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Sample records for compressed fcc crystals

  1. Vacancy behavior in a compressed fcc Lennard-Jones crystal

    SciTech Connect

    Beeler, J.R. Jr.

    1981-12-01

    This computer experiment study concerns the determination of the stable vacancy configuration in a compressed fcc Lennard-Jones crystal and the migration of this defect in a compressed crystal. Isotropic and uniaxial compression stress conditions were studied. The isotropic and uniaxial compression magnitudes employed were 0.94 less than or equal to eta less than or equal to 1.5, and 1.0 less than or equal to eta less than or equal to 1.5, respectively. The site-centered vacancy (SCV) was the stable vacancy configuration whenever cubic symmetry was present. This includes all of the isotropic compression cases and the particular uniaxial compression case (eta = ..sqrt..2) that give a bcc structure. In addition, the SCV was the stable configuration for uniaxial compression eta < 1.29. The out-of-plane split vacancy (SV-OP) was the stable vacancy configuration for uniaxial compression 1.29 < eta less than or equal to 1.5 and was the saddle-point configuration for SCV migration when the SCV was the stable form. For eta > 1.20, the SV-OP is an extended defect and, therefore, a saddle point for SV-OP migration could not be determined. The mechanism for the transformation from the SCV to the SV-OP as the stable form at eta = 1.29 appears to be an alternating sign (101) and/or (011) shear process.

  2. Nucleation of hcp and fcc phases in bcc iron under uniform compression: classical molecular dynamics simulations.

    PubMed

    Wang, B T; Shao, J L; Zhang, G C; Li, W D; Zhang, P

    2010-11-03

    By classical molecular dynamics simulations employing an embedded atom method potential, we have simulated the bcc to hcp/fcc structural transition in single-crystal iron under uniform compression. Results showed that the transition pressure is different from uniaxial compression and shock loading. The transformation occurs on a picosecond timescale and the transition time decreases along with the increase of pressure. The nucleation and growth of the hcp and fcc phases under constant pressure and temperature are analyzed in detail. The nucleation planes, all belonging to the {110}(bcc) family and parallel to the three compression directions [100], [010], and [001], have been observed. About 20% bcc atoms have transformed to fcc phase under pressure just over the critical point, and under higher pressure the fraction of the fcc phase increases steadily to exceed that of the hcp phase. We have investigated the transition mechanism of iron from initial bcc to hcp/fcc and found that the transition mainly consists of compression, rotation, and shuffle.

  3. Theoretical analysis of the channel die compression test—II. First- and second-order analysis of orientation [110] [00 overline1] [ overline110] in F.C.C. crystals

    NASA Astrophysics Data System (ADS)

    Havner, K. S.; Sue, P. L.

    I NTHIS paper we present a general formulation of the analysis of the channel die compression test for single crystals, to second order in the applied compressive load increment. Specific first- and second-order analyses of f.c.c. crystals in orientation [110] [00 overline1] [ overline110] are carried out for the same four hardening rules considered in S UE and H AVNER (1984). These are Taylor hardening, a 2-parameter empirical rule, the "simple theory" (H AVNER and S HALBY, 1977), and a modification of the simple theory introduced by P EIRCE, A SARO and N EEDLEMAN (1982). In particular, we address the analysis of lattice rotation about the loading axis for each of these theories. Such rotation was a prominent feature of the deformation of a copper crystal in this orientation in experiments by W ONSIEWICZ and C HIN (1970). We establish that all theories permit this rotation consistent with the first- and second-order channel die constraints. Regarding the issue of lattice stability, a fundamental difference between the present orientation and those analyzed in S UE and H AVNER (1984) is uncovered and discussed. We close with a strong recommendation for a new series of channel die experiments.

  4. FCC-HCP coexistence in dense thermo-responsive microgel crystals

    NASA Astrophysics Data System (ADS)

    Karthickeyan, D.; Joshi, R. G.; Tata, B. V. R.

    2017-06-01

    Analogous to hard-sphere suspensions, monodisperse thermo-responsive poly (N-isopropyl acrylamide) (PNIPAM) microgel particles beyond a volume fraction (ϕ) of 0.5 freeze into face centered cubic (FCC)-hexagonal close packed (HCP) coexistence under as prepared conditions and into an FCC structure upon annealing. We report here FCC-HCP coexistence to be stable in dense PNIPAM microgel crystals (ϕ > 0.74) with particles in their deswollen state (referred to as osmotically compressed microgel crystals) and the FCC structure with particles in their swollen state by performing annealing studies with different cooling rates. The structure of PNIPAM microgel crystals is characterized using static light scattering technique and UV-Visible spectroscopy and dynamics by dynamic light scattering (DLS). DLS studies reveal that the particle motion is diffusive at short times in crystals with ϕ < 0.74 and sub-diffusive at short times in PNIPAM crystals with ϕ > 0.74. The observed sub-diffusive behavior at short times is due to the overlap (interpenetration) of the dangling polymer chains between the shells of neighbouring PNIPAM microgel particles. Overlap is found to disappear upon heating the crystals well above their melting temperature, Tm due to reduction in the particle size. Annealing studies confirm that the overlap of dangling polymer chains between the shells of neighbouring PNIPAM spheres is responsible for the stability of FCC-HCP coexistence observed in osmotically compressed PNIPAM microgel crystals. Results are discussed in the light of recent reports of stabilizing the HCP structure in hard sphere crystals by adding interacting polymer chains.

  5. Phase-field-crystal model for fcc ordering.

    PubMed

    Wu, Kuo-An; Adland, Ari; Karma, Alain

    2010-06-01

    We develop and analyze a two-mode phase-field-crystal model to describe fcc ordering. The model is formulated by coupling two different sets of crystal density waves corresponding to <111> and <200> reciprocal lattice vectors, which are chosen to form triads so as to produce a simple free-energy landscape with coexistence of crystal and liquid phases. The feasibility of the approach is demonstrated with numerical examples of polycrystalline and (111) twin growth. We use a two-mode amplitude expansion to characterize analytically the free-energy landscape of the model, identifying parameter ranges where fcc is stable or metastable with respect to bcc. In addition, we derive analytical expressions for the elastic constants for both fcc and bcc. Those expressions show that a nonvanishing amplitude of [200] density waves is essential to obtain mechanically stable fcc crystals with a nonvanishing tetragonal shear modulus (C11-C12)/2. We determine the model parameters for specific materials by fitting the peak liquid structure factor properties and solid-density wave amplitudes following the approach developed for bcc [K.-A. Wu and A. Karma, Phys. Rev. B 76, 184107 (2007)]. This procedure yields reasonable predictions of elastic constants for both bcc Fe and fcc Ni using input parameters from molecular dynamics simulations. The application of the model to two-dimensional square lattices is also briefly examined.

  6. Molecular dynamics simulations of hcp/fcc nucleation and growth in bcc iron driven by uniaxial compression.

    PubMed

    Wang, B T; Shao, J L; Zhang, G C; Li, W D; Zhang, P

    2009-12-02

    Molecular dynamics simulations have been performed to study the structural transition in bcc iron under uniaxial strain loading. We found that the transition pressures are less dependent on the crystal orientations, ∼14 GPa for [001], [011], and [111] loadings. However, the pressure interval of a mixed phase for [011] loading is much shorter than loading along other orientations. In addition, the temperature increased amplitude for [001] loading is evidently lower than other orientations. The nucleation and growth of the hcp/fcc phases, and their crystal orientation dependence, were analyzed in detail, where the atom structure was presented by the topological medium-range-order analysis. For [001] compression, the hcp structure occurs first and grows into a laminar morphology in the (011)(bcc) plane with some fcc atoms as an intermediate structure. For loading along [011] and [111] directions, both hcp and fcc structure nucleation and growth along the {110}(bcc) planes are observed; their morphology is also discussed.

  7. Atomistically-informed Dislocation Dynamics in fcc Crystals

    SciTech Connect

    Martinez, E; Marian, J; Arsenlis, T; Victoria, M; Perlado, J M

    2006-09-06

    We develop a nodal dislocation dynamics (DD) model to simulate plastic processes in fcc crystals. The model explicitly accounts for all slip systems and Burgers vectors observed in fcc systems, including stacking faults and partial dislocations. We derive simple conservation rules that describe all partial dislocation interactions rigorously and allow us to model and quantify cross-slip processes, the structure and strength of dislocation junctions and the formation of fcc-specific structures such as stacking fault tetrahedra. The DD framework is built upon isotropic non-singular linear elasticity, and supports itself on information transmitted from the atomistic scale. In this fashion, connection between the meso and micro scales is attained self-consistently with core parameters fitted to atomistic data. We perform a series of targeted simulations to demonstrate the capabilities of the model, including dislocation reactions and dissociations and dislocation junction strength. Additionally we map the four-dimensional stress space relevant for cross-slip and relate our findings to the plastic behavior of monocrystalline fcc metals.

  8. Solution based synthesis of simple fcc Si nano-crystals under ambient conditions.

    PubMed

    Balcı, Mustafa H; Sæterli, Ragnhild; Maria, Jerome; Lindgren, Mikael; Holmestad, Randi; Grande, Tor; Einarsrud, Mari-Ann

    2013-02-28

    We demonstrate for the first time that simple face-centered cubic (fcc) silicon nano-crystals can be produced by a solution based bottom-up synthesis route under ambient conditions. Simple fcc Si nano-crystals (2-7 nm) were prepared at room temperature by using sodium cyclopentadienide as a reducing agent for silicon tetrachloride. Photoluminescence emission at 550 nm was observed for the fcc silicon nano-crystals upon excitation at 340 nm, indicating that fcc Si nano-crystals were exhibiting direct bandgap like semiconductor properties with very fast radiative recombination rates. The new synthesis route makes possible the production and study of simple fcc polymorphs of Si nano-crystals with an easy alteration of surface termination groups.

  9. Germanium FCC structure from a colloidal crystal template

    SciTech Connect

    Miguez, H.; Meseguer, F.; Lopez, C.; Holgado, M.; Andreasen, G.; Mifsud, A.; Fornes, V.

    2000-05-16

    Here, the authors show a method to fabricate a macroporous structure in which the pores, essentially identical, arrange regularly in a face-centered cubic (FCC) lattice. The result is a network of air spheres in a germanium medium. This structure presents the highest dielectric contrast ({epsilon}{sub Ge}/{epsilon}{sub air} = 16) ever achieved in the optical regime in such periodic structures, which could result in important applications in photonics. The authors employ solid silica colloidal crystals (opals) as templates within which a cyclic germanium growth process is carried out. Thus, the three-dimensional periodicity of the host is inherited by the guest. Afterward, the silica is removed and a germanium opal replica is obtained.

  10. Local elastic constants in thin films of an fcc crystal.

    PubMed

    van Workum, Kevin; de Pablo, Juan J

    2003-03-01

    In this work we present a formalism for the calculation of the local elastic constants in inhomogeneous systems based on a method of planes. Unlike previous work, this formalism does not require the partitioning of the system into a set of finite volumes over which average elastic constants are calculated. Results for the calculation of the local elastic constants of a nearest-neighbor Lennard-Jones fcc crystal in the bulk and in a thin film are presented. The local constants are calculated at exact planes of the (001) face of the crystal. The average elastic constants of the bulk system are also computed and are consistent with the local constants. Additionally we present the local stress profiles in the thin film when a small uniaxial strain is applied. The resulting stress profile compares favorably with the stress profile predicted via the local elastic constants. The surface melting of a model for argon for which experimental and simulation data are available is also studied within the framework of this formalism.

  11. Random hcp and fcc structures in thermoresponsive microgel crystals.

    PubMed

    Brijitta, J; Tata, B V R; Joshi, R G; Kaliyappan, T

    2009-08-21

    Monodisperse thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles having a diameter of 520 nm were synthesized by free-radical precipitation polymerization and centrifuged to obtain a concentrated suspension. The centrifuged mother suspension was made to self-order into a crystalline state by repeated annealing beyond the volume phase transition (VPT) of the particles. We report here the three-dimensional (3D) real space structure, determined using a confocal laser scanning microscope, of PNIPAM microgel crystal samples prepared by two different recrystallized routes: (1) solidifying a shear melted colloidal liquid (referred as as-prepared sample) and (2) slow cooling of a colloidal liquid (referred as recrystallized sample). We have recorded images of several regions of the crystal with each region containing 15 horizontal crystal planes for determining the in-plane [two-dimensional (2D)] and 3D pair-correlation functions. The 2D pair-correlation function g(r) revealed hexagonal long-range order of particles in the layers with a lattice constant of 620 nm. The analysis of stacking sequence of layers recorded on as-prepared sample has revealed the existence of stacking disorder with an average stacking probability alpha approximately 0.42. This value of alpha together with the analysis of 3D pair-correlation function determined from particle positions revealed the structure of microgel crystals in the as-prepared sample to be random hexagonal close packing. We report the first observation of a split second peak in the 3D g(r) of the microgel crystals obtained from a shear melted liquid. Upon melting the sample above VPT and recrystallizing it the split second peak disappeared and the crystals are found to have a face centered cubic (fcc) structure with alpha approximately 0.95. From simulations, the split second peak is shown to arise from the displacement of some of the B-planes from the ideal hcp positions. The present results are discussed in

  12. Response of FCC and BCC Metals to High-Amplitude Dynamic Compression

    NASA Astrophysics Data System (ADS)

    Meyers, Marc; Remington, Bruce; Maddox, Brian; Bringa, Eduardo; Park, Hye-Sook; Lu, Chia-Hui

    2013-06-01

    The experimentally observed response of FCC and BCC metals to high-amplitude compressive waves is compared with analytical predictions using constitutive models based on dislocations and twinning and with molecular dynamics simulations. In FCC metals (Cu and Ni), the predictions of dislocation densities from a homogeneous nucleation model are close to those of molecular dynamics simulations. Both are orders of magnitude higher than experimentally observed residual dislocation densities. MD calculations predict a drastic decrease in dislocation densities upon unloading, bringing the values in agreement with measurements. For BCC metals (Ta), on the residual densities are close to predictions of Orowan dislocation multiplication. Due to the much higher Peierls-Nabarro stress, the MD simulations predict much lower dislocation densities than in FCC metals subjected to similar pressures. At higher amplitudes, both FCC and BCC metals experience extensive twinning. The threshold pressure for twinning is successfully modeled by constitutive model based on a critical shear stress for twinning, at the imposed strain rate and temperature. Research funded by UCOP/UC Labs Program.

  13. Simulation of mechanical performance of nanoporous FCC copper under compression with pores mimicking several crystalline arrays

    NASA Astrophysics Data System (ADS)

    Cui, Yi; Chen, Zengtao

    2017-08-01

    The mechanical performance of porous metal with assembly of pores mimicking typical crystalline structures is studied via atomistic simulation and finite element method. The pore lattices are made with the same orientation as the face-centered cubic (FCC) copper lattice. The compression is applied in the [0 0 1] direction. Under the same initial porosity and identical pore size, pores assembled in diamond array result in a superior stress response under compression. The sample with pores assembled in body-centered cubic array, whose surface-to-volume ratio is close to that of either FCC or hexagonally close-packed (HCP) array, has a yet much higher yield stress. However, the FCC- and HCP-structured nanoporous samples exhibit a greater hardening effect. The Lubarda model for critical stress to trigger dislocation emission is extended to the nanoporous geometry numerically. The magnitude and distribution of shear stress on the slip plane are found crucial to dislocation activities. No strong correlation between dislocation formation and early densification of nanoporous geometry is found. Through comparing the yielding and hardening behavior among differently structured nanoporous samples, new understanding could be established on their mechanical performance. Enhanced structural integrity could better support their diverse applications by design.

  14. Preparation and characterization of Co single-crystal thin films with hcp, fcc and bcc structures

    SciTech Connect

    Ohtake, Mitsuru; Yabuhara, Osamu; Higuchi, Jumpei; Futamoto, Masaaki

    2011-04-01

    Co crystals with three different structures are realized in the form of single-crystal thin films hetero-epitaxially grown on single-crystal substrates by ultrahigh vacuum rf magnetron sputtering. hcp-, fcc-, and bcc-Co single-crystal films are formed on Cr(211){sub bcc}, Cu(100){sub fcc}, and GaAs(110){sub B3}, respectively. The film growth process is studied by RHEED, and the lattice constants of these Co films are determined by x-ray diffraction. The magnetization properties of these thin films are reflecting the magnetocrystalline anisotropies of Co crystals with the easy magnetization axes along hcp<0001>, fcc<111>, and bcc<100> directions.

  15. Kinetics study of crystallization with the disorder-bcc-fcc phase transition of charged colloidal dispersions.

    PubMed

    Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Du, Xuan; Liu, Lixia

    2011-06-21

    Structure transformation (disorder-bcc-fcc) in charged colloidal dispersions, as a manifestation of the Ostwald's step rule, was confirmed by means of reflection spectrum (RS) measurements in our previous study. By taking advantage of a reflection spectrum containing plenty of information about the crystallization behaviors, time-dependent changes of parameters associated with the crystal structure and composition during the disorder-bcc-fcc transition are reported by treating the data from RS in this article. In addition, Avrami's model is adopted to analyze the transition process and investigate the transition rate. On the basis of the above investigations, associated kinetic features of crystallization with the disorder-bcc-fcc transition are described.

  16. Multilayer Relaxation and Surface Energies of FCC and BCC Metals Using Equivalent Crystal Theory

    NASA Technical Reports Server (NTRS)

    Rodriguez, Agustin M.; Bozzolo, Guillermo; Ferrante, John

    1993-01-01

    The multilayer relaxation of fcc and bcc metal surfaces is calculated using equivalent crystal theory. The results for changes in interplanar spacings of planes close to the surface and the ensuing surface energies are discussed in reference to other theoretical results and compared to available experimental data. The calculation includes high-index surfaces for which no other theoretical results are known.

  17. Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Knudsen, Erik; Swanson, Gregory R.; Duke, Gregory; Ham-Battista, Gilda

    2004-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent high cycle fatigue (HCF) failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and non-crystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is presented for evaluating the subsurface stresses in the elastic half-space, based on the adaptation of a stress function method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis (FEA). Effects of crystal orientation on stress response and fatigue life are examined. Obtaining accurate subsurface stress results for anisotropic single crystal contact problems require extremely refined three-dimensional (3-D) finite element grids, especially in the edge of contact region. Obtaining resolved shear stresses (RSS) on the principal slip planes also involves

  18. Void growth and coalescence in triaxial stress fields in irradiated FCC single crystals

    NASA Astrophysics Data System (ADS)

    Ling, Chao; Tanguy, Benoît; Besson, Jacques; Forest, Samuel; Latourte, Felix

    2017-08-01

    Void growth and coalescence, known as main mechanisms of ductile fracture, are investigated for irradiated FCC single crystals. Finite element simulations of voided unit cells are performed with a single crystal plasticity model accounting for strain hardening and softening associated with irradiation-induced defects. The simulations predict a rather brittle overall behavior for the voided irradiated single crystal at high stress triaxiality, with a large amount of local plastic deformation, which is consistent with experimental observations reported in the literature for stainless steels irradiated in fast reactors. Compared with unirradiated single crystals, irradiated crystals exhibit a higher void growth rate leading to an earlier void coalescence, which is caused by a stronger plastic slip localization in the region near the voids.

  19. Dynamic stability of fcc crystals under isotropic loading from first principles.

    PubMed

    Rehák, Petr; Cerný, Miroslav; Pokluda, Jaroslav

    2012-05-30

    Lattice dynamics and stability of four fcc crystals (Al, Ir, Pt and Au) under isotropic (hydrostatic) tensile loading are studied from first principles using the linear response method and the harmonic approximation. The results reveal that, contrary to former expectations, strengths of all the studied crystals are limited by instabilities related to soft phonons with finite or vanishing wavevectors. The critical strains associated with such instabilities are remarkably lower than those related to the volumetric instability. On the other hand, the corresponding reduction of the tensile strength is by 20% at the most. An analysis of elastic stability conditions is also performed and the results obtained by means of both approaches are compared.

  20. Geometry explains the large difference in the elastic properties of fcc and hcp crystals of hard spheres.

    PubMed

    Sushko, Nazar; van der Schoot, Paul

    2005-12-01

    As is well known, hard-sphere crystals of the fcc and hcp type differ very little in their thermodynamic properties. Nonetheless, recent computer simulations by Pronk and Frenkel indicate that the elastic response to mechanical deformation of these two types of crystal are quite different [S. Pronk and D. Frenkel, Phys. Rev. Lett. 90, 255501 (2003)]. By invoking a geometrical argument put forward by Martin some time ago [R. M. Martin, Phys. Rev. B 6, 4546 (1972)], we suggest that this is largely due to the different symmetries of the fcc and hcp crystal structures. Indeed, we find that elastic constants of the fcc hard-sphere crystal can be mapped onto the equivalent ones of the hcp crystal to very high accuracy, as a comparison with the computer simulation data of Pronk and Frenkel shows. The same procedure applied to density functional theoretical predictions for the elastic properties of the fcc hard-sphere crystal also produces remarkably accurate predictions for those of the hcp hard-sphere crystal.

  1. Universal relationships for the phonon spectra in BCC, FCC, and HCP crystals with a short-range interatomic interaction

    SciTech Connect

    Vaks, V. G. Zhuravlev, I. A.; Zabolotskii, A. D.

    2012-03-15

    The frequencies of the phonon branches that correspond to the vibrations of the close-packed atomic planes in bcc, fcc, and hcp crystals with short-range interatomic interaction are shown to be described by a universal relationship, which only contains two parameters for each branch, for any polarization {lambda}. These phonon branches correspond to the ({xi}, {xi}, 0) direction in bcc crystals, the ({xi}, {xi}, {xi}) direction in fcc crystals, and the (0, 0, {xi}) direction in hcp crystals. This universal relationship can only be violated by long-range interactions, namely, the interactions outside the sixth coordination shell in a bcc crystal, the fifth coordination shell in an fcc crystal, and the eleventh or tenth coordination shell in an hcp crystal. The effect of these long-range interactions for each phonon branch can be quantitatively characterized by certain parameters {Delta}{sub n{lambda}}, which are simply expressed in terms of the frequencies of three phonons of the branch. The values of these parameters are presented for all bcc, fcc, and hcp metals whose phonon spectra are measured. In most cases, the proposed relationships for the frequencies are found to be fulfilled accurate to several percent. In the cases where the {Delta}{sub n{lambda}} parameters are not small, they can give substantial information on the type and scale of long-range interaction effects in various metals.

  2. Identifying self-interstitials of bcc and fcc crystals in molecular dynamics

    NASA Astrophysics Data System (ADS)

    Bukkuru, S.; Bhardwaj, U.; Warrier, M.; Rao, A. D. P.; Valsakumar, M. C.

    2017-02-01

    Identification of self-interstitials in molecular dynamics (MD) simulations is of critical importance. There exist several criteria for identifying the self-interstitial. Most of the existing methods use an assumed cut-off value for the displacement of an atom from its lattice position to identify the self-interstitial. The results obtained are affected by the chosen cut-off value. Moreover, these chosen cut-off values are independent of temperature. We have developed a novel unsupervised learning algorithm called Max-Space Clustering (MSC) to identify an appropriate cut-off value and its dependence on temperature. This method is compared with some widely used methods such as effective sphere (ES) method and nearest neighbor sphere (NNS) method. The cut-off radius obtained using our method shows a linear variation with temperature. The value of cut-off radius and its temperature dependence is derived for five bcc (Cr, Fe, Mo, Nb, W) and six fcc (Ag, Au, Cu, Ni, Pd, Pt) crystals. It is seen that the ratio of the cut-off values "r" to the lattice constant "a" lies between 0.23 and 0.3 at 300 K and this ratio is on an average smaller for the fcc crystals. Collision cascade simulations are carried out for Primary knock-on Atom (PKA) energies of 5 keV in Fe (at 300 K and 1000 K) and W (at 300 K and 2500 K) and the results are compared using the various methods.

  3. Flow-induced alignment of (100) fcc thin film colloidal crystals.

    PubMed

    Joy, Midhun; Muangnapoh, Tanyakorn; Snyder, Mark A; Gilchrist, James F

    2015-09-28

    The realization of structural diversity in colloidal crystals obtained by self-assembly techniques remains constrained by thermodynamic considerations and current limits on our ability to alter structure over large scales using imposed fields and confinement. In this work, a convective-based procedure to fabricate multi-layer colloidal crystal films with extensive square-like symmetry is enabled by periodic substrate motion imposed during the continuous assembly. The formation of film-spanning domains of (100) fcc symmetry as a result of added vibration is robust across a range of micron-scale monosized spherical colloidal suspensions (e.g., polystyrene, silica) as well as substrate surface chemistries (e.g., hydrophobic, hydrophilic). The generation of extensive single crystalline (100) fcc domains as large as 15 mm(2) and covering nearly 40% of the colloidal crystalline film is possible by simply tuning coating conditions and multi-layer film thickness. Preferential orientation of the square-packed domains with respect to the direction of deposition is attributed to domain generation based upon a shear-related mechanism. Visualization during assembly gives clues toward the mechanism of this flow-driven self-assembly method.

  4. Surface energy and work function of fcc and bcc crystals: Density functional study

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Wang, Shao-Qing

    2014-12-01

    The surface energies and work functions for six close-packed surfaces of 19 common fcc and bcc metals in the periodic table have been systematically calculated by means of the density functional theory (DFT) method. The accuracy of the results is established in comparison with the experimental and other theoretical values. The variations of work functions with the surface crystallographic orientation display a good regularity. For alkali metals, the work functions follow the sequence Φ(110) > Φ(133) > Φ(311) > Φ(120) > Φ(100) > Φ(111). But for the same crystal structure of bcc transition metals (Nb, Mo, Ta, W), the order is Φ(110) > Φ(133) > Φ(120) > Φ(111) > Φ(311) > Φ(100). The work functions for 3d, 4d and 5d transition fcc metals also display an obvious regularity and ordered as Φ(111) > Φ(100) > Φ(211) > Φ(123) > Φ(310) > Φ(110). Particular attention is paid to the surface energies anisotropy with the same crystal structure metals and the variations present a good regularity, too. Especially, a roughly inverse proportional relationship between the surface energy and work function is found.

  5. Quantum calculation of disordered length in fcc single crystals using channelling techniques

    NASA Astrophysics Data System (ADS)

    Abu-Assy, M. K.

    2006-04-01

    Lattices of face-centred cubic crystals (fcc), due to irradiation processes, may become disordered in stable configurations like the dumb-bell configuration (DBC) or body-centred interstitial (BCI). In this work, a quantum mechanical treatment for the calculation of transmission coefficients of channelled positrons from their bound states in the normal lattice regions into the allowed bound states in the disordered regions is given as a function of the length of the disordered regions. In order to obtain more reliable results, higher anharmonic terms in the planar channelling potential are considered in the calculations by using first-order perturbation theory where new bound states have been found. The calculations were executed in the energy range 10 200 MeV of the incident positron on a copper single crystal in the planar direction (100).

  6. Size effects on plasticity and fatigue microstructure evolution in FCC single crystals

    NASA Astrophysics Data System (ADS)

    El-Awady, Jaafar Abbas

    In aircraft structures and engines, fatigue damage is manifest in the progressive emergence of distributed surface cracks near locations of high stress concentrations. At the present time, reliable methods for prediction of fatigue crack initiation are not available, because the phenomenon starts at the atomic scale. Initiation of fatigue cracks is associated with the formation of Persistent slip bands (PSBs), which start at certain critical conditions inside metals with specific microstructure dimensions. The main objective of this research is to develop predictive computational capabilities for plasticity and fatigue damage evolution in finite volumes. In that attempt, a dislocation dynamics model that incorporates the influence of free and internal interfaces on dislocation motion is presented. The model is based on a self-consistent formulation of 3-D Parametric Dislocation Dynamics (PDD) with the Boundary Element method (BEM) to describe dislocation motion, and hence microscopic plastic flow in finite volumes. The developed computer models are bench-marked by detailed comparisons with the experimental data, developed at the Wright-Patterson Air Force Lab (WP-AFRL), by three dimensional large scale simulations of compression loading on micro-scale samples of FCC single crystals. These simulation results provide an understanding of plastic deformation of micron-size single crystals. The plastic flow characteristics as well as the stress-strain behavior of simulated micropillars are shown to be in general agreement with experimental observations. New size scaling aspects of plastic flow and work-hardening are identified through the use of these simulations. The flow strength versus the diameter of the micropillar follows a power law with an exponent equal to -0.69. A stronger correlation is observed between the flow strength and the average length of activated dislocation sources. This relationship is again a power law, with an exponent -0.85. Simulation results

  7. Fcc r arrow bct phase transition in Th at extreme compressions: Theory

    SciTech Connect

    Eriksson, O. ); Soederlind, P. ); Wills, J.M. )

    1992-06-01

    The experimentally observed fcc{r arrow}bct crystallographic phase transition in Th, at {similar to}1 Mbar, is reproduced by means of full-potential, linear-muffin-tin-orbitals calculations. Both the calculated volume and pressure for which the transition occurs, agrees with the experimental data. The calculated pressure dependence of the {ital c}/{ital a} ratio of the bct structure is also in good agreement wtih experimental data. Calculations for La predict the fcc phase to be stable over the bct phase up to {similar to}7 Mbar.

  8. Ideal compressive strength of fcc Co, Ni, and Ni-rich alloys along the <001 > direction: A first-principles study

    NASA Astrophysics Data System (ADS)

    Breidi, A.; Fries, S. G.; Ruban, A. V.

    2016-04-01

    We perform density functional theory based first-principles calculations to identify promising alloying elements (X ) capable of enhancing the compressive uniaxial theoretical (ideal) strength of the fcc Ni-matrix along the <001 > direction. The alloying element belongs to a wide range of 3 d ,4 d , and 5 d series with nominal composition of 6.25 at. %. Additionally, a full elastic study is carried to investigate the ideal strength of fcc Ni and fcc Co. Our results indicate that the most desirable alloying elements are those with half d -band filling, namely, Os, Ir, Re, and Ru.

  9. Elastic properties of compressed rare-gas crystals in a model of deformable atoms

    NASA Astrophysics Data System (ADS)

    Gorbenko, Ie. Ie.; Troitskaya, E. P.; Pilipenko, E. A.

    2017-01-01

    The elastic properties of compressed Ne, Ar, Kr, and Xe rare-gas crystals were studied in a model of deformable and polarizable atoms. The second-order Fuchs elasticity moduli, their pressure derivatives, and the Zener elastic anisotropy ratio were calculated with allowance for three-body interaction and quadrupole deformation in electron shells within a wide pressure range. Comparison with the experiment and results of other authors was performed. In xenon at a compression of 0.6, the shear modulus B 44 was observed to become zero, thus corresponding to the FCC-HCP transition at 75 GPa.

  10. Ambient Compression-Compression Fatigue Behavior of Magnesium Single Crystal

    NASA Astrophysics Data System (ADS)

    Li, Qizhen

    2014-01-01

    A magnesium single crystal sample with a near orientation was tested at room temperature under compression-compression cyclic loading, and the microstructure was characterized to disclose the involved deformation mechanisms. No plastic deformation region appeared on the stress-strain curve during the cyclic loading. The stress-strain curve stabilized at the first cycle, the strain range for each cycle fluctuated slightly around a constant value, and the mean strain for each cycle was in a narrow range from 0.0846 to 0.0863 during the whole test. The ratcheting strain rate decreased exponentially from ~0.0003, and reached a relatively small and stable value of about zero. The observed deformation mechanisms were prismatic slip, compression twinning, and tension twinning. The prismatic dislocation slip roughened the cylindrical sample surface by forming extrusions and intrusions, and small cracks were also observed on the surface.

  11. Crystal plasticity finite element modelling of low cycle fatigue in fcc metals

    NASA Astrophysics Data System (ADS)

    Grilli, Nicolò; Janssens, Koenraad G. F.; Van Swygenhoven, Helena

    2015-11-01

    A new dislocation-based model for low cycle fatigue in fcc metals at a length scale smaller than the feature size of the dislocation structures is presented. It uses the crystal plasticity finite element method and dislocation densities as internal variables. Equations for the dipole distance distribution, for the double cross slip mechanism and a new dislocation multiplication law are introduced, which can predict the emergence of vein and channel structures starting from a randomly perturbed dislocation distribution. The characteristics of these structures in copper and aluminium, as well as the mechanical properties, are compared with experiments. Compared with existing density-based theories, the capability to reproduce dislocation patterning is a significant step forward.

  12. Orientation dependence of the plastic slip near notches in ductile FCC single crystals

    NASA Astrophysics Data System (ADS)

    Crone, W. C.; Shield, T. W.; Creuziger, A.; Henneman, B.

    2004-01-01

    Results from experiments conducted on copper FCC single crystals are reported. Two symmetric crystallographic orientations and four nonsymmetric crystallographic orientations were tested. The slip line fields that form near a pre-existing notch in these specimens were observed. The changes in these patterns as the orientation of the notch in the crystal is rotated in an {101} plane are discussed. Sectors of similar slip line patterns are identified and the type of boundaries between these sectors are discussed. A type of sector boundary called mixed kink is identified. Specimen orientations that differ by 90° are found to have different slip line patterns, contrary to the predictions of perfectly plastic slip line theory. The locations of the first slip lines to form are compared to the predictions obtained using anisotropic linear elastic stress field solutions and the initial plane-strain yield surfaces. It is found that comparison of these surface slip line fields to plane strain crack tip solutions in the annular region between 350 and 750 μm is justified. The differences in anisotropic elastic solutions for orientations that are 90° apart explain the lack of agreement with perfectly plastic slip line theory.

  13. Crystal Dynamics of (delta) fcc Pu-Ga by High Resolution Inelastic X-Ray Scattering

    SciTech Connect

    Wong, J; Krisch, M; Farber, D; Occelli, F; Xu, R; Chiang, T C; Clatterbuck, D; Schwartz, A J; Wall, M; Boro, C

    2004-09-28

    We have used a microbeam on large grain sample concept to carry out an inelastic x-ray scattering experiment to map the full phonon dispersion curves of an fcc {delta}-phase Pu-Ga alloy. This approach obviates experimental difficulties with conventional inelastic neutron scattering due to the high absorption cross section of the common {sup 239}Pu isotope and the non-availability of large (mm size) single crystal materials for Pu and its alloys. A classical Born von-Karman force constant model was used to model the experimental results, and no less than 4th nearest neighbor interactions had to be included to account for the observation. Several unusual features including, a large elastic anisotropy, a small shear elastic modulus, (C{sub 11}-C{sub 12})/2, a Kohn-like anomaly in the T{sub 1}[011] branch, and a pronounced softening of the T[111] branch towards the L point in the Brillouin are found. These features can be related to the phase transitions of plutonium and to strong coupling between the crystal structure and the 5f valence instabilities. Our results represent the first full phonon dispersions ever obtained for any Pu-bearing material, thus ending a 40-year quest for this fundamental data. The phonon data also provide a critical test for theoretical treatments of highly correlated 5f electron systems as exemplified by recent dynamical mean field theory (DMFT) calculations for {delta}-plutonium.

  14. Gravitational compression dynamics of charged colloidal crystals.

    PubMed

    Murai, Masako; Okuzono, Tohru; Yamamoto, Masaaki; Toyotama, Akiko; Yamanaka, Junpei

    2012-03-15

    We examine the compression of charged colloidal crystals under the influence of gravitational force by monitoring the spatiotemporal variations of Bragg diffraction from the crystal lattice. We use the dilute aqueous dispersions of colloidal silica particles (diameter=216 nm, charge number=733, a particle volume fraction φ=0.06) in the presence of 5-15 μM sodium chloride. The sedimentation profiles of the colloidal crystals along the crystal height are determined by in situ fiber optics reflection spectroscopy. The time evolutions of the sedimentation profiles are calculated by numerical simulations based on a phenomenological continuum model that explicitly incorporates the electrostatic interparticle interactions. The simulation results correctly describe the experiments at sufficiently high ionic strength. Copyright © 2012 Elsevier Inc. All rights reserved.

  15. Solidification and fcc to metastable hcp phase transition in krypton under variable compression rates

    NASA Astrophysics Data System (ADS)

    Chen, Jing-Yin; Yoo, Choong-Shik; Evans, William J.; Liermann, Hanns-Peter; Cynn, Hyunchae; Kim, Minseob; Jenei, Zsolt

    2014-10-01

    We present time-resolved synchrotron x-ray diffraction measurements to study kinetics associated with the liquid-solid and solid-solid high-pressure phase transitions in Kr under dynamic loading in a dynamic-diamond anvil cell. The results show a strong compression-rate dependence of the solidification/melting process in liquid Kr. The analysis of the compression-rate dependent melting/solidification, using an Avrami equation with the parameter n =1, indicates a spontaneous nucleation and one-dimensional growth mechanism. In contrast, the face-centered-cubic to metastable hexagonal close-packed transition in solid Kr occurs rapidly at ˜0.8 GPa near the melting line, which has negligible compression-rate dependence within the range of compression rates studied (0.004-13 GPa /s).

  16. Crystal-momentum dispersion of ultrafast spin change in fcc Co

    PubMed Central

    Si, M. S.; Li, J. Y.; Yang, D. Z.; Xue, D. S.; Zhang, G. P.

    2014-01-01

    Nearly twenty years ago, Beaurepaire and coworkers showed that when an ultrafast laser impinges on a ferromagnet, its spin moment undergoes a dramatic change, but how it works remains a mystery. While the current experiment is still unable to resolve the minute details of the spin change, crystal momentum-resolved techniques have long been used to analyze the charge dynamics in superconductors and strongly correlated materials. Here we extend it to probe spin moment change in the entire three-dimensional Brillouin zone for fcc Co. Our results indeed show a strong spin activity along the Δ line, supporting a prior experimental finding. The spin active pockets coalesce into a series of spin surfaces that follow the Fermi surfaces. We predict two largest spin change pockets which have been elusive to experiments: one pocket is slightly below the Δ line and the other is along the Λ line and close to the L point. Our theory presents an opportunity for the time-, spin- and momentum-resolve photoemission technique. PMID:24852331

  17. Single-crystal adsorption calorimetry and density functional theory of CO chemisorption on fcc Co{110}.

    PubMed

    Liao, Kristine; Fiorin, Vittorio; Gunn, David S D; Jenkins, Stephen J; King, David A

    2013-03-21

    Using single-crystal adsorption calorimetry (SCAC) and density functional theory (DFT), the interaction of carbon monoxide on fcc Co{110} is reported for the first time. The results indicate that adsorption is consistent with molecular chemisorption at all coverages. The initial heat of adsorption of 140 kJ mol(-1) is found in the range of heat values calorimetrically measured on other ferromagnetic metal surfaces, such as nickel and iron. DFT adsorption energies are in good agreement with the experimental results, and comparison between SCAC and DFT for CO on other ferromagnetic surfaces is made. The calculated dissociation barrier of 2.03 eV implies that dissociation at 300 K is unlikely even at the lowest coverage. At high coverages during the adsorption-desorption steady state regime, a pre-exponential factor for CO desorption of 1.2 × 10(17) s(-1) is found, implying a localised molecular adsorbed state prior to desorption in contrast to what we found with Ni surfaces. This result highlights the importance of the choice of the pre-exponential factor in evaluating the activation energy for desorption.

  18. Crystal-momentum dispersion of ultrafast spin change in fcc Co.

    PubMed

    Si, M S; Li, J Y; Yang, D Z; Xue, D S; Zhang, G P

    2014-05-23

    Nearly twenty years ago, Beaurepaire and coworkers showed that when an ultrafast laser impinges on a ferromagnet, its spin moment undergoes a dramatic change, but how it works remains a mystery. While the current experiment is still unable to resolve the minute details of the spin change, crystal momentum-resolved techniques have long been used to analyze the charge dynamics in superconductors and strongly correlated materials. Here we extend it to probe spin moment change in the entire three-dimensional Brillouin zone for fcc Co. Our results indeed show a strong spin activity along the Δ line, supporting a prior experimental finding. The spin active pockets coalesce into a series of spin surfaces that follow the Fermi surfaces. We predict two largest spin change pockets which have been elusive to experiments: one pocket is slightly below the Δ line and the other is along the Λ line and close to the L point. Our theory presents an opportunity for the time-, spin- and momentum-resolve photoemission technique.

  19. Theory and practice of “shape spectroscopy” of local FCC structures in computer simulations of nucleation and crystallization

    NASA Astrophysics Data System (ADS)

    Mitus, A. C.; Smolej, F.; Hahn, H.; Patashinski, A. Z.

    1996-02-01

    Starting from the previously developed probabilistic method for recognition of structures of small clusters of atoms undergoing thermal fluctuations, we derive simple algorithms for the very detailed study of local face-centered-cubic (FCC) arrangements of the atoms, directly in a configuration of atoms when it is being simulated. This includes (i) an algorithm for a local identification of FCC-like clusters, with the discussion of its reliability, and (ii) an algorithm for the calculation of the relative orientational correlations between the clusters. As an illustration, the method is used for studying nucleation and growth of an FCC phase in a rapidly quenched melt of 4000 Lennard-Jones atoms. On the basis of this analysis, we propose two trial hypotheses about (i) the existence of “slow” and “quick” regimes during the nucleation and growth and (ii) that in the intermediate stages of nucleation and crystallization the FCC-like local order appears rather in two-, than in three-dimensional aggregates.

  20. 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.

  1. 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.

  2. Origin of tension-compression asymmetry in ultrafine-grained fcc metals

    NASA Astrophysics Data System (ADS)

    Tsuru, T.

    2017-08-01

    A mechanism of anomalous tension-compression (T-C) asymmetry in ultrafine-grained (UFG) metals is proposed using large-scale atomistic simulations and dislocation theory. Unlike coarse-grained metals, UFG Al exhibits remarkable T-C asymmetry of the yield stress. The atomistic simulations reveal that the yield event is not related to intragranular dislocations but caused by dislocation nucleation from the grain boundaries (GBs). The dislocation core structure associated with the stacking fault energy in Al is strongly affected by the external stress compared with Cu; specifically, high tensile stress stabilizes the dissociation into partial dislocations. These dislocations are more likely to be nucleated from GBs and form deformation twins from an energetic viewpoint. The mechanism, which is different from well-known mechanisms for nanocrystalline and amorphous metals, is unique to high-strength UFG metals and can explain the difference in T-C asymmetry between UFG Cu and Al.

  3. Wulff polyhedra derived from morse potentials and crystal habits of bcc and fcc metal particles

    NASA Astrophysics Data System (ADS)

    Saito, Yahachi

    1981-05-01

    Using the broken-bond method and the pairwise potentials of Morse type, relative surface energies were calculated to derive the Wulff polyhedra for bcc and fcc metals. When only the first and the second nearest neighbour interactions are taken into account, the resulting Wulff polyhedron is a rhombic dodecahedron truncated by {100} faces and an octahedron truncated by {100} and {100} faces for bcc and fcc metals, respectively. The truncation degrees calculated are in good agreement with those measured from smoke particles grown in an atmosphere of rarefied inactive gas. The effect of the higher order terms of interactions is simply to make the edges and corners round.

  4. Probing Microplasticity in Small-Scale FCC Crystals via Dynamic Mechanical Analysis

    NASA Astrophysics Data System (ADS)

    Ni, Xiaoyue; Papanikolaou, Stefanos; Vajente, Gabriele; Adhikari, Rana X.; Greer, Julia R.

    2017-04-01

    In small-scale metallic systems, collective dislocation activity has been correlated with size effects in strength and with a steplike plastic response under uniaxial compression and tension. Yielding and plastic flow in these samples is often accompanied by the emergence of multiple dislocation avalanches. Dislocations might be active preyield, but their activity typically cannot be discerned because of the inherent instrumental noise in detecting equipment. We apply alternate current load perturbations via dynamic mechanical analysis during quasistatic uniaxial compression experiments on single crystalline Cu nanopillars with diameters of 500 nm and compute dynamic moduli at frequencies 0.1, 0.3, 1, and 10 Hz under progressively higher static loads until yielding. By tracking the collective aspects of the oscillatory stress-strain-time series in multiple samples, we observe an evolving dissipative component of the dislocation network response that signifies the transition from elastic behavior to dislocation avalanches in the globally preyield regime. We postulate that microplasticity, which is associated with the combination of dislocation avalanches and slow viscoplastic relaxations, is the cause of the dependency of dynamic modulus on the driving rate and the quasistatic stress. We construct a continuum mesoscopic dislocation dynamics model to compute the frequency response of stress over strain and obtain a consistent agreement with experimental observations. The results of our experiments and simulations present a pathway to discern and quantify correlated dislocation activity in the preyield regime of deforming crystals.

  5. Fabrication of FCC-SiO{sub 2} colloidal crystals using the vertical convective self-assemble method

    SciTech Connect

    Castañeda-Uribe, O. A.; Salcedo-Reyes, J. C.; Méndez-Pinzón, H. A.; Pedroza-Rodríguez, A. M.

    2014-05-15

    In order to determine the optimal conditions for the growth of high-quality 250 nm-SiO{sub 2} colloidal crystals by the vertical convective self-assemble method, the Design of Experiments (DoE) methodology is applied. The influence of the evaporation temperature, the volume fraction, and the pH of the colloidal suspension is studied by means of an analysis of variance (ANOVA) in a 3{sup 3} factorial design. Characteristics of the stacking lattice of the resulting colloidal crystals are determined by scanning electron microscopy and angle-resolved transmittance spectroscopy. Quantitative results from the statistical test show that the temperature is the most critical factor influencing the quality of the colloidal crystal, obtaining highly ordered structures with FCC stacking lattice at a growth temperature of 40°C.

  6. Cascaded photonic crystal fibers for three-stage soliton compression.

    PubMed

    Li, Qian; Cheng, Zihao

    2016-11-01

    Cascaded higher-order soliton compression in photonic crystal fibers (PCFs) is demonstrated, where both the hyperbolic secant and Gaussian input pulses are considered. Detailed fiber designs for three-stage higher-order soliton compression where soliton order is three or non-integer are presented. A highest compression factor of 221.32 has been achieved with only 49.48% pedestal energy.

  7. Static and shock compressibility of TATB molecular crystal

    NASA Astrophysics Data System (ADS)

    Degtyarev, A. A.; Smirnov, E. B.; Kostitsin, O. V.; Stankevich, A. V.; Muzyrya, A. K.; Ten, K. A.; Pruuel, E. R.; Kashkarov, A. O.; Batretdinova, L. H.

    2016-11-01

    The paper presents analysis of experimental data on hydrostatic and shock-wave compression of TATB energy-saturated material. The semi-empirical Mie-Grüneisen equation of state was used to describe thermodynamic properties of metastable molecular crystals without considering phase transitions. The equation of state describes experimental data on isothermal compression of a molecular crystal, and this data are obtained using the powder diffraction method. The Hugoniot curve expression plausibly describes shock-compression data on the studied material having various initial porosities.

  8. Why FCC

    NASA Technical Reports Server (NTRS)

    Angele, W.

    1972-01-01

    Summaries are given of design characteristics and various advantages of FCC use. The information is presented in tables that include the following headings: (1) mechanical design, (2) electrical design, (3) manufacturing advantages, (4) inspection and reliability, and (5) cost savings. In addition, the results are summarized of a Saturn 4B FCC-RWC comparison study.

  9. The evolution of machining-induced surface of single-crystal FCC copper via nanoindentation

    PubMed Central

    2013-01-01

    The physical properties of the machining-induced new surface depend on the performance of the initial defect surface and deformed layer in the subsurface of the bulk material. In this paper, three-dimensional molecular dynamics simulations of nanoindentation are preformed on the single-point diamond turning surface of single-crystal copper comparing with that of pristine single-crystal face-centered cubic copper. The simulation results indicate that the nucleation of dislocations in the nanoindentation test on the machining-induced surface and pristine single-crystal copper is different. The dislocation embryos are gradually developed from the sites of homogeneous random nucleation around the indenter in the pristine single-crystal specimen, while the dislocation embryos derived from the vacancy-related defects are distributed in the damage layer of the subsurface beneath the machining-induced surface. The results show that the hardness of the machining-induced surface is softer than that of pristine single-crystal copper. Then, the nanocutting simulations are performed along different crystal orientations on the same crystal surface. It is shown that the crystal orientation directly influences the dislocation formation and distribution of the machining-induced surface. The crystal orientation of nanocutting is further verified to affect both residual defect generations and their propagation directions which are important in assessing the change of mechanical properties, such as hardness and Young's modulus, after nanocutting process. PMID:23641932

  10. The evolution of machining-induced surface of single-crystal FCC copper via nanoindentation.

    PubMed

    Zhang, Lin; Huang, Hu; Zhao, Hongwei; Ma, Zhichao; Yang, Yihan; Hu, Xiaoli

    2013-05-04

    The physical properties of the machining-induced new surface depend on the performance of the initial defect surface and deformed layer in the subsurface of the bulk material. In this paper, three-dimensional molecular dynamics simulations of nanoindentation are preformed on the single-point diamond turning surface of single-crystal copper comparing with that of pristine single-crystal face-centered cubic copper. The simulation results indicate that the nucleation of dislocations in the nanoindentation test on the machining-induced surface and pristine single-crystal copper is different. The dislocation embryos are gradually developed from the sites of homogeneous random nucleation around the indenter in the pristine single-crystal specimen, while the dislocation embryos derived from the vacancy-related defects are distributed in the damage layer of the subsurface beneath the machining-induced surface. The results show that the hardness of the machining-induced surface is softer than that of pristine single-crystal copper. Then, the nanocutting simulations are performed along different crystal orientations on the same crystal surface. It is shown that the crystal orientation directly influences the dislocation formation and distribution of the machining-induced surface. The crystal orientation of nanocutting is further verified to affect both residual defect generations and their propagation directions which are important in assessing the change of mechanical properties, such as hardness and Young's modulus, after nanocutting process.

  11. Temperature Dependence of the Mechanical Properties of Equiatomic Solid Solution Alloys with FCC Crystal Structures

    DOE PAGES

    Wu, Zhenggang; Bei, Hongbin; Pharr, George M.; ...

    2014-10-03

    We found that compared to decades-old theories of strengthening in dilute solid solutions, the mechanical behavior of concentrated solid solutions is relatively poorly understood. A special subset of these materials includes alloys in which the constituent elements are present in equal atomic proportions, including the high-entropy alloys of recent interest. A unique characteristic of equiatomic alloys is the absence of “solvent” and “solute” atoms, resulting in a breakdown of the textbook picture of dislocations moving through a solvent lattice and encountering discrete solute obstacles. Likewise, to clarify the mechanical behavior of this interesting new class of materials, we investigate heremore » a family of equiatomic binary, ternary and quaternary alloys based on the elements Fe, Ni, Co, Cr and Mn that were previously shown to be single-phase face-centered cubic (fcc) solid solutions. The alloys were arc-melted, drop-cast, homogenized, cold-rolled and recrystallized to produce equiaxed microstructures with comparable grain sizes. Tensile tests were performed at an engineering strain rate of 10-3 s-1 at temperatures in the range 77–673 K. Unalloyed fcc Ni was processed similarly and tested for comparison. The flow stresses depend to varying degrees on temperature, with some (e.g. NiCoCr, NiCoCrMn and FeNiCoCr) exhibiting yield and ultimate strengths that increase strongly with decreasing temperature, while others (e.g. NiCo and Ni) exhibit very weak temperature dependencies. Moreover, to better understand this behavior, the temperature dependencies of the yield strength and strain hardening were analyzed separately. Lattice friction appears to be the predominant component of the temperature-dependent yield stress, possibly because the Peierls barrier height decreases with increasing temperature due to a thermally induced increase of dislocation width. In the early stages of plastic flow (5–13% strain, depending on material), the temperature

  12. Temperature Dependence of the Mechanical Properties of Equiatomic Solid Solution Alloys with FCC Crystal Structures

    SciTech Connect

    Wu, Zhenggang; Bei, Hongbin; Pharr, George M.; George, Easo P.

    2014-10-03

    We found that compared to decades-old theories of strengthening in dilute solid solutions, the mechanical behavior of concentrated solid solutions is relatively poorly understood. A special subset of these materials includes alloys in which the constituent elements are present in equal atomic proportions, including the high-entropy alloys of recent interest. A unique characteristic of equiatomic alloys is the absence of “solvent” and “solute” atoms, resulting in a breakdown of the textbook picture of dislocations moving through a solvent lattice and encountering discrete solute obstacles. Likewise, to clarify the mechanical behavior of this interesting new class of materials, we investigate here a family of equiatomic binary, ternary and quaternary alloys based on the elements Fe, Ni, Co, Cr and Mn that were previously shown to be single-phase face-centered cubic (fcc) solid solutions. The alloys were arc-melted, drop-cast, homogenized, cold-rolled and recrystallized to produce equiaxed microstructures with comparable grain sizes. Tensile tests were performed at an engineering strain rate of 10-3 s-1 at temperatures in the range 77–673 K. Unalloyed fcc Ni was processed similarly and tested for comparison. The flow stresses depend to varying degrees on temperature, with some (e.g. NiCoCr, NiCoCrMn and FeNiCoCr) exhibiting yield and ultimate strengths that increase strongly with decreasing temperature, while others (e.g. NiCo and Ni) exhibit very weak temperature dependencies. Moreover, to better understand this behavior, the temperature dependencies of the yield strength and strain hardening were analyzed separately. Lattice friction appears to be the predominant component of the temperature-dependent yield stress, possibly because the Peierls barrier height decreases with increasing temperature due to a thermally induced increase of dislocation width. In the early stages of plastic flow (5–13% strain, depending on material), the

  13. Metal-organic pathways for anisotropic growth of a highly symmetrical crystal structure: example of the fcc Ni.

    PubMed

    Mourdikoudis, Stefanos; Collière, Vincent; Amiens, Catherine; Fau, Pierre; Kahn, Myrtil L

    2013-11-05

    The control of the metallic nanocrystal shape is of prime importance for a wide variety of applications. We report a detailed research work on metal-organic chemical routes for the synthesis of a highly symmetrical crystal structure. In particular, this study shows the key parameters ensuring the anisotropic growth of nickel nanostructures (fcc crystal). Numerous reaction conditions are investigated (precursors, solvents, temperature, reducing agents, reaction time, and types and ratios of surfactants, such as alkyl amines, carboxylic acids, and phosphine oxides), and their effects on the size and shape of the final product are reported. The role of the growth modifiers and the structuring of the reaction media on the anisotropic growth are demonstrated. This metal-organic approach generates several novel anisotropic nanostructures in a wide size range depending on the reaction conditions. In this way, nanomaterials with reproducible size, shape, and composition are obtained with good yield. Transmission electron microscopy techniques (TEM and HRTEM) are the principal methods for monitoring the morphology.

  14. Dislocation structure and deformation hardening alloy fcc single crystals at the mesolevel

    NASA Astrophysics Data System (ADS)

    Teplyakova, L. A.; Kunitsyna, T. S.; Koneva, N. A.; Kozlov, E. V.; Kondratyuk, A. A.; Zboikova, N. A.; Kakushkin, Yu A.; Iakhin, A. A.

    2016-11-01

    The article presents the evaluation results of impacts of various strengthening mechanisms to flow stress. Such evaluations were made on the basis of the measured parameters of the dislocation substructure formed in monocrystals of [001]-Ni3Fe alloy deformed by compression within the stage II. It was found that the main impact to deformation resistance in the alloys with net substructure is made by the mechanism of dislocation impediment, which is caused by contact interaction between moving dislocations and forest dislocations.

  15. Nucleation of liquid droplets and voids in a stretched Lennard-Jones fcc crystal.

    PubMed

    Baidakov, Vladimir G; Tipeev, Azat O

    2015-09-28

    The method of molecular dynamics simulation has been used to investigate the phase decay of a metastable Lennard-Jones face-centered cubic crystal at positive and negative pressures. It is shown that at high degrees of metastability, crystal decay proceeds through the spontaneous formation and growth of new-phase nuclei. It has been found that there exists a certain boundary temperature. Below this temperature, the crystal phase disintegrates as the result of formation of voids, and above, as a result of formation of liquid droplets. The boundary temperature corresponds to the temperature of cessation of a crystal-liquid phase equilibrium when the melting line comes in contact with the spinodal of the stretched liquid. The results of the simulations are interpreted in the framework of classical nucleation theory. The thermodynamics of phase transitions in solids has been examined with allowance for the elastic energy of stresses arising owing to the difference in the densities of the initial and the forming phases. As a result of the action of elastic forces, at negative pressures, the boundary of the limiting superheating (stretching) of a crystal approaches the spinodal, on which the isothermal bulk modulus of dilatation becomes equal to zero. At the boundary of the limiting superheating (stretching), the shape of liquid droplets and voids is close to the spherical one.

