Li, Minghai; Liu, Yongsheng; Bansil, Rama
2010-08-28
The kinetics of the transformation from the hexagonal packed cylinder (hex) phase to the face-centered-cubic (fcc) phase was simulated using Brownian dynamics for an ABA triblock copolymer in a selective solvent for the A block. The kinetics was obtained by instantaneously changing either the temperature of the system or the well-depth of the Lennard-Jones potential. Detailed analysis showed that the transformation occurred via a rippling mechanism. The simulation results indicated that the order-order transformation was a nucleation and growth process when the temperature of the system instantly jumped from 0.8 to 0.5. The time evolution of the structure factor obtained by Fourier transformation showed that the peak intensities of the hex and fcc phases could be fit well by an Avrami equation.
Assembly of body-centered cubic crystals in hard spheres.
Xu, W-S; Sun, Z-Y; An, L-J
2011-05-01
We investigate the crystallization of monodisperse hard spheres confined by two square patterned substrates (possessing the basic character of the body-centered cubic (bcc) crystal structure) at varying substrate separations via molecular dynamics simulation. Through slowly increasing the density of the system, we find that crystallization under the influence of square patterned substrates can set in at lower densities compared with the homogeneous crystallization. As the substrate separation decreases, the density, where crystallization occurs (i.e., pressure drops), becomes small. Moreover, two distinct regimes are identified in the plane of bcc particle fraction and density for the separation range investigated. For large substrate separations, the bcc particle fraction displays a local maximum as the density is increased, and the resulting formed crystals have a polycrystalline structure. However, and more importantly, another situation emerges for small substrate separations: the capillary effects (stemming from the presence of two substrates) overwhelm the bulk driving forces (stemming from the spontaneous thermal fluctuations in the bulk) during the densification, eventually resulting in the formation of a defect-free bcc crystal (unstable with respect to the bulk hard-sphere crystals) by using two square patterned substrates.
The quantization of the radii of coordination spheres cubic crystals and cluster systems
NASA Astrophysics Data System (ADS)
Melnikov, G.; Emelyanov, S.; Ignatenko, N.; Ignatenko, G.
2016-02-01
The article deals with the creation of an algorithm for calculating the radii of coordination spheres and coordination numbers cubic crystal structure and cluster systems in liquids. Solution has important theoretical value since it allows us to calculate the amount of coordination in the interparticle interaction potentials, to predict the processes of growth of the crystal structures and processes of self-organization of particles in the cluster system. One option accounting geometrical and quantum factors is the use of the Fibonacci series to construct a consistent number of focal areas for cubic crystals and cluster formation in the liquid.
Diffusion spectrum MRI using body-centered-cubic and half-sphere sampling schemes.
Kuo, Li-Wei; Chiang, Wen-Yang; Yeh, Fang-Cheng; Wedeen, Van Jay; Tseng, Wen-Yih Isaac
2013-01-15
The optimum sequence parameters of diffusion spectrum MRI (DSI) on clinical scanners were investigated previously. However, the scan time of approximately 30 min is still too long for patient studies. Additionally, relatively large sampling interval in the diffusion-encoding space may cause aliasing artifact in the probability density function when Fourier transform is undertaken, leading to estimation error in fiber orientations. Therefore, this study proposed a non-Cartesian sampling scheme, body-centered-cubic (BCC), to avoid the aliasing artifact as compared to the conventional Cartesian grid sampling scheme (GRID). Furthermore, the accuracy of DSI with the use of half-sphere sampling schemes, i.e. GRID102 and BCC91, was investigated by comparing to their full-sphere sampling schemes, GRID203 and BCC181, respectively. In results, smaller deviation angle and lower angular dispersion were obtained by using the BCC sampling scheme. The half-sphere sampling schemes yielded angular precision and accuracy comparable to the full-sphere sampling schemes. The optimum b(max) was approximately 4750 s/mm(2) for GRID and 4500 s/mm(2) for BCC. In conclusion, the BCC sampling scheme could be implemented as a useful alternative to the GRID sampling scheme. Combination of BCC and half-sphere sampling schemes, that is BCC91, may potentially reduce the scan time of DSI from 30 min to approximately 14 min while maintaining its precision and accuracy.
Kinetic pathways of sphere-to-cylinder transition in diblock copolymer melt under electric field.
Ly, D Q; Pinna, M; Honda, T; Kawakatsu, T; Zvelindovsky, A V M
2013-02-21
Phase transition from body-centered-cubic spheres to cylinders in a diblock copolymer melt under an external electric field is investigated by means of real-space dynamical self-consistent field theory. Different phase transition kinetic pathways and different cylindrical domains arrangements of the final phase are observed depending on the strength and direction of the applied electric field. Various transient states have been identified depending on the electric field being applied along [111], [100], and [110] directions. The electric field should be above a certain threshold value in order the transition to occur. A "dynamic critical exponent" of the transition is found to be about 3/2, consistent with other order-order transitions in diblock copolymers under electric field.
Thermodynamic signature of the dynamic glass transition in hard spheres.
Hermes, Michiel; Dijkstra, Marjolein
2010-03-17
We use extensive event-driven molecular dynamics simulations to study the thermodynamic, structural and dynamic properties of hard-sphere glasses. We determine the equation of state of the metastable fluid branch for hard spheres with a size polydispersity of 10%. Our results show a clear jump in the slope of the isothermal compressibility. The observation of a thermodynamic signature at the transition from a metastable fluid to a glassy state is analogous to the abrupt change in the specific heat or thermal expansion coefficient as observed for molecular liquids at the glass transition. The dynamic glass transition becomes more pronounced and shifts to higher densities for longer equilibration times.
Echoes of the Glass Transition in Athermal Soft Spheres
NASA Astrophysics Data System (ADS)
Morse, Peter K.; Corwin, Eric I.
2017-09-01
Recent theoretical advances have led to the creation of a unified phase diagram for the thermal glass and athermal jamming transitions. This diagram makes clear that, while related, the mode-coupling—or dynamic—glass transition is distinct from the jamming transition, occurring at a finite temperature and significantly lower density than the jamming transition. Nonetheless, we demonstrate a prejamming transition in athermal frictionless spheres which occurs at the same density as the mode-coupling transition and is marked by percolating clusters of locally rigid particles. At this density in both the thermal and athermal systems, individual motions of an extensive number of particles become constrained, such that only collective motion is possible. This transition, which is well below jamming, exactly matches the definition of collective behavior at the dynamical transition of glasses. Thus, we reveal that the genesis of rigidity in both thermal and athermal systems is governed by the same underlying topological transition in their shared configuration space.
Ytterbium: Transition at High Pressure from Face-Centered Cubic to Body-Centered Cubic Structure.
Hall, H T; Barnett, J D; Merrill, L
1963-01-11
Pressure of 40,000 atmospheres at 25 degrees C induces a phase transformation in ytterbium metal; the face-centered cubic structure changes to body-centered cubic. The radius of the atom changes from 1.82 to 1.75 A. At the same time the atom's volume decreases by 11 percent and the volume, observed macroscopically, decreases 3.2 percent.
Photoluminescence and electronic transitions in cubic silicon nitride
Museur, Luc; Zerr, Andreas; Kanaev, Andrei
2016-01-01
A spectroscopic study of cubic silicon nitride (γ-Si3N4) at cryogenic temperatures of 8 K in the near IR - VUV range of spectra with synchrotron radiation excitation provided the first experimental evidence of direct electronic transitions in this material. The observed photoluminescence (PL) bands were assigned to excitons and excited and centers formed after the electron capture by neutral structural defects. The excitons are weakly quenched on neutral and strongly on charged defects. The fundamental band-gap energy of 5.05 ± 0.05 eV and strong free exciton binding energy ~0.65 eV were determined. The latter value suggests a high efficiency of the electric power transformation in light in defect-free crystals. Combined with a very high hardness and exceptional thermal stability in air, our results indicate that γ-Si3N4 has a potential for fabrication of robust and efficient photonic emitters. PMID:26725937
Photoluminescence and electronic transitions in cubic silicon nitride.
Museur, Luc; Zerr, Andreas; Kanaev, Andrei
2016-01-04
A spectroscopic study of cubic silicon nitride (γ-Si3N4) at cryogenic temperatures of 8 K in the near IR - VUV range of spectra with synchrotron radiation excitation provided the first experimental evidence of direct electronic transitions in this material. The observed photoluminescence (PL) bands were assigned to excitons and excited and centers formed after the electron capture by neutral structural defects. The excitons are weakly quenched on neutral and strongly on charged defects. The fundamental band-gap energy of 5.05 ± 0.05 eV and strong free exciton binding energy ~0.65 eV were determined. The latter value suggests a high efficiency of the electric power transformation in light in defect-free crystals. Combined with a very high hardness and exceptional thermal stability in air, our results indicate that γ-Si3N4 has a potential for fabrication of robust and efficient photonic emitters.
Photoluminescence and electronic transitions in cubic silicon nitride
NASA Astrophysics Data System (ADS)
Museur, Luc; Zerr, Andreas; Kanaev, Andrei
2016-01-01
A spectroscopic study of cubic silicon nitride (γ-Si3N4) at cryogenic temperatures of 8 K in the near IR - VUV range of spectra with synchrotron radiation excitation provided the first experimental evidence of direct electronic transitions in this material. The observed photoluminescence (PL) bands were assigned to excitons and excited and centers formed after the electron capture by neutral structural defects. The excitons are weakly quenched on neutral and strongly on charged defects. The fundamental band-gap energy of 5.05 ± 0.05 eV and strong free exciton binding energy ~0.65 eV were determined. The latter value suggests a high efficiency of the electric power transformation in light in defect-free crystals. Combined with a very high hardness and exceptional thermal stability in air, our results indicate that γ-Si3N4 has a potential for fabrication of robust and efficient photonic emitters.
NASA Astrophysics Data System (ADS)
Sun, Jiu-Xun; Cai, Ling-Cang; Wu, Qiang; Jin, Ke
2013-09-01
Based on the expansion and extension of the virial equation of state (EOS) of hard-sphere fluids solved by the Percus-Yevick integration equation, a universal cubic (UC) EOS is developed. The UC EOS is applied to model hard-sphere and Lennard-Jones (LJ) fluids, simple Ar and N2 liquids at low temperatures, and supercritical Ar and N2 fluids at high temperatures, as well as ten solids, respectively. The three parameters are determined for the hard-sphere fluid by fitting molecular dynamics (MD) simulation data of the third to eighth virial coefficients in the literature; for other fluids by fitting isothermal compression data; and for solids by using the Einstein model. The results show that the UC EOS gives better results than the Carnahan-Starling EOS for compressibility of hard-sphere fluids. The Helmholtz free energy and internal energy for LJ fluids are predicted and compared with MD simulation data. The calculated pressures for simple Ar and N2 liquids are compared with experimental data. The agreement is fairly good. Eight three-parameter EOSs are applied to describe isothermals of ten typical solids. It is shown that the UC EOS gives the best precision with correct behavior at high-pressure limitation. The UC EOS considering thermal effects is used to analytically evaluate the isobaric thermal expansivity and isothermal compressibility coefficients. The results are in good agreement with experimental data.
Anomalous dynamics at the hard-sphere glass transition.
Kwaśniewski, Paweł; Fluerasu, Andrei; Madsen, Anders
2014-11-21
We use X-ray photon correlation spectroscopy to study the dynamics of hard sphere suspensions and report the emergence of ergodicity restoring anomalous intermittent relaxation modes in the highest concentration suspension that is estimated to be above the glass transition concentration. We associate these phenomena with non-thermal stress induced relaxations and support our interpretation by a direct comparison of the results with predictions of the mode coupling theory.
NASA Astrophysics Data System (ADS)
Tang, Chengchun; Bando, Yoshio; Huang, Yang; Zhi, Chunyi; Golberg, Dmitri; Xu, Xuewen; Zhao, Jianling; Li, YangXian
2010-03-01
Cubic spinel structured gallium oxynitride has been synthesized through the reaction of metallic gallium and water in the presence of organic ethylenediamine. The relative content of the mixed solvent of water and ethylenediamine controls the product morphology and structure. A novel well-defined nanoporous structure has finally been obtained, whose large surface area and peculiar surface chemistry will generate novel physical and chemical properties. As an example, lithium intercalation properties for prospective applications in lithium ion batteries are demonstrated in this work.
NASA Astrophysics Data System (ADS)
Sun, Jiu-Xun; Wu, Qiang; Cai, Ling-Cang; Jin, Ke
2013-11-01
A universal cubic equation of state (UC EOS) is proposed based on a modification of the virial Percus-Yevick (PY) integral equation EOS for hard-sphere fluid. The UC EOS is extended to multi-component hard-sphere mixtures based on a modification of Lebowitz solution of PY equation for hard-sphere mixtures. And expressions of the radial distribution functions at contact (RDFC) are improved with the form as simple as the original one. The numerical results for the compressibility factor and RDFC are in good agreement with the simulation results. The average errors of the compressibility factor relative to MC data are 3.40%, 1.84% and 0.92% for CP3P, BMCSL equations and UC EOS, respectively. The UC EOS is a unique cubic one with satisfactory precision among many EOSs in the literature both for pure and mixture fluids of hard spheres.
Shape transitions in soft spheres regulated by elasticity
NASA Astrophysics Data System (ADS)
Fogle, Craig; Rowat, Amy; Levine, Alex; Rudnick, Joseph
2014-03-01
Soft core shell structures abound in nature. Examples of these structures, comprised of a thin outer membrane bounding an elastic core, include raisins, gel-filled vesicles, and a variety of membrane-bound organelles in the cell. We study the elasticity-driven morphological transitions of spherical core shell structures when either their surface area is increased or their interior volume is decreased. We demonstrate a transition, which is related to the Euler buckling, from the spherical initial shape to a lower symmetry one. We discuss the dependence of the critical excess surface area (relative to that of a bounding sphere) for buckling, the internal stresses in the core, and the symmetry of the buckled state on the elastic parameters of the system. We compare these predictions to a variety of observed morphological transitions in hard and soft materials, and discuss extensions of this work to growing viscoelastic media.
Multiple reentrant glass transitions in confined hard-sphere glasses
NASA Astrophysics Data System (ADS)
Mandal, Suvendu; Lang, Simon; Gross, Markus; Oettel, Martin; Raabe, Dierk; Franosch, Thomas; Varnik, Fathollah
2014-07-01
Glass-forming liquids exhibit a rich phenomenology upon confinement. This is often related to the effects arising from wall-fluid interactions. Here we focus on the interesting limit where the separation of the confining walls becomes of the order of a few particle diameters. For a moderately polydisperse, densely packed hard-sphere fluid confined between two smooth hard walls, we show via event-driven molecular dynamics simulations the emergence of a multiple reentrant glass transition scenario upon a variation of the wall separation. Using thermodynamic relations, this reentrant phenomenon is shown to persist also under constant chemical potential. This allows straightforward experimental investigation and opens the way to a variety of applications in micro- and nanotechnology, where channel dimensions are comparable to the size of the contained particles. The results are in line with theoretical predictions obtained by a combination of density functional theory and the mode-coupling theory of the glass transition.
Deformation-induced structural transition in body-centred cubic molybdenum
Wang, S. J.; Wang, H.; Du, K.; Zhang, W.; Sui, M. L.; Mao, S. X.
2014-01-01
Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama–Wassermann and Kurdjumov–Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions. PMID:24603655
Deformation-induced structural transition in body-centred cubic molybdenum
NASA Astrophysics Data System (ADS)
Wang, S. J.; Wang, H.; Du, K.; Zhang, W.; Sui, M. L.; Mao, S. X.
2014-03-01
Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions.
Deformation-induced structural transition in body-centred cubic molybdenum.
Wang, S J; Wang, H; Du, K; Zhang, W; Sui, M L; Mao, S X
2014-03-07
Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions.
Mechanism of the body-centered cubic--hexagonal close-packed phase transition in iron.
Bassett, W A; Huang, E
1987-11-06
The transition from body-centered cubic to hexagonal close-packed phase in iron has been studied in a diamond anvil cell with synchrotron radiation. The hexagonal close-packed phase, when it first appears, has a ratio of lattice parameters that is significantly larger than normal. This is attributed to a displacive mechanism that causes a distortion of the hexagonal close-packed structure in a body-centered cubic matrix. The hexagonal close-packed phase adjacent to a boundary with the body-centered cubic phase is stretched in the c direction and compressed in the a direction when it first forms.
Squeezing of a periodic emulsion through a cubic lattice of spheres
NASA Astrophysics Data System (ADS)
Zinchenko, Alexander Z.; Davis, Robert H.
2008-04-01
Squeezing of a periodic, highly concentrated emulsion of deformable drops through a dense, simple cubic array of solid spherical particles at zero Reynolds number is simulated by considering one drop in a periodic cell. The particles are rigidly held in space. The drops with nondeformed diameter comparable with the particle size (and considerably larger than the interparticle constrictions) squeeze under a specified average pressure gradient. This three dimensional problem serves as a useful prototype model of drop-solid interaction for emulsion flow through granular materials. The solution allows us to study permeabilities for both phases in detail and determine the critical conditions when the drop phase flow stops due to blockage in the pores by capillary forces. The algorithm employs a boundary-integral formulation with periodic Green's function, Hebeker representation for solid-particle contributions, and recent desingularization tools [A. Z. Zinchenko and R. H. Davis, J. Fluid Mech. 564, 227 (2006)] to alleviate difficulties with lubrication. Calculations are challenging in that tens of thousands of boundary elements per surface and 10 000-20 000 time steps are required for near-critical squeezing conditions, and the use of multipole acceleration is crucial to make such simulations feasible. The results are presented for 36% and 50% concentrated emulsions flowing through an array of almost packed particles, at drop-to-medium viscosity ratios of 1 and 4. Scaling for the squeezing time of the drop phase at near-criticial capillary numbers is extracted from the calculations. For all the simulated cases, the drops move, on average, faster than the continuous phase.
Jamming transition and inherent structures of hard spheres and disks.
Ozawa, Misaki; Kuroiwa, Takeshi; Ikeda, Atsushi; Miyazaki, Kunimasa
2012-11-16
Recent studies show that volume fractions φ(J) at the jamming transition of frictionless hard spheres and disks are not uniquely determined but exist over a continuous range. Motivated by this observation, we numerically investigate the dependence of φ(J) on the initial configurations of the parent fluid equilibrated at a volume fraction φ(eq), before compressing to generate a jammed packing. We find that φ(J) remains constant when φ(eq) is small but sharply increases as φ(eq) exceeds the dynamic transition point which the mode-coupling theory predicts. We carefully analyze configurational properties of both jammed packings and parent fluids and find that, while all jammed packings remain isostatic, the increase of φ(J) is accompanied with subtle but distinct changes of local orders, a static length scale, and an exponent of the finite-size scaling. These results are consistent with the scenario of the random first-order transition theory of the glass transition.
Phase Transition of a Structure II Cubic Clathrate Hydrate to a Tetragonal Form.
Takeya, Satoshi; Fujihisa, Hiroshi; Yamawaki, Hiroshi; Gotoh, Yoshito; Ohmura, Ryo; Alavi, Saman; Ripmeester, John A
2016-08-01
The crystal structure and phase transition of cubic structure II (sII) binary clathrate hydrates of methane (CH4 ) and propanol are reported from powder X-ray diffraction measurements. The deformation of host water cages at the cubic-tetragonal phase transition of 2-propanol+CH4 hydrate, but not 1-propanol+CH4 hydrate, was observed below about 110 K. It is shown that the deformation of the host water cages of 2-propanol+CH4 hydrate can be explained by the restriction of the motion of 2-propanol within the 5(12) 6(4) host water cages. This result provides a low-temperature structure due to a temperature-induced symmetry-lowering transition of clathrate hydrate. This is the first example of a cubic structure of the common clathrate hydrate families at a fixed composition.
Torija, Maria A; Choi, Soo-Hyung; Lodge, Timothy P; Bates, Frank S
2011-05-19
Small-angle X-ray diffraction experiments have uncovered a remarkable mechanism of grain alignment during plastic deformation of ordered sphere-forming diblock copolymer micelles when subjected to large amplitude dynamic shearing. A nearly monodisperse poly(styrene-b-ethylene-alt-propylene) (SEP) diblock copolymer with block molecular weights of 42,000 and 60,000 was mixed with squalane (C(30)H(62)), an EP selective solvent, at a concentration of 10 wt%. After high temperature annealing, the sample formed an ordered polydomain morphology containing glassy S cores at room temperature. SAXS powder patterns confirm body-centered cubic (BCC) symmetry and reveal the development of a complex array of two-dimensionally resolved Bragg reflections following the application, and cessation, of oscillatory shearing. These diffraction results are interpreted on the basis of the classic mechanism of crystalline slip, which accounts for plastic deformation of ductile materials such as metals. Four distinct slip systems are shown to be active in this work, suggesting a robust basis for deforming and mixing of soft ordered solids.
Fair cubic transition between two circles with one circle inside or tangent to the other
NASA Astrophysics Data System (ADS)
Dimulyo, Sarpono; Habib, Zulfiqar; Sakai, Manabu
2009-08-01
This paper describes a method for joining two circles with a C-shaped and an S-shaped transition curve, composed of a cubic Bézier segment. As an extension of our previous work; we show that a single cubic curve can be used for blending or for a transition curve preserving G 2 continuity regardless of the distance of their centers and magnitudes of the radii which is an advantage. Our method with shape parameter provides freedom to modify the shape in a stable manner.
Collapse transition of short polymers on simple cubic lattice
NASA Astrophysics Data System (ADS)
Jaleel, Asweel Ahmed A.; Satyanarayana, S. V. M.
2016-10-01
Denatured proteins and polymers exhibit two types of conformations in solution. Extended coil conformation and compact globule conformation. There is a phase transition associated with these conformation change as a function of temperature or solvent concentration etc. These phase transition is usually studied using Self Avoiding Walk(SAW). We have generated Self avoiding walk using chain growth algorithm. Here we have compared our generated density of states with Exact enumerated data of the same. Also we have presented the Pseudo order parameter method to identify collapse temperature. The results are compared with Partition function zero analysis.
Pollen Patterning as a Brazovskii Phase Transition on a Sphere
NASA Astrophysics Data System (ADS)
Lavrentovich, Maxim; Horsley, Eric; Radja, Asja; Sweeney, Alison; Kamien, Randall
Pollen grains acquire intricate, varied surface patterns during development. The patterns are reproducible within a single plant species, and yet exhibit a wide variation among species, despite having similar developmental steps. We model this pattern formation on spherical grains as a phase transition to a spatially modulated phase, characterized by an unstable wavelength λ0. On the infinite, flat plane, the patterned phase consists of uniform stripes, as shown by Brazovskii. We find that, by contrast, the patterns may be much more varied on a spherical surface because the topological defects which must be present in the pattern may be accommodated in a variety of ways. This variation may explain the wide range of observed pollen patterns. We also argue that the first-order character of the transition may be responsible for the robust reproducibility of the patterns in a single plant species. Finally, we compute the free energy difference between the unpatterned, smooth phase and various patterned phases on the sphere. These calculations point toward possible future experimental tests of our model.
2014-09-09
ISS040-E-139549 (9 Sept. 2014) --- In the International Space Station’s Kibo laboratory, NASA astronaut Reid Wiseman, Expedition 40 crew member, works with the bowling ball-sized satellites known as SPHERES (Synchronized Position Hold Engage Reorient Experimental Satellites) to study how liquids behave inside containers in microgravity. The experiment, named SPHERES-Slosh, maneuvers the tiny satellites similar to an actual spacecraft with an externally mounted tank and observes the interaction between the sloshing fluid and the tank/vehicle dynamics.
2013-08-08
Astronaut Karen Nyberg, Expedition 36 flight engineer, conducts a session with the bowling-ball-sized free-flying satellite known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES in the International Space Stations Japanese Experiment Module (JEM) Kibo laboratory. Also sent as Twitter message.
2009-07-11
ISS020-E-019064 (11 July 2009) --- NASA astronaut Michael Barratt (left) and Japan Aerospace Exploration Agency (JAXA) astronaut Koichi Wakata, both Expedition 20 flight engineers, perform a check of the Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) Beacon / Beacon Tester in the Destiny laboratory of the International Space Station.
2009-07-13
ISS020-E-018319 (11 July 2009) --- NASA astronaut Michael Barratt (left) and Japan Aerospace Exploration Agency (JAXA) astronaut Koichi Wakata, both Expedition 20 flight engineers, perform a check of the Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) Beacon / Beacon Tester in the Destiny laboratory of the International Space Station.
2009-07-11
ISS020-E-019069 (11 July 2009) --- Japan Aerospace Exploration Agency (JAXA) astronaut Koichi Wakata, Expedition 20 flight engineer, is pictured near three Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) floating freely in the Harmony node of the International Space Station.
2009-07-13
ISS020-E-018324 (11 July 2009) --- NASA astronaut Michael Barratt (left) and Japan Aerospace Exploration Agency (JAXA) astronaut Koichi Wakata, both Expedition 20 flight engineers, perform a check of the Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) Beacon / Beacon Tester in the Destiny laboratory of the International Space Station.
2009-06-26
ISS020-E-014670 (26 June 2009) --- Japan Aerospace Exploration Agency (JAXA) astronaut Koichi Wakata, Expedition 20 flight engineer, is pictured near two Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) floating freely in the Harmony node of the International Space Station.
2009-07-13
ISS020-E-018325 (11 July 2009) --- NASA astronaut Michael Barratt (left) and Japan Aerospace Exploration Agency (JAXA) astronaut Koichi Wakata, both Expedition 20 flight engineers, perform a check of the Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) Beacon / Beacon Tester in the Destiny laboratory of the International Space Station.
2009-07-11
ISS020-E-019059 (11 July 2009) --- NASA astronaut Michael Barratt, Expedition 20 flight engineer, writes notes while performing a check of the Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) Beacon / Beacon Tester in the Destiny laboratory of the International Space Station.
2013-08-08
ISS036-E-029545 (7 Aug. 2013) --- In the International Space Station’s Kibo laboratory, NASA astronaut Karen Nyberg, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Nyberg and NASA astronaut Chris Cassidy (not pictured) put the miniature satellites through their paces for a dry run of the SPHERES Zero Robotics tournament scheduled for Aug. 13. Teams of middle school students from Florida, Georgia, Idaho and Massachusetts will gather at the Massachusetts Institute of Technology in Cambridge to see which teams’ algorithms do the best job of commanding the free-flying robots through a series of maneuvers and objectives.
2013-08-08
ISS036-E-029521 (7 Aug. 2013) --- In the International Space Station’s Kibo laboratory, NASA astronaut Karen Nyberg, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Nyberg and NASA astronaut Chris Cassidy (not pictured) put the miniature satellites through their paces for a dry run of the SPHERES Zero Robotics tournament scheduled for Aug. 13. Teams of middle school students from Florida, Georgia, Idaho and Massachusetts will gather at the Massachusetts Institute of Technology in Cambridge to see which teams’ algorithms do the best job of commanding the free-flying robots through a series of maneuvers and objectives.
2013-08-08
ISS036-E-029539 (7 Aug. 2013) --- In the International Space Station’s Kibo laboratory, NASA astronaut Karen Nyberg, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Nyberg and NASA astronaut Chris Cassidy (not pictured) put the miniature satellites through their paces for a dry run of the SPHERES Zero Robotics tournament scheduled for Aug. 13. Teams of middle school students from Florida, Georgia, Idaho and Massachusetts will gather at the Massachusetts Institute of Technology in Cambridge to see which teams’ algorithms do the best job of commanding the free-flying robots through a series of maneuvers and objectives.
2013-08-08
ISS036-E-029522 (7 Aug. 2013) --- In the International Space Station’s Kibo laboratory, NASA astronaut Karen Nyberg, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Nyberg and NASA astronaut Chris Cassidy (not pictured) put the miniature satellites through their paces for a dry run of the SPHERES Zero Robotics tournament scheduled for Aug. 13. Teams of middle school students from Florida, Georgia, Idaho and Massachusetts will gather at the Massachusetts Institute of Technology in Cambridge to see which teams’ algorithms do the best job of commanding the free-flying robots through a series of maneuvers and objectives.
On structural transitions in a discontinuous micellar cubic phase loaded with sodium diclofenac.
Efrat, R; Aserin, A; Garti, N
2008-05-01
An intermediate mesophase of lyotropic liquid crystalline structure from the ternary mixtures of glycerol monooleate, water, and ethanol was recently characterized in our lab. This mesophase, termed Q(L), consists of discrete discontinuous micelles arranged in a cubic array. The Q(L) phase can solubilize very significant loads of water-insoluble anti-inflamatory drug sodium diclofenac (Na-DFC). Close examination of the internal structures of the lyotropic liquid structure upon increasing the solubilization loads reveals the existence of three structural transitions controlled by the Na-DFC levels. Up to 0.4 wt% Na-DFC, the Q(L) structure remains intact with some influence on the hydration of the headgroups and on the intermicellar forces. However, at 0.8 to 1.2 wt% Na-DFC, the discontinuous micellar cubic phase is transformed into a more condensed mesophase of a bicontinuous cubic phase. At > or =1.2 wt% Na-DFC, the cubic phase is converted into a lamellar phase (L(alpha)). Within 5.5 to 7.3 wt% Na-DFC the mesophase is progressively transformed into a less ordered lamellar structure. At 12 wt% Na-DFC crystals tend to precipitate out. At low Na-DFC concentrations the drug behaves like a lyotropic or kosmotropic salt and can salt-out the surfactant from its water layer, but at higher levels it behaves like a hydrotropic, chaotropic salt and can salt-in the surfactant. The Na-DFC location and position within the interface as well as its polarization and partial ionization are strongly affected by its solubilization contents and the structure that it is inducing. In the cubic phase the drug is located less close to the hydration layer while once transition occurs it is exposed more to the water layer and the surfactant headgroups.
Manaka, Hirotaka; Yagi, Genta; Miura, Yoko
2016-07-01
Optical birefringence imaging systems demonstrate a high potential for comprehensively investigating various phase transitions. To completely demonstrate such abilities, the temperature dependence of birefringence (Δn) was measured in Δn ≃ 0 materials (i.e., cubic crystals with imperfect crystallization) via a background subtraction method. As a result, highly accurate birefringence imaging at 384 × 288 pixels was obtained using phase transition processes as well as varying temperatures visually characterized by the spatial distribution of not only the retardance level but also the optical fast-axis azimuth.
NASA Astrophysics Data System (ADS)
Manaka, Hirotaka; Yagi, Genta; Miura, Yoko
2016-07-01
Optical birefringence imaging systems demonstrate a high potential for comprehensively investigating various phase transitions. To completely demonstrate such abilities, the temperature dependence of birefringence (Δn) was measured in Δn ≃ 0 materials (i.e., cubic crystals with imperfect crystallization) via a background subtraction method. As a result, highly accurate birefringence imaging at 384 × 288 pixels was obtained using phase transition processes as well as varying temperatures visually characterized by the spatial distribution of not only the retardance level but also the optical fast-axis azimuth.
Nature of the cubic to tetragonal phase transition in methylammonium lead iodide perovskite.
Saidi, Wissam A; Choi, Joshua J
2016-10-14
Hybrid organic-inorganic perovskites, as well as the perovskites in general, are known for their phase complexity evidenced by the stabilization of different polymorphs, and thus an understanding of their regions of stability and transitions can be important for their photovoltaic and optoelectronic technologies. Here we use a multiscale approach based on first-principles calculations with van der Waals corrections and classical force-field molecular dynamics to determine the finite-temperature properties of the tetragonal and cubic phases of CH3NH3PbI3. Temperature effects are implicitly included using the quasi-harmonic approximation that can describe anharmonic behavior due to thermal expansion through the dependence of the harmonic frequencies on structural parameters. Our finite-temperature free-energy surfaces predict the lattice and elastic moduli evolution with temperature, and show in particular that the calculated lattice parameters of the cubic and tetragonal phases are to within 1% of experimental values. Further, our results show that the phonons are the major contributing factor for stabilizing the cubic phase at high temperatures mainly due to the low-energy phonon modes that are associated with the inorganic lattice. On the other hand, the configurational entropy due to CH3NH3(+) rotational degrees of freedom is slightly more favored in the cubic phase and amounts to less than 0.2% of the T = 0 K free-energy difference between the two phases.
Nature of the cubic to tetragonal phase transition in methylammonium lead iodide perovskite
NASA Astrophysics Data System (ADS)
Saidi, Wissam A.; Choi, Joshua J.
2016-10-01
Hybrid organic-inorganic perovskites, as well as the perovskites in general, are known for their phase complexity evidenced by the stabilization of different polymorphs, and thus an understanding of their regions of stability and transitions can be important for their photovoltaic and optoelectronic technologies. Here we use a multiscale approach based on first-principles calculations with van der Waals corrections and classical force-field molecular dynamics to determine the finite-temperature properties of the tetragonal and cubic phases of CH3NH3PbI3. Temperature effects are implicitly included using the quasi-harmonic approximation that can describe anharmonic behavior due to thermal expansion through the dependence of the harmonic frequencies on structural parameters. Our finite-temperature free-energy surfaces predict the lattice and elastic moduli evolution with temperature, and show in particular that the calculated lattice parameters of the cubic and tetragonal phases are to within 1% of experimental values. Further, our results show that the phonons are the major contributing factor for stabilizing the cubic phase at high temperatures mainly due to the low-energy phonon modes that are associated with the inorganic lattice. On the other hand, the configurational entropy due to CH3NH3+ rotational degrees of freedom is slightly more favored in the cubic phase and amounts to less than 0.2% of the T = 0 K free-energy difference between the two phases.
Non--Cubic Symmetry of the Electronic Response in AFM Late Transition--Metal Oxides.
NASA Astrophysics Data System (ADS)
Posternak, M.; Baldereschi, A.; Massidda, S.; Resta, R.
1998-03-01
The late transition--metal monoxides (MnO, FeO, CoO, NiO) have the rocksalt structure in their paramagnetic phase, while below the Neel temperature a weak structural distortion accompanies an AFM ordering of type II. Therefore, it is generally assumed that most nonmagnetic (i.e. spin--integrated) crystalline properties are essentially cubic: we give here convincing evidence of the contrary. We focus on the half--filled d shell oxide MnO as the most suitable case study, on which we perform accurate ab--initio, all--electron calculations, within different one--particle schemes. In order to study the symmetry lowering due to AFM ordering, we assume an ideal cubic geometry throughout. The calculated TO frequencies and Born effective charge tensor do not have cubic symmetry. The standard LSD severely exaggerates the deviations from cubic symmetry, confirming its unreliability for calculating properties of insulating AFM oxides, while a model self--energy correction scheme(S. Massidda et al.), Phys. Rev. B 55, 13494 (1997). reduces considerably the anisotropy. We also explain the origin and the magnitude of this effect in terms of the mixed charge--transfer/Mott--Hubbard character of MnO.
NASA Astrophysics Data System (ADS)
Sun, Jiu-Xun; Jin, Ke; Cai, Ling-Cang; Wu, Qiang
2014-08-01
The equation of state (EOS) for hard-sphere fluid derived from compressibility routes of Percus-Yevick theory (PYC) is extended. The two parameters are determined by fitting well-known virial coefficients of pure fluid. The extended cubic EOS can be directly extended to multi-component mixtures, merely demanding the EOS of mixtures also is cubic and combining two physical conditions for the radial distribution functions at contact (RDFC) of mixtures. The calculated virial coefficients of pure fluid and predicted compressibility factors and RDFC for both pure fluid and mixtures are excellent as compared with the simulation data. The values of RDFC for mixtures with extremely large size ratio 10 are far better than the BGHLL expressions in literature.
Cubic to tetragonal phase transition of Tm{sup 3+} doped nanocrystals in oxyfluoride glass ceramics
Li, Yiming; Fu, Yuting; Shi, Yahui; Zhang, Xiaoyu; Yu, Hua E-mail: yuhua@nankai.edu.cn; Zhao, Lijuan E-mail: yuhua@nankai.edu.cn
2016-02-15
Tm{sup 3+} ions doped β-PbF{sub 2} nanocrystals in oxyfluoride glass ceramics with different doping concentrations and thermal temperatures are prepared by a traditional melt-quenching and thermal treatment method to investigate the structure and the phase transition of Tm{sup 3+} doped nanocrystals. The structures are characterized by X-ray diffraction Rietveld analysis and confirmed with numerical simulation. The phase transitions are proved further by the emission spectra. Both of the doping concentration and thermal temperature can induce an O{sub h} to D{sub 4h} site symmetry distortion and a cubic to tetragonal phase transition. The luminescence of Tm{sup 3+} doped nanocrystals at 800 nm was modulated by the phase transition of the surrounding crystal field.
Superionic-Superionic Phase Transitions in Body-Centered Cubic H2O Ice
NASA Astrophysics Data System (ADS)
Hernandez, Jean-Alexis; Caracas, Razvan
2016-09-01
From first-principles molecular dynamics, we investigate the relation between the superionic proton conduction and the behavior of the O - H ⋯O bond (ice VII' to ice X transition) in body-centered-cubic (bcc) H2O ice between 1300 and 2000 K and up to 300 GPa. We bring evidence that there are three distinct phases in the superionic bcc stability field. A first superionic phase characterized by extremely fast diffusion of highly delocalized protons (denoted VII'' hereinafter) is stable at low pressures. A first-order transition separates this phase from a superionic VII' , characterized by a finite degree of localization of protons along the nonsymmetric O - H ⋯O bonds. The transition is identified in structural, energetic, and elastic analysis. Upon further compression a second-order phase transition leads to the superionic ice X with symmetric O - H - O bonds.
Superionic-Superionic Phase Transitions in Body-Centered Cubic H_{2}O Ice.
Hernandez, Jean-Alexis; Caracas, Razvan
2016-09-23
From first-principles molecular dynamics, we investigate the relation between the superionic proton conduction and the behavior of the O─H⋯O bond (ice VII^{'} to ice X transition) in body-centered-cubic (bcc) H_{2}O ice between 1300 and 2000 K and up to 300 GPa. We bring evidence that there are three distinct phases in the superionic bcc stability field. A first superionic phase characterized by extremely fast diffusion of highly delocalized protons (denoted VII^{''} hereinafter) is stable at low pressures. A first-order transition separates this phase from a superionic VII^{'}, characterized by a finite degree of localization of protons along the nonsymmetric O─H⋯O bonds. The transition is identified in structural, energetic, and elastic analysis. Upon further compression a second-order phase transition leads to the superionic ice X with symmetric O─H─O bonds.
Distortion induced magnetic phase transition in cubic BaFeO3
NASA Astrophysics Data System (ADS)
Rahman, Gul; Morbec, Juliana M.; Ferradás, Rubén; García-Suárez, Víctor M.; English, Niall J.
2016-03-01
The electronic and magnetic structures of cubic BaFeO3 (BFO) in the ferromagnetic (FM) and antiferromagnetic (AFM) states are studied using density functional theory (DFT) with the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), with and without a Coulomb U term. Our LSDA/GGA and LSDA+U/GGA+U results show that cubic BFO has a FM ground state, in agreement with recent experimental studies. Two types of distortions, denoted as D1 and D2, are considered. The source of the distortion in the D1 (D2) case is the displacement of the oxygen (iron) atoms from their equilibrium positions. FM to ferrimagnetic (FIM) and FM to AFM magnetic phase transitions are found in the D1 and D2 distortions, respectively. Larger strains are required for the FM-AFM transition as compared to the FM-FIM. DFT+U calculations also show that the magnetic moments dramatically decrease at large strains due to strong overlapping between the iron and oxygen atoms. The origin of these transitions is discussed in terms of a competition between double exchange and superexchange interactions. From these results it is possible to conclude that oxygen and iron displacements are responsible for the magnetic phase transitions and the reduction of the magnetic moments in BFO.
Isotropic-nematic transition for hard rods on a three-dimensional cubic lattice
NASA Astrophysics Data System (ADS)
Gschwind, A.; Klopotek, M.; Ai, Y.; Oettel, M.
2017-07-01
Using grand-canonical Monte Carlo (GCMC) simulations, we investigate the isotropic-nematic phase transition for hard rods of size L ×1 ×1 on a three-dimensional cubic lattice. We observe such a transition for L ≥6 . For L =6 , the nematic state has a negative order parameter, reflecting the co-occurrence of two dominating orientations. For L ≥7 , the nematic state has a positive order parameter, corresponding to the dominance of one orientation. We investigate rod lengths up to L =25 and find evidence for a very weakly first-order isotropic-nematic transition, while we cannot completely rule out a second-order transition. It was not possible to detect a density jump at the transition, despite using large systems containing several 105 particles. The probability density distributions P (Q ) from the GCMC simulations near the transition are very broad, pointing to strong fluctuations. Our results complement earlier results on the demixing (pseudonematic) transition for an equivalent system in two dimensions, which is presumably of Ising type and occurs for L ≥7 . We compare our results to lattice fundamental measure theory (FMT) and find that FMT strongly overestimates nematic order and consequently predicts a strong first-order transition. The rod packing fraction of the nematic coexisting states, however, agree reasonably well between FMT and GCMC.
First principles calculations of mechanical properties of cubic 5d transition metal monocarbides
NASA Astrophysics Data System (ADS)
Yang, Jun; Gao, Faming
2012-09-01
The electronic and elastic properties of cubic 5d transition metal monocarbides in rocksalt, cesium chloride, and zinc blende structures have been studied by first principles calculations. The calculations show that the incompressibility for ReC in cesium chloride structure is even higher than that of diamond under pressure (above 89 GPa). The transformation pressure from zinc blende structure to rocksalt structure takes place at about 47 GPa for PtC. HfC-NaCl, ReC-CsCl, and HfC-ZnS have the smallest metallicity, leading to higher hardness. A valence electron number of 8/cell may be a stable valence shell configuration for 5d transition metal monocarbides in rocksalt and zinc blende structures.
Large volume collapse observed in the phase transition in cubic PbCrO[subscript 3] perovskite
Xiao, Wansheng; Tan, Dayong; Xiong, Xiaolin; Liu, Jing; Xu, Jian
2010-08-27
When cubic PbCrO{sub 3} perovskite (Phase I) is squeezed up to {approx}1.6 GPa at room temperature, a previously undetected phase (Phase II) has been observed with a 9.8% volume collapse. Because the structure of Phase II can also be indexed into a cubic perovskite as Phase I, the transition between Phases I and II is a cubic to cubic isostructural transition. Such a transition appears independent of the raw materials and synthesizing methods used for the cubic PbCrO{sub 3} perovskite sample. In contrast to the high-pressure isostructural electronic transition that appears in Ce and SmS, this transition seems not related with any change of electronic state, but it could be possibly related on the abnormally large volume and compressibility of the PbCrO{sub 3} Phase I. The physical mechanism behind this transition and the structural and electronic/magnetic properties of the condensed phases are the interesting issues for future studies.
The structural origin of the hard-sphere glass transition in granular packing
Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie
2015-09-28
Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden’ polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleation process, similar to that of the random first-order transition theory. In conclusion, our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses.
The structural origin of the hard-sphere glass transition in granular packing
Xia, Chengjie; Li, Jindong; Cao, Yixin; ...
2015-09-28
Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden’ polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleationmore » process, similar to that of the random first-order transition theory. In conclusion, our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses.« less
The structural origin of the hard-sphere glass transition in granular packing
Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie
2015-01-01
Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden' polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleation process, similar to that of the random first-order transition theory. Our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses. PMID:26412008
Cubic-tetragonal phase transition in KMnF3: excess entropy and spontaneous strain
NASA Astrophysics Data System (ADS)
Hayward, S. A.; Romero, F. J.; Gallardo, M. C.; del Cerro, J.; Gibaud, A.; Salje, E. K. H.
2000-02-01
The transition between cubic and tetragonal phases in KMnF3 has been studied by x-ray diffraction rocking curves and calorimetry. Comparison of the excess entropy with the order parameter Q obtained from spontaneous strain shows that the mean field relationship icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> Sicons/Journals/Common/propto" ALT="propto" ALIGN="TOP"/> Q 2 is obeyed to within experimental error. The data are fitted to a Landau free energy expression icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> G = 1/2 A (T -TC )Q 2 +(1/4) BQ 4 +(1/6)CQ 6 , with A = 2.781 J K-1 mol-1 , B = -57.63 J mol-1 , C = 574.2 J mol-1 , TC = 185.76 K. No significant excess specific heat is found at T >>TC .
Intermittency and transition to chaos in the cubical lid-driven cavity flow
NASA Astrophysics Data System (ADS)
Loiseau, J.-Ch; Robinet, J.-Ch; Leriche, E.
2016-12-01
Transition from steady state to intermittent chaos in the cubical lid-driven cavity flow is investigated numerically. Fully three-dimensional stability analyses have revealed that the flow experiences an Andronov-Poincaré-Hopf bifurcation at a critical Reynolds number Re c = 1914. As for the 2D-periodic lid-driven cavity flows, the unstable mode originates from a centrifugal instability of the primary vortex core. A Reynolds-Orr analysis reveals that the unstable perturbation relies on a combination of the lift-up and anti lift-up mechanisms to extract its energy from the base flow. Once linearly unstable, direct numerical simulations show that the flow is driven toward a primary limit cycle before eventually exhibiting intermittent chaotic dynamics. Though only one eigenpair of the linearized Navier-Stokes operator is unstable, the dynamics during the intermittencies are surprisingly well characterized by one of the stable eigenpairs.
NASA Astrophysics Data System (ADS)
Hamano, Katsumi; Hirotsu, Shunsuke
1980-01-01
Phenomenological equations are derived which interrelate the anomalies in various thermodynamic quantities above the transition point of a cubic-to-tetragonal phase transition caused by an instability of a triply degenerate soft mode. The anomalous part of the Gibbs free energy is assumed to be a simple sum of the three parts which represent the contributions from the three fluctuation components. A cylindrical approximation is adopted to each of the three contributions by taking into account the symmetry of the fluctuations. The theory predicts that the adiabatic elastic compliances, s11s, s12s, and also s11s-s12s should exhibit anomalies proportional to the anomaly in the specific heat at constant pressure. This is in marked contrast with the result of the generalized Pippard equations derived by Garland, and by Janovec. The new equations are successfully tested for KMnF3, CsPbCl3, and CsPbBr3. The β-γ transition of NH4Br is also discussed.
Aerodynamic drag of a transiting sphere by large-scale tomographic-PIV
NASA Astrophysics Data System (ADS)
Terra, W.; Sciacchitano, A.; Scarano, F.
2017-07-01
A method is introduced to measure the aerodynamic drag of moving objects such as ground vehicles or athletes in speed sports. Experiments are conducted as proof-of-concept that yield the aerodynamic drag of a sphere towed through a square duct in stagnant air. The drag force is evaluated using large-scale tomographic PIV and invoking the time-average momentum equation within a control volume in a frame of reference moving with the object. The sphere with 0.1 m diameter moves at a velocity of 1.45 m/s, corresponding to a Reynolds number of 10,000. The measurements in the wake of the sphere are conducted at a rate of 500 Hz within a thin volume of approximately 3 × 40 × 40 cubic centimeters. Neutrally buoyant helium-filled soap bubbles are used as flow tracers. The terms composing the drag are related to the flow momentum, the pressure and the velocity fluctuations and they are separately evaluated. The momentum and pressure terms dominate the momentum budget in the near wake up to 1.3 diameters downstream of the model. The pressure term decays rapidly and vanishes within 5 diameters. The term due to velocity fluctuations contributes up to 10% to the drag. The measurements yield a relatively constant value of the drag coefficient starting from 2 diameters downstream of the sphere. At 7 diameters the measurement interval terminates due to the finite length of the duct. Error sources that need to be accounted for are the sphere support wake and blockage effects. The above findings can provide practical criteria for the drag evaluation of generic bluff objects with this measurement technique.
NASA Astrophysics Data System (ADS)
Aray, Yosslen; Paredes, Ricardo; Álvarez, Luis Javier; Martiz, Alejandro
2017-06-01
The electron density localization in insulator and semiconductor elemental cubic materials with diamond structure, carbon, silicon, germanium, and tin, and good metallic conductors with face centered cubic structure such as α-Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au, was studied using a localized electrons detector defined in the local moment representation. Our results clearly show an opposite pattern of the electron density localization for the cubic ceramic and transition metal materials. It was found that, for the elemental ceramic materials, the zone of low electron localization is very small and is mainly localized on the atomic basin edges. On the contrary, for the transition metals, there are low-valued localized electrons detector isocontours defining a zone of highly delocalized electrons that extends throughout the material. We have found that the best conductors are those in which the electron density at this low-value zone is the lowest.
NASA Astrophysics Data System (ADS)
Torres, Juan F.; Henry, Daniel; Komiya, Atsuki; Maruyama, Shigenao
2015-08-01
The transition from the complex Rayleigh-Bénard convection to the simple heated-from-the-sides configuration in a cubical cavity filled with a Newtonian fluid is numerically studied. The cavity is tilted by an angle θ around its lower horizontal edge and is heated and cooled from two opposite tilted sides. We first analyze the effect of a marginal inclination angle on quasi-Rayleigh-Bénard convection (θ ≈0∘ ), which is a realistic physical approximation to the ideal Rayleigh-Bénard convection. We then yield the critical angles where multiple solutions that were initially found for θ ≈0∘ disappear, eventually resulting in the single steady roll solution found in the heated-from-the-sides configuration (θ =90∘ ). We confirm the existence of critical angles during the transition θ :0∘→90∘ , and we demonstrate that such angles are a consequence of either singularities or collisions of bifurcation points in the Rayleigh-number-θ parameter space. We finally derive the most important critical angles corresponding to any Newtonian fluid of Prandtl number greater than that of air.
Torres, Juan F; Henry, Daniel; Komiya, Atsuki; Maruyama, Shigenao
2015-08-01
The transition from the complex Rayleigh-Bénard convection to the simple heated-from-the-sides configuration in a cubical cavity filled with a Newtonian fluid is numerically studied. The cavity is tilted by an angle θ around its lower horizontal edge and is heated and cooled from two opposite tilted sides. We first analyze the effect of a marginal inclination angle on quasi-Rayleigh-Bénard convection (θ≈0∘), which is a realistic physical approximation to the ideal Rayleigh-Bénard convection. We then yield the critical angles where multiple solutions that were initially found for θ≈0∘ disappear, eventually resulting in the single steady roll solution found in the heated-from-the-sides configuration (θ=90∘). We confirm the existence of critical angles during the transition θ:0∘→90∘, and we demonstrate that such angles are a consequence of either singularities or collisions of bifurcation points in the Rayleigh-number-θ parameter space. We finally derive the most important critical angles corresponding to any Newtonian fluid of Prandtl number greater than that of air.
Hard sphere-like glass transition in eye lens α-crystallin solutions
Savin, Gabriela; Bucciarelli, Saskia; Dorsaz, Nicolas; Thurston, George M.; Stradner, Anna; Schurtenberger, Peter
2014-01-01
We study the equilibrium liquid structure and dynamics of dilute and concentrated bovine eye lens α-crystallin solutions, using small-angle X-ray scattering, static and dynamic light scattering, viscometry, molecular dynamics simulations, and mode-coupling theory. We find that a polydisperse Percus–Yevick hard-sphere liquid-structure model accurately reproduces both static light scattering data and small-angle X-ray scattering liquid structure data from α-crystallin solutions over an extended range of protein concentrations up to 290 mg/mL or 49% vol fraction and up to ca. 330 mg/mL for static light scattering. The measured dynamic light scattering and viscosity properties are also consistent with those of hard-sphere colloids and show power laws characteristic of an approach toward a glass transition at α-crystallin volume fractions near 58%. Dynamic light scattering at a volume fraction beyond the glass transition indicates formation of an arrested state. We further perform event-driven molecular dynamics simulations of polydisperse hard-sphere systems and use mode-coupling theory to compare the measured dynamic power laws with those of hard-sphere models. The static and dynamic data, simulations, and analysis show that aqueous eye lens α-crystallin solutions exhibit a glass transition at high concentrations that is similar to those found in hard-sphere colloidal systems. The α-crystallin glass transition could have implications for the molecular basis of presbyopia and the kinetics of molecular change during cataractogenesis. PMID:25385638
Size dependent transition enthalpy in PbTiO3 nanoparticles due to a cubic surface layer
NASA Astrophysics Data System (ADS)
Ma, Wenhui
2013-05-01
Size dependence of transition enthalpy observed in ferroelectric PbTiO3 nanoparticles has been shown to result from volume averaging or the surface dilution effect rather than size induced reduction of spontaneous polarization at the first-order phase transition temperature. The PbTiO3 nanoparticles are suggested to be composed of a cubic surface layer with size independent thickness and a ferroelectric core having nonzero and size independent spontaneous polarization at the transition point. Based on a surface layer model, thickness of the cubic surface layer at the Curie temperature is estimated to be around 5-8 nm for PbTiO3 nanoparticles from the literature-reported transition enthalpy data. The present analyses indicate that the size effect in ferroelectrics is possibly a surface related extrinsic effect.
Fluence dependence of the ultrafast transition from the A7 to the simple cubic structure in arsenic
NASA Astrophysics Data System (ADS)
Huntemann, Nils; Zijlstra, Eeuwe S.; Garcia, Martin E.
2009-07-01
We extend a previous theoretical study, in which we have predicted that a solid-solid phase transition can be induced by a laser in arsenic under pressure, to higher fluences. In particular, we compute the fluence that is needed to induce an ultrafast structural transition from the A7 to the simple cubic phase as a function of the applied pressure. We further discuss the possibility of ultrafast, laser-induced melting.
Phase transition induced by a shock wave in hard-sphere and hard-disk systems.
Zhao, Nanrong; Sugiyama, Masaru; Ruggeri, Tommaso
2008-08-07
Dynamic phase transition induced by a shock wave in hard-sphere and hard-disk systems is studied on the basis of the system of Euler equations with caloric and thermal equations of state. First, Rankine-Hugoniot conditions are analyzed. The quantitative classification of Hugoniot types in terms of the thermodynamic quantities of the unperturbed state (the state before a shock wave) and the shock strength is made. Especially Hugoniot in typical two possible cases (P-1 and P-2) of the phase transition is analyzed in detail. In the case P-1 the phase transition occurs between a metastable liquid state and a stable solid state, and in the case P-2 the phase transition occurs through coexistence states, when the shock strength changes. Second, the admissibility of the two cases is discussed from a viewpoint of the recent mathematical theory of shock waves, and a rule with the use of the maximum entropy production rate is proposed as the rule for selecting the most probable one among the possible cases, that is, the most suitable constitutive equation that predicts the most probable shock wave. According to the rule, the constitutive equation in the case P-2 is the most promising one in the dynamic phase transition. It is emphasized that hard-sphere and hard-disk systems are suitable reference systems for studying shock wave phenomena including the shock-induced phase transition in more realistic condensed matters.
Multiscale modeling of crowdion and vacancy defects in body-centered-cubic transition metals
Derlet, P. M.; Nguyen-Manh, D.
