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.
Ferromagnetic Ground States in Face-Centered Cubic Hubbard Clusters.
Souza, T X R; Macedo, C A
2016-01-01
In this study, the ground state energies of face-centered cubic Hubbard clusters are analyzed using the Lanczos method. Examination of the ground state energy as a function of the number of particle per site n showed an energy minimum for face-centered cubic structures. This energy minimum decreased in n with increasing coulombic interaction parameter U. We found that the ground state energy had a minimum at n = 0.6, when U = 3W, where W denotes the non-interacting energy bandwidth and the face-centered cubic structure was ferromagnetic. These results, when compared with the properties of nickel, shows strong similarity with other finite temperature analyses in the literature and supports the Hirsh's conjecture that the interatomic direct exchange interaction dominates in driving the system into a ferromagnetic phase. PMID:27583653
Direct Numerical Simulation of turbulent flow in a porous, face centered cubic cell
NASA Astrophysics Data System (ADS)
He, Xiaoliang; Apte, Sourabh; Wood, Brian
2014-11-01
DNS of flow through a 3D, periodic, face centered cubic (FCC) unit cell geometry at Re = 300 , 550, and 950 based on diameter is performed. This low porosity arrangement of spheres is characterized by rapid flow expansions and contractions, and thus features an early onset to turbulence. The simulations are performed using a fictitious domain approach [Apte et al., J. Comp. Physics 2009], which uses non-body conforming Cartesian grids, with resolution up to D / Δ = 250 (3543 cells total). The results are used to investigate the structure of turbulence in the Eulerian and Lagrangian frames, the distribution and budget of turbulent kinetic energy, and the characteristics of the energy spectrum in complex packed beds and porous media. The porescale flow physics, which are important to properties such as bulk mixing performance and permeability, are investigated. Specifically, the data generated is being used to understand the important turbulence characteristics in low porosity packed beds of relevance for heat tranfer applications in chemical/nuclear reactors. Funding: NSF Project Number 1336983.
Resistance calculation of the face-centered cubic lattice: Theory and experiment
NASA Astrophysics Data System (ADS)
Owaidat, M. Q.
2013-12-01
The effective resistance between two arbitrary lattice points in an infinite, face-centered cubic lattice network of identical resistors is calculated using the lattice Green's function method. Theoretical results have been verified experimentally by constructing actual finite networks of resistors. This problem could be useful in undergraduate courses (e.g., advanced mathematical methods course) and would provide a good example for introducing the concept of Green's function.
Phonon densities of states of face-centered-cubic Ni-Fe alloys
Lucas, Matthew; Mauger, L; Munoz, Jorge A.; Halevy, I; Horwath, J; Semiatin, S L; Leontsev, S. O.; Stone, Matthew B; Abernathy, Douglas L; Xiao, Yuming; Chow, P; Fultz, B.
2013-01-01
Inelastic neutron scattering and nuclear resonant inelastic x-ray scattering were used to determine the phonon densities of states of face-centered-cubic Ni-Fe alloys. Increasing Fe concentration results in an average softening of the phonon modes. Chemical ordering of the Ni0.72Fe0.28 alloy results in a reduction of the partial vibrational entropy of the Fe atoms but does not significantly change the partial vibrational entropy of the Ni atoms. Changes in the phonon densities of states with composition and chemical ordering are discussed and analyzed with a cluster expansion method.
High dose effects in neutron irradiated face-centered cubic metals
Garner, F.A.; Toloczko, M.B.
1993-06-01
During neutron irradiation, most face-centered cubic metals and alloys develop saturation or quasi-steady state microstructures. This, in turn, leads to saturation levels in mechanical properties and quasi-steady state rates of swelling and creep deformation. Swelling initially plays only a small role in determining these saturation states, but as swelling rises to higher levels, it exerts strong feedback on the microstructure and its response to environmental variables. The influence of swelling, either directly or indirectly via second order mechanisms, such as elemental segregation to void surfaces, eventually causes major changes, not only in irradiation creep and mechanical properties, but also on swelling itself. The feedback effects of swelling on irradiation creep are particularly complex and lead to problems in applying creep data derived from highly pressurized creep tubes to low stress situations, such as fuel pins in liquid metal reactors.
Bufford, Daniel C.; Wang, Morris; Liu, Yue; Lu, Lei
2016-04-01
The remarkable properties of nanotwinned (NT) face-centered-cubic (fcc) metals arise directly from twin boundaries, the structures of which can be initially determined by growth twinning during the deposition process. When we understand the synthesis process and its relation to the resulting microstructure, and ultimately to material properties, we realize how key it is to understanding and utilizing these materials. Furthermore, our article presents recent studies on electrodeposition and sputtering methods that produce a high density of nanoscale growth twins in fcc metals. Nanoscale growth twins tend to form spontaneously in monolithic and alloyed fcc metals with lower stacking-fault energies, whilemore » engineered approaches are necessary for fcc metals with higher stacking-fault energies. Finally, growth defects and other microstructural features that influence nanotwin behavior and stability are introduced here, and future challenges in fabricating NT materials are highlighted.« less
Anisotropy of tensile strength and fracture mode of perfect face-centered-cubic crystals
NASA Astrophysics Data System (ADS)
Wang, R. F.; Xu, J.; Qu, R. T.; Liu, Z. Q.; Zhang, Z. F.
2015-06-01
This study presents an effective method to calculate the ideal tensile strength of six face-centered-cubic (fcc) crystals (Cu, Au, Ni, Pt, Al, and Ir) along an arbitrary tensile direction by considering the coupling effect of normal stress and shear stress on a given crystallographic plane. Meanwhile, the fracture modes of the six crystals can also be derived from the competition between shear and cleavage fracture along different crystallographic planes. The results show that both the intrinsic factors (the ideal shear strength and cleavage strength of low-index planes) and the orientation may affect the tensile strength and fracture modes of ideal fcc crystals, which may give the reliable strength limit of fcc metals and well interpret the observed high strength in nano-scale mechanical experiments.
Rolling-induced Face Centered Cubic Titanium in Hexagonal Close Packed Titanium at Room Temperature
NASA Astrophysics Data System (ADS)
Wu, H. C.; Kumar, A.; Wang, J.; Bi, X. F.; Tomé, C. N.; Zhang, Z.; Mao, S. X.
2016-04-01
Combining transmission electron microscopes and density functional theory calculations, we report the nucleation and growth mechanisms of room temperature rolling induced face-centered cubic titanium (fcc-Ti) in polycrystalline hexagonal close packed titanium (hcp-Ti). Fcc-Ti and hcp-Ti take the orientation relation: <0001>hcp||<001>fcc and , different from the conventional one. The nucleation of fcc-Ti is accomplished via pure-shuffle mechanism with a minimum stable thickness of three atomic layers, and the growth via shear-shuffle mechanisms through gliding two-layer disconnections or pure-shuffle mechanisms through gliding four-layer disconnections. Such phase transformation offers an additional plastic deformation mode comparable to twinning.
Formation of recrystallization cube texture in high purity face-centered cubic metal sheets
Mao, W.
1999-10-01
An investigation on recrystallization textures in high purity face-centered cubic (fcc) aluminum, copper, and nickel indicated that the cube texture is a unique dominant final texture. In a macroview of rolling deformation, a balanced activation of four slip systems can result in certain stability of some substructure with cube orientation in the deformed matrix. In the stable substructure the dislocation density is very low, and the dislocation configuration is rather simple in comparison to other orientations so that the cube substructure can easily be transformed into cube recrystallization nuclei by a recovery process. A high orientation gradient and correspondingly high angle boundaries to the deformed matrix are usually expected around the cube nuclei, which, therefore, grow rapidly. After the primary recrystallization, the size of cube grains is much larger than the grains with other orientations, which will be expensed as the cube grains grow further, so that the cube texture can finally become a dominant texture component.
Anisotropic Size-Dependent Plasticity in Face-Centered Cubic Micropillars Under Torsion
NASA Astrophysics Data System (ADS)
Ryu, Ill; Cai, Wei; Nix, William D.; Gao, Huajian
2016-01-01
Three-dimensional dislocation dynamics (DD) simulations are performed to investigate the size-dependent plasticity in submicron face-centered cubic (FCC) micropillars under torsion. By using a previously implemented surface nucleation algorithm within DD, we show that the plastic behavior of FCC micropillars under torsion is strongly affected by the crystallographic orientation: In <110> oriented submicron pillars, coaxial dislocations nucleate and pile up near the axis, leading to homogeneous deformation along the pillars. In contrast, in <100> and <111> oriented pillars, heterogeneous plasticity has been observed due to the formation of localized dislocation arrays. As a result of the existence of a coaxial slip plane in <110> oriented pillars, stronger size-dependent plasticity is observed in this case compared with those in other orientations.
Atomic Mobilities in the Ag-Cu-Sn Face-Centered Cubic Lattice
NASA Astrophysics Data System (ADS)
Gierlotka, W.; Chen, Y. H.; Haque, M. A.; Rahman, M. A.
2012-12-01
Knowledge of atomic mobilities is necessary to predict the evolution of microstructure. The theoretical description of atomic mobilities is connected to the chemical potentials of the components in a given phase. A new thermodynamic description of the quaternary Ag-Cu-In-Sn system was recently published, and it is clear that a new description of the mobilities is also necessary. Based on the available literature and using Dictra software, optimization of the mobility parameters of silver, copper, and tin in the face-centered cubic phase was carried out. The results were compared with relevant data from literature as well as with our own experimental results. Good agreement between calculations and experiment was obtained.
Rolling-induced Face Centered Cubic Titanium in Hexagonal Close Packed Titanium at Room Temperature
Wu, H. C.; Kumar, A.; Wang, J.; Bi, X. F.; Tomé, C. N.; Zhang, Z.; Mao, S. X.
2016-01-01
Combining transmission electron microscopes and density functional theory calculations, we report the nucleation and growth mechanisms of room temperature rolling induced face-centered cubic titanium (fcc-Ti) in polycrystalline hexagonal close packed titanium (hcp-Ti). Fcc-Ti and hcp-Ti take the orientation relation: 〈0001〉hcp||〈001〉fcc and , different from the conventional one. The nucleation of fcc-Ti is accomplished via pure-shuffle mechanism with a minimum stable thickness of three atomic layers, and the growth via shear-shuffle mechanisms through gliding two-layer disconnections or pure-shuffle mechanisms through gliding four-layer disconnections. Such phase transformation offers an additional plastic deformation mode comparable to twinning. PMID:27067515
NASA Astrophysics Data System (ADS)
Kumar Ray, Atish
There exists considerable debate in the texture community about whether grain interactions are a necessary factor to explain the development of deformation textures in polycrystalline metals. Computer simulations indicate that grain interactions play a significant role, while experimental evidence shows that the material type and starting orientation are more important in the development of texture and microstructure. A balanced review of the literature on face-centered cubic metals shows that the opposing viewpoints have developed due to the lack of any complete experimental study which considers both the intrinsic (material type and starting orientation) and extrinsic (grain interaction) factors. In this study, a novel method was developed to assemble ideally orientated crystalline aggregates in 99.99% aluminum (Al) or copper (Cu) to experimentally evaluate the effect of grain interactions on room temperature deformation texture. Ideal orientations relevant to face-centered cubic rolling textures, Cube {100} <001>, Goss {110} <001>, Brass {110} <11¯2> and Copper {112} <111¯> were paired in different combinations and deformed by plane strain compression to moderate strain levels of 1.0 to 1.5. Orientation dependent mechanical behavior was distinguishable from that of the neighbor-influenced behavior. In interacting crystals the constraint on the rolling direction shear strains (gammaXY , gammaXZ) was found to be most critical to show the effect of interactions via the evolution of local microstructure and microtexture. Interacting crystals with increasing deformations were observed to gradually rotate towards the S-component, {123} <634>. Apart from the average lattice reorientations, the interacting crystals also developed strong long-range orientation gradients inside the bulk of the crystal, which were identified as accumulating misorientations across the deformation boundaries. Based on a statistical procedure using quaternions, the orientation and
NASA Astrophysics Data System (ADS)
Salcedo-Reyes, Juan Carlos
2012-01-01
A quantitative kinematic analysis, of the refraction properties of face-centered-cubic and hexagonal close-packed 250 nm-SiO2-based colloidal crystals, was performed using the plane wave expansion method. The angle-dependent effective refractive index, for different frequencies, was calculated taking into account the continuity of the tangential component of the wave vector across the interface and the energy conservation principle as well. The results demonstrate that the unusual optical properties, of the close packed SiO2-based colloidal crystals, depend strongly on the sphere-packing symmetry rather than from the material itself.
Numerical Modeling of the Stability of Face-Centered Cubic Metals with High Vacancy Concentration
Brian P. Somerday; M. I. Baskes
1998-12-01
The objective of this research is to assess the possibility of forming an atomically porous structure in a low-density metal, e.g., Al with vacancies up to 0.20/lattice site; and to examine the effects of hydrogen and vacancy concentration on the stability of an atomically porous structure that has been experimentally produced in nickel. The approach involves numerical modeling using the Embedded-Atom Method (EAM). High vacancy concentrations cause the Al lattice to disorder at 300K. In contrast, Ni retains the face-centered-cubic structure at 300K for vacancy concentrations up to 0.15 Vac/lattice site. Unexpectedly, the lattice with 0.15 Vac/lattice site is more stable than the lattice with 0.10 or 0.20 Vac/lattice site. The Ni systems with 0.10 and 0.15 Vac/lattice site exhibit domains consisting of uniform lattice rotations. The Ni lattice with 0.15 Vac/lattice site is more stable with an initial distribution of random vacancies compared to ordered vacancies. The equilibrium lattice structures of Ni a d Al containing vacancies and H are less ordered to structures with vacancies only at 300K.
Stacking fault energy of face-centered cubic metals: thermodynamic and ab initio approaches.
Li, Ruihuan; Lu, Song; Kim, Dongyoo; Schönecker, Stephan; Zhao, Jijun; Kwon, Se Kyun; Vitos, Levente
2016-10-01
The formation energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking fault energy (SFE) of fcc metals and alloys using thermodynamic calculations. It is often assumed that the contribution of the planar fault energy to the SFE has the same order of magnitude as the bulk part, and thus the lack of precise information about it can become the limiting factor in thermodynamic predictions. Here, we differentiate between the interfacial energy for the coherent fcc(1 1 1)/hcp(0 0 0 1) interface and the 'pseudo-interfacial energy' that enters the thermodynamic expression for the SFE. Using first-principles calculations, we determine the coherent and pseudo-interfacial energies for six elemental metals (Al, Ni, Cu, Ag, Pt, and Au) and three paramagnetic Fe-Cr-Ni alloys. Our results show that the two interfacial energies significantly differ from each other. We observe a strong chemistry dependence for both interfacial energies. The calculated pseudo-interfacial energies for the Fe-Cr-Ni steels agree well with the available literature data. We discuss the effects of strain on the description of planar faults via thermodynamic and ab initio approaches. PMID:27484794
Order-by-disorder effects in antiferromagnets on face-centered cubic lattice
NASA Astrophysics Data System (ADS)
Batalov, L. A.; Syromyatnikov, A. V.
2016-09-01
We discuss the role of quantum fluctuations in Heisenberg antiferromagnets on face-centered cubic lattice with small dipolar interaction in which the next-nearest-neighbor exchange coupling dominates over the nearest-neighbor one. It is well known that a collinear magnetic structure which contains (111) ferromagnetic planes arranged antiferromagnetically along one of the space diagonals of the cube is stabilized in this model via order-by-disorder mechanism. On the mean-field level, the dipolar interaction forces spin to lie within (111) planes. By considering 1 / S corrections to the ground state energy, we demonstrate that quantum fluctuations lead to an anisotropy within (111) planes favoring three equivalent directions for the staggered magnetization (e.g., [ 11 2 bar ], [ 1 2 bar 1 ], and [ 2 bar 11 ] directions for (111) plane). Such in-plane anisotropy was obtained experimentally in related materials MnO, α-MnS, α-MnSe, EuTe, and EuSe. We find that the order-by-disorder mechanism can contribute significantly to the value of the in-plane anisotropy in EuTe. Magnon spectrum is also derived in the first order in 1 / S.
Deformation twinning evolution from a single crystal in a face-centered-cubic ternary alloy
Zhang, Zhenyu; Yang, Song; Guo, Dongming; Yuan, Boya; Guo, Xiaoguang; Zhang, Bi; Huo, Yanxia
2015-01-01
Deformation twinning evolution from a single crystal is conducted by molecular dynamics simulations, to elucidate a twinned face-centered-cubic alloy in an experiment with hardness up to 100 times as that of single crystals, and with ductility simultaneously. Critical twinning stress of cadmium zinc telluride (CdZnTe or CZT) calculated is 1.38 GPa. All the twin boundaries are along the (11-1) orientation, except the one with the (-111) plane that supports the indentation, interpreting the unidirectional and boundary-free characteristics, confirmed in the experiment. Three twin thicknesses after unloading are 3.2, 3.5, and 16 nm, which is consistent with the experimentally repeated pattern of a lamellar twin with thickness larger than 12.7 nm, followed by one or several twins with thicknesses smaller than 12.7 nm. An inverse triangle of a twin combining with three twins generate a synergistic strengthening effect through the hardening and softening functions, illuminating the ultrahigh hardness demonstrated in the experiment. Twinning takes place in loading, and detwinning occurs in unloading, which expounds the high ductility observed in the experiment. PMID:26060979
Quantitative modeling of solute drag by vacancies in face-centered-cubic alloys
NASA Astrophysics Data System (ADS)
Garnier, Thomas; Trinkle, Dallas R.; Nastar, Maylise; Bellon, Pascal
2014-04-01
Transport coefficients, the elements of the so-called Onsager matrix, are essential quantities for modeling solid-state kinetics controlled by diffusion. In a face-centered-cubic structure, drag of solute atoms by vacancies can be caused by solute-vacancy binding at nearest neighbors. In order to investigate solute drag in alloys with interactions up to the third-nearest-neighbor sites, we extend an analytic method: the self-consistent mean field method. With this method, we calculate the Onsager matrix of model alloys to identify kinetic effects arising from individual and collective jump frequencies and assess the results on select cases using atomic kinetic Monte Carlo simulations. Using preexisting density functional theory data from various sources, we show that many impurities have low-temperature solute drag before changing to solute exchange at high temperatures. We evaluate the transition temperature for these alloys between these two regimes and compare the results with available experimental data. Some disagreement is found, which can be due both to experimental and numerical shortcomings. In order to guide diffusion calculations, the sensitivity of the Onsager matrix to the range of the kinetic correlation and to the input density functional theory data is studied.
Multiple Bragg diffraction at W point in the face centered cubic photonic crystals
NASA Astrophysics Data System (ADS)
Nair, Rajesh V.; Jagatap, Bhagawantrao N.
2015-01-01
We report the experimental observation of multiple Bragg diffraction that occurs when the tip of the incident wave vector lies on a line joining the L and W points in the Brillouin zone of a face-centered cubic (FCC) photonic crystal. The multiple Bragg diffraction is analyzed for photonic crystals with different lattice constants and refractive index contrasts. Angle-dependent reflectance spectroscopy indicates strong hybridization of diffraction resonances when the tip of the incident wave vector crosses the W point and the multiple Bragg diffraction is seen to be extended over an angular range of 8 deg around the W point. We also observe a new diffraction resonance in the short-wavelength region for wave vectors shifting toward the W point in the hexagonal facet of the FCC Brillouin zone. Each diffraction resonance is fitted using the Bragg's law for different planes in the FCC photonic crystal taking into account the internal angle between the planes. The diffraction resonances in the multiple Bragg diffraction regime are assigned to FCC crystal planes with Miller indices (111), (200), (1¯11), and (220). Our results have implications for diverse kinds of wave propagations in periodic structures and applications in light emission, sensing, and structural color pigments.
Deformation twinning evolution from a single crystal in a face-centered-cubic ternary alloy.
Zhang, Zhenyu; Yang, Song; Guo, Dongming; Yuan, Boya; Guo, Xiaoguang; Zhang, Bi; Huo, Yanxia
2015-01-01
Deformation twinning evolution from a single crystal is conducted by molecular dynamics simulations, to elucidate a twinned face-centered-cubic alloy in an experiment with hardness up to 100 times as that of single crystals, and with ductility simultaneously. Critical twinning stress of cadmium zinc telluride (CdZnTe or CZT) calculated is 1.38 GPa. All the twin boundaries are along the (11-1) orientation, except the one with the (-111) plane that supports the indentation, interpreting the unidirectional and boundary-free characteristics, confirmed in the experiment. Three twin thicknesses after unloading are 3.2, 3.5, and 16 nm, which is consistent with the experimentally repeated pattern of a lamellar twin with thickness larger than 12.7 nm, followed by one or several twins with thicknesses smaller than 12.7 nm. An inverse triangle of a twin combining with three twins generate a synergistic strengthening effect through the hardening and softening functions, illuminating the ultrahigh hardness demonstrated in the experiment. Twinning takes place in loading, and detwinning occurs in unloading, which expounds the high ductility observed in the experiment. PMID:26060979
Zhao, Ming; Figueroa-Cosme, Legna; Elnabawy, Ahmed O; Vara, Madeline; Yang, Xuan; Roling, Luke T; Chi, Miaofang; Mavrikakis, Manos; Xia, Younan
2016-08-10
Nanocages have received considerable attention in recent years for catalytic applications owing to their high utilization efficiency of atoms and well-defined facets. Here we report, for the first time, the synthesis of Ru cubic nanocages with ultrathin walls, in which the atoms are crystallized in a face-centered cubic (fcc) rather than hexagonal close-packed (hcp) structure. The key to the success of this synthesis is to ensure layer-by-layer deposition of Ru atoms on the surface of Pd cubic seeds by controlling the reaction temperature and the injection rate of a Ru(III) precursor. By selectively etching away the Pd from the Pd@Ru core-shell nanocubes, we obtain Ru nanocages with an average wall thickness of 1.1 nm or about six atomic layers. Most importantly, the Ru nanocages adopt an fcc crystal structure rather than the hcp structure observed in bulk Ru. The synthesis has been successfully applied to Pd cubic seeds with different edge lengths in the range of 6-18 nm, with smaller seeds being more favorable for the formation of Ru shells with a flat, smooth surface due to shorter distance for the surface diffusion of the Ru adatoms. Self-consistent density functional theory calculations indicate that these unique fcc-structured Ru nanocages might possess promising catalytic properties for ammonia synthesis compared to hcp Ru(0001), on the basis of strengthened binding of atomic N and substantially reduced activation energies for N2 dissociation, which is the rate-determining step for ammonia synthesis on hcp Ru catalysts. PMID:27458871
Wang-Landau sampling in face-centered-cubic hydrophobic-hydrophilic lattice model proteins
NASA Astrophysics Data System (ADS)
Liu, Jingfa; Song, Beibei; Yao, Yonglei; Xue, Yu; Liu, Wenjie; Liu, Zhaoxia
2014-10-01
Finding the global minimum-energy structure is one of the main problems of protein structure prediction. The face-centered-cubic (fcc) hydrophobic-hydrophilic (HP) lattice model can reach high approximation ratios of real protein structures, so the fcc lattice model is a good choice to predict the protein structures. The lacking of an effective global optimization method is the key obstacle in solving this problem. The Wang-Landau sampling method is especially useful for complex systems with a rough energy landscape and has been successfully applied to solving many optimization problems. We apply the improved Wang-Landau (IWL) sampling method, which incorporates the generation of an initial conformation based on the greedy strategy and the neighborhood strategy based on pull moves into the Wang-Landau sampling method to predict the protein structures on the fcc HP lattice model. Unlike conventional Monte Carlo simulations that generate a probability distribution at a given temperature, the Wang-Landau sampling method can estimate the density of states accurately via a random walk, which produces a flat histogram in energy space. We test 12 general benchmark instances on both two-dimensional and three-dimensional (3D) fcc HP lattice models. The lowest energies by the IWL sampling method are as good as or better than those of other methods in the literature for all instances. We then test five sets of larger-scale instances, denoted by the S, R, F90, F180, and CASP target instances on the 3D fcc HP lattice model. The numerical results show that our algorithm performs better than the other five methods in the literature on both the lowest energies and the average lowest energies in all runs. The IWL sampling method turns out to be a powerful tool to study the structure prediction of the fcc HP lattice model proteins.
