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.
Zhu, Yong-zheng; Cao, Yan-ling; Li, Zhi-hui; Ding, Juan; Liu, Jun-song; Chi, Yuan-bin
2007-02-01
With the help of self-assembly, thermal sintering, selective etching techniques and sol-gel process, the non-close packed (ncp) face-centered cubic (fcc) photonic crystals of titanium dioxide (TiO2) hollow spheres connected by TiO2 cylindrical tubes have been fabricated using silica template. The photonic bandgap calculations indicate that the ncp structure of TiO2 hollow spheres was easier to open the pseudogaps than close packed system at the lowest energy.
The glass transition in binary mixtures of hard colloidal spheres
NASA Astrophysics Data System (ADS)
Williams, S. R.; van Megen, W.
2000-06-01
Particle dynamics have been measured by dynamic light scattering for mixtures of colloidal particles with hard sphere interactions. The diameter ratio (small:large) is 0.6. The optical properties of the suspended particles are such that the relative contrast of the two species is very sensitive to temperature, a feature we exploit to obtain the three partial intermediate scattering functions. The glass transition is identified by the onset of structural arrest, or the arrest of the alpha process, on the time scale of the experiment. This is observed in the one-component suspension at the packing fraction 0.57. Introduction of the smaller particles, at fixed packing fraction, releases the alpha process, ie, the glass melts. Increasing the fraction of smaller particles speeds up the alpha process but interestingly, increases its amplitude. .
Structural and magnetic transitions in cubic Mn3Ga.
Kharel, P; Huh, Y; Al-Aqtash, N; Shah, V R; Sabirianov, R F; Skomski, R; Sellmyer, D J
2014-03-26
The structural, magnetic and electron-transport properties of cubic Mn3Ga have been investigated. The alloys prepared by arc melting and melt-spinning show an antiferromagnetic spin order at room temperature but undergo coupled structural and magnetic phase transitions at 600 and 800 K. First-principles calculations show that the observed magnetic properties are consistent with that of a cubic Mn3Ga crystallizing in the disordered Cu3Au-type structure. The samples exhibit metallic electron transport with a resistance minimum near 30 K, followed by a logarithmic upturn below the minimum. The observed anomaly in the low-temperature resistivity has been discussed as a consequence of electron scattering at the low-lying excitations of the structurally disordered Mn3Ga lattice.
Pollen Patterning as a Brazovskii Phase Transition on a Sphere
NASA Astrophysics Data System (ADS)
Lavrentovich, Maxim; Horsley, Eric; Radja, Asja; Sweeney, Alison; Kamien, Randall
Pollen grains acquire intricate, varied surface patterns during development. The patterns are reproducible within a single plant species, and yet exhibit a wide variation among species, despite having similar developmental steps. We model this pattern formation on spherical grains as a phase transition to a spatially modulated phase, characterized by an unstable wavelength λ0. On the infinite, flat plane, the patterned phase consists of uniform stripes, as shown by Brazovskii. We find that, by contrast, the patterns may be much more varied on a spherical surface because the topological defects which must be present in the pattern may be accommodated in a variety of ways. This variation may explain the wide range of observed pollen patterns. We also argue that the first-order character of the transition may be responsible for the robust reproducibility of the patterns in a single plant species. Finally, we compute the free energy difference between the unpatterned, smooth phase and various patterned phases on the sphere. These calculations point toward possible future experimental tests of our model.
Photoluminescence and electronic transitions in cubic silicon nitride
Museur, Luc; Zerr, Andreas; Kanaev, Andrei
2016-01-01
A spectroscopic study of cubic silicon nitride (γ-Si3N4) at cryogenic temperatures of 8 K in the near IR - VUV range of spectra with synchrotron radiation excitation provided the first experimental evidence of direct electronic transitions in this material. The observed photoluminescence (PL) bands were assigned to excitons and excited and centers formed after the electron capture by neutral structural defects. The excitons are weakly quenched on neutral and strongly on charged defects. The fundamental band-gap energy of 5.05 ± 0.05 eV and strong free exciton binding energy ~0.65 eV were determined. The latter value suggests a high efficiency of the electric power transformation in light in defect-free crystals. Combined with a very high hardness and exceptional thermal stability in air, our results indicate that γ-Si3N4 has a potential for fabrication of robust and efficient photonic emitters. PMID:26725937
Ising-like phase transition of an n-component Eulerian face-cubic model.
Ding, Chengxiang; Guo, Wenan; Deng, Youjin
2013-11-01
By means of Monte Carlo simulations and a finite-size scaling analysis, we find a critical line of an n-component Eulerian face-cubic model on the square lattice and the simple cubic lattice in the region v>1, where v is the bond weight. The phase transition belongs to the Ising universality class independent of n. The critical properties of the phase transition can also be captured by the percolation of the complement of the Eulerian graph. PMID:24329232
Ising-like phase transition of an n-component Eulerian face-cubic model
NASA Astrophysics Data System (ADS)
Ding, Chengxiang; Guo, Wenan; Deng, Youjin
2013-11-01
By means of Monte Carlo simulations and a finite-size scaling analysis, we find a critical line of an n-component Eulerian face-cubic model on the square lattice and the simple cubic lattice in the region v>1, where v is the bond weight. The phase transition belongs to the Ising universality class independent of n. The critical properties of the phase transition can also be captured by the percolation of the complement of the Eulerian graph.
The structural origin of the hard-sphere glass transition in granular packing
Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie
2015-09-28
Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden’ polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleation process, similar to that of the random first-order transition theory. In conclusion, our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses.
The structural origin of the hard-sphere glass transition in granular packing
Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie
2015-09-28
Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden’ polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleationmore » process, similar to that of the random first-order transition theory. In conclusion, our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses.« less
The structural origin of the hard-sphere glass transition in granular packing
Xia, Chengjie; Li, Jindong; Cao, Yixin; Kou, Binquan; Xiao, Xianghui; Fezzaa, Kamel; Xiao, Tiqiao; Wang, Yujie
2015-01-01
Glass transition is accompanied by a rapid growth of the structural relaxation time and a concomitant decrease of configurational entropy. It remains unclear whether the transition has a thermodynamic origin, and whether the dynamic arrest is associated with the growth of a certain static order. Using granular packing as a model hard-sphere glass, we show the glass transition as a thermodynamic phase transition with a ‘hidden' polytetrahedral order. This polytetrahedral order is spatially correlated with the slow dynamics. It is geometrically frustrated and has a peculiar fractal dimension. Additionally, as the packing fraction increases, its growth follows an entropy-driven nucleation process, similar to that of the random first-order transition theory. Our study essentially identifies a long-sought-after structural glass order in hard-sphere glasses. PMID:26412008
Reese, Caleb W.; Strango, Zachariah I.; Dell, Zachary R.; Tristram-Nagle, Stephanie; Harper, Paul E.
2015-01-01
Using DSC (differential scanning calorimetry), we measure the kinetics of the cubic-HII phase transition of monoolein in bulk sucrose solutions. We find that the transition temperature is dramatically lowered, with each 1 mol/kg of sucrose concentration dropping the transition by 20 °C. The kinetics of this transition also slow greatly with increasing sucrose concentration. For low sucrose concentrations, the kinetics are asymmetric, with the cooling (HII-cubic) transition taking twice as long as the heating (cubic-HII) transition. This asymmetry in transition times is reduced for higher sucrose concentrations. The cooling transition (cubic-HII) exhibits Avrami exponents in the range of 2 to 2.5 and the heating transition shows Avrami exponents ranging from 1 to 3. A classical Avrami interpretation would be that these processes occur via a one or two dimensional pathway with variable nucleation rates. A non-classical perspective would suggest that these exponents reflect the time dependence of pore formation (cooling) and destruction (heating). New density measurements of monoolein show that the currently accepted value is about 5% too low; this has substantial implications for electron density modeling. Structural calculations indicate that the head group area and lipid length in the cubic-HII transition shrink by about 12 % and 4 % respectively; this reduction is practically the same as that seen in a lipid with a very different molecular structure (rac-di-12:0 β-GlcDAG) that makes the same transition. Thermodynamic considerations suggest there is a hydration shell about one water molecule thick in front of the lipid head groups in both the cubic and HII phases. PMID:25758637
Deformation-induced structural transition in body-centred cubic molybdenum
Wang, S. J.; Wang, H.; Du, K.; Zhang, W.; Sui, M. L.; Mao, S. X.
2014-01-01
Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama–Wassermann and Kurdjumov–Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions. PMID:24603655
Deformation-induced structural transition in body-centred cubic molybdenum.
Wang, S J; Wang, H; Du, K; Zhang, W; Sui, M L; Mao, S X
2014-03-07
Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions.
Deformation-induced structural transition in body-centred cubic molybdenum.
Wang, S J; Wang, H; Du, K; Zhang, W; Sui, M L; Mao, S X
2014-01-01
Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama-Wassermann and Kurdjumov-Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions. PMID:24603655
Phase Transition of a Structure II Cubic Clathrate Hydrate to a Tetragonal Form.
Takeya, Satoshi; Fujihisa, Hiroshi; Yamawaki, Hiroshi; Gotoh, Yoshito; Ohmura, Ryo; Alavi, Saman; Ripmeester, John A
2016-08-01
The crystal structure and phase transition of cubic structure II (sII) binary clathrate hydrates of methane (CH4 ) and propanol are reported from powder X-ray diffraction measurements. The deformation of host water cages at the cubic-tetragonal phase transition of 2-propanol+CH4 hydrate, but not 1-propanol+CH4 hydrate, was observed below about 110 K. It is shown that the deformation of the host water cages of 2-propanol+CH4 hydrate can be explained by the restriction of the motion of 2-propanol within the 5(12) 6(4) host water cages. This result provides a low-temperature structure due to a temperature-induced symmetry-lowering transition of clathrate hydrate. This is the first example of a cubic structure of the common clathrate hydrate families at a fixed composition. PMID:27346760
On metal-insulator transition in cubic fullerides
NASA Astrophysics Data System (ADS)
Iwahara, Naoya; Chibotaru, Liviu
The interplay between degenerate orbital and electron correlation is a key to characterize the electronic phases in, for example, transition metal compounds and alkali-doped fullerides. Besides, the degenerate orbital couples to spin and lattice degrees of freedom ,giving rise to exotic phenomena. Here, we develop the self-consistent Gutzwiller approach for the simultaneous treatment of the Jahn-Teller effect and electron correlation, and apply the methodology to reveal the nature of the ground electronic state of fullerides. For small Coulomb repulsion on site U, the fulleride is quasi degenerate correlated metal. With increase of U, we found the quantum phase transition from the metallic phase to JT split phase. In the latter, the Mott transition (MT) mainly develops in the half-filled subband, whereas the empty and the completely filled subbands are almost uninvolved. Therefore, we can qualify the metal-insulator transition in fullerides as an orbital selective MT induced by JT effect.
Phonon softening induced cubic-to-tetragonal phase transition in ReO3
NASA Astrophysics Data System (ADS)
Liu, Yaming; Zhang, Niu; Jia, Yu; Sun, Qiang; Chao, Mingju
2015-10-01
Within density functional theory, the structural, electronic and lattice dynamical properties of ReO3 in cubic Pm-3m and tetragonal P4/mbm phases are studied by using quasiharmonic approximation. The enthalpy-pressure curves show that a phase transition may take place at 5.0 kbar and the nonexistence of imaginary frequency in phonon dispersions demonstrates the two phases are dynamically stable under proper conditions. With the increase of pressure, an obvious softening of M3 mode at M point appears in cubic phase, and a cubic-to-tetragonal phase transition is accompanied with the presence of negative frequency in M3 mode at 5.0 kbar. In detail, one type of O atoms displaced from x = 0.2500 to x = 0.2401, which corresponds to the softening of M3 mode, are responsible for the phase transition. Our theoretical results show that ReO3 can exist in the tetragonal P4/mbm phase, and a cubic-to-tetragonal phase transition will appear at around 5.0 kbar.
Zhang, Fan; An, Yongling; Zhai, Wei; Gao, Xueping; Feng, Jinkui; Ci, Lijie; Xiong, Shenglin
2015-10-15
Highlights: • The hollow Co{sub 2}SiO{sub 4}, MnSiO{sub 3} and CuSiO{sub 3} were successfully prepared by a facile hydrothermal method using SiO{sub 2} nanosphere. • The hollow Co{sub 2}SiO{sub 4}, MnSiO{sub 3} and CuSiO{sub 3} were tested as anode materials for lithium batteries. • The hollow Co{sub 2}SiO{sub 4}, MnSiO{sub 3} and CuSiO{sub 3} delivered superior electrochemical performance. • The lithium storage mechanism is probe via cyclic voltammetry and XPS. - Abstract: A series of transition metal silicate hollow spheres, including cobalt silicate (Co{sub 2}SiO{sub 4}), manganese silicate (MnSiO{sub 3}) and copper silicate (CuSiO{sub 3}.2H{sub 2}O, CuSiO{sub 3} as abbreviation in the text) were prepared via a simple and economic hydrothermal method by using silica spheres as chemical template. Time-dependent experiments confirmed that the resultants formed a novel type of hierarchical structure, hollow spheres assembled by numerous one-dimensional (1D) nanotubes building blocks. For the first time, the transition metal silicate hollow spheres were characterized as novel anode materials of Li-ion battery, which presented superior lithium storage capacities, cycle performance and rate performance. The 1D nanotubes assembly and hollow interior endow this kind of material facilitate fast lithium ion and electron transport and accommodate the big volume change during the conversion reactions. Our study shows that low-cost transition metal silicate with rationally designed nanostructures can be promising anode materials for high capacity lithium-ion battery.
NASA Astrophysics Data System (ADS)
Hanifpour, M.; Francois, N.; Robins, V.; Kingston, A.; Vaez Allaei, S. M.; Saadatfar, M.
2015-06-01
Here we present an experimental and numerical investigation on the grain-scale geometrical and mechanical properties of partially crystallized structures made of macroscopic frictional grains. Crystallization is inevitable in arrangements of monosized hard spheres with packing densities exceeding Bernal's limiting density ϕBernal≈0.64 . We study packings of monosized hard spheres whose density spans over a wide range (0.59 <ϕ <0.72 ) . These experiments harness x-ray computed tomography, three-dimensional image analysis, and numerical simulations to access precisely the geometry and the 3D structure of internal forces within the sphere packings. We show that clear geometrical transitions coincide with modifications of the mechanical backbone of the packing both at the grain and global scale. Notably, two transitions are identified at ϕBernal≈0.64 and ϕc≈0.68 . These results provide insights on how geometrical and mechanical features at the grain scale conspire to yield partially crystallized structures that are mechanically stable.
Hanifpour, M; Francois, N; Robins, V; Kingston, A; Allaei, S M Vaez; Saadatfar, M
2015-06-01
Here we present an experimental and numerical investigation on the grain-scale geometrical and mechanical properties of partially crystallized structures made of macroscopic frictional grains. Crystallization is inevitable in arrangements of monosized hard spheres with packing densities exceeding Bernal's limiting density ϕ(Bernal)≈0.64. We study packings of monosized hard spheres whose density spans over a wide range (0.59<ϕ<0.72). These experiments harness x-ray computed tomography, three-dimensional image analysis, and numerical simulations to access precisely the geometry and the 3D structure of internal forces within the sphere packings. We show that clear geometrical transitions coincide with modifications of the mechanical backbone of the packing both at the grain and global scale. Notably, two transitions are identified at ϕ(Bernal)≈0.64 and ϕ(c)≈0.68. These results provide insights on how geometrical and mechanical features at the grain scale conspire to yield partially crystallized structures that are mechanically stable. PMID:26172700
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.
The Dynamics of Disorder-Order Transition in Hard Sphere Colloidal Dispersions
NASA Technical Reports Server (NTRS)
Chaikin, Paul M.; Zhu, Jixiang; Cheng, Zhengdong; Phan, See-Eng; Russel, William B.; Lant, Christian T.; Doherty, Michael P.; Meyer, William V.; Rogers, Richard; Cannell, D. S.; Ottewill, R. H.
1998-01-01
The Physics of Hard Spheres Experiment (PHaSE) seeks a complete understanding of the entropically driven disorder-order transition in hard sphere colloidal dispersions. The light scattering instrument designed for flight collects Bragg and low angle light scattering in the forward direction via a CCD camera and performs conventional static and dynamic light scattering at 10-160 deg. through fiber optic cables. Here we report on the kinetics of nucleation and growth extracted from time-resolved Bragg images and measurements of the elastic modulus of crystalline phases obtained by monitoring resonant responses to sinusoidal forcing through dynamic light scattering. Preliminary analysis of the former indicates a significant difference from measurements on the ground, while the latter confirms nicely laboratory experiments with the same instrument and predictions from computer simulations.
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.
On structural transitions in a discontinuous micellar cubic phase loaded with sodium diclofenac.
Efrat, R; Aserin, A; Garti, N
2008-05-01
An intermediate mesophase of lyotropic liquid crystalline structure from the ternary mixtures of glycerol monooleate, water, and ethanol was recently characterized in our lab. This mesophase, termed Q(L), consists of discrete discontinuous micelles arranged in a cubic array. The Q(L) phase can solubilize very significant loads of water-insoluble anti-inflamatory drug sodium diclofenac (Na-DFC). Close examination of the internal structures of the lyotropic liquid structure upon increasing the solubilization loads reveals the existence of three structural transitions controlled by the Na-DFC levels. Up to 0.4 wt% Na-DFC, the Q(L) structure remains intact with some influence on the hydration of the headgroups and on the intermicellar forces. However, at 0.8 to 1.2 wt% Na-DFC, the discontinuous micellar cubic phase is transformed into a more condensed mesophase of a bicontinuous cubic phase. At > or =1.2 wt% Na-DFC, the cubic phase is converted into a lamellar phase (L(alpha)). Within 5.5 to 7.3 wt% Na-DFC the mesophase is progressively transformed into a less ordered lamellar structure. At 12 wt% Na-DFC crystals tend to precipitate out. At low Na-DFC concentrations the drug behaves like a lyotropic or kosmotropic salt and can salt-out the surfactant from its water layer, but at higher levels it behaves like a hydrotropic, chaotropic salt and can salt-in the surfactant. The Na-DFC location and position within the interface as well as its polarization and partial ionization are strongly affected by its solubilization contents and the structure that it is inducing. In the cubic phase the drug is located less close to the hydration layer while once transition occurs it is exposed more to the water layer and the surfactant headgroups.
Manaka, Hirotaka; Yagi, Genta; Miura, Yoko
2016-07-01
Optical birefringence imaging systems demonstrate a high potential for comprehensively investigating various phase transitions. To completely demonstrate such abilities, the temperature dependence of birefringence (Δn) was measured in Δn ≃ 0 materials (i.e., cubic crystals with imperfect crystallization) via a background subtraction method. As a result, highly accurate birefringence imaging at 384 × 288 pixels was obtained using phase transition processes as well as varying temperatures visually characterized by the spatial distribution of not only the retardance level but also the optical fast-axis azimuth. PMID:27475562
NASA Astrophysics Data System (ADS)
Manaka, Hirotaka; Yagi, Genta; Miura, Yoko
2016-07-01
Optical birefringence imaging systems demonstrate a high potential for comprehensively investigating various phase transitions. To completely demonstrate such abilities, the temperature dependence of birefringence (Δn) was measured in Δn ≃ 0 materials (i.e., cubic crystals with imperfect crystallization) via a background subtraction method. As a result, highly accurate birefringence imaging at 384 × 288 pixels was obtained using phase transition processes as well as varying temperatures visually characterized by the spatial distribution of not only the retardance level but also the optical fast-axis azimuth.
Nature of the cubic to tetragonal phase transition in methylammonium lead iodide perovskite
NASA Astrophysics Data System (ADS)
Saidi, Wissam A.; Choi, Joshua J.
2016-10-01
Hybrid organic-inorganic perovskites, as well as the perovskites in general, are known for their phase complexity evidenced by the stabilization of different polymorphs, and thus an understanding of their regions of stability and transitions can be important for their photovoltaic and optoelectronic technologies. Here we use a multiscale approach based on first-principles calculations with van der Waals corrections and classical force-field molecular dynamics to determine the finite-temperature properties of the tetragonal and cubic phases of CH3NH3PbI3. Temperature effects are implicitly included using the quasi-harmonic approximation that can describe anharmonic behavior due to thermal expansion through the dependence of the harmonic frequencies on structural parameters. Our finite-temperature free-energy surfaces predict the lattice and elastic moduli evolution with temperature, and show in particular that the calculated lattice parameters of the cubic and tetragonal phases are to within 1% of experimental values. Further, our results show that the phonons are the major contributing factor for stabilizing the cubic phase at high temperatures mainly due to the low-energy phonon modes that are associated with the inorganic lattice. On the other hand, the configurational entropy due to CH3NH3+ rotational degrees of freedom is slightly more favored in the cubic phase and amounts to less than 0.2% of the T = 0 K free-energy difference between the two phases.
