polarization vectors were first calculated using a lattice dynamical model in order to derive in a second step the analytical expression of the angular momentum density arising from the inelastic light scattering by quasi-phonons. The numerical results of the calculated angle dependent mode electric fields and the induced spin angular moments as well as the transferred torques were analyzed with regard to some typical behaviors of the interacting modes and it is shown that the fluctuations of the effective charges is their main origin.

Strain-modulated anisotropy of quantum transport properties in single-layer silicene: Spin and valley filtering

NASA Astrophysics Data System (ADS)

Farokhnezhad, M.; Esmaeilzadeh, M.; Shakouri, Kh.

2017-11-01

Strained two-dimensional crystals often offer novel physical properties that are usable to improve their electronic performance. Here we show by the theory of elasticity combined with the tight-binding approximation that local strains in silicene can open up new prospects for generating fully polarized spin and valley currents. The trajectory of electrons flowing through locally strained regions obeys the same behavior as light waves propagating in uniaxial anisotropic materials. The refraction angle of electrons at local strain boundaries exhibits a strong dependence on the valley degree of freedom, allowing for valley filtering based on the strain direction. The ability to control the spin polarization direction additionally requires a perpendicular electric field to be involved in combination with the local strain. Further similarities of the problem with optics of anisotropic materials are elucidated and possible applications in spin- and valleytronic nanodevices are discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aldosary, Mohammed; Li, Junxue; Tang, Chi

30-80 nm thick yttrium iron garnet (YIG) films are grown by pulsed laser deposition on a 5 nm thick sputtered Pt atop gadolinium gallium garnet substrate (GGG) (110). Upon post-growth rapid thermal annealing, single crystal YIG(110) emerges as if it were epitaxially grown on GGG(110) despite the presence of the intermediate Pt film. The YIG surface shows atomic steps with the root-mean-square roughness of 0.12 nm on flat terraces. Both Pt/YIG and GGG/Pt interfaces are atomically sharp. The resulting YIG(110) films show clear in-plane uniaxial magnetic anisotropy with a well-defined easy axis along 〈001〉 and a peak-to-peak ferromagnetic resonance linewidth of 7.5 Oe atmore » 9.32 GHz, similar to YIG epitaxially grown on GGG. Both spin Hall magnetoresistance and longitudinal spin Seebeck effects in the inverted bilayers indicate excellent Pt/YIG interface quality.« less

New structures of Fe3S for rare-earth-free permanent magnets

NASA Astrophysics Data System (ADS)

Yu, Shu; Zhao, Xin; Wu, Shunqing; Nguyen, Manh Cuong; Zhu, Zi-zhong; Wang, Cai-Zhuang; Ho, Kai-Ming

2018-02-01

We applied an adaptive genetic algorithm (AGA) to search for low-energy crystal structures of Fe3S. A number of structures with energies lower than that of the experimentally reported Pnma and I-4 structures have been obtained from our AGA searches. These low-energy structures can be classified as layer-motif and column-motif structures. In the column-motif structures, Fe atoms self-assemble into rods with a bcc type of underlying lattice, which are separated by the holes terminated by S atoms. In the layer-motif structures, the bulk Fe is broken into slabs of several layers passivated by S atoms. Magnetic property calculations showed that the column-motif structures exhibit reasonably high uniaxial magnetic anisotropy. In addition, we examined the effect of Co doping to Fe3S and found that magnetic anisotropy can be enhanced through Co doping.

Elastic anomaly and aging of new type of incommensurate phase transition in ferroelectric barium sodium niobate

NASA Astrophysics Data System (ADS)

Christy, Yohanes; Matsumoto, Kazuya; Kojima, Seiji

2015-07-01

The lattice instability of the incommensurate (IC) phase transition of uniaxial ferroelectric Ba2NaNb5O15 (BNN) was investigated by micro-Brillouin scattering. Spectra of the longitudinal acoustic (LA) mode were observed from room temperature to 750 K. In the vicinity of the IC phase transition temperature TIC = 573 K, elastic anomalies in the form of a sharp peak in the sound velocity and thermal hysteresis during the heating and cooling cycle were observed. During this transition, the crystal point group changed from tetragonal 4mm to orthorhombic 2mm along with the IC modulation. In order to deepen our understanding of the thermal hysteresis, aging experiment in the IC phase was conducted. We can conclude that the appearance of thermal hysteresis related to the relaxation of ferroelastic strain is related to the feature of the new type III IC phase transition mechanism of BNN.