  16. Shear moduli in bcc-fcc structure transition of colloidal crystals.

    PubMed

    Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Zhu, Ruzeng

    2015-10-14

    Shear moduli variation in the metastable-stable structure transition of charged colloidal crystals was investigated by the combination techniques of torsional resonance spectroscopy and reflection spectrometer. Modulus of the system increases with the proceeding of the transition process and it finally reaches the maximum value at the end of the transition. For colloidal crystals in stable state, the experimental moduli show good consistence with theoretical expectations. However, in the transition process, the moduli are much smaller than theoretical ones and this can be chalked up to crystalline imperfection in the transition state.

  17. Shear moduli in bcc-fcc structure transition of colloidal crystals

    NASA Astrophysics Data System (ADS)

    Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Zhu, Ruzeng

    2015-10-01

    Shear moduli variation in the metastable-stable structure transition of charged colloidal crystals was investigated by the combination techniques of torsional resonance spectroscopy and reflection spectrometer. Modulus of the system increases with the proceeding of the transition process and it finally reaches the maximum value at the end of the transition. For colloidal crystals in stable state, the experimental moduli show good consistence with theoretical expectations. However, in the transition process, the moduli are much smaller than theoretical ones and this can be chalked up to crystalline imperfection in the transition state.

  18. Nonlinear femtosecond pulse compression in cholesteric liquid crystals (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Liu, Yikun; Zhou, Jianying; Lin, Tsung-Hsien; Khoo, Iam-Choon

    2016-09-01

    Liquid crystals materials have the advantage of having a large nonlinear coefficient, but the response time is slow, normally up to several minisecond. This makes it is hard to apply in ultra fast optical devices. Recently, fentosecond (fs) nonlinear effect in choleteric liquid crystals is reported, nonlinear coefficient in the scale of 10-12 cm2/W is achieved. Base on this effect, in this work, fentosecond pulse compression technique in a miniature choleteric liquid crystal is demonstrated1,2. Cholesteric liquid crystals (CLC) is a kind of 1-dimensional phontonic structure with helical periodic. In a 10 μm thick CLC, femtosecond pulse with 100 fs is compressed to about 50 fs. CLC sample in planar texture with 500μm thick cell gap is further fabricated. In this sample, femtosecond pulse with 847 fs can be compressed to 286 fs. Due to the strong dispersion at the edge of photonic band gap, femtosecond pulse stretching and compensation can be achieve. In this experiment, laser pulse with duration 90 fs is stretched to above 2 picosecond in the first CLC sample and re-compressed to 120 fs in the second sample. Such technique might be applied in chirp pulse amplification. In conclusion, we report ultra fast nonlinear effect in cholesteric liquid crystals. Due to the strong dispersion and nonlinearity of CLC, femtosecond pulse manipulating devices can be achieved in the scale of micrometer.

  19. Lattice rotation patterns and strain gradient effects in FCC single crystals under spherical indentation

    SciTech Connect

    Gao, Y. F.; Larson, B. C.; Lee, J.H.; Nicola, L; Tischler, J.Z.; Pharr, G. M.

    2015-06-01

    Strain gradient effects are commonly modeled as the origin of the size dependence of material strength, such as the dependence of indentation hardness on contact depth and spherical indenter radius. However, studies on the microstructural comparisons of experiments and theories are limited. First, we have extended a strain gradient Mises-plasticity model to its crystal plasticity version and implemented a finite element method to simulate the load-displacement response and the lattice rotation field of Cu single crystals under spherical indentation. The strain gradient simulations demonstrate that the forming of distinct sectors of positive and negative angles in the lattice rotation field is governed primarily by the slip geometry and crystallographic orientations, depending only weakly on strain gradient effects, although hardness depends strongly on strain gradients. Second, the lattice rotation simulations are compared quantitatively with micron resolution, three-dimensional X-ray microscopy (3DXM) measurements of the lattice rotation fields under 100mN force, 100 mu m radius spherical indentations in < 111 >, < 110 >, and < 001 > oriented Cu single crystals. Third, noting the limitation of continuum strain gradient crystal plasticity models, two-dimensional discrete dislocation simulation results suggest that the hardness in the nanocontact regime is governed synergistically by a combination of strain gradients and source-limited plasticity. However, the lattice rotation field in the discrete dislocation simulations is found to be insensitive to these two factors but to depend critically on dislocation obstacle densities and strengths.

  20. Nucleation of liquid droplets and voids in a stretched Lennard-Jones fcc crystal

    SciTech Connect

    Baidakov, Vladimir G. Tipeev, Azat O.

    2015-09-28

    The method of molecular dynamics simulation has been used to investigate the phase decay of a metastable Lennard-Jones face-centered cubic crystal at positive and negative pressures. It is shown that at high degrees of metastability, crystal decay proceeds through the spontaneous formation and growth of new-phase nuclei. It has been found that there exists a certain boundary temperature. Below this temperature, the crystal phase disintegrates as the result of formation of voids, and above, as a result of formation of liquid droplets. The boundary temperature corresponds to the temperature of cessation of a crystal–liquid phase equilibrium when the melting line comes in contact with the spinodal of the stretched liquid. The results of the simulations are interpreted in the framework of classical nucleation theory. The thermodynamics of phase transitions in solids has been examined with allowance for the elastic energy of stresses arising owing to the difference in the densities of the initial and the forming phases. As a result of the action of elastic forces, at negative pressures, the boundary of the limiting superheating (stretching) of a crystal approaches the spinodal, on which the isothermal bulk modulus of dilatation becomes equal to zero. At the boundary of the limiting superheating (stretching), the shape of liquid droplets and voids is close to the spherical one.

  1. Inferring elastic properties of an fcc crystal from displacement correlations: sub-space projection and statistical artifacts

    NASA Astrophysics Data System (ADS)

    Hasan, Asad; Maloney, Craig

    2013-03-01

    We compute the effective dispersion and density of states (DOS) of two-dimensional sub-regions of three dimensional face centered cubic (FCC) crystals with both a direct projection-inversion technique and a Monte Carlo simulation based on a common Hamiltonian. We study sub-regions of both (111) and (100) planes. For any direction of wavevector, we show an anomalous ω2 ~ q scaling regime at low q where ω2 is the energy associated with a mode of wavenumber q. This scaling should give rise to an anomalous DOS, Dω, at low ω: Dω ~ω3 rather than the conventional Debye result: Dω ~ω2 . The DOS for the (100) sub-region looks to be consistent with Dω ~ω3 , while the (111) shows something closer to the Debye result at the smallest frequencies. Our Monte Carlo simulation shows that finite sampling artifacts act as an effective disorder and bias the Dω in the same way as the finite size artifacts, giving a behavior closer to Dω ~ω2 than Dω ~ω3 . These results should have an important impact on interpretation of recent studies of colloidal solids where two-point displacement correlations can be obtained in real-space via microscopy.

  2. Microstructurally Based Cross-slip Mechanisms and Their Effects on Dislocation Microstructure Evolution in fcc Crystals

    DTIC Science & Technology

    2015-01-01

    pp. 655–677. [13] F.J. Humphreys, P.B. Hirsch, The deformation of single crystals of copper and copper -zinc alloys containing alumina particles. ii...stress- orientation dependence in pure copper , Acta Metall. 27 (9) (1979) 1477–1486. [20] J. Bonneville, G. Vanderschaeve, A study of cross slip in the...cross- slipping activation parameters in pure copper , Acta Metall. 36 (1988) 1989–2002. [22] O. Couteau, T. Kruml, J.-L. Martin, About the activation

  3. Dislocation-kinetic analysis of FCC and BCC crystal spallation under shock-wave loading

    NASA Astrophysics Data System (ADS)

    Malygin, G. A.; Ogarkov, S. L.; Andriyash, A. V.

    2015-09-01

    Within the dislocation-kinetic model of the formation and propagation of shock waves in crystals under their intense shock-wave loading, the crystal spallation mechanism at micro- and macrolevels has been discussed taking into account published empirical data. It has been shown that the spallation time t f for Cu, Ni, α-Fe, and Ta crystals in the time interval of 10-6-10-9 s at the macroscopic level changes with variations in the wave pressure σ as , where = is the plastic strain rate according to the Swegle-Grady relation; K f , K σ, and ɛ f = K f K σ ≈ 3-5% are the pressure-independent spallation coefficients and strain, respectively; and E is the Young's modulus. At the microlevel, the dislocation-kinetic calculation of plastic zones around pore nuclei as stress concentrators and plastic strain localization regions at the shock wave front has been performed. It has been shown that the pore coalescence and spall fracture formation result from the superposition of shear stresses and plastic deformations in interpore spacings when the latter decrease to a size of the order of two pore sizes.

  4. Shock compression of [001] single crystal silicon

    SciTech Connect

    Zhao, S.; Remington, B.; Hahn, E. N.; Kad, B.; Bringa, E. M.; Meyers, M. A.

    2016-03-14

    Silicon is ubiquitous in our advanced technological society, yet our current understanding of change to its mechanical response at extreme pressures and strain-rates is far from complete. This is due to its brittleness, making recovery experiments difficult. High-power, short-duration, laser-driven, shock compression and recovery experiments on [001] silicon (using impedance-matched momentum traps) unveiled remarkable structural changes observed by transmission electron microscopy. As laser energy increases, corresponding to an increase in peak shock pressure, the following plastic responses are are observed: surface cleavage along {111} planes, dislocations and stacking faults; bands of amorphized material initially forming on crystallographic orientations consistent with dislocation slip; and coarse regions of amorphized material. Molecular dynamics simulations approach equivalent length and time scales to laser experiments and reveal the evolution of shock-induced partial dislocations and their crucial role in the preliminary stages of amorphization. Furthermore, application of coupled hydrostatic and shear stresses produce amorphization below the hydrostatically determined critical melting pressure under dynamic shock compression.

  5. Shock compression of [001] single crystal silicon

    DOE PAGES

    Zhao, S.; Remington, B.; Hahn, E. N.; ...

    2016-03-14

    Silicon is ubiquitous in our advanced technological society, yet our current understanding of change to its mechanical response at extreme pressures and strain-rates is far from complete. This is due to its brittleness, making recovery experiments difficult. High-power, short-duration, laser-driven, shock compression and recovery experiments on [001] silicon (using impedance-matched momentum traps) unveiled remarkable structural changes observed by transmission electron microscopy. As laser energy increases, corresponding to an increase in peak shock pressure, the following plastic responses are are observed: surface cleavage along {111} planes, dislocations and stacking faults; bands of amorphized material initially forming on crystallographic orientations consistent withmore » dislocation slip; and coarse regions of amorphized material. Molecular dynamics simulations approach equivalent length and time scales to laser experiments and reveal the evolution of shock-induced partial dislocations and their crucial role in the preliminary stages of amorphization. Furthermore, application of coupled hydrostatic and shear stresses produce amorphization below the hydrostatically determined critical melting pressure under dynamic shock compression.« less

  6. Shock compression of [001] single crystal silicon

    NASA Astrophysics Data System (ADS)

    Zhao, S.; Hahn, E. N.; Kad, B.; Remington, B. A.; Bringa, E. M.; Meyers, M. A.

    2016-05-01

    Silicon is ubiquitous in our advanced technological society, yet our current understanding of change to its mechanical response at extreme pressures and strain-rates is far from complete. This is due to its brittleness, making recovery experiments difficult. High-power, short-duration, laser-driven, shock compression and recovery experiments on [001] silicon (using impedance-matched momentum traps) unveiled remarkable structural changes observed by transmission electron microscopy. As laser energy increases, corresponding to an increase in peak shock pressure, the following plastic responses are are observed: surface cleavage along {111} planes, dislocations and stacking faults; bands of amorphized material initially forming on crystallographic orientations consistent with dislocation slip; and coarse regions of amorphized material. Molecular dynamics simulations approach equivalent length and time scales to laser experiments and reveal the evolution of shock-induced partial dislocations and their crucial role in the preliminary stages of amorphization. Application of coupled hydrostatic and shear stresses produce amorphization below the hydrostatically determined critical melting pressure under dynamic shock compression.

  7. Inferring elastic properties of an fcc crystal from displacement correlations: Subspace projection and statistical artifacts

    NASA Astrophysics Data System (ADS)

    Hasan, A.; Maloney, C. E.

    2014-12-01

    We compute the effective dispersion and vibrational density of states (DOS) of two-dimensional subregions of three-dimensional face-centered-cubic crystals using both a direct projection-inversion technique and a Monte Carlo simulation based on a common underlying Hamiltonian. We study both a (111) and (100) plane. We show that for any given direction of wave vector, both (111) and (100) show an anomalous ω2˜q regime at low q where ω2 is the energy associated with the given mode and q is its wave number. The ω2˜q scaling should be expected to give rise to an anomalous DOS, Dω, at low ω : Dω˜ω3 rather than the conventional Debye result: Dω˜ω2 . The DOS for (100) looks to be consistent with Dω˜ω3 , while (111) shows something closer to the conventional Debye result at the smallest frequencies. In addition to the direct projection-inversion calculation, we perform Monte Carlo simulations to study the effects of finite sampling statistics. We show that finite sampling artifacts act as an effective disorder and bias Dω, giving a behavior closer to Dω˜ω2 than Dω˜ω3 . These results should have an important impact on the interpretation of recent studies of colloidal solids where the two-point displacement correlations can be obtained directly in real-space via microscopy.

  8. Inferring elastic properties of an fcc crystal from displacement correlations: subspace projection and statistical artifacts.

    PubMed

    Hasan, A; Maloney, C E

    2014-12-01

    We compute the effective dispersion and vibrational density of states (DOS) of two-dimensional subregions of three-dimensional face-centered-cubic crystals using both a direct projection-inversion technique and a Monte Carlo simulation based on a common underlying Hamiltonian. We study both a (111) and (100) plane. We show that for any given direction of wave vector, both (111) and (100) show an anomalous ω(2)∼q regime at low q where ω(2) is the energy associated with the given mode and q is its wave number. The ω(2)∼q scaling should be expected to give rise to an anomalous DOS, D(ω), at low ω: D(ω)∼ω(3) rather than the conventional Debye result: D(ω)∼ω(2). The DOS for (100) looks to be consistent with D(ω)∼ω(3), while (111) shows something closer to the conventional Debye result at the smallest frequencies. In addition to the direct projection-inversion calculation, we perform Monte Carlo simulations to study the effects of finite sampling statistics. We show that finite sampling artifacts act as an effective disorder and bias D(ω), giving a behavior closer to D(ω)∼ω(2) than D(ω)∼ω(3). These results should have an important impact on the interpretation of recent studies of colloidal solids where the two-point displacement correlations can be obtained directly in real-space via microscopy.

  9. Alignment and Stiffening of Liquid Crystal Elastomers under Dynamic Compression

    NASA Astrophysics Data System (ADS)

    Agrawal, Aditya; Patra, Prabir; Ajayan, Pulickel; Chapman, Walter; Verduzco, Rafael

    2013-03-01

    Biological tissues have the remarkable ability to remodel and repair in response to disease, injury, and mechanical stresses, a phenomenon known ``functional adaptation'' or ``remodeling''. Herein, we report similar behavior in polydomain liquid crystal elastomers. Liquid crystal elastomers dramatically increase in stiffness by up to 90 % under low-amplitude, repetitive (dynamic) compression. By studying a systematic series of materials, we demonstrate that the stiffness increase is directly influenced by the liquid crystal content of the elastomers, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through a combination of rheological measurements, polarizing optical microscopy and 2-D X-ray diffraction, we demonstrate that self-stiffening arises due to rotations of the nematic director in response to dynamic compression, and show that the behavior is consistent with the theory for nematic rubber elasticity. Previous work with liquid crystal elastomers has focused primarily on `soft elastic' deformations at large strains, but our findings indicate rich behavior at previously overlooked low-strain, dynamic deformations.

  10. Infrared predetection dynamic range compression via photorefractive crystals

    NASA Technical Reports Server (NTRS)

    Liu, Hua-Kuang; Cheng, Li-Jen

    1988-01-01

    The theoretical basis and practical implementation of a predetection dynamic-range compression technique for IR sensor systems are discussed. The approach takes advantage of the nonlinear intensity dependence of the gain coefficient in photorefractive crystals. Its feasibility is demonstrated in numerical computations using the experimental data of Cheng and Partovi (1986) on two-wave mixing in GaAs at 1.15 micron wavelength.

  11. Epitaxial growth of fcc-Co{sub x}Ni{sub 100-x} thin films on MgO(110) single-crystal substrates

    SciTech Connect

    Ohtake, Mitsuru; Nukaga, Yuri; Sato, Yoichi; Futamoto, Masaaki; Kirino, Fumiyoshi

    2009-12-15

    Co{sub x}Ni{sub 100-x} (x=100, 80, 20, 0 at. %) epitaxial thin films were prepared on MgO(110) single-crystal substrates heated at 300 deg. C by ultrahigh vacuum molecular beam epitaxy. The growth mechanism is discussed based on lattice strain and crystallographic defects. CoNi(110) single-crystal films with a fcc structure are obtained for all compositions. Co{sub x}Ni{sub 100-x} film growth follows the Volmer-Weber mode. X-ray diffraction analysis indicates that the out-of-plane and the in-plane lattice spacings of the Co{sub x}Ni{sub 100-x} films are in agreement within +-0.5% with the values of the respective bulk Co{sub x}Ni{sub 100-x} crystals, suggesting that the strain in the film is very small. High-resolution cross-sectional transmission microscopy shows that an atomically sharp boundary is formed between a Co(110){sub fcc} film and a MgO(110) substrate, where periodical misfit dislocations are preferentially introduced in the film at the Co/MgO interface. The presence of such periodical misfit dislocations relieves the strain caused by the lattice mismatch between the film and the substrate.

  12. Shock compression experiments on Lithium Deuteride single crystals.

    SciTech Connect

    Knudson, Marcus D.; Desjarlais, Michael Paul; Lemke, Raymond W.

    2014-10-01

    S hock compression exper iments in the few hundred GPa (multi - Mabr) regime were performed on Lithium Deuteride (LiD) single crystals . This study utilized the high velocity flyer plate capability of the Sandia Z Machine to perform impact experiments at flyer plate velocities in the range of 17 - 32 km/s. Measurements included pressure, density, and temperature between %7E200 - 600 GPa along the Principal Hugoniot - the locus of end states achievable through compression by large amplitude shock waves - as well as pressure and density of re - shock states up to %7E900 GPa . The experimental measurements are compared with recent density functional theory calculations as well as a new tabular equation of state developed at Los Alamos National Labs.

  13. Resonance compression of an acoustic beam in a crystal

    SciTech Connect

    Alshits, V. I. Bessonov, D. A.; Lyubimov, V. N.

    2016-04-15

    The resonance excitation of an intense acoustic beam in a crystal is described for a special geometry of pump-wave reflection from the crystal surface. The resonance appears in the vicinity of the total internal reflection angle under the condition that the wave field in a compressed reflected beam propagating almost parallel to the surface is close to the volume eigenmode satisfying the free boundary condition. Criteria for the existence of such modes are considered in detail. Conversion conditions are analyzed under which a “parasitic” reflected wave of the same branch as the incident wave is absent and entire energy from the incident wave falls within a narrow intense acoustic beam of another branch. It is shown that, when the surface is chosen parallel to the crystal symmetry plane, the conversion criterion is reduced to the sole condition on the elastic moduli of the medium. Analysis is performed by analytic and numerical methods for skew cuts of monoclinic, rhombic, trigonal, and hexagonal crystals, when the boundary is the symmetry plane, while the sagittal plane has no symmetry. A number of crystals are found in which resonance excitation is very close to conversion.

  14. Resonance compression of an acoustic beam in a crystal

    NASA Astrophysics Data System (ADS)

    Alshits, V. I.; Bessonov, D. A.; Lyubimov, V. N.

    2016-04-01

    The resonance excitation of an intense acoustic beam in a crystal is described for a special geometry of pump-wave reflection from the crystal surface. The resonance appears in the vicinity of the total internal reflection angle under the condition that the wave field in a compressed reflected beam propagating almost parallel to the surface is close to the volume eigenmode satisfying the free boundary condition. Criteria for the existence of such modes are considered in detail. Conversion conditions are analyzed under which a "parasitic" reflected wave of the same branch as the incident wave is absent and entire energy from the incident wave falls within a narrow intense acoustic beam of another branch. It is shown that, when the surface is chosen parallel to the crystal symmetry plane, the conversion criterion is reduced to the sole condition on the elastic moduli of the medium. Analysis is performed by analytic and numerical methods for skew cuts of monoclinic, rhombic, trigonal, and hexagonal crystals, when the boundary is the symmetry plane, while the sagittal plane has no symmetry. A number of crystals are found in which resonance excitation is very close to conversion.

  15. Shock Compression of Metal Crystals: A Comparison of Eulerian and Lagrangian Elastic-Plastic Theories

    DTIC Science & Technology

    2014-11-01

    Shock Compression of Metal Crystals: A Comparison of Eulerian and Lagrangian Elastic- Plastic Theories by JD Clayton ARL-RP-0513...of Metal Crystals: A Comparison of Eulerian and Lagrangian Elastic- Plastic Theories JD Clayton Weapons and Materials Research Directorate, ARL...SUBTITLE Shock Compression of Metal Crystals: A Comparison of Eulerian and Lagrangian Elastic- Plastic Theories 5a. CONTRACT NUMBER 5b. GRANT

  16. Dislocation Multiplication by Single Cross Slip for FCC at Submicron Scales

    NASA Astrophysics Data System (ADS)

    Cui, Yi-Nan; Liu, Zhan-Li; Zhuang, Zhuo

    2013-04-01

    The operation mechanism of single cross slip multiplication (SCSM) is investigated by studying the response of one dislocation loop expanding in face-centered-cubic (FCC) single crystal using three-dimensional discrete dislocation dynamic (3D-DDD) simulation. The results show that SCSM can trigger highly correlated dislocation generation in a short time, which may shed some light on understanding the large strain burst observed experimentally. Furthermore, we find that there is a critical stress and material size for the operation of SCSM, which agrees with that required to trigger large strain burst in the compression tests of FCC micropillars.

  17. Insulating fcc YH

    SciTech Connect

    Molen, S. J. van der; Nagengast, D. G.; Gogh, A. T. M. van; Kalkman, J.; Kooij, E. S.; Rector, J. H.; Griessen, R.

    2001-06-15

    We study the structural, optical, and electrical properties of Mg{sub z}Y{sub 1{minus}z} switchable mirrors upon hydrogenation. It is found that the alloys disproportionate into essentially pure YH{sub 3{minus}{delta}} and MgH{sub 2} with the crystal structure of YH{sub 3{minus}{delta}} dependent on the Mg concentration z. For 0{lt}z{lt}0.1, both hcp and fcc YH{sub 3{minus}{delta}} are observed, whereas for z{ge}0.1 only cubic YH{sub 3{minus}{delta}} is present. Interestingly, cubic YH{sub 3{minus}{delta}} is expanded compared to YH{sub 2}, in disagreement with theoretical predictions. From optical and electrical measurements we conclude that cubic YH{sub 3{minus}{delta}} is a transparent insulator with properties similar to hexagonal YH{sub 3{minus}{delta}}. Our results are inconsistent with calculations predicting fcc YH{sub 3{minus}{delta}} to be metallic, but they are in good agreement with recent GW calculations on both hcp and fcc YH{sub 3}. Finally, we find an increase in the effective band gap of the hydrided Mg{sub z}Y{sub 1{minus}z} alloys with increasing z. Possibly this is due to quantum confinement effects in the small YH{sub 3} clusters.

  18. Dependence of Initial Grain Orientation on the Evolution of Anisotropy in FCC and BCC Metals Using Crystal Plasticity and Texture Analysis

    NASA Astrophysics Data System (ADS)

    Raja, Daniel Selvakumar

    Abundant experimental analyses and theoretical computational analyses that had been performed on metals to understand anisotropy and its evolution and its dependence on initial orientation of grains have failed to provide theories that can be used in macro-scale plasticity. Ductile metals fracture after going through a large amount of plastic deformation, during which the anisotropy of the material changes significantly. Processed metal sheets or slabs possess anisotropy due to textures produced by metal forming processes (such as drawing, bending and press braking). Metals that were initially isotropic possess anisotropy after undergoing forming processes, i.e., through texture formation due to large amount of plastic deformation before fracture. It is therefore essential to consider the effect of anisotropy to predict the characteristics of fracture and plastic flow performances in the simulation of ductile fracture and plastic flow of materials. Crystal plasticity simulations carried out on grains at the meso-scale level with different initial orientations (ensembles) help to derive the evolution of anisotropy at the macro-scale level and its dependence on initial orientation of grains. This paper investigates the evolution of anisotropy in BCC and FCC metals and its dependence on grain orientation using crystal plasticity simulations and texture analysis to reveal the mechanics behind the evolution of anisotropy. A comparison of anisotropy evolution between BCC and FCC metals is made through the simulation, which can be used to propose the theory of anisotropy evolution in macro-scale plasticity. Keywords: ensembles; grains; initial orientation; anisotropy; evolution of anisotropy; crystal plasticity; textures; homogeneity; isotropy; inelastic; equivalent strain.

  19. Impact sensitivity and crystal lattice compressibility/free space.

    PubMed

    Politzer, Peter; Murray, Jane S

    2014-05-01

    There is considerable evidence, which we discuss, indicating that compressibility and available free space in the crystal lattice are among the factors that govern the sensitivity of an explosive compound. Expanding and extending earlier work, we demonstrate, for 25 explosives, that there is an overall general tendency for greater impact sensitivity as the estimated free space per molecule increases. More specific relationships can be discerned by looking at subgroups of the compounds. The nitramine sensitivities, most of which are quite high, increase nearly linearly but only very gradually with free space. The nitroaromatics cover a wide range of sensitivities but all have an approximately similar intermediate level of free space. The remaining types of compounds show a reasonable sensitivity-free space relationship with one outlier: FOX-7 (1,1-diamino-2,2-dinitroethylene).

  20. Observation of soliton compression in silicon photonic crystals

    PubMed Central

    Blanco-Redondo, A.; Husko, C.; Eades, D.; Zhang, Y.; Li, J.; Krauss, T.F.; Eggleton, B.J.

    2014-01-01

    Solitons are nonlinear waves present in diverse physical systems including plasmas, water surfaces and optics. In silicon, the presence of two photon absorption and accompanying free carriers strongly perturb the canonical dynamics of optical solitons. Here we report the first experimental demonstration of soliton-effect pulse compression of picosecond pulses in silicon, despite two photon absorption and free carriers. Here we achieve compression of 3.7 ps pulses to 1.6 ps with <10 pJ energy. We demonstrate a ~1-ps free-carrier-induced pulse acceleration and show that picosecond input pulses are critical to these observations. These experiments are enabled by a dispersion-engineered slow-light photonic crystal waveguide and an ultra-sensitive frequency-resolved electrical gating technique to detect the ultralow energies in the nanostructured device. Strong agreement with a nonlinear Schrödinger model confirms the measurements. These results further our understanding of nonlinear waves in silicon and open the way to soliton-based functionalities in complementary metal-oxide-semiconductor-compatible platforms. PMID:24423977

  1. Spin rotation and depolarization of high-energy particles in crystals at LHC and FCC energies. The possibility to measure the anomalous magnetic moments of short-lived particles and quadrupole moment of Ω -hyperon

    NASA Astrophysics Data System (ADS)

    Baryshevsky, V. G.

    2017-07-01

    The phenomena of spin rotation and depolarization of high-energy particles in crystals in the range of high energies that will be available at Hadron Collider (LHC) and Future Circular Collider (FCC) provides a unique possibility of measuring the anomalous magnetic moment of charged and neutral charm and beauty hyperons and quadrupole moment of Ω -hyperon. Crystals with polarized nuclei give opportunities for measuring spin-dependent interactions of short lived particles with nuclei and measurement of a particle polarization.

  2. Crystal Plasticity Analysis on Compressive Loading of Magnesium with Suppression of Twinning

    NASA Astrophysics Data System (ADS)

    Mayama, Tsuyoshi; Ohashi, Tetsuya; Higashida, Kenji; Kawamura, Yoshihito

    The compressive loading behavior of single crystals and bicrystals of magnesium without consideration of deformation twinning has been investigated by crystal plasticity finite element analysis with the aim of fundamental understanding of kink band formation in magnesium alloys with long period stacking ordered structure (LPSO) phase. The basal plane of the single crystal model is set to be parallel to the compressive direction. The result of the compressive loading analysis of single crystals indicates the significant influence of suppression of twinning on the activation of nonbasal slip systems and stress-strain behavior. The compressive analysis of symmetric bicrystal is also performed to clarify the influence of the angle between basal plane and the loading axis. The influence of the introduction of grain boundary and the slight change of crystal orientation is discussed in terms of activated deformation modes.

  3. A physically based constitutive model for FCC single crystals with a single state variable per slip system

    NASA Astrophysics Data System (ADS)

    Demir, Eralp

    2017-01-01

    A new, simple and physically consistent dislocation-density-based continuum model is developed in a large-strain crystal plasticity framework. All the constitutive laws are expressed in a simple and unique way in terms of a single state variable dislocation density. The proposed physically based model predicts experimental single-crystal stress-strain curves along different crystal directions more accurately than a classical model with widely accepted constitutive laws. The polycrystal texture predictions from the dislocation-density-based and classical models having the same single-crystal stress-strain characteristics are in good agreement with the classical model when Taylor-type homogenization is used in conjunction with enough number of grains.

  4. Compression of Single-Crystal Orthopyroxene to 60GPa

    NASA Astrophysics Data System (ADS)

    Finkelstein, G. J.; Dera, P. K.; Holl, C. M.; Dorfman, S. M.; Duffy, T. S.

    2010-12-01

    Orthopyroxene ((Mg,Fe)SiO3) is one of the dominant phases in Earth’s upper mantle - it makes up ~20% of the upper mantle by volume. At high pressures and temperatures, this phase undergoes several well-characterized phase transitions. However, when compressed at low temperature and high-pressure, orthopyroxene is predicted to exhibit metastable behavior(1). Previous researchers have found orthoenstatite (Mg endmember of orthopyroxene) persists up to ~10 GPa, and diffraction(2-3), Raman(4), and elasticity(5) experiments suggest a phase transition above this pressure to an as-yet unidentified structure. While earlier diffraction data has surprisingly only been evaluated for structural information to ~9 GPa(2), changes in high-pressure Raman spectra to ~70 GPa indicate that several more high-pressure phase transitions in orthopyroxene are likely, including at least one change in Si-coordination(6). We have recently conducted exploratory experiments to further elucidate the high-pressure behavior of orthopyroxene. Compressing a single crystal of Fe-rich orthopyroxene (Fe0.66Mg0.24Ca0.05SiO3) using a diamond anvil cell, we observe phase transitions at ~10, 14, and 30 GPa, with the new phases having monoclinic, orthorhombic, and orthorhombic symmetries, respectively. While the first two transitions do not show a significant change in volume, the phase transition at ~30 GPa shows a large decrease in volume, which is consistent with a change in Si coordination number to mixed 4- and 6-fold coordination. References: [1] S. Jahn, American Mineralogist 93, 528-532 (2008). [2] R. J. Angel, J. M. Jackson, American Mineralogist 87, 558-561 (2002). [3] R. J. Angel, D. A. Hugh-Jones, Journal of Geophysical Research-Solid Earth 99, 19,777-19,783 (1994). [4] G. Serghiou, Journal of Raman Spectroscopy 34, 587-590 (2003). [5] J. Kung et al., Physics of the Earth and Planetary Interiors 147, 27-44 (2004). [6] G. Serghiou, A. Chopelas, R. Boehler, Journal of Physics: Condensed

  5. Phase field theory of interfaces and crystal nucleation in a eutectic system of fcc structure: I. Transitions in the one-phase liquid region.

    PubMed

    Tóth, Gyula I; Gránásy, László

    2007-08-21

    The phase field theory (PFT) has been applied to predict equilibrium interfacial properties and nucleation barrier in the binary eutectic system Ag-Cu using double well and interpolation functions deduced from a Ginzburg-Landau expansion that considers fcc (face centered cubic) crystal symmetries. The temperature and composition dependent free energies of the liquid and solid phases are taken from CALculation of PHAse Diagrams-type calculations. The model parameters of PFT are fixed so as to recover an interface thickness of approximately 1 nm from molecular dynamics simulations and the interfacial free energies from the experimental dihedral angles available for the pure components. A nontrivial temperature and composition dependence for the equilibrium interfacial free energy is observed. Mapping the possible nucleation pathways, we find that the Ag and Cu rich critical fluctuations compete against each other in the neighborhood of the eutectic composition. The Tolman length is positive and shows a maximum as a function of undercooling. The PFT predictions for the critical undercooling are found to be consistent with experimental results. These results support the view that heterogeneous nucleation took place in the undercooling experiments available at present. We also present calculations using the classical droplet model [classical nucleation theory (CNT)] and a phenomenological diffuse interface theory (DIT). While the predictions of the CNT with a purely entropic interfacial free energy underestimate the critical undercooling, the DIT results appear to be in a reasonable agreement with the PFT predictions.

  6. Effect of compression force on the crystal properties of erythromycin acistrate tablets.

    PubMed

    Riippi, M; Tanninen, V; Yliruusi, J

    2000-11-01

    The crystal properties of compressed and powdered erythromycin acistrate tablets were studied by the X-ray powder diffraction (XRPD) method. Detailed analysis of X-ray powder diffraction line profiles was performed. Diffraction peak intensities and full width at half maximum (FWHM) values of the peaks corresponding to three different crystal lattice directions were determined. Crystallite size was calculated by Scherrer's equation using the data of integral breadth of the peaks. The preferred orientation of the crystallites is also discussed. According to the results, the crystallite size increased on the tablet surface after a small compression force (4 kN) in all crystal lattice directions studied. Even small compression forces caused recrystallization. With higher compression forces (8-18 kN) the crystallite size and the FWHM values remained rather constant. After the compression force of 18 kN the peaks in different crystal lattice directions behaved differently. In the lattice directions of diffraction maxima 2 and 3, the effect was the same with the small (4 kN) and the high compression force (22 kN). Further recrystallization occurred with 22 kN. However, in the crystal lattice direction of diffraction maximum 1 at the compression force of 8 kN the crystallite broke and crystallinity decreased. These were not seen in the powdered tablet samples. It could be concluded that the effect of compression force on the crystal properties of erythromycin acistrate tablets was seen on the tablet surface but not in the powdered tablets. Compression force also affected the preferred orientation of crystallites on the tablet surface and especially in the lattice direction of diffraction maximum 3. This was not seen in the powdered tablets.

  7. Development of a numerical procedure for mixed mode K-solutions and fatigue crack growth in FCC single crystal superalloys

    NASA Astrophysics Data System (ADS)

    Ranjan, Srikant

    2005-11-01

    Fatigue-induced failures in aircraft gas turbine and rocket engine turbopump blades and vanes are a pervasive problem. Turbine blades and vanes represent perhaps the most demanding structural applications due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and jet engines because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. These materials have orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Computation of stress intensity factors (SIFs) and the ability to model fatigue crack growth rate at single crystal cracks subject to mixed-mode loading conditions are important parts of developing a mechanistically based life prediction for these complex alloys. A general numerical procedure has been developed to calculate SIFs for a crack in a general anisotropic linear elastic material subject to mixed-mode loading conditions, using three-dimensional finite element analysis (FEA). The procedure does not require an a priori assumption of plane stress or plane strain conditions. The SIFs KI, KII, and KIII are shown to be a complex function of the coupled 3D crack tip displacement field. A comprehensive study of variation of SIFs as a function of crystallographic orientation, crack length, and mode-mixity ratios is presented, based on the 3D elastic orthotropic finite element modeling of tensile and Brazilian Disc (BD) specimens in specific crystal orientations. Variation of SIF through the thickness of the specimens is also analyzed. The resolved shear stress intensity coefficient or effective SIF, Krss, can be computed as a function of crack tip SIFs and the

  8. The possibility to measure the magnetic moments of short-lived particles (charm and beauty baryons) at LHC and FCC energies using the phenomenon of spin rotation in crystals

    NASA Astrophysics Data System (ADS)

    Baryshevsky, V. G.

    2016-06-01

    The use of spin rotation effect in bent crystals for measuring the magnetic moment of short-lived particles in the range of LHC and FCC energies is considered. It is shown that the estimated number of produced baryons that are captured into a bent crystal grows as ∼γ 3 / 2 with increasing particle energy. Hence it may be concluded that the experimental measurement of magnetic moments of short-lived particles using the spin rotation effect is feasible at LHC and higher energies (for LHC energies, e.g., the running time required for measuring the magnetic moment of Λc+ is 2 ÷ 16 hours).

  9. Segmentation Effect on Inhomogeneity of [110]-Single Crystal Deformation

    NASA Astrophysics Data System (ADS)

    Lychagin, D. V.; Nesterenko, E. A. Alfyorova V. P.

    2016-08-01

    This work presents a detailed analysis of segmentation process in FCC single crystals with compression axis [110] and side faces( ̅110) and (001) considering effect of octahedral shear crystal-geometry and basic stress concentrators. Sequence of meso-band systems formation on side faces is determined. Macro-segmentation patterns are specified, that are common to the FCC single crystals under investigation. It is proved that rectangular shape of highly compressed crystals, elongated in direction of operating planes, is conditioned by orientation symmetry of compression axis, single crystal side faces and shears directions, which are characteristic for the given orientation. The specified patterns are characteristic only for the samples with initial height-to-width ratio equal to 2. When varying sample height relative to the initial one, segmentation patterns will also vary due to crystal geometry variations.

  10. Minor element partitioning between fcc Fe metal and Fe-S liquid at high pressure: The role of crystal lattice strain

    NASA Astrophysics Data System (ADS)

    Stewart, Andrew J.; van Westrenen, Wim; Schmidt, Max W.; Günther, D.

    2009-07-01

    We present a new approach to model element distribution between solid and liquid metal phases, based on experimentally determined data for the partitioning of P, S, selected transition metals, and chalcophile elements between face-centred cubic (fcc) Fe and Fe-S liquid at pressures of 9, 15 and 23 GPa and temperatures between 1523 and 1773 K. Solid/liquid partition coefficients ( D) for the transition metals V, Cr, Mn, Fe, Co, and Ni range from a minimum D of 0.16-0.64 for V to a maximum D of 1.1-1.2 for Co, indicating modest but significant fractionation. D for the chalcophile elements Cu, Zn, Ga, Sn, and Pb varies from 0.029-0.051 for DPb up to 1.6-2.4 for DGa and for non-metals from 0.02-0.04 for S to 0.23-0.66 for P. A modified lattice strain model (as in common use for silicate mineral-melt partitioning) describes the variations in D values for the first row transition metals through the deviance in metal radius from the ideal site radius of Fe in solid metal, indicating that these metals all substitute into the iron site of the solid phase. Variations in D values for the chalcophile elements can also be rationalized using a lattice strain model, but chalcophiles occupy a different site in the solid metal, probably related to the presence of sulphur defects. We show that the lattice strain model can be applied to previously published low pressure experimental data, as well as to third-row transition metals as to first-row transition metals and chalcophiles. The fact that solid-liquid metal D values are amenable to interpretation using lattice strain models paves the way for the development of a new class of element partitioning models applicable to metallic core crystallization processes.

  11. Reduce FCC corrosion

    SciTech Connect

    Walker, H.B.

    1984-01-01

    Efficiency of fluid catalytic cracking (FCC) vapor recovery units can be significantly reduced by corrosion and fouling. The fundamentals of FCC light ends corrosion, including diagnoses, control and monitoring of hydrogen blistering, general metal loss, pitting, erosion and under-deposit attack are discussed, relating actual unit problems to effective treatment program solutions.

  12. Improving the intensity and efficiency of compressed echo in rare-earth-ion-doped crystal

    NASA Astrophysics Data System (ADS)

    Xiu-Rong, Ma; Yu-Qing, Liang; Song, Wang; Shuang-Gen, Zhang; Yun-Long, Shan

    2016-07-01

    We investigate the intensity and efficiency of a compressed echo, which is important in arbitrary waveform generation (AWG). A new model of compressed echo is proposed based on the optical Bloch equations, which exposes much more detailed parameters than the conventional model, such as the time delay of the chirp lasers, the nature of the rare-earth-ion-doped crystal, etc. According to the novel model of compressed echo, we find that reducing the time delay of the chirp lasers and scanning the lasers around the center frequency of the inhomogeneously broadened spectrum, while utilizing a crystal with larger coherence time and excitation lifetime can improve the compressed echo’s intensity and efficiency. The theoretical analysis is validated by numerical simulations. Project supported by Special Funds for Scientific and Technological Innovation Projects in Tianjin, China (Grant No. 10FDZDGX00400) and the Tianjin Research Program of Application Foundation and Advanced Technology, China (Grant No. 15JCQNJC01100).

  13. Equation of state and thermodynamic functions for the fcc soft-core multiple-Yukawa solid and application to fullerenes with compressible molecular radius

    NASA Astrophysics Data System (ADS)

    Sun, Jiu-Xun

    2007-01-01

    The generalized free volume theory is applied to the soft-core multiple-Yukawa solid, and the hard-core multiple-Yukawa is included in as a special case. The expressions for equation of state and internal energy are derived. The formalism developed is applied to the C60 , C76 , and C84 solids. The effective diameter of C60 molecule is taken as the experimental value; the parameters of the double Yukawa (DY) potential for carbon-carbon atoms are determined through fitting the experimental data of cohesive energy, the lattice constant, and the compression curve of C60 solid at ambient temperature. The effective diameter of C76 and C84 molecules are determined through fitting the experimental lattice constants at ambient temperature. The numerical results of C60 solid from the soft-core DY potential are in good agreement with the experiments, including the lattice constant and compression curve. The lattice constant versus temperature relationship for C76 and C84 solids calculated from the DY potential is qualitatively in accordance with experimental data as same as the Girifalco potential. The compression curve of the C84 solid calculated from the DY potential deviates from and is softer than the experimental data available. The reason for deviation is discussed, and it is concluded that the influence of compressibility of fullerene molecules to thermophysical quantities is important at high-pressure conditions.

  14. Avalanches, plasticity, and ordering in colloidal crystals under compression.

    PubMed

    McDermott, D; Reichhardt, C J Olson; Reichhardt, C

    2016-06-01

    Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.

  15. Molecular Dynamics Simulation of FCC Metallic Nanowires: A Review

    NASA Astrophysics Data System (ADS)

    Lao, Jijun; Naghdi Tam, Mehdi; Pinisetty, Dinesh; Gupta, Nikhil

    2013-02-01

    Molecular dynamic simulation studies are reviewed to understand the influence of strain rate, temperature, and cross-section size on the mechanical properties of face-centered cubic (FCC) metallic nanowires (MNWs). The yield stress of FCC MNWs is found to be 100 times higher than that of the corresponding bulk metals. The yield strain and fracture stress of MNWs are also found to be significantly higher compared with those of the bulk metals. The influence of deformation mechanisms (slip and twinning) on the mechanical properties of FCC MNWs is discussed. FCC MNWs are found to exhibit novel structural reorientation, phase transformation, elastic recovery, pseudoelasticity, and shape memory effect. MNWs with body-centered cubic (BCC) and hexagonal closed-packed crystal structures are compared with the FCC MNWs. Pseudoelasticity was also observed in BCC MNWs similar to that of FCC MNWs. Dense nano-twin arrays were found in Mg nanowires despite the high twin boundary energy.

  16. Hydrostatic Compression of 2,4,6,8,10,12 hexanitrohexaaza isowurtzitane (CL20) Co Crystals

    DTIC Science & Technology

    2016-12-01

    improved properties.1,2 Co-crystals are solid state materials comprising 2 (or more) molecular components that interact via noncovalent interactions...of the co-crystal’s stability to that of the individual components .6,7 However, other critical material properties such as the response of EM co...Hydrostatic Compression of 2,4,6,8,10,12- hexanitrohexaaza-isowurtzitane (CL20) Co-Crystals by DeCarlos Taylor Weapons and Materials

  17. On the localization of plastic strain under compression of LiF crystals

    NASA Astrophysics Data System (ADS)

    Barannikova, S. A.; Nadezhkin, M. V.; Zuev, L. B.

    2010-07-01

    The plastic flow localization patterns for alkali halide LiF crystals under compression have been investigated. The main spatiotemporal regularities of the strain localization at different stages of deformation hardening in the single crystals have been established. The relation has been traced between the orientation of localized strain zones and the crystallography of slip systems of the test specimens studied simultaneously by the double-exposure speckle photography and photoelasticity methods.

  18. Acoustic Emission Analysis of Plane Strain-Compressed Mg Single Crystals

    NASA Astrophysics Data System (ADS)

    Drozdenko, Daria; Dobroň, Patrik; Knapek, Michal; Letzig, Dietmar; Bohlen, Jan; Chmelík, František

    Mg single crystals with three different crystallographic orientations have been channel die (plane strain) compressed at applied rate of 10-3s-1 and at room temperature. The concurrent acoustic emission (AE) measurement was used as a method to analyze the dislocation dynamic during plastic deformation of Mg single crystals. The AE count rate and the maximum amplitudes of the AE event were correlated with stress-strain curves to determine the activity of various deformation mechanisms. The presence of large AE signals in the first stage of plastic deformation in single crystals with favorable orientation for (10.2)-twinning indicates twin nucleation and subsequent decrease of the AE activity, which can be connected with twin growth and collective dislocation processes. Compression along the c-axis (hard deformation mode) produces almost no AE activity.

  19. A Study of the Crystallization, Melting, and Foaming Behaviors of Polylactic Acid in Compressed CO2

    PubMed Central

    Zhai, Wentao; Ko, Yoorim; Zhu, Wenli; Wong, Anson; Park, Chul B.

    2009-01-01

    The crystallization and melting behaviors of linear polylactic acid (PLA) treated by compressed CO2 was investigated. The isothermal crystallization test indicated that while PLA exhibited very low crystallization kinetics under atmospheric pressure, CO2 exposure significantly increased PLA’s crystallization rate; a high crystallinity of 16.5% was achieved after CO2 treatment for only 1 min at 100 °C and 6.89 MPa. One melting peak could be found in the DSC curve, and this exhibited a slight dependency on treatment times, temperatures, and pressures. PLA samples tended to foam during the gas release process, and a foaming window as a function of time and temperature was established. Based on the foaming window, crystallinity, and cell morphology, it was found that foaming clearly reduced the needed time for PLA’s crystallization equilibrium. PMID:20054476

  20. Thermoreversible, epitaxial fcc<-->bcc transitions in block copolymer solutions.

    PubMed

    Bang, Joona; Lodge, Timothy P; Wang, Xiaohui; Brinker, Kristin L; Burghardt, Wesley R

    2002-11-18

    Uncharged block copolymer micelles display thermoreversible transitions between close-packed and bcc lattices for a range of concentration, solvent selectivity, and copolymer composition. Using small-angle x-ray scattering on shear-oriented solutions, highly aligned fcc crystals are seen to transform epitaxially to bcc crystals, with fcc/bcc orientational relationships that are well established in martensitic transformations in metals. The transition is driven by decreasing solvent selectivity with increasing temperature, inducing solvent penetration of the micellar core.

  1. An approach to engineer paracetamol crystals by antisolvent crystallization technique in presence of various additives for direct compression.

    PubMed

    Kaialy, Waseem; Larhrib, Hassan; Chikwanha, Brian; Shojaee, Saeed; Nokhodchi, Ali

    2014-04-10

    Paracetamol is a popular over-the-counter analgesic and a challenging model drug due to its poor technological and biopharmaceutical properties such as flowability, compressibility, compactibility and wettability. This work was aimed to alter the crystal habit of paracetamol from elongated to polyhedral-angular via particle engineering whilst maintaining the stable polymorphic form (form I: monoclinic form). The engineered paracetamol crystals obtained in the present investigation showed better technological and biopharmaceutical properties in comparison to the commercial paracetamol. Engineered paracetamol crystals were obtained using antisolvent crystallization technique in the presence of various concentrations (0.1, 0.5 and 1%, w/w) of additives, namely, polyvinyl alcohol (PVA), Avicel PH 102 (microcrystalline cellulose), Brij 58, methylcellulose (MC) and polyethylene glycol having different molecular weights (PEGs 1500, 6000 and 8000). Paracetamols crystallized in the presence of Avicel (or physically mixed with Avicel), Brij 58 and PEG 6000 demonstrated the best compactibility over a range of compaction pressures. Brij-crystallized paracetamol provided the fastest dissolution rate among all the paracetamol batches. Paracetamols crystallized in the presence of PVA or Avicel, or physically mixed with Avicel demonstrated a reduced degree of crystallinity in comparison to the other paracetamols. This study showed that the type, the grade and the concentration of additives could influence the physical stability such as flow, crystallinity and polymorphic transformation of paracetamol, the technological and biopharmaceutical properties of paracetamol. Stable polymorphic form of paracetamol with optimal tableting characteristics can be achieved through particle engineering.

  2. Global existence and incompressible limit in critical spaces for compressible flow of liquid crystals

    NASA Astrophysics Data System (ADS)

    Bie, Qunyi; Cui, Haibo; Wang, Qiru; Yao, Zheng-An

    2017-10-01

    The Cauchy problem for the compressible flow of nematic liquid crystals in the framework of critical spaces is considered. We first establish the existence and uniqueness of global solutions provided that the initial data are close to some equilibrium states. This result improves the work by Hu and Wu (SIAM J Math Anal 45(5):2678-2699, 2013) through relaxing the regularity requirement of the initial data in terms of the director field. Based on the global existence, we then consider the incompressible limit problem for ill prepared initial data. We prove that as the Mach number tends to zero, the global solution to the compressible flow of liquid crystals converges to the solution to the corresponding incompressible model in some function spaces. Moreover, the accurate converge rates are obtained.

  3. Peculiarities of high-temperature superelasticity in Ni-Fe-Ga single crystals in compression

    NASA Astrophysics Data System (ADS)

    Timofeeva, E. E.; Panchenko, E. Yu.; Chumlyakov, Yu. I.; Maier, H. J.; Gerstein, G.

    2017-03-01

    The high-temperature superelasticity and temperature dependence of the yield stress of 14M and L10 martensite in [001]-oriented single crystals of Ni54Fe19Ga27 (at %) in compression alloy have been studied. As the temperature increases, the sequence of stress-induced martensitic transformations (MTs) changes from L21-14M to L21-L10. The yield stress of L10 martensite weakly depends on the temperature and is 1.7 times lower than that of 14M martensite. The temperature interval of superelasticity in [001]-oriented single crystals of Ni54Fe19Ga27 under compression is determined by the growth of critical stresses with increasing temperature, the coefficient of strain-hardening, and the yield stress of L10 martensite.

  4. The hierarchical characterization of deformation heterogeneities in compressed metal single crystals

    NASA Astrophysics Data System (ADS)

    Magid, Karen Ruth

    Plastic deformation is an inherently heterogeneous process whose understanding is still incomplete after more than 50 years of study. The traditional methods of analysis look at both bulk material deformation and properties and the microscale features which comprise the inherent deformation processes. A large amount of information occurring on the mesoscale, from 1 to 100 microns, has not been analyzed. Here we present the results from an x-ray diffraction technique with submicron spatial resolution used to analyze compressed metal single crystals. The mesoscopic structure of the inhomogeneous macroscopic deformation pattern was explored with selected area diffraction, using a focused synchrotron radiation polychromatic beam with a resolution of 1-3 mum. Single crystals of copper, molybdenum, and zinc were oriented for single slip tested to ˜2-14% strain in nearly uniaxial compression, using a specifically designed 6 degree of freedom compressive test device. The macroscopic strain field was monitored during the test by optical image correlation methods that mapped the strain field with a spatial resolution of about 100 mum. The copper and molybdenum crystals deformed unexpectedly, exhibiting significant amounts of secondary slip activity alongside the primary slip. Areas of interest from adjacent faces were identified from the image correlation and mapped for their orientation, excess defect density, and shear stress. The mesoscopic defect structure in the copper specimens consisted of broad, somewhat irregular primary bands that lay nominally parallel to (111), in an almost periodic distribution with a period of about 30 mum. These primary bands were dominant even in the region of conjugate strain. There were also broad conjugate defect bands, almost precisely perpendicular to the primary bands that tended to bridge primary bands and terminate at them. In addition, a tantalum bicrystal, previously compressed and characterized using electron back

  5. Atomistic study of pyramidal slips in pure magnesium single crystal under nano-compression

    NASA Astrophysics Data System (ADS)

    Tang, Xiao-Zhi; Guo, Ya-Fang; Xu, Shuang; Wang, Yue-Sheng

    2015-07-01

    Pyramidal slip mechanism plays an important role in c-axis micro-compression of hexagonal closed-packed metals. In this article, the detailed slip paths, respectively, on ? and ? planes in magnesium single crystal are given by molecular dynamics. The pyramidal slip on ? plane is suggested to consist of an edge-type partial dislocation and opposite basal movements on neighbouring basal planes, while the ? slip dissociation is achieved by two partial dislocations with a strip of stacking fault. Results imply that the slip on ? plane is more likely to nucleate with a relatively easy dissociation type comparing to the one on ? plane. No twinning is found under c-axis compression by examining the stepwise movement of atoms involved, fully supporting the recent experimental observations of micro-compression and the theoretical analysis on twinning formation proposed by our previous work.

  6. On self-diffusion and surface energy upon compression or tension of an iron crystal

    NASA Astrophysics Data System (ADS)

    Magomedov, M. N.

    2013-03-01

    The dependences of the activation parameters (formation of vacancies and self-diffusion) and specific surface energy on the volume fraction ( V/ V 0) are calculated in terms of the Mie-Lenard-Jones pair potential of interatomic interaction for bcc-Fe along the 300-K and 3000-K isotherms. It is shown that under strong compressions ( V/ V 0 < 1) or tensions ( V/ V 0 > 1), the surface energy has a negative value, which must lead to the crystal structure fragmentation.

  7. Multiple slip in copper single crystals deformed in compression under uniaxial stress

    SciTech Connect

    Florando, J N; LeBlanc, M M; Lassila, D H

    2006-11-30

    Uniaxial compression experiments on copper single crystals, oriented to maximize the shear for one slip system, show some unexpected results. In addition to the expected activity on the primary slip system, the results show appreciable activity perpendicular to the primary system. The magnitude of the activity orthogonal to the primary varies from being equal to the primary for the as-fabricated samples to 1/5 of the primary in the samples annealed after fabrication.

  8. Analysis of compression behavior of a [011] Ta single crystal with orientation imaging microscopy and crystal plasticity

    SciTech Connect

    Adams, B L; Campbell, G H; King, W E; Lassila, D H; Stolken, J S; Sun, S; Swartz, A J

    1999-02-03

    High-purity tantalum single crystal cylinders oriented with [011] parallel to the cylinder axis were deformed 10, 20, and 30 percent in compression. The engineering stress-strain curve exhibited an up-turn at strains greater than {approximately}20% while the samples took on an ellipsoidal shape during testing, elongated along the [100] direction with almost no dimensional change along [0{bar 1}1]. Two orthogonal planes were selected for characterization using Orientation Imaging Microscopy (OIM): one plane containing [100] and [011] (longitudinal) and the other in the plane containing [0{bar 1}1] and [011] (transverse). OIM revealed patterns of alternating crystal rotations that develop as a function of strain and exhibit evolving length scales. The spacing and magnitude of these alternating misorientations increases in number density and decreases in spacing with increasing strain. Classical crystal plasticity calculations were performed to simulate the effects of compression deformation with and without the presence of friction. The calculated stress-strain response, local lattice reorientations, and specimen shape are compared with experiment.

  9. Electrical impedance of FCC

    NASA Technical Reports Server (NTRS)

    Liu, Y. S.

    1972-01-01

    The electrical characteristics of FCC are investigated in the context of multiple transmission lines theory. Analytical expressions for the coefficients of capacitance of conductors in a single cable are obtained. Numerical values calculated with these expressions are in good agreement with experimental data. Crosstalk, attenuation constants and phase angles of the current and voltage in flat conductor cable are also calculated.

  10. The FCC and Broadcasting.

    ERIC Educational Resources Information Center

    Federal Communications Commission, Washington, DC.