2007-08-01
We investigate the structure and mobility of single self-interstitial atom and vacancy defects in body-centered-cubic transition metals forming groups 5B (vanadium, niobium, and tantalum) and 6B (chromium, molybdenum, and tungsten) of the Periodic Table. Density-functional calculations show that in all these metals the axially symmetric <111> self-interstitial atom configuration has the lowest formation energy. In chromium, the difference between the energies of the <111> and the <110> self-interstitial configurations is very small, making the two structures almost degenerate. Local densities of states for the atoms forming the core of crowdion configurations exhibit systematic widening of the ''local'' d band and an upward shift of the antibonding peak. Using the information provided by electronic structure calculations, we derive a family of Finnis-Sinclair-type interatomic potentials for vanadium, niobium, tantalum, molybdenum, and tungsten. Using these potentials, we investigate the thermally activated migration of self-interstitial atom defects in tungsten. We rationalize the results of simulations using analytical solutions of the multistring Frenkel-Kontorova model describing nonlinear elastic interactions between a defect and phonon excitations. We find that the discreteness of the crystal lattice plays a dominant part in the picture of mobility of defects. We are also able to explain the origin of the non-Arrhenius diffusion of crowdions and to show that at elevated temperatures the diffusion coefficient varies linearly as a function of absolute temperature.
Transition to a time-dependent state of fluid flow in the wake of a sphere.
Gumowski, K; Miedzik, J; Goujon-Durand, S; Jenffer, P; Wesfreid, J E
2008-05-01
In this paper, the results of laboratory investigation about the flow behind the sphere in the range of 150
First-order layering and critical wetting transitions in nonadditive hard-sphere mixtures.
Hopkins, Paul; Schmidt, Matthias
2011-05-01
Using fundamental-measure density functional theory we investigate entropic wetting in an asymmetric binary mixture of hard spheres with positive nonadditivity. We consider a general planar hard wall, where preferential adsorption is induced by a difference in closest approach of the different species and the wall. Close to bulk fluid-fluid coexistence, the phase rich in the minority component adsorbs either through a series of first-order layering transitions, where an increasing number of liquid layers adsorbs sequentially, or via a critical wetting transition, where a thick film grows continuously.
Zhang, Fan; An, Yongling; Zhai, Wei; Gao, Xueping; Feng, Jinkui; Ci, Lijie; Xiong, Shenglin
2015-10-15
Highlights: • The hollow Co{sub 2}SiO{sub 4}, MnSiO{sub 3} and CuSiO{sub 3} were successfully prepared by a facile hydrothermal method using SiO{sub 2} nanosphere. • The hollow Co{sub 2}SiO{sub 4}, MnSiO{sub 3} and CuSiO{sub 3} were tested as anode materials for lithium batteries. • The hollow Co{sub 2}SiO{sub 4}, MnSiO{sub 3} and CuSiO{sub 3} delivered superior electrochemical performance. • The lithium storage mechanism is probe via cyclic voltammetry and XPS. - Abstract: A series of transition metal silicate hollow spheres, including cobalt silicate (Co{sub 2}SiO{sub 4}), manganese silicate (MnSiO{sub 3}) and copper silicate (CuSiO{sub 3}.2H{sub 2}O, CuSiO{sub 3} as abbreviation in the text) were prepared via a simple and economic hydrothermal method by using silica spheres as chemical template. Time-dependent experiments confirmed that the resultants formed a novel type of hierarchical structure, hollow spheres assembled by numerous one-dimensional (1D) nanotubes building blocks. For the first time, the transition metal silicate hollow spheres were characterized as novel anode materials of Li-ion battery, which presented superior lithium storage capacities, cycle performance and rate performance. The 1D nanotubes assembly and hollow interior endow this kind of material facilitate fast lithium ion and electron transport and accommodate the big volume change during the conversion reactions. Our study shows that low-cost transition metal silicate with rationally designed nanostructures can be promising anode materials for high capacity lithium-ion battery.
Dynamics of Disorder-Order Transitions in Hard Sphere Colloidal Dispersions in micro-g
NASA Technical Reports Server (NTRS)
Zhu, J. X.; Li, M.; Phan, S. E.; Russel, W. B.; Chaikin, Paul M.; Rogers, Rick; Meyers, W.
1996-01-01
We performed a series of experiments on 0.518 millimeter PMMA spheres suspended in an index matching mixture of decalin and tetralin the microgravity environment provided by the Shuttle Columbia on mission STS-73. The samples ranged in concentration from 0.49 to 0.62. volume fraction (phi) of spheres, which covers the range in which liquid, coexistence, solid and glass phases are expected from Earth bound experiments. Light scattering was used to probe the static structure, and the particle dynamics. Digital and 35 mm photos provided information on the morphology of the crystals. In general, the crystallites grew considerably larger (roughly an order of magnitude larger) than the same samples with identical treatment in 1 g. The dynamic light scattering shows the typical short time diffusion and long time caging effects found in 1 g. The surprises that were encountered in microgravity include the preponderance of random hexagonal close packed (RHCP) structures and the complete absence of the expected face centered cubic (FCC) structure, existence of large dendritic crystals floating in the coexistence samples (where liquid and solid phases coexist) and the rapid crystallization of samples which exist only in glass phase under the influence of one g. These results suggest that colloidal crystal growth is profoundly effected by gravity in yet unrecognized ways. We suspect that the RCHP structure is related to the nonequilibrium growth that is evident from the presence of dendrites. An analysis of the dendritic growth instabilities is presented within the framework of the Ackerson-Schatzel equation.
NASA Technical Reports Server (NTRS)
Zhu, Ji-Xiang; Chaikin, P. M.; Li, Min; Russel, W. B.; Ottewill, R. H.; Rogers, R.; Meyer, W. V.
1998-01-01
Classical hard spheres have long served as a paradigm for our understanding of the structure of liquids, crystals, and glasses and the transitions between these phases. Ground-based experiments have demonstrated that suspensions of uniform polymer colloids are near-ideal physical realizations of hard spheres. However, gravity appears to play a significant and unexpected role in the formation and structure of these colloidal crystals. In the microgravity environment of the Space Shuttle, crystals grow purely via random stacking of hexagonal close-packed planes, lacking any of the face-centered cubic (FCC) component evident in crystals grown in 1 g beyond melting and allowed some time to settle. Gravity also masks 33-539 the natural growth instabilities of the hard sphere crystals which exhibit striking dendritic arms when grown in microgravity. Finally, high volume fraction "glass" samples which fail to crystallize after more than a year in 1 g begin nucleation after several days and fully crystallize in less than 2 weeks on the Space Shuttle.
NASA Technical Reports Server (NTRS)
Zhu, Ji-Xiang; Chaikin, P. M.; Li, Min; Russel, W. B.; Ottewill, R. H.; Rogers, R.; Meyer, W. V.
1998-01-01
Classical hard spheres have long served as a paradigm for our understanding of the structure of liquids, crystals, and glasses and the transitions between these phases. Ground-based experiments have demonstrated that suspensions of uniform polymer colloids are near-ideal physical realizations of hard spheres. However, gravity appears to play a significant and unexpected role in the formation and structure of these colloidal crystals. In the microgravity environment of the Space Shuttle, crystals grow purely via random stacking of hexagonal close-packed planes, lacking any of the face-centered cubic (FCC) component evident in crystals grown in 1 g beyond melting and allowed some time to settle. Gravity also masks 33-539 the natural growth instabilities of the hard sphere crystals which exhibit striking dendritic arms when grown in microgravity. Finally, high volume fraction "glass" samples which fail to crystallize after more than a year in 1 g begin nucleation after several days and fully crystallize in less than 2 weeks on the Space Shuttle.
NASA Astrophysics Data System (ADS)
Hanifpour, M.; Francois, N.; Robins, V.; Kingston, A.; Vaez Allaei, S. M.; Saadatfar, M.
2015-06-01
Here we present an experimental and numerical investigation on the grain-scale geometrical and mechanical properties of partially crystallized structures made of macroscopic frictional grains. Crystallization is inevitable in arrangements of monosized hard spheres with packing densities exceeding Bernal's limiting density ϕBernal≈0.64 . We study packings of monosized hard spheres whose density spans over a wide range (0.59 <ϕ <0.72 ) . These experiments harness x-ray computed tomography, three-dimensional image analysis, and numerical simulations to access precisely the geometry and the 3D structure of internal forces within the sphere packings. We show that clear geometrical transitions coincide with modifications of the mechanical backbone of the packing both at the grain and global scale. Notably, two transitions are identified at ϕBernal≈0.64 and ϕc≈0.68 . These results provide insights on how geometrical and mechanical features at the grain scale conspire to yield partially crystallized structures that are mechanically stable.
Tang, T-Y Dora; Brooks, Nicholas J; Jeworrek, Christoph; Ces, Oscar; Terrill, Nick J; Winter, Roland; Templer, Richard H; Seddon, John M
2012-09-11
Monoacylglycerol based lipids are highly important model membrane components and attractive candidates for drug encapsulation and as delivery agents. However, optimizing the properties of these lipids for applications requires a detailed understanding of the thermodynamic factors governing the self-assembled structures that they form. Here, we report on the effects of hydrostatic pressure, temperature, and water composition on the structural behavior and stability of inverse lyotropic liquid crystalline phases adopted by monolinolein (an unsaturated monoacylglycerol having cis-double bonds at carbon positions 9 and 12) under limited hydration conditions. Six pressure-temperature phase diagrams have been determined using small-angle X-ray diffraction at water contents between 15 wt % and 27 wt % water, in the range 10-40 °C and 1-3000 bar. The gyroid bicontinuous cubic (Q(II)(G)) phase is formed at low pressure and high temperatures, transforming to a fluid lamellar (L(α)) phase at high pressures and low temperature via a region of Q(II)(G)/L(α) coexistence. Pressure stabilizes the lamellar phase over the Q(II)(G) phase; at fixed pressure, increasing the water content causes the coexistence region to move to lower temperature. These trends are consistent throughout the hydration range studied. Moreover, at fixed temperature, increasing the water composition increases the pressure at which the Q(II)(G) to L(α) transition takes place. We discuss the qualitative effect of pressure, temperature, and water content on the stability of the Q(II)(G) phase.
NASA Astrophysics Data System (ADS)
Patrykiejew, A.; Sokołowski, S.; Zientarski, T.; Binder, K.
1998-03-01
The results of Monte Carlo simulation of two-dimensional films formed on the (110) face of a face-centered-cubic crystal are presented. Systems with different corrugation of the gas-solid potential and different size of adsorbed atoms are discussed. It is demonstrated that even small changes in the gas-solid potential corrugation considerably affect the inner structure of the low-temperature ordered phases and the location of the order-disorder phase transition.
First-order patterning transitions on a sphere as a route to cell morphology.
Lavrentovich, Maxim O; Horsley, Eric M; Radja, Asja; Sweeney, Alison M; Kamien, Randall D
2016-05-10
We propose a general theory for surface patterning in many different biological systems, including mite and insect cuticles, pollen grains, fungal spores, and insect eggs. The patterns of interest are often intricate and diverse, yet an individual pattern is robustly reproducible by a single species and a similar set of developmental stages produces a variety of patterns. We argue that the pattern diversity and reproducibility may be explained by interpreting the pattern development as a first-order phase transition to a spatially modulated phase. Brazovskii showed that for such transitions on a flat, infinite sheet, the patterns are uniform striped or hexagonal. Biological objects, however, have finite extent and offer different topologies, such as the spherical surfaces of pollen grains. We consider Brazovskii transitions on spheres and show that the patterns have a richer phenomenology than simple stripes or hexagons. We calculate the free energy difference between the unpatterned state and the many possible patterned phases, taking into account fluctuations and the system's finite size. The proliferation of variety on a sphere may be understood as a consequence of topology, which forces defects into perfectly ordered phases. The defects are then accommodated in different ways. We also argue that the first-order character of the transition is responsible for the reproducibility and robustness of the pattern formation.
Glass Transition and Re-entrant Melting in a Polydisperse Hard-Sphere Fluid
NASA Astrophysics Data System (ADS)
Tokuyama, Michio; Terada, Yayoi
2006-05-01
Extensive molecular dynamics simulations are performed for a hard-sphere fluid at 6% polydispersity. The simulation results are then analyzed based on the mean-field theory proposed recently by Tokuyama (Physica A 364, 23-62 (2006)). The phase diagram and the dynamic behavior are investigated fully in each phase. It is then found that as the volume fraction φ is increased, a supercooled liquid phase appears at the supercooled point φβ (≃ 0.5524) and a transition from supercooled liquid to crystal then occurs at the melting volume fraction φm(1) (≃ 0.5625). As φ is further increased, a transition from crystal to supercooled liquid (re-entrant melting) is also observed at the second melting volume fraction φm(2) (≃ 0.5770) within a waiting time tw = 7 × 104t0, where t0 is a time for a particle to move over a distance of a particle radius with an average velocity. The glass transition is thus predicted to occur at the glass transition volume fraction φg (≃ 0.6005). The various aspects obtained in our study is quite similar to those in the experiment for the suspension of hard spheres, including the logarithmic growth of the mean-square displacement in fast-β stage, the non-singular behavior of the long-time self-diffusion coefficient, and the non divergence of any characteristic times, such as the α- and β-relaxation times.
First-order patterning transitions on a sphere as a route to cell morphology
Lavrentovich, Maxim O.; Horsley, Eric M.; Radja, Asja; Sweeney, Alison M.; Kamien, Randall D.
2016-01-01
We propose a general theory for surface patterning in many different biological systems, including mite and insect cuticles, pollen grains, fungal spores, and insect eggs. The patterns of interest are often intricate and diverse, yet an individual pattern is robustly reproducible by a single species and a similar set of developmental stages produces a variety of patterns. We argue that the pattern diversity and reproducibility may be explained by interpreting the pattern development as a first-order phase transition to a spatially modulated phase. Brazovskii showed that for such transitions on a flat, infinite sheet, the patterns are uniform striped or hexagonal. Biological objects, however, have finite extent and offer different topologies, such as the spherical surfaces of pollen grains. We consider Brazovskii transitions on spheres and show that the patterns have a richer phenomenology than simple stripes or hexagons. We calculate the free energy difference between the unpatterned state and the many possible patterned phases, taking into account fluctuations and the system’s finite size. The proliferation of variety on a sphere may be understood as a consequence of topology, which forces defects into perfectly ordered phases. The defects are then accommodated in different ways. We also argue that the first-order character of the transition is responsible for the reproducibility and robustness of the pattern formation. PMID:27102872
The Dynamics of Disorder-Order Transition in Hard Sphere Colloidal Dispersions
NASA Technical Reports Server (NTRS)
Chaikin, Paul M.; Zhu, Jixiang; Cheng, Zhengdong; Phan, See-Eng; Russel, William B.; Lant, Christian T.; Doherty, Michael P.; Meyer, William V.; Rogers, Richard; Cannell, D. S.;
1998-01-01
The Physics of Hard Spheres Experiment (PHaSE) seeks a complete understanding of the entropically driven disorder-order transition in hard sphere colloidal dispersions. The light scattering instrument designed for flight collects Bragg and low angle light scattering in the forward direction via a CCD camera and performs conventional static and dynamic light scattering at 10-160 deg. through fiber optic cables. Here we report on the kinetics of nucleation and growth extracted from time-resolved Bragg images and measurements of the elastic modulus of crystalline phases obtained by monitoring resonant responses to sinusoidal forcing through dynamic light scattering. Preliminary analysis of the former indicates a significant difference from measurements on the ground, while the latter confirms nicely laboratory experiments with the same instrument and predictions from computer simulations.
Ionic and Optical Properties of Methylammonium Lead Iodide Perovskite across the Tetragonal-Cubic Structural Phase Transition.
Hoque, Md Nadim Ferdous; Islam, Nazifah; Li, Zhen; Ren, Guofeng; Zhu, Kai; Fan, Zhaoyang
2016-09-22
Practical hybrid perovskite solar cells (PSCs) must endure temperatures above the tetragonal-cubic structural phase transition of methylammonium lead iodide (MAPbI3 ). However, the ionic and optical properties of MAPbI3 in such a temperature range, and particularly, dramatic changes in these properties resulting from a structural phase transition, are not well studied. Herein, we report a striking contrast at approximately 45 °C in the ionic/electrical properties of MAPbI3 owing to a change of the ion activation energy from 0.7 to 0.5 eV, whereas the optical properties exhibit no particular transition except for the steady increase of the bandgap with temperature. These observations can be explained by the "continuous" nature of perovskite phase transition. We speculate that the critical temperature at which the ionic/electrical properties change, although related to crystal symmetry variation, is not necessarily the same temperature as when tetragonal-cubic structural phase transition occurs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Hoque, Md Nadim Ferdous; Islam, Nazifah; Li, Zhen; Ren, Guofeng; Zhu, Kai; Fan, Zhaoyang
2016-09-01
Practical hybrid perovskite solar cells (PSCs) must endure temperatures above the tetragonal-cubic structural phase transition of methylammonium lead iodide (MAPbI3). However, the ionic and optical properties of MAPbI3 in such a temperature range, and particularly, dramatic changes in these properties resulting from a structural phase transition, are not well studied. Herein, we report a striking contrast at approximately 45 degrees C in the ionic/electrical properties of MAPbl3 owing to a change of the ion activation energy from 0.7 to 0.5 eV, whereas the optical properties exhibit no particular transition except for the steady increase of the bandgap with temperature. These observations can be explained by the 'continuous' nature of perovskite phase transition. We speculate that the critical temperature at which the ionic/electrical properties change, although related to crystal symmetry variation, is not necessarily the same temperature as when tetragonal-cubic structural phase transition occurs.
Three-dimensional kinetic Monte Carlo simulations of cubic transition metal nitride thin film growth
NASA Astrophysics Data System (ADS)
Nita, F.; Mastail, C.; Abadias, G.
2016-02-01
A three-dimensional kinetic Monte Carlo (KMC) model has been developed and used to simulate the microstructure and growth morphology of cubic transition metal nitride (TMN) thin films deposited by reactive magnetron sputtering. Results are presented for the case of stoichiometric TiN, chosen as a representative TMN prototype. The model is based on a NaCl-type rigid lattice and includes deposition and diffusion events for both N and Ti species. It is capable of reproducing voids and overhangs, as well as surface faceting. Simulations were carried out assuming a uniform flux of incoming particles approaching the surface at normal incidence. The ballistic deposition model is parametrized with an interaction parameter r0 that mimics the capture distance at which incoming particles may stick on the surface, equivalently to a surface trapping mechanism. Two diffusion models are implemented, based on the different ways to compute the site-dependent activation energy for hopping atoms. The influence of temperature (300-500 K), deposition flux (0.1-100 monolayers/s), and interaction parameter r0 (1.5-6.0 Å) on the obtained growth morphology are presented. Microstructures ranging from highly porous, [001]-oriented straight columns with smooth top surface to rough columns emerging with different crystallographic facets are reproduced, depending on kinetic restrictions, deposited energy (seemingly captured by r0), and shadowing effect. The development of facets is a direct consequence of the diffusion model which includes an intrinsic (minimum energy-based) diffusion anisotropy, although no crystallographic diffusion anisotropy was explicitly taken into account at this stage. The time-dependent morphological evolution is analyzed quantitatively to extract the growth exponent β and roughness exponent α , as indicators of kinetic roughening behavior. For dense TiN films, values of α ≈0.7 and β =0.24 are obtained in good agreement with existing experimental data. At this
Wallez, Gilles; Raison, Philippe E; Dacheux, Nicolas; Clavier, Nicolas; Bykov, Denis; Delevoye, Laurent; Popa, Karin; Bregiroux, Damien; Fitch, Andrew N; Konings, Rudy J M
2012-04-02
The AnP(2)O(7) diphosphates (An = Th, U, Np, Pu) have been synthesized by various routes depending on the stability of the An(IV) cation and its suitability for the unusual octahedral environment. Synchrotron and X-ray diffraction, thermal analysis, Raman spectroscopy, and (31)P nuclear magnetic resonance reveal them as a new family of diphosphates which probably includes the recently studied CeP(2)O(7). Although they adopt at high temperature the same cubic archetypal cell as the other known MP(2)O(7) diphosphates, they differ by a very faint triclinic distortion at room temperature that results from an ordering of the P(2)O(7) units, as shown using high-resolution synchrotron diffraction for UP(2)O(7). The uncommon triclinic-cubic phase transition is first order, and its temperature is very sensitive to the ionic radius of An(IV). The conflicting effects which control the thermal variations of the P-O-P angle are responsible for a strong expansion of the cell followed by a contraction at higher temperature. This inversion of expansion occurs at a temperature significantly higher than the phase transition, at variance with the parent compounds with smaller M(IV) cations in which the two phenomena coincide. As shown by various approaches, the P-O(b)-P linkage remains bent in the cubic form.
Chong, Ketpin; Deng, Yuru
2012-01-01
Biological membranes are generally perceived as phospholipid bilayer structures that delineate in a lamellar form the cell surface and intracellular organelles. However, much more complex and highly convoluted membrane organizations are ubiquitously present in many cell types under certain types of stress, states of disease, or in the course of viral infections. Their occurrence under pathological conditions make such three-dimensionally (3D) folded and highly ordered membranes attractive biomarkers. They have also stimulated great biomedical interest in understanding the molecular basis of their formation. Currently, the analysis of such membrane arrangements, which include tubulo-reticular structures (TRS) or cubic membranes of various subtypes, is restricted to electron microscopic methods, including tomography. Preservation of membrane structures during sample preparation is the key to understand their true 3D nature. This chapter discusses methods for appropriate sample preparations to successfully examine and analyze well-preserved highly ordered membranes by electron microscopy. Processing methods and analysis conditions for green algae (Zygnema sp.) and amoeba (Chaos carolinense), mammalian cells in culture and primary tissue cells are described. We also discuss methods to identify cubic membranes by transmission electron microscopy (TEM) with the aid of a direct template matching method and by computer simulation. A 3D analysis of cubic cell membrane topology by electron tomography is described as well as scanning electron microscopy (SEM) to investigate surface contours of isolated mitochondria with cubic membrane arrangement.
Probing the equilibrium dynamics of colloidal hard spheres above the mode-coupling glass transition.
Brambilla, G; El Masri, D; Pierno, M; Berthier, L; Cipelletti, L; Petekidis, G; Schofield, A B
2009-02-27
We use dynamic light scattering and computer simulations to study equilibrium dynamics and dynamic heterogeneity in concentrated suspensions of colloidal hard spheres. Our study covers an unprecedented density range and spans seven decades in structural relaxation time, tau(alpha0, including equilibrium measurements above phi(c), the location of the glass transition deduced from fitting our data to mode-coupling theory. Instead of falling out of equilibrium, the system remains ergodic above phi(c) and enters a new dynamical regime where tau(alpha) increases with a functional form that was not anticipated by previous experiments, while the amplitude of dynamic heterogeneity grows slower than a power law with tau(alpha), as found in molecular glass formers close to the glass transition.
Structure and phase transition of BiFeO{sub 3} cubic micro-particles prepared by hydrothermal method
Zhou, Jian-Ping; Yang, Ruo-Lin; Xiao, Rui-Juan; Chen, Xiao-Ming; Deng, Chao-Yong
2012-11-15
Graphical abstract: Bismuth ferrite (BiFeO{sub 3}) cubic micro-particles with smooth surfaces were synthesized. BiFeO{sub 3} has a hexagonal perovskite structure with a space group R3c below 370 °C and rhombohedral perovskite structure with a space group R3m below 755 °C, undergoes a phase transition in the temperature range of 755–817 °C to a cubic structure, then decompose to liquid and Fe{sub 2}O{sub 3} above 939 °C. Highlights: ► BiFeO{sub 3} micro-particles with smooth surface were synthesized by hydrothermal method. ► BiFeO{sub 3} enjoys hexagonal structure with well element ratio and chemical valence. ► BiFeO{sub 3} transition from rhombohedral phase to cubic phase lasts 60 °C. -- Abstract: Single-phase bismuth ferrite (BiFeO{sub 3}) powders were synthesized with a hydrothermal method by controlling the experimental conditions carefully. The powder structure, morphology and composition were characterized by using X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscope, Raman measurement and X-ray photoelectron spectroscopy. The particles change from irregular agglomerations to regular cubes with increasing KOH concentration. The large BiFeO{sub 3} cubic particles enjoy much smooth surfaces with well-matched element ratio (Bi:Fe:O = 1:1:3) and chemical valence (Bi{sup 3+}, Fe{sup 3+} and O{sup 2−}). The high temperature XRD and differential scanning calorimetry show that BiFeO{sub 3} powders have a hexagonal perovskite structure with a space group R3c below 370 °C and a rhombohedral structure with a space group R3m below 755 °C. BiFeO{sub 3} undergoes a phase transition in the temperature range of 755–817 °C from rhombohedral structure to a cubic phase, then decomposes to liquid and Fe{sub 2}O{sub 3} above 939 °C.
Behera, Pallavi Suhasinee; Vasanthavel, S.; Ponnilavan, V.; Kannan, S.
2015-05-15
The present study reports the effect of gadolinium (Gd{sup 3+}) in zirconia-silica (ZrO{sub 2}-SiO{sub 2}) binary oxides. The pure ZrO{sub 2}-SiO{sub 2} synthesized at 1100 °C was tetragonal. The addition of Gd{sup 3+} in the concentration range of 5%–10% resulted in the formation of t-ZrO{sub 2}, whereas higher contents of Gd{sup 3+} led to the formation of cubic ZrO{sub 2} (c-ZrO{sub 2}). The presence of Gd{sup 3+} also affected the lattice parameters of both t-ZrO{sub 2} and c-ZrO{sub 2}. Magnetic studies confirmed a steady increase in the paramagnetic behaviour with increasing content of Gd{sup 3+}. - Graphical abstract: t-ZrO{sub 2} to c-ZrO{sub 2} phase transition influenced by Gd{sup 3+} content. - Highlights: • Sol-gel synthesis of Gd{sup 3+} added SiO{sub 2}-ZrO{sub 2} binary oxides. • Significant role of Gd{sup 3+} content in the tetragonal and cubic stabilization of ZrO{sub 2}. • Phase stability of either tetragonal or cubic stabilization till 1100 °C. • Gd{sup 3+} additions ensured additional paramagnetic behaviour in SiO{sub 2}-ZrO{sub 2} binary oxide.
Banerjee, M; Rai, Archana
2007-06-01
Nanocrystalline cubic CuFe2O4 have been prepared by co-precipitation method. The experimental conditions have been controlled to produce CuFe2O4 with particle size 18 nm, 7.2 nm, and 3.2 nm as calculated by Scherrer formula. Room temperature Mössbauer spectra show that 18 nm and 7.2 nm CuFe2O4 exhibit ferrimagnetism while 3.2 nm CuFe2O4 exhibits superparamagnetism. The cationic distribution calculated using Mössbauer spectra confirm to the cubic structure confirming the findings of XRD study. XPS data corroborates the finding. Low temperature Mössbauer measurements on 3.2 nm particles show gradual transformation to ferrimagnetic state.
Salt induced lamellar to bicontinuous cubic phase transitions in cationic nanoparticles.
Muir, Benjamin W; Zhen, Guoliang; Gunatillake, Pathiraja; Hartley, Patrick G
2012-03-22
The development of improved methods to allow the low energy production of cubic phase forming nanoparticles (cubosomes) is highly desired. The lamellar to hexagonal and cubic phase change of these lipid nanoparticles has previously been induced via the lowering of pH and the addition of calcium ions to anionic lipid nanoparticles. We have developed a method to produce low polydispersity cubosomes without the requirement of high energy input such as shear, sonication or homogenization under physiological conditions. We have found that the simple addition of phosphate buffered saline solution to aqueous dispersions of cationic liposome vesicles made with phytantriol results in the spontaneous formation of cubosomes after vortex mixing. This finding demonstrates the potential of utilizing this technique to incorporate shear and temperature sensitive compounds into cubosomes under extremely mild conditions for biomedical and nanotechnological applications.
NASA Astrophysics Data System (ADS)
Liu, Qihang; Zunger, Alex
2017-04-01
We show that the previously predicted "cubic Dirac fermion," composed of six conventional Weyl fermions including three with left-handed and three with right-handed chirality, is realized in a specific, stable solid state system that has been made years ago, but was not appreciated as a "cubically dispersed Dirac semimetal" (CDSM). We identify the crystal symmetry constraints and find the space group P 63/m as one of the two that can support a CDSM, of which the characteristic band crossing has linear dispersion along the principle axis but cubic dispersion in the plane perpendicular to it. We then conduct a material search using density functional theory, identifying a group of quasi-one-dimensional molybdenum monochalcogenide compounds AI(MoXVI)3 (AI=Na , K, Rb, In, Tl; XVI=S , Se, Te) as ideal CDSM candidates. Studying the stability of the A (MoX) 3 family reveals a few candidates such as Rb (MoTe) 3 and Tl (MoTe) 3 that are predicted to be resilient to Peierls distortion, thus retaining the metallic character. Furthermore, the combination of one dimensionality and metallic nature in this family provides a platform for unusual optical signature—polarization-dependent metallic vs insulating response.
Importance of many-body correlations in glass transition: An example from polydisperse hard spheres
NASA Astrophysics Data System (ADS)
Leocmach, Mathieu; Russo, John; Tanaka, Hajime
2013-03-01
Most of the liquid-state theories, including glass-transition theories, are constructed on the basis of two-body density correlations. However, we have recently shown that many-body correlations, in particular, bond orientational correlations, play a key role in both the glass transition and the crystallization transition. Here we show, with numerical simulations of supercooled polydisperse hard spheres systems, that the length-scale associated with any two-point spatial correlation function does not increase toward the glass transition. A growing length-scale is instead revealed by considering many-body correlation functions, such as correlators of orientational order, which follows the length-scale of the dynamic heterogeneities. Despite the growing of crystal-like bond orientational order, we reveal that the stability against crystallization with increasing polydispersity is due to an increasing population of icosahedral arrangements of particles. Our results suggest that, for this type of systems, many-body correlations are a manifestation of the link between the vitrification and the crystallization phenomena. Whether a system is vitrified or crystallized can be controlled by the degree of frustration against crystallization, polydispersity in this case.
Li,M.; Liu, Y.; Nie, H.; Bansil, R.; Steinhart, M.
2007-01-01
Time-resolved small-angle X-ray scattering (SAXS) was used to examine the kinetics of the transition from hexagonal (hex) cylinders to body-centered cubic (bcc) spheres at various temperatures in poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) in mineral oil, a selective solvent for the middle ethylene-co-butylene (EB) block. Temperature-ramp SAXS and rheology measurements show the hex to bcc order-order transition (OOT) at 127 C and order-disorder transition (ODT) at 180 C. We also observed the metastability limit of hex in bcc with a spinodal temperature, Ts 150 C. The OOT exhibits three stages and occurs via a nucleation and growth mechanism when the final temperature Tf < Ts. Spinodal decomposition in a continuous ordering system was seen when Ts < Tf < TODT. We observed that hex cylinders transform to disordered spheres via a transient bcc state. We develop a geometrical model of coupled anisotropic fluctuations and calculate the scattering which shows very good agreement with the SAXS data. The splitting of the primary peak into two peaks when the cylinder spacing and modulation wavelength are incommensurate predicted by the model is confirmed by analysis of the SAXS data.
Tuning the sphere-to-rod transition in the self-assembly of thermoresponsive polymer hybrids.
Lee, Jangwook; Park, Honghyun; Jeong, Eun Ju; Kwark, Young-Je; Lee, Kuen Yong
2015-12-01
Nano-scale drug delivery systems have undergone extensive development, and control of size and structure is critical for regulation of their biological responses and therapeutic efficacy. Amphiphilic polymers that form self-assembled structures in aqueous media have been investigated and used for the diagnosis and therapy of various diseases, including cancer. Here, we report the design and fabrication of thermoresponsive polymeric micelles from alginate conjugated with poly(N-isopropylacrylamide) (PNIPAAm). Alginate-PNIPAAm hybrids formed self-aggregated structures in response to temperature changes near body temperature. A structural transition from micellar spheres to rods of alginate-PNIPAAm hybrids was observed depending on the molecular weight of PNIPAAm and the polymer concentration. Additionally, hydrogels with nanofibrous structures were formed by simply increasing the polymer concentration. This approach to controlling the structure of polymer micelles from nanoparticles to fibrous hydrogels may be useful in applications in drug delivery and tissue engineering.
Transition to complex dynamics in the cubic lid-driven cavity
NASA Astrophysics Data System (ADS)
Wu, Ke; Lopez, Juan M.; Welfert, Bruno D.; Yalim, Jason
2016-11-01
The cubic lid-drive cavity flow is simulated numerically by a Chebyshev collocation method, focusing on the onset of unsteadiness. The onset is directly to intermittent chaos. This has been reported by others in 2014, but they were unable to explain why, in such a simple geometry at quite modest Reynolds numbers (Re 1930), the flow should go from being steady directly to intermittent chaos. In this presentation, we show that the reason has three components: instability of the steady flow is subcritical, breaking of the reflection symmetry about the spanwise midplane, and spanwise confinement. These ingredients lead to there being no locally attracting states for Re beyond which the steady state loses stability, and the intermittent bursts are excursions shadowing unstable and stable manifolds of the (unstable) saddle local states. We show that this comes about because the instability of the steady state is close to a subcritical double Hopf bifurcation, and note that very recent theory on such bifurcations shows that they have associated dynamics that captures all the observed complexity in the cubic lid-driven cavity in the neighborhood of its primary instability.
NASA Astrophysics Data System (ADS)
Cao, Wenwu
1987-09-01
Perovskite compounds, ABX(,3), have been studied both experimentally and theoretically above and below the cubic-tetragonal improper ferroelastic phase transition. The second order elastic constants of Potassium Manganese Fluoride KMnF(,3) were measured as function of temperature in the cubic prototype phase. Along 100 and 110 the two longitudinal modes were measured from 190 K to 430 K, and the two independent transverse modes from 190 K to 350 K. Strong anomalies were observed near the phase transition (T(,c) = 186 K). The three independent pressure derivatives of the elastic constants were measured from 200 K to 400 K and also show anomalous behavior near T(,c). By means of second harmonic generation, the nonlinearity parameter was measured in 100 , 110 and 111 from 298 K to 348 K. In this temperature range, all six independent third order elastic constants have been determined. Above 320 K the second and third order elastic constants show linear temperature dependence. The values pertaining to the static crystal were obtained by linear extrapolation to T = 0 from the high temperature region where the effect of the phase transition has subsided. A Landau-Ginzburg continuum model for the interphase boundaries in the heterotype phase has been developed. It includes nonlinear local terms and nonlocal gradient terms for the three-component primary order parameter (the rotation angles of the BX(,6) octahedra). By means of group theoretical methods, the gradient coefficients have been expressed in terms of the nonlinear dispersion of the soft phonon mode near the R-point. Analytic and numerical kink-type soliton solutions for both antiphase and twin boundaries were obtained. According to this model, the symmetry in the center of the twin boundary should be trigonal (rather than cubic, as for a proper ferroelastic). Numerical application to Strontium Titanate, SrTiO(,3), shows that at T = 0 the domain wall thickness is 12 (ANGSTROM), and the domain wall energy density
Ma, Long; Peng, Jing; Wu, Changzheng; He, Linghui; Ni, Yong
2017-03-28
Nanotube formation in low-temperature solution has attracted intense interest since the 1990s. How to disclose the in-depth physicochemical nature of nanotubes and pursue new available chemical strategies is still highly desirable but remains a challenge. Here, we report that sphere-to-tube transition triggered by inverse Plateau-Rayleigh instability can be a chemical route for scalable production of nanotubes. As a proof of concept, formation of a phosphorus nitride (PN) nanotube and various hierarchical nanotube architectures by coalescence of the PN hollow spheres is achieved under systematic solvothermal reaction. The combination of theoretical analysis and dynamic simulation elucidates that the inverse Plateau-Rayleigh instability driven by the competition between curvature elasticity and surface energy is responsible for the PN nanotube formation observed in experiments. We anticipate that the sphere-to-tube transition provides a paradigm for nanotube synthesis for practical applications.
Campbell, J L; Williams, C V; Eisemann, J H
2004-11-01
Differences in dietary profiles and gastrointestinal (GI) morphologies observed across lemur species suggest that there may be variation in patterns of digesta flow through the GI tract related to the method of digesta processing. Using radio-opaque barium-impregnated polyethylene spheres (BIPS), we characterized such patterns in four lemur species: Varecia variegata (VV), Eulemur fulvus (EF), Propithecus verreauxi (PV), and Hapalemur griseus (HG) (n = 2 per species). After an initial radiograph was taken under light sedation, the animals were fed the BIPS together with a small meal. A combination of 30 small (1.5 mm) and 10 large (5 mm) BIPS was administered. Radiographs were then taken on a species-dependent basis up to 48 hr post-dosage. For small BIPS, the gastric transit time (GTT; time of first exit of BIPS from stomach) was 0.25-2 hr for VV, EF, and HG, and approximately 10 hr for PV. The oro-rectal transit time (ORTT; time of first appearance in the rectum) was < 2 hr for VV and EF, and 24.0 hr for PV and HG. The intestinal transit time (ITT, measured as ORTT - GTT) was < 1.5 hr for VV and EF, and approximately 14 hr and 22 hr for PV and HG, respectively. These data suggest that the GTT of digesta as measured with BIPS was rapid for VV, EF, and HG. For VV and EF, the ORTT and ITT were also rapid, while for HG they were much slower. PV was characterized by delayed GTT, and a more rapid ITT compared to HG. Thus, patterns of flow for PV and HG, despite similar ORTT, differed in that HG emptied BIPS more rapidly and ITT was slower. The flow of BIPS did not differ for VV and EF. These data reveal new information in addition to the total tract transit time, and complement existing knowledge regarding anatomy and diet.
NASA Astrophysics Data System (ADS)
Logothetidis, S.; Petalas, J.; Cardona, M.; Moustakas, T. D.
1994-12-01
The optical properties of cubic and hexagonal GaN thin films, grown by electron-cyclotron resonance microwave plasma-assisted molecular-beam epitaxy on silicon and sapphire substrates, respectively, have been studied at photon energies up to 25 eV with conventional and synchrotron-radiation spectroscopic ellipsometry. The fundamental gaps of the two polytypes are located at different energies, namely at 3.25 and 3.43 eV for cubic and hexagonal GaN. Analysis of the dielectric function of the two phases in the region 4.5-9.5 eV with appropriate models yields the energy location and broadening of the observed critical points. These critical points are assigned to specific points in the zinc-blende and wurtzite Brillouin zones, respectively, making use of the latest published band-structure studies and a comparison is made between the corresponding results for GaN, GaAs, and GaP. Measurements in the temperature range from 80 to 650 K provide the temperature dependence of these parameters. The features observed in the reflectivity spectra of hexagonal GaN are discussed in relation to other works. Kramers-Kronig analysis of the reflectivity between 0 and 33 eV of the hexagonal polytype verifies the existence of a broad feature centered at 14 eV. Finally, average properties, such as the effective ir dielectric constant and the effective number of valence electrons per atom are calculated for the two polytypes and compared to GaAs and GaP.
Oka, Toshihiko; Saiki, Takahiro; Alam, Jahangir Md; Yamazaki, Masahito
2016-02-09
Electrostatic interaction is an important factor for phase transitions between lamellar liquid-crystalline (Lα) and inverse bicontinuous cubic (QII) phases. We investigated the effect of temperature on the low-pH-induced Lα to double-diamond cubic (QII(D)) phase transition in dioleoylphosphatidylserine (DOPS)/monoolein (MO) using time-resolved small-angle X-ray scattering with a stopped-flow apparatus. Under all conditions of temperature and pH, the Lα phase was directly transformed into an intermediate inverse hexagonal (HII) phase, and subsequently the HII phase slowly converted to the QII(D) phase. We obtained the rate constants of the initial step (i.e., the Lα to HII phase transition) and of the second step (i.e., the HII to QII(D) phase transition) using the non-negative matrix factorization method. The rate constant of the initial step increased with temperature. By analyzing this result, we obtained the values of its apparent activation energy, Ea (Lα → HII), which did not change with temperature but increased with an increase in pH. In contrast, the rate constant of the second step decreased with temperature at pH 2.6, although it increased with temperature at pH 2.7 and 2.8. These results indicate that the value of Ea (HII → QII(D)) at pH 2.6 increased with temperature, but the values of Ea (HII → QII(D)) at pH 2.7 and 2.8 were constant with temperature. The values of Ea (HII → QII(D)) were smaller than those of Ea (Lα → HII) at the same pH. We analyzed these results using a modified quantitative theory on the activation energy of phase transitions of lipid membranes proposed initially by Squires et al. (Squires, A. M.; Conn, C. E.; Seddon, J. M.; Templer, R. H. Soft Matter 2009, 5, 4773). On the basis of these results, we discuss the mechanism of this phase transition.
Shock-induced phase transition in systems of hard spheres with internal degrees of freedom
NASA Astrophysics Data System (ADS)
Taniguchi, Shigeru; Mentrelli, Andrea; Zhao, Nanrong; Ruggeri, Tommaso; Sugiyama, Masaru
2010-06-01
Shock waves and shock-induced phase transitions are theoretically and numerically studied on the basis of the system of Euler equations with caloric and thermal equations of state for a system of hard spheres with internal degrees of freedom. First, by choosing the unperturbed state (the state before the shock wave) in the liquid phase, the Rankine-Hugoniot conditions are studied and their solutions are classified on the basis of the phase of the perturbed state (the state after the shock wave), being a shock-induced phase transition possible under certain conditions. With this regard, the important role of the internal degrees of freedom is shown explicitly. Second, the admissibility (stability) of shock waves is studied by means of the results obtained by Liu in the theory of hyperbolic systems. It is shown that another type of instability of a shock wave can exist even though the perturbed state is thermodynamically stable. Numerical calculations have been performed in order to confirm the theoretical results in the case of admissible shocks and to obtain the actual evolution of the wave profiles in the case of inadmissible shocks (shock splitting phenomena).
NASA Astrophysics Data System (ADS)
Sun, Jiu-Xun; Wu, Qiang; Cai, Ling-Cang; Jin, Ke
2014-06-01
A generalized cubic (GC) equation of state (EOS) with two independent parameters is proposed. The GC EOS can include EOS from both virial and compressibility routes of Percus-Yevick theory in it as special cases. The two parameters are determined by fitting well-known virial coefficients of pure fluid. The generalized cubic EOS can be directly and consistently extended to multi-component mixtures merely demanding of the EOS of mixtures also is cubic, and combining two strict physical conditions for the radial distribution functions at contact (RDFC) of mixtures. The calculated virial coefficients of pure fluid and predicted compressibility factors and RDFC for both pure fluid and mixtures are excellent as compared with the simulation data. The values of RDFC for mixtures with extremely large size ratio are far better than the expressions in literature.
NASA Astrophysics Data System (ADS)
Soucasse, L.; Rivière, Ph.; Soufiani, A.; Xin, S.; Le Quéré, P.
2014-02-01
The transition to unsteadiness and the dynamics of weakly turbulent natural convection, coupled to wall or gas radiation in a differentially heated cubical cavity with adiabatic lateral walls, are studied numerically. The working fluid is air with small contents of water vapor and carbon dioxide whose infrared spectral radiative properties are modelled by the absorption distribution function model. A pseudo spectral Chebyshev collocation method is used to solve the flow field equations and is coupled to a direct ray tracing method for radiation transport. Flow structures are identified by means of either the proper orthogonal decomposition or the dynamic mode decomposition methods. We first retrieve the classical mechanism of transition to unsteadiness without radiation, characterized by counter-rotating streamwise-oriented vortices generated at the exit of the vertical boundary layers. Wall radiation through a transparent medium leads to a homogenization of lateral wall temperatures and the resulting transition mechanism is similar to that obtained with perfectly conducting lateral walls. The transition is due to an unstable stratification upstream the vertical boundary layers and is characterized by periodically oscillating transverse rolls of axis perpendicular to the main flow. When molecular gas radiation is accounted for, no periodic solution is found and the transition to unsteadiness displays complex structures with chimneys-like rolls whose axes are again parallel to the main flow. The origin of this instability is probably due to centrifugal forces, as suggested previously for the case without radiation. Above the transition to unsteadiness, at Ra = 3 × 108, it is shown that both wall and gas radiation significantly intensify turbulent fluctuations, decrease the thermal stratification in the core of the cavity, and increase the global circulation.
Soucasse, L.; Rivière, Ph.; Soufiani, A.; Xin, S.
2014-02-15
The transition to unsteadiness and the dynamics of weakly turbulent natural convection, coupled to wall or gas radiation in a differentially heated cubical cavity with adiabatic lateral walls, are studied numerically. The working fluid is air with small contents of water vapor and carbon dioxide whose infrared spectral radiative properties are modelled by the absorption distribution function model. A pseudo spectral Chebyshev collocation method is used to solve the flow field equations and is coupled to a direct ray tracing method for radiation transport. Flow structures are identified by means of either the proper orthogonal decomposition or the dynamic mode decomposition methods. We first retrieve the classical mechanism of transition to unsteadiness without radiation, characterized by counter-rotating streamwise-oriented vortices generated at the exit of the vertical boundary layers. Wall radiation through a transparent medium leads to a homogenization of lateral wall temperatures and the resulting transition mechanism is similar to that obtained with perfectly conducting lateral walls. The transition is due to an unstable stratification upstream the vertical boundary layers and is characterized by periodically oscillating transverse rolls of axis perpendicular to the main flow. When molecular gas radiation is accounted for, no periodic solution is found and the transition to unsteadiness displays complex structures with chimneys-like rolls whose axes are again parallel to the main flow. The origin of this instability is probably due to centrifugal forces, as suggested previously for the case without radiation. Above the transition to unsteadiness, at Ra = 3 × 10{sup 8}, it is shown that both wall and gas radiation significantly intensify turbulent fluctuations, decrease the thermal stratification in the core of the cavity, and increase the global circulation.
Short- and long-range ordering during the phase transition of the Zn6Sc 1/1 cubic approximant
NASA Astrophysics Data System (ADS)
Yamada, Tsunetomo; Euchner, Holger; Pay Gómez, Cesar; Takakura, Hiroyuki; Tamura, Ryuji; de Boissieu, Marc
2013-05-01
Using in situ x-ray scattering and synchrotron radiation, we have experimentally elucidated the mechanism of the cubic to monoclinic phase transition in the Zn6Sc 1/1 approximant to an icosahedral quasicrystal. The high-temperature cubic phase is described as a bcc packing of a large Tsai-type icosahedral cluster whose center is occupied by an orientationally disordered Zn4 tetrahedron. A clear monoclinic distortion has been found to take place within 2 K around Tc = 157 K, in excellent agreement with the observed anomalies in the electrical resistivity and heat capacity. Also, a rapid variation of the super-structure reflection intensity is observed. The low-temperature monoclinic phase, as determined by single-crystal x-ray diffraction at 40 K, has been confirmed to consist of ordered Zn4 tetrahedra, oriented in an anti-parallel way along the [\\bar {1}0 1] direction. Above Tc, a diffuse scattering signal is observed at the position of the super-structure reflections, which evidences that a short-range ordering of the Zn4 tetrahedra takes place. In a way similar to a second-order phase transition, the correlation length describing this short-range ordering increases rapidly when the temperature diminishes and almost diverges when the temperature is close to Tc, going from 200 Å at 220 K to reach the very large value of 1200 Å at 161 K. Finally, using single-crystal x-ray diffraction, the atomic structure of the low-temperature monoclinic super-structure (space group C2/c) could be solved. The ordering of the Zn4 tetrahedra is accompanied by a strong distortion of the surrounding shells.
Transition to complex dynamics in the cubic lid-driven cavity
NASA Astrophysics Data System (ADS)
Lopez, Juan M.; Welfert, Bruno D.; Wu, Ke; Yalim, Jason
2017-07-01
The onset of time dependence in the cubic lid-driven cavity is surprisingly complicated, given the simplicity of the geometry and the modest value of the Reynolds number at which it occurs. The onset is characterized by finite-amplitude oscillations that appear to be stable for long times, but are subjected to intermittent bursts at irregular times during which the reflection symmetry about the spanwise midplane is broken. The complex dynamics are shown to be intimately related to the subcritical nature of the instability of the steady basic state. We use a spectral collocation numerical technique, solving both in the full three-dimensional space and in the symmetric subspace, and use selective frequency damping and Arnoldi iterations about the unstable basic state to determine its bifurcations. Edge tracking is also used to investigate a number of time-dependent saddle states. Putting all this together, we show that the complex dynamics are organized by two successive Hopf bifurcations, the first of which is shown to be subcritical. All local states are unstable in the full space at higher Reynolds numbers, leading to the intermittent bursting behavior.
NASA Astrophysics Data System (ADS)
Nestler, Tina; Potzger, Kay; Stöcker, Hartmut; Abendroth, Barbara; Strohmeyer, Ralph; Zierer, Robert; Meyer, Dirk C.
2011-10-01
Electrical properties of SrTiO3 single crystal samples treated by an anisotropic surface annealing technique under reducing conditions have been investigated in the temperature range of 35 K-300 K. Optical and atomic force microscopy show that annealing gives rise to polycrystallization and the formation of colored dendritic structures. Carrier concentrations and mobilities determined by Hall measurements as well as resistivities detected by van der Pauw measurements show the expected metallic behavior due to oxygen vacancy doping. Moreover, the temperature dependent resistivities indicate a cubic-to-tetragonal phase transition, which to our knowledge has not been reported before. Additionally, the transition occurred up to 53 K above the known bulk transition temperature T C at 105 K with a hysteresis up to a temperature of 220 K. Both phenomena possibly arise from dislocations and associated strain fields introduced by surface annealing that are assumed to lower the free energy of the tetragonal phase and simultaneously pin tetragonal domains. Thus, microregions of the tetragonal phase persist above T C causing the hysteresis in resistivity up to ˜12%. This effect possibly provides new chances for future oxide based non-volatile data-storage devices.
NASA Astrophysics Data System (ADS)
Lechman, Jeremy; Pierce, Flint
2012-02-01
Diffusive transport is a ubiquitous process that is typically understood in terms of a classical random walk of non-interacting particles. Here we present the results for a model of hard-sphere colloids in a Newtonian incompressible solvent at various volume fractions below the ordering transition (˜50%). We numerically simulate the colloidal systems via Fast Lubrication Dynamics -- a Brownian Dynamics approach with corrected mean-field hydrodynamic interactions. Colloid-colloid interactions are also included so that we effectively solve a system of interacting Langevin equations. The results of the simulations are analyzed in terms of the diffusion coefficient as a function of time with the early and late time diffusion coefficients comparing well with experimental results. An interpretation of the full time dependent behavior of the diffusion coefficient and mean-squared displacement is given in terms of a continuous time random walk. Therefore, the deterministic, continuum diffusion equation which arises from the discrete, interacting random walkers is presented. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Chess, David J.; Billings, Eric; Covian, Raúl; Glancy, Brian; French, Stephanie; Taylor, Joni; de Bari, Heather; Murphy, Elizabeth; Balaban, Robert S.
2013-01-01
Recent evidence suggests that the activity of mitochondrial oxidative phosphorylation Complexes (MOPC) is modulated at multiple sites. Herein, a method of optically monitoring electron distribution within and between MOPC is described using a center-mounted sample in an integrating sphere (to minimize scattering effects) with a rapid-scanning spectrometer. The redox-sensitive MOPC absorbances (~465 to 630 nm) were modeled using linear least squares analysis with individual chromophore spectra. Classical mitochondrial activity transitions (e.g., ADP-induced increase in oxygen consumption) were used to characterize this approach. Most notable in these studies was the observation that intermediates of the catalytic cycle of cytochrome oxidase are dynamically modulated with metabolic state. The MOPC redox state, along with measurements of oxygen consumption and mitochondrial membrane potential, was used to evaluate the conductances of different sections of the electron transport chain. This analysis then was applied to mitochondria isolated from rabbit hearts subjected to ischemia-reperfusion (I/R). Surprisingly, I/R resulted in an inhibition of all measured MOPC conductances, suggesting a coordinated down-regulation of mitochondrial activity with this well-established cardiac perturbation. PMID:23665273
Leal, Cecília; Ewert, Kai K.; Bouxsein, Nathan F.; Shirazi, Rahau S.; Li, Youli; Safinya, Cyrus R.
2012-01-01
Lyotropic phases of amphiphiles are a prototypical example of self-assemblies. Their structure is generally determined by amphiphile shape and their phase transitions are primarily governed by composition. In this paper, we demonstrate a new paradigm for membrane shape control where the electrostatic coupling of charged membranes to short DNA (sDNA), with tunable temperature-dependent end-to-end stacking interactions, enables switching between the inverted gyroid cubic structure (QIIG) and the inverted hexagonal phase (HIIC). We investigated the structural shape transitions induced in the QIIG phase upon complexation with a series of sDNAs (5, 11, 24, and 48 bp) with three types of end structure (“sticky” adenine (A)–thymine (T) (dAdT) overhangs, no overhang (blunt), and “nonsticky” dTdT overhangs) using synchrotron small-angle X-ray scattering. Very short 5 bp sDNA with dAdT overhangs and blunt ends induce coexistence of the QIIG and the HIIC phase, with the fraction of QIIG increasing with temperature. Phase coexistence for blunt 5 bp sDNA is observed from 27 °C to about 65 °C, where the HIIC phase disappears and the temperature dependence of the lattice spacing of the QIIG phase indicates that the sDNA duplexes melt into single strands. The only other sDNA for which melting is observed is 5 bp sDNA with dTdT overhangs, which forms the QIIG phase throughout the studied range of temperature (27 °C to 85.2 °C). The longer 11 bp sDNA forms coexisting QIIG and HIIC phases (with the fraction of QIIG again increasing with temperature) only for “nonsticky” dTdT overhangs, while dAdT overhangs and blunt ends exclusively template the HIIC phase. For 24 and 48 bp sDNAs the HIIC phase replaces the QIIG phase at all investigated temperatures, independent of sDNA end structure. Our work demonstrates how the combined effects of sDNA length and end structure (which determine the temperature-dependent stacking length) tune the phase behavior of the complexes
NASA Astrophysics Data System (ADS)
Yurtseven, H.; Kiraci, A.
2017-01-01
The damping constant Γsp due to the pseudospin-phonon coupling is calculated as a function of temperature using the pseudospin-phonon coupled model and the energy fluctuation model close to the tetragonal-cubic transition (TC = 1443 K) in SrZrO3. Using the observed Raman frequencies and the linewidth (FWHM) of the soft modes (Eg and A1g) from the literature, predictions of both models studied, are examined for the tetragonal-cubic transition in this crystalline system. Values of the activation energy U are extracted and also the inverse relaxation time is predicted as a function of temperature close to the phase transition studied in SrZrO3. Divergence behaviour of the damping constant (FWHM) of the soft modes is predicted from both models as also observed experimentally when TC is approached from the tetragonal to the cubic phase in SrZrO3. The relaxation time also diverges close to the TC in this crystal. It is indicated that the tetragonal-cubic transition is of a second order as predicted from both models studied here, as also observed experimentally in SrZrO3.