NASA Astrophysics Data System (ADS)
Xiao, X.; Liang, J. H.; Chen, B. L.; Li, J. X.; Ma, D. H.; Ding, Z.; Wu, Y. Z.
2015-07-01
Face-centered-cubic cobalt films are epitaxially grown on insulating LaAlO3(001) substrates by molecular beam epitaxy. Transport measurements are conducted in different current directions relative to the crystal axes. We find that the temperature dependent anisotropic magnetoresistance ratio strongly depends on the current direction. However, the anomalous Hall effect shows isotropic behavior independent of the current direction. Our results demonstrate the interplay between the current direction and the crystalline lattice in single-crystalline ferromagnetic films. A phenomenological analysis is presented to interpret the experimental data.
Xiao, X.; Liang, J. H.; Chen, B. L.; Li, J. X.; Ding, Z.; Wu, Y. Z.; Ma, D. H.
2015-07-28
Face-centered-cubic cobalt films are epitaxially grown on insulating LaAlO{sub 3}(001) substrates by molecular beam epitaxy. Transport measurements are conducted in different current directions relative to the crystal axes. We find that the temperature dependent anisotropic magnetoresistance ratio strongly depends on the current direction. However, the anomalous Hall effect shows isotropic behavior independent of the current direction. Our results demonstrate the interplay between the current direction and the crystalline lattice in single-crystalline ferromagnetic films. A phenomenological analysis is presented to interpret the experimental data.
Low-temperature thermostatics of face-centered-cubic metallic hydrogen
NASA Technical Reports Server (NTRS)
Caron, L. G.
1974-01-01
The thermostatic properties of a high-symmetry phase of metallic hydrogen with atomic sphere radius between 0.1 and 1.5 bohr are studied, with special emphasis accorded to electronic screening and quantum proton motion. The electron-proton and proton-proton interactions receive a perturbation treatment based on the Singwi dielectric function, while the proton motion is handled by self-consistent harmonic approximation. Quantum behavior is found to be less pronounced than expected, and nuclear magnetism is absent. The phonon spectrum is, however, affected by screening and large proton motion. The zero-point vibrational energy and the superconducting critical temperature are below previous estimates. The crystalline-defect formation energies are a few times the Debye energy, which implies that defects contribute significantly to melting at the lower particle densities.
Bao, Luyao; Hu, Haibao; Wen, Jun; Sepri, Paavo; Luo, Kai
2016-01-01
A liquid in the vicinity of a solid-liquid interface (SLI) may exhibit complex structures. In this study, we used molecular dynamics simulations demonstrating for the first time that the liquid adjacent to the SLI can have a two-level structure in some cases: a major structure and a minor structure. Through a time-averaging process of molecular motions, we identified the type of the liquid structure by calculating positions of the maximum liquid density in three spatial dimensions, and these positions were found to distribute in many dispersed zones (called high-density zones (HDZs)). The major structure appears throughout the SLI, while the minor structure only occurs significantly within the third layer. Instead of the previously reported body-centered cubic (BCC) or face-centered-cubic (FCC) types, the major structure was found to show a body-centered tetragonal (BCT) type. The adjacent HDZs are connected by specific junctions, demonstrating that atoms diffuse along some particular high probability paths from one HDZ to another. By considering the three-dimensional liquid density distribution from the continuum point of view, more complete details of the structure and diffusive behavior of liquids in the SLI are also possible to be revealed. PMID:27430188
NASA Astrophysics Data System (ADS)
Bao, Luyao; Hu, Haibao; Wen, Jun; Sepri, Paavo; Luo, Kai
2016-07-01
A liquid in the vicinity of a solid-liquid interface (SLI) may exhibit complex structures. In this study, we used molecular dynamics simulations demonstrating for the first time that the liquid adjacent to the SLI can have a two-level structure in some cases: a major structure and a minor structure. Through a time-averaging process of molecular motions, we identified the type of the liquid structure by calculating positions of the maximum liquid density in three spatial dimensions, and these positions were found to distribute in many dispersed zones (called high-density zones (HDZs)). The major structure appears throughout the SLI, while the minor structure only occurs significantly within the third layer. Instead of the previously reported body-centered cubic (BCC) or face-centered-cubic (FCC) types, the major structure was found to show a body-centered tetragonal (BCT) type. The adjacent HDZs are connected by specific junctions, demonstrating that atoms diffuse along some particular high probability paths from one HDZ to another. By considering the three-dimensional liquid density distribution from the continuum point of view, more complete details of the structure and diffusive behavior of liquids in the SLI are also possible to be revealed.
Effects of stacking fault energy on defect formation process in face-centered cubic metals
NASA Astrophysics Data System (ADS)
Okita, Taira; Yang, Yingjuan; Hirabayashi, Junichi; Itakura, Mitsuhiro; Suzuki, Katsuyuki
2016-05-01
To elucidate the effect of stacking fault energies (SFEs) on defect formation by the collision cascade process for face-centred cubic metals, we used six sets of interatomic potentials with different SFEs while keeping the other properties almost identical. Molecular dynamic simulations of the collision cascade were carried out using these potentials with primary knock-on atom energies (EPKA) of 10 and 20 keV at 100 K. Neither the number of residual defects nor the size distributions for both self-interstitial atom (SIA) type and vacancy type clusters were affected by the difference in the SFE. In the case of EPKA = 20 keV, the ratio of glissile SIA clusters increased as the SFE decreased, which was not expected by a prediction based on the classical dislocation theory. The trend did not change after annealing at 1100 K for 100 ps. For vacancy clusters, few stacking fault tetrahedrons (SFTs) formed before the annealing. However, lower SFEs tended to increase the SFT fraction after the annealing, where large vacancy clusters formed at considerable densities. The findings of this study can be used to characterise the defect formation process in low SFE metals such as austenitic stainless steels.
NASA Astrophysics Data System (ADS)
Kudryavtsev, Y. V.; Perekos, A. E.; Uvarov, N. V.; Kolchiba, M. R.; Synoradzki, K.; Dubowik, J.
2016-05-01
Magnetic and transport properties of near stoichiometric metastable FexMnyGaz alloys (46 ≤ x ≤ 52, 17 ≤ y ≤ 25, 26 ≤ z ≤ 30) with face-centered cubic (FCC), body-centered cubic (BCC), and two-phase (FCC + BCC) structures are investigated. The experimental results are analyzed in terms of first-principles calculations of stoichiometric Fe2MnGa alloy with the L21, L12, and the tetragonally distorted L21 structural orderings. It is shown that the pure BCC and FCC phases have distinct magnetic and transport properties. Two-phase Fe2MnGa alloys have magnetic and transport properties typical of the mixed BCC and FCC phases. Among the investigated alloys, Fe46Mn24Ga30 has a martensitic transformation accompanied with significant changes of its magnetic and transport properties.
Extended Peierls-Nabarro model for cross slip in face centered cubic metals
NASA Astrophysics Data System (ADS)
Ramirez, Benjamin R.
dislocation configurations are approximated by a network of cubic parametric splines with tangent continuity. The first approximation of cross-slip activation energy for zero stress was performed by using a non-singular dislocation theory with a core parameter determined from an atomistic method (Peierls-Nabarro approach). An energy barrier of 1.9 [eV] is determined for Cu at the saddle point, which is in good agreement with values determined by other models, including those of Puschl and Escaig. Furthermore, a refinement of the proposed model is developed by representing the Shockley partials with fractional dislocations and adding lattice restoring forces to the dislocations, which are determined from ab-initio methods. Thus, this calculation gives a value of 1.43 [eV] for the cross-slip activation energy, which is in excellent agreement with the activation energy determined from the Bonneville-Escaig experimental value of 1.11 +/- 0.37 [eV]. Finally, a cross-slip scenario with pile-up dislocations on the glide plane is simulated to show the versatility of the proposed model for more realistic dislocation arrangements.
NASA Astrophysics Data System (ADS)
Liu, Jingfa; Song, Beibei; Liu, Zhaoxia; Huang, Weibo; Sun, Yuanyuan; Liu, Wenjie
2013-11-01
Protein structure prediction (PSP) is a classical NP-hard problem in computational biology. The energy-landscape paving (ELP) method is a class of heuristic global optimization algorithm, and has been successfully applied to solving many optimization problems with complex energy landscapes in the continuous space. By putting forward a new update mechanism of the histogram function in ELP and incorporating the generation of initial conformation based on the greedy strategy and the neighborhood search strategy based on pull moves into ELP, an improved energy-landscape paving (ELP+) method is put forward. Twelve general benchmark instances are first tested on both two-dimensional and three-dimensional (3D) face-centered-cubic (fcc) hydrophobic-hydrophilic (HP) lattice models. The lowest energies by ELP+ are as good as or better than those of other methods in the literature for all instances. Then, five sets of larger-scale instances, denoted by S, R, F90, F180, and CASP target instances on the 3D FCC HP lattice model are tested. The proposed algorithm finds lower energies than those by the five other methods in literature. Not unexpectedly, this is particularly pronounced for the longer sequences considered. Computational results show that ELP+ is an effective method for PSP on the fcc HP lattice model.
Lattice Green functions: the d-dimensional face-centered cubic lattice, d = 8, 9, 10, 11, 12
NASA Astrophysics Data System (ADS)
Hassani, S.; Koutschan, Ch; Maillard, J.-M.; Zenine, N.
2016-04-01
We previously reported on a recursive method to generate the expansion of the lattice Green function (LGF) of the d-dimensional face-centered cubic lattice (fcc). The method was used to generate many coefficients for d=7 and the corresponding linear differential equation has been obtained. In this paper, we show the strength and the limit of the method by producing the series and the corresponding linear differential equations for d=8,9,10,11,12. The differential Galois groups of these linear differential equations are shown to be symplectic for d=8,10,12 and orthogonal for d=9,11. The recursion relation naturally provides a two-dimensional array {t}d(n,j) where only the coefficients {t}d(n,0) correspond to the coefficients of the LGF of the d-dimensional fcc. The coefficients {t}d(n,j) are associated to D-finite bivariate series annihilated by linear partial differential equations that we analyze. Dedicated to Guttmann, for his 70th birthday.
Magnetic cluster expansion model for random and ordered magnetic face-centered cubic Fe-Ni-Cr alloys
NASA Astrophysics Data System (ADS)
Lavrentiev, M. Yu.; Wróbel, J. S.; Nguyen-Manh, D.; Dudarev, S. L.; Ganchenkova, M. G.
2016-07-01
A Magnetic Cluster Expansion model for ternary face-centered cubic Fe-Ni-Cr alloys has been developed, using DFT data spanning binary and ternary alloy configurations. Using this Magnetic Cluster Expansion model Hamiltonian, we perform Monte Carlo simulations and explore magnetic structures of alloys over the entire range of compositions, considering both random and ordered alloy structures. In random alloys, the removal of magnetic collinearity constraint reduces the total magnetic moment but does not affect the predicted range of compositions where the alloys adopt low-temperature ferromagnetic configurations. During alloying of ordered fcc Fe-Ni compounds with Cr, chromium atoms tend to replace nickel rather than iron atoms. Replacement of Ni by Cr in ordered alloys with high iron content increases the Curie temperature of the alloys. This can be explained by strong antiferromagnetic Fe-Cr coupling, similar to that found in bcc Fe-Cr solutions, where the Curie temperature increase, predicted by simulations as a function of Cr concentration, is confirmed by experimental observations. In random alloys, both magnetization and the Curie temperature decrease abruptly with increasing chromium content, in agreement with experiment.
NASA Astrophysics Data System (ADS)
Kimizuka, Hajime; Ogata, Shigenobu
We investigated the H diffusivity in face-centered cubic Pd and Al by performing path-integral molecular dynamics (PIMD) modeling in the framework of density functional theory (DFT); in our calculations, we took nuclear quantum effects into consideration. The DFT results showed that the H-migration barriers (Em) in Pd and Al exhibited similar values (approximately 0.16 eV), while the H atoms were stable at octahedral (O) sites for Pd and at tetrahedral (T) sites for Al. The PIMD-based free-energy profiles for H migration between the O-site and T-site were evaluated using the thermodynamic integration of the centroid forces at 150-600 K. We confirmed that the quantum effects significantly affected the Em and the difference between the energies of the H atom at the O-site and the T-site (EO - T); The Em and EO - T values in Pd at 300 K increased by 32% and 98%, respectively, relative to the classical limit. On the other hand, the Em and ET - O (i.e., -EO - T) values in Al at 300 K decreased by 3% and 41%, respectively. This suggested that the quantum nature of H nuclei was essential for understanding the H-diffusion kinetics in these metals even above ambient temperature.
NASA Astrophysics Data System (ADS)
Mirkhani, Hamidreza; Joshi, Shailendra P.
2014-08-01
Nanotwinned (nt) metals are an important subset of nanostructured materials because they exhibit impressive strength and ductility. Several recent investigations on nt face-centered-cubic (FCC) metals indicate that their macroscopic responses emerge from complex microscopic mechanisms that are dominated by dislocation-TB interactions. Under applied stimulus, nt microstructures evolve through migration of twin boundaries (TBs) that may have implications on the material strength and stability. This work focuses on modeling TB migration within finite element framework in an explicit manner and studying its effects on the micromechanics of twinned FCC metals under quasi-static loading conditions. The theoretical setting is developed using three-dimensional single crystal plasticity as a basis wherein the plastic slip on the {111}<1bar10> slip systems in an FCC crystal structure is modeled as visco-plastic behavior. Owing to their governing role, twins are modeled as discrete lamellas with full crystallographic anisotropy. To model TB migration, an additional visco-plastic slip-law for twinning partial systems ({111}<112bar>) based on the nucleation and motion of twin partial dislocations is introduced. This size-dependent constitutive law is presumed to prevail in the vicinity of the TB and naturally facilitates TB migration when combined with a twinning condition that is based on the accrual of the necessary shear strain. The constitutive development is implemented within a finite element framework through a User Material (UMAT) facility within ABAQUS/STANDARD®. Detailed micromechanics simulations on model microstructures involving single-grained and polycrystalline topologies are presented.
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.
NASA Astrophysics Data System (ADS)
Somasi, Sweta; Khomami, Bamin; Lovett, Ronald
2000-09-01
On a thermodynamic path proposed by Lutsko, Wolf, and Yip, a solid is transformed at fixed density into an ideal gas. The accuracy of molecular dynamics simulation results for the free energy of solids using this path is compromised by the presence of a singularity on the path and by the nonergodic behavior of the ideal gas. We present calculations of the third law free energies of the face-centered-cubic (fcc) and hexagonal-close-packed (hcp) solids of argon (modeled as a Lennard-Jones system) to illustrate how the singularity and the nonergodic dynamics introduce errors. Strategies for removing the singularity and the nonergodic dynamics are presented. Finally, an analytic expansion around the ideal state is developed to provide an alternate route to the free energy of those states for which simulation estimates give large statistical uncertainties. The quantitative errors in these new approaches to the simulation of the free energy of a solid are given.
Gloss, Jonas; Shah Zaman, Sameena; Jonner, Jakub; Novotny, Zbynek; Schmid, Michael; Varga, Peter; Urbánek, Michal
2013-12-23
Metastable face-centered cubic (fcc) Fe/Cu(100) thin films are good candidates for ion-beam magnetic patterning due to their magnetic transformation upon ion-beam irradiation. However, pure fcc Fe films undergo spontaneous transformation when their thickness exceeds 10 ML. This limit can be extended to approximately 22 ML by deposition of Fe at increased CO background pressures. We show that much thicker films can be grown by alloying with Ni for stabilizing the fcc γ phase. The amount of Ni necessary to stabilize nonmagnetic, transformable fcc Fe films in dependence on the residual background pressure during the deposition is determined and a phase diagram revealing the transformable region is presented.
Wu, Zhenggang; Gao, Y. F.; Bei, Hongbin
2015-07-25
To understand the fundamental deformation mechanisms of compositionally complex alloys, single crystals of a multi-component equiatomic FeNiCoCr alloy with face-centered cubic (FCC) structure were grown for mechanical studies. Similarly to typical FCC pure metals, slip trace analyses indicate that dislocation slips take place on (1 1 1) planes along [11¯0] directions. The critical resolved shear stress (CRSS) obeys the Schmid law at both 77 and 293 K, and tension–compression asymmetry is not observed. Although this material slips in a normal FCC manner both at 293 and 77 K, compared to typical FCC metals the CRSS’s strong temperature dependence is abnormal.
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.
NASA Astrophysics Data System (ADS)
Zhu, Linli; Qu, Shaoxing; Guo, Xiang; Lu, Jian
2015-03-01
Hierarchical twin lamellae in polycrystalline face-centered cubic (fcc) metals possess a possibility to achieve higher strength with keeping an acceptable elongation. The present work is concerned with the analysis of twin spacing and grain size-dependent plastic performance in hierarchically nanotwinned fcc metals using a generalized strain-gradient plasticity model. The dislocation density-based physical model for constitutive description of nanotwinned fcc metals is expanded for the hierarchical structures of nanotwins. The strengthening mechanism and the failure behavior in these hierarchical nanostructures are studied to evaluate the strength and ductility. Moreover, the transition twin spacing between the strengthening and softening is obtained in different order of twin lamellae. A dislocation-based model on nucleating deformation twins is presented to predict the critical twin spacing in the lowest twin lamellae for generating the subordinate twin lamellae. Our simulation results demonstrate that the existence of the hierarchical nanotwins gives rise to a significant enhancement in the strength, and the resulting global flow stresses are sensitive to the twin spacings of the hierarchical twin lamellae and the grain size. Two softening stages are observed with variation of twin spacing, and the relevant transition twin spacing depends on the microstructural size in hierarchically nanotwinned metals. We further find that the predicted failure strain decreases with decreasing the twin spacing, which is quite different from the case of the individually nanotwinned fcc metals. The critical twin spacing for generating subordinate twins also depends on the twin spacing of superordinate twin lamellae and the grain size. These findings suggest that the high yield strength and good ductility can be achieved by optimizing the grain size and the twin spacings in the hierarchical twins.
NASA Astrophysics Data System (ADS)
Cheng, Wei-Chun; Jou, Shyan-Kay; Chiu, Chuei-Fu
2005-07-01
We discovered a new silicon nitride with cubic symmetry formed in the silicon at the Ta/Si interface of the TaN/Ta/Si(100) thin film system when the silicon wafer was annealed at 500 or 600°C. The cubic silicon nitride grew into the silicon crystal in the shape of an inverse pyramid after the annealing process. The boundary planes of the inverse pyramid were the \\{111\\} planes of the silicon crystal. The orientation relationship between the silicon nitride and silicon crystal is cubic to cubic. The lattice constant of the new silicon nitride is a=0.5548 nm and is about 2.2% larger than that of the silicon crystal.
NASA Astrophysics Data System (ADS)
Proust, Gwénaëlle; Kalidindi, Surya R.
2006-08-01
Microstructure-sensitive design (MSD) is a novel mathematical framework that facilitates a rigorous consideration of the material microstructure as a continuous design variable in the engineering design enterprise [Adams, B.L., Henrie, A., Henrie, B., Lyon, M., Kalidindi, S.R., Garmestani, H., 2001. Microstructure-sensitive design of a compliant beam. J. Mech. Phys. Solids 49(8), 1639-1663; Adams, B.L., Lyon, M., Henrie, B., 2004. Microstructures by design: linear problems in elastic-plastic design. Int. J. Plasticity 20(8-9), 1577-1602; Kalidindi, S.R., Houskamp, J.R., Lyons, M., Adams, B.L., 2004. Microstructure sensitive design of an orthotropic plate subjected to tensile load. Int. J. Plasticity 20(8-9), 1561-1575]. MSD employs spectral representations of the local state distribution functions in describing the microstructure quantitatively, and these in turn enable development of invertible linkages between microstructure and effective properties using established homogenization (composite) theories. As a natural extension of the recent publications in MSD, we provide in this paper a detailed account of the methods that can be readily used by mechanical designers to construct first-order elastic-plastic property closures. The main focus in this paper is on the crystallographic texture (also called Orientation Distribution Function or ODF) as the main microstructural parameter controlling the elastic and yield properties of cubic (fcc and bcc) polycrystalline metals. The following specific advances are described in this paper: (i) derivation of rigorous first-order bounds for the off-diagonal terms of the effective elastic stiffness tensor and their incorporation in the MSD framework, (ii) delineation of the union of the property closures corresponding to both the upper and lower bound theories resulting in comprehensive first-order closures, (iii) development of generalized and readily usable expressions for effective anisotropic elastic-plastic properties
NASA Technical Reports Server (NTRS)
Tatarenko, Valentine A.; Tsysman, Constantin L.; Oltarzhevskaya, Yelena T.