Molecular-dynamic study of the influence of temperature on the process of metallic nanocrystals fracture

NASA Astrophysics Data System (ADS)

Demianenko, A. M.; Golovnev, I. F.; Golovneva, E. I.

2017-10-01

The behavior of the fracture processes of a metal nanostructure under deformation in the temperature range 0-550 K was investigated by the molecular dynamics method. An ideal copper crystal was used as a sample in the form of a rectangular parallelepiped with the number of crystalline cells nx = 50, ny = nz = 5 along the corresponding axes. The deformation was carried out by uniaxial stretching of the sample between two clamps (movable and fixed) with a constant speed. The stretching rate varied from 50 to 500 m/s. To describe the interatomic interaction, the Voter many-body EAM potential was used. The effect of temperature on macro characteristics of fracture (the fracture place, the number of fragments formed, the stress on the clamps), and also on the kinetic characteristics (fracture rate, time of formation of maximum stress values on the clamps, mass transfer phenomena and formation of the fracture neck) were revealed.

New structures of Fe3S for rare-earth-free permanent magnets

DOE PAGES

Yu, Shu; Zhao, Xin; Wu, Shunqing; ...

2018-02-25

We applied adaptive genetic algorithm (AGA) to search for low-energy crystal structures of Fe 3S. A number of structures with energies lower than that of the experimentally reported Pnma and I-4 structures have been obtained from our AGA searches. These low-energy structures can be classified as layer-motif and column-motif structures. In the column-motif structures, Fe atoms self-assemble into rods with bcc type of underlying lattice, which are separated by the holes terminated by S atoms. In the layer-motif structures, the bulk Fe is broken into slabs of several layers passivated by S atoms. Magnetic properties calculations showed that the column-motifmore » structures exhibit reasonably high uniaxial magnetic anisotropy. In addition, we examined the effect of Co doping to Fe 3S and found magnetic anisotropy can be enhanced through Co doping.« less

Lattice-level observation of the elastic-to-plastic relaxation process with subnanosecond resolution in shock-compressed Ta using time-resolved in situ Laue diffraction

DOE PAGES

Wehrenberg, C. E.; Comley, A. J.; Barton, N. R.; ...

2015-09-29

We report direct lattice level measurements of plastic relaxation kinetics through time-resolved, in-situ Laue diffraction of shock-compressed single-crystal [001] Ta at pressures of 27-210 GPa. For a 50 GPa shock, a range of shear strains is observed extending up to the uniaxial limit for early data points (<0.6 ns) and the average shear strain relaxes to a near steady state over ~1 ns. For 80 and 125 GPa shocks, the measured shear strains are fully relaxed already at 200 ps, consistent with rapid relaxation associated with the predicted threshold for homogeneous nucleation of dislocations occurring at shock pressure ~65 GPa.more » The relaxation rate and shear stresses are used to estimate the dislocation density and these quantities are compared to the Livermore Multiscale Strength model as well as various molecular dynamics simulations.« less

Symmetry breaking and electrical frustration during tip-induced polarization switching in the non-polar cut of lithium niobate single crystals

DOE PAGES

Ievlev, Anton; Alikin, Denis O.; Morozovska, A. N.; ...

2014-12-15

Polarization switching in ferroelectric materials is governed by a delicate interplay between bulk polarization dynamics and screening processes at surfaces and domain walls. Here we explore the mechanism of tip-induced polarization switching in the non-polar cuts of uniaxial ferroelectrics. In this case, in-plane component of polarization vector switches, allowing for detailed observations of resultant domain morphologies. We observe surprising variability of resultant domain morphologies stemming from fundamental instability of formed charged domain wall and associated electric frustration. In particular, we demonstrate that controlling vertical tip position allows the polarity of the switching to be controlled. This represents very unusual formmore » of symmetry breaking where mechanical motion in vertical direction controls the lateral domain growth. The implication of these studies for ferroelectric devices and domain wall electronics are discussed.« less

Measured iron-gallium alloy tensile properties under magnetic fields

NASA Astrophysics Data System (ADS)

Yoo, Jin-Hyeong; Flatau, Alison B.