Cubic to tetragonal phase transition of Tm3+ doped nanocrystals in oxyfluoride glass ceramics
NASA Astrophysics Data System (ADS)
Li, Yiming; Zhao, Lijuan; Fu, Yuting; Shi, Yahui; Zhang, Xiaoyu; Yu, Hua
2016-02-01
Tm3+ ions doped β-PbF2 nanocrystals in oxyfluoride glass ceramics with different doping concentrations and thermal temperatures are prepared by a traditional melt-quenching and thermal treatment method to investigate the structure and the phase transition of Tm3+ doped nanocrystals. The structures are characterized by X-ray diffraction Rietveld analysis and confirmed with numerical simulation. The phase transitions are proved further by the emission spectra. Both of the doping concentration and thermal temperature can induce an Oh to D4h site symmetry distortion and a cubic to tetragonal phase transition. The luminescence of Tm3+ doped nanocrystals at 800 nm was modulated by the phase transition of the surrounding crystal field.
Superionic-Superionic Phase Transitions in Body-Centered Cubic H2O Ice
NASA Astrophysics Data System (ADS)
Hernandez, Jean-Alexis; Caracas, Razvan
2016-09-01
From first-principles molecular dynamics, we investigate the relation between the superionic proton conduction and the behavior of the O - H ⋯O bond (ice VII' to ice X transition) in body-centered-cubic (bcc) H2O ice between 1300 and 2000 K and up to 300 GPa. We bring evidence that there are three distinct phases in the superionic bcc stability field. A first superionic phase characterized by extremely fast diffusion of highly delocalized protons (denoted VII'' hereinafter) is stable at low pressures. A first-order transition separates this phase from a superionic VII' , characterized by a finite degree of localization of protons along the nonsymmetric O - H ⋯O bonds. The transition is identified in structural, energetic, and elastic analysis. Upon further compression a second-order phase transition leads to the superionic ice X with symmetric O - H - O bonds.
Tuning the sphere-to-rod transition in the self-assembly of thermoresponsive polymer hybrids.
Lee, Jangwook; Park, Honghyun; Jeong, Eun Ju; Kwark, Young-Je; Lee, Kuen Yong
2015-12-01
Nano-scale drug delivery systems have undergone extensive development, and control of size and structure is critical for regulation of their biological responses and therapeutic efficacy. Amphiphilic polymers that form self-assembled structures in aqueous media have been investigated and used for the diagnosis and therapy of various diseases, including cancer. Here, we report the design and fabrication of thermoresponsive polymeric micelles from alginate conjugated with poly(N-isopropylacrylamide) (PNIPAAm). Alginate-PNIPAAm hybrids formed self-aggregated structures in response to temperature changes near body temperature. A structural transition from micellar spheres to rods of alginate-PNIPAAm hybrids was observed depending on the molecular weight of PNIPAAm and the polymer concentration. Additionally, hydrogels with nanofibrous structures were formed by simply increasing the polymer concentration. This approach to controlling the structure of polymer micelles from nanoparticles to fibrous hydrogels may be useful in applications in drug delivery and tissue engineering.
Bao, Shanshan; Hua, Zheng; Wang, Xiaoyong; Zhou, Yong; Zhang, Chunfeng; Tu, Wenguang; Zou, Zhigang; Xiao, Min
2012-12-17
In this report, we studied the optical properties of hybrid spherical structures consisting of alternating nanosheets of titania (TiO(2)) and graphene oxide (GO) prepared by a layer-by-layer self-assembly technique. Compared to samples with only TiO(2) spheres or GO nanosheets, a blue-to-red light emission band emerges and persists in this novel composite material even after it was further reduced through microwave irradiation. From detailed time-resolved measurements and energy-level structure modeling, this unexpected fluorescent feature was attributed to the indirect optical transitions between TiO(2) and the localized sp(2) domains of GO in a charge-separated configuration.
Constraining turbulence mixing strength in transitional discs with planets using SPHERE and ALMA
NASA Astrophysics Data System (ADS)
de Juan Ovelar, M.; Pinilla, P.; Min, M.; Dominik, C.; Birnstiel, T.
2016-06-01
We investigate the effect that the turbulent mixing strength parameter αturb plays on near-infrared polarimetric and sub-millimetre interferometric imaging observations of transitional discs (TDs) with a gap carved by a planet. We generate synthetic observations of these objects with ALMA and VLT/SPHERE-ZIMPOL by combining hydrodynamical, dust evolution, radiative transfer and instrument models for values of α _{turb}=[10^{-4}, 10^{-3}, 10^{-2}]. We find that, through a combination of effects on the viscosity of the gas, the turbulent mixing and dust evolution processes, αturb strongly affects the morphology of the dust distribution that can be traced with these observations. We constrain the value of αturb to be within an order of magnitude of 10-3 in TD sources that show cavities in sub-mm continuum images while featuring continuous distribution of dust or smaller cavities in NIR-polarimetric images.
Falling to Floating Transitions of Solid Spheres in a Bubbly Fluid
NASA Astrophysics Data System (ADS)
Higley, Michael; Belmonte, Andrew
2007-11-01
We present experimental observations of the trajectories and average velocities of solid spheres falling through a curtain of rising bubbles in water. For the quiescent case (no bubbles), the Reynolds numbers are on the order of 1,000, and the average terminal velocity is determined by the form (inertial) drag. The main effect of the bubbles is to slow down the spheres. In some regimes (larger or heavier spheres), the paths followed by the spheres in the bubble stream are nearly indistinguishable from their paths without bubbles. In other regimes (smaller or lighter spheres), an apparently random lateral motion is the dominant feature.
NASA Astrophysics Data System (ADS)
Lechman, Jeremy; Pierce, Flint
2012-02-01
Diffusive transport is a ubiquitous process that is typically understood in terms of a classical random walk of non-interacting particles. Here we present the results for a model of hard-sphere colloids in a Newtonian incompressible solvent at various volume fractions below the ordering transition (˜50%). We numerically simulate the colloidal systems via Fast Lubrication Dynamics -- a Brownian Dynamics approach with corrected mean-field hydrodynamic interactions. Colloid-colloid interactions are also included so that we effectively solve a system of interacting Langevin equations. The results of the simulations are analyzed in terms of the diffusion coefficient as a function of time with the early and late time diffusion coefficients comparing well with experimental results. An interpretation of the full time dependent behavior of the diffusion coefficient and mean-squared displacement is given in terms of a continuous time random walk. Therefore, the deterministic, continuum diffusion equation which arises from the discrete, interacting random walkers is presented. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Note: Sound velocity of a soft sphere model near the fluid-solid phase transition.
Khrapak, Sergey A
2016-03-28
The quasilocalized charge approximation is applied to estimate the sound velocity of simple soft sphere fluid with the repulsive inverse-power-law interaction. The obtained results are discussed in the context of the sound velocity of the hard-sphere system and of liquid metals at the melting temperature. PMID:27036483
Magnetic phase transitions of spin-1 ultracold bosons in a cubic optical lattice
NASA Astrophysics Data System (ADS)
Li, Yongqiang; He, Liang; Hofstetter, Walter
2016-03-01
We investigate strongly correlated spin-1 ultracold bosons with antiferromagnetic interactions in a cubic optical lattice, based on bosonic dynamical mean-field theory. Rich phase diagrams of the system are mapped out at both zero and finite temperature, and in particular the existence of a spin-singlet condensate is established. Interestingly, at finite temperature, we find that the superfluid can be heated into a Mott insulator with even (odd) filling via a first- (second-) order phase transition, analogous to the Pomeranchuk effect in 3He. Moreover, for typical experimental setups, we estimate the critical temperature (entropy) for different ordered phases and our results suggest that direct experimental observation of these phases is promising.
NASA Astrophysics Data System (ADS)
Torres, Juan F.; Henry, Daniel; Komiya, Atsuki; Maruyama, Shigenao
2015-08-01
The transition from the complex Rayleigh-Bénard convection to the simple heated-from-the-sides configuration in a cubical cavity filled with a Newtonian fluid is numerically studied. The cavity is tilted by an angle θ around its lower horizontal edge and is heated and cooled from two opposite tilted sides. We first analyze the effect of a marginal inclination angle on quasi-Rayleigh-Bénard convection (θ ≈0∘ ), which is a realistic physical approximation to the ideal Rayleigh-Bénard convection. We then yield the critical angles where multiple solutions that were initially found for θ ≈0∘ disappear, eventually resulting in the single steady roll solution found in the heated-from-the-sides configuration (θ =90∘ ). We confirm the existence of critical angles during the transition θ :0∘→90∘ , and we demonstrate that such angles are a consequence of either singularities or collisions of bifurcation points in the Rayleigh-number-θ parameter space. We finally derive the most important critical angles corresponding to any Newtonian fluid of Prandtl number greater than that of air.
ERIC Educational Resources Information Center
Chiung, Wi-vun Taiffalo
2007-01-01
The Han sphere, including Vietnam, Korea, Japan, Taiwan and China, adopted Han characters and classical Han writing as the official written language before the 20th century. However, great changes came with the advent of the 20th century. After World War II, Han characters in Vietnam and Korea were officially replaced by the romanised "Chu Quoc…
Zhang, Jingyan; Ge, Zhishen; Jiang, Xiaoze; Hassan, P A; Liu, Shiyong
2007-12-15
The kinetics and mechanism of sphere-to-rod transitions of sodium alkyl sulfate micelles induced by hydrotropic salt, p-toluidine hydrochloride (PTHC), were investigated by stopped-flow with light scattering detection. Spherical sodium dodecyl sulfate (SDS) micelles transform into short ellipsoidal shapes at low salt concentrations ([PTHC]/[SDS], chi(PTHC)=0.3 and 0.4). Upon stopped-flow mixing aqueous solutions of spherical SDS micelles with PTHC, the scattered light intensity gradually increases with time. Single exponential fitting of the dynamic traces leads to characteristic relaxation time, tau(g), for the growth process from spherical to ellipsoidal micelles, and it increases with increasing SDS concentrations. This suggests that ellipsoidal micelles might be produced by successive insertion of unimers into spherical micelles, similar to the case of formation of spherical micelles as suggested by Aniansson-Wall (A-W) theory. At chi(PTHC) > or = 0.5, rod-like micelles with much higher axial ratio form. The scattered light intensity exhibits an initially abrupt increase and then levels off. The dynamic curves can be well fitted with single exponential functions, and the obtained tau(g) decreases with increasing SDS concentration. Thus, the growth from spherical to rod-like micelles might proceed via fusion of spherical micelles, in agreement with mechanism proposed by Ikeda et al. At chi(PTHC)=0.3 and 0.6, the apparent activation energies obtained from temperature dependent kinetic studies for the micellar growth are 40.4 and 3.6 kJ/mol, respectively. The large differences between activation energies for the growth from spherical to ellipsoidal micelles at low chi(PTHC) and the sphere-to-rod transition at high chi(PTHC) further indicate that they should follow different mechanisms. Moreover, the sphere-to-rod transition kinetics of sodium alkyl sulfate with varying hydrophobic chain lengths (n=10, 12, 14, and 16) are also studied. The longer the carbon chain
Zhang, Jingyan; Ge, Zhishen; Jiang, Xiaoze; Hassan, P A; Liu, Shiyong
2007-12-15
The kinetics and mechanism of sphere-to-rod transitions of sodium alkyl sulfate micelles induced by hydrotropic salt, p-toluidine hydrochloride (PTHC), were investigated by stopped-flow with light scattering detection. Spherical sodium dodecyl sulfate (SDS) micelles transform into short ellipsoidal shapes at low salt concentrations ([PTHC]/[SDS], chi(PTHC)=0.3 and 0.4). Upon stopped-flow mixing aqueous solutions of spherical SDS micelles with PTHC, the scattered light intensity gradually increases with time. Single exponential fitting of the dynamic traces leads to characteristic relaxation time, tau(g), for the growth process from spherical to ellipsoidal micelles, and it increases with increasing SDS concentrations. This suggests that ellipsoidal micelles might be produced by successive insertion of unimers into spherical micelles, similar to the case of formation of spherical micelles as suggested by Aniansson-Wall (A-W) theory. At chi(PTHC) > or = 0.5, rod-like micelles with much higher axial ratio form. The scattered light intensity exhibits an initially abrupt increase and then levels off. The dynamic curves can be well fitted with single exponential functions, and the obtained tau(g) decreases with increasing SDS concentration. Thus, the growth from spherical to rod-like micelles might proceed via fusion of spherical micelles, in agreement with mechanism proposed by Ikeda et al. At chi(PTHC)=0.3 and 0.6, the apparent activation energies obtained from temperature dependent kinetic studies for the micellar growth are 40.4 and 3.6 kJ/mol, respectively. The large differences between activation energies for the growth from spherical to ellipsoidal micelles at low chi(PTHC) and the sphere-to-rod transition at high chi(PTHC) further indicate that they should follow different mechanisms. Moreover, the sphere-to-rod transition kinetics of sodium alkyl sulfate with varying hydrophobic chain lengths (n=10, 12, 14, and 16) are also studied. The longer the carbon chain
Angelov, Borislav; Angelova, Angelina; Mutafchieva, Rada; Lesieur, Sylviane; Vainio, Ulla; Garamus, Vasil M; Jensen, Grethe V; Pedersen, Jan Skov
2011-02-28
The encapsulation and release of peptides, proteins, nucleic acids, and drugs in nanostructured lipid carriers depend on the type of the self-assembled liquid-crystalline organization and the structural dimensions of the aqueous and membraneous compartments, which can be tuned by the multicomponent composition of the systems. In this work, small-angle X-ray scattering (SAXS) investigation is performed on the 'melting' transition of the bicontinuous double diamond cubic phase, formed by pure glycerol monooleate (MO), upon progressive inclusion of varying fractions of pharmaceutical-grade glycerol monooleate (GO) in the hydrated system. The self-assembled MO/GO mixtures are found to form diamond (Pn3m) inverted cubic, inverted hexagonal (H(II)), and sponge (L(3)) phases at ambient temperature in excess of aqueous medium without heat treatment. Mixing of the inverted-cubic-phase-forming MO and the sponge-phase-forming GO components, in equivalent proportions (50/50 w/w), yields an inverted hexagonal (H(II)) phase nanostructured carrier. Scattering models are applied for fitting of the experimental SAXS patterns and identification of the structural changes in the aqueous and lipid bilayer subcompartments. The possibility of transforming, at ambient temperature (20 °C), the bicontinuous cubic nanostructures into inverted hexagonal (H(II)) or sponge (L(3)) mesophases may facilitate novel biomedical applications of the investigated liquid crystalline self-assemblies. PMID:21079857
Three-dimensional kinetic Monte Carlo simulations of cubic transition metal nitride thin film growth
NASA Astrophysics Data System (ADS)
Nita, F.; Mastail, C.; Abadias, G.
2016-02-01
A three-dimensional kinetic Monte Carlo (KMC) model has been developed and used to simulate the microstructure and growth morphology of cubic transition metal nitride (TMN) thin films deposited by reactive magnetron sputtering. Results are presented for the case of stoichiometric TiN, chosen as a representative TMN prototype. The model is based on a NaCl-type rigid lattice and includes deposition and diffusion events for both N and Ti species. It is capable of reproducing voids and overhangs, as well as surface faceting. Simulations were carried out assuming a uniform flux of incoming particles approaching the surface at normal incidence. The ballistic deposition model is parametrized with an interaction parameter r0 that mimics the capture distance at which incoming particles may stick on the surface, equivalently to a surface trapping mechanism. Two diffusion models are implemented, based on the different ways to compute the site-dependent activation energy for hopping atoms. The influence of temperature (300-500 K), deposition flux (0.1-100 monolayers/s), and interaction parameter r0 (1.5-6.0 Å) on the obtained growth morphology are presented. Microstructures ranging from highly porous, [001]-oriented straight columns with smooth top surface to rough columns emerging with different crystallographic facets are reproduced, depending on kinetic restrictions, deposited energy (seemingly captured by r0), and shadowing effect. The development of facets is a direct consequence of the diffusion model which includes an intrinsic (minimum energy-based) diffusion anisotropy, although no crystallographic diffusion anisotropy was explicitly taken into account at this stage. The time-dependent morphological evolution is analyzed quantitatively to extract the growth exponent β and roughness exponent α , as indicators of kinetic roughening behavior. For dense TiN films, values of α ≈0.7 and β =0.24 are obtained in good agreement with existing experimental data. At this
Meng, Xiuqing; Wu, Fengmin; Chen, Zhanghui; Li, Shu-Shen; Chen, Zhuo; Li, Jingbo E-mail: swei@nrel.gov; Wu, Junqiao; Wei, Su-Huai E-mail: swei@nrel.gov
2013-12-16
We demonstrate in this work controllable synthesis of cubic InN nanocrystals through Mn doping. We show that the pristine nanocrystal has the wurtzite structure, but can be converted into the zinc-blende (ZB) structure when it is doped with Mn. Our first-principles calculations show that the phase transition is caused by the stronger p-d coupling between the host p valence state and the impurity d level in the ZB structure, which makes the hole generation in the ZB structure easier. Quantum confinement in the nanocrystals further enhanced this effect. This observation lays an important foundation for defects control of crystal phases.
Behera, Pallavi Suhasinee; Vasanthavel, S.; Ponnilavan, V.; Kannan, S.
2015-05-15
The present study reports the effect of gadolinium (Gd{sup 3+}) in zirconia-silica (ZrO{sub 2}-SiO{sub 2}) binary oxides. The pure ZrO{sub 2}-SiO{sub 2} synthesized at 1100 °C was tetragonal. The addition of Gd{sup 3+} in the concentration range of 5%–10% resulted in the formation of t-ZrO{sub 2}, whereas higher contents of Gd{sup 3+} led to the formation of cubic ZrO{sub 2} (c-ZrO{sub 2}). The presence of Gd{sup 3+} also affected the lattice parameters of both t-ZrO{sub 2} and c-ZrO{sub 2}. Magnetic studies confirmed a steady increase in the paramagnetic behaviour with increasing content of Gd{sup 3+}. - Graphical abstract: t-ZrO{sub 2} to c-ZrO{sub 2} phase transition influenced by Gd{sup 3+} content. - Highlights: • Sol-gel synthesis of Gd{sup 3+} added SiO{sub 2}-ZrO{sub 2} binary oxides. • Significant role of Gd{sup 3+} content in the tetragonal and cubic stabilization of ZrO{sub 2}. • Phase stability of either tetragonal or cubic stabilization till 1100 °C. • Gd{sup 3+} additions ensured additional paramagnetic behaviour in SiO{sub 2}-ZrO{sub 2} binary oxide.
Chong, Ketpin; Deng, Yuru
2012-01-01
Biological membranes are generally perceived as phospholipid bilayer structures that delineate in a lamellar form the cell surface and intracellular organelles. However, much more complex and highly convoluted membrane organizations are ubiquitously present in many cell types under certain types of stress, states of disease, or in the course of viral infections. Their occurrence under pathological conditions make such three-dimensionally (3D) folded and highly ordered membranes attractive biomarkers. They have also stimulated great biomedical interest in understanding the molecular basis of their formation. Currently, the analysis of such membrane arrangements, which include tubulo-reticular structures (TRS) or cubic membranes of various subtypes, is restricted to electron microscopic methods, including tomography. Preservation of membrane structures during sample preparation is the key to understand their true 3D nature. This chapter discusses methods for appropriate sample preparations to successfully examine and analyze well-preserved highly ordered membranes by electron microscopy. Processing methods and analysis conditions for green algae (Zygnema sp.) and amoeba (Chaos carolinense), mammalian cells in culture and primary tissue cells are described. We also discuss methods to identify cubic membranes by transmission electron microscopy (TEM) with the aid of a direct template matching method and by computer simulation. A 3D analysis of cubic cell membrane topology by electron tomography is described as well as scanning electron microscopy (SEM) to investigate surface contours of isolated mitochondria with cubic membrane arrangement.