1995-01-01
The calculations in a majority of previous works for the fulleride (AqC-60) crystals were performed within the framework of the rigid-lattice model, neglecting the distortion relaxation of the host fullerene (C-60) crystal caused by the interstitial alkali-metal (A) cations. However, an each cation is a source of a static distortion field, and the resulting field is a superposition of such fields generated by all cations. This is a reason why the host-crystal distortions depend on the A-cations configurations, i.e. on a type of a spatial bulk distribution of interstitial cations. The given paper seeks to find a functional relation between the amplitudes of the doping-induced structure-distortion waves and of static concentration ones. A semiphenomenological model is constructed here within the scope of statistical-thermodynamic treatment and using the lattice-statistics simulation method(*). In this model the effects due to the presence of q solute A cations over available interstices (per unit cell) on the static inherent reorientation and/or displacements of the solvent molecules from the 'average-lattice' sites' as well as on the lattice parameter a of a elastically-anysotropic 'cubic' C-60 crystal are taken into account.
Tatarenko, V.A.; Tsysman, C.L.; Oltarzhevskaya, Y.T.
1994-12-31
The calculations in a majority of previous works for the fulleride (AqC{sub 60}) crystals were performed within the framework of the rigid-lattice model, neglecting the distoration relaxation of the host fullerene (C{sub 60}) crystal caused by the interstitial alkali-metal (A) cations. However, an each cation is a source of a static distoration field, and the resulting field is a superposition of such fields generated by all cations. This is a reason why the host-crystal distortions depend on the A-cations configurations, i.e. on a type of a spatial bulk distribution of interstitial cations. This paper seeks to find a functional relation between the amplitudes of the doping-induced structure-distortion waves and of statistic concentration ones. A semiphenomenological model is constructed here within the scope of statistical-thermodynamic treatment and using the lattice-statistics simulation method. In this model the effects due to the presence of q solute A cations over available interstices (per unit cell) on the statistic inherent reorientation and/or displacements of the solvent molecules from the average-lattice sites as well as on the lattice parameter a of the elastically-anysotropic cubic C{sub 60} crystal are taken into account.
Li, Yingyu; Yi, Jinhui; Kruk, Michal
2015-09-01
The unit-cell size and pore diameter as functions of temperature are investigated in the syntheses of FDU-12 silicas with face-centered cubic structure templated by Pluronic (PEO-PPO-PEO) block copolymer micelles swollen by toluene. The temperature range in which the unit-cell size and pore size strongly increase as temperature decreases is correlated with the critical micelle temperature (CMT) of the surfactant. While Pluronic F127 affords a wide range of unit-cell parameters (28-51 nm) and pore diameters (16-32 nm), it renders moderately enlarged pore sizes at 25 °C. The use of Pluronic F108 with higher CMT affords FDU-12 with very large unit-cell size (∼49 nm) and large pore diameter (27 nm) at 23 °C. Large unit-cell size (40-41 nm) and pore size (22 nm) were obtained even at 25 °C. The application of Pluronics F87 and F88 with much smaller molecular weights and higher CMTs also allows one to synthesize FDU-12 with quite large unit-cell parameters and pore sizes at room temperature. The present work demonstrates that one can judiciously select Pluronic surfactants with appropriate CMT to shift the temperature range in which the pore diameter is readily tunable. PMID:26178137
NASA Astrophysics Data System (ADS)
Bray, D. W.; Howe, J. M.
1996-11-01
The face-centered cubic/hexagonal close-packed (fcc/hcp) martensite phase transformation in a Co-31.8 wt pct Ni alloy was studied by high-resolution transmission electron microscopy (HRTEM). The HRTEM was used to study the structure and properties of intersections between martensite plates and other defects observed in the alloy such as stacking fault tetrahedra (SFT) and Z-type defects. The HRTEM was also used to attempt to determine if various proposed mechanisms for the fcc/hcp martensite transformation were operating. There is evidence to suggest that the reflection mechanism proposed by Bollmann and the dipole mechanism proposed by Hirth are active in the fcc/hcp martensitic transformation, although the evidence is not completely certain in either case. Growth of the hcp phase by a four- or six-plane mechanism as proposed by Mahajan et al. is possible in theory but was not observed in this study. Transformation by previously proposed pole mechanisms was also not observed in this study, although evidence for a new type of pole mechanism was found. The formation of SFT along the fcc/hcp martensite interface was observed to occur by the cross-slip of Shockley partial dislocations out of the fcc/hcp interface onto conjugate fcc matrix planes, followed by further cross-slip to form the SFT, as previously observed for grain boundaries in fcc alloys.
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.
Numerical simulation of a shear-thinning fluid through packed spheres
NASA Astrophysics Data System (ADS)
Liu, Hai Long; Moon, Jong Sin; Hwang, Wook Ryol
2012-12-01
Flow behaviors of a non-Newtonian fluid in spherical microstructures have been studied by a direct numerical simulation. A shear-thinning (power-law) fluid through both regular and randomly packed spheres has been numerically investigated in a representative unit cell with the tri-periodic boundary condition, employing a rigorous three-dimensional finite-element scheme combined with fictitious-domain mortar-element methods. The present scheme has been validated for the classical spherical packing problems with literatures. The flow mobility of regular packing structures, including simple cubic (SC), body-centered cubic (BCC), face-centered cubic (FCC), as well as randomly packed spheres, has been investigated quantitatively by considering the amount of shear-thinning, the pressure gradient and the porosity as parameters. Furthermore, the mechanism leading to the main flow path in a highly shear-thinning fluid through randomly packed spheres has been discussed.
NASA Astrophysics Data System (ADS)
Cardenas, M. Bayani
2009-12-01
The transition from non-Fickian to Fickian macroscale transport is explicitly demonstrated for an increasing array of three-dimensional pores with vortices in between a lattice of cubic packed spheres by microscale finite element Navier-Stokes flow and transport simulations. Solute residence time distribution begins with a power law for one pore but gradually and eventually transforms to an exponential distribution typical of classic dispersive transport after about ten pores. Parameter fitting of an analytical solution to the 1-D advection-dispersion equation using the simulated breakthrough curves leads to fitted pore velocities within 1% of actual values and an asymptotic fitted dispersion coefficient after a few pores. Therefore, after dozens of pores, bulk transport can be described by the advection-dispersion equation. Persistent vortices in similarly structured porous media subjected to similar grain-scale Reynolds and Peclet numbers may have minimal contribution to anomalous transport observed at larger scales.
Hynninen, Antti-Pekka; Dijkstra, Marjolein
2005-04-01
Phase diagrams of hard and soft spheres with a fixed dipole moment are determined by calculating the Helmholtz free energy using simulations. The pair potential is given by a dipole-dipole interaction plus a hard-core and a repulsive Yukawa potential for soft spheres. Our system models colloids in an external electric or magnetic field, with hard spheres corresponding to uncharged and soft spheres to charged colloids. The phase diagram of dipolar hard spheres shows fluid, face-centered-cubic (fcc), hexagonal-close-packed (hcp), and body-centered-tetragonal (bct) phases. The phase diagram of dipolar soft spheres exhibits, in addition to the above mentioned phases, a body-centered-orthorhombic (bco) phase, and it agrees well with the experimental phase diagram [Nature (London) 421, 513 (2003)]. Our results show that bulk hcp, bct, and bco crystals can be realized experimentally by applying an external field. PMID:15904046
Torija, Maria A.; Choi, Soo-Hyung; Lodge, Timothy P.; Bates, Frank S.
2013-03-07
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{sub 30}H{sub 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.
ERIC Educational Resources Information Center
Hawkins, John A.; Rittenhouse, Jeffrey L.; Soper, Linda M.; Rittenhouse, Robert C.
2008-01-01
One of the most important crystal structures adopted by metals is characterized by the "abcabc"...stacking of close-packed layers. This structure is commonly referred to in textbooks as the cubic close-packed (ccp) or face-centered cubic (fcc) structure, since the entire lattice can be generated by replication of a face-centered cubic unit cell…
Adlakha, I; Solanki, K N
2015-01-01
We present a systematic study to elucidate the role of triple junctions (TJs) and their constituent grain boundaries on the structural stability of nanocrystalline materials. Using atomistic simulations along with the nudge elastic band calculations, we explored the atomic structural and thermodynamic properties of TJs in three different fcc materials. We found that the magnitude of excess energy at a TJ was directly related to the atomic density of the metal. Further, the vacancy binding and migration energetics in the vicinity of the TJ were examined as they play a crucial role in the structural stability of NC materials. The resolved line tension which takes into account the stress buildup at the TJ was found to be a good measure in predicting the vacancy binding tendency near the TJ. The activation energy for vacancy migration along the TJ was directly correlated with the measured excess energy. Finally, we show that the resistance for vacancy diffusion increased for TJs with larger excess stored energy and the defect mobility at some TJs is slower than their constituent GBs. Hence, our results have general implications on the diffusional process in NC materials and provide new insight into stabilizing NC materials with tailored TJs. PMID:25732834
NASA Astrophysics Data System (ADS)
Adlakha, I.; Solanki, K. N.
2015-03-01
We present a systematic study to elucidate the role of triple junctions (TJs) and their constituent grain boundaries on the structural stability of nanocrystalline materials. Using atomistic simulations along with the nudge elastic band calculations, we explored the atomic structural and thermodynamic properties of TJs in three different fcc materials. We found that the magnitude of excess energy at a TJ was directly related to the atomic density of the metal. Further, the vacancy binding and migration energetics in the vicinity of the TJ were examined as they play a crucial role in the structural stability of NC materials. The resolved line tension which takes into account the stress buildup at the TJ was found to be a good measure in predicting the vacancy binding tendency near the TJ. The activation energy for vacancy migration along the TJ was directly correlated with the measured excess energy. Finally, we show that the resistance for vacancy diffusion increased for TJs with larger excess stored energy and the defect mobility at some TJs is slower than their constituent GBs. Hence, our results have general implications on the diffusional process in NC materials and provide new insight into stabilizing NC materials with tailored TJs.
Thermal plasma processed ferro-magnetically ordered face-centered cubic iron at room temperature
NASA Astrophysics Data System (ADS)
Raut, Suyog A.; Kanhe, Nilesh S.; Bhoraskar, S. V.; Das, A. K.; Mathe, V. L.
2014-10-01
Here, we report tailor made phase of iron nanoparticles using homogeneous gas phase condensation process via thermal plasma route. It was observed that crystal lattice of nano-crystalline iron changes as a function of operating parameters of the plasma reactor. In the present investigation iron nanoparticles have been synthesized in presence of argon at operating pressures of 125-1000 Torr and fixed plasma input DC power of 6 kW. It was possible to obtain pure fcc, pure bcc as well as the mixed phases for iron nanoparticles in powder form as a function of operating pressure. The as synthesized product was characterized for understanding the structural and magnetic properties by using X-ray diffraction, vibrating sample magnetometer, and Mössbauer spectroscopy. The data reveal that fcc phase is ferromagnetically ordered with high spin state, which is unusual whereas bcc phase is found to be ferromagnetic as usual. Finally, the structural and magnetic properties are co-related.
Molecular dynamic simulation for nanometric cutting of single-crystal face-centered cubic metals
2014-01-01
In this work, molecular dynamics simulations are performed to investigate the influence of material properties on the nanometric cutting of single crystal copper and aluminum with a diamond cutting tool. The atomic interactions in the two metallic materials are modeled by two sets of embedded atom method (EAM) potential parameters. Simulation results show that although the plastic deformation of the two materials is achieved by dislocation activities, the deformation behavior and related physical phenomena, such as the machining forces, machined surface quality, and chip morphology, are significantly different for different materials. Furthermore, the influence of material properties on the nanometric cutting has a strong dependence on the operating temperature. PMID:25426007
Adlakha, I.; Solanki, K. N.
2015-01-01
We present a systematic study to elucidate the role of triple junctions (TJs) and their constituent grain boundaries on the structural stability of nanocrystalline materials. Using atomistic simulations along with the nudge elastic band calculations, we explored the atomic structural and thermodynamic properties of TJs in three different fcc materials. We found that the magnitude of excess energy at a TJ was directly related to the atomic density of the metal. Further, the vacancy binding and migration energetics in the vicinity of the TJ were examined as they play a crucial role in the structural stability of NC materials. The resolved line tension which takes into account the stress buildup at the TJ was found to be a good measure in predicting the vacancy binding tendency near the TJ. The activation energy for vacancy migration along the TJ was directly correlated with the measured excess energy. Finally, we show that the resistance for vacancy diffusion increased for TJs with larger excess stored energy and the defect mobility at some TJs is slower than their constituent GBs. Hence, our results have general implications on the diffusional process in NC materials and provide new insight into stabilizing NC materials with tailored TJs. PMID:25732834
Molecular dynamic simulation for nanometric cutting of single-crystal face-centered cubic metals.
Huang, Yanhua; Zong, Wenjun
2014-01-01
In this work, molecular dynamics simulations are performed to investigate the influence of material properties on the nanometric cutting of single crystal copper and aluminum with a diamond cutting tool. The atomic interactions in the two metallic materials are modeled by two sets of embedded atom method (EAM) potential parameters. Simulation results show that although the plastic deformation of the two materials is achieved by dislocation activities, the deformation behavior and related physical phenomena, such as the machining forces, machined surface quality, and chip morphology, are significantly different for different materials. Furthermore, the influence of material properties on the nanometric cutting has a strong dependence on the operating temperature. PMID:25426007
In situ observation of deformation processes in nanocrystalline face-centered cubic metals
Kobler, Aaron; Brandl, Christian; Hahn, Horst
2016-01-01
Summary The atomistic mechanisms active during plastic deformation of nanocrystalline metals are still a subject of controversy. The recently developed approach of combining automated crystal orientation mapping (ACOM) and in situ straining inside a transmission electron microscope was applied to study the deformation of nanocrystalline PdxAu1− x thin films. This combination enables direct imaging of simultaneously occurring plastic deformation processes in one experiment, such as grain boundary motion, twin activity and grain rotation. Large-angle grain rotations with ≈39° and ≈60° occur and can be related to twin formation, twin migration and twin–twin interaction as a result of partial dislocation activity. Furthermore, plastic deformation in nanocrystalline thin films was found to be partially reversible upon rupture of the film. In conclusion, conventional deformation mechanisms are still active in nanocrystalline metals but with different weighting as compared with conventional materials with coarser grains. PMID:27335747
In situ observation of deformation processes in nanocrystalline face-centered cubic metals.
Kobler, Aaron; Brandl, Christian; Hahn, Horst; Kübel, Christian
2016-01-01
The atomistic mechanisms active during plastic deformation of nanocrystalline metals are still a subject of controversy. The recently developed approach of combining automated crystal orientation mapping (ACOM) and in situ straining inside a transmission electron microscope was applied to study the deformation of nanocrystalline Pd x Au1- x thin films. This combination enables direct imaging of simultaneously occurring plastic deformation processes in one experiment, such as grain boundary motion, twin activity and grain rotation. Large-angle grain rotations with ≈39° and ≈60° occur and can be related to twin formation, twin migration and twin-twin interaction as a result of partial dislocation activity. Furthermore, plastic deformation in nanocrystalline thin films was found to be partially reversible upon rupture of the film. In conclusion, conventional deformation mechanisms are still active in nanocrystalline metals but with different weighting as compared with conventional materials with coarser grains. PMID:27335747
Thermal plasma processed ferro-magnetically ordered face-centered cubic iron at room temperature
Raut, Suyog A.; Kanhe, Nilesh S.; Bhoraskar, S. V.; Mathe, V. L.; Das, A. K.
2014-10-28
Here, we report tailor made phase of iron nanoparticles using homogeneous gas phase condensation process via thermal plasma route. It was observed that crystal lattice of nano-crystalline iron changes as a function of operating parameters of the plasma reactor. In the present investigation iron nanoparticles have been synthesized in presence of argon at operating pressures of 125–1000 Torr and fixed plasma input DC power of 6 kW. It was possible to obtain pure fcc, pure bcc as well as the mixed phases for iron nanoparticles in powder form as a function of operating pressure. The as synthesized product was characterized for understanding the structural and magnetic properties by using X-ray diffraction, vibrating sample magnetometer, and Mössbauer spectroscopy. The data reveal that fcc phase is ferromagnetically ordered with high spin state, which is unusual whereas bcc phase is found to be ferromagnetic as usual. Finally, the structural and magnetic properties are co-related.
Dynamic self-assembly of non-Brownian spheres studied by molecular dynamics simulations
NASA Astrophysics Data System (ADS)
Carvente, O.; Salazar-Cruz, M.; Peñuñuri, F.; Ruiz-Suárez, J. C.
2016-02-01
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 body-centered-tetragonal or face-centered-cubic 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 that may be in the core of crystal nucleation. Around the isothermal point, a sudden growth of granular clusters having the maximum coordination number takes place, indicating the outcome of a first-order phase transition. We propose a heuristic equation that successfully describes the dynamic evolution of the local packing fraction in terms of the local granular temperature, along the entire crystallization process.
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)
NASA Astrophysics Data System (ADS)
Wang, Lin; An, Xizhong; Wang, Defeng; Qian, Quan
2016-01-01
Quantitative characterization on the topological and metrical properties of radical subunits (polyhedra) for two new ternary hard sphere crystals was studied. These two ideal crystalline structures are numerically constructed by filling small and medium spheres into interstices (corresponding to regular tetrahedral and octahedral pores) of perfect face centered cubic (FCC) and hexagonal close packed (HCP) crystals formed by the packing of large spheres. Topological properties such as face number, edge number, vertex number of each radical polyhedron (RP), edge number of each RP face and metrical properties such as volume, surface area, total perimeter and pore volume of each RP, area and perimeter of each RP face were analyzed and compared. The results show that even though the overall packing densities for FCC and HCP ternary crystals are the same, different characteristics of radical polyhedra for corresponding spheres in these two crystals can be identified. That is, in the former structure RPs are more symmetric than those in the latter; the orientations of corresponding RP in the latter are twice as many as that in the former. Moreover, RP topological and metrical properties in the HCP ternary crystal are much more complicated than those in the FCC ternary crystal. These differences imply the structure and property differences of these two ternary crystals. Analyses of RPs provide intensive understanding of pores in the structure.
Self-consistent phonon theory of the crystallization and elasticity of attractive hard spheres.
Shin, Homin; Schweizer, Kenneth S
2013-02-28
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. PMID:23464163
Force distribution/transmission in amorphous and crystalline packings of spheres
NASA Astrophysics Data System (ADS)
An, Xizhong; Huang, Fei
2013-06-01
In this paper, the discrete element modeling (DEM) was used to study the force distributions/transmissions in the packings of amorphous and crystalline states generated by equal spheres subjected to an external load (of a large sphere) applied on the top of a packing. Crystalline packings such as {100}-and {111}-oriented face centered cubic (FCC), hexagonal close packed (HCP) and body centered cubic (BCC) were considered. The results show that the forces among the particles in these packings are quite different, with different force chains identified with different structures. For amorphous packings, the force chain supporting the external load gives a conical shape. The force chain in a crystalline packing is mainly of a pyramid shape and the forces therein are transmitted along the crystalline lattice. For {100}-FCC, {111}-FCC, and BCC other than HCP, the forces transmit along straight lines with different orientations. In crystalline packings, the forces in the chains are uniformly distributed in each layer and decrease linearly with the height. The force distributions in amorphous and crystalline granular packings are structure-dependent.
NASA Astrophysics Data System (ADS)
Gungor, M. Rauf; Maroudas, Dimitrios
2005-06-01
A comprehensive computational analysis is reported of the atomistic mechanisms of strain relaxation and failure in free-standing Cu thin films under applied biaxial tensile strain for strain levels up to 6%. The analysis focuses on nanometer-scale-thick films with a preexisting void extending across the film thickness and the film plane oriented normal to the [111] crystallographic direction. Our computational study is based on isothermal-isostrain large-scale molecular-dynamics simulations within an embedded-atom-method parametrization for Cu. Our analysis has revealed various regimes in the film's mechanical response as the applied strain level increases. Within the considered strain range, after an elastic response at a low strain (<2%), void growth is the major strain relaxation mechanism mediated by the emission of perfect screw dislocation pairs from the void surface and subsequent dislocation propagation; as a result, a plastic zone forms around the void. Plastic deformation is accompanied by the glide motion of the dislocations emitted from the void surface, void surface morphological transitions, formation of a step pattern on the film's surfaces, dislocation jogging, vacancy generation due to gliding jogged dislocations, dislocation-vacancy interactions, vacancy pipe diffusion along dislocation cores, as well as dislocation-dislocation interactions. The increase in film surface roughness with increasing strain eventually leads to nucleation and propagation from the film surfaces of threading dislocation loops, which ultimately break up when they reach the opposite free surface of the thin film.
NASA Astrophysics Data System (ADS)
Chen, Jian; Deng, Xin; Gong, Manfeng; Liu, Wei; Wu, Shanghua
2016-09-01
This paper systematically investigated a set of functionally graded WC-TiC-Mo-Co cemented carbides with modified surface layer (called fcc-rich surface layer in this study), which is mainly composed of fcc phases (Ti(CN) and TiN) and WC. Nitridation at liquid phase sintering temperature is the key process making this fcc-rich surface layer. The functionally graded WC-TiC-Mo-Co cemented carbides synthesized in this study show 3 layer structure: the outer layer, i.e. the fcc-rich surface layer; the intermediate layer, which is characterized by abnormally large WC and high Co content; and the inner layer. It was found that TiC is the most critical component for the formation of fcc-rich surface layer. The higher content of TiC results in the thicker fcc-rich outer layer, higher (Ti(CN) and TiN) content in the outer layer, and higher hardness of the fcc-rich outer layer. The formation of this fcc-rich surface layer is mainly due to the nitridation process between Ti and N, which leads to the diffusion of Ti outwards (from the inside of the sample to the surface) and the subsequent migration of liquid cobalt inwards (from surface to the inside of the sample). The three-layer structure developed in this study provides the excellent combination of high wear resistance and high toughness, which is favorable for some applications.