    This report outlines the Federal Communications Commission's (FCC) regulatory authority over the licensing and operation of commercial, educational, and public broadcasting in the United States. Also described are rules and regulations governing the program content and advertising, in relation to the fairness doctrine, free speech, and public…

  11. Temperature rise of installed FCC

    NASA Technical Reports Server (NTRS)

    Hankins, J. D.

    1976-01-01

    Report discusses temperature profiles of installed FCC for wood and tile surfaces. Three-conductor FCC was tested at twice nominal current-carrying capacity over bare floor and under carpet, with result indicating that temperature rise is not a linear function of current with FCC at this level.

  12. The FCC in Fiscal 1971.

    ERIC Educational Resources Information Center

    Federal Communications Commission, Washington, DC.

    Fiscal 1971 saw major actions by the Federal Communications Commission (FCC) in all areas of its jurisdiction. In broadcasting, the FCC proposed new renewal rules and policies and issued a number of significant rulings on Fairness Doctrine matters. A policy statement outlining FCC cable television plans was submitted to the Congress. In the common…

  13. X-Ray Diffraction From Shocked Crystals: Experiments and Predications of Molecular Dynamics Simulations

    SciTech Connect

    Rosolankova, K; Kalantar, D H; Belak, J F; Bringa, E M; Caturla, M J; Hawreliak, J; Holian, B L; Kadau, K; Lomdahl, P S; Germann, T C; Ravelo, R; Sheppard, J; Wark, J S

    2003-09-24

    When a crystal is subjected to shock compression beyond its Hugoniot Elastic Limit (HEL), the deformation it undergoes is composed of elastic and plastic strain components. In situ time-dependent X-ray diffraction, which allows direct measurement of lattice spacings, can be used to investigate such phenomena. This paper presents recent experimental results of X-ray diffraction from shocked fcc crystals. Comparison is made between experimental data and simulated X-ray diffraction using a post-processor to Molecular Dynamics (MD) simulations of shocked fcc crystals.

  14. Ginzburg-Landau-type multiphase field model for competing fcc and bcc nucleation.

    PubMed

    Tóth, G I; Morris, J R; Gránásy, L

    2011-01-28

    We address crystal nucleation and fcc-bcc phase selection in alloys using a multiphase field model that relies on Ginzburg-Landau free energies of the liquid-fcc, liquid-bcc, and fcc-bcc subsystems, and determine the properties of the nuclei as a function of composition, temperature, and structure. With a realistic choice for the free energy of the fcc-bcc interface, the model predicts well the fcc-bcc phase-selection boundary in the Fe-Ni system.

  15. Solvent effect on tolbutamide crystallization induced by compressed CO 2 as antisolvent

    NASA Astrophysics Data System (ADS)

    Subra-Paternault, P.; Roy, C.; Vrel, D.; Vega-Gonzalez, A.; Domingo, C.

    2007-11-01

    The aim of this work is to investigate the crystallization of tolbutamide induced by the addition of compressed carbon dioxide, with a particular focus on the role of the liquor solvent on the product characteristics. Crystals morphology and sizes were documented by microscopy and laser diffraction, respectively; since tolbutamide exists in four polymorph forms, characterizations by powder X-rays diffraction, differential scanning calorimetry and Raman spectroscopy were carried out. When processed from acetone or ethyl acetate, the drug crystallizes as polyedres and in a crystal lattice typical of Form III. If ethanol is added to acetone, Form I appears in the powder and becomes predominant for a content of 29% (in mol) and above; at the same time, mean particles size decreases. However, ethanol improves the solubilization of tolbutamide in the formed CO 2-solvent mixture, and is thus not favourable to a good yield of production. Mixtures of acetone with poor solvents such as diethyl ether and water were tested out; both enable the recovery of a mixture of Forms I and III, but with no significant improvement in sizes or yields compared with pure acetone or acetone-ethanol mixtures. Finally, the comparison with crystals obtained by evaporation indicates that the solvent itself was the main cause of the crystal phase observed, rather than the supercritical treatment.

  16. Effects of molecular geometry on the properties of compressed diamondoid crystals

    DOE PAGES

    Yang, Fan; Lin, Yu; Baldini, Maria; ...

    2016-11-01

    Diamondoids are an intriguing group of carbon-based nanomaterials, which combine desired properties of inorganic nanomaterials and small hydrocarbon molecules with atomic-level uniformity. In this Letter, we report the first comparative study on the effect of pressure on a series of diamondoid crystals with systematically varying molecular geometries and shapes, including zero-dimensional (0D) adamantane; one-dimensional (1D) diamantane, [121]tetramantane, [123]tetramantane, and [1212]pentamantane; two-dimensional (2D) [12312]hexamantane; and three-dimensional (3D) triamantane and [1(2,3)4]pentamantane. We find the bulk moduli of these diamondoid crystals are strongly dependent on the diamondoids’ molecular geometry with 3D [1(2,3)4]pentamantane being the least compressible and 0D adamantane being the most compressible.more » These diamondoid crystals possess excellent structural rigidity and are able to sustain large volume deformation without structural failure even after repetitive pressure loading cycles. These properties are desirable for constructing cushioning devices. Furthermore, we also demonstrate that lower diamondoids outperform the conventional cushioning materials in both the working pressure range and energy absorption density.« less

  17. Effects of molecular geometry on the properties of compressed diamondoid crystals

    SciTech Connect

    Yang, Fan; Lin, Yu; Baldini, Maria; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Mao, Wendy L.

    2016-11-01

    Diamondoids are an intriguing group of carbon-based nanomaterials, which combine desired properties of inorganic nanomaterials and small hydrocarbon molecules with atomic-level uniformity. In this Letter, we report the first comparative study on the effect of pressure on a series of diamondoid crystals with systematically varying molecular geometries and shapes, including zero-dimensional (0D) adamantane; one-dimensional (1D) diamantane, [121]tetramantane, [123]tetramantane, and [1212]pentamantane; two-dimensional (2D) [12312]hexamantane; and three-dimensional (3D) triamantane and [1(2,3)4]pentamantane. We find the bulk moduli of these diamondoid crystals are strongly dependent on the diamondoids’ molecular geometry with 3D [1(2,3)4]pentamantane being the least compressible and 0D adamantane being the most compressible. These diamondoid crystals possess excellent structural rigidity and are able to sustain large volume deformation without structural failure even after repetitive pressure loading cycles. These properties are desirable for constructing cushioning devices. Furthermore, we also demonstrate that lower diamondoids outperform the conventional cushioning materials in both the working pressure range and energy absorption density.

  18. FCC catalyst selection

    SciTech Connect

    Carter, G.D.L. ); McElhiney, G. )

    1989-09-01

    This paper discusses a commonly used technique for comparing FCC catalytic selectivities based on the ASTM microactivity test (MAT) procedure, ASTM D-3907-80. In its original form the ASTM test provides only very limited information on selectivity. However, extension of the ASTM MAT procedure by using additional product analyses gives a microselectivity test capable of providing detailed yield structure information. This modified MAT procedure thus provides a cost-effective and rapid means of comparing many catalysts.

  19. Shock compression experiments on Lithium Deuteride (LiD) single crystals

    DOE PAGES

    Knudson, M. D.; Desjarlais, M. P.; Lemke, R. W.

    2016-12-21

    Shock compression experiments in the few hundred GPa (multi-Mbar) regime were performed on Lithium Deuteride single crystals. This study utilized the high velocity flyer plate capability of the Sandia Z Machine to perform impact experiments at flyer plate velocities in the range of 17–32 km/s. Measurements included pressure, density, and temperature between ~190 and 570 GPa along the Principal Hugoniot—the locus of end states achievable through compression by large amplitude shock waves—as well as pressure and density of reshock states up to ~920 GPa. As a result, the experimental measurements are compared with density functional theory calculations, tabular equation ofmore » state models, and legacy nuclear driven results that have been reanalyzed using modern equations of state for the shock wave standards used in the experiments.« less

  20. Shock compression experiments on Lithium Deuteride (LiD) single crystals

    SciTech Connect

    Knudson, M. D.; Desjarlais, M. P.; Lemke, R. W.

    2016-12-21

    Shock compression experiments in the few hundred GPa (multi-Mbar) regime were performed on Lithium Deuteride single crystals. This study utilized the high velocity flyer plate capability of the Sandia Z Machine to perform impact experiments at flyer plate velocities in the range of 17–32 km/s. Measurements included pressure, density, and temperature between ~190 and 570 GPa along the Principal Hugoniot—the locus of end states achievable through compression by large amplitude shock waves—as well as pressure and density of reshock states up to ~920 GPa. As a result, the experimental measurements are compared with density functional theory calculations, tabular equation of state models, and legacy nuclear driven results that have been reanalyzed using modern equations of state for the shock wave standards used in the experiments.

  1. Shock compression experiments on Lithium Deuteride (LiD) single crystals

    SciTech Connect

    Knudson, M. D.; Desjarlais, M. P.; Lemke, R. W.

    2016-12-21

    Shock compression experiments in the few hundred GPa (multi-Mabr) regime were performed on Lithium Deuteride (LiD) single crystals. This study utilized the high velocity flyer plate capability of the Sandia Z Machine to perform impact experiments at flyer plate velocities in the range of 17-32 km/s. Measurements included pressure, density, and temperature between ~200-600 GPa along the Principal Hugoniot – the locus of end states achievable through compression by large amplitude shock waves – as well as pressure and density of re - shock states up to ~900 GPa. Lastly, the experimental measurements are compared with recent density functional theory calculations as well as a new tabular equation of state developed at Los Alamos National Labs.

  2. Crystal structure of graphite under room-temperature compression and decompression

    SciTech Connect

    Wang, Yuejian; Panzik, Joseph E.; Kiefer, Boris; Lee, Kanani K.M.

    2012-10-23

    Recently, sophisticated theoretical computational studies have proposed several new crystal structures of carbon (e.g., bct-C{sub 4}, H-, M-, R-, S-, W-, and Z-carbon). However, until now, there lacked experimental evidence to verify the predicted high-pressure structures for cold-compressed elemental carbon at least up to 50 GPa. Here we present direct experimental evidence that this enigmatic high-pressure structure is currently only consistent with M-carbon, one of the proposed carbon structures. Furthermore, we show that this phase transition is extremely sluggish, which led to the observed broad x-ray diffraction peaks in previous studies and hindered the proper identification of the post-graphite phase in cold-compressed carbon.

  3. Nanosecond homogeneous nucleation and crystal growth in shock-compressed SiO2

    NASA Astrophysics Data System (ADS)

    Shen, Yuan; Jester, Shai; Qi, Tingting; Reed, Evan

    Understanding the kinetics of shock-compressed SiO2 is of great importance for mitigating optical damage for high-intensity lasers and for understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high-pressure phases of this material, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing multiscale molecular dynamics studies of shock-compressed fused silica and quartz, we find that silica transforms into a poor glass former that subsequently exhibits ultrafast crystallization within a few nanoseconds. We also find that, as a result of the formation of such an intermediate disordered phase, the transition between silica polymorphs obeys a homogeneous reconstructive nucleation and grain growth model. Moreover, we construct a quantitative model of nucleation and grain growth, and compare its predictions with stishovite grain sizes observed in laser-induced damage and meteoroid impact events.

  4. Nanosecond homogeneous nucleation and crystal growth in shock-compressed SiO2.

    PubMed

    Shen, Yuan; Jester, Shai B; Qi, Tingting; Reed, Evan J

    2016-01-01

    Understanding the kinetics of shock-compressed SiO2 is of great importance for mitigating optical damage for high-intensity lasers and for understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high-pressure phases of this material, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing multiscale molecular dynamics studies of shock-compressed fused silica and quartz, we find that silica transforms into a poor glass former that subsequently exhibits ultrafast crystallization within a few nanoseconds. We also find that, as a result of the formation of such an intermediate disordered phase, the transition between silica polymorphs obeys a homogeneous reconstructive nucleation and grain growth model. Moreover, we construct a quantitative model of nucleation and grain growth, and compare its predictions with stishovite grain sizes observed in laser-induced damage and meteoroid impact events.

  5. Nanosecond homogeneous nucleation and crystal growth in shock-compressed SiO2

    NASA Astrophysics Data System (ADS)

    Shen, Yuan; Jester, Shai B.; Qi, Tingting; Reed, Evan J.

    2016-01-01

    Understanding the kinetics of shock-compressed SiO2 is of great importance for mitigating optical damage for high-intensity lasers and for understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high-pressure phases of this material, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing multiscale molecular dynamics studies of shock-compressed fused silica and quartz, we find that silica transforms into a poor glass former that subsequently exhibits ultrafast crystallization within a few nanoseconds. We also find that, as a result of the formation of such an intermediate disordered phase, the transition between silica polymorphs obeys a homogeneous reconstructive nucleation and grain growth model. Moreover, we construct a quantitative model of nucleation and grain growth, and compare its predictions with stishovite grain sizes observed in laser-induced damage and meteoroid impact events.

  6. Shock compression experiments on Lithium Deuteride (LiD) single crystals

    SciTech Connect

    Knudson, Marcus D.; Desjarlais, Michael P.; Lemke, Raymond W.

    2014-10-01

    Shock compression experiments in the few hundred GPa (multi-Mabr) regime were performed on Lithium Deuteride (LiD) single crystals. This study utilized the high velocity flyer plate capability of the Sandia Z Machine to perform impact experiments at flyer plate velocities in the range of 17-32 km/s. Measurements included pressure, density, and temperature between ~200-600 GPa along the Principal Hugoniot – the locus of end states achievable through compression by large amplitude shock waves – as well as pressure and density of re - shock states up to ~900 GPa. Lastly, the experimental measurements are compared with recent density functional theory calculations as well as a new tabular equation of state developed at Los Alamos National Labs.

  7. Miniature Compressive Ultra-spectral Imaging System Utilizing a Single Liquid Crystal Phase Retarder

    PubMed Central

    August, Isaac; Oiknine, Yaniv; AbuLeil, Marwan; Abdulhalim, Ibrahim; Stern, Adrian

    2016-01-01

    Spectroscopic imaging has been proved to be an effective tool for many applications in a variety of fields, such as biology, medicine, agriculture, remote sensing and industrial process inspection. However, due to the demand for high spectral and spatial resolution it became extremely challenging to design and implement such systems in a miniaturized and cost effective manner. Using a Compressive Sensing (CS) setup based on a single variable Liquid Crystal (LC) retarder and a sensor array, we present an innovative Miniature Ultra-Spectral Imaging (MUSI) system. The LC retarder acts as a compact wide band spectral modulator. Within the framework of CS, a sequence of spectrally modulated images is used to recover ultra-spectral image cubes. Using the presented compressive MUSI system, we demonstrate the reconstruction of gigapixel spatio-spectral image cubes from spectral scanning shots numbering an order of magnitude less than would be required using conventional systems. PMID:27004447

  8. Miniature Compressive Ultra-spectral Imaging System Utilizing a Single Liquid Crystal Phase Retarder

    NASA Astrophysics Data System (ADS)

    August, Isaac; Oiknine, Yaniv; Abuleil, Marwan; Abdulhalim, Ibrahim; Stern, Adrian

    2016-03-01

    Spectroscopic imaging has been proved to be an effective tool for many applications in a variety of fields, such as biology, medicine, agriculture, remote sensing and industrial process inspection. However, due to the demand for high spectral and spatial resolution it became extremely challenging to design and implement such systems in a miniaturized and cost effective manner. Using a Compressive Sensing (CS) setup based on a single variable Liquid Crystal (LC) retarder and a sensor array, we present an innovative Miniature Ultra-Spectral Imaging (MUSI) system. The LC retarder acts as a compact wide band spectral modulator. Within the framework of CS, a sequence of spectrally modulated images is used to recover ultra-spectral image cubes. Using the presented compressive MUSI system, we demonstrate the reconstruction of gigapixel spatio-spectral image cubes from spectral scanning shots numbering an order of magnitude less than would be required using conventional systems.

  9. Shock compression experiments on Lithium Deuteride (LiD) single crystals

    NASA Astrophysics Data System (ADS)

    Knudson, M. D.; Desjarlais, M. P.; Lemke, R. W.

    2016-12-01

    Shock compression experiments in the few hundred GPa (multi-Mbar) regime were performed on Lithium Deuteride single crystals. This study utilized the high velocity flyer plate capability of the Sandia Z Machine to perform impact experiments at flyer plate velocities in the range of 17-32 km/s. Measurements included pressure, density, and temperature between ˜190 and 570 GPa along the Principal Hugoniot—the locus of end states achievable through compression by large amplitude shock waves—as well as pressure and density of reshock states up to ˜920 GPa. The experimental measurements are compared with density functional theory calculations, tabular equation of state models, and legacy nuclear driven results that have been reanalyzed using modern equations of state for the shock wave standards used in the experiments.

  10. Shock compression experiments on Lithium Deuteride (LiD) single crystals

    DOE PAGES

    Knudson, M. D.; Desjarlais, M. P.; Lemke, R. W.

    2016-12-21

    Shock compression experiments in the few hundred GPa (multi-Mabr) regime were performed on Lithium Deuteride (LiD) single crystals. This study utilized the high velocity flyer plate capability of the Sandia Z Machine to perform impact experiments at flyer plate velocities in the range of 17-32 km/s. Measurements included pressure, density, and temperature between ~200-600 GPa along the Principal Hugoniot – the locus of end states achievable through compression by large amplitude shock waves – as well as pressure and density of re - shock states up to ~900 GPa. Lastly, the experimental measurements are compared with recent density functional theorymore » calculations as well as a new tabular equation of state developed at Los Alamos National Labs.« less

  11. 1100 to 1500 K Slow Plastic Compressive Behavior of NiAl-xCr Single Crystals

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel; Darolia, Ram

    2003-01-01

    The compressive properties of near <001> and <111> oriented NiAl-2Cr single crystals and near <011> oriented NiAl-6Cr samples have been measured between 1100 and 1500 K. The 2Cr addition produced significant solid solution strengthening in NiAl, and the <111> and <001> single crystals possessed similar strengths. The 6Cr crystals were not stronger than the 2Cr versions. At 1100 and 1200 K plastic flow in all three Cr-modified materials was highly dependent on stress with exponents > 10. The <011> oriented 6Cr alloy exhibited a stress exponent of about 8 at 1400 and 1500 K; whereas both <001> and <111> NiAl-2Cr crystals possessed stress exponents near 3 which is indicative of a viscous dislocation glide creep mechanism. While the Cottrell-Jaswon solute drag model predicted creep rates within a factor of 3 at 1500 K for <001>-oriented NiAl-2Cr; this mechanism greatly over predicted creep rates for other orientations and at 1400 K for <001> crystals.

  12. The elastic properties and stability of fcc-Fe and fcc-FeNi alloys at inner-core conditions

    NASA Astrophysics Data System (ADS)

    Martorell, Benjamí; Brodholt, John; Wood, Ian G.; Vočadlo, Lidunka

    2015-07-01

    The agreement between shear wave velocities for the Earth's inner core observed from seismology with those derived from mineral physics is considerably worse than for any other region of the Earth. Furthermore, there is still debate as to the phase of iron present in the inner core, particularly when alloying with nickel and light elements is taken into account. To investigate the extent to which the mismatch between seismology and mineral physics is a function of either crystal structure and/or the amount of nickel present, we have used ab initio molecular dynamics simulations to calculate the elastic constants and seismic velocities (Vp and Vs) of face centred cubic (fcc) iron at Earth's inner core pressures (360 GPa) and at temperatures up to ˜7000 K. We find that Vp for fcc iron (fcc-Fe) is very similar to that for hexagonal close packed (hcp) iron at all temperatures. In contrast, Vs for fcc-Fe is significantly higher than in hcp-Fe, with the difference increasing with increasing temperature; the difference between Vs for the core (from seismology) and Vs for fcc-Fe exceeds 40 per cent. These results are consistent with previous work at lower temperatures. We have also investigated the effect of 6.5 and 13 atm% Ni in fcc-Fe. We find that Ni only slightly reduces Vp and Vs (e.g. by 2 per cent in Vs for 13 atm% Ni at 5500 K), and cannot account for the difference between the velocities observed in the core and those of pure fcc-Fe. We also tried to examine pre-melting behaviour in fcc-Fe, as reported in hcp-Fe by extending the study to very high temperatures (at which superheating may occur). However, we find that fcc-Fe spontaneously transforms to other hcp-like structures before melting; two hcp-like structures were found, both of hexagonal symmetry, which may most easily be regarded as being derived from an hcp crystal with stacking faults. That the structure did not transform to a true hcp phase is likely as a consequence of the limited size of the

  13. Relationship between burgers vectors of dislocations and plastic strain localization patterns in compression-strained alkali halide crystals

    NASA Astrophysics Data System (ADS)

    Barannikova, S. A.; Nadezhkin, M. V.; Zuev, L. B.

    2011-08-01

    Plastic strain localization patterns in compression-strained alkali halide (NaCl, KCl, and LiF) crystals have been studied using a double-exposure speckle photography technique. The main parameters of strain localization autowaves at the linear stages of deformation hardening in alkali halide crystals have been determined. A quantitative relationship between the macroscopic parameters of plastic flow localization and microscopic parameters of strained alkali halide crystals has been established.

  14. Plasticity of Micrometer-Scale Single-Crystals in Compression: A Critical Review (PREPRINT)

    DTIC Science & Technology

    2008-10-01

    AFRL-RX-WP-TP-2008-4326 PLASTICITY OF MICROMETER-SCALE SINGLE- CRYSTALS IN COMPRESSION: A CRITICAL REVIEW (PREPRINT) Michael D. Uchic... Michael D. Uchic and Dennis M. Dimiduk (AFRL/RXLMD) Paul A. Shade (The Ohio State University) 5d. PROJECT NUMBER 4347 5e. TASK NUMBER RG 5f...a critical review    Michael  D. Uchic1, Paul A. Shade2, and Dennis M. Dimiduk1    1 Air Force Research Laboratory, Materials & Manufacturing

  15. Strain localization in <111> single crystals of Hadfield steel under compressive load

    NASA Astrophysics Data System (ADS)

    Astafurova, E. G.; Zakharova, G. G.; Melnikov, E. V.

    2010-07-01

    A study of strain localization under compression of <111> Hadfield steel single crystals at room temperature was done by light and transmission electron microscopy. At epsilon<1%, macro shear bands (MSB) form that have non-crystallographic and complex non-linear habit planes and are the results of the interaction of dislocation slip on conjugate slip planes. Mechanical twinning was experimentally found inside the MSB. After the stage of MSBs formation, deformation develops with high strain hardening coefficient and corresponds to interaction of slip and twinning inside as well as outside the MSBs.

  16. Experiments with phase transitions at very high pressure. [compressed solidifed gases, semiconductors, superconductors, and molecular crystals

    NASA Technical Reports Server (NTRS)

    Spain, I. L.

    1983-01-01

    Diamond cells were constructed for use to 1 Mbar. A refrigerator for cooling diamond cells was adapted for studies between 15 and 300 K. A cryostat for superconductivity studies between 1.5 to 300 K was constructed. Optical equipment was constructed for fluorescence, transmission, and reflectance studies. X-ray equipment was adapted for use with diamond cells. Experimental techniques were developed for X-ray diffraction studies using synchrotron radiation. AC susceptibility techniques were developed for detecting superconducting transitions. The following materials were studied: compressed solidified gases (Xe, Ar), semiconductors (Ge, Si, GaAs), superconductors (Nb3Ge, Nb3Si, Nb3As, CuCl), molecular crystals (I).

  17. Ultrafast tilting of the dispersion of a photonic crystal and adiabatic spectral compression of light pulses.

    PubMed

    Beggs, Daryl M; Krauss, Thomas F; Kuipers, L; Kampfrath, Tobias

    2012-01-20

    We demonstrate, by theory and experiment, the ultrafast tilting of the dispersion curve of a photonic-crystal waveguide following the absorption of a femtosecond pump pulse. By shaping the pump-beam cross section with a nanometric shadow mask, different waveguide eigenmodes acquire different spatial overlap with the perturbing pump, leading to a local flattening of the dispersion by up to 11%. We find that such partial mode perturbation can be used to adiabatically compress the spectrum of a light pulse traveling through the waveguide.

  18. Synthesis of 4H/fcc-Au@Metal Sulfide Core-Shell Nanoribbons.

    PubMed

    Fan, Zhanxi; Zhang, Xiao; Yang, Jian; Wu, Xue-Jun; Liu, Zhengdong; Huang, Wei; Zhang, Hua

    2015-09-02

    Although great advances on the synthesis of Au-semiconductor heteronanostructures have been achieved, the crystal structure of Au components is limited to the common face-centered cubic (fcc) phase. Herein, we report the synthesis of 4H/fcc-Au@Ag2S core-shell nanoribbon (NRB) heterostructures from the 4H/fcc Au@Ag NRBs via the sulfurization of Ag. Remarkably, the obtained 4H/fcc-Au@Ag2S NRBs can be further converted to a novel class of 4H/fcc-Au@metal sulfide core-shell NRB heterostructures, referred to as 4H/fcc-Au@MS (M = Cd, Pb or Zn), through the cation exchange. We believe that these novel 4H/fcc-Au@metal sulfide NRB heteronanostructures may show some promising applications in catalysis, surface enhanced Raman scattering, solar cells, photothermal therapy, etc.

  19. Growth of defect-free colloidal hard-sphere crystals using colloidal epitaxy

    NASA Astrophysics Data System (ADS)

    Dasgupta, Tonnishtha; Edison, John R.; Dijkstra, Marjolein

    2017-02-01

    Using event-driven Brownian dynamics simulations, we investigate the epitaxial growth of hard-sphere crystals with a face-centered-cubic (fcc) structure on the three densest cross-sectional planes of the fcc: (i) fcc (100), (ii) fcc (111), and (iii) fcc (110). We observe that for high settling velocities, large fcc crystals with very few extended defects grow on the fcc (100) template. Our results show good agreement with the experiments of Jensen et al. [Soft Matter 9, 320 (2013)], who observed such large fcc crystals upon centrifugation on an fcc (100) template. We also compare the quality of the fcc crystal formed on the fcc (111) and fcc (110) templates with that of the fcc (100) template and conclude that the latter yields the best crystal. We also briefly discuss the dynamical behavior of stacking faults that occur in the sediments.

  20. Growth of defect-free colloidal hard-sphere crystals using colloidal epitaxy.

    PubMed

    Dasgupta, Tonnishtha; Edison, John R; Dijkstra, Marjolein

    2017-02-21

    Using event-driven Brownian dynamics simulations, we investigate the epitaxial growth of hard-sphere crystals with a face-centered-cubic (fcc) structure on the three densest cross-sectional planes of the fcc: (i) fcc (100), (ii) fcc (111), and (iii) fcc (110). We observe that for high settling velocities, large fcc crystals with very few extended defects grow on the fcc (100) template. Our results show good agreement with the experiments of Jensen et al. [Soft Matter 9, 320 (2013)], who observed such large fcc crystals upon centrifugation on an fcc (100) template. We also compare the quality of the fcc crystal formed on the fcc (111) and fcc (110) templates with that of the fcc (100) template and conclude that the latter yields the best crystal. We also briefly discuss the dynamical behavior of stacking faults that occur in the sediments.

  1. Technique for compressing light intensity ranges utilizing a specifically designed liquid crystal notch filter

    DOEpatents

    Rushford, Michael C.

    1988-01-01

    A pin hole camera assembly for use in viewing an object having a relatively large light intensity range, for example a crucible containing molten metal in an atomic vapor laser isotope separation (AVLIS) system is disclosed herein. The assembly includes means for optically compressing the light intensity range appearing at its input sufficient to make it receivable and decipherable by a standard video camera. To accomplish this, the assembly utilizes the combination of interference filter and a liquid crystal notch filter. The latter which preferably includes a cholesteric liquid crystal arrangement is configured to pass light at all wavelengths, except a relatively narrow wavelength band which defines the filter's notch, and includes means for causing the notch to vary to at least a limited extent with the intensity of light at its light incidence surface.

  2. Negative linear compressibility in a crystal of α-BiB3O6

    NASA Astrophysics Data System (ADS)

    Kang, Lei; Jiang, Xingxing; Luo, Siyang; Gong, Pifu; Li, Wei; Wu, Xiang; Li, Yanchun; Li, Xiaodong; Chen, Chuangtian; Lin, Zheshuai

    2015-08-01

    Negative linear compressibility (NLC), a rare and important mechanical effect with many application potentials, in a crystal of α-BiB3O6 (BIBO) is comprehensively investigated using first-principles calculations and high-pressure synchrotron X-ray diffraction experiments. The results indicate that the BIBO crystal exhibits the second largest NLC among all known inorganic materials over a broad pressure range. This unusual NLC behaviour is due to the rotation and displacement of the rigid [BO3] and [BO4] building units that result in hinge motion in an umbrella-like topology. More importantly, the parallel-polar lone-pair electrons on the Bi3+ cations act as “umbrella stands” to withstand the B-O hinges, thus significantly enhancing the NLC effect. BIBO presents a unique example of a “collapsible umbrella” mechanism for achieving NLC, which could be applied to other framework materials with lone-pair electrons.

  3. Negative linear compressibility in a crystal of α-BiB3O6

    PubMed Central

    Kang, Lei; Jiang, Xingxing; Luo, Siyang; Gong, Pifu; Li, Wei; Wu, Xiang; Li, Yanchun; Li, Xiaodong; Chen, Chuangtian; Lin, Zheshuai

    2015-01-01

    Negative linear compressibility (NLC), a rare and important mechanical effect with many application potentials, in a crystal of α-BiB3O6 (BIBO) is comprehensively investigated using first-principles calculations and high-pressure synchrotron X-ray diffraction experiments. The results indicate that the BIBO crystal exhibits the second largest NLC among all known inorganic materials over a broad pressure range. This unusual NLC behaviour is due to the rotation and displacement of the rigid [BO3] and [BO4] building units that result in hinge motion in an umbrella-like topology. More importantly, the parallel-polar lone-pair electrons on the Bi3+ cations act as “umbrella stands” to withstand the B-O hinges, thus significantly enhancing the NLC effect. BIBO presents a unique example of a “collapsible umbrella” mechanism for achieving NLC, which could be applied to other framework materials with lone-pair electrons. PMID:26305262

  4. First principles calculation of the mechanical compression of two organic molecular crystals.

    PubMed

    Zerilli, Frank J; Kuklja, Maija M

    2006-04-20

    The mechanical compression curves for the organic molecular crystals 1,1-diamino-2,2-dinitroethylene and beta-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (beta-HMX) are calculated using the Hartree-Fock approximation to the solutions of the many-body Schrödinger equation for a periodic system as implemented in the computer program CRYSTAL. No correction was made for basis set superposition error. The equilibrium lattice parameters are reproduced to within 1% of reported experimental values. Pressure values on the isotherm also agree well with reported experimental values. To obtain accurate results, the relaxation of all the atomic coordinates as well as the lattice parameters under a fixed volume constraint was required.

  5. Electromechanical properties of high coupling single crystals under large electric drive and uniaxial compression.

    PubMed

    Amin, Ahmed

    2005-10-01

    This work investigates the 33-mode electromechanical response of relaxor-ferroelectric lead magnesium niobate-lead titanate (PMN-PT) single crystals when driven with large fields approximately 0.4 MV/m under a combined direct current (DC) field and mechanical bias similar to those used in the design of sound projectors. It demonstrates that the remarkable small signal length extensional coupling (k33 > 0.90) and other electromechanical properties of morphotropic PMN-PT single crystals prevail under large drive. The observed k33 roll-off at 42 MPa compressive stress is analyzed in terms of the recent structural data and the high-order Devonshire theory of possible ferroelectric-ferroelectric transition trajectories.

  6. Orientation imaging microscopy investigation of the compression deformation of a [011] ta single crystal

    SciTech Connect

    Adams, B L; Campbell, G H; King, W E; Lassila, D H; Stolken, J S; Sun, S; Swartz, A J.

    1999-01-08

    High-purity tantalum single crystal cylinders oriented with [110] parallel to the cylinder axis were deformed 10, 20, and 30 percent in compression. The samples were subsequently sectioned for characterization using Orientation Imaging Microscopy (O I) along two orthogonal sectioning planes: one in the plane containing [001] and [110] (longitudinal) and the other in the plane containing [1[anti 1]0] and[110] (transverse). To examine local lattice rotations, the Euler angles relative to a reference angle at the section center were decomposed to their in-plane and out-of-plane components. The in-plane and out-of-plane misorientation maps for all compression tests reveal inhomogeneous deformation everywhere and particularly large lattice rotations in the comers of the longitudinal section. Of particular interest are the observed alternating orientation changes. This suggests the existence of networks of dislocations with net alternating sign that are required to accommodate the observed rotations. Rotation maps from the transverse section are distinctly different in appearance from those in the longitudinal plane. However, the rotation maps confirm that the rotations observed above were about the [1[anti 1]0] axis. Alternating orientation changes are also observed on this section. Results will be directly compared with crystal rotations predicted using finite element methods and reviewed in light of the LLNL Multiscale Materials Modeling Program.

  7. Orientation imaging microscopy investigation of the compression deformation of a [011] ta single crystal

    SciTech Connect

    Adams, B L; Campbell, G H; King, W E; Lassila, D H; Stolken, J S; Sun, S; Swartz, A J

    1999-01-08

    High-purity tantalum single crystal cylinders oriented with [110] parallel to the cylinder axis were deformed 10, 20, and 30 percent in compression. The samples were subsequently sectioned for characterization using Orientation Imaging Microscopy (O&I) along two orthogonal sectioning planes: one in the plane containing [001] and [110] (longitudinal) and the other in the plane containing [1{anti 1}0] and[110] (transverse). To examine local lattice rotations, the Euler angles relative to a reference angle at the section center were decomposed to their in-plane and out-of-plane components. The in-plane and out-of-plane misorientation maps for all compression tests reveal inhomogeneous deformation everywhere and particularly large lattice rotations in the comers of the longitudinal section. Of particular interest are the observed alternating orientation changes. This suggests the existence of networks of dislocations with net alternating sign that are required to accommodate the observed rotations. Rotation maps from the transverse section are distinctly different in appearance from those in the longitudinal plane. However, the rotation maps confirm that the rotations observed above were about the [1{anti 1}0] axis. Alternating orientation changes are also observed on this section. Results will be directly compared with crystal rotations predicted using finite element methods and reviewed in light of the LLNL Multiscale Materials Modeling Program.

  8. Nanosecond Timescale Homogeneous Nucleation and Crystal Growth in Shock-Compressed SiO2

    NASA Astrophysics Data System (ADS)

    Shen, Yuan; Barak, Shai; Qi, Tingting; Reed, Evan

    2015-06-01

    Understanding the kinetics of shock compressed SiO2 is of great importance for mitigating optical damage for high intensity lasers and understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high pressure crystal phases, but the kinetics and microscopic mechanisms are yet to be elucidated. The latter are particularly relevant for this material which has long-lived metastable states. Enabled by million atom multiscale shock technique (MSST) molecular dynamics studies of shock compressed fused silica and quartz using variations on the BKS analytical potential, we discover here that crystallization occurs within as little as a few nanoseconds. In surprising contrast to shock induced solid-solid phase transformations in metals, we find that the transition from quartz obeys a diffusion mediated homogeneous nucleation and growth model due to formation of an intermediate disordered phase. We construct a quantitative model of diffusion mediated nucleation and growth kinetics and compare to stishovite grain sizes observed in laser damage events and near the Barringer Crater. We also study the effect of quantum nuclear effects using the quantum bath MSST and find that shock temperatures are shifted up to 500 K from classical values.

  9. Twinning in nanocrystalline fcc and bcc metals

    NASA Astrophysics Data System (ADS)

    Boyko, Vladimir S.; Kezerashvili, Roman Ya.

    2013-03-01

    The deformation twinning in nanocrystalline (nc) face-centered cubic (fcc) metals, body-centered cubic (bcc) metals, and in nc Si is analyzed. The phenomenological approach is used to make a bridge between microscopical mechanisms of twin nucleation and macroscopical characteristics of twinning with different crystal structures and to calculate the grain size range of the twinning propensity, the requisite external stress for twinning propagation in nc polycrystals, and the grain size at which the slip begins to prevail over the twinning. The developed approach allows to derive analytical expressions and estimate lower and and upper limits of grain sizes at which a twinning propensity is occurred. Results of calculations for the nc fcc metals Al, Cu, Ni, Pd, Au, nc bcc metals Ta, Fe, Mo, W, Nb, and nc diamond-cubic Si are compared with the experimental data, otherwise predictions are made.

  10. Hydrous Ringwoodite: Clarifying Defect Mechanisms Through Combined Single-Crystal Refinement, Compressibility, and IR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Panero, W. R.; Smyth, J. R.; Jacobsen, S. D.; Frost, D. J.; Reaman, D. M.; Pigott, J. S.; Thomas, S.; Liu, Z.

    2009-12-01

    Incorporation of hydrogen into mantle silicates reduces bulk density and compressibility by varying amounts through associated defects. As the stiffest of the olivine polymorphs, ringwoodite should experience the greatest effects of hydration. We have synthesized Mg ringwoodite (γ-Mg2SiO4) with 2.6 wt% H2O at 20 GPa and 1250°C in the 5000 ton multi-anvil press at Bayerisches Geoinstitut and refined the crystal structure at ambient conditions from single-crystal X-ray diffraction data. The unit cell length is 8.0829(3) Å. The hydration mechanism is principally by octahedral cation vacancy with possible minor tetrahedral vacancy at a ratio of ~7:1. To further clarify the defect mechanism, we report low-temperature, ambient-pressure FTIR together with room temperature compression in a quasi-hydrostatic neon pressure medium to 23 GPa. FTIR spectra of this sample as well as one with about half the water content show three primary overlapping OH stretching bands at 2534, 3125, and 3622 cm-1 at ambient pressure and 300 K. Cooling to 11 K shows just 3% reduction of the width of the main 3125 cm-1 OH band, whereas the peak width reduction was recovered upon heating to room temperature. The sample with the lower water content shows splitting of the primary 3125 cm-1 peak, to 3089 and 3263 cm-1 at temperatures below 120 K. We interpret these results to indicate that the high water storage capacity of ringwoodite results from a combination of multiple bonding sites and loosely bound hydrogen dominated by cation vacancies. The 300 K isothermal bulk modulus (K0) and its pressure derivative (K’=dK0/dP) are 160.7(1.1) GPa and 5.0(2) respectively. Compared with nominally anhydrous ringwoodite, we observe a 12% decrease in the bulk modulus and a measurable increase in K’. The data indicate some evidence οf a change in compression mechanism at ~15 GPa, possibly resulting from a shift from initial compression of vacancies to more uniform compression of the structure

  11. Phase field theory of interfaces and crystal nucleation in a eutectic system of fcc structure: II. Nucleation in the metastable liquid immiscibility region.

    PubMed

    Tóth, Gyula I; Gránásy, László

    2007-08-21

    In the second part of our paper, we address crystal nucleation in the metastable liquid miscibility region of eutectic systems that is always present, though experimentally often inaccessible. While this situation resembles the one seen in single component crystal nucleation in the presence of a metastable vapor-liquid critical point addressed in previous works, it is more complex because of the fact that here two crystal phases of significantly different compositions may nucleate. Accordingly, at a fixed temperature below the critical point, six different types of nuclei may form: two liquid-liquid nuclei: two solid-liquid nuclei; and two types of composite nuclei, in which the crystalline core has a liquid "skirt," whose composition falls in between the compositions of the solid and the initial liquid phases, in addition to nuclei with concentric alternating composition shells of prohibitively high free energy. We discuss crystalline phase selection via exploring/identifying the possible pathways for crystal nucleation.

  12. Two techniques for temporal pulse compression in gas-filled hollow-core kagomé photonic crystal fiber.

    PubMed

    Mak, K F; Travers, J C; Joly, N Y; Abdolvand, A; Russell, P St J

    2013-09-15

    We demonstrate temporal pulse compression in gas-filled kagomé hollow-core photonic crystal fiber (PCF) using two different approaches: fiber-mirror compression based on self-phase modulation under normal dispersion, and soliton effect self-compression under anomalous dispersion with a decreasing pressure gradient. In the first, efficient compression to near-transform-limited pulses from 103 to 10.6 fs was achieved at output energies of 10.3 μJ. In the second, compression from 24 to 6.8 fs was achieved at output energies of 6.6 μJ, also with near-transform-limited pulse shapes. The results illustrate the potential of kagomé-PCF for postprocessing the output of fiber lasers. We also show that, using a negative pressure gradient, ultrashort pulses can be delivered directly into vacuum.

  13. The FCC: A Research Tool.

    ERIC Educational Resources Information Center

    Wilson, Paul

    The numerous forms filed with the Federal Communications Commission (FCC) provide information about a variety of topics. Basic licensing information that is available concerns engineering, ownership, and equal employment opportunity. The FCC's broadcast bureau collects information about programing, the ascertainment of community needs, public…

  14. Commercial FCC License Study Guide.

    ERIC Educational Resources Information Center

    Swearer, Harvey F.

    Jobs in radio arts, from serviceman to station engineer, are easier to get if one has a recommendation of the U.S. Government in the form of a license from the Federal Communications Commission (FCC). This study guide for FCC radiotelephone licenses is designed to thoroughly prepare the applicant for any radiotelephone exam and to serve as a…

  15. Long-time behavior of solution for the compressible nematic liquid crystal flows in R3

    NASA Astrophysics Data System (ADS)

    Gao, Jincheng; Tao, Qiang; Yao, Zheng-an

    2016-08-01

    In this paper, we investigate the global existence and long-time behavior of classical solution for the compressible nematic liquid crystal flows in three-dimensional whole space. First of all, the global existence of classical solution is established under the condition that the initial data are close to the constant equilibrium state in HN (R3) (N ≥ 3)-framework. Then, one establishes algebraic time decay for the classical solution by weighted energy method. Finally, the algebraic decay rate of classical solution in Lp (R3)-norm with 2 ≤ p ≤ ∞ and optimal decay rate of their spatial derivative in L2 (R3)-norm are obtained if the initial perturbation belong to L1 (R3) additionally.

  16. Molecular Dynamics Modelling of Laser-Pulse Compression of a Ta single crystal with dislocations

    NASA Astrophysics Data System (ADS)

    Ruestes, Carlos; Remington, Tane; Bringa, Eduardo; Meyers, Marc; Remington, Bruce

    2013-06-01

    The nanoindentation of a defect-free Ta [001] single crystal is studied by Molecular Dynamics simulations. The potential by, an EFS potential, and a recent EAM potential by are tested and their results analyzed in terms of dislocation slip planes. Dislocations emitted from the indented zone interact forming prismatic loops. The Ta dislocated structure is then subjected to shock compression induced by a piston hitting the sample at various speeds. The shock-induced dislocation generation and motion mechanisms are studied in order to compare to on-going experiments. This research was funded by ANPCyT PRH, PICT2008-1325, PICT2009-0092, SecTyP UNCuyo 06/M035 and UC Research Lab grants.

  17. Virus-mediated FCC iron nanoparticle induced synthesis of uranium dioxide nanocrystals.

    PubMed

    Ling, Tao; Yu, Huimin; Shen, Zhongyao; Wang, Hui; Zhu, Jing

    2008-03-19

    A reducing system involving M13 virus-mediated FCC Fe nanoparticles was employed to achieve uranium reduction and synthesize uranium dioxide nanocrystals. Here we show that metastable face-centered cubic (FCC) Fe nanoparticles were fabricated around the surface of the M13 virus during the specific adsorption of the virus towards Fe ions under a reduced environment. The FCC phase of these Fe nanoparticles was confirmed by careful TEM characterization. Moreover, this virus-mediated FCC Fe nanoparticle system successfully reduced contaminable U(VI) into UO(2) crystals with diameters of 2-5 nm by a green and convenient route.

  18. Enhancement of superconductivity in FeSe thin crystals induced by biaxial compressive strain

    NASA Astrophysics Data System (ADS)

    Wang, X. F.; Zhang, Z. T.; Wang, W. K.; Zhou, Y. H.; Kan, X. C.; Chen, X. L.; Gu, C. C.; Zhang, L.; Pi, L.; Yang, Z. R.; Zhang, Y. H.

    2017-06-01

    We report on the enhancement of superconductivity in FeSe thin crystals induced by in-plane biaxial compressive strain, with an underlying scotch tape as an in-situ strain generator. It is found that, due to the compressive strain, the superconducting transition temperature Tc ≈ 9 K of FeSe is increased by 30%-40% and the upper critical field Hc2(0) ≈ 14.8 T is increased by ∼ 20%. In parallel, the T*, which characterizes an onset of enhanced spin fluctuations, is raised up from 69 K to 87 K. On the other hand, the structural transition temperature Ts ≈ 94 K, below which an orthorhombic structure and an electronic nematic phase settle in, is suppressed down by ∼ 5 K. These findings reveal clear evolutions of the orders/fluctuations under strain effect in FeSe, the structurally simplest iron-based superconductor where the lattice/spin/charge degrees of freedom are closely coupled to one another. Moreover, the presented research provides a simple and clean way to manipulate the superconductivity in the layered iron compounds and may promote applications in related materials.

  19. Shock compression and release of a-axis magnesium single crystals: Anisotropy and time dependent inelastic response

    NASA Astrophysics Data System (ADS)

    Renganathan, P.; Winey, J. M.; Gupta, Y. M.

    2017-01-01

    To gain insight into inelastic deformation mechanisms for shocked hexagonal close-packed (hcp) metals, particularly the role of crystal anisotropy, magnesium (Mg) single crystals were subjected to shock compression and release along the a-axis to 3.0 and 4.8 GPa elastic impact stresses. Wave profiles measured at several thicknesses, using laser interferometry, show a sharply peaked elastic wave followed by the plastic wave. Additionally, a smooth and featureless release wave is observed following peak compression. When compared with wave profiles measured previously for c-axis Mg [Winey et al., J. Appl. Phys. 117, 105903 (2015)], the elastic wave amplitudes for a-axis Mg are lower for the same propagation distance, and less attenuation of elastic wave amplitude is observed for a given peak stress. The featureless release wave for a-axis Mg is in marked contrast to the structured features observed for c-axis unloading. Numerical simulations, using a time-dependent anisotropic modeling framework, showed that the wave profiles calculated using prismatic slip or (10 1 ¯ 2 ) twinning, individually, do not match the measured compression profiles for a-axis Mg. However, a combination of slip and twinning provides a good overall match to the measured compression profiles. In contrast to compression, prismatic slip alone provides a reasonable match to the measured release wave profiles; (10 1 ¯ 2 ) twinning due to its uni-directionality is not activated during release. The experimental results and wave profile simulations for a-axis Mg presented here are quite different from the previously published c-axis results, demonstrating the important role of crystal anisotropy in the time-dependent inelastic deformation of Mg single crystals under shock compression and release.

  20. Shock compression and release of a-axis magnesium single crystals: Anisotropy and time dependent inelastic response

    DOE PAGES

    Renganathan, P.; Winey, J. M.; Gupta, Y. M.

    2017-01-19

    Here, to gain insight into inelastic deformation mechanisms for shocked hexagonal close-packed (hcp) metals, particularly the role of crystal anisotropy, magnesium (Mg) single crystals were subjected to shock compression and release along the a-axis to 3.0 and 4.8 GPa elastic impact stresses. Wave profiles measured at several thicknesses, using laser interferometry, show a sharply peaked elastic wave followed by the plastic wave. Additionally, a smooth and featureless release wave is observed following peak compression. When compared to wave profiles measured previously for c-axis Mg, the elastic wave amplitudes for a-axis Mg are lower for the same propagation distance, and less attenuation of elastic wave amplitude is observed for a given peak stress. The featureless release wave for a-axis Mg is in marked contrast to the structured features observed for c-axis unloading. Numerical simulations, using a time-dependent anisotropic modeling framework, showed that the wave profiles calculated using prismatic slip or (10more » $$\\bar{1}$$2) twinning, individually, do not match the measured compression profiles for a-axis Mg. However, a combination of slip and twinning provides a good overall match to the measured compression profiles. In contrast to compression,prismatic slip alone provides a reasonable match to the measured release wave profiles; (10$$\\bar{1}$$2) twinning due to its uni-directionality is not activated during release. The experimental results and wave profile simulations for a-axis Mg presented here are quite different from the previously published c-axis results, demonstrating the important role of crystal anisotropy on the time-dependent inelastic deformation of Mg single crystals under shock compression and release.« less

  1. Surface and crystalline analysis of aluminum oxide single crystal treated by quasistationary compression plasma flow

    SciTech Connect

    Maletic, S.; Popovic, D.M.; Cubrovic, V.; Zekic, A.A.; Dojcilovic, J.

    2012-04-15

    Highlights: Black-Right-Pointing-Pointer The effects of treatment of Al{sub 2}O{sub 3} (0001) surface by CPF are analyzed. Black-Right-Pointing-Pointer Oriented low-dimensional structures are occurred for the treated Al{sub 2}O{sub 3} crystal. Black-Right-Pointing-Pointer The dimension of these ripples are 1 {mu}m and the distance between them is about 10 {mu}m. Black-Right-Pointing-Pointer The ripple-shaped structures contain a higher percentage of oxygen than the surroundings. Black-Right-Pointing-Pointer Results could promote CPF as a tool for producing organized oxygen-rich structures. -- Abstract: Material such as aluminum oxide (Al{sub 2}O{sub 3}) is important in electronics industry. On the other hand, plasma is one of the most efficient and sophisticated tools for materials processing. In this work a treatment of Al{sub 2}O{sub 3} (0001) surface by quasistationary compression plasma flow (CPF) is analyzed in detail. Offline metrology was performed using dielectric measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). Oriented low-dimensional periodic structures are occurred for the plasma treated Al{sub 2}O{sub 3} single crystal. In the paper is reported that these oriented ripple-shaped structures contain a higher percentage of oxygen than the surrounding crystal surface. This could be the framework for usage of CPF as a tool in manufacturing of surfaces containing the highly organized oxygen-rich structures.

  2. Structural transformation between bcc and fcc in Fe-Ni nanoparticle during heating process

    NASA Astrophysics Data System (ADS)

    Li, Guojian; Sui, Xudong; Qin, Xuesi; Ma, Yonghui; Wang, Kai; Wang, Qiang

    2016-10-01

    Phase transformation between bcc and fcc in Fe-Ni nanoparticle has been studied by using molecular dynamics simulation with an embedded atom method. The transformation has been explored by designing the nanoparticles with different initial structures, sizes and elemental distributions at various Ni concentrations. The results show that the structural transformation is strongly related to the Ni content and elemental distribution. Initial fcc structure transforms to bcc for a lower Ni content and bcc transforms to fcc for a higher Ni content. The transformation is accompanied with a sharp reduction in energy even for the nanoparticle with a large size. Furthermore, lattice distortion first occurs before the transformation. The transformation from fcc to bcc is occurred by elongating fcc (100) to bcc (110) and that from bcc to fcc by compressing bcc (110) to fcc (100). The reason is that the nanoparticle has a low energy state for bcc structure with a lower Ni content and also for fcc structure with a higher Ni content. The coexistence of bcc and fcc phases appears with the change of elemental distribution.

  3. Status and availability of FCC hardware

    NASA Technical Reports Server (NTRS)

    Romriell, G. K.

    1973-01-01

    The source availability of FCC and/or FCC connectors was surveyed. The results for the following areas are presented: (1) cost of FCC versus standard round cable, (2) qualification status, (3) size of wire available in FCC, (4) availability of hermetic connectors for FCC, (5) conversion from flat cable to round cable and visa versa, (6) availability of shielded flat cable for RF usage, (7) termination techniques, and (8) repair techniques.

  4. Nucleation of fcc Ta when heating thin films

    DOE PAGES

    Janish, Matthew T.; Mook, William M.; Carter, C. Barry

    2014-10-25

    Thin tantalum films have been studied during in-situ heating in a transmission electron microscope. Diffraction patterns from the as-deposited films were typical of amorphous materials. Crystalline grains were observed to form when the specimen was annealed in-situ at 450°C. Particular attention was addressed to the formation and growth of grains with the face-centered cubic (fcc) crystal structure. As a result, these observations are discussed in relation to prior work on the formation of fcc Ta by deformation and during thin film deposition.

  5. Tension-compression asymmetry of the stress-strain response in aged single crystal and polycrystalline NiTi

    SciTech Connect

    Gall, K.; Sehitoglu, H.; Chumlyakov, Y.I.; Kireeva, I.V.

    1999-03-10

    The purpose of this work is to thoroughly understand tension-compression asymmetry in precipitated NiTi using unique experimental results and micro-mechanical modeling. For the first time, tensile and compressive stress-strain behaviors were established on aged single crystals ([100], [110], and [111] orientations) and polycrystalline NiTi. The single crystal and polycrystalline Ti-50.8 at.% Ni materials were given both peak aged and over aged heat treatments. The drawn polycrystalline NiTi has a strong texture of the {l_angle}111{r_angle}{l_brace}110{r_brace} type, thus it deformed in a manner consistent with the [111] single crystals. In contrast to the phenomenological theory of martensitic transformations (analogous to Schmid`s law), the critical resolved shear stress required to trigger the transformation, {tau}{sub crss}, in the peak-aged single crystals was dependent on both the stress direction and crystallographic orientation. Using micro-mechanical modeling, the deviation from Schmid`s law was attributed to the unique orientation relationship that exists between the Ti{sub 3}Ni{sub 4} precipitates (their coherent stress fields) and the 24 martensite correspondence variant pairs. The over-aged single crystals generally obeyed Schmid`s law within experimental error, consistent with the proposed micro-mechanical model. Qualitatively, the tension-compression asymmetry and orientation dependence of the recoverable strain level, {var_epsilon}{sub 0}, was consistent with the phenomenological theory for martensitic transformations. However, the peak- and over-aged single crystals generally both demonstrated smaller {var_epsilon}{sub 0} magnitudes than predicted. The differences for both crystals were attributed to the inhibition of martensite detwinning coupled with several unique microstructural effects.

  6. Ferromagnetic Fe on Cu(001) throughout the fcc-like phase: arguing from the viewpoint of the electronic structure.

    PubMed

    Donath, M; Pickel, M; Schmidt, A B; Weinelt, M

    2009-04-01

    The scientific enthusiasm for ultrathin Fe films on Cu(001) has now lasted for more than 20 years. Is there ferromagnetic iron with a face-centred cubic (fcc) structure? Does ferromagnetism in Fe hinge on the body-centred cubic (bcc) structure? In this contribution, we try to establish that the electron system gives evidence of ferromagnetic behaviour with fcc-like electronic bands. We examine a crystal-induced surface state, which is characteristic of fcc surface order. Furthermore, we compare electronic signatures of fcc and bcc: the d-band exchange splitting, image-potential-state energies and the work function. We conclude that, from the viewpoint of the electronic structure, Fe on Cu(001) is found to be ferromagnetic throughout the fcc-like phase. This result raises a new question: how much deviation from the relaxed fcc order is acceptable without losing the electronic signature of fcc?

  7. Real time synchrotron x-ray diffraction measurements to determine material strength of shocked single crystals following compression and release

    SciTech Connect

    Turneaure, Stefan J.; Gupta, Y.M.

    2009-09-15

    We present a method to use real time, synchrotron x-ray diffraction measurements to determine the strength of shocked single crystals following compression and release during uniaxial strain loading. Aluminum and copper single crystals shocked along [111] were examined to peak stresses ranging from 2 to 6 GPa. Synchrotron x rays were used to probe the longitudinal lattice strains near the rear free surface (16 and 5 {micro}m depths for Al and Cu, respectively) of the metal crystals following shock compression and release. The 111 diffraction peaks showed broadening indicating a heterogeneous microstructure in the released state. The diffraction peaks also shifted to lower Bragg angles relative to the ambient Bragg angle; the magnitude of the shift increased with increasing impact stress. The Bragg angle shifts and appropriate averaging procedures were used to determine the macroscopic or continuum strength following compression and release. For both crystals, the strengths upon release increased with increasing impact stress and provide a quantitative measure of the strain hardening that occurs in Al(111) and Cu(111) during the shock and release process. Our results for Al(111) are in reasonable agreement with a previous determination based solely on continuum measurements. Two points are noteworthy about the developments presented here: Synchrotron x rays are needed because they provide the resolution required for analyzing the data in the released state; the method presented here can be extended to the shocked state but will require additional measurements.