Liu, Kong; Li, Huanyuan; Lu, Yuan; Wang, Ruijuan; Bei, Fengli; Lu, Lude; Han, Qiaofeng; Wu, Xiaodong
2016-04-20
The combination of a simple modification of the sample addition method to generate a sort of continuously accumulated external stimulation with only minute increments in amplitude and the introduction of probe molecules (herein aniline) within the micelle allow the direct continuous in situ spectroscopic monitoring of possible micellar transitions. In this way, a sphere-to-ellipsoid and further an ellipsoid-to-bilayer micellar transition of sodium dodecyl sulfate (SDS) induced by camphor sulfuric acid (CSA) is observed to experience four stages in the time sequence: (i) the accumulated protons released from CSA in the hydration layer of the micelle stimulate the rearrangement of SDS micelles; (ii) the micelles transform into ellipsoidal shapes as evidenced by the characteristic chemical shift anisotropy and the corresponding molecular dynamic properties from probe molecules; (iii) further protonation of aniline induces the micelle to turn into lamellar structures; (iv) aniline is freed from the micelle while leaving the SDS bilayers undistorted. Moreover, polyaniline nanosheets incorporating SDS bilayers in sandwich structures, which can display excellent capacitive behavior at relatively high current densities for the fabricated supercapacitors, are prepared from the aniline oriented by the bending energy of the SDS bilayers. PMID:26996652
Polireddy, Kishore; Dong, Ruochen; McDonald, Peter R.; Wang, Tao; Luke, Brendan; Chen, Ping; Broward, Melinda; Roy, Anuradha; Chen, Qi
2016-01-01
Background Pancreatic cancer has an enrichment of stem-like cancer cells (CSCs) that contribute to chemoresistant tumors prone to metastasis and recurrence. Drug screening assays based on cytotoxicity cannot identify specific CSC inhibitors, because CSCs comprise only a small portion of cancer cell population, and it is difficult to propagate stable CSC populations in vitro for high-throughput screening (HTS) assays. Based on the important role of cancer cell epithelial-to-mesenchymal transition (EMT) in promoting CSCs, we hypothesized that inhibition of EMT can be a useful strategy for inhibiting CSCs, and therefore a feasible approach for HTS can be built for identification of CSC inhibitors, based on assays detecting EMT inhibition. Methods An immunofluorescent assay was established and optimized for HTS to identify compounds that enhance E-cadherin expression, as a hallmark of inhibition of EMT. Four chemical libraries containing 41,472 compounds were screened in PANC-1 pancreatic cancer cell line. Positive hits were validated for EMT and CSC inhibition in vitro using sphere formation assay, western blotting, immune fluorescence, and scratch assay. Results Initial hits were refined to 73 compounds with a secondary screening, among which 17 exhibited concentration dependent induction of E-cadherin expression. Six compounds were selected for further study which belonged to 2 different chemical structural clusters. A novel compound 1-(benzylsulfonyl) indoline (BSI, Compound #38) significantly inhibited pancreatic cancer cell migration and invasion. BSI inhibited histone deacetylase, increased histone 4 acetylation preferably, resulting in E-cadherin up-regulation. BSI effectively inhibited tumor spheres formation. Six more analogues of BSI were tested for anti-migration and anti-CSC activities. Conclusion This study demonstrated a feasible approach for discovery of agents targeting EMT and CSCs using HTS, and identified a class of novel chemicals that could be
Fully reversible shape transition of soft spheres in elastomeric polymer opal films.
Schäfer, Christian G; Smolin, Daniel A; Hellmann, Goetz P; Gallei, Markus
2013-09-10
Core-interlayer-shell (CIS) beads featuring noncross-linked hard cores were used to prepare large and well-defined elastomeric opal films with remarkably distinct iridescent reflection colors. The matrix of the opal films was cross-linked by UV-irradiation after compression molding of the CIS beads mixed with a bifunctional monomer. Stress-induced deformation of the embedded PS cores lead to hexagonally arranged spheroid oblates with an aspect ratio of 2.5. Optical characterization shows that bead deformation provokes a tremendous photonic band gap shift of about 160 nm. Fully reversible shape transition from the spheroid oblates back to the spherical beads and hence full recovery of the original photonic band gap can be achieved. PMID:23947686
Natural convection between two concentric spheres - Transition toward a multicellular flow
NASA Astrophysics Data System (ADS)
Caltagirone, J.-P.; Mojtabi, A.; Combarnous, M.
1980-03-01
A moderate temperature difference maintained between two concentric spherical surfaces induces, in steady state, unicellular toroidal movements in the enclosed fluid. Beyond a critical temperature difference, the flow becomes unstable and the convective phenomena rearrange into counter-rotating toroidal cells. A two-dimensional axisymmetric numerical model confirms the existence of a unicellular regime and shows that, beyond the critical conditions and for the same set of parameters, two convergent solutions can be obtained. One is unicellular and the other is bicellular; in the latter, the additional cell appears at the top of the layer. The initial conditions determine which one of these two will be established. This transition is investigated as a function of several parameters and the results are compared with the experimental results in the literature.
Oka, Toshihiko; Saiki, Takahiro; Alam, Jahangir Md; Yamazaki, Masahito
2016-02-01
Electrostatic interaction is an important factor for phase transitions between lamellar liquid-crystalline (Lα) and inverse bicontinuous cubic (QII) phases. We investigated the effect of temperature on the low-pH-induced Lα to double-diamond cubic (QII(D)) phase transition in dioleoylphosphatidylserine (DOPS)/monoolein (MO) using time-resolved small-angle X-ray scattering with a stopped-flow apparatus. Under all conditions of temperature and pH, the Lα phase was directly transformed into an intermediate inverse hexagonal (HII) phase, and subsequently the HII phase slowly converted to the QII(D) phase. We obtained the rate constants of the initial step (i.e., the Lα to HII phase transition) and of the second step (i.e., the HII to QII(D) phase transition) using the non-negative matrix factorization method. The rate constant of the initial step increased with temperature. By analyzing this result, we obtained the values of its apparent activation energy, Ea (Lα → HII), which did not change with temperature but increased with an increase in pH. In contrast, the rate constant of the second step decreased with temperature at pH 2.6, although it increased with temperature at pH 2.7 and 2.8. These results indicate that the value of Ea (HII → QII(D)) at pH 2.6 increased with temperature, but the values of Ea (HII → QII(D)) at pH 2.7 and 2.8 were constant with temperature. The values of Ea (HII → QII(D)) were smaller than those of Ea (Lα → HII) at the same pH. We analyzed these results using a modified quantitative theory on the activation energy of phase transitions of lipid membranes proposed initially by Squires et al. (Squires, A. M.; Conn, C. E.; Seddon, J. M.; Templer, R. H. Soft Matter 2009, 5, 4773). On the basis of these results, we discuss the mechanism of this phase transition.
Oka, Toshihiko; Saiki, Takahiro; Alam, Jahangir Md; Yamazaki, Masahito
2016-02-01
Electrostatic interaction is an important factor for phase transitions between lamellar liquid-crystalline (Lα) and inverse bicontinuous cubic (QII) phases. We investigated the effect of temperature on the low-pH-induced Lα to double-diamond cubic (QII(D)) phase transition in dioleoylphosphatidylserine (DOPS)/monoolein (MO) using time-resolved small-angle X-ray scattering with a stopped-flow apparatus. Under all conditions of temperature and pH, the Lα phase was directly transformed into an intermediate inverse hexagonal (HII) phase, and subsequently the HII phase slowly converted to the QII(D) phase. We obtained the rate constants of the initial step (i.e., the Lα to HII phase transition) and of the second step (i.e., the HII to QII(D) phase transition) using the non-negative matrix factorization method. The rate constant of the initial step increased with temperature. By analyzing this result, we obtained the values of its apparent activation energy, Ea (Lα → HII), which did not change with temperature but increased with an increase in pH. In contrast, the rate constant of the second step decreased with temperature at pH 2.6, although it increased with temperature at pH 2.7 and 2.8. These results indicate that the value of Ea (HII → QII(D)) at pH 2.6 increased with temperature, but the values of Ea (HII → QII(D)) at pH 2.7 and 2.8 were constant with temperature. The values of Ea (HII → QII(D)) were smaller than those of Ea (Lα → HII) at the same pH. We analyzed these results using a modified quantitative theory on the activation energy of phase transitions of lipid membranes proposed initially by Squires et al. (Squires, A. M.; Conn, C. E.; Seddon, J. M.; Templer, R. H. Soft Matter 2009, 5, 4773). On the basis of these results, we discuss the mechanism of this phase transition. PMID:26766583
Soucasse, L.; Rivière, Ph.; Soufiani, A.; Xin, S.
2014-02-15
The transition to unsteadiness and the dynamics of weakly turbulent natural convection, coupled to wall or gas radiation in a differentially heated cubical cavity with adiabatic lateral walls, are studied numerically. The working fluid is air with small contents of water vapor and carbon dioxide whose infrared spectral radiative properties are modelled by the absorption distribution function model. A pseudo spectral Chebyshev collocation method is used to solve the flow field equations and is coupled to a direct ray tracing method for radiation transport. Flow structures are identified by means of either the proper orthogonal decomposition or the dynamic mode decomposition methods. We first retrieve the classical mechanism of transition to unsteadiness without radiation, characterized by counter-rotating streamwise-oriented vortices generated at the exit of the vertical boundary layers. Wall radiation through a transparent medium leads to a homogenization of lateral wall temperatures and the resulting transition mechanism is similar to that obtained with perfectly conducting lateral walls. The transition is due to an unstable stratification upstream the vertical boundary layers and is characterized by periodically oscillating transverse rolls of axis perpendicular to the main flow. When molecular gas radiation is accounted for, no periodic solution is found and the transition to unsteadiness displays complex structures with chimneys-like rolls whose axes are again parallel to the main flow. The origin of this instability is probably due to centrifugal forces, as suggested previously for the case without radiation. Above the transition to unsteadiness, at Ra = 3 × 10{sup 8}, it is shown that both wall and gas radiation significantly intensify turbulent fluctuations, decrease the thermal stratification in the core of the cavity, and increase the global circulation.
Tabira, Y.; Withers, R.L.; Barry, J.C.; Elcoro, L.
2001-06-01
The relationship between the ordering characteristic of the pyrochlore structure type and that characteristic of the ''defect fluorite'' structure type (immediately on either side of two phase regions separating the two structure types) in a range of rare earth sesquioxide-stabilized cubic zirconias was investigated by electron diffraction and imaging. Systematic structural change as a function of composition and relative size of the constituent metal ions is highlighted, and a multi-q to single-q = {1/2} [111]* model is proposed for the observed pyrochlore-to-defect fluorite phase transition. Strain introduced into the close-packed {l_brace}111{r_brace} metal ion planes of the defect fluorite average structure by the local cation and oxygen vacancy distribution is pointed to as the likely origin of the observed behavior.
NASA Astrophysics Data System (ADS)
Reiss, Howard; Manzanares, José A.
2016-09-01
Using several theoretical toolsldots (i) the nucleation theorem, (ii) an equivalent cavity, (iii) the reversible work of adding a cavity to an open hard sphere system, and (iv) the theory of "stability"... the authors estimated the density at which the hard sphere freezing transition occurs. No direct involvement of the equilibrium solid phase is involved. The reduced density \\uppi a^3ρ _f/6 (where a is the hard sphere diameter and ρ _f is the actual density at which freezing occurs) is found to be 0.4937 while the value obtained by computer simulation is 0.494. The agreement is good, but the new method still contains some approximation. However, the approximation is based on the idea that at a density just below ρ _f the fluid adopts a distorted structure resembling the solid, but different enough so that long-range order vanishes. Initial loss of stability may not be involved in every fluid-solid transition, but it may be an early step in the hard sphere and related systems.
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.
Leal, Cecília; Ewert, Kai K.; Bouxsein, Nathan F.; Shirazi, Rahau S.; Li, Youli; Safinya, Cyrus R.
2012-01-01
Lyotropic phases of amphiphiles are a prototypical example of self-assemblies. Their structure is generally determined by amphiphile shape and their phase transitions are primarily governed by composition. In this paper, we demonstrate a new paradigm for membrane shape control where the electrostatic coupling of charged membranes to short DNA (sDNA), with tunable temperature-dependent end-to-end stacking interactions, enables switching between the inverted gyroid cubic structure (QIIG) and the inverted hexagonal phase (HIIC). We investigated the structural shape transitions induced in the QIIG phase upon complexation with a series of sDNAs (5, 11, 24, and 48 bp) with three types of end structure (“sticky” adenine (A)–thymine (T) (dAdT) overhangs, no overhang (blunt), and “nonsticky” dTdT overhangs) using synchrotron small-angle X-ray scattering. Very short 5 bp sDNA with dAdT overhangs and blunt ends induce coexistence of the QIIG and the HIIC phase, with the fraction of QIIG increasing with temperature. Phase coexistence for blunt 5 bp sDNA is observed from 27 °C to about 65 °C, where the HIIC phase disappears and the temperature dependence of the lattice spacing of the QIIG phase indicates that the sDNA duplexes melt into single strands. The only other sDNA for which melting is observed is 5 bp sDNA with dTdT overhangs, which forms the QIIG phase throughout the studied range of temperature (27 °C to 85.2 °C). The longer 11 bp sDNA forms coexisting QIIG and HIIC phases (with the fraction of QIIG again increasing with temperature) only for “nonsticky” dTdT overhangs, while dAdT overhangs and blunt ends exclusively template the HIIC phase. For 24 and 48 bp sDNAs the HIIC phase replaces the QIIG phase at all investigated temperatures, independent of sDNA end structure. Our work demonstrates how the combined effects of sDNA length and end structure (which determine the temperature-dependent stacking length) tune the phase behavior of the complexes
NASA Astrophysics Data System (ADS)
Freitas, F. L.; Marques, M.; Teles, L. K.
2016-08-01
We provide approximate quasiparticle-corrected band gap energies for quaternary cubic and hexagonal AlxGayIn1-x-yN semiconductor alloys, employing a cluster expansion method to account for the inherent statistical disorder of the system. Calculated values are compared with photoluminescence measurements and discussed within the currently accepted model of emission in these materials by carrier localization. It is shown that bowing parameters are larger in the cubic phase, while the range of band gap variation is bigger in the hexagonal one. Experimentally determined transition energies are mostly consistent with band-to-band excitations.
NASA Astrophysics Data System (ADS)
van Westen, Thijs; Vlugt, Thijs J. H.; Gross, Joachim
2014-01-01
An analytical equation of state (EoS) is derived to describe the isotropic (I) and nematic (N) phase of linear- and partially flexible tangent hard-sphere chain fluids and their mixtures. The EoS is based on an extension of Onsager's second virial theory that was developed in our previous work [T. van Westen, B. Oyarzún, T. J. H. Vlugt, and J. Gross, J. Chem. Phys. 139, 034505 (2013)]. Higher virial coefficients are calculated using a Vega-Lago rescaling procedure, which is hereby generalized to mixtures. The EoS is used to study (1) the effect of length bidispersity on the I-N and N-N phase behavior of binary linear tangent hard-sphere chain fluid mixtures, (2) the effect of partial molecular flexibility on the binary phase diagram, and (3) the solubility of hard-sphere solutes in I- and N tangent hard-sphere chain fluids. By changing the length bidispersity, two types of phase diagrams were found. The first type is characterized by an I-N region at low pressure and a N-N demixed region at higher pressure that starts from an I-N-N triphase equilibrium. The second type does not show the I-N-N equilibrium. Instead, the N-N region starts from a lower critical point at a pressure above the I-N region. The results for the I-N region are in excellent agreement with the results from molecular simulations. It is shown that the N-N demixing is driven both by orientational and configurational/excluded volume entropy. By making the chains partially flexible, it is shown that the driving force resulting from the configurational entropy is reduced (due to a less anisotropic pair-excluded volume), resulting in a shift of the N-N demixed region to higher pressure. Compared to linear chains, no topological differences in the phase diagram were found. We show that the solubility of hard-sphere solutes decreases across the I-N phase transition. Furthermore, it is shown that by using a liquid crystal mixture as the solvent, the solubility difference can by maximized by tuning the
Murtazaev, A. K.; Ramazanov, M. K.; Kassan-Ogly, F. A.; Kurbanova, D. R.
2015-01-15
Phase transitions in the antiferromagnetic Ising model on a body-centered cubic lattice are studied on the basis of the replica algorithm by the Monte Carlo method and histogram analysis taking into account the interaction of next-to-nearest neighbors. The phase diagram of the dependence of the critical temperature on the intensity of interaction of the next-to-nearest neighbors is constructed. It is found that a second-order phase transition is realized in this model in the investigated interval of the intensities of interaction of next-to-nearest neighbors.
NASA Astrophysics Data System (ADS)
López-Sánchez, Erik; Estrada-Álvarez, César D.; Pérez-Ángel, Gabriel; Méndez-Alcaraz, José Miguel; González-Mozuelos, Pedro; Castañeda-Priego, Ramón
2013-09-01
Asymmetric binary mixtures of hard-spheres exhibit several interesting thermodynamic phenomena, such as multiple kinds of glassy states. When the degrees of freedom of the small spheres are integrated out from the description, their effects are incorporated into an effective pair interaction between large spheres known as the depletion potential. The latter has been widely used to study both the phase behavior and dynamic arrest of the big particles. Depletion forces can be accounted for by a contraction of the description in the multicomponent Ornstein-Zernike equation [R. Castañeda-Priego, A. Rodríguez-López, and J. M. Méndez-Alcaraz, Phys. Rev. E 73, 051404 (2006)], 10.1103/PhysRevE.73.051404. Within this theoretical scheme, an approximation for the difference between the effective and bare bridge functions is needed. In the limit of infinite dilution, this difference is irrelevant and the typical Asakura-Osawa depletion potential is recovered. At higher particle concentrations, however, this difference becomes important, especially where the shell of first neighbors is formed, and, as shown here, cannot be simply neglected. In this work, we use a variant of the Verlet expression for the bridge functions to highlight their importance in the calculation of the depletion potential at high densities and close to the spinodal decomposition. We demonstrate that the modified Verlet closure predicts demixing in binary mixtures of hard spheres for different size ratios and compare its predictions with both liquid state and density functional theories, computer simulations, and experiments. We also show that it provides accurate correlation functions even near the thermodynamic instability; this is explicitly corroborated with results of molecular dynamics simulations of the whole mixture. Particularly, our findings point toward a possible universal behavior of the depletion potential around the spinodal line.
Epitaxial growth of ordered and disordered granular sphere packings.
Panaitescu, Andreea; Kudrolli, Arshad
2014-09-01
We demonstrate that epitaxy can be used to obtain a wide range of ordered to disordered granular packings by simply changing the deposition flux. We show that a defect-free face-centered-cubic (fcc) monocrystal can be obtained by depositing athermal granular spheres randomly into a container with a templated surface in a gravitational field without direct manipulation. This packing corresponds to the maximum sphere packing fraction and is obtained when the substrate is templated corresponding to the (100) plane of a fcc crystal and the container side is an integer multiple of the sphere diameter. We find that the maximum sphere packing is obtained when the deposited grains come to rest, one at a time, without damaging the substrate. A transition to a disordered packing is observed when the flux is increased. Using micro x-ray computed tomography, we find that defects nucleate at the boundaries of the container in which the packing is grown as grains cooperatively come to rest above their local potential minimum. This leads to a transition from ordered to disordered loose packings that grow in the form of an inverted cone, with the apex located at the defect nucleation site. We capture the observed decrease in order using a minimal model in which a defect leads to growth of further defects in the neighboring sites in the layer above with a probability that increases with the deposition flux.