Investigation of the Metallic State in Cubic FeGe beyond its Quantum Phase Transition
NASA Astrophysics Data System (ADS)
Wilhelm, Heribert
2007-03-01
FeGe and MnSi are prominent examples where the Dzyaloshinskii-Moriya interaction causes a modulation of the ferromagnetic structure as a consequence of the lack of inversion symmetry in the B20 structure (space group P213 ). In FeGe, helimagnetism sets in through a first order phase transition at TC=280,K with a saturated moment of m=1 μB per Fe atom. The helical modulation has a period of about 700,åand propagates along the spiral propagation vector k [1 0 0]. It alters its direction to k[1 1 1] at T2 211-245,K without a change in the period. In MnSi, however, the helical order occurs below TC=29,K. The modulation has a wavelength of 175,åand the ordered moments of about m=0.4,B per Mn atom are perpendicular to k[1 1 1]. It is well established that the second order phase transition is driven first order for a sufficiently weak magnetic interaction close to the critical pressure, pc=1.46,GPa. In light of these structural and magnetic similarities between FeGe and MnSi, a volume compression in FeGe could tune its TC to zero temperature with the chance to reveal peculiar electronic ground state properties at the verge of the magnetic order. Indeed, the electrical resistivity measurements, ρ(T) , show a suppression of the helical order at pc 19 ,GPa. The strong deviations from a Fermi-liquid behavior in a wide pressure range above pc suggest that the suppression of TC disagrees with the standard notion of a quantum critical phase transition. Our band-structure calculations suggest that disorder due to zero-point motion is strong enough to close the narrow gap expected for compressed FeGe, stabilizing a new magnetic ground state above pc. An anomaly observed at TX in the ρ(T) curves recorded above pc might be related to this magnetic phase. The isothermal structural data at low temperature revealed a discontinuous change in the pressure dependence of the shortest Fe-Ge interatomic distance close to the TC(p) phase line. The (T,V) phase diagram will be discussed
Zhang, Jie; Huang, Rong; Wei, Fenfen; Cheng, Guosheng; Kong, Tao
2014-11-17
The phase transition of Bi-doped (∼3 at. %) GeTe nanowires from a rhombohedral (R) to a face-centered cubic (C) structure was observed in in situ high-temperature X-ray diffraction. The promotion of high-temperature R-C phase transition by a doping approach was revealed. Ab initio energy calculations of doped GeTe at various Bi doping concentrations were performed to interpret the promoted temperature-induced phase transitions. Those results indicated that the total energy differences between R and C structures of doped GeTe decreased as Bi doping concentrations increased, which facilitated R-C phase transitions.
Interplay between cubic and hexagonal phases in block copolymer solutions.
Park, Moon Jeong; Char, Kookheon; Bang, Joona; Lodge, Timothy P
2005-02-15
The phase behavior of a symmetric styrene-isoprene (SI) diblock copolymer in a styrene-selective solvent, diethylphthalate, was investigated by in situ small-angle X-ray scattering on isotropic and shear-oriented solutions and by rheology and birefringence. A remarkable new feature in this phase diagram is the coexistence of both body-centered cubic (bcc) and hexagonally close-packed (hcp) sphere phases, in a region between close-packed spheres (cps) and hexagonally packed cylinders (hex) over the concentration range phi approximately 0.33-0.45. By focusing on the transitions among these various ordered phases during heating and cooling cycles, we observed a strong hysteresis: supercooled cylinders persisted upon cooling. The stability of these supercooled cylinders is quite dependent on concentration, and for phi > or = 0.40, the supercooled cylinders do not revert to spheres even after quiescent annealing for 1 month. The spontaneous formation of spheres due to the dissociation of cylinders is kinetically hindered in this case, and the system is apparently not amenable to any pretransitional fluctuations of cylinders prior to the cylinder-to-sphere transition. This contrasts with the case of cylinders transforming to spheres upon heating in the melt. The application of large amplitude shear to the supercooled cylinders is effective in restoring the equilibrium sphere phases.
Freitas, F. L. Marques, M.; Teles, L. K.
2016-08-15
We provide approximate quasiparticle-corrected band gap energies for quaternary cubic and hexagonal Al{sub x}Ga{sub y}In{sub 1–x–y}N semiconductor alloys, employing a cluster expansion method to account for the inherent statistical disorder of the system. Calculated values are compared with photoluminescence measurements and discussed within the currently accepted model of emission in these materials by carrier localization. It is shown that bowing parameters are larger in the cubic phase, while the range of band gap variation is bigger in the hexagonal one. Experimentally determined transition energies are mostly consistent with band-to-band excitations.
The effect of disorder in Ba{sub 2}YTaO{sub 6} on the tetragonal to cubic phase transition
Zhou, Qingdi; Kennedy, Brendan J.; Kimpton, Justin A.
2011-04-15
Synchrotron X-ray diffraction and Raman spectroscopy have been used to study the structure of the complex perovskite Ba{sub 2}YTaO{sub 6}, at temperatures down to 100 K. Where the Ta and Y cations exhibit long-range rock-salt like ordering, Ba{sub 2}YTaO{sub 6} displays a continuous phase transition from a high temperature cubic structure, described in space group Fm3-bar m, to a tetragonal, I4/m, structure near 260 K. This transition is inhibited if extensive disorder and/or vacancies are/is present in the sample. -- Graphical abstract: The tetragonal-cubic phase transition observed in the cation ordered double perovskite Ba{sub 2}YTaO{sub 6} is inhibited when these are disordered. Display Omitted Highlights: {yields} Double perovskite Ba{sub 2}YTaO{sub 6} characterised by XRD and Raman spectroscopy. {yields} Cubic-tetragonal transition in Ba{sub 2}YTaO{sub 6} studied. {yields} Impact of disorder on the structure and phase transitions established.
Brouwers, H J H
2007-10-01
The geometrical stability of the three lattices of the cubic crystal system, viz. face-centered cubic (fcc), body-centered cubic (bcc), and simple cubic (sc), consisting of bimodal discrete hard spheres, and the transition to amorphous packing is studied. First, the random close packing (rcp) fraction of binary mixtures of amorphously packed spheres is recapitulated. Next, the packing of a binary mixture of hard spheres in randomly disordered cubic structures is analyzed, resulting in original analytical expressions for the unit cell volume and the packing fraction, and which are also valid for the other five crystal systems. The bimodal fcc lattice parameter appears to be in close agreement with empirical hard sphere data from literature, and this parameter could be used to distinguish the size mismatch effect from all other effects in distorted binary lattices of materials. Here, as a first model application, bimodal amorphous and crystalline fcc/bcc packing fractions are combined, yielding the optimum packing configuration, which depends on mixture composition and diameter ratio only. Maps of the closest packing mode are established and applied to colloidal mixtures of polydisperse spheres and to binary alloys of bcc, fcc, and hcp metals. The extensive comparison between the analytical expressions derived here and the published numerical and empirical data yields good agreement. Hence, it is seen that basic space-filling theories on "simple" noninteracting hard spheres are a valuable tool for the study of crystalline materials.
NASA Astrophysics Data System (ADS)
Brouwers, H. J. H.
2007-10-01
The geometrical stability of the three lattices of the cubic crystal system, viz. face-centered cubic (fcc), body-centered cubic (bcc), and simple cubic (sc), consisting of bimodal discrete hard spheres, and the transition to amorphous packing is studied. First, the random close packing (rcp) fraction of binary mixtures of amorphously packed spheres is recapitulated. Next, the packing of a binary mixture of hard spheres in randomly disordered cubic structures is analyzed, resulting in original analytical expressions for the unit cell volume and the packing fraction, and which are also valid for the other five crystal systems. The bimodal fcc lattice parameter appears to be in close agreement with empirical hard sphere data from literature, and this parameter could be used to distinguish the size mismatch effect from all other effects in distorted binary lattices of materials. Here, as a first model application, bimodal amorphous and crystalline fcc/bcc packing fractions are combined, yielding the optimum packing configuration, which depends on mixture composition and diameter ratio only. Maps of the closest packing mode are established and applied to colloidal mixtures of polydisperse spheres and to binary alloys of bcc, fcc, and hcp metals. The extensive comparison between the analytical expressions derived here and the published numerical and empirical data yields good agreement. Hence, it is seen that basic space-filling theories on “simple” noninteracting hard spheres are a valuable tool for the study of crystalline materials.
Fischer, T; Vink, R L C
2010-03-17
Computer simulations of first-order phase transitions using 'standard' toroidal boundary conditions are generally hampered by exponential slowing down. This is partly due to interface formation, and partly due to shape transitions. The latter occur when droplets become large such that they self-interact through the periodic boundaries. On a spherical simulation topology, however, shape transitions are absent. We expect that by using an appropriate bias function, exponential slowing down can be largely eliminated. In this work, these ideas are applied to the two-dimensional Widom-Rowlinson mixture confined to the surface of a sphere. Indeed, on the sphere, we find that the number of Monte Carlo steps needed to sample a first-order phase transition does not increase exponentially with system size, but rather as a power law τ α V(α), with α≈2.5, and V the system area. This is remarkably close to a random walk for which α(RW) = 2. The benefit of this improved scaling behavior for biased sampling methods, such as the Wang-Landau algorithm, is investigated in detail.
Mills, P; Snabre, P
2009-11-01
We consider the steady shear flow of a homogeneous and dense assembly of hard spheres suspended in a Newtonian viscous fluid. In a first part, a mean-field approach based on geometric arguments is used to determine the viscous dissipation in a dense isotropic suspension of smooth hard spheres and the hydrodynamic contribution to the suspension viscosity. In a second part, we consider the coexistence of transient solid clusters coupled to regions with free flowing particles near the jamming transition. The fraction of particles in transient clusters is derived through the Landau-Ginzburg concepts for first-order phase transition with an order parameter corresponding to the proportion of "solid" contacts. A state equation for the fraction of particle-accessible volume is introduced to derive the average normal stresses and a constitutive law that relates the total shear stress to the shear rate. The analytical expression of the average normal stresses well accounts for numerical or experimental evaluation of the particle pressure and non-equilibrium osmotic pressure in a dense sheared suspension. Both the friction level between particles and the suspension dilatancy are shown to determine the singularity of the apparent shear viscosity and the flow stability near the jamming transition. The model further predicts a Newtonian behavior for a concentrated suspension of neutrally buoyant particles and no shear thinning behavior in relation with the shear liquefaction of transient solid clusters.
ERIC Educational Resources Information Center
Chiung, Wi-vun Taiffalo
2007-01-01
The Han sphere, including Vietnam, Korea, Japan, Taiwan and China, adopted Han characters and classical Han writing as the official written language before the 20th century. However, great changes came with the advent of the 20th century. After World War II, Han characters in Vietnam and Korea were officially replaced by the romanised "Chu…
Zhang, Jingyan; Ge, Zhishen; Jiang, Xiaoze; Hassan, P A; Liu, Shiyong
2007-12-15
The kinetics and mechanism of sphere-to-rod transitions of sodium alkyl sulfate micelles induced by hydrotropic salt, p-toluidine hydrochloride (PTHC), were investigated by stopped-flow with light scattering detection. Spherical sodium dodecyl sulfate (SDS) micelles transform into short ellipsoidal shapes at low salt concentrations ([PTHC]/[SDS], chi(PTHC)=0.3 and 0.4). Upon stopped-flow mixing aqueous solutions of spherical SDS micelles with PTHC, the scattered light intensity gradually increases with time. Single exponential fitting of the dynamic traces leads to characteristic relaxation time, tau(g), for the growth process from spherical to ellipsoidal micelles, and it increases with increasing SDS concentrations. This suggests that ellipsoidal micelles might be produced by successive insertion of unimers into spherical micelles, similar to the case of formation of spherical micelles as suggested by Aniansson-Wall (A-W) theory. At chi(PTHC) > or = 0.5, rod-like micelles with much higher axial ratio form. The scattered light intensity exhibits an initially abrupt increase and then levels off. The dynamic curves can be well fitted with single exponential functions, and the obtained tau(g) decreases with increasing SDS concentration. Thus, the growth from spherical to rod-like micelles might proceed via fusion of spherical micelles, in agreement with mechanism proposed by Ikeda et al. At chi(PTHC)=0.3 and 0.6, the apparent activation energies obtained from temperature dependent kinetic studies for the micellar growth are 40.4 and 3.6 kJ/mol, respectively. The large differences between activation energies for the growth from spherical to ellipsoidal micelles at low chi(PTHC) and the sphere-to-rod transition at high chi(PTHC) further indicate that they should follow different mechanisms. Moreover, the sphere-to-rod transition kinetics of sodium alkyl sulfate with varying hydrophobic chain lengths (n=10, 12, 14, and 16) are also studied. The longer the carbon chain
Murtazaev, A. K.; Ramazanov, M. K.; Kassan-Ogly, F. A.; Kurbanova, D. R.
2015-01-15
Phase transitions in the antiferromagnetic Ising model on a body-centered cubic lattice are studied on the basis of the replica algorithm by the Monte Carlo method and histogram analysis taking into account the interaction of next-to-nearest neighbors. The phase diagram of the dependence of the critical temperature on the intensity of interaction of the next-to-nearest neighbors is constructed. It is found that a second-order phase transition is realized in this model in the investigated interval of the intensities of interaction of next-to-nearest neighbors.
NASA Astrophysics Data System (ADS)
An, Xi-Zhong
2007-08-01
Micro structures of equal sphere packing (ranging from loose to dense packing) generated numerically by discrete element method under different vibration conditions are characterized using Voronoi/Delaunay tessellation, which is applied on a wide range of packing densities. The analysis on micro properties such as the total perimeter, surface area, and the face number distribution of each Voronoi polyhedron, and the pore size distribution in each Voronoi/Delaunay subunit is systematically carried out. The results show that with the increasing density of sphere packing, the Voronoi/Delaunay pore size distribution is narrowed. That indicates large pores to be gradually substituted by small uniformed ones during densification. Meanwhile, the distributions of face number, total perimeter, and surface area of Voronoi polyhedra at high packing densities tend to be narrower and higher, which is in good agreement with those in random loose packing.
NASA Astrophysics Data System (ADS)
Yang, Lin-Hong; Dong, Hong-Xing; Sun, Zheng; Sun, Liao-Xin; Shen, Xue-Chu; Chen, Zhang-Hai
2011-08-01
We report an experimental study on the temperature-induced phase transition of three-dimensional nanosheet-based flower-like microspheres (NBFMs) of In2O3. Using InOOH as precursor, rhombohedral-In2O3 NBFMs are fabricated. Temperature-induced phase transition of In2O3 NBFMs from a rhombohedral (rh) structure to a body-centered cubic (bcc) structure is examined by Raman spectroscopy and x-ray diffraction. The critical phase transition temperature is found to be about 500°C. Photoluminescence (PL) spectra of In2O3 are measured before annealing and after annealing at different temperatures. The PL spectral results provide further evidence for the phase transition, confirming the fabrication of bcc-In2O3 NBFMs via a simple annealing method.
NASA Astrophysics Data System (ADS)
Wei, Yong-Kai; Ge, Ni-Na; Chen, Xiang-Rong; Ji, Guang-Fu; Cai, Ling-Cang; Gu, Zhuo-Wei
2014-03-01
The phase transition, thermoelastic, lattice dynamic, and thermodynamic properties of the cubic metallic phase AlH3 were obtained within the density-function perturbation theory. The calculated elastic modulus and phonon dispersion curves under various pressures at 0 K indicate the cubic phase is both mechanically and dynamically stable above 73 GPa. The superconducting transition temperature Tc was calculated using the Allen-Dynes modification of the McMillan formula based on BCS theory. The calculations show that Tc for the cubic phase AlH3 is 8.5 K (μ*=0.1) at the onset of this phase (73 GPa), while decreases to 5.7 K at 80 GPa and almost disappears at 110 GPa, consisting with experimental phenomenon that there was no superconducting transition observed down to 4 K over a wide pressure range 110-164 GPa. It is found that the soft phonon mode for branch 1, namely, the lowest acoustic mode, plays a crucial role in elevating the total EPC parameter λ of cubic AlH3. And the evolution of Tc with pressure follows the corresponding change of this soft mode, i.e. this mode is responsible for the disappearance of Tc in experiments. Meanwhile, the softening of this lowest acoustic mode originates from the electronic momentum transfer from M to R point. This phenomenon provides an important insight into why drastic changes in the diffraction pattern were observed in the pressure range of 63-73 GPa in Goncharenko's experiments. Specifically, once finite electronic temperature effects are included, we find that dynamical instabilities can be removed in the phonon dispersion for P ≥63 GPa, rendering the metastability of this phase in the range of 63-73 GPa, and Tc (15.4 K) becomes remarkably high under the lowest possible pressure (63 GPa) compared with that of under 73 GPa (8.5 K). Our calculations open the possibility that finite temperature may allow cubic AlH3 to be dynamically stabilized even for pressures below 73 GPa. It is reasonable to deduced that if special
Monte Carlo simulations of the solid-liquid transition in hard spheres and colloid-polymer mixtures.
Zykova-Timan, T; Horbach, J; Binder, K
2010-07-07
Monte Carlo simulations at constant pressure are performed to study coexistence and interfacial properties of the liquid-solid transition in hard spheres and in colloid-polymer mixtures. The latter system is described as a one-component Asakura-Oosawa (AO) model where the polymer's degrees of freedom are incorporated via an attractive part in the effective potential for the colloid-colloid interactions. For the considered AO model, the polymer reservoir packing fraction is eta(p) (r)=0.1 and the colloid-polymer size ratio is q[triple bond]sigma(p)/sigma=0.15 (with sigma(p) and sigma as the diameter of polymers and colloids, respectively). Inhomogeneous solid-liquid systems are prepared by placing the solid fcc phase in the middle of a rectangular simulation box, creating two interfaces with the adjoined bulk liquid. By analyzing the growth of the crystalline region at various pressures and for different system sizes, the coexistence pressure p(co) is obtained, yielding p(co)=11.576 k(B)T/sigma(3) for the hard-sphere system and p(co)=8.00 k(B)T/sigma(3) for the AO model (with k(B) as the Boltzmann constant and T as the temperature). Several order parameters are introduced to distinguish between solid and liquid phases and to describe the interfacial properties. From the capillary-wave broadening of the solid-liquid interface, the interfacial stiffness is obtained for the (100) crystalline plane, giving the values gamma approximately 0.49 k(B)T/sigma(2) for the hard-sphere system and gamma approximately 0.95 k(B)T/sigma(2) for the AO model.
Monte Carlo simulations of the solid-liquid transition in hard spheres and colloid-polymer mixtures
NASA Astrophysics Data System (ADS)
Zykova-Timan, T.; Horbach, J.; Binder, K.
2010-07-01
Monte Carlo simulations at constant pressure are performed to study coexistence and interfacial properties of the liquid-solid transition in hard spheres and in colloid-polymer mixtures. The latter system is described as a one-component Asakura-Oosawa (AO) model where the polymer's degrees of freedom are incorporated via an attractive part in the effective potential for the colloid-colloid interactions. For the considered AO model, the polymer reservoir packing fraction is ηpr=0.1 and the colloid-polymer size ratio is q ≡σp/σ=0.15 (with σp and σ as the diameter of polymers and colloids, respectively). Inhomogeneous solid-liquid systems are prepared by placing the solid fcc phase in the middle of a rectangular simulation box, creating two interfaces with the adjoined bulk liquid. By analyzing the growth of the crystalline region at various pressures and for different system sizes, the coexistence pressure pco is obtained, yielding pco=11.576 kBT/σ3 for the hard-sphere system and pco=8.00 kBT/σ3 for the AO model (with kB as the Boltzmann constant and T as the temperature). Several order parameters are introduced to distinguish between solid and liquid phases and to describe the interfacial properties. From the capillary-wave broadening of the solid-liquid interface, the interfacial stiffness is obtained for the (100) crystalline plane, giving the values γ˜≈0.49 kBT/σ2 for the hard-sphere system and γ˜≈0.95 kBT/σ2 for the AO model.
NASA Astrophysics Data System (ADS)
Pundt, A.; Dornheim, M.; Guerdane, M.; Teichler, H.; Ehrenberg, H.; Reetz, M. T.; Jisrawi, N. M.
2002-06-01
An in situ synchrotron radiation study of quasi-free five nanometer-sized palladium clusters during hydrogen absorption is combined with molecular dynamics simulations to investigate the structural development. In the diffraction patterns, strong intensity changes are found that provide evidence for a structural phase transformation that is significantly different from the α α' Pd H bulk phase transition. The structural transition is reversible and driven by the hydrogen concentration. The intensity changes are consistent with a cubic-to-icosahedral structural phase transition obtained in molecular dynamical simulations using embedded-atom-method potentials.
NASA Astrophysics Data System (ADS)
Mishra, Vikash; Sagdeo, Archna; Kumar, Vipin; Warshi, M. Kamal; Rai, Hari Mohan; Saxena, S. K.; Roy, Debesh R.; Mishra, Vinayak; Kumar, Rajesh; Sagdeo, P. R.
2017-08-01
Temperature dependent diffuse reflectance spectroscopy measurements were carried out on polycrystalline samples of BaTiO3 across the tetragonal to cubic structural phase transition temperature (TP). The values of various optical parameters such as band gap (Eg), Urbach energy (Eu), and Urbach focus (E0) were estimated in the temperature range of 300 K to 480 K. It was observed that with increasing temperature, Eg decreases and shows a sharp anomaly at TP. First principle studies were employed in order to understand the observed change in Eg due to the structural phase transition. Near TP, there exist two values of E0, suggesting the presence of electronic heterogeneity. Further, near TP, Eu shows metastability, i.e., the value of Eu at temperature T is not constant but is a function of time (t). Interestingly, it is observed that the ratio of Eu (t=0)/Eu (t = tm), almost remains constant at 300 K (pure tetragonal phase) and at 450 K (pure cubic phase), whereas this ratio decreases close to the transition temperature, which confirms the presence of electronic metastability in the pure BaTiO3. The time dependence of Eu, which also shows an influence of the observed metastability can be fitted with the stretched exponential function, suggesting the presence of a dynamic heterogeneous electronic disorder in the sample across TP. First principle studies suggest that the observed phase coexistence may be due to a very small difference between the total cohesive energy of the tetragonal and the cubic structure of BaTiO3. The present work implies that the optical studies may be a sensitive probe of disorder/heterogeneity in the sample.
Santos, Andrés; López de Haro, Mariano; Yuste, Santos B
2010-05-28
Different theoretical approaches for the thermodynamic properties and the equation of state for multicomponent mixtures of nonadditive hard spheres in d dimensions are presented in a unified way. These include the theory by Hamad, our previous formulation, the original MIX1 theory, a recently proposed modified MIX1 theory, as well as a nonlinear extension of the MIX1 theory proposed in this paper. Explicit expressions for the compressibility factor, Helmholtz free energy, and second, third, and fourth virial coefficients are provided. A comparison is carried out with recent Monte Carlo data for the virial coefficients of asymmetric mixtures and with available simulation data for the compressibility factor, the critical consolute point, and the liquid-liquid coexistence curves. The merits and limitations of each theory are pointed out.
Topology trivialization transition in random non-gradient autonomous ODEs on a sphere
NASA Astrophysics Data System (ADS)
Fyodorov, Y. V.
2016-12-01
We calculate the mean total number of equilibrium points in a system of N random autonomous ODEs introduced by Cugliandolo et al [17] to describe non-relaxational glassy dynamics on the high-dimensional sphere. In doing it we suggest a new approach which allows such a calculation to be done most straightforwardly, and is based on efficiently incorporating the Langrange multiplier into the Kac-Rice framework. Analysing the asymptotic behaviour for large N we confirm that the phenomenon of ‘topology trivialization’ revealed earlier for other systems holds also in the present framework with nonrelaxational dynamics. Namely, by increasing the variance of the random ‘magnetic field’ term in dynamical equations we find a ‘phase transition’ from the exponentially abundant number of equilibria down to just two equilibria. Classifying the equilibria in the nontrivial phase by stability remains an open problem.
NASA Astrophysics Data System (ADS)
Santos, Andrés; López de Haro, Mariano; Yuste, Santos B.
2010-05-01
Different theoretical approaches for the thermodynamic properties and the equation of state for multicomponent mixtures of nonadditive hard spheres in d dimensions are presented in a unified way. These include the theory by Hamad, our previous formulation, the original MIX1 theory, a recently proposed modified MIX1 theory, as well as a nonlinear extension of the MIX1 theory proposed in this paper. Explicit expressions for the compressibility factor, Helmholtz free energy, and second, third, and fourth virial coefficients are provided. A comparison is carried out with recent Monte Carlo data for the virial coefficients of asymmetric mixtures and with available simulation data for the compressibility factor, the critical consolute point, and the liquid-liquid coexistence curves. The merits and limitations of each theory are pointed out.
Thermodynamic properties of lattice hard-sphere models.
Panagiotopoulos, A Z
2005-09-08
Thermodynamic properties of several lattice hard-sphere models were obtained from grand canonical histogram- reweighting Monte Carlo simulations. Sphere centers occupy positions on a simple cubic lattice of unit spacing and exclude neighboring sites up to a distance sigma. The nearestneighbor exclusion model, sigma = radical2, was previously found to have a second-order transition. Models with integer values of sigma = 1 or 2 do not have any transitions. Models with sigma = radical3 and sigma = 3 have weak first-order fluid-solid transitions while those with sigma = 2 radical2, 2 radical3, and 3 radical2 have strong fluid-solid transitions. Pressure, chemical potential, and density are reported for all models and compared to the results for the continuum, theoretical predictions, and prior simulations when available.
Boujnah, M.; Zaari, H.; El Kenz, A.; Labrim, H.; Benyoussef, A.; Mounkachi, O.
2014-03-28
The electronic structure, magnetic, and optical properties in cubic crystalline phase of Zr{sub 1−x}TM{sub x}O{sub 2} (TM = V, Mn, Fe, and Co) at x = 6.25% are studied using density functional theory with the Generalized Gradient Approximation and the modified Becke-Johnson of the exchange-correlation energy and potential. In our calculations, the zirconia is a p-type semiconductor and has a large band gap. We evaluated the possibility of long-range magnetic order for transition metal ions substituting Zr. Our results show that ferromagnetism is the ground state in V, Mn, and Fe-doped ZrO{sub 2} and have a high value of energy in Mn-doped ZrO{sub 2}. However, in Co-doped ZrO{sub 2}, antiferromagnetic ordering is more stable than the ferromagnetic one. The exchange interaction mechanism has been discussed to explain the responsible of this stability. Moreover, it has been found that the V, Mn, and Fe transition metals provide half-metallic properties considered to be the leading cause, responsible for ferromagnetism. Furthermore, the optical absorption spectra in the TM -doped cubic ZrO{sub 2} are investigated.
Phase diagram of Hertzian spheres
NASA Astrophysics Data System (ADS)
Pàmies, Josep C.; Cacciuto, Angelo; Frenkel, Daan
2009-07-01
We report the phase diagram of interpenetrating Hertzian spheres. The Hertz potential is purely repulsive, bounded at zero separation, and decreases monotonically as a power law with exponent 5/2, vanishing at the overlapping threshold. This simple functional describes the elastic interaction of weakly deformable bodies and, therefore, it is a reliable physical model of soft macromolecules, like star polymers and globular micelles. Using thermodynamic integration and extensive Monte Carlo simulations, we computed accurate free energies of the fluid phase and a large number of crystal structures. For this, we defined a general primitive unit cell that allows for the simulation of any lattice. We found multiple re-entrant melting and first-order transitions between crystals with cubic, trigonal, tetragonal, and hexagonal symmetries.
Wilding, Nigel B; Sollich, Peter
2010-12-14
The statistical mechanics of phase transitions in dense systems of polydisperse particles presents distinctive challenges to computer simulation and analytical theory alike. The core difficulty, namely, dealing correctly with particle size fractionation between coexisting phases, is set out in the context of a critique of previous simulation work on such systems. Specialized Monte Carlo simulation techniques and moment free energy method calculations, capable of treating fractionation exactly, are then described and deployed to study the fluid-solid transition of an assembly of repulsive spherical particles described by a top-hat "parent" distribution of particle sizes. The cloud curve delineating the solid-fluid coexistence region is mapped as a function of the degree of polydispersity δ, and the properties of the incipient "shadow" phases are presented. The coexistence region is found to shift to higher densities as δ increases, but does not exhibit the sharp narrowing predicted by many theories and some simulations.
Entropically dirven phase transitions in mixtures of colloidal rods and spheres.
NASA Astrophysics Data System (ADS)
Fraden, Seth
2001-03-01
We have prepared a homologous series of filamentous viruses with varying contour length using molecular cloning techniques. These viruses are monodisperse enough to form a stable smectic phase. Two systems are studied. The first system consists of viruses to which polymers are covalently attached to the virus surface. Through studies of the isotropic - cholesteric phase transition we demonstrate that covalently attached polymers alter the effective diameter of the virus and we have produced mixtures of viruses whose ratio of effective diameters varies by a factor of five. The second system is composed of mixtures of rod-like viruses and non-absorbing polymers. With this system we study the kinetics of the isotropic - smectic phase transition and describe observations of a number of novel metastable structures of unexpected complexity. Preprints are available online at www.elsie.brandeis.edu and at http://xxx.lanl.gov/abs/cond-mat/0010269.
Alsobrook, Andera N.; Hauser, B. G.; Hupp, Joseph T.; Alekseev, Evgeny V.; Depmeier, Wulf; Albrecht-Schmitt, Thomas E.
2010-11-01
Four heterobimetallic U(VI)/M(II) (M = Mn, Co, Cd) carboxyphosphonates have been synthesized. M_{2}[(UO_{2})_{6}(PO_{3}CH_{2}CO_{2})_{3}O_{3}(OH)(H_{2}O)_{2}]·16H_{2}O (M = Mn(II), Co(II), and Cd(II)) adopt cubic three-dimensional network structures with large cavities approximately 16 Å in diameter that are filled with co-crystallized water molecules. [Cd_{3}(UO_{2})_{6}(PO_{3}CH_{2}CO_{2})_{6}(H_{2}O)_{13}]·6H^{2 }O forms a rhombohedral channel structure with hydrated Cd(II) within the channels. The cubic compound (Co) displays differential gas absorption with a surface area for CO_{2} uptake of 40 m^{2 }g^{-1} at 273 K, and no uptake of N_{2} at 77 K.
Testing giant planet formation in the transitional disk of SAO 206462 using deep VLT/SPHERE imaging
NASA Astrophysics Data System (ADS)
Maire, A.-L.; Stolker, T.; Messina, S.; Müller, A.; Biller, B. A.; Currie, T.; Dominik, C.; Grady, C. A.; Boccaletti, A.; Bonnefoy, M.; Chauvin, G.; Galicher, R.; Millward, M.; Pohl, A.; Brandner, W.; Henning, T.; Lagrange, A.-M.; Langlois, M.; Meyer, M. R.; Quanz, S. P.; Vigan, A.; Zurlo, A.; van Boekel, R.; Buenzli, E.; Buey, T.; Desidera, S.; Feldt, M.; Fusco, T.; Ginski, C.; Giro, E.; Gratton, R.; Hubin, N.; Lannier, J.; Le Mignant, D.; Mesa, D.; Peretti, S.; Perrot, C.; Ramos, J. R.; Salter, G.; Samland, M.; Sissa, E.; Stadler, E.; Thalmann, C.; Udry, S.; Weber, L.
2017-05-01
Context. The SAO 206462 (HD 135344B) disk is one of the few known transitional disks showing asymmetric features in scattered light and thermal emission. Near-infrared scattered-light images revealed two bright outer spiral arms and an inner cavity depleted in dust. Giant protoplanets have been proposed to account for the disk morphology. Aims: We aim to search for giant planets responsible for the disk features and, in the case of non-detection, to constrain recent planet predictions using the data detection limits. Methods: We obtained new high-contrast and high-resolution total intensity images of the target spanning the Y to the K bands (0.95-2.3 μm) using the VLT/SPHERE near-infrared camera and integral field spectrometer. Results: The spiral arms and the outer cavity edge are revealed at high resolutions and sensitivities without the need for aggressive image post-processing techniques, which introduce photometric biases. We do not detect any close-in companions. For the derivation of the detection limits on putative giant planets embedded in the disk, we show that the knowledge of the disk aspect ratio and viscosity is critical for the estimation of the attenuation of a planet signal by the protoplanetary dust because of the gaps that these putative planets may open. Given assumptions on these parameters, the mass limits can vary from 2-5 to 4-7 Jupiter masses at separations beyond the disk spiral arms. The SPHERE detection limits are more stringent than those derived from archival NaCo/L' data and provide new constraints on a few recent predictions of massive planets (4-15 MJ) based on the spiral density wave theory. The SPHERE and ALMA data do not favor the hypotheses on massive giant planets in the outer disk (beyond 0.6''). There could still be low-mass planets in the outer disk and/or planets inside the cavity. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 095.C
Polireddy, Kishore; Dong, Ruochen; McDonald, Peter R.; Wang, Tao; Luke, Brendan; Chen, Ping; Broward, Melinda; Roy, Anuradha; Chen, Qi
2016-01-01
Background Pancreatic cancer has an enrichment of stem-like cancer cells (CSCs) that contribute to chemoresistant tumors prone to metastasis and recurrence. Drug screening assays based on cytotoxicity cannot identify specific CSC inhibitors, because CSCs comprise only a small portion of cancer cell population, and it is difficult to propagate stable CSC populations in vitro for high-throughput screening (HTS) assays. Based on the important role of cancer cell epithelial-to-mesenchymal transition (EMT) in promoting CSCs, we hypothesized that inhibition of EMT can be a useful strategy for inhibiting CSCs, and therefore a feasible approach for HTS can be built for identification of CSC inhibitors, based on assays detecting EMT inhibition. Methods An immunofluorescent assay was established and optimized for HTS to identify compounds that enhance E-cadherin expression, as a hallmark of inhibition of EMT. Four chemical libraries containing 41,472 compounds were screened in PANC-1 pancreatic cancer cell line. Positive hits were validated for EMT and CSC inhibition in vitro using sphere formation assay, western blotting, immune fluorescence, and scratch assay. Results Initial hits were refined to 73 compounds with a secondary screening, among which 17 exhibited concentration dependent induction of E-cadherin expression. Six compounds were selected for further study which belonged to 2 different chemical structural clusters. A novel compound 1-(benzylsulfonyl) indoline (BSI, Compound #38) significantly inhibited pancreatic cancer cell migration and invasion. BSI inhibited histone deacetylase, increased histone 4 acetylation preferably, resulting in E-cadherin up-regulation. BSI effectively inhibited tumor spheres formation. Six more analogues of BSI were tested for anti-migration and anti-CSC activities. Conclusion This study demonstrated a feasible approach for discovery of agents targeting EMT and CSCs using HTS, and identified a class of novel chemicals that could be
Phase transitions and marginal ensemble equivalence for freely evolving flows on a rotating sphere.
Herbert, C; Dubrulle, B; Chavanis, P H; Paillard, D
2012-05-01
The large-scale circulation of planetary atmospheres such as that of the Earth is traditionally thought of in a dynamical framework. Here we apply the statistical mechanics theory of turbulent flows to a simplified model of the global atmosphere, the quasigeostrophic model, leading to nontrivial equilibria. Depending on a few global parameters, the structure of the flow may be either a solid-body rotation (zonal flow) or a dipole. A second-order phase transition occurs between these two phases, with associated spontaneous symmetry breaking in the dipole phase. This model allows us to go beyond the general theory of marginal ensemble equivalence through the notion of Goldstone modes.
NASA Astrophysics Data System (ADS)
Behera, Pallavi Suhasinee; Vasanthavel, S.; Ponnilavan, V.; Kannan, S.
2015-05-01
The present study reports the effect of gadolinium (Gd3+) in zirconia-silica (ZrO2-SiO2) binary oxides. The pure ZrO2-SiO2 synthesized at 1100 °C was tetragonal. The addition of Gd3+ in the concentration range of 5%-10% resulted in the formation of t-ZrO2, whereas higher contents of Gd3+ led to the formation of cubic ZrO2 (c-ZrO2). The presence of Gd3+ also affected the lattice parameters of both t-ZrO2 and c-ZrO2. Magnetic studies confirmed a steady increase in the paramagnetic behaviour with increasing content of Gd3+.
Glycerol prevents dehydration in lipid cubic phases.
Richardson, S J; Staniec, P A; Newby, G E; Rawle, J L; Slaughter, A R; Terrill, N J; Elliott, J M; Squires, A M
2015-07-21
Lipid cubic phase samples dry out and undergo phase transitions when exposed to air. We demonstrate experimentally and theoretically that adding glycerol controllably lowers the humidity at which cubic phases form. These results broaden the potential applications of cubic phases and open up the potential of a new humidity-responsive nanomaterial.
NASA Astrophysics Data System (ADS)
Clerc, M.; Levelut, A. M.; Sadoc, J. F.
1991-10-01
In order to approach the fascinating structure of the cubic mesophases, we study phase transitions involving them and another mesophases with simpler structures. In the first part, we give some results obtained in the C_{12}EO_6/water binary system, that exhibits the most frequent case of bicontinuous cubic mesophase, with space group Ia3d, and two transitions toward the hexagonal and lamellar mesophases. X-ray scattering experiments and some optical observations in polarized light are presented for oriented single-domains of the mesophases. In the second part, we propose some topological arguments to explain the transformations involved at these two transitions and propose some possible fluctuations associated with them. les phases cubiques dans les systèmes eau/savon sont un exemple tout à fait remarquable d'organisation moléculaire entre liquides. Nous présentons ici une étude de transitions de phases entre elles et d'autres phases de structure beaucoup moins complexe, en montrant comment la structure cubique peut se déduire de celle des autres. Dans la première partie, nous présentons les résultats obtenus pour le système modèle C_{12}EO_6/eau, qui offre le cas le plus fréquent de phase cubique bicontinue, de groupe d'espace Ia3d, ainsi que deux transitions vers les phases hexagonale et lamellaire. Des clichés de diffraction des rayons X aux petits angles ont été obtenus pour des échantillons orientés de ces phases, mettant en particulier en évidence les fluctuations des structures observées, par la présence de “diffusions diffuses" entre les réflexions de Bragg. Dans la seconde partie, nous exposons une analyse détaillée des changements de topologie intervenant lors de ces deux transitions, puis discutons des fluctuations pouvant leur être associées, à la lumière des observations précédentes.
Deng, Yuru; Kohlwein, Sepp D; Mannella, Carmen A
2002-05-01
Large free-living amoeba (Chaos carolinensis) can survive in spring water without food intake for several weeks. Starvation is associated with a dramatic change in mitochondrial cristae from random tubular to ordered (paracrystalline) cubic morphology. Whole-cell polarography was used to monitor changes in respiratory activity during fasting. Basal respiration per cell decreased progressively during starvation, while the cyanide-resistant fraction increased. Spectrofluorometric assay of H2O2 and reactive oxygen species (ROS) in cell lysates (using the dye 2',7'-dichlorofluorescein diacetate) indicates greater H2O2 and ROS generation in starved than in fed cells. Fluorescence microscopy of intact cells incubated with the same dye demonstrates that H2O2 and ROS tend to accumulate in vacuoles. A remarkable generation of O2 observed with starved cells after addition of KCN may be explained by release of H2O2 from these compartments into the cytosol, where it can react with catalase. Together, these observations suggest that fasting increases oxidative stress in the amoeba and that this organism has several protective mechanisms to deal with it, including activation of a plantlike alternative oxidase. The hypothesis is forwarded that the cubic structural transition of the mitochondrial inner membrane represents another protective mechanism, reducing oxidative damage by enhancing the efflux of H2O2 and ROS and by reducing the susceptibility of membrane lipids to the oxidants.
NASA Astrophysics Data System (ADS)
Giampietri, Alessio; Drera, Giovanni; Píš, Igor; Magnano, Elena; Sangaletti, Luigi
2016-09-01
The epitaxial growth of cubic BiFeO3 ultrathin films on SrTiO3 (001) substrates by off-axis RF sputtering is demonstrated, suitable to X-ray spectroscopies interface investigation. X-ray photoelectron diffraction is used as a tool to probe the long-range crystal order and to track the transition from amorphous to epitaxial growth as a function of deposition parameters. Further spectroscopic measurements, in particular, X-ray linear dichroism on the Fe L 3 , 2 edge, confirm the heteroepitaxial growth of BiFeO3 and clearly indicate a 3+ valence state for the iron cation. Finally, XPS is used to reconstruct the band alignment diagram, which results in a staggered configuration with a remarkable energy shift of the SrTiO3 band edges which can ultimately favor the n-type doping of SrTiO3.
Kumar, Satish; Kumar, Dhirendra; Rathore, Ajay Kumar; Sathe, V. G.
2016-05-23
BaTiO{sub 3} [BTO] films have been grown on LaAlO{sub 3} (LAO) substrate using pulse laser deposition technique. The film is found highly oriented, possess 400 nm thickness and single phase in nature. However, the out-of-plane lattice parameter of the film obtained from the x-ray diffraction was found to be lower when compared to bulk compound indicating towards strain reversal. The Raman spectra recorded at room temperature showed that the film is tetragonal with C4v symmetry. Raman spectra collected at high temperatures for the film and the bulk compound showed that the tetragonal to cubic transition temperature in film is enhanced by 100 K.
Discovery of a Frank-Kasper sigma phase in sphere-forming block copolymer melts.
Lee, Sangwoo; Bluemle, Michael J; Bates, Frank S
2010-10-15
Sphere-forming block copolymers are known to self-assemble into body-centered cubic crystals near the order-disorder transition temperature. Small-angle x-ray scattering and transmission electron microscopy experiments on diblock and tetrablock copolymer melts have revealed an equilibrium phase characterized by a large tetragonal unit cell containing 30 microphase-separated spheres. This structure, referred to as the sigma (σ) phase by Frank and Kasper more than 50 years ago, nucleates and grows from the body-centered cubic phase similar to its occurrence in metal alloys and is a crystal approximant to dodecagonal quasicrystals. Formation of the σ phase in undiluted linear block copolymers (and certain branched dendrimers) appears to be mediated by macromolecular packing frustration, an entropic contribution to the interparticle interactions that control the sphere-packing geometry.
Zhang, Yin; Chen, Chen; Gao, Ran; Xia, Feng; Li, YueSheng; Che, Renchao
2015-11-02
Phase stability of the ferroelectric materials at high temperature is extremely important to their device performance. Ba{sub x}Sr{sub 1−x}TiO{sub 3} (BST) nanoparticles with different Sr contents (x = 1, 0.91, 0.65, 0.4, and 0) are prepared by a facile hydrothermal method. Using Raman spectroscopy and transmission electron microscopy (TEM) analyses under in situ heating conditions (up to 300 °C), the phase transitions of BST nanoparticles between 25 °C and 280 °C are comprehensively investigated. The original Curie temperature of BST nanoparticles decreases abruptly with the increase in Sr content, which is more obvious than in the bulk or film material. Besides, an abnormal phase transition from cubic to tetragonal structure is observed from BST nanoparticles and the transition temperature rises along with the increase in Sr content. Direct TEM evidences including a slight lattice distortion have been provided. Differently, BaTiO{sub 3} nanoparticles remained in the tetragonal phase during the above temperature ranges.
NASA Astrophysics Data System (ADS)
Vives, Eduard; Baró, Jordi; Gallardo, María Carmen; Martín-Olalla, José-María; Romero, Francisco Javier; Driver, Sarah L.; Carpenter, Michael A.; Salje, Ekhard K. H.; Stipcich, Marcelo; Romero, Ricardo; Planes, Antoni
2016-07-01
We studied the two-step martensitic transition of a Cu-Al-Ni shape-memory alloy by calorimetry, acoustic emission (AE), and resonant ultrasound spectroscopy (RUS) measurements. The transition occurs under cooling from the cubic (β , F m 3 m ) parent phase near 242 K to a mixture of orthorhombic 2 H and monoclinic 18 R phases. Heating leads first to the back transformation of small 18 R domains to β and/or 2 H near 255 K, and then to the transformation 2 H to β near 280 K. The total transformation enthalpy is Δ HT=328 ±10 J/mol and is observed as one large latent heat peak under cooling. The back-transformation entropy under heating breaks down into a large component 18 R to β at 255 K and a smaller, smeared component of the transformation 2 H to β near 280 K. The proportions inside the phase mixture depend on the thermal history of the sample. The elastic response of the sample is dominated by large elastic softening during cooling. The weakening of the elastic shear modulus shows a peak at 242 K, which is typical for the formation of complex microstructures. Cooling the sample further leads to additional changes of the microstructure and domain wall freezing, which is seen by gradual elastic hardening and increasing damping of the RUS signal. Heating from 220 K to room temperature leads to elastic anomalies due to the initial transformation, which is now shifted to high temperatures. The transition is smeared over a wider temperature interval and shows strong elastic damping. The shear modulus of the cubic phase is recovered at 280 K. The phase transformation leads to avalanches, which were recorded by AE and by time-resolved calorimetry. The cooling transition shows very extended avalanche signals in calorimetry with power-law distributions. Cooling and heating runs show AE signals over a large temperature interval above 260 K. Splitting the transformation into two martensite phases leads to power-law exponents ɛ ˜2 (β ↔ 18 R ) and ɛ ˜1.5 (β ↔ 2
NASA Astrophysics Data System (ADS)
Lee, S. C.; Youngblood, N.; Jiang, Y. B.; Peterson, E. J.; Stark, C. J. M.; Detchprohm, T.; Wetzel, C.; Brueck, S. R. J.
2015-12-01
The incorporation of In on the non-polar, piezoelectric-free (001) facet of cubic (c-) GaN epitaxially grown over a Si(001) substrate by metal-organic vapor phase epitaxy is reported. Relying on a hexagonal (h-) to c-phase transformation during epitaxy on an 800 nm-wide, Si(111)-faceted v-groove patterned into the substrate, the GaN epilayer at cross sectional view retains a triangular c-phase inside a chevron-shaped h-phase that results in a top surface bounded by a (001) facet parallel to Si(001) at the center and ( 1 1 ¯ 01 ) facets at both edges. A stack of five, ˜3 nm-thick, InxGa1-xN/GaN quantum wells (QWs) was deposited on the double-phased top surface. The c-phase region up to the QWs keeps extremely small misfit (˜0.002) to the fully relaxed h-GaN underneath it and is in tensile stress implying undefected by the h-c phase interface. The In incorporation on a strained non-polar (001) of c-GaN is comparable with that on totally relaxed semi-polar ( 1 1 ¯ 01 ) of h-GaN without noticeable adatom migration across the phase boundary, and sufficient to provide the room-temperature green emission at 496 nm from the c-InxGa1-xN/GaN QWs on Si(001) in photoluminescence.
Cheng, Jinguang; Kweon, K. E.; Larregola, S. A.; ...
2015-01-26
The perovskite PbCrO3 is an antiferromagnetic insulator. But, the fundamental interactions leading to the insulating state in this single-valent perovskite are unclear. Moreover, the origin of the unprecedented volume drop observed at a modest pressure of P = 1.6 GPa remains an outstanding problem. Our report shows a variety of in situ pressure measurements including electron transport properties, X-ray absorption spectrum, and crystal structure study by X-ray and neutron diffraction. These studies reveal key information leading to the elucidation of the physics behind the insulating state and the pressure-induced transition. Furthermore, we argue that a charge disproportionation 3Cr4+ → 2Cr3+more » + Cr6+ in association with the 6s-p hybridization on the Pb2+ is responsible for the insulating ground state of PbCrO3 at ambient pressure and the charge disproportionation phase is suppressed under pressure to give rise to a metallic phase at high pressure. The model is well supported by density function theory plus the correlation energy U (DFT + U) calculations.« less
NASA Astrophysics Data System (ADS)
Vatansever, Erol
2017-05-01
By means of Monte Carlo simulation method with Metropolis algorithm, we elucidate the thermal and magnetic phase transition behaviors of a ferrimagnetic core/shell nanocubic system driven by a time dependent magnetic field. The particle core is composed of ferromagnetic spins, and it is surrounded by an antiferromagnetic shell. At the interface of the core/shell particle, we use antiferromagnetic spin-spin coupling. We simulate the nanoparticle using classical Heisenberg spins. After a detailed analysis, our Monte Carlo simulation results suggest that present system exhibits unusual and interesting magnetic behaviors. For example, at the relatively lower temperature regions, an increment in the amplitude of the external field destroys the antiferromagnetism in the shell part of the nanoparticle, leading to a ground state with ferromagnetic character. Moreover, particular attention has been dedicated to the hysteresis behaviors of the system. For the first time, we show that frequency dispersions can be categorized into three groups for a fixed temperature for finite core/shell systems, as in the case of the conventional bulk systems under the influence of an oscillating magnetic field.
NASA Astrophysics Data System (ADS)
Chung, S.; Malherbe, J. G.; Amokrane, S.
2015-11-01
We study by Monte Carlo simulation the model of a binary mixture of neutral and dipolar hard spheres confined between two widely separated planar walls and subjected to a uniform external field. The goal is to investigate the structural response and the phase transitions of a fluid of hard-sphere-like colloids dispersed in a low-permittivity solvent under the combined effect of geometrical confinement and applied field. In a wide slab, the direction of the field, either normal or perpendicular to the walls, remains one of the most important factors that govern the response of the mixture: in normal field, a wide variety of structural effects are evidenced, including partial wetting or drying of the wall; in parallel field, phase separation is favoured with a specific population of the region close to the wall and a clear separation of the two species. These results suggest possible means to modulate the response of the confined fluid for specific needs.
NASA Astrophysics Data System (ADS)
Stolker, T.; Dominik, C.; Avenhaus, H.; Min, M.; de Boer, J.; Ginski, C.; Schmid, H. M.; Juhasz, A.; Bazzon, A.; Waters, L. B. F. M.; Garufi, A.; Augereau, J.-C.; Benisty, M.; Boccaletti, A.; Henning, Th.; Langlois, M.; Maire, A.-L.; Ménard, F.; Meyer, M. R.; Pinte, C.; Quanz, S. P.; Thalmann, C.; Beuzit, J.-L.; Carbillet, M.; Costille, A.; Dohlen, K.; Feldt, M.; Gisler, D.; Mouillet, D.; Pavlov, A.; Perret, D.; Petit, C.; Pragt, J.; Rochat, S.; Roelfsema, R.; Salasnich, B.; Soenke, C.; Wildi, F.
2016-11-01
Context. The protoplanetary disk around the F-type star HD 135344B (SAO 206462) is in a transition stage and shows many intriguing structures both in scattered light and thermal (sub-)millimeter emission which are possibly related to planet formation processes. Aims: We aim to study the morphology and surface brightness of the disk in scattered light to gain insight into the innermost disk regions, the formation of protoplanets, planet-disk interactions traced in the surface and midplane layers, and the dust grain properties of the disk surface. Methods: We have carried out high-contrast polarimetric differential imaging (PDI) observations with VLT/SPHERE and obtained polarized scattered light images with ZIMPOL in the R and I-bands and with IRDIS in the Y and J-bands. The scattered light images and surface brightness profiles are used to study in detail structures in the disk surface and brightness variations. We have constructed a 3D radiative transfer model to support the interpretation of several detected shadow features. Results: The scattered light images reveal with unprecedented angular resolution and sensitivity the spiral arms as well as the 25 au cavity of the disk. Multiple shadow features are discovered on the outer disk with one shadow only being present during the second observation epoch. A positive surface brightness gradient is observed in the stellar irradiation corrected (r2-scaled) images in southwest direction possibly due to an azimuthally asymmetric perturbation of the temperature and/or surface density by the passing spiral arms. The disk integrated polarized flux, normalized to the stellar flux, shows a positive trend towards longer wavelengths which we attribute to large (2πa ≳ λ) aggregate dust grains in the disk surface. Part of the non-azimuthal polarization signal in the Uφ image of the J-band observation can be attributed to multiple scattering in the disk. Conclusions: The detected shadow features and their possible variability
Jammed lattice sphere packings
NASA Astrophysics Data System (ADS)
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-12-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.
Sadakane, Masahiro; Sasaki, Keisuke; Nakamura, Hiroki; Yamamoto, Takashi; Ninomiya, Wataru; Ueda, Wataru
2012-12-21
We demonstrate that the glass-transition temperature (T(g)) of a polymer sphere template is a crucial factor in the production of three-dimensionally ordered macroporous (3DOM) materials. Metal nitrate dissolved in ethylene glycol-methanol was infiltrated into the void of a face-centered, close-packed colloidal crystal of poly(methyl methacrylate) (PMMA)-based spheres. The metal nitrate reacts with EG to form a metal oxalate (or metal glycoxylate) solid (nitrate oxidation) in the void of the template when the metal nitrate-EG-PMMA composite is heated. Further heating converts metal oxalate to metal oxide and removes PMMA to form 3DOM materials. We investigated the effect of T(g) of PMMA templates and obtained clear evidence that the solidification temperature of the metal precursor solution (i.e., nitration oxidation temperature) should be lower than the T(g) of the polymer spheres to obtain a well-ordered 3DOM structure.
van Westen, Thijs; Vlugt, Thijs J H; Gross, Joachim
2014-01-21
An analytical equation of state (EoS) is derived to describe the isotropic (I) and nematic (N) phase of linear- and partially flexible tangent hard-sphere chain fluids and their mixtures. The EoS is based on an extension of Onsager's second virial theory that was developed in our previous work [T. van Westen, B. Oyarzún, T. J. H. Vlugt, and J. Gross, J. Chem. Phys. 139, 034505 (2013)]. Higher virial coefficients are calculated using a Vega-Lago rescaling procedure, which is hereby generalized to mixtures. The EoS is used to study (1) the effect of length bidispersity on the I-N and N-N phase behavior of binary linear tangent hard-sphere chain fluid mixtures, (2) the effect of partial molecular flexibility on the binary phase diagram, and (3) the solubility of hard-sphere solutes in I- and N tangent hard-sphere chain fluids. By changing the length bidispersity, two types of phase diagrams were found. The first type is characterized by an I-N region at low pressure and a N-N demixed region at higher pressure that starts from an I-N-N triphase equilibrium. The second type does not show the I-N-N equilibrium. Instead, the N-N region starts from a lower critical point at a pressure above the I-N region. The results for the I-N region are in excellent agreement with the results from molecular simulations. It is shown that the N-N demixing is driven both by orientational and configurational/excluded volume entropy. By making the chains partially flexible, it is shown that the driving force resulting from the configurational entropy is reduced (due to a less anisotropic pair-excluded volume), resulting in a shift of the N-N demixed region to higher pressure. Compared to linear chains, no topological differences in the phase diagram were found. We show that the solubility of hard-sphere solutes decreases across the I-N phase transition. Furthermore, it is shown that by using a liquid crystal mixture as the solvent, the solubility difference can by maximized by tuning the
Fisicaro, Emilia; Compari, Carlotta; Duce, Elenia; Contestabili, Cristina; Viscardi, Guido; Quagliotto, Pierluigi
2005-02-10
The apparent and partial molar enthalpies, apparent molar volumes, and adiabatic compressibilities at 298 K of the aqueous solutions of the cationic gemini surfactants propanediyl-alpha,omega-bis(octyldimethylammonium bromide) (8-3-8) and propanediyl-alpha,omega-bis(dodecyldimethylammonium bromide) (12-3-12) have been measured as a function of concentration. The trends of the partial molar enthalpies versus concentration are the first well documented thermodynamic evidence of sphere to rod transition in the micellar phase, involving a detectable quantity of heat, and allow the determination of the change in enthalpy associated with this transition. The changes in enthalpies upon micellization and for the sphere to elongated micelles transition, DeltaH(s)(-->)(r), have been obtained from the experimental data by using a pseudo-phase transition approach: -1.5 kJ mol(-1) for 8-3-8 and -3.9 kJ mol(-1) for 12-3-12. No evidence of the above transition is found in the trends of volumetric properties versus m. The apparent adiabatic molar compressibilities for the compounds under investigation are also reported here for the first time: a negative group contribution for the methylene group is evaluated, when the surfactants are present in solution as a single molecule, reflecting its solvation structure. In the micellar phase, the -CH(2)- group contribution becomes positive. A value of 1.17 x 10(-3) cm(3) bar(-1) mol(-1) for the change in adiabatic molar compressibility upon micellization is obtained. The lower values of the methylene group contributions to the volumetric properties for the monomers support the hypothesis of partial association of the chains before the cmc.