Kamiko, M.; Nose, K.; Suenaga, R.; Kyuno, K.; Koo, J.-W.; Ha, J.-G.
2013-12-28
The influence of Ti seed layers on the structure of self-organized Ag nanodots, obtained with a Ti seed-layer-assisted thermal agglomeration method, has been investigated. The samples were grown on MgO(001) single crystal substrates by RF magnetron sputter deposition. The samples were deposited at room temperature and post-annealed at 350 °C for 4 h while maintaining the chamber vacuum conditions. The results of atomic force microscopy (AFM) observations indicated that the insertion of the Ti seed layer (0.6–5.0 nm) between the MgO substrate and Ag layer promotes the agglomeration process, forming the nanodot array. Comparisons between the AFM images revealed that the size of the Ag nanodots was increased with an increase in the Ti seed layer thickness. The atomic concentration of the film surface was confirmed by X-ray photoelectron spectroscopy (XPS). The XPS result suggested that the nanodot surface mainly consisted of Ag. Moreover, X-ray diffraction results proved that the initial deposition of the Ti seed layer (0.6–5.0 nm) onto MgO(001) prior to the Ag deposition yielded high-quality fcc-Ag(001) oriented epitaxial nanodots. The optical absorbance spectra of the fabricated Ag nanodots with various Ti seed layer thicknesses were obtained in the visible light range.
Sesé, Luis M; Bailey, Lorna E
2007-04-28
The structural features of the quantum hard-sphere system in the region of the fluid-face-centered-cubic-solid transition, for reduced number densities 0.45
NASA Astrophysics Data System (ADS)
Edison, John R.; Dasgupta, Tonnishtha; Dijkstra, Marjolein
2016-08-01
We study the phase behaviour of a binary mixture of colloidal hard spheres and freely jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and co-workers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures.
Edison, John R; Dasgupta, Tonnishtha; Dijkstra, Marjolein
2016-08-01
We study the phase behaviour of a binary mixture of colloidal hard spheres and freely jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and co-workers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures. PMID:27497577
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.
Effects of periodicity on flow and dispersion through closely packed fixed beds of spheres
NASA Astrophysics Data System (ADS)
Reynolds, A. M.
2002-02-01
A lattice-Boltzmann formulation is used to investigate the effects of ``periodicity'' (geometry) on fluid flow and tracer-particle dispersion through fixed beds of spheres comprising of closely packed layers. In the ``period-1'' arrangement, spheres in the adjacent layers contact at their poles while the ``period-2'' and ``period-3'' arrangements correspond to hexagonal and faced-centered cubic close packing. For all three packing arrangements, there is a transition with increasing Reynolds number from a power law to a log-normal distribution of kinetic energies and, velocity and vorticity become more closely aligned giving rise to helical tracer-particle trajectories. It is suggested that these flow characteristics, unlike the stability of flow and the distribution of helicity, are largely insensitive to geometry, even when the geometry creates direct channels through the pack bed orientated along the gradient in applied pressure. For steady flows and strongly turbulent flows, such channels are predicted to provide direct routes for dispersion through a packed bed, while for weakly turbulent flows they influence dispersion primarily by destabilizing the flow and thereby promoting dispersion throughout a bed. The dispersion of tracer-particles released from a source located on or close to a ``stagnation streamline'' is predicted to be faster than ballistic in the near field and the transition to long-time Fickian diffusion is predicted to be distinguished by a regime of subdiffusion.
Wang, L.; Bei, Hongbin; Li, T.; Gao, Y. F.; George, Easo P; Nieh, T. G.
2011-01-01
Nanoindentation tests were performed on single crystals of Mo and Ni. The critical shear stress for the first pop-in was {approx}1/7 of the shear modulus in both crystals. The dependence of pop-in probability on load was understood in terms of a thermally activated dislocation nucleation process. Comparison of the activation energies suggests nucleation of full dislocations in Mo and partial dislocations in Ni. The activation energy analysis also offers information on the specific slip system on which dislocations are nucleated.
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)
Filion, L.; Hermes, M.; Ni, R.; Dijkstra, M.
2010-12-01
Over the last number of years several simulation methods have been introduced to study rare events such as nucleation. In this paper we examine the crystal nucleation rate of hard spheres using three such numerical techniques: molecular dynamics, forward flux sampling, and a Bennett-Chandler-type theory where the nucleation barrier is determined using umbrella sampling simulations. The resulting nucleation rates are compared with the experimental rates of Harland and van Megen [Phys. Rev. E 55, 3054 (1997)], Sinn et al. [Prog. Colloid Polym. Sci. 118, 266 (2001)], Schätzel and Ackerson [Phys. Rev. E 48, 3766 (1993)], and the predicted rates for monodisperse and 5% polydisperse hard spheres of Auer and Frenkel [Nature 409, 1020 (2001)]. When the rates are examined in units of the long-time diffusion coefficient, we find agreement between all the theoretically predicted nucleation rates, however, the experimental results display a markedly different behavior for low supersaturation. Additionally, we examined the precritical nuclei arising in the molecular dynamics, forward flux sampling, and umbrella sampling simulations. The structure of the nuclei appears independent of the simulation method, and in all cases, the nuclei contains on average significantly more face-centered-cubic ordered particles than hexagonal-close-packed ordered particles.
NASA Technical Reports Server (NTRS)
Reed, W. B.
1972-01-01
The sphere launcher was designed to eject a 200 lb, 15 in. diameter sphere from a space vehicle or missile, at a velocity of 58 ft/sec without imparting excessive lateral loads to the vehicle. This launching is accomplished with the vehicle operating in vacuum conditions and under a 9 g acceleration. Two principal elements are used: a high thrust, short burn time rocket motor and two snubbers for reducing the lateral loads to acceptable limits.
Nonclassical Nucleation in a Solid-Solid Transition of Confined Hard Spheres
NASA Astrophysics Data System (ADS)
Qi, Weikai; Peng, Yi; Han, Yilong; Bowles, Richard K.; Dijkstra, Marjolein
2015-10-01
A solid-solid phase transition of colloidal hard spheres confined between two planar hard walls is studied using a combination of molecular dynamics and Monte Carlo simulation. The transition from a solid consisting of five crystalline layers with square symmetry (5 □ ) to a solid consisting of four layers with triangular symmetry (4 △ ) is shown to occur through a nonclassical nucleation mechanism that involves the initial formation of a precritical liquid cluster, within which the cluster of the stable 4 △ phase grows. Free-energy calculations show that the transition occurs in one step, crossing a single free-energy barrier, and that the critical nucleus consists of a small 4 △ solid cluster wetted by a metastable liquid. In addition, the liquid cluster and the solid cluster are shown to grow at the planar hard walls. We also find that the critical nucleus size increases with supersaturation, which is at odds with classical nucleation theory. The △-solid-like cluster is shown to contain both face-centered-cubic and hexagonal-close-packed ordered particles.
Wang, S.; Wang, M.P.; Chen, C.; Xiao, Z.; Jia, Y.L.; Li, Z.; Wang, Z.X.
2014-05-01
The orientation dependence of the deformation microstructure has been investigated in commercial pure molybdenum. After deformation, the dislocation boundaries of compressed molybdenum can be classified, similar to that in face-centered cubic metals, into three types: dislocation cells (Type 2), and extended planar boundaries parallel to (Type 1) or not parallel to (Type 3) a (110) trace. However, it shows a reciprocal relationship between face-centered cubic metals and body-centered cubic metals on the orientation dependence of the deformation microstructure. The higher the strain, the finer the microstructure is and the smaller the inclination angle between extended planar boundaries and the compression axis is. - Highlights: • A reciprocal relationship between FCC metals and BCC metals is confirmed. • The dislocation boundaries can be classified into three types in compressed Mo. • The dislocation characteristic of different dislocation boundaries is different.
Physics of Hard Spheres Experiment: Significant and Quantitative Findings Made
NASA Technical Reports Server (NTRS)
Doherty, Michael P.
2000-01-01
(Earth's gravity), and the emergence of face-centered-cubic (FCC) crystals late in the coarsening process (as small crystallites lost particles to the slow ripening of large crystallites). Significant quantitative findings from the microgravity experiments have been developed describing complex interactions among crystallites during the growth process, as concentration fields overlap in the surrounding disordered phase. Time-resolved Bragg scattering under microgravity captures one effect of these interactions quite conclusively for the sample at a volume fraction of 0.528. From the earliest time until the sample is almost fully crystalline, the size and overall crystallinity grow monotonically, but the number of crystallites per unit volume (number density) falls. Apparently nucleation is slower than the loss of crystallites because of the transfer of particles from small to large crystals. Thus, coarsening occurs simultaneously with growth, rather than following the completion of nucleation and growth as is generally assumed. In the same sample, an interesting signature appears in the apparent number density of crystallites and the volume fraction within the crystallites shortly before full crystallinity is reached. A brief upturn in both indicates the creation of more domains of the size of the average crystallite simultaneous with the compression of the crystallites. Only the emergence of dendritic arms offers a reasonable explanation. The arms would be "seen" by the light scattering as separate domains whose smaller radii of curvature would compress the interior phase. In fiscal year 1999, numerous papers, a doctoral dissertation, and the PHaSE final report were produced. Although this flight project has been completed, plans are in place for a follow-on colloid experiment by Chaikin and Russel that employs a light microscope within Glenn's Fluids and Combustion Facility on the International Space Station. PHaSE is providing us with a deeper understanding of the
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.
NASA Astrophysics Data System (ADS)
Aref'eva, L. P.; Shebzukhova, I. G.
2016-07-01
A technique for the evaluation of the electron work function of metallic single crystals and the electron work function anisotropy has been developed in the framework of the electron-statistical method. The surface energy and the electron work function have been calculated for crystal faces of allotropic modifications of 4 d- and 5 d-metals. A change in the electron work function due to the allotropic transformations has been estimated, and the periodic dependence of the electron work function has been determined. It has been shown that the results obtained using the proposed technique correlate with the available experimental data for polycrystals.
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.
NASA Astrophysics Data System (ADS)
Bocchini, Peter J.
High-temperature structural alloys for aerospace and energy applications have long been dominated by Ni-based superalloys, whose high-temperature strength and creep resistance can be attributed to a two-phase microstructure consisting of a large volume fraction of ordered gamma'(L12)-precipitates embedded in a disordered gamma(f.c.c.)-matrix. These alloys exhibit excellent mechanical behavior and thermal stability, but after decades of incremental improvement, are nearing the theoretical limit of their operating temperatures. In 2006, an analogous gamma(f.c.c.) + gamma'(L12) microstructure was identified in the Co-Al-W ternary system with liquidus and solidus temperatures 50-150 °C higher than conventional Ni-based superalloys. The work herein focuses on assessing the effects of alloying additions on microstructure and mechanical behavior in an effort to lay the foundations for understanding this emerging alloy system. A variety of Co-based superalloys are investigated in order to study fundamental materials properties and to address key engineering challenges. Coarsening rate constants and temporal exponents are measured for gamma'(L1 2)-precipitates in a ternary Co-Al-W alloy aged at 650 °C and 750 °C. A series of Co-Al-W-B-Zr alloys are cast to study the influence of segregation of B and Zr to grain boundaries (GBs) on mechanical properties. Co-Ni-Al-W-Ti alloys with various amounts of Al, W, and Ti are cast in order to fabricate Co-based superalloys with decreased density and increased gamma'(L1 2)-solvus temperature. 2-D dislocation dynamics modeling is employed to predict how gamma'(L12)-precipitate size and volume fraction affect the mechanical properties of Ni- and Co-based superalloys. Compositional information such as phase concentrations, partitioning behavior, and GB segregation are measured with local electrode atom probe (LEAP) tomography in alloys with fine microstructures and with scanning electron microscope (SEM) electron dispersive x-ray spectroscopy (EDS) in alloys with coarse microstructures. High-temperature mechanical properties are determined with compression creep at 850 °C and flow stress tests conducted between room temperature and 900 °C. gamma'(L12)-solvus temperature, as well as solidus and liquidus temperatures, are measured with differential thermal analysis (DTA). B and Zr strongly segregate to GBs in Co-Al-W-B-Zr alloys. B additions of 0.05 at. % result in micron-sized GB-precipitates that improve creep strength by two orders of magnitude. Segregation of B or Zr in amounts where GB-precipitates do not form, have no effect on creep strength over a ternary Co-Al-W alloy. The concurrent addition of B and Zr improves creep strength, though to a lesser degree than in alloys containing GB-borides. Ti is an effective substitute for W and Al in Co-Ni-Al-W alloys where density is decreased by 9 % and solvus is increased to 1137 °C in a Co-10Ni-5Al-5W-8Ti at. % alloy compared to 982 °C in a Co-10Ni-9Al-9W at. % alloy. Further investigation of reducing W in a Co-10Ni-6Al-xW-6Ti at. % (x=6, 4, 2, 0) alloys ascertain that, with the addition of Ti, gamma'(L12)-precipitates can form in a wider composition range than in ternary Co-Al-W alloys. 2-D dislocation dynamics simulations are in good agreement with experimental measurements for binary Ni-Al and ternary Co-Al-W alloys. General trends in strengthening are captured for higher order Ni-Al-Cr and Ni-Al-Cr-W alloys.
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.
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...
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…
NASA Astrophysics Data System (ADS)
Chaney, A.; Lu, Lei; Stern, A.
2015-09-01
We show that fuzzy spheres are solutions of Lorentzian Ishibashi-Kawai-Kitazawa-Tsuchiya-type matrix models. The solutions serve as toy models of closed noncommutative cosmologies where big bang/crunch singularities appear only after taking the commutative limit. The commutative limit of these solutions corresponds to a sphere embedded in Minkowski space. This "sphere" has several novel features. The induced metric does not agree with the standard metric on the sphere, and, moreover, it does not have a fixed signature. The curvature computed from the induced metric is not constant, has singularities at fixed latitudes (not corresponding to the poles) and is negative. Perturbations are made about the solutions, and are shown to yield a scalar field theory on the sphere in the commutative limit. The scalar field can become tachyonic for a range of the parameters of the theory.
Wu, Dong; Junyan, Zhang; Huang, J C; Bei, Hongbin; Nieh, Tai-Gang
2013-01-01
Nanocrystalline Cr (nc-Cr) was synthesized by electrodeposition. Samples with various grain sizes (19 57 nm) were prepared by annealing the as-deposited sample. Microstructures were examined using X-ray and electron microscopy, and the mechanical prop- erties were evaluated using nanoindentation. The strength of nc-Cr samples apparently obeyed the classical Hall Petch relationship. It was found that hardening potency caused by grain refinement was generally higher in body-centered cubic metals than that in face-centered cubic and hexagonal close-packed metals. A possible explanation was offered.
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.
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)
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 ...
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.
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.
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.
Acoustic band gaps of three-dimensional periodic polymer cellular solids with cubic symmetry
NASA Astrophysics Data System (ADS)
Chen, Yanyu; Yao, Haimin; Wang, Lifeng
2013-07-01
The band structure and sound attenuation of the triply periodic co-continuous composite materials with simple cubic lattice, body-centered cubic lattice, and face-centered cubic lattice consisting of PMMA and air are investigated using finite element method. Complete band gaps are found in these structures and the width of band gaps is depending on volume fraction. It is shown that the width of band gaps along different directions in the first irreducible Brillouin zone enlarges as the volume fraction increases from 0.2 to 0.7. The largest complete band gap widths of the three types of co-continuous structures are 0.29, 0.54, and 0.55, respectively. As the complete band gaps appear in audible range of frequencies, these triply periodic co-continuous composite materials can be utilized to control noise.
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.
Piecewise Cubic Interpolation Package
Energy Science and Technology Software Center (ESTSC)
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)more » 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.« less
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.
Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; Shen, Bo; Wu, Liheng; Zhang, Sen; Lu, Gang; Wu, Zhongbiao; Sun, Shouheng
2015-10-04
We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe_{3}O_{4} NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO_{4} with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly, our study offers a general approach to enhance Pd catalysis in acid for ORB.
Zhu, Huiyuan; Jiang, Guangming; Zhang, Xu; Shen, Bo; Wu, Liheng; Zhang, Sen; Lu, Gang; Wu, Zhongbiao; Sun, Shouheng
2015-10-04
We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) via reductive annealing of core/shell Pd/Fe3O4 NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at similar to 8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4 with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Lastly, our study offersmore » a general approach to enhance Pd catalysis in acid for ORB.« less
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.
NASA Astrophysics Data System (ADS)
Claudi, R.; Gratton, R.; Desidera, S.; Maire, A.-L.; Mesa, D.; Turatto, M.; Baruffolo, A.; Cascone, E.; De Caprio, V.; D'Orazi, V.; Fantinel, D.; Giro, E.; Salasnich, B.; Scuderi, S.; Sissa, E.; Beuzit, J.-L.; Mouillet, D.
The Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) facility mounted at ESO-VLT aims at discovering giant extrasolar planets in the proximity of bright stars and characterising them through spectroscopic and polarimetric observations. SPHERE is a complete system with a core made of an extreme-Adaptive Optics (XAO) turbulence correction, a pupil tracker and NIR and Visible coronagraph devices. At its back end, a differential dual imaging camera (IRDIS) and an integral field spectrograph (IFS) work in the Near Infrared (NIR) (0.95 < lambda < 2.32 μm) while a high resolution polarization camera covers the visible domain (0.6 < lambda < 0.9 μm). The IFS is a low resolution spectrograph (R˜50) that operates in the near IR (0.95< lambda < 1.6 μm), an optimal wavelength range for the detection of planetary features, over a field of view of about 1.7 × 1.7 square arcsecs. From spectra it is possible to reconstruct monochromatic images with high contrast (10-6 at 0.5 arcsec) and high spatial resolution, well inside the star PSF. The commissioning of the instrument ended in October 2014 and ESO has already offered SPHERE to the community. In this paper several results obtained during the commissioning and science verification phase are described.
Myers, B.F.; Montgomery, F.C.; Morris, R.N.
1993-08-01
The equivalent sphere model, which is widely used in calculating the release of fission gases from nuclear fuel, is idealized. The model is based on the diffusion of fission products in and their escape from a homogeneous sphere of fuel; the fission products are generated at a constant rate and undergo radiodecay. The fuel is assumed to be a set of spherical particles with a common radius. The value of the radius is such that the surface-to-volume ratio, S/V, of the set of spherical particles is the same as the S/V of the fuel mass of interest. The release rate depends on the dimensionless quantity {lambda}a{sup 2}/D where {lambda} is the radiodecay constant, a, the equivalent sphere radius and D, the diffusion coefficient. In the limit {lambda}t {much_gt} 1, the steady-state fractional release for isotopes with half-lives less than about 5 d is given by the familiar relation R/B = 3{radical}D/{lambda}a{sup 2} (1). For the spherical particles, S/V = 3/a. However, in important cases, the assumption of a single value of a is inappropriate. Examples of configurations for which multiple values of a are appropriate include powders, hydrolyzed fuel kernels, normally configured HTR fuel particles and perhaps, fuel kernels alone. In the latter case, one can imagine a distribution of values of a whose mean yields the value appropriate for agreement of Eq. (1) with measurement.
Ultraviolet characterization of integrating spheres.
Shaw, Ping-Shine; Li, Zhigang; Arp, Uwe; Lykke, Keith R
2007-08-01
We have studied the performance of polytetrafluoroethylene integrating spheres in the ultraviolet (UV) region with wavelengths as short as 200 nm. Two techniques were used for this study; first, the spectral throughput of an integrating sphere irradiated by a deuterium lamp was analyzed by a monochromator. Second, a UV laser beam was directed into an integrating sphere, and spectrally dispersed laser induced fluorescence was studied. Significant absorption and fluorescence features were observed in the UV region and attributed to the contamination in the integrating sphere. We demonstrate that integrating spheres are easily contaminated by environmental pollutants such as polycyclic aromatic hydrocarbons emitted from engine exhaust. Baking of the contaminated integrating sphere can reverse some but not all of the effects caused by contaminants. The implications for using integrating spheres for UV measurement are discussed. PMID:17676122
Ultraviolet characterization of integrating spheres
NASA Astrophysics Data System (ADS)
Shaw, Ping-Shine; Li, Zhigang; Arp, Uwe; Lykke, Keith R.
2007-08-01
We have studied the performance of polytetrafluoroethylene integrating spheres in the ultraviolet (UV) region with wavelengths as short as 200 nm. Two techniques were used for this study; first, the spectral throughput of an integrating sphere irradiated by a deuterium lamp was analyzed by a monochromator. Second, a UV laser beam was directed into an integrating sphere, and spectrally dispersed laser induced fluorescence was studied. Significant absorption and fluorescence features were observed in the UV region and attributed to the contamination in the integrating sphere. We demonstrate that integrating spheres are easily contaminated by environmental pollutants such as polycyclic aromatic hydrocarbons emitted from engine exhaust. Baking of the contaminated integrating sphere can reverse some but not all of the effects caused by contaminants. The implications for using integrating spheres for UV measurement are discussed.
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.
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.
Observation of Body-Centered Cubic Gold Nanocluster.
Liu, Chao; Li, Tao; Li, Gao; Nobusada, Katsuyuki; Zeng, Chenjie; Pang, Guangsheng; Rosi, Nathaniel L; Jin, Rongchao
2015-08-17
The structure of nanoparticles plays a critical role in dictating their material properties. Gold is well known to adopt face-centered cubic (fcc) structure. Herein we report the first observation of a body-centered cubic (bcc) gold nanocluster composed of 38 gold atoms protected by 20 adamantanethiolate ligands and two sulfido atoms ([Au38S2(SR)20], where R=C10H15) as revealed by single-crystal X-ray crystallography. This bcc structure is in striking contrast with the fcc structure of bulk gold and conventional Au nanoparticles, as well as the bi-icosahedral structure of [Au38(SCH2CH2Ph)24]. The bcc nanocluster has a distinct HOMO-LUMO gap of ca. 1.5 eV, much larger than the gap (0.9 eV) of the bi-icosahedral [Au38(SCH2CH2Ph)24]. The unique structure of the bcc gold nanocluster may be promising in catalytic applications. PMID:26136241
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.