  8. Crystal structure of HgGa{sub 2}Se{sub 4} under compression

    SciTech Connect

    Gomis, Oscar; Vilaplana, Rosario; Manjón, Francisco Javier; Santamaría-Pérez, David [Departamento de Química Física I, Universidad Complutense de Madrid, MALTA Consolider Team, Avenida Complutense s Departamento de Física Aplicada-ICMUV, MALTA Consolider Team, Universidad de Valencia, Edificio de Investigación, C Errandonea, Daniel [Departamento de Física Aplicada-ICMUV, MALTA Consolider Team, Universidad de Valencia, Edificio de Investigación, C and others

    2013-06-01

    Highlights: ► Single crystals of HgGa{sub 2}Se{sub 4} with defect-chalcopyrite structure were synthesized. ► HgGa{sub 2}Se{sub 4} exhibits a phase transition to a disordered rock salt structure at 17 GPa. ► HgGa{sub 2}Se{sub 4} undergoes a phase transition below 2.1 GPa to a disordered zinc blende. - Abstract: We report on high-pressure x-ray diffraction measurements up to 17.2 GPa in mercury digallium selenide (HgGa{sub 2}Se{sub 4}). The equation of state and the axial compressibilities for the low-pressure tetragonal phase have been determined and compared to related compounds. HgGa{sub 2}Se{sub 4} exhibits a phase transition on upstroke toward a disordered rock-salt structure beyond 17 GPa, while on downstroke it undergoes a phase transition below 2.1 GPa to a phase that could be assigned to a metastable zinc-blende structure with a total cation-vacancy disorder. Thermal annealing at low- and high-pressure shows that kinetics plays an important role on pressure-driven transitions.

  9. Direct nanomechanical measurement of layer thickness and compressibility of smectic liquid crystals.

    PubMed

    Carbone, Giovanni; Zappone, Bruno; Barberi, Riccardo; Bartolino, Roberto; Musevic, Igor

    2011-05-01

    Using an atomic force microscope (AFM) we confined a smectic-A liquid crystal (LC) between a flat glass plate and a 10-μm glass sphere attached to the free end of the AFM cantilever. Both surfaces were treated with a surfactant that induces normal alignment of the LC molecules. We measured the force F acting on the cantilever while varying the plate-sphere distance D with subnanometer precision. For D < 50 nm, the force was periodically oscillating and decayed as D was increased. Analyzing the force in the framework of a simple model of elastic deformation of the smectic layers, we have evaluated the undeformed layer thickness a(0) and compressibility modulus B. Compared to other techniques used to determine a(0) and B, AFM measurements are faster and require a much smaller amount (microliters) of LC. Moreover, they are based on purely mechanical deformations of the LC structure and do not require any static or radiative electromagnetic field.

  10. C-Axis Compression of Magnesium Single Crystals: Multi-Scale Dislocation Dynamics Analyses

    NASA Astrophysics Data System (ADS)

    Jaber, Wassim; Shehadeh, Mu'tasem

    Hexagonal-closed packed materials (HCP) materials has attracted interest recently due to their unique physical and mechanical properties. The low density and the high strength to weight ratio of such materials make them excellent candidates to save structural weight and consequently fuel consumption in both automotive and aircraft fields. However, the deformation behavior of HCP metals hasn't been completely understood as prior work still lack a detailed understanding on the activation of slip planes and twinning. In addition, the work-hardening behavior and the effect of temperature and strain rate are not yet well-established. This work aims at investigating the deformation mechanisms in magnesium single crystals using Multiscale Dislocation Dynamics Plasticity (MDDP) model. In particular, we focus on modeling the deformation behavior under c-axis compression loading. Several Simulations have been carried out to study the effect of dislocation mobility dependence on the dislocation character and its consequences on the evolution of the dislocation density, the dislocation microstructure, and the hardening behavior. Preliminary results show that the experimentally observed hardening behavior can be reproduced by using linear interpolation of the mobility such that screw segments are stationary and edge segments are highly mobile.

  11. Dynamic mechanical response of magnesium single crystal under compression loading: Experiments, model, and simulations

    NASA Astrophysics Data System (ADS)

    Li, Qizhen

    2011-05-01

    Magnesium single crystal samples are compressed at room temperature under quasistatic (˜0.001 s-1) loading in a universal testing machine and dynamic (430, 1000, and 1200 s-1) loading in a split Hopkinson pressure bar system. Stress-strain curves show that (a) the fracture strain slightly increases with the strain rate; and (b) the maximum strength and strain hardening rate increase significantly when the testing changes from quasistatic to dynamic, although they do not vary much when the strain rate for dynamic testing varies in the range of 430-1200 s-1. The operation of the secondary pyramidal slip system is the dominating deformation mechanism, which leads to a fracture surface with an angle of ˜42° with respect to the loading axial direction. A theoretical material model based on Johnson-Cook law is also derived. The model includes the strain hardening and strain rate hardening terms, and provides the stress-strain relations matching with the experimental results. Finite element simulations for the strain rates used in the experiments predict the mechanical responses of the material that agree well with the experimental data.

  12. Microstructure evolution and strain localization in Cu and Cu-8Al single crystals subjected to channel-die compression.

    PubMed

    Lewandowska, Małgorzata; Swiatnicki, Wiesław; Piatkowski, Andrzej; Jasienski, Zdzisław

    2006-09-01

    Single crystals of pure Cu and Cu-8%Al with two initial orientations, {112}111 and {112}110, were subjected to monotonic compression in channel-die at room temperature (293 K). The dislocation microstructure and local crystallography were investigated by transmission electron microscopy after different amounts of deformation. Various factors, such as initial single crystal orientation, chemical composition and amount of plastic deformation, were analysed in order to determine their influence on the microstructure evolution, local orientation variations and strain localization phenomena.

  13. Elevated temperature tension, compression and creep-rupture behavior of (001)-oriented single crystal superalloy PWA 1480

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G.; Miner, Robert V.

    1987-01-01

    Tensile and compressive flow behavior at various temperatures and strain rates, and tensile creep rupture behavior at 850 and 1050 C and various stresses were studied for (001)-oriented single crystals of the Ni-base superalloy PWA 1480. At temperatures up to 760 C, the flow stress is insensitive to strain rate and of greater magnitude in tension than in compression. At temperatures of 800 C and above, the flow stress decreases continuously with decreasing strain rate and the tension/compression anisotropy diminishes. The second stage creep rate and rupture time exhibited power law relationships with the applied stress for both 850 and 1050 C, however with different stress dependencies. The stress exponent for the steady state creep rate was about 7 at 1050 C, but much higher at 850 C, about 12. Directional coarsening of the gamma' phase occurred during creep at 1050 C, but not at 850 C.

  14. Controlled FCC/on-top binding of H/Pt(111) using surface stress

    NASA Astrophysics Data System (ADS)

    Shuttleworth, I. G.

    2016-08-01

    The preferred binding site of H/Pt(111) has been shown to be change from the on-top to FCC as the Pt(111) surface goes approximately from a state of compressive to tensile strain. A chemical analysis of the system has shown that for both FCC and on-top bound cases the H ssbnd Pt s and H ssbnd Pt d interactions have a similar importance in determining the preferred binding position. It has been seen that FCC-bound H forms a distinct state below the Pt d-band, whereas the on-top bound H does not.

  15. Compression-induced crystallization of amorphous indomethacin in tablets: characterization of spatial heterogeneity by two-dimensional X-ray diffractometry.

    PubMed

    Thakral, Naveen K; Mohapatra, Sarat; Stephenson, Gregory A; Suryanarayanan, Raj

    2015-01-05

    Tablets of amorphous indomethacin were compressed at 10, 25, 50, or 100 MPa using either an unlubricated or a lubricated die and stored individually at 35 °C in sealed Mylar pouches. At selected time points, tablets were analyzed by two-dimensional X-ray diffractometry (2D-XRD), which enabled us to profile the extent of drug crystallization in tablets, in both the radial and axial directions. To evaluate the role of lubricant, magnesium stearate was used as "internal" and/or "external" lubricant. Indomethacin crystallization propensity increased as a function of compression pressure, with 100 MPa pressure causing crystallization immediately after compression (detected using synchrotron radiation). However, the drug crystallization was not uniform throughout the tablets. In unlubricated systems, pronounced crystallization at the radial surface could be attributed to die wall friction. The tablet core remained substantially amorphous, irrespective of the compression pressure. Lubrication of the die wall with magnesium stearate, as external lubricant, dramatically decreased drug crystallization at the radial surface. The spatial heterogeneity in drug crystallization, as a function of formulation composition and compression pressure, was systematically investigated. When formulating amorphous systems as tablets, the potential for compression induced crystallization warrants careful consideration. Very low levels of crystallization on the tablet surface, while profoundly affecting product performance (decrease in dissolution rate), may not be readily detected by conventional analytical techniques. Early detection of crystallization could be pivotal in the successful design of a dosage form where, in order to obtain the desired bioavailability, the drug may be in a high energy state. Specialized X-ray diffractometric techniques (2D; use of high intensity synchrotron radiation) enabled detection of very low levels of drug crystallization and revealed the heterogeneity in

  16. Single crystal plastic behavior of a single-phase, face-center-cubic-structured, equiatomic FeNiCrCo alloy

    DOE PAGES

    Wu, Zhenggang; Gao, Y. F.; Bei, Hongbin

    2015-07-25

    To understand the fundamental deformation mechanisms of compositionally complex alloys, single crystals of a multi-component equiatomic FeNiCoCr alloy with face-centered cubic (FCC) structure were grown for mechanical studies. Similarly to typical FCC pure metals, slip trace analyses indicate that dislocation slips take place on (1 1 1) planes along [11¯0] directions. The critical resolved shear stress (CRSS) obeys the Schmid law at both 77 and 293 K, and tension–compression asymmetry is not observed. Although this material slips in a normal FCC manner both at 293 and 77 K, compared to typical FCC metals the CRSS’s strong temperature dependence is abnormal.

  17. Single crystal plastic behavior of a single-phase, face-center-cubic-structured, equiatomic FeNiCrCo alloy

    SciTech Connect

    Wu, Zhenggang; Gao, Y. F.; Bei, Hongbin

    2015-07-25

    To understand the fundamental deformation mechanisms of compositionally complex alloys, single crystals of a multi-component equiatomic FeNiCoCr alloy with face-centered cubic (FCC) structure were grown for mechanical studies. Similarly to typical FCC pure metals, slip trace analyses indicate that dislocation slips take place on (1 1 1) planes along [11¯0] directions. The critical resolved shear stress (CRSS) obeys the Schmid law at both 77 and 293 K, and tension–compression asymmetry is not observed. Although this material slips in a normal FCC manner both at 293 and 77 K, compared to typical FCC metals the CRSS’s strong temperature dependence is abnormal.

  18. FCC-ee: Energy Calibration

    SciTech Connect

    Koratzinos, M.; Blondel, A.; Gianfelice-Wendt, E.; Zimmermann, F.

    2015-06-02

    The FCC-ee aims to improve on electroweak precision measurements, with goals of 100 ke V on the Z mass and width, and a fraction of MeV on the W mass. Compared to LEP, this implies a much improved knowledge of the center-of-mass energy when operating at the Z peak and WW threshold. This can be achieved by making systematic use of resonant depolarization. A number of issues have been identified, due in particular to the long polarization times. However the smaller emittance and energy spread of FCC-ee with respect to LEP should help achieve a much improved performance.

  19. FCC and the Sunshine Act.

    ERIC Educational Resources Information Center

    Weiss, Kenneth

    The Sunshine Act, designed to encourage open meetings to increase public understanding of the governmental decision-making process, went into effect in March 1977. A total of 50 agencies, including the Federal Communications Commission (FCC), are subject to the provisions of the Sunshine Act. The act lists 10 exemptions, any of which can result in…

  20. FCC, CATV, ETV, and ITFS.

    ERIC Educational Resources Information Center

    Schwartz, Louis; Woods, Robert A.

    Actions taken in 1970 by the Federal Communications Commission (FCC) are reviewed and discussed in this paper. These actions include amendment of educational broadcast rules for the first time in 17 years, decisions in the area of educational programing, a decision regarding the ultra high frequency (UHF)-land mobile dilemma, and a promise to…

  1. Positive and negative linear compressibility and electronic properties of energetic and porous hybrid crystals with nitrate anions.

    PubMed

    Korabel'nikov, D V; Zhuravlev, Yu N

    2016-12-07

    The structural and electronic properties of energetic nitrates with organic cations (uronium and 3,3'-diamino-4,4'-azo-1,2,4-triazole) and a metal-organic framework crystal [Ag(ethylenediamine)]NO3 have been investigated using density functional theory including van der Waals interactions. It is found that the linear compressibility of urea nitrate is positive and anisotropic (a ≈ b < c), whereas 3,3'-diamino-4,4'-azo-1,2,4-triazole nitrate and [Ag(ethylenediamine)]NO3 show both positive and negative linear compressibility along the b, c and a-axes, respectively. Negative linear compressibility is correlated with the expansion of hydrogen bonds. The band gaps of considered crystals are different, which is related to the difference in the nature (anionic, cationic or mixed) of upper valence and lower unoccupied electronic states. The band gap of 3,3'-diamino-4,4'-azo-1,2,4-triazole nitrate is the smallest and nonlinearly decreases with pressure.

  2. The spray drying of acetazolamide as method to modify crystal properties and to improve compression behaviour.

    PubMed

    Di Martino, P; Scoppa, M; Joiris, E; Palmieri, G F; Andres, C; Pourcelot, Y; Martelli, S

    2001-02-01

    Acetazolamide shows a very poor compression ability and tablets must usually be produced through a wet granulation process. However, the possibility to obtain pure acetazolamide for direct compression could be interesting for industrial application. With the scope to obtain a material for direct compression, three different crystallisation methods were chosen, with respect to acetazolamide solvent solubility. (a) Acetazolamide was dissolved in an ammonia solution and then spray dried. It was possible to characterise the spherical particles as a mixture of two polymorphic forms, I and II by Powder X-ray diffraction study. (b) Pure form I was obtained by slowly cooling to room temperature a boiling water solution. (c) Pure form II, the marketed form, was obtained by neutralisation of an ammonia solution. Their compression behaviour was investigated firstly by a rotary press. Whilst pure polymorphic forms I and II could not be compressed, the spray dried particles showed very good compression properties. In fact, tablets were obtained only by spray dried particles, which show very good properties under compression and the absence of capping tendency. On the other hand, it was impossible to obtain tablets from polymorphic forms I and II, whatever compression pressures were used. In order to explain their densification mechanism, a single-punch tablet machine, equipped for the measurement of the upper punch displacement in the die, was used. From calculated Heckel's parameters, it was demonstrated that the spray dried material shows a greater particle rearrangement in the initial stage of compression due to its spherical habit and minor wrinkledness of particle surface. The crystalline structure due to the presence of polymorphic forms I and II concur to lowering the intrinsic elasticity of the material. This fact avoids the risk of the rupturing the interpaticulate bonds, which are formed during the compression, concurring to the consolidation of the tablet.

  3. Photonic band-gap and defect modes of a one-dimensional photonic crystal under localized compression

    NASA Astrophysics Data System (ADS)

    Sánchez, A.; Porta, A. V.; Orozco, S.

    2017-05-01

    The rupture of periodicity caused by one defect (defect layer) in a one-dimensional photonic crystal (1DPhC) results in a narrow transmission spectral line in the photonic band-gap, and the field distribution shows a strong confinement in the proximity of the defect layer. In this work, we present a theoretical model to calculate the frequency of defect modes caused by defect layers induced by localized mechanical stress. Two periodical arrangements were studied: one with layers of poly(methyl-methacrylate) (PMMA) and polystyrene (PS), PMMA-PS; the other with layers of PMMA and fused silica (SiO2), PMMA-SiO2. The defect layers were induced by localized compression (tension). The frequencies of the defect modes were calculated using elasto-optical theory and plane wave expansion and perturbation methods. Numerical results show that the frequency of the defect mode increases (decreases) when the compression (tension) increases. Based on the theoretical model developed, we show that compression of n layers of a 1DPhC induces n defect modes whose frequencies depend on the compression magnitude in the case of normal incidence of electromagnetic waves, in accordance with the results reported for other types of defect layers. The methodology shows the feasibility of the plane wave expansion and perturbation methods to study the frequency of the defect modes. Both periodical arrangements are suitable for designing mechanically tunable (1DPhC)-based narrow pass band filters and narrow reflectors in the (60, 65) THz range.

  4. Deformation mechanisms of olivine single crystals compressed at 300 MPa and 800-1100°C

    NASA Astrophysics Data System (ADS)

    Cordier, Patrick; Demouchy, Sylvie; Mussi, Alexandre; Tommasi, Andrea

    2013-04-01

    Rheology of mantle rocks at lithospheric temperatures remains poorly constrained, since most experimental studies on creep mechanisms of olivine single crystals ((MgFe)2SiO4, Pbnm) and polycrystalline olivine aggregates were performed at high-temperatures (T >> 1200oC). In this study, we have performed deformation experiments on oriented single crystals of San Carlos olivine and polycrystalline olivine aggregate at temperatures relevant of the uppermost mantle (ranging from 800o to 1090oC) in tri-axial compression. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at various constant strain rates (from 7 × 10-6 s-1 to 1 × 10-4 s-1). Mechanical tests yield differential stresses ranging from 88 to 1076 MPa. All samples were deformed at constant displacement rate and for finite strains ranging from 4 to 23 %, to provide insight into possible effects of hardening, softening or stick-and-slip. The single crystals were compressed along several crystallographic directions to test the possibility of activating different slip systems (e.g. [100](001), [001](100), [001](010) and [100](010)). We will present the characterization of the dislocation microstructures performed in the TEM.

  5. Evaluating optical properties of real photonic crystal fibers with compressed sensing based on non-subsampled contourlet transform

    NASA Astrophysics Data System (ADS)

    Shen, Yan; Liu, Jing; Lou, Shuqin; Hou, Ya-Li; Chen, Houjin

    2017-09-01

    A real photonic crystal fibers (PCFs) evaluation approach based on compressed sensing with non-subsampled contourlet transform (NSCT) and the total variation model is proposed for modeling optical properties of the real PCFs. The classical images of a commercial large mode area PCF and polarization-maintaining PCF are used to verify the effectiveness of the proposed method. Experimental results demonstrate that the cross section images of real PCFs are rebuilt effectively by using only 36% image data for evaluating the optical properties with the same accuracy as by 100% data. To the best of our knowledge, this is the instance of applying the compressed sensing with the NSCT and total variation to reconstruct the cross section images of PCFs for quickly evaluating the optical properties of real PCFs without the requirement of long fiber samples and expensive measurement apparatuses.

  6. Structure and Magnetism in fcc Magnetic Metals on (001) Diamond

    NASA Astrophysics Data System (ADS)

    Wolf, J. A.; Krebs, J. J.; Idzerda, Y. U.; Prinz, G. A.; Kemner, K. M.

    1996-03-01

    We have prepared single crystal face centered cubic (fcc) magnetic transition metal films (Co, Ni, Fe) on (001) diamonds, the thickness of the films varying from ~1nm to over 100nm. The crystalline quality and fourfold symmetry of these layers was monitored in-situ during film growth with RHEED and a chemical analysis was performed using Auger spectroscopy. In addition, the structure of the samples was investigated ex-situ using X-ray diffraction and EXAFS, demonstrating the single crystal, fcc (001) structure throughout the entire film. The magnetic characterization of the Co-, Ni- and Fe-films was carried out with Ferromagnetic Resonance (FMR) and Superconducting Quantum Interference Device (SQUID) hysteresis loops, yielding information on the cubic anisotropy constant K_1, the magnetic moment M and the magnetization reversal. The Co displays extremely high quality growth and magnetic characteristics up to thicknesses well in excess of 100nm, while the Ni is tetragonally distorted resulting in an out-of-plane anisotropy component. The fcc Fe is only stable up to ~2nm before the transition to the bcc crystal structure starts.

  7. The Mechanism of Orientation Dependence of Cyclic Stability of Superelesticity in NiFeGaCo Single Crystals Under Compression

    NASA Astrophysics Data System (ADS)

    Timofeeva, E. E.; Panchenko, E. Yu.; Vetoshkina, N. G.; Chumlyakov, Yu. I.; Tagiltsev, A. I.; Eftifeeva, A. S.; Maier, H.

    2016-12-01

    Using single crystals of the Ni49Fe18Ga27Co6 (at.%) alloy, oriented along [001]- and [123]-directions, cyclic stability of superelasticity is investigated in isothermal loading/unloading cycles at T = Af +(12-15) K (100 cycles) under compressive stress as a function of given strain per cycle, presence of disperse γ-phase particles measuring 5-10 μm, austenitic (B2 or L21) and stress-induced martensitic crystal structure (14M or L10). It is shown that single-phase L21-crystals demonstrate high cyclic stability during L21-14M-transitions with narrow hysteresises Δσ < 50 MPa in the absence of detwinning of the martensite. During the development of L21-14M stress-induced transformation, the reversible energy ΔGrev for these crystals exceeds the dissipated energy ΔGirr, and ΔGrev/ΔGirr = 1.7-1.8. A significant degradation of superelasticity is observed in [123]-oriented crystals during the development of L21-14M-L10-transformations followed by detwinning of the L10-martensite crystals and heterophase (B2+γ) single crystals, irrespective of their orientation during the B2-L10-transition. In the latter case, martensitic transformations are characterized by a wide stress hysteresis Δσ ≥ 80 MPa and the dissipated energy exceeds the reversible energy ΔGrev/ΔGirr = 0.5. The empirical criterion, relying on the analysis of the reversible-to-irreversible energy ratio, ΔGrev/ΔGirr, during stressinduced martensitic transformations, can be used to predict the cyclic stability of superelasticity in NiFeGaCo alloys subjected to different types of heat treatment.

  8. An electron microscopy study of dislocation structures in Mg single crystals compressed along [0 0 0 1] at room temperature

    DOE PAGES

    Kumar, K. S.; Chisholm, Matthew F.; Geng, J.; ...

    2016-01-09

    We compressed Mg single crystals along [0 0 0 1] at room temperature to various stress levels (40, 80, 120, 160 and 320 MPa) and the evolution of dislocation structure with stress increment was investigated by TEM slip is confirmed to be the dominant deformation mode; the predominance of edge dislocation debris lying along the <1 0more » $$\\bar{1}$$ 0> implies that screw dislocations are more mobile than their edge counterpart. The edge dislocation may dissociate into and dislocations, and the latter can extend further on the basal plane and bound a basal-stacking fault.« less

  9. An electron microscopy study of dislocation structures in Mg single crystals compressed along [0 0 0 1] at room temperature

    SciTech Connect

    Kumar, K. S.; Chisholm, Matthew F.; Geng, J.; Mishra, R. K.

    2016-01-09

    We compressed Mg single crystals along [0 0 0 1] at room temperature to various stress levels (40, 80, 120, 160 and 320 MPa) and the evolution of dislocation structure with stress increment was investigated by TEM slip is confirmed to be the dominant deformation mode; the predominance of edge dislocation debris lying along the <1 0 $\\bar{1}$ 0> implies that screw dislocations are more mobile than their edge counterpart. The edge dislocation may dissociate into and dislocations, and the latter can extend further on the basal plane and bound a basal-stacking fault.

  10. Molecular dynamics simulation on generalized stacking fault energies of FCC metals under preloading stress

    NASA Astrophysics Data System (ADS)

    Zhang, Liang; Cheng, Lü; Kiet, Tieu; Zhao, Xing; Pei, Lin-Qing; Guillaume, Michal

    2015-08-01

    Molecular dynamics (MD) simulations are performed to investigate the effects of stress on generalized stacking fault (GSF) energy of three fcc metals (Cu, Al, and Ni). The simulation model is deformed by uniaxial tension or compression in each of [111], [11-2], and [1-10] directions, respectively, before shifting the lattice to calculate the GSF curve. Simulation results show that the values of unstable stacking fault energy (γusf), stable stacking fault energy (γsf), and unstable twin fault energy (γutf) of the three elements can change with the preloaded tensile or compressive stress in different directions. The ratio of γsf/γusf, which is related to the energy barrier for full dislocation nucleation, and the ratio of γutf/γusf, which is related to the energy barrier for twinning formation are plotted each as a function of the preloading stress. The results of this study reveal that the stress state can change the energy barrier of defect nucleation in the crystal lattice, and thereby can play an important role in the deformation mechanism of nanocrystalline material. Project supported by Australia Research Council Discovery Projects (Grant No. DP130103973). L. Zhang, X. Zhao and L. Q. Pei were financially supported by the China Scholarship Council (CSC).

  11. Three-Dimensional Crystal Plasticity Finite Element Simulation of Hot Compressive Deformation Behaviors of 7075 Al Alloy

    NASA Astrophysics Data System (ADS)

    Li, Lei-Ting; Lin, Y. C.; Li, Ling; Shen, Lu-Ming; Wen, Dong-Xu

    2015-03-01

    Three-dimensional crystal plasticity finite element (CPFE) method is used to investigate the hot compressive deformation behaviors of 7075 aluminum alloy. Based on the grain morphology and crystallographic texture of 7075 aluminum alloy, the microstructure-based representative volume element (RVE) model was established by the pole figure inversion approach. In order to study the macroscopic stress-strain response and microstructural evolution, the CPFE simulations are performed on the established microstructure-based RVE model. It is found that the simulated stress-strain curves and deformation texture well agree with the measured results of 7075 aluminum alloy. With the increasing deformation degree, the remained initial weak Goss texture component tends to be strong and stable, which may result in the steady flow stress. The grain orientation and grain misorientation have significant effects on the deformation heterogeneity during hot compressive deformation. In the rolling-normal plane, the continuity of strain and misorientation can maintain across the low-angle grain boundaries, while the discontinuity of strain and misorientation is observed at the high-angle grain boundaries. The simulated results demonstrate that the developed CPFE model can well describe the hot compressive deformation behaviors of 7075 aluminum alloy under elevated temperatures.

  12. Polymorphism and decomposition of HE single crystals: Insight from static and shock compression experiments

    NASA Astrophysics Data System (ADS)

    Dreger, Z. A.

    2014-05-01

    Understanding the reactive behaviour of high explosive (HE) crystals at thermo-mechanical conditions generated by shock-waves is an important step toward understanding shock-wave initiation of these crystals. Despite the significant differences in time scales and loading rates, static high pressure and high temperature (HP-HT) experiments can provide key results regarding structural and chemical processes in HE crystals at pressures and temperatures relevant to shock initiation. Here, we present selected examples for utilizing optical spectroscopy to understand molecular processes in HE crystals at static HP-HT conditions to gain insight into their shock initiation mechanisms. The relevant results obtained from static studies up to 15 GPa and 700 K on polymorphism and decomposition are presented for cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN). This work demonstrates that the static HP-HT results in conjunction with shock-wave experiments provide an important approach to elucidate processes related to the initiation of shocked HE crystals, including polymorphic transitions, conformational changes, identification of crystal phases at decomposition, and mechanisms governing shock induced decomposition.

  13. Role of five-fold twin boundary on the enhanced mechanical properties of fcc Fe nanowires.

    PubMed

    Wu, J Y; Nagao, S; He, J Y; Zhang, Z L

    2011-12-14

    The role of 5-fold twin boundary on the structural and mechanical properties of fcc Fe nanowire under tension is explored by classical molecular dynamics. Twin-stabilized fcc nanowire with various diameters (6-24 nm) are examined by tension tests at several temperatures ranging from 0.01 to 1100 K. Significant increase in the Young's modulus of the smaller nanowires is revealed to originate from the central area of quinquefoliolate-like stress-distribution over the 5-fold twin, rather than from the surface tension that is often considered as the main source of such size-effects found in nanostructures. Because of the excess compressive stress caused by crossing twin-boundaries, the atoms in the center behave stiffer than those in bulk and even expand laterally under axial tension, providing locally negative Poisson's ratio. The yield strength of nanowire is also enhanced by the twin boundary that suppresses dislocation nucleation within a fcc twin-domain; therefore, the plasticity of nanowire is initiated by strain-induced fcc→bcc phase transformation that destroys the twin structure. After the yield, the nucleated bcc phase immediately spreads to the entire area, and forms a multigrain structure to realize ductile deformation followed by necking. As temperature elevated close to the critical temperature between bcc and fcc phases, the increased stability of fcc phase competes with the phase transformation under tension, and hence dislocation nucleations in fcc phase are observed exclusively at the highest temperature in our study.

  14. Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2

    PubMed Central

    Gleason, A. E.; Bolme, C. A.; Lee, H. J.; Nagler, B.; Galtier, E.; Milathianaki, D.; Hawreliak, J.; Kraus, R. G.; Eggert, J. H.; Fratanduono, D. E.; Collins, G. W.; Sandberg, R.; Yang, W.; Mao, W. L.

    2015-01-01

    Pressure- and temperature-induced phase transitions have been studied for more than a century but very little is known about the non-equilibrium processes by which the atoms rearrange. Shock compression generates a nearly instantaneous propagating high-pressure/temperature condition while in situ X-ray diffraction (XRD) probes the time-dependent atomic arrangement. Here we present in situ pump–probe XRD measurements on shock-compressed fused silica, revealing an amorphous to crystalline high-pressure stishovite phase transition. Using the size broadening of the diffraction peaks, the growth of nanocrystalline stishovite grains is resolved on the nanosecond timescale just after shock compression. At applied pressures above 18 GPa the nuclueation of stishovite appears to be kinetically limited to 1.4±0.4 ns. The functional form of this grain growth suggests homogeneous nucleation and attachment as the growth mechanism. These are the first observations of crystalline grain growth in the shock front between low- and high-pressure states via XRD. PMID:26337754

  15. Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2

    DOE PAGES

    Gleason, A. E.; Bolme, C. A.; Lee, H. J.; ...

    2015-09-04

    Pressure- and temperature-induced phase transitions have been studied for more than a century but very little is known about the non-equilibrium processes by which the atoms rearrange. Shock compression generates a nearly instantaneous propagating high-pressure/temperature condition while in situ X-ray diffraction (XRD) probes the time-dependent atomic arrangement. Here we present in situ pump–probe XRD measurements on shock-compressed fused silica, revealing an amorphous to crystalline high-pressure stishovite phase transition. Using the size broadening of the diffraction peaks, the growth of nanocrystalline stishovite grains is resolved on the nanosecond timescale just after shock compression. At applied pressures above 18 GPa the nuclueationmore » of stishovite appears to be kinetically limited to 1.4 ± 0.4 ns. The functional form of this grain growth suggests homogeneous nucleation and attachment as the growth mechanism. As a result, these are the first observations of crystalline grain growth in the shock front between low- and high-pressure states via XRD.« less

  16. Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2.

    PubMed

    Gleason, A E; Bolme, C A; Lee, H J; Nagler, B; Galtier, E; Milathianaki, D; Hawreliak, J; Kraus, R G; Eggert, J H; Fratanduono, D E; Collins, G W; Sandberg, R; Yang, W; Mao, W L

    2015-09-04

    Pressure- and temperature-induced phase transitions have been studied for more than a century but very little is known about the non-equilibrium processes by which the atoms rearrange. Shock compression generates a nearly instantaneous propagating high-pressure/temperature condition while in situ X-ray diffraction (XRD) probes the time-dependent atomic arrangement. Here we present in situ pump-probe XRD measurements on shock-compressed fused silica, revealing an amorphous to crystalline high-pressure stishovite phase transition. Using the size broadening of the diffraction peaks, the growth of nanocrystalline stishovite grains is resolved on the nanosecond timescale just after shock compression. At applied pressures above 18 GPa the nuclueation of stishovite appears to be kinetically limited to 1.4±0.4 ns. The functional form of this grain growth suggests homogeneous nucleation and attachment as the growth mechanism. These are the first observations of crystalline grain growth in the shock front between low- and high-pressure states via XRD.

  17. Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2

    NASA Astrophysics Data System (ADS)

    Gleason, A. E.; Bolme, C. A.; Lee, H. J.; Nagler, B.; Galtier, E.; Milathianaki, D.; Hawreliak, J.; Kraus, R. G.; Eggert, J. H.; Fratanduono, D. E.; Collins, G. W.; Sandberg, R.; Yang, W.; Mao, W. L.

    2015-09-01

    Pressure- and temperature-induced phase transitions have been studied for more than a century but very little is known about the non-equilibrium processes by which the atoms rearrange. Shock compression generates a nearly instantaneous propagating high-pressure/temperature condition while in situ X-ray diffraction (XRD) probes the time-dependent atomic arrangement. Here we present in situ pump-probe XRD measurements on shock-compressed fused silica, revealing an amorphous to crystalline high-pressure stishovite phase transition. Using the size broadening of the diffraction peaks, the growth of nanocrystalline stishovite grains is resolved on the nanosecond timescale just after shock compression. At applied pressures above 18 GPa the nuclueation of stishovite appears to be kinetically limited to 1.4+/-0.4 ns. The functional form of this grain growth suggests homogeneous nucleation and attachment as the growth mechanism. These are the first observations of crystalline grain growth in the shock front between low- and high-pressure states via XRD.

  18. Time-resolved Raman spectroscopy of shock compressed single crystal HMX

    NASA Astrophysics Data System (ADS)

    Scharff, R. J.; Whitley, V. H.; Stahl, D. B.; Dattelbaum, D. M.

    2009-06-01

    Shock initiation of an energetic organic solid is generally considered to proceed via a mechanism through which low frequency acoustic phonons are upconverted to higher frequency bond stretching vibrations in the crystal. To elucidate changes in molecular structure under shock loading, a series of well defined gas gun driven plate impact experiments coupled to time-resolved Raman spectroscopy were performed on single crystal β-HMX. We will also present progress in obtaining temperature measurements in the shocked material using a Stokes/anti-Stokes intensity ratio method.

  19. The FCC and the Electric Church.

    ERIC Educational Resources Information Center

    Abrams, Michael F.

    This newsletter focuses on the relationship between the Federal Communications Commission (FCC) and religious broadcasters. It traces the history of that relationship and discusses some of the pressures put on both. It includes a discussion of a recent avalanche of mail at the FCC supporting the church on the airways. It also summarizes some of…

  20. New FCC Goal in Ownership Regulation.

    ERIC Educational Resources Information Center

    Rappaport, Josh

    By first describing the historical stance of the Federal Communications Commission (FCC) toward ownership of broadcast facilities and then describing the FCC's most recent policy statements, this report compares the differing viewpoints and recognizes that the new value or goal that seems to have been established conflicts with the past emphasis…

  1. The FCC and the Electric Church.

    ERIC Educational Resources Information Center

    Abrams, Michael F.

    This newsletter focuses on the relationship between the Federal Communications Commission (FCC) and religious broadcasters. It traces the history of that relationship and discusses some of the pressures put on both. It includes a discussion of a recent avalanche of mail at the FCC supporting the church on the airways. It also summarizes some of…

  2. Demonstration of an ultraviolet stimulated Brillouin scattering pulse compressed hundred picosecond laser in LiB3O5 crystals

    NASA Astrophysics Data System (ADS)

    Bai, Zhenxu; Wang, Yulei; Lu, Zhiwei; Jiang, Li; Yuan, Hang; Liu, Zhaohong

    2017-08-01

    A hundred picosecond ultraviolet (UV) laser is demonstrated with a pulse duration of less than 200 ps and peak power of 0.6 GW. With a hundred picosecond stimulated Brillouin scattering compressed pulse as the fundamental light, the UV output at 355 nm is obtained by extra-cavity sum-frequency-mixing in two LiB3O5 crystals. Maximum UV energy was 100 mJ when the incident energy was 280 mJ, yielding an optical-to-optical efficiency of 35.7%. This result is of interest for the generation of high energy sub-nanosecond UV lasers which finds applications in shock ignition and industrial processing.

  3. Global well-posedness and decay of smooth solutions to the non-isothermal model for compressible nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Guo, Boling; Xi, Xiaoyu; Xie, Binqiang

    2017-02-01

    The Cauchy problem for the three-dimensional non-isothermal model for compressible nematic liquid crystals is considered. Existence of global-in-time smooth solutions is established provided that the initial datum is close to a steady state (ρ bar , 0 , d bar , θ bar). By using the Lq-Lp estimates and the Fourier splitting method, if the initial perturbation is small in H3-norm and bounded in Lq (q ∈ [ 1 ,6/5)) norm, we obtain the optimal decay rates for the first and second order spatial derivatives of solutions. In addition, the third and fourth order spatial derivatives of director field d in L2-norm are achieved.

  4. Formulation Development of Spherical Crystal Agglomerates of Itraconazole for Preparation of Directly Compressible Tablets with Enhanced Bioavailability.

    PubMed

    Fadke, Janki; Desai, Jagruti; Thakkar, Hetal

    2015-12-01

    The objective of the present work was to formulate tablet dosage form of itraconazole with enhanced bioavailability. Spherical crystal agglomerates (SCA) of itraconazole prepared by quasi emulsification solvent diffusion method using Soluplus and polyethylene glycol 4000 (PEG 4000) showed increased solubility (540 μg/ml) in 0.1 N hydrochloric acid as compared to pure drug (12 μg/ml). A Fourier transform infrared (FTIR) study indicated compatibility of drug with the excipients. The developed SCA were spherical with smooth surface having an average size of 412 μm. The significantly improved micromeritic properties compared to the plain drug suggested its suitability for direct compression. The antifungal activity of itraconazole was retained in the SCA form as evidenced from the results of the disc diffusion method. The optimized SCA formulation could be easily compressed into tablet with desirable characteristics of hardness (5 kg/cm(2)) and disintegration time (6.3 min). The in vitro dissolution studies showed significant difference in the dissolution profiles of pure drug (21%) and SCA formulation (85%) which was even greater than that of marketed preparation (75%). In vivo pharmacokinetic showed significant enhancement in C max and AUC0-t with relative bioavailability of 225%. The SCA formulation seems to be promising for enhancement of oral bioavailability of itraconazole.

  5. Dual-phase steel sheets under cyclic tension-compression to large strains: Experiments and crystal plasticity modeling

    NASA Astrophysics Data System (ADS)

    Zecevic, Milovan; Korkolis, Yannis P.; Kuwabara, Toshihiko; Knezevic, Marko

    2016-11-01

    In this work, we develop a physically-based crystal plasticity model for the prediction of cyclic tension-compression deformation of multi-phase materials, specifically dual-phase (DP) steels. The model is elasto-plastic in nature and integrates a hardening law based on statistically stored dislocation density, localized hardening due to geometrically necessary dislocations (GNDs), slip-system-level kinematic backstresses, and annihilation of dislocations. The model further features a two level homogenization scheme where the first level is the overall response of a two-phase polycrystalline aggregate and the second level is the homogenized response of the martensite polycrystalline regions. The model is applied to simulate a cyclic tension-compression-tension deformation behavior of DP590 steel sheets. From experiments, we observe that the material exhibits a typical decreasing hardening rate during forward loading, followed by a linear and then a non-linear unloading upon the load reversal, the Bauschinger effect, and changes in hardening rate during strain reversals. To predict these effects, we identify the model parameters using a portion of the measured data and validate and verify them using the remaining data. The developed model is capable of predicting all the particular features of the cyclic deformation of DP590 steel, with great accuracy. From the predictions, we infer and discuss the effects of GNDs, the backstresses, dislocation annihilation, and the two-level homogenization scheme on capturing the cyclic deformation behavior of the material.

  6. Amplifying and compressing optical filter based on one-dimensional ternary photonic crystal structure containing gain medium

    NASA Astrophysics Data System (ADS)

    Jamshidi-Ghaleh, Kazem; Ebrahimpour, Zeinab; Moslemi, Fatemeh

    2015-07-01

    The transmission spectrum properties of the one-dimensional ternary photonic crystal (1DTPC) structure, composed of dielectric (D), metal (M) and gain (G) materials, with three different arrangements of (DGM)N, (GDM)N and (DMG)N, where N is the number of periodicity, were investigated. Two full photonic band gaps and N-1 resonant peaks, localized between them, were observed on transmittance spectra on near-UV spectrum region. When the gained layer was placed in front of the metal, the peaks appeared with higher resolution. There is a peak, localized on the higher band-edge of the first gap, which shows very interesting property than the other peaks. Thus, it amplifies and compresses faster with increase in the N and strength of the gain coefficient. The effects of the gain coefficient and periodicity number are graphically illustrated. This communication presents a PC structure that can be a good candidate to design an amplifying and compressing single or multi-channel optical filter in the UV region.

  7. Apparatus and method for determining microscale interactions based on compressive sensors such as crystal structures

    DOEpatents

    McAdams, Harley; AlQuraishi, Mohammed

    2015-04-21

    Techniques for determining values for a metric of microscale interactions include determining a mesoscale metric for a plurality of mesoscale interaction types, wherein a value of the mesoscale metric for each mesoscale interaction type is based on a corresponding function of values of the microscale metric for the plurality of the microscale interaction types. A plurality of observations that indicate the values of the mesoscale metric are determined for the plurality of mesoscale interaction types. Values of the microscale metric are determined for the plurality of microscale interaction types based on the plurality of observations and the corresponding functions and compressed sensing.

  8. Relative stability of the FCC and HCP polymorphs with interacting polymers.

    PubMed

    Mahynski, Nathan A; Kumar, Sanat K; Panagiotopoulos, Athanassios Z

    2015-01-14

    Recent work [Mahynski et al., Nat. Commun., 2014, 5, 4472] has demonstrated that the addition of long linear homopolymers thermodynamically biases crystallizing hard-sphere colloids to produce the hexagonal close-packed (HCP) polymorph over the closely related face-centered cubic (FCC) structure when the polymers and colloids are purely repulsive. In this report, we investigate the effects of thermal interactions on each crystal polymorph to explore the possibility of stabilizing the FCC crystal structure over the HCP. We find that the HCP polymorph remains at least as stable as its FCC counterpart across the entire range of interactions we explored, where interactions were quantified by the reduced second virial coefficient, -1.50 < B < 1.01. This metric conveniently characterizes the crossover from entropically to energetically dominated systems at B ≈ 0. While the HCP relies on its octahedral void arrangement for enhanced stability when B > 0, its tetrahedral voids produce a similar effect when B < 0 (i.e. when energetics dominate). Starting from this, we derive a mean-field expression for the free energy of an infinitely-dilute polymer adsorbed in the crystal phase for nonzero B. Our results reveal that co-solute biasing of a single polymorph can still be observed in experimentally realizable scenarios when the colloids and polymers have attractive interactions, and provide a possible explanation for the experimental finding that pure FCC crystals are elusive in these binary mixtures.

  9. The Strength of Single Crystal Copper under Uniaxial Shock Compression at Mbar pressures

    SciTech Connect

    Murphy, W; Higginbotham, A; Kimminau, G; Barbrel, B; Bringa, E; Hawreliak, J; Koenig, M; McBarron, W; Meyers, M; Nagler, B; Ozaki, N; Park, N; Remington, B; Rothman, S; Vinko, S M; Whitcher, T; Wark, J

    2009-05-21

    In situ x-ray diffraction has been used to measure the shear strain (and thus strength) of single crystal copper shocked to Mbar pressures along the [001] and [111] axes. These direct shear strain measurements indicate shear strengths at these ultra-high strain rates (of order 10{sup 9} s{sup -1}) of a few GPa, which are both broadly in agreement with the extrapolation of lower strain-rate data and with non-equilibrium molecular dynamics simulations.

  10. Synthesis of 4H/fcc Noble Multimetallic Nanoribbons for Electrocatalytic Hydrogen Evolution Reaction.

    PubMed

    Fan, Zhanxi; Luo, Zhimin; Huang, Xiao; Li, Bing; Chen, Ye; Wang, Jie; Hu, Yanling; Zhang, Hua

    2016-02-03

    Noble multimetallic nanomaterials, if only consisting of Au, Ag, Pt, and Pd, typically adopt the high-symmetry face-centered cubic (fcc) structure. Here for the first time, by using the 4H/fcc Au@Ag nanoribbons (NRBs) as seeds, we report the synthesis of 4H/fcc trimetallic Au@PdAg core-shell NRBs via the galvanic reaction method under ambient conditions. Moreover, this strategy can also be used to synthesize 4H/fcc trimetallic Au@PtAg and quatermetallic Au@PtPdAg core-shell NRBs. Impressively, for the first time, these alloy shells, i.e., PdAg, PtAg, and PtPdAg, epitaxially grown on the 4H/fcc Au core with novel 4H hexagonal phase were successfully synthesized. Remarkably, the obtained 4H/fcc Au@PdAg NRBs exhibit excellent electrocatalytic activity toward the hydrogen evolution reaction, which is even quite close to that of the commercial Pt black. We believe that our findings here may provide a novel strategy for the crystal-structure-controlled synthesis of advanced functional noble multimetallic nanomaterials with various promising applications.

  11. Electronic Structure of Crystalline Buckyballs: fcc-C60

    NASA Astrophysics Data System (ADS)

    Jalali-Asadabadi, Saeid; Ghasemikhah, E.; Ouahrani, T.; Nourozi, B.; Bayat-Bayatani, M.; Javanbakht, S.; Aliabad, H. A. Rahnamaye; Ahmad, Iftikhar; Nematollahi, J.; Yazdani-Kachoei, M.

    2016-01-01

    The electronic properties of pristine fcc-C60 are calculated by utilizing a variety of density functional theory (DFT) approaches including the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA), PBE-GGA+DFT-D3(vdW), Engel and Vosko GGA (EV-GGA), GGA plus Hubbard U parameter (GGA+U), hybrids Becke-Perdew-Wang hybrid functional (B3PW91), Becke-Lee-Yang-Parr hybrid functional (B3LYP), the PBE exchange-correlation functional (PBE0), and Tran and Blaha regular and non-regular modified Becke and Johnson (TB-mBJ) potential within a DFT frame work using augmented plane waves plus local orbital method. The comparison of the calculated results with the experimental values shows that the non-regular TB-mBJ method reproduces a correct experimental direct band gap of 2.12 eV at X symmetry for this compound. The effectiveness of this theoretical approach in the reproduction of the experimental band gap is due to the proper treatment of the electrons in the interstitial region of the crystal. Our results show that the C60 clusters are weakly interacting with each other in the fcc crystal. This study also reveals that the five-fold degeneracies of the isolated C60 molecule due to its icosahedral symmetry are completely lifted at an X symmetry point by the crystal field.

  12. Shock compression modeling of metallic single crystals: comparison of finite difference, steady wave, and analytical solutions

    SciTech Connect

    Lloyd, Jeffrey T.; Clayton, John D.; Austin, Ryan A.; McDowell, David L.

    2015-07-10

    Background: The shock response of metallic single crystals can be captured using a micro-mechanical description of the thermoelastic-viscoplastic material response; however, using a such a description within the context of traditional numerical methods may introduce a physical artifacts. Advantages and disadvantages of complex material descriptions, in particular the viscoplastic response, must be framed within approximations introduced by numerical methods. Methods: Three methods of modeling the shock response of metallic single crystals are summarized: finite difference simulations, steady wave simulations, and algebraic solutions of the Rankine-Hugoniot jump conditions. For the former two numerical techniques, a dislocation density based framework describes the rate- and temperature-dependent shear strength on each slip system. For the latter analytical technique, a simple (two-parameter) rate- and temperature-independent linear hardening description is necessarily invoked to enable simultaneous solution of the governing equations. For all models, the same nonlinear thermoelastic energy potential incorporating elastic constants of up to order 3 is applied. Results: Solutions are compared for plate impact of highly symmetric orientations (all three methods) and low symmetry orientations (numerical methods only) of aluminum single crystals shocked to 5 GPa (weak shock regime) and 25 GPa (overdriven regime). Conclusions: For weak shocks, results of the two numerical methods are very similar, regardless of crystallographic orientation. For strong shocks, artificial viscosity affects the finite difference solution, and effects of transverse waves for the lower symmetry orientations not captured by the steady wave method become important. The analytical solution, which can only be applied to highly symmetric orientations, provides reasonable accuracy with regards to prediction of most variables in the final shocked state but, by construction, does not provide insight

  13. Shock compression modeling of metallic single crystals: comparison of finite difference, steady wave, and analytical solutions

    DOE PAGES

    Lloyd, Jeffrey T.; Clayton, John D.; Austin, Ryan A.; ...

    2015-07-10

    Background: The shock response of metallic single crystals can be captured using a micro-mechanical description of the thermoelastic-viscoplastic material response; however, using a such a description within the context of traditional numerical methods may introduce a physical artifacts. Advantages and disadvantages of complex material descriptions, in particular the viscoplastic response, must be framed within approximations introduced by numerical methods. Methods: Three methods of modeling the shock response of metallic single crystals are summarized: finite difference simulations, steady wave simulations, and algebraic solutions of the Rankine-Hugoniot jump conditions. For the former two numerical techniques, a dislocation density based framework describes themore » rate- and temperature-dependent shear strength on each slip system. For the latter analytical technique, a simple (two-parameter) rate- and temperature-independent linear hardening description is necessarily invoked to enable simultaneous solution of the governing equations. For all models, the same nonlinear thermoelastic energy potential incorporating elastic constants of up to order 3 is applied. Results: Solutions are compared for plate impact of highly symmetric orientations (all three methods) and low symmetry orientations (numerical methods only) of aluminum single crystals shocked to 5 GPa (weak shock regime) and 25 GPa (overdriven regime). Conclusions: For weak shocks, results of the two numerical methods are very similar, regardless of crystallographic orientation. For strong shocks, artificial viscosity affects the finite difference solution, and effects of transverse waves for the lower symmetry orientations not captured by the steady wave method become important. The analytical solution, which can only be applied to highly symmetric orientations, provides reasonable accuracy with regards to prediction of most variables in the final shocked state but, by construction, does not provide

  14. The strength of single crystal copper under uniaxial shock compression at 100 GPa

    NASA Astrophysics Data System (ADS)

    Murphy, W. J.; Higginbotham, A.; Kimminau, G.; Barbrel, B.; Bringa, E. M.; Hawreliak, J.; Kodama, R.; Koenig, M.; McBarron, W.; Meyers, M. A.; Nagler, B.; Ozaki, N.; Park, N.; Remington, B.; Rothman, S.; Vinko, S. M.; Whitcher, T.; Wark, J. S.

    2010-02-01

    In situ x-ray diffraction has been used to measure the shear strain (and thus strength) of single crystal copper shocked to 100 GPa pressures at strain rates over two orders of magnitude higher than those achieved previously. For shocks in the [001] direction there is a significant associated shear strain, while shocks in the [111] direction give negligible shear strain. We infer, using molecular dynamics simulations and VISAR (standing for 'velocity interferometer system for any reflector') measurements, that the strength of the material increases dramatically (to ~1 GPa) for these extreme strain rates.

  15. Quadrupole deformation of electron shells in the lattice dynamics of compressed rare-gas crystals

    NASA Astrophysics Data System (ADS)

    Troitskaya, E. P.; Chabanenko, Val. V.; Zhikharev, I. V.; Gorbenko, Ie. Ie.; Pilipenko, E. A.

    2012-06-01

    The lattice dynamics of rare-gas crystals has been constructed taking into account the deformation of electron shells of the atoms of the dipole and quadrupole types, depending on the displacement of the nuclei. The obtained equations of lattice vibrations have been investigated in the long-wavelength approximation. The role played by the three-body interaction and the deformation of the electron shells in the violation of the Cauchy relation has been discussed. The calculated Birch elastic moduli for Xe and deviations from the Cauchy relation are in good agreement with the available experimental data over a wide range of pressures.

  16. Dynamic range compression/expansion of light beams by photorefractive crystals

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen (Inventor); Liu, Hua-Kuang (Inventor)

    1988-01-01

    An apparatus is provided which greatly reduces the intensity of bright portions of an image while only moderately reducing the brightness of dimmer portions of the image, to thereby compress the range of light intensities to facilitate detection of the image. The apparatus includes a light detector device formed by a chip of photorefractive material. A 2-D array of light beams from an object to be detected passes through a beam splitter to form two arrays of light beams. The two arrays are directed at different angles against a surface of the chip of photorefractive material, the two arrays of light beams forming coincident images on the surface. One of the 2-D arrays of beams emerging from an opposite surface of the chip has a lower range of intensities, to facilitate detection of the object despite very bright spots in its image. The other array of light beams emerging from the chip has a greater range of intensities than the unprocessed image of the object.

  17. Dynamic range compression/expansion of light beams by photorefractive crystals

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen (Inventor); Liu, Hua-Kuang (Inventor)

    1988-01-01

    An apparatus is provided which greatly reduces the intensity of bright portions of an image while only moderately reducing the brightness of dimmer portions of the image, to thereby compress the range of light intensities to facilitate detection of the image. The apparatus includes a light detector device formed by a chip of photorefractive material. A 2-D array of light beams from an object to be detected passes through a beam splitter to form two arrays of light beams. The two arrays are directed at different angles against a surface of the chip of photorefractive material, the two arrays of light beams forming coincident images on the surface. One of the 2-D arrays of beams emerging from an opposite surface of the chip has a lower range of intensities, to facilitate detection of the object despite very bright spots in its image. The other array of light beams emerging from the chip has a greater range of intensities than the unprocessed image of the object.

  18. Compression of single-crystal magnesium oxide to 118 GPa and a ruby pressure gauge for helium pressure media

    SciTech Connect

    Jacobsen, S.D.; Holl, C.M.; Adams, K.A.; Fischer, R.A.; Martin, E.S.; Bina, C.R.; Lin, J.-F.; Prakapenka, V.B.; Kubo, A.; Dera, P.

    2008-11-13

    The pressure-volume equation of state (EoS) of single-crystal MgO has been studied in diamond-anvil cells loaded with helium to 118 GPa and in a non-hydrostatic KCl pressure medium to 87 GPa using monochromatic synchrotron X-ray diffraction. A third-order Birch-Murnaghan fit to the non-hydrostatic P-V data (KCl medium) yields typical results for the initial volume, V{sub 0} = 74.698(7) {angstrom}{sup 3}, bulk modulus, K{sub T0} = 164(1) GPa, and pressure derivative, K' = 4.05(4), using the non-hydrostatic ruby pressure gauge of Mao et al. (1978). However, compression of MgO in helium yields V{sub 0} = 74.697(6) {angstrom}{sup 3}, K{sub T0} = 159.6(6) GPa, and K' = 3.74(3) using the quasi-hydrostatic ruby gauge of Mao et al. (1986). In helium, the fitted equation of state of MgO underdetermines the pressure by 8% at 100 GPa when compared with the primary MgO pressure scale of Zha et al. (2000), with K{sub T0} = 160.2 GPa and K' = 4.03. The results suggest that either the compression mechanism of MgO changes above 40 GPa (in helium), or the ruby pressure gauge requires adjsutment for the softer helium pressure medium. We propose a ruby pressure gauge for helium based on shift of the ruby-R{sub 1} fluorescence line ({Delta}{lambda}/{lambda}{sub 0}) and the primary MgO pressure scale, with P (GPa) = A/B{l_brace}[1 + ({Delta}{lambda}/{lambda}{sub 0})]B - 1{r_brace}, where A is fixed to 1904 GPa and B = 10.32(7).

  19. 47 CFR 80.417 - FCC Rules and Regulations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false FCC Rules and Regulations. 80.417 Section 80... STATIONS IN THE MARITIME SERVICES Station Documents § 80.417 FCC Rules and Regulations. The Commission's... available on the Commission's web site at www.fcc.gov or ftp.fcc.gov....

  20. In Situ Mechanical Behavior of Mineral Crystals in Human Cortical Bone under Compressive Load Using Synchrotron X-Ray Scattering Techniques

    PubMed Central

    Giri, Bijay; Almer, Jon D.; Dong, X. Neil; Wang, Xiaodu

    2012-01-01

    Mineral crystals, the major strength-bearing component of bone, are aligned in longitudinal bone with (00l) axes preferentially along the longitudinal axis, which in concert with crystal anisotropy leads to macroscopic anisotropy in mechanical behavior. Thus, it is of great interest to delineate the contributions of different subsets of mineral crystals as a function of orientation, on the bulk mechanical behavior of bone. Using a unique synergistic approach combining a progressive loading scheme and synchrotron X-ray scattering techniques, human cortical bone specimens were loaded in compression to examine the in situ mechanical behavior of mineral crystals as the function of orientation. The orientation distribution of mineral crystals was quantitatively estimated by measuring the X-ray diffraction intensity from the crystallographic (002) plane in different orientations. In addition, the average longitudinal (c-axis), transverse (a-axis), and shear strains of the subset of mineral crystals aligned in each orientation were determined by measuring the lattice deformation in the crystals normal to three distinct crystallographic planes (i.e. 002, 310, and 213). The experimental results indicated that the in situ strain and stress of mineral crystals varied with orientation. The normal strain and stress exerted on the longitudinally aligned mineral crystals were markedly greater than those on the transversely oriented crystals, whereas the shear stress reached a maximum for the crystals aligned in ±30° with respect to the loading direction, which coincided with the long axis of bone. The maximum principal strain and stress were observed in the mineral crystals oriented along the loading axis, with a similar trend observed in the maximum shear strain and stress. By examining their in situ behavior, the contribution of mineral crystals to load bearing and the bulk behavior of bone are discussed. PMID:22982959

  1. Compression of single-crystal magnesium oxide to 118 GPa and a ruby pressure gauge for helium pressure media

    NASA Astrophysics Data System (ADS)

    Jacobsen, S. D.; Holl, C. M.; Adams, K. A.; Fischer, R. A.; Martin, E. S.; Bina, C. R.; Lin, J.; Prakapenka, V. B.; Kubo, A.; Dera, P.