Quadratic and Cubic Transition Elements
1980-11-01
WATERVLIET, N. Y. 12189 AMCMS No. 611102H600011 DA Project No. 1L161102AH60 PRON No. 1A0215601A1A DTIC QUALTTY INSPECTBD 3 APPROVED FOR...AMCMS No. 611102H600011 DA Project No. 1L161102AH60 PRON No. 1A0215601A1A 12. REPORT DATE November 1980 13. NUMBER OF PAGES 19 IB. SECURITY
2014-06-18
ISS040-E-014147 (18 June 2014) --- In the International Space Station's Kibo laboratory, NASA astronauts Steve Swanson (foreground), Expedition 40 commander; and Reid Wiseman, flight engineer, conduct test runs of the SPHERES-Slosh experiment, using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The SPHERES-Slosh investigation uses small robotic satellites on the space station to examine how liquids move around inside containers in microgravity.
2014-06-18
ISS040-E-014536 (18 June 2014) --- In the International Space Station's Kibo laboratory, NASA astronauts Steve Swanson (left), Expedition 40 commander; and Reid Wiseman, flight engineer, conduct test runs of the SPHERES-Slosh experiment, using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The SPHERES-Slosh investigation uses small robotic satellites on the space station to examine how liquids move around inside containers in microgravity.
2014-06-18
ISS040-E-014615 (18 June 2014) --- In the International Space Station's Kibo laboratory, NASA astronauts Steve Swanson (top), Expedition 40 commander; and Reid Wiseman, flight engineer, conduct test runs of the SPHERES-Slosh experiment, using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The SPHERES-Slosh investigation uses small robotic satellites on the space station to examine how liquids move around inside containers in microgravity.
2014-06-18
ISS040-E-014444 (18 June 2014) --- In the International Space Station's Kibo laboratory, NASA astronauts Steve Swanson (left), Expedition 40 commander; and Reid Wiseman, flight engineer, conduct test runs of the SPHERES-Slosh experiment, using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The SPHERES-Slosh investigation uses small robotic satellites on the space station to examine how liquids move around inside containers in microgravity.
2014-06-18
ISS040-E-013914 (18 June 2014) --- In the International Space Station's Kibo laboratory, NASA astronauts Steve Swanson (left), Expedition 40 commander; and Reid Wiseman, flight engineer, conduct test runs of the SPHERES-Slosh experiment, using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The SPHERES-Slosh investigation uses small robotic satellites on the space station to examine how liquids move around inside containers in microgravity.
2014-06-18
ISS040-E-015415 (18 June 2014) --- In the International Space Station's Kibo laboratory, NASA astronauts Steve Swanson, Expedition 40 commander; and Reid Wiseman (partially obscured), flight engineer, conduct test runs of the SPHERES-Slosh experiment, using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The SPHERES-Slosh investigation uses small robotic satellites on the space station to examine how liquids move around inside containers in microgravity.
2014-06-18
ISS040-E-013952 (18 June 2014) --- In the International Space Station's Kibo laboratory, NASA astronaut Reid Wiseman, Expedition 40 flight engineer, enters data in a computer during test runs of the SPHERES-Slosh experiment, using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES (out of frame). The SPHERES-Slosh investigation uses small robotic satellites on the space station to examine how liquids move around inside containers in microgravity.
López-Sánchez, Erik; Estrada-Álvarez, César D; Pérez-Ángel, Gabriel; Méndez-Alcaraz, José Miguel; González-Mozuelos, Pedro; Castañeda-Priego, Ramón
2013-09-14
Asymmetric binary mixtures of hard-spheres exhibit several interesting thermodynamic phenomena, such as multiple kinds of glassy states. When the degrees of freedom of the small spheres are integrated out from the description, their effects are incorporated into an effective pair interaction between large spheres known as the depletion potential. The latter has been widely used to study both the phase behavior and dynamic arrest of the big particles. Depletion forces can be accounted for by a contraction of the description in the multicomponent Ornstein-Zernike equation [R. Castañeda-Priego, A. Rodríguez-López, and J. M. Méndez-Alcaraz, Phys. Rev. E 73, 051404 (2006)]. Within this theoretical scheme, an approximation for the difference between the effective and bare bridge functions is needed. In the limit of infinite dilution, this difference is irrelevant and the typical Asakura-Osawa depletion potential is recovered. At higher particle concentrations, however, this difference becomes important, especially where the shell of first neighbors is formed, and, as shown here, cannot be simply neglected. In this work, we use a variant of the Verlet expression for the bridge functions to highlight their importance in the calculation of the depletion potential at high densities and close to the spinodal decomposition. We demonstrate that the modified Verlet closure predicts demixing in binary mixtures of hard spheres for different size ratios and compare its predictions with both liquid state and density functional theories, computer simulations, and experiments. We also show that it provides accurate correlation functions even near the thermodynamic instability; this is explicitly corroborated with results of molecular dynamics simulations of the whole mixture. Particularly, our findings point toward a possible universal behavior of the depletion potential around the spinodal line.
NASA Astrophysics Data System (ADS)
López-Sánchez, Erik; Estrada-Álvarez, César D.; Pérez-Ángel, Gabriel; Méndez-Alcaraz, José Miguel; González-Mozuelos, Pedro; Castañeda-Priego, Ramón
2013-09-01
Asymmetric binary mixtures of hard-spheres exhibit several interesting thermodynamic phenomena, such as multiple kinds of glassy states. When the degrees of freedom of the small spheres are integrated out from the description, their effects are incorporated into an effective pair interaction between large spheres known as the depletion potential. The latter has been widely used to study both the phase behavior and dynamic arrest of the big particles. Depletion forces can be accounted for by a contraction of the description in the multicomponent Ornstein-Zernike equation [R. Castañeda-Priego, A. Rodríguez-López, and J. M. Méndez-Alcaraz, Phys. Rev. E 73, 051404 (2006)], 10.1103/PhysRevE.73.051404. Within this theoretical scheme, an approximation for the difference between the effective and bare bridge functions is needed. In the limit of infinite dilution, this difference is irrelevant and the typical Asakura-Osawa depletion potential is recovered. At higher particle concentrations, however, this difference becomes important, especially where the shell of first neighbors is formed, and, as shown here, cannot be simply neglected. In this work, we use a variant of the Verlet expression for the bridge functions to highlight their importance in the calculation of the depletion potential at high densities and close to the spinodal decomposition. We demonstrate that the modified Verlet closure predicts demixing in binary mixtures of hard spheres for different size ratios and compare its predictions with both liquid state and density functional theories, computer simulations, and experiments. We also show that it provides accurate correlation functions even near the thermodynamic instability; this is explicitly corroborated with results of molecular dynamics simulations of the whole mixture. Particularly, our findings point toward a possible universal behavior of the depletion potential around the spinodal line.
Saito, Kazuya; Shinhara, Takashi; Nakamoto, Tadahiro; Kutsumizu, Shoichi; Yano, S; Sorai, Michio
2002-03-01
Heat capacity of a thermotropic mesogen ANBC(22) (4(')-alkoxy-3(')-nitrobiphenyl-4-carboxylic acid with 22 carbon atoms in alkyl chain) showing two cubic mesophases was measured by adiabatic calorimetry between 13 and 480 K. Excess enthalpies and entropies due to phase transitions were determined. A small thermal anomaly due to the cubic Im3m-->cubic Ia3d phase transition was successfully detected. Through an analysis of chain-length dependence of the entropy of transition, the sequence of two cubic mesophases (with space groups Ia3d and Im3m) is deduced for thermotropic mesogens ANBC(n). It is shown that the disorder of the core arrangement decreases in the order of Sm-C-->cubic (Im3m)-->cubic (Ia3d) while that of the chain in the reverse order cubic (Ia3d)-->cubic (Im3m)-->Sm C.
NASA Astrophysics Data System (ADS)
Chen, L.; Fan, J. L.; Gong, H. R.
2017-03-01
Molecular dynamic simulation is used to systematically find out the effects of the size and shape of nanoparticles on phase transition and mechanical properties of W nanomaterials. It is revealed that the body-centered cubic (BCC) to face-centered cubic (FCC) phase transition could only happen in cubic nanoparticles of W, instead of the shapes of sphere, octahedron, and rhombic dodecahedron, and that the critical number to trigger the phase transition is 5374 atoms. Simulation also shows that the FCC nanocrystalline W should be prevented due to its much lower tensile strength than its BCC counterpart and that the octahedral and rhombic dodecahedral nanoparticles of W, rather than the cubic nanoparticles, should be preferred in terms of phase transition and mechanical properties. The derived results are discussed extensively through comparing with available observations in the literature to provide a deep understanding of W nanomaterials.
Rhombohedral-cubic transition in Li 0.2Na 0.3La 0.5TiO 3 perovskite
NASA Astrophysics Data System (ADS)
Varez, Alejandro; Fernandez-Díaz, Maria T.; Sanz, Jesus
2004-12-01
High-temperature behavior of the fast ionic conductor Li 0.2Na 0.3La 0.5TiO 3 has been investigated by neutron powder diffraction between 300 and 1073 K. The Rietveld analysis of diffraction patterns showed around 1000 K a change from rhombohedral ( R3¯c) to cubic ( Pm3 m) symmetry. During the heating, the tilting of octahedra along the [111] direction of the cubic perovskite decreased and the rhombic distortion of oxygen square windows that relates contiguous A-sites of the perovskite was eliminated. The influence of the octahedral tilting on Li mobility is finally discussed.
2014-06-18
ISS040-E-014468 (18 June 2014) --- In the International Space Station's Kibo laboratory, NASA astronauts Steve Swanson (left), Expedition 40 commander; and Reid Wiseman, flight engineer, conduct test runs of the SPHERES-Slosh experiment, using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The SPHERES-Slosh investigation uses small robotic satellites on the space station to examine how liquids move around inside containers in microgravity. Russian cosmonaut Maxim Suraev (bottom right), flight engineer, looks on.
Electronic structure of nonstoichiometric cubic hydrides
Switendick, A.C.
1980-01-01
Using the supercell approach we have calculated the electronic structure of Y/sub 4/H/sub 8/, Y/sub 4/H/sub 9/, Y/sub 4/H/sub 11/, and Y/sub 4/H/sub 12/ as prototypic of nonstoichiometric cubic di- and trihydrides. The nature of the interaction between the yttrium and the octahedral and tetrahedral hydrogens is shown by the relative amount of charge contained in the crystal spheres. Each added hydrogen lowers one band which was already partially filled. The charge on both the octahedral and tetrahedral sites is very similar and significantly more than is contained in a comparable atomic sphere.
Dereymaker, Aswin; Van Den Mooter, Guy
2015-05-01
Fluid bed coating has been proposed in the past as an alternative technology for manufacturing of drug-polymer amorphous solid dispersions, or so-called glass solutions. It has the advantage of being a one-step process, and thus omitting separate drying steps, addition of excipients, or manipulation of the dosage form. In search of an adequate sample preparation method for modulated differential scanning calorimetry analysis of beads coated with glass solutions, glass transition broadening and decrease of the glass transition temperature (Tg ) were observed with increasing particle size of crushed coated beads and crushed isolated films of indomethacin (INDO) and polyvinylpyrrolidone (PVP). Substituting INDO with naproxen gave comparable results. When ketoconazole was probed or the solvent in INDO-PVP films was switched to dichloromethane (DCM) or a methanol-DCM mixture, two distinct Tg regions were observed. Small particle sizes had a glass transition in the high Tg region, and large particle sizes had a glass transition in the low Tg region. This particle size-dependent glass transition was ascribed to different residual solvent amounts in the bulk and at the surface of the particles. A correlation was observed between the deviation of the Tg from that calculated from the Gordon-Taylor equation and the amount of residual solvent at the Tg of particles with different sizes. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.
Direct detection of scattered light gaps in the transitional disk around HD 97048 with VLT/SPHERE
NASA Astrophysics Data System (ADS)
Ginski, C.; Stolker, T.; Pinilla, P.; Dominik, C.; Boccaletti, A.; de Boer, J.; Benisty, M.; Biller, B.; Feldt, M.; Garufi, A.; Keller, C. U.; Kenworthy, M.; Maire, A. L.; Ménard, F.; Mesa, D.; Milli, J.; Min, M.; Pinte, C.; Quanz, S. P.; van Boekel, R.; Bonnefoy, M.; Chauvin, G.; Desidera, S.; Gratton, R.; Girard, J. H. V.; Keppler, M.; Kopytova, T.; Lagrange, A.-M.; Langlois, M.; Rouan, D.; Vigan, A.
2016-11-01
Aims: We studied the well-known circumstellar disk around the Herbig Ae/Be star HD 97048 with high angular resolution to reveal undetected structures in the disk which may be indicative of disk evolutionary processes such as planet formation. Methods: We used the IRDIS near-IR subsystem of the extreme adaptive optics imager SPHERE at the ESO/VLT to study the scattered light from the circumstellar disk via high resolution polarimetry and angular differential imaging. Results: We imaged the disk in unprecedented detail and revealed four ring-like brightness enhancements and corresponding gaps in the scattered light from the disk surface with radii between 39 au and 341 au. We derived the inclination and position angle as well as the height of the scattering surface of the disk from our observational data. We found that the surface height profile can be described by a single power law up to a separation 270 au. Using the surface height profile we measured the scattering phase function of the disk and found that it is consistent with theoretical models of compact dust aggregates. We discuss the origin of the detected features and find that low mass (≤1 MJup) nascent planets are a possible explanation. Based on data collected at the European Southern Observatory, Chile (ESO Programs 096.C-0248, 096.C-0241, 077.C-0106).
Bloch, Rebecca A; Cronin, Kimberly; Hoover, John P; Pechman, Robert D; Payton, Mark E
2010-03-01
Barium impregnated polyethylene spheres (BIPS) are used in small animal medicine as an alternative to barium sulfate for radiographic studies of the gastrointestinal tract. To determine the usefulness of BIPS as an alternative to barium suspension in measuring gastrointestinal (GI) transit time for avian species, ventrodorsal radiographs were used to follow the passage of BIPS and 30% barium sulfate suspension through the GI tracts of domestic pigeons (Columba livia). Gastrointestinal transit times of thirty 1.5-mm BIPS administered in moistened gelatin capsules and 30% barium sulfate suspension gavaged into the crop were compared in 6 pigeons. Although the barium suspension passed out of the GI tract of all pigeons within 24 hours, the 1.5-mm BIPS remained in the ventriculus for 368.0 +/- 176.8 hours and did not clear the GI tract for 424.0 +/- 204.6 hours. Although the times for passage of BIPS and 30% barium sulfate suspension from the crop into the ventriculus were not significantly different (P = .14), the times for passage of BIPS from the ventriculus into the large intestine-cloaca and for clearance from the GI tract of the pigeons were significantly longer (P < .001) than for the 30% barium sulfate suspension. From the results of this study, we conclude that BIPS are not useful for radiographically evaluating GI transit times in pigeons and are unlikely to be useful in other avian species that have a muscular ventriculus. BIPS may or may not be useful for evaluating GI transit times in species that lack a muscular ventriculus.
NASA Technical Reports Server (NTRS)
Deveikis, William D.; Walker, Robert W.
1961-01-01
A wind-tunnel investigation was made to determine heat-transfer distributions on three steel sphere-ellipsoid bodies with surface roughnesses of 5, 100, and 200 microinches. Tests were conducted in the Langley 9- by 6-foot thermal structures tunnel at a Mach number of 3.0, free-stream Reynolds numbers (based on model spherical diameter) of 4.25 x 10(exp 6) and 2.76 x l0(exp 6), and at a stagnation temperature of 650 F. Pressure distributions were obtained also on a fourth model. The results indicated that the combination of surface roughness and boundary-layer cooling tended to promote early transition and nullify the advantages attributable to the blunt shape of the model for reducing local temperatures. Good correlation between experimental heating rates and those calculated from laminar theory was achieved up to the start of boundary-layer transition. The correlation also was good with the values predicted by turbulent theory for surface stations downstream from the 45 deg. station.
Phase diagram of elastic spheres.
Athanasopoulou, L; Ziherl, P
2017-02-15
Experiments show that polymeric nanoparticles often self-assemble into several non-close-packed lattices in addition to the face-centered cubic lattice. Here, we explore theoretically the possibility that the observed phase sequences may be associated with the softness of the particles, which are modeled as elastic spheres interacting upon contact. The spheres are described by two finite-deformation theories of elasticity, the modified Saint-Venant-Kirchhoff model and the neo-Hookean model. We determine the range of indentations where the repulsion between the spheres is pairwise additive and agrees with the Hertz theory. By computing the elastic energies of nine trial crystal lattices at densities far beyond the Hertzian range, we construct the phase diagram and find the face- and body-centered cubic lattices as well as the A15 lattice and the simple hexagonal lattice, with the last two being stable at large densities where the spheres are completely faceted. These results are qualitatively consistent with observations, suggesting that deformability may indeed be viewed as a generic property that determines the phase behavior in nanocolloidal suspensions.
Flores-Ruiz, Hugo M; Naumis, Gerardo G
2009-10-21
Using molecular dynamics at constant pressure, the relationship between the excess of low frequency vibrational modes (known as the boson peak) and the glass transition is investigated for a truncated Lennard-Jones potential. It is observed that the quadratic mean displacement is enhanced by such modes, as predicted using a harmonic Hamiltonian for metastable states. As a result, glasses loose mechanical stability at lower temperatures than the corresponding crystal, since the Lindemann criteria are observed, as is also deduced from density functional theory. Finally, we found that the average force and elastic constant are reduced in the glass due to such excess of modes. The ratio between average elastic constants can be approximated using the 2/3 rule between melting and glass transition temperatures.
Piecewise Cubic Interpolation Package
Fritsch, F. N.; LLNL,
1982-04-23
PCHIP (Piecewise Cubic Interpolation Package) is a set of subroutines for piecewise cubic Hermite interpolation of data. It features software to produce a monotone and "visually pleasing" interpolant to monotone data. Such an interpolant may be more reasonable than a cubic spline if the data contain both 'steep' and 'flat' sections. Interpolation of cumulative probability distribution functions is another application. In PCHIP, all piecewise cubic functions are represented in cubic Hermite form; that is, f(x) is determined by its values f(i) and derivatives d(i) at the breakpoints x(i), i=1(1)N. PCHIP contains three routines - PCHIM, PCHIC, and PCHSP to determine derivative values, six routines - CHFEV, PCHFE, CHFDV, PCHFD, PCHID, and PCHIA to evaluate, differentiate, or integrate the resulting cubic Hermite function, and one routine to check for monotonicity. A FORTRAN 77 version and SLATEC version of PCHIP are included.
2014-07-25
ISS040-E-079355 (25 July 2014) --- In the International Space Station?s Kibo laboratory, NASA astronaut Steve Swanson (foreground), Expedition 40 commander; and European Space Agency astronaut Alexander Gerst, flight engineer, conduct a session with a trio of soccer-ball-sized robots known as the Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The free-flying robots were equipped with stereoscopic goggles called the Visual Estimation and Relative Tracking for Inspection of Generic Objects, or VERTIGO, to enable the SPHERES to perform relative navigation based on a 3D model of a target object.
2014-07-25
ISS040-E-079332 (25 July 2014) --- In the International Space Station?s Kibo laboratory, NASA astronaut Steve Swanson (foreground), Expedition 40 commander; and European Space Agency astronaut Alexander Gerst, flight engineer, conduct a session with a trio of soccer-ball-sized robots known as the Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The free-flying robots were equipped with stereoscopic goggles called the Visual Estimation and Relative Tracking for Inspection of Generic Objects, or VERTIGO, to enable the SPHERES to perform relative navigation based on a 3D model of a target object.
2014-07-25
ISS040-E-079129 (25 July 2014) --- In the International Space Station?s Kibo laboratory, NASA astronaut Steve Swanson (left), Expedition 40 commander; and European Space Agency astronaut Alexander Gerst, flight engineer, conduct a session with a trio of soccer-ball-sized robots known as the Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The free-flying robots were equipped with stereoscopic goggles called the Visual Estimation and Relative Tracking for Inspection of Generic Objects, or VERTIGO, to enable the SPHERES to perform relative navigation based on a 3D model of a target object.
2014-07-25
ISS040-E-079083 (25 July 2014) --- In the International Space Station?s Kibo laboratory, NASA astronaut Steve Swanson, Expedition 40 commander, enters data in a computer in preparation for a session with a trio of soccer-ball-sized robots known as the Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The free-flying robots were equipped with stereoscopic goggles called the Visual Estimation and Relative Tracking for Inspection of Generic Objects, or VERTIGO, to enable the SPHERES to perform relative navigation based on a 3D model of a target object.
2014-07-25
ISS040-E-079910 (25 July 2014) --- In the International Space Station?s Kibo laboratory, NASA astronaut Steve Swanson (left), Expedition 40 commander; and European Space Agency astronaut Alexander Gerst, flight engineer, conduct a session with a trio of soccer-ball-sized robots known as the Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The free-flying robots were equipped with stereoscopic goggles called the Visual Estimation and Relative Tracking for Inspection of Generic Objects, or VERTIGO, to enable the SPHERES to perform relative navigation based on a 3D model of a target object.
Chandrasekhar, Vadapalli; Dey, Atanu; Senapati, Tapas; Sañudo, E Carolina
2012-01-21
The reaction of VCl(3) with 3,5-dimethylpyrazole (3,5-Me(2)PzH) and trichloromethylphosphonic/tert-butylphosphonic acid in the presence of triethylamine as a hydrogen chloride scavenger afforded the tetranuclear V(IV) assemblies, [(VO)(4)(3,5-Me(2)PzH)(8)(CCl(3)PO(3))(4)] (1) and [(VO)(4)(3,5-Me(2)PzH)(4)(t-BuPO(3))(4)] (2). Both of these compounds possess a distorted cubic framework structures containing V(IV) ions and phosphorus atoms in the alternate corners of the cube. The edges of the cube contain oxygen atoms derived from the phosphonate ligand. The phosphonate ligand in both of these compounds is dianionic and helps to bind to three V(IV) centers. The faces of the cubic ensembles contain puckered V(2)P(2)O(4) eight-membered rings. The V(IV) center in 1 is six-coordinate in a distorted octahedral geometry while in 2 it is five-coordinate in a distorted square-pyramidal geometry. Magnetic studies carried out on 1 and 2 reveal that the V(IV) centers are anti-ferromagnetically coupled to each other, albeit weakly, through the mediation of the phosphonate ligands.
Bond-orientational analysis of hard-disk and hard-sphere structures.
Senthil Kumar, V; Kumaran, V
2006-05-28
We report the bond-orientational analysis results for the thermodynamic, random, and homogeneously sheared inelastic structures of hard-disks and hard-spheres. The thermodynamic structures show a sharp rise in the order across the freezing transition. The random structures show the absence of crystallization. The homogeneously sheared structures get ordered at a packing fraction higher than the thermodynamic freezing packing fraction, due to the suppression of crystal nucleation. On shear ordering, strings of close-packed hard-disks in two dimensions and close-packed layers of hard-spheres in three dimensions, oriented along the velocity direction, slide past each other. Such a flow creates a considerable amount of fourfold order in two dimensions and body-centered-tetragonal (bct) structure in three dimensions. These transitions are the flow analogs of the martensitic transformations occurring in metals due to the stresses induced by a rapid quench. In hard-disk structures, using the bond-orientational analysis we show the presence of fourfold order. In sheared inelastic hard-sphere structures, even though the global bond-orientational analysis shows that the system is highly ordered, a third-order rotational invariant analysis shows that only about 40% of the spheres have face-centered-cubic (fcc) order, even in the dense and near-elastic limits, clearly indicating the coexistence of multiple crystalline orders. When layers of close-packed spheres slide past each other, in addition to the bct structure, the hexagonal-close-packed (hcp) structure is formed due to the random stacking faults. Using the Honeycutt-Andersen pair analysis and an analysis based on the 14-faceted polyhedra having six quadrilateral and eight hexagonal faces, we show the presence of bct and hcp signatures in shear ordered inelastic hard-spheres. Thus, our analysis shows that the dense sheared inelastic hard-spheres have a mixture of fcc, bct, and hcp structures.
Melting temperature of colloidal crystals of polystyrene spheres
NASA Astrophysics Data System (ADS)
Okubo, Tsuneo
1991-09-01
The melting temperature (Tm) of colloidal crystals of polystyrene spheres has been measured by the reflection spectroscopy as a function of sphere concentration. Seven kinds of spheres their diameters ranging from 85 to 212 nm, and their monodispersity indices (standard deviation of spheres divided by the mean diameter) between 0.014 and 0.26, are used after further purification and deionization processes. A phase diagram, including liquid-like and crystal-like (body-centered-cubic and face-centered-cubic lattices) structures, is obtained as a function of Tm against sphere concentration. The data of Tm are analyzed successfully with the theory of Williams, Crandall, and Wojtowicz, and the heat and entropy of melting are estimated. Tm values are consistent with the theory of Robbins and co-workers which treats the repulsive Yukawa potential between colloidal spheres.
NASA Astrophysics Data System (ADS)
de Boer, J.; Salter, G.; Benisty, M.; Vigan, A.; Boccaletti, A.; Pinilla, P.; Ginski, C.; Juhasz, A.; Maire, A.-L.; Messina, S.; Desidera, S.; Cheetham, A.; Girard, J. H.; Wahhaj, Z.; Langlois, M.; Bonnefoy, M.; Beuzit, J.-L.; Buenzli, E.; Chauvin, G.; Dominik, C.; Feldt, M.; Gratton, R.; Hagelberg, J.; Isella, A.; Janson, M.; Keller, C. U.; Lagrange, A.-M.; Lannier, J.; Menard, F.; Mesa, D.; Mouillet, D.; Mugrauer, M.; Peretti, S.; Perrot, C.; Sissa, E.; Snik, F.; Vogt, N.; Zurlo, A.; SPHERE Consortium
2016-11-01
Context. The effects of a planet sculpting the disk from which it formed are most likely to be found in disks that are in transition between being classical protoplanetary and debris disks. Recent direct imaging of transition disks has revealed structures such as dust rings, gaps, and spiral arms, but an unambiguous link between these structures and sculpting planets is yet to be found. Aims: We aim to find signs of ongoing planet-disk interaction and study the distribution of small grains at the surface of the transition disk around RX J1615.3-3255 (RX J1615). Methods: We observed RX J1615 with VLT/SPHERE. From these observations, we obtained polarimetric imaging with ZIMPOL (R'-band) and IRDIS (J), and IRDIS (H2H3) dual-band imaging with simultaneous spatially resolved spectra with the IFS (YJ). Results: We image the disk for the first time in scattered light and detect two arcs, two rings, a gap and an inner disk with marginal evidence for an inner cavity. The shapes of the arcs suggest that they are probably segments of full rings. Ellipse fitting for the two rings and inner disk yield a disk inclination i = 47 ± 2° and find semi-major axes of 1.50 ± 0.01'' (278 au), 1.06 ± 0.01'' (196 au) and 0.30 ± 0.01'' (56 au), respectively. We determine the scattering surface height above the midplane, based on the projected ring center offsets. Nine point sources are detected between 2.1'' and 8.0'' separation and considered as companion candidates. With NACO data we recover four of the nine point sources, which we determine to be not co-moving, and therefore unbound to the system. Conclusions: We present the first detection of the transition disk of RX J1615 in scattered light. The height of the rings indicate limited flaring of the disk surface, which enables partial self-shadowing in the disk. The outermost arc either traces the bottom of the disk or it is another ring with semi-major axis ≳ 2.35'' (435 au). We explore both scenarios, extrapolating the complete
2013-07-05
ISS036-E-015549 (5 July 2013) --- In the International Space Station’s Kibo laboratory, NASA astronaut Chris Cassidy, Expedition 36 flight engineer, watches as he devotes some time with the long-running SPHERES experiment, also known as Synchronized Position Hold Engage and Reorient Experimental Satellites. The experiment is run in conjunction with students who program bowling ball-sized satellites using algorithms. The free-floating satellites are programmed to perform maneuvers potentially influencing the design of future missions.
Banik, Mayukh; El-Khoury, Patrick Z; Nag, Amit; Rodriguez-Perez, Alejandro; Guarrottxena, Nekane; Bazan, Guillermo C; Apkarian, Vartkess A
2012-11-27
By taking advantage of the tensor nature of surface-enhanced Raman scattering (SERS), we track trajectories of the linker molecule and a CO molecule chemisorbed at the hot spot of a nano-dumbbell consisting of dibenzyldithio-linked silver nanospheres. The linear Stark shift of CO serves as an absolute gauge of the local field, while the polyatomic spectra characterize the vector components of the local field. We identify surface-enhanced Raman optical activity due to a transient asperity in the nanojunction in an otherwise uneventful SERS trajectory. During fusion of the spheres, we observe sequential evolution of the enhanced spectra from dipole-coupled Raman to quadrupole- and magnetic dipole-coupled Raman, followed by a transition from line spectra to band spectra, and the full reversal of the sequence. From the spectrum of CO, the sequence can be understood to track the evolution of the junction plasmon resonance from dipolar to quadrupolar to charge transfer as a function of intersphere separation, which evolves at a speed of ∼1 Å/min. The crossover to the conduction limit is marked by the transition of line spectra to Stark-broadened and shifted band spectra. As the junction closes on CO, the local field reaches 1 V/Å, limited to a current of 1 electron per vibrational cycle passing through the molecule, with associated Raman enhancement factor via the charge transfer plasmon resonance of 10(12). The local field identifies that a sharp protrusion is responsible for room-temperature chemisorption of CO on silver. The asymmetric phototunneling junction, Ag-CO-Ag, driven by the frequency-tunable charge transfer plasmon of the dumbbell antenna, combines the design elements of an ideal rectifying photocollector.
NASA Astrophysics Data System (ADS)
Salje, Ekhard K. H.; Zhang, Ming; Zhang, Huali
2009-08-01
Precursor effects were observed in KMnF3 using infrared hard-mode spectroscopy. The intensity of the infrared-active mode near 265 cm-1 follows the thermodynamic order parameter, Q, in the tetragonal phase (I4/mcm). An additional weak signal is found in the cubic phase (Pm\\bar {3}m ). The order parameter step at To = 185.95 K (L = 0.129 J g-1) is smeared with excess intensity due to the tetragonal short range order extending to T>215 K. The intensity follows the predictions of Landau theory with a defect field Gdefect = -hQ, h = 6 J mol-1. The observed excess intensities are compared with the appearance of precursor elastic softening. It is concluded that the precursor softening and the local tetragonal short range order are likely to be related to an extended defect structure, such as a tweed pattern, which may be stabilized by extrinsic defects.
Cubic topological Kondo insulators.
Alexandrov, Victor; Dzero, Maxim; Coleman, Piers
2013-11-27
Current theories of Kondo insulators employ the interaction of conduction electrons with localized Kramers doublets originating from a tetragonal crystalline environment, yet all Kondo insulators are cubic. Here we develop a theory of cubic topological Kondo insulators involving the interaction of Γ(8) spin quartets with a conduction sea. The spin quartets greatly increase the potential for strong topological insulators, entirely eliminating the weak topological phases from the diagram. We show that the relevant topological behavior in cubic Kondo insulators can only reside at the lower symmetry X or M points in the Brillouin zone, leading to three Dirac cones with heavy quasiparticles.
B═B and B≡E (E = N and o) multiple bonds in the coordination sphere of late transition metals.
Brand, Johannes; Braunschweig, Holger; Sen, Sakya S
2014-01-21
Because of their unusual structural and bonding motifs, multiply bonded boron compounds are fundamentally important to chemists, leading to enormous research interest. To access these compounds, researchers have introduced sterically demanding ligands that provide kinetic as well as electronic stability. A conceptually different approach to the synthesis of such compounds involves the use of an electron-rich, coordinatively unsaturated transition metal fragment. To isolate the plethora of borane, boryl, and borylene complexes, chemists have also used the coordination sphere of transition metals to stabilize reactive motifs in these molecules. In this Account, we summarize our results showing that increasingly synthetically challenging targets such as iminoboryl (B≡N), oxoboryl (B≡O), and diborene (B═B) fragments can be stabilized in the coordination sphere of late transition metals. This journey began with the isolation of two new iminoboryl ligands trans-[(Cy3P)2(Br)M(B≡N(SiMe3))] (M = Pd, Pt) attached to palladium and platinum fragments. The synthesis involved oxidative addition of the B-Br bond in (Me3Si)2N═BBr2 to [M(PCy3)2] (M = Pt, Pd) and the subsequent elimination of Me3SiBr at room temperature. Variation of the metal, the metal-bound coligands, and the substituent at the nitrogen atom afforded a series of analogous iminoboryl complexes. Following the same synthetic strategy, we also synthesized the first oxoboryl complex trans-[(Cy3P)2BrPt(BO)]. The labile bromide ligand adjacent to platinum makes the complex a viable candidate for further substitution reactions, which led to a number of new oxoboryl complexes. In addition to allowing us to isolate these fundamental compounds, the synthetic strategy is very convenient and minimizes byproducts. We also discuss the reaction chemistry of these types of compounds. In addition to facilitating the isolation of compounds with B≡E (E = N, O) triple bonds, the platinum fragment can also stabilize a
Accurate monotone cubic interpolation
NASA Technical Reports Server (NTRS)
Huynh, Hung T.
1991-01-01
Monotone piecewise cubic interpolants are simple and effective. They are generally third-order accurate, except near strict local extrema where accuracy degenerates to second-order due to the monotonicity constraint. Algorithms for piecewise cubic interpolants, which preserve monotonicity as well as uniform third and fourth-order accuracy are presented. The gain of accuracy is obtained by relaxing the monotonicity constraint in a geometric framework in which the median function plays a crucial role.
NASA Astrophysics Data System (ADS)
Mukherji, Debashis; Strunz, Pavel; Piegert, Sebastian; Gilles, Ralph; Hofmann, Michael; Hölzel, Markus; Rösler, Joachim
2012-06-01
Co-Re-based alloys have been developed to supplement the Ni-base superalloys used in gas turbine applications at high temperatures (1473 K [1200 °C] bare metal temperature). Unlike other commercial Co-based alloys, the Co matrix in the Co-Re alloys has a stable hexagonal close-packed (hcp) structure at room temperature. In situ neutron diffraction measurements on experimental Co-Re alloys hardened by carbide precipitates showed that the matrix undergoes an hcp ⇆ face-centered cubic (fcc) allotropic transformation after heating to high temperatures. Furthermore, it was found that this transformation has a large hysteresis (~100 K). Thermodynamic calculations were undertaken to study the high-temperature phase stability and transformations in the complex multicomponent, multiphase Co-Re-Cr-C system with or without the addition of Ta. The results show that the minor phases (Cr23C6-type carbides and the Cr2Re3-type σ phase) play an important role in the hcp ⇆ fcc hysteresis by influencing the partitioning of Cr and Re between the matrix and the other phases.
Weisemoeller, T.; Bertram, F.; Gevers, S.; Greuling, A.; Deiter, C.; Tobergte, H.; Neumann, M.; Wollschlaeger, J.; Giussani, A.; Schroeder, T.
2009-06-15
Films of hexagonal praseodymium sesquioxide (h-Pr{sub 2}O{sub 3}) were deposited on Si(111) by molecular beam epitaxy and thereafter annealed in 1 atm oxygen at different temperatures, ranging from 100 to 700 deg. C. The films of the samples annealed at 300 deg. C or more were transformed to PrO{sub 2} with B-oriented Fm3m structure, while films annealed at lower temperatures kept the hexagonal structure. The films are composed of PrO{sub 2} and PrO{sub 2-d}elta species, which coexist laterally and are tetragonally distorted due to the interaction at the interface between oxide film and Si substrate. Compared to PrO{sub 2}, PrO{sub 2-d}elta has the same cubic structure but with oxygen vacancies. The oxygen vacancies are partly ordered and increase the vertical lattice constant of the film, whereas the lateral lattice constant is almost identical for both species and on all samples. The latter lattice constant matches the lattice constant of the originally crystallized hexagonal praseodymium sesquioxide. That means that no long range reordering of the praseodymium atoms takes place during the phase transformation.
Salje, Ekhard K H; Zhang, Ming; Zhang, Huali
2009-08-19
Precursor effects were observed in KMnF(3) using infrared hard-mode spectroscopy. The intensity of the infrared-active mode near 265 cm(-1) follows the thermodynamic order parameter, Q, in the tetragonal phase (I4/mcm). An additional weak signal is found in the cubic phase ([Formula: see text]). The order parameter step at T(o) = 185.95 K (L = 0.129 J g(-1)) is smeared with excess intensity due to the tetragonal short range order extending to T>215 K. The intensity follows the predictions of Landau theory with a defect field G(defect) = -hQ, h = 6 J mol(-1). The observed excess intensities are compared with the appearance of precursor elastic softening. It is concluded that the precursor softening and the local tetragonal short range order are likely to be related to an extended defect structure, such as a tweed pattern, which may be stabilized by extrinsic defects.
Voronoi neighbor statistics of hard-disks and hard-spheres
NASA Astrophysics Data System (ADS)
Kumar, V. Senthil; Kumaran, V.
2005-08-01
The neighbor distribution in hard-sphere and hard-disk fluids is analyzed using Voronoi tessellation. The statistical measures analyzed are the nth neighbor coordination number (Cn), the nth neighbor distance distribution [fn(r )], and the distribution of the number of Voronoi faces (Pn). These statistics are sensitive indicators of microstructure, and they distinguish thermodynamic and annealed structures. A sharp rise in the hexagon population marks the onset of hard-disk freezing transition, and Cn decreases sharply to the hexagonal lattice values. In hard-disk random structures the pentagon and heptagon populations remain significant even at high volume fraction. In dense hard-sphere (three-dimensional) structures at the freezing transition, C1 is close to 14, instead of the value of 12 expected for a face-centered-cubic lattice. This is found to be because of a topological instability, where a slight perturbation of the positions in the centers of a pair of particles transforms a vertex in the Voronoi polyhedron into a Voronoi surface. We demonstrate that the pair distribution function and the equation-of-state obtained from Voronoi tessellation are equal to those obtained from thermodynamic calculations. In hard-sphere random structures, the dodecahedron population decreases with increasing density. To demonstrate the utility of the neighbor analysis, we estimate the effective hard-sphere diameter of the Lennard-Jones fluid by identifying the diameter of the spheres in the hard-sphere fluid which has C1 equal to that for the Lennard-Jones fluid. The estimates are within 2% deviation from the theoretical results of Barker-Henderson and Weeks-Chandler-Andersen.
NASA Technical Reports Server (NTRS)
Martinez, Andres; Benavides, Jose Victor; Ormsby, Steve L.; GuarnerosLuna, Ali
2014-01-01
Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) are bowling-ball sized satellites that provide a test bed for development and research into multi-body formation flying, multi-spacecraft control algorithms, and free-flying physical and material science investigations. Up to three self-contained free-flying satellites can fly within the cabin of the International Space Station (ISS), performing flight formations, testing of control algorithms or as a platform for investigations requiring this unique free-flying test environment. Each satellite is a self-contained unit with power, propulsion, computers, navigation equipment, and provides physical and electrical connections (via standardized expansion ports) for Principal Investigator (PI) provided hardware and sensors.
Melting temperature of colloidal crystals of monodisperse silica spheres
NASA Astrophysics Data System (ADS)
Okubo, Tsuneo
1992-02-01
Melting temperature (Tm) of colloidal crystals of monodisperse silica spheres has been measured by the reflection spectroscopy as a function of sphere concentration. Spheres of their diameters of 110 and 178 nm from electron microscopy, and their monodispersity indices (standard deviation of sphere diameter divided by the mean diameter) of 0.041 and 0.05, respectively, are used after purification and deionization processes. Transformation from the body-centered cubic lattice to the face-centered cubic lattice subphases are observed as the suspension temperature rises. A phase diagram including liquid-like and crystal-like structures is obtained in the presence of ion-exchange resins or sodium chloride. The Tm values observed are analyzed with the theory of Crandall et al. successfully. The Tm values are also consistent with the theory of Robbins et al., which treats the repulsive Yukawa potential between colloidal spheres.
Burrell, Anthony K; McCleskey, Thomas Mark; Jia, Quanxi; Mueller, Alexander H; Luo, Hongmei
2013-04-30
A polymer-assisted deposition process for deposition of epitaxial cubic metal nitride films and the like is presented. The process includes solutions of one or more metal precursor and soluble polymers having binding properties for the one or more metal precursor. After a coating operation, the resultant coating is heated at high temperatures under a suitable atmosphere to yield metal nitride films and the like. Such films can be used as templates for the development of high quality cubic GaN based electronic devices.
NASA Astrophysics Data System (ADS)
Li, Tengfei; Liu, Tianmo; Wei, Hongmei; Hussain, Shahid; Wang, Jinxing; Zeng, Wen; Peng, Xianghe; Wang, Zhongchang
2015-11-01
The twin boundary energies of TiN, ZrN, HfN, TiC, ZrC, HfC, VC, NbC and TaC and the adhesion energies of twin interfaces and interfaces of TiN/ZrN, VC/TiC and TiN/TiC were calculated using first-principles methods. A new route in the preparation of mechanically superhard films has been proposed by introducing twin into the multilayer of transition-metal nitrides and carbides.
Cubic colloidal platinum nanoparticles
Ahmadi, T.S.; Wang, Z.L.; Henglein, A.; El-Sayed, M.A.
1996-06-01
Cubic platinum nanoparticles (4-18 nm) have been synthesized for the first time in solution by the controlled reduction of K{sub 2}PtCl{sub 4} with hydrogen gas in the presence of sodium polyacrylate as a capping material. The nanoparticles are found to have fcc structures, similar to the bulk metal with (100) facets.
Henry Spelter
2002-01-01
Noted forest products industry researcher and writer says the conversion factor traditionally used to convert logs measured in board feet to cubic meters has risen. In the U.S., most timber is measured in terms of board feet. The log scales currently in use to estimate lumber recovery from roundwood, however, were created in the 19th century according to sawmill...
Self-consistent phonon theory of the crystallization and elasticity of attractive hard spheres
NASA Astrophysics Data System (ADS)
Shin, Homin; Schweizer, Kenneth S.
2013-02-01
We propose an Einstein-solid, self-consistent phonon theory for the crystal phase of hard spheres that interact via short-range attractions. The approach is first tested against the known behavior of hard spheres, and then applied to homogeneous particles that interact via short-range square well attractions and the Baxter adhesive hard sphere model. Given the crystal symmetry, packing fraction, and strength and range of attractive interactions, an effective harmonic potential experienced by a particle confined to its Wigner-Seitz cell and corresponding mean square vibrational amplitude are self-consistently calculated. The crystal free energy is then computed and, using separate information about the fluid phase free energy, phase diagrams constructed, including a first-order solid-solid phase transition and its associated critical point. The simple theory qualitatively captures all the many distinctive features of the phase diagram (critical and triple point, crystal-fluid re-entrancy, low-density coexistence curve) as a function of attraction range, and overall is in good semi-quantitative agreement with simulation. Knowledge of the particle localization length allows the crystal shear modulus to be estimated based on elementary ideas. Excellent predictions are obtained for the hard sphere crystal. Expanded and condensed face-centered cubic crystals are found to have qualitatively different elastic responses to varying attraction strength or temperature. As temperature increases, the expanded entropic solid stiffens, while the energy-controlled, fully-bonded dense solid softens.
Avarvari, N; Faulques, E; Fourmigué, M
2001-05-21
PhSb(dmit) (dmit(2)(-), 4,5-dithiolato-1,3-dithiole-2-thione), the first neutral organo-antimony dithiolene complex, has been synthesized by addition of PhSbCl(2) on a suspension of Na(2)(dmit). The complex was characterized by spectroscopic ((1)H and (13)C NMR and IR) methods and elemental analysis. Its crystal structure was determined by X-ray diffraction at room temperature in the monoclinic P2(1)/c space group, with a = 12.580(3), b = 8.9756(18), c = 15.905(3) A, beta = 109.06(3) degrees, V = 1697.5(6) A(3), Z = 4. A coordinating THF molecule was found in the structure and the coordination geometry around the antimony atom is of distorted pseudopentagonal bipyramid type, if taking into account the Sb.O and secondary Sb.S interactions, as well as the stereochemically active 5s(2) lone pair. The intermolecular Sb.S and S.S contacts, shorter than the sum of van der Waals radii of corresponding atoms, lead to the formation of a three-dimensional polymeric network in the solid state. A second X-ray diffraction experiment, performed at 85 K, revealed a very similar monoclinic unit cell with the noncentrosymmetrical space group P2(1) with a = 12.613(3), b = 8.9876(18), c = 15.109(3) A, beta = 107.01(3) degrees, V = 1637.8(6), Z = 4. The structural differences with the first one are basically due to the rotation of the THF ligand in the coordination sphere of the antimony center, leading to the loss of every inversion center found at room temperature. A temperature variable X-ray diffraction study on a PhSb(dmit) single-crystal allowed the detection, with a remarkable accuracy, of two successive first-order phase transitions, the first occurring at T = 162.5 K, while the second was observed at T = 182.5 K. Subsequently, a third set of X-ray data was collected at 180 K and the resulting structure (monoclinic, P2(1)/c, a = 16.736(3), b = 8.9653(18), c = 33.132(7) A, beta = 91.98(3) degrees, V = 4968.2(17), Z = 12) derives from the two others by a common b axis, a 3-fold
2012-12-27
vacancy concentration to stabilize the cubic structure [22,23]. Substitution on the Zr (4þ) site will not block the Li-ion pathways and thus leads to...contamination from alumina crucibles [10,17]. Later Al was intentionally added [18,19] and a dense (relative density > 90%) material with a cubic ... structure was ob- tained. Geiger et al. [17] have suggested that Al substitutes for Li and thereby stabilizes the cubic phase. A similar stabilization of
Martín, Victoria Isabel; Rodríguez, Amalia; Graciani, María del Mar; Robina, Inmaculada; Moyá, María Luisa
2010-06-17
The micellization and micellar growth in pure aqueous alkanediyl-alpha-omega-bis(dodecyldimethylammonium) bromide, 12-s-12,2Br(-) (with s = 2,5,6,8,10,12), and N-decanoyl-N-methylglucamide MEGA10 solutions and their mixtures are investigated at 303 K. Application of different theoretical approaches to the binary mixtures shows a nonideal behavior. It also shows that the spacer length does not play an important role in the attractive interactions shown by the mixed systems. The sphere-to-rod morphological transition in the pure dimeric micellar solutions is studied at 303 K. From comparison of these results with those at 298 K the key role played by the spacer in the micellar growth is shown. The spacer length controls not only the surfactant concentration at which the morphological transition happens but also the sign of the enthalpy change accompanying the sphere-to-rod equilibrium. Spacers with an even number of methylenes show smaller C* values than those with an odd number of -CH(2)- units. An endothermic enthalpy change is found for even spacers whereas an exothermic enthalpy change is found for odd spacers. To the authors knowledge, this is the first time this experimental trend has been shown. Addition of MEGA10 diminishes the tendency of the aggregates to grow. An increment in the solution mole fraction of MEGA10 makes the formation of elongated micelles difficult. Microviscosity measurements provide additional information about the influence of the MEGA10 content on the sphere-to-rod transition.
NASA Astrophysics Data System (ADS)
Roundy, David; Kraig, Robert E.; Cohen, Marvin L.
2002-03-01
Scientists have long pondered why the simple cubic structure is so rarely seen in nature. Only one element forms the simple cubic structure: polonium. There are `proofs' dating back to 1954 that the simple cubic lattice should be unstable. We will attempt to address the question of why polonium takes the simple cubic structure by means of ab initio calculations using the pseudopotential density functional method. We will discuss the electronic structure of polonium in relation to its crystal structure.
NASA Astrophysics Data System (ADS)
Iyo, A.; Hira, K.; Tokiwa, K.; Tanaka, Y.; Hase, I.; Yanagisawa, T.; Takeshita, N.; Kihou, K.; Lee, C. H.; Shirage, P. M.; Raychaudhuri, P.; Eisaki, H.
2014-02-01
We have investigated superconductivity and structure in a gold-antimony-tellurium ternary alloy system (AuxSb1-x-yTey) synthesized under high pressure. We found that Au0.125Sb0.75Te0.125 and AuSb6Te when crystallized in simple cubic structures (α-Po type), which are reported to be semiconductors above 20 K, are superconductors with a transition temperature (Tc) of 6.7 K. The structure and Tc are mapped on an Au-Sb-Te triangular diagram. A β-Po-type rhombohedral structure appears before the crystal structure changes from As type (Sb) to α-Po type. Superconductivity is observed in the β-Po-type structure as well as in the α-Po-type structure. Tc increases with decreasing Te concentration toward the Te-free Au-Sb end of the diagram. A Tc of 8.1 K was achieved for the Au-Sb alloy with a typical composition of Au0.15Sb0.85. This Tc value is the highest among materials with the α-Po-type structure under ambient pressure. Our Au0.125Sb0.75Te0.125 sample exhibits a weak metallic behavior in resistivity. The discrepancy in the normal state resistivity behaviors between the previous study and ours must originate from a difference in the number of lattice defects in the samples.
2013-01-01
added [18,19] and a dense (relative density > 90%) material with a cubic structure was ob- tained. Geiger et al. [17] have suggested that Al substitutes...5þ) on the 16a site (Zr 4þ), that reduces the Li content and/or increases Li vacancy concentration to stabilize the cubic structure [22,23
Nontrivial topology of cubic alkali bismuthides
NASA Astrophysics Data System (ADS)
Rusinov, I. P.; Sklyadneva, I. Yu.; Heid, R.; Bohnen, K.-P.; Petrov, E. K.; Koroteev, Yu. M.; Echenique, P. M.; Chulkov, E. V.
2017-06-01
We report an ab initio study of the effect of pressure on vibrational and electronic properties of K3Bi and Rb3Bi in the cubic F m 3 ¯m structure. It is shown that the high-temperature cubic phase of K3Bi and Rb3Bi is dynamically unstable at T =0 but can be stabilized by pressure. The electronic spectra of alkali bismuthides are found to possess the bulk band touching at the Brillouin zone center and an inverted spin-orbit bulk band structure. Upon hydrostatic compression the compounds transform from the topologically nontrivial semimetal (K3Bi )/metal (Rb3Bi ) into a trivial semiconductor (metal) with a conical Dirac-type dispersion of electronic bands at the point of the topological transition. In K3Bi the dynamical stabilization occurs before the system undergoes the topological phase transition.
Simulation of rotary-drum and repose tests for frictional spheres and rigid sphere clusters
Walton, O.R.; Braun, R.L.
1993-11-01
The effects of rotation rate and interparticle friction on the bulk flow behavior in rotating horizontal cylinders are studied via particle-dynamic simulations. Assemblies of inelastic, frictional spheres and rigid sphere clusters are utilized, and rotation rates from quasistatic to centrifuging are examined. Flow phenomena explored include size segregation, avalanching, slumping and centrifuging. Simulated drum flows with two sizes of frictional spheres showed very rapid segregation of species perpendicular to the drum axis; however, simulations of up to 10 revolutions, utilizing periodic-boundary ends, did not exhibit the experimentally observed axial segregation into stripes. Angles of repose for uniform-sized spheres in slowly rotating cylinders varied from 13 to 31 degrees as the friction coefficient varied from 0.02 to 1.0. For simulated rotation rates higher than the threshold to obtain uniform flow conditions, the apparent angle of repose increases as the rotation rats increases, consistent with experiments. Also, simulations with rigid clusters of 4 spheres in a tetrahedral shape or 8 spheres in a cubical arrangement, demonstrate that particle shape strongly influences the repose angle. Simulations of cubical 8-sphere clusters, with a surface coefficient of friction of 0.1, produced apparent angles of repose exceeding 35 degrees, compared to 23 degrees for assemblies of single spheres interacting with the same force model parameters. Centrifuging flows at very high rotation rates exist as stationary beds moving exactly as the outer rotating wall. At somewhat slower speeds the granular bed remains in contact with the wall but exhibits surface sliding down the rising inner bed surface, moving a short distance on each revolution. At still slower speeds particles rain from the surface of the upper half of the rotating bed.
Radiation of non-relativistic particle on a conducting sphere and a string of spheres
NASA Astrophysics Data System (ADS)
Shul'ga, N. F.; Syshchenko, V. V.; Larikova, E. A.
2017-07-01
The radiation resulting from the uniform motion of a charged particle by (or through) metal sphere is considered. The simple but rigorous description of the radiation process is developed for the case of non-relativistic particle and perfectly conducting sphere by the way of the method of images known from electrostatics. The spectral-angular and spectral densities of the diffraction and transition radiation on the single sphere are computed. The Smith-Purcell radiation caused by motion of the particle parallel to the periodic string of spheres is also considered.
Strain tuning of topological band order in cubic semiconductors
Feng, wanxiang; Zhu, Wenguang; Weitering, Hanno; Stocks, George Malcolm; Yao, yugui; Xiao, Di
2012-01-01
We theoretically explore the possibility of tuning the topological order of cubic diamond/zinc-blende semi- conductors with external strain. Based on a simple tight-binding model, we analyze the evolution of the cubic semiconductor band structure under hydrostatic or biaxial lattice expansion, by which a generic guiding princi- ple is established that biaxial lattice expansion can induce a topological phase transition of small band-gap cubic semiconductors via a band inversion and symmetry breaking at point. Using density functional theory cal- culations, we demonstrate that a prototype topological trivial semiconductor, InSb, is converted to a nontrivial topological semiconductor with a 2% 3% biaxial lattice expansion.
Rheological properties of Cubic colloidal suspensions
NASA Astrophysics Data System (ADS)
Boromand, Arman; Maia, Joao
2016-11-01
Colloidal and non-colloidal suspensions are ubiquitous in many industrial application. There are numerous studies on these systems to understand and relate their complex rheological properties to their microstructural evolution under deformation. Although most of the experimental and simulation studies are centered on spherical particles, in most of the industrial applications the geometry of the colloidal particles deviate from the simple hard sphere and more complex geometries exist. Recent advances in microfabrication paved the way to fabricate colloidal particles with complex geometries for applications in different areas such as drug delivery where the fundamental understanding of their dynamics has remained unexplored. In this study, using dissipative particle dynamics, we investigate the rheological properties of cubic (superball) particles which are modeled as the cluster of core-modified DPD particles. Explicit representation of solvent particles in the DPD scheme will conserve the full hydrodynamic interactions between colloidal particles. Rheological properties of these cubic suspensions are investigated in the dilute and semi-dilute regimes. The Einstein and Huggins coefficients for these particles with different superball exponent will be calculate which represent the effect of single particle's geometry and multibody interactions on viscosity, respectively. The response of these suspensions is investigated under simple shear and oscillatory shear where it is shown that under oscillation these particles tend to form crystalline structure giving rise to stronger shear-thinning behavior recently measured experimentally.