2004-07-01

Tension testing is used to identify Galfenol material properties under low level DC magnetic bias fields. Dog bone shaped specimens of single crystal Fe100-xGax, where 17<=x<=33, underwent tensile testing along two crystalographic axis orientations, [110] and [100]. The material properties being investigated and calculated from measured quantities are: Young's modulus and Poisson's ratio. Data are presented that demonstrate the dependence of these material properties on applied magnetic field levels and provide a preliminary assessment of the trends in material properties for performance under varied operating conditions. The elastic properties of Fe-Ga alloys were observed to be increasingly anisotropic with rising Ga content for the stoichiometries examined. The largest elastic anisotropies were manifested in [110] Poisson's ratios of as low as -0.63 in one specimen. This negative Poisson's ratio creates a significant in-plane auxetic behavior that could be exploited in applications that capitalize on unique area effects produced under uniaxial loading.

Second harmonic generation of off axial vortex beam in the case of walk-off effect

NASA Astrophysics Data System (ADS)

Chen, Shunyi; Ding, Panfeng; Pu, Jixiong

2016-07-01

Process of off axial vortex beam propagating in negative uniaxial crystal is investigated in this work. Firstly, we get the formulae of the normalized electric field and calculate the location of vortices for second harmonic beam in two type of phase matching. Then, numerical analysis verifies that the intensity distribution and location of vortices of the first order original vortex beam depend on the walk-off angle and off axial magnitude. It is shown that, in type I phase matching, the distribution of vortices is symmetrical about the horizontal axis, the separation distance increases as the off axial magnitude increases or the off axial magnitude deceases. However, in type II phase matching, the vortices are symmetrical along with some vertical axis, and increase of the walk-off angle or off axial magnitude leads to larger separation distance. Finally, the case of high order original off axial vortex beam is also investigated.

Large Strain Behaviour of ZEK100 Magnesium Alloy at Various Strain Rates

NASA Astrophysics Data System (ADS)

Lévesque, Julie; Kurukuri, Srihari; Mishra, Raja; Worswick, Michael; Inal, Kaan

A constitutive framework based on a rate-dependent crystal plasticity theory is employed to simulate large strain deformation in hexagonal closed-packed metals that deform by slip and twinning. The model allows the twinned zones and the parent matrix to rotate independently. ZEK100 magnesium alloy sheets which significant texture weakening compared to AZ31 sheets are investigated using the model. There is considerable in-plane anisotropy and tension compression asymmetry in the flow behavior of ZEK100. Simulations of uniaxial tension in different directions at various strain rates and the accompanying texture evolution are performed and they are in very good agreement with experimental measurements. The effect of strain rate on the activation of the various slip systems and twinning show that differences in the strain rate dependence of yield stress and Rvalues in ZEK100 have their origin in the activation of different deformation mechanisms.

Core structure and dynamics of non-Abelian vortices in a biaxial nematic spinor Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Borgh, Magnus O.; Ruostekoski, Janne

2016-05-01

We demonstrate that multiple interaction-dependent defect core structures as well as dynamics of non-Abelian vortices can be realized in the biaxial nematic (BN) phase of a spin-2 atomic Bose-Einstein condensate (BEC). An experimentally simple protocol may be used to break degeneracy with the uniaxial nematic phase. We show that a discrete spin-space symmetry in the core may be reflected in a breaking of its spatial symmetry. The discrete symmetry of the BN order parameter leads to non-commuting vortex charges. We numerically simulate reconnection of non-Abelian vortices, demonstrating formation of the obligatory rung vortex. In addition to atomic BECs, non-Abelian vortices are theorized in, e.g., liquid crystals and cosmic strings. Our results suggest the BN spin-2 BEC as a prime candidate for their realization. We acknowledge financial support from the EPSRC.

Calculation of gyrotropy coefficients in media with low-pitch helical structures

NASA Astrophysics Data System (ADS)

Dhaouadi, H.; Trabelsi, F.; Riahi, O.; Othman, T.