NASA Astrophysics Data System (ADS)
Wei, Yong-Kai; Ge, Ni-Na; Chen, Xiang-Rong; Ji, Guang-Fu; Cai, Ling-Cang; Gu, Zhuo-Wei
2014-03-01
The phase transition, thermoelastic, lattice dynamic, and thermodynamic properties of the cubic metallic phase AlH3 were obtained within the density-function perturbation theory. The calculated elastic modulus and phonon dispersion curves under various pressures at 0 K indicate the cubic phase is both mechanically and dynamically stable above 73 GPa. The superconducting transition temperature Tc was calculated using the Allen-Dynes modification of the McMillan formula based on BCS theory. The calculations show that Tc for the cubic phase AlH3 is 8.5 K (μ*=0.1) at the onset of this phase (73 GPa), while decreases to 5.7 K at 80 GPa and almost disappears at 110 GPa, consisting with experimental phenomenon that there was no superconducting transition observed down to 4 K over a wide pressure range 110-164 GPa. It is found that the soft phonon mode for branch 1, namely, the lowest acoustic mode, plays a crucial role in elevating the total EPC parameter λ of cubic AlH3. And the evolution of Tc with pressure follows the corresponding change of this soft mode, i.e. this mode is responsible for the disappearance of Tc in experiments. Meanwhile, the softening of this lowest acoustic mode originates from the electronic momentum transfer from M to R point. This phenomenon provides an important insight into why drastic changes in the diffraction pattern were observed in the pressure range of 63-73 GPa in Goncharenko's experiments. Specifically, once finite electronic temperature effects are included, we find that dynamical instabilities can be removed in the phonon dispersion for P ≥63 GPa, rendering the metastability of this phase in the range of 63-73 GPa, and Tc (15.4 K) becomes remarkably high under the lowest possible pressure (63 GPa) compared with that of under 73 GPa (8.5 K). Our calculations open the possibility that finite temperature may allow cubic AlH3 to be dynamically stabilized even for pressures below 73 GPa. It is reasonable to deduced that if special
Wei, Yong-Kai; Ge, Ni-Na; Chen, Xiang-Rong E-mail: cyfjkf@caep.ac.cn; Ji, Guang-Fu E-mail: cyfjkf@caep.ac.cn; Cai, Ling-Cang; Gu, Zhuo-Wei
2014-03-28
The phase transition, thermoelastic, lattice dynamic, and thermodynamic properties of the cubic metallic phase AlH{sub 3} were obtained within the density-function perturbation theory. The calculated elastic modulus and phonon dispersion curves under various pressures at 0 K indicate the cubic phase is both mechanically and dynamically stable above 73 GPa. The superconducting transition temperature T{sub c} was calculated using the Allen-Dynes modification of the McMillan formula based on BCS theory. The calculations show that T{sub c} for the cubic phase AlH{sub 3} is 8.5 K (μ{sup *}=0.1) at the onset of this phase (73 GPa), while decreases to 5.7 K at 80 GPa and almost disappears at 110 GPa, consisting with experimental phenomenon that there was no superconducting transition observed down to 4 K over a wide pressure range 110–164 GPa. It is found that the soft phonon mode for branch 1, namely, the lowest acoustic mode, plays a crucial role in elevating the total EPC parameter λ of cubic AlH{sub 3}. And the evolution of T{sub c} with pressure follows the corresponding change of this soft mode, i.e. this mode is responsible for the disappearance of T{sub c} in experiments. Meanwhile, the softening of this lowest acoustic mode originates from the electronic momentum transfer from M to R point. This phenomenon provides an important insight into why drastic changes in the diffraction pattern were observed in the pressure range of 63–73 GPa in Goncharenko's experiments. Specifically, once finite electronic temperature effects are included, we find that dynamical instabilities can be removed in the phonon dispersion for P≥63 GPa, rendering the metastability of this phase in the range of 63–73 GPa, and T{sub c} (15.4 K) becomes remarkably high under the lowest possible pressure (63 GPa) compared with that of under 73 GPa (8.5 K). Our calculations open the possibility that finite temperature may allow cubic AlH{sub 3} to be
Dereymaker, Aswin; Van Den Mooter, Guy
2015-05-01
Fluid bed coating has been proposed in the past as an alternative technology for manufacturing of drug-polymer amorphous solid dispersions, or so-called glass solutions. It has the advantage of being a one-step process, and thus omitting separate drying steps, addition of excipients, or manipulation of the dosage form. In search of an adequate sample preparation method for modulated differential scanning calorimetry analysis of beads coated with glass solutions, glass transition broadening and decrease of the glass transition temperature (Tg ) were observed with increasing particle size of crushed coated beads and crushed isolated films of indomethacin (INDO) and polyvinylpyrrolidone (PVP). Substituting INDO with naproxen gave comparable results. When ketoconazole was probed or the solvent in INDO-PVP films was switched to dichloromethane (DCM) or a methanol-DCM mixture, two distinct Tg regions were observed. Small particle sizes had a glass transition in the high Tg region, and large particle sizes had a glass transition in the low Tg region. This particle size-dependent glass transition was ascribed to different residual solvent amounts in the bulk and at the surface of the particles. A correlation was observed between the deviation of the Tg from that calculated from the Gordon-Taylor equation and the amount of residual solvent at the Tg of particles with different sizes.
Boujnah, M.; Zaari, H.; El Kenz, A.; Labrim, H.; Benyoussef, A.; Mounkachi, O.
2014-03-28
The electronic structure, magnetic, and optical properties in cubic crystalline phase of Zr{sub 1−x}TM{sub x}O{sub 2} (TM = V, Mn, Fe, and Co) at x = 6.25% are studied using density functional theory with the Generalized Gradient Approximation and the modified Becke-Johnson of the exchange-correlation energy and potential. In our calculations, the zirconia is a p-type semiconductor and has a large band gap. We evaluated the possibility of long-range magnetic order for transition metal ions substituting Zr. Our results show that ferromagnetism is the ground state in V, Mn, and Fe-doped ZrO{sub 2} and have a high value of energy in Mn-doped ZrO{sub 2}. However, in Co-doped ZrO{sub 2}, antiferromagnetic ordering is more stable than the ferromagnetic one. The exchange interaction mechanism has been discussed to explain the responsible of this stability. Moreover, it has been found that the V, Mn, and Fe transition metals provide half-metallic properties considered to be the leading cause, responsible for ferromagnetism. Furthermore, the optical absorption spectra in the TM -doped cubic ZrO{sub 2} are investigated.
Angelov, Borislav; Angelova, Angelina; Vainio, Ulla; Garamus, Vasil M; Lesieur, Sylviane; Willumeit, Regine; Couvreur, Patrick
2009-04-01
To generate nanostructured vehicles with tunable internal organization, the structural phase behavior of a self-assembled amphiphilic mixture involving poly(ethylene glycol) monooleate (MO-PEG) and glycerol monooleate (MO) is studied in excess aqueous medium by time-resolved small-angle X-ray scattering (SAXS) in the temperature range from 1 to 68 degrees C. The SAXS data indicate miscibility of the two components in lamellar and nonlamellar soft-matter nanostructures. The functionalization of the MO assemblies by a MO-PEG amphiphile, which has a flexible large hydrophilic moiety, appears to hinder the epitaxial growth of a double diamond (D) cubic lattice from the lamellar (L) bilayer structure during the thermal phase transition. The incorporated MO-PEG additive is found to facilitate the formation of structural intermediates. They exhibit greater characteristic spacings and large diffusive scattering in broad temperature and time intervals. Their features are compared with those of swollen long-living intermediates in MO/octylglucoside assemblies. A conclusion can be drawn that long-living intermediate states can be equilibrium stabilized in two- or multicomponent amphiphilic systems. Their role as cubic phase precursors is to smooth the structural distortions arising from curvature mismatch between flat and curved regions. The considered MO-PEG functionalized assemblies may be useful for preparation of sterically stabilized liquid-crystalline nanovehicles for confinement of therapeutic biomolecules. PMID:19708151
NASA Astrophysics Data System (ADS)
Shirokov, V. B.; Shakhovoy, R. A.; Razumnaya, A. G.; Yuzyuk, Yu. I.
2015-07-01
A phenomenological thermodynamic theory of BaxSr1-xTiO3 (BST-x) thin films epitaxially grown on (111)-oriented cubic substrates is developed using the Landau-Devonshire approach. The group-theoretical analysis of the low-symmetry phases was performed taking into account two order parameters: the polarization related to ionic shifts in polar zone-center F1u mode and the out-of-phase rotation of TiO6 octahedra corresponding to the R25 zone-boundary mode in the parent cubic phase P m 3 ¯ m . The eight-order thermodynamic potential for BST-x solid solutions was developed and analyzed. We constructed the "concentration-misfit strain" phase diagram for BST-x thin films at room temperature and found that polar rhombohedral R3m phase with the polarization normal to the substrate is stable for x > 0.72 and negative misfit strains, while ferroelectric monoclinic C2 and Cm phases with in-plane polarization are stable for much smaller x and positive or slightly negative misfit strains. We constructed the "temperature-misfit strain" phase diagrams for several concentrations (x = 1, 0.8, 0.6, 0.4, and 0.2). Systematic changes of the phase transition lines between the paraelectric and ferroelectric phases are discussed. The phase diagrams are useful for practical applications in thin-film engineering.
Zhang, Yin; Chen, Chen; Gao, Ran; Xia, Feng; Li, YueSheng; Che, Renchao
2015-11-02
Phase stability of the ferroelectric materials at high temperature is extremely important to their device performance. Ba{sub x}Sr{sub 1−x}TiO{sub 3} (BST) nanoparticles with different Sr contents (x = 1, 0.91, 0.65, 0.4, and 0) are prepared by a facile hydrothermal method. Using Raman spectroscopy and transmission electron microscopy (TEM) analyses under in situ heating conditions (up to 300 °C), the phase transitions of BST nanoparticles between 25 °C and 280 °C are comprehensively investigated. The original Curie temperature of BST nanoparticles decreases abruptly with the increase in Sr content, which is more obvious than in the bulk or film material. Besides, an abnormal phase transition from cubic to tetragonal structure is observed from BST nanoparticles and the transition temperature rises along with the increase in Sr content. Direct TEM evidences including a slight lattice distortion have been provided. Differently, BaTiO{sub 3} nanoparticles remained in the tetragonal phase during the above temperature ranges.
Banik, Mayukh; El-Khoury, Patrick Z; Nag, Amit; Rodriguez-Perez, Alejandro; Guarrottxena, Nekane; Bazan, Guillermo C; Apkarian, Vartkess A
2012-11-27
By taking advantage of the tensor nature of surface-enhanced Raman scattering (SERS), we track trajectories of the linker molecule and a CO molecule chemisorbed at the hot spot of a nano-dumbbell consisting of dibenzyldithio-linked silver nanospheres. The linear Stark shift of CO serves as an absolute gauge of the local field, while the polyatomic spectra characterize the vector components of the local field. We identify surface-enhanced Raman optical activity due to a transient asperity in the nanojunction in an otherwise uneventful SERS trajectory. During fusion of the spheres, we observe sequential evolution of the enhanced spectra from dipole-coupled Raman to quadrupole- and magnetic dipole-coupled Raman, followed by a transition from line spectra to band spectra, and the full reversal of the sequence. From the spectrum of CO, the sequence can be understood to track the evolution of the junction plasmon resonance from dipolar to quadrupolar to charge transfer as a function of intersphere separation, which evolves at a speed of ∼1 Å/min. The crossover to the conduction limit is marked by the transition of line spectra to Stark-broadened and shifted band spectra. As the junction closes on CO, the local field reaches 1 V/Å, limited to a current of 1 electron per vibrational cycle passing through the molecule, with associated Raman enhancement factor via the charge transfer plasmon resonance of 10(12). The local field identifies that a sharp protrusion is responsible for room-temperature chemisorption of CO on silver. The asymmetric phototunneling junction, Ag-CO-Ag, driven by the frequency-tunable charge transfer plasmon of the dumbbell antenna, combines the design elements of an ideal rectifying photocollector. PMID:23092179
Lin, Tsanglang; Chen, Sowhsin ); Gabriel, N.E.; Roberts, M.F. )
1990-01-25
The solubilization of tributyrin by rodlike diheptanoylphosphatidylcholine (diheptanoyl-PC) micelles has been studied by small-angle neutron-scattering techniques. A rod to sphere transition is observed from the measured angular distribution of neutron-scattering intensities. The transition is from the rodlike micelle to a globular mixed micelle which has tributyrin molecules at the core surrounded by an outer shell of diheptanoyl-PC molecules. When the molar ratio of tributyrin to diheptanoyl-PC is increased beyond 0.18, all rodlike diheptanoyl-PC micelles are transformed into globular mixed micelles. The size of these globular mixed micelles increases with increasing tributyrin concentration in the simple micelle region up to the solubility limit. The small-angle neutron scattering data were analyzed to obtain the structural parameters of the mixed micelles. It is found that the growth of the mixed micelles does not follow a constant available surface area model or a constant palisade layer thickness model. If the model is modified to include tributyrin molecules at the surface of the mixed micelle, the growth behavior can be explained. For the tributyrin/diheptanoyl-PC molar ratio less than 0.18, rodlike micelles are found to coexist with globular mixed micelles. By fitting the neutron scattering data in the middle Q range, it is possible to determine the size and number density of the mixed micelles in the coexistence region. The results of analyzing the small-angle neutron scattering data in the coexistence region. The results of analyzing the small-angle neutron scattering data in the coexistence region show that some tributyrin molecules are solubilized by the rodlike dipheptanoyl-PC micelles and only part of the added tributyrin forms globular micelles.
NASA Astrophysics Data System (ADS)
Vives, Eduard; Baró, Jordi; Gallardo, María Carmen; Martín-Olalla, José-María; Romero, Francisco Javier; Driver, Sarah L.; Carpenter, Michael A.; Salje, Ekhard K. H.; Stipcich, Marcelo; Romero, Ricardo; Planes, Antoni
2016-07-01
We studied the two-step martensitic transition of a Cu-Al-Ni shape-memory alloy by calorimetry, acoustic emission (AE), and resonant ultrasound spectroscopy (RUS) measurements. The transition occurs under cooling from the cubic (β , F m 3 m ) parent phase near 242 K to a mixture of orthorhombic 2 H and monoclinic 18 R phases. Heating leads first to the back transformation of small 18 R domains to β and/or 2 H near 255 K, and then to the transformation 2 H to β near 280 K. The total transformation enthalpy is Δ HT=328 ±10 J/mol and is observed as one large latent heat peak under cooling. The back-transformation entropy under heating breaks down into a large component 18 R to β at 255 K and a smaller, smeared component of the transformation 2 H to β near 280 K. The proportions inside the phase mixture depend on the thermal history of the sample. The elastic response of the sample is dominated by large elastic softening during cooling. The weakening of the elastic shear modulus shows a peak at 242 K, which is typical for the formation of complex microstructures. Cooling the sample further leads to additional changes of the microstructure and domain wall freezing, which is seen by gradual elastic hardening and increasing damping of the RUS signal. Heating from 220 K to room temperature leads to elastic anomalies due to the initial transformation, which is now shifted to high temperatures. The transition is smeared over a wider temperature interval and shows strong elastic damping. The shear modulus of the cubic phase is recovered at 280 K. The phase transformation leads to avalanches, which were recorded by AE and by time-resolved calorimetry. The cooling transition shows very extended avalanche signals in calorimetry with power-law distributions. Cooling and heating runs show AE signals over a large temperature interval above 260 K. Splitting the transformation into two martensite phases leads to power-law exponents ɛ ˜2 (β ↔ 18 R ) and ɛ ˜1.5 (β ↔ 2
Observation of a possible charge-density-wave transition in cubic Ce3Co4Sn13
NASA Astrophysics Data System (ADS)
Lue, C. S.; Liu, H. F.; Hsu, S.-L.; Chu, M. W.; Liao, H. Y.; Kuo, Y. K.
2012-05-01
We report an observation of a first-order phase transition in Ce3Co4Sn13 by means of the specific heat, electrical resistivity, Seebeck coefficient, and thermal conductivity, as well as 59Co nuclear magnetic resonance (NMR) measurements. The phase transition has been evidenced by marked features near To≃155 K in all measured physical quantities except for magnetic susceptibility. This excludes a magnetic origin for the observed phase transition. In addition, x-ray diffraction results below and above To confirm the absence of a structural change, suggesting that the peculiar phase transition is possibly related to an electronic origin and/or electron-lattice coupling such as the formation of a charge density wave (CDW). As a matter of fact, the disappearance of the double-peak feature of 59Co NMR central lines below To can be realized as the spatial modulation of the electric field gradient due to incommensurate CDW superlattices. Also, a distinct peak found in the spin-lattice relaxation rate near To manifests a phase transition and its feature can be accounted for by the thermally driven normal modes of the CDW. From the NMR analyses, we obtained a consistent picture that the change of electronic structures below To is mainly due to the weakening of p-d hybridization. Such an effect could result in possible electron-lattice instability and, thus, the formation of a CDW state in Ce3Co4Sn13.
Phase Transitions in Thin Block Copolymer Films
Kramer, Edward J.
2010-10-08
David Turnbull's experiments and theoretical insights paved the way for much of our modern understanding of phase transitions in materials. In recognition of his contributions, this lecture will concentrate on phase transitions in a material system not considered by Turnbull, thin diblock copolymer films. Well-ordered block copolymer films are attracting increasing interest as we attempt to extend photolithography to smaller dimensions. In the case of diblock copolymer spheres, an ordered monolayer is hexagonal, but the ordered bulk is body-centered cubic (bcc). There is no hexagonal plane in the bcc structure, so a phase transition must occur as n, the number of layers of spheres in the film, increases. How this phase transition occurs with n and how it can be manipulated is the subject of the first part of my presentation. In the second part of the talk, I show that monolayers of diblock copolymer spheres and cylinders undergo order-to-disorder transitions that differ greatly from those of the bulk. These ordered 2D monolayers are susceptible to phonon-generated disorder as well as to thermal generation of defects, such as dislocations, which, while they are line defects in 3D, are point defects in 2D. The results are compared to the theories of melting of 2D crystals (spheres) and of 2D smectic liquid crystals (cylinders), a comparison that will allow us to understand most, but not all, of the features of these order-disorder transitions that occur as the temperature is increased.
Monoclinic sphere packings. I. Invariant, univariant and bivariant lattice complexes.
Sowa, Heidrun; Fischer, Werner
2016-05-01
All homogeneous sphere packings were derived that refer to the two invariant, the four univariant and the three bivariant lattice complexes belonging to the monoclinic crystal system. In total, sphere packings of 29 types have been found. Only for five types is the maximal inherent symmetry of their sphere packings monoclinic whereas the inherent symmetry is orthorhombic for nine types, tetragonal for five types, hexagonal for six types and cubic for four types. PMID:27126112
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.
Ab initio study of the cubic-to-hexagonal phase transition promoted by interstitial hydrogen in iron
NASA Astrophysics Data System (ADS)
Castedo, A.; Sanchez, J.; Fullea, J.; Andrade, M. C.; de Andres, P. L.
2011-09-01
Using ab initio density-functional theory, we study the role of interstitial hydrogen on the energetics of the phase transformation of iron from bcc to hcp along Bain’s pathway. The impurity creates an internal stress field that can be released through a tetragonal distortion of the lattice, promoting the bcc (ferromagnetic) → fcc (frustrated antiferromagnetic) → hcp (ferromagnetic) transition. The transformation between crystal systems is accompanied by a drastic magnetic reorganization and sudden variations of the unit cell volume, which can be one of the reasons for embrittlement and mechanical failure of iron upon hydrogen adsorption.
ERIC Educational Resources Information Center
Lipp, Alan
2000-01-01
Presents a classification of factorable cubics and shows how the associated factor graphs determine domains of disconnected branches and furnish a skeletal framework for the number and shape of the branches. Illustrates three dimensional visualization and examines level curves and spikes of surfaces. (KHR)
Liu, Z T Y; Zhou, X; Khare, S V; Gall, D
2014-01-15
We report systematic results from ab initio calculations with density functional theory on three cubic structures, zincblende (zb), rocksalt (rs) and cesium chloride (cc), of the ten 3d transition metal nitrides. We computed lattice constants, elastic constants, their derived moduli and ratios that characterize mechanical properties. Experimental measurements exist in the literature of lattice constants for rs-ScN, rs-TiN and rs-VN and of elastic constants for rs-TiN and rs-VN, all of which are in good agreement with our computational results. Similarly, computed Vickers hardness (HV) values for rs-TiN and rs-VN are consistent with earlier experimental results. Several trends were observed in our rich data set of 30 compounds. All nitrides, except for zb-CrN, rs-MnN, rs-FeN, cc-ScN, cc-CrN, cc-NiN and cc-ZnN, were found to be mechanically stable. A clear correlation in the atomic density with the bulk modulus (B) was observed with maximum values of B around FeN, MnN and CrN. The shear modulus, Young's modulus, HV and indicators of brittleness showed similar trends and all showed maxima for cc-VN. The calculated value of HV for cc-VN was about 30 GPa, while the next highest values were for rs-ScN and rs-TiN, about 24 GPa. A relation (H(V) is proportional to θ(D)(2)) between HV and Debye temperature (θD) was investigated and verified for each structure type. A tendency for anti-correlation of the elastic constant C44, which strongly influences stability and hardness, with the number of electronic states around the Fermi energy was observed.
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.
Fabrication of long lasting phosphorescence glass spheres
NASA Astrophysics Data System (ADS)
Lv, Hao; Liu, Aimei; Tong, Jufang; Yi, Xunong; Li, Qianguang
2008-12-01
The long lasting phosphorescence glass spheres doped with Eu2O3 and Dy2O3 were prepared under the reducing atmosphere and characterized. XRD analysis indicated the glass spheres exhibited the typical diffraction peaks of SrAl2O4: Eu2+, Dy3+. The emission spectra of the glass spheres showed broad bands peaking at 510nm. The excitation spectra of the glass spheres showed broad bands ranging from 300 to 480nm. These are believed due to the 5d4f-->4f transitions of Eu2+ in the SrAl2O4: Eu2+, Dy3+ phosphors. The afterglow luminescence of the glass spheres excited by a 40W fluorescence lamp for 30min can be observed in the dark for about 15h with the naked eye.
Hypervelocity flow over spheres
NASA Astrophysics Data System (ADS)
Wen, Chihyung
The nature of the nonequilibrium flow of dissociating gases over spheres was investigated experimentally, numerically and theoretically. A series of experiments with three different gases, nitrogen, air and carbon dioxide, was performed in the shock tunnel T5 at GALCIT. Five spheres of different radii equipped with thermocouples for surface heat flux measurements were used. The state-of-the-art numerical method by Candler (1988) was used to conduct a parallel study which strongly complemented the experimental and theoretical efforts.Experimental heat flux measurements are presented. Good agreement was observed among the measured stagnation point heat transfer rates, computational results and Fay and Riddell's theoretical predictions. For nitrogen and air, the measured heat flux distributions were also in good agreement with numerical computation results and Lees' theory. For carbon dioxide, large deviations were observed. Early transition tripped by surface roughness is a possible cause for the deviation of heat flux distribution from the theory. The experimental differential interferograms were compared with the images constructed from computational flowfields. Good agreement of fringe pattern and shock shape was observed.An analytical solution is obtained for inviscid hypervelocity dissociating flow over spheres. The solution explains the correlation between the dimensionless stand-off distance and the dimensionless reaction rate parameter previously observed by Hornung (1972) for nitrogen. The physics of the correlation can be shown as the binary scaling. Based on the solution, a new dimensionless reaction rate parameter is defined to generalize Hornung's correlation for more complex gases than nitrogen. Experimental and numerical results confirm the new correlation.The effect of nonequilibrium recombination downstream of a curved two-dimensional shock was also addressed. An analytical solution for an ideal dissociating gas was obtained, giving an expression for
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.