Percolation of disordered jammed sphere packings
NASA Astrophysics Data System (ADS)
Ziff, Robert M.; Torquato, Salvatore
2017-02-01
We determine the site and bond percolation thresholds for a system of disordered jammed sphere packings in the maximally random jammed state, generated by the Torquato–Jiao algorithm. For the site threshold, which gives the fraction of conducting versus non-conducting spheres necessary for percolation, we find {{p}\\text{c}}=0.3116(3) , consistent with the 1979 value of Powell 0.310(5) and identical within errors to the threshold for the simple-cubic lattice, 0.311 608, which shares the same average coordination number of 6. In terms of the volume fraction ϕ, the threshold corresponds to a critical value {φ\\text{c}}=0.199 . For the bond threshold, which apparently was not measured before, we find {{p}\\text{c}}=0.2424(3) . To find these thresholds, we considered two shape-dependent universal ratios involving the size of the largest cluster, fluctuations in that size, and the second moment of the size distribution; we confirmed the ratios’ universality by also studying the simple-cubic lattice with a similar cubic boundary. The results are applicable to many problems including conductivity in random mixtures, glass formation, and drug loading in pharmaceutical tablets.
Rahman, M Shahinur; Changez, M; Samal, Shashadhar; Lee, Jae-Suk
2007-11-01
The effect of solvent compositions on the micellization behaviors of amphiphilic poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate) (PHIC-b-P2VP-b-PHIC) rod-coil-rod triblock copolymer was studied. In absolute methanol the block copolymer formed hollow spherical micelles. These micelles transformed into giant-tubes by simply changing the solvent composition. With 20% THF in CH3OH hollow spheres got interconnected and formed species that are precursors of the giant tubes. When the composition of THF reached 50-70%, long giant tubes are formed. Further increasing THF content in the mixed solvent, fragmentation of the wall of the tubes was observed. In absolute THF, which is the common solvent for both the blocks, the usual phase separation occurred. TEM image of the giant tubes stained with iodine showed that the core of the tubes is made from PHIC rod block.
ERIC Educational Resources Information Center
Agnew, Jeanne L.; Choike, James R.
1987-01-01
Mathematical observations are made about some continuous curves, called transitions, encountered in well-known experiences. The transition parabola, the transition spiral, and the sidestep maneuver are presented. (MNS)
Archaic artifacts resembling celestial spheres
NASA Astrophysics Data System (ADS)
Dimitrakoudis, S.; Papaspyrou, P.; Petoussis, V.; Moussas, X.
We present several bronze artifacts from the Archaic Age in Greece (750-480 BC) that resemble celestial spheres or forms of other astronomical significance. They are studied in the context of the Dark Age transition from Mycenaean Age astronomical themes to the philosophical and practical revival of astronomy in the Classical Age with its plethora of astronomical devices. These artifacts, mostly votive in nature are spherical in shape and appear in a variety of forms their most striking characteristic being the depiction of meridians and/or an equator. Most of those artifacts come from Thessaly, and more specifically from the temple of Itonia Athena at Philia, a religious center of pan-Hellenic significance. Celestial spheres, similar in form to the small artifacts presented in this study, could be used to measure latitudes, or estimate the time at a known place, and were thus very useful in navigation.
Multiply charged monopoles in cubic dimer model
NASA Astrophysics Data System (ADS)
Ganesh Jaya, Sreejith; Powell, Stephen
2015-03-01
The classical cubic dimer model is a 3D statistical mechanical system whose degrees of freedom are dimers that occupy the edges between nearest neighbour vertices of a cubic lattice. Dimer occupancies are subject to the local constraint that every vertex is associated with exactly one dimer. In the presence of an aligning interaction, it is known that the system exhibits an unconventional continuous thermal phase transition from a symmetry broken columnar phase to a Coulomb-phase. The transition is in the NCCP1 universality class, which also describes the Neel-VBS transition in the JQ model and the S =1/2 Heisenberg model with suppression of hedgehog defects. Using Monte-Carlo simulations of a pair of defects in a background of fluctuating dimers, we calculate the scaling exponents for fugacities of monopole defects of charge Q = 2 and 3 at this critical point. Our estimates suggest that Q = 3 monopoles are relevant and could therefore drive the JQ model away from the NCCP1 critical point on a hexagonal lattice.
2014-01-22
ISS038-E-033888 (22 Jan. 2014) --- A new experiment using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES, already on the station, is featured in this image photographed by an Expedition 38 crew member in the International Space Station's Kibo laboratory. For the SPHERES-Slosh experiment, two SPHERES robots are attached to opposite ends of a metal frame holding a plastic tank with green-colored water. The new hardware for the SPHERES-Slosh study was delivered to the station aboard Orbital Sciences' Cygnus cargo craft on Jan. 12.
The Smart SPHERES space robot (Synchronized Position Hold, Engage, Reorient, Experimental Satellites) equipped with an Android smartphone performs a video survey inside of the International Space S...
DISE: directed sphere exclusion.
Gobbi, Alberto; Lee, Man-Ling
2003-01-01
The Sphere Exclusion algorithm is a well-known algorithm used to select diverse subsets from chemical-compound libraries or collections. It can be applied with any given distance measure between two structures. It is popular because of the intuitive geometrical interpretation of the method and its good performance on large data sets. This paper describes Directed Sphere Exclusion (DISE), a modification of the Sphere Exclusion algorithm, which retains all positive properties of the Sphere Exclusion algorithm but generates a more even distribution of the selected compounds in the chemical space. In addition, the computational requirement is significantly reduced, thus it can be applied to very large data sets.
2014-01-22
ISS038-E-033890 (22 Jan. 2014) --- In the International Space Station's Kibo laboratory, NASA astronaut Mike Hopkins, Expedition 38 flight engineer, works with a new experiment using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES, which are already on the station. For the SPHERES-Slosh experiment, two SPHERES robots are attached to opposite ends of a metal frame holding the plastic tank with the green-colored water. The new hardware for the SPHERES-Slosh study was delivered to the station aboard Orbital Sciences' Cygnus cargo craft on Jan. 12.
ERIC Educational Resources Information Center
Nathanson, Jeanne H., Ed.
1993-01-01
This theme issue on transitions for individuals with disabilities contains nine papers discussing transition programs and issues. "Transition Issues for the 1990s," by Michael J. Ward and William D. Halloran, discusses self-determination, school responsibility for transition, continued educational engagement of at-risk students, and service…
Colloidal alloys with preassembled clusters and spheres
NASA Astrophysics Data System (ADS)
Ducrot, Étienne; He, Mingxin; Yi, Gi-Ra; Pine, David J.
2017-06-01
Self-assembly is a powerful approach for constructing colloidal crystals, where spheres, rods or faceted particles can build up a myriad of structures. Nevertheless, many complex or low-coordination architectures, such as diamond, pyrochlore and other sought-after lattices, have eluded self-assembly. Here we introduce a new design principle based on preassembled components of the desired superstructure and programmed nearest-neighbour DNA-mediated interactions, which allows the formation of otherwise unattainable structures. We demonstrate the approach using preassembled colloidal tetrahedra and spheres, obtaining a class of colloidal superstructures, including cubic and tetragonal colloidal crystals, with no known atomic analogues, as well as percolating low-coordination diamond and pyrochlore sublattices never assembled before.
Multiscale mesh generation on the sphere
NASA Astrophysics Data System (ADS)
Lambrechts, Jonathan; Comblen, Richard; Legat, Vincent; Geuzaine, Christophe; Remacle, Jean-François
2008-12-01
A method for generating computational meshes for applications in ocean modeling is presented. The method uses a standard engineering approach for describing the geometry of the domain that requires meshing. The underlying sphere is parametrized using stereographic coordinates. Then, coastlines are described with cubic splines drawn in the stereographic parametric space. The mesh generation algorithm builds the mesh in the parametric plane using available techniques. The method enables to import coastlines from different data sets and, consequently, to build meshes of domains with highly variable length scales. The results include meshes together with numerical simulations of various kinds.
MINIMAL IMMERSIONS OF SPHERES INTO SPHERES
Do Carmo, Manfredo P.; Wallach, Nolan R.
1969-01-01
In this paper we announce a qualitative description of an important class of closed n-dimensional submanifolds of the m-dimensional sphere, namely, those which locally minimize the n-area in the same way that geodesics minimize the arc length and are themselves locally n-spheres of constant radius r; those r that may appear are called admissible. It is known that for n = 2 each admissible r determines a unique element of the above class. The main result here is that for each n ≥ 3 and each admissible r ≥ [unk]8 there exists a continuum of distinct such submanifolds. PMID:16591771
Brouwers, H J H
2008-07-01
In a previous paper analytical equations were derived for the packing fraction of crystalline structures consisting of bimodal randomly placed hard spheres [H. J. H. Brouwers, Phys. Rev. E 76, 041304 (2007)]. The bimodal packing fraction was derived for the three crystalline cubic systems: viz., face-centered cubic, body-centered cubic, and simple cubic. These three equations appeared also to be applicable to all 14 Bravais lattices. Here it is demonstrated, accounting for the number of distorted bonds in the building blocks and using graph theory, that one general packing equation can be derived, valid again for all lattices. This expression is validated and applied to the process of amorphization.
Infrared cubic dielectric resonator metamaterial.
Sinclair, Michael B.; Brener, Igal; Peters, David William; Ginn, James Cleveland, III; Ten Eyck, Gregory A.
2010-06-01
Dielectric resonators are an effective means to realize isotropic, low-loss optical metamaterials. As proof of this concept, a cubic resonator is analytically designed and then tested in the long-wave infrared.
ERIC Educational Resources Information Center
Szekely, George
2011-01-01
This article describes an art lesson that allows students to set up and collect sphere canvases. Spheres move art away from a rectangular canvas into a dimension that requires new planning and painting. From balls to many other spherical canvases that bounce, roll, float and fly, art experiences are envisioned by students. Even if adults recognize…
Liquid hydrogen sphere project
2011-06-22
A 107,000-gallon liquid hydrogen sphere no longer needed at Stennis Space Center is barged through the facility locks June 21. The rocket engine test facility has teamed with the Mississippi Department of Marine Resource to place the sphere in offshore waters as an artificial reef.
ERIC Educational Resources Information Center
Szekely, George
2011-01-01
This article describes an art lesson that allows students to set up and collect sphere canvases. Spheres move art away from a rectangular canvas into a dimension that requires new planning and painting. From balls to many other spherical canvases that bounce, roll, float and fly, art experiences are envisioned by students. Even if adults recognize…
Ogawa, Ryoji; Miwa, Yohei; Kutsumizu, Shoichi
2015-08-06
Changes in intermolecular interactions and molecular geometry for two kinds of thermotropic cubic mesogenes, 4'-n-alkoxy-3'-nitrobiphenyl-4-carboxlic acid (denoted as ANBC-n, where n represents the number of carbon atoms in the alkoxy group) and 1,2-bis(4'-n-alkoxybenzoyl)hydrazines (BABH-n), at liquid crystal (LC) phase transitions were revealed utilizing the frequency shifts in Fourier transform infrared (FT-IR) bands as a guide. The ANBC-n and BABH-n form two kinds of bicontinuous cubic (Cub(bi)), Ia3d and Im3m types, and smectic LC phases depending on the length of the alkyl chain and temperature. In the present work, two kinds of phase transitions, i.e., smectic C ↔ Ia3d-Cub(bi) phase transition for the ANBC-16 and BABH-9 and Ia3d-Cub(bi) ↔ Im3m-Cub(bi) phase transition for the BABH-13 and BABH-16, were examined, and the experimental result was compared to the entropy changes predicted by the quasibinary picture model. In this model, it is postulated that the basic units in the BABH-n and ANBC-n, i.e., the "chain" and "core", would contribute to the phase transition entropy in different ways. A conclusion of the FT-IR result shows the adequacy of this model for the behavior of the alkyl chain. On the other hand, the FT-IR result suggested that entropy changes for the "core" predicted by this model are not directly related to changes in the intermolecular interactions between the aromatic cores of the LC molecules at the phase transitions.
Phase behaviour of deionized binary mixtures of charged colloidal spheres.
Lorenz, Nina J; Schöpe, Hans Joachim; Reiber, Holger; Palberg, Thomas; Wette, Patrick; Klassen, Ina; Holland-Moritz, Dirk; Herlach, Dieter; Okubo, Tsuneo
2009-11-18
We review recent work on the phase behaviour of binary charged sphere mixtures as a function of particle concentration and composition. Both size ratios Γ and charge ratios Λ are varied over a wide range. Unlike the case for hard spheres, the long-ranged Coulomb interaction stabilizes the crystal phase at low particle concentrations and shifts the occurrence of amorphous solids to particle concentrations considerably larger than the freezing concentration. Depending on Γ and Λ, we observe upper azeotrope, spindle, lower azeotrope and eutectic types of phase diagrams, all known well from metal systems. Most solids are of body centred cubic structure. Occasionally stoichiometric compounds are formed at large particle concentrations. For very low Γ, entropic effects dominate and induce a fluid-fluid phase separation. Since for charged spheres the charge ratio Λ is also decisive for the type of phase diagram, future experiments with charge variable silica spheres are suggested.
PREPARATION OF HIGH-DENSITY THORIUM OXIDE SPHERES
McNees, R.A. Jr.; Taylor, A.J.
1963-12-31
A method of preparing high-density thorium oxide spheres for use in pellet beds in nuclear reactors is presented. Sinterable thorium oxide is first converted to free-flowing granules by means such as compression into a compact and comminution of the compact. The granules are then compressed into cubes having a density of 5.0 to 5.3 grams per cubic centimeter. The cubes are tumbled to form spheres by attrition, and the spheres are then fired at 1250 to 1350 deg C. The fired spheres are then polished and fired at a temperature above 1650 deg C to obtain high density. Spherical pellets produced by this method are highly resistant to mechanical attrition hy water. (AEC)
ERIC Educational Resources Information Center
Field, David; And Others
1992-01-01
Includes four articles: "Career Aspirations" (Field); "Making the Transition to a New Curriculum" (Baker, Householder); "How about a 'Work to School' Transition?" (Glasberg); and "Technological Improvisation: Bringing CNC to Woodworking" (Charles, McDuffie). (SK)
Effective interatomic potential for body-centered-cubic metals
Wang, Y.R.; Boercker, D.B.
1995-07-01
An effective interatomic potential suitable for all body-centered-cubic (bcc) metals is developed based on the embedded atom method. The potential predicts all major anomalies displayed in the phonon spectra of the bcc transition metals, as well as the large relaxation of the (100) surface of V, Nb, and Ta. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
NASA Technical Reports Server (NTRS)
Benavides, Jose
2014-01-01
SPHERES is a facility of the ISS National Laboratory with three IVA nano-satellites designed and delivered by MIT to research estimation, control, and autonomy algorithms. Since Fall 2010, The SPHERES system is now operationally supported and managed by NASA Ames Research Center (ARC). A SPHERES Program Office was established and is located at NASA Ames Research Center. The SPHERES Program Office coordinates all SPHERES related research and STEM activities on-board the International Space Station (ISS), as well as, current and future payload development. By working aboard ISS under crew supervision, it provides a risk tolerant Test-bed Environment for Distributed Satellite Free-flying Control Algorithms. If anything goes wrong, reset and try again! NASA has made the capability available to other U.S. government agencies, schools, commercial companies and students to expand the pool of ideas for how to test and use these bowling ball-sized droids. For many of the researchers, SPHERES offers the only opportunity to do affordable on-orbit characterization of their technology in the microgravity environment. Future utilization of SPHERES as a facility will grow its capabilities as a platform for science, technology development, and education.
NASA Astrophysics Data System (ADS)
Shaulov, S. B.; Besshapov, S. P.; Kabanova, N. V.; Sysoeva, T. I.; Antonov, R. A.; Anyuhina, A. M.; Bronvech, E. A.; Chernov, D. V.; Galkin, V. I.; Tkaczyk, W.; Finger, M.; Sonsky, M.
2009-12-01
The expedition carried out in March, 2008 to Lake Baikal became an important stage in the development of the SPHERE experiment. During the expedition the SPHERE-2 installation was hoisted, for the first time, on a tethered balloon, APA, to a height of 700 m over the lake surface covered with ice and snow. A series of test measurements were made. Preliminary results of the data processing are presented. The next plan of the SPHERE experiment is to begin a set of statistics for constructing the CR spectrum in the energy range 10-10 eV.
2013-11-04
ISS037-E-025870 (4 Nov. 2013) --- In the International Space Station?s Kibo laboratory, NASA astronaut Michael Hopkins, Expedition 37 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Surrounding the two SPHERES mini-satellites is ring-shaped hardware known as the Resonant Inductive Near-field Generation System, or RINGS. SPHERES-RINGS seeks to demonstrate wireless power transfer between satellites at a distance for enhanced operations.
2013-11-04
ISS037-E-025872 (4 Nov. 2013) --- In the International Space Station?s Kibo laboratory, NASA astronaut Michael Hopkins, Expedition 37 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Surrounding the two SPHERES mini-satellites is ring-shaped hardware known as the Resonant Inductive Near-field Generation System, or RINGS. SPHERES-RINGS seeks to demonstrate wireless power transfer between satellites at a distance for enhanced operations.
2013-11-04
ISS037-E-025866 (4 Nov. 2013) --- In the International Space Station?s Kibo laboratory, NASA astronaut Michael Hopkins, Expedition 37 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Surrounding the two SPHERES mini-satellites is ring-shaped hardware known as the Resonant Inductive Near-field Generation System, or RINGS. SPHERES-RINGS seeks to demonstrate wireless power transfer between satellites at a distance for enhanced operations.
2013-11-04
ISS037-E-025868 (4 Nov. 2013) --- In the International Space Station?s Kibo laboratory, NASA astronaut Michael Hopkins, Expedition 37 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Surrounding the two SPHERES mini-satellites is ring-shaped hardware known as the Resonant Inductive Near-field Generation System, or RINGS. SPHERES-RINGS seeks to demonstrate wireless power transfer between satellites at a distance for enhanced operations.
2013-11-04
ISS037-E-025879 (4 Nov. 2013) --- In the International Space Station?s Kibo laboratory, NASA astronaut Michael Hopkins, Expedition 37 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Surrounding the two SPHERES mini-satellites is ring-shaped hardware known as the Resonant Inductive Near-field Generation System, or RINGS. SPHERES-RINGS seeks to demonstrate wireless power transfer between satellites at a distance for enhanced operations.
NASA Public Affairs Officer Kelly Humphries conducts a phone interview with Mark Micire, SPHERES Engineering Manager at Ames Research Center. Questions? Ask us on Twitter @NASA_Johnson and include ...
Electromagnetically revolving sphere viscometer
NASA Astrophysics Data System (ADS)
Hosoda, Maiko; Sakai, Keiji
2014-12-01
In this paper, we propose a new method of low viscosity measurement, in which the rolling of a probe sphere on the flat solid bottom of a sample cell is driven remotely and the revolution speed of the probe in a sample liquid gives the viscosity measurements. The principle of this method is based on the electromagnetically spinning technique that we developed, and the method is effective especially for viscosity measurements at levels below 100 mPa·s with an accuracy higher than 1%. The probe motion is similar to that in the well-known rolling sphere (ball) method. However, our system enables a steady and continuous measurement of viscosity, which is problematic using the conventional method. We also discuss the limits of the measurable viscosity range common to rolling-sphere-type viscometers by considering the accelerating motion of a probe sphere due to gravity, and we demonstrate the performance of our methods.
NASA Technical Reports Server (NTRS)
Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)
1986-01-01
The improved, heterogeneous catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitably formed of a shell (12) of metal such as aluminum having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be, itself, catalytic or the catalyst can be coated onto the sphere as a layer (16), suitably platinum or iron, which may be further coated with a layer (18) of activator or promoter. The density of the spheres (30) can be uniformly controlled to a preselected value within .+-.10 percent of the density of the fluid reactant such that the spheres either remain suspended or slowly fall or rise through the liquid reactant.
NASA Technical Reports Server (NTRS)
Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)
1989-01-01
The improved, heterogeneous catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitably formed of a shell (12) of metal such as aluminum having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be, itself, catalytic or the catalyst can be coated onto the sphere as a layer (16), suitably platinum or iron, which may be further coated with a layer (18) of activator or promoter. The density of the spheres (30) can be uniformly controlled to a preselected value within .+-.10 percent of the density of the fluid reactant such that the spheres either remain suspended or slowly fall or rise through the liquid reactant.
Catalytic, hollow, refractory spheres
NASA Technical Reports Server (NTRS)
Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)
1987-01-01
Improved, heterogeneous, refractory catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitable formed of a shell (12) of refractory such as alumina having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be itself catalytic or a catalytically active material coated onto the sphere as a layer (16), suitably platinum or iron, which may be further coated with a layer (18) of activator or promoter. The density of the spheres (30) can be uniformly controlled to a preselected value within .+-.10 percent of the density of the fluid reactant such that the spheres either remain suspended or slowly fall or rise through the liquid reactant.
2016-06-30
iss048e017435 (6/30/2016) --- Commander Jeff Williams monitors bowling ball-sized internal satellites known as SPHERES (Synchronized Position Hold, Engage, Reorient, Experimental Satellites) during a maintenance run in the Japanese Kibo Laboratory Module.
2000-10-25
The John C. Stennis Space Center's visitor center, StenniSphere, is one of Mississippi's leading tourist attractions and features a 14,000-square-foot interactive review of Stennis Space Center's role in America's space program. Designed to entertain while educating, StenniSphere includes informative displays and exhibits from NASA, the Naval Meteorology and Oceanography Command, and other resident agencies located at Stennis Space Center in Hancock County, Miss.
NASA Technical Reports Server (NTRS)
2000-01-01
The John C. Stennis Space Center's visitor center, StenniSphere, is one of Mississippi's leading tourist attractions and features a 14,000-square-foot interactive review of Stennis Space Center's role in America's space program. Designed to entertain while educating, StenniSphere includes informative displays and exhibits from NASA, the Naval Meteorology and Oceanography Command, and other resident agencies located at Stennis Space Center in Hancock County, Miss.
2007-03-24
ISS014-E-17880 (24 March 2007) --- This medium close-up view shows three bowling-ball-sized free-flying satellites called Synchronized Position Hold, Engage, Reorient, Experimental Satellites (SPHERES) in the Destiny laboratory of the International Space Station. SPHERES were designed to test control algorithms for spacecraft by performing autonomous rendezvous and docking maneuvers inside the station. The results are important for multi-body control and in designing constellation and array spacecraft configurations.
NASA Astrophysics Data System (ADS)
Sun, Xiaochun
The armillary sphere was perhaps the most important type of astronomical instrument in ancient China. It was first invented by Luoxia Hong in the first century BC. After Han times, the structure of the armillary sphere became increasingly sophisticated by including more and more rings representing various celestial movements as recognized by the Chinese astronomers. By the eighth century, the Chinese armillary sphere consisted of three concentric sets of rings revolving on the south-north polar axis. The relative position of the rings could be adjusted to reflect the precession of the equinoxes and the regression of the Moon's nodes along the ecliptic. To counterbalance the defect caused by too many rings, Guo Shoujing from the late thirteenth century constructed the Simplified Instruments which reorganized the rings of the armillary sphere into separate instruments for measuring equatorial coordinates and horizontal coordinates. The armillary sphere was still preserved because it was a good illustration of celestial movements. A fifteenth-century replica of Guo Shoujing's armillary sphere still exists today.
NASA Astrophysics Data System (ADS)
Minguzzi, E.
2017-03-01
We investigate spacetimes whose light cones could be anisotropic. We prove the equivalence of the structures: (a) Lorentz-Finsler manifold for which the mean Cartan torsion vanishes, (b) Lorentz-Finsler manifold for which the indicatrix (observer space) at each point is a convex hyperbolic affine sphere centered on the zero section, and (c) pair given by a spacetime volume and a sharp convex cone distribution. The equivalence suggests to describe (affine sphere) spacetimes with this structure, so that no algebraic-metrical concept enters the definition. As a result, this work shows how the metric features of spacetime emerge from elementary concepts such as measure and order. Non-relativistic spacetimes are obtained replacing proper spheres with improper spheres, so the distinction does not call for group theoretical elements. In physical terms, in affine sphere spacetimes the light cone distribution and the spacetime measure determine the motion of massive and massless particles (hence the dispersion relation). Furthermore, it is shown that, more generally, for Lorentz-Finsler theories non-differentiable at the cone, the lightlike geodesics and the transport of the particle momentum over them are well defined, though the curve parametrization could be undefined. Causality theory is also well behaved. Several results for affine sphere spacetimes are presented. Some results in Finsler geometry, for instance in the characterization of Randers spaces, are also included.
ERIC Educational Resources Information Center
Thompson, Sandy, Ed.; And Others
1990-01-01
This "feature issue" focuses on transition from school to adult life for persons with disabilities. Included are "success stories," brief program descriptions, and a list of resources. Individual articles include the following titles and authors: "Transition: An Energizing Concept" (Paul Bates); "Transition…
NASA Astrophysics Data System (ADS)
Nabil, Dhifallah; Hehlen, Bernard; El Marssi, Mimoun; Mohamed, Dammak; Khemakhem, Hamadi
2016-12-01
This paper presents a survey of soft modes and their relationship to structural phase transitions. After introducing the concept of a soft mode, the origin of softening is considered from a lattice-dynamical point. The Landau theory approach to structural transitions is then discussed, followed by a generalization of the soft-mode concept through the use of the dynamic order-parameter susceptibility. The hyper-Raman spectra in the cubic phase of (Ba0.8Sr0.2)Ti0.95(Zn1/3Nb2/3)0.05O3 are studied with special emphasis on the lowest-frequency phonon mode. The spectral structure is found to change above the Curie temperature (303-873 K). Soft modes were put forward by Cochran and Anderson about 50 years ago as an explanation of structural phase transitions. Extending Landau's theory of phase transitions, their prediction was that the square of the frequency of the soft mode was proportional to ω0 (T) = C √{ T - TC } where Tc is the transition temperature.
Amaya, Andrew J.; Pathak, Harshad; Modak, Viraj P.; ...
2017-06-28
Using an X-ray laser, we investigated the crystal structure of ice formed by homogeneous ice nucleation in deeply supercooled water nanodrops (r ≈ 10 nm) at ~225 K. The nanodrops were formed by condensation of vapor in a supersonic nozzle, and the ice was probed within 100 μs of freezing using femtosecond wide-angle X-ray scattering at the Linac Coherent Light Source free-electron X-ray laser. The X-ray diffraction spectra indicate that this ice has a metastable, predominantly cubic structure; the shape of the first ice diffraction peak suggests stacking-disordered ice with a cubicity value, χ, in the range of 0.78 ±more » 0.05. The cubicity value determined here is higher than those determined in experiments with micron-sized drops but comparable to those found in molecular dynamics simulations. Lastly, the high cubicity is most likely caused by the extremely low freezing temperatures and by the rapid freezing, which occurs on a ~1 μs time scale in single nanodroplets.« less
ERIC Educational Resources Information Center
Khonsari, Michael M.; Horn, Douglas
1990-01-01
An algorithm is described for generating smooth curves of first-order continuity. The algorithm is composed of several cubic Bezier curves joined together at the user defined control points. Introduced is a tension control parameter which can be set thus providing additional flexibility in the design of free-form curves. (KR)
Cubication of Conservative Nonlinear Oscillators
ERIC Educational Resources Information Center
Belendez, Augusto; Alvarez, Mariela L.; Fernandez, Elena; Pascual, Immaculada
2009-01-01
A cubication procedure of the nonlinear differential equation for conservative nonlinear oscillators is analysed and discussed. This scheme is based on the Chebyshev series expansion of the restoring force, and this allows us to approximate the original nonlinear differential equation by a Duffing equation in which the coefficients for the linear…
Cubication of Conservative Nonlinear Oscillators
ERIC Educational Resources Information Center
Belendez, Augusto; Alvarez, Mariela L.; Fernandez, Elena; Pascual, Immaculada
2009-01-01
A cubication procedure of the nonlinear differential equation for conservative nonlinear oscillators is analysed and discussed. This scheme is based on the Chebyshev series expansion of the restoring force, and this allows us to approximate the original nonlinear differential equation by a Duffing equation in which the coefficients for the linear…
Cubic Unit Cell Construction Kit.
ERIC Educational Resources Information Center
Mattson, Bruce
2000-01-01
Presents instructions for building a simple interactive unit-cell construction kit that allows for the construction of simple, body-centered, and face-centered cubic lattices. The lit is built from inexpensive and readily available materials and can be built in any number of sizes. (WRM)
Superconductivity in cubic noncentrosymmetric PdBiSe Crystal
NASA Astrophysics Data System (ADS)
Joshi, B.; Thamizhavel, A.; Ramakrishnan, S.
2015-03-01
Mixing of spin singlet and spin triplet superconducting pairing state is expected in noncentrosymmetric superconductors (NCS) due to the inherent presence of Rashba-type antisymmetric spin-orbit coupling. Unlike low symmetry (tetragonal or monoclinic) NCS, parity is isotropicaly broken in space for cubic NCS and can additionally lead to the coexistence of magnetic and superconducting state under certain conditions. Motivated with such enriched possibility of unconventional superconducting phases in cubic NCS we are reporting successful formation of single crystalline cubic noncentrosymmetric PdBiSe with lattice parameter a = 6.4316 Å and space group P21 3 (space group no. 198) which undergoes to superconducting transition state below 1.8 K as measured by electrical transport and AC susceptibility measurements. Significant strength of Rashba-type antisymmetric spin-orbit coupling can be expected for PdBiSe due to the presence of high Z (atomic number) elements consequently making it potential candidate for unconventional superconductivity.
Maximizing cubic phase gallium nitride surface coverage on nano-patterned silicon (100)
NASA Astrophysics Data System (ADS)
Liu, R.; Bayram, C.
2016-07-01
Here we investigate the hexagonal-to-cubic phase transition in metalorganic-chemical-vapor-deposition-grown gallium nitride enabled via silicon (100) nano-patterning. Electron backscatter diffraction and depth-resolved cathodoluminescence experiments show complete cubic phase GaN surface coverage when GaN deposition thickness ( hc ), etch depth ( td ), and opening width ( p ) obey hc≈1.06 p -0.75 td ; in line with a geometrical model based on crystallography. Cubic GaN uniformity is studied via electron backscatter diffraction and cathodoluminescence measurements. Atomic force microscopy reveals a smooth cubic GaN surface. Phase-transition cubic GaN shows promising optical and structural quality for integrated photonic devices.
Sphere-supported thin film electroluminescent technology
NASA Astrophysics Data System (ADS)
Xiang, Yingwei
A new Sphere-Supported Thin Film Electroluminescent (SSTFEL) technology is developed based on a novel device structure containing numerous spherical BaTiO3 particles embedded in a polypropylene matrix with top and bottom area exposed. A TFEL phosphor stack deposited on the top area of the spherical BaTiO3 particles emits light through the same mechanism as conventional flat TFEL devices. Flexibility is realized by the polypropylene matrix. SSTFEL technology provides the first flexible and rollable light-emitting devices based on the TFEL mechanism. Besides the superior flexibility, SSTFEL technology enables high post-annealing temperature for the phosphor up to approximately 1200°C, which permits a wide range of TFEL phosphors to be exploited. After sintering at a temperature higher than 920°C, the spray-dried cubic BaTiO3 spheres have tetragonal phase. The relative dielectric constant of the BaTiO3 spheres depends on the grain size that is mainly controlled by the sintering temperature. Software simulation and experimental measurements indicate that the relative dielectric constant of the BaTiO 3 spheres reaches above 4000 after sintering at 1170° for 2 hours. Assuming angle alpha varying from 0° (top of the BaTiO3 sphere) to 180° (bottom of the BaTiO3 sphere), the phosphor stack sputtered on a BaTiO3 sphere has a nearly uniform thickness with a variation less than +/-2.5% when alpha is between 0° and 25°. When alpha increases from 25° to 45°, the thickness of the phosphor stack gradually decreases up to 12.5%. Software simulation shows that the electric field in the central plane of the phosphor stack increases 18% from the pole to the edge of the light-emitting cap on the BaTiO3 sphere. Experimental results reveal that, instead of the variation in electric field, the nature of the surface of the BaTiO3 spheres before the sputtering process primarily influences the electroluminescent properties of the SSTFEL devices. A new Indium-Tin-Oxide (ITO
Evolution of cubic membranes as antioxidant defence system.
Deng, Yuru; Almsherqi, Zakaria A
2015-08-06
Possibly the best-characterized cubic membrane transition has been observed in the mitochondrial inner membranes of free-living giant amoeba (Chaos carolinense). In this ancient organism, the cells are able to survive in extreme environments such as lack of food, thermal and osmolarity fluctuations and high levels of reactive oxygen species. Their mitochondrial inner membranes undergo rapid changes in three-dimensional organization upon food depletion, providing a valuable model to study this subcellular adaptation. Our data show that cubic membrane is enriched with unique ether phospholipids, plasmalogens carrying very long-chain polyunsaturated fatty acids. Here, we propose that these phospholipids may not only facilitate cubic membrane formation but may also provide a protective shelter to RNA. The potential interaction of cubic membrane with RNA may reduce the amount of RNA oxidation and promote more efficient protein translation. Thus, recognizing the role of cubic membranes in RNA antioxidant systems might help us to understand the adaptive mechanisms that have evolved over time in eukaryotes.
Evolution of cubic membranes as antioxidant defence system
Deng, Yuru; Almsherqi, Zakaria A.
2015-01-01
Possibly the best-characterized cubic membrane transition has been observed in the mitochondrial inner membranes of free-living giant amoeba (Chaos carolinense). In this ancient organism, the cells are able to survive in extreme environments such as lack of food, thermal and osmolarity fluctuations and high levels of reactive oxygen species. Their mitochondrial inner membranes undergo rapid changes in three-dimensional organization upon food depletion, providing a valuable model to study this subcellular adaptation. Our data show that cubic membrane is enriched with unique ether phospholipids, plasmalogens carrying very long-chain polyunsaturated fatty acids. Here, we propose that these phospholipids may not only facilitate cubic membrane formation but may also provide a protective shelter to RNA. The potential interaction of cubic membrane with RNA may reduce the amount of RNA oxidation and promote more efficient protein translation. Thus, recognizing the role of cubic membranes in RNA antioxidant systems might help us to understand the adaptive mechanisms that have evolved over time in eukaryotes. PMID:26464785
Gravity theory through affine spheres
NASA Astrophysics Data System (ADS)
Minguzzi, E.
2017-08-01
In this work it is argued that in order to improve our understanding of gravity and spacetime our most successful theory, general relativity, must be destructured. That is, some geometrical assumptions must be dropped and recovered just under suitable limits. Along this line of thought we pursue the idea that the roundness of the light cone, and hence the isotropy of the speed of light, must be relaxed and that, in fact, the shape of light cones must be regarded as a dynamical variable. Mathematically, we apply some important results from affine differential geometry to this problem, the idea being that in the transition we should preserve the identification of the spacetime continuum with a manifold endowed with a cone structure and a spacetime volume form. To that end it is suggested that the cotangent indicatrix (dispersion relation) must be described by an equation of Monge-Ampère type determining a hyperbolic affine sphere, at least whenever the matter content is negligible. Non-relativistic spacetimes fall into this description as they are recovered whenever the center of the affine sphere is at infinity. In the more general context of Lorentz-Finsler theories it is shown that the lightlike unparametrized geodesic flow is completely determined by the distribution of light cones. Moreover, the transport of lightlike momenta is well defined though there could be no notion of affine parameter. Finally, we show how the perturbed indicatrix can be obtained from the perturbed light cone.
Diagnosis of a poorly performing liquid hydrogen bulk storage sphere
NASA Astrophysics Data System (ADS)
Krenn, Angela Gray
2012-06-01
There are two 3,218 cubic meter (850,000 gallon) Liquid Hydrogen (LH2) storage spheres used to support the Space Shuttle Program; one residing at Launch Pad A, the other at Launch Pad B. The Sphere at Pad B had a high boiloff rate when brought into service in the 1960s. In 2001, the daily commodity loss was approximately double that of the Pad A sphere, and well above the maximum allowed by the specification. After being re-painted in the 1990s a "cold spot" appeared on the outer sphere that resulted in poor paint bonding and mold formation. Thermography was used to characterize the area, and the boiloff rate was continually evaluated. All evidence suggested that the high boiloff rate was caused by an excessive heat leak into the inner sphere due to an insulation void in the annulus. Pad B was recently taken out of service, which provided a unique opportunity to perform a series of visual inspections of the insulation. Boroscope examinations revealed a large Perlite void in the region where the cold spot was apparent. Perlite was then trucked in and offloaded into the annular void region until full. The sphere has not yet been brought back into service.
NASA Astrophysics Data System (ADS)
Holmes-Cerfon, Miranda; Gortler, Steven; Brenner, Michael
2014-03-01
We have enumerated all the ways to arrange n <= 13+ spheres as a cluster that is nonlinearly rigid. We have discovered many packings that are hypostatic, namely they have fewer than the 3n-6 contacts required to be linearly rigid. Simple scaling arguments explain why these are thermodynamically important when the spheres are colloids interacting with a short-range potential. We discuss these clusters, as well as other surprises that came up along the way. (''+'' means we have enumerated only a particular kind of cluster for n=14, 15, and beyond.)
2014-07-25
ISS040-E-080130 (25 July 2014) --- In the International Space Station?s Kibo laboratory, European Space Agency astronaut Alexander Gerst, Expedition 40 flight engineer, conducts a session with a trio of soccer-ball-sized robots known as the Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. The free-flying robots were equipped with stereoscopic goggles called the Visual Estimation and Relative Tracking for Inspection of Generic Objects, or VERTIGO, to enable the SPHERES to perform relative navigation based on a 3D model of a target object.
Cubic Icosahedra? A Problem in Assigning Symmetry
ERIC Educational Resources Information Center
Lloyd, D. R.
2010-01-01
There is a standard convention that the icosahedral groups are classified separately from the cubic groups, but these two symmetry types have been conflated as "cubic" in some chemistry textbooks. In this note, the connection between cubic and icosahedral symmetries is examined, using a simple pictorial model. It is shown that octahedral and…
Solving Cubic Equations by Polynomial Decomposition
ERIC Educational Resources Information Center
Kulkarni, Raghavendra G.
2011-01-01
Several mathematicians struggled to solve cubic equations, and in 1515 Scipione del Ferro reportedly solved the cubic while participating in a local mathematical contest, but did not bother to publish his method. Then it was Cardano (1539) who first published the solution to the general cubic equation in his book "The Great Art, or, The Rules of…
Cubic Icosahedra? A Problem in Assigning Symmetry
ERIC Educational Resources Information Center
Lloyd, D. R.
2010-01-01
There is a standard convention that the icosahedral groups are classified separately from the cubic groups, but these two symmetry types have been conflated as "cubic" in some chemistry textbooks. In this note, the connection between cubic and icosahedral symmetries is examined, using a simple pictorial model. It is shown that octahedral and…
2013-09-04
ISS036-E-039685 (4 Sept. 2013) --- In the International Space Station's Kibo laboratory, European Space Agency astronaut Luca Parmitano, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
2013-08-13
ISS036-E-031684 (13 Aug. 2013) --- In the International Space Station’s Kibo laboratory, NASA astronaut Chris Cassidy, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
2013-09-04
ISS036-E-039743 (4 Sept. 2013) --- In the International Space Station's Kibo laboratory, European Space Agency astronaut Luca Parmitano, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
2013-08-13
ISS036-E-031668 (13 Aug. 2013) --- In the International Space Station’s Kibo laboratory, NASA astronaut Karen Nyberg, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
2013-08-13
ISS036-E-031698 (13 Aug. 2013) --- In the International Space Station’s Kibo laboratory, NASA astronaut Chris Cassidy, Expedition 36 flight engineer, poses for a photo while conducting a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
2013-09-04
ISS036-E-039697 (4 Sept. 2013) --- In the International Space Station's Kibo laboratory, European Space Agency astronaut Luca Parmitano, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
2013-08-13
ISS036-E-032134 (13 Aug. 2013) --- In the International Space Station?s Kibo laboratory, NASA astronaut Chris Cassidy, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
2013-08-13
ISS036-E-032138 (13 Aug. 2013) --- In the International Space Station?s Kibo laboratory, NASA astronaut Chris Cassidy, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
2013-08-13
ISS036-E-032180 (13 Aug. 2013) --- In the International Space Station?s Kibo laboratory, NASA astronaut Chris Cassidy, Expedition 36 flight engineer, conducts a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
2013-11-10
ISS038-E-000078 (10 Nov. 2013) --- In the International Space Station?s Kibo laboratory, Japan Aerospace Exploration Agency astronaut Koichi Wakata, Expedition 38 flight engineer, poses for a photo while conducting a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES.
Storing Chemicals in Packed Spheres
NASA Technical Reports Server (NTRS)
Wang, T. G.; Elleman, D. D.
1986-01-01
Reactants released by crushing or puncturing. Agglomerated gas-filled spheres hexagonally close packed and sintered or glued together into rods strung together at ends. Rods fed into crushing machine to release material in spheres as needed.
Zhang, Kelvin H L; Bourlange, Anne; Egdell, Russell G; Collins, Stephen P; Bean, Richard J; Robinson, Ian K; Cowley, Roger A
2012-08-28
The growth of In(2)O(3) on cubic Y-stabilized ZrO(2)(001) by molecular beam epitaxy leads to formation of nanoscale islands which may tilt relative to the substrate in order to help accommodate the 1.7% tensile mismatch between the epilayer and the substrate. High-resolution synchrotron-based X-ray diffraction has been used in combination with atomic force microscopy to probe the evolution in island morphology, orientation, and tilt with island size. Very small islands formed at low substrate coverage are highly strained but exhibit no tilt, while intermediate islands are tilted randomly in all directions, giving rise to distinctive doughnut-shaped structure in three-dimensional reciprocal space isosurfaces. The largest islands with lateral sizes on the order of 1 μm tilt away from the four equivalent in-plane <110> directions, giving three-dimensional scattering isosurfaces dominated by structure at the four corners of a square. Spatially resolved reciprocal space mapping using an X-ray beam with dimensions on the order of 1 μm suggests that the four-fold symmetry observed using a larger beam arises from averaging over an ensemble of islands, each with an individual tilt down one direction, rather than from the coexistence of differently tilted domains within a given island.
Chemical potential of a test hard sphere of variable size in a hard-sphere fluid
NASA Astrophysics Data System (ADS)
Heyes, David M.; Santos, Andrés
2016-12-01
The Labík and Smith Monte Carlo simulation technique to implement the Widom particle insertion method is applied using Molecular Dynamics (MD) instead to calculate numerically the insertion probability, P0(η ,σ0) , of tracer hard-sphere (HS) particles of different diameters, σ0, in a host HS fluid of diameter σ and packing fraction, η , up to 0.5. It is shown analytically that the only polynomial representation of -ln P0 (η ,σ0) consistent with the limits σ0→0 and σ0→∞ has necessarily a cubic form, c0(η ) +c1(η ) σ0 /σ +c2(η ) (σ0/σ ) 2 +c3(η ) (σ0/σ ) 3 . Our MD data for -ln P0 (η ,σ0) are fitted to such a cubic polynomial and the functions c0(η ) and c1(η ) are found to be statistically indistinguishable from their exact solution forms. Similarly, c2(η ) and c3(η ) agree very well with the Boublík-Mansoori-Carnahan-Starling-Leland and Boublík-Carnahan-Starling-Kolafa formulas. The cubic polynomial is extrapolated (high density) or interpolated (low density) to obtain the chemical potential of the host fluid, or σ0→σ , as β μex =c0+c1+c2+c3 . Excellent agreement between the Carnahan-Starling and Carnahan-Starling-Kolafa theories with our MD data is evident.
Photon-pair generation in arrays of cubic nonlinear waveguides.
Solntsev, Alexander S; Sukhorukov, Andrey A; Neshev, Dragomir N; Kivshar, Yuri S
2012-11-19
We study photon-pair generation in arrays of cubic nonlinear waveguides through spontaneous four-wave mixing. We analyze numerically the quantum statistics of photon pairs at the array output as a function of waveguide dispersion and pump beam power. We show flexible spatial quantum state control such as pump-power-controlled transition between bunching and anti-bunching correlations due to nonlinear self-focusing.
Packings of a charged line on a sphere
NASA Astrophysics Data System (ADS)
Alben, Silas
2008-12-01
We find equilibrium configurations of open and closed lines of charge on a sphere, and track them with respect to varying sphere radius. Closed lines transition from a circle to a spiral-like shape through two low-wave-number bifurcations—“baseball seam” and “twist”—which minimize Coulomb energy. The spiral shape is the unique stable equilibrium of the closed line. Other unstable equilibria arise through tip-splitting events. An open line transitions smoothly from an arc of a great circle to a spiral as the sphere radius decreases. Under repulsive potentials with faster-than-Coulomb power-law decay, the spiral is tighter in initial stages of sphere shrinkage, but at later stages of shrinkage the equilibria for all repulsive potentials converge on a spiral with uniform spacing between turns. Multiple stable equilibria of the open line are observed.
Electromechanical polishing of metal spheres
Miller, N.E.; Engelhaupt, D.E.
1980-04-01
Equipment has been developed to electromechanically polish metal spheres. Mechanical polishing is accomplished by the action of three cup-shaped laps which rotate against the sphere. An abrasive slurry containing an electrolyte is continuously applied to the sphere and laps. Electrochemical etching is accomplished by applying a positive potential to two of the laps and a negative potential to the third.
Large attractive depletion interactions in soft repulsive-sphere binary mixtures.
Cinacchi, Giorgio; Martínez-Ratón, Yuri; Mederos, Luis; Navascués, Guillermo; Tani, Alessandro; Velasco, Enrique
2007-12-07
We consider binary mixtures of soft repulsive spherical particles and calculate the depletion interaction between two big spheres mediated by the fluid of small spheres, using different theoretical and simulation methods. The validity of the theoretical approach, a virial expansion in terms of the density of the small spheres, is checked against simulation results. Attention is given to the approach toward the hard-sphere limit and to the effect of density and temperature on the strength of the depletion potential. Our results indicate, surprisingly, that even a modest degree of softness in the pair potential governing the direct interactions between the particles may lead to a significantly more attractive total effective potential for the big spheres than in the hard-sphere case. This might lead to significant differences in phase behavior, structure, and dynamics of a binary mixture of soft repulsive spheres. In particular, a perturbative scheme is applied to predict the phase diagram of an effective system of big spheres interacting via depletion forces for a size ratio of small and big spheres of 0.2; this diagram includes the usual fluid-solid transition but, in the soft-sphere case, the metastable fluid-fluid transition, which is probably absent in hard-sphere mixtures, is close to being stable with respect to direct fluid-solid coexistence. From these results, the interesting possibility arises that, for sufficiently soft repulsive particles, this phase transition could become stable. Possible implications for the phase behavior of real colloidal dispersions are discussed.
Weighted cubic and biharmonic splines
NASA Astrophysics Data System (ADS)
Kvasov, Boris; Kim, Tae-Wan
2017-01-01
In this paper we discuss the design of algorithms for interpolating discrete data by using weighted cubic and biharmonic splines in such a way that the monotonicity and convexity of the data are preserved. We formulate the problem as a differential multipoint boundary value problem and consider its finite-difference approximation. Two algorithms for automatic selection of shape control parameters (weights) are presented. For weighted biharmonic splines the resulting system of linear equations can be efficiently solved by combining Gaussian elimination with successive over-relaxation method or finite-difference schemes in fractional steps. We consider basic computational aspects and illustrate main features of this original approach.
Sticky surface: sphere-sphere adhesion dynamics
Sircar, Sarthok; Younger, John G.; Bortz, David M.
2014-01-01
We present a multi-scale model to study the attachment of spherical particles with a rigid core, coated with binding ligands and suspended in the surrounding, quiescent fluid medium. This class of fluid-immersed adhesion is widespread in many natural and engineering settings, particularly in microbial surface adhesion. Our theory highlights how the micro-scale binding kinetics of these ligands, as well as the attractive / repulsive surface potential in an ionic medium affects the eventual macro-scale size distribution of the particle aggregates (flocs). The bridge between the micro-macro model is made via an aggregation kernel. Results suggest that the presence of elastic ligands on the particle surface lead to the formation of larger floc aggregates via efficient inter-floc collisions (i.e., non-zero sticking probability, g). Strong electrolytic composition of the surrounding fluid favors large floc formation as well. The kernel for the Brownian diffusion for hard spheres is recovered in the limit of perfect binding effectiveness (g → 1) and in a neutral solution with no dissolved salts. PMID:25159830
Dendritic Growth of Hard-Sphere Crystals. Experiment 34
NASA Technical Reports Server (NTRS)
Russel, W. B.; Chaikin, P. M.; Zhu, Ji-Xiang; Meyer, W. V.; Rogers, R.
1998-01-01
Recent observations of the disorder-order transition for colloidal hard spheres under microgravity revealed dendritic crystallites roughly 1-2 mm in size for samples in the coexistence region of the phase diagram. Order-of-magnitude estimates rationalize the absence of large or dendritic crystals under normal gravity and their stability to annealing in microgravity. A linear stability analysis of the Ackerson and Schaetzel model for crystallization of hard spheres establishes the domain of instability for diffusion-limited growth at small supersaturations. The relationship between hard-sphere and molecular crystal growth is established and exploited to relate the predicted linear instability to the well-developed dendrites observed.
Absolute multilateration between spheres
NASA Astrophysics Data System (ADS)
Muelaner, Jody; Wadsworth, William; Azini, Maria; Mullineux, Glen; Hughes, Ben; Reichold, Armin
2017-04-01
Environmental effects typically limit the accuracy of large scale coordinate measurements in applications such as aircraft production and particle accelerator alignment. This paper presents an initial design for a novel measurement technique with analysis and simulation showing that that it could overcome the environmental limitations to provide a step change in large scale coordinate measurement accuracy. Referred to as absolute multilateration between spheres (AMS), it involves using absolute distance interferometry to directly measure the distances between pairs of plain steel spheres. A large portion of each sphere remains accessible as a reference datum, while the laser path can be shielded from environmental disturbances. As a single scale bar this can provide accurate scale information to be used for instrument verification or network measurement scaling. Since spheres can be simultaneously measured from multiple directions, it also allows highly accurate multilateration-based coordinate measurements to act as a large scale datum structure for localized measurements, or to be integrated within assembly tooling, coordinate measurement machines or robotic machinery. Analysis and simulation show that AMS can be self-aligned to achieve a theoretical combined standard uncertainty for the independent uncertainties of an individual 1 m scale bar of approximately 0.49 µm. It is also shown that combined with a 1 µm m-1 standard uncertainty in the central reference system this could result in coordinate standard uncertainty magnitudes of 42 µm over a slender 1 m by 20 m network. This would be a sufficient step change in accuracy to enable next generation aerospace structures with natural laminar flow and part-to-part interchangeability.
Krogh, M.; Painter, J.; Hansen, C.
1996-10-01
Sphere rendering is an important method for visualizing molecular dynamics data. This paper presents a parallel algorithm that is almost 90 times faster than current graphics workstations. To render extremely large data sets and large images, the algorithm uses the MIMD features of the supercomputers to divide up the data, render independent partial images, and then finally composite the multiple partial images using an optimal method. The algorithm and performance results are presented for the CM-5 and the M.
Density-functional theory for fluid-solid and solid-solid phase transitions.
Bharadwaj, Atul S; Singh, Yashwant
2017-03-01
We develop a theory to describe solid-solid phase transitions. The density functional formalism of classical statistical mechanics is used to find an exact expression for the difference in the grand thermodynamic potentials of the two coexisting phases. The expression involves both the symmetry conserving and the symmetry broken parts of the direct pair correlation function. The theory is used to calculate phase diagram of systems of soft spheres interacting via inverse power potentials u(r)=ε(σ/r)^{n}, where parameter n measures softness of the potential. We find that for 1/n<0.154 systems freeze into the face centered cubic (fcc) structure while for 1/n≥0.154 the body-centred-cubic (bcc) structure is preferred. The bcc structure transforms into the fcc structure upon increasing the density. The calculated phase diagram is in good agreement with the one found from molecular simulations.
Transparent polycrystalline cubic silicon nitride
NASA Astrophysics Data System (ADS)
Nishiyama, Norimasa; Ishikawa, Ryo; Ohfuji, Hiroaki; Marquardt, Hauke; Kurnosov, Alexander; Taniguchi, Takashi; Kim, Byung-Nam; Yoshida, Hidehiro; Masuno, Atsunobu; Bednarcik, Jozef; Kulik, Eleonora; Ikuhara, Yuichi; Wakai, Fumihiro; Irifune, Tetsuo
2017-03-01
Glasses and single crystals have traditionally been used as optical windows. Recently, there has been a high demand for harder and tougher optical windows that are able to endure severe conditions. Transparent polycrystalline ceramics can fulfill this demand because of their superior mechanical properties. It is known that polycrystalline ceramics with a spinel structure in compositions of MgAl2O4 and aluminum oxynitride (γ-AlON) show high optical transparency. Here we report the synthesis of the hardest transparent spinel ceramic, i.e. polycrystalline cubic silicon nitride (c-Si3N4). This material shows an intrinsic optical transparency over a wide range of wavelengths below its band-gap energy (258 nm) and is categorized as one of the third hardest materials next to diamond and cubic boron nitride (cBN). Since the high temperature metastability of c-Si3N4 in air is superior to those of diamond and cBN, the transparent c-Si3N4 ceramic can potentially be used as a window under extremely severe conditions.
Hardness of cubic solid solutions
Gao, Faming
2017-01-01
We demonstrate that a hardening rule exists in cubic solid solutions with various combinations of ionic, covalent and metallic bonding. It is revealed that the hardening stress ∆τFcg is determined by three factors: shear modulus G, the volume fraction of solute atoms fv, and the size misfit degree δb. A simple hardening correlation in KCl-KBr solid-solution is proposed as ∆τFcg = 0.27 G. It is applied to calculate the hardening behavior of the Ag-Au, KCl-KBr, InP-GaP, TiN-TiC, HfN-HfC, TiC-NbC and ZrC-NbC solid-solution systems. The composition dependence of hardness is elucidated quantitatively. The BN-BP solid-solution system is quantitatively predicted. We find a hardening plateau region around the x = 0.55–0.85 in BNxP1−x, where BNxP1−x solid solutions are far harder than cubic BN. Because the prediction is quantitative, it sets the stage for a broad range of applications. PMID:28054659
Transparent polycrystalline cubic silicon nitride.
Nishiyama, Norimasa; Ishikawa, Ryo; Ohfuji, Hiroaki; Marquardt, Hauke; Kurnosov, Alexander; Taniguchi, Takashi; Kim, Byung-Nam; Yoshida, Hidehiro; Masuno, Atsunobu; Bednarcik, Jozef; Kulik, Eleonora; Ikuhara, Yuichi; Wakai, Fumihiro; Irifune, Tetsuo
2017-03-17
Glasses and single crystals have traditionally been used as optical windows. Recently, there has been a high demand for harder and tougher optical windows that are able to endure severe conditions. Transparent polycrystalline ceramics can fulfill this demand because of their superior mechanical properties. It is known that polycrystalline ceramics with a spinel structure in compositions of MgAl2O4 and aluminum oxynitride (γ-AlON) show high optical transparency. Here we report the synthesis of the hardest transparent spinel ceramic, i.e. polycrystalline cubic silicon nitride (c-Si3N4). This material shows an intrinsic optical transparency over a wide range of wavelengths below its band-gap energy (258 nm) and is categorized as one of the third hardest materials next to diamond and cubic boron nitride (cBN). Since the high temperature metastability of c-Si3N4 in air is superior to those of diamond and cBN, the transparent c-Si3N4 ceramic can potentially be used as a window under extremely severe conditions.