NASA Astrophysics Data System (ADS)
Peng, Gan Chew; Hin, Pooi Ah; Ho, C. K.
2015-12-01
The power-normal distribution given in Yeo and Johnson in year 2000 is a unimodal distribution with wide ranges of skewness and kurtosis. A shortcoming of the power-normal distribution is that the negative and positve parts of the underlying random variable have to be specified by two different expressions of the standard normal random variable. In this paper, we construct a new distribution, called the cubic-normal distribution, via a single polynomial expression in cubic root function. Apart from having the properties which are similar to those of the power-normal distribution, this cubic-normal distribution can be developed into a multivariate version which is more attractive from the theoretical and computational points of view.
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.
Dynamical tachyons on fuzzy spheres
NASA Astrophysics Data System (ADS)
Berenstein, David; Trancanelli, Diego
2011-05-01
We study the spectrum of off-diagonal fluctuations between displaced fuzzy spheres in the Berenstein-Maldacena-Nastase plane wave matrix model. The displacement is along the plane of the fuzzy spheres. We find that when two fuzzy spheres intersect at angles, classical tachyons develop and that the spectrum of these modes can be computed analytically. These tachyons can be related to the familiar Nielsen-Olesen instabilities in Yang-Mills theory on a constant magnetic background. Many features of the problem become more apparent when we compare with maximally supersymmetric Yang-Mills theory on a sphere, of which this system is a truncation. We also set up a simple oscillatory trajectory on the displacement between the fuzzy spheres and study the dynamics of the modes as they become tachyonic for part of the oscillations. We speculate on their role regarding the possible thermalization of the system.
Dynamical tachyons on fuzzy spheres
Berenstein, David; Trancanelli, Diego
2011-05-15
We study the spectrum of off-diagonal fluctuations between displaced fuzzy spheres in the Berenstein-Maldacena-Nastase plane wave matrix model. The displacement is along the plane of the fuzzy spheres. We find that when two fuzzy spheres intersect at angles, classical tachyons develop and that the spectrum of these modes can be computed analytically. These tachyons can be related to the familiar Nielsen-Olesen instabilities in Yang-Mills theory on a constant magnetic background. Many features of the problem become more apparent when we compare with maximally supersymmetric Yang-Mills theory on a sphere, of which this system is a truncation. We also set up a simple oscillatory trajectory on the displacement between the fuzzy spheres and study the dynamics of the modes as they become tachyonic for part of the oscillations. We speculate on their role regarding the possible thermalization of the system.
Periodically oscillating plasma sphere
Park, J.; Nebel, R.A.; Stange, S.; Murali, S. Krupakar
2005-05-15
The periodically oscillating plasma sphere, or POPS, is a novel fusion concept first proposed by D. C. Barnes and R. A. Nebel [Fusion Technol. 38, 28 (1998)]. POPS utilizes the self-similar collapse of an oscillating ion cloud in a spherical harmonic oscillator potential well formed by electron injection. Once the ions have been phase-locked, their coherent motion simultaneously produces very high densities and temperatures during the collapse phase of the oscillation. A requirement for POPS is that the electron injection produces a stable harmonic oscillator potential. This has been demonstrated in a gridded inertial electrostatic confinement device and verified by particle simulation. Also, the POPS oscillation has been confirmed experimentally through observation that the ions in the potential well exhibit resonance behavior when driven at the POPS frequency. Excellent agreement between the observed POPS frequencies and the theoretical predictions has been observed for a wide range of potential well depths and three different ion species. Practical applications of POPS require large plasma compressions. These large compressions have been observed in particle simulations, although space charge neutralization remains a major issue.
NASA Astrophysics Data System (ADS)
Avgin, I.; Boukahil, A.; Huber, D. L.
2015-11-01
Using the coherent potential approximation, we investigate the optical absorption and the density of states of Frenkel exciton systems on simple, body centered, and face centered cubic lattices with nearest-neighbor interactions and a Gaussian distribution of transition frequencies (i.e. Gaussian diagonal disorder). The analysis is based on an elliptic integral approach with a variety of variances. The results for the simple cubic lattice are in good agreement with the finite array calculations of Schreiber and Toyozawa. Our findings suggest that the coherent potential approximation can be useful in interpreting the optical properties of cubic crystals where the optically excited states are Frenkel excitons with the dominant interactions limited to nearest-neighbors.
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...
NASA Astrophysics Data System (ADS)
Chesneau, O.; Schmid, H.-M.; Carbillet, M.; Chiavassa, A.; Abe, L.; Mouillet, D.
2013-05-01
SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument for the VLT is optimized towards reaching the highest contrast in a limited field of view and at short distances from the central star, thanks to an extreme AO system. SPHERE is very well suited to study the close environment of Betelgeuse, and has a strong potential for detecting the ejection activity around this key red supergiant.
Ancient Celestial Spheres from Greece
NASA Astrophysics Data System (ADS)
Dimitrakoudis, S.; Papaspyrou, P.; Petoussis, V.; Moussas, X.
2006-08-01
We present several ancient celestial spheres from the 8th century B.C. found throughout Greece, mainly in Thessaly, at the temple of Itonia Athena, but also in Olympia and other places. These celestial spheres have an axis, equator and several meridians and they have several markings with the symbol of stars (today's symbol for the Sun) $\\odot$. Such instruments could have been used to measure the time, the latitude of a location, or the coordinates of stars.
NASA Astrophysics Data System (ADS)
Shoockron, Joseph
1989-06-01
This work deals with the analysis and calculation of the critical angle for the ricochet of a sphere off water. The critical angle is defined as the maximum incidence angle of a sphere over water which enables it to ricochet. This work presents the development and calculation of the forces acting on the sphere during its entry into the water. Since the critical angle is very sensitive to the hydrodynamic forces, the accurate development and calculation of these forces has been emphasized in some previous methods. There is a simple empirical formula for calculation of the critical angle, which is theta(sub c) = 18 deg/square root of zeta, where theta(sub c) is the critical angle and zeta is the ratio between the density of the sphere and the density of the water. Likewise, there are works which give a theoretical basis to the above-mentioned formula. This formula does not depend on the incidence velocity of the sphere or on the sphere radius, these being parameters that affect the critical angle. In this work it is verified that the critical angle depends on these added parameters, in the form of the F(sub r) number, where F(sub r) = V(exp 2)/Rg.
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.)
Exchange stiffness, magnetization, and spin waves in cubic and hexagonal phases of cobalt
Liu, X.; Steiner, M.M.; Sooryakumar, R.; Prinz, G.A.; Farrow, R.F.; Harp, G.
1996-05-01
We utilize Brillouin light scattering to investigate the magnetic properties of the hexagonal-close-packed as well as the body- and face-centered cubic phases of elemental cobalt stabilized as thin epilayers. Expressions for the dependence of the surface and bulk magnons on applied magnetic field and in-plane propagation direction yield the exchange stiffness constant {ital D}, saturation magnetization {ital M}, and magnetic anisotropy fields of the cobalt atoms synthesized in these distinct crystal structures. Estimates of {ital D} and {ital M} are also calculated from the electronic band structure for the different crystalline phases. Satisfactory agreement is found between theory and experiment. The implications of these results towards our understanding of magnetic properties of itinerant ferromagnets are discussed. {copyright} {ital 1996 The American Physical Society.}
Phonon frequencies and elastic constants of cubic Pu from electronic structure theory
Straub, G.K.
1996-11-01
The phonon frequencies and elastic constants of plutonium are calculated using a model for the electronic structure that treats the valance electrons as a pseudopotential and the f-electrons in tight-binding theory. An effective interaction between ions is presented with electron screening treated in the Thomas-Fermi approximation and the f-electrons contributing bonding and repulsive terms to the potential. The phonon frequencies and elastic constants are calculated using the face-centered cubic lattice structure for both the {alpha}-, and {delta}-phases of Pu. The electronic structure predicts the qualitative behavior of the elastic constants and the transverse branches of the phonon dispersion curves in agreement with experimental values of the elastic constants for B-phase Pu.
Higher-order elasticity of cubic metals in the embedded-atom method
NASA Astrophysics Data System (ADS)
Chantasiriwan, Somchart; Milstein, Frederick
1996-06-01
The higher-order elasticity of cubic metals in the framework of the embedded-atom method (EAM) is investigated. Proper groupings of the second- and third-order elastic moduli are shown to yield expressions that depend solely on either the electron density function or the pair potential and which therefore facilitate the construction of EAM models. This formulation also makes evident some important restrictions on the EAM functions and lattice summations. In order for the EAM to model the anharmonic properties accurately, (a) at least the third-nearest-neighbor interactions must be included in the expressions for the cohesive energies of both the body-centered-cubic and face-centered-cubic metals and (b) an electron density function of an inverse power form, as has been employed previously, generally is not valid. Specific EAM models are constructed for a diverse selection of metals (i.e., aluminum, copper, sodium, and molybdenum). These models identically reproduce the respective second- and third-order elastic moduli, as well as the binding energy, atomic volume, unrelaxed vacancy formation energy, and Rose's universal equation of state. They also provide reasonable phonon frequency spectra and structural energy differences
Particle linear theory on a self-gravitating perturbed cubic Bravais lattice
Marcos, B.
2008-08-15
Discreteness effects are a source of uncontrolled systematic errors of N-body simulations, which are used to compute the evolution of a self-gravitating fluid. We have already developed the so-called ''particle linear theory''(PLT), which describes the evolution of the position of self-gravitating particles located on a perturbed simple cubic lattice. It is the discrete analogue of the well-known (Lagrangian) linear theory of a self-gravitating fluid. Comparing both theories permits us to quantify precisely discreteness effects in the linear regime. It is useful to develop the PLT also for other perturbed lattices because they represent different discretizations of the same continuous system. In this paper we detail how to implement the PLT for perturbed cubic Bravais lattices (simple, body, and face-centered) in a cubic simulation box. As an application, we will study the discreteness effects--in the linear regime--of N-body simulations for which initial conditions have been set up using these different lattices.
NASA Astrophysics Data System (ADS)
Russier, V.
2016-07-01
The low temperature behavior of densely packed interacting spherical single domain nanoparticles (MNP) is investigated by Monte Carlo simulations in the framework of an effective one spin model. The particles are distributed through a hard sphere like distribution with periodic boundary conditions and interact through the dipole dipole interaction (DDI) with an anisotropy energy including both cubic and uniaxial symmetry components. The cubic component is shown to play a sizable role on the value of the blocking temperature Tb only when the MNP easy axes are parallel to the cubic easy direction ([111] direction for a negative cubic anisotropy constant). The nature of the collective low temperature state, either ferromagnetic or spin glass like, is found to depend on the ratio of the anisotropy to the dipolar energies characterizing partly the disorder in the system.
NASA Astrophysics Data System (ADS)
Stewart, Cameron; Najjar, Fady; Stewart, D. Scott; Bdzil, John
2012-11-01
Modern-engineered high explosive (HE) materials can consist of a matrix of solid, inert particles embedded into an HE charge. When this charge is detonated, intense shock waves are generated. As these intense shocks interact with the inert particles, large deformations occur in the particles while the incident shock diffracts around the particle interface. We will present results from a series of 3-D DNS of an intense shock interacting with unit-cube configurations of inert particles embedded into nitromethane. The LLNL multi-physics massively parallel hydrodynamics code ALE3D is used to carry out high-resolution (4 million nodes) simulations. Three representative unit-cube configurations are considered: primitive cubic, face-centered and body-centered cubic for two particle material types of varying impedance ratios. Previous work has only looked at in-line particles configurations. We investigate the time evolution of the unit cell configurations, vorticity being generated by the shock interaction, as well as the velocity and acceleration of the particles until they reach the quasi-steady regime. LLNL-ABS-567694. CSS was supported by a summer internship through the HEDP program at LLNL. FMN's work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Simple manipulator for rotating spheres.
Weinstein, B W; Hendricks, C D; Ward, C M; Willenborg, D L
1978-06-01
We describe a simple device for rapidly rotating a small sphere to any orientation for inspection of the surface. The ball is held between two small, flat surfaces and rolls as the surfaces are moved differentially parallel to one another. PMID:18699214
Laflamme-Sanders, Alexandra; Zhu, Mu
2008-11-01
LAGO is an efficient kernel algorithm designed specifically for the rare target detection problem. However, unlike other kernel algorithms, LAGO cannot be easily used with many domain-specific kernels. We solve this problem by first providing a unified framework for LAGO and clarifying its basic principle, and then applying that principle on the unit sphere instead of in the Euclidean space. PMID:18775643
NASA Astrophysics Data System (ADS)
Hale, L. M.; Zhou, X. W.; Zimmerman, J. A.; Moody, N. R.; Ballarini, R.; Gerberich, W. W.
2009-10-01
Compliant substrate technology offers an effective approach to grow high-quality multilayered films, of importance to microelectronics and microelectromechanical systems devices. By using a thin, soft substrate to relieve the mismatch strain of an epitaxial film, the critical thickness of misfit dislocation formation in the overlayer is effectively increased. Experiments have indicated that stiff films deposited onto Si substrates can delaminate at the interface. However, the atomic mechanisms of the deformation and the fracture of the films have not been well studied. Here, we have applied molecular dynamics simulations to study the delamination of a stiff body-centered-cubic crystalline film from a compliant Si substrate due to tensile loading. The observed mechanical behavior is shown to be relatively independent of small changes in temperature, loading rate, and system size. Fracture occurs at the interface between the two materials resulting in nearly atomically clean surfaces. Dislocations are seen to nucleate in the body-centered-cubic film prior to delamination. At higher strains, a phase change to a face centered cubic is observed within the body-centered-cubic film, facilitating extensive dislocation growth and interaction. The various defects that form prior to fracture are discussed and related to the mechanical properties of the system.
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...
Tessellating the Sphere with Regular Polygons
ERIC Educational Resources Information Center
Soto-Johnson, Hortensia; Bechthold, Dawn
2004-01-01
Tessellations in the Euclidean plane and regular polygons that tessellate the sphere are reviewed. The regular polygons that can possibly tesellate the sphere are spherical triangles, squares and pentagons.
Eddy currents in a conducting sphere
NASA Technical Reports Server (NTRS)
Bergman, John; Hestenes, David
1986-01-01
This report analyzes the eddy current induced in a solid conducting sphere by a sinusoidal current in a circular loop. Analytical expressions for the eddy currents are derived as a power series in the vectorial displacement of the center of the sphere from the axis of the loop. These are used for first order calculations of the power dissipated in the sphere and the force and torque exerted on the sphere by the electromagnetic field of the loop.
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)
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.
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. PMID:25768504
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.
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.
Hard sphere packings within cylinders.
Fu, Lin; Steinhardt, William; Zhao, Hao; Socolar, Joshua E S; Charbonneau, Patrick
2016-02-23
Arrangements of identical hard spheres confined to a cylinder with hard walls have been used to model experimental systems, such as fullerenes in nanotubes and colloidal wire assembly. Finding the densest configurations, called close packings, of hard spheres of diameter σ in a cylinder of diameter D is a purely geometric problem that grows increasingly complex as D/σ increases, and little is thus known about the regime for D > 2.873σ. In this work, we extend the identification of close packings up to D = 4.00σ by adapting Torquato-Jiao's adaptive-shrinking-cell formulation and sequential-linear-programming (SLP) technique. We identify 17 new structures, almost all of them chiral. Beyond D ≈ 2.85σ, most of the structures consist of an outer shell and an inner core that compete for being close packed. In some cases, the shell adopts its own maximum density configuration, and the stacking of core spheres within it is quasiperiodic. In other cases, an interplay between the two components is observed, which may result in simple periodic structures. In yet other cases, the very distinction between the core and shell vanishes, resulting in more exotic packing geometries, including some that are three-dimensional extensions of structures obtained from packing hard disks in a circle. PMID:26843132
Generating perfect fluid spheres in general relativity
NASA Astrophysics Data System (ADS)
Boonserm, Petarpa; Visser, Matt; Weinfurtner, Silke
2005-06-01
Ever since Karl Schwarzschild’s 1916 discovery of the spacetime geometry describing the interior of a particular idealized general relativistic star—a static spherically symmetric blob of fluid with position-independent density—the general relativity community has continued to devote considerable time and energy to understanding the general-relativistic static perfect fluid sphere. Over the last 90 years a tangle of specific perfect fluid spheres has been discovered, with most of these specific examples seemingly independent from each other. To bring some order to this collection, in this article we develop several new transformation theorems that map perfect fluid spheres into perfect fluid spheres. These transformation theorems sometimes lead to unexpected connections between previously known perfect fluid spheres, sometimes lead to new previously unknown perfect fluid spheres, and in general can be used to develop a systematic way of classifying the set of all perfect fluid spheres.
BDA: A novel method for identifying defects in body-centered cubic crystals
Möller, Johannes J.; Bitzek, Erik
2016-01-01
The accurate and fast identification of crystallographic defects plays a key role for the analysis of atomistic simulation output data. For face-centered cubic (fcc) metals, most existing structure analysis tools allow for the direct distinction of common defects, such as stacking faults or certain low-index surfaces. For body-centered cubic (bcc) metals, on the other hand, a robust way to identify such defects is currently not easily available. We therefore introduce a new method for analyzing atomistic configurations of bcc metals, the BCC Defect Analysis (BDA). It uses existing structure analysis algorithms and combines their results to uniquely distinguish between typical defects in bcc metals. In essence, the BDA method offers the following features:•Identification of typical defect structures in bcc metals.•Reduction of erroneously identified defects by iterative comparison to the defects in the atom's neighborhood.•Availability as ready-to-use Python script for the widespread visualization tool OVITO [http://ovito.org]. PMID:27114926
BDA: A novel method for identifying defects in body-centered cubic crystals.
Möller, Johannes J; Bitzek, Erik
2016-01-01
The accurate and fast identification of crystallographic defects plays a key role for the analysis of atomistic simulation output data. For face-centered cubic (fcc) metals, most existing structure analysis tools allow for the direct distinction of common defects, such as stacking faults or certain low-index surfaces. For body-centered cubic (bcc) metals, on the other hand, a robust way to identify such defects is currently not easily available. We therefore introduce a new method for analyzing atomistic configurations of bcc metals, the BCC Defect Analysis (BDA). It uses existing structure analysis algorithms and combines their results to uniquely distinguish between typical defects in bcc metals. In essence, the BDA method offers the following features:•Identification of typical defect structures in bcc metals.•Reduction of erroneously identified defects by iterative comparison to the defects in the atom's neighborhood.•Availability as ready-to-use Python script for the widespread visualization tool OVITO [http://ovito.org]. PMID:27114926
Steel and titanium hollow sphere foams
Hurysz, K.M.; Clark, J.L.; Nagel, A.R.; Lee, K.J.; Cochran, J.K.; Sanders, T.H. Jr.; Hardwicke, C.U.
1998-12-31
Metal hollow sphere foams are fabricated by bonding millimeter sized metal alloy hollow spheres at points of contact. The spheres are formed as powder shells from slurries. For stainless steel spheres, the starting powder is a mixture of iron and chromium oxide. Thermal treatment in hydrogen reduces the oxides to Fe/Cr alloys with less than 2% porosity in sphere walls. The nominal composition is close to that of 405 stainless. Carburization in CO/CO{sub 2} atmosphere followed by heat treatment produces foams of either 410 or 420 type stainless steels depending on carbon content. Compressive stress-strain behavior was measured on point contact bonded stainless foams both before and after carburization. Hardness measurements on steel sphere walls were used to estimate the yield strength. Relative strengths of the foams were positioned between open and closed cell models. This was encouraging because bonding in the foams was less than optimum and the hollow sphere walls contained defects. As processing improves, strengths should increase. To produce titanium alloy spheres, the starting powder is titanium alloy hydride. Thermal treatment in an inert atmosphere decomposes the hydride and sinters the titanium powder in the sphere walls to greater than 96% relative density. Both titanium and Ti-6V-4V spheres and foams have been produced. Oxygen contents are a concern for titanium compositions and processing is being altered to reduce oxygen levels to increase ductility.
Perturbative Casimir Energies of Spheres
NASA Astrophysics Data System (ADS)
Barton, G.
The Casimir energies of single bodies (as opposed to the interaction between mutually disjoint bodies) have accumulated deceptive folklore which this talk will try to exorcise, by mean of calculations for atomic solids that, though optically dilute, are realistically dispersive. This is easy, because quantum electrodynamics then yields identically the same energy as one gets from the properly retarded interatomic potentials. The problem of regularizing (nominal) divergences turns out to be quite distinct from the appropriate process of renormalization: simply discarding all nominally divergent contributions would prevent one from understanding the physics. Contrary to legend, the pertinent Casimir energies for dielectric spheres are attractive.
Brittle onset of monodispersed magmatic suspensions: from spheres to spheroid
NASA Astrophysics Data System (ADS)
Cordonnier, B.; Kaus, B.; Manga, M.; Caricchi, L.; Pistone, M.; Castro, J.; Hess, K.-U.; Gottschaller, S.; Dingwell, D. B.; Burlini, L.
2012-04-01
post-processing are all performed under MATLAB. For the largest meshes, the computation has been performed with the help of the BRUTUS cluster at ETH Zurich. For solving the system of equation we used the MILAMIN solver and extended it from 2-D to 3-D by the use of Crouzeix-Raviart type elements. MILAMIN is a native MATLAB implementation, which takes advantage of Tim Davi's SuiteSparse package. Here we solve the incompressible Stokes equations. We tested random to structured configurations (Simple Cubic, Body Centered Cubic and Face Centered Cubic) for different particle orientations from random to aligned. These numerical simulations allow us to estimate the stress concentration in magmas due to the presence of the crystals. Our results first confirm the hydrodynamics effects on the flow of elongated particles. The calculated apparent viscosity of the material versus the crystal fraction confirms an early increase for the suspensions viscosity with elongated particles. More importantly, the stress localization due to the particles suggests that the melt will start cracking for a relatively lower bulk stress. Finally, the experimental trend is supported by the numerical simulations, which highlight the importance of the critical packing fraction in addition to the maximum packing fraction. The combination of experimental results and numerical modeling allow us to characterize the physical processes responsible for the failure of particle bearing suspensions and characterize the effect of fraction and shape on the brittle-ductile transition.