    2008-12-01

    Magnesium oxide (MgO, periclase) is among the most widely studied standard materials for testing experimental and theoretical methods of determining elastic properties. Because of its simple structure and geophysical relevance, knowledge of accurate elastic properties of MgO pertains to problems ranging from experimental pressure scales to interpreting Earth's seismic structure. The pressure-volume equation of state (EoS) of single-crystal MgO has been studied in diamond-anvil cells loaded with helium to 118 GPa and in a non-hydrostatic KCl pressure medium to 87 GPa using monochromatic synchrotron X-ray diffraction at GSECARS (Sector 13, APS). A third-order Birch-Murnaghan fit to the non-hydrostatic P-V data (KCl medium) yields typical results for the initial volume, V0=74.698(7)Å3, bulk modulus, KT0=164(1)GPa, and pressure derivative, K'=4.05(4) using the non-hydrostatic ruby pressure gauge of Mao et al. (1978). However, compression of MgO in helium yields V0=74.697(6)Å3, KT0=159.6(6)GPa, and K'=3.74(3) using the quasi-hydrostatic ruby gauge of Mao et al. (1986). In helium, the fitted equation of state of MgO underdetermines the pressure by 8% at 100 GPa when compared with the primary MgO pressure scale of Zha et al. (2000), with KT0=160.2GPa and K'=4.03. The results suggest that either the compression mechanism of MgO changes above 40 GPa (in helium), or the ruby pressure gauge requires adjustment for the softer helium pressure medium. We provide a revised ruby pressure gauge for helium pressure media against the primary MgO pressure scale, which will be useful for future high-pressure crystallographic studies of minerals compressed with helium in the 25-140 GPa range of the lower mantle.

  2. Low voltage FCC for home and business

    NASA Technical Reports Server (NTRS)

    Wolf, L.

    1972-01-01

    A thin pressure-sensitive FCC for low voltage usage is described. It is recommended for installing in speakers, intercoms, doorbells, burglar alarms, and clocks, without running wires between walls. The specifications are given.

  3. Military and aerospace applications of FCC

    NASA Technical Reports Server (NTRS)

    Swanson, C.

    1972-01-01

    Military and NASA programs are discussed in which FCC were used. Included are Saturn 4, Pegasus satellites solar, array for Skylab orbital workshop, Poseidon missiles, MK 48 torpedo fire control, and Lunar Surveyor.

  4. Low voltage FCC for home and business

    NASA Technical Reports Server (NTRS)

    Wolf, L.

    1972-01-01

    A thin pressure-sensitive FCC for low voltage usage is described. It is recommended for installing in speakers, intercoms, doorbells, burglar alarms, and clocks, without running wires between walls. The specifications are given.

  5. 78 FR 69415 - Proposed Changes to FCC Form 499-A, FCC Form 499-Q, and Accompanying Instructions.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-19

    ... COMMISSION Proposed Changes to FCC Form 499-A, FCC Form 499-Q, and Accompanying Instructions. AGENCY: Federal... to (1) the annual Telecommunications Reporting Worksheet, FCC Form 499-A (Form 499-A) and... quarterly Telecommunications Reporting Worksheet, FCC Form 499-Q (Form 499-Q) and accompanying...

  6. Ferromagnetic properties of fcc Gd thin films

    SciTech Connect

    Bertelli, T. P. Passamani, E. C.; Larica, C.; Nascimento, V. P.; Takeuchi, A. Y.

    2015-05-28

    Magnetic properties of sputtered Gd thin films grown on Si (100) substrates kept at two different temperatures were investigated using X-ray diffraction, ac magnetic susceptibility, and dc magnetization measurements. The obtained Gd thin films have a mixture of hcp and fcc structures, but with their fractions depending on the substrate temperature T{sub S} and film thickness x. Gd fcc samples were obtained when T{sub S} = 763 K and x = 10 nm, while the hcp structure was stabilized for lower T{sub S} (300 K) and thicker film (20 nm). The fcc structure is formed on the Ta buffer layer, while the hcp phase grows on the fcc Gd layer as a consequence of the lattice relaxation process. Spin reorientation phenomenon, commonly found in bulk Gd species, was also observed in the hcp Gd thin film. This phenomenon is assumed to cause the magnetization anomalous increase observed below 50 K in stressed Gd films. Magnetic properties of fcc Gd thin films are: Curie temperature above 300 K, saturation magnetization value of about 175 emu/cm{sup 3}, and coercive field of about 100 Oe at 300 K; features that allow us to classify Gd thin films, with fcc structure, as a soft ferromagnetic material.

  7. Non-Newtonian Crystal- and Bubble-Rich Lava Rheology in Compression

    NASA Astrophysics Data System (ADS)

    Lavallee, Y.; Hess, K.; Cordonnier, B.; Dingwell, D. B.

    2006-12-01

    Volcanic eruption models are still hampered by the lack of multiphase magmatic rheology laws. Fortunately, the lack of sufficient rheological data for lavas bearing crystals and vesicles is now being systematically experimentally addressed. Most rheological models consider suspension rheology according to the Einstein- Roscoe equation or a modification of it. This approach does not contain a Non-Newtonian description (strain- rate dependence). Here, experiments using high-load, high-temperature uniaxial apparatus were carried out to simulate multiphase lava deformation under stresses ranging from 1 to 70 MPa. Samples from Unzen, Colima, Anak Krakatau and Bezymianny (containing 30, 50, 70 and 80 % phenocrysts, and 5, 8, 23 and 9 % vesicles, respectively) were chosen for this study. Obtained results reveal that multiphase lavas behave as pseudo-plastic fluids exhibiting an important component of shear thinning. The viscosity of all lavas decreases exponentially by ca. 1.5 log units between the strain rates of 10-6 and 10-3 s-1; point at which viscous heating and micro-cracking begin to be detected. The strong exponential dependence of the viscosity on strain rate holds the promise of yielding a Non-Newtonian rheology law and consequentially challenges the completeness of the Einstein-Roscoe equation to treat suspension rheology in volcanic eruption models.

  8. Elastic-plastic and phase transition of zinc oxide single crystal under shock compression

    SciTech Connect

    Liu, Xun; Mashimo, Tsutomu Li, Wei; Zhou, Xianming; Sekine, Toshimori

    2015-03-07

    The Hugoniot data for zinc oxide (ZnO) single crystals were measured up to 80 GPa along both the 〈112{sup ¯}0〉 (a-axis) and 〈0001〉 (c-axis) directions using a velocity interferometer system for any reflector and inclined-mirror method combined with a powder gun and two-stage light gas gun. The Hugoniot-elastic limits of ZnO were determined to be 10.5 and 11.5 GPa along the a- and c-axes, respectively. The wurtzite (B4) to rocksalt (B1) phase transition pressures along the a- and c-axes are 12.3 and 14.4 GPa, respectively. Shock velocity (U{sub s}) versus particle velocity (U{sub p}) relation of the final phase is given by the following relationship: U{sub s} (km/s) = 2.76 + 1.51U{sub p} (km/s). Based on the Debye-Grüneisen model and Birch-Murnaghan equation of state (EOS), we discuss the EOS of the B1 phase ZnO. The bulk modulus (K{sub 0}) and its pressure derivative (K{sub 0}′) are estimated to be K{sub 0} = 174 GPa and K{sub 0}′ = 3.9, respectively.

  9. Shock wave compression of hexagonal-close-packed metal single crystals: Time-dependent, anisotropic elastic-plastic response of beryllium

    SciTech Connect

    Winey, J. M.; Gupta, Y. M.

    2014-07-21

    Understanding and modeling the response of hcp metals to high stress impulsive loading is challenging because the lower crystal symmetry, compared to cubic metals, results in a significantly more complex material response. To gain insight into the inelastic deformation of hcp metals subjected to high dynamic stresses, shock wave compression of single crystals provides a useful approach because different inelastic deformation mechanisms can be examined selectively by shock compression along different crystal orientations. As a representative example, we report, here, on wave propagation simulations for beryllium (Be) single crystals shocked along the c-axis, a-axis, and several low-symmetry directions to peak stresses reaching 7 GPa. The simulations utilized a time-dependent, anisotropic material model that incorporated dislocation dynamics, deformation twinning, and shear cracking based descriptions of inelastic deformation. The simulation results showed good overall agreement with measured wave profiles for all the different crystal orientations examined [Pope and Johnson, J. Appl. Phys. 46, 720 (1975)], including features arising from wave mode coupling due to the highly anisotropic inelastic response of Be. This good agreement demonstrates that the measured profiles can be understood in terms of dislocation slip along basal, prismatic, and pyramidal planes, together with deformation twinning along (101{sup ¯}2) planes. Our results show that the response of shocked Be single crystals involves the simultaneous operation of multiple, distinct inelastic deformation mechanisms for all orientations except the c-axis. For shocked c-axis Be, the measured wave profiles do not provide good discrimination between pyramidal slip and other inelastic deformation mechanisms, such as shear cracking. The findings presented here provide insight into the complex inelastic deformation response of shocked Be single crystals and are expected to be useful for other hcp crystals

  10. Appropriate deposition parameters for formation of fcc Co-Ni alloy nanowires during electrochemical deposition process

    NASA Astrophysics Data System (ADS)

    Mukhtar, Aiman; Shahzad Khan, Babar; Mehmood, Tahir

    2016-12-01

    The effect of deposition potential on the crystal structure and composition of Co-Ni alloy nanowires is studied by XRD, FE-SEM and EDX. The alloy nanowires deposited at -3.2 V are metastable fcc phase Co-Ni. The alloy nanowires deposited at -1.8 V are hcp phase Co-Ni. The formation of the metastable fcc alloy nanowires can be attributed to smaller critical clusters formed at the high potential as the smaller critical clusters favor fcc structure because of the significant surface energy effect. The content of Co inside nanowires increases with increasing potential. This can be understood by the polarization curves of depositing Co and Ni nanowires, which show that the current density ratio of Ni to Co at low potential has larger value than that at high potential.

  11. Catalytic reforming of heart cut fcc naphthas

    SciTech Connect

    Gerritsen, L.A.

    1985-03-01

    The anticipated lead phasedown in the USA and the growing demand for unleaded gasoline will require a higher gasoline pool octane number. One of the possibilities to achieve this increase of pool octane will be catalytic reforming of FCC naphtha. In this paper we evaluate the effects of FCC naphtha reforming on the reformer operation and gasoline pool volume for various lead phasedown scenarios. High-stability reforming catalysts, like TPR-8/CK-522 TRILOBE catalyst, will be required to maintain acceptable cycle lengths at the more severe reformer operating conditions. The properties and octane distribution of FCC naphtha are discussed, as well as its hydrotreating with high-active NiMo catalysts.

  12. Ru nanoframes with an fcc structure and enhanced catalytic properties

    SciTech Connect

    Ye, Haihang; Wang, Qingxiao; Catalano, Massimo; Lu, Ning; Vermeylen, Joseph; Kim, Moon J.; Liu, Yuzi; Sun, Yugang; Xia, Xiaohu

    2016-03-21

    Noble-metal nanoframes are of great interest to many applications due to their unique open structures. Among various noble metals, Ru has never been made into nanoframes. In this study, we report for the first time an effective method based on seeded growth and chemical etching for the facile synthesis of Ru nanoframes with high purity. The essence of this approach is to induce the preferential growth of Ru on the corners and edges of Pd truncated octahedra as the seeds by kinetic control. The resultant Pd–Ru core–frame octahedra could be easily converted to Ru octahedral nanoframes of ~2 nm in thickness by selectively removing the Pd cores through chemical etching. Most importantly, in this approach the face-centered cubic (fcc) crystal structure of Pd seeds was faithfully replicated by Ru that usually takes an hcp structure. Furthermore, the fcc Ru nanoframes showed higher catalytic activities toward the reduction of p-nitrophenol by NaBH4 and the dehydrogenation of ammonia borane compared with hcp Ru nanowires with roughly the same thickness.

  13. Ru nanoframes with an fcc structure and enhanced catalytic properties

    DOE PAGES

    Ye, Haihang; Wang, Qingxiao; Catalano, Massimo; ...

    2016-03-21

    Noble-metal nanoframes are of great interest to many applications due to their unique open structures. Among various noble metals, Ru has never been made into nanoframes. In this study, we report for the first time an effective method based on seeded growth and chemical etching for the facile synthesis of Ru nanoframes with high purity. The essence of this approach is to induce the preferential growth of Ru on the corners and edges of Pd truncated octahedra as the seeds by kinetic control. The resultant Pd–Ru core–frame octahedra could be easily converted to Ru octahedral nanoframes of ~2 nm inmore » thickness by selectively removing the Pd cores through chemical etching. Most importantly, in this approach the face-centered cubic (fcc) crystal structure of Pd seeds was faithfully replicated by Ru that usually takes an hcp structure. Furthermore, the fcc Ru nanoframes showed higher catalytic activities toward the reduction of p-nitrophenol by NaBH4 and the dehydrogenation of ammonia borane compared with hcp Ru nanowires with roughly the same thickness.« less

  14. Ru Nanoframes with an fcc Structure and Enhanced Catalytic Properties.

    PubMed

    Ye, Haihang; Wang, Qingxiao; Catalano, Massimo; Lu, Ning; Vermeylen, Joseph; Kim, Moon J; Liu, Yuzi; Sun, Yugang; Xia, Xiaohu

    2016-04-13

    Noble-metal nanoframes are of great interest to many applications due to their unique open structures. Among various noble metals, Ru has never been made into nanoframes. In this study, we report for the first time an effective method based on seeded growth and chemical etching for the facile synthesis of Ru nanoframes with high purity. The essence of this approach is to induce the preferential growth of Ru on the corners and edges of Pd truncated octahedra as the seeds by kinetic control. The resultant Pd-Ru core-frame octahedra could be easily converted to Ru octahedral nanoframes of ∼2 nm in thickness by selectively removing the Pd cores through chemical etching. Most importantly, in this approach the face-centered cubic (fcc) crystal structure of Pd seeds was faithfully replicated by Ru that usually takes an hcp structure. The fcc Ru nanoframes showed higher catalytic activities toward the reduction of p-nitrophenol by NaBH4 and the dehydrogenation of ammonia borane compared with hcp Ru nanowires with roughly the same thickness.

  15. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 1 2014-10-01 2014-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  16. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  17. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  18. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 1 2013-10-01 2013-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  19. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  20. Current Policy Problems at the FCC.

    ERIC Educational Resources Information Center

    Wiley, Richard E.

    In the past year the Federal Communications Commission (FCC) has instituted new programs and initiatives designed to improve the exchange of information between the Commission and the research and academic community. An Office of Plans and Policy has been formed. As a result of the Future Planning Conference held last year, a research project is…

  1. Deformation Heterogeneity and Texture Evolution of NiTiFe Shape Memory Alloy Under Uniaxial Compression Based on Crystal Plasticity Finite Element Method

    NASA Astrophysics Data System (ADS)

    Liang, Yulong; Jiang, Shuyong; Zhang, Yanqiu; Zhao, Yanan; Sun, Dong; Zhao, Chengzhi

    2017-04-01

    Crystal plastic finite element method (CPFEM) is used to simulate microstructural evolution, texture evolution and macroscopic stress-strain response of polycrystalline NiTiFe shape memory alloy (SMA) with B2 austenite phase during compression deformation. A novel two-dimensional polycrystalline finite element model based on electron back-scattered diffraction (EBSD) experiment data is developed to represent virtual grain structures of polycrystalline NiTiFe SMA. In the present study, CPFEM plays a significant role in predicting texture evolution and macroscopic stress-strain response of NiTiFe SMA during compression deformation. The simulated results are in good agreement with the experimental ones. It can be concluded that intragranular and intergranular strain heterogeneities are of great importance in guaranteeing plastic deformation compatibility of NiTiFe SMA. CPFEM is able to capture the evolution of grain boundaries with various misorientation angles for NiTiFe SMA subjected to the various compression deformation degrees. During uniaxial compression of NiTiFe SMA, the microstructure evolves into high-energy substructure and consequently the well-defined subgrains are formed. Furthermore, the grain boundaries and the subgrain boundaries are approximately aligned with the direction in which metal flows.

  2. Effects of Co doping on the metamagnetic states of the ferromagnetic fcc Fe-Co alloy.

    PubMed

    Ortiz-Chi, Filiberto; Aguayo, Aarón; de Coss, Romeo

    2013-01-16

    The evolution of the metamagnetic states in the ferromagnetic face centered cubic (fcc) Fe(1-x)Co(x) alloy as a function of Co concentration has been studied by means of first-principles calculations. The ground state properties were obtained using the full-potential linear augmented plane wave method and the generalized gradient approximation for the exchange-correlation functional. The alloying was modeled using the virtual crystal approximation and the magnetic states were obtained from the calculations of the total energy as a function of the spin moment, using the fixed spin moment method. For ferromagnetic fcc Fe, the binding-energy curve shows metamagnetic behavior, with two minima corresponding to a small-volume, low-spin (LS) state and a large-volume, high-spin (HS) state, which are separated by a small energy (E(LS) ≲ E(HS)). The evolution of the magnetic moment, the exchange integral (J), and the binding-energy curve is analyzed in the whole range of Co concentrations (x). The magnetic moment corresponding to the HS state decreases monotonically from 2.6 μ(B)/atom in fcc Fe to 1.7 μ(B)/atom in fcc Co. In contrast, the exchange integral for the HS state shows a maximum at around x = 0.45. The thermal dependence of the lattice parameter is evaluated with a method based on statistical mechanics using the binding-energy curve as an effective potential. It is observed that the behavior of the lattice parameter with temperature is tuned by Co doping, from negative thermal expansion in fcc Fe to positive thermal expansion in fcc Co, through the modification of the energetics of the metamagnetic states.

  3. 47 CFR 74.3 - FCC inspections of stations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false FCC inspections of stations. 74.3 Section 74.3... Services in Part 74 § 74.3 FCC inspections of stations. (a) The licensee of a station authorized under this part must make the station available for inspection by representatives of the FCC during the...

  4. Inside the FCC: A Guide for Information Seekers.

    ERIC Educational Resources Information Center

    Le Duc, Don R., Ed.; Krasnow, Erwin G., Ed.

    1975-01-01

    To aid the public in obtaining information and documents from the files of the Federal Communications Commission (FCC) this guide, written with assistance from the FCC staff, explains which office to approach and in what form to make the request. Ways to obtain informaion by visiting the FCC are explained along with methods for obtaining…

  5. 47 CFR 73.1225 - Station inspections by FCC.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Station inspections by FCC. 73.1225 Section 73... BROADCAST SERVICES Rules Applicable to All Broadcast Stations § 73.1225 Station inspections by FCC. (a) The... FCC during the station's business hours, or at any time it is in operation. (b) In the course of...

  6. Single-crystal elastic constants of disordered and ordered FePd

    NASA Astrophysics Data System (ADS)

    Ichitsubo, Tetsu; Tanaka, Katsushi

    2004-12-01

    Single-crystal elastic constants of A1 (fcc disordered) and single-variant L10-ordered FePd alloy are presented. The ordered phase consisting of single-variant domains was formed using the compression method proposed by our previous paper [T. Ichitsubo, M. Nakamoto, K. Tanaka, and M. Koiwa, Mater. Trans. JIM 39, 24 (1998)]. A complete set of elastic constants has been determined with the resonance ultrasound spectroscopy technique. The disordered alloy exhibits common features of usual fcc metals, and the ordered alloy clearly shows a tetragonal elastic anisotropy, c11

  7. Air-guided photonic-crystal-fiber pulse-compression delivery of multimegawatt femtosecond laser output for nonlinear-optical imaging and neurosurgery

    NASA Astrophysics Data System (ADS)

    Lanin, Aleksandr A.; Fedotov, Il'ya V.; Sidorov-Biryukov, Dmitrii A.; Doronina-Amitonova, Lyubov V.; Ivashkina, Olga I.; Zots, Marina A.; Sun, Chi-Kuang; Ömer Ilday, F.; Fedotov, Andrei B.; Anokhin, Konstantin V.; Zheltikov, Aleksei M.

    2012-03-01

    Large-core hollow photonic-crystal fibers (PCFs) are shown to enable a fiber-format air-guided delivery of ultrashort infrared laser pulses for neurosurgery and nonlinear-optical imaging. With an appropriate dispersion precompensation, an anomalously dispersive 15-μm-core hollow PCF compresses 510-fs, 1070-nm light pulses to a pulse width of about 110 fs, providing a peak power in excess of 5 MW. The compressed PCF output is employed to induce a local photodisruption of corpus callosum tissues in mouse brain and is used to generate the third harmonic in brain tissues, which is captured by the PCF and delivered to a detector through the PCF cladding.

  8. Formation of fivefold axes in the FCC-metal nanoclusters

    NASA Astrophysics Data System (ADS)

    Myasnichenko, Vladimir S.; Starostenkov, Mikhail D.

    2012-11-01

    Formation of atomistic structures of metallic Cu, Au, Ag clusters and bimetallic Cu-Au clusters was studied with the help of molecular dynamics using the many-body tight-binding interatomic potential. The simulation of the crystallization process of clusters with the number of atoms ranging from 300 to 1092 was carried out. The most stable configurations of atoms in the system, corresponding to the minimum of potential energy, was found during super-fast cooling from 1000 K. Atoms corresponding to fcc, hcp, and Ih phases were identified by the method of common neighbor analysis. Incomplete icosahedral core can be discovered at the intersection of one of the Ih axes with the surface of monometallic cluster. The decahedron-shaped structure of bimetallic Cu-Au cluster with seven completed icosahedral cores was obtained. The principles of the construction of small bimetallic clusters with icosahedral symmetry and increased fractal dimensionality were offered.

  9. First-principles study of the thermodynamics of hydrogen-vacancy interaction in fcc iron

    SciTech Connect

    Nazarov, R.; Hickel, T.; Neugebauer, J.

    2010-12-01

    The interaction of vacancies and hydrogen in an fcc iron bulk crystal was studied combining thermodynamic concepts with ab initio calculations and considering various magnetic structures. We show that up to six H atoms can be trapped by a monovacancy. All of the studied point defects (single vacancy, H in interstitial positions, and H-vacancy complexes) cause an anisotropic elastic field in antiferromagnetic fcc iron and significantly change the local and total magnetization of the system. The proposed thermodynamical model allows the determination of the equilibrium vacancy concentration and the concentration of dissolved hydrogen for a given temperature and H chemical potential in the reservoir. For H-rich conditions a dramatic increase in the vacancy concentration in the crystal is found.

  10. Regeneration of Hydrotreating and FCC Catalysts

    SciTech Connect

    CM Wai; JG Frye; JL Fulton; LE Bowman; LJ Silva; MA Gerber

    1999-09-30

    Hydrotreating, hydrocracking, and fluid catalytic cracking (FCC) catalysts are important components of petroleum refining processes. Hydrotreating and hydrocracking catalysts are used to improve the yield of high-quality light oil fractions from heavier crude oil and petroleum feedstocks containing high levels of impurities. FCC catalysts improve the yield of higher octane gasoline from crude oil. Residuum hydrotreating and cracking catalysts are susceptible to irreversible deactivation caused by adsorption of sulfur and by metals impurities, such as vanadium and nickel. The gradual buildup of these impurities in a hydrotreating catalyst eventually plugs the pores and deactivates it. Nickel and vanadium adversely affect the behavior of cracking catalysts, reducing product yield and quality. Replacing deactivated catalysts represents a significant cost in petroleum refining. Equally important are the costs and potential liabilities associated with treating and disposing spent catalysts. For example, recent US Environmental Protection Agency rulings have listed spent hydrotreating and hydrorefining catalysts as hazardous wastes. FCC catalysts, though more easily disposed of as road-base or as filler in asphalt and cement, are still an economic concern mainly because of the large volumes of spent catalysts generated. New processes are being considered to increase the useful life of catalysts or for meeting more stringent disposal requirements for spent catalysts containing metals. This report discusses a collaborative effort between Pacific Northwest National Laboratory (PNNL) and Phillips Petroleum, Inc., to identify promising chemical processes for removing metals adhered to spent hydrodesulfurization (HDS, a type of hydrotreating catalyst) and FCC catalysts. This study, conducted by PNNL, was funded by the US Department of Energy's Bartlesville Project Office. Fresh and spent catalysts were provided by Phillips Petroleum. The FCC catalyst was a rare-earth exchanged

  11. Variation in electromagnetic radiation during plastic deformation under tension and compression of metals

    NASA Astrophysics Data System (ADS)

    Singh, Ranjana; Lal, S. P.; Misra, Ashok

    2014-06-01

    This paper presents some significant variations in the intermittent electromagnetic radiation (EMR) during plastic deformation under tension and compression of some metals with selected crystal structure, viz. zinc, hexagonal closed packed (hcp), copper, face-centred cubic (fcc: stacking fault energy 0.08 J/m2), aluminium (fcc: stacking fault energy 0.2 J/m2) and 0.18 % carbon steel, body-centred cubic (bcc). The intermittent EMR signals starting near yielding are either oscillatory or exponential under both modes of deformation except a very few intermediate signals, random in nature, in zinc under compression. The number and amplitude of EMR signals exhibit marked variations under tension and compression. The smooth correlation between elastic strain energy release rate and average EMR energy release rate suggests a novel technique to determine the fracture toughness of metals. The first EMR emission amplitude and EMR energy release rate occurring near the yield increase, but maximum EMR energy burst frequency decreases almost linearly with increase in Debye temperature of the metals under tension while all EMR parameters decrease nonlinearly under compression. These results can be developed into a new technique to evaluate dislocation velocity. The EMR amplitude and energy release rate of the first EMR emission vary parabolically showing a maxima with increase in electronic heat constant of the metals under tension while they first sharply decrease and then become asymptotic during compression. However, the variation in EMR maximum energy burst frequency is apparently similar under both modes of deformation. These results strongly suggest that the mechanism of EMR emission during plastic deformation of metals involves not only the interaction of conduction electrons with the lattice periodic potential as presented in the previous theoretical models but also the interaction of conduction electrons with phonons. However, during crack propagation and fracture

  12. Recycled plastics in FCC feedstocks: Specific contributions

    SciTech Connect

    Puente, G. de la; Sedran, U.A.; Arandes, J.M.

    1997-11-01

    Following a tertiary recycling option for plastics focused on the FCC process, styrene-based polymers were dissolved in benzene and injected over fresh and equilibrium samples of a commercial FCC catalyst. Reaction times were up to 12 s in a discontinuous fluidized bed reactor at 550 C. The major reaction products were ethylbenzene, benzene, toluene, and styrene, and the production of coke was very significant. A reaction mechanism which includes polymer thermal cracking, surface oligomerization of styrene molecules, and further cracking, in parallel to hydrogen-transfer reactions, was delineated based on the comparison of the catalytic behaviors of the different samples. Increases in the yields of ethylbenzene, styrene, and coke are predictable for the industrial conditions.

  13. Manufacturing and quality control of FCC harnesses

    NASA Technical Reports Server (NTRS)

    Malohm, W. L.; Vandergriff, J.

    1972-01-01

    The Saturn 5 program contractors encountered many technological challenges and problems relative to inter-connecting wiring and cabling during the development stages of the Saturn program. The knowledge gained from solving these problems, plus recently developed state-of-the-art techniques, materials, and processes were documented in a report prepared for NASA/MSFC. The portions of that report which deal with FCC harnesses are presented.

  14. Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. 3: Tension-compression anisotropy

    NASA Technical Reports Server (NTRS)

    Miner, R. V.; Gaab, T. P.; Gayda, J.; Hemker, K. J.

    1985-01-01

    Single crystal superalloy specimens with various crystallographic directions along their axes were tested in compression at room temperature, 650, 760, 870, and 980 deg C. These results are compared with the tensile behavior studied previously. The alloy, Rene N4, was developed for gas turbine engine blades and has the nominal composition 3.7 Al, 4.2 Ti, 4 Ta, 0.5 Nb, 6 W, 1.5 Mo 9 Cr. 7.5 Co, balance Ni, in weight percent. Slip trace analysis showed that primary cube slip occurred even at room temperature for the 111 specimens. With increasing test temperature more orientations exhibited primary cube slip, until at 870 deg C only the 100 and 011 specimens exhibited normal octahedral slip. The yield strength for octahedral slip was numerically analysed using a model proposed by Lall, Chin, and Pope to explain deviations from Schmid's Law in the yielding behavior of a single phase Gamma prime alloy, Ni3(Al, Nb). The Schmid's Law deviations in Rene N4 were found to be largely due to a tension-compression anisotropy. A second effect, which increases trength for orientations away from 001, was found to be small in Rene N4. Analysis of recently published data on the single crystal superalloy PWA 1480 yielded the same result.

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

    SciTech Connect

    Aman, Amjad; Orlovskaya, Nina; Chen, Yan; Lugovy, Mykola; Reece, Michael J.; Ma, Dong; Stoica, Alexandru D.; An, Ke

    2014-07-07

    The dynamics of texture formation, changes in crystal structure, and stress accommodation mechanisms have been studied in perovskite-type R3⁻c rhombohedral LaCoO₃ during uniaxial compression using in-situ neutron diffraction. The in-situ neutron diffraction revealed the complex crystallographic changes causing the texture formation and significant straining along certain crystallographic directions during compression, which are responsible for the appearance of hysteresis and non-linear ferroelastic deformation in the 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 hysteresis loop was closed and no further irrecoverable strain appeared after deformation. The significant texture formation is responsible for an increase in the Young's modulus of LaCoO₃ at high compressive stresses, ranging from 76 GPa at the very beginning of the loading to 194 GPa at 900 MPa at the beginning of the unloading curve.

  16. Computer simulation of FCC riser reactors.

    SciTech Connect

    Chang, S. L.; Golchert, B.; Lottes, S. A.; Petrick, M.; Zhou, C. Q.

    1999-04-20

    A three-dimensional computational fluid dynamics (CFD) code, ICRKFLO, was developed to simulate the multiphase reacting flow system in a fluid catalytic cracking (FCC) riser reactor. The code solve flow properties based on fundamental conservation laws of mass, momentum, and energy for gas, liquid, and solid phases. Useful phenomenological models were developed to represent the controlling FCC processes, including droplet dispersion and evaporation, particle-solid interactions, and interfacial heat transfer between gas, droplets, and particles. Techniques were also developed to facilitate numerical calculations. These techniques include a hybrid flow-kinetic treatment to include detailed kinetic calculations, a time-integral approach to overcome numerical stiffness problems of chemical reactions, and a sectional coupling and blocked-cell technique for handling complex geometry. The copyrighted ICRKFLO software has been validated with experimental data from pilot- and commercial-scale FCC units. The code can be used to evaluate the impacts of design and operating conditions on the production of gasoline and other oil products.

  17. Ultrafast visualization of crystallization and grain growth in shock-compressed SiO2

    SciTech Connect

    Gleason, A. E.; Bolme, C. A.; Lee, H. J.; Nagler, B.; Galtier, E.; Milathianaki, D.; Hawreliak, J.; Kraus, R. G.; Eggert, J. H.; Fratanduono, D. E.; Collins, G. W.; Sandberg, R.; Yang, W.; Mao, W. L.

    2015-09-04

    Pressure- and temperature-induced phase transitions have been studied for more than a century but very little is known about the non-equilibrium processes by which the atoms rearrange. Shock compression generates a nearly instantaneous propagating high-pressure/temperature condition while in situ X-ray diffraction (XRD) probes the time-dependent atomic arrangement. Here we present in situ pump–probe XRD measurements on shock-compressed fused silica, revealing an amorphous to crystalline high-pressure stishovite phase transition. Using the size broadening of the diffraction peaks, the growth of nanocrystalline stishovite grains is resolved on the nanosecond timescale just after shock compression. At applied pressures above 18 GPa the nuclueation of stishovite appears to be kinetically limited to 1.4 ± 0.4 ns. The functional form of this grain growth suggests homogeneous nucleation and attachment as the growth mechanism. As a result, these are the first observations of crystalline grain growth in the shock front between low- and high-pressure states via XRD.

  18. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... (CB Rule 28) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: CB, 1270 Fairfield Road...

  19. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... (R/C Rule 25) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: R/C, 1270 Fairfield Road...

  20. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... (R/C Rule 25) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: R/C, 1270 Fairfield Road...

  1. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... (CB Rule 28) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: CB, 1270 Fairfield Road...

  2. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... (R/C Rule 25) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: R/C, 1270 Fairfield Road...

  3. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... (CB Rule 28) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: CB, 1270 Fairfield Road...

  4. A novel approach to octane enhancement via FCC catalysis

    SciTech Connect

    Yanik, S.J.; Campagna, R.J.; Demmel, E.J.; Humphries, A.P.

    1985-03-01

    The development of FCC catalysts containing the shape selective zeolite, ZSM-5, has been successfully completed. Both experimental and commercial results have demonstrated that significant octane enhancement can be achieved using these FCC catalysts. The Z catalysts reduce FCC gasoline yield, but total C/sub 3//sup +/ liquid yields increase. Total prime products yields also increase if sufficient alkylation capacity is available. Significant economic benefits are achieved. Because of Filtrol's flexible catalyst production process, ZSM-5 can be included in all grades of Filtrol's FCC catalysts. These new materials are now commercially available.

  5. Stacking fault energy in FCC plutonium with multiple reference states in the modified embedded atom method

    NASA Astrophysics Data System (ADS)

    Valone, S. M.; Baskes, M. I.; Rudin, S. P.

    2012-03-01

    Basic concepts from the multi-reference state formalism for determining the functions for the modified embedded atom method (MEAM) are adopted to modeling elemental plutonium (Pu). In the case of elemental Pu, the focus is on the background electron density. Here we utilize a portion of the formalism that determines the structure of the background density necessary to capture correct phase ordering between fcc and ideal hcp crystal structures. The critical information comes from cold curves, that is the energy/volume relationships, for these phases. Practically speaking, the energy difference between these two phases determines the stacking fault energy of the material. At the same time, the simple monoclinic phase of elemental Pu also becomes higher in energy at the equilibrium volume of the fcc phase. The new model is based on first-principles electronic structure calculations and captures the basic phase ordering of those calculations.

  6. Temperature and orientation dependent plasticity features of Cu and Al single crystals under axial compression. 1: Lattice rotation effects and true hardening stages

    SciTech Connect

    Mecif, A.; Bacroix, B.; Franciosi, P.

    1997-01-01

    Compressive axial loadings are performed on differently oriented aluminium and copper single crystals between room temperature and 0.9 times the melting temperature. In this first part of the work, attention is paid to the influence on the hardening evolution of the type of active strain mechanisms and the associated lattice rotations. The lattice rotation amplitudes for unstable orientations decrease when the temperature increases and almost vanish above 0.7 T{sub m}. Octahedral straight slip traces evolve into weavy and distant ones, and occurrence of non-octahedral slip is observed. The stress-strain curves are resolved on the dominant octahedral slip system. The comparison for different orientations of this reference hardening modulus allows to separate lattice rotation effects and true hardening stages. This representation allows to estimate to what extent hardening characteristics can be considered as orientation independent. Part II, devoted to quantitative analyses on these hardening parameters, will follow.

  7. MD simulation of steady shock-wave fronts with phase transition in single-crystal iron

    NASA Astrophysics Data System (ADS)

    Zhakhovsky, V. V.; Migdal, K. P.; Inogamov, N. A.; Anisimov, S. I.

    2017-01-01

    Overdriven shock waves propagating in main crystallographic directions of single-crystal bcc iron were studied with moving-window molecular dynamics (MD) technique. To simulate correctly the shock-induced bcc-to-hcp phase transition in iron a new EAM potential fitted to the cold pressure curves and pressure transition at 13 GPa was developed with the stress matching method. We demonstrate that structure of shock fronts depends on orientation of crystal. A peculiar structure of steady shock-wave front in [100] direction is observed. While the ultra-fast α → ɛ transition initiated in uniaxially compressed crystal along [100] in elastic zone transforms bcc completely to hcp phase, transformation in other directions is performed only partially with production of metastable composition of nanometer-sized bcc-hcp-fcc grains.

  8. Mechanical Properties and Microstructure of the CoCrFeMnNi High Entropy Alloy Under High Strain Rate Compression

    NASA Astrophysics Data System (ADS)

    Wang, Bingfeng; Fu, Ao; Huang, Xiaoxia; Liu, Bin; Liu, Yong; Li, Zezhou; Zan, Xiang

    2016-07-01

    The equiatomic CoCrFeMnNi high entropy alloy, which crystallizes in the face-centered cubic (FCC) crystal structure, was prepared by the spark plasma sintering technique. Dynamic compressive tests of the CoCrFeMnNi high entropy alloy were deformed at varying strain rates ranging from 1 × 103 to 3 × 103 s-1 using a split-Hopkinson pressure bar (SHPB) system. The dynamic yield strength of the CoCrFeMnNi high entropy alloy increases with increasing strain rate. The Zerilli-Armstrong (Z-A) plastic model was applied to model the dynamic flow behavior of the CoCrFeMnNi high entropy alloy, and the constitutive relationship was obtained. Serration behavior during plastic deformation was observed in the stress-strain curves. The mechanism for serration behavior of the alloy deformed at high strain rate is proposed.

  9. Ground state searches in fcc intermetallics

    SciTech Connect

    Wolverton, C.; de Fontaine, D.; Ceder, G.; Dreysse, H.

    1991-12-01

    A cluster expansion is used to predict the fcc ground states, i.e., the stable phases at zero Kelvin as a function of composition, for alloy systems. The intermetallic structures are not assumed, but derived regorously by minimizing the configurational energy subject to linear constraints. This ground state search includes pair and multiplet interactions which spatially extend to fourth nearest neighbor. A large number of these concentration-independent interactions are computed by the method of direct configurational averaging using a linearized-muffin-tin orbital Hamiltonian cast into tight binding form (TB-LMTO). The interactions, derived without the use of any adjustable or experimentally obtained parameters, are compared to those calculated via the generalized perturbation method extention of the coherent potential approximation within the context of a KKR Hamiltonian (KKR-CPA-GPM). Agreement with the KKR-CPA-GPM results is quite excellent, as is the comparison of the ground state results with the fcc-based portions of the experimentally-determined phase diagrams under consideration.

  10. Ground state searches in fcc intermetallics

    SciTech Connect

    Wolverton, C.; de Fontaine, D. ); Ceder, G. ); Dreysse, H. . Lab. de Physique du Solide)

    1991-12-01

    A cluster expansion is used to predict the fcc ground states, i.e., the stable phases at zero Kelvin as a function of composition, for alloy systems. The intermetallic structures are not assumed, but derived regorously by minimizing the configurational energy subject to linear constraints. This ground state search includes pair and multiplet interactions which spatially extend to fourth nearest neighbor. A large number of these concentration-independent interactions are computed by the method of direct configurational averaging using a linearized-muffin-tin orbital Hamiltonian cast into tight binding form (TB-LMTO). The interactions, derived without the use of any adjustable or experimentally obtained parameters, are compared to those calculated via the generalized perturbation method extention of the coherent potential approximation within the context of a KKR Hamiltonian (KKR-CPA-GPM). Agreement with the KKR-CPA-GPM results is quite excellent, as is the comparison of the ground state results with the fcc-based portions of the experimentally-determined phase diagrams under consideration.

  11. Thermodynamic stability and structural properties of cluster crystals formed by amphiphilic dendrimers

    NASA Astrophysics Data System (ADS)

    Lenz, Dominic A.; Mladek, Bianca M.; Likos, Christos N.; Blaak, Ronald

    2016-05-01

    We pursue the goal of finding real-world examples of macromolecular aggregates that form cluster crystals, which have been predicted on the basis of coarse-grained, ultrasoft pair potentials belonging to a particular mathematical class [B. M. Mladek et al., Phys. Rev. Lett. 46, 045701 (2006)]. For this purpose, we examine in detail the phase behavior and structural properties of model amphiphilic dendrimers of the second generation by means of monomer-resolved computer simulations. On augmenting the density of these systems, a fluid comprised of clusters that contain several overlapping and penetrating macromolecules is spontaneously formed. Upon further compression of the system, a transition to multi-occupancy crystals takes place, the thermodynamic stability of which is demonstrated by means of free-energy calculations, and where the FCC is preferred over the BCC-phase. Contrary to predictions for coarse-grained theoretical models in which the particles interact exclusively by effective pair potentials, the internal degrees of freedom of these molecules cause the lattice constant to be density-dependent. Furthermore, the mechanical stability of monodisperse BCC and FCC cluster crystals is restricted to a bounded region in the plane of cluster occupation number versus density. The structural properties of the dendrimers in the dense crystals, including their overall sizes and the distribution of monomers are also thoroughly analyzed.

  12. 76 FR 10827 - Modernizing the FCC Form 477 Data Program

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-28

    ... submitting comments. Federal Communications Commission's Web Site: http://fjallfoss.fcc.gov/ecfs2/ . Follow... available on the Commission's Web site at http://www.fcc.gov . Pursuant to Sec. Sec. 1.415 and 1.419 of the... . Filers should follow the instructions provided on the Web site for submitting comments. For ECFS...

  13. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Where to contact the FCC. 95.117 Section 95.117 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES General Mobile Radio Service (GMRS) § 95.117 Where to contact the FCC. Additional GMRS...

  14. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Where to contact the FCC. 95.117 Section 95.117 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES General Mobile Radio Service (GMRS) § 95.117 Where to contact the FCC. Additional GMRS...

  15. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Where to contact the FCC. 95.117 Section 95.117 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES General Mobile Radio Service (GMRS) § 95.117 Where to contact the FCC. Additional GMRS...

  16. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Where to contact the FCC. 95.117 Section 95.117 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES General Mobile Radio Service (GMRS) § 95.117 Where to contact the FCC. Additional GMRS...

  17. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Where to contact the FCC. 95.117 Section 95.117 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES General Mobile Radio Service (GMRS) § 95.117 Where to contact the FCC. Additional GMRS...

  18. 47 CFR 76.1714 - FCC rules and regulations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false FCC rules and regulations. 76.1714 Section 76.1714 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES MULTICHANNEL VIDEO AND CABLE TELEVISION SERVICE Documents to be Maintained for Inspection § 76.1714 FCC...

  19. 47 CFR 73.4000 - Listing of FCC policies.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Listing of FCC policies. 73.4000 Section 73... BROADCAST SERVICES Rules Applicable to All Broadcast Stations § 73.4000 Listing of FCC policies. The following sections list, solely for the purpose of reference and convenience, certain Policies of the...

  20. Characterization of x-ray imaging crystal spectrometer for high-resolution spatially-resolved x-ray Thomson scattering measurements in shock-compressed experiments

    NASA Astrophysics Data System (ADS)

    Lu, J.; Hill, K. W.; Bitter, M.; Pablant, N. A.; Delgado-Aparicio, L. F.; Efthimion, P. C.; Lee, H. J.; Zastrau, U.

    2017-01-01

    We have proposed, designed and built a dual-channel x-ray imaging crystal spectrometer (XICS) for spectrally- and spatially-resolved x-ray Thomson scattering (XRTS) measurements in the Matter in Extreme Conditions (MEC) end station at the Linac Coherent Light Source (LCLS). This spectrometer employs two spherically-bent germanium (Ge) 220 crystals, which are combined to form a large aperture dispersive element with a spectral bandwidth of 300 eV that enables both the elastic and inelastic x-ray scattering peaks to be simultaneously measured. The apparatus and its characterization are described. A resolving power of 1900 was demonstrated and a spatial resolution of 12 μm was achieved in calibration tests. For XRTS measurements, a narrow-bandwidth (ΔE/E<0.003) LCLS x-ray free electron laser (XFEL) beam at 5.07 keV was used to probe a dense carbon plasma produced in shock-compressed samples of different forms of carbon. Preliminary results of the scattering experiments from Pyrolytic Graphite samples that illustrate the utility of the instrument are presented.

  1. Crystal structures and compressibility of novel iron borides Fe2B7 and FexB50 synthesized at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Bykova, E.; Gou, H.; Bykov, M.; Hanfland, M.; Dubrovinsky, L.; Dubrovinskaia, N.

    2015-10-01

    We present here a detailed description of the crystal structures of novel iron borides, Fe2B7 and FexB50 with various iron content (x=1.01(1), 1.04(1), 1.32(1)), synthesized at high pressures and high temperatures. As revealed by high-pressure single-crystal X-ray diffraction, the structure of Fe2B7 possesses short incompressible B-B bonds, which make it as stiff as diamond in one crystallographic direction. The volume compressibility of Fe2B7 (the bulk modulus K0= 259(1.8) GPa, K0‧= 4 (fixed)) is even lower than that of FeB4 and comparable with that of MnB4, known for high bulk moduli among 3d metal borides. FexB50 adopts the structure of the tetragonal δ-B, in which Fe atoms occupy an interstitial position. FexB50 does not show considerable anisotropy in the elastic behavior.

  2. Saddle-point equilibrium lines between fcc and bcc phases in Al and Ca from first principles

    NASA Astrophysics Data System (ADS)

    Qiu, S. L.; Marcus, P. M.

    2013-10-01

    Phase equilibrium lines (denoted ph-eq lines) of face-centered-cubic (fcc) and body-centered-cubic (bcc) phases, as well as saddle-point equilibrium lines (denoted sp-eq lines) in Al and Ca are studied by first-principles total-energy calculations. For a non-vibrating crystal of Al we determine the transition pressure p t = 2.62 Mbar from fcc to bcc phase. The sp-eq line lies between the two ph-eq lines, merges with the bcc-eq line at V = 61 au3/atom ( p = 1.64 Mbar) and with the fcc-eq line at V = 42.4 au3/atom ( p = 5.50 Mbar), gives the Gibbs free energy barrier ΔG = 0.64 mRy/atom at p t . The bcc phase is unstable below 1.64 Mbar, while the fcc phase is unstable above 5.50 Mbar. In a non-vibrating crystal of Ca two sp-eq lines (denoted sp1-eq line and sp2-eq line, respectively) are found corresponding to two phase transitions: one is from fcc to bcc at p t1 = 89.6 kbar, the other is from bcc to fcc at p t2 = 787 kbar. The sp1-eq line merges with the bcc-eq line at V = 231 au3/atom ( p = 50 kbar) and with the fcc-eq line at V = 183 au3/atom ( p = 174 kbar), gives a barrier of Δ G 1 = 0.62 mRy/atom at p t1. The sp2-eq line merges with the bcc-eq line at V = 90 au3/atom ( p = 981 kbar) and with the fcc-eq line at V = 110 au3/atom ( p = 624 kbar), gives a barrier of Δ G 2 = 1.1 mRy/atom at p t2. The bcc phase is stable in the range from 50 kbar to 981 kbar but unstable outside this range, while the fcc phase is unstable in the range from 174 to 624 kbar but stable outside this range. This work confirms all the features of the sp-eq line described in our recent work [S.L. Qiu, P.M. Marcus, J. Phys.: Condens. Matter 24, 225501 (2012)] and finds two additional features: (1) there are two sp-eq lines corresponding to the two phase transitions between fcc and bcc phases in Ca; (2) fcc phase of Ca is unstable between the two merge points on the fcc-eq line but stable beyond them, while bcc phase of Ca is stable between the two merge points on the bcc-eq line but

  3. Detection of the Impact of Ice Crystal Accretion in an Aircraft Engine Compression System During Dynamic Operation

    NASA Technical Reports Server (NTRS)

    May, Ryan D.; Simon, Donald L.; Guo, Ten-Huei

    2014-01-01

    The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation community. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. Here a detection algorithm is developed which has the capability to detect the impact of ice accretion in the Low Pressure Compressor of an aircraft engine during steady flight as well as during changes in altitude. Unfortunately, the algorithm as implemented was not able to distinguish throttle changes from ice accretion and thus more work remains to be done.

  4. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  5. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  6. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  7. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  8. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  9. Microcalorimetry of oxygen adsorption on fcc Co{110}.

    PubMed

    Liao, Kristine; Fiorin, Vittorio; Jenkins, Stephen J; King, David A

    2012-05-28

    The coverage dependent heats of adsorption and sticking probabilities for oxygen on fcc Co{110} have been measured at 300 K using single crystal adsorption calorimetry (SCAC). Initial adsorption is consistent with dissociative chemisorption at low coverage followed by oxide formation above 0.6 ML coverage. The initial heat of adsorption of 633 kJ mol(-1) is similar to heat values calorimetrically measured on other ferromagnetic metal surfaces, such as nickel and iron. As the coverage increases, the heat of adsorption and sticking probability drop very rapidly up to the onset of oxidation. As already observed for other oxygen-metal surface systems, strong lateral adatom repulsions are responsible for the transition from the chemisorption regime to oxide film formation at higher coverage. The heat of oxide formation at the onset is 475 kJ mol(-1), which is consistent with the formation of CoO crystallites. The oxide film formation is discussed in terms of nucleation and island growth, and the Mott-Cabrera mechanisms, the latter being evidenced by the relatively constant heat of adsorption and sticking probability in contrast to the nickel and iron oxidation cases.

  10. Microstructure and mechanical properties of bulk highly faulted fcc/hcp nanostructured cobalt microstructures

    SciTech Connect

    Barry, Aliou Hamady; Dirras, Guy; Schoenstein, Frederic; Tétard, Florent; Jouini, Noureddine

    2014-05-01

    Nanostructured cobalt powders with an average particle size of 50 nm were synthesized using a polyol method and subsequently consolidated by spark plasma sintering (SPS). SPS experiments performed at 650 °C with sintering times ranging from 5 to 45 min under a pressure of 100 MPa, yielded to dense bulk nanostructured cobalt (relative density greater than 97%). X-ray diffraction patterns of the as-prepared powders showed only a face centered cubic (fcc) crystalline phase, whereas the consolidated samples exhibited a mixture of both fcc and hexagonal close packed (hcp) phases. Transmission electron microscopy observations revealed a lamellar substructure with a high density of nanotwins and stacking faults in every grain of the sintered samples. Room temperature compression tests, carried out at a strain rate of 10{sup −3} s{sup −1}, yielded to highest strain to fracture values of up to 5% for sample of holding time of 15 min, which exhibited a yield strength of 1440 MPa, an ultimate strength as high as 1740 MPa and a Young's modulus of 205 GPa. The modulus of elasticity obtained from the nanoindentation tests, ranges from 181 to 218 GPa. The lowest modulus value of 181 GPa was obtained for the sample with the highest sintering time (45 min), which could be related to mass density loss as a consequence of trapped gases releasing. - Highlights: • Co nanopowder (50 nm) was prepared by reduction in polyol medium. • SPS was used to process bulk nanostructured Co specimens. • Microstructures were made of intricate fcc/hcp, along with nanotwins and SFs. • High strengths and moderate compressive ductility were obtained. • Deformation mechanisms related to complex interplay of different length scales.

  11. Crack Tip Dislocation Nucleation in FCC Solids

    NASA Astrophysics Data System (ADS)

    Knap, J.; Sieradzki, K.

    1999-02-01

    We present results of molecular dynamic simulations aimed at examining crack tip dislocation emission in fcc solids. The results are analyzed in terms of recent continuum formulations of this problem. In mode II, Au, Pd, and Pt displayed a new unanticipated mechanism of crack tip dislocation emission involving the creation of a pair of Shockley partials on a slip plane one plane below the crack plane. In mode I, for all the materials examined, Rice's continuum formulation [J. Mech. Phys. Solids 40, 239 (1992)] underestimated the stress intensity for dislocation emission by almost a factor of 2. Surface stress corrections to the emission criterion brought the agreement between continuum predictions and simulations to within 20%.

  12. Structure and magnetism in fcc magnetic transition metals on (001) diamond (abstract)

    NASA Astrophysics Data System (ADS)

    Wolf, J. A.; Krebs, J. J.; Idzerda, Y. U.; Prinz, G. A.; Kemner, K. M.

    1996-04-01

    We have prepared single crystal face centered cubic (fcc) magnetic transition metal films (Co,Ni,Fe) on (001) diamonds, the thickness of the films varying between a few tenths of a nanometer to over 100 nm. The crystalline quality and fourfold symmetry of these layers was monitored in situ during the film growth with RHEED and a chemical analysis was performed using Auger spectroscopy. In addition, the structure of the samples was investigated ex situ using X-ray diffraction and EXAFS, demonstrating the single crystal, fcc (001) structure throughout each entire film. The magnetic characterization was performed with Ferromagnetic Resonance (FMR) and Superconducting Quantum Interference Device (SQUID) hysteresis loops. The saturation magnetization of the Co films is only slightly lower than the literature values. The coercive fields are very small (˜25 Oe) and the magnetization reversal very sharp. The FMR yielded a fourfold anisotropy comparable to literature values. The observation of the first standing spinwaves underlines the good quality. The Ni films are tetragonally distorted due to the 1.2% mismatch. The FMR data indicate a significant perpendicular anisotropy slightly smaller than 4πM, the fourfold in-plane anisotropy being comparable to the bulk value. The saturation magnetization is reduced by 30% compared to bulk values, probably due to nickel-carbide which was observed in the XRD data from some samples. Neither the in-plane <110> nor the in-plane <100> axis show an easy axis behavior and both require fields in excess of 6000 Oe to saturate, the coercive fields being about 200 Oe. The RHEED patterns of the Fe films show single crystal growth with a lattice constant comparable to diamond, indicating an fcc structure. A similar structural and magnetic characterization of these films will also be presented.

  13. Comparison of void strengthening in fcc and bcc metals : large-scale atomic-level modelling.

    SciTech Connect

    Osetskiy, Yury N; Bacon, David J

    2005-01-01

    Strengthening due to voids can be a significant radiation effect in metals. Treatment of this by elasticity theory of dislocations is difficult when atomic structure of the obstacle and dislocation is influential. In this paper, we report results of large-scale atomic-level modelling of edge dislocation-void interaction in fcc (copper) and bcc (iron) metals. Voids of up to 5 nm diameter were studied over the temperature range from 0 to 600 K. We demonstrate that atomistic modelling is able to reveal important effects, which are beyond the continuum approach. Some arise from features of the dislocation core and crystal structure, others involve dislocation climb and temperature effects.

  14. Data Compression.

    ERIC Educational Resources Information Center

    Bookstein, Abraham; Storer, James A.

    1992-01-01

    Introduces this issue, which contains papers from the 1991 Data Compression Conference, and defines data compression. The two primary functions of data compression are described, i.e., storage and communications; types of data using compression technology are discussed; compression methods are explained; and current areas of research are…

  15. Stability of the fcc structure in block copolymer systems.

    PubMed

    Nonomura, Makiko

    2008-11-19

    The stability of the face-centered cubic (fcc) structure in microphase separated copolymers is investigated by a coarse-grained approach. Direct simulations of the equation for the microphase separation in three dimensions indicate that there is a narrow area above a certain degree of segregation in the phase diagram, where the fcc structure is the most stable structure. By employing the mode expansion, we have confirmed that the fcc structure can form as a metastable structure even in the weak segregation regime.

  16. Graphene oxide-templated synthesis of ultrathin or tadpole-shaped au nanowires with alternating hcp and fcc domains.

    PubMed

    Huang, Xiao; Li, Shaozhou; Wu, Shixin; Huang, Yizhong; Boey, Freddy; Gan, Chee Lip; Zhang, Hua

    2012-02-14

    Ultrathin Au nanowires (AuNWs) and tadpole-shaped nanowires are synthesized on graphene oxide (GO) sheet templates. For the first time, 1.6 nm-diameter AuNWs are shown to contain hexagonal close-packed (hcp) crystal domains, and the tadpole-shaped nanowires exhibit alternating sets of hcp and face-centered cubic (fcc) structures, associated with variation in wire thickness.