Vacancy Relaxation in Cubic Crystals
NASA Technical Reports Server (NTRS)
Girifalco, L. A.; Weizer, V. G.
1960-01-01
The configuration of the atoms surrounding a vacancy in four face-centered cubic and three body-centered cubic metals has been computed, using a pairwise, central-force model in which the energy of interaction between two atoms was taken to have the form of a Morse function. Only radial relaxations were considered. The first and second nearest-neighbor relaxations for the face-centered systems were found to be: Pb (1.42,-0.43), Ni (2.14,-0.39), Cu(2.24,-0.40) and Ca (2.73,-0.41, expressed in percentages of normal distances. For the body-centered systems the relaxations out to the fourth nearest neighbors to the vacancy were: Fe (6.07,-2.12, -0.25, -), Ba (7.85, -2.70, 0.70, -0.33) and Na (10.80, -3.14, 3.43, -0.20). The positive signs indicate relaxation toward the vacancy and the negative signs indicate relaxation away from the vacancy. The energies of relaxation (eV) are: Pb (0.162), Ni (0.626), Cu (0.560), Ca (0.400), Fe (1.410), Ba (0.950) and Na (0.172).
Transparent polycrystalline cubic silicon nitride
Nishiyama, Norimasa; Ishikawa, Ryo; Ohfuji, Hiroaki; Marquardt, Hauke; Kurnosov, Alexander; Taniguchi, Takashi; Kim, Byung-Nam; Yoshida, Hidehiro; Masuno, Atsunobu; Bednarcik, Jozef; Kulik, Eleonora; Ikuhara, Yuichi; Wakai, Fumihiro; Irifune, Tetsuo
2017-01-01
Glasses and single crystals have traditionally been used as optical windows. Recently, there has been a high demand for harder and tougher optical windows that are able to endure severe conditions. Transparent polycrystalline ceramics can fulfill this demand because of their superior mechanical properties. It is known that polycrystalline ceramics with a spinel structure in compositions of MgAl2O4 and aluminum oxynitride (γ-AlON) show high optical transparency. Here we report the synthesis of the hardest transparent spinel ceramic, i.e. polycrystalline cubic silicon nitride (c-Si3N4). This material shows an intrinsic optical transparency over a wide range of wavelengths below its band-gap energy (258 nm) and is categorized as one of the third hardest materials next to diamond and cubic boron nitride (cBN). Since the high temperature metastability of c-Si3N4 in air is superior to those of diamond and cBN, the transparent c-Si3N4 ceramic can potentially be used as a window under extremely severe conditions. PMID:28303948
Hardness of cubic solid solutions
NASA Astrophysics Data System (ADS)
Gao, Faming
2017-01-01
We demonstrate that a hardening rule exists in cubic solid solutions with various combinations of ionic, covalent and metallic bonding. It is revealed that the hardening stress ∆τFcg is determined by three factors: shear modulus G, the volume fraction of solute atoms fv, and the size misfit degree δb. A simple hardening correlation in KCl-KBr solid-solution is proposed as ∆τFcg = 0.27 G. It is applied to calculate the hardening behavior of the Ag-Au, KCl-KBr, InP-GaP, TiN-TiC, HfN-HfC, TiC-NbC and ZrC-NbC solid-solution systems. The composition dependence of hardness is elucidated quantitatively. The BN-BP solid-solution system is quantitatively predicted. We find a hardening plateau region around the x = 0.55-0.85 in BNxP1-x, where BNxP1-x solid solutions are far harder than cubic BN. Because the prediction is quantitative, it sets the stage for a broad range of applications.
Nam, Ki Min; Park, Joon T
2014-12-01
The stabilization and growth of a non-native structure, hexagonal wurtzite MnO (h-MnO), is explored via kinetic control of manganese precursor on a carbon sphere template. MnO is most stable in the cubic rock-salt structure (c-MnO), and a number of studies have focused on the synthesis and properties of this rock-salt phase. However, h-MnO has not been fully characterized before our work. Prolonged heating at a relatively low temperature yields c-MnO, whereas rapid heating of the reaction mixture at reflux produces h-MnO in the presence of carbon spheres. The effect of benzyl amine concentration on the formation of two different oxidation states (c-MnO and t-Mn3O4) was examined as well. Moreover, the structural stability of the manganese oxides and phase transition of MnO in terms of the wurtzite to rock-salt structural transformation have been investigated.
Automated reasoning about cubic curves.
Padmanabhan, R.; McCune, W.; Mathematics and Computer Science; Univ. of Manitoba
1995-01-01
It is well known that the n-ary morphisms defined on projective algebraic curves satisfy some strong local-to-global equational rules of derivation not satisfied in general by universal algebras. For example, every rationally defined group law on a cubic curve must be commutative. Here we extract from the geometry of curves a first order property (gL) satisfied by all morphisms defined on these curves such that the equational consequences known for projective curves can be derived automatically from a set of six rules (stated within the first-order logic with equality). First, the rule (gL) is implemented in the theorem-proving program Otter. Then we use Otter to automatically prove some incidence theorems on projective curves without any further reference to the underlying geometry or topology of the curves.
Two-dimensional cubic convolution.
Reichenbach, Stephen E; Geng, Frank
2003-01-01
The paper develops two-dimensional (2D), nonseparable, piecewise cubic convolution (PCC) for image interpolation. Traditionally, PCC has been implemented based on a one-dimensional (1D) derivation with a separable generalization to two dimensions. However, typical scenes and imaging systems are not separable, so the traditional approach is suboptimal. We develop a closed-form derivation for a two-parameter, 2D PCC kernel with support [-2,2] x [-2,2] that is constrained for continuity, smoothness, symmetry, and flat-field response. Our analyses, using several image models, including Markov random fields, demonstrate that the 2D PCC yields small improvements in interpolation fidelity over the traditional, separable approach. The constraints on the derivation can be relaxed to provide greater flexibility and performance.
Chiral Surface Twists and Skyrmion Stability in Nanolayers of Cubic Helimagnets.
Leonov, A O; Togawa, Y; Monchesky, T L; Bogdanov, A N; Kishine, J; Kousaka, Y; Miyagawa, M; Koyama, T; Akimitsu, J; Koyama, Ts; Harada, K; Mori, S; McGrouther, D; Lamb, R; Krajnak, M; McVitie, S; Stamps, R L; Inoue, K
2016-08-19
Theoretical analysis and Lorentz transmission electron microscopy (LTEM) investigations in an FeGe wedge demonstrate that chiral twists arising near the surfaces of noncentrosymmetric ferromagnets [Meynell et al., Phys. Rev. B 90, 014406 (2014)] provide a stabilization mechanism for magnetic Skyrmion lattices and helicoids in cubic helimagnet nanolayers. The magnetic phase diagram obtained for freestanding cubic helimagnet nanolayers shows that magnetization processes differ fundamentally from those in bulk cubic helimagnets and are characterized by the first-order transitions between modulated phases. LTEM investigations exhibit a series of hysteretic transformation processes among the modulated phases, which results in the formation of the multidomain patterns.
Chiral Surface Twists and Skyrmion Stability in Nanolayers of Cubic Helimagnets
NASA Astrophysics Data System (ADS)
Leonov, A. O.; Togawa, Y.; Monchesky, T. L.; Bogdanov, A. N.; Kishine, J.; Kousaka, Y.; Miyagawa, M.; Koyama, T.; Akimitsu, J.; Koyama, Ts.; Harada, K.; Mori, S.; McGrouther, D.; Lamb, R.; Krajnak, M.; McVitie, S.; Stamps, R. L.; Inoue, K.
2016-08-01
Theoretical analysis and Lorentz transmission electron microscopy (LTEM) investigations in an FeGe wedge demonstrate that chiral twists arising near the surfaces of noncentrosymmetric ferromagnets [Meynell et al., Phys. Rev. B 90, 014406 (2014)] provide a stabilization mechanism for magnetic Skyrmion lattices and helicoids in cubic helimagnet nanolayers. The magnetic phase diagram obtained for freestanding cubic helimagnet nanolayers shows that magnetization processes differ fundamentally from those in bulk cubic helimagnets and are characterized by the first-order transitions between modulated phases. LTEM investigations exhibit a series of hysteretic transformation processes among the modulated phases, which results in the formation of the multidomain patterns.
Singh, M. N.; Sinha, A. K. Ghosh, Haranath
2015-08-15
We report anomalous x-ray diffraction studies on Co ferrite with composition Co{sub 1.5}Fe{sub 1.5}O{sub 4} to obtain the distribution of transition metal ions in tetrahedral and octahedral sites. We synthesize spinel oxide (Co{sub 1.5}Fe{sub 1.5}O{sub 4}) through co-precipitation and subsequent annealing route. The imaginary part (absorption) of the energy dependent anomalous form factor is measured and the real part is calculated theoretically through Kramers–Krönig transformation to analyze anomalous x-ray diffraction peak intensities. Fe and Co K-edge x-ray absorption near edge structure (XANES) spectra are used to estimate charge states of transition metals. Our analysis, within experimental errors, suggests 44% of the tetrahedral sites contain Co in +2 oxidation state and the rest 56% sites contain Fe in +2 and +3 oxidation states. Similarly, 47% of the octahedral sites contain Fe in +3 oxidation states, whereas, the rest of the sites contain Co in +2 and +3 oxidation states. While a distinct pre-edge feature in the Fe K-edge XANES is observed, Co pre-edge remains featureless. Implications of these results to magnetism are briefly discussed.
Phase diagram of highly asymmetric binary hard-sphere mixtures.
Dijkstra, M; van Roij, R; Evans, R
1999-05-01
We study the phase behavior and structure of highly asymmetric binary hard-sphere mixtures. By first integrating out the degrees of freedom of the small spheres in the partition function we derive a formal expression for the effective Hamiltonian of the large spheres. Then using an explicit pairwise (depletion) potential approximation to this effective Hamiltonian in computer simulations, we determine fluid-solid coexistence for size ratios q=0.033, 0.05, 0.1, 0.2, and 1.0. The resulting two-phase region becomes very broad in packing fractions of the large spheres as q becomes very small. We find a stable, isostructural solid-solid transition for q< or =0.05 and a fluid-fluid transition for q< or =0.10. However, the latter remains metastable with respect to the fluid-solid transition for all size ratios we investigate. In the limit q-->0 the phase diagram mimics that of the sticky-sphere system. As expected, the radial distribution function g(r) and the structure factor S(k) of the effective one-component system show no sharp signature of the onset of the freezing transition and we find that at most points on the fluid-solid boundary the value of S(k) at its first peak is much lower than the value given by the Hansen-Verlet freezing criterion. Direct simulations of the true binary mixture of hard spheres were performed for q > or =0.05 in order to test the predictions from the effective Hamiltonian. For those packing fractions of the small spheres where direct simulations are possible, we find remarkably good agreement between the phase boundaries calculated from the two approaches-even up to the symmetric limit q=1 and for very high packings of the large spheres, where the solid-solid transition occurs. In both limits one might expect that an approximation which neglects higher-body terms should fail, but our results support the notion that the main features of the phase equilibria of asymmetric binary hard-sphere mixtures are accounted for by the effective
Hard Spheres on the Primitive Surface
NASA Astrophysics Data System (ADS)
Dotera, Tomonari; Takahashi, Yusuke
2015-03-01
Recently hierarchical structures associated with the gyroid in several soft-matter systems have been reported. One of fundamental questions is regular arrangement or tiling on minimal surfaces. We have found certain numbers of hard spheres per unit cell on the gyroid surface are entropically self-organized. Here, new results for the primitive surface are presented. 56/64/72 per unit cell on the primitive minimal surface are entropically self-organized. Numerical evidences for the fluid-solid transition as a function of hard sphere radius are obtained in terms of the acceptance ratio of Monte Carlo moves and order parameters. These arrangements, which are the extensions of the hexagonal arrangement on a flat surface, can be viewed as hyperbolic tiling on the Poincaré disk with a negative Gaussian curvature.
2013-05-23
ISS036-E-003308(23 May 2013) --- Onboard the International Space Station, Expedition 36 Flight Engineer Chris Cassidy, NASA astronaut, watches from just out of frame as he devotes some time with the long-running SPHERES experiment, also known as Synchronized Position Hold Engage and Reorient Experimental Satellites. The experiment is run in conjunction with students who program bowling ball-sized satellites using algorithms. The free-floating satellites are programmed to perform maneuvers potentially influencing the design of future missions.
Krogh, M.; Hansen, C.; Painter, J.; de Verdiere, G.C.
1995-05-01
Sphere rendering is an important method for visualizing molecular dynamics data. This paper presents a parallel divide-and-conquer algorithm that is almost 90 times faster than current graphics workstations. To render extremely large data sets and large images, the algorithm uses the MIMD features of the supercomputers to divide up the data, render independent partial images, and then finally composite the multiple partial images using an optimal method. The algorithm and performance results are presented for the CM-5 and the T3D.
Microstructural characterization of random packings of cubic particles
Malmir, Hessam; Sahimi, Muhammad; Tabar, M. Reza Rahimi
2016-01-01
Understanding the properties of random packings of solid objects is of critical importance to a wide variety of fundamental scientific and practical problems. The great majority of the previous works focused, however, on packings of spherical and sphere-like particles. We report the first detailed simulation and characterization of packings of non-overlapping cubic particles. Such packings arise in a variety of problems, ranging from biological materials, to colloids and fabrication of porous scaffolds using salt powders. In addition, packing of cubic salt crystals arise in various problems involving preservation of pavements, paintings, and historical monuments, mineral-fluid interactions, CO2 sequestration in rock, and intrusion of groundwater aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We have developed a version of the random sequential addition algorithm to generate such packings, and have computed a variety of microstructural descriptors, including the radial distribution function, two-point probability function, orientational correlation function, specific surface, and mean chord length, and have studied the effect of finite system size and porosity on such characteristics. The results indicate the existence of both spatial and orientational long-range order in the packing, which is more distinctive for higher packing densities. The maximum packing fraction is about 0.57. PMID:27725736
Microstructural characterization of random packings of cubic particles
Malmir, Hessam; Sahimi, Muhammad; Tabar, M. Reza Rahimi
2016-10-11
Understanding the properties of random packings of solid objects is of critical importance to a wide variety of fundamental scientific and practical problems. The great majority of the previous works focused, however, on packings of spherical and sphere-like particles. We report the first detailed simulation and characterization of packings of non-overlapping cubic particles. Such packings arise in a variety of problems, ranging from biological materials, to colloids and fabrication of porous scaffolds using salt powders. In addition, packing of cubic salt crystals arise in various problems involving preservation of pavements, paintings, and historical monuments, mineral-fluid interactions, CO2 sequestration in rock,more » and intrusion of groundwater aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We have developed a version of the random sequential addition algorithm to generate such packings, and have computed a variety of microstructural descriptors, including the radial distribution function, two-point probability function, orientational correlation function, specific surface, and mean chord length, and have studied the effect of finite system size and porosity on such characteristics. Here, the results indicate the existence of both spatial and orientational long-range order in the packing, which is more distinctive for higher packing densities.« less
Microstructural characterization of random packings of cubic particles
Malmir, Hessam; Sahimi, Muhammad; Tabar, M. Reza Rahimi
2016-10-11
Understanding the properties of random packings of solid objects is of critical importance to a wide variety of fundamental scientific and practical problems. The great majority of the previous works focused, however, on packings of spherical and sphere-like particles. We report the first detailed simulation and characterization of packings of non-overlapping cubic particles. Such packings arise in a variety of problems, ranging from biological materials, to colloids and fabrication of porous scaffolds using salt powders. In addition, packing of cubic salt crystals arise in various problems involving preservation of pavements, paintings, and historical monuments, mineral-fluid interactions, CO_{2} sequestration in rock, and intrusion of groundwater aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We have developed a version of the random sequential addition algorithm to generate such packings, and have computed a variety of microstructural descriptors, including the radial distribution function, two-point probability function, orientational correlation function, specific surface, and mean chord length, and have studied the effect of finite system size and porosity on such characteristics. Here, the results indicate the existence of both spatial and orientational long-range order in the packing, which is more distinctive for higher packing densities.
Microstructural characterization of random packings of cubic particles
NASA Astrophysics Data System (ADS)
Malmir, Hessam; Sahimi, Muhammad; Tabar, M. Reza Rahimi
2016-10-01
Understanding the properties of random packings of solid objects is of critical importance to a wide variety of fundamental scientific and practical problems. The great majority of the previous works focused, however, on packings of spherical and sphere-like particles. We report the first detailed simulation and characterization of packings of non-overlapping cubic particles. Such packings arise in a variety of problems, ranging from biological materials, to colloids and fabrication of porous scaffolds using salt powders. In addition, packing of cubic salt crystals arise in various problems involving preservation of pavements, paintings, and historical monuments, mineral-fluid interactions, CO2 sequestration in rock, and intrusion of groundwater aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We have developed a version of the random sequential addition algorithm to generate such packings, and have computed a variety of microstructural descriptors, including the radial distribution function, two-point probability function, orientational correlation function, specific surface, and mean chord length, and have studied the effect of finite system size and porosity on such characteristics. The results indicate the existence of both spatial and orientational long-range order in the packing, which is more distinctive for higher packing densities. The maximum packing fraction is about 0.57.
Dynamic Self-assembly of Non-Brownian Spheres.
NASA Astrophysics Data System (ADS)
Salazar, J. Marcos; Simon, J. Marc; Ruiz-Suárez, J. Carlos; Peñuñuri, Francisco; Carvente, Osvaldo
2017-06-01
Granular self-assembly of confined non-Brownian spheres under gravity is studied by Molecular Dynamics simulations. Starting from a disordered phase, dry or cohesive spheres organize, by vibrational annealing into BCT or FCC structures, respectively. During the self-assembling process, isothermal and isodense points are observed. The existence of such points indicates that both granular temperature and packing fraction undergo an inversion process. Around the isothermal point, a sudden growth of beads having the maximum coordination number takes place. We show by a density fluctuation analysis that a transition form a disordered phase to a crystalline structure may be associated to a first-order transition.
Slip and flow of hard-sphere colloidal glasses.
Ballesta, P; Besseling, R; Isa, L; Petekidis, G; Poon, W C K
2008-12-19
We study the flow of concentrated hard-sphere colloidal suspensions along smooth, nonstick walls using cone-plate rheometry and simultaneous confocal microscopy. In the glass regime, the global flow shows a transition from Herschel-Bulkley behavior at large shear rate to a characteristic Bingham slip response at small rates, absent for ergodic colloidal fluids. Imaging reveals both the "solid" microstructure during full slip and the local nature of the "slip to shear" transition. Both the local and global flow are described by a phenomenological model, and the associated Bingham slip parameters exhibit characteristic scaling with size and concentration of the hard spheres.
Interactions between uniformly magnetized spheres
NASA Astrophysics Data System (ADS)
Edwards, Boyd F.; Riffe, D. M.; Ji, Jeong-Young; Booth, William A.
2017-02-01
We use simple symmetry arguments suitable for undergraduate students to demonstrate that the magnetic energy, forces, and torques between two uniformly magnetized spheres are identical to those between two point magnetic dipoles. These arguments exploit the equivalence of the field outside of a uniformly magnetized sphere with that of a point magnetic dipole, and pertain to spheres of arbitrary sizes, positions, and magnetizations. The point dipole/sphere equivalence for magnetic interactions may be useful in teaching and research, where dipolar approximations for uniformly magnetized spheres can now be considered to be exact. The work was originally motivated by interest in the interactions between collections of small neodymium magnetic spheres used as desk toys.
Reversible Nanoparticle Cubic Lattices in Blue Phase Liquid Crystals.
Gharbi, Mohamed Amine; Manet, Sabine; Lhermitte, Julien; Brown, Sarah; Milette, Jonathan; Toader, Violeta; Sutton, Mark; Reven, Linda
2016-03-22
Blue phases (BPs), a distinct class of liquid crystals (LCs) with 3D periodic ordering of double twist cylinders involving orthogonal helical director twists, have been theoretically studied as potential templates for tunable colloidal crystals. Here, we report the spontaneous formation of thermally reversible, cubic crystal nanoparticle (NP) assemblies in BPs. Gold NPs, functionalized to be highly miscible in cyanobiphenyl-based LCs, were dispersed in BP mixtures and characterized by polarized optical microscopy and synchrotron small-angle X-ray scattering (SAXS). The NPs assemble by selectively migrating to periodic strong trapping sites in the BP disclination lines. The NP lattice, remarkably robust given the small particle size (4.5 nm diameter), is commensurate with that of the BP matrix. At the BP I to BP II phase transition, the NP lattice reversibly switches between two different cubic structures. The simultaneous presence of two different symmetries in a single material presents an interesting opportunity to develop novel dynamic optical materials.
NASA Astrophysics Data System (ADS)
Hall, Brian C.; Mitchell, Jeffrey J.
2002-03-01
We describe a family of coherent states and an associated resolution of the identity for a quantum particle whose classical configuration space is the d-dimensional sphere Sd. The coherent states are labeled by points in the associated phase space T*(Sd). These coherent states are not of Perelomov type but rather are constructed as the eigenvectors of suitably defined annihilation operators. We describe as well the Segal-Bargmann representation for the system, the associated unitary Segal-Bargmann transform, and a natural inversion formula. Although many of these results are in principle special cases of the results of Hall and Stenzel, we give here a substantially different description based on ideas of Thiemann and of Kowalski and Rembieliński. All of these results can be generalized to a system whose configuration space is an arbitrary compact symmetric space. We focus on the sphere case in order to carry out the calculations in a self-contained and explicit way.
NASA Technical Reports Server (NTRS)
2009-01-01
Students from Xavier University Preparatory School in New Orleans view the newest exhibit at StenniSphere, the visitor center at NASA's John C. Stennis Space Center - Science on a Sphere, a 68-inch global presentation of planetary data. StenniSphere is only the third NASA visitor center to offer the computer system, which uses four projectors to display data on a globe and present a dynamic, revolving, animated view of Earth and other planets.
2009-03-31
Students from Xavier University Preparatory School in New Orleans view the newest exhibit at StenniSphere, the visitor center at NASA's John C. Stennis Space Center - Science on a Sphere, a 68-inch global presentation of planetary data. StenniSphere is only the third NASA visitor center to offer the computer system, which uses four projectors to display data on a globe and present a dynamic, revolving, animated view of Earth and other planets.
Magnetic spheres in microwave cavities
NASA Astrophysics Data System (ADS)
Zare Rameshti, Babak; Cao, Yunshan; Bauer, Gerrit E. W.
2015-06-01
We apply Mie scattering theory to study the interaction of magnetic spheres with microwaves in cavities beyond the magnetostatic and rotating wave approximations. We demonstrate that both strong and ultrastrong coupling can be realized for stand alone magnetic spheres made from yttrium iron garnet (YIG), acting as an efficient microwave antenna. The eigenmodes of YIG spheres with radii of the order mm display distinct higher angular momentum character that has been observed in experiments.
Heterogeneous crystallization of hard spheres on patterned substrates
NASA Astrophysics Data System (ADS)
Xu, Wen-Sheng; Sun, Zhao-Yan; An, Li-Jia
2010-04-01
We report a numerical investigation of the crystallization of monodisperse hard spheres on different patterned substrates. We find that the duration of a metastable fluid state, which may last for relatively long time in the homogeneous crystallization, can be deeply reduced or almost eliminated when a substrate is used as the seed of crystallization. In the presence of the square patterned substrate, which has the basic character of the body-centered cubic (bcc) crystal structure, a transient bcc crystal phase was observed, suggesting that the bcc structure could be possible to be stabilized by the square patterned substrates. The process of crystallization becomes complicated when the patterned substrate is incommensurate with the bulk crystal. Furthermore, a purely face-centered cubic or hexagonal close packed crystal phase with stacking faults can be generated by using a certain patterned substrate without other factors such as gravity.
Bulk and wetting phenomena in a colloidal mixture of hard spheres and platelets.
Harnau, L; Dietrich, S
2005-01-01
Density functional theory is used to study binary colloidal fluids consisting of hard spheres and thin platelets in their bulk and near a planar hard wall. This system exhibits liquid-liquid coexistence of a phase that is rich in spheres (poor in platelets) and a phase that is poor in spheres (rich in platelets). For the mixture near a planar hard wall, we find that the phase rich in spheres wets the wall completely upon approaching the liquid demixing binodal from the sphere-poor phase, provided the concentration of the platelets is smaller than a threshold value which marks a first-order wetting transition at coexistence. No layering transitions are found, in contrast to recent studies on binary mixtures of spheres and nonadsorbing polymers or thin hard rods.
Numerical simulation of negative Magnus force on a rotating sphere
NASA Astrophysics Data System (ADS)
Muto, Masaya; Tsubokura, Makoto; Oshima, Nobuyuki
2010-11-01
Flow characteristics and fluid force on a sphere rotating along with axis perpendicular to mean air flow were investigated using Large Eddy Simulation at two different Reynolds numbers of 10,000 and 200,000. As a result of simulation, opposite flow characteristics around the sphere and displacement of the separation point were visualized depending on the Reynolds number even though the sphere rotates at the same rotation speed according to the Reynolds number. When Reynolds number is 10,000, flow characteristics agree with the flow field explained in the Magnus effect. However sphere rotates at the same rotation speed while increasing Reynolds number to 200,000, separation point moves in opposite direction and wake appears in the different direction. The reason of the negative Magnus force was discussed in terms of the boundary layer transition on the surface.
Cubic spline functions for curve fitting
NASA Technical Reports Server (NTRS)
Young, J. D.
1972-01-01
FORTRAN cubic spline routine mathematically fits curve through given ordered set of points so that fitted curve nearly approximates curve generated by passing infinite thin spline through set of points. Generalized formulation includes trigonometric, hyperbolic, and damped cubic spline fits of third order.
Modified cubic convolution resampling for Landsat
NASA Technical Reports Server (NTRS)
Prakash, A.; Mckee, B.
1985-01-01
An overview is given of Landsat Thematic Mapper resampling technique, including a modification of the well-known cubic convolution interpolator (nearest neighbor interpolation) used to provide geometric correction for TM data. Post launch study has shown that the modified cubic convolution interpolator can selectively enhance or suppress frequency bands in the output image. This selectivity is demonstrated on TM Band 3 imagery.
Cubic spline functions for curve fitting
NASA Technical Reports Server (NTRS)
Young, J. D.
1972-01-01
FORTRAN cubic spline routine mathematically fits curve through given ordered set of points so that fitted curve nearly approximates curve generated by passing infinite thin spline through set of points. Generalized formulation includes trigonometric, hyperbolic, and damped cubic spline fits of third order.
Ustinov, E A
2017-01-21
The paper aims at a comparison of techniques based on the kinetic Monte Carlo (kMC) and the conventional Metropolis Monte Carlo (MC) methods as applied to the hard-sphere (HS) fluid and solid. In the case of the kMC, an alternative representation of the chemical potential is explored [E. A. Ustinov and D. D. Do, J. Colloid Interface Sci. 366, 216 (2012)], which does not require any external procedure like the Widom test particle insertion method. A direct evaluation of the chemical potential of the fluid and solid without thermodynamic integration is achieved by molecular simulation in an elongated box with an external potential imposed on the system in order to reduce the particle density in the vicinity of the box ends. The existence of rarefied zones allows one to determine the chemical potential of the crystalline phase and substantially increases its accuracy for the disordered dense phase in the central zone of the simulation box. This method is applicable to both the Metropolis MC and the kMC, but in the latter case, the chemical potential is determined with higher accuracy at the same conditions and the number of MC steps. Thermodynamic functions of the disordered fluid and crystalline face-centered cubic (FCC) phase for the hard-sphere system have been evaluated with the kinetic MC and the standard MC coupled with the Widom procedure over a wide range of density. The melting transition parameters have been determined by the point of intersection of the pressure-chemical potential curves for the disordered HS fluid and FCC crystal using the Gibbs-Duhem equation as a constraint. A detailed thermodynamic analysis of the hard-sphere fluid has provided a rigorous verification of the approach, which can be extended to more complex systems.
NASA Astrophysics Data System (ADS)
Ustinov, E. A.
2017-01-01
The paper aims at a comparison of techniques based on the kinetic Monte Carlo (kMC) and the conventional Metropolis Monte Carlo (MC) methods as applied to the hard-sphere (HS) fluid and solid. In the case of the kMC, an alternative representation of the chemical potential is explored [E. A. Ustinov and D. D. Do, J. Colloid Interface Sci. 366, 216 (2012)], which does not require any external procedure like the Widom test particle insertion method. A direct evaluation of the chemical potential of the fluid and solid without thermodynamic integration is achieved by molecular simulation in an elongated box with an external potential imposed on the system in order to reduce the particle density in the vicinity of the box ends. The existence of rarefied zones allows one to determine the chemical potential of the crystalline phase and substantially increases its accuracy for the disordered dense phase in the central zone of the simulation box. This method is applicable to both the Metropolis MC and the kMC, but in the latter case, the chemical potential is determined with higher accuracy at the same conditions and the number of MC steps. Thermodynamic functions of the disordered fluid and crystalline face-centered cubic (FCC) phase for the hard-sphere system have been evaluated with the kinetic MC and the standard MC coupled with the Widom procedure over a wide range of density. The melting transition parameters have been determined by the point of intersection of the pressure-chemical potential curves for the disordered HS fluid and FCC crystal using the Gibbs-Duhem equation as a constraint. A detailed thermodynamic analysis of the hard-sphere fluid has provided a rigorous verification of the approach, which can be extended to more complex systems.
Panoramic stereo sphere vision
NASA Astrophysics Data System (ADS)
Feng, Weijia; Zhang, Baofeng; Röning, Juha; Zong, Xiaoning; Yi, Tian
2013-01-01
Conventional stereo vision systems have a small field of view (FOV) which limits their usefulness for certain applications. While panorama vision is able to "see" in all directions of the observation space, scene depth information is missed because of the mapping from 3D reference coordinates to 2D panoramic image. In this paper, we present an innovative vision system which builds by a special combined fish-eye lenses module, and is capable of producing 3D coordinate information from the whole global observation space and acquiring no blind area 360°×360° panoramic image simultaneously just using single vision equipment with one time static shooting. It is called Panoramic Stereo Sphere Vision (PSSV). We proposed the geometric model, mathematic model and parameters calibration method in this paper. Specifically, video surveillance, robotic autonomous navigation, virtual reality, driving assistance, multiple maneuvering target tracking, automatic mapping of environments and attitude estimation are some of the applications which will benefit from PSSV.
Hairy black holes in cubic quasi-topological gravity
NASA Astrophysics Data System (ADS)
Dykaar, Hannah; Hennigar, Robie A.; Mann, Robert B.
2017-05-01
We construct a class of five dimensional black hole solutions to cubic quasi-topological gravity with conformal scalar hair and study their thermodynamics. We find these black holes provide the second example of black hole λ-lines: a line of second order (continuous) phase transitions, akin to the fluid/superfluid transition of 4He. Examples of isolated critical points are found for spherical black holes, marking the first in the literature to date. We also find various novel and interesting phase structures, including an isolated critical point occurring in conjunction with a double reentrant phase transition. The AdS vacua of the theory are studied, finding ghost-free configurations where the scalar field takes on a non-zero constant value, in notable contrast to the five dimensional Lovelock case.
Bidispersed Sphere Packing on Spherical Surfaces
NASA Astrophysics Data System (ADS)
Atherton, Timothy; Mascioli, Andrew; Burke, Christopher
Packing problems on spherical surfaces have a long history, originating in the classic Thompson problem of finding the ground state configuration of charges on a sphere. Such packings contain a minimal number of defects needed to accommodate the curvature; this is predictable using the Gauss-Bonnet theorem from knowledge of the topology of the surface and the local symmetry of the ordering. Famously, the packing of spherical particles on a sphere contains a 'scar' transition, where additional defects over those required by topology appear above a certain critical number of particles and self-organize into chains or scars. In this work, we study the packing of bidispersed packings on a sphere, and hence determine the interaction of bidispersity and curvature. The resultant configurations are nearly crystalline for low values of bidispersity and retain scar-like structures; these rapidly become disordered for intermediate values and approach a so-called Appollonian limit at the point where smaller particles can be entirely accommodated within the voids left by the larger particles. We connect our results with studies of bidispersed packings in the bulk and on flat surfaces from the literature on glassy systems and jamming. Supported by a Cottrell Award from the Research Corporation for Science Advancement.
Rainbow Scattering by a Coated Sphere
NASA Technical Reports Server (NTRS)
Lock, James A.; Jamison, J. Michael; Lin, Chih-Yang
1994-01-01
We examine the behavior of the first-order rainbow for a coated sphere by using both ray theory and Aden-Kerker wave theory as the radius of the core alpha(sub 12) and the thickness of the coating beta are varied. As the ratio beta/alpha(sub 12) increases from 10(sup -4) to 0.33, we find three classes of rainbow phenomena that cannot occur for a homogeneous-sphere rainbow. For beta/alpha(sub 12) approx less than 10(sup -3), the rainbow intensity is an oscillatory function of the coating thickness, for beta/alpha(sub 12) approx. 10(sup -2), the first-order rainbow breaks into a pair of twin rainbows, and for beta/alpha(sub 12) approx. 0.33, various rainbow-extinction transitions occur. Each of these effects is analyzed, and their physical interpretations are given. A Debye series decomposition of coated-sphere partial-wave scattering amplitudes is also performed and aids in the analysis.
Yashima, Masatomo; Ishizawa, Nobuo; Yoshimura, Masahiro . Research Lab. of Engineering Materials)
1993-03-01
The tetragonal-to-cubic phase transition of rapidly quenched 12 mol% ErO[sub 1.5]-ZrO[sub 2] was investigated in situ using high-temperature X-ray diffraction. Rapid quenching of the melt yielded a small oxygen ion displacement and a small tetragonality, axial ratio c/a. Although the tetragonality of the as-quenched specimen increased with temperature up to about 1,000C, it became independent of temperature on cooling to room temperature from about 1,000C and reheating up to 1,000C. The tetragonality decreased continuously with temperature above 1,000C and became unity at about 1,400C. The atomic coordination z for the oxygen ion, which expresses the displacement from its ideal site in the fluorite-type structure, increased with temperature and became 1.4 at about 1,400C. The tetragonality increased with annealing time through a thermal activation, which could explain the compositional dependence of the tetragonality in rapidly quenched ZrO[sub 2]-RO[sub 1.5] samples (R = rare earths).
A staggered overset grid method for resolved simulation of incompressible flow around moving spheres
NASA Astrophysics Data System (ADS)
Vreman, A. W.
2017-03-01
An overset grid method for resolved simulation of incompressible (turbulent) flows around moving spherical particles is presented. The Navier-Stokes equations in spherical coordinates are solved on body-fitted spherical polar grids attached to the moving spheres. These grids are overset on a fixed Cartesian background grid, where the Navier-Stokes equations in Cartesian coordinates are solved. The standard second-order staggered finite difference scheme is used on each grid. The velocities and pressures on different grids are coupled by third-order Lagrange interpolations. The method, implemented in the form of a Message Passing Interface parallel program, has been validated for a range of flows around spheres. In a first validation section, the results of simulations of four Stokes flows around a single moving sphere are compared with classical analytical results. The first three cases are the flows due to a translating, an oscillating sphere and a rotating sphere. The numerically produced velocity and pressure fields appear to converge to the corresponding (transient) analytical solutions in the maximum norm. The fourth Stokes case is the flow due to an instantaneously accelerated sphere. For this case, the results are compared with the corresponding numerical solution of the Basset-Boussinesq-Oseen equation. In a second validation section, results of three Navier-Stokes flows around one or more moving spheres are presented. These test configurations are a moving face-centered cubic array of spheres, laminar channel flow with a falling a sphere, and freely moving small spheres in a Taylor-Green flow. Results for the flow with the falling sphere are compared with the results from the literature on immersed boundary methods.
Chemical potential of a test hard sphere of variable size in a hard-sphere fluid.
Heyes, David M; Santos, Andrés
2016-12-07
The Labík and Smith Monte Carlo simulation technique to implement the Widom particle insertion method is applied using Molecular Dynamics (MD) instead to calculate numerically the insertion probability, P0(η,σ0), of tracer hard-sphere (HS) particles of different diameters, σ0, in a host HS fluid of diameter σ and packing fraction, η, up to 0.5. It is shown analytically that the only polynomial representation of -lnP0(η,σ0) consistent with the limits σ0→0 and σ0→∞ has necessarily a cubic form, c0(η)+c1(η)σ0/σ+c2(η)(σ0/σ)(2)+c3(η)(σ0/σ)(3). Our MD data for -lnP0(η,σ0) are fitted to such a cubic polynomial and the functions c0(η) and c1(η) are found to be statistically indistinguishable from their exact solution forms. Similarly, c2(η) and c3(η) agree very well with the Boublík-Mansoori-Carnahan-Starling-Leland and Boublík-Carnahan-Starling-Kolafa formulas. The cubic polynomial is extrapolated (high density) or interpolated (low density) to obtain the chemical potential of the host fluid, or σ0→σ, as βμ(ex)=c0+c1+c2+c3. Excellent agreement between the Carnahan-Starling and Carnahan-Starling-Kolafa theories with our MD data is evident.
Ultrahard nanotwinned cubic boron nitride.
Tian, Yongjun; Xu, Bo; Yu, Dongli; Ma, Yanming; Wang, Yanbin; Jiang, Yingbing; Hu, Wentao; Tang, Chengchun; Gao, Yufei; Luo, Kun; Zhao, Zhisheng; Wang, Li-Min; Wen, Bin; He, Julong; Liu, Zhongyuan
2013-01-17
Cubic boron nitride (cBN) is a well known superhard material that has a wide range of industrial applications. Nanostructuring of cBN is an effective way to improve its hardness by virtue of the Hall-Petch effect--the tendency for hardness to increase with decreasing grain size. Polycrystalline cBN materials are often synthesized by using the martensitic transformation of a graphite-like BN precursor, in which high pressures and temperatures lead to puckering of the BN layers. Such approaches have led to synthetic polycrystalline cBN having grain sizes as small as ∼14 nm (refs 1, 2, 4, 5). Here we report the formation of cBN with a nanostructure dominated by fine twin domains of average thickness ∼3.8 nm. This nanotwinned cBN was synthesized from specially prepared BN precursor nanoparticles possessing onion-like nested structures with intrinsically puckered BN layers and numerous stacking faults. The resulting nanotwinned cBN bulk samples are optically transparent with a striking combination of physical properties: an extremely high Vickers hardness (exceeding 100 GPa, the optimal hardness of synthetic diamond), a high oxidization temperature (∼1,294 °C) and a large fracture toughness (>12 MPa m(1/2), well beyond the toughness of commercial cemented tungsten carbide, ∼10 MPa m(1/2)). We show that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall-Petch effect below a critical grain size or the twin thickness of ∼10-15 nm found in metals and alloys.
Gu, Qilin; Zhu, Kongjun; Sun, Qiaomei; Liu, Jinsong; Wang, Jing; Qiu, Jinhao; Wang, John
2016-12-07
Structural modification, especially the stabilization of metastable phases at room temperature, has emerged as an effective strategy to understand their stabilization mechanism and improve their functional properties. In this work, a facile solvothermal approach is developed to synthesize metastable sodium niobate (NaNbO3) crystals with the cubic symmetry. XRD, Raman and TEM results all confirmed the selective synthesis of cubic and orthorhombic NaNbO3via adjustment of the reaction medium. The fact that traditional hydrothermal synthesis often yields orthorhombic NaNbO3 inspires us to elucidate the formation mechanism of cubic NaNbO3 with respect to the solvent effect. With the increasing post-calcination temperature, the as-synthesized cubic NaNbO3 gradually transforms into the orthorhombic structure, which is understood to be a recrystallization behavior, as evidenced by the XRD and TEM results. The organic molecules retained in the NaNbO3 nanocrystals, as suggested by UV-vis, FT-IR and TGA-MS results, have contributed to the stabilization of the metastable structure, demonstrated by the different temperature-induced phase transition behaviors in air and argon atmospheres, where the phase transition from cubic to orthorhombic would take place at a relatively higher temperature in argon. This work provides an alternative approach to synthesize cubic NaNbO3 nanocrystals, and the understanding of the stabilization mechanism could pave a new pathway for fabricating metastable materials.
Theoretical analysis of motion of a microparticle in an optically created cubic potential
NASA Astrophysics Data System (ADS)
Šiler, Martin; Jákl, Petr; Filip, Radim; Ryabov, Artem; Zemánek, Pavel
2016-12-01
The noise-to-signal transitions are considered as interesting processes in physics as they might transform environmental noise to useful mechanical effects. Previously, we theoretically analyzed stochastic noise-to-signal transition, first passage times, and other stochastic quantities of overdamped Brownian motion of a nanoparticle in the cubic potential. Here we present a feasibility study showing that the cubic potential can be successfully obtained in a pair of overlapping optical tweezers even in the case of a dielectric microparticle having radius comparable to the trapping wavelength.
Conn, Charlotte E.; Ces, Oscar; Mulet, Xavier; Seddon, John M.; Templer, Richard H.; Finet, Stephanie; Winter, Roland
2006-03-17
The liquid crystalline lamellar (L{sub {alpha}}) to double-diamond inverse bicontinuous cubic (Q{sub II}{sup D}) phase transition for the amphiphile monoelaidin in excess water exhibits a remarkable sequence of structural transformations for pressure or temperature jumps. Our data imply that the transition dynamics depends on a coupling between changes in molecular shape and the geometrical and topological constraints of domain size. We propose a qualitative model for this coupling based on theories of membrane fusion via stalks and existing knowledge of the structure and energetics of bicontinuous cubic phases.
Identity Development in the Learning Sphere among Japanese First-Year University Students
ERIC Educational Resources Information Center
Sugimura, Kazumi; Shimizu, Noriko
2011-01-01
Identity development in the learning sphere is an important identity-defining issue for Japanese adolescents during the transition from high school to university. The present study reports a preliminary feasibility evaluation of an intervention program designed to facilitate identity formation in the learning sphere. 179 Japanese university…
Cubic and Hexagonal Liquid Crystals as Drug Delivery Systems
Chen, Yulin; Ma, Ping; Gui, Shuangying
2014-01-01
Lipids have been widely used as main constituents in various drug delivery systems, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers, and lipid-based lyotropic liquid crystals. Among them, lipid-based lyotropic liquid crystals have highly ordered, thermodynamically stable internal nanostructure, thereby offering the potential as a sustained drug release matrix. The intricate nanostructures of the cubic phase and hexagonal phase have been shown to provide diffusion controlled release of active pharmaceutical ingredients with a wide range of molecular weights and polarities. In addition, the biodegradable and biocompatible nature of lipids demonstrates the minimum toxicity and thus they are used for various routes of administration. Therefore, the research on lipid-based lyotropic liquid crystalline phases has attracted a lot of attention in recent years. This review will provide an overview of the lipids used to prepare cubic phase and hexagonal phase at physiological temperature, as well as the influencing factors on the phase transition of liquid crystals. In particular, the most current research progresses on cubic and hexagonal phases as drug delivery systems will be discussed. PMID:24995330
Cubic and hexagonal liquid crystals as drug delivery systems.
Chen, Yulin; Ma, Ping; Gui, Shuangying
2014-01-01
Lipids have been widely used as main constituents in various drug delivery systems, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers, and lipid-based lyotropic liquid crystals. Among them, lipid-based lyotropic liquid crystals have highly ordered, thermodynamically stable internal nanostructure, thereby offering the potential as a sustained drug release matrix. The intricate nanostructures of the cubic phase and hexagonal phase have been shown to provide diffusion controlled release of active pharmaceutical ingredients with a wide range of molecular weights and polarities. In addition, the biodegradable and biocompatible nature of lipids demonstrates the minimum toxicity and thus they are used for various routes of administration. Therefore, the research on lipid-based lyotropic liquid crystalline phases has attracted a lot of attention in recent years. This review will provide an overview of the lipids used to prepare cubic phase and hexagonal phase at physiological temperature, as well as the influencing factors on the phase transition of liquid crystals. In particular, the most current research progresses on cubic and hexagonal phases as drug delivery systems will be discussed.
Superconductivity of sodium tungsten bronze with cubic structure
NASA Astrophysics Data System (ADS)
Garif'yanov, N. N.; Khlebnikov, S. Ya.; Khlebnikov, I. S.; Garifullin, I. A.
1996-02-01
Sodium tungsten bronze Na x WO3 with cubic structure is reported to exhibit bulk superconductivity at sodium content 0.16≤ x≤0.4. The superconducting transition temperature T c and the temperature dependence of the critical field H c2 have been measured for the samples with different x. It was concluded that the enhancement of T c at low x-values occurs due to softening of the phonon spectrum. The possible reason for positive curvature of the H c2 vs T curve is discussed.
Cubical Sets and Trace Monoid Actions
Husainov, Ahmet A.
2013-01-01
This paper is devoted to connections between trace monoids and cubical sets. We prove that the category of trace monoids is isomorphic to the category of generalized tori and it is a reflective subcategory of the category of cubical sets. Adjoint functors between the categories of cubical sets and trace monoid actions are constructed. These functors carry independence preserving morphisms in the independence preserving morphisms. This allows us to build adjoint functors between the category of weak asynchronous systems and the category of higher dimensional automata. PMID:24453827
Structure of the body-centered cubic phase of lipid systems.
Saludjian, P; Reiss-Husson, F
1980-12-01
A new model is proposed for the structure of the body-centered cubic phase of lipid systems. Infinite rods of polar groups (and water) are arranged with axes parallel to the four cubic [unk]1 1 1[unk] directions. The hydrocarbon chains fill the space between the rods to form a continuous matrix. With this unified topology, the model explains satisfactorily the x-ray diffraction patterns of strontium soaps, lecithin, galactolipids, potassium soaps, and hexadecyltrimethylammonium bromide and explains the transition between cubic/H(II) phases. The paradoxical thermal effects on the lipid cubic phase, in particular the decrease of unit cell dimensions with increasing temperature, can be explained with the proposed model by mechanisms similar to those used for the monodimensional and bidimensional (mesomorphic) phases.
Fast Monte Carlo algorithm for supercooled soft spheres.
Grigera, T S; Parisi, G
2001-04-01
We present a nonlocal Monte Carlo algorithm with particle swaps that greatly accelerates thermalization of soft sphere binary mixtures in the glassy region. Our first results show that thermalization of systems of hundreds of particles is achievable, and find behavior compatible with a thermodynamic glass transition.
Topological lifetimes of polydisperse colloidal hard spheres at a wall.
Dullens, Roel P A; Kegel, Willem K
2005-01-01
Confocal scanning laser microscopy was used to study the behavior of dense suspensions of model colloidal hard spheres at a single wall. Due to the slight polydispersity, our system shows a reentrant melting transition at high densities involving a hexatic structure [Phys. Rev. Lett 92, 195702 (2004)
Negative thermal expansion materials related to cubic zirconium tungstate
NASA Astrophysics Data System (ADS)
Lind, Cora
2001-12-01
A non-hydrolytic sol-gel method for the preparation of ZrW2O 8 was developed. A new trigonal polymorph was discovered, which is structurally related to trigonal ZrMO2O8 and MnRe2O 8 as evidenced by powder x-ray diffraction and EXAFS studies. Seeding of the starting mixtures with cubic ZrW2O8 promoted crystallization of the cubic phase instead of trigonal material. Dehydration of ZrW2O7(OH)2·2H 2O gave cubic ZrW2O8 at 650°C, and a modification of this route led to the discovery of the new NTE materials cubic ZrMo 2O8 and HfMo2O8. These compounds crystallize in the same temperature range as the more stable trigonal AMo2O 8 polymorphs. To facilitate preparation of phase pure cubic molybdates, the influence of precursor chemistry on the crystallization behavior was investigated. The synthesis was extended to the solid solution system ZrxHf 1-xMoyW2-yO8 (0 ≤ x ≤ 1, 0 ≤ y ≤ 2). All compounds showed negative thermal expansion between 77 and 573 K. High-pressure in situ diffraction experiments were conducted on several AM2O8 polymorphs. With the exception of monoclinic ZrMo2O8, all materials underwent at least one pressure induced phase transition. Quasi-hydrostatic experiments on cubic AMo 2O8 led to a reversible transition to a new high-pressure structure, while low-pressure amorphization was observed under non-hydrostatic conditions. Isothermal kinetic studies of the cubic to trigonal transformation for ZrMo2O8 were carried out on four samples. Apparent activation energies of 170--290 kJ/mol were obtained using an Avrami model in combination with an Arrhenius analysis. This corresponds to 5% conversion levels after one year at temperatures between 220 and 315°C. Ex situ studies showed that the conversion at lower temperatures was considerably slower than what would be expected from extrapolation of the kinetic data. Drop solution calorimetry was carried out on several polymorphs of ZrMo 2O8, HfMo2O8 and ZrW2O 8. Only monoclinic ZrMo2O8 was enthalpically
Why GPCRs behave differently in cubic and lamellar lipidic mesophases
2012-01-01
Recent successes in the crystallographic determination of structures of transmembrane proteins in the G protein-coupled receptor (GPCR) family have established the lipidic cubic phase (LCP) environment as the medium of choice for growing structure-grade crystals by the method termed “in meso”. The understanding of in meso crystallogenesis is currently at a descriptive level. To enable an eventual quantitative, energy-based description of the nucleation and crystallization mechanism, we have examined the properties of the lipidic cubic phase system and the dynamics of the GPCR rhodopsin reconstituted into the LCP with coarse-grained molecular dynamics simulations with the Martini force-field. Quantifying the differences in the hydrophobic/hydrophilic exposure of the GPCR to lipids in the cubic and lamellar phases, we found that the highly curved geometry of the cubic phase provides more efficient shielding of the protein from unfavorable hydrophobic exposure, which leads to a lesser hydrophobic mismatch and less unfavorable hydrophobic–hydrophilic interactions between the protein and lipid–water interface in the LCP, compared to the lamellar phase. Since hydrophobic mismatch is considered a driving force for oligomerization, the differences in exposure mismatch energies between the LCP and the lamellar structures suggest that the latter provide a more favorable setting in which GPCRs can oligomerize as a prelude to nucleation and crystal growth. These new findings lay the foundation for future investigations of in meso crystallization mechanisms related to the transition from the LCP to the lamellar phase and studies aimed at an improved rational approach for generating structure-quality crystals of membrane proteins. PMID:22931253
Laser range profile of spheres
NASA Astrophysics Data System (ADS)
Gong, Yanjun; Wang, Mingjun; Gong, Lei
2016-09-01
Profile information about a three-dimensional target can be obtained by laser range profile (LRP). A mathematical LRP model from rough sphere is presented. LRP includes laser one-dimensional range profile and laser two-dimensional range profile. A target coordinate system and an imaging coordinate system are established, the mathematical model of the range profile is derived in the imaging coordinate system. The mathematical model obtained has nothing to do with the incidence direction of laser. It is shown that the laser range profile of the sphere is independent of the incidence direction of laser. This is determined by the symmetry of the sphere. The laser range profile can reflect the shape and material properties of the target. Simulations results of LRP about some spheres are given. Laser range profile of sphere, whose surface material with diffuse lambertian reflectance, is given in this paper. Laser one-dimensional range profile of sphere, whose surface mater with diffuse materials whose retro-reflectance can be modeled closely with an exponential term that decays with increasing incidence angles, is given in this paper. Laser range profiles of different pulse width of sphere are given in this paper. The influences of geometric parameters, pulse width on the range profiles are analyzed.
Biomechanical Analysis with Cubic Spline Functions
ERIC Educational Resources Information Center
McLaughlin, Thomas M.; And Others
1977-01-01
Results of experimentation suggest that the cubic spline is a convenient and consistent method for providing an accurate description of displacement-time data and for obtaining the corresponding time derivatives. (MJB)
Biomechanical Analysis with Cubic Spline Functions
ERIC Educational Resources Information Center
McLaughlin, Thomas M.; And Others
1977-01-01
Results of experimentation suggest that the cubic spline is a convenient and consistent method for providing an accurate description of displacement-time data and for obtaining the corresponding time derivatives. (MJB)
Mastracchio during SPHERES Vertigo Experiment
2014-01-24
ISS038-E-035434 (23 Jan. 2014) --- NASA astronaut Rick Mastracchio, Expedition 38 flight engineer, works with a pair of basketball-sized, free-flying satellites known Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES, in the Kibo laboratory of the International Space Station. For this experiment session, the crew members equipped one of the two SPHERES with a pair of stereoscopic goggles dubbed the Visual Estimation and Relative Tracking for Inspection of Generic Objects, or VERTIGO. As the second SPHERES tumbled and spun, the VERTIGO-equipped robot attempted to map it and perform relative navigation around it.
Mastracchio during SPHERES Vertigo Experiment
2014-01-23
ISS038-E-035432 (23 Jan. 2014) --- NASA astronaut Rick Mastracchio, Expedition 38 flight engineer, works with a pair of basketball-sized, free-flying satellites known Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES, in the Kibo laboratory of the International Space Station. For this experiment session, the crew members equipped one of the two SPHERES with a pair of stereoscopic goggles dubbed the Visual Estimation and Relative Tracking for Inspection of Generic Objects, or VERTIGO. As the second SPHERES tumbled and spun, the VERTIGO-equipped robot attempted to map it and perform relative navigation around it.
2014-07-10
ISS040-E-059478 (10 July 2014) --- In the International Space Station's Kibo laboratory, European Space Agency astronaut Alexander Gerst (left) and NASA astronaut Reid Wiseman, both Expedition 40 flight engineers, conduct a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Surrounding the two SPHERES mini-satellites is ring-shaped hardware known as the Resonant Inductive Near-field Generation System, or RINGS. SPHERES-RINGS seeks to demonstrate wireless power transfer between satellites at a distance for enhanced operations.
2014-07-10
ISS040-E-059467 (10 July 2014) --- In the International Space Station's Kibo laboratory, European Space Agency astronaut Alexander Gerst and NASA astronaut Reid Wiseman (mostly obscured), both Expedition 40 flight engineers, conduct a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Surrounding the two SPHERES mini-satellites is ring-shaped hardware known as the Resonant Inductive Near-field Generation System, or RINGS. SPHERES-RINGS seeks to demonstrate wireless power transfer between satellites at a distance for enhanced operations.
2014-07-10
ISS040-E-059344 (10 July 2014) --- In the International Space Station’s Kibo laboratory, NASA astronaut Reid Wiseman (left) and European Space Agency astronaut Alexander Gerst, both Expedition 40 flight engineers, conduct a session with a pair of bowling-ball-sized free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES. Surrounding the two SPHERES mini-satellites is ring-shaped hardware known as the Resonant Inductive Near-field Generation System, or RINGS. SPHERES-RINGS seeks to demonstrate wireless power transfer between satellites at a distance for enhanced operations.