2018-04-01

Chiral smectic liquid crystals are known for their huge optical activity due to the precession of the anisotropic dielectric tensor around the helicoidal axis. For an oblique direction of the propagating wave, the helix acts as a grating which splits an incident beam in different directions as long as the pitch is not too small with respect to the light wavelength. When the pitch of the helix is smaller than the wavelength, the effect of the helix is a renormalization of the gyrotropic coefficients (g⊥ and g∥) of the resulting uniaxial medium. We report here on a method to compute these coefficients in that limit. Resolution of the Maxwell equations, using a perturbative approach, gives expressions for g⊥ and g∥ as a power development of the ratio (p/λ ) . The various terms of these developments coincide with the approximate expressions of these coefficients known in the literature.

High-temperature ultrasonic characterization of the mechanical and microstructural behavior of a fibrous composite with a magnesium lithium aluminum silicate glass-ceramic matrix

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cutard, T.; Huger, M.; Fargeot, D.

The mechanical behavior and the microstructural modifications of a SiC-fiber-reinforced magnesium lithium aluminum silicate glass-ceramic (SiC/MASL) have been characterized by ultrasonic measurement of uniaxial Young`s modulus at high temperature. Under vacuum, long isothermal agings in the 750--1,000 C temperature range have shown matrix modifications in terms of crystallization of residual glassy phases, and of phase transformations in the Li{sub 2}O-Al{sub 2}O{sub 3}-SiO{sub 2} system. In air, long isothermal agings performed under the same conditions have led to the same matrix transformations but in competition with oxidation mechanisms of the carbon fiber-matrix interphase. All of these matrix and/or interface transformations havemore » been confirmed by X-ray diffraction analysis, scanning electron microscopy, scanning acoustic microscopy, and microindentation tests.« less

Magnetic properties of epitaxial bismuth ferrite-garnet mono- and bilayers

NASA Astrophysics Data System (ADS)

Semuk, E. Yu.; Berzhansky, V. N.; Prokopov, A. R.; Shaposhnikov, A. N.; Karavainikov, A. V.; Salyuk, O. Yu.; Golub, V. O.

2015-11-01

Magnetic properties of Bi1.5Gd1.5Fe4.5Al0.5O12 (84 nm) and Bi2.8Y0.2Fe5O12 (180 nm) films epitaxially grown on gallium-gadolinium garnet (GGG) single crystal (111) substrate as well as Bi1.5Gd1.5Fe4.5Al0.5O12/Bi2.8Y0.2Fe5O12 bilayer were investigated using ferromagnetic resonance technique. The mismatch of the lattice parameters of substrate and magnetic layers leads to formation of adaptive layers which affect on the high order anisotropy constant of the films but practically do not affect on uniaxial perpendicular magnetic anisotropy The magnetic properties of the bilayer film were explained in supposition of strong exchange coupling between magnetic layers taking into account film-film and film-substrate elastic interaction.

Correlations of oriented ice and precipitation in marine midlatitude low clouds using collocated CloudSat, CALIOP, and MODIS observations

NASA Astrophysics Data System (ADS)

Ross, Alexa; Holz, Robert E.; Ackerman, Steven A.

2017-08-01

In April 2006, the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) launched aboard the CALIPSO satellite and into the A-Train constellation of satellites with its transmitter pointed near nadir. This proved problematic due to specular reflection from horizontally oriented ice crystals occurring more frequently than expected. Because the specular backscatter from oriented ice crystals has large attenuated backscatter and almost no depolarization, the standard lidar inversions cannot be applied. To mitigate this issue, the CALIOP transmitter was moved to 3° off nadir in November 2007. Though problematic for global CALIOP retrievals, the sensitivity to oriented ice during the first year of observations provides a unique data set to investigate scenes of this ice crystal signature. This study focuses on the CALIOP-oriented signature that occurs in midlatitude ocean regions whose cloud tops are relatively warm and low, existing below 6 km. A significant seasonal dependence is found in the Northern Hemisphere with up to 19% of clouds below 6 km yielding specular reflection by CALIOP during the colder months. In contrast, the Southern Hemisphere lacks such seasonal dependence and sees fewer oriented ice crystals. Using collocated CloudSat observations with both CALIOP and Moderate Resolution Imaging Spectroradiometer (MODIS), we investigate the correlations of the oriented signature with MODIS cloud properties. Comparing with CloudSat precipitation retrievals, we find that the oriented signature is strongly correlated with surface precipitation with 64% of CALIOP-oriented ice crystal cases precipitating compared to 40% for nonoriented cases.