  17. High-pressure behavior of fcc phase FeHx

    NASA Astrophysics Data System (ADS)

    Thompson, E. C.; Chidester, B.; Fischer, R. A.; Prakapenka, V.; Bi, W.; Alp, E. E.; Campbell, A. J.

    2015-12-01

    Earth's core is composed of iron with the inclusion of light elements to compensate for the difference between seismically obtained densities and the density of pure Fe at relevant pressure and temperature conditions. As the most abundant and lightest element in the solar system, hydrogen is a plausible contributor to this core density deficit. Nearly stoichiometric iron hydride (FeHx) has been shown to result from the reaction of Fe and hydrous silicates, and is stable up to at least 80 GPa [1]. Iron hydride formation at Earth's surface is unlikely because the equilibrium hydrogen solubility in iron at atmospheric conditions is prohibitively low, yet as hydrogen solubility increases with pressure, so does the likelihood of FeHx formation within the Earth's interior [2]. Recent experimental and ab initio attempts disagree on the equation of state parameters needed to describe the compressional behavior of FeHx [3-5]. The work presented here combines synchrotron x-ray diffraction of laser-heated diamond anvil cell compressed samples with high-pressure, ambient temperature nuclear resonant inelastic scattering (NRIXS) and synchrotron Mössbauer spectroscopy (SMS) to better constrain the behavior of the fcc phase of FeHx at elevated pressures and temperatures. By pairing P-V-T data for iron hydride with the sound velocity information available through high-pressure NRIXS studies, we can better understand the degree to which hydrogen may contribute to the density deficit of Earth's iron core. [1] Antonov et al. (1998) J. Alloys Compd. 264, 214-222 [2] Fukai and Akimoto (1983) Proc. Japan Acad. 59, 158-162 [3] Pépin et al. (2014) Phys. Rev. Lett. 265504, 1-5 [4] Hirao (2004) Geophys. Res. Lett. 31, L06616 [5] Badding et al. (1991) Science. 253, 421-424

  18. Elemental vacancy diffusion database from high-throughput first-principles calculations for fcc and hcp structures

    NASA Astrophysics Data System (ADS)

    Angsten, Thomas; Mayeshiba, Tam; Wu, Henry; Morgan, Dane

    2014-01-01

    This work demonstrates how databases of diffusion-related properties can be developed from high-throughput ab initio calculations. The formation and migration energies for vacancies of all adequately stable pure elements in both the face-centered cubic (fcc) and hexagonal close packing (hcp) crystal structures were determined using ab initio calculations. For hcp migration, both the basal plane and z-direction nearest-neighbor vacancy hops were considered. Energy barriers were successfully calculated for 49 elements in the fcc structure and 44 elements in the hcp structure. These data were plotted against various elemental properties in order to discover significant correlations. The calculated data show smooth and continuous trends when plotted against Mendeleev numbers. The vacancy formation energies were plotted against cohesive energies to produce linear trends with regressed slopes of 0.317 and 0.323 for the fcc and hcp structures respectively. This result shows the expected increase in vacancy formation energy with stronger bonding. The slope of approximately 0.3, being well below that predicted by a simple fixed bond strength model, is consistent with a reduction in the vacancy formation energy due to many-body effects and relaxation. Vacancy migration barriers are found to increase nearly linearly with increasing stiffness, consistent with the local expansion required to migrate an atom. A simple semi-empirical expression is created to predict the vacancy migration energy from the lattice constant and bulk modulus for fcc systems, yielding estimates with errors of approximately 30%.

  19. A crystal plasticity model incorporating the effects of precipitates in superalloys: Application to tensile, compressive, and cyclic deformation of Inconel 718

    DOE PAGES

    Ghorbanpour, Saeede; Zecevic, Milovan; Kumar, Anil; ...

    2017-09-14

    An elasto-plastic polycrystal plasticity model is developed and applied to an Inconel 718 (IN718) superalloy that was produced by additive manufacturing (AM). The model takes into account the contributions of solid solution, precipitates shearing, and grain size and shape effects into the initial slip resistance. Non-Schmid effects and backstress are also included in the crystal plasticity model for activating slip. The hardening law for the critical resolved shear stress is based on the evolution of dislocation density. In using the same set of material and physical parameters, the model is compared against a suite of compression, tension, and large-strain cyclicmore » mechanical test data applied in different AM build directions. We demonstrate that the model is capable of predicting the particularities of both monotonic and cyclic deformation to large strains of the alloy, including decreasing hardening rate during monotonic loading, the non-linear unloading upon the load reversal, the Bauschinger effect, the hardening rate change during loading in the reverse direction as well as plastic anisotropy and the concomitant microstructure evolution. It is anticipated that the general model developed here can be applied to other multiphase alloys containing precipitates.« less

  20. 47 CFR 1.8001 - FCC Registration Number (FRN).

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... unique identifying number that is assigned to entities doing business with the Commission. (b) The FRN is obtained through the Commission Registration System (CORES) over the Internet at the CORES link at www.fcc...

  1. Reformulated gasoline will change FCC operations and catalysts

    SciTech Connect

    Stokes, G.M.; Wear, C.C.; Suarez, W.; Young, G.W. )

    1990-07-02

    Operation of fluid catalytic cracking units (FCCUs) will be significantly affected by new regulations that will in all probability require gasoline to be produced with lower aromatics and olefins contents, lower vapor pressure, and a minimum oxygen content. This paper reports on a study conducted to better define the basic relationship between operating variables, including catalyst and naphtha quality, in the context of reformulated gasoline. The study helped to define specific operating strategies, potential problem areas, and opportunities for improved FCC unit and catalyst technologies. FCC feedstock quality can have a significant influence on the composition of FCC naphtha. However, even extremely paraffinic or aromatic feeds can yield substantial levels of both olefins and aromatics in FCC naphtha, particularly when compared to the levels proposed in a reformulated gasoline pool.

  2. Compression behavior of orthorhombic paracetamol.

    PubMed

    Joiris, E; Di Martino, P; Berneron, C; Guyot-Hermann, A M; Guyot, J C

    1998-07-01

    Orthorhombic crystals of paracetamol exhibit good technological properties during compression. The purpose of this study was to investigate the compression behavior of this substance and to compare it to that of monoclinic paracetamol. From the crystal structure, it could be hypothesized that sliding planes are present in the orthorhombic form, and could be responsible for an increase in crystal plasticity. Compression of pure orthorhombic or monoclinic paracetamol tablets was carried out on a fully instrumented single punch machine. Data was used to establish Heckel's profiles. Images of compressed crystals were obtained by scanning electron microscopy. Tabletability of the orthorhombic crystals was far better than that of the monoclinic ones, and capping was not observed even at high compression pressure. Compared to the monoclinic form, orthorhombic paracetamol exhibited greater fragmentation at low pressure, increased plastic deformation at higher pressure, and lower elastic recovery during decompression. Plastic behavior was confirmed by SEM - micrographs showing that crystals folded under pressure. A compactibility study showed that the nature of interparticle bonds was similar for both polymorphs, the number of bonds being greater for orthorhombic paracetamol. Unlike the monoclinic form, orthorhombic paracetamol is suitable for the direct compression process. The crystalline structure accounts for its better compression behavior, because of the presence of sliding planes.

  3. Selection of the Space Station Freedom (SSF) Flat Collector Circuit (FCC) insulation material

    NASA Technical Reports Server (NTRS)

    Emerson, Dawn

    1994-01-01

    The topics are presented in viewgraph form and include the following: function of the Space Station Freedom (SSF) Flat Collector Circuit (FCC); requirements of the FCC which affect the selection of the insulation material; data to support the selection of the FCC insulation material; development history; modified design; coverlay testing; effects on modified design on FCC; arc tracking tests performed on FCC; and arc tracking test results.

  4. Low-cycle fatigue-cracking mechanisms in fcc crystalline materials

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Qu, S.; Duan, Q. Q.; Wu, S. D.; Li, S. X.; Wang, Z. G.; Zhang, Z. F.

    2011-01-01

    The low-cycle fatigue (LCF) cracking behavior in various face-centered-cubic (fcc) crystalline materials, including Cu single crystals, bicrystals and polycrystals, Cu-Al and Cu-Zn alloys, ultrafine-grained (UFG) Al-Cu and Cu-Zn alloys, was systematically investigated and reviewed. In Cu single crystals, fatigue cracking always nucleates along slip bands and deformation bands. The large-angle grain boundary (GB) becomes the preferential site in bicrystals and polycrystals. In addition, fatigue cracking can also nucleate along slip bands and twin boundaries (TBs) in polycrystalline materials. However, shear bands and coarse deformation bands are observed to the preferential sites for fatigue cracking in UFG materials with a large number of GBs. Based on numerous observations on fatigue-cracking behavior, the fatigue-cracking mechanisms along slip bands, GBs, TBs, shear bands and deformation bands were systematically compared and classified into two types, i.e. shear crack and impingement crack. Finally, these fatigue-cracking behaviors are discussed in depth for a better understanding of their physical nature and the transition from intergranular to transgranular cracking in various fcc crystalline materials. These comprehensive results for fatigue damage mechanisms should significantly aid in obtaining the optimum design to further strengthen and toughen metallic materials in practice.

  5. A self-consistent plasticity theory for modeling the thermo-mechanical properties of irradiated FCC metallic polycrystals

    NASA Astrophysics Data System (ADS)

    Xiao, Xiazi; Song, Dingkun; Xue, Jianming; Chu, Haijian; Duan, Huiling

    2015-05-01

    A self-consistent theoretical framework is developed to model the thermo-mechanical behaviors of irradiated face-centered cubic (FCC) polycrystalline metals at low to intermediate homologous temperatures. In this model, both irradiation and temperature effects are considered at the grain level with the assist of a tensorial plasticity crystal model, and the elastic-visocoplastic self-consistent method is applied for the scale transition from individual grains to macroscopic polycrystals. The proposed theory is applied to analyze the mechanical behaviors of irradiated FCC copper. It is found that: (1) the numerical results match well with experimental data, which includes the comparison of results for single crystals under the load in different directions, and for polycrystals with the influences of irradiation and temperature. Therefore, the feasibility and accuracy of the present model are well demonstrated. (2) The main irradiation effects including irradiation hardening, post-yield softening, strain-hardening coefficient (SHC) dropping and the non-zero stress offset are all captured by the proposed model. (3) The increase of temperature results in the decrease of yield strength and SHC. The former is attributed to the weakened dislocation-defect interaction, while the latter is due to the temperature-strengthened dynamic recovery of dislocations through the thermally activated mechanism. The present model may provide a theoretical guide to predict the thermo-mechanical behaviors of irradiated FCC metals for the selection of structural materials in nuclear equipment.

  6. Isentropic Compression of Argon

    SciTech Connect

    H. Oona; J.C. Solem; L.R. Veeser, C.A. Ekdahl; P.J. Rodriquez; S.M. Younger; W. Lewis; W.D. Turley

    1997-08-01

    We are studying the transition of argon from an insulator to a conductor by compressing the frozen gas isentropically to pressures at which neighboring atomic orbitals overlap sufficiently to allow some electron motion between atoms. Argon and the other rare gases have closed electron shells and therefore remain montomic, even when they solidify. Their simple structure makes it likely that any measured change in conductivity is due to changes in the atomic structure, not in molecular configuration. As the crystal is compressed the band gap closes, allowing increased conductivity. We have begun research to determine the conductivity at high pressures, and it is our intention to determine the compression at which the crystal becomes a metal.

  7. Temperature dependence of the crystal structure and g-values of trans-diaquabis(methoxyacetato)copper(II): evidence for a thermal equilibrium between complexes with tetragonally elongated and compressed geometries.

    PubMed

    Simmons, Charles J; Stratemeier, Horst; Hitchman, Michael A; Reinen, Dirk; Masters, Vanessa M; Riley, Mark J

    2011-06-06

    The crystal structures of trans-diaquabis(methoxyacetato)copper(II) and the isostructural nickel(II) complex have been determined over a wide temperature range. In conjunction with the reported behavior of the g-values, the structural data suggest that the copper(II) compound exhibits a thermal equilibrium between three structural forms, two having orthorhombically distorted, tetragonally elongated geometries but with the long and intermediate bonds to different atoms, and the third with a tetragonally compressed geometry. This is apparently the first reported example of a copper(II) complex undergoing an equilibrium between tetragonally elongated and compressed forms. The optical spectrum of single crystals of the copper(II) compound is used to obtain metal-ligand bonding parameters which yield the g-values of the compressed form of the complex and hence the proportions of the complex in each structural form at every temperature. When combined with estimates of the Jahn-Teller distortions of the different forms, the latter produce excellent agreement with the observed temperature dependence of the bond lengths. The behavior of an infrared combination band is consistent with such a thermal equilibrium, as is the temperature dependence of the thermal ellipsoid parameters and the XAFS. The potential surfaces of the different forms of the copper(II) complex have been calculated by a model based upon Jahn-Teller coupling. It is suggested that cooperative effects may cause the development of the population of tetragonally compressed complexes, and the crystal packing is consistent with this hypothesis, though the present model may oversimplify the diversity of structural forms present at high temperature. © 2011 American Chemical Society

  8. High resolution transmission electron microscopy characterization of fcc --> 9R transformation in nanocrystalline palladium films due to hydriding

    NASA Astrophysics Data System (ADS)

    Amin-Ahmadi, Behnam; Idrissi, Hosni; Delmelle, Renaud; Pardoen, Thomas; Proost, Joris; Schryvers, Dominique

    2013-02-01

    Sputtered nanocrystalline palladium thin films with nanoscale growth twins have been subjected to hydriding cycles. The evolution of the twin boundaries has been investigated using high resolution transmission electron microscopy. Surprisingly, the ∑3{112} incoherent twin boundaries dissociate after hydriding into two phase boundaries bounding a 9R phase. This phase which corresponds to single stacking faults located every three {111} planes in the fcc Pd structure was not expected because of the high stacking fault energy of Pd. This observation is connected to the influence of the Hydrogen on the stacking fault energy of palladium and the high compressive stresses building up during hydriding.

  9. Color octet electron search potential of FCC based e–p colliders

    NASA Astrophysics Data System (ADS)

    Acar, Y. C.; Kaya, U.; Oner, B. B.; Sultansoy, S.

    2017-04-01

    Resonant production of color octet electrons, e 8, at the FCC based e–p colliders is analyzed. It is shown that e-FCC will cover much a wider region of e 8 masses compared to the LHC. Moreover, with the highest electron beam energy, the e 8 search potential of the e-FCC exceeds that of the FCC p–p collider. If e 8 is discovered earlier by the FCC p–p collider, e-FCC will give an opportunity to handle very important additional information. For example, the compositeness scale can be probed up to the hundreds of TeV region.

  10. DNABIT Compress - Genome compression algorithm.

    PubMed

    Rajarajeswari, Pothuraju; Apparao, Allam

    2011-01-22

    Data compression is concerned with how information is organized in data. Efficient storage means removal of redundancy from the data being stored in the DNA molecule. Data compression algorithms remove redundancy and are used to understand biologically important molecules. We present a compression algorithm, "DNABIT Compress" for DNA sequences based on a novel algorithm of assigning binary bits for smaller segments of DNA bases to compress both repetitive and non repetitive DNA sequence. Our proposed algorithm achieves the best compression ratio for DNA sequences for larger genome. Significantly better compression results show that "DNABIT Compress" algorithm is the best among the remaining compression algorithms. While achieving the best compression ratios for DNA sequences (Genomes),our new DNABIT Compress algorithm significantly improves the running time of all previous DNA compression programs. Assigning binary bits (Unique BIT CODE) for (Exact Repeats, Reverse Repeats) fragments of DNA sequence is also a unique concept introduced in this algorithm for the first time in DNA compression. This proposed new algorithm could achieve the best compression ratio as much as 1.58 bits/bases where the existing best methods could not achieve a ratio less than 1.72 bits/bases.

  11. Impact of magnetic fluctuations on lattice excitations in fcc nickel.

    PubMed

    Körmann, Fritz; Ma, Pui-Wai; Dudarev, Sergei L; Neugebauer, Jörg

    2016-02-24

    The spin-space averaging formalism is applied to compute atomic forces and phonon spectra for magnetically excited states of fcc nickel. Transverse and longitudinal magnetic fluctuations are taken into account by a combination of magnetic special quasi random structures and constrained spin-density-functional theory. It turns out that for fcc Ni interatomic force constants and phonon spectra are almost unaffected by both kinds of spin fluctuations. Given the computational expense to simulate coupled magnetic and atomic fluctuations, this insight facilitates computational modeling of magnetic alloys such as Ni-based superalloys.

  12. Investigation of primary static recrystallization in a NiTiFe shape memory alloy subjected to cold canning compression using the coupling crystal plasticity finite element method with cellular automaton

    NASA Astrophysics Data System (ADS)

    Zhang, Yanqiu; Jiang, Shuyong; Hu, Li; Zhao, Yanan; Sun, Dong

    2017-10-01

    The behavior of primary static recrystallization (SRX) in a NiTiFe shape memory alloy (SMA) subjected to cold canning compression was investigated using the coupling crystal plasticity finite element method (CPFEM) with the cellular automaton (CA) method, where the distribution of the dislocation density and the deformed grain topology quantified by CPFEM were used as the input for the subsequent SRX simulation performed using the CA method. The simulation results were confirmed by the experimental ones in terms of microstructures, average grain size and recrystallization fraction, which indicates that the proposed coupling method is well able to describe the SRX behavior of the NiTiFe SMA. The results show that the dislocation density exhibits an inhomogeneous distribution in the deformed sample and the recrystallization nuclei mainly concentrate on zones where the dislocation density is relatively higher. An increase in the compressive deformation degree leads to an increase in nucleation rate and a decrease in grain boundary spaces in the compression direction, which reduces the growth spaces for the SRX nuclei and impedes their further growth. In addition, both the mechanisms of local grain refinement in the incomplete SRX and the influence of compressive deformation degree on the grain size of SRX were vividly illustrated by the corresponding physical models.

  13. Influence of compressive stress and electric field on the stability of [ 011 ] poled and [ 0 1 xAF 1 ] oriented 31-mode PZN-0.055PT single crystals

    NASA Astrophysics Data System (ADS)

    Heitmann, Adam A.; Stace, Joseph A.; Lim, Leong-Chew; Amin, Ahmed H.

    2016-06-01

    The effect of compressive stress, in the presence of an electrical field along the [ 011 ] direction, on the phase transition stability of [ 0 1 ¯ 1 ] oriented and [ 011 ] poled relaxor (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) single crystals in the transverse length extensional 31-mode geometry is investigated. The thermal, electrical, and mechanical stability range for operation lacking elastic instabilities is identified and compared with conventional 33 and 32-mode geometries with the near morphotropic composition of x ˜ 0.055. It is found that the 31-mode geometry retains the stable, room temperature ferroelectric rhombohedral (R) symmetry up to and exceeding compressive stresses, along the [ 0 1 ¯ 1 ] direction, of 90 MPa under zero field conditions. Under zero stress conditions, a phase transformation from the stable rhombohedral symmetry to the low symmetry ferroelectric orthorhombic (O) phase occurs in the presence of an electric field of 0.85 MV/m. Stabilization of the R-O phase transformation against electric field drive occurs as a function of compressive prestress, similar to the 33-mode geometry. And, under sufficiently large compressive stress, an R-T (or R-MA-T) transformation is identified and discussed.

  14. Bulk Nanostructured FCC Steels With Enhanced Radiation Tolerance

    SciTech Connect

    Zhang, Xinghang; Hartwig, K. Ted; Allen, Todd; Yang, Yong

    2012-10-27

    The objective of this project is to increase radiation tolerance in austenitic steels through optimization of grain size and grain boundary (GB) characteristics. The focus will be on nanocrystalline austenitic Fe-Cr-Ni alloys with an fcc crystal structure. The long-term goal is to design and develop bulk nanostructured austenitic steels with enhanced void swelling resistance and substantial ductility, and to enhance their creep resistance at elevated temperatures via GB engineering. The combination of grain refinement and grain boundary engineering approaches allows us to tailor the material strength, ductility, and resistance to swelling by 1) changing the sink strength for point defects, 2) by increasing the nucleation barriers for bubble formation at GBs, and 3) by changing the precipitate distributions at boundaries. Compared to ferritic/martensitic steels, austenitic stainless steels (SS) possess good creep and fatigue resistance at elevated temperatures, and better toughness at low temperature. However, a major disadvantage of austenitic SS is that they are vulnerable to significant void swelling in nuclear reactors, especially at the temperatures and doses anticipated in the Advanced Burner Reactor. The lack of resistance to void swelling in austenitic alloys led to the switch to ferritic/martensitic steels as the preferred material for the fast reactor cladding application. Recently a type of austenitic stainless steel, HT-UPS, was developed at ORNL, and is expected to show enhanced void swelling resistance through the trapping of point defects at nanometersized carbides. Reducing the grain size and increasing the fraction of low energy grain boundaries should reduce the available radiation-produced point defects (due to the increased sink area of the grain boundaries), should make bubble nucleation at the boundaries less likely (by reducing the fraction of high-energy boundaries), and improve the strength and ductility under radiation by producing a higher

  15. Phase stability of ternary fcc and bcc Fe-Cr-Ni alloys

    NASA Astrophysics Data System (ADS)

    Wróbel, Jan S.; Nguyen-Manh, Duc; Lavrentiev, Mikhail Yu.; Muzyk, Marek; Dudarev, Sergei L.

    2015-01-01

    The phase stability of fcc and bcc magnetic binary Fe-Cr, Fe-Ni, and Cr-Ni alloys, and ternary Fe-Cr-Ni alloys is investigated using a combination of density functional theory (DFT), cluster expansion (CE), and magnetic cluster expansion (MCE) approaches. Energies, magnetic moments, and volumes of more than 500 alloy structures have been evaluated using DFT, and the predicted most stable configurations are compared with experimental observations. Deviations from the Vegard law in fcc Fe-Cr-Ni alloys, resulting from the nonlinear variation of atomic magnetic moments as functions of alloy composition, are observed. The accuracy of the CE model is assessed against the DFT data, where for ternary Fe-Cr-Ni alloys the cross-validation error is found to be less than 12 meV/atom. A set of cluster interaction parameters is defined for each alloy, where it is used for predicting new ordered alloy structures. The fcc Fe2CrNi phase with Cu2NiZn -like crystal structure is predicted to be the global ground state of ternary Fe-Cr-Ni alloys, with the lowest chemical ordering temperature of 650 K. DFT-based Monte Carlo (MC) simulations are applied to the investigation of order-disorder transitions in Fe-Cr-Ni alloys. The enthalpies of formation of ternary alloys predicted by MC simulations at 1600 K, combined with magnetic correction derived from MCE, are in excellent agreement with experimental values measured at 1565 K. The relative stability of fcc and bcc phases is assessed by comparing the free energies of alloy formation. The evaluation of the free energies involved the application of a dedicated algorithm for computing the configurational entropies of the alloys. Chemical order is analyzed, as a function of temperature and composition, in terms of the Warren-Cowley short-range order (SRO) parameters and effective chemical pairwise interactions. In addition to compositions close to binary intermetallic phases CrNi2, FeNi, FeNi3, and FeNi8, pronounced chemical order is found

  16. Fcc-bcc transition for Yukawa interactions determined by applied strain deformation.

    PubMed

    Hoy, Robert S; Robbins, Mark O

    2004-05-01

    Calculations of the work required to transform between bcc and fcc phases yield a high-precision bcc-fcc transition line for monodisperse point Yukawa (screened-Coulomb) systems. Our results agree qualitatively but not quantitatively with recently published simulations and phenomenological criteria for the bcc-fcc transition. In particular, the bcc-fcc-fluid triple point lies at a higher inverse screening length than previously reported.

  17. Folding tool for preparing FCC molded-plug terminations

    NASA Technical Reports Server (NTRS)

    Campbell, E. C.; Chambers, C. M.

    1971-01-01

    Assemblies consist of window piece, conductor spacer, insulator, outer seal, and molded portion that integrates all components. Preparation of FCC for molded plug termination requires that terminated ends of conductors in each cable be accurately folded simultaneously into spacer end and groove.

  18. Fixture for multiple-FCC chemical stripping and plating

    NASA Technical Reports Server (NTRS)

    Angele, W.; Norton, W. E.

    1971-01-01

    For chemical stripping, lead tape applied near ends to be stripped protects insulation. Taped ends are submerged half way in stripping solution. For electroplating, both ends of FCC are stripped - top ends for electric contact, others for submersion in electroplating solution.

  19. Congress, the FCC and Children's Television Regulation: A Shift in the Balance of Power.

    ERIC Educational Resources Information Center

    Markin, Karen

    The Federal Communications Commission (FCC) of the late 1980s appeared to pursue its own agenda of broadcast deregulation, notwithstanding congressional pressures. The apparent power shift is evident in a case study of the interactions between Congress and the FCC on the subject of children's television. In the early 1970s, the FCC tended to…

  20. 76 FR 12308 - Modernizing the FCC Form 477 Data Program; Correction

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-07

    ... COMMISSION 47 CFR Parts 1, 20, and 43 Modernizing the FCC Form 477 Data Program; Correction AGENCY: Federal... FCC Form 477. Inadvertently the Comment Filing Procedures section of the February 28, 2011 publication... February 28, 2011 (76 FR 10827) relating to the modernization of the FCC Form 477. The document (FR...

  1. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  2. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 4 2013-10-01 2013-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  3. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 4 2011-10-01 2011-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  4. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 4 2012-10-01 2012-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  5. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 4 2014-10-01 2014-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  6. Compression embedding

    DOEpatents

    Sandford, II, Maxwell T.; Handel, Theodore G.; Bradley, Jonathan N.

    1998-01-01

    A method and apparatus for embedding auxiliary information into the digital representation of host data created by a lossy compression technique and a method and apparatus for constructing auxiliary data from the correspondence between values in a digital key-pair table with integer index values existing in a representation of host data created by a lossy compression technique. The methods apply to data compressed with algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as ordered sequences of blocks containing integer indices having redundancy and uncertainty of value by one unit, allowing indices which are adjacent in value to be manipulated to encode auxiliary data. Also included is a method to improve the efficiency of lossy compression algorithms by embedding white noise into the integer indices. Lossy compression methods use loss-less compression to reduce to the final size the intermediate representation as indices. The efficiency of the loss-less compression, known also as entropy coding compression, is increased by manipulating the indices at the intermediate stage. Manipulation of the intermediate representation improves lossy compression performance by 1 to 10%.

  7. Compression embedding

    DOEpatents

    Sandford, M.T. II; Handel, T.G.; Bradley, J.N.

    1998-07-07

    A method and apparatus for embedding auxiliary information into the digital representation of host data created by a lossy compression technique and a method and apparatus for constructing auxiliary data from the correspondence between values in a digital key-pair table with integer index values existing in a representation of host data created by a lossy compression technique are disclosed. The methods apply to data compressed with algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as ordered sequences of blocks containing integer indices having redundancy and uncertainty of value by one unit, allowing indices which are adjacent in value to be manipulated to encode auxiliary data. Also included is a method to improve the efficiency of lossy compression algorithms by embedding white noise into the integer indices. Lossy compression methods use loss-less compression to reduce to the final size the intermediate representation as indices. The efficiency of the loss-less compression, known also as entropy coding compression, is increased by manipulating the indices at the intermediate stage. Manipulation of the intermediate representation improves lossy compression performance by 1 to 10%. 21 figs.

  8. Microstructural Characterization of Dislocation Networks During Harper-Dorn Creep of fcc, bcc, and hcp Metals and Alloys

    SciTech Connect

    Przystupa, Marek A.

    2007-12-13

    temperatures, (2) time invariant and (3) identical to the distributions obtained previously for Harper-Dorn creep. This has never been shown before and confirms our theoretical expectations that evolution of the dislocation networks during annealing and H-D creep is governed by the same growth law. Obtained results were also used to predict H-D steady creep rates from annealing kinetics data using equations of the dislocation network theory. For the three considered stresses the theory predicts systematically smaller creep rates by the average factor of 4.5. Considering that the creep rates have been predicted from the annealing data alone and without any adjustable parameters, this results shout be considered as outstanding. In case of hcp zinc the samples were pre-deformed in compression at constant stress of 4 MPa at temperature of 573 K and subsequently annealed at the same temperature. During annealing samples readily recrystallized, but it was possible to obtain information on the link length distributions from several unrecrystallized grains. The results showed that the scaled link length distributions were time invariant and similar to those of the aluminum. The annealing studies on bcc tin were also curtailed by the concurrent recrystallization. It was only possible to obtain link length distribution for samples deformed in compression at constant load of 2 MPa at 423 K after unloading. The link length distribution was also in this case similar to that of the aluminum and zinc. These results suggest that the scaled link length distribution is universal and the same for the three considered crystal structures. This supports theoretical findings of these studies that appropriately scaled dislocation link length distribution should both universal and time invariant. We have also investigated the possibility of using alternative methods of estimating local dislocation densities from etch pits which could give more precise estimates of the dislocation link-lengths. The two

  9. Indium-defect interactions in FCC and BCC metals studied using the modified embedded atom method

    NASA Astrophysics Data System (ADS)

    Zacate, M. O.

    2016-12-01

    With the aim of developing a transferable potential set capable of predicting defect formation, defect association, and diffusion properties in a wide range of intermetallic compounds, the present study was undertaken to test parameterization strategies for determining empirical pair-wise interaction parameters in the modified embedded atom method (MEAM) developed by Baskes and coworkers. This report focuses on indium-solute and indium-vacancy interactions in FCC and BCC metals, for which a large set of experimental data obtained from perturbed angular correlation measurements is available for comparison. Simulation results were found to be in good agreement with experimental values after model parameters had been adjusted to reproduce as best as possible the following two sets of quantities: (1) lattice parameters, formation enthalpies, and bulk moduli of hypothetical equiatomic compounds with the NaCl crystal structure determined using density functional theory and (2) dilute solution enthalpies in metals as predicted by Miedema's semi-empirical model.

  10. Compression embedding

    DOEpatents

    Sandford, M.T. II; Handel, T.G.; Bradley, J.N.

    1998-03-10

    A method of embedding auxiliary information into the digital representation of host data created by a lossy compression technique is disclosed. The method applies to data compressed with lossy algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as integer indices having redundancy and uncertainty in value by one unit. Indices which are adjacent in value are manipulated to encode auxiliary data. By a substantially reverse process, the embedded auxiliary data can be retrieved easily by an authorized user. Lossy compression methods use loss-less compressions known also as entropy coding, to reduce to the final size the intermediate representation as indices. The efficiency of the compression entropy coding, known also as entropy coding is increased by manipulating the indices at the intermediate stage in the manner taught by the method. 11 figs.

  11. Compression embedding

    DOEpatents

    Sandford, II, Maxwell T.; Handel, Theodore G.; Bradley, Jonathan N.

    1998-01-01

    A method of embedding auxiliary information into the digital representation of host data created by a lossy compression technique. The method applies to data compressed with lossy algorithms based on series expansion, quantization to a finite number of symbols, and entropy coding. Lossy compression methods represent the original data as integer indices having redundancy and uncertainty in value by one unit. Indices which are adjacent in value are manipulated to encode auxiliary data. By a substantially reverse process, the embedded auxiliary data can be retrieved easily by an authorized user. Lossy compression methods use loss-less compressions known also as entropy coding, to reduce to the final size the intermediate representation as indices. The efficiency of the compression entropy coding, known also as entropy coding is increased by manipulating the indices at the intermediate stage in the manner taught by the method.

  12. Precipitate Rafting in a Polycrystalline Superalloy During Compression Creep

    NASA Astrophysics Data System (ADS)

    Altincekic, Arun; Balikci, Ercan

    2014-12-01

    Rafting is an industrially and scientifically important phenomenon for precipitate-strengthened alloys utilized at high temperatures. Although this phenomenon is observed in polycrystalline alloys as well, the literature lacks scientific work on rafting in polycrystals. Scientific work is usually conducted on single-crystal superalloys. Being one of the many polycrystalline nickel-base superalloys, IN738LC has a good high-temperature strength and hot corrosion resistance. Coherency strains between the FCC gamma matrix ( γ)- and L12 gamma prime ( γ')-precipitate phase particles mainly provide the high-temperature strength in IN738LC. Conical IN738LC specimens have been aged under compression for various times [24, 192, 480, and 960 hours at 1223 K (950 °C) and 12, 24, 192, and 480 hours at 1323 K (1050 °C)] in order to observe the morphological evolution of the γ' precipitate microstructure. Dislocations play a determining role in morphological changes. Fingerprints of matrix dislocations in the form of indentations on γ' precipitates have been identified by scanning electron microscope. Precipitate morphology has become more complex through dissolution/merging as temperature, aging time, and stress have increased. The precipitate morphology has evolved toward rafting at appropriate strain, temperature, and time. Localized slip bands have marked the beginning of rafting. The rafts have been observed at around a 45 deg angle away from the load direction. For higher stress positions, there is a trend toward N-type rafting which is expected of a positive misfit alloy under compression. Rafts eventually have collapsed due to severe creep deformation.

  13. Compressive Holography

    NASA Astrophysics Data System (ADS)

    Lim, Se Hoon

    Compressive holography estimates images from incomplete data by using sparsity priors. Compressive holography combines digital holography and compressive sensing. Digital holography consists of computational image estimation from data captured by an electronic focal plane array. Compressive sensing enables accurate data reconstruction by prior knowledge on desired signal. Computational and optical co-design optimally supports compressive holography in the joint computational and optical domain. This dissertation explores two examples of compressive holography: estimation of 3D tomographic images from 2D data and estimation of images from under sampled apertures. Compressive holography achieves single shot holographic tomography using decompressive inference. In general, 3D image reconstruction suffers from underdetermined measurements with a 2D detector. Specifically, single shot holographic tomography shows the uniqueness problem in the axial direction because the inversion is ill-posed. Compressive sensing alleviates the ill-posed problem by enforcing some sparsity constraints. Holographic tomography is applied for video-rate microscopic imaging and diffuse object imaging. In diffuse object imaging, sparsity priors are not valid in coherent image basis due to speckle. So incoherent image estimation is designed to hold the sparsity in incoherent image basis by support of multiple speckle realizations. High pixel count holography achieves high resolution and wide field-of-view imaging. Coherent aperture synthesis can be one method to increase the aperture size of a detector. Scanning-based synthetic aperture confronts a multivariable global optimization problem due to time-space measurement errors. A hierarchical estimation strategy divides the global problem into multiple local problems with support of computational and optical co-design. Compressive sparse aperture holography can be another method. Compressive sparse sampling collects most of significant field

  14. Nonlinear compression of an ultrashort-pulse thulium-based fiber laser to sub-70  fs in Kagome photonic crystal fiber.

    PubMed

    Gebhardt, M; Gaida, C; Hädrich, S; Stutzki, F; Jauregui, C; Limpert, J; Tünnermann, A

    2015-06-15

    Nonlinear pulse compression of ultrashort pulses is an established method for reducing the pulse duration and increasing the pulse peak power beyond the intrinsic limits of a given laser architecture. In this proof-of-principle experiment, we demonstrate nonlinear compression of the pulses emitted by a high-repetition-rate thulium-based fiber CPA system. The initial pulse duration of about 400 fs has been shortened to <70  fs with 19.7 μJ of pulse energy, which corresponds to about 200 MW of pulse peak power.

  15. Compressive spectroscopy by spectral modulation

    NASA Astrophysics Data System (ADS)

    Oiknine, Yaniv; August, Isaac; Stern, Adrian

    2017-05-01

    We review two compressive spectroscopy techniques based on modulation in the spectral domain that we have recently proposed. Both techniques achieve a compression ratio of approximately 10:1, however each with a different sensing mechanism. The first technique uses a liquid crystal cell as a tunable filter to modulate the spectral signal, and the second technique uses a Fabry-Perot etalon as a resonator. We overview the specific properties of each of the techniques.

  16. Polymorphic crystals selected in the nucleation stage

    NASA Astrophysics Data System (ADS)

    Zhang, Hui-Jun; Peng, Shu-Ming; Zhou, Xiao-Song; Ju, Xin

    2014-08-01

    Molecular dynamics simulations are used to explore the atomic mechanism of formation of polymorphic crystals. Cooling the Lennard-Jones systems, we observe that the system almost always evolves into a polymorphic crystal with either fivefold-symmetric stacking faults or single-direction stacking faults. The detailed analysis reveals that such an evolution depends on the configuration of fcc/hcp concomitance in the nucleation stage. A defect-induced model is then introduced to illustrate these two evolution routes. Through calculating the formation energies of the defective critical nuclei, we find that the polymorphic crystals seem to be determined by their critical nuclei, in which the relatively lower formation energy ensures the preponderance of the fivefold-symmetric cluster. Before the nucleation, we observe that thermal fluctuations prefer hcp-like particles over fcc-like ones while in the nucleation and growth stage this preference reverses. Notably, an extended step rule of Ostwald is seemingly suitable to characterise the growth process because of the temporary hcp layers appearing among fcc layers in the growth stage. Although the crystalline cluster with single-direction stacking faults has higher growth rate and structural order than its competitor, the component (fcc and hcp) proportion of the final crystals is almost always constant regardless of the polymorphic type. Our finding renews the understanding of the polymorphism of crystals, and possibly draws more attention of people intending to control the polymorphic structures through nucleation.

  17. Post-riser quench improves FCC yields, profitability

    SciTech Connect

    Quinn, G.P.; Silverman, M.A.

    1996-01-15

    Performance tests of a post-riser quench system have shown increases in gasoline yield; reductions in fuel gas, butadienes, and pentadienes; and improved oxidation stability of FCC gasoline. Following commercial trials in six of Amoco Petroleum Products` refineries for some 10 years, the system is now being installed by other refiners. Elimination of post-riser thermal cracking is essential to achieving the most desirable product slate. Most of Amoco`s FCC units (FCCUs) have rough-cut cyclone systems in which there is significant vapor residence time in the disengaging vessel. To overcome this problem Amoco chose to reduce the temperature in the dilute phase. This technology involves quenching the dilute phase, thereby reducing the thermal cracking rates. The approach is very effective and virtually eliminates post-riser cracking. This paper reviews this design.

  18. The crystal structure of iron at the inner core

    NASA Astrophysics Data System (ADS)

    Tateno, S.; Hirose, K.; Ohishi, Y.; Tatsumi, Y.

    2010-12-01

    The Earth’s solid inner core is mainly composed of iron. Thus the crystal structure of iron is of prime importance for understanding the nature of solid inner core. Despite many efforts to investigate phase relations of iron have by dynamic and static compression, and theoretical calculation, consensus on the stable phase at the inner core condition has never been achieved. While hcp-Fe can persist to core pressures at 300 K, a phase transition at elevated temperature is a possibility. Both theory and experiments proposed different forms of iron at simultaneously high P-T conditions, which include bcc, face-centered-cubic (fcc), and hcp structures. The structure of iron has never been examined experimentally at the inner core P-T conditions (>330 GPa and ≥5000 K), because such extreme conditions could only be achieved by shock-wave compression experiments. Based on static compression experiments in a laser-heated diamond-anvil cell (DAC), we determined the structure of iron up to 377 GPa and 5700 K. Iron powder and thermal insulation layers of SiO2 glass were loaded into a hole of a pre-indented rhenium gasket placed in the For experiments beyond 300 GPa, the double-beveled diamond anvils with 40-μm culets were used, and accordingly the sample size was limited to about 20 μm. Heating was performed from both sides of the sample by employing two single mode, Yb fiber lasers with output power up to 100 W each with flat-top beam shaping optics to minimize temperature gradient across the sample. Angle-dispersive x-ray diffraction measurements were conducted at BL10XU of SPring-8. Six separate sets of experiments were conducted in a wide P-T range from 135 GPa and 2690 K to 377 GPa and 5700 K. We observed crystal growth and hence the stability of hcp-Fe at these P-T conditions with no evidence for a phase transition to bcc nor fcc iron phases. The c/a axial ratio of hcp-Fe at high temperature was also studied, which has significant effect on the nature of the

  19. Spectroscopic insight for tablet compression.

    PubMed

    Lakio, S; Ylinärä, H; Antikainen, O; Räikkönen, H; Yliruusi, J

    2015-02-01

    Tablet compression process has been studied over the years from various perspectives. However what exactly happens to material during compression is still unknown. In this study a novel compression die which enables real-time spectroscopic measurements during the compression of material is represented. Both near infrared and Raman spectroscope probes can be attached to the die. In this study the usage of the die is demonstrated by using Raman spectroscopy. Eicosane, d-glucose anhydrate, α-lactose monohydrate and xylitol were used in the study because their compression behavior and bonding properties during compression were assumed to be different. The intensity of the Raman signal changed during compression with all of the materials. However, the intensity changes were different within the materials. The biggest differences were within the xylitol spectra. It was noticed that some peaks disappeared with higher compression pressures indicating that the pressure affected variously on different bonds in xylitol structure. These reversible changes were supposed to relate the changes in conformation and crystal structure. As a conclusion, the die was found to be a significant addition for studying compression process in real-time. It can help to reveal Process induced transformations (PITs) occurring during powder compaction.

  20. Attrition Resistant Fischer-Tropsch Catalysts Based on FCC Supports

    SciTech Connect

    Adeyiga, Adeyinka

    2010-02-05

    Commercial spent fluid catalytic cracking (FCC) catalysts provided by Engelhard and Albemarle were used as supports for Fe-based catalysts with the goal of improving the attrition resistance of typical F-T catalysts. Catalysts with the Ruhrchemie composition (100 Fe/5 Cu/4.2 K/25 spent FCC on mass basis) were prepared by wet impregnation. XRD and XANES analysis showed the presence of Fe{sub 2}O{sub 3} in calcined catalysts. FeC{sub x} and Fe{sub 3}O{sub 4} were present in the activated catalysts. The metal composition of the catalysts was analyzed by ICP-MS. F-T activity of the catalysts activated in situ in CO at the same conditions as used prior to the attrition tests was measured using a fixed bed reactor at T = 573 K, P = 1.38 MPa and H{sub 2}:CO ratio of 0.67. Cu and K promoted Fe supported over Engelhard provided spent FCC catalyst shows relatively good attrition resistance (8.2 wt% fines lost), high CO conversion (81%) and C{sub 5}+ hydrocarbons selectivity (18.3%).

  1. Magnetism in bcc and fcc Fe with carbon and manganese.

    PubMed

    Medvedeva, N I; Van Aken, D; Medvedeva, J E

    2010-08-11

    Density functional theory calculations were performed to study the structure and magnetic properties of bcc (α) and fcc (γ) Fe with 3 at.% carbon and manganese impurities. We find that all bcc-based Fe, Fe-C and Fe-Mn-C phases exhibit a ferromagnetic (FM) ground state, while the antiferromagnetic double-layer (AFMD) state is lowest in energy within the collinear spin approach in fcc Fe, Fe-C and Fe-Mn-C phases. However, the carbon and manganese impurities affect the local magnetic interactions significantly. The states with opposite manganese magnetic moments are quasi-degenerate in bcc Fe-Mn alloy, whereas octa-site carbon stabilizes ferromagnetic coupling of the nearest manganese atom with the Fe host. We demonstrate that the antiferromagnetic (AFM) fcc Fe-C and Fe-Mn-C alloys are intrinsically inhomogeneous magnetic systems. Carbon frustrates the local magnetic order by reorientation of magnetic moments of the nearest Mn and Fe atoms, and favors their ferromagnetic coupling. The competition between ferromagnetic and antiferromagnetic Fe-Fe and Fe-Mn interactions and the local magnetovolume instability near carbon may give rise to the spin-glass-like regions observed in austenitic Fe-Mn-C alloys.

  2. Formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters.

    PubMed

    Li, Guojian; Wang, Qiang; Sui, Xudong; Wang, Kai; Wu, Chun; He, Jicheng

    2015-09-07

    The formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters has been studied by molecular dynamics simulation using an embedded atom method. Structural evolution of the clusters, coalesced under varying temperature, Ni content and substrate conditions, was explored by interatomic energy, snapshots, pair distribution functions and bond order parameters. The results show that the formation of bcc and fcc is strongly related to Ni content, substrate and coalescence temperature. Free clusters coalesced at 1200 K form bcc at lower Ni contents with fcc forming at higher Ni concentrations and no observable coexistence of bcc and fcc. Differences in coalescence at 1000 K result from the coexistence of bcc and fcc within the Ni range of 50-70%. Free clusters supported on disordered Ni substrates were shown to transform from spherical morphology to islands of supported clusters with preferred epitaxial orientation. The Ni content required to form bcc and fcc coexistence on supported clusters at 1000 K decreased to 30-50% Ni. Free clusters possessing bcc and fcc generally stacked along the bcc (110) and fcc (111) facets, whereas supported clusters stacked along the (111) bcc and (100) fcc planes. Structural transformation was induced by clusters containing greater numbers of atoms. Spread over the substrate enhanced interatomic energy, order substrates affect the epitaxial growth direction and increase the melting points of the supported clusters. This study can be used to predict the nature of fcc and bcc formation in Fe-Ni films.

  3. Phase transition from fcc to bcc structure of the Cu-clusters during nanocrystallization of Fe85.2Si1B9P4Cu0.8 soft magnetic alloy

    NASA Astrophysics Data System (ADS)

    Nishijima, Masahiko; Matsuura, Makoto; Takenaka, Kana; Takeuchi, Akira; Ofuchi, Hironori; Makino, Akihiro

    2014-05-01

    A role of Cu on the nanocrystallization of an Fe85.2Si1B9P4Cu0.8 alloy was investigated by X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM). The Cu K-edge XAFS results show that local structure around Cu is disordered for the as-quenched sample whereas it changes to fcc-like structure at 613 K. The fcc Cu-clusters are, however, thermodynamically unstable and begin to transform into bcc structure at 638 K. An explicit bcc structure is observed for the sample annealed at 693 K for 600 s in which TEM observation shows that precipitated bcc-Fe crystallites with ˜12 nm are homogeneously distributed. The bcc structure of the Cu-clusters transforms into the fcc-type again at 973 K, which can be explained by the TEM observations; Cu segregates at grain boundaries between bcc-Fe crystallites and Fe3(B,P) compounds. Combining the XAFS results with the TEM observations, the structure transition of the Cu-clusters from fcc to bcc is highly correlated with the preliminary precipitation of the bcc-Fe which takes place prior to the onset of the first crystallization temperature, Tx1 = 707 K. Thermodynamic analysis suggests that an interfacial energy density γ between an fcc-Cu cluster and bcc-Fe matrix dominates at a certain case over the structural energy between fcc and bcc Cu, ΔGfcc - bcc, which causes phase transition of the Cu clusters from fcc to bcc structure.

  4. Interplay between crystallization and glass transition in binary Lennard-Jones mixtures

    NASA Astrophysics Data System (ADS)

    Banerjee, Atreyee; Chakrabarty, Suman; Bhattacharyya, Sarika Maitra

    2013-09-01

    In this work we explore the interplay between crystallization and glass transition in different binary mixtures by changing their inter-species interaction length and also the composition. We find that only those systems which form bcc crystal in the equimolar mixture and whose global structure for larger xA (xA = 0.6, where xA is the mole fraction of the bigger particles) is a mixed fcc + bcc phase, do not crystallize at this higher composition. However, the systems whose equimolar structure is a variant of fcc (NaCl type crystal) and whose global structure at larger xA is a mixed NaCl + fcc phase, crystallize easily to this mixed structure. We find that the stability against crystallization of this "bcc zone" is due to the frustration between the locally preferred structure (LPS) and the mixed bcc + fcc crystal. Our study suggests that when the global structure is a mixed crystal where a single species contributes to both the crystal forms and where the two crystal forms have large difference in some order parameter related to that species then this induces frustration between the LPS and the global structure. This frustration makes the systems good glass former. When xA is further increased (0.70 ⩽ xA < 0.90) the systems show a tendency towards mixed fcc crystal formation. However, the "bcc zone" even for this higher composition is found to be sitting at the bottom of a V shaped phase diagram formed by two different variants of the fcc crystal structure, leading to its stability against crystallization.

  5. Interplay between crystallization and glass transition in binary Lennard-Jones mixtures.

    PubMed

    Banerjee, Atreyee; Chakrabarty, Suman; Bhattacharyya, Sarika Maitra

    2013-09-14

    In this work we explore the interplay between crystallization and glass transition in different binary mixtures by changing their inter-species interaction length and also the composition. We find that only those systems which form bcc crystal in the equimolar mixture and whose global structure for larger x(A) (x(A) = 0.6, where x(A) is the mole fraction of the bigger particles) is a mixed fcc + bcc phase, do not crystallize at this higher composition. However, the systems whose equimolar structure is a variant of fcc (NaCl type crystal) and whose global structure at larger x(A) is a mixed NaCl + fcc phase, crystallize easily to this mixed structure. We find that the stability against crystallization of this "bcc zone" is due to the frustration between the locally preferred structure (LPS) and the mixed bcc + fcc crystal. Our study suggests that when the global structure is a mixed crystal where a single species contributes to both the crystal forms and where the two crystal forms have large difference in some order parameter related to that species then this induces frustration between the LPS and the global structure. This frustration makes the systems good glass former. When x(A) is further increased (0.70 ≤ x(A) < 0.90) the systems show a tendency towards mixed fcc crystal formation. However, the "bcc zone" even for this higher composition is found to be sitting at the bottom of a V shaped phase diagram formed by two different variants of the fcc crystal structure, leading to its stability against crystallization.

  6. Atomic force imaging of the surface of a FCC after thermal and hydrothermal treatments

    SciTech Connect

    Occelli, M.L.; Gould, S.A.G.; Baldiraghi, F.; Leoncini, S.

    1996-10-01

    An atomic force microscope (AFM) operating in a contact mode was used to observe surface variations in FCC resulting from aging. AFM images of a commercial FCC sample before and after steam-aging have been compared with those of the same FCC after use in a major refinery. Large scale (5 {mu}m x 5 {mu}m) images reveal that the FCC surface is formed by platelets and platelet aggregates and that the catalyst microporosity result mainly from elongated and narrow spacings between these plates. Steam-aging does not seem to greatly change the FCC surface architecture. However, in the corresponding equilibrium catalyst (containing several metals impurities) the FCC surface roughness decreases. Atomic scale images were obtained for all the samples examined. The hexagonal symmetry observed in these images is consistent with the structure of the silicate layer in Kaolin, a major component of these types of catalysts.

  7. A general kinetic-flow coupling model for FCC riser flow simulation.

    SciTech Connect

    Chang, S. L.

    1998-05-18

    A computational fluid dynamic (CFD) code has been developed for fluid catalytic cracking (FCC) riser flow simulation. Depending on the application of interest, a specific kinetic model is needed for the FCC flow simulation. This paper describes a method to determine a kinetic model based on limited pilot-scale test data. The kinetic model can then be used with the CFD code as a tool to investigate optimum operating condition ranges for a specific FCC unit.

  8. 47 CFR 11.21 - State and Local Area plans and FCC Mapbook.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... must be followed by EAS Participants' personnel, emergency officials, and National Weather Service (NWS... are consistent with national plans, FCC regulations, and EAS operation. (a) The State EAS...

  9. 47 CFR 11.21 - State and Local Area plans and FCC Mapbook.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... must be followed by EAS Participants' personnel, emergency officials, and National Weather Service (NWS... are consistent with national plans, FCC regulations, and EAS operation. (a) The State EAS...

  10. Moessbauer spectroscopy evidence of a spinodal mechanism for the thermal decomposition of fcc FeCu

    SciTech Connect

    Crespo, P. |; Barro, M.J.; Hernando, A.; Escorial, A.G.; Menendez, N.; Tornero, J.D.; Barandiaran, J.M.

    1998-07-24

    Moessbauer spectroscopy shows the existence of compositional fluctuations, where different Fe environments coexist, during decomposition upon heat treatment of metastable f.c.c. FeCu solid solution. The presence of isolated Fe atoms in the Cu matrix, f.c.c. Fe{sub rich}Cu, f.c.c. FeCu{sub rich} and b.c.c. Fe has been detected in early decomposition stages. At later decomposition stages, low temperature Moessbauer spectroscopy indicates the presence of a broad distribution of Curie temperatures, coexisting with isolated Fe atoms in the Cu matrix, f.c.c. Fe and b.c.c. Fe.

  11. Shock compression and quasielastic release in tantalum

    SciTech Connect

    Johnson, J.N.; Hixson, R.S.; Tonks, D.L.; Gray, G.T. III

    1993-06-01

    Previous studies of quasielastic release in shock-loaded FCC metals have shown a strong influence of the defect state on the leading edge, or first observable arrival, of release wave, due to large density of pinned dislocation segments behind the shock front, their relatively large pinning separation, and a very short response time as determined by drag coefficient in shock-compressed state. This effect is entirely equivalent to problems associated with elastic moduli determination using ultrasonic methods. This is particularly true for FCC metals, which have an especially low Peierls stress, or inherent lattice resistance, that has little influence in pinning dislocation segments and inhibiting anelastic deformation. BCC metals, on the other hand, have a large Peierls stress that essentially holds dislocation segments in place at low net applied shear stresses and thus allows fully elastic deformation to occur in the complete absence of anelastic behavior. Shock-compression and release experiments have been performed on tantalum (BCC), with the observation that the leading release disturbance is indeed elastic. This conclusion is established by examination of experimental VISAR records taken at the tantalum/sapphire (window) interface in a symmetric-impact experiment which subjects the sample to a peak longitudinal stress of approximately 7.3 GPa, in comparison with characteristic code calculations.

  12. Preliminary design of FCC-ee pre-injector complex

    NASA Astrophysics Data System (ADS)

    Ogur, S.; Barnyakov, A.; Furukawa, K.; Iida, N.; Levichev, A.; Miyahara, F.; Nikiforov, D.; Oide, K.; Papaphilippou, Y.; Zimmermann, F.

    2017-07-01

    The design of a 100 km circular e + e - collider with extremely high luminosity is an important component of the global Future Circular Collider (FCC) study hosted by CERN. FCC-ee is being designed to serve as Z, W, H and top factory, covering beam energies from 45.6 to 175 GeV. For the injectors, the Z-operation is the most challenging mode, due to the high total charge and low equilibrium emittance in the collider at this energy. Thus, fulfilling the Z-mode will also meet the demands for all other modes of FCC-ee. This goal can be achieved by using a 6 GeV NC linac with an S-band RF frequency of 2.856 GHz and a repetition rate of 100 Hz. This linac will accelerate two bunches per RF pulse, each with a charge of 6.5 nC. Positrons will be generated by sending 4.46 GeV e - onto a hybrid target so that the e + created can still be accelerated to 1.54 GeV in the remaining part of the same linac. The emittance of the e + beam will then shrink to the nm level in a 1.54 GeV damping ring. After damping, the e + will be reinjected into the linac and accelerated to 6 GeV. The e - and e + will then be accelerated alternately to 45.6 GeV in the booster, before they are injected into the collider.

  13. Colloidal Crystal Growth Monitored By Bragg Diffraction Interference Fringes

    PubMed Central

    Bohn, Justin J.; Tikhonov, Alexander; Asher, Sanford A.

    2010-01-01

    We monitor the crystal growth kinetics of crystallization of a shear melted crystalline colloidal array (CCA). The fcc CCA heterogeneously nucleates at the flow cell wall surface. We examined the evolution of the (111) Bragg diffraction peak, and, for the first time, quantitatively monitored growth by measuring the temporal evolution of the Bragg diffraction interference fringes. Modeling of the evolution of the fringe patterns exposes the time dependence of the increasing crystal thickness. The initial diffusion driven linear growth is followed by ripening-driven growth. Between 80 to 90 μM NaCl concentrations the fcc crystals first linearly grow at rates between 1.9 and 4.2 μm/sec until they contact homogeneously nucleated crystals in the bulk. At lower salt concentrations interference fringes are not visible because the strong electrostatic interactions between particles result in high activation barriers, preventing defect annealing and leading to a lower crystal quality. The fcc crystals melt to a liquid phase at >90 μM NaCl concentrations. Increasing NaCl concentrations slows the fcc CCA growth rate consistent with the expectation of the classical Wilson-Frenkel growth theory. The final thickness of wall nucleated CCA is determined by the competition between growth of heterogeneously and homogenously nucleated CCA and increases with higher NaCl concentrations. PMID:20542277

  14. Software for Mathematical Modeling of Plastic Deformation in FCC Metals

    NASA Astrophysics Data System (ADS)

    Petelin, A. E.; Eliseev, A. S.