A note on cubic convolution interpolation.
Meijering, Erik; Unser, Michael
2003-01-01
We establish a link between classical osculatory interpolation and modern convolution-based interpolation and use it to show that two well-known cubic convolution schemes are formally equivalent to two osculatory interpolation schemes proposed in the actuarial literature about a century ago. We also discuss computational differences and give examples of other cubic interpolation schemes not previously studied in signal and image processing.
Great Plains makes 100 billion cubic feet
Not Available
1987-03-01
The Great Plains coal gasification plant on January 18, 1987 produced its 100 billionth cubic foot of gas since start-up July 28, 1984. Owned by the Department of Energy and operated by ANG Coal Gasification Company, the plant uses the Lurgi process to produce about 50 billion cubic feet per year of gas from five million tons per year of lignite. The plant has been performing at well above design capacity.
Inner- and outer-sphere metal coordination in blue copper proteins.
Warren, Jeffrey J; Lancaster, Kyle M; Richards, John H; Gray, Harry B
2012-10-01
Blue copper proteins (BCPs) comprise classic cases of Nature's profound control over the electronic structures and chemical reactivity of transition metal ions. Early studies of BCPs focused on their inner coordination spheres, that is, residues that directly coordinate Cu. Equally important are the electronic and geometric perturbations to these ligands provided by the outer coordination sphere. In this tribute to Hans Freeman, we review investigations that have advanced the understanding of how inner-sphere and outer-sphere coordination affects biological Cu properties.
Electrostatic swelling of bicontinuous cubic lipid phases.
Tyler, Arwen I I; Barriga, Hanna M G; Parsons, Edward S; McCarthy, Nicola L C; Ces, Oscar; Law, Robert V; Seddon, John M; Brooks, Nicholas J
2015-04-28
Lipid bicontinuous cubic phases have attracted enormous interest as bio-compatible scaffolds for use in a wide range of applications including membrane protein crystallisation, drug delivery and biosensing. One of the major bottlenecks that has hindered exploitation of these structures is an inability to create targeted highly swollen bicontinuous cubic structures with large and tunable pore sizes. In contrast, cubic structures found in vivo have periodicities approaching the micron scale. We have been able to engineer and control highly swollen bicontinuous cubic phases of spacegroup Im3m containing only lipids by (a) increasing the bilayer stiffness by adding cholesterol and (b) inducing electrostatic repulsion across the water channels by addition of anionic lipids to monoolein. By controlling the composition of the ternary mixtures we have been able to achieve lattice parameters up to 470 Å, which is 5 times that observed in pure monoolein and nearly twice the size of any lipidic cubic phase reported previously. These lattice parameters significantly exceed the predicted maximum swelling for bicontinuous cubic lipid structures, which suggest that thermal fluctuations should destroy such phases for lattice parameters larger than 300 Å.
NASA Astrophysics Data System (ADS)
Chen, Hong-Bo; Cao, Yan-Ling; Zhu, Yong-Zheng; Wang, Yan-Ping; Chi, Yuan-Bin
2006-05-01
We report a photonic crystal model, which consists of hollow spheres located at face-centered cubic lattice sites and each sphere connected to all of its 12 nearest neighbors by cylindrical rods. Theoretical calculations show that this kind of structure exhibits two large complete photonic band gaps. The maximum relative gap sizes reach 17.3% between the eighth and ninth bands, and 15.1% between the 13th and 14th bands for a dielectric contrast of 11.9, and the minimal dielectric contrasts needed to open the two gaps are 5.8 and 7.3, respectively, which are lower than that of other face-centered cubic photonic crystal structures.
Transport coefficients of hard sphere fluids
NASA Astrophysics Data System (ADS)
Sigurgeirsson, H.; Heyes, D. M.
New calculations have been made of the self-diffusion coefficient D, the shear viscosity ηs , the bulk viscosity ηb and thermal conductivity λ of the hard sphere fluid, using molecular dynamics (MD) computer simulation. A newly developed hard sphere MD scheme was used to model the hard sphere fluid over a wide range up to the glass transition (~0.57 packing fraction). System sizes of up to 32 000 hard spheres were considered. This set of transport coefficient data was combined with others taken from the literature to test a number of previously proposed analytical formulae for these quantities together with some new ones given here. Only the self-diffusion coefficient showed any substantial n dependence for N > 500 at equilibrium fluid densities ( ξ < 0.494). D increased with N , especially at intermediate densities in the range ξ ~ 0.3-0.35. The expression for the packing fraction dependence of D proposed by Speedy, R. J., 1987, Molec. Phys. , 62 , 509 was shown to fit these data well for N ~ 500 particle systems. We found that the packing fraction ξ dependence of the two viscosities and thermal conductivity, generically denoted by X , were represented well by the simple formula X/X0 = 1/[1 -( ξ / gr;1)]m within the equilibrium fluid range 0 < ξ <0.493. This formula has two disposable parameters, ξ1 and m, and X0 is the value of the property X in the limit of zero density. This expression has the same form as the Krieger-Dougherty formula (Kreiger, I. M., 1972,Adv. Colloid. Interface Sci. , 3, 111) which is used widely in the colloid literature to represent the packing fraction dependence of the Newtonian shear viscosity of monodisperse colloidal near-hard spheres. Of course, in the present case, X0 was the dilute gas transport coefficient of the pure liquid rather than the solvent viscosity. It was not possible to fit the transport coefficient normalized by their Enskog values with such a simple expression because these ratios are typically of order
Cubic TiO2 as a potential light absorber in solar-energy conversion
NASA Astrophysics Data System (ADS)
Mattesini, M.; de Almeida, J. S.; Dubrovinsky, L.; Dubrovinskaia, N.; Johansson, B.; Ahuja, R.
2004-09-01
Materials are currently sought for use in the photo-induced decomposition of water on crystalline electrodes. Titanium dioxide is valuable in this respect. The electronic structural properties of cubic TiO2 polymorphs were investigated by means of first-principles methods. We demonstrate that both fluorite- and pyrite-type TiO2 have important optical absorptive transitions in the region of the visible light. A cubic TiO2 phase that can efficiently absorb the sunlight would be an important candidate material for the development of the solar cells. Also, we present results on the Ti L edges for the two different titania forms. We predict that a qualitative spectroscopic discrimination of the cubic polymorphs can be achieved by following the Ti 2p→3d x-ray transitions.
Hopkins during SPHERES Slosh Run
2014-01-22
ISS038-E-033884 (22 Jan. 2014) --- In the International Space Station's Kibo laboratory, NASA astronaut Mike Hopkins, Expedition 38 flight engineer, holds a plastic container partially filled with green-colored water which will be used in a new experiment using the soccer-ball-sized, free-flying satellites known as Synchronized Position Hold, Engage, Reorient, Experimental Satellites, or SPHERES, which are already on the station. For the SPHERES-Slosh experiment, two SPHERES robots are attached to opposite ends of a metal frame holding the plastic tank with the green-colored water. The new hardware for the SPHERES-Slosh study was delivered to the station aboard Orbital Sciences' Cygnus cargo craft on Jan. 12.
Frontal Impact of Rolling Spheres.
ERIC Educational Resources Information Center
Domenech, A.; Casasus, E.
1991-01-01
A model of the inelastic collision between two spheres rolling along a horizontal track is presented, taking into account the effects of frictional forces at impact. This experiment makes possible direct estimates of the coefficients of restitution and friction. (Author)
Science off the Sphere: Bistronauts
International Space Station Expedition 30 astronaut Don Pettit demonstrates physics in space for 'Science off the Sphere.' Through a partnership between NASA and the American Physical Society you c...
Polyimide nanocomposites based on cubic zirconium tungstate
NASA Astrophysics Data System (ADS)
Ramasubramanian Sharma, Gayathri
2009-12-01
In this research, cubic zirconium tungstate (ZrW2O8) was used as a filler to reduce the CTE of polyimides (PI), and the effect of ZrW2O8 nanoparticles on the bulk polymer properties was studied. Polyimides are high performance polymers with exceptional thermal stability, and there is a need for PIs with low CTEs for high temperature applications. The nanofiller, cubic ZrW2O8, is well known for its isotropic negative thermal expansion (NTE) over a wide temperature range from -272.7 to 777°C. The preparation of nanocomposites involved the synthesis of ZrW 2O8 nanofiller, engineering the polymer-filler interface using linker groups and optimization of processing strategies to prepare free-standing PI nanocomposite films. A hydrothermal method was used to synthesize ZrW 2O8 nanoparticles. Polyimide-ZrW2O8 interface interaction was enhanced by covalently bonding linker moieties to the surface of ZrW2O8 nanoparticles. Specifically, ZrW 2O8 nanoparticles were functionalized with two different linker groups: (1) a short aliphatic silane, and (2) low molecular weight PI. The surface functionalization was confirmed using X-ray photoelectron spectroscopy and thermal gravimetric analysis (TGA). Reprecipitation blending was used to prepare the freestanding PI-ZrW2O8 nanocomposite films with up to 15 volume% filler loading. SEM images showed the improvements in polymer-filler wetting behavior achieved using interface engineering. SEM images indicated that there was better filler dispersion in the PI matrix using reprecipitation blending, compared to the filler dispersion achieved in the nanocomposites prepared using conventional blending technique. The structure-property relationships in PI-ZrW2O8 nanocomposites were investigated by studying the thermal degradation, glass transition, tensile and thermal expansion properties of the nanocomposites. The properties were studied as a function of filler loading and interface linker groups. Addition of ZrW2O8 nanoparticles did not
Confined disordered strictly jammed binary sphere packings
NASA Astrophysics Data System (ADS)
Chen, D.; Torquato, S.
2015-12-01
Disordered jammed packings under confinement have received considerably less attention than their bulk counterparts and yet arise in a variety of practical situations. In this work, we study binary sphere packings that are confined between two parallel hard planes and generalize the Torquato-Jiao (TJ) sequential linear programming algorithm [Phys. Rev. E 82, 061302 (2010), 10.1103/PhysRevE.82.061302] to obtain putative maximally random jammed (MRJ) packings that are exactly isostatic with high fidelity over a large range of plane separation distances H , small to large sphere radius ratio α , and small sphere relative concentration x . We find that packing characteristics can be substantially different from their bulk analogs, which is due to what we term "confinement frustration." Rattlers in confined packings are generally more prevalent than those in their bulk counterparts. We observe that packing fraction, rattler fraction, and degree of disorder of MRJ packings generally increase with H , though exceptions exist. Discontinuities in the packing characteristics as H varies in the vicinity of certain values of H are due to associated discontinuous transitions between different jammed states. When the plane separation distance is on the order of two large-sphere diameters or less, the packings exhibit salient two-dimensional features; when the plane separation distance exceeds about 30 large-sphere diameters, the packings approach three-dimensional bulk packings. As the size contrast increases (as α decreases), the rattler fraction dramatically increases due to what we call "size-disparity" frustration. We find that at intermediate α and when x is about 0.5 (50-50 mixture), the disorder of packings is maximized, as measured by an order metric ψ that is based on the number density fluctuations in the direction perpendicular to the hard walls. We also apply the local volume-fraction variance στ2(R ) to characterize confined packings and find that these
Confined disordered strictly jammed binary sphere packings.
Chen, D; Torquato, S
2015-12-01
Disordered jammed packings under confinement have received considerably less attention than their bulk counterparts and yet arise in a variety of practical situations. In this work, we study binary sphere packings that are confined between two parallel hard planes and generalize the Torquato-Jiao (TJ) sequential linear programming algorithm [Phys. Rev. E 82, 061302 (2010)] to obtain putative maximally random jammed (MRJ) packings that are exactly isostatic with high fidelity over a large range of plane separation distances H, small to large sphere radius ratio α, and small sphere relative concentration x. We find that packing characteristics can be substantially different from their bulk analogs, which is due to what we term "confinement frustration." Rattlers in confined packings are generally more prevalent than those in their bulk counterparts. We observe that packing fraction, rattler fraction, and degree of disorder of MRJ packings generally increase with H, though exceptions exist. Discontinuities in the packing characteristics as H varies in the vicinity of certain values of H are due to associated discontinuous transitions between different jammed states. When the plane separation distance is on the order of two large-sphere diameters or less, the packings exhibit salient two-dimensional features; when the plane separation distance exceeds about 30 large-sphere diameters, the packings approach three-dimensional bulk packings. As the size contrast increases (as α decreases), the rattler fraction dramatically increases due to what we call "size-disparity" frustration. We find that at intermediate α and when x is about 0.5 (50-50 mixture), the disorder of packings is maximized, as measured by an order metric ψ that is based on the number density fluctuations in the direction perpendicular to the hard walls. We also apply the local volume-fraction variance σ(τ)(2)(R) to characterize confined packings and find that these packings possess essentially the
Analysis of principal nested spheres.
Jung, Sungkyu; Dryden, Ian L; Marron, J S
2012-09-01
A general framework for a novel non-geodesic decomposition of high-dimensional spheres or high-dimensional shape spaces for planar landmarks is discussed. The decomposition, principal nested spheres, leads to a sequence of submanifolds with decreasing intrinsic dimensions, which can be interpreted as an analogue of principal component analysis. In a number of real datasets, an apparent one-dimensional mode of variation curving through more than one geodesic component is captured in the one-dimensional component of principal nested spheres. While analysis of principal nested spheres provides an intuitive and flexible decomposition of the high-dimensional sphere, an interesting special case of the analysis results in finding principal geodesics, similar to those from previous approaches to manifold principal component analysis. An adaptation of our method to Kendall's shape space is discussed, and a computational algorithm for fitting principal nested spheres is proposed. The result provides a coordinate system to visualize the data structure and an intuitive summary of principal modes of variation, as exemplified by several datasets.
Analysis of principal nested spheres
Jung, Sungkyu; Dryden, Ian L.; Marron, J. S.
2012-01-01
Summary A general framework for a novel non-geodesic decomposition of high-dimensional spheres or high-dimensional shape spaces for planar landmarks is discussed. The decomposition, principal nested spheres, leads to a sequence of submanifolds with decreasing intrinsic dimensions, which can be interpreted as an analogue of principal component analysis. In a number of real datasets, an apparent one-dimensional mode of variation curving through more than one geodesic component is captured in the one-dimensional component of principal nested spheres. While analysis of principal nested spheres provides an intuitive and flexible decomposition of the high-dimensional sphere, an interesting special case of the analysis results in finding principal geodesics, similar to those from previous approaches to manifold principal component analysis. An adaptation of our method to Kendall’s shape space is discussed, and a computational algorithm for fitting principal nested spheres is proposed. The result provides a coordinate system to visualize the data structure and an intuitive summary of principal modes of variation, as exemplified by several datasets. PMID:23843669
Phase diagrams of colloidal spheres with a constant zeta-potential.
Smallenburg, Frank; Boon, Niels; Kater, Maarten; Dijkstra, Marjolein; van Roij, René
2011-02-21
We study suspensions of colloidal spheres with a constant zeta-potential within Poisson-Boltzmann theory, quantifying the discharging of the spheres with increasing colloid density and decreasing salt concentration. We use the calculated renormalized charge of the colloids to determine their pairwise effective screened-Coulomb repulsions. Bulk phase diagrams in the colloid concentration-salt concentration representation follow, for various zeta-potentials, by a mapping onto published fits of phase boundaries of point-Yukawa systems. Although the resulting phase diagrams do feature face-centered cubic and body-centered cubic phases, they are dominated by the (re-entrant) fluid phase due to the colloidal discharging with increasing colloid concentration and decreasing salt concentration.
Cubic mesoporous titanium phosphonates with multifunctionality.
Ma, Tian-Yi; Lin, Xiu-Zhen; Yuan, Zhong-Yong
2010-07-26
Cubic mesoporous titanium phosphonate materials with bridged organic groups inside the framework were synthesized by means of a one-pot hydrothermal autoclaving process, with the assistance of cationic surfactant cetyltrimethylammonium bromide. 1-Hydroxyethylidene-1,1-diphosphonic acid was used as the coupling molecule. A typical cubic mesophase with surface area of 1052 m(2) g(-1) and pore size of 2.6 nm was confirmed by XRD, TEM, and N(2) sorption analysis. The organophosphonate groups were homogeneously incorporated in the network of the mesoporous solids, as revealed by FTIR and magic-angle spinning (MAS) NMR spectroscopy, and thermogravimetry and differential scanning calorimetry (TG-DSC) measurements. The synthesized hydroxyethylidene-bridged cubic mesoporous titanium phosphonates proved to be thermally stable up to 350 degrees C, with a well-preserved hybrid framework and cubic mesoporous architecture. The obtained cubic mesophase could be transformed into a hexagonal mesophase by simply adjusting the molar ratios of the added raw materials, namely, a Ti/P molar ratio of 1:4 and a CTAB/Ti molar ratio of 1.9-2.3 for the cubic phase and Ti/P molar ratio of 3:4 and CTAB/Ti molar ratio of 0.1-0.4 for the hexagonal phase. The cubic hybrid materials could be used as efficient photocatalysts for the photodegradation of rhodamine B. Moreover, they were also used for adsorption of CO(2) and heavy metal ions and exhibited a significant capture amount of around 1.0 mmol g(-1) for CO(2) molecules at 35 degrees C and high adsorption capacity of 28.5 micromol g(-1) for Cu(2+) ions with good reusability, which demonstrated their promising potential in environmental remediation.
NASA Astrophysics Data System (ADS)
Carrillo-Cabrera, Wilder; Curda, Jan; Peters, Karl; von Schnering, Hans Georg
1999-10-01
La4(C2)2Ge was obtained as a minor component from the reaction of the elements in corundum crucibles enclosed in stainless steel ampoules at 1360 K. The compound is gray with metallic luster. The crystal structure (space group Ioverline43d (No. 220); a=8.995(1) Å; Z=4; R(F)=0.033, Rw(F2)=0.061 for 106 reflections (all data) with 2θmax=50° measured on four-circle diffractometer) may be described as a 3D framework of condensed La8 dodecahedra (bisdisphenoids) centered by Ge atoms and C2 dumbbells (d(C-C)=1.22 Å). La4(C2)2Ge and the previous reported cubic compounds La2C3≙La4(C2)3, "La5C1.5Ge3" ≙La4(C2)0.60Ge2.40, and La4Ge3 demonstrate the existence of a large range of homogeneity La4[(C2)1-xGex]3 between the yellow transparent ethenide (4-) La2C3 and La4Ge3. In the series, the C2 dumbbells are replaced by Ge atoms, corresponding with the formal charges C4-2, Ge4-, and La3+. These mixed crystals (Pearson symbol cI28⇔40) represent a continuous transition between the structure types cI40 (Rb4O6/Pu2C3) and cI28 (Th3P4). The results are discussed together with the general trends in the members of both structures types.
Rakhimov, Abdulla; Askerzade, Iman N
2014-09-01
We have shown that the critical temperature of a Bose-Einstein condensate to a normal phase transition of noninteracting bosons in cubic optical lattices has a linear dependence on the filling factor, especially at large densities. The condensed fraction exhibits a linear power law dependence on temperature in contrast to the case of ideal homogeneous Bose gases.
Structural Instability and Superconductivity of the Defect Cubic Structure δ-MoC1-x
NASA Astrophysics Data System (ADS)
Athanasiou, N. S.
In this work we report the formation, characterization and superconducting transition temperatures (Tc) of homogeneous and single-phase ternary crystalline molybdenum-carbon based compounds. The required samples were prepared by conventional solidification (arc-melting). The stabilization of the cubic δ-MoC1-x phase was successfully done by substituting Mo or C by small additions (about 1-5 at.%) of B, Ti, Zr, Ru, Hf, W, Re or Os. All substitutions of B or transition metals to pure δ-MoC1-x phase result in a decrease of the transition temperature. The transition temperature of the single-cubic δ-MoC1-x phase (prepared by different techniques for comparison reasons) increases from 10.15 K to 14.7 K with increasing C/Mo ratio in the homogeneity range of 0.65 ≤ C/Mo ≤ 0.75.
Physics of Hard Spheres Experiment: Significant and Quantitative Findings Made
NASA Technical Reports Server (NTRS)
Doherty, Michael P.
2000-01-01
Direct examination of atomic interactions is difficult. One powerful approach to visualizing atomic interactions is to study near-index-matched colloidal dispersions of microscopic plastic spheres, which can be probed by visible light. Such spheres interact through hydrodynamic and Brownian forces, but they feel no direct force before an infinite repulsion at contact. Through the microgravity flight of the Physics of Hard Spheres Experiment (PHaSE), researchers have sought a more complete understanding of the entropically driven disorder-order transition in hard-sphere colloidal dispersions. The experiment was conceived by Professors Paul M. Chaikin and William B. Russel of Princeton University. Microgravity was required because, on Earth, index-matched colloidal dispersions often cannot be density matched, resulting in significant settling over the crystallization period. This settling makes them a poor model of the equilibrium atomic system, where the effect of gravity is truly negligible. For this purpose, a customized light-scattering instrument was designed, built, and flown by the NASA Glenn Research Center at Lewis Field on the space shuttle (shuttle missions STS 83 and STS 94). This instrument performed both static and dynamic light scattering, with sample oscillation for determining rheological properties. Scattered light from a 532- nm laser was recorded either by a 10-bit charge-coupled discharge (CCD) camera from a concentric screen covering angles of 0 to 60 or by sensitive avalanche photodiode detectors, which convert the photons into binary data from which two correlators compute autocorrelation functions. The sample cell was driven by a direct-current servomotor to allow sinusoidal oscillation for the measurement of rheological properties. Significant microgravity research findings include the observation of beautiful dendritic crystals, the crystallization of a "glassy phase" sample in microgravity that did not crystallize for over 1 year in 1g
Porous Ceramic Spheres From Cation Exchange Beads
NASA Technical Reports Server (NTRS)
Dynys, Fred
2005-01-01
This document is a slide presentation that examines the use of a simple templating process to produce hollow ceramic spheres with a pore size of 1 to 10 microns. Using ion exchange process it was determined that the method produces porous ceramic spheres with a unique structure: (i.e., inner sphere surrounded by an outer sphere.)
Interpolation by two-dimensional cubic convolution
NASA Astrophysics Data System (ADS)
Shi, Jiazheng; Reichenbach, Stephen E.
2003-08-01
This paper presents results of image interpolation with an improved method for two-dimensional cubic convolution. Convolution with a piecewise cubic is one of the most popular methods for image reconstruction, but the traditional approach uses a separable two-dimensional convolution kernel that is based on a one-dimensional derivation. The traditional, separable method is sub-optimal for the usual case of non-separable images. The improved method in this paper implements the most general non-separable, two-dimensional, piecewise-cubic interpolator with constraints for symmetry, continuity, and smoothness. The improved method of two-dimensional cubic convolution has three parameters that can be tuned to yield maximal fidelity for specific scene ensembles characterized by autocorrelation or power-spectrum. This paper illustrates examples for several scene models (a circular disk of parametric size, a square pulse with parametric rotation, and a Markov random field with parametric spatial detail) and actual images -- presenting the optimal parameters and the resulting fidelity for each model. In these examples, improved two-dimensional cubic convolution is superior to several other popular small-kernel interpolation methods.
Superconductivity in doped cubic silicon
NASA Astrophysics Data System (ADS)
Bustarret, E.; Marcenat, C.; Achatz, P.; Kačmarčik, J.; Lévy, F.; Huxley, A.; Ortéga, L.; Bourgeois, E.; Blase, X.; Débarre, D.; Boulmer, J.
2006-11-01
Although the local resistivity of semiconducting silicon in its standard crystalline form can be changed by many orders of magnitude by doping with elements, superconductivity has so far never been achieved. Hybrid devices combining silicon's semiconducting properties and superconductivity have therefore remained largely underdeveloped. Here we report that superconductivity can be induced when boron is locally introduced into silicon at concentrations above its equilibrium solubility. For sufficiently high boron doping (typically 100p.p.m.) silicon becomes metallic. We find that at a higher boron concentration of several per cent, achieved by gas immersion laser doping, silicon becomes superconducting. Electrical resistivity and magnetic susceptibility measurements show that boron-doped silicon (Si:B) made in this way is a superconductor below a transition temperature Tc~0.35K, with a critical field of about 0.4T. Ab initio calculations, corroborated by Raman measurements, strongly suggest that doping is substitutional. The calculated electron-phonon coupling strength is found to be consistent with a conventional phonon-mediated coupling mechanism. Our findings will facilitate the fabrication of new silicon-based superconducting nanostructures and mesoscopic devices with high-quality interfaces.
Demixing in binary mixtures of apolar and dipolar hard spheres.
Almarza, N G; Lomba, E; Martín, C; Gallardo, A
2008-12-21
We study the demixing transition of mixtures of equal size hard spheres and dipolar hard spheres using computer simulation and integral equation theories. Calculations are carried out at constant pressure, and it is found that there is a strong correlation between the total density and the composition. The critical temperature and the critical total density are found to increase with pressure. The critical mole fraction of the dipolar component on the contrary decreases as pressure is augmented. These qualitative trends are reproduced by the theoretical approaches that on the other hand overestimate by far the value of the critical temperature. Interestingly, the critical parameters for the liquid-vapor equilibrium extrapolated from the mixture results in the limit of vanishing neutral hard sphere concentration agree rather well with recent estimates based on the extrapolation of charged hard dumbbell phase equilibria when dumbbell elongation shrinks to zero [G. Ganzenmuller and P. J. Camp, J. Chem. Phys. 126, 191104 (2007)].
Yashima, Masatomo; Ishizawa, Nobuo; Yoshimura, Masahiro . Research Lab. of Engineering Materials)
1993-03-01
The cubic-tetragonal phase transition of 14 mol% ErO[sub 1.5]-ZrO[sub 2] was investigated through high-temperature powder X-ray diffraction. A new tetragonal form without tetragonality, t[double prime]-ZrO[sub 2], was taken into consideration, although only two forms of t- and t[prime]-ZrO[sub 2] have previously been distinguished. The metastable t[double prime]-ZrO[sub 2], which could be obtained by rapid quenching of 14 mol% ErO[sub 1.5]-ZrO[sub 2] melts, partially changed into t[prime]-ZrO[sub 2] through a thermal activation process above 500C. The t[prime]-ZrO[sub 2] continuously changed into t[double prime]-ZrO[sub 2] or transformed into cubic phase at about 1,200C. The t[prime]-t[double prime] change occurred reversibly below 1,100C.
Superhard BC3 in cubic diamond structure
Zhang, Miao; Liu, Hanyu; Li, Quan; ...
2015-01-06
We solve the crystal structure of recently synthesized cubic BC3 using an unbiased swarm structure search, which identifies a highly symmetric BC3 phase in the cubic diamond structure (d–BC3) that contains a distinct B-B bonding network along the body diagonals of a large 64-atom unit cell. Simulated x-ray diffraction and Raman peaks of d–BC3 are in excellent agreement with experimental data. Calculated stress-strain relations of d–BC3 demonstrate its intrinsic superhard nature and reveal intriguing sequential bond-breaking modes that produce superior ductility and extended elasticity, which are unique among superhard solids. Here, the present results establish the first boron carbide inmore » the cubic diamond structure with remarkable properties, and these new findings also provide insights for exploring other covalent solids with complex bonding configurations.« less
Image reconstruction by parametric cubic convolution
NASA Technical Reports Server (NTRS)
Park, S. K.; Schowengerdt, R. A.
1983-01-01
Cubic convolution, which has been discussed by Rifman and McKinnon (1974), was originally developed for the reconstruction of Landsat digital images. In the present investigation, the reconstruction properties of the one-parameter family of cubic convolution interpolation functions are considered and thee image degradation associated with reasonable choices of this parameter is analyzed. With the aid of an analysis in the frequency domain it is demonstrated that in an image-independent sense there is an optimal value for this parameter. The optimal value is not the standard value commonly referenced in the literature. It is also demonstrated that in an image-dependent sense, cubic convolution can be adapted to any class of images characterized by a common energy spectrum.
Possible significance of cubic water-ice, H2O-Ic, in the atmospheric water cycle of Mars
NASA Technical Reports Server (NTRS)
Gooding, James L.
1988-01-01
The possible formation and potential significance of the cubic ice polymorph on Mars is discussed. When water-ice crystallizes on Earth, the ambient conditions of temperature and pressure result in the formation of the hexagonal ice polymorph; however, on Mars, the much lower termperature and pressures may permit the crystallization of the cubic polymorph. Cubic ice has two properties of possible importance on Mars: it is an excellant nucleator of other volatiles (such as CO2), and it undergoes an exothermic transition to hexagonal ice at temperatures above 170 K. These properties may have significant implications for both martian cloud formation and the development of the seasonal polar caps.
Self-assembly in colloidal hard-sphere systems
NASA Astrophysics Data System (ADS)
Filion, L. C.
2011-01-01
In this thesis, we examine the phase behaviour and nucleation in a variety of hard-sphere systems. In Chapter 1 we present a short introduction and describe some of the simulation techniques used in this thesis. One of the main difficulties in predicting the phase behaviour in colloidal, atomic and nanoparticle systems is in determining the stable crystalline phases. To address this problem, in Chapters 2 and 4 we present two different methods for predicting possible crystal phases. In Chapter 2, we apply a genetic algorithm to binary hard-sphere mixtures and use it to predict the best-packed structures for this system. In Chapter 4 we present a novel method based on Monte Carlo simulations to predict possible crystalline structures for a variety of models. When the possible phases are known, full free-energy calculations can be used to predict the phase diagrams. This is the focus of Chapters 3 and 5. In Chapter 3, we examine the phase behaviour for binary hard-sphere mixtures with size ratios of the large and small spheres between 0.74 and 0.85. Between size ratios 0.76 and 0.84 we find regions where the binary Laves phases are stable, in addition to monodisperse face-centered-cubic (FCC) crystals of the large and small spheres and a binary liquid. For size ratios 0.74 and 0.85 we find only the monodisperse FCC crystals and the binary liquid. In Chapter 5 we examine the phase behaviour of binary hard-sphere mixtures with size ratios between 0.3 and 0.42. In this range, we find an interstitial solid solution (ISS) to be stable, as well as FCC crystals of the small and large spheres, and a binary fluid. The ISS phase consists of an FCC crystal of the large particles with some of the octahedral holes filled by smaller particles. We show that this filling fraction can be tuned from 0 to 100%. Additionally, we examine the diffusive properties of the small particles in the ISS for size ratio 0.3. In contrast to most systems, we find a region where the diffusion
Purely cubic action for string field theory
NASA Technical Reports Server (NTRS)
Horowitz, G. T.; Lykken, J.; Rohm, R.; Strominger, A.
1986-01-01
It is shown that Witten's (1986) open-bosonic-string field-theory action and a closed-string analog can be written as a purely cubic interaction term. The conventional form of the action arises by expansion around particular solutions of the classical equations of motion. The explicit background dependence of the conventional action via the Becchi-Rouet-Stora-Tyutin operator is eliminated in the cubic formulation. A closed-form expression is found for the full nonlinear gauge-transformation law.
Diffuse reflectivity measurement using cubic cavity.
Yu, Jia; Zhang, Y G; Gao, Qiang; Hu, Gang; Zhang, Z G; Wu, S H
2014-04-01
A method for measuring diffuse reflectivity using cubic cavity based on the variable port fraction method was developed by measuring oxygen P11 line at 762 nm using tunable diode laser absorption spectroscopy. An experimental method to determine the additional path length l0 was presented. We measured the diffuse reflectivity of a cubic cavity with scattering coatings of different thickness. The error of diffuse reflectivity was reduced from 0.004 to 0.0003 when the diffuse reflectivity increased from 0.867(4) to 0.9887(3). A simulation result manifests that the error of diffuse reflectivity has the potential to be further reduced at higher diffuse reflectivity.
Cubic trihedral corner entanglement for a free scalar
NASA Astrophysics Data System (ADS)
Hayward Sierens, Lauren E.; Bueno, Pablo; Singh, Rajiv R. P.; Myers, Robert C.; Melko, Roger G.
2017-07-01
We calculate the universal contribution to the α -Rényi entropy from a cubic trihedral corner in the boundary of the entangling region in 3 +1 dimensions for a massless free scalar. The universal number vα is manifest as the coefficient of a scaling term that is logarithmic in the size of the entangling region. Our numerical calculations find that this universal coefficient has both larger magnitude and the opposite sign to that induced by a smooth spherical entangling boundary in 3 +1 dimensions, for which there is a well-known subleading logarithmic scaling. Despite these differences, up to the uncertainty of our finite-size lattice calculations, the functional dependence of the trihedral coefficient vα on the Rényi index α is indistinguishable from that for a sphere, which is known analytically for a massless free scalar. We comment on the possible source of this α dependence arising from the general structure of (3 +1 ) -dimensional conformal field theories, and suggest calculations past the free scalar which could further illuminate the general structure of the trihedral divergence in the Rényi entropy.
Sphere forming method and apparatus
NASA Technical Reports Server (NTRS)
Youngberg, C. L.; Miller, C. G.; Stephens, J. B.; Finnerty, A. A. (Inventor)
1983-01-01
A system is provided for forming small accurately spherical objects. Preformed largely spherical objects are supported at the opening of a conduit on the update of hot gas emitted from the opening, so the object is in a molten state. The conduit is suddenly jerked away at a downward incline, to allow the molten object to drop in free fall, so that surface tension forms a precise sphere. The conduit portion that has the opening, lies in a moderate vacuum chamber, and the falling sphere passes through the chamber and through a briefly opened valve into a tall drop tower that contains a lower pressure, to allow the sphere to cool without deformation caused by falling through air.
The phase space of the focused cubic Schroedinger equation: A numerical study
Burlakov, Yuri O.
1998-05-01
In a paper of 1988 [41] on statistical mechanics of the nonlinear Schroedinger equation, it was observed that a Gibbs canonical ensemble associated with the nonlinear Schroedinger equation exhibits behavior reminiscent of a phase transition in classical statistical mechanics. The existence of a phase transition in the canonical ensemble of the nonlinear Schroedinger equation would be very interesting and would have important implications for the role of this equation in modeling physical phenomena; it would also have an important bearing on the theory of weak solutions of nonlinear wave equations. The cubic Schroedinger equation, as will be shown later, is equivalent to the self-induction approximation for vortices, which is a widely used equation of motion for a thin vortex filament in classical and superfluid mechanics. The existence of a phase transition in such a system would be very interesting and actually very surprising for the following reasons: in classical fluid mechanics it is believed that the turbulent regime is dominated by strong vortex stretching, while the vortex system described by the cubic Schroedinger equation does not allow for stretching. In superfluid mechanics the self-induction approximation and its modifications have been used to describe the motion of thin superfluid vortices, which exhibit a phase transition; however, more recently some authors concluded that these equations do not adequately describe superfluid turbulence, and the absence of a phase transition in the cubic Schroedinger equation would strengthen their argument. The self-induction approximation for vortices takes into account only very localized interactions, and the existence of a phase transition in such a simplified system would be very unexpected. In this thesis the authors present a numerical study of the phase transition type phenomena observed in [41]; in particular, they find that these phenomena are strongly related to the splitting of the phase space into
Experimental and numerical study on bubble-sphere interaction near a rigid wall
NASA Astrophysics Data System (ADS)
Li, S.; Zhang, A. M.; Han, R.; Liu, Y. Q.
2017-09-01
This study is concerned with the interaction between a violently oscillating bubble and a movable sphere with comparable size near a rigid wall, which is an essential physical phenomenon in many applications such as cavitation, underwater explosion, ultrasonic cleaning, and biomedical treatment. Experiments are performed in a cubic water tank, and the underwater electric discharge technique (580 V DC) is employed to generate a bubble that is initiated between a rigid wall and a sphere in an axisymmetric configuration. The bubble-sphere interactions are captured using a high-speed camera operating at 52 000 frames/s. A classification of the bubble-sphere interaction is proposed, i.e., "weak," "intermediate," and "strong" interactions, identified with three distinct bubble shapes at the maximum volume moment. In the numerical simulations, the boundary integral method and the auxiliary function method are combined to establish a full coupling model that decouples the mutual dependence between the force and the sphere motion. The main features of bubble dynamics in different experiments are well reproduced by our numerical model. Meanwhile, the pressure and velocity fields are also provided for clarifying the associated mechanisms. The effects of two dimensionless standoff parameters, namely, γs (defined as ds/Rm, where ds is the minimum distance between the initial bubble center and the sphere surface and Rm is the maximum bubble radius) and γw (defined as dw/Rm, where dw is the distance between the initial bubble center and the rigid wall), are also discussed.
Vacancy-induced mechanical stabilization of cubic tungsten nitride
NASA Astrophysics Data System (ADS)
Balasubramanian, Karthik; Khare, Sanjay; Gall, Daniel
2016-11-01
First-principles methods are employed to determine the structural, mechanical, and thermodynamic reasons for the experimentally reported cubic WN phase. The defect-free rocksalt phase is both mechanically and thermodynamically unstable, with a negative single crystal shear modulus C44=-86 GPa and a positive enthalpy of formation per formula unit Hf=0.623 eV with respect to molecular nitrogen and metallic W. In contrast, WN in the NbO phase is stable, with C44=175 GPa and Hf=-0.839 eV . A charge distribution analysis reveals that the application of shear strain along [100] in rocksalt WN results in an increased overlap of the t2 g orbitals which causes electron migration from the expanded to the shortened W-W <110 > bond axes, yielding a negative shear modulus due to an energy reduction associated with new bonding states 8.1-8.7 eV below the Fermi level. A corresponding shear strain in WN in the NbO phase results in an energy increase and a positive shear modulus. The mechanical stability transition from the NaCl to the NbO phase is explored using supercell calculations of the NaCl structure containing Cv=0 %-25 % cation and anion vacancies, while keeping the N-to-W ratio constant at unity. The structure is mechanically unstable for Cv<5 % . At this critical vacancy concentration, the isotropic elastic modulus E of cubic WN is zero, but increases steeply to E =445 GPa for Cv=10 % , and then less steeply to E =561 GPa for Cv=25 % . Correspondingly, the hardness estimated using Tian's model increases from 0 to 15 to 26 GPa as Cv increases from 5% to 10% to 25%, indicating that a relatively small vacancy concentration stabilizes the cubic WN phase and that the large variations in reported mechanical properties of WN can be attributed to relatively small changes in Cv.
Vortex-induced vibrations of a sphere
NASA Astrophysics Data System (ADS)
Govardhan, R. N.; Williamson, C. H. K.
2005-05-01
There are many studies on the vortex-induced vibrations of a cylindrical body, but almost none concerned with such vibrations for a sphere, despite the fact that tethered bodies are a common configuration. In this paper, we study the dynamics of an elastically mounted or tethered sphere in a steady flow, employing displacement, force and vorticity measurements. Within a particular range of flow speeds, where the oscillation frequency (f) is of the order of the static-body vortex shedding frequency (f_{vo}), there exist two modes of periodic large-amplitude oscillation, defined as modes I and II, separated by a transition regime exhibiting non-periodic vibration. The dominant wake structure for both modes is a chain of streamwise vortex loops on alternating sides of the wake. Further downstream, the heads of the vortex loops pinch off to form a sequence of vortex rings. We employ an analogy with the lift on an aircraft that is associated with its trailing vortex pair (of strength Gamma(*) and spacing b(*) ), and thereby compute the rate of change of impulse for the streamwise vortex pair, yielding the vortex force coefficient (cvortex): [ cvortex = {8}/{pi} {U^*_{v}}b^*( - Gamma^*). ] This calculation yields predicted forces in reasonable agreement with direct measurements on the sphere. This is significant because it indicates that the principal vorticity dynamics giving rise to vortex-induced vibration for a sphere are the motions of these streamwise vortex pairs. The Griffin plot, showing peak amplitudes as a function of the mass damping (m(*zeta) ), exhibits a good collapse of data, indicating a maximum response of around 0.9 diameters. Following recent studies of cylinder vortex-induced vibration, we deduce the existence of a critical mass ratio, m(*_{crit}) {≈} 0.6, below which large-amplitude vibrations are predicted to persist to infinite normalized velocities. An unexpected large-amplitude and highly periodic mode (mode III) is found at distinctly higher
A monotonicity conjecture for real cubic maps
Dawson, S.P.; Galeeva, R.; Milnor, J.; Tresser, C.
1993-12-01
This will be an outline of work in progress. We study the conjecture that the topological entropy of a real cubic map depends ``monotonely`` on its parameters, in the sense that each locus of constant entropy in parameter space is a connected set. This material will be presented in more detail in a later paper.
Sound velocity anisotropy in cubic crystals
NASA Technical Reports Server (NTRS)
Tsang, T.; Park, H. Y.
1983-01-01
Simple analytical expressions may be derived for sound velocities in cubic crystals by using lattice harmonics or functions which are invariant under the crystal symmetry operations. These expressions are in good agreement with the exact results for typical crystals such as metallic iron and potassium fluoride.
Magnetic ground states in nanocuboids of cubic magnetocrystalline anisotropy
NASA Astrophysics Data System (ADS)
Bonilla, F. J.; Lacroix, L.-M.; Blon, T.
2017-04-01
Flower and easy-axis vortex states are well-known magnetic configurations that can be stabilized in small particles. However, <111> vortex (V<111>), i.e. a vortex state with its core axis along the hard-axis direction, has been recently evidenced as a stable configuration in Fe nanocubes of intermediate sizes in the flower/vortex transition. In this context, we present here extensive micromagnetic simulations to determine the different magnetic ground states in ferromagnetic nanocuboids exhibiting cubic magnetocrystalline anisotropy (MCA). Focusing our study in the single-domain/multidomain size range (10-50 nm), we showed that V<111> is only stable in nanocuboids exhibiting peculiar features, such as a specific size, shape and magnetic environment, contrarily to the classical flower and easy-axis vortex states. Thus, to track experimentally these V<111> states, one should focused on (i) nanocuboids exhibiting a nearly perfect cubic shape (size distorsion <12%) made of (ii) a material which combines a zero or positive MCA and a high saturation magnetization, such as Fe or FeCo; and (iii) a low magnetic field environment, V<111> being only observed in virgin or remanent states.
Field theory and anisotropy of a cubic ferromagnet near the Curie point
NASA Astrophysics Data System (ADS)
Kudlis, A.; Sokolov, A. I.
2017-02-01
It is known that critical fluctuations can change the effective anisotropy of a cubic ferromagnet near the Curie point. If the crystal undergoes a phase transition into the orthorhombic phase and the initial anisotropy is not too strong, then the effective anisotropy acquires the universal value A* = v*/ u* at T c, where u* and v* are the coordinates of the cubic fixed point of the renormalization group equations in the scaling equation of state and expressions for nonlinear susceptibilities. Using the pseudo-ɛ-expansion method, we find the numerical value of the anisotropy parameter A at the critical point. Padé resummation of the six-loop pseudo-ɛ-expansions for u*, v*, and A* leads to the estimate A* = 0.13 ± 0.01, giving evidence that observation of anisotropic critical behavior of cubic ferromagnets in physical and computer experiments is entirely possible.
Pronounced negative thermal expansion from a simple structure: cubic ScF(3).
Greve, Benjamin K; Martin, Kenneth L; Lee, Peter L; Chupas, Peter J; Chapman, Karena W; Wilkinson, Angus P
2010-11-10
Scandium trifluoride maintains a cubic ReO(3) type structure down to at least 10 K, although the pressure at which its cubic to rhombohedral phase transition occurs drops from >0.5 GPa at ∼300 K to 0.1-0.2 GPa at 50 K. At low temperatures it shows strong negative thermal expansion (NTE) (60-110 K, α(l) ≈ -14 ppm K(-1)). On heating, its coefficient of thermal expansion (CTE) smoothly increases, leading to a room temperature CTE that is similar to that of ZrW(2)O(8) and positive thermal expansion above ∼1100 K. While the cubic ReO(3) structure type is often used as a simple illustration of how negative thermal expansion can arise from the thermally induced rocking of rigid structural units, ScF(3) is the first material with this structure to provide a clear experimental illustration of this mechanism for NTE.
Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography
NASA Astrophysics Data System (ADS)
Demurtas, Davide; Guichard, Paul; Martiel, Isabelle; Mezzenga, Raffaele; Hébert, Cécile; Sagalowicz, Laurent
2015-11-01
Bulk and dispersed cubic liquid crystalline phases (cubosomes), present in the body and in living cell membranes, are believed to play an essential role in biological phenomena. Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications. Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures. It is demonstrated that the interior is constituted of a perfect bicontinuous cubic phase, while the outside shows interlamellar attachments, which represent a transition state between the liquid crystalline interior phase and the outside vesicular structure. Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase. This is crucial to understand and enhance controlled release of target molecules and calls for a revision of postulated transport mechanisms from cubosomes to the aqueous phase.
Pressure-induced phase transformations in cubic Gd[subscript 2]O[subscript 3
Bai, Ligang; Liu, Jing; Li, Xiaodong; Jiang, Sheng; Xiao, Wansheng; Li, Yanchun; Tang, Lingyun; Zhang, Yufeng; Zhang, Dechun
2009-10-21
High-pressure transformation and compression behavior of Gd{sub 2}O{sub 3} were investigated using synchrotron radiation x-ray diffraction in a diamond anvil cell up to 44 GPa at room temperature. The structural transformation from a cubic to a monoclinic phase occurred during the sample precompression process. Phase transitions from both the cubic and the monoclinic polymorphs to a hexagonal structure were observed. The hexagonal phase was stable up to the highest pressure in this study and was not quenchable and transformed to a monoclinic phase after pressure release. The bulk moduli of Gd{sub 2}O{sub 3} for the cubic, monoclinic, and hexagonal phases were obtained by fitting the compression data to the Birch-Murnaghan equation of state. Moreover, an anomaly of the hexagonal type Gd{sub 2}O{sub 3} was observed.
Effect of pressure on itinerant magnetism and spin disorder in cubic FeGe.
Pulikkotil, J J; Auluck, S; Rout, P K; Budhani, R C
2012-03-07
The results of ab initio calculations of the pressure dependence of Fe magnetism in cubic FeGe are presented. We find that when the pressure-volume scale is set by means of generalized gradient approximation total energies and magnetism is described by means of the local density approximation, the critical pressure at which the magnetic phase transition occurs is estimated at ≈18 GPa, which is in good agreement with experiments. Using the disordered local moment method we find a localized to itinerant model cross-over of Fe magnetism in cubic FeGe, as a function of volume. Moreover, our calculations also suggest subtle signatures of longitudinal spin fluctuations in cubic FeGe, and that the stiffness parameter softens with increasing pressure. We associate the retention of metallicity in FeGe under pressure with the spin-disorder scattering. The effect of spin-orbit coupling on the electronic structure is also discussed.
Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography
Demurtas, Davide; Guichard, Paul; Martiel, Isabelle; Mezzenga, Raffaele; Hébert, Cécile; Sagalowicz, Laurent
2015-01-01
Bulk and dispersed cubic liquid crystalline phases (cubosomes), present in the body and in living cell membranes, are believed to play an essential role in biological phenomena. Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications. Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures. It is demonstrated that the interior is constituted of a perfect bicontinuous cubic phase, while the outside shows interlamellar attachments, which represent a transition state between the liquid crystalline interior phase and the outside vesicular structure. Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase. This is crucial to understand and enhance controlled release of target molecules and calls for a revision of postulated transport mechanisms from cubosomes to the aqueous phase. PMID:26573367
Jammed Ellipsoids Beat Jammed Spheres
NASA Astrophysics Data System (ADS)
Chaikin, Paul; Donev, Aleksandar; Man, Weining; Cisse, Ibrahim; Stillinger, Frank; Torquato, Salvatore
2004-03-01
We have performed experiments and computer simulations on random packings of ellipsoids. The experiments on M^textregistered Milk Chocolate candies (spheroids with aspect ratio ˜ 1.91:1) indicate a packing fraction 0.68-0.7 considerably higher than that for random sphere packings (0.64). Moreover the number of contacting neighbors is measured as Z ˜ 9.8, close to the isostatic result of twice the number of degrees of freedom f, Z=2f, per particle. For spheres f=3, Z ˜ 6, for ellipsoids of revolution f=5, Z ˜ 10, and for general ellipsoids Z ˜ 12. Simulations, for spheroids support this observation and show a remarkable downward cusp-like behavior for packing fraction vs aspect ratio with a local minimum for spheres. Experiments on general ellipsoids also show high packing fractions and simulations yield orientationally disordered ellipsoid packings up to a density of 0.75, i.e., exceeding even the densest crystal packing of spheres.
Neuroscience in the public sphere.
O'Connor, Cliodhna; Rees, Geraint; Joffe, Helene
2012-04-26
The media are increasingly fascinated by neuroscience. Here, we consider how neuroscientific discoveries are thematically represented in the popular press and the implications this has for society. In communicating research, neuroscientists should be sensitive to the social consequences neuroscientific information may have once it enters the public sphere. Copyright © 2012 Elsevier Inc. All rights reserved.
Improved linings for integrating spheres
NASA Technical Reports Server (NTRS)
Fergerson, P. O.; French, B. O.
1970-01-01
Sphere surface is covered with plain weave of glass fibers coated with polytetrafluoroethylene and one or two layers of magnesium oxide vapor. The resultant lining is suitable for measurement of radiation in the ultraviolet, visible, and near-infrared wavelengths, is not damage prone, and is easily cleaned.
Room temperature quantum emission from cubic silicon carbide nanoparticles.
Castelletto, Stefania; Johnson, Brett C; Zachreson, Cameron; Beke, David; Balogh, István; Ohshima, Takeshi; Aharonovich, Igor; Gali, Adam
2014-08-26
The photoluminescence (PL) arising from silicon carbide nanoparticles has so far been associated with the quantum confinement effect or to radiative transitions between electronically active surface states. In this work we show that cubic phase silicon carbide nanoparticles with diameters in the range 45-500 nm can host other point defects responsible for photoinduced intrabandgap PL. We demonstrate that these nanoparticles exhibit single photon emission at room temperature with record saturation count rates of 7 × 10(6) counts/s. The realization of nonclassical emission from SiC nanoparticles extends their potential use from fluorescence biomarker beads to optically active quantum elements for next generation quantum sensing and nanophotonics. The single photon emission is related to single isolated SiC defects that give rise to states within the bandgap.
Dogic; Frenkel; Fraden
2000-09-01
There is increasing evidence that entropy can induce microphase separation in binary fluid mixtures interacting through hard particle potentials. One such phase consists of alternating two-dimensional liquidlike layers of rods and spheres. We study the transition from a uniform miscible state to this ordered state using computer simulations, and compare results to experiments and theory. We conclude the following: (1) There is stable entropy driven microphase separation in mixtures of parallel rods and spheres. (2) Adding spheres smaller than the rod length decreases the total volume fraction needed for the formation of a layered phase, and therefore small spheres effectively stabilize the layered phase; the opposite is true for large spheres. (3) The degree of this stabilization increases with increasing rod length.
Hansen-Goos, Hendrik; Mortazavifar, Mostafa; Oettel, Martin; Roth, Roland
2015-05-01
Based on Santos' general solution for the scaled-particle differential equation [Phys. Rev. E 86, 040102(R) (2012)], we construct a free-energy functional for the hard-sphere system. The functional is obtained by a suitable generalization and extension of the set of scaled-particle variables using the weighted densities from Rosenfeld's fundamental measure theory for the hard-sphere mixture [Phys. Rev. Lett. 63, 980 (1989)]. While our general result applies to the hard-sphere mixture, we specify remaining degrees of freedom by requiring the functional to comply with known properties of the pure hard-sphere system. Both for mixtures and pure systems, the functional can be systematically extended following the lines of our derivation. We test the resulting functionals regarding their behavior upon dimensional reduction of the fluid as well as their ability to accurately describe the hard-sphere crystal and the liquid-solid transition.
ERIC Educational Resources Information Center
Nikitina, N. N.
2010-01-01
Present-day Russia is characterized by a resolute transition to the innovative path of development in all spheres of economic and social life, and that includes the sphere of education. The processes that took place in Russian education in the 1990s, which can be characterized as a time of "precipitous innovation," were, to some extent,…
ERIC Educational Resources Information Center
Nikitina, N. N.
2010-01-01
Present-day Russia is characterized by a resolute transition to the innovative path of development in all spheres of economic and social life, and that includes the sphere of education. The processes that took place in Russian education in the 1990s, which can be characterized as a time of "precipitous innovation," were, to some extent,…
Space-time CFTs from the Riemann sphere
NASA Astrophysics Data System (ADS)
Adamo, Tim; Monteiro, Ricardo; Paulos, Miguel F.
2017-08-01
We consider two-dimensional chiral, first-order conformal field theories governing maps from the Riemann sphere to the projective light cone inside Minkowski space — the natural setting for describing conformal field theories in two fewer dimensions. These theories have a SL(2) algebra of local bosonic constraints which can be supplemented by additional fermionic constraints depending on the matter content of the theory. By computing the BRST charge associated with gauge fixing these constraints, we find anomalies which vanish for specific target space dimensions. These critical dimensions coincide precisely with those for which (biadjoint) cubic scalar theory, gauge theory and gravity are classically conformally invariant. Furthermore, the BRST cohomology of each theory contains vertex operators for the full conformal multiplets of single field insertions in each of these space-time CFTs. We give a prescription for the computation of three-point functions, and compare our formalism with the scattering equations approach to on-shell amplitudes.
Entropy of hard spheres in the close-packing limit
NASA Astrophysics Data System (ADS)
Noya, Eva G.; Almarza, Noé G.
2015-05-01
The Helmholtz free energies of the face-centred cubic (FCC) and hexagonal close packed (HCP) hard-sphere solids in the close-packing limit have been evaluated using two different approaches based on the Einstein crystal method. Different system sizes and orientations of the crystal with respect to the simulation box have been investigated, both methods giving free energies that are consistent within statistical uncertainty. Our results show that for a given orientation of the crystal and system size, the FCC crystal is always slightly more stable than the HCP, the free-energy difference remaining practically constant with the number of particles up to the thermodynamic limit. In agreement with previous calculations, it is found that the free-energy difference between the HCP and FCC crystals at close packing in the thermodynamic limit is 0.001 164(8) NkBT.
Science off the Sphere: Fun with Antibubbles
International Space Station Expedition 30 astronaut Don Pettit injects air bubbles inside a sphere of water to demonstrate physics in space for 'Science off the Sphere.' Through a partnership betwe...
Face-Centered-Cubic Nanostructured Polymer Foams
NASA Astrophysics Data System (ADS)
Cui, C.; Baughman, R. H.; Liu, L. M.; Zakhidov, A. A.; Khayrullin, I. I.
1998-03-01
Beautifully iridescent polymer foams having Fm-3m cubic symmetry and periodicities on the scale of the wavelength of light have been synthesized by the templating of porous synthetic opals. These fabrication processes involve the filling of porous SiO2 opals (with typical cubic lattice parameters of 250 nm) with either polymers or polymer precursors, polymerization of the precursors if necessary, and removal of the fcc array of SiO2 balls to provide an all-polymer structure. The structures of these foams are similar to periodic minimal surfaces, although the Gaussian curvature can have both positive and negative values. Depending upon whether the internal surfaces of the opal are polymer filled or polymer coated, the polymer replica has either one or two sets of independent channels. We fill these channels with semiconductors, metals, or superconductors to provide electronic and optical materials with novel properties dependent on the nanoscale periodicity.