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...
NASA Technical Reports Server (NTRS)
Elleman, Daniel D. (Inventor); Wang, Taylor G. (Inventor)
1989-01-01
Systems are described for using multiple closely-packed spheres. In one system for passing fluid, a multiplicity of spheres lie within a container, with all of the spheres having the same outside diameter and with the spheres being closely nested in one another to create multiple interstitial passages of a known size and configuration and smooth walls. The container has an inlet and outlet for passing fluid through the interstitial passages formed between the nested spheres. The small interstitial passages can be used to filter out material, especially biological material such as cells in a fluid, where the cells can be easily destroyed if passed across sharp edges. The outer surface of the spheres can contain a material that absorbs a constitutent in the flowing fluid, such as a particular contamination gas, or can contain a catalyst to chemically react the fluid passing therethrough, the use of multiple small spheres assuring a large area of contact of these surfaces of the spheres with the fluid. In a system for storing and releasing a fluid such as hydrogen as a fuel, the spheres can include a hollow shell containing the fluid to be stored, and located within a compressable container that can be compressed to break the shells and release the stored fluid.
Phukon, Aparajita; Ray, Sudipta; Sahu, Kalyanasis
2016-07-01
How does microscopic organization of an organized assembly alter during macroscopic structural transition? The question may be important to ascertain driving forces responsible for such transitions. Didodecyldimethylammonium bromide (DDAB)/water/cyclohexane reverse micelle is an attractive assembly that undergoes structural transition from rod to spherical shape when the amount of water loading, w0 ([water]/[surfactant]), exceeds a particular value (w0 ∼ 8). Here, we intend to investigate the effect of the morphological change upon interfacial hydration using steady-state and time-resolved fluorescence measurements. The anionic fluorophore 8-hydroxypyrene-1,3,6-trisulfonate (HPTS or pyranine) is expected to be trapped within the positively charged RM interface. The fluorophore can undergo excited-state proton transfer (ESPT) in the presence of water and, thus, is able to provide insight on the level of hydration within the interface. The ESPT process is markedly inhibited within the interface at low w0 and gradually favored with increase of w0. The time-resolved fluorescence decays could be best analyzed by assuming distribution of HPTS over two distinct interfacial regions- partly hydrated and mostly dehydrated. The relative population of the two regions varies distinctly at low w0 (<6) and high w0 (>6) regimes. Moreover, fluorescence anisotropy (steady-state and time-resolved) varies differently with respect to w0, before and after the transition point (w0 ∼ 8). PMID:27292367
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.
NASA Astrophysics Data System (ADS)
Pastore, G.; Bernu, B.; Hansen, J. P.; Hiwatari, Y.
1988-07-01
Using molecular-dynamics (MD) data on a binary-alloy model, we have computed the self (incoherent) -part of the density autocorrelation functions of both species in the supercooled liquid and near the glass transition, over an extensive range of wave numbers. Standard theoretical models of liquid-state theory fail to reproduce the data, while the Chudley-Elliott jump diffusion model yields reasonable results in the glass range. With a suitable scaling of the time axis, the data for different temperatures can be brought onto a single master curve, which is well fitted by a Kohlrausch (``stretched-exponential'') function with a wave-number-dependent exponent.
ERIC Educational Resources Information Center
Field, David; And Others
1992-01-01
Includes four articles: "Career Aspirations" (Field); "Making the Transition to a New Curriculum" (Baker, Householder); "How about a 'Work to School' Transition?" (Glasberg); and "Technological Improvisation: Bringing CNC to Woodworking" (Charles, McDuffie). (SK)
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 ...
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.
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.
Weisemoeller, T.; Bertram, F.; Gevers, S.; Greuling, A.; Deiter, C.; Tobergte, H.; Neumann, M.; Wollschlaeger, J.; Giussani, A.; Schroeder, T.
2009-06-15
Films of hexagonal praseodymium sesquioxide (h-Pr{sub 2}O{sub 3}) were deposited on Si(111) by molecular beam epitaxy and thereafter annealed in 1 atm oxygen at different temperatures, ranging from 100 to 700 deg. C. The films of the samples annealed at 300 deg. C or more were transformed to PrO{sub 2} with B-oriented Fm3m structure, while films annealed at lower temperatures kept the hexagonal structure. The films are composed of PrO{sub 2} and PrO{sub 2-d}elta species, which coexist laterally and are tetragonally distorted due to the interaction at the interface between oxide film and Si substrate. Compared to PrO{sub 2}, PrO{sub 2-d}elta has the same cubic structure but with oxygen vacancies. The oxygen vacancies are partly ordered and increase the vertical lattice constant of the film, whereas the lateral lattice constant is almost identical for both species and on all samples. The latter lattice constant matches the lattice constant of the originally crystallized hexagonal praseodymium sesquioxide. That means that no long range reordering of the praseodymium atoms takes place during the phase transformation.
NASA Astrophysics Data System (ADS)
Gilliland, Ronald L.
Transits of the planets Mercury and especially Venus have been exciting events in the development of astronomy over the past few hundred years. Just two years ago the first transiting extra-solar planet, HD 209458b, was discovered, and subsequent studies during transit have contributed fundamental new knowledge. From the photometric light curve during transit one obtains a basic confirmation that the radial velocity detected object is indeed a planet by allowing precise determination of its mass and radius relative to these stellar quantities. From study of spectroscopic changes during transit it has been possible to probe for individual components of the transiting planets atmosphere. Planet transits are likely to become a primary tool for detection of new planets, especially other Earth-like planets with the Kepler Discovery Mission. Looking ahead, the additional aperture of the James Webb Space Space Telescope promises to allow the first possibility of studying the atmosphere of extra-solar Earth-analogue planets, perhaps even providing the first evidence of direct relevance to the search for signs of life on other planets.
Cherstvy, A G; Winkler, R G
2011-06-28
A universal description is presented for weak adsorption of flexible polyelectrolyte chains onto oppositely charged planar and curved surfaces. It is based on the WKB (Wentzel-Kramers-Brillouin) quantum mechanical method for the Green function equation in the ground state dominance limit. The approach provides a unified picture for the scaling behavior of the critical characteristics of polyelectrolyte adsorption and the thickness of the adsorbed polymer layer formed adjacent to the interface. We find, particularly at low-salt conditions, that curved convex surfaces necessitate much larger surface charge densities to trigger polyelectrolyte adsorption, as compared to a planar interface in the same solution. In addition, we demonstrate that the different surface geometries yield very distinct scaling laws for the critical surface charge density required to initiate chain adsorption. Namely, in the low-salt limit, the surface charge density scales cubical with the inverse Debye screening length for a plane, quadratic for an adsorbing cylinder, and linear for a sphere. As the radius of surface curvature grows, the parameter of critical chain adsorption onto a rod and a sphere turns asymptotically into that of a planar interface. The transition occurs when the radius of surface curvature becomes comparable to the Debye screening length. The general scaling trends derived appear to be consistent with the complex-formation experiments of polyelectrolyte chains with oppositely charged spherical and cylindrical micelles. Finally, the WKB results are compared with the existing theories of polyelectrolyte adsorption and future perspectives are outlined.
Piecewise Cubic Interpolation Package
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
NASA Astrophysics Data System (ADS)
Heyes, D. M.; Clarke, S. M.; Brańka, A. C.
2009-11-01
Molecular dynamics simulations have been used to compute physical properties of model fluids in which the particles interacted via the soft-sphere pair potential (SSP) ϕ(r )=ɛ(σ /r)n, where ɛ and σ are the characteristic energy and distance, respectively. The emphasis is on small values of n, tending to the lower theromodynamically allowed bound of 3+. An accurate equation of state for the SSP fluid is obtained, consisting of two terms, and as n→3+, the compressibility factor, Z tends to Z =B2ζn /3 for ζ >0, where B2 is the second virial coefficient, and ζ =πNσ3/6V is a nominal packing fraction for N particles in volume V. A simple formula for the position of the first peak in the radial distribution function in the soft particle limit is proposed and shown to agree with the simulation data. The fluid phase velocity autocorrelation function at fluid-solid coexistence becomes more oscillatory as n decreases. Values for the self-diffusion coefficient D and shear viscosity η were calculated as a function of n and density, and these were used to estimate the n-dependence of an ideal glass transition. The glass transition shifts relatively further into the solid part of the phase diagram as softness (˜1/n) increases. D decreases by ca. 75% and η increases by about a factor of 3 along the fluid-solid coexistence line from n =∞ to 3.25. Non-Gaussian behavior was calculated from the particle displacements as a function of particle softness. A screened soft-sphere potential, SSSP, was introduced to explore the effects for small n of the long range part of the potential in relation to the scale of the local structure. The SSSP with suitable analytic form and parameters can give statistically indistinguishable results from the full SSP for the static properties, D and η.
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.
The role of thickness transitions in convective assembly.
Meng, Linli; Wei, Hong; Nagel, Anthony; Wiley, Benjamin J; Scriven, L E; Norris, David J
2006-10-01
Here we examine the microscopic details of convective assembly, a process in which thin colloidal crystals are deposited on a substrate from suspensions of nearly monodisperse spheres. Previously, such crystals have been shown to exhibit a strong tendency toward the face-centered cubic structure, which is difficult to explain on thermodynamic grounds. Using real-time microscopic visualization, electron microscopy, and scanning confocal microscopy, we obtain clues about the crystallization mechanism. Our results indicate that the regions at which a growing crystal transitions from n to n + 1 layers can play an important and previously unrecognized role in the crystallization. For thin crystals, we show both from experiment and through simple modeling that these transition regions can generate specific crystal structures. In thicker crystals, the crystallization is more complicated, but the transition regions must still be considered before a complete understanding of convective assembly can be obtained.
Sticky surface: sphere-sphere adhesion dynamics
Sircar, Sarthok; Younger, John G.; Bortz, David M.
2014-01-01
We present a multi-scale model to study the attachment of spherical particles with a rigid core, coated with binding ligands and suspended in the surrounding, quiescent fluid medium. This class of fluid-immersed adhesion is widespread in many natural and engineering settings, particularly in microbial surface adhesion. Our theory highlights how the micro-scale binding kinetics of these ligands, as well as the attractive / repulsive surface potential in an ionic medium affects the eventual macro-scale size distribution of the particle aggregates (flocs). The bridge between the micro-macro model is made via an aggregation kernel. Results suggest that the presence of elastic ligands on the particle surface lead to the formation of larger floc aggregates via efficient inter-floc collisions (i.e., non-zero sticking probability, g). Strong electrolytic composition of the surrounding fluid favors large floc formation as well. The kernel for the Brownian diffusion for hard spheres is recovered in the limit of perfect binding effectiveness (g → 1) and in a neutral solution with no dissolved salts. PMID:25159830
Packings of a charged line on a sphere
NASA Astrophysics Data System (ADS)
Alben, Silas
2008-12-01
We find equilibrium configurations of open and closed lines of charge on a sphere, and track them with respect to varying sphere radius. Closed lines transition from a circle to a spiral-like shape through two low-wave-number bifurcations—“baseball seam” and “twist”—which minimize Coulomb energy. The spiral shape is the unique stable equilibrium of the closed line. Other unstable equilibria arise through tip-splitting events. An open line transitions smoothly from an arc of a great circle to a spiral as the sphere radius decreases. Under repulsive potentials with faster-than-Coulomb power-law decay, the spiral is tighter in initial stages of sphere shrinkage, but at later stages of shrinkage the equilibria for all repulsive potentials converge on a spiral with uniform spacing between turns. Multiple stable equilibria of the open line are observed.
Packings of a charged line on a sphere.
Alben, Silas
2008-12-01
We find equilibrium configurations of open and closed lines of charge on a sphere, and track them with respect to varying sphere radius. Closed lines transition from a circle to a spiral-like shape through two low-wave-number bifurcations-"baseball seam" and "twist"-which minimize Coulomb energy. The spiral shape is the unique stable equilibrium of the closed line. Other unstable equilibria arise through tip-splitting events. An open line transitions smoothly from an arc of a great circle to a spiral as the sphere radius decreases. Under repulsive potentials with faster-than-Coulomb power-law decay, the spiral is tighter in initial stages of sphere shrinkage, but at later stages of shrinkage the equilibria for all repulsive potentials converge on a spiral with uniform spacing between turns. Multiple stable equilibria of the open line are observed.
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.
Cubic topological Kondo insulators.
Alexandrov, Victor; Dzero, Maxim; Coleman, Piers
2013-11-27
Current theories of Kondo insulators employ the interaction of conduction electrons with localized Kramers doublets originating from a tetragonal crystalline environment, yet all Kondo insulators are cubic. Here we develop a theory of cubic topological Kondo insulators involving the interaction of Γ(8) spin quartets with a conduction sea. The spin quartets greatly increase the potential for strong topological insulators, entirely eliminating the weak topological phases from the diagram. We show that the relevant topological behavior in cubic Kondo insulators can only reside at the lower symmetry X or M points in the Brillouin zone, leading to three Dirac cones with heavy quasiparticles.
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.
Sowa
2000-05-01
A structure forming a cubic primitive lattice cP may be deformed into a structure forming a cubic body-centred lattice cI in the space group Cmcm at position 4(c) m2m 0,y,1/4. If in related structures the sites are alternately occupied by unlike atoms, the NaCl and the CsCl types occur, respectively. The corresponding phase transition can be described as a deformation of a heterogeneous sphere packing in the subgroup Pmmn (a,-c,b) of Cmcm. All sphere configurations with symmetry Cmcm 4(c) m2m were derived. On the basis of this information, further possibilities for phase transitions that also correspond to sphere-packing deformations were found with this symmetry. Two of them possibly may take place in metals. The first one leads from a primitive hexagonal lattice to a hexagonal close packing, the other from a cubic body-centred lattice also to a hexagonal close packing.
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.
Vacancy-dependent stability of cubic and wurtzite Ti1−xAlxN
Euchner, H.; Mayrhofer, P.H.
2015-01-01
While it is well-known that supersaturated cubic-structured Ti1−xAlxN can be prepared by physical vapor deposition, the impact of point defects on formation process and cubic to wurtzite transition is largely unexplored. Irrespective of point defects, ab initio calculations correctly predict the Al concentration of the cubic to wurtzite transition. By means of density functional theory we show that vacancies on metal and/or non-metal sites only slightly affect the cubic to wurtzite transition region, whereas they clearly affect the physical properties. PMID:26412921
Slip and flow of hard-sphere colloidal glasses.
Ballesta, P; Besseling, R; Isa, L; Petekidis, G; Poon, W C K
2008-12-19
We study the flow of concentrated hard-sphere colloidal suspensions along smooth, nonstick walls using cone-plate rheometry and simultaneous confocal microscopy. In the glass regime, the global flow shows a transition from Herschel-Bulkley behavior at large shear rate to a characteristic Bingham slip response at small rates, absent for ergodic colloidal fluids. Imaging reveals both the "solid" microstructure during full slip and the local nature of the "slip to shear" transition. Both the local and global flow are described by a phenomenological model, and the associated Bingham slip parameters exhibit characteristic scaling with size and concentration of the hard spheres.
Numerical simulation of negative Magnus force on a rotating sphere
NASA Astrophysics Data System (ADS)
Muto, Masaya; Tsubokura, Makoto; Oshima, Nobuyuki
2010-11-01
Flow characteristics and fluid force on a sphere rotating along with axis perpendicular to mean air flow were investigated using Large Eddy Simulation at two different Reynolds numbers of 10,000 and 200,000. As a result of simulation, opposite flow characteristics around the sphere and displacement of the separation point were visualized depending on the Reynolds number even though the sphere rotates at the same rotation speed according to the Reynolds number. When Reynolds number is 10,000, flow characteristics agree with the flow field explained in the Magnus effect. However sphere rotates at the same rotation speed while increasing Reynolds number to 200,000, separation point moves in opposite direction and wake appears in the different direction. The reason of the negative Magnus force was discussed in terms of the boundary layer transition on the surface.
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.
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
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
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.
Bidispersed Sphere Packing on Spherical Surfaces
NASA Astrophysics Data System (ADS)
Atherton, Timothy; Mascioli, Andrew; Burke, Christopher
Packing problems on spherical surfaces have a long history, originating in the classic Thompson problem of finding the ground state configuration of charges on a sphere. Such packings contain a minimal number of defects needed to accommodate the curvature; this is predictable using the Gauss-Bonnet theorem from knowledge of the topology of the surface and the local symmetry of the ordering. Famously, the packing of spherical particles on a sphere contains a 'scar' transition, where additional defects over those required by topology appear above a certain critical number of particles and self-organize into chains or scars. In this work, we study the packing of bidispersed packings on a sphere, and hence determine the interaction of bidispersity and curvature. The resultant configurations are nearly crystalline for low values of bidispersity and retain scar-like structures; these rapidly become disordered for intermediate values and approach a so-called Appollonian limit at the point where smaller particles can be entirely accommodated within the voids left by the larger particles. We connect our results with studies of bidispersed packings in the bulk and on flat surfaces from the literature on glassy systems and jamming. Supported by a Cottrell Award from the Research Corporation for Science Advancement.
Rainbow Scattering by a Coated Sphere
NASA Technical Reports Server (NTRS)
Lock, James A.; Jamison, J. Michael; Lin, Chih-Yang
1994-01-01
We examine the behavior of the first-order rainbow for a coated sphere by using both ray theory and Aden-Kerker wave theory as the radius of the core alpha(sub 12) and the thickness of the coating beta are varied. As the ratio beta/alpha(sub 12) increases from 10(sup -4) to 0.33, we find three classes of rainbow phenomena that cannot occur for a homogeneous-sphere rainbow. For beta/alpha(sub 12) approx less than 10(sup -3), the rainbow intensity is an oscillatory function of the coating thickness, for beta/alpha(sub 12) approx. 10(sup -2), the first-order rainbow breaks into a pair of twin rainbows, and for beta/alpha(sub 12) approx. 0.33, various rainbow-extinction transitions occur. Each of these effects is analyzed, and their physical interpretations are given. A Debye series decomposition of coated-sphere partial-wave scattering amplitudes is also performed and aids in the analysis.
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
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.
Anisotropy of a cubic ferromagnet at criticality
NASA Astrophysics Data System (ADS)
Kudlis, A.; Sokolov, A. I.
2016-10-01
Critical fluctuations change the effective anisotropy of cubic ferromagnet near the Curie point. If the crystal undergoes phase transition into orthorhombic phase and the initial anisotropy is not too strong, reduced anisotropy of nonlinear susceptibility acquires at Tc the universal value δ4*=2/v* 3 (u*+v*) where u* and v* are coordinates of the cubic fixed point on the flow diagram of renormalization group equations. In the paper, the critical value of the reduced anisotropy is estimated within the pseudo-ɛ expansion approach. The six-loop pseudo-ɛ expansions for u*, v*, and δ4* are derived for the arbitrary spin dimensionality n . For cubic crystals (n =3 ) higher-order coefficients of the pseudo-ɛ expansions obtained turn out to be so small that use of simple Padé approximants yields reliable numerical results. Padé resummation of the pseudo-ɛ series for u*, v*, and δ4* leads to the estimate δ4*=0.079 ±0.006 , indicating that detection of the anisotropic critical behavior of cubic ferromagnets in physical and computer experiments is certainly possible.
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...
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
Mutifuntional GdPO4:Eu3+ hollow spheres: synthesis and magnetic and luminescent properties.
Zhang, Lihui; Yin, Meili; You, Hongpeng; Yang, Mei; Song, Yanhua; Huang, Yeju
2011-11-01
Mondispersed submicrometer GdPO(4):Eu(3+) hollow spheres were synthesized via an effective one-pot hydrothermal process. These hollow spheres have the average diameter of 200 nm, and the shell thickness is about 20 nm. The surface of the spheres consists of a number of nanorods with diameters of about 10 nm and lengths of about 50-80 nm. Both magnetic and luminescent properties of the obtained Eu(3+)-doped GdPO(4) hollow spheres were investigated. The hysteresis plot (M-H) analysis result indicates their paramagnetic property. The fluorescence spectra demonstrate that they emit orange-red color light originated from the (5)D(0) → (7)F(J) transitions of the Eu(3+) ions. Therefore, the obtained GdPO(4) hollow spheres hold promise for encapsulate drugs with controlled release. Moreover, the GdPO(4):Eu(3+) hollow spheres are attributes for bimodal magnetic resonance imaging (MRI)/optical bioimaging labeling.