Optical-strain characteristics of anisotropic polymer films fabricated from a liquid crystal diacrylate

NASA Astrophysics Data System (ADS)

Escuti, Michael J.; Cairns, Darran R.; Crawford, Gregory P.

2004-03-01

The optomechanical characteristics of oriented polymer films made from a photopolymerizable liquid crystal diacrylate (BASF LC242) were examined, with general implications for oriented films of similar materials being used and considered for display-component applications. The birefringence of these uniaxial films before and after polymerization was determined by measuring the retardation between crossed polarizers, (resulting in Δn=0.142±0.002 at 633 nm for the cured polymer films). Optical-strain characteristics were also determined by measuring the transmittance of the films between crossed polarizers at two wavelengths (612 and 633 nm) during the application of a monotonically increasing tensile strain. Under the conservative assumption that Poisson's ratio is constant for the relatively small strains in our experiment, we develop a strained-waveplate model to detect changes in birefringence directly from the modulation in transmittance with increasing strain. We show that strain applied along the axis of the polymer chains did not substantially affect the birefringence, and strain applied perpendicularly caused only a slight decrease (˜1% decrease for 10% strain). These results highlight the robustness of fully polymerized reactive mesogen optical films to withstand the moderate strains anticipated during manufacturing processes and in-service deformation caused by bending or impact.

Electrically activated artificial muscles made with liquid crystal elastomers

NASA Astrophysics Data System (ADS)

Shahinpoor, Mohsen

2000-06-01

Composites of monodomain nematic liquid crystal elastomers and a conducting material distributed within their network are shown to exhibit large deformations, i.e. contraction, expansion, bending with strains of over 200% and appreciable force, by Joule heating through electrical activation. The electrical activation of the conducting material induces a rapid Joule heating in the sample leading to a nematic to isotropic phase transition where the elastomer of dimensions 32 mm x 7 mm x 0.4 mm contracted in less than a second. The cooling process, isotropic to nematic transition where the elastomer expands back to its original length, was slow and took 8 seconds. The material studied here is a highly novel liquid crystalline co-elastomer, invented and developed by Heino Finkelmann and co-workers at Albert-Ludwigs-Universitaet in Freiburg, Germany. The material is such that in which the mesogenic units are in both the side chains and the main chains of the elastomer. This co-elastomer was then mechanically loaded to induce a uniaxial network anisotropy before the cross-linking reaction was completed. These samples were then made into a composite with a conducting material such as dispersed silver particles or graphite fibers. The final samples was capable of undergoing more than 200% reversible strain in a few seconds.

Using Neutron Diffraction to Investigate Texture Evolution During Consolidation of Deuterated Triaminotrinitrobenzene (d-TATB) Explosive Powder

DOE PAGES

Luscher, Darby J.; Yeager, John D.; Clausen, Bjørn; ...

2017-05-14

Triaminotrinitrobenzene (TATB) is a highly anisotropic molecular crystal used in several plastic-bonded explosive (PBX) formulations. A complete understanding of the orientation distribution of TATB particles throughout a PBX charge is required to understand spatially variable, anisotropic macroscale properties of the charge. Although texture of these materials can be measured after they have been subjected to mechanical or thermal loads, measuring texture evolution in situ is important in order to identify mechanisms of crystal deformation and reorientation used to better inform thermomechanical models. Neutron diffraction measurements were used to estimate crystallographic reorientation while deuterated TATB (d-TATB) powder was consolidated into amore » cylindrical pellet via a uniaxial die-pressing operation at room temperature. Both the final texture of the pressed pellet and the in situ evolution of texture during pressing were measured, showing that the d-TATB grains reorient such that (001) poles become preferentially aligned with the pressing direction. A compaction model is used to predict the evolution of texture in the pellet during the pressing process, finding that the original model overpredicted the texture strength compared to these measurements. The theory was extended to account for initial particle shape and pore space, bringing the results into good agreement with the data.« less