Wavelets based on Hermite cubic splines
NASA Astrophysics Data System (ADS)
Cvejnová, Daniela; Černá, Dana; Finěk, Václav
2016-06-01
In 2000, W. Dahmen et al. designed biorthogonal multi-wavelets adapted to the interval [0,1] on the basis of Hermite cubic splines. In recent years, several more simple constructions of wavelet bases based on Hermite cubic splines were proposed. We focus here on wavelet bases with respect to which both the mass and stiffness matrices are sparse in the sense that the number of nonzero elements in any column is bounded by a constant. Then, a matrix-vector multiplication in adaptive wavelet methods can be performed exactly with linear complexity for any second order differential equation with constant coefficients. In this contribution, we shortly review these constructions and propose a new wavelet which leads to improved Riesz constants. Wavelets have four vanishing wavelet moments.
Coating a Sphere With Evaporated Metal
NASA Technical Reports Server (NTRS)
Strayer, D. M.; Jackson, H. W.; Gatewood, J. R.
1986-01-01
In vacuum coating apparatus, metal evaporated onto sphere from small source located some distance away. Sphere held in path of metal vapor while rotated about axis that rocks back and forth. One tilting motion particularly easy to produce is sinusoidal rocking with frequency much lower than rotational frequency. Apparatus developed for coating single-crystal sapphire spheres with niobium.
NASA Astrophysics Data System (ADS)
Koiller, J.; Ehlers, K.
2007-04-01
“Rubber” coated bodies rolling over a surface satisfy a no-twist condition in addition to the no slip condition satisfied by “marble” coated bodies [1]. Rubber rolling has an interesting differential geometric appeal because the geodesic curvatures of the curves on the surfaces at corresponding points are equal. The associated distribution in the 5 dimensional configuration space has 2 3 5 growth (these distributions were first studied by Cartan; he showed that the maximal symmetries occurs for rubber rolling of spheres with 3:1 diameters ratio and materialize the exceptional group G 2). The 2 3 5 nonholonomic geometries are classified in a companion paper [2] via Cartan’s equivalence method [3]. Rubber rolling of a convex body over a sphere defines a generalized Chaplygin system [4 8] with SO(3) symmetry group, total space Q = SO(3) × S 2 and base S 2, that can be reduced to an almost Hamiltonian system in T* S 2 with a non-closed 2-form ωNH. In this paper we present some basic results on the sphere-sphere problem: a dynamically asymmetric but balanced sphere of radius b (unequal moments of inertia I j but with center of gravity at the geometric center), rubber rolling over another sphere of radius a. In this example ωNH is conformally symplectic [9]: the reduced system becomes Hamiltonian after a coordinate dependent change of time. In particular there is an invariant measure, whose density is the determinant of the reduced Legendre transform, to the power p = 1/2( b/a - 1). Using sphero-conical coordinates we verify the result by Borisov and Mamaev [10] that the system is integrable for p = -1/2 (ball over a plane). They have found another integrable case [11] corresponding to p = -3/2 (rolling ball with twice the radius of a fixed internal ball). Strikingly, a different set of sphero-conical coordinates separates the Hamiltonian in this case. No other integrable cases with different I j are known.
Use of Pom Pons to Illustrate Cubic Crystal Structures.
ERIC Educational Resources Information Center
Cady, Susan G.
1997-01-01
Describes a method that uses olefin pom pons to illustrate cubic crystal structure. Facilitates hands-on examination of different packing arrangements such as hexagonal close-packed and cubic close-packed structures. (JRH)
Use of Pom Pons to Illustrate Cubic Crystal Structures.
ERIC Educational Resources Information Center
Cady, Susan G.
1997-01-01
Describes a method that uses olefin pom pons to illustrate cubic crystal structure. Facilitates hands-on examination of different packing arrangements such as hexagonal close-packed and cubic close-packed structures. (JRH)
Cubic Polynomials with Rational Roots and Critical Points
ERIC Educational Resources Information Center
Gupta, Shiv K.; Szymanski, Waclaw
2010-01-01
If you want your students to graph a cubic polynomial, it is best to give them one with rational roots and critical points. In this paper, we describe completely all such cubics and explain how to generate them.
Cubic Polynomials with Rational Roots and Critical Points
ERIC Educational Resources Information Center
Gupta, Shiv K.; Szymanski, Waclaw
2010-01-01
If you want your students to graph a cubic polynomial, it is best to give them one with rational roots and critical points. In this paper, we describe completely all such cubics and explain how to generate them.
Effect of cubic aeroelastic nonlinearities on flutter
NASA Astrophysics Data System (ADS)
Berci, M.
2017-07-01
The effect of cubic aero-structural nonlinearities on aeroelastic flutter instability is here investigated. Focusing on the unstable flutter mode, the exact amplitude and frequency of the arising limit cycle oscillations are determined analytically. Both harmonic balance and multiple scales methods are adopted and perfect agreement of the explicit results is demonstrated, for the case of small perturbations of the aircraft speed in the neighborhood of the flutter instability.
Quasiparticle Interference on Cubic Perovskite Oxide Surfaces
NASA Astrophysics Data System (ADS)
Okada, Yoshinori; Shiau, Shiue-Yuan; Chang, Tay-Rong; Chang, Guoqing; Kobayashi, Masaki; Shimizu, Ryota; Jeng, Horng-Tay; Shiraki, Susumu; Kumigashira, Hiroshi; Bansil, Arun; Lin, Hsin; Hitosugi, Taro
2017-08-01
We report the observation of coherent surface states on cubic perovskite oxide SrVO3(001 ) thin films through spectroscopic-imaging scanning tunneling microscopy. A direct link between the observed quasiparticle interference patterns and the formation of a dx y -derived surface state is supported by first-principles calculations. We show that the apical oxygens on the topmost VO2 plane play a critical role in controlling the coherent surface state via modulating orbital state.
Deposition Of Cubic BN On Diamond Interlayers
NASA Technical Reports Server (NTRS)
Ong, Tiong P.; Shing, Yuh-Han
1994-01-01
Thin films of polycrystalline, pure, cubic boron nitride (c-BN) formed on various substrates, according to proposal, by chemical vapor deposition onto interlayers of polycrystalline diamond. Substrate materials include metals, semiconductors, and insulators. Typical substrates include metal-cutting tools: polycrystalline c-BN coats advantageous for cutting ferrous materials and for use in highly oxidizing environments-applications in which diamond coats tend to dissolve in iron or be oxidized, respectively.
Deposition Of Cubic BN On Diamond Interlayers
NASA Technical Reports Server (NTRS)
Ong, Tiong P.; Shing, Yuh-Han
1994-01-01
Thin films of polycrystalline, pure, cubic boron nitride (c-BN) formed on various substrates, according to proposal, by chemical vapor deposition onto interlayers of polycrystalline diamond. Substrate materials include metals, semiconductors, and insulators. Typical substrates include metal-cutting tools: polycrystalline c-BN coats advantageous for cutting ferrous materials and for use in highly oxidizing environments-applications in which diamond coats tend to dissolve in iron or be oxidized, respectively.
Cubic pencils of lines and bivariate interpolation
NASA Astrophysics Data System (ADS)
Carnicer, J. M.; Gasca, M.
2008-10-01
Cubic pencils of lines are classified up to projectivities. Explicit formulae for the addition of lines on the set of nonsingular lines of the pencils are given. These formulae can be used for constructing planar generalized principal lattices, which are sets of points giving rise to simple Lagrange formulae in bivariate interpolation. Special attention is paid to the irreducible nonsingular case, where elliptic functions are used in order to express the addition in a natural form.
Two-Dimensional Melting of Colloidal Hard Spheres
NASA Astrophysics Data System (ADS)
Thorneywork, Alice L.; Abbott, Joshua L.; Aarts, Dirk G. A. L.; Dullens, Roel P. A.
2017-04-01
We study the melting of quasi-two-dimensional colloidal hard spheres by considering a tilted monolayer of particles in sedimentation-diffusion equilibrium. In particular, we measure the equation of state from the density profiles and use time-dependent and height-resolved correlation functions to identify the liquid, hexatic, and crystal phases. We find that the liquid-hexatic transition is first order and that the hexatic-crystal transition is continuous. Furthermore, we directly measure the width of the liquid-hexatic coexistence gap from the fluctuations of the corresponding interface, and thereby experimentally establish the full phase behavior of hard disks.
Periodic surfaces and cubic phases in mixtures of oil, water, and surfactant
NASA Astrophysics Data System (ADS)
Ciach, Alina; Hołyst, Robert
1999-02-01
We study a ternary mixture of oil, water, and surfactant in the case of equal volume fractions of oil and water using the Landau-Ginzburg model derived from a lattice model of this ternary mixture. We concentrate on a phase region close to a coexistence line between microemulsion and cubic phases. In our model the bicontinuous cubic phases exist in a narrow window of the volume fraction of surfactant ρs≈0.6. The sequence of phase transitions is L→G→D→P→C as we increase ρs along the cubic-microemulsion bifurcation line. Here L stands for the lamellar phase and C for the cubic micellar phase. The gyroid G, primitive P, and diamond D phases are all bicontinuous. The transitions weakly depend on the temperature. The increase of ρs is accompanied by the increase of the surface area per unit volume. In the case of fluctuating monolayers the interface is diffused and the average area of the monolayer per unit volume is larger than the "projected area," i.e., the area of the surface describing the average position of the monolayer, per unit volume. The effect is the strongest in the L and the weakest in the C structure.
Statistical properties of two interacting soft spheres in a hard spherical pore
NASA Astrophysics Data System (ADS)
Kim, Soon-Chul
2015-06-01
The structure and thermodynamics of two soft spheres, whose interactions include the soft repulsion and attraction, confined in a hard spherical pore have been considered. The exact partition function, one-body density, and equation of state have been obtained using the Fourier transform method. The pore-size and potential dependence of the structural and thermodynamic properties have been investigated. The two penetrable square-well spheres shows a negative compressibility of the van der Waals type, which imitates the phase transition of many particle system. The van der Waals instability for two penetrable square-well spheres has been studied.
Numerical simulation of a sphere moving down an incline with identical spheres placed equally apart
Ling, Chi-Hai; Jan, Chyan-Deng; Chen, Cheng-lung; Shen, Hsieh Wen
1992-01-01
This paper describes a numerical study of an elastic sphere moving down an incline with a string of identical spheres placed equally apart. Two momentum equations and a moment equation formulated for the moving sphere are solved numerically for the instantaneous velocity of the moving sphere on an incline with different angles of inclination. Input parameters for numerical simulation include the properties of the sphere (the radius, density, Poison's ratio, and Young's Modulus of elasticity), the coefficient of friction between the spheres, and a damping coefficient of the spheres during collision.
NASA Astrophysics Data System (ADS)
Sknepnek, Rastko; Henkes, Silke
2015-02-01
We show that coupling to curvature nontrivially affects collective motion in active systems, leading to motion patterns not observed in flat space. Using numerical simulations, we study a model of self-propelled particles with polar alignment and soft repulsion confined to move on the surface of a sphere. We observe a variety of motion patterns with the main hallmarks being polar vortex and circulating band states arising due to the incompatibility between spherical topology and uniform motion—a consequence of the "hairy ball" theorem. We provide a detailed analysis of density, velocity, pressure, and stress profiles in the circulating band state. In addition, we present analytical results for a simplified model of collective motion on the sphere showing that frustration due to curvature leads to stable elastic distortions storing energy in the band.
46 CFR 160.035-9 - Cubic capacity of lifeboats.
Code of Federal Regulations, 2010 CFR
2010-10-01
... 46 Shipping 6 2010-10-01 2010-10-01 false Cubic capacity of lifeboats. 160.035-9 Section 160.035-9...: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Lifeboats for Merchant Vessels § 160.035-9 Cubic capacity of... its cubic capacity. (1) Length (L). The length is the distance in feet from the inside of the...
46 CFR 160.035-9 - Cubic capacity of lifeboats.
Code of Federal Regulations, 2011 CFR
2011-10-01
... 46 Shipping 6 2011-10-01 2011-10-01 false Cubic capacity of lifeboats. 160.035-9 Section 160.035-9...: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Lifeboats for Merchant Vessels § 160.035-9 Cubic capacity of... its cubic capacity. (1) Length (L). The length is the distance in feet from the inside of the...
Northeastern forest survey revised cubic-foot volume equations
Charles T. Scott
1981-01-01
Cubic-foot volume equations are presented for the 17 species groups used in the forest survey of the 14 northeastern states. The previous cubic- foot volume equations were simple linear in form; the revised cubic-foot volume equations are nonlinear.
NASA Astrophysics Data System (ADS)
Barrera, Ruben G.; Mendoza, Carlos I.; Fuchs, Ronald
1998-03-01
A theory for the energy loss of electrons travelling parallel to a semiinfinite system of polarizable spheres has been recently reported(R. Fuchs, C. I. Mendoza, R. G. Barrera and J. L. Carrillo, Physica A, 241, 29(1997).). In this theory a spectral representation of the surface response is explicitly constructed. Here we apply this theory to a cubic array of identical spheres using a numerical approach. Our results are compared with previous calculations(J. B. Pendry and L. M. Moreno, Phys. Rev. B 50, 5062 (1994)), (C. I. Mendoza, R. G. Barrera and R. Fuchs, Phys. Rev. B (submitted).).
Principal Fibrations from Noncommutative Spheres
NASA Astrophysics Data System (ADS)
Landi, Giovanni; Suijlekom, Walter Van
2005-11-01
We construct noncommutative principal fibrations Sθ7→Sθ4 which are deformations of the classical SU(2) Hopf fibration over the four sphere. We realize the noncommutative vector bundles associated to the irreducible representations of SU(2) as modules of coequivariant maps and construct corresponding projections. The index of Dirac operators with coefficients in the associated bundles is computed with the Connes-Moscovici local index formula. "The algebra inclusion is an example of a not-trivial quantum principal bundle."
Light Scattering by Charged Spheres.
1988-01-29
Wyman Graduate Student: Mr. Alan Chu %"% ,’A% 4, % .1 % 70 References , % -- Arnold S. and N. Hessel , 1985: Photoemission from Single...position of the natural resonances of a sphere are used to determine its size or its chemical * composition ( Arnold , 1980; Lettieri, 1984). High...us very helpful suggestions during the program. We also kept close scientific contact with Dr. Arnold of the Polytechnic Institute of New York, and
1992-12-16
12 = (K,, + )- (29) K 2 (see [3]). The parameter KM represents the amplitude of the periodic curva - ture function and sm denotes the value at which K...Additamentum De curvis elasticis. Methodus Inveniendi Lineas Curvas Maximi Minimive Proprietate Gaudentes, Ser. 1., Vol. 24, Lausanne 1744. 17 [10...Mathematical Theory of Elasticity. 4th. ed., Cambridge University Press, 1927. [12] G. Nielson. Bernstein/ Bezier Curves and Splines on Spheres based upon
Dense, collisional, shearing flows of compliant spheres
NASA Astrophysics Data System (ADS)
Jenkins, James; Berzi, Diego
2017-06-01
We outline the development of theory to describe, dense, collisional shearing flows of identical compliant spheres. We begin with two simple theories: one for rigid, nearly elastic spheres that interact through instantaneous, binary collisions; the other for compliant spheres that interact through multiple, enduring contacts. We then join the two extremes by adding compliance to the collisions and collisions to the spheres in enduring contact. Finally, we compare the predictions of the resulting theory with the results of discrete numerical simulations of steady, homogeneous shearing of compliant frictional spheres.
Homogeneous sphere packings with triclinic symmetry.
Fischer, W; Koch, E
2002-11-01
All homogeneous sphere packings with triclinic symmetry have been derived by studying the characteristic Wyckoff positions P -1 1a and P -1 2i of the two triclinic lattice complexes. These sphere packings belong to 30 different types. Only one type exists that has exclusively triclinic sphere packings and no higher-symmetry ones. The inherent symmetry of part of the sphere packings is triclinic for 18 types. Sphere packings of all but six of the 30 types may be realized as stackings of parallel planar nets.
Structure and phase behaviors of confined two penetrable soft spheres
NASA Astrophysics Data System (ADS)
Kim, Eun-Young; Kim, Soon-Chul
2016-04-01
We study the phase behaviors of two penetrable soft spheres, whose interactions include the soft repulsion and attraction, in a hard spherical pore. The exact partition function, one-body density, and equation of state for the confined two penetrable soft spheres have been calculated using the Fourier transform method. The phase diagrams have been determined from the negative compressibility of the van der Waals type, which imitates the phase transition of many particle system. The addition of the soft repulsion and attraction beyond the soft-core potential gives rise to the van der Waals instability. The soft attraction beyond the soft-core potential significantly enhances the van der Waals instability, whereas the soft repulsion reduces the van der Waals instability. For two hard spheres and hard square-well spheres, the van der Waals instability is not observed. However, the addition of a short-range soft repulsion beyond the hard-core gives rise to the van der Waals instability.
Crystallizing hard-sphere glasses by doping with active particles.
Ni, Ran; Cohen Stuart, Martien A; Dijkstra, Marjolein; Bolhuis, Peter G
2014-09-21
Crystallization and vitrification are two different routes to form a solid. Normally these two processes suppress each other, with the glass transition preventing crystallization at high density (or low temperature). This is even true for systems of colloidal hard spheres, which are commonly used as building blocks for novel functional materials with potential applications, e.g. photonic crystals. By performing Brownian dynamics simulations of glassy systems consisting of mixtures of active and passive hard spheres, we show that the crystallization of such hard-sphere glasses can be dramatically promoted by doping the system with small amounts of active particles. Surprisingly, even hard-sphere glasses of packing fraction up to ϕ = 0.635 crystallize, which is around 0.5% below the random close packing at ϕ ≃ 0.64. Our results suggest a novel way of fabricating crystalline materials from (colloidal) glasses. This is particularly important for materials that get easily kinetically trapped in glassy states, and the crystal nucleation hardly occurs.
Galileon hairs of Dyson spheres, Vainshtein's coiffure and hirsute bubbles
NASA Astrophysics Data System (ADS)
Kaloper, Nemanja; Padilla, Antonio; Tanahashi, Norihiro
2011-10-01
We study the fields of spherically symmetric thin shell sources, a.k.a. Dyson spheres, in a fully nonlinear covariant theory of gravity with the simplest galileon field. We integrate exactly all the field equations once, reducing them to first order nonlinear equations. For the simplest galileon, static solutions come on six distinct branches. On one, a Dyson sphere surrounds itself with a galileon hair, which far away looks like a hair of any Brans-Dicke field. The hair changes below the Vainshtein scale, where the extra galileon terms dominate the minimal gradients of the field. Their hair looks more like a fuzz, because the galileon terms are suppressed by the derivative of the volume determinant. It shuts off the `hair bunching' over the `angular' 2-sphere. Hence the fuzz remains dilute even close to the source. This is really why the Vainshtein's suppression of the modifications of gravity works close to the source. On the other five branches, the static solutions are all singular far from the source, and shuttered off from asymptotic infinity. One of them, however, is really the self-accelerating branch, and the singularity is removed by turning on time dependence. We give examples of regulated solutions, where the Dyson sphere explodes outward, and its self-accelerating side is nonsingular. These constructions may open channels for nonperturbative transitions between branches, which need to be addressed further to determine phenomenological viability of multi-branch gravities.
Crystallizing hard-sphere glasses by doping with active particles
NASA Astrophysics Data System (ADS)
Ni, Ran; Cohen Stuart, Martien A.; Dijkstra, Marjolein; Bolhuis, Peter G.
Crystallization and vitrification are two different routes to form a solid. Normally these two processes suppress each other, with the glass transition preventing crystallization at high density (or low temperature). This is even true for systems of colloidal hard spheres, which are commonly used as building blocks for novel functional materials with potential applications, e.g. photonic crystals. By performing Brownian dynamics simulations of glassy systems consisting of mixtures of active and passive hard spheres, we show that the crystallization of such hard-sphere glasses can be dramatically promoted by doping the system with small amounts of active particles. Surprisingly, even hard-sphere glasses of packing fraction up to $\\phi = 0.635$ crystallize, which is around $0.5\\%$ below the random close packing at $\\phi \\simeq 0.64$. Our results suggest a novel way of fabricating crystalline materials from (colloidal) glasses. This is particularly important for materials that get easily kinetically trapped in glassy states, and crystal nucleation hardly occurs.
Liu, Hanyu; Tse, John S.; Hu, Michael Y.; ...
2015-10-27
The pressure-induced amorphization and subsequent recrystallization of SnI4 have been investigated using first principles molecular dynamics calculations together with high-pressure 119Sn nuclear resonant inelastic x-ray scattering measurements. Above ~8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ~64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI4 under ambient conditions. Although high pressure structures of SnI4 were thought to be determined by random packing of equal-sized spheres,more » we detected electron charge transfer in each phase. As a result, this charge transfer results in a crystal structure packing determined by larger than expected iodine atoms. (C) 2015 AIP Publishing LLC.« less
Density-functional theory for fluid-solid and solid-solid phase transitions
NASA Astrophysics Data System (ADS)
Bharadwaj, Atul S.; Singh, Yashwant
2017-03-01
We develop a theory to describe solid-solid phase transitions. The density functional formalism of classical statistical mechanics is used to find an exact expression for the difference in the grand thermodynamic potentials of the two coexisting phases. The expression involves both the symmetry conserving and the symmetry broken parts of the direct pair correlation function. The theory is used to calculate phase diagram of systems of soft spheres interacting via inverse power potentials u (r ) =ɛ "close="1 /n )">σ /r n , where parameter n measures softness of the potential. We find that for 1 /n ≥0.154 the body-centred-cubic (bcc) structure is preferred. The bcc structure transforms into the fcc structure upon increasing the density. The calculated phase diagram is in good agreement with the one found from molecular simulations.
Imai, M; Yoshida, I; Iwaki, T; Nakaya, K
2005-01-22
We have investigated the static and dynamic structures of nonionic surfactant micelles, a C(12)E(8)/water binary system, during the disorder-order transition using small angle x-ray scattering, static light scattering, and dynamic light scattering techniques. In the disordered phase, the micelles have spherical shape and intermicellar interactions are governed by the hard core and weak long ranged attractive potentials. With increase of the micellar concentration, the disordered micelles transform to the three characteristic ordered micellar phases, a hexagonally close packed lattice, a body centered cubic lattice, and an A15 lattice having area-minimizing structure. The stability of these phases is well explained by balance of a close packing rule and a minimal-area rule proposed by Ziherl and Kamien [Phys. Rev. Lett. 85, 3528 (2000)]. The role of hydrodynamic interactions in surfactant micellar solutions was compared with that in hard sphere colloidal particle suspensions.
Persson, Gerd; Edlund, Håkan; Lindblom, Göran
2003-01-01
Using synchrotron X-ray diffraction the thermal behaviour was studied of the cubic phases in the 1-monooleoyl-rac-glycerol (MO)/n-octyl-beta-d-glucopyranoside (OG)/2H2O system with 58 or 45 wt % MO concentration and varying OG/2H2O contents. These MO contents correspond to a Pn3m cubic single-phase or a Pn3m cubic phase in excess water on the binary MO/water axis of the ternary phase diagram. The cubic liquid crystalline phases are stable with small fractions of OG, while higher OG concentrations trigger a cubic-to-lamellar phase transition. Moreover, with increasing OG concentration the initial Pn3m structure is completely converted to an Ia3d structure prior to the Lalpha phase being formed. Upon heating this effect is reversed, resulting in an Ia3d-to-Pn3m phase transition. For some samples additional peaks were observed in the diffractograms upon heating, resulting from the metastability notoriously shown by bicontinuous cubic phases. This judgement is supported by the fact that upon cooling these peaks were absent. Remarkably, both the Ia3d and the Pn3m cubic structures could be in equilibrium with excess water in this ternary system. A comparison is made with previous results on n-dodecyl-beta-d-maltoside (DM), showing that cubic phases with OG have higher thermal and compositional stability than with DM.
Growth and characterization of cubic and non-cubic Ge nanocrystals
Mukherjee, S.; Pradhan, A.; Bhunia, S.; Mukherjee, S.; Maitra, T.; Nayak, A.
2016-05-06
Germanium nanocrystals with tetragonal (ST-12) and diamond like cubic (Ge-I) phases have been selectively grown by controlling the ionization and electrostatic potential of Ge clusters in an ion cluster beam deposition system. Predominantly tetragonal nanocrystals were obtained when grown using neutral clusters. The percentage of cubic phase increased when grown by ionizing the clusters and accelerating them towards substrates by applying electrostatic bias in the range of 1.5 –2.5 kV. Raman spectroscopic measurement showed strong peak at 275 cm{sup −1} and 300 cm{sup −1} for tetragonal and cubic Ge nanocrystals, respectively. TEM measurements showed crystalline lattice fringes of both type of the nanocrystals. The selected area electron diffraction patterns showed (111) and (210) as the dominating lattice planes for tetragonal nanocrystals while the cubic phases had (111), (311) and (331) as the prominent lattice planes. The optical absorption edge redshifted from 1.75 to 1.55 eV as the percentage of the cubic phases increased in the NC composition in the composite film.
Shear Yielding and Shear Jamming of Dense Hard Sphere Glasses
NASA Astrophysics Data System (ADS)
Urbani, Pierfrancesco; Zamponi, Francesco
2017-01-01
We investigate the response of dense hard sphere glasses to a shear strain in a wide range of pressures ranging from the glass transition to the infinite-pressure jamming point. The phase diagram in the density-shear strain plane is calculated analytically using the mean-field infinite-dimensional solution. We find that just above the glass transition, the glass generically yields at a finite shear strain. The yielding transition in the mean-field picture is a spinodal point in presence of disorder. At higher densities, instead, we find that the glass generically jams at a finite shear strain: the jamming transition prevents yielding. The shear yielding and shear jamming lines merge in a critical point, close to which the system yields at extremely large shear stress. Around this point, highly nontrivial yielding dynamics, characterized by system-spanning disordered fractures, is expected.
Tunable photoluminescence in monodisperse silica spheres.
Kong, Deyan; Zhang, Cuimiao; Xu, Zhenhe; Li, Guogang; Hou, Zhiyao; Lin, Jun
2010-12-15
The nanometer-scale luminescent monodisperse silica spheres have been prepared by a water/oil (W/O) microemulsion method and the size of these spheres changed with the different concentrations of 3-aminopropyltriethoxysilane (APTES). The luminescent monodisperse silica spheres at the submicrometer scale have been prepared via Stöber method and the particles size increased with the increase of the amino concentrations. After calcination, all silica spheres do not change obviously in size. The annealed silica spheres contain C impurities and O defects, which resulted in the luminescence of silica spheres. The spheres showed variations in emission due to the different size and the concentration of organosiloxane precursors. Therefore, the emission can be tuned finely via the change of organosiloxane precursor and the size of samples. Copyright © 2010 Elsevier Inc. All rights reserved.
NASA Astrophysics Data System (ADS)
Narayanan, Rajesh; Vojta, Thomas
2001-01-01
We study the quantum phase transition of an itinerant antiferromagnet with cubic anisotropy in the presence of quenched disorder, paying particular attention to the locally ordered spatial regions that form in the Griffiths region. We derive an effective action where these rare regions are described in terms of static annealed disorder. A one-loop renormalization-group analysis of the effective action shows that for order-parameter dimensions p<4, the rare regions destroy the conventional critical behavior, and the renormalized disorder flows to infinity. For order-parameter dimensions p>4, the critical behavior is not influenced by the rare regions; it is described by the conventional dirty cubic fixed point. We also discuss the influence of the rare regions on the fluctuation-driven first-order transition in this system.
Large negative thermal expansion in the cubic phase of CaMn7O12
NASA Astrophysics Data System (ADS)
Gautam, K.; Shukla, D. K.; Francoual, S.; Bednarcik, J.; Mardegan, J. R. L.; Liermann, H.-P.; Sankar, R.; Chou, F. C.; Phase, D. M.; Strempfer, J.
2017-04-01
Observations of multiferroicity and giant improper ferroelectricity in CaMn7O12 invigorated the research on this material. Delicate structural changes have been reported to cause ferroelectricity in the magnetically ordered state of CaMn7O12 as well as high-temperature crystallographic transformations. Through high-resolution synchrotron x-ray diffraction experiments we show for the first time the large negative thermal expansion (NTE) behavior of the cubic phase of CaMn7O12 . A large NTE coefficient αL for a temperature window of around 60 K is inferred for the cubic phase in the phase coexistence region during the high-temperature structural transition. It is explained using quasirigid unit modes. We also observe a large phase coexistence region of about 100 K across the high-temperature first-order structural transition, which is different from previous reports.
Interplay between lattice dynamics and the low-pressure phase of simple cubic polonium
NASA Astrophysics Data System (ADS)
Zaoui, A.; Belabbes, A.; Ahuja, R.; Ferhat, M.
2011-04-01
Low-pressure structural properties of simple cubic polonium are explored through first-principles density-functional theory based relativistic total energy calculations using pseudopotentials and plane-wave basis set, as well as linear-response theory. We have found that Po undergoes structural phase transition at low pressure near 2 GPa, where the element transforms from simple cubic to a mixture of two trigonal phases namely, hR1 (α=86°) and hR2 (α=97.9°) structures. The lattice dynamics calculations provide strong support for the observed phase transition, and show the dynamical stability (instability) of the hR2 (hR1) phase.
Spontaneous Graphitization of Ultrathin Cubic Structures: A Computational Study
NASA Astrophysics Data System (ADS)
Sorokin, Pavel B.; Kvashnin, Alexander G.; Zhu, Zhen; Tománek, David
2014-12-01
Results based on {\\em ab initio} density functional calculations indicate a general graphitization tendency in ultrathin slabs of cubic diamond, boron nitride, and many other cubic structures including rocksalt. Whereas such compounds often show an energy preference for cubic rather than layered atomic arrangements in the bulk, the surface energy of layered systems is commonly lower than that of their cubic counterparts. We determine the critical slab thickness for a range of systems, below which a spontaneous conversion from a cubic to a layered graphitic structure occurs, driven by surface energy reduction in surface-dominated structures.
Cubic Phases in Phosphatidylcholine-Cholesterol Mixtures: Cholesterol as Membrane 'Fusogen'
Tenchov, Boris G.; MacDonald, Robert C.; Siegel, David P.
2010-01-18
X-ray diffraction reveals that mixtures of some unsaturated phosphatidylcholines (PCs) with cholesterol (Chol) readily form inverted bicontinuous cubic phases that are stable under physiological conditions. This effect was studied in most detail for dioleoyl PC/Chol mixtures with molar ratios of 1:1 and 3:7. Facile formation of Im3m and Pn3m phases with lattice constants of 30-50nm and 25-30nm, respectively, took place in phosphate-buffered saline, in sucrose solution, and in water near the temperature of the L{alpha}HII transition of the mixtures, as well as during cooling of the HII phase. Once formed, the cubic phases displayed an ability to supercool and replace the initial L{sub {alpha}} phase over a broad range of physiological temperatures. Conversion into stable cubic phases was also observed for mixtures of Chol with dilinoleoyl PC but not for mixtures with palmitoyl-linoleoyl PC or palmitoyl-oleoyl PC, for which only transient cubic traces were recorded at elevated temperatures. A saturated, branched-chain PC, diphytanoyl PC, also displayed a cubic phase in mixture with Chol. Unlike the PEs, the membrane PCs are intrinsically nonfusogenic lipids: in excess water they only form lamellar phases and not any of the inverted phases on their own. Thus, the finding that Chol induces cubic phases in mixtures with unsaturated PCs may have important implications for its role in fusion. In ternary mixtures, saturated PCs and sphingomyelin are known to separate into liquid-ordered domains along with Chol. Our results thus suggest that unsaturated PCs, which are excluded from these domains, could form fusogenic domains with Chol. Such a dual role of Chol may explain the seemingly paradoxical ability of cell membranes to simultaneously form rigid, low-curvature raft-like patches while still being able to undergo facile membrane fusion.
Phase equilibria in polydisperse nonadditive hard-sphere systems.
Paricaud, Patrice
2008-08-01
Colloidal particles naturally exhibit a size polydispersity that can greatly influence their phase behavior in solution. Nonadditive hard-sphere (NAHS) mixtures are simple and well-suited model systems to represent phase transitions in colloid systems. Here, we propose an analytical equation of state (EOS) for NAHS fluid mixtures, which can be straightforwardly applied to polydisperse systems. For positive values of the nonadditivity parameter Delta the model gives accurate predictions of the simulated fluid-fluid coexistence curves and compressibility factors. NPT Monte Carlo simulations of the mixing properties of the NAHS symmetric binary mixture with Delta>0 are reported. It is shown that the enthalpy of mixing is largely positive and overcomes the positive entropy of mixing when the pressure is increased, leading to a fluid-fluid phase transition with a lower critical solution pressure. Phase equilibria in polydisperse systems are predicted with the model by using the density moment formalism [P. Sollich, Adv. Chem. Phys. 116, 265 (2001)]. We present predictions of the cloud and shadow curves for polydisperse NAHS systems composed of monodisperse spheres and polydisperse colloid particles. A fixed nonadditivity parameter Delta > 0 is assumed between the monodisperse and polydisperse spheres, and a Schulz distribution is used to represent the size polydispersity. Polydispersity is found to increase the extent of the immiscibility region. The predicted cloud and shadow curves depend dramatically on the upper cutoff diameter sigmac of the Schulz distribution, and three-phase equilibria can occur for large values of sigmac.
Liquid water in the domain of cubic crystalline ice Ic
NASA Technical Reports Server (NTRS)
Jenniskens, P.; Banham, S. F.; Blake, D. F.; McCoustra, M. R.
1997-01-01
Vapor-deposited amorphous water ice when warmed above the glass transition temperature (120-140 K), is a viscous liquid which exhibits a viscosity vs temperature relationship different from that of liquid water at room temperature. New studies of thin water ice films now demonstrate that viscous liquid water persists in the temperature range 140-210 K. where it coexists with cubic crystalline ice. The liquid character of amorphous water above the glass transition is demonstrated by (1) changes in the morphology of water ice films on a nonwetting surface observed in transmission electron microscopy (TEM) at around 175 K during slow warming, (2) changes in the binding energy of water molecules measured in temperature programmed desorption (TPD) studies, and (3) changes in the shape of the 3.07 micrometers absorption band observed in grazing angle reflection-absorption infrared spectroscopy (RAIRS) during annealing at high temperature. whereby the decreased roughness of the water surface is thought to cause changes in the selection rules for the excitation of O-H stretch vibrations. Because it is present over such a wide range of temperatures, we propose that this form of liquid water is a common material in nature. where it is expected to exist in the subsurface layers of comets and on the surfaces of some planets and satellites.
Liquid water in the domain of cubic crystalline ice Ic.
Jenniskens, P; Banham, S F; Blake, D F; McCoustra, M R
1997-07-22
Vapor-deposited amorphous water ice when warmed above the glass transition temperature (120-140 K), is a viscous liquid which exhibits a viscosity vs temperature relationship different from that of liquid water at room temperature. New studies of thin water ice films now demonstrate that viscous liquid water persists in the temperature range 140-210 K. where it coexists with cubic crystalline ice. The liquid character of amorphous water above the glass transition is demonstrated by (1) changes in the morphology of water ice films on a nonwetting surface observed in transmission electron microscopy (TEM) at around 175 K during slow warming, (2) changes in the binding energy of water molecules measured in temperature programmed desorption (TPD) studies, and (3) changes in the shape of the 3.07 micrometers absorption band observed in grazing angle reflection-absorption infrared spectroscopy (RAIRS) during annealing at high temperature. whereby the decreased roughness of the water surface is thought to cause changes in the selection rules for the excitation of O-H stretch vibrations. Because it is present over such a wide range of temperatures, we propose that this form of liquid water is a common material in nature. where it is expected to exist in the subsurface layers of comets and on the surfaces of some planets and satellites.
Liquid water in the domain of cubic crystalline ice Ic
NASA Technical Reports Server (NTRS)
Jenniskens, P.; Banham, S. F.; Blake, D. F.; McCoustra, M. R.
1997-01-01
Vapor-deposited amorphous water ice when warmed above the glass transition temperature (120-140 K), is a viscous liquid which exhibits a viscosity vs temperature relationship different from that of liquid water at room temperature. New studies of thin water ice films now demonstrate that viscous liquid water persists in the temperature range 140-210 K. where it coexists with cubic crystalline ice. The liquid character of amorphous water above the glass transition is demonstrated by (1) changes in the morphology of water ice films on a nonwetting surface observed in transmission electron microscopy (TEM) at around 175 K during slow warming, (2) changes in the binding energy of water molecules measured in temperature programmed desorption (TPD) studies, and (3) changes in the shape of the 3.07 micrometers absorption band observed in grazing angle reflection-absorption infrared spectroscopy (RAIRS) during annealing at high temperature. whereby the decreased roughness of the water surface is thought to cause changes in the selection rules for the excitation of O-H stretch vibrations. Because it is present over such a wide range of temperatures, we propose that this form of liquid water is a common material in nature. where it is expected to exist in the subsurface layers of comets and on the surfaces of some planets and satellites.
Cherenkov and Scintillation Properties of Cubic Zirconium
NASA Technical Reports Server (NTRS)
Christl, M.J.; Adams, J.H.; Parnell, T.A.; Kuznetsov, E.N.
2008-01-01
Cubic zirconium (CZ) is a high index of refraction (n =2.17) material that we have investigated for Cherenkov counter applications. Laboratory and proton accelerator tests of an 18cc sample of CZ show that the expected fast Cherenkov response is accompanied by a longer scintillation component that can be separated by pulse shaping. This presents the possibility of novel particle spectrometers which exploits both properties of CZ. Other high index materials being examined for Cherenkov applications will be discussed. Results from laboratory tests and an accelerator exposure will be presented and a potential application in solar energetic particle instruments will be discussed
Craniofacial Reconstruction Using Rational Cubic Ball Curves
Majeed, Abdul; Mt Piah, Abd Rahni; Gobithaasan, R. U.; Yahya, Zainor Ridzuan
2015-01-01
This paper proposes the reconstruction of craniofacial fracture using rational cubic Ball curve. The idea of choosing Ball curve is based on its robustness of computing efficiency over Bezier curve. The main steps are conversion of Digital Imaging and Communications in Medicine (Dicom) images to binary images, boundary extraction and corner point detection, Ball curve fitting with genetic algorithm and final solution conversion to Dicom format. The last section illustrates a real case of craniofacial reconstruction using the proposed method which clearly indicates the applicability of this method. A Graphical User Interface (GUI) has also been developed for practical application. PMID:25880632
Two-layer tubes from cubic crystals
NASA Astrophysics Data System (ADS)
Goldstein, R. V.; Gorodtsov, V. A.; Lisovenko, D. S.; Volkov, M. A.
2016-12-01
Effective Young's moduli and Poisson's ratios of two-layer tubes from cubic crystals have been analyzed theoretically. It is shown (using derived formulas for numerical estimates) that the mechanical properties of two-layer tube composites from auxetics and nonauxetics are not described by the mixture rule. It is demonstrated that the deviation of the effective modulus from the mixture rule predictions rapidly increases with an increase in Young's modulus of the nonauxetic components of a composite. It is established that, combining auxetics and nonauxetics in layered tubes, one can obtain, depending on the packing order in layers, either a strong increase or a decrease in auxeticity.
Cherenkov and Scintillation Properties of Cubic Zirconium
NASA Technical Reports Server (NTRS)
Christl, M.J.; Adams, J.H.; Parnell, T.A.; Kuznetsov, E.N.
2008-01-01
Cubic zirconium (CZ) is a high index of refraction (n =2.17) material that we have investigated for Cherenkov counter applications. Laboratory and proton accelerator tests of an 18cc sample of CZ show that the expected fast Cherenkov response is accompanied by a longer scintillation component that can be separated by pulse shaping. This presents the possibility of novel particle spectrometers which exploits both properties of CZ. Other high index materials being examined for Cherenkov applications will be discussed. Results from laboratory tests and an accelerator exposure will be presented and a potential application in solar energetic particle instruments will be discussed
Scaling for hard-sphere colloidal glasses near jamming
NASA Astrophysics Data System (ADS)
Zargar, Rojman; DeGiuli, Eric; Bonn, Daniel
2016-12-01
Hard-sphere colloids are model systems in which to study the glass transition and universal properties of amorphous solids. Using covariance matrix analysis to determine the vibrational modes, we experimentally measure here the scaling behavior of the density of states, shear modulus, and mean-squared displacement (MSD) in a hard-sphere colloidal glass. Scaling the frequency with the boson-peak frequency, we find that the density of states at different volume fractions all collapse on a single master curve, which obeys a power law in terms of the scaled frequency. Below the boson peak, the exponent is consistent with theoretical results obtained by real-space and phase-space approaches to understanding amorphous solids. We find that the shear modulus and the MSD are nearly inversely proportional, and show a singular power-law dependence on the distance from random close packing. Our results are in very good agreement with the theoretical predictions.
Cubic membranes: a structure-based design for DNA uptake.
Almsherqi, Zakaria; Hyde, Stephen; Ramachandran, Malarmathy; Deng, Yuru
2008-09-06
Cubic membranes are soft three-dimensional crystals found within cell organelles in a variety of living systems, despite the aphorism of Fedorov: 'crystallization is death'. They consist of multi-bilayer lipid-protein stacks, folded onto anticlastic surfaces that resemble triply periodic minimal surfaces, forming highly swollen crystalline sponges. Although cubic membranes have been observed in numerous cell types and under different pathophysiological conditions, knowledge about the formation and potential function(s) of non-lamellar, cubic structures in biological systems is scarce. We report that mitochondria with this cubic membrane organization isolated from starved amoeba Chaos carolinense interact sufficiently with short segments of phosphorothioate oligonucleotides (PS-ODNs) to give significant ODNs uptake. ODNs condensed within the convoluted channels of cubic membrane by an unknown passive targeting mechanism. Moreover, the interaction between ODNs and cubic membrane is sufficient to retard electrophoretic mobility of the ODN component in the gel matrix. These ODN-cubic membrane complexes are readily internalized within the cytoplasm of cultured mammalian cells. Transmission electron microscopic analysis confirms ODNs uptake by cubic membranes and internalization of ODN-cubic membrane complexes into the culture cells. Cubic membranes thus may offer a new, potentially benign medium for gene transfection.
Floating behavior of hydrophobic glass spheres.
Liu, Xinjie; Wang, Xiaolong; Liang, Yongmin; Zhou, Feng
2009-08-15
When a hydrophobic solid sphere is floating on water or salt solutions with different concentrations, it is at equilibrium under the impact of gravity, buoyancy force, and curvature force, the component of surface tension in the vertical direction. We have changed the diameters of the spheres and the concentrations of the two selected salts, NaCl and NaNO(3), to study the floating behaviors of these spheres and the contributions of surface tension and buoyancy force to their floatation. Generally speaking, the surface tension plays a more important role than the buoyancy force when the gravity is small, but the buoyancy force plays an identical or a more important role when the spheres are big enough. The wettability of the spheres significantly influences the height below the contact perimeter especially in salt solutions. The theoretical calculation meniscus slope angles at the sphere three-phase contact line are in agreement with experimental results.
Sphere-Pac Evaluation for Transmutation
Icenhour, A.S.
2005-05-19
The U.S. Department of Energy Advanced Fuel Cycle Initiative (AFCI) is sponsoring a project at Oak Ridge National Laboratory with the objective of conducting the research and development necessary to evaluate the use of sphere-pac transmutation fuel. Sphere-pac fuels were studied extensively in the 1960s and 1970s. More recently, this fuel form is being studied internationally as a potential plutonium-burning fuel. For transmutation fuel, sphere-pac fuels have potential advantages over traditional pellet-type fuels. This report provides a review of development efforts related to the preparation of sphere-pac fuels and their irradiation tests. Based on the results of these tests, comparisons with pellet-type fuels are summarized, the advantages and disadvantages of using sphere-pac fuels are highlighted, and sphere-pac options for the AFCI are recommended. The Oak Ridge National Laboratory development activities are also outlined.
NASA Astrophysics Data System (ADS)
Degtyareva, Valentina F.; Afonikova, Nataliya S.
2013-01-01
Binary alloy phases of the noble metals with the main group elements are analyzed in relation to the body centered cubic structure with distortions, vacancies and superlattices. The stability of these distorted phases is studied in terms of the Fermi sphere-Brillouin-Jones zone interaction within the nearly free-electron model in order to understand the importance of the band structure energy contribution to the overall crystal energy. Examination of Brillouin-Jones zone configurations with respect to the Fermi sphere for several representative phases has shown how significant the electron energy contribution is in forming the distorted structures with superlattices and ordered vacancies. This approach may be useful for understanding the complex structures recently found in compressed simple alkali metals.
van 't Hag, Leonie; Li, Xu; Meikle, Thomas G; Hoffmann, Søren V; Jones, Nykola C; Pedersen, Jan Skov; Hawley, Adrian M; Gras, Sally L; Conn, Charlotte E; Drummond, Calum J
2016-07-12
Nanostructured bicontinuous lipidic cubic phases are used for the encapsulation of proteins in a range of applications such as in meso crystallization of transmembrane proteins and as drug delivery vehicles. The retention of the nanoscale order of the cubic phases subsequent to protein incorporation, as well as retention of the protein structure and function, is essential for all of these applications. Herein synthetic peptides (WALP21, WALPS53, and WALPS73) with a common α-helical hydrophobic domain, but varying hydrophilic loop size, were designed to systematically examine the effect of peptide structure and charge on bicontinuous cubic phases. The effect of the cubic phases on the secondary structure of the peptides was also investigated. The incorporation of the WALP peptides in cubic phases formed by a range of lipids showed that hydrophobic mismatch of the peptides with the lipid bilayers, the hydrophilic domain size, and peptide charge were all significant factors determining the response of the lipid nanomaterial to protein insertion. As charge repulsion had the most significant effect on the phase transitions observed, we suggest that buffer pH and salt concentration must be carefully considered to ensure cubic mesophase retention. Importantly, the WALP peptides were found to have a different conformation depending on the local lipid environment. Such structural changes could potentially affect membrane protein function, which is crucial for both current and prospective applications.
Absence of Metallic Conductivity in Tetragonal and Cubic PbVO3 at High Pressure
NASA Astrophysics Data System (ADS)
Belik, Alexei A.; Yamauchi, Touru; Ueda, Hiroaki; Ueda, Yutaka; Yusa, Hitoshi; Hirao, Naohisa; Azuma, Masaki
2014-07-01
Transport properties of PbVO3, a material whose structural and electronic properties bear similarities with high-temperature copper superconductors, were investigated between 2 and 300 K and in the pressure range of 0.1 MPa and 11.3 GPa. There is a structural phase transition from about 2 GPa at room temperature from a super-tetragonal phase to a cubic phase with a significant drop of resistivity by about 5 orders of magnitude. Nevertheless, the cubic phase exhibited a semiconducting behavior of resistivity between 2 and 300 K up to 11.3 GPa. The pressure dependence of lattice parameters of the tetragonal and cubic phases was in very good agreement with results of first-principle calculations from http://dx.doi.org/10.1088/0953-8984/24/43/435403, J. Phys.: Condens. Matter 24, 435403 (2012). Fitting with the Birch-Murnaghan equation of states gave a bulk modulus K0 = 38.0(1.1) GPa and a unit cell volume V0 = 67.63(6) Å3 for the tetragonal phase and K0 = 179.5(1.4) GPa and V0 = 58.272(14) Å3 for the cubic phase.
The cubic phase of phosphatidylethanolamine film by small angle x-ray scattering
NASA Astrophysics Data System (ADS)
Sun, Run Guang; Zhang, Jing
2004-02-01
Using small angle x-ray scattering, we have investigated the effects of polyvinylpyrrolidone (PVP) and oleic acid (OA) on the structures of the cubic phase of 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) films. At lower PVP concentrations, DEPE-PVP mixed films existed in two cubic phases. With increasing PVP concentration in the DEPE-PVP mixed phase, a phase transition from Q229 (Im3m) to Q224 (Pn3m) occurred. The effect of addition of OA to a DEPE-PVP mixed phase was also determined using a certain fixed amount. At 0.5 mol% OA, the presence of low amounts of OA allows the DEPE-PVP-OA system to organize in a cubic Q229 phase. At 1.0 mol% OA, the presence of larger amounts of OA induces formation of coexisting Q229 and Q224 phases. At 1.5 mol% OA, the presence of even larger amounts of OA promotes formation of a cubic Q224 phase in the DEPE-PVP-OA mixture.
Magnetic and thermodynamic properties of face-centered cubic Fe-Ni alloys.
Lavrentiev, M Yu; Wróbel, J S; Nguyen-Manh, D; Dudarev, S L
2014-08-14
A model lattice ab initio parameterized Heisenberg-Landau magnetic cluster expansion Hamiltonian spanning a broad range of alloy compositions and a large variety of chemical and magnetic configurations has been developed for face-centered cubic Fe-Ni alloys. The thermodynamic and magnetic properties of the alloys are explored using configuration and magnetic Monte Carlo simulations over a temperature range extending well over 1000 K. The predicted face-centered cubic-body-centered cubic coexistence curve, the phase stability of ordered Fe3Ni, FeNi, and FeNi3 intermetallic compounds, and the predicted temperatures of magnetic transitions simulated as functions of alloy composition agree well with experimental observations. Simulations show that magnetic interactions stabilize the face-centered cubic phase of Fe-Ni alloys. Both the model Hamiltonian simulations and ab initio data exhibit a particularly large number of magnetic configurations in a relatively narrow range of alloy compositions corresponding to the occurrence of the Invar effect.
Sphere Drag and Heat Transfer.
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-07-20
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-01-01
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body. PMID:26189698
Porous Ceramic Spheres from Ion Exchange Resin
NASA Technical Reports Server (NTRS)
Dynys, Fred
2005-01-01
A commercial cation ion exchange resin, cross-linked polystyrene, has been successfully used as a template to fabricate 20 to 50 micron porous ceramic spheres. Ion exchange resins have dual template capabilities. Pore architecture of the ceramic spheres can be altered by changing the template pattern. Templating can be achieved by utilizing the internal porous structure or the external surface of the resin beads. Synthesis methods and chemical/physical characteristics of the ceramic spheres will be reported.
Process for making hollow carbon spheres
Luhrs, Claudia C.; Phillips, Jonathan; Richard, Monique N.; Knapp, Angela Michelle
2013-04-16
A hollow carbon sphere having a carbon shell and an inner core is disclosed. The hollow carbon sphere has a total volume that is equal to a volume of the carbon shell plus an inner free volume within the carbon shell. The inner free volume is at least 25% of the total volume. In some instances, a nominal diameter of the hollow carbon sphere is between 10 and 180 nanometers.
Microgravity and the Formation of Latex Spheres
NASA Technical Reports Server (NTRS)
1982-01-01
This set of photographs illustrates the value of microgravity in the formation of latex spheres. The image at left shows irregular spheres produced on Earth, while the photograph at right shows uniform spheres produced during the STS-3 mission, March 22 - 30, 1982, in the Monodisperse Latex Reactor, developed by the Marshall Space Flight Center and Lehigh University. The Marshall-managed MLR experiment demonstrated the feasibility of producing monodisperse polystyrene latex microspheres in space and their application to medicine and industry.
Simulation of Flow for an Immersed Sphere
2016-12-01
creating an unlikely physical realization of the flow field around the sphere. Two measures are implemented to prevent this problem from occurring. First...AFRL-RW-EG-TR-2016-092 Simulation of Flow for an Immersed Sphere Pedro A. Lopez-Fernandez Ralph K. Tatum Douglas...AND SUBTITLE 5a. CONTRACT NUMBER Simulation of Flow for an Immersed Sphere 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 62602F
Microgravity and the Formation of Latex Spheres
NASA Technical Reports Server (NTRS)
1982-01-01
This set of photographs illustrates the value of microgravity in the formation of latex spheres. The image at left shows irregular spheres produced on Earth, while the photograph at right shows uniform spheres produced during the STS-3 mission, March 22 - 30, 1982, in the Monodisperse Latex Reactor, developed by the Marshall Space Flight Center and Lehigh University. The Marshall-managed MLR experiment demonstrated the feasibility of producing monodisperse polystyrene latex microspheres in space and their application to medicine and industry.
Aperture correction for a sphere interferometer
NASA Astrophysics Data System (ADS)
Arnold Nicolaus, R.; Bönsch, Gerhard
2009-12-01
Considerations have been made to derive a correction for the diameter measurements of a sphere by means of a special sphere interferometer. This correction is caused by the finite diameter of the light source acting as the entrance 'pinhole' aperture in the light collimating system. The finite diameter has the effect that the wave which is incident on the sphere is a superposition of spherical waves which are slightly inclined with respect to each other. The resulting correction is essential for high accuracy dimensional measurements of silicon spheres to determine the Avogadro constant—a new determination of which is a contribution to a new definition of the kilogram.
Chimera grid simulations of falling spheres
NASA Astrophysics Data System (ADS)
Hauser, Thomas; Schauerhamer, Daniel
2007-11-01
Many applications involve modeling a system with moving objects larger than the grid, such as air pollution, combustion systems, accident simulations, chemical and agricultural processes. The chimera grid approach is an efficient approach to solve such problems. Simulations of one sphere falling under the influence of gravity and suction through an orifice will be presented. Additionally, we will demonstrate collisions between two moving spheres. In this simulation the setup is the same as in the one sphere case, but two spheres are placed side by side. Both are released to be acted upon by gravity, the suction, and each other.
Macromolecule-Induced Clustering of Hard Spheres.
Chatterjee, Avik Prasun
2001-06-01
The connectivity Ornstein-Zernike formalism, together with the polymer reference interaction site model (PRISM), is employed to describe connectivity and network formation in mixtures of spheres and polymers. Results are presented for the percolation of spheres induced by both flexible coil-like and rigid rod-like linear polymers; the Percus-Yevick (PY) approximation is used throughout. Our results are compared with predictions based on the adhesive hard sphere (AHS) model, and correlations with the polymer-mediated second virial coefficient between spheres are discussed. Copyright 2001 Academic Press.
Small-world networks on a sphere
NASA Astrophysics Data System (ADS)
Corso, Gilberto; Torres Cruz, Claudia P.
2017-01-01
The Small-World Network on a Sphere SWNS is a non-crossing network that has no hubs and presents the small-world property diam log N with diam being the maximal distance between any two vertices and N being the number of vertices. The SWNS is constructed using a partition of the sphere and the parallels are regular sections of the sphere with constant latitude. The number of cells on the parallels, however, increases exponentially from the pole to the equator of the sphere. We analytically compute the distribution of connectivity, the clustering coefficient and the SWNS distances. The resilience of the model against selective attacks is also discussed.
Method for producing small hollow spheres
Hendricks, Charles D. [Livermore, CA
1979-01-09
Method for producing small hollow spheres of glass, metal or plastic, wherein the sphere material is mixed with or contains as part of the composition a blowing agent which decomposes at high temperature (T .gtorsim. 600.degree. C). As the temperature is quickly raised, the blowing agent decomposes and the resulting gas expands from within, thus forming a hollow sphere of controllable thickness. The thus produced hollow spheres (20 to 10.sup.3 .mu.m) have a variety of application, and are particularly useful in the fabrication of targets for laser implosion such as neutron sources, laser fusion physics studies, and laser initiated fusion power plants.