Zhang, Genqiang; Lou, Xiong Wen David
2014-08-18
Complex hollow structures of transition metal oxides, especially mixed metal oxides, could be promising for different applications such as lithium ion batteries. However, it remains a great challenge to fabricate well-defined hollow spheres with multiple shells for mixed transition metal oxides. Herein, we have developed a new "penetration-solidification-annealing" strategy which can realize the synthesis of various mixed metal oxide multi-shelled hollow spheres. Importantly, it is found that multi-shelled hollow spheres possess impressive lithium storage properties with both high specific capacity and excellent cycling stability. Specifically, the carbon-coated CoMn2O4 triple-shelled hollow spheres exhibit a specific capacity of 726.7 mA h g(-1) and a nearly 100 % capacity retention after 200 cycles. The present general strategy could represent a milestone in design and synthesis of mixed metal oxide complex hollow spheres and their promising uses in different areas.
Zhang, Genqiang; Lou, Xiong Wen David
2014-08-18
Complex hollow structures of transition metal oxides, especially mixed metal oxides, could be promising for different applications such as lithium ion batteries. However, it remains a great challenge to fabricate well-defined hollow spheres with multiple shells for mixed transition metal oxides. Herein, we have developed a new "penetration-solidification-annealing" strategy which can realize the synthesis of various mixed metal oxide multi-shelled hollow spheres. Importantly, it is found that multi-shelled hollow spheres possess impressive lithium storage properties with both high specific capacity and excellent cycling stability. Specifically, the carbon-coated CoMn2O4 triple-shelled hollow spheres exhibit a specific capacity of 726.7 mA h g(-1) and a nearly 100 % capacity retention after 200 cycles. The present general strategy could represent a milestone in design and synthesis of mixed metal oxide complex hollow spheres and their promising uses in different areas. PMID:24962932
An Unusual Rolling-Sphere Phenomenon.
ERIC Educational Resources Information Center
Cromer, Alan
1996-01-01
Discusses the theory behind a study of motion where a hollow plastic sphere racing against a steel sphere in two parallel sections of inclined channeling always reaches the bottom first; once on the floor, however, the steel sphere travels faster, speeding past the plastic sphere when both are about one meter from the base of the track. (JRH)
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.)
Demixing in binary mixtures of apolar and dipolar hard spheres
NASA Astrophysics Data System (ADS)
Almarza, N. G.; Lomba, E.; Martín, C.; Gallardo, A.
2008-12-01
We study the demixing transition of mixtures of equal size hard spheres and dipolar hard spheres using computer simulation and integral equation theories. Calculations are carried out at constant pressure, and it is found that there is a strong correlation between the total density and the composition. The critical temperature and the critical total density are found to increase with pressure. The critical mole fraction of the dipolar component on the contrary decreases as pressure is augmented. These qualitative trends are reproduced by the theoretical approaches that on the other hand overestimate by far the value of the critical temperature. Interestingly, the critical parameters for the liquid-vapor equilibrium extrapolated from the mixture results in the limit of vanishing neutral hard sphere concentration agree rather well with recent estimates based on the extrapolation of charged hard dumbbell phase equilibria when dumbbell elongation shrinks to zero [G. Ganzenmüller and P. J. Camp, J. Chem. Phys. 126, 191104 (2007)].
The viscosity of colloidal spheres in deionized suspensions
NASA Astrophysics Data System (ADS)
Okubo, Tsuneo
1987-12-01
Viscosities of colloidal spheres, i.e., colloidal silica (diameter 8 and 45 nm) and monodisperse polystyrene latices (diameter 85 to 780 nm), are measured in deionized (``salt-free'') suspensions and in the presence of a small amount of NaCl. The reduced viscosities (specific viscosity divided by concentration) of deionized silica (diameter 8 nm) are much higher than would be expected by Einstein's prediction and decrease sharply with increasing concentration. A sharp peak is observed in the reduced viscosity vs concentration curves of deionized colloidal silica of 45 nm diameter and the deionized latex spheres. The peak corresponds to the transition between ``liquid-like'' and ``crystal-like'' structures. These results show that electrostatic intersphere repulsion and the elongated Debye-screening length around the colloidal spheres are essential to explain the extraordinary properties.
Physics of Hard Spheres Experiment: Significant and Quantitative Findings Made
NASA Technical Reports Server (NTRS)
Doherty, Michael P.
2000-01-01
Direct examination of atomic interactions is difficult. One powerful approach to visualizing atomic interactions is to study near-index-matched colloidal dispersions of microscopic plastic spheres, which can be probed by visible light. Such spheres interact through hydrodynamic and Brownian forces, but they feel no direct force before an infinite repulsion at contact. Through the microgravity flight of the Physics of Hard Spheres Experiment (PHaSE), researchers have sought a more complete understanding of the entropically driven disorder-order transition in hard-sphere colloidal dispersions. The experiment was conceived by Professors Paul M. Chaikin and William B. Russel of Princeton University. Microgravity was required because, on Earth, index-matched colloidal dispersions often cannot be density matched, resulting in significant settling over the crystallization period. This settling makes them a poor model of the equilibrium atomic system, where the effect of gravity is truly negligible. For this purpose, a customized light-scattering instrument was designed, built, and flown by the NASA Glenn Research Center at Lewis Field on the space shuttle (shuttle missions STS 83 and STS 94). This instrument performed both static and dynamic light scattering, with sample oscillation for determining rheological properties. Scattered light from a 532- nm laser was recorded either by a 10-bit charge-coupled discharge (CCD) camera from a concentric screen covering angles of 0 to 60 or by sensitive avalanche photodiode detectors, which convert the photons into binary data from which two correlators compute autocorrelation functions. The sample cell was driven by a direct-current servomotor to allow sinusoidal oscillation for the measurement of rheological properties. Significant microgravity research findings include the observation of beautiful dendritic crystals, the crystallization of a "glassy phase" sample in microgravity that did not crystallize for over 1 year in 1g
Localization accuracy of sphere fiducials in computed tomography images
NASA Astrophysics Data System (ADS)
Kobler, Jan-Philipp; Díaz Díaz, Jesus; Fitzpatrick, J. Michael; Lexow, G. Jakob; Majdani, Omid; Ortmaier, Tobias
2014-03-01
In recent years, bone-attached robots and microstereotactic frames have attracted increasing interest due to the promising targeting accuracy they provide. Such devices attach to a patient's skull via bone anchors, which are used as landmarks during intervention planning as well. However, as simulation results reveal, the performance of such mechanisms is limited by errors occurring during the localization of their bone anchors in preoperatively acquired computed tomography images. Therefore, it is desirable to identify the most suitable fiducials as well as the most accurate method for fiducial localization. We present experimental results of a study focusing on the fiducial localization error (FLE) of spheres. Two phantoms equipped with fiducials made from ferromagnetic steel and titanium, respectively, are used to compare two clinically available imaging modalities (multi-slice CT (MSCT) and cone-beam CT (CBCT)), three localization algorithms as well as two methods for approximating the FLE. Furthermore, the impact of cubic interpolation applied to the images is investigated. Results reveal that, generally, the achievable localization accuracy in CBCT image data is significantly higher compared to MSCT imaging. The lowest FLEs (approx. 40 μm) are obtained using spheres made from titanium, CBCT imaging, template matching based on cross correlation for localization, and interpolating the images by a factor of sixteen. Nevertheless, the achievable localization accuracy of spheres made from steel is only slightly inferior. The outcomes of the presented study will be valuable considering the optimization of future microstereotactic frame prototypes as well as the operative workflow.
Sphere forming method and apparatus
NASA Technical Reports Server (NTRS)
Youngberg, C. L.; Miller, C. G.; Stephens, J. B.; Finnerty, A. A. (Inventor)
1983-01-01
A system is provided for forming small accurately spherical objects. Preformed largely spherical objects are supported at the opening of a conduit on the update of hot gas emitted from the opening, so the object is in a molten state. The conduit is suddenly jerked away at a downward incline, to allow the molten object to drop in free fall, so that surface tension forms a precise sphere. The conduit portion that has the opening, lies in a moderate vacuum chamber, and the falling sphere passes through the chamber and through a briefly opened valve into a tall drop tower that contains a lower pressure, to allow the sphere to cool without deformation caused by falling through air.
Computational polymer physics: Hard-sphere chain in solvent systems
NASA Astrophysics Data System (ADS)
Gautam, Avinash; Gavazzi, Daniel; Taylor, Mark
2009-10-01
In this work we present results for chain conformation in two simple chain-in-solvent systems constructed from hard-sphere monomers of diameter D. The first system consists of a flexible chain of fused hard spheres (i.e., bond length L=D) in a monomeric hard-sphere solvent. The second system consists of a flexible tangent hard-sphere chain (L=D) in a dimeric hard-sphere solvent with L=D. These systems are studied using Monte Carlo simulations which employ both single-site crankshaft and multi-site pivot moves to sample the configuration space of the chain. We report chain structure, in terms of site-site probability functions, as a function of solvent density. In all cases, increasing solvent density leads to an overall compression of the chain. At high solvent density the chain conformation is closely coupled to the local solvent structure and we speculate that incommensurate structures may lead to interesting conformational transitions.
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.
Anisotropic cubic curvature couplings
NASA Astrophysics Data System (ADS)
Bailey, Quentin G.
2016-09-01
To complement recent work on tests of spacetime symmetry in gravity, cubic curvature couplings are studied using an effective field theory description of spacetime-symmetry breaking. The associated mass-dimension-eight coefficients for Lorentz violation studied do not result in any linearized gravity modifications and instead are revealed in the first nonlinear terms in an expansion of spacetime around a flat background. We consider effects on gravitational radiation through the energy loss of a binary system and we study two-body orbital perturbations using the post-Newtonian metric. Some effects depend on the internal structure of the source and test bodies, thereby breaking the weak equivalence principle for self-gravitating bodies. These coefficients can be measured in Solar-System tests, while binary-pulsar systems and short-range gravity tests are particularly sensitive.
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.
ERIC Educational Resources Information Center
Nikitina, N. N.
2010-01-01
Present-day Russia is characterized by a resolute transition to the innovative path of development in all spheres of economic and social life, and that includes the sphere of education. The processes that took place in Russian education in the 1990s, which can be characterized as a time of "precipitous innovation," were, to some extent, an…
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
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.
NASA Astrophysics Data System (ADS)
Mattner, Trent; Chong, Min; Joubert, Peter
2000-11-01
Vortical flow past a sphere in a constant diameter pipe was studied experimentally in a guide vane apparatus similar to those used in fundamental experimental studies of vortex breakdown. The initial effect of swirl was to shorten the downstream separation bubble. For a small range of the swirl intensity, an almost stagnant upstream separation bubble formed. As the swirl intensity was increased, the bubble became unstable and an unsteady spiral formed. At high swirl intensity there was a mean recirculation region which penetrated far upstream while the flow on the downstream hemisphere was attached. Measurements of the velocity field were obtained using laser Doppler velocimetry. Analysis of these results suggests that the onset of upstream separation is associated with the formation of a negative azimuthal vorticity component which slows the axial flow near the axis of symmetry. This is consistent with inviscid distortion of the vortex filaments in the diverging flow approaching the sphere.
Polyolefin cubic silsesquioxane nanocomposites
NASA Astrophysics Data System (ADS)
Zheng, Lei
This thesis focuses on the synthesis and characterization of polyolefin nanocomposites containing polyhedral oligomeric silsesquioxane (POSS) units. Two copolymerization methods were developed utilizing either ring-opening metathesis polymerization or metallocene-catalyzed reactions to incorporate cubic silsesquioxane into polyolefins. Ring-opening metathesis copolymerizations of cyclooctene and the POSS-norbornylene macromonomer have been performed using Grubbs' catalyst RuCl2(=CHPh)(PCy3)2. Random copolymers have been prepared and characterized with POSS loadings as high as 55 wt%. Diimide reduction of these copolymers affords polyethylene-POSS random copolymers. Polyethylene (PE) and isotactic polypropylene (PP) copolymers incorporating POSS have also been prepared using a metallocene/methylaluminoxane (MAO) cocatalyst system. A wide range of POSS concentrations was obtained in these polyolefin POSS copolymers under mild conditions; up to 56 wt% for PE-POSS copolymers and 73 wt% for PP-POSS copolymers were prepared. Copolymerizations of styrene and the POSS-styryl macromonomer have been performed using CpTiCl 3 in conjunction with MAO. Random copolymers of syndiotactic polystyrene and POSS copolymers have been formed and characterized. Novel nanocomposites of PE-POSS have been characterized using Wide Angle X-ray Scattering (WAXS). From both line broadening of the diffraction maxima and also the oriented diffraction in a drawn sample, we conclude that POSS forms anisotropically shaped crystallites. On the basis of this result, a novel approach to obtain nanocomposites containing inorganic nanolayers is proposed. Cubic silsesquioxane (POSS) nanoparticles are used to achieve the nanolayered "clay-like" structure through controlled self-assembly. The organic polymer, covalently connected to POSS, is intended to regulate the POSS crystallization into a two-dimensional lattice. The concept is demonstrated by random copolymers of polybutadiene and POSS. The data from
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.
Underwater implosion of glass spheres.
Turner, Stephen E
2007-02-01
Underwater implosion experiments were conducted with thin-wall glass spheres to determine the influence that structural failure has on the pressure pulse. Four experiments were conducted with glass spheres having an outside diameter of 7.62 cm, thickness of 0.762 mm, and an estimated buckling pressure of 7.57 MPa. The experiments were performed in a pressure vessel at a hydrostatic pressure of 6.996 MPa. The average peak pressure of the implosion pressure pulse was 26.1 MPa, measured at a radial distance of 10.16 cm from the sphere center. A computational fluid structure interaction model was developed to assess how the failure rate of the glass structure influences the pressure time history. The model employed a specified glass failure sequence that is uniform in time and space. It was found that for the conditions of the test, a glass failure rate of 275 m/s provided a reasonable representation of the test data. The test data and the model results show that the failure time history of the structure has a significant influence on an implosion pressure pulse. Computational prediction of an implosion pressure pulse needs to include the failure time history of the structure; otherwise it will overpredict the pressure time history.
Mechanical Deformability of Biological Membranes and the Sphering of the Erythrocyte
Adams, K. H.
1973-01-01
Equations of mechanical equilibrium are applied to the erythrocyte membrane in the normal, hypotonically swollen, and sphered configurations. The hydrostatic pressure drop across the normal cell membrane is shown to be zero for all biconcave shapes if the membrane thickness is uniform. This result leads to the conclusion that the membrane tension is uniform and is a function of membrane potential. A two-dimensional fluid film model for the membrane is introduced to describe the unusual deformability of the erythrocyte during sphering in hypotonic solutions. The model predicts a smooth transition from the biconcave shape to a perfect sphere. PMID:4697234
Infrared cubic dielectric resonator metamaterial.
Sinclair, Michael B.; Brener, Igal; Peters, David William; Ginn, James Cleveland, III; Ten Eyck, Gregory A.
2010-06-01
Dielectric resonators are an effective means to realize isotropic, low-loss optical metamaterials. As proof of this concept, a cubic resonator is analytically designed and then tested in the long-wave infrared.
Use of Pom Pons To Illustrate Cubic Crystal Structures
NASA Astrophysics Data System (ADS)
Cady, Susan G.
1997-07-01
In general chemistry classes, students are introduced to the ways in which atoms are arranged in cubic crystal structures. Transposing the textbook illustrations into three dimensional structures is difficult for some students. This transitions is easier if a three dimensional model is available for examination. Several 3D models are cited. A quick to assemble, inexpensive, colorful, and durable alternative to these models and styrofoam balls is the use of olefin pom pons. Different sized pom pons can be used to demonstrate how the atomic radius will vary when comparing the different types of cubic crystal unit cells. Being made of a coarse material, pom pons can be stacked to illustrate different packing arrangements such as hexagonal close-packed and cubic close-packed structures. Pom pons make great atoms.
Superconductivity in cubic noncentrosymmetric PdBiSe Crystal
NASA Astrophysics Data System (ADS)
Joshi, B.; Thamizhavel, A.; Ramakrishnan, S.
2015-03-01
Mixing of spin singlet and spin triplet superconducting pairing state is expected in noncentrosymmetric superconductors (NCS) due to the inherent presence of Rashba-type antisymmetric spin-orbit coupling. Unlike low symmetry (tetragonal or monoclinic) NCS, parity is isotropicaly broken in space for cubic NCS and can additionally lead to the coexistence of magnetic and superconducting state under certain conditions. Motivated with such enriched possibility of unconventional superconducting phases in cubic NCS we are reporting successful formation of single crystalline cubic noncentrosymmetric PdBiSe with lattice parameter a = 6.4316 Å and space group P21 3 (space group no. 198) which undergoes to superconducting transition state below 1.8 K as measured by electrical transport and AC susceptibility measurements. Significant strength of Rashba-type antisymmetric spin-orbit coupling can be expected for PdBiSe due to the presence of high Z (atomic number) elements consequently making it potential candidate for unconventional superconductivity.
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.
Evolution of cubic membranes as antioxidant defence system
Deng, Yuru; Almsherqi, Zakaria A.
2015-01-01
Possibly the best-characterized cubic membrane transition has been observed in the mitochondrial inner membranes of free-living giant amoeba (Chaos carolinense). In this ancient organism, the cells are able to survive in extreme environments such as lack of food, thermal and osmolarity fluctuations and high levels of reactive oxygen species. Their mitochondrial inner membranes undergo rapid changes in three-dimensional organization upon food depletion, providing a valuable model to study this subcellular adaptation. Our data show that cubic membrane is enriched with unique ether phospholipids, plasmalogens carrying very long-chain polyunsaturated fatty acids. Here, we propose that these phospholipids may not only facilitate cubic membrane formation but may also provide a protective shelter to RNA. The potential interaction of cubic membrane with RNA may reduce the amount of RNA oxidation and promote more efficient protein translation. Thus, recognizing the role of cubic membranes in RNA antioxidant systems might help us to understand the adaptive mechanisms that have evolved over time in eukaryotes. PMID:26464785
Stimulus-responsive azobenzene supramolecules: fibers, gels, and hollow spheres.
Lee, Sumi; Oh, Seungwhan; Lee, Joosub; Malpani, Yashwardhan; Jung, Young-Sik; Kang, Baotao; Lee, Jin Yong; Ozasa, Kazunari; Isoshima, Takashi; Lee, Sang Yun; Hara, Masahiko; Hashizume, Daisuke; Kim, Jong-Man
2013-05-14
Novel, stimulus-responsive supramolecular structures in the form of fibers, gels, and spheres, derived from an azobenzene-containing benzenetricarboxamide derivative, are described. Self-assembly of tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxamide (Azo-1) in aqueous organic solvent systems results in solvent dependent generation of microfibers (aq DMSO), gels (aq DMF), and hollow spheres (aq THF). The results of a single crystal X-ray diffraction analysis of Azo-1 (crystallized from a mixture of DMSO and H2O) reveal that it possesses supramolecular columnar packing along the b axis. Data obtained from FTIR analysis and density functional theory (DFT) calculation suggest that multiple hydrogen bonding modes exist in the Azo-1 fibers. UV irradiation of the microfibers, formed in aq DMSO, causes complete melting while regeneration of new fibers occurs upon visible light irradiation. In addition to this photoinduced and reversible phase transition, the Azo-1 supramolecules display a reversible, fiber-to-sphere morphological transition upon exposure to pure DMSO or aq THF. The role played by amide hydrogen bonds in the morphological changes occurring in Azo-1 is demonstrated by the behavior of the analogous, ester-containing tris(4-((E)-phenyldiazenyl)phenyl)benzene-1,3,5-tricarboxylate (Azo-2) and by the hydrogen abstraction in the presence of fluoride anions. PMID:23597134
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.
The dynamic sphere test problem
Chabaud, Brandon M.; Brock, Jerry S.; Smith, Brandon M.
2012-05-16
In this manuscript we define the dynamic sphere problem as a spherical shell composed of a homogeneous, linearly elastic material. The material exhibits either isotropic or transverse isotropic symmetry. When the problem is formulated in material coordinates, the balance of mass equation is satisfied automatically. Also, the material is assumed to be kept at constant temperature, so the only relevant equation is the equation of motion. The shell has inner radius r{sub i} and outer radius r{sub o}. Initially, the shell is at rest. We assume that the interior of the shell is a void and we apply a time-varying radial stress on the outer surface.
Structural evolution in the packing of uniform spheres.
Tian, Z A; Dong, K J; Yu, A B
2014-03-01
Structural analysis is very important to understanding the physics of atomic or particle systems of various types. However, properly characterizing the structures at different packing fraction ρ is still a challenge. Here we analyze the local structure, in terms of the so-called common-neighbor-subcluster (CNS), of sphere packings with ρ ∈ (0.2, 0.74). We show that although complicated in structure, there are totally 39 kinds of CNSs of which 12 are dominant. The evolution of these CNSs with the increase of ρ is quantified, and the rules governing the evolution are explored. The results are found to be useful in constructing a comprehensive picture about the critical states and their transition in sphere packing.