Visual attention on the sphere.
Bogdanova, Iva; Bur, Alexandre; Hugli, Heinz
2008-11-01
Human visual system makes an extensive use of visual attention in order to select the most relevant information and speed-up the vision process. Inspired by visual attention, several computer models have been developed and many computer vision applications rely today on such models. However, the actual algorithms are not suitable to omnidirectional images, which contain a significant amount of geometrical distortion. In this paper, we present a novel computational approach that performs in spherical geometry and thus is suitable for omnidirectional images. Following one of the actual models of visual attention, the spherical saliency map is obtained by fusing together intensity, chromatic, and orientation spherical cue conspicuity maps that are themselves obtained through multiscale analysis on the sphere. Finally, the consecutive maxima in the spherical saliency map represent the spots of attention on the sphere. In the experimental part, the proposed method is then compared to the standard one using a synthetic image. Also, we provide examples of spots detection in real omnidirectional scenes which show its advantages. Finally, an experiment illustrates the homogeneity of the detected visual attention in omnidirectional images. PMID:18854253
NASA Astrophysics Data System (ADS)
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-07-01
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.
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
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.
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.
Impingement of Water Droplets on a Sphere
NASA Technical Reports Server (NTRS)
Dorsch, Robert G.; Saper, Paul G.; Kadow, Charles F.
1955-01-01
Droplet trajectories about a sphere in ideal fluid flow were calculated. From the calculated droplet trajectories the droplet impingement characteristics of the sphere were determined. Impingement data and equations for determining the collection efficiency, the area, and the distribution of impingement are presented in terms of dimensionless parameters. The range of flight and atmospheric conditions covered in the calculations was extended considerably beyond the range covered by previously reported calculations for the sphere.
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.
Preparation of thorium-uranium gel spheres
Spence, R.D.; Haas, P.A.
1980-01-01
Ceramic oxide spheres with diameters of 15 to 1500 ..mu..m are being evaluated for fabrication of power reactor fuel rods. (Th,U)O/sub 2/ spheres can be prepared by internal or external chemical gelation of nitrate solutions or oxide sols. Two established external gelation techniques were tested but proved to be unsatisfactory for the intended application. Established internal gelation techniques for UO/sub 2/ spheres were applied with minor modifications to make 75% ThO/sub 2/-25% UO/sub 2/ spheres that sinter to diameters of 200 to 1400 ..mu..m (99% T.D.).
Science off the Sphere: Earth in Infrared
International Space Station Expedition 30 astronaut Don Pettit views cities, agricultural areas and deserts using an infrared camera for 'Science off the Sphere.' Through a partnership between NASA...
Photonic crystals from multiply-coated spheres
NASA Astrophysics Data System (ADS)
Chan, Che Ting
2000-03-01
We show theoretically and experimentally that photonic band gaps can be realized using metal or metal-coated spheres as building blocks. Robust photonic gaps exist in any periodic structure built from such spheres when the filling ratio of the spheres exceeds a threshold, and they are not sensitive to the symmetry or the global long range order, with stacking faults cause almost no degradation. Good agreement between theory and experiment is obtained in the microwave regime. The gaps persist even in a random packing of such spheres. Calculations show that the approach can be scaled up to IR and optical frequencies.
Unexpected ricochet of spheres off water
NASA Astrophysics Data System (ADS)
Shlien, D. J.
1994-08-01
A sphere was observed to apparently ricochet off the free surface of water at incident angles as large as 45° while the expected (empirical/analytical) maximum angle to the horizontal for ricochet was 6°. Closer examination of the process revealed that the cavitating sphere penetrated the liquid to depths as great as 35 sphere diameters. Under certain circumstances the sphere was also observed to leave the liquid in a direction close to the incoming direction; that is, the sphere ricocheted backwards! This peculiar behavior was found to be a result of an unintentional spin applied to the sphere upon launching. By crudely modelling the process, the sphere path is qualitatively predicted. It was found that the drag and lift coefficients required to model the trajectory data were several times smaller than those obtained for the non-cavitating case or for the non-spinning case. If more precise sphere trajectory data were available, this experiment could be used to measure the lift and drag coefficients of a spinning and cavitating sphere.
Method for producing small hollow spheres
Hendricks, C.D.
1979-01-09
Method is disclosed 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 [approx gt] 600 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. 1 fig.
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.
Hollow Spheres in Composite Materials and Metallic Hollow Sphere Composites (MHSC)
NASA Astrophysics Data System (ADS)
Baumeister, Erika; Molitor, Martin
The newly developed metallic hollow spheres are used in combination with a polymeric matrix for producing metallic hollow-sphere-composites (MSHC), which have been developed for mechanical engineering applications in the “InnoZellMet” project.
Tandem spheres in hypersonic flow
Laurence, Stuart J; Deiterding, Ralf; Hornung, Hans G
2009-01-01
The problem of determining the forces acting on a secondary body when it is travelling at some point within the shocked region created by a hypersonic primary body is of interest in such situations as store or stage separation, re-entry of multiple vehicles, and atmospheric meteoroid fragmentation. The current work is concerned with a special case of this problem, namely that in which both bodies are spheres and are stationary with respect to one another. We first present an approximate analytical model of the problem; subsequently, numerical simulations are described and results are compared with those from the analytical model. Finally, results are presented from a series of experiments in the T5 hypervelocity shock tunnel in which a newly-developed force-measurement technique was employed.
The Circle and Sphere as Great Equalizers.
ERIC Educational Resources Information Center
Schwartzman, Steven
1991-01-01
From the equality of the ratios of the surface areas and volumes of a sphere and its circumscribed cylinder, the exploration of theorems relating the ratios of surface areas and volumes of a sphere and other circumscribed solids in three dimensions, and analogous questions relating two-dimensional concepts of perimeter and area is recounted. (MDH)
Electric dipoles on the Bloch sphere
NASA Astrophysics Data System (ADS)
Vutha, Amar C.
2015-03-01
The time evolution of a two-level quantum mechanical system can be geometrically described using the Bloch sphere. By mapping the Bloch sphere evolution onto the dynamics of oscillating electric dipoles, we provide a physically intuitive link between classical electromagnetism and the electric dipole transitions of atomic and molecular physics.
The "Magical" Sphere: Uncovering the Secret
ERIC Educational Resources Information Center
Petruševski, Vladimir M.; Bukleski, Miha
2006-01-01
A red sphere is seen at the bottom of a sealed glass tube filled with a colorless, transparent liquid. Holding the tube for a short period makes the sphere rise slowly from the bottom until it finally floats on the surface of the liquid. Instructions for preparing the demonstration are given, together with an explanation of the phenomenon. A…
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…
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…
Impact into Coarse Grained Spheres
NASA Technical Reports Server (NTRS)
Barnouin-Jha, O. S.; Cintala, M.; Crawford, D. A.
2005-01-01
Several experimental studies [1,2,3] indicate that differences in the grain size of the target relative to the projectile could influence the cratering process. Impacts into coarse sand grains of size comparable to the projectile show some discrepancies with existing relationships for crater growth [e.g. 4]. Similarly, targets of ne grained, uniform in diameter glass spheres show differences in crater depth, transient crater diameter, and volume of ejecta excavated as a function of grain size [2,3]. The purpose of this work is to continue investigating how the relative grain size may influence early time coupling between a projectile and target, with implications for subsequent ejecta excavation and crater growth. In previous efforts we used numerical techniques to focus on the propagation of shock waves in coarse, granular media emphasizing the influence of relative grain size on crater growth, ejecta production, cratering efficiency, target strength, and crater shape [5,6,7]. In this study, we use experimental techniques - in part as a reality check for the numerical studies - to report on how coarse grained targets might influence ejecta excavation and crater shape. This body of work possesses important implications for ejecta excavation and cratering efficiency on asteroids that may possess rubble pile-like structures, and on planets that may possess either pre-fractured surfaces or large-scale heterogeneities in shock impedance.
Ceramic Spheres From Cation Exchange Beads
NASA Technical Reports Server (NTRS)
Dynys, F. W.
2003-01-01
Porous ZrO2 and hollow TiO2 spheres were synthesized from a strong acid cation exchange resin. Spherical cation exchange beads, polystyrene based polymer, were used as a morphological-directing template. Aqueous ion exchange reaction was used to chemically bind (ZrO)(2+) ions to the polystyrene structure. The pyrolysis of the polystyrene at 600 C produces porous ZrO2 spheres with a surface area of 24 sq m/g with a mean sphere size of 42 microns. Hollow TiO2 spheres were synthesized by using the beads as a micro-reactor. A direct surface reaction - between titanium isopropoxide and the resin beads forms a hydrous TiO2 shell around the polystyrene core. The pyrolysis of the polystyrene core at 600 C produces hollow anatase spheres with a surface area of 42 sq m/g with a mean sphere size of 38 microns. The formation of ceramic spheres was studied by XRD, SEM and B.E.T. nitrogen adsorption measurements.
Induced differentiation inhibits sphere formation in neuroblastoma.
Craig, Brian T; Rellinger, Eric J; Alvarez, Alexandra L; Dusek, Haley L; Qiao, Jingbo; Chung, Dai H
2016-08-19
Neuroblastoma arises from the neural crest, the precursor cells of the sympathoadrenal axis, and differentiation status is a key prognostic factor used for clinical risk group stratification and treatment strategies. Neuroblastoma tumor-initiating cells have been successfully isolated from patient tumor samples and bone marrow using sphere culture, which is well established to promote growth of neural crest stem cells. However, accurate quantification of sphere-forming frequency of commonly used neuroblastoma cell lines has not been reported. Here, we show that MYCN-amplified neuroblastoma cell lines form spheres more frequently than non-MYCN-amplified cell lines. We also show that sphere formation is directly sensitive to cellular differentiation status. 13-cis-retinoic acid is a clinically used differentiating agent that induces a neuronal phenotype in neuroblastoma cells. Induced differentiation nearly completely blocked sphere formation. Furthermore, sphere formation was specifically FGF-responsive and did not respond to increasing doses of EGF. Taken together, these data suggest that sphere formation is an accurate method of quantifying the stemness phenotype in neuroblastoma. PMID:27297102
NASA Astrophysics Data System (ADS)
Cheng, Hongbo
2015-08-01
The Casimir energies for plate-sphere system and sphere-sphere systems under PFA in the presence of one extra compactified universal dimension are analyzed. We find that the Casimir energy between a plate and a sphere in the case of sphere-based PFA is divergent. The Casimir energy of plate-sphere system in the case of plate-based PFA is finite and keeps negative. The extra-dimension corrections to the Casimir energy will be more manifest if the sphere is larger or farther away from the plate. It is shown that the negative Casimir energy for two spheres is also associated with the sizes of spheres and extra space. The larger spheres and the longer distance between them make the influence from the additional dimension stronger.
Flow around spheres by dissipative particle dynamics
NASA Astrophysics Data System (ADS)
Chen, Shuo; Phan-Thien, Nhan; Khoo, Boo Cheong; Fan, Xi Jun
2006-10-01
The dissipative particle dynamics (DPD) method is used to study the flow behavior past a sphere. The sphere is represented by frozen DPD particles while the surrounding fluids are modeled by simple DPD particles (representing a Newtonian fluid). For the surface of the sphere, the conventional model without special treatment and the model with specular reflection boundary condition proposed by Revenga et al. [Comput. Phys. Commun. 121-122, 309 (1999)] are compared. Various computational domains, in which the sphere is held stationary at the center, are investigated to gage the effects of periodic conditions and walls for Reynolds number (Re)=0.5 and 50. Two types of flow conditions, uniform flow and shear flow are considered, respectively, to study the drag force and torque acting on the stationary sphere. It is found that the calculated drag force imposed on the sphere based on the model with specular reflection is slightly lower than the conventional model without special treatment. With the conventional model the drag force acting on the sphere is in better agreement with experimental correlation obtained by Brown and Lawler [J. Environ. Eng. 129, 222 (2003)] for the case of larger radius up to Re of about 5. The computed torque also approaches the analytical Stokes value when Re <1. For a force-free and torque-free sphere, its motion in the flow is captured by solving the translational and rotational equations of motion. The effects of different DPD parameters (a, γ, and σ) on the drag force and torque are studied. It shows that the dissipative coefficient (γ) mainly affects the drag force and torque, while random and conservative coefficient have little influence on them. Furthermore the settling of a single sphere in square tube is investigated, in which the wall effect is considered. Good agreement is found with the experiments of Miyamura et al. [Int. J. Multiphase Flow 7, 31 (1981)] and lattice-Boltzmann simulation results of Aidun et al. [J. Fluid Mech
Numerical Simulations of Falling Sphere Viscometry Experiments.
NASA Astrophysics Data System (ADS)
O Dwyer, L.; Kellogg, L. H.; Lesher, C. E.
2007-12-01
The falling sphere technique based on Stokes' law is widely used to determine the viscosities of geologically relevant melts at high pressures. Stokes' law is valid when a rigid sphere falls slowly and steadily through a stationary and infinite Newtonian medium of uniform properties. High-pressure falling sphere experiments however, usually involve dropping a dense, refractory sphere through a liquid contained by a cylindrical capsule of finite size. The sphere velocity is influenced by the walls (Faxen correction) and ends of the capsule, and possible convective motion of the fluid. Efforts are made to minimize thermal gradients in laboratory experiments, but small temperature differences within the capsule can lead to convection complicating interpretation. We utilize GALE (Moresi et al., 2003;), a finite element particle-in-cell code, to examine these factors in numerical models of conditions similar to those of high-pressure experiments. Our modeling considers a three- dimensional box or cylinder containing a cluster of particles that represent the dense sphere in laboratory experiments surrounded by low viscosity particles representing the melt. GALE includes buoyancy forces, heat flow, and viscosity variations so our model can be used to assess the effects of the capsule's walls and ends, and the consequences of thermal gradients on the sphere's velocity and trajectory. Comparisons between our numerical simulations and real-time falling sphere experiments involving lower viscosity molten komatiite are made to assess the validity of Stokes' law with the standard Faxen correction included, and formulations considering end effects. The modeling also permits an evaluation of the uncertainties in recovering accurate liquid viscosities from Stokes' law when a dense sphere falls through a convecting low viscosity melt. It also allows us to assess acceleration to a terminal velocity that can provide constraints on melt viscosity in experiments in which the terminal
Manipulator for rotating and examining small spheres
Weinstein, Berthold W. [Livermore, CA; Willenborg, David L. [Livermore, CA
1980-02-12
A manipulator which provides fast, accurate rotational positioning of a small sphere, such as an inertial confinement fusion target, which allows inspecting of the entire surface of the sphere. The sphere is held between two flat, flexible tips which move equal amounts in opposite directions. This provides rolling of the ball about two orthogonal axes without any overall translation. The manipulator may be controlled, for example, by an x- and y-axis driven controlled by a mini-computer which can be programmed to generate any desired scan pattern.
Manipulator for rotating and examining small spheres
Weinstein, B.W.; Willenborg, D.L.
1980-02-12
A manipulator is disclosed which provides fast, accurate rotational positioning of a small sphere, such as an inertial confinement fusion target, which allows inspecting of the entire surface of the sphere. The sphere is held between two flat, flexible tips which move equal amounts in opposite directions. This provides rolling of the ball about two orthogonal axes without any overall translation. The manipulator may be controlled, for example, by an x- and y-axis driven controlled by a mini-computer which can be programmed to generate any desired scan pattern. 8 figs.
Integrating Sphere Alkali-Metal Vapor Cells
NASA Astrophysics Data System (ADS)
McGuyer, Bart; Ben-Kish, Amit; Jau, Yuan-Yu; Happer, William
2010-03-01
An integrating sphere is an optical multi-pass cavity that uses diffuse reflection to increase the optical path length. Typically applied in photometry and radiometry, integrating spheres have previously been used to detect trace gases and to cool and trap alkali-metal atoms. Here, we investigate the potential for integrating spheres to enhance optical absorption in optically thin alkali-metal vapor cells. In particular, we consider the importance of dielectric effects due to a glass container for the alkali-metal vapor. Potential applications include miniature atomic clocks and magnetometers, where multi-passing could reduce the operating temperature and power consumption.
Superelastic carbon spheres under high pressure
NASA Astrophysics Data System (ADS)
Li, Meifen; Guo, Junjie; Xu, Bingshe
2013-03-01
We report a superelastic deformation behavior of carbon spheres by the in situ Raman spectroscopy in a high-pressure diamond anvil cell. The carbon spheres produced by arc discharging in toluene have a mean diameter of 200 nm and an onion-like multilayer graphitic structure. We find that the elastic coefficients, during both the compression and decompression processes, remain a constant up to 10 GPa, indicating a superior high-pressure structural stability. Such superelastic behavior is related to the isotropic and concentric configuration of carbon spheres and provides additional insight into improving the microscopic mechanical properties of small-scale particles.
Separate spheres and indirect benefits
Brock, Dan W
2003-01-01
On any plausible account of the basis for health care resource prioritization, the benefits and costs of different alternative resource uses are relevant considerations in the prioritization process. Consequentialists hold that the maximization of benefits with available resources is the only relevant consideration. Non-consequentialists do not reject the relevance of consequences of benefits and costs, but insist that other considerations, and in particular the distribution of benefits and costs, are morally important as well. Whatever one's particular account of morally justified standards for the prioritization of different health interventions, we must be able to measure those interventions' benefits and costs. There are many theoretical and practical difficulties in that measurement, such as how to weigh extending life against improving health and quality of life as well as how different quality of life improvements should be valued, but they are not my concern here. This paper addresses two related issues in assessing benefits and costs for health resource prioritization. First, should benefits be restricted only to health benefits, or include as well other non health benefits such as economic benefits to employers from reducing the lost work time due to illness of their employees? I shall call this the Separate Spheres problem. Second, should only the direct benefits, such as extending life or reducing disability, and direct costs, such as costs of medical personnel and supplies, of health interventions be counted, or should other indirect benefits and costs be counted as well? I shall call this the Indirect Benefits problem. These two issues can have great importance for a ranking of different health interventions by either a cost/benefit or cost effectiveness analysis (CEA) standard. PMID:12773217
#4 Simulated Solar Sphere from Data - Interpolated
Rotating solar sphere made from a combination of imagery from the two STEREO spacecraft, together with simultaneous data from the Solar Dynamic Observatory.This movie is made from data taken on Jan...
Science off the Sphere: Lenses and Vortices
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...
Elastic spheres can walk on water
NASA Astrophysics Data System (ADS)
Belden, Jesse; Hurd, Randy C.; Jandron, Michael A.; Bower, Allan F.; Truscott, Tadd T.
2016-02-01
Incited by public fascination and engineering application, water-skipping of rigid stones and spheres has received considerable study. While these objects can be coaxed to ricochet, elastic spheres demonstrate superior water-skipping ability, but little is known about the effect of large material compliance on water impact physics. Here we show that upon water impact, very compliant spheres naturally assume a disk-like geometry and dynamic orientation that are favourable for water-skipping. Experiments and numerical modelling reveal that the initial spherical shape evolves as elastic waves propagate through the material. We find that the skipping dynamics are governed by the wave propagation speed and by the ratio of material shear modulus to hydrodynamic pressure. With these insights, we explain why softer spheres skip more easily than stiffer ones. Our results advance understanding of fluid-elastic body interaction during water impact, which could benefit inflatable craft modelling and, more playfully, design of elastic aquatic toys.
Acoustic levitation of a large solid sphere
NASA Astrophysics Data System (ADS)
Andrade, Marco A. B.; Bernassau, Anne L.; Adamowski, Julio C.
2016-07-01
We demonstrate that acoustic levitation can levitate spherical objects much larger than the acoustic wavelength in air. The acoustic levitation of an expanded polystyrene sphere of 50 mm in diameter, corresponding to 3.6 times the wavelength, is achieved by using three 25 kHz ultrasonic transducers arranged in a tripod fashion. In this configuration, a standing wave is created between the transducers and the sphere. The axial acoustic radiation force generated by each transducer on the sphere was modeled numerically as a function of the distance between the sphere and the transducer. The theoretical acoustic radiation force was verified experimentally in a setup consisting of an electronic scale and an ultrasonic transducer mounted on a motorized linear stage. The comparison between the numerical and experimental acoustic radiation forces presents a good agreement.
Science off the Sphere: Knitting Needles
International Space Station Expedition 30 astronaut Don Pettit uses knitting needles and water droplets to demonstrate physics in space for 'Science off the Sphere.' Through a partnership between N...
Science off the Sphere: Thin Film Physics
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...
Entanglement entropy across a deformed sphere
NASA Astrophysics Data System (ADS)
Mezei, Márk
2015-02-01
I study the entanglement entropy (EE) across a deformed sphere in conformal field theories (CFTs). I show that the sphere (locally) minimizes the universal term in EE among all shapes. In the work of Allais and Mezei [Phys. Rev. D 91, 046002 (2015)] it was derived that the sphere is a local extremum, by showing that the contribution linear in the deformation parameter is absent. In this paper I demonstrate that the quadratic contribution is positive and is controlled by the coefficient of the stress tensor two-point function, CT. Such a minimization result contextualizes the fruitful relation between the EE of a sphere and the number of degrees of freedom in field theory. I work with CFTs with gravitational duals, where all higher curvature couplings are turned on. These couplings parametrize conformal structures in stress tensor n -point functions; hence I show the result for infinitely many CFT examples.
Elastic spheres can walk on water
Belden, Jesse; Hurd, Randy C.; Jandron, Michael A.; Bower, Allan F.; Truscott, Tadd T.