Using Neutron Diffraction to Investigate Texture Evolution During Consolidation of Deuterated Triaminotrinitrobenzene (d-TATB) Explosive Powder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luscher, Darby J.; Yeager, John D.; Clausen, Bjørn

Triaminotrinitrobenzene (TATB) is a highly anisotropic molecular crystal used in several plastic-bonded explosive (PBX) formulations. A complete understanding of the orientation distribution of TATB particles throughout a PBX charge is required to understand spatially variable, anisotropic macroscale properties of the charge. Although texture of these materials can be measured after they have been subjected to mechanical or thermal loads, measuring texture evolution in situ is important in order to identify mechanisms of crystal deformation and reorientation used to better inform thermomechanical models. Neutron diffraction measurements were used to estimate crystallographic reorientation while deuterated TATB (d-TATB) powder was consolidated into amore » cylindrical pellet via a uniaxial die-pressing operation at room temperature. Both the final texture of the pressed pellet and the in situ evolution of texture during pressing were measured, showing that the d-TATB grains reorient such that (001) poles become preferentially aligned with the pressing direction. A compaction model is used to predict the evolution of texture in the pellet during the pressing process, finding that the original model overpredicted the texture strength compared to these measurements. The theory was extended to account for initial particle shape and pore space, bringing the results into good agreement with the data.« less

Temperature-independent zero-birefringence polymer for liquid crystal displays

NASA Astrophysics Data System (ADS)

Shikanai, M. D.; Tagaya, A.; Koike, Y.

2016-03-01

A polymer film that shows almost no orientational birefringence even when the polymer main chain is in an oriented state and almost no temperature dependence of orientational birefringence in the temperature range from around -40 to 85 °C was prepared. This temperature range is important because it is where in-car liquid crystal displays (LCDs) are generally used; therefore, it is desirable to have constant orientational birefringence over this range. We suggest a method to compensate for the intrinsic birefringence and temperature coefficient of intrinsic birefringence of individual polymers by copolymerizing monomers of homopolymers that display opposite signs of the two parameters described above. Analysis of four types of polymers, methyl methacrylate (MMA), 2,2,2-trifluoroethyl methacrylate, benzyl methacrylate (BzMA), and phenyl methacrylate (PhMA), reveal that they possess both positive and negative signs of their temperature coefficient of intrinsic birefringence. Using this approach, we prepare P(MMA/PhMA/BzMA) (39:23:38 wt. %), which exhibits almost no intrinsic birefringence and almost no temperature dependence of intrinsic birefringence. The retardation of this polymer film when drawn uniaxially scarcely changed (between 0.3 and 0.8 nm) between 12 and 70 °C, which is small enough not to cause image degradation in LCDs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, J. P.; Wang, Y. D.; Hao, Y. L.

Two main explanations exist for the deformation mechanisms in Ti-Nb-based gum metals, i.e. the formation of reversible nanodisturbance and reversible stress-induced martensitic transformation. In this work, we used the in situ synchrotron-based high-energy X-ray diffuse-scattering technique to reveal the existence of a specific deformation mechanism, i.e. deformation-induced spatially confined martensitic transformations, in Ti-24Nb-4Zr-8Sn-0.10O single crystals with cubic 13 parent phase, which explains well some anomalous mechanical properties of the alloy such as low elastic modulus and nonlinear superelasticity. Two kinds of nanosized martensites with different crystal structures were found during uniaxial tensile loading along the [11 0](beta) axis at roommore » temperature and 190 K, respectively. The detailed changes in the martensitic phase transformation characteristics and the transformation kinetics were experimentally observed at different temperatures. The domain switch from non-modulated martensite to a modulated one occurred at 190 K, with its physical origin attributed to the heterogeneity of local phonon softening depending on temperature and inhomogeneous composition in the parent phase. An in-depth understanding of the formation of stress-induced spatially confined nanosized martensites with a large gradient in chemical composition may benefit designs of high-strength and high-ductility alloys. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Guozheng, E-mail: guozhengkang@home.swjtu.edu.cn; Dong, Yawei; Liu, Yujie