When do jammed sphere packings have a valid linear regime?
NASA Astrophysics Data System (ADS)
Goodrich, Carl; Liu, Andrea; Nagel, Sidney
2014-03-01
The physics of jamming can be studied in its purest form in packings of soft spheres at zero temperature. One of the successes of this approach is that bulk material properties, such as the elastic moduli or density of normal modes, can be predicted solely from the distance of the system to the jamming transition. Such properties are both defined and measured in the linear-response regime. It is thus tacitly assumed that the harmonic approximation to the local energy landscape can capture the meaningful physics, and it is therefore essential to delineate when this assumption is valid. We will examine the regime of validity of the harmonic approximation in jammed sphere packings as a function of system size and density. We will also discuss the crossover from linear response of the zero-temperature jammed solid to thermal behavior at nonzero temperatures.
Sphere Drag and Heat Transfer.
Duan, Zhipeng; He, Boshu; Duan, Yuanyuan
2015-07-20
Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.
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
Porous Ceramic Spheres from Ion Exchange Resin
NASA Technical Reports Server (NTRS)
Dynys, Fred
2005-01-01
A commercial cation ion exchange resin, cross-linked polystyrene, has been successfully used as a template to fabricate 20 to 50 micron porous ceramic spheres. Ion exchange resins have dual template capabilities. Pore architecture of the ceramic spheres can be altered by changing the template pattern. Templating can be achieved by utilizing the internal porous structure or the external surface of the resin beads. Synthesis methods and chemical/physical characteristics of the ceramic spheres will be reported.
Process for making hollow carbon spheres
Luhrs, Claudia C.; Phillips, Jonathan; Richard, Monique N.; Knapp, Angela Michelle
2013-04-16
A hollow carbon sphere having a carbon shell and an inner core is disclosed. The hollow carbon sphere has a total volume that is equal to a volume of the carbon shell plus an inner free volume within the carbon shell. The inner free volume is at least 25% of the total volume. In some instances, a nominal diameter of the hollow carbon sphere is between 10 and 180 nanometers.
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.
Capturing dynamic cation hopping in cubic pyrochlores
NASA Astrophysics Data System (ADS)
Brooks Hinojosa, Beverly; Asthagiri, Aravind; Nino, Juan C.
2011-08-01
In direct contrast to recent reports, density functional theory predicts that the most stable structure of Bi2Ti2O7 pyrochlore is a cubic Fd3¯m space group by accounting for atomic displacements. The displaced Bi occupies the 96g(x,x,z) Wyckoff position with six equivalent sites, which create multiple local minima. Using nudged elastic band method, the transition states of Bi cation hopping between equivalent minima were investigated and an energy barrier between 0.11 and 0.21 eV was determined. Energy barriers associated with the motion of Bi between equivalent sites within the 96g Wyckoff position suggest the presence of dielectric relaxation in Bi2Ti2O7.
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.
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.
The water entry of decelerating spheres
NASA Astrophysics Data System (ADS)
Aristoff, Jeffrey M.; Truscott, Tadd T.; Techet, Alexandra H.; Bush, John W. M.
2010-03-01
We present the results of a combined experimental and theoretical investigation of the vertical impact of low-density spheres on a water surface. Particular attention is given to characterizing the sphere dynamics and the influence of its deceleration on the shape of the resulting air cavity. A theoretical model is developed which yields simple expressions for the pinch-off time and depth, as well as the volume of air entrained by the sphere. Theoretical predictions compare favorably with our experimental observations, and allow us to rationalize the form of water-entry cavities resulting from the impact of buoyant and nearly buoyant spheres.
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...
Liu, Hanyu; Tse, John S.; Hu, Michael Y.; Bi, Wenli; Zhao, Jiyong; Alp, E. Ercan; Pasternak, Moshe; Taylor, R. Dean; Lashley, Jason C.
2015-10-27
The pressure-induced amorphization and subsequent recrystallization of SnI4 have been investigated using first principles molecular dynamics calculations together with high-pressure 119Sn nuclear resonant inelastic x-ray scattering measurements. Above ~8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ~64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI4 under ambient conditions. Although high pressure structures of SnI4 were thought to be determined by random packing of equal-sized spheres,more » we detected electron charge transfer in each phase. As a result, this charge transfer results in a crystal structure packing determined by larger than expected iodine atoms. (C) 2015 AIP Publishing LLC.« less
Dynamics of hard sphere colloidal dispersions
NASA Technical Reports Server (NTRS)
Zhu, J. X.; Chaikin, Paul M.; Phan, S.-E.; Russel, W. B.
1994-01-01
Our objective is to perform on homogeneous, fully equilibrated dispersions the full set of experiments characterizing the transition from fluid to solid and the properties of the crystalline and glassy solid. These include measurements quantifying the nucleation and growth of crystallites, the structure of the initial fluid and the fully crystalline solid, and Brownian motion of particles within the crystal, and the elasticity of the crystal and the glass. Experiments are being built and tested for ideal microgravity environment. Here we describe the ground based effort, which exploits a fluidized bed to create a homogeneous, steady dispersion for the studies. The differences between the microgravity environment and the fluidized bed is gauged by the Peclet number Pe, which measures the rate of convection/sedimentation relative to Brownian motion. We have designed our experiment to accomplish three types of measurements on hard sphere suspensions in a fluidized bed: the static scattering intensity as a function of angle to determine the structure factor, the temporal autocorrelation function at all scattering angles to probe the dynamics, and the amplitude of the response to an oscillatory forcing to deduce the low frequency viscoelasticity. Thus the scattering instrument and the colloidal dispersion were chosen such as that the important features of each physical property lie within the detectable range for each measurement.
2012-01-01
Terahertz (THz) time-domain spectroscopy is carried out for micro/nanostructured periodic Au/dielectric sphere arrays on Si substrate. We find that the metal-insulator transition can be achieved in THz bandwidth via varying sample parameters such as the thickness of the Au shell and the diameter of the Au/dielectric sphere. The Au/polystyrene sphere arrays do not show metallic THz response when the Au shell thickness is larger than 10 nm and the sphere diameter is smaller than 500 nm. This effect is in sharp contrast to the observations in flat Au films on Si substrate. Interestingly, the Au/polystyrene sphere arrays with a 5-nm-thick Au shell show extraordinary THz absorption bands or metallic optical conductance when the diameter of the sphere is larger than 200 nm. This effect is related to the quantum confinement effect in which the electrons in the structure are trapped in the sphere potential well of the gold shell. PMID:23190688
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.
Verma, Anurag; Ford, David M
2011-05-01
The free-energy difference between coexisting solid and liquid phases is studied in the context of classical density functional theory (DFT). A bridge function is used to represent the higher-order (n>2) terms in the perturbative expansion of the excess Helmholtz free energy, and the values of this bridge function within the solid lattice are determined by inversion using literature Monte Carlo simulation results. Four potential models, specifically hard-sphere and inverse twelfth-, sixth-, and fourth-power repulsive, are studied. The face-centered cubic (fcc) solid is considered for the hard-sphere and inverse twelfth- and sixth-power potentials, while the body-centered cubic (bcc) solid is considered for the inverse sixth- and fourth-power potentials. For a given solid structure there is a remarkable similarity among the bridge functions for different potentials that is analogous to the universality in the sum of elementary diagrams, or bridge functions, of liquid-state theory as originally observed by Rosenfeld and Ashcroft [Phys. Rev. A 20, 1208 (1979)]. In further analogy with liquid-state theory, the bridge functions in the present problem are plotted as functionals of the second-order convolution term in the perturbative expansion. In each case, the plot indicates a unique functionality in the dense regions of the solid near the lattice sites but a scattered and nonunique behavior in the void regions. Interestingly, knowledge of the functional relationship in the unique region near the lattice sites seems to be sufficient to quantitatively model the solid-fluid phase transition. These qualitative observations are true for both fcc and bcc solid phases, although there are some quantitative differences between them. The findings suggest that pursuit of a closure-based DFT of solid-fluid transitions may be profitable. PMID:21728493
Chiral Surface Twists and Skyrmion Stability in Nanolayers of Cubic Helimagnets
NASA Astrophysics Data System (ADS)
Leonov, A. O.; Togawa, Y.; Monchesky, T. L.; Bogdanov, A. N.; Kishine, J.; Kousaka, Y.; Miyagawa, M.; Koyama, T.; Akimitsu, J.; Koyama, Ts.; Harada, K.; Mori, S.; McGrouther, D.; Lamb, R.; Krajnak, M.; McVitie, S.; Stamps, R. L.; Inoue, K.
2016-08-01
Theoretical analysis and Lorentz transmission electron microscopy (LTEM) investigations in an FeGe wedge demonstrate that chiral twists arising near the surfaces of noncentrosymmetric ferromagnets [Meynell et al., Phys. Rev. B 90, 014406 (2014)] provide a stabilization mechanism for magnetic Skyrmion lattices and helicoids in cubic helimagnet nanolayers. The magnetic phase diagram obtained for freestanding cubic helimagnet nanolayers shows that magnetization processes differ fundamentally from those in bulk cubic helimagnets and are characterized by the first-order transitions between modulated phases. LTEM investigations exhibit a series of hysteretic transformation processes among the modulated phases, which results in the formation of the multidomain patterns.
Chiral Surface Twists and Skyrmion Stability in Nanolayers of Cubic Helimagnets.
Leonov, A O; Togawa, Y; Monchesky, T L; Bogdanov, A N; Kishine, J; Kousaka, Y; Miyagawa, M; Koyama, T; Akimitsu, J; Koyama, Ts; Harada, K; Mori, S; McGrouther, D; Lamb, R; Krajnak, M; McVitie, S; Stamps, R L; Inoue, K
2016-08-19
Theoretical analysis and Lorentz transmission electron microscopy (LTEM) investigations in an FeGe wedge demonstrate that chiral twists arising near the surfaces of noncentrosymmetric ferromagnets [Meynell et al., Phys. Rev. B 90, 014406 (2014)] provide a stabilization mechanism for magnetic Skyrmion lattices and helicoids in cubic helimagnet nanolayers. The magnetic phase diagram obtained for freestanding cubic helimagnet nanolayers shows that magnetization processes differ fundamentally from those in bulk cubic helimagnets and are characterized by the first-order transitions between modulated phases. LTEM investigations exhibit a series of hysteretic transformation processes among the modulated phases, which results in the formation of the multidomain patterns. PMID:27588877
Singh, M. N.; Sinha, A. K. Ghosh, Haranath
2015-08-15
We report anomalous x-ray diffraction studies on Co ferrite with composition Co{sub 1.5}Fe{sub 1.5}O{sub 4} to obtain the distribution of transition metal ions in tetrahedral and octahedral sites. We synthesize spinel oxide (Co{sub 1.5}Fe{sub 1.5}O{sub 4}) through co-precipitation and subsequent annealing route. The imaginary part (absorption) of the energy dependent anomalous form factor is measured and the real part is calculated theoretically through Kramers–Krönig transformation to analyze anomalous x-ray diffraction peak intensities. Fe and Co K-edge x-ray absorption near edge structure (XANES) spectra are used to estimate charge states of transition metals. Our analysis, within experimental errors, suggests 44% of the tetrahedral sites contain Co in +2 oxidation state and the rest 56% sites contain Fe in +2 and +3 oxidation states. Similarly, 47% of the octahedral sites contain Fe in +3 oxidation states, whereas, the rest of the sites contain Co in +2 and +3 oxidation states. While a distinct pre-edge feature in the Fe K-edge XANES is observed, Co pre-edge remains featureless. Implications of these results to magnetism are briefly discussed.
Modeling the "glass" transition in proteins.
Sitnitsky, A E
2002-02-01
A model of a protein as a disordered system of identical spherical particles (which imitate protein side chains) interacting with each other via a repulsive soft sphere potential U(r) infinity r(-beta) is constructed. The particles undergo the conformational motion (CM) within their own harmonic conformational potentials around some mean equilibrium positions ascribed by the tertiary structure of the protein. A first principles calculation of the positional correlation functions for the CM is carried out. The general analysis is exemplified by the case in which the mean equilibrium positions of the particles form a cubic tightly-packed (face- centered) lattice (each particle has 12 nearest neighbors) with the step b(hydr) =6.6 A (the average distance between the centers of mass of hydrated protein subunits). The model yields dramatic slowing down of the relaxation with the decrease of temperature followed by a sharp glass transition at some crossover temperature T(c) < 200 K. At the transition the liquid-like dynamic behavior (the correlation functions tend to zero with time) is altered by the glass-like one (the correlation functions tend with time to some non-zero limit). In the liquid-like region above the crossover temperature the relaxation exhibits distinct alpha-process following the beta-one. The glass transition results from the interaction of the particles. Thus the model suggests that namely direct interactions of the fragments of protein structure rather than protein-solvent interactions are the origin of the phenomenon of the glass transition. The known increase of T(c) up to 300 K at dehydration of the protein is attributed to the known concomitant compression of the globule upon drying by about 4-6% so that positions of individual atoms displace by about 0.6 A (modeled by the decrease of the step of the lattice b by 0.6 A so that b(dehydr)=6 A). The model suggests that the solvent influences the phenomenon of the glass transition indirectly
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)
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…
Anomalous slowing down in the metastable liquid of hard spheres
NASA Astrophysics Data System (ADS)
Dzugutov, M.
2002-03-01
It is demonstrated that a straightforward extension of the Arrhenius law accurately describes diffusion in the thermodynamically stable liquid of hard spheres. A sharp negative deviation from this behavior is observed as the liquid is compressed beyond its stability limit. This dynamical anomaly can be compared with the nonlinear slowing down characteristic of the supercooled dynamics regime in liquids with continuous interaction. It is suggested that the observed dynamical transition is caused by long-time decomposition of the configuration space. This interpretation is corroborated by the observation of characteristic anomalies in the geometry of a particle trajectory in the metastable domain.
Cubication of Conservative Nonlinear Oscillators
ERIC Educational Resources Information Center
Belendez, Augusto; Alvarez, Mariela L.; Fernandez, Elena; Pascual, Immaculada
2009-01-01
A cubication procedure of the nonlinear differential equation for conservative nonlinear oscillators is analysed and discussed. This scheme is based on the Chebyshev series expansion of the restoring force, and this allows us to approximate the original nonlinear differential equation by a Duffing equation in which the coefficients for the linear…
Cubic Unit Cell Construction Kit.
ERIC Educational Resources Information Center
Mattson, Bruce
2000-01-01
Presents instructions for building a simple interactive unit-cell construction kit that allows for the construction of simple, body-centered, and face-centered cubic lattices. The lit is built from inexpensive and readily available materials and can be built in any number of sizes. (WRM)
He II heat transfer through random packed spheres: Pressure drop
NASA Astrophysics Data System (ADS)
Vanderlaan, M. H.; Van Sciver, S. W.
2014-09-01
Heat flow induced pressure drop through superfluid helium (He II) contained in porous media is examined. In this experiment, heat was applied to one side of a He II column containing a random pack of uniform size polyethylene spheres. Measured results include steady state pressure drops across the random packs of spheres (nominally 35 μm, 49 μm, and 98 μm diameter) for different heat inputs. Laminar, turbulent, and transition fluid flow regimes are examined. The laminar permeability and equivalent channel shape factor are compared to our past studies of the temperature drop through He II in the same porous media of packed spheres. Results from the pressure drop experiments are more accurate than temperature drop experiments due to reduced measurement errors achieved with the pressure transducer. Turbulent results are fitted to models with empirically derived friction factors. A turbulent model considering only dynamic pressure losses in the normal fluid yields the most consistent friction factors. The addition of the laminar and turbulent heat flow equations into a unifying prediction fits all regimes to within 10%.
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…
Hydrophobic Surfactant Proteins Induce a Phosphatidylethanolamine to Form Cubic Phases
Chavarha, Mariya; Khoojinian, Hamed; Schulwitz, Leonard E.; Biswas, Samares C.; Rananavare, Shankar B.; Hall, Stephen B.
2010-01-01
Abstract The hydrophobic surfactant proteins SP-B and SP-C promote rapid adsorption of pulmonary surfactant to an air/water interface. Previous evidence suggests that they achieve this effect by facilitating the formation of a rate-limiting negatively curved stalk between the vesicular bilayer and the interface. To determine whether the proteins can alter the curvature of lipid leaflets, we used x-ray diffraction to investigate how the physiological mixture of these proteins affects structures formed by 1-palmitoyl-2-oleoyl phosphatidylethanolamine, which by itself undergoes the lamellar-to-inverse hexagonal phase transition at 71°C. In amounts as low as 0.03% (w:w) and at temperatures as low as 57°C, the proteins induce formation of bicontinuous inverse cubic phases. The proteins produce a dose-related shift of diffracted intensity to the cubic phases, with minimal evidence of other structures above 0.1% and 62°C, but no change in the lattice-constants of the lamellar or cubic phases. The induction of the bicontinuous cubic phases, in which the individual lipid leaflets have the same saddle-shaped curvature as the hypothetical stalk-intermediate, supports the proposed model of how the surfactant proteins promote adsorption. PMID:20409474
Dynamic mirror-symmetry breaking in bicontinuous cubic phases.
Dressel, Christian; Liu, Feng; Prehm, Marko; Zeng, Xiangbing; Ungar, Goran; Tschierske, Carsten
2014-11-24
Chiral segregation of enantiomers or chiral conformers of achiral molecules during self-assembly in well-ordered crystalline superstructures has fascinated chemists since Pasteur. Here we report spontaneous mirror-symmetry breaking in cubic phases formed by achiral multichain-terminated diphenyl-2,2'-bithiophenes. It was found that stochastic symmetry breaking is a general phenomenon observed in bicontinuous cubic liquid crystal phases of achiral rod-like compounds. In all compounds studied the Im3̄m cubic phase is always chiral, while the Ia3̄d phase is achiral. These intriguing observations are explained by propagation of homochiral helical twist across the entire networks through helix matching at network junctions. In the Ia3̄d phase the opposing chiralities of the two networks cancel, but not so in the three-networks Im3̄m phase. The high twist in the Im3̄m phase explains its previously unrecognized chirality, as well as the origin of this complex structure and the transitions between the different cubic phases.
Dynamic Mirror-Symmetry Breaking in Bicontinuous Cubic Phases**
Dressel, Christian; Liu, Feng; Prehm, Marko; Zeng, Xiangbing; Ungar, Goran; Tschierske, Carsten
2014-01-01
Chiral segregation of enantiomers or chiral conformers of achiral molecules during self-assembly in well-ordered crystalline superstructures has fascinated chemists since Pasteur. Here we report spontaneous mirror-symmetry breaking in cubic phases formed by achiral multichain-terminated diphenyl-2,2′-bithiophenes. It was found that stochastic symmetry breaking is a general phenomenon observed in bicontinuous cubic liquid crystal phases of achiral rod-like compounds. In all compounds studied the ${{\\it Im}\\bar 3m}$ cubic phase is always chiral, while the ${Ia\\bar 3d}$ phase is achiral. These intriguing observations are explained by propagation of homochiral helical twist across the entire networks through helix matching at network junctions. In the ${Ia\\bar 3d}$ phase the opposing chiralities of the two networks cancel, but not so in the three-networks ${{\\it Im}\\bar 3m}$ phase. The high twist in the ${{\\it Im}\\bar 3m}$ phase explains its previously unrecognized chirality, as well as the origin of this complex structure and the transitions between the different cubic phases. PMID:25257551
Anomalies, conformal manifolds, and spheres
NASA Astrophysics Data System (ADS)
Gomis, Jaume; Hsin, Po-Shen; Komargodski, Zohar; Schwimmer, Adam; Seiberg, Nathan; Theisen, Stefan
2016-03-01
The two-point function of exactly marginal operators leads to a universal contribution to the trace anomaly in even dimensions. We study aspects of this trace anomaly, emphasizing its interpretation as a sigma model, whose target space {M} is the space of conformal field theories (a.k.a. the conformal manifold). When the underlying quantum field theory is supersymmetric, this sigma model has to be appropriately supersymmetrized. As examples, we consider in some detail {N}=(2,2) and {N}=(0,2) supersymmetric theories in d = 2 and {N}=2 supersymmetric theories in d = 4. This reasoning leads to new information about the conformal manifolds of these theories, for example, we show that the manifold is Kähler-Hodge and we further argue that it has vanishing Kähler class. For {N}=(2,2) theories in d = 2 and {N}=2 theories in d = 4 we also show that the relation between the sphere partition function and the Kähler potential of {M} follows immediately from the appropriate sigma models that we construct. Along the way we find several examples of potential trace anomalies that obey the Wess-Zumino consistency conditions, but can be ruled out by a more detailed analysis.