2016-01-01
Incited by public fascination and engineering application, water-skipping of rigid stones and spheres has received considerable study. While these objects can be coaxed to ricochet, elastic spheres demonstrate superior water-skipping ability, but little is known about the effect of large material compliance on water impact physics. Here we show that upon water impact, very compliant spheres naturally assume a disk-like geometry and dynamic orientation that are favourable for water-skipping. Experiments and numerical modelling reveal that the initial spherical shape evolves as elastic waves propagate through the material. We find that the skipping dynamics are governed by the wave propagation speed and by the ratio of material shear modulus to hydrodynamic pressure. With these insights, we explain why softer spheres skip more easily than stiffer ones. Our results advance understanding of fluid-elastic body interaction during water impact, which could benefit inflatable craft modelling and, more playfully, design of elastic aquatic toys. PMID:26842860
Catalytic, hollow, refractory spheres, conversions with them
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
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.
StenniSphere reopens after Hurricane Katrina
NASA Technical Reports Server (NTRS)
2006-01-01
StenniSphere reopened Jan. 18, 2006, almost five months after Hurricane Katrina damaged the basement of the building that houses the visitor center. Thanks to the staff's careful preparations before the storm, no artifacts or exhibits were harmed.
Elastic spheres can walk on water.
Belden, Jesse; Hurd, Randy C; Jandron, Michael A; Bower, Allan F; Truscott, Tadd T
2016-01-01
Incited by public fascination and engineering application, water-skipping of rigid stones and spheres has received considerable study. While these objects can be coaxed to ricochet, elastic spheres demonstrate superior water-skipping ability, but little is known about the effect of large material compliance on water impact physics. Here we show that upon water impact, very compliant spheres naturally assume a disk-like geometry and dynamic orientation that are favourable for water-skipping. Experiments and numerical modelling reveal that the initial spherical shape evolves as elastic waves propagate through the material. We find that the skipping dynamics are governed by the wave propagation speed and by the ratio of material shear modulus to hydrodynamic pressure. With these insights, we explain why softer spheres skip more easily than stiffer ones. Our results advance understanding of fluid-elastic body interaction during water impact, which could benefit inflatable craft modelling and, more playfully, design of elastic aquatic toys. PMID:26842860
Please comply: the water entry of soft spheres
NASA Astrophysics Data System (ADS)
Belden, Jesse; Hurd, Randy; Fanning, Tate; Jandron, Michael; Rekos, John; Bower, Allan; Truscott, Tadd
2015-11-01
The typical phenomena associated with sphere water impact are significantly altered when the sphere material is highly compliant rather than rigid. We describe the water impact physics of homogenous and hollow elastic spheres. The homogeneous spheres undergo large oscillatory deformations throughout entry that carve nested disturbances into the normally smooth air cavity, altering cavity shape and pinch off. Using an analytical model, we relate the maximum sphere deformation to the material properties and impact velocity. This characteristic deformation is used to reconcile the differences between cavities formed by compliant and rigid spheres. In addition to the nested disturbances seen with the homogeneous spheres, we observe azimuthal irregularities on the cavity during water entry of hollow elastic spheres. Based on experiments and finite-element modeling, we suggest that these disturbances are initiated by vibration mode shapes excited in the hollow spheres upon impact. For all sphere types, we compare the forces throughout water entry to the rigid sphere case.
Liouville Quantum Gravity on the Riemann Sphere
NASA Astrophysics Data System (ADS)
David, François; Kupiainen, Antti; Rhodes, Rémi; Vargas, Vincent
2016-03-01
In this paper, we rigorously construct Liouville Quantum Field Theory on the Riemann sphere introduced in the 1981 seminal work by Polyakov. We establish some of its fundamental properties like conformal covariance under PSL{_2({C})}-action, Seiberg bounds, KPZ scaling laws, KPZ formula and the Weyl anomaly formula. We also make precise conjectures about the relationship of the theory to scaling limits of random planar maps conformally embedded onto the sphere.
Approximating spheroid inductive responses using spheres
Smith, J. Torquil; Morrison, H. Frank
2003-12-12
The response of high permeability ({mu}{sub r} {ge} 50) conductive spheroids of moderate aspect ratios (0.25 to 4) to excitation by uniform magnetic fields in the axial or transverse directions is approximated by the response of spheres of appropriate diameters, of the same conductivity and permeability, with magnitude rescaled based on the differing volumes, D.C. magnetizations, and high frequency limit responses of the spheres and modeled spheroids.
Hollow sphere ceramic particles for abradable coatings
Longo, F.N.; Bader, N.F. III; Dorfman, M.R.
1984-05-22
A hollow sphere ceramic flame spray powder is disclosed. The desired constituents are first formed into agglomerated particles in a spray drier. Then the agglomerated particles are introduced into a plasma flame which is adjusted so that the particles collected are substantially hollow. The hollow sphere ceramic particles are suitable for flame spraying a porous and abradable coating. The hollow particles may be selected from the group consisting of zirconium oxide and magnesium zirconate.
Inverse Magnus effect on a rotating sphere
NASA Astrophysics Data System (ADS)
Kim, Jooha; Park, Hyungmin; Choi, Haecheon; Yoo, Jung Yul
2011-11-01
In this study, we investigate the flow characteristics of rotating spheres in the subcritical Reynolds number (Re) regime by measuring the drag and lift forces on the sphere and the two-dimensional velocity in the wake. The experiment is conducted in a wind tunnel at Re = 0 . 6 ×105 - 2 . 6 ×105 and the spin ratio (ratio of surface velocity to the free-stream velocity) of 0 (no spin) - 0.5. The drag coefficient on a stationary sphere remains nearly constant at around 0.52. However, the magnitude of lift coefficient is nearly zero at Re < 2 . 0 ×105 , but rapidly increases to 0.3 and then remains constant with further increasing Reynolds number. On the other hand, with rotation, the lift coefficient shows negative values, called inverse Magnus effect, depending on the magnitudes of the Reynolds number and spin ratio. The velocity field measured from a particle image velocimetry (PIV) indicates that non-zero lift coefficient on a stationary sphere at Re > 2 . 0 ×105 results from the asymmetry of separation line, whereas the inverse Magnus effect for the rotating sphere results from the differences in the boundary-layer growth and separation along the upper and lower sphere surfaces. Supported by the WCU, Converging Research Center and Priority Research Centers Program, NRF, MEST, Korea.
NASA Astrophysics Data System (ADS)
Navruz, N.
2001-02-01
The aim of the present study is to discuss the infinitesimal deformation (ID) approach’s application and practical applicability. Therefore, ID theory was reformulated and applied to the face centered cubic (fcc) to body centered tetragonal (bct) martensitic transformation for the case of the (110) [bar 110] slip system as the lattice invariant shear (LIS). The analytical solutions for the habit plane orientation, the magnitude of the lattice invariant shear, the orientation relation between parent and product phases, etc. were derived for fcc to bct martensitic transformation in an Fe-7 pct Al-2 pct C alloy. In order to compare with phenomenological theory’s results, crystallographic parameters were also calculated by using Wechsler, Lieberman, and Read (W-L-R) phenomenological theory. Agreement between the two results obtained from ID approach and W-L-R theory was found to be excellent.
A Unit Cell Laboratory Experiment: Marbles, Magnets, and Stacking Arrangements
ERIC Educational Resources Information Center
Collins, David C.
2011-01-01
An undergraduate first-semester general chemistry laboratory experiment introducing face-centered, body-centered, and simple cubic unit cells is presented. Emphasis is placed on the stacking arrangement of solid spheres used to produce a particular unit cell. Marbles and spherical magnets are employed to prepare each stacking arrangement. Packing…
Terminal energy distribution of blast waves from bursting spheres
NASA Technical Reports Server (NTRS)
Adamczyk, A. A.; Strehlow, R. A.
1977-01-01
The calculation results for the total energy delivered to the surroundings by the burst of an idealized massless sphere containing an ideal gas are presented. The logic development of various formulas for sphere energy is also presented. For all types of sphere bursts the fraction of the total initial energy available in the sphere that is delivered to the surroundings is shown to lie between that delivered for the constant pressure addition of energy to a source region and that delivered by isentropic expansion of the sphere. The relative value of E sub/Q increases at fixed sphere pressure/surrounding pressure as sphere temperature increases because the velocity of sound increases.
The Separate Spheres Model of Gendered Inequality
Miller, Andrea L.; Borgida, Eugene
2016-01-01
Research on role congruity theory and descriptive and prescriptive stereotypes has established that when men and women violate gender stereotypes by crossing spheres, with women pursuing career success and men contributing to domestic labor, they face backlash and economic penalties. Less is known, however, about the types of individuals who are most likely to engage in these forms of discrimination and the types of situations in which this is most likely to occur. We propose that psychological research will benefit from supplementing existing research approaches with an individual differences model of support for separate spheres for men and women. This model allows psychologists to examine individual differences in support for separate spheres as they interact with situational and contextual forces. The separate spheres ideology (SSI) has existed as a cultural idea for many years but has not been operationalized or modeled in social psychology. The Separate Spheres Model presents the SSI as a new psychological construct characterized by individual differences and a motivated system-justifying function, operationalizes the ideology with a new scale measure, and models the ideology as a predictor of some important gendered outcomes in society. As a first step toward developing the Separate Spheres Model, we develop a new measure of individuals’ endorsement of the SSI and demonstrate its reliability, convergent validity, and incremental predictive validity. We provide support for the novel hypotheses that the SSI predicts attitudes regarding workplace flexibility accommodations, income distribution within families between male and female partners, distribution of labor between work and family spheres, and discriminatory workplace behaviors. Finally, we provide experimental support for the hypothesis that the SSI is a motivated, system-justifying ideology. PMID:26800454
The Separate Spheres Model of Gendered Inequality.
Miller, Andrea L; Borgida, Eugene
2016-01-01
Research on role congruity theory and descriptive and prescriptive stereotypes has established that when men and women violate gender stereotypes by crossing spheres, with women pursuing career success and men contributing to domestic labor, they face backlash and economic penalties. Less is known, however, about the types of individuals who are most likely to engage in these forms of discrimination and the types of situations in which this is most likely to occur. We propose that psychological research will benefit from supplementing existing research approaches with an individual differences model of support for separate spheres for men and women. This model allows psychologists to examine individual differences in support for separate spheres as they interact with situational and contextual forces. The separate spheres ideology (SSI) has existed as a cultural idea for many years but has not been operationalized or modeled in social psychology. The Separate Spheres Model presents the SSI as a new psychological construct characterized by individual differences and a motivated system-justifying function, operationalizes the ideology with a new scale measure, and models the ideology as a predictor of some important gendered outcomes in society. As a first step toward developing the Separate Spheres Model, we develop a new measure of individuals' endorsement of the SSI and demonstrate its reliability, convergent validity, and incremental predictive validity. We provide support for the novel hypotheses that the SSI predicts attitudes regarding workplace flexibility accommodations, income distribution within families between male and female partners, distribution of labor between work and family spheres, and discriminatory workplace behaviors. Finally, we provide experimental support for the hypothesis that the SSI is a motivated, system-justifying ideology. PMID:26800454
Robotics Programming Competition Spheres, Russian Part
NASA Astrophysics Data System (ADS)
Sadovski, Andrei; Kukushkina, Natalia; Biryukova, Natalia
2016-07-01
Spheres" such name was done to Russian part of the Zero Robotics project which is a student competition devoted to programming of SPHERES (SPHERES - Synchronized Position Hold Engage and Reorient Experimental Satellites are the experimental robotics devices which are capable of rotation and translation in all directions, http://ssl.mit.edu/spheres/), which perform different operations on the board of International Space Station. Competition takes place online on http://zerorobotics.mit.edu. The main goal is to develop a program for SPHERES to solve an annual challenge. The end of the tournament is the real competition in microgravity on the board of ISS with a live broadcast. The Russian part of the tournament has only two years history but the problems, organization and specific are useful for the other educational projects especially for the international ones. We introduce the history of the competition, its scientific and educational goals in Russia and describe the participation of Russian teams in 2014 and 2015 tournaments. Also we discuss the organizational problems.
SPHERES flight operations testing and execution
NASA Astrophysics Data System (ADS)
Mohan, Swati; Saenz-Otero, Alvar; Nolet, Simon; Miller, David W.; Sell, Steven
2009-10-01
Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) is a formation flight testing facility consisting of three satellites operating inside the International Space Station (ISS). The goal is to use the long term microgravity environment of the ISS to mature formation flight and docking algorithms. The operations processes of SPHERES have also matured over the course of the first seven test sessions. This paper describes the evolution of the SPHERES program operations processes from conception to implementation to refinement through flight experience. Modifications to the operations processes were based on experience and feedback from Marshall Space Flight Center Payload Operations Center, USAF Space Test Program office at Johnson Space Center, and the crew of Expedition 13 (first to operate SPHERES on station). Important lessons learned were on aspects such as test session frequency, determination of session success, and contingency operations. This paper describes the tests sessions; then it details the lessons learned, the change in processes, and the impact on the outcome of later test sessions. SPHERES had very successful initial test sessions which allowed for modification and tailoring of the operations processes to streamline the code delivery and to tailor responses based on flight experiences.
Thermodynamic properties of non-conformal soft-sphere fluids with effective hard-sphere diameters.
Rodríguez-López, Tonalli; del Río, Fernando
2012-01-28
In this work we study a set of soft-sphere systems characterised by a well-defined variation of their softness. These systems represent an extension of the repulsive Lennard-Jones potential widely used in statistical mechanics of fluids. This type of soft spheres is of interest because they represent quite accurately the effective intermolecular repulsion in fluid substances and also because they exhibit interesting properties. The thermodynamics of the soft-sphere fluids is obtained via an effective hard-sphere diameter approach that leads to a compact and accurate equation of state. The virial coefficients of soft spheres are shown to follow quite simple relationships that are incorporated into the equation of state. The approach followed exhibits the rescaling of the density that produces a unique equation for all systems and temperatures. The scaling is carried through to the level of the structure of the fluids. PMID:22158949
Physics of the granite sphere fountain
NASA Astrophysics Data System (ADS)
Snoeijer, Jacco H.; der Weele, Ko van
2014-11-01
A striking example of levitation is encountered in the "kugel fountain" where a granite sphere, sometimes weighing over a ton, is kept aloft by a thin film of flowing water. In this paper, we explain the working principle behind this levitation. We show that the fountain can be viewed as a giant ball bearing and thus forms a prime example of lubrication theory. It is demonstrated how the viscosity and flow rate of the fluid determine (i) the remarkably small thickness of the film supporting the sphere and (ii) the surprisingly long time it takes for rotations to damp out. The theoretical results compare well with measurements on a fountain holding a granite sphere of one meter in diameter. We close by discussing several related cases of levitation by lubrication.
Impact of a superhydrophobic sphere onto water.
Lee, Duck-Gyu; Kim, Ho-Young
2008-01-01
When a water drop hits a superhydrophobic solid surface, it bounces off the substrate like an elastic ball. Here we show that when a tiny superhydrophobic solid sphere impacts with water, it can bounce off the free surface just as it impacts with an elastic membrane. The motion of a sinking sphere is analytically calculated by solving a potential flow whose free boundary is determined by the Young-Laplace equation. To find conditions under which the solid sphere should sink, bounce off, or oscillate upon impact with water, we construct simple scaling laws which are shown to agree well with experimentally found boundaries between the distinct impact behaviors in a regime map based on dimensionless parameters. PMID:17999546
Geometrical characterization of hard-sphere systems.
Richard, P; Oger, L; Troadec, J P; Gervois, A
1999-10-01
By using molecular dynamics simulations on a large number of hard spheres and the Voronoï tessellation we characterize hard-sphere systems geometrically at any packing fraction eta along the different branches of the phase diagram. Crystallization of disordered packings occurs only for a small range of packing fraction. For the other packing fractions the system behaves as either a fluid (stable or metastable) or a glass. We have studied the evolution of the statistics of the Voronoï tessellation during crystallization and characterized the apparition of order by an order parameter (Q(6)) built from spherical harmonics. PMID:11970312
Strength Measurement of Ceramic Spheres Using a Diametrally Compressed "C-Sphere" Specimen
Wereszczak, Andrew A; Jadaan, Osama M.; Kirkland, Timothy Philip
2007-01-01
A "C-sphere" flexure strength specimen geometry was conceived and developed to measure the hoop tensile strength of bearing-grade silicon nitride (Si3N4) balls. Because such a strength can be measured, the important study of surface-located strength-limiting flaws in ceramic sphere is also enabled with this specimen. A slot is machined into the balls to a set depth to produce the C-sphere geometry. A simple, monotonically increasing uniaxial compressive force produces a hoop tensile stress at the C-sphere's outer surface that ultimately initiates fracture. The strength is determined using the combination of failure load, C-sphere geometry, and finite element analysis. Additionally, the stress field was used to determine C-sphere effective areas and effective volumes as a function of Weibull modulus. To demonstrate this new specimen, C-sphere flexure strength distributions were determined for three commercially available bearing-grade Si3N4 materials (NBD200, SN101C, and TSN-03NH), and differences among their characteristic strengths and Weibull moduli were found.
Supersymmetric cubic Galileons have ghosts
NASA Astrophysics Data System (ADS)
Koehn, Michael; Lehners, Jean-Luc; Ovrut, Burt A.
2013-07-01
Galileons are higher-derivative theories of a real scalar which nevertheless admit second-order equations of motion. They have interesting applications as dark energy models and in early universe cosmology, and have been conjectured to arise as descriptions of brane dynamics in string theory. In the present paper, we study the bosonic sector of globally N=1 supersymmetric extensions of the cubic Galileon Lagrangian in detail. Supersymmetry requires that the Galileon scalar now becomes paired with a second real scalar field. We prove that the presence of this second scalar causes the equations of motion to become higher than second order, thus leading to the appearance of ghosts. We also analyze the energy scales up to which, in an effective field theory description, the ghosts can be tamed.
Spheres: from Ground Development to ISS Operations
NASA Technical Reports Server (NTRS)
Katterhagen, A.
2016-01-01
SPHERES (Synchronized Position Hold Engage and Reorient Experimental Satellites) is an internal International Space Station (ISS) Facility that supports multiple investigations for the development of multi-spacecraft and robotic control algorithms. The SPHERES National Lab Facility aboard ISS is managed and operated by NASA Ames Research Center (ARC) at Moffett Field California. The SPHERES Facility on ISS consists of three self-contained eight-inch diameter free-floating satellites which perform the various flight algorithms and serve as a platform to support the integration of experimental hardware. SPHERES has served to mature the adaptability of control algorithms of future formation flight missions in microgravity (6 DOF (Degrees of Freedom) / long duration microgravity), demonstrate key close-proximity formation flight and rendezvous and docking maneuvers, understand fault diagnosis and recovery, improve the field of human telerobotic operation and control, and lessons learned on ISS have significant impact on ground robotics, mapping, localization, and sensing in three-dimensions - among several other areas of study.
Electromagnetic resonant modes of dielectric sphere bilayers
NASA Astrophysics Data System (ADS)
Andueza, A.; Pérez-Conde, J.; Sevilla, J.
2015-05-01
Sphere bilayers have been proposed as promising structures for electromagnetic management in photonic crystal devices. These arrangements are made of two intertwined subsets of spheres of different size and refractive index, one subset filling the interstitial sites of the other. We present a systematic study of the electromagnetic resonant modes of the bilayers, in comparison with those of the constituent subsets of spheres. Three samples were built with glass and Teflon spheres and their transmission spectra measured in the microwave range (10-25 GHz). Simulations with finite integration time-domain method are in good agreement with experiments. Results show that the bilayer presents the same resonances as one of the subsets but modified by the presence of the other in its resonant frequencies and in the electric field distributions. As this distortion is not very large, the number of resonances in a selected spectral region is determined by the dominant subset. The degree of freedom that offers the bilayer could be useful to fine tune the resonances of the structure for different applications. A map of modes useful to guide this design is also presented. Scale invariance of Maxwell equations allows the translation of these results in the microwave range to the visible region; hence, some possible applications are discussed in this framework.
Propulsion of a Two-Sphere Swimmer.
Klotsa, Daphne; Baldwin, Kyle A; Hill, Richard J A; Bowley, R M; Swift, Michael R
2015-12-11
We describe experiments and simulations demonstrating the propulsion of a neutrally buoyant swimmer that consists of a pair of spheres attached by a spring, immersed in a vibrating fluid. The vibration of the fluid induces relative motion of the spheres which, for sufficiently large amplitudes, can lead to motion of the center of mass of the two spheres. We find that the swimming speed obtained from both experiment and simulation agree and collapse onto a single curve if plotted as a function of the streaming Reynolds number, suggesting that the propulsion is related to streaming flows. There appears to be a critical onset value of the streaming Reynolds number for swimming to occur. We observe a change in the streaming flows as the Reynolds number increases, from that generated by two independent oscillating spheres to a collective flow pattern around the swimmer as a whole. The mechanism for swimming is traced to a strengthening of a jet of fluid in the wake of the swimmer. PMID:26705658
Electromagnetic resonant modes of dielectric sphere bilayers
Andueza, A. Pérez-Conde, J.; Sevilla, J.
2015-05-28
Sphere bilayers have been proposed as promising structures for electromagnetic management in photonic crystal devices. These arrangements are made of two intertwined subsets of spheres of different size and refractive index, one subset filling the interstitial sites of the other. We present a systematic study of the electromagnetic resonant modes of the bilayers, in comparison with those of the constituent subsets of spheres. Three samples were built with glass and Teflon spheres and their transmission spectra measured in the microwave range (10–25 GHz). Simulations with finite integration time-domain method are in good agreement with experiments. Results show that the bilayer presents the same resonances as one of the subsets but modified by the presence of the other in its resonant frequencies and in the electric field distributions. As this distortion is not very large, the number of resonances in a selected spectral region is determined by the dominant subset. The degree of freedom that offers the bilayer could be useful to fine tune the resonances of the structure for different applications. A map of modes useful to guide this design is also presented. Scale invariance of Maxwell equations allows the translation of these results in the microwave range to the visible region; hence, some possible applications are discussed in this framework.
DNS of Swirling Flow Past a Sphere
NASA Astrophysics Data System (ADS)
Higgins, Keith; Ooi, Andrew; Chong, Min; Balachandar, S.