    2017-08-01

    The question on the necessity of software implementation in the study of plastic deformation in FCC metals with the use of mathematical modeling methods is investigated. This article describes the implementation features and the possibility of using the software Dislocation Dynamics of Crystallographic Slip (DDCS). The software has an advanced user interface and is designed for users without an extensive experience in IT-technologies. Parameter values of the mathematical model, obtained from field experiments and accumulated in a special database, are used in DDCS to carry out computational experiments. Moreover, the software is capable of accumulating bibliographic information used in research.

  15. Polarization Issues in the $e\\pm$ FCC

    SciTech Connect

    Gianfelice-Wendt, E.

    2015-08-10

    After the Higgs boson discovery at LHC, the international physics community is considering the next energy frontier circular collider (FCC). A pp collider of 100 km with a center of mass energy of about 100 TeV is believed to have the necessary discovery potential. The same tunnel could host first a e+e- collider with beam energy ranging between 45 and 175 GeV. In this paper preliminary considerations on the possibility of self-polarization for the e± beams are presented.

  16. Synchrotron radiation backgrounds for the FCC-hh experiments

    NASA Astrophysics Data System (ADS)

    Collamati, F.; Boscolo, M.; Burkhardt, H.; Kersevan, R.

    2017-07-01

    In this paper we present a detailed analysis of the Synchrotron Radiation emitted by the 50 TeV protons of the FCC-hh in the last bending and quadrupole magnets upstream of the interaction region. We discuss the characteristics of this radiation in terms of power, flux, photon spectrum and fans with and without crossing angle for comparison. We mainly focus our study on the fraction of photons that may hit the detector, with a full tracking in GEANT4 that simulates the interaction within the central beam pipe.

  17. Deformation twinning mechanisms in FCC and HCP metals

    SciTech Connect

    Wang, Jian; Tome, Carlos N; Beyerlein, Irene J; Misra, Amit; Mara, N

    2011-01-31

    We report the recent work on twinning and detwinning in fcc and hcp metals based on the in situ and ex situ TEM observations and molecular dynamics simulations. Three aspects are discussed in this paper. (1) Detwinning in single-phase Cu with respect to growth twins, (2) deformation twinning in Ag-Cu composites, and (3) deformation twinning mechanisms in hcp metals. The main conclusion is that atomic structures of interfaces (twin boundaries, two-phases interface, and grain boundaries) play a crucial role in nucleating and propagating of deformation twins.

  18. Alkali cation specific adsorption onto fcc(111) transition metal electrodes.

    PubMed

    Mills, J N; McCrum, I T; Janik, M J

    2014-07-21

    The presence of alkali cations in electrolyte solutions is known to impact the rate of electrocatalytic reactions, though the mechanism of such impact is not conclusively determined. We use density functional theory (DFT) to examine the specific adsorption of alkali cations to fcc(111) electrode surfaces, as specific adsorption may block catalyst sites or otherwise impact surface catalytic chemistry. Solvation of the cation-metal surface structure was investigated using explicit water models. Computed equilibrium potentials for alkali cation adsorption suggest that alkali and alkaline earth cations will specifically adsorb onto Pt(111) and Pd(111) surfaces in the potential range of hydrogen oxidation and hydrogen evolution catalysis in alkaline solutions.

  19. Collisional viscosity of FCC particles in a CFB

    SciTech Connect

    Gidaspow, D.; Lu Huilin

    1996-09-01

    Particle velocity distributions were measured for a flow of 75-{micro}m FCC (fluidized catalytic cracking) particles in a CFB (circulating fluidized bed) using a new video-digital camera technique. From the spread of particle histograms, a random oscillating particle velocity was determined. This random velocity was used to compute the powder viscosity with the help of dense-phase kinetic theory of granular flow. There was excellent agreement between this kinetic-theory measurement and previous macroscopic viscosity measurements. The dimensionless group kinematic viscosity divided by the oscillating velocity and particle diameter correlated all available data as a function of particle volume fraction.

  20. Video Compression

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Optivision developed two PC-compatible boards and associated software under a Goddard Space Flight Center Small Business Innovation Research grant for NASA applications in areas such as telerobotics, telesciences and spaceborne experimentation. From this technology, the company used its own funds to develop commercial products, the OPTIVideo MPEG Encoder and Decoder, which are used for realtime video compression and decompression. They are used in commercial applications including interactive video databases and video transmission. The encoder converts video source material to a compressed digital form that can be stored or transmitted, and the decoder decompresses bit streams to provide high quality playback.

  1. Preparation and characterization of Co epitaxial thin films on Al2O3(0001) single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Yabuhara, Osamu; Ohtake, Mitsuru; Nukaga, Yuri; Futamoto, Masaaki

    2011-01-01

    Co epitaxial thin films were prepared on Al2O3(0001) single-crystal substrates in a substrate temperature range between 50 and 500 °C by ultra high vacuum molecular beam epitaxy. Effects of substrate temperature on the structure and the magnetic properties of the films were investigated. The films grown at temperatures lower than 150 °C consist of fcc- Co(111) crystal. With increasing the substrate temperature, hcp-Co(0001) crystal coexists with the fcc crystal and the volume ratio of hcp to fcc crystal increases. The films prepared at temperatures higher than 250 °C consist primarily of hcp crystal. The film growth seems to follow island-growth mode. The films consisting primarily of hcp crystal show perpendicular magnetic anisotropy. The domain structure and the magnetization properties are influenced by the magnetocrystalline anisotropy and the shape anisotropy caused by the film surface roughness.

  2. Influence of test temperature on the size effect in molybdenum small-scale compression pillars

    NASA Astrophysics Data System (ADS)

    Schneider, A. S.; Frick, C. P.; Arzt, E.; Clegg, W. J.; Korte, S.

    2013-06-01

    Previous research has shown that body-centred cubic (bcc) metals exhibit a smaller size dependence of strength than what is commonly observed in face-centred cubic (fcc) metals. This work investigates compression testing of focused ion beam-manufactured molybdenum pillars ranging in size from 300 nm to 5 μm, both above and below its critical temperature at 300 and 500 K. At 500 K the size effect is found to be consistent with what is observed in fcc metals, owing to the increased mobility of screw dislocations.

  3. Compression stockings

    MedlinePlus

    ... knee bend. Compression Stockings Can Be Hard to Put on If it's hard for you to put on the stockings, try these tips: Apply lotion ... your legs, but let it dry before you put on the stockings. Use a little baby powder ...

  4. The effect of feedstock additives on FCC catalyst deactivation

    SciTech Connect

    Hughes, R.; Koon, C.L.; McGhee, B.

    1995-12-31

    Fluid catalytic cracking is a major petroleum refining process and because of this the deactivation of FCC catalysts by coke deposition has been the subject of considerable investigation during the past 50 years. Nevertheless, a lack of understanding of the fundamental understanding of processes leading to coke formation still exists. Basic studies using Zeolites have usually involved excessively high levels of coke deposits compared to normal FCC operation. The present study addresses coke formation at realistic levels of 0.5 to 1.0% w/w using a standard MAT reactor in which concentrations of 1% and 10% of various additives were added to the n-hexadecane feedstock. These additives included, quinoline, phenanthrene, benzofuran, thianaphthene and indene. The coke formed was characterised by mass spectrometry and was significantly aliphatic in nature, the amount formed increasing in the order quinoline, phenanthrene, thianaphthene, benzofuran, indene. Quinoline acts primarily as a poison, whereas the other additives tend to promote coke formation in n-hexadecane cracking.

  5. Key elements in optimizing catalyst selections for resid FCC units

    SciTech Connect

    Yanik, S.J.; O`Connor, P.

    1995-09-01

    Achieving the optimum activity and yield structure from a commercial Resid FCC Unit (RFCC) is essential to maximizing profitability in today`s modern refinery. Proper catalyst selection is a key element in this optimization. This paper is written to provide FCC Process Engineers with an understanding of some basic elements of RFCC operation. The necessity of using realistic evaluation methods to assure proper RFCC catalyst selection is explained. The differences between Activity limited and Delta Coke limited RFCC operations are elucidated and the related catalyst performance requirements are discussed. The effect of the catalyst to oil ratio on conversion and on catalyst site utilization and poisoning plays a key role in the transition of an RFCC unit from Catalyst Activity limited regime to a Cat-to-Oil limited regime. For the Activity limited operation the catalyst resistance to poisons with the appropriate feedstock will be the most important selection criteria. For the Delta Coke limited operation, a reduction of the commercial delta coke of the catalyst will be crucial. The types of commercial delta coke are discussed and methods for their evaluation are suggested. In both cases the use of realistic catalyst evaluation methods and feedstock will be essential in order to arrive at the correct catalyst selection. Finally, commercial data comparisons illustrate the improvements in product value that can be achieved when the proper catalyst is chosen.

  6. Ultrasmall-angle X-ray scattering analysis of photonic crystal structure

    SciTech Connect

    Abramova, V. V.; Sinitskii, A. S.; Grigor'eva, N. A.; Grigor'ev, S. V.; Belov, D. V.; Petukhov, A. V.; Mistonov, A. A.; Vasil'eva, A. V.; Tret'yakov, Yu. D.

    2009-07-15

    The results of an ultrasmall-angle X-ray scattering study of iron(III) oxide inverse opal thin films are presented. The photonic crystals examined are shown to have fcc structure with amount of stacking faults varying among the samples. The method used in this study makes it possible to easily distinguish between samples with predominantly twinned fcc structure and nearly perfect fcc stacking. The difference observed between samples fabricated under identical conditions is attributed to random layer stacking in the self-assembled colloidal crystals used as templates for fabricating the inverse opals. The present method provides a versatile tool for analyzing photonic crystal structure in studies of inverse opals made of various materials, colloidal crystals, and three-dimensional photonic crystals of other types.

  7. Diversity of Voice? The FCC's Bright-Line "Anti-Monopoly" Rule.

    ERIC Educational Resources Information Center

    Haddock, David D.; Polsby, Daniel D.

    The Federal Communications Commission (FCC) has long had rules that prohibit anyone from owning more than one television station in any given location. Two of the stated purposes behind the FCC's anti-monopoly rules are to foster diversity of programming for the sake of First Amendment interests, and to promote programming among media outlets in…

  8. 47 CFR 2.1076 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 1 2014-10-01 2014-10-01 false FCC inspection and submission of equipment for... ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Declaration of Conformity § 2.1076 FCC inspection and submission of equipment for testing. (a)...

  9. 76 FR 69738 - Revised 2011 Annual Telecommunications Reporting Worksheet (FCC Form 499-A) and Accompanying...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-09

    ... COMMISSION Revised 2011 Annual Telecommunications Reporting Worksheet (FCC Form 499-A) and Accompanying... Competition Bureau released the revised Telecommunications Reporting Worksheet (FCC Form 499-A) and... Competition Bureau, Telecommunications Access Policy Division, at (202) 418-7400 or via the Internet...

  10. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  11. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  12. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  13. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  14. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  15. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station license...

  16. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station license...

  17. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station license...

  18. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station license...

  19. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station license...

  20. 47 CFR 64.1110 - State notification of election to administer FCC rules.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 3 2010-10-01 2010-10-01 false State notification of election to administer FCC rules. 64.1110 Section 64.1110 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... Telecommunications Service Providers § 64.1110 State notification of election to administer FCC rules. (a)...

  1. On Campus Web-Monitoring Rules, Colleges and the FCC Have a Bad Connection

    ERIC Educational Resources Information Center

    Hartle, Terry W.

    2006-01-01

    A regulation issued by the US Federal Communications Commission (FCC) requires facilities-based Internet services providers who operate their own equipment, including colleges, to make their Internet systems compliant with a statute known as the Communications Assistance for Law Enforcement Act (Calea) by April 2007. However, the FCC does not…

  2. Inequities in Mass Communication Law: The FCC's Application of the Duopoly Rule to Public Broadcasting.

    ERIC Educational Resources Information Center

    Avery, Robert K.

    A three-part petition was filed in December 1974 with the Federal Communications Commission (FCC) which presented the first serious threat to public broadcasters' exemption from the FCC's multiple-ownership rules. The petition requested a revision of the rules that permit multiple ownership of noncommercial educational stations within a single…

  3. The Impact of Public Affairs Programming Regulation: A Study of the FCC's Effectiveness.

    ERIC Educational Resources Information Center

    Chamberlin, Bill F.

    1979-01-01

    Explores the effectiveness of the Federal Communications Commission (FCC) public affairs program regulation through analysis of annual reports for 75 television stations, examining amount of time for public issues programing, amount of local affairs programing, total prime time programing, and whether FCC standards are met. (CWM)

  4. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In ITU...

  5. The FCC, The Coverage Principle of the Fairness Doctrine and the First Amendment.

    ERIC Educational Resources Information Center

    Chamberlin, Bill F.

    This review of the history of the coverage principle developed by the Federal Communications Commission (FCC) concludes that government regulation of mass media program content can be dangerous and that the coverage principle needs to be abolished. The first section of the report discusses the FCC's interpretation of the 1934 Communications Act…

  6. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In...

  7. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In...

  8. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In...

  9. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In...

  10. Outstanding compressive creep strength in Cr/Ir-codoped (Mo0.85Nb0.15)Si2 crystals with the unique cross-lamellar microstructure.

    PubMed

    Hagihara, Koji; Ikenishi, Takaaki; Araki, Haruka; Nakano, Takayoshi

    2017-06-21

    A (Mo0.85Nb0.15)Si2 crystal with an oriented, lamellar, C40/C11b two-phase microstructure is a promising ultrahigh-temperature (UHT) structural material, but its low room-temperature fracture toughness and low high-temperature strength prevent its practical application. As a possibility to overcome these problems, we first found a development of unique "cross-lamellar microstructure", by the cooping of Cr and Ir. The cross-lamellar microstructure consists of a rod-like C11b-phase grains that extend along a direction perpendicular to the lamellar interface in addition to the C40/C11b fine lamellae. In this study, the effectiveness of the cross-lamellar microstructure for improving the high-temperature creep deformation property, being the most essential for UHT materials, was examined by using the oriented crystals. The creep rate significantly reduced along a loading orientation parallel to the lamellar interface. Furthermore, the degradation in creep strength for other loading orientation that is not parallel to the lamellar interface, which has been a serious problem up to now, was also suppressed. The results demonstrated that the simultaneous improvement of high-temperature creep strength and room temperature fracture toughness can be first accomplished by the development of unique cross-lamellar microstructure, which opens a potential avenue for the development of novel UHT materials as alternatives to existing Ni-based superalloys.

  11. In situ TEM observation of FCC Ti formation at elevated temperatures

    DOE PAGES

    Yu, Qian; Kacher, Josh; Gammer, Christoph; ...

    2017-07-04

    Pure Ti traditionally exhibits the hexagonal closed packed (HCP) crystallographic structure under ambient conditions and the body centered cubic (BCC) structure at elevated temperatures. In addition to these typical structures for Ti alloys, the presence of a face centered cubic (FCC) phase associated with thin films, interfaces, or high levels of plastic deformation has occasionally been reported. Here in this paper we show that small FCC precipitates form in freestanding thin foils during in situ transmission electron microscope (TEM) heating and we discuss the potential origins of the FCC phase in light of the in situ observations. This FCC phasemore » was found to be stable upon cooling and under ambient conditions, which allowed us to explore its mechanical properties and stability via nanomechanical in situ TEM testing. It was found that FCC platelets within the HCP matrix phase were stable under mechanical deformation and exhibited similar mechanical deformation behavior as the parent HCP phase.« less

  12. Combined influences of micro-pillar geometry and substrate constraint on microplastic behavior of compressed single-crystal micro-pillar: Two-dimensional discrete dislocation dynamics modeling

    NASA Astrophysics Data System (ADS)

    Ouyanga, Chaojun; Lia, Zhenhuan; Huanga, Minsheng; Hua, Lili; Houa, Chuantao

    2009-11-01

    2D discrete dislocation dynamic modeling of compressed micro-pillars attached on a huge base is executed to study the size-dependent microplastic behavior of micro-pillars and the corresponding size effect. In addition to the conventional dimensional parameters of the micro-pillar such as the micro-pillar size and the height-to-width ratio, the micro-pillar taper angle and the dislocation slip plane orientation angle in the micro-pillar are also considered to address the size effect and its rich underlying mechanism. Computational results show that there are at least two operating mechanisms responsible for the plastic behavior of micro-pillars. One is associated with the dislocation free slip-out from the micro-pillar sidewall; the other is related to the dislocation pile-up at the base and the top end of the pillar. The overall mechanism governing the size effect of the micro-pillar rests with multi-factors, including the micro-pillar size, the height-to-width ratio, the micro-pillar taper and the slip plane orientation angle; however, whether the "free slip band" exists or not is the most important denotation. The well-known Schmid law still validates in the slender micro-pillars due to existence of the free slip band, whereas it may fail in the podgier micro-pillars due to absence of the free slip band; as a result, a complicated even "reverse" size effect appears.

  13. Complexity and Fermi surface deformation in compressed lithium

    NASA Astrophysics Data System (ADS)

    Rodriguez-Prieto, A.; Bergara, A.; Silkin, V. M.; Echenique, P. M.

    2006-11-01

    Recently reported structural complexity and enhanced temperature superconducting transitions in lithium under pressure have increased the interest in light alkalies, otherwise considered as simple and well-known systems under normal conditions. Here we present an analysis of the pressure-induced Fermi surface deformation in lithium and its relation to the observed complexity. According to our calculations, the Fermi surface becomes increasingly anisotropic with pressure and at 8GPa contacts the Brillouin zone boundary inducing a Hume-Rothery mechanism explaining the bcc-fcc transition. Around 30GPa increasing cooper-like necks and an extended nesting are observed in the Fermi surface in the fcc phase, enhancing the electronic susceptibility response function and inducing a strong phonon softening. This softening, besides preluding the transition to complex structures and providing a better understanding of the observed superconductivity, is expected to induce other yet unexplored anomalies in compressed lithium.

  14. Numerical study of the process of plastic deformation localization by an example of high-speed compression of a hollow single crystal cylinder

    NASA Astrophysics Data System (ADS)

    Dmitriev, A. I.; Nikonov, A. Yu.; Bondar', M. P.

    2016-11-01

    The effect of the crystallographic orientation of a single crystal hollow cylinder on features of creation and evolution of plastic deformation in it under conditions of high-speed axisymmetric load is studied. An advantage of the proposed loading scheme is the simultaneous implementation of all loading variants within the chosen crystallographic base plane of the cylinder and reaching different degrees of deformation over the cross section of the sample. Using the molecular-dynamic modeling, the difference in deformation properties of the loaded sample has been shown depending on the chosen crystallographic orientation of the base plane. Results of the investigation can be used to understand the main mechanisms of the plastic deformation of crystalline bodies.

  15. Grain Size Dependence of Uniform Elongation in Single-Phase FCC/BCC Metals

    NASA Astrophysics Data System (ADS)

    Liu, Haiting; Shen, Yao; Ma, Jiawei; Zheng, Pengfei; Zhang, Lei

    2016-09-01

    We studied the dependence of uniform elongation on grain size in the range of submicron to millimeter for single-phase FCC/BCC metals by reviewing recent experimental results and applying crystal plasticity finite element method simulation. In the order of increasing grain size, uniform elongation can be divided into three stages, namely low elongation stage, nearly constant elongation stage, and decreased elongation with large scatters stage. Low elongation stage features a dramatic increase near the critical grain size at the end of the stage, which is primarily attributed to the emergence of dislocation cell size transition from ultrafine to mid-size grain. Other factors can be neglected due to their negligible influence on overall variation trend. In nearly constant elongation stage, uniform elongation remains unchanged at a high level in general. As grain size keeps growing, uniform elongation starts decreasing and becomes scattered upon a certain grain size, indicating the initiation of decreased elongation with large scatters stage. It is shown that the increase is not linear or smooth but rather sharp at the end of low elongation stage, leading to a wider range in nearly constant elongation stage. The grain size dependence of uniform elongation can serve as a guiding principle for designing small uniaxial tensile specimens for mechanical testing, where size effect matters in most cases.

  16. Evolution of fcc Cu clusters and their structure changes in the soft magnetic Fe85.2Si1B9P4Cu0.8 (NANOMET) and FINEMET alloys observed by X-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Matsuura, M.; Nishijima, M.; Takenaka, K.; Takeuchi, A.; Ofuchi, H.; Makino, A.

    2015-05-01

    It is known that Cu plays an essential role in reducing the grain size of precipitated bcc Fe(Si) nanocrystallites in a nanocrystalline soft-magnetic Fe85.2Si1B9P4Cu0.8 (NANOMET®) alloys like as an Fe73.5Si13.5B9Nb3Cu1 (FINEMET®). However, significant differences are there between two alloys; NANOMET has much higher iron content (˜85%) than FINEMET (73.5%) and the former contains P instead of Nb for the latter. In the present work, the local structure around Cu in FINEMET was measured by X-ray absorption fine structure (XAFS) at 20 K and compared with those of NANOMET during nanocrystallization. Definite differences between NANOMET and FINEMET are found in the way of the evolution of Cu clusters during nanocrystallization. In FINEMET, an fcc structure of Cu is recognized in an as-quenched ribbon indicating existence of a small number of Cu clusters or a very small size of Cu clusters which is stable up to 450 °C, while the fcc Cu clusters are developed rapidly above 450 °C. An fcc structure of the Cu clusters in FINEMET is retained all the way to the end of the nanocrystallization. On the contrary, for NANOMET the local structure around Cu changes in a sequence as "amorphous → fcc → bcc → fcc" by annealing. The reasons of such different behaviors of the local structure around Cu during nanocrystallization are discussed in terms of different contributions of Cu clusters in bcc Fe precipitation between FINEMET and NANOMET. A significantly fast crystallization process with an extraordinary large heat release can be another reason for the transition of the local structure around Cu from fcc to bcc for NANOMET.

  17. Diffusion and segregation of niobium in fcc-nickel.

    PubMed

    Connétable, Damien; Ter-Ovanessian, Benoît; Andrieu, Éric

    2012-03-07

    Niobium is one of the major alloying elements, among the refractory elements, contributing to the strengthening of superalloys. Consequently, data about its behavior and its migration mechanism in fcc-Ni are essential knowledge to understand and control the strengthening in such alloys. We present in this work Nb interactions, solubility and diffusion in Ni performed by using the GGA approximation of the density functional theory. The substituted site is found to be the most favorable configuration in comparison to the tetrahedral and octahedral sites. The effect of temperature on solubility is discussed taking into account the thermal expansion of the lattice parameter and the vibrational contribution. Its diffusion mechanism is also discussed and compared to the literature. We finally discuss the segregation of Nb atoms on a Σ(5)-(012) symmetric tilt grain boundary.

  18. Developing of a test procedure to evaluate FCC catalyst regenerability

    SciTech Connect

    Murthy, V.L.N.; Debnath, S.; Bao, M.R.

    1995-12-31

    FCC catalyst comprises various active ingredients e.g. Y Zeolites, ZSM-5 and other medium pore Zeolites, active, matrix etc. with wide variation in Zeolite/matrix ratio and pore size distribution. The effect of pore size distribution on the accessibility of the active sites is a subject for intensive research at present. The accessibility of these active sites has a major effect on the overall reaction and regeneration kinetics. Catalyst regenerability is a very important factor particularly for moderate and low temperature regenerators, since it directly effects the CRC (Coke on-Regenerated Catalyst) value. The regenerability of catalyst is critical to minimize the overall catalyst inventory. Unfortunately, till date, there is no suitable laboratory equipment available to test catalyst regenerability.

  19. Full tunability of strain along the fcc-bcc bain path in epitaxial films and consequences for magnetic properties.

    PubMed

    Buschbeck, J; Opahle, I; Richter, M; Rössler, U K; Klaer, P; Kallmayer, M; Elmers, H J; Jakob, G; Schultz, L; Fähler, S

    2009-11-20

    Strained coherent film growth is commonly either limited to ultrathin films or low strains. Here, we present an approach to achieve high strains in thicker films, by using materials with inherent structural instabilities. As an example, 50 nm thick epitaxial films of the Fe70Pd30 magnetic shape memory alloy are examined. Strained coherent growth on various substrates allows us to adjust the tetragonal distortion from c/a{bct}=1.09 to 1.39, covering most of the Bain transformation path from fcc to bcc crystal structure. Magnetometry and x-ray circular dichroism measurements show that the Curie temperature, orbital magnetic moment, and magnetocrystalline anisotropy change over broad ranges.

  20. An ab initio study of the fcc and hcp structures of helium.

    PubMed

    Røeggen, I

    2006-05-14

    The hexagonal close packed (hcp) and face centered cubic (fcc) structures of helium are studied by using a new ab initio computational model for large complexes comprising small subsystems. The new model is formulated within the framework of the energy incremental scheme. In the calculation of intra- and intersystem energies, model systems are introduced. To each subsystem associated is a set of partner subsystems defined by a vicinity criterion. In the independent calculations of intra- and intersystem energies, the calculations are performed on model subsystems defined by the subsystems considered and their partner subsystems. A small and a large basis set are associated with each subsystem. For partner subsystems in a model system, the small basis set is adopted. By introducing a particular decomposition scheme, the intermolecular potential is written as a sum of effective one-body potentials. The binding energy per atom in an infinite crystal of atoms is the negative value of this one-body potential. The one-body potentials for hcp and fcc structures are calculated for the following nearest neighbor distances (d0): 4.6, 5.1, 5.4, 5.435, 5.5, 5.61, and 6.1 a.u. The equilibrium distance is 5.44 a.u. for both structures. The equilibrium dimer distance is 5.61 a.u. For the larger distances, i.e., d0 > 5.4 a.u., the difference of the effective one-body potentials for the two structures is less than 0.2 microE(h). However, the hcp structure has the lowest effective one-body potential for all the distances considered. For the smallest distance the difference in the effective one-body potential is 3.9 microE(h). Hence, for solid helium, i.e., helium under high pressure, the hcp structure is the preferred one. The error in the calculated effective one-body potential for the distance d0 = 5.61 a.u. is of the order of 1 microE(h) (approximately 0.5%).

  1. Highly anisotropic exchange interactions of jeff=12 iridium moments on the fcc lattice in La2BIrO6 (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

  2. Highly anisotropic exchange interactions of jeff=1/2 iridium moments on the fcc lattice in La2B IrO6 (B =Mg ,Zn )

    NASA Astrophysics Data System (ADS)

    Aczel, A. A.; Cook, A. M.; Williams, T. J.; Calder, S.; Christianson, A. D.; Cao, G.-X.; Mandrus, D.; Kim, Yong-Baek; Paramekanti, A.

    2016-06-01

    We have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites La2ZnIrO6 and La2MgIrO6 , which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated jeff=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 jeff=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. 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.

  3. Phase transition from fcc to bcc structure of the Cu-clusters during nanocrystallization of Fe{sub 85.2}Si{sub 1}B{sub 9}P{sub 4}Cu{sub 0.8} soft magnetic alloy

    SciTech Connect

    Nishijima, Masahiko; Matsuura, Makoto; Takenaka, Kana; Takeuchi, Akira; Makino, Akihiro; Ofuchi, Hironori

    2014-05-15

    A role of Cu on the nanocrystallization of an Fe{sub 85.2}Si{sub 1}B{sub 9}P{sub 4}Cu{sub 0.8} alloy was investigated by X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM). The Cu K-edge XAFS results show that local structure around Cu is disordered for the as-quenched sample whereas it changes to fcc-like structure at 613 K. The fcc Cu-clusters are, however, thermodynamically unstable and begin to transform into bcc structure at 638 K. An explicit bcc structure is observed for the sample annealed at 693 K for 600 s in which TEM observation shows that precipitated bcc-Fe crystallites with ∼12 nm are homogeneously distributed. The bcc structure of the Cu-clusters transforms into the fcc-type again at 973 K, which can be explained by the TEM observations; Cu segregates at grain boundaries between bcc-Fe crystallites and Fe{sub 3}(B,P) compounds. Combining the XAFS results with the TEM observations, the structure transition of the Cu-clusters from fcc to bcc is highly correlated with the preliminary precipitation of the bcc-Fe which takes place prior to the onset of the first crystallization temperature, T{sub x1} = 707 K. Thermodynamic analysis suggests that an interfacial energy density γ between an fcc-Cu cluster and bcc-Fe matrix dominates at a certain case over the structural energy between fcc and bcc Cu, ΔG{sub fcc} {sub −} {sub bcc}, which causes phase transition of the Cu clusters from fcc to bcc structure.

  4. Lattice dynamics of wurtzite and rocksalt AlN under high pressure: Effect of compression on the crystal anisotropy of wurtzite-type semiconductors

    NASA Astrophysics Data System (ADS)

    Manjón, Francisco Javier; Errandonea, Daniel; Romero, Aldo Humberto; Garro, Núria; Serrano, Jorge; Kuball, Martin

    2008-05-01

    Raman spectra of aluminum nitride (AlN) under pressure have been measured up to 25GPa , i.e., beyond the onset of the wurtzite-to-rocksalt phase transition around 20GPa . The experimental pressure coefficients for all the Raman-active modes of the wurtzite phase are reported and compared to those obtained from ab initio lattice dynamical calculations, as well as to previous experimental and theoretical results. The pressure coefficients of all the Raman-active modes in wurtzite-type semiconductors (AlN, GaN, InN, ZnO, and BeO), as well as the relatively low bulk modulus and phase transition pressure in wurtzite AlN, are discussed in the light of the pressure dependence of the structural crystal anisotropy in wurtzite semiconductors. On pressure release, AlN partially returns to the wurtzite phase below 1.3GPa but the presence of a rocksalt phase in AlN was observed at pressures as low as 1.3GPa , as evidenced by comparing the experimental Raman spectra to calculated one- and two-phonon densities of states of the rocksalt phase.

  5. Faceting and commensurability in crystal structures of colloidal thin films.

    PubMed

    Ramiro-Manzano, F; Meseguer, F; Bonet, E; Rodriguez, I

    2006-07-14

    This Letter investigates the influence of finite size effects on the particle arrangement of thin film colloidal crystals. A rich variety of crystallographic faceting with large single domain microcrystallites is shown. Optical reflectance experiments together with scanning electron microscopy permit the identification of the crystal symmetry and the facet orientation, as well as the exact number of monolayers. When the cell thickness is not commensurable with a high symmetry layering, particles arrange themselves in a periodic distribution of (111)- and (100)-orientated face centered cubic (fcc) microcrystallites separated by planar defects. These structures can be described as a fcc ordering orientated along a vicinal surface, modified by a periodic distribution of fcc (111) stacking faults.

  6. Ab initio lattice stability of fcc and hcp Fe-Mn random alloys.

    PubMed

    Gebhardt, T; Music, D; Hallstedt, B; Ekholm, M; Abrikosov, I A; Vitos, L; Schneider, J M

    2010-07-28

    We have studied the lattice stability of face centred cubic (fcc) versus hexagonal close packed (hcp) Fe-Mn random alloys using ab initio calculations. In the calculations we considered the antiferromagnetic order of local moments, which for fcc alloys models the magnetic configuration of this phase at room temperature (below its Néel temperature) as well as their complete disorder, corresponding to paramagnetic fcc and hcp alloys. For both cases, the results are consistent with our thermodynamic calculations, obtained within the Calphad approach. For the room temperature magnetic configuration, the cross-over of the total energies of the hcp phase and the fcc phase of Fe-Mn alloys is at the expected Mn content, whereas for the magnetic configuration above the fcc Néel temperature, the hcp lattice is more stable within the whole composition range studied. The increase of the total energy difference between hcp and antiferromagnetic fcc due to additions of Mn as well as the stabilizing effect of antiferromagnetic ordering on the fcc phase are well displayed. These results are of relevance for understanding the deformation mechanisms of these random alloys.

  7. Interactions of multiphase hydrodynamics, droplet evaporation, and chemical kinetics in FCC riser reactors.

    SciTech Connect

    Chang, S. L.

    1998-02-17

    A computational fluid dynamics (CFD) computer code, ICRKFLO, has been developed for flow simulation of fluid catalytic cracking (FCC) riser reactors, which convert crude oil into gasoline and other valuable products. The FCC flow, especially in the entry region, is a three-phase reacting flow including hot catalyst particles, inert lift gas, and feed oil droplets. The impact of the hydrodynamics processes of heat transfer, droplet evaporation, and mixing on the chemical kinetics or riser performance can be significant. ICRKFLO was used to evaluate the impact of these processes on the performance of an advanced FCC unit. The code solves for major flow properties of all three phases in an FCC riser, with models governing the transport of catalyst particles and feed oil droplet, the vaporization of the feed oil droplets, the cracking of the oil vapor, and the formation and deposition of coke on particles. First, the code was validated against available test data of a pilot-scale FCC unit. Then, flow calculations for the FCC unit were performed. Computational results indicate that the heat transfer and droplet vaporization processes have a significant impact on the performance of a pilot-scale FCC unit. The impact is expected to be even greater on commercial scale units.

  8. A first-principles study of the phase stability of fcc-based Ti-Al alloys

    SciTech Connect

    Asta, M. . Dept. of Materials Science and Mineral Engineering); de Fontaine, D. . Dept. of Materials Science and Mineral Engineering Lawrence Berkeley Lab., CA ); van Schilfgaarde, M. ); Sluiter, M. (Lawrence Livermore National Lab., CA (Un

    1992-04-01

    In this paper we present results of a first-principles phase stability study of fcc-based Ti-Al alloys. In particular the full-potential linear muffin tin orbital method has been used to determine heats of format on and other zero-temperature properties of 9 fcc ordered superstructures as well as fcc and hcp Ti, and fcc Al. From these results a set of effective cluster interactions are determined which are used in a cluster variation method calculation of the thermodynamic properties and the composition-temperature phase diagram of fcc-based alloys.

  9. Compressed convolution

    NASA Astrophysics Data System (ADS)

    Elsner, Franz; Wandelt, Benjamin D.

    2014-01-01

    We introduce the concept of compressed convolution, a technique to convolve a given data set with a large number of non-orthogonal kernels. In typical applications our technique drastically reduces the effective number of computations. The new method is applicable to convolutions with symmetric and asymmetric kernels and can be easily controlled for an optimal trade-off between speed and accuracy. It is based on linear compression of the collection of kernels into a small number of coefficients in an optimal eigenbasis. The final result can then be decompressed in constant time for each desired convolved output. The method is fully general and suitable for a wide variety of problems. We give explicit examples in the context of simulation challenges for upcoming multi-kilo-detector cosmic microwave background (CMB) missions. For a CMB experiment with detectors with similar beam properties, we demonstrate that the algorithm can decrease the costs of beam convolution by two to three orders of magnitude with negligible loss of accuracy. Likewise, it has the potential to allow the reduction of disk space required to store signal simulations by a similar amount. Applications in other areas of astrophysics and beyond are optimal searches for a large number of templates in noisy data, e.g. from a parametrized family of gravitational wave templates; or calculating convolutions with highly overcomplete wavelet dictionaries, e.g. in methods designed to uncover sparse signal representations.

  10. In Situ Determination of BCC-, FCC- and HPC-Iron Textures at Simultaneous High- Pressure and -Temperature by Means of the Resistive Heated Radial Diffraction Diamond Anvil Cell (RH-RD-DAC): Implications for the iron core.

    NASA Astrophysics Data System (ADS)

    Liermann, H.; Merkel, S.; Miyagi, L.; Wenk, H.; Shen, G.; Cynn, H.; Evans, W. J.

    2008-12-01

    Radial diffraction in the diamond anvil cell (DAC) has long been used to determine the stress state of materials under non-hydrostatic compression. This technique is also a major tool to investigate textures and infer deformation mechanisms in the earth mantle and core. However, most of these experiments have been conducted at ambient temperatures and therefore the results of these measurements may be difficult to extrapolate to the deep Earth. Here, we present texture data collected at HPCAT sector 16 BMD of the Advanced Photon Source during the plastic deformation of BCC-, FCC- and HPC-iron at simultaneous high-pressure and temperature in the new Resistive Heated Radial Diffraction Diamond Anvil Cell (RH-RD-DAC). Initial results from Rietveld refinements in MAUD indicate that BCC- iron develops a mixed {100} and {111} texture that remains active during heating. Latter is compatible with previous observations on BCC-iron and interpreted as slip along {110}<111>. Texture obtained after formation of FCC-iron at simultaneous high- pressure and temperatures show a pronounced maximum at {110} with minima at {100} and {111}. This texture is typical for FCC metals in compression with slip on {111}<110>. Processing of the HCP-iron textures at high-pressure and -temperature are under way. We will discuss the implications that the experimental results have for the deformation mechanisms of iron at pressure temperature conditions of the inner core.

  11. Crystal structures and compressibility of novel iron borides Fe{sub 2}B{sub 7} and Fe{sub x}B{sub 50} synthesized at high pressure and high temperature

    SciTech Connect

    Bykova, E.; Gou, H.; Bykov, M.; Hanfland, M.; Dubrovinsky, L.; Dubrovinskaia, N.

    2015-10-15

    We present here a detailed description of the crystal structures of novel iron borides, Fe{sub 2}B{sub 7} and Fe{sub x}B{sub 50} with various iron content (x=1.01(1), 1.04(1), 1.32(1)), synthesized at high pressures and high temperatures. As revealed by high-pressure single-crystal X-ray diffraction, the structure of Fe{sub 2}B{sub 7} possesses short incompressible B–B bonds, which make it as stiff as diamond in one crystallographic direction. The volume compressibility of Fe{sub 2}B{sub 7} (the bulk modulus K{sub 0}= 259(1.8) GPa, K{sub 0}′= 4 (fixed)) is even lower than that of FeB{sub 4} and comparable with that of MnB{sub 4}, known for high bulk moduli among 3d metal borides. Fe{sub x}B{sub 50} adopts the structure of the tetragonal δ-B, in which Fe atoms occupy an interstitial position. Fe{sub x}B{sub 50} does not show considerable anisotropy in the elastic behavior. - Graphical abstract: Crystal structures of novel iron borides, Fe{sub 2}B{sub 7} and Fe{sub x}B{sub 50} (x=1.01(1), 1.04(1), 1.32(1)). - Highlights: • Novel iron borides, Fe{sub 2}B{sub 7} and Fe{sub x}B{sub 50}, were synthesized under HPHT conditions. • Fe{sub 2}B{sub 7} has a unique orthorhombic structure (space group Pbam). • Fe{sub 2}B{sub 7} possesses short incompressible B–B bonds that results in high bulk modulus. • Fe{sub x}B{sub 50} adopts the structure of the tetragonal δ-B composed of B{sub 12} icosahedra. • In Fe{sub x}B{sub 50} intraicosahedral bonds are stiffer than intericosahedral ones.

  12. Attrition resistant catalysts and sorbents based on heavy metal poisoned FCC catalysts

    DOEpatents

    Gangwal, Santosh; Jothimurugesan, Kandaswamy

    1999-01-01

    A heavy metal poisoned, spent FCC catalyst is treated by chemically impregnating the poisoned catalyst with a new catalytic metal or metal salt to provide an attrition resistant catalyst or sorbent for a different catalytic or absorption processes, such as catalysts for Fischer-Tropsh Synthesis, and sorbents for removal of sulfur gasses from fuel gases and flue-gases. The heavy metal contaminated FCC catalyst is directly used as a support for preparing catalysts having new catalytic properties and sorbents having new sorbent properties, without removing or "passivating" the heavy metals on the spent FCC catalyst as an intermediate step.

  13. Attrition resistant catalysts and sorbents based on heavy metal poisoned FCC catalysts

    DOEpatents

    Gangwal, S.; Jothimurugesan, K.

    1999-07-27

    A heavy metal poisoned, spent FCC catalyst is treated by chemically impregnating the poisoned catalyst with a new catalytic metal or metal salt to provide an attrition resistant catalyst or sorbent for a different catalytic or absorption process, such as catalysts for Fischer-Tropsh Synthesis, and sorbents for removal of sulfur gases from fuel gases and flue-gases. The heavy metal contaminated FCC catalyst is directly used as a support for preparing catalysts having new catalytic properties and sorbents having new sorbent properties, without removing or passivating the heavy metals on the spent FCC catalyst as an intermediate step.

  14. Martensitic fcc-to-hcp transformation observed in xenon at high pressure.

    PubMed

    Cynn, H; Yoo, C S; Baer, B; Iota-Herbei, V; McMahan, A K; Nicol, M; Carlson, S

    2001-05-14

    Angle-resolved x-ray diffraction patterns of Xe to 127 GPa indicate that the fcc-to-hcp transition occurs martensitically between 3 and 70 GPa in diamond-anvil cells without an intermediate phase. These data also reveal that the transition occurs by the introduction of stacking disorder in the fcc lattice at low pressure, which grows into hcp domains with increasing pressure. The small energy difference between the hcp and the fcc structures may allow the two phases to coexist over a wide pressure range. Evidence of similar stacking disorder and incipient growth of an hcp phase are also observed in solid Kr.

  15. First-principles calculations of free energies of unstable phases: the case of fcc W.

    PubMed

    Ozolins, V

    2009-02-13

    Ab initio molecular dynamics simulations are used to solve the long-standing problem of calculating the free energies of unstable phases, such as fcc W. We find that fcc W is mechanically unstable with respect to long-wavelength shear at all temperatures considered (T>2500 K), while the short-wavelength phonon modes are anharmonically stabilized. The calculated fcc-bcc enthalpy and entropy differences at T=3500 K (308 meV and 0.74k_{B} per atom, respectively) agree well with the recent values derived from analysis of experimental data.

  16. Antiferromagnetic resonance in the Mott insulator fcc-Cs3C60.

    PubMed

    Suzuki, Yuta; Shibasaki, Seiji; Kubozono, Yoshihiro; Kambe, Takashi

    2013-09-11

    The magnetic ground state of the fcc phase of the Mott insulator Cs3C60 was studied using a low-temperature electron spin resonance technique, and antiferromagnetic resonance (AFMR) below 1.57 K was directly observed at ambient pressure. The AFMR modes for the fcc phase of Cs3C60 were investigated using a conventional two-sublattice model with uniaxial anisotropy, and the spin-flop field was determined to be 4.7 kOe at 1.57 K. The static magnetic exchange interactions and anisotropy field for fcc-Cs3C60 were also estimated.

  17. Observation of continuous and reversible bcc-fcc phase transformation in Ag/V multilayers

    SciTech Connect

    Wei, Q. M.; Liu, X.-Y.; Misra, A.

    2011-03-14

    A continuous and reversible bcc-fcc phase transformation via a rotation of bcc(110) or fcc(111) planes is observed in the Bain orientation relationship in a sputter deposited V/Ag multilayers using high resolution transmission electron microscopy and analyzed using molecular dynamics simulations. As a result of the continuous phase transformation, an intermediate bct phase connecting the bcc and fcc phases coexists, giving rise to the Bain path. The periodic displacement of atoms occurs in every two adjacent Ag and V layers. The alternating shear stress created by misfit strain is responsible for generating such transformation.

  18. Formation of Superlattices of Gold Nanoparticles Using Ostwald Ripening in Emulsions: Transition from fcc to bcc Structure.

    PubMed

    Schmitt, Julien; Hajiw, Stéphanie; Lecchi, Amélie; Degrouard, Jéril; Salonen, Anniina; Impéror-Clerc, Marianne; Pansu, Brigitte

    2016-06-30

    An efficient method to form 3D superlattices of gold nanoparticles inside oil emulsion droplets is presented. We demonstrate that this method relies on Ostwald ripening, a well-known phenomenon occurring during the aging of emulsions. The key point is that the nanoparticle concentration inside the smaller droplets is increasing very slowly with time, thus inducing the crystallization of the nanoparticles into superlattices. Using oil-in-water emulsions doped with hydrophobic gold nanoparticles, we demonstrate that this method is efficient for different types of oils (toluene, cyclohexane, dodecane, and hexadecane). 3D superlattices of the nanoparticles are obtained, with dimensions reaching a hundred nanometers. The kinetics of the crystallization depends on the solubility of the oil in water but also on the initial concentration of the gold nanoparticles in oil. This method also provides an innovative way to obtain the complete phase diagram of nanoparticle suspensions with concentration. Indeed, during this slow crystallization process, a transition from a disordered suspension to a fcc structure is observed, followed by a transition toward a bcc structure. This evolution with time provides key results to understand the role played by the ligands located at the surface of the nanoparticles in order to control the type of superlattices which are formed.

  19. Orientation relations in aluminide coatings on single crystals of nickel superalloys

    NASA Astrophysics Data System (ADS)

    Khayutin, S. G.

    2008-03-01

    The crystallographic orientation of NiAl refractory coatings on the surface of single crystals of high-temperature nickel alloy ZhS32 is studied. The orientation relation between single-crystal substrates based on an fcc γ-phase and coatings based on a bcc β-phase is studied.

  20. Spin frustration and magnetic ordering in the Mott insulating fcc-Cs3C60

    NASA Astrophysics Data System (ADS)

    Kasahara, Yuichi; Takeuchi, Yuki; Itou, Tatsuaki; Iwasa, Yoshihiro; Arcon, Denis; Rosseinsky, Matthew; Prassides, Kosmas

    2014-03-01

    The low-temperature magnetic state at ambient pressure has been investigated by specific heat and nuclear magnetic resonance (NMR) measurements in face-centered-cubic (fcc-) Cs3C60, which is characterized by a Mott insulating state with S = 1 / 2 spins in C603- anions and a geometrical spin frustration inherent in the fcc lattice. Specific heat exhibited no sharp anomaly down to 0.4 K, but both magnetic specific heat and NMR relaxation rate revealed a broad peak around 2.5 K, indicating that the reported antiferromagnetic ordering is accompanied by a gradual freezing of electronic spins with distributed transition temperatures. These results are unexpected in the conventional fcc antiferromagnets. Interplay of geometrical frustration, orientational disorder of C60 molecules, and weak Mottness gives rise to the unique magnetic ground state in fcc-Cs3C60.

  1. 76 FR 20976 - Wireline Competition Bureau Releases 2011 Annual Telecommunications Reporting Worksheet (FCC Form...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-04-14

    ... COMMISSION Wireline Competition Bureau Releases 2011 Annual Telecommunications Reporting Worksheet (FCC Form.... SUMMARY: In this document, the Wireline Competition Bureau released the revised annual Telecommunications... (describing a filer's principal telecommunications activities) into Appendix B. (5) Noting that...

  2. Lattice parameters of fcc binary alloys using a new semiempirical method

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Ferrante, John

    1992-01-01

    A new method is presented for the calculation of heats of formation, lattice parameters and cohesive energies of binary alloys. The method is applied to some fcc alloys and compared with experimental data, as well as other semiempirical results.

  3. 47 CFR 0.409 - Commission policy on private printing of FCC forms.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... ORGANIZATION General Information General § 0.409 Commission policy on private printing of FCC forms. The... in quality to the original document, without change to the page size, image size, configuration...

  4. First Principles Theory of the hcp-fcc Phase Transition in Cobalt.

    PubMed

    Lizárraga, Raquel; Pan, Fan; Bergqvist, Lars; Holmström, Erik; Gercsi, Zsolt; Vitos, Levente

    2017-06-19

    Identifying the forces that drive a phase transition is always challenging. The hcp-fcc phase transition that occurs in cobalt at ~700 K has not yet been fully understood, although early theoretical studies have suggested that magnetism plays a main role in the stabilization of the fcc phase at high temperatures. Here, we perform a first principles study of the free energies of these two phases, which we break into contributions arising from the vibration of the lattice, electronic and magnetic systems and volume expansion. Our analysis of the energy of the phases shows that magnetic effects alone cannot drive the fcc-hcp transition in Co and that the largest contribution to the stabilization of the fcc phase comes from the vibration of the ionic lattice. By including all the contributions to the free energy considered here we obtain a theoretical transition temperature of 825 K.

  5. 78 FR 44121 - FCC Extends Reply Comment Dates for Indecency Cases Policy

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-07-23

    ... From the Federal Register Online via the Government Publishing Office FEDERAL COMMUNICATIONS COMMISSION FCC Extends Reply Comment Dates for Indecency Cases Policy AGENCY: Federal Communications Commission. ACTION: Notice. SUMMARY: In this document, the Federal Communications Commission Enforcement...

  6. 78 FR 34099 - FCC Extends Pleading Cycle for Indecency Cases Policy

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-06

    ... From the Federal Register Online via the Government Publishing Office FEDERAL COMMUNICATIONS COMMISSION FCC Extends Pleading Cycle for Indecency Cases Policy AGENCY: Federal Communications Commission. ACTION: Notice. SUMMARY: In this document, the Federal Communications Commission Enforcement Bureau and...

  7. Crystal collimator systems for high energy frontier

    NASA Astrophysics Data System (ADS)

    Sytov, A. I.; Tikhomirov, V. V.; Lobko, A. S.

    2017-07-01

    Crystalline collimators can potentially considerably improve the cleaning performance of the presently used collimator systems using amorphous collimators. A crystal-based collimation scheme which relies on the channeling particle deflection in bent crystals has been proposed and extensively studied both theoretically and experimentally. However, since the efficiency of particle capture into the channeling regime does not exceed ninety percent, this collimation scheme partly suffers from the same leakage problems as the schemes using amorphous collimators. To improve further the cleaning efficiency of the crystal-based collimation system to meet the requirements of the FCC, we suggest here a double crystal-based collimation scheme, to which the second crystal is introduced to enhance the deflection of the particles escaping the capture to the channeling regime in its first crystal. The application of the effect of multiple volume reflection in one bent crystal and of the same in a sequence of crystals is simulated and compared for different crystal numbers and materials at the energy of 50 TeV. To enhance also the efficiency of use of the first crystal of the suggested double crystal-based scheme, we propose: the method of increase of the probability of particle capture into the channeling regime at the first crystal passage by means of fabrication of a crystal cut and the method of the amplification of nonchanneled particle deflection through the multiple volume reflection in one bent crystal, accompanying the particle channeling by a skew plane. We simulate both of these methods for the 50 TeV FCC energy.

  8. Growth and micromagnetism of self-assembled epitaxial fcc(111) cobalt dots.

    PubMed

    Fruchart, O; Masseboeuf, A; Toussaint, J C; Bayle-Guillemaud, P

    2013-12-11

    We develop the self-assembly of epitaxial submicrometer-sized face-centered-cubic (fcc) Co(111) dots using pulsed laser deposition. The dots display atomically flat facets, from which the ratios of surface and interface energies for fcc Co are deduced. Zero-field magnetic structures are investigated with magnetic force and Lorentz microscopies, revealing vortex-based flux-closure patterns. A good agreement is found with micromagnetic simulations.

  9. Detection of helium bubble formation at fcc-bcc interfaces using neutron reflectometry

    NASA Astrophysics Data System (ADS)

    Kashinath, A.; Wang, P.; Majewski, J.; Baldwin, J. K.; Wang, Y. Q.; Demkowicz, M. J.

    2013-07-01

    We use neutron reflectometry to find the critical helium (He) fluence required to form He bubbles at interfaces between fcc and bcc metals. Our findings are in agreement with previous experimental as well as modeling results and provide evidence for the presence of stable He platelets at fcc-bcc interfaces prior to bubble formation. The stable storage of He in interfacial platelets may provide the basis for the design of materials with increased resistance to He-induced degradation.

  10. Scaling Laws and Critical Properties for fcc and hcp Metals.

    PubMed

    Desgranges, Caroline; Widhalm, Leanna; Delhommelle, Jerome

    2016-06-16

    The determination of the critical parameters of metals has remained particularly challenging both experimentally, because of the very large temperatures involved, and theoretically, because of the many-body interactions that take place in metals. Moreover, experiments have shown that these systems exhibit an unusually strong asymmetry of their binodal. Recent theoretical work has led to new similarity laws, based on the calculation of the Zeno line and of the underlying Boyle parameters, which provided results for the critical properties of atomic and molecular systems in excellent agreement with experiments. Using the recently developed expanded Wang-Landau (EWL) simulation method, we evaluate the grand-canonical partition function, over a wide range of conditions, for 11 fcc and hcp metals (Ag, Al, Au, Be, Cu, Ir, Ni, Pb, Pd, Pt, and Rh), modeled with a many-body interaction potential. This allows us to calculate the binodal, Zeno line, and Boyle parameters and, in turn, obtain the critical properties for these systems. We also propose two scaling laws for the enthalpy and entropy of vaporization, and identify critical exponents of 0.4 and 1.22 for these two laws, respectively.

  11. Orbitide Composition of the Flax Core Collection (FCC).

    PubMed

    Burnett, Peta-Gaye Gillian; Olivia, Clara Marisa; Okinyo-Owiti, Denis Paskal; Reaney, Martin John Tarsisius

    2016-06-29

    The flax (Linum usitatissimum L.) core collection (FCC) was regenerated in Saskatoon, Saskatchewan and Morden, Manitoba in 2009. Seed orbitide content and composition from successfully propagated plants of 391 accessions were analyzed using high-throughput analyses employing high-performance liquid chromatography (HPLC) with reverse-phase monolithic HPLC columns and diode array detection (HPLC-DAD). Seed from plants regenerated in Morden had comparatively higher orbitide content than those grown in Saskatoon. Concentrations of orbitides encoded by contig AFSQ01016651.1 (1, 3, and 8) were higher than those encoded by AFSQ01025165.1 (6, 13, and 17) for most accessions in both locations. The cultivar 'Primus' from Poland and an unnamed accession (CN 101580 of unknown origin) exhibited the highest ratio of sum of [1,3,8] to a sum of [6,13,17]. Conversely, the lowest orbitide concentrations and ratio of [1,3,8] to [6,13,17] were observed in cultivars 'Hollandia' and 'Z 11637', both from The Netherlands. Orbitide expression did not correlate with flax morphological and other chemical traits.

  12. Multiscale modeling of radiation effects in fcc and bcc metals

    SciTech Connect

    Alonso, E; Caturla, M; Diaz de la Rubia, T; Felter, T; Fluss, M; Perlado, J; Wall, M; Wirth, B

    1999-07-15

    The prospect of using computer simulations to calculate radiation-induced defect production and its influence on microstructure evolution and mechanical property changes during prolonged irradiation of nuclear materials has been a beckoning, yet elusive goal for many years. However, the enormous progress achieved in computational physics for calculating reliable, yet tractable interatomic potentials, coupled with vast improvements in computational power have brought this hope to near reality. In order to develop modeling and simulation tools for predicting the irradiation response of nuclear structural materials, models must be implemented and tested across all relevant length and time scales. We discuss the development and implementation of a modeling methodology that consists of the linkage and hierarchical use of ab initio electronic structure calculations, molecular dynamics (MD) simulations, and kinetic Monte Carlo (KMC) simulations. This methodology can describe length and time scales from nanometers to hundreds of microns and from picoseconds to years, respectively. The ideas are demonstrated in two applications. First, we describe simulations that describe the irradiation and subsequent isochronal annealing of Pb, a low melting point fcc metal, and compare the results to experiments. Second, we show how these methods can be used to investigate damage production and freely migrating defect formation in irradiated V, the key component of candidate low activation alloys for fusion energy applications.