Anomalies, conformal manifolds, and spheres
Gomis, Jaume; Hsin, Po-Shen; Komargodski, Zohar; Schwimmer, Adam; Seiberg, Nathan; Theisen, Stefan
2016-03-04
The two-point function of exactly marginal operators leads to a universal contribution to the trace anomaly in even dimensions. We study aspects of this trace anomaly, emphasizing its interpretation as a sigma model, whose target space $M$ is the space of conformal field theories (a.k.a. the conformal manifold). When the underlying quantum field theory is supersymmetric, this sigma model has to be appropriately supersymmetrized. As examples, we consider in some detail $N$ = (2; 2) and $N$ = (0; 2) supersymmetric theories in d = 2 and $N$ = 2 supersymmetric theories in d = 4. This reasoning leads tomore » new information about the conformal manifolds of these theories, for example, we show that the manifold is K ahler-Hodge and we further argue that it has vanishing K ahler class. For $N$ = (2; 2) theories in d = 2 and N = 2 theories in d = 4 we also show that the relation between the sphere partition function and the K ahler potential of $M$ follows immediately from the appropriate sigma models that we construct. Ultimately, along the way we find several examples of potential trace anomalies that obey the Wess-Zumino consistency conditions, but can be ruled out by a more detailed analysis.« less
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
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
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.
The water entry of decelerating spheres
NASA Astrophysics Data System (ADS)
Aristoff, Jeffrey; Truscott, Tadd; Techet, Alexandra; Bush, John
2009-11-01
We present the results of a combined experimental and theoretical investigation of the vertical impact of low-density spheres on a water surface. Particular attention is given to characterizing the sphere dynamics and the influence of its deceleration on the shape of the resulting air cavity. A theoretical model is developed that yields simple expressions for the pinch-off time and depth. Theoretical predictions compare favorably with our experimental observations, and allow us to rationalize the form of water-entry cavities resulting from the impact of buoyant and nearly buoyant spheres.
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.
Microstructural characterization of random packings of cubic particles
Malmir, Hessam; Sahimi, Muhammad; Tabar, M. Reza Rahimi
2016-01-01
Understanding the properties of random packings of solid objects is of critical importance to a wide variety of fundamental scientific and practical problems. The great majority of the previous works focused, however, on packings of spherical and sphere-like particles. We report the first detailed simulation and characterization of packings of non-overlapping cubic particles. Such packings arise in a variety of problems, ranging from biological materials, to colloids and fabrication of porous scaffolds using salt powders. In addition, packing of cubic salt crystals arise in various problems involving preservation of pavements, paintings, and historical monuments, mineral-fluid interactions, CO2 sequestration in rock, and intrusion of groundwater aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We have developed a version of the random sequential addition algorithm to generate such packings, and have computed a variety of microstructural descriptors, including the radial distribution function, two-point probability function, orientational correlation function, specific surface, and mean chord length, and have studied the effect of finite system size and porosity on such characteristics. The results indicate the existence of both spatial and orientational long-range order in the packing, which is more distinctive for higher packing densities. The maximum packing fraction is about 0.57. PMID:27725736
Microstructural characterization of random packings of cubic particles
NASA Astrophysics Data System (ADS)
Malmir, Hessam; Sahimi, Muhammad; Tabar, M. Reza Rahimi
2016-10-01
Understanding the properties of random packings of solid objects is of critical importance to a wide variety of fundamental scientific and practical problems. The great majority of the previous works focused, however, on packings of spherical and sphere-like particles. We report the first detailed simulation and characterization of packings of non-overlapping cubic particles. Such packings arise in a variety of problems, ranging from biological materials, to colloids and fabrication of porous scaffolds using salt powders. In addition, packing of cubic salt crystals arise in various problems involving preservation of pavements, paintings, and historical monuments, mineral-fluid interactions, CO2 sequestration in rock, and intrusion of groundwater aquifers by saline water. Not much is known, however, about the structure and statistical descriptors of such packings. We have developed a version of the random sequential addition algorithm to generate such packings, and have computed a variety of microstructural descriptors, including the radial distribution function, two-point probability function, orientational correlation function, specific surface, and mean chord length, and have studied the effect of finite system size and porosity on such characteristics. The results indicate the existence of both spatial and orientational long-range order in the packing, which is more distinctive for higher packing densities. The maximum packing fraction is about 0.57.
Structural disorder and anomalous diffusion in random packing of spheres
Palombo, M.; Gabrielli, A.; Servedio, V. D. P.; Ruocco, G.; Capuani, S.
2013-01-01
Nowadays Nuclear Magnetic Resonance diffusion (dNMR) measurements of water molecules in heterogeneous systems have broad applications in material science, biophysics and medicine. Up to now, microstructural rearrangement in media has been experimentally investigated by studying the diffusion coefficient (D(t)) behavior in the tortuosity limit. However, this method is not able to describe structural disorder and transitions in complex systems. Here we show that, according to the continuous time random walk framework, the dNMR measurable parameter α, quantifying the anomalous regime of D(t), provides a quantitative characterization of structural disorder and structural transition in heterogeneous systems. To demonstrate this, we compare α measurements obtained in random packed monodisperse micro-spheres with Molecular Dynamics simulations of disordered porous media and 3D Monte Carlo simulation of particles diffusion in these kind of systems. Experimental results agree well with simulations that correlate the most used parameters and functions characterizing the disorder in porous media. PMID:24022264
Liu, H.; Tse, J. S.; Hu, M. Y.; Bi, W.; Zhao, J.; Alp, E. E.; Pasternak, M.; Taylor, R. D.; Lashley, J. C.
2015-10-28
The pressure-induced amorphization and subsequent recrystallization of SnI{sub 4} have been investigated using first principles molecular dynamics calculations together with high-pressure {sup 119}Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI{sub 4} under ambient conditions. Although high pressure structures of SnI{sub 4} were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.
Liu, Hanyu; Tse, John S.; Hu, Michael Y.; Bi, Wenli; Zhao, Jiyong; Alp, E. Ercan; Pasternak, Moshe; Taylor, R. Dean; Lashley, Jason C.
2015-10-27
The pressure-induced amorphization and subsequent recrystallization of SnI_{4} have been investigated using first principles molecular dynamics calculations together with high-pressure ^{119}Sn nuclear resonant inelastic x-ray scattering measurements. Above ~8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ~64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI_{4} under ambient conditions. Although high pressure structures of SnI_{4} were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. As a result, this charge transfer results in a crystal structure packing determined by larger than expected iodine atoms. (C) 2015 AIP Publishing LLC.
Conn, Charlotte E.; Ces, Oscar; Mulet, Xavier; Seddon, John M.; Templer, Richard H.; Finet, Stephanie; Winter, Roland
2006-03-17
The liquid crystalline lamellar (L{sub {alpha}}) to double-diamond inverse bicontinuous cubic (Q{sub II}{sup D}) phase transition for the amphiphile monoelaidin in excess water exhibits a remarkable sequence of structural transformations for pressure or temperature jumps. Our data imply that the transition dynamics depends on a coupling between changes in molecular shape and the geometrical and topological constraints of domain size. We propose a qualitative model for this coupling based on theories of membrane fusion via stalks and existing knowledge of the structure and energetics of bicontinuous cubic phases.
Equation of state for the soft-sphere fluid from a direct summation of the virial series
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1993-04-01
An equation of state for the inverse-twelfth-power soft-sphere fluid is obtained by direct summation of the virial series. To do so, a generalization of the Carnahan-Starling method for obtaining the equation of state of the hard-sphere fluid is used. The equation of state obtained in this way reproduces accurately the simulation data for both the stable and metastable fluid regions. Agreement remains good up to the neighborhood of the glass transition where the equation of state predicts that the soft-sphere fluid becomes unstable.
Cationic Phospholipids Forming Cubic Phases: Lipoplex Structure and Transfection Efficiency
Koynova, Rumiana; Wang, Li; MacDonald, Robert C.
2008-10-29
The transfection activity and the phase behavior of two novel cationic O-alkyl-phosphatidylcholines, 1,2-dioleoyl-sn-glycero-3-hexylphosphocholine (C6-DOPC) and 1,2-dierucoyl-sn-glycero-3-ethylphosphocholine (di22:1-EPC), have been examined with the aim of more completely understanding the mechanism of lipid-mediated DNA delivery. Both lipids form cubic phases: C6-DOPC in the entire temperature range from -10 to 90 C, while di22:1-EPC exhibits an irreversible lamellar-cubic transition between 50 and 70 C on heating. The lipoplexes formed by C6-DOPC arrange into hexagonal phase, while the lipoplexes of di22:1-EPC are lamellar. Both lipids exhibit lower transfection activity than the lamellar-forming 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine (EDOPC). Thus, for the studied cationic phospholipid-DNA systems, the lipoplex phase state is a factor that does not seem to correlate with transfection activity. The parameter that exhibits better correlation with the transfection activity within the present data set is the phase state of the lipid dispersion prior to the addition of DNA. Thus, the lamellar lipid dispersion (EDOPC) produces more efficient lipoplexes than the dispersion with coexisting lamellar and cubic aggregates (diC22:1-EPC), which is even more efficient than the purely cubic dispersions (C6-DOPC; diC22:1-EPC after heating). It could be inferred from these data and from previous research that cubic phase lipid aggregates are unlikely to be beneficial to transfection. The lack of correlation between the phase state of lipoplexes and their transfection activity observed within the present data set does not mean that lipid phase state is generally unimportant for lipofection: a viewpoint now emerging from our previous studies is that the critical factor in lipid-mediated transfection is the structural evolution of lipoplexes within the cell, upon interacting and mixing with cellular lipids.
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
Reversible Nanoparticle Cubic Lattices in Blue Phase Liquid Crystals.
Gharbi, Mohamed Amine; Manet, Sabine; Lhermitte, Julien; Brown, Sarah; Milette, Jonathan; Toader, Violeta; Sutton, Mark; Reven, Linda
2016-03-22
Blue phases (BPs), a distinct class of liquid crystals (LCs) with 3D periodic ordering of double twist cylinders involving orthogonal helical director twists, have been theoretically studied as potential templates for tunable colloidal crystals. Here, we report the spontaneous formation of thermally reversible, cubic crystal nanoparticle (NP) assemblies in BPs. Gold NPs, functionalized to be highly miscible in cyanobiphenyl-based LCs, were dispersed in BP mixtures and characterized by polarized optical microscopy and synchrotron small-angle X-ray scattering (SAXS). The NPs assemble by selectively migrating to periodic strong trapping sites in the BP disclination lines. The NP lattice, remarkably robust given the small particle size (4.5 nm diameter), is commensurate with that of the BP matrix. At the BP I to BP II phase transition, the NP lattice reversibly switches between two different cubic structures. The simultaneous presence of two different symmetries in a single material presents an interesting opportunity to develop novel dynamic optical materials.
Swelling of Bicontinuous Cubic Phases in Guerbet Glycolipid: Effects of Additives.
Salim, Malinda; Wan Iskandar, Wan Farah Nasuha; Patrick, Melonney; Zahid, N Idayu; Hashim, Rauzah
2016-06-01
Inverse bicontinuous cubic phases of lyotropic liquid crystal self-assembly have received much attention in biomedical, biosensing, and nanotechnology applications. An Ia3d bicontinuous cubic based on the gyroid G-surface can be formed by the Guerbet synthetic glucolipid 2-hexyl-decyl-β-d-glucopyranoside (β-Glc-OC6C10) in excess water. The small water channel diameter of this cubic phase could provide nanoscale constraints in encapsulation of large molecules and crystallization of membrane proteins, hence stresses the importance of water channel tuning ability. This work investigates the swelling behavior of lyotropic self-assembly of β-Glc-OC6C10 which could be controlled and modulated by different surfactants as a hydration-modulating agent. Our results demonstrate that addition of nonionic glycolipid octyl-β-d-glucopyranoside (β-Glc-OC8) at 20 and 25 mol % gives the largest attainable cubic water channel diameter of ca. 62 Å, and formation of coacervates which may be attributed to a sponge phase were seen at 20 mol % octyl-β-d-maltopyranoside (β-Mal-OC8). Swelling of the cubic water channel can also be attained in charged surfactant-doped systems dioctyl sodium sulfosuccinate (AOT) and hexadecyltrimethylammonium bromide (CTAB), of which phase transition occurred from cubic to a lamellar phase. Destabilization of the cubic phase to an inverse hexagonal phase was observed when a high amount of charged lecithin (LEC) and stearylamine (SA) was added to the lipid self-assembly. PMID:27183393
#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...
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.
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: 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...
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.
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...
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...
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
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.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Shenoy, S. R.; Lookman, T.; Saxena, A.
2010-10-01
We consider ferroelastic first-order phase transitions with NOP order-parameter strains entering Landau free energies as invariant polynomials that have NV structural-variant Landau minima. The total free energy includes (seemingly innocuous) harmonic terms, in the n=6-NOP nonorder-parameter strains. Four three-dimensional (3D) transitions are considered, tetragonal/orthorhombic, cubic/tetragonal, cubic/trigonal, and cubic/orthorhombic unit-cell distortions, with, respectively, NOP=1 , 2, 3, and 2; and NV=2 , 3, 4, and 6. Five two-dimensional (2D) transitions are also considered, as simpler examples. Following Barsch and Krumhansl, we scale the free energy to absorb most material-dependent elastic coefficients into an overall prefactor, by scaling in an overall elastic energy density; a dimensionless temperature variable; and the spontaneous-strain magnitude at transition λ≪1 . To leading order in λ the scaled Landau minima become material independent, in a kind of “quasiuniversality.” The scaled minima in NOP -dimensional order-parameter space, fall at the center and at the NV corners, of a transition-specific polyhedron inscribed in a sphere, whose radius is unity at transition. The “polyhedra” for the four 3D transitions are, respectively, a line, a triangle, a tetrahedron, and a hexagon. We minimize the n terms harmonic in the nonorder-parameter strains, by substituting solutions of the “no dislocation” St Venant compatibility constraints, and explicitly obtain power-law anisotropic, order-parameter interactions, for all transitions. In a reduced discrete-variable description, the competing minima of the Landau free energies induce unit-magnitude pseudospin vectors, with NV+1 values, pointing to the polyhedra corners and the (zero-value) center. The total scaled free energies then become ZNV+1 clocklike pseudospin Hamiltonians, with temperature-dependent local Landau terms, nearest-neighbor Ginzburg couplings, and power-law St Venant
Structure of the body-centered cubic phase of lipid systems
Saludjian, Pedro; Reiss-Husson, Françoise
1980-01-01
A new model is proposed for the structure of the body-centered cubic phase of lipid systems. Infinite rods of polar groups (and water) are arranged with axes parallel to the four cubic [unk]1 1 1[unk] directions. The hydrocarbon chains fill the space between the rods to form a continuous matrix. With this unified topology, the model explains satisfactorily the x-ray diffraction patterns of strontium soaps, lecithin, galactolipids, potassium soaps, and hexadecyltrimethylammonium bromide and explains the transition between cubic/HII phases. The paradoxical thermal effects on the lipid cubic phase, in particular the decrease of unit cell dimensions with increasing temperature, can be explained with the proposed model by mechanisms similar to those used for the monodimensional and bidimensional (mesomorphic) phases. Images PMID:16592934
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.
Sun, Xiaoran; Zhang, Hongwei; Zhou, Liang; Huang, Xiaodan; Yu, Chengzhong
2016-07-01
Here, ZnFe2 O4 double-shell hollow microspheres are designed to accommodate the large volume expansion during lithiation. A facile and efficient vapor-phase polymerization method has been developed to coat the ZnFe2 O4 hollow spheres with polypyrrole (PPY). The thin PPY coating improves not only the electronic conductivity but also the structural integrity, and thus the cycling stability of the ZnFe2 O4 hollow spheres. Our work sheds light on how to enhance the electrochemical performance of transition metal oxide-based anode materials by designing delicate nanostructures. PMID:27259158
Model energy landscapes of low-temperature fluids: Dipolar hard spheres.
Matyushov, Dmitry V
2007-07-01
An analytical model of non-Gaussian energy landscape of low-temperature fluids is developed based on the thermodynamics of the fluid of dipolar hard spheres. The entire excitation profile of the liquid, from the high-temperature liquid to the point of ideal-glass transition, has been obtained from Monte Carlo simulations. The fluid of dipolar hard spheres loses stability close to the point of ideal-glass transition transforming via a first-order transition into a columnar liquid phase of dipolar chains locally arranged in a body-centered-tetragonal order. Significant non-Gaussianity of the energy landscape is responsible for narrowing of the distribution of potential energies and energies of inherent structures with decreasing temperature. We suggest that the proposed functionality of the enumeration function is widely applicable to both polar and nonpolar low-temperature liquids.
Collinear swimmer propelling a cargo sphere at low Reynolds number.
Felderhof, B U
2014-11-01
The swimming velocity and rate of dissipation of a linear chain consisting of two or three little spheres and a big sphere is studied on the basis of low Reynolds number hydrodynamics. The big sphere is treated as a passive cargo, driven by the tail of little spheres via hydrodynamic and direct elastic interaction. The fundamental solution of Stokes equations in the presence of a sphere with a no-slip boundary condition, as derived by Oseen, is used to model the hydrodynamic interactions between the big sphere and the little spheres.
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
Phase diagram for a cubic-Q interacting boson model Hamiltonian: Signs of triaxiality
Fortunato, L.; Alonso, C. E.; Arias, J. M.; Garcia-Ramos, J. E.; Vitturi, A.
2011-07-15
An extension of the Interacting Boson Model that includes the cubic (QxQxQ){sup (0)} term is proposed. The potential energy surface for the cubic quadrupole interaction is explicitly calculated within the coherent state formalism using the complete ({chi}-dependent) expression for the quadrupole operator. The Q-cubic term is found to depend on the asymmetry deformation parameter {gamma} as a linear combination of cos(3{gamma}) and cos{sup 2}(3{gamma}) terms, thereby allowing for triaxiality. The phase diagram of the model in the large N limit is explored: The orders of the phase transition surfaces that define the phase diagram are described, and the possible nuclear equilibrium shapes are established. It is found that for this particular Hamiltonian, contrary to expectations, there is only a very tiny region of triaxiality, and that the transition from prolate to oblate shapes is so fast that, in most cases, the onset of triaxiality might go unnoticed.
Feng, Dong-xia; Nguyen, Anh V
2016-03-01
Floating objects on the air-water interfaces are central to a number of everyday activities, from walking on water by insects to flotation separation of valuable minerals using air bubbles. The available theories show that a fine sphere can float if the force of surface tension and buoyancies can support the sphere at the interface with an apical angle subtended by the circle of contact being larger than the contact angle. Here we show that the pinning of the contact line at the sharp edge, known as the Gibbs inequality condition, also plays a significant role in controlling the stability and detachment of floating spheres. Specifically, we truncated the spheres with different angles and used a force sensor device to measure the force of pushing the truncated spheres from the interface into water. We also developed a theoretical modeling to calculate the pushing force that in combination with experimental results shows different effects of the Gibbs inequality condition on the stability and detachment of the spheres from the water surface. For small angles of truncation, the Gibbs inequality condition does not affect the sphere detachment, and hence the classical theories on the floatability of spheres are valid. For large truncated angles, the Gibbs inequality condition determines the tenacity of the particle-meniscus contact and the stability and detachment of floating spheres. In this case, the classical theories on the floatability of spheres are no longer valid. A critical truncated angle for the transition from the classical to the Gibbs inequality regimes of detachment was also established. The outcomes of this research advance our understanding of the behavior of floating objects, in particular, the flotation separation of valuable minerals, which often contain various sharp edges of their crystal faces. PMID:26837262
Feng, Dong-xia; Nguyen, Anh V
2016-03-01
Floating objects on the air-water interfaces are central to a number of everyday activities, from walking on water by insects to flotation separation of valuable minerals using air bubbles. The available theories show that a fine sphere can float if the force of surface tension and buoyancies can support the sphere at the interface with an apical angle subtended by the circle of contact being larger than the contact angle. Here we show that the pinning of the contact line at the sharp edge, known as the Gibbs inequality condition, also plays a significant role in controlling the stability and detachment of floating spheres. Specifically, we truncated the spheres with different angles and used a force sensor device to measure the force of pushing the truncated spheres from the interface into water. We also developed a theoretical modeling to calculate the pushing force that in combination with experimental results shows different effects of the Gibbs inequality condition on the stability and detachment of the spheres from the water surface. For small angles of truncation, the Gibbs inequality condition does not affect the sphere detachment, and hence the classical theories on the floatability of spheres are valid. For large truncated angles, the Gibbs inequality condition determines the tenacity of the particle-meniscus contact and the stability and detachment of floating spheres. In this case, the classical theories on the floatability of spheres are no longer valid. A critical truncated angle for the transition from the classical to the Gibbs inequality regimes of detachment was also established. The outcomes of this research advance our understanding of the behavior of floating objects, in particular, the flotation separation of valuable minerals, which often contain various sharp edges of their crystal faces.
Recent researches on the air resistance of spheres
NASA Technical Reports Server (NTRS)
Flachsbart, O
1928-01-01
The following conclusions on air resistance of spheres are drawn: 1) disturbances in front of the sphere and even single fine wires affect the critical Reynolds Number; 2) disturbances around the