The uniaxial ratchetting of Ti–6Al–4V alloy with two phases (i.e., primary hexagonal close packed (HCP) α and secondary body-centered cubic (BCC) β phases) was investigated by macroscopic and microscopic experiments at room temperature. Firstly, the effects of cyclic softening/hardening feature, applied mean stress and stress amplitude on the uniaxial ratchetting of the alloy were discussed. The macroscopic investigation of Ti–6Al–4V alloy presents obvious strain-amplitude-dependent cyclic softening, as well as a three-staged evolution curve with regard to the ratchetting strain rate. The ratchetting depends greatly on the applied mean stress and stress amplitude while the ratchetting strain increases with the increasingmore » applied mean stress and stress amplitude. Then, the evolution of dislocation patterns and deformation twinning during the uniaxial ratchetting of two-phase Ti–6Al–4V alloy were observed using transmission electron microscopy (TEM). The microscopic observation shows that deformation twinning occurs in the primary α phase and its amount increases gradually during the uniaxial ratchetting. Simultaneously, the planar dislocation evolves from discrete lines to some dislocation nets and parallel lines with the increasing number of cycles. The deformation twinning in the primary α phase is one of main contributions to the uniaxial ratchetting of Ti–6Al–4V alloy, and should be considered in the construction of corresponding constitutive model. - Highlights: • A three-staged ratchetting occurs in the stress-controlled cyclic tests of Ti–6Al–4V alloy. • Dislocation patterns change from discrete lines to nets and parallel lines. • Deformation twinning occurs during the uniaxial ratchetting. • Both dislocation slipping and twinning are the causes of ratchetting.« less

Optical gain tuning within IR region in type-II In0.5Ga0.5As0.8P0.2/GaAs0.5Sb0.5 nano-scale heterostructure under external uniaxial strain

NASA Astrophysics Data System (ADS)

Singh, A. K.; Rathi, Amit; Riyaj, Md.; Bhardwaj, Garima; Alvi, P. A.

2017-11-01

Quaternary and ternary alloy semiconductors offer an extra degree of flexibility in terms of bandgap tuning. Modifications in the wave functions and alterations in optical transitions in quaternary and ternary QW (quantum well) heterostructures due to external uniaxial strain provide valuable insights on the characteristics of the heterostructure. This paper reports the optical gain in strained InGaAsP/GaAsSb type-II QW heterostructure (well width = 20 Å) under external uniaxial strain at room temperature (300 K). The entire heterostructure is supposed to be grown on InP substrate pseudomorphically. Band structure, wave functions, energy dispersion and momentum matrix elements of the heterostructure have been computed. 6 × 6 diagonalised k → ·p → Hamiltonian matrix of the system is evaluated and Luttinger-Kohn model has been applied for the band structure and wavefunction calculations. TE mode optical gain spectrum in the QW-heterostructure under uniaxial strain along [110] is calculated. Optical gain of the heterostructure as a function of 2D carrier density and temperature variation is investigated. The variation of the peak optical gain as a function of As and Sb fractions in InGaAsP as a barrier and GaAsSb as a well respectively is exhibited. For a charge carrier injection of 5 ×1012 /cm2 , the TE optical gain is 3952 cm-1 at room temperature under no external uniaxial strain. Significant increase in TE mode optical gain is observed under high external uniaxial strain (1, 5 and 10 GPa) along [110] within IR (Infrared region) region.

Matrix assisted laser desorption ionization time-of-flight mass spectrometry: Velocity measurements using orthogonal and axial injection and applications to characterization of wheat proteins

NASA Astrophysics Data System (ADS)

Dworschak, Ragnar G.