  13. High speed, high temperature electrical characterization of phase change materials: metastable phases, crystallization dynamics, and resistance drift

    NASA Astrophysics Data System (ADS)

    Dirisaglik, Faruk; Bakan, Gokhan; Jurado, Zoila; Muneer, Sadid; Akbulut, Mustafa; Rarey, Jonathan; Sullivan, Lindsay; Wennberg, Maren; King, Adrienne; Zhang, Lingyi; Nowak, Rebecca; Lam, Chung; Silva, Helena; Gokirmak, Ali

    2015-10-01

    During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K.During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05512a

  14. Deformation of Single Crystal Molybdenum at High Pressure

    SciTech Connect

    Bonner, B P; Aracne, C; Farber, D L; Boro, C O; Lassila, D H

    2004-02-24

    Single crystal samples of micron dimensions oriented in the [001] direction were shortened 10 to 40% in uniaxial compression with superposed hydrostatic pressure to begin investigation of how the onset of yielding evolves with pressure. A testing machine based on opposed anvil geometry with precision pneumatic control of the applied force and capability to measure sub micron displacements was developed to produce shape changing deformation at pressure. The experiments extend observations of pressure dependent deformation to {approx}5Gpa at shortening rates of {approx}2*10{sup -4}. Samples have been recovered for post run characterization and analysis to determine if deformation mechanisms are altered by pressure. Experiments under hydrostatic pressure provide insight into the nature of materials under extreme conditions, and also provide a means for altering deformation behavior in a controlled fashion. The approach has a long history demonstrating that pressure enhances ductility in general, and produces enhanced hardening relative to that expected from normal cold work in the BCC metals Mo, Ta and Nb{sup 2}. The pressure hardening is in excess of that predicted from the measured increase in shear modulus at pressure, and therefore is likely due to a dislocation mechanism, such as suppression of kink pair formation or the interaction of forest dislocation cores, and not from lattice resistance. The effect has not been observed in FCC metals, suggesting a fundamental difference between deformation mechanisms at pressure for the two classes. The purpose of this letter is to investigate the origin of pressure hardening with new experiments that extend the pressure range beyond 3 GPa, the upper limit of conventional large sample (1cm{sup 3}) testing methods. Most previous high pressure deformation studies have been on poly crystals, relying on model dependent analysis to infer the maximum deviatoric stress that a deformed sample can support. In one experiment, a

  15. Dynamic-Range Compression For Infrared Imagery

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Liu, Hua-Kuang

    1989-01-01

    Photorefractive crystals covering detectors prevent saturation. To make full use of information in image, desirable to compress dynamic range of input intensity to within region of approximately linear response of detector. Dynamic-range compression exhibited by measurements of attenuation in photorefractive GaAs. Effective dynamic-range-compressor plate, film, or coating reduces apparent contrast of scene imaged on detector plane to within dynamic range of detectors; original image contrast or intensity data recovered subsequently in electronic image processing because range-compression function and inverse known.

  16. High speed, high temperature electrical characterization of phase change materials: metastable phases, crystallization dynamics, and resistance drift.

    PubMed

    Dirisaglik, Faruk; Bakan, Gokhan; Jurado, Zoila; Muneer, Sadid; Akbulut, Mustafa; Rarey, Jonathan; Sullivan, Lindsay; Wennberg, Maren; King, Adrienne; Zhang, Lingyi; Nowak, Rebecca; Lam, Chung; Silva, Helena; Gokirmak, Ali

    2015-10-28

    During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K.

  17. The frustrated fcc antiferromagnet Ba2 YOsO6: Structural characterization, magnetic properties and neutron scattering studies

    DOE PAGES

    Kermarrec, E.; Marjerrison, Casey A.; Thompson, C. M.; ...

    2015-02-26

    Here we report the crystal structure, magnetization, and neutron scattering measurements on the double perovskite Ba2 YOsO6. The Fmmore » $$\\bar{3}$$m space group is found both at 290 K and 3.5 K with cell constants a0=8.3541(4) Å and 8.3435(4) Å, respectively. Os5+ (5d3) ions occupy a nondistorted, geometrically frustrated face-centered-cubic (fcc) lattice. A Curie-Weiss temperature θ ~₋700 K suggests the presence of a large antiferromagnetic interaction and a high degree of magnetic frustration. A magnetic transition to long-range antiferromagnetic order, consistent with a type-I fcc state below TN~69 K, is revealed by magnetization, Fisher heat capacity, and elastic neutron scattering, with an ordered moment of 1.65(6) μB on Os5+. The ordered moment is much reduced from either the expected spin-only value of ~3 μB or the value appropriate to 4d3 Ru5+ in isostructural Ba2 YRuO6 of 2.2(1) μB, suggesting a role for spin-orbit coupling (SOC). Triple-axis neutron scattering measurements of the order parameter suggest an additional first-order transition at T=67.45 K, and the existence of a second-ordered state. We find time-of-flight inelastic neutron results reveal a large spin gap Δ~17 meV, unexpected for an orbitally quenched, d3 electronic configuration. In conclusion, we discuss this in the context of the ~5 meV spin gap observed in the related Ru5+,4d3 cubic double perovskite Ba2YRuO6, and attribute the ~3 times larger gap to stronger SOC present in this heavier, 5d, osmate system.« less

  18. Thallium under extreme compression

    NASA Astrophysics Data System (ADS)

    Cazorla, C.; MacLeod, S. G.; Errandonea, D.; Munro, K. A.; McMahon, M. I.; Popescu, C.

    2016-11-01

    We present a combined theoretical and experimental study of the high-pressure behavior of thallium. X-ray diffraction experiments have been carried out at room temperature (RT) up to 125 GPa using diamond-anvil cells (DACs), nearly doubling the pressure range of previous experiments. We have confirmed the hcp-fcc transition at 3.5 GPa and determined that the fcc structure remains stable up to the highest pressure attained in the experiments. In addition, HP-HT experiments have been performed up to 8 GPa and 700 K by using a combination of XRD and a resistively heated DAC. Information on the phase boundaries is obtained, as well as crystallographic information on the HT bcc phase. The equation of state (EOS) for different phases is reported. Ab initio calculations have also been carried out considering several potential high-pressure structures. They are consistent with the experimental results and predict that, among the structures considered in the calculations, the fcc structure of thallium is stable up to 4.3 TPa. Calculations also predict the post-fcc phase to have a close-packed orthorhombic structure above 4.3 TPa.

  19. Thallium under extreme compression.

    PubMed

    Cazorla, C; MacLeod, S G; Errandonea, D; Munro, K A; McMahon, M I; Popescu, C

    2016-11-09

    We present a combined theoretical and experimental study of the high-pressure behavior of thallium. X-ray diffraction experiments have been carried out at room temperature (RT) up to 125 GPa using diamond-anvil cells (DACs), nearly doubling the pressure range of previous experiments. We have confirmed the hcp-fcc transition at 3.5 GPa and determined that the fcc structure remains stable up to the highest pressure attained in the experiments. In addition, HP-HT experiments have been performed up to 8 GPa and 700 K by using a combination of XRD and a resistively heated DAC. Information on the phase boundaries is obtained, as well as crystallographic information on the HT bcc phase. The equation of state (EOS) for different phases is reported. Ab initio calculations have also been carried out considering several potential high-pressure structures. They are consistent with the experimental results and predict that, among the structures considered in the calculations, the fcc structure of thallium is stable up to 4.3 TPa. Calculations also predict the post-fcc phase to have a close-packed orthorhombic structure above 4.3 TPa.

  20. Cubic to tetragonal crystal lattice reconstruction during ordering or decomposition

    SciTech Connect

    Cheong, Byung-kl

    1992-09-01

    This thesis studied thermodynamic stability and morphology of product phases in diffusional phase transformations involving cubic-to-tetragonal crystal lattice reconstructions. Two different kinds of diffusional transformations were examined: L1{sub 0} ordering (fcc to fct lattice change) and decomposition of off-stoichiometric B2 ordering alloys accompanying bcc to fcc Bain transformation. In the first case, Fe-45 at.% Pd alloys were studied by TEM; in the second, the Bain strain relaxation during decomposition of hyper-eutectoid Cu-9.04 wt% Be alloy was studied. CuAu and InMg were also studied.

  1. Phase diagram of power law and Lennard-Jones systems: Crystal phases

    SciTech Connect

    Travesset, Alex

    2014-10-28

    An extensive characterization of the low temperature phase diagram of particles interacting with power law or Lennard-Jones potentials is provided from Lattice Dynamical Theory. For power law systems, only two lattice structures are stable for certain values of the exponent (or softness) (A15, body centered cube (bcc)) and two more (face centered cubic (fcc), hexagonal close packed (hcp)) are always stable. Among them, only the fcc and bcc are equilibrium states. For Lennard-Jones systems, the equilibrium states are either hcp or fcc, with a coexistence curve in pressure and temperature that shows reentrant behavior. The hcp solid never coexists with the liquid. In all cases analyzed, for both power law and Lennard-Jones potentials, the fcc crystal has higher entropy than the hcp. The role of anharmonic terms is thoroughly analyzed and a general thermodynamic integration to account for them is proposed.

  2. Phase diagram of power law and Lennard-Jones systems: Crystal phases

    SciTech Connect

    Travesset, Alex

    2014-10-28

    An extensive characterization of the low temperature phase diagram of particles interacting with power law or Lennard-Jones potentials is provided from Lattice Dynamical Theory. For power law systems, only two lattice structures are stable for certain values of the exponent (or softness) (A15, body centered cube (bcc)) and two more (face centered cubic (fcc), hexagonal close packed (hcp)) are always stable. Among them, only the fcc and bcc are equilibrium states. For Lennard-Jones systems, the equilibrium states are either hcp or fcc, with a coexistence curve in pressure and temperature that shows reentrant behavior. The hcp solid never coexists with the liquid. In all cases analyzed, for both power law and Lennard-Jones potentials, the fcc crystal has higher entropy than the hcp. The role of anharmonic terms is thoroughly analyzed and a general thermodynamic integration to account for them is proposed.

  3. Phase diagram of power law and Lennard-Jones systems: Crystal phases

    NASA Astrophysics Data System (ADS)

    Travesset, Alex

    2014-10-01

    An extensive characterization of the low temperature phase diagram of particles interacting with power law or Lennard-Jones potentials is provided from Lattice Dynamical Theory. For power law systems, only two lattice structures are stable for certain values of the exponent (or softness) (A15, body centered cube (bcc)) and two more (face centered cubic (fcc), hexagonal close packed (hcp)) are always stable. Among them, only the fcc and bcc are equilibrium states. For Lennard-Jones systems, the equilibrium states are either hcp or fcc, with a coexistence curve in pressure and temperature that shows reentrant behavior. The hcp solid never coexists with the liquid. In all cases analyzed, for both power law and Lennard-Jones potentials, the fcc crystal has higher entropy than the hcp. The role of anharmonic terms is thoroughly analyzed and a general thermodynamic integration to account for them is proposed.

  4. Phase diagram of power law and Lennard-Jones systems: crystal phases.

    PubMed

    Travesset, Alex

    2014-10-28

    An extensive characterization of the low temperature phase diagram of particles interacting with power law or Lennard-Jones potentials is provided from Lattice Dynamical Theory. For power law systems, only two lattice structures are stable for certain values of the exponent (or softness) (A15, body centered cube (bcc)) and two more (face centered cubic (fcc), hexagonal close packed (hcp)) are always stable. Among them, only the fcc and bcc are equilibrium states. For Lennard-Jones systems, the equilibrium states are either hcp or fcc, with a coexistence curve in pressure and temperature that shows reentrant behavior. The hcp solid never coexists with the liquid. In all cases analyzed, for both power law and Lennard-Jones potentials, the fcc crystal has higher entropy than the hcp. The role of anharmonic terms is thoroughly analyzed and a general thermodynamic integration to account for them is proposed.

  5. Aluminum exchanged sepiolite as components of FCC catalysts

    SciTech Connect

    Corma, A.; Fornes, V.; Mifsud, A.; Perez-Pariente, J. )

    1990-08-01

    Sepiolite is a fibrous magnesium silicate, which is formed of talc-like ribbons arranged in such a way that the tetrahedral sheet is continuous but inverts apical directions in adjacent ribbons. In this way, channels of 10.8 {times} 4.0 {angstrom} in a cross-section perpendicular to the length of the fiber (C axis) are generated. The average fiber length of the mineral varies between 0.5 and 1.0 {mu}m, and reagent molecules have only access to a small portion of the interior of the channels. Natural or acid leached sepiolite have been found useful for vanadium passivation in FCC catalysts. The authors have modified the sepiolite in order to improve the textural characteristics, while removing the Mg{sup 2+} ions of the border and introducing other cations which can give acid properties to this material. Conclusions are as follows: (1) It is possible to prepare, by a conventional treatment, sepiolites in which the magnesium at the borders of the channels has been substituted by Al{sup 3+}. (2) These samples show a much higher acidity and hydrothermal stability than natural sepiolites, being most of the acidity in the range of mild strengths. (3) Aluminic sepiolites, while being good for vanadium passivation, do not present the inconvenience due to Mg migrations to the zeolite (if in the same particle) shown by natural sepiolite. (4) They present a good gasoil cracking activity and selectivity, specially useful for bottoms conversion. All these characteristics make aluminum sepiolites materials worth testing in a larger scale for catalytic cracking of residues.

  6. High resolution electron microscopy of interfaces in fcc materials

    SciTech Connect

    Merkle, K.L.

    1990-08-01

    Modern high-resolution electron microscopy (HREM) instruments, which are capable of a point-to-point resolution of better than 0.2 nm, have allowed atomic-scale observations of a variety of internal interfaces. The application of the HREM technique to fcc model systems for the purpose of addressing a number of interface issues will be examined in this paper. Atomic structure observations for heterophase interfaces of metal/metal and metal/metal-oxide systems as well as HREM studies of grain boundaries in NiO and Au will be discussed with emphasis on generic structural features and the role of the interface plane. Comparisons between observed interface structures and atomistic computer modeling results have shown agreements for some interfaces, as well as certain differences in others. A number of structural features are common to both metal and oxide grain boundaries, as well as certain heterophase boundaries. Of particular importance in close-packed solids appears to be the tendency to preserve, as much as possible, local atomic coordination, giving rise to atomically well-matched regions that alternate along the interface with regions of misfit. It is commonly observed that heterophase interfaces are being preferentially formed on dense-packed planes. Low-index planes are also frequently observed in asymmetric grain boundaries. In addition to the observation of misfit dislocations in heterophase boundaries, misfit-dislocation-like defects have also been found in asymmetric, incommensurate grain boundaries. The tendency for maintaining coherence between dense-packed planes across the interface has resulted in the formation of novel three-dimensional GB structures. HREM observations have brought new insights into the correlations between macroscopic geometry, interfacial energy, and microscopic atomic relaxations.

  7. Monte Carlo Studies of the Fcc Ising Model.

    NASA Astrophysics Data System (ADS)

    Polgreen, Thomas Lee

    Monte Carlo simulations are performed on the antiferromagnetic fcc Ising model which is relevant to the binary alloy CuAu. The model exhibits a first-order ordering transition as a function of temperature. The lattice free energy of the model is determined for all temperatures. By matching free energies of the ordered and disordered phases, the transition temperature is determined to be T(,t) = 1.736 J where J is the coupling constant of the model. The free energy as determined by series expansion and the Kikuchi cluster variation method is compared with the Monte Carlo results. These methods work well for the ordered phase, but not for the disordered phase. A determination of the pair correlation in the disordered phase along the {100} direction indicates a correlation length of (DBLTURN) 2.5a at the phase transition. The correlation length exhibits mean-field-like temperature dependence. The Cowley-Warren short range order parameters are determined as a function of temperature for the first twelve nearest-neighbor shells of this model. The Monte Carlo results are used to determine the free parameter in a mean-field-like class of theories described by Clapp and Moss. The ability of these theories to predict ratios between pair potentials is tested with these results. In addition, evidence of a region of heterophase fluctuations is presented in agreement with x-ray diffuse scattering measurements on Cu(,3)Au. The growth of order following a rapid quench from disorder is studied by means of a dynamic Monte Carlo simulation. The results compare favorably with the Landau theory proposed by Chan for temperatures near the first-order phase transition. For lower temperatures, the results are in agreement with the theories of Lifshitz and Allen and Chan. In the intermediate temperature range, our extension of Chan's theory is able to explain our simulation results and recent experimental results.

  8. Diffusion-controlled anisotropic growth of stable and metastable crystal polymorphs in the phase-field crystal model.

    PubMed

    Tegze, G; Gránásy, L; Tóth, G I; Podmaniczky, F; Jaatinen, A; Ala-Nissila, T; Pusztai, T

    2009-07-17

    We use a simple density functional approach on a diffusional time scale, to address freezing to the body-centered cubic (bcc), hexagonal close-packed (hcp), and face-centered cubic (fcc) structures. We observe faceted equilibrium shapes and diffusion-controlled layerwise crystal growth consistent with two-dimensional nucleation. The predicted growth anisotropies are discussed in relation with results from experiment and atomistic simulations. We also demonstrate that varying the lattice constant of a simple cubic substrate, one can tune the epitaxially growing body-centered tetragonal structure between bcc and fcc, and observe a Mullins-Sekerka-Asaro-Tiller-Grinfeld-type instability.

  9. Sensitivity to grain discretization of the simulated crystal stress distributions in FCC polycrystals

    NASA Astrophysics Data System (ADS)

    Ritz, H.; Dawson, P. R.

    2009-01-01

    An elastoviscoplastic finite element model of aluminum alloys is used to compare mechanical response among meshes formed with several different grain shapes. Tetrahedral elements are used to form grains of cubic, rhombic dodecahedral and truncated octahedral shape. The influence of the grain shape on the aggregate response is examined in terms of the stress variation and the aggregate elastic moduli. While elastic anisotropy in the bulk material is not found to be dependent on grain shape, consistent trends are observed in intragranular and intergranular stress distributions across these mesh definitions.

  10. The length change of a dislocation junction in FCC-single crystals under stress

    NASA Astrophysics Data System (ADS)

    Kurinnaya, Raisa; Zgolich, Marina; Starenchenko, Vladimir; Sadritdinova, Gulnora

    2016-01-01

    The product of dislocation reactions among dislocations of non-coplanar slip systems are dislocation junctions. The paper presents the study on the length change of dislocation junctions under stress. It is revealed that dislocation junctions can be destructed by merging of triple dislocation nodes at certain inclination angles of the glide dislocation and the forest dislocation to the junction line and the corresponding lengths of free segments of intersecting dislocations. Dislocation junctions formed at an arbitrary intersection of segments of the reacting dislocation are investigated. The geometry of the intersection of segments of reacting dislocations, at which dislocation junctions are not completely destructed under stress but cease to be an obstacle for further motion of the glide dislocation, is determined. Such junctions remain in the shear zone, presenting an obstacle to other glide dislocations. Conditions under which the length of the dislocation junction increases with an increase in the stress exceeding the original length are found. The formed extended barrier becomes too strong for the acting stress. Higher stresses are required in order to destruct it. The probability of completely destructible junctions under stress, the probability of non-destructible junctions that remain in the shear zone and replenish the density of dislocation debris, as well as the probability of formation of long strong junctions, which are barriers capable of limiting the shear zone, are determined.

  11. High Temperature Properties of the Fcc Metallic Crystals in the Anharmonic Approximation

    DTIC Science & Technology

    2001-01-01

    interactions were approximated by the Morse and Lennard - Jones pair potential functions. Unfortunately, the parameters of these potentials were...Au) we take as a model of interatomic interactions the (alpha,m) Buckingham, (n,m) Lennard - Jones and (alpha,beta) Morse pair potentials with the

  12. Isomorph invariance of the structure and dynamics of classical crystals

    NASA Astrophysics Data System (ADS)

    Albrechtsen, Dan E.; Olsen, Andreas E.; Pedersen, Ulf R.; Schrøder, Thomas B.; Dyre, Jeppe C.

    2014-09-01

    This paper shows by computer simulations that some crystalline systems have curves in their thermodynamic phase diagrams, so-called isomorphs, along which structure and dynamics in reduced units are invariant to a good approximation. The crystals are studied in a classical-mechanical framework, which is generally a good description except significantly below melting. The existence of isomorphs for crystals is validated by simulations of particles interacting via the Lennard-Jones pair potential arranged into a face-centered cubic (fcc) crystalline structure; the slow vacancy-jump dynamics of a defective fcc crystal is also shown to be isomorph invariant. In contrast, a NaCl crystal model does not exhibit isomorph invariances. Other systems simulated, though in less detail, are the Wahnström binary Lennard-Jones crystal with the MgZn2 Laves crystal structure, monatomic fcc crystals of particles interacting via the Buckingham pair potential and via a purely repulsive pair potential diverging at a finite separation, an ortho-terphenyl molecular model crystal, and SPC/E hexagonal ice. Except for NaCl and ice, the crystals simulated all have isomorphs. Based on previous simulations of liquid models, we conjecture that crystalline solids with isomorphs include most or all formed by atoms or molecules interacting via metallic or van der Waals forces, whereas covalently bonded or hydrogen-bonded crystals are not expected to have isomorphs; crystals of ions or dipolar molecules constitute a limiting case for which isomorphs are only expected when the Coulomb interactions are relatively weak. We briefly discuss the consequences of the findings for theories of melting and crystallization.

  13. Turbulence in Compressible Flows

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Lecture notes for the AGARD Fluid Dynamics Panel (FDP) Special Course on 'Turbulence in Compressible Flows' have been assembled in this report. The following topics were covered: Compressible Turbulent Boundary Layers, Compressible Turbulent Free Shear Layers, Turbulent Combustion, DNS/LES and RANS Simulations of Compressible Turbulent Flows, and Case Studies of Applications of Turbulence Models in Aerospace.

  14. Turbulence in Compressible Flows

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Lecture notes for the AGARD Fluid Dynamics Panel (FDP) Special Course on 'Turbulence in Compressible Flows' have been assembled in this report. The following topics were covered: Compressible Turbulent Boundary Layers, Compressible Turbulent Free Shear Layers, Turbulent Combustion, DNS/LES and RANS Simulations of Compressible Turbulent Flows, and Case Studies of Applications of Turbulence Models in Aerospace.

  15. Crystal Structure of Cold Compressed Graphite

    NASA Astrophysics Data System (ADS)

    Amsler, Maximilian; Flores-Livas, José A.; Lehtovaara, Lauri; Balima, Felix; Ghasemi, S. Alireza; Machon, Denis; Pailhès, Stéphane; Willand, Alexander; Caliste, Damien; Botti, Silvana; San Miguel, Alfonso; Goedecker, Stefan; Marques, Miguel A. L.

    2012-02-01

    Through a systematic structural search we found an allotrope of carbon with Cmmm symmetry which we predict to be more stable than graphite for pressures above 10 GPa. This material, which we refer to as Z-carbon, is formed by pure sp3 bonds and it provides an explanation to several features in experimental x-ray diffraction and Raman spectra of graphite under pressure. The transition from graphite to Z-carbon can occur through simple sliding and buckling of graphene sheets. Our calculations predict that Z-carbon is a transparent wide band-gap semiconductor with a hardness comparable to diamond.

  16. Phononic crystals of poroelastic spheres

    NASA Astrophysics Data System (ADS)

    Alevizaki, A.; Sainidou, R.; Rembert, P.; Morvan, B.; Stefanou, N.

    2016-11-01

    An extension of the layer-multiple-scattering method to phononic crystals of poroelastic spheres immersed in a fluid medium is developed. The applicability of the method is demonstrated on specific examples of close-packed fcc crystals of submerged water-saturated meso- and macroporous silica microspheres. It is shown that, by varying the pore size and/or the porosity, the transmission, reflection, and absorption spectra of finite slabs of these crystals are significantly altered. Strong absorption, driven by the slow waves in the poroelastic material and enhanced by multiple scattering, leads to negligible transmittance over an extended frequency range, which might be useful for practical applications in broadband acoustic shielding. The results are analyzed by reference to relevant phononic dispersion diagrams in the viscous and inertial coupling limits, and a consistent interpretation of the underlying physics is provided.

  17. Molecular dynamics simulations of the mechanisms controlling the propagation of bcc/fcc semi-coherent interfaces in iron

    NASA Astrophysics Data System (ADS)

    Ou, X.; Sietsma, J.; Santofimia, M. J.

    2016-06-01

    Molecular dynamics simulations have been used to study the effects of different orientation relationships between fcc and bcc phases on the bcc/fcc interfacial propagation in pure iron systems at 300 K. Three semi-coherent bcc/fcc interfaces have been investigated. In all the cases, results show that growth of the bcc phase starts in the areas of low potential energy and progresses into the areas of high potential energy at the original bcc/fcc interfaces. The phase transformation in areas of low potential energy is of a martensitic nature while that in the high potential energy areas involves occasional diffusional jumps of atoms.

  18. The hcp to fcc transformation path of scandium trihydride under high pressure.

    PubMed

    Pakornchote, T; Pinsook, U; Bovornratanaraks, T

    2014-01-15

    We used density functional theory to calculate the phase stability of the hcp (hexagonal close packed) and the fcc (face centered cubic) structures of ScH3. The hcp form is stable up to 22 GPa according to the generalized gradient approximation calculation. Then the fcc form becomes energetically more stable. In order to provide insight into the phase transition mechanism, we modeled the hcp to fcc transition by sliding the hcp basal planes, i.e. (001)h planes, in such a way that the ABABAB sequence of the hcp form is altered into the ABCABC sequence of the fcc form. This sliding was suggested by the experiment. The configurations of these sliding steps are our proposed intermediate configurations, whose symmetry group is the Cm group. By using the Cm crystallography, we can match the d-spacings from the lattice planes of the hcp and fcc forms and the intermediate planes measured from the experiment. We also calculated the enthalpy per step, from which the energy barrier between the two phases at various pressures was derived. The barrier at 35 GPa is 0.370 eV per formula or 0.093 eV/atom. The movements of the hydrogen atoms during the hcp to intermediate phase transition are consistent with the result from the Raman spectra.

  19. Unique Bonding Properties of the Au36(SR)24 Nanocluster with FCC-Like Core.

    PubMed

    Chevrier, Daniel M; Chatt, Amares; Zhang, Peng; Zeng, Chenjie; Jin, Rongchao

    2013-10-03

    The recent discovery on the total structure of Au36(SR)24, which was converted from biicosahedral Au38(SR)24, represents a surprising finding of a face-centered cubic (FCC)-like core structure in small gold-thiolate nanoclusters. Prior to this finding, the FCC feature was only expected for larger (nano)crystalline gold. Herein, we report results on the unique bonding properties of Au36(SR)24 that are associated with its FCC-like core structure. Temperature-dependent X-ray absorption spectroscopy (XAS) measurements at the Au L3-edge, in association with ab initio calculations, show that the local structure and electronic behavior of Au36(SR)24 are of more molecule-like nature, whereas its icosahedral counterparts such as Au38(SR)24 and Au25(SR)18 are more metal-like. Moreover, site-specific S K-edge XAS studies indicate that the bridging motif for Au36(SR)24 has different bonding behavior from the staple motif from Au38(SR)24. Our findings highlight the important role of "pseudo"-Au4 units within the FCC-like Au28 core in interpreting the bonding properties of Au36(SR)24 and suggest that FCC-like structure in gold thiolate nanoclusters should be treated differently from its bulk counterpart.

  20. Compression Freezing Kinetics of Water to Ice VII

    DOE PAGES

    Gleason, A. E.; Bolme, C. A.; Galtier, E.; ...

    2017-07-11

    Time-resolved x-ray diffraction (XRD) of compressed liquid water shows transformation to ice VII in 6 nsec, revealing crystallization rather than amorphous solidification during compression freezing. Application of classical nucleation theory indicates heterogeneous nucleation and one-dimensional (e.g., needlelike) growth. In conclusion, these first XRD data demonstrate rapid growth kinetics of ice VII with implications for fundamental physics of diffusion-mediated crystallization and thermodynamic modeling of collision or impact events on ice-rich planetary bodies.

  1. Compression Freezing Kinetics of Water to Ice VII

    NASA Astrophysics Data System (ADS)

    Gleason, A. E.; Bolme, C. A.; Galtier, E.; Lee, H. J.; Granados, E.; Dolan, D. H.; Seagle, C. T.; Ao, T.; Ali, S.; Lazicki, A.; Swift, D.; Celliers, P.; Mao, W. L.

    2017-07-01

    Time-resolved x-ray diffraction (XRD) of compressed liquid water shows transformation to ice VII in 6 nsec, revealing crystallization rather than amorphous solidification during compression freezing. Application of classical nucleation theory indicates heterogeneous nucleation and one-dimensional (e.g., needlelike) growth. These first XRD data demonstrate rapid growth kinetics of ice VII with implications for fundamental physics of diffusion-mediated crystallization and thermodynamic modeling of collision or impact events on ice-rich planetary bodies.

  2. Crystallographic dependence of CO activation on cobalt catalysts: HCP versus FCC.

    PubMed

    Liu, Jin-Xun; Su, Hai-Yan; Sun, Da-Peng; Zhang, Bing-Yan; Li, Wei-Xue

    2013-11-06

    Identifying the structure sensitivity of catalysts in reactions, such as Fischer-Tropsch synthesis from CO and H2 over cobalt catalysts, is an important yet challenging issue in heterogeneous catalysis. Based on a first-principles kinetic study, we find for the first time that CO activation on hexagonal close-packed (HCP) Co not only has much higher intrinsic activity than that of face centered-cubic (FCC) Co but also prefers a different reaction route, i.e., direct dissociation with HCP Co but H-assisted dissociation on the FCC Co. The origin is identified from the formation of various denser yet favorable active sites on HCP Co not available for FCC Co, due to their distinct crystallographic structure and morphology. The great dependence of the activity on the crystallographic structure and morphology of the catalysts revealed here may open a new avenue for better, stable catalysts with maximum mass-specific reactivity.

  3. Interdiffusion and Diffusion Mobility for fcc Ni-Co-Al Alloys

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Zhu, Naqiong; Wang, Hao; Lu, Xiao-Gang

    2016-12-01

    Ternary fcc Ni-Co-Al diffusion couples annealed at 1173 K (900 °C), 1373 K (1100 °C), and 1573 K (1300 °C) have been studied by using electron probe microanalysis. The interdiffusion coefficients were extracted using the Sauer-Freise and Whittle-Green methods from the measured concentration profiles of binary and ternary diffusion couples, respectively. Based on the diffusion coefficients reported in the literature and those determined in the present work, the diffusion mobilities for fcc Ni-Co-Al alloys were assessed. In general, reasonable agreements were reached and the resulted mobility database can be used to study the diffusion behavior of the ternary fcc Ni-Co-Al alloys in a wide composition range.

  4. Hydrodynamics and catalytic reactions in the riser of a FCC plant

    SciTech Connect

    Derouin, C.; van Landeghem, F.; Turlier, P.; Bernard, J.R.

    1996-12-31

    The hydrodynamic characteristics of the riser of a FCC plants are investigated in a cold pilot plant. The results are checked and completed with measurements made in real operating FCC units. In both cases, tracing of the gas, velocity probes and {gamma}-tomography were used. The gas and solid velocity profiles are described by using a plug flow model with radial dispersion. The gas velocity profile is formally represented by an Ostwald - de Waele type equation; the radial and axial solid concentration profile is fitted to data obtained in the real plant. The kinetics of the reactions occurring during catalytic cracking are investigated in a MAT equipment and are represented by a 19 lumps model including deactivation by coking of the catalyst. A combination of this reaction model with the hydrodynamic model is able to predict with a satisfactory precision the yields of the different product families obtained in an industrial FCC unit. 12 refs., 3 tabs.

  5. Reducing the formation of FIB-induced FCC layers on Cu-Zn-Al austenite.

    PubMed

    Zelaya, Eugenia; Schryvers, Dominique

    2011-01-01

    The irradiation effects of thinning a sample of a Cu-Zn-Al shape memory alloy to electron transparency by a Ga(+) focused ion beam were investigated. This thinning method was compared with conventional electropolishing and Ar(+) ion milling. No implanted Ga was detected but surface FCC precipitation was found as a result of the focused ion beam sample preparation. Decreasing the irradiation dose by lowering the energy and current of the Ga(+) ions did not lead to a complete disappearance of the FCC structure. The latter could only be removed after gentle Ar(+) ion milling of the sample. It was further concluded that the precipitation of the FCC is independent of the crystallographic orientation of the surface.

  6. Interdiffusion and Diffusion Mobility for fcc Ni-Co-Al Alloys

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Zhu, Naqiong; Wang, Hao; Lu, Xiao-Gang

    2017-03-01

    Ternary fcc Ni-Co-Al diffusion couples annealed at 1173 K (900 °C), 1373 K (1100 °C), and 1573 K (1300 °C) have been studied by using electron probe microanalysis. The interdiffusion coefficients were extracted using the Sauer-Freise and Whittle-Green methods from the measured concentration profiles of binary and ternary diffusion couples, respectively. Based on the diffusion coefficients reported in the literature and those determined in the present work, the diffusion mobilities for fcc Ni-Co-Al alloys were assessed. In general, reasonable agreements were reached and the resulted mobility database can be used to study the diffusion behavior of the ternary fcc Ni-Co-Al alloys in a wide composition range.

  7. Correlation-induced anomalies and extreme sensitivity in fcc-Pu

    SciTech Connect

    Chen, Shao-ping

    2008-01-01

    We have used GGA + U density functional theory to study the effects of correlation on the properties of fcc Pu. We found that the structural and elastic properties of fcc-Pu are highly sensitive to the Hubbard U parameter. Within an interval of 0.05 eV of the U parameter, the equilibrium lattice constants of fcc-Pu can change from 0.42 to 0.47 nm. While the bulk modulus can drop by a factor of 5 to 10. The pressure derivative, dB/dp, of the bulk modulus can rise dramatically from 5 to 15 and then drop to the negative values before recovering to the more normal values. These observations are partially supported by existing experiments and the prediction of a negative dB/dp need to be tested in future experiments.

  8. Progress towards next generation hadron colliders: FCC-hh, HE-LHC, and SPPC

    NASA Astrophysics Data System (ADS)

    Zimmermann, Frank; EuCARD-2 Extreme Beams Collaboration; Future Circular Collider (FCC) Study Collaboration

    2017-01-01

    A higher-energy circular proton collider is generally considered to be the only path available in this century for exploring energy scales well beyond the reach of the Large Hadron Collider (LHC) presently in operation at CERN. In response to the 2013 Update of the European Strategy for Particle Physics and aligned with the 2014 US ``P5'' recommendations, the international Future Circular Collider (FCC) study, hosted by CERN, is designing such future frontier hadron collider. This so-called FCC-hh will provide proton-proton collisions at a centre-of-mass energy of 100 TeV, with unprecedented luminosity. The FCC-hh energy goal is reached by combining higher-field, 16 T magnets, based on Nb3Sn superconductor, and a new 100 km tunnel connected to the LHC complex. In addition to the FCC-hh proper, the FCC study is also exploring the possibility of a High-Energy LHC (HE-LHC), with a centre-of-mass energy of 25-27 TeV, as could be achieved in the existing 27 km LHC tunnel using the FCC-hh magnet technology. A separate design effort centred at IHEP Beijing aims at developing and constructing a similar collider in China, with a smaller circumference of about 54 km, called SPPC. Assuming even higher-field 20 T magnets, by relying on high-temperature superconductor, the SPPC could reach a c.m. energy of about 70 TeV. This presentation will report the motivation and the present status of the R&D for future hadron colliders, a comparison of the three designs under consideration, the major challenges, R&D topics, the international technology programs, and the emerging global collaboration. Work supported by the European Commission under Capacities 7th Framework Programme project EuCARD-2, Grant Agreement 312453, and the HORIZON 2020 project EuroCirCol, Grant Agreement 654305.

  9. Transition-sized Au92 nanoparticle bridging non-fcc-structured gold nanoclusters and fcc-structured gold nanocrystals.

    PubMed

    Liao, Lingwen; Chen, Jishi; Wang, Chengming; Zhuang, Shengli; Yan, Nan; Yao, Chuanhao; Xia, Nan; Li, Lingling; Bao, Xiaoli; Wu, Zhikun

    2016-10-04

    Herein, we report the intriguing structure, optical absorption and electrochemical properties of the transition-sized Au92(TBBT)44 (Au92 for short, TBBT = 4-tert-butylbenzenethiolate) nanoparticle. An interesting observation is the 4H phase array of Au92 nanoparticles in the unit cells of single crystals.

  10. Dissipation by a crystallization process

    NASA Astrophysics Data System (ADS)

    Dorosz, Sven; Voigtmann, Thomas; Schilling, Tanja

    2016-01-01

    We discuss crystallization as a non-equilibrium process. In a system of hard spheres under compression at a constant rate, we quantify the amount of heat that is dissipated during the crystallization process. We interpret the dissipation as arising from the resistance of the system against phase transformation. An intrinsic compression rate is identified that separates a quasi-static regime from one of rapidly driven crystallization. In the latter regime the system crystallizes more easily, because new relaxation channels are opened, at the cost of forming a higher fraction of non-equilibrium crystal structures. We rationalize the change in the crystallization mechanism by analogy with shear thinning, in terms of a kinetic competition between near-equilibrium relaxation and external driving.

  11. Learning in compressed space.

    PubMed

    Fabisch, Alexander; Kassahun, Yohannes; Wöhrle, Hendrik; Kirchner, Frank

    2013-06-01

    We examine two methods which are used to deal with complex machine learning problems: compressed sensing and model compression. We discuss both methods in the context of feed-forward artificial neural networks and develop the backpropagation method in compressed parameter space. We further show that compressing the weights of a layer of a multilayer perceptron is equivalent to compressing the input of the layer. Based on this theoretical framework, we will use orthogonal functions and especially random projections for compression and perform experiments in supervised and reinforcement learning to demonstrate that the presented methods reduce training time significantly. Copyright © 2013 Elsevier Ltd. All rights reserved.

  12. Optomechanics of two- and three-dimensional soft photonic crystals

    NASA Astrophysics Data System (ADS)

    Krishnan, Dwarak

    Soft photonic crystals are a class of periodic dielectric structures that undergo highly nonlinear deformation due to strain or other external stimulus such as temperature, pH etc. This can in turn dramatically affect optical properties such as light transmittance. Moreover certain classes of lithographically fabricated structures undergo some structural distortion due to the effects of processing, eventually affecting the optical properties of the final photonic crystal. In this work, we study the deformation mechanics of soft photonic crystal structures using realistic physics-based models and leverage that understanding to explain the optomechanics of actual 2-D and 3-D soft photonic crystals undergoing similar symmetry breaking nonlinear deformations. We first study the optomechanics of two classes of 3-D soft photonic crystals: (1) hydrogel and (2) elastomer based material systems. The hydrogel based inverse face-centered-cubic structure undergoes swelling with change in pH of the surrounding fluid. The inverse structure is a network of bulky domains with thin ligament-like connections, and it undergoes a pattern transformation from FCC to L11 as a result of swelling. A continuum scale poroelasticity based coupled fluid-diffusion FEM model is developed to accurately predict this mechanical behavior. Light transmittance simulation results qualitatively explain the experimentally observed trends in the optical behavior with pH change. The elastomer based, lithographically fabricated material experiences shrinkage induced distortion upon processing. This behavior is modeled using FEM with the material represented by a neo-Hookean constitutive law. The light transmittance calculations for normal incidence are carried out using the transfer matrix method and a good comparison is obtained for the positions of first and second order reflectance peaks. A unit cell based approach is taken to compute the photonic bandstructure to estimate light propagation through the

  13. Deformation Banding and Grain Refinement in FCC Materials

    DTIC Science & Technology

    2003-03-01

    recent review of observed textures in common deformation processes is provided by Hosford [Ref. 66] and Kocks et al [Ref. 67]. In general, plastic...Sevillano et al. [Ref. 65]. Hosford [Ref. 66] and Kocks et al. [Ref. 67] have provided a more recent review of textures found in association with...Aernoudt, Progress in Materials Science, vol. 25, pp. 69-412, 1980. 66. W.F. Hosford , The Mechanics of Crystals and Textured Polycrystals, pp. 128- 138

  14. Observation of the fcc-to-hcp transition in ensembles of argon nanoclusters.

    PubMed

    Krainyukova, N V; Boltnev, R E; Bernard, E P; Khmelenko, V V; Lee, D M; Kiryukhin, V

    2012-12-14

    Macroscopic ensembles of weakly interacting argon nanoclusters are studied using x-ray diffraction in low vacuum. As the clusters grow by fusion with increasing temperature, their structure transforms from essentially face-centered cubic (fcc) to hexagonal close packed as the cluster size approaches ~10(5) atoms. The transformation involves intermediate orthorhombic phases. These data confirm extant theoretical predictions. They also indicate that growth kinetics and spatial constraints might play an important role in the formation of the fcc structure of bulk rare-gas solids, which still remains puzzling.

  15. Magnetic phases of fcc Fe films in the 5{endash}11 monolayer thickness range

    SciTech Connect

    Escorcia-Aparicio, E.J.; Choi, H.J.; Kawakami, R.K.; Qiu, Z.Q.

    1998-07-01

    Using the methods of artificial roughening and interfacial doping, we investigated the effects of film roughness and interdiffusion on the formation of the magnetic phase of the fcc Fe film in the Fe/Co/Cu(100) system. We found that it is the degree of film roughness that determines the magnetic phase of the fcc Fe film in the 5{endash}11 monolayer thickness range, and that the interdiffusion plays no appreciable role in the formation of the magnetic phase. {copyright} {ital 1998} {ital The American Physical Society}

  16. Effects of Dynamic Impact Loading on Microstructure of FCC (TWIP) Steel

    DTIC Science & Technology

    2014-08-01

    Gazder, 2011, Texture evolution of cold rolled and annealed Fe-24 Mn-3 Al-2Si-1Ni-0.06C TWIP steel , Mater Sci. Eng. A, 528, 4537-4549. 13. J.K. Kim, L...representatively in the current investigation. Figure 9(a) shows the typical rolling texture components in FCC alloys [12] as reference, consisting of ideal...Figure 9: (1 1 1) pole figures of the (a) ideal rolling texture components in FCC materials, and (b) original, (c) Specimen 1, (d) Specimen 2, (e

  17. Beam-beam and electron cloud effects in CEPC/FCC-ee

    NASA Astrophysics Data System (ADS)

    Ohmi, Kazuhito

    2016-11-01

    We discuss beam dynamics issues in CEPC/FCC-ee, especially focusing on the beam-beam and electron cloud effects. Beamstrahlung is strong in extreme high energy collision such as Higgs and top factory. Beam-beam simulations considering beamstrahlung are now ready. Several points of beam-beam effects for FCC-ee are presented. Electron cloud effects are serious for high current positron machine, especially in Z factory that many bunches are stored. Analytical estimate for threshold of electron density and electron build-up for CEPC are presented.

  18. Micromagnetic simulations of interacting dipoles on an fcc lattice: application to nanoparticle assemblies.

    PubMed

    Plumer, M L; van Lierop, J; Southern, B W; Whitehead, J P

    2010-07-28

    Micromagnetic simulations are used to examine the effects of cubic and axial anisotropy, magnetostatic interactions and temperature on M-H loops for a collection of magnetic dipoles on fcc and sc lattices. We employ a simple model of interacting dipoles that represent single-domain particles in an attempt to explain recent experimental data on ordered arrays of magnetoferritin nanoparticles that demonstrate the crucial role of interactions between particles in an fcc lattice. Significant agreement between the simulation and experimental results is achieved, and the impact of intra-particle degrees of freedom and surface effects on thermal fluctuations is investigated.

  19. Molecular dynamics study of melting and fcc-bcc transitions in Xe.

    PubMed

    Belonoshko, A B; Ahuja, R; Johansson, B

    2001-10-15

    We have investigated the phase diagram of Xe over a wide pressure-temperature range by molecular dynamics. The calculated melting curve is in good agreement with earlier experimental data. At a pressure of around 25 GPa and a temperature of about 2700 K we find a triple fcc-bcc liquid point. The calculated fcc-bcc boundary is in nice agreement with the experimental points, which, however, were interpreted as melting. This finding suggests that the transition from close-packed to bcc structure might be more common at high pressure and high temperature than was previously anticipated.

  20. Compression in leg ulcer treatment: inelastic compression.

    PubMed

    Mosti, Giovanni

    2014-05-01

    Compression therapy is extremely effective in promoting ulcer healing. Which material to use, if elastic or inelastic, is still a matter of debate. This paper will provide an overview on the recent findings in compression therapy mainly for venous or mixed ulcers which are the great majority of leg ulcers. In this paper it will be demonstrated that inelastic compression has been proved to be significantly more effective than elastic compression in reducing venous reflux, increasing venous pumping function and decreasing ambulatory venous hypertension. In addition it is comfortable, well accepted by patients and achieved an extremely high healing rate in venous ulcers. With reduced pressure inelastic compression is able to improve venous pumping function in patients with mixed ulcers without affecting but improving the arterial inflow. It will be also clearly shown that studies claiming a better effect of elastic compression compared to inelastic in favouring healing rate have significant methodological flaws making their conclusions at least doubtful. In conclusion inelastic- is significantly more effective than elastic compression in reducing ambulatory venous hypertension which is the main pathophysiological determinant of venous ulcers and demonstrated to be very effective in getting ulcer healing. New multicentric, randomized and controlled studies, without methodological flaws, will be necessary to prove that elastic- is at least as effective as inelastic compression or, maybe, more effective. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

  1. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  2. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  3. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  4. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  5. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  6. Tailoring of crystal phase and Néel temperature of cobalt monoxides nanocrystals with synthetic approach conditions

    NASA Astrophysics Data System (ADS)

    Ravindra, A. V.; Behera, B. C.; Padhan, P.; Lebedev, O. I.; Prellier, W.

    2014-07-01

    Cobalt monoxide (CoO) nanocrystals were synthesized by thermal decomposition of cobalt oleate precursor in a high boiling point organic solvent 1-octadecene. The X-ray diffraction pattern and transmission electron microscopy studies suggest that pure face-centered-cubic (fcc) phase of CoO can be synthesized in the temperature range of 569-575 K. Thermolysis product at higher synthesis temperature 585 K is a mixture of fcc and hexagonal-closed-packed (hcp) phases. These nanocrystals are single crystals of CoO and exhibit mixture of two types of morphologies; one is nearly spherical with 5-25 nm diameter, and other one is 5-10 nm thick flake. The pure fcc-CoO nanocrystals show enhanced, and mixture of fcc- and hcp-CoO nanocrystals show reduced antiferromagnetic ordering temperature. Such results provide new opportunities for optimizing and enhancing the properties and performance of cobalt oxide nanomaterials.

  7. Microbunching and RF Compression

    SciTech Connect

    Venturini, M.; Migliorati, M.; Ronsivalle, C.; Ferrario, M.; Vaccarezza, C.

    2010-05-23

    Velocity bunching (or RF compression) represents a promising technique complementary to magnetic compression to achieve the high peak current required in the linac drivers for FELs. Here we report on recent progress aimed at characterizing the RF compression from the point of view of the microbunching instability. We emphasize the development of a linear theory for the gain function of the instability and its validation against macroparticle simulations that represents a useful tool in the evaluation of the compression schemes for FEL sources.

  8. Compressed gas manifold

    DOEpatents

    Hildebrand, Richard J.; Wozniak, John J.

    2001-01-01

    A compressed gas storage cell interconnecting manifold including a thermally activated pressure relief device, a manual safety shut-off valve, and a port for connecting the compressed gas storage cells to a motor vehicle power source and to a refueling adapter. The manifold is mechanically and pneumatically connected to a compressed gas storage cell by a bolt including a gas passage therein.

  9. Compressible turbulent mixing: Effects of compressibility.

    PubMed

    Ni, Qionglin

    2016-04-01

    We studied by numerical simulations the effects of compressibility on passive scalar transport in stationary compressible turbulence. The turbulent Mach number varied from zero to unity. The difference in driven forcing was the magnitude ratio of compressive to solenoidal modes. In the inertial range, the scalar spectrum followed the k^{-5/3} scaling and suffered negligible influence from the compressibility. The growth of the Mach number showed (1) a first reduction and second enhancement in the transfer of scalar flux; (2) an increase in the skewness and flatness of the scalar derivative and a decrease in the mixed skewness and flatness of the velocity-scalar derivatives; (3) a first stronger and second weaker intermittency of scalar relative to that of velocity; and (4) an increase in the intermittency parameter which measures the intermittency of scalar in the dissipative range. Furthermore, the growth of the compressive mode of forcing indicated (1) a decrease in the intermittency parameter and (2) less efficiency in enhancing scalar mixing. The visualization of scalar dissipation showed that, in the solenoidal-forced flow, the field was filled with the small-scale, highly convoluted structures, while in the compressive-forced flow, the field was exhibited as the regions dominated by the large-scale motions of rarefaction and compression.

  10. Compression of nanowires using a flat indenter: diametrical elasticity measurement.

    PubMed

    Wang, Zhao; Mook, William M; Niederberger, Christoph; Ghisleni, Rudy; Philippe, Laetitia; Michler, Johann

    2012-05-09

    A new experimental approach for the characterization of the diametrical elastic modulus of individual nanowires is proposed by implementing a micro/nanoscale diametrical compression test geometry, using a flat punch indenter. A 250 nm diameter single crystal silicon nanowire is compressed inside of a scanning electron microscope. Since silicon is highly anisotropic, the wire crystal orientation in the compression axis is determined by electron backscatter diffraction. In order to analyze the load-displacement compression data, a two-dimensional analytical closed-form solution based on a classical contact model is proposed. The results of the analytical model are compared with those of finite element simulations and to the experimental diametrical compression results and show good agreement.

  11. Negative linear compressibility in common materials

    NASA Astrophysics Data System (ADS)

    Miller, W.; Evans, K. E.; Marmier, A.

    2015-06-01

    Negative linear compressibility (NLC) is still considered an exotic property, only observed in a few obscure crystals. The vast majority of materials compress axially in all directions when loaded in hydrostatic compression. However, a few materials have been observed which expand in one or two directions under hydrostatic compression. At present, the list of materials demonstrating this unusual behaviour is confined to a small number of relatively rare crystal phases, biological materials, and designed structures, and the lack of widespread availability hinders promising technological applications. Using improved representations of elastic properties, this study revisits existing databases of elastic constants and identifies several crystals missed by previous reviews. More importantly, several common materials—drawn polymers, certain types of paper and wood, and carbon fibre laminates—are found to display NLC. We show that NLC in these materials originates from the misalignment of polymers/fibres. Using a beam model, we propose that maximum NLC is obtained for misalignment of 26°. The existence of such widely available materials increases significantly the prospects for applications of NLC.

  12. Negative linear compressibility in common materials

    SciTech Connect

    Miller, W.; Evans, K. E.; Marmier, A.

    2015-06-08

    Negative linear compressibility (NLC) is still considered an exotic property, only observed in a few obscure crystals. The vast majority of materials compress axially in all directions when loaded in hydrostatic compression. However, a few materials have been observed which expand in one or two directions under hydrostatic compression. At present, the list of materials demonstrating this unusual behaviour is confined to a small number of relatively rare crystal phases, biological materials, and designed structures, and the lack of widespread availability hinders promising technological applications. Using improved representations of elastic properties, this study revisits existing databases of elastic constants and identifies several crystals missed by previous reviews. More importantly, several common materials-drawn polymers, certain types of paper and wood, and carbon fibre laminates-are found to display NLC. We show that NLC in these materials originates from the misalignment of polymers/fibres. Using a beam model, we propose that maximum NLC is obtained for misalignment of 26°. The existence of such widely available materials increases significantly the prospects for applications of NLC.

  13. Elastic constants of random solid solutions by SQS and CPA approaches: the case of fcc Ti-Al.

    PubMed

    Tian, Li-Yun; Hu, Qing-Miao; Yang, Rui; Zhao, Jijun; Johansson, Börje; Vitos, Levente

    2015-08-12

    Special quasi-random structure (SQS) and coherent potential approximation (CPA) are techniques widely employed in the first-principles calculations of random alloys. Here we scrutinize these approaches by focusing on the local lattice distortion (LLD) and the crystal symmetry effects. We compare the elastic parameters obtained from SQS and CPA calculations, taking the random face-centered cubic (fcc) Ti(1-x)Al(x) (0 ≤ x ≤ 1) alloy as an example of systems with components showing different electronic structures and bonding characteristics. For the CPA and SQS calculations, we employ the Exact Muffin-Tin Orbitals (EMTO) method and the pseudopotential method as implemented in the Vienna Ab initio Simulation Package (VASP), respectively. We show that the predicted trends of the VASP-SQS and EMTO-CPA parameters against composition are in good agreement with each other. The energy associated with the LLD increases with x up to x = 0.625 ~ 0.750 and drops drastically thereafter. The influence of the LLD on the lattice constants and C12 elastic constant is negligible. C11 and C44 decrease after atomic relaxation for alloys with large LLD, however, the trends of C11 and C44 are not significantly affected. In general, the uncertainties in the elastic parameters associated with the symmetry lowering turn out to be superior to the differences between the two techniques including the effect of LLD.

  14. Interface effect of magnetic properties in Ni nanoparticles with a hcp core and fcc shell structure.

    PubMed

    Choo, Seongmin; Lee, Kyujoon; Jo, Younghun; Yoon, Seon-Mi; Choi, Jae-Young; Kim, Jea-Young; Park, Jea-Hoon; Lee, Kyung-Jin; Lee, Jong-Heun; Jung, Myung-Hwa

    2011-07-01

    We have fabricated hexagonal close-packed (hcp) Ni nanoparticles covered by a face-centered cubic (fcc) Ni surface layer by polyol method. The magnetic properties have been investigated as a function of temperature and applied magnetic field. The magnetic behavior reveals that the system should be divided magnetically into three distinct phases with different origins. The fcc Ni phase on the shell contributes to the superparamagnetism through a wide temperature range up to 360 K. The hcp Ni phase at the core is associated with antiferromagnetic nature below 12 K. These observations are in good agreement with the X-ray absorption spectroscopy and magnetic circular dichroism measurements. In our particular case, the unique hcp core and fcc shell structure gives rise to an additional anomaly at 20 K in the zero-field-cooled magnetization curve. Its position is barely affected by the magnetic field but its structure disappears above 30 kOe, showing a metamagnetic transition in the magnetization versus magnetic field curve. This new phase originates from the magnetic exchange at the interface between the hcp and fcc Ni sublattices.

  15. Nitrogen Chemistry and Coke Transformation of FCC Coked Catalyst during the Regeneration Process

    PubMed Central

    Shi, Junjun; Guan, Jianyu; Guo, Dawei; Zhang, Jiushun; France, Liam John; Wang, Lefu; Li, Xuehui

    2016-01-01

    Regeneration of the coked catalyst is an important process of fluid catalytic cracking (FCC) in petroleum refining, however, this process will emit environmentally harmful gases such as nitrogen and carbon oxides. Transformation of N and C containing compounds in industrial FCC coke under thermal decomposition was investigated via TPD and TPO to examine the evolved gaseous species and TGA, NMR and XPS to analyse the residual coke fraction. Two distinct regions of gas evolution are observed during TPD for the first time, and they arise from decomposition of aliphatic carbons and aromatic carbons. Three types of N species, pyrrolic N, pyridinic N and quaternary N are identified in the FCC coke, the former one is unstable and tends to be decomposed into pyridinic and quaternary N. Mechanisms of NO, CO and CO2 evolution during TPD are proposed and lattice oxygen is suggested to be an important oxygen resource. Regeneration process indicates that coke-C tends to preferentially oxidise compared with coke-N. Hence, new technology for promoting nitrogen-containing compounds conversion will benefit the in-situ reduction of NO by CO during FCC regeneration. PMID:27270486

  16. Exchange coupled L10-FePt/fcc-FePt nanomagnets: Synthesis, characterization and magnetic properties

    NASA Astrophysics Data System (ADS)

    Srivastava, Sachchidanand; Gajbhiye, Namdeo S.

    2016-03-01

    We report synthesis, characterization and magnetic properties of exchange-coupled L10-FePt/fcc-FePt nanomagnets. Structural and morphological characterization of exchange-coupled L10-FePt/fcc-FePt was carried out by powder X-ray diffraction, Mössbauer spectroscopy and transmission electron microscopy. Rietveld refinement of powder X-ray diffraction pattern has been used to quantify L10-FePt and fcc-FePt phases present in samples. Room temperature Mössbauer spectroscopy showed sextets of both L10-FePt and fcc-FePt phases with their respective hyperfine interaction parameters. Transmission electron microscopic (TEM and HRTEM) images confirmed nanocrystalline nature of exchange-coupled nanomagnets with particle size ranges from 15 nm to 50 nm after annealing for different time at 700 °C. Room temperature magnetic studies showed ferromagnetic nature of nanomagnets and maximum energy product (BH)max~10.92 MGOe was obtained for sample containing 89.0% volume fraction of L10-FePt phase.

  17. Special Report: FCC Program Offers Schools and Libraries Steep Telecommunications Discounts.

    ERIC Educational Resources Information Center

    Crowe, Thomas K.

    1998-01-01

    In the Telecommunications Act of 1996, Congress directed the Federal Communications Commission (FCC) to establish the Universal Service program to provide financial support for communications services for all K-12 schools/libraries. A Washington telecommunications attorney discusses eligible services and the application process, and offers tips…

  18. 47 CFR 2.956 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false FCC inspection and submission of equipment for testing. 2.956 Section 2.956 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  19. 47 CFR 2.1076 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 1 2013-10-01 2013-10-01 false FCC inspection and submission of equipment for testing. 2.1076 Section 2.1076 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  20. 47 CFR 2.1076 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false FCC inspection and submission of equipment for testing. 2.1076 Section 2.1076 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...