2001-11-01
Experimental investigations into the swirling flow past a sphere have revealed a range of surprising and complex flow phenomena. These results have advanced our understanding in applications such as particle entrainment and the combustion of fuel droplets. Renewed interest in this problem has been kindled by recent experimental observations. (Mattner et al. 2001, submitted for review to J. Fluid Mech.) This has motivated the development of a fully spectral direct numerical simulation of the three-dimensional time-dependent swirling flow past a sphere. The effect of swirl on the various transitions in the wake structure behind a sphere is unknown. The main objective of our study is to identify transitions that occur with increasing Reynolds number and swirl strength. Firstly, we show the effect of swirl strength on the axisymmetric sphere wake and drag. Then, using a three-dimensional simulation, we examine the effect of swirl on the time histories of the lift, drag and velocities. We hope to show some visualisations of the topology of the 3D wake flow using the invariants of the velocity gradient tensor.
Steel Spheres and Skydiver--Terminal Velocity
ERIC Educational Resources Information Center
Costa Leme, J.; Moura, C.; Costa, Cintia
2009-01-01
This paper describes the use of open source video analysis software in the study of the relationship between the velocity of falling objects and time. We discuss an experiment in which a steel sphere falls in a container filled with two immiscible liquids. The motion is similar to that of a skydiver falling through air.
Exact Interior Solutions for Charged Fluid Spheres
NASA Astrophysics Data System (ADS)
Patel, L. K.; Tikekar, R.; Sabu, M. C.
1997-04-01
A new method is discussed to obtain the interior solution of Einstein-Maxwell equations for a charged static sphere from a known particular solutions of a similar kind. Beginning with a charged fluid interior solution reported by Patel and Pandya [11], a new interior Reissner-Nordström metric is obtained using this method and physical aspects of it are extensively discussed.
Conforming quadrilaterals meshes on the cubed sphere.
Taylor, Mark A.; Levy, Michael Nathan; Overfelt, James Robert
2010-08-01
The cubed sphere geometry, obtained by inscribing a cube in a sphere and mapping points between the two surfaces using a gnomonic (central) projection, is commonly used in atmospheric models because it is free of polar singularities and is well-suited for parallel computing. Global meshes on the cubed-sphere typically project uniform (square) grids from each face of the cube onto the sphere, and if refinement is desired then it is done with non-conforming meshes - overlaying the area of interest with a finer uniform mesh, which introduces so-called hanging nodes on edges along the boundary of the fine resolution area. An alternate technique is to tile each face of the cube with quadrilaterals without requiring the quads to be rectangular. These meshes allow for refinement in areas of interest with a conforming mesh, providing a smoother transition between high and low resolution portions of the grid than non-conforming refinement. The conforming meshes are demonstrated in HOMME, NCAR's High Order Method Modeling Environment, where two modifications have been made: the dependence on uniform meshes has been removed, and the ability to read arbitrary quadrilateral meshes from a previously-generated file has been added. Numerical results come from a conservative spectral element method modeling a selection of the standard shallow water test cases.
Metal-Matrix/Hollow-Ceramic-Sphere Composites
NASA Technical Reports Server (NTRS)
Baker, Dean M.
2011-01-01
A family of metal/ceramic composite materials has been developed that are relatively inexpensive, lightweight alternatives to structural materials that are typified by beryllium, aluminum, and graphite/epoxy composites. These metal/ceramic composites were originally intended to replace beryllium (which is toxic and expensive) as a structural material for lightweight mirrors for aerospace applications. These materials also have potential utility in automotive and many other terrestrial applications in which there are requirements for lightweight materials that have high strengths and other tailorable properties as described below. The ceramic component of a material in this family consists of hollow ceramic spheres that have been formulated to be lightweight (0.5 g/cm3) and have high crush strength [40.80 ksi (.276.552 MPa)]. The hollow spheres are coated with a metal to enhance a specific performance . such as shielding against radiation (cosmic rays or x rays) or against electromagnetic interference at radio and lower frequencies, or a material to reduce the coefficient of thermal expansion (CTE) of the final composite material, and/or materials to mitigate any mismatch between the spheres and the matrix metal. Because of the high crush strength of the spheres, the initial composite workpiece can be forged or extruded into a high-strength part. The total time taken in processing from the raw ingredients to a finished part is typically 10 to 14 days depending on machining required.
The Sphere of Women in Colonial America.
ERIC Educational Resources Information Center
Cook, Robert
This project is a unit of six lessons designed to study and understand the roles and expectations of women in the colonial period. The unit provides an historical perspective on those expectations, examines how both men and women viewed the sphere of women, and how enlightened thought on this topic began to emerge during this revolutionary time.…
Experimentation on recurrent sphere collision with Audacity
NASA Astrophysics Data System (ADS)
Muradoglu, Murat; Ng, Enoch Ming Wei; Ng, Tuck Wah
2014-11-01
Under the theme of collisions that occur repeatedly, we conducted easy and inexpensive experiments of rebounding spheres and Newton’s cradle with two spheres to determine the coefficients of restitution using the sound record feature in modern laptops and a free and open source software called Audacity. In the rebounding sphere experiment, the coefficients of restitution of the golf and ping pong balls used were found to be 0.727 ± 0.025 and 0.816 ± 0.041 respectively. With the Netwon’s cradle experiment, the coefficient of restitution of two steel sphere balls was found to be 0.987 ± 0.003. The contrasts in the results obtained from both experiments permit the operational principles of a pendulum to be emphasized, and engagements to be made to consider the transfer of kinetic energy in the form of vibrational energy of the bodies’ constituents. Using a one-dimensional two-mass model with spring and damper linkages to account for harmonic motions that occur during impact, we found it possible to perform a simple analysis to account for this, and how it can be linked to high energy transfer modes such as the phenomenon of resonance and impedance matching.
ERIC Educational Resources Information Center
Pelton, Joseph N.
2002-01-01
Discusses the survival of the human race in the Third Millennium. Considers environmental issues; shifting from a focus on economic growth to human development; the rate of technological change; the e-sphere, which goes beyond a global village to a global brain; technology in education and in health care; and educational reform. (LRW)
Some analytical models of radiating collapsing spheres
Herrera, L.; Di Prisco, A; Ospino, J.
2006-08-15
We present some analytical solutions to the Einstein equations, describing radiating collapsing spheres in the diffusion approximation. Solutions allow for modeling physical reasonable situations. The temperature is calculated for each solution, using a hyperbolic transport equation, which permits to exhibit the influence of relaxational effects on the dynamics of the system.
Propulsion of a two-sphere swimmer
NASA Astrophysics Data System (ADS)
Klotsa, Daphne; Baldwin, Kyle; Hill, Richard; Bowley, Roger; Swift, Michael
We describe experiments and simulations demonstrating the propulsion of a neutrally-buoyant macroscopic swimming robot that consists of a pair of spheres attached by a spring, immersed in a vibrating fluid. The vibration of the fluid induces relative motion of the spheres which, for sufficiently large amplitudes, can lead to motion of the center of mass of the two spheres. We find that the swimming speed obtained from both experiment and simulation agree and collapse onto a single curve if plotted as a function of the streaming Reynolds number, suggesting that the propulsion is related to streaming flows. There appears to be a critical onset value of the streaming Reynolds number for swimming to occur. We observe a change in the streaming flows as the Reynolds number increases, from that generated by two independent oscillating spheres to a collective flow pattern around the swimmer as a whole. The mechanism for swimming is traced to a strengthening of a jet of fluid in the wake of the swimmer.
Generalized Vaidya spacetime for cubic gravity
NASA Astrophysics Data System (ADS)
Ruan, Shan-Ming
2016-03-01
We present a kind of generalized Vaidya solution of a new cubic gravity in five dimensions whose field equations in spherically symmetric spacetime are always second order like the Lovelock gravity. We also study the thermodynamics of its spherically symmetric apparent horizon and get its entropy expression and generalized Misner-Sharp energy. Finally, we present the first law and second law hold in this gravity. Although all the results are analogous to those in Lovelock gravity, we in fact introduce the contribution of a new cubic term in five dimensions where the cubic Lovelock term is just zero.
Generalized orbital angular momentum Poincaré sphere
NASA Astrophysics Data System (ADS)
Chithrabhanu, P.; Reddy, Salla Gangi; Anwar, Ali; Singh, R. P.
2015-06-01
We construct a orbital angular momentum (OAM) Poincaŕe sphere in which we can represent 2-D superposition states of arbitrary OAM. In addition, we represent the mixed states of OAM as non separable states inside the sphere. We also give an experimental set up to generate all points on this sphere.
Viscosity of concentrated suspensions of sphere/rod mixtures
Mor, R.; Gottlieb, M.; Graham, A.L.; Mondy, L.A.
1996-05-01
This paper discusses the viscosity of concentrated suspensions of sphere/rod mixtures by adopting the Thomas relations for spheres and Milliken`s for randomly oriented rods with aspect ratio of 20. The relative viscosity of a mixed suspension may now be calculated for any combination of rods (of aspect ratio 20) and spheres.
21 CFR 886.3320 - Eye sphere implant.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Eye sphere implant. 886.3320 Section 886.3320 Food... DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An eye sphere implant is a device intended to be implanted in the eyeball to occupy space following the...
21 CFR 886.3320 - Eye sphere implant.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Eye sphere implant. 886.3320 Section 886.3320 Food... DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An eye sphere implant is a device intended to be implanted in the eyeball to occupy space following the...
21 CFR 886.3320 - Eye sphere implant.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Eye sphere implant. 886.3320 Section 886.3320 Food... DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An eye sphere implant is a device intended to be implanted in the eyeball to occupy space following the...
Bidirectional reflection effects in practical integrating spheres.
Mahan, J R; Walker, J A; Stancil, M M
2015-10-20
Integrating spheres play a central role in radiometric instrument calibration, surface optical property measurement, and radiant source characterization. Our work involves a simulation, based on the Monte Carlo ray-trace (MCRT) of bidirectional reflections within a practical integrating sphere pierced with two viewing ports. We used data from the literature to create an empirical model for the bidirectional reflection distribution function (BRF) of Spectralon suitable for use in the MCRT environment. The ratio of power escaping through the two openings is shown to vary linearly with wall absorptivity for both diffuse and bidirectional reflections. The sensitivity of this ratio to absorptivity is shown to be less when reflections are weakly bidirectional. PMID:26560384
Improved method for producing small hollow spheres
Rosencwaig, A.; Koo, J.C.; Dressler, J.L.
An improved method and apparatus for producing small hollow spheres of glass having an outer diameter ranging from about 100..mu.. to about 500..mu.. with a substantially uniform wall thickness in the range of about 0.5 to 20..mu.. are described. The method involves introducing aqueous droplets of a glass-forming solution into a long vertical drop oven or furnace having varying temperature regions.
From Noncommutative Sphere to Nonrelativistic Spin
NASA Astrophysics Data System (ADS)
Deriglazov, Alexei A.
2010-02-01
Reparametrization invariant dynamics on a sphere, being parameterized by angular momentum coordinates, represents an example of noncommutative theory. It can be quantized according to Berezin-Marinov prescription, replacing the coordinates by Pauli matrices. Following the scheme, we present two semiclassical models for description of spin without use of Grassman variables. The first model implies Pauli equation upon the canonical quantization. The second model produces nonrelativistic limit of the Dirac equation implying correct value for the electron spin magnetic moment.
Equilibrium configurations of degenerate fluid spheres
Whitman, P.G.
1985-04-01
Equilibrium configurations of degenerate fluid spheres which assume a polytropic form in the ultrahigh-density regime are considered. We show that analytic solutions more general than those of Misner and Zapolsky exist which possess the asymptotic equation of state. Simple expressions are derived which indicate this nature of the fluids in the extreme relativistic limit, and the stability of these interiors is considered in the asymptotic region.
Diffusion processes in general relativistic radiating spheres
Barreto, W.; Herrera, L.; Santos, N.O.; Universidad Central de Venezuela, Caracas; Observatorio Nacional do Brasil, Rio de Janeiro )
1989-09-01
The influence of diffusion processes on the dynamics of general relativistic radiating spheres is systematically studied by means of two examples. Differences between the streaming-out limit and the diffusion limit are exhibited, for both models, through the evolution curves of dynamical variables. In particular it is shown the Bondi mass decreases, for both models, in the diffusion limit as compared with its value at the streaming-out regime. 15 refs.
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. PMID:25790335
Integrating spheres for improved skin photodynamic therapy.
Glennie, Diana L; Farrell, Thomas J; Hayward, Joseph E; Patterson, Michael S
2010-01-01
The prescribed radiant exposures for photodynamic therapy (PDT) of superficial skin cancers are chosen empirically to maximize the success of the treatment while minimizing adverse reactions for the majority of patients. They do not take into account the wide range of tissue optical properties for human skin, contributing to relatively low treatment success rates. Additionally, treatment times can be unnecessarily long for large treatment areas if the laser power is not sufficient. Both of these concerns can be addressed by the incorporation of an integrating sphere into the irradiation apparatus. The light fluence rate can be increased by as much as 100%, depending on the tissue optical properties. This improvement can be determined in advance of treatment by measuring the reflectance from the tissue through a side port on the integrating sphere, allowing for patient-specific treatment times. The sphere is also effective at improving beam flatness, and reducing the penumbra, creating a more uniform light field. The side port reflectance measurements are also related to the tissue transport albedo, enabling an approximation of the penetration depth, which is useful for real-time light dosimetry. PMID:21054127
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.
Broadband Electromagnetic Transparency by Graded Metamaterial Sphere
NASA Astrophysics Data System (ADS)
Sun, L.; Yu, K. W.
2010-03-01
We have investigated the scattering of electromagnetic waves from a radially inhomogeneous metamaterial sphere whose dielectric permittivity is described by the graded Drude model ɛs(r)=1-φp^2(r)/2̂. The radial position dependent plasma frequency depends on r as φp^2=1/2-c(r/r0)^n, where c and n are positive constants and r0 is the radius of the sphere. The electromagnetic field distribution has been calculated within the full-wave Mie scattering theory. When n=2, exact analytic solutions can be obtained in terms of confluent Heun function and confluent hypergeometric function of Kummer. This allows us to obtain the full-wave total scattering cross section analytically from the scattering field amplitudes. While the total scattering cross section Qs depends on both the graded plasma frequency profile and the frequency of the incident electromagnetic wave, it is found that Qs can achieve extremely small values over a broad frequency band and graded parameters. The analytic solutions allow us to assess the conditions for achieving broadband electromagnetic transparency in the metamaterial sphere and make tunable electromagnetic transparency feasible.
Method for producing small hollow spheres
Rosencwaig, Allen; Koo, Jackson C.; Dressler, John L.
1981-01-01
A method for producing small hollow spheres of glass having an outer diameter ranging from about 100.mu. to about 500.mu. with a substantially uniform wall thickness in the range of about 0.5-20.mu.. The method involves introducing aqueous droplets of a glass-forming solution into a long vertical drop oven or furnace having varying temperature regions. In one embodiment, one of the temperature regions is lower than both the preceeding region and the subsequent region. One region utilizes a temperature of at least 200.degree. C. higher than the melting point of the glass-forming material in the solution and, for example, may be at least 3 times higher than the temperature of the preceeding region. In addition, there is a sharp temperature gradient between these regions. As each droplet of solution passes through a first region it forms into a gel membrane having a spherical shape and encapsulates the rest of the drop retained in the elastic outer surface and the water entrapped within diffuses rapidly through the thin gel membrane which causes more of the glass-forming material to go out of solution and is incorporated into the gel membrane causing it to grow in size and become hollow. thus produced hollow glass sphere has a sphericity, concentricity, and wall uniformity of better than 5%. The sphere is capable of retaining material of up to at least 100 atmospheres therein over long periods of time. In one embodiment.
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.
Rainbow scattering by a coated sphere.
Lock, J A; Jamison, J M; Lin, C Y
1994-07-20
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 a(12) and the thickness of the coating δ are varied. As the ratio δ/a(12) increases from 10(-4) to 0.33, we find three classes of rainbow phenomena that cannot occur for a homogeneous-sphere rainbow. For δ/a(12) ≲ 10(-3), the rainbow intensity is an oscillatory function of the coating thickness, for δ/a(12) ≈ 10(-2), the first-order rainbow breaks into a pair of twin rainbows, and for δ/a(12) ≈ 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. PMID:20935838
Technology Transfer Automated Retrieval System (TEKTRAN)
Sticky red spheres can be used to capture western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), but whether they capture more flies than yellow spheres and panels is poorly known. The objective of this study was to compare fly captures on red spheres versus yellow traps so...
Evaporative coating of a sphere from a point source
NASA Technical Reports Server (NTRS)
Strayer, D. M.; Jackson, H. W.; Gatewood, J. R.
1984-01-01
To optimize the procedure for evaporating a metal film onto a sphere, calculations of the film thickness distribution for various motions of the sphere have been carried out. These calculations, including shadowing effects of sphere support rods, are presented in this paper. Also, an apparatus and procedure for the evaporative coating of a sphere are described. A comparison of measured thickness with the calculated values is made for one example of sphere motion. The implications of the calculated results for coating techniques are discussed.
Alexander, Jenolyn F; Kozlovskaya, Veronika; Chen, Jun; Kuncewicz, Thomas; Kharlampieva, Eugenia; Godin, Biana
2015-12-01
Blood-borne objects display a nonspherical shape with in-flow dimensions much larger than the vascular endothelial fenestrations, yet, at the diseased state, are able to traverse through these fenestrations owing to their elasticity. The role of physical parameters including shape and elasticity in the behavior of objects found in the tumor microenvironment needs to be understood to ultimately enhance chemotherapy and minimize its side effects. In this study, sphere- and cube-shaped biocompatible elastic microparticles (EM) made via layer-by-layer assembly of hydrogen-bonded tannic acid/poly(N-vinylpyrrolidone) (TA/PVPON) as hollow polymer shells and their rigid core-shell precursors (RM) are explored. In contrast to rigid five-bilayer (TA/PVPON) core shells, hollow elastic shells are unrecognized by J774A.1 macrophages, yet interact with endothelial and breast cancer cells. Internalization of cubical shells is fivefold more efficient by HMVEC (human microvascular endothelial cells) and sixfold and 2.5-fold more efficient by MDA-MB-231 and by SUM159 (breast cancer cells), respectively, compared to spherical shells. The interaction of cubical (TA/PVPON)5 shells with endothelial cells is similar under 10 s(-1) (characteristic of tumor vasculature) and 100 s(-1) shear rate (normal vasculature) while it is decreased at 100 s(-1) shear rate for the spherical shells. Our data suggest that cubical geometry promotes interaction of particles with breast cancer cells, while elasticity prevents engulfment by phagocytic cells in the tumor microenvironment. PMID:26424126
Random sphere packing model of heterogeneous propellants
NASA Astrophysics Data System (ADS)
Kochevets, Sergei Victorovich
It is well recognized that combustion of heterogeneous propellants is strongly dependent on the propellant morphology. Recent developments in computing systems make it possible to start three-dimensional modeling of heterogeneous propellant combustion. A key component of such large scale computations is a realistic model of industrial propellants which retains the true morphology---a goal never achieved before. The research presented develops the Random Sphere Packing Model of heterogeneous propellants and generates numerical samples of actual industrial propellants. This is done by developing a sphere packing algorithm which randomly packs a large number of spheres with a polydisperse size distribution within a rectangular domain. First, the packing code is developed, optimized for performance, and parallelized using the OpenMP shared memory architecture. Second, the morphology and packing fraction of two simple cases of unimodal and bimodal packs are investigated computationally and analytically. It is shown that both the Loose Random Packing and Dense Random Packing limits are not well defined and the growth rate of the spheres is identified as the key parameter controlling the efficiency of the packing. For a properly chosen growth rate, computational results are found to be in excellent agreement with experimental data. Third, two strategies are developed to define numerical samples of polydisperse heterogeneous propellants: the Deterministic Strategy and the Random Selection Strategy. Using these strategies, numerical samples of industrial propellants are generated. The packing fraction is investigated and it is shown that the experimental values of the packing fraction can be achieved computationally. It is strongly believed that this Random Sphere Packing Model of propellants is a major step forward in the realistic computational modeling of heterogeneous propellant of combustion. In addition, a method of analysis of the morphology of heterogeneous
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
Heng, Ri-Liang; Sy, Ki Cheong; Pilon, Laurent
2015-01-01
This study demonstrates that the absorption and scattering cross sections and asymmetry factor of randomly oriented and optically soft bispheres, quadspheres, and circular rings of spheres, with either monodisperse or polydisperse monomers, can be approximated by an equivalent coated sphere with identical volume and average projected area. This approximation could also apply to the angle-dependent scattering matrix elements for monomer size parameter less than 0.1. However, it quickly deteriorated with increasing monomer number and/or size parameter. It was shown to be superior to previously proposed approximations considering a volume equivalent homogeneous sphere and a coated sphere with identical volume and surface area. These results provide a rapid and accurate way of predicting the radiation characteristics of bispheres, quadspheres, and rings of spheres representative of various unicellular and multicellular cyanobacteria considered for producing food supplements, biofuels, and fertilizers. They could also be used in inverse methods for retrieving the monomers' optical properties, morphology, and/or concentration. PMID:26366489
NASA Astrophysics Data System (ADS)
Liu, Fei; Xu, Guanghua; Zhang, Qing; Liang, Lin; Liu, Dan
2015-11-01
As one of the Geometrical Product Specifications that are widely applied in industrial manufacturing and measurement, sphericity error can synthetically scale a 3D structure and reflects the machining quality of a spherical workpiece. Following increasing demands in the high motion performance of spherical parts, sphericity error is becoming an indispensable component in the evaluation of form error. However, the evaluation of sphericity error is still considered to be a complex mathematical issue, and the related research studies on the development of available models are lacking. In this paper, an intersecting chord method is first proposed to solve the minimum circumscribed sphere and maximum inscribed sphere evaluations of sphericity error. This new modelling method leverages chord relationships to replace the characteristic points, thereby significantly reducing the computational complexity and improving the computational efficiency. Using the intersecting chords to generate a virtual centre, the reference sphere in two concentric spheres is simplified as a space intersecting structure. The position of the virtual centre on the space intersecting structure is determined by characteristic chords, which may reduce the deviation between the virtual centre and the centre of the reference sphere. In addition,two experiments are used to verify the effectiveness of the proposed method with real datasets from the Cartesian coordinates. The results indicate that the estimated errors are in perfect agreement with those of the published methods. Meanwhile, the computational efficiency is improved. For the evaluation of the sphericity error, the use of high performance computing is a remarkable change.