Orthogonal-injection was introduced to allow continuous ion sources to be coupled to time-of-flight mass spectrometers, but also demonstrated promising features for pulsed sources such as MALDI. We tested the feasibility of using a simple implementation orthogonal injection TOF with a MALDI source without collisional cooling. The experiment demonstrated that high resolution is achievable in principle in such an instrument, but only with impractical sacrifices in intensity. Subsequent work in this laboratory has demonstrated that the addition of collisional cooling makes orthogonal MALDI not only feasible, but advantageous in several respects. The instrument used for the above feasibility test was well-suited for measurements of initial velocity distributions in MALDI, avoiding problems of field penetration and questions of timescale of the plume expansion that seemed to produce rather conflicting results in axial TOF measurements. Average initial velocities of peptides and proteins above about 1000 daltons were found to be largely mass independent around 800 m/s, plus or minus about 15% depending on the matrix used. This result is slightly higher, but still quite consistent with earlier measurements using axial TOF with the field-free method (˜750 m/s), but a factor of two higher than the first reports using the delayed-extraction method. The experiments also showed that in contrast to the average velocity, the width of the velocity distribution increases significantly with increasing mass. The matrix velocity measurements confirm earlier experiments that show the benzoic acid derivatives have generally higher velocities than the cinnamic acid derivatives. Measurements of the velocity component in the direction back toward the laser with different sample orientations suggest that the surface orientation is the main determiner of the plume direction. On the other hand, preliminary measurements using the field-free method in the axial TOF geometry show higher velocities of matrix and analyte ions for more normal laser incidence, and for single crystals parallel to the sample surface compared to polycrystalline surfaces, suggesting the orientation of the crystal face with respect to the incident laser direction plays a role in the desorption process. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS) was used to analyse the protein composition in several common and durum wheat varieties. Mass spectra were obtained directly from crude and partially purified wheat gliadin and reduced glutenin subunit fractions. Mass spectra of the gliadins and the low molecular weight glutenin subunits show a complex pattern of proteins in the 30--40 kDa range. The observed gliadin patterns showed some promise for variety identification. The mass spectra of the high molecular weight glutenin subunits are much simpler and the complete high molecular weight subunit profile can be determined directly from a single mass spectrum. This may prove particularly useful in wheat breeding programs for rapid identification of lines containing subunits associated with superior quality.

Impact of tensile strain on the thermal transport of zigzag hexagonal boron nitride nanoribbon: An equilibrium molecular dynamics study

NASA Astrophysics Data System (ADS)

Navid, Ishtiaque Ahmed; Intisar Khan, Asir; Subrina, Samia

2018-02-01

The thermal conductivity of single layer strained hexagonal boron nitride nanoribbon (h-BNNR) has been computed using the Green—Kubo formulation of Equilibrium Molecular Dynamics (EMD) simulation. We have investigated the impact of strain on thermal transport of h-BNNR by varying the applied tensile strain from 1% upto 5% through uniaxial loading. The thermal conductivity of h-BNNR decreases monotonically with the increase of uniaxial tensile strain keeping the sample size and temperature constant. The thermal conductivity can be reduced upto 86% for an applied uniaxial tensile strain of 5%. The impact of temperature and width variation on the thermal conductivity of h-BNNR has also been studied under different uniaxial tensile strain conditions. With the increase in temperature, the thermal conductivity of strained h-BNNR exhibits a decaying characteristics whereas it shows an opposite pattern with the increasing width. Such study would provide a good insight on the strain tunable thermal transport for the potential device application of boron nitride nanostructures.

Cryogenic System for Neutron Scattering Experiments with In Situ Pressure Tuning Mechanism: Response of the Antiferromagnetism of URu2Si2 to Uniaxial Stress

NASA Astrophysics Data System (ADS)

Kawarazaki, Shuzo; Uwatoko, Yoshiya; Yokoyama, Makoto; Okita, Yuji; Tabata, Yoshikazu; Taniguchi, Toshifumi; Amitsuka, Hiroshi

2002-10-01

A handy insertable device to manipulate hydrostatic pressure or uniaxial stress on a sample in a cryostat for neutron scattering experiments is described. The pressure that is generated in a miniature hydraulic oil-cylinder on the top of the inserting stick is transmitted to the sample via a long piston-cylinder unit made of a thick stainless-steel tube and a fiber-reinforced plastics (FRP) rod. One can thus in situ tune the pressure or the stress on the sample without handling the pressure-cell at room temperature outside the cryostat. The device is designed to fit into the ILL-type Orange cryostat so that it can be used in many neutron scattering facilities. A newly designed uniaxial-stress cell and hydrostatic pressure cell to be used with this system are also described. The result of measurement of the hysteresis effect of uniaxial stress on the antiferromagnetism of URu2Si2 at 1.4 K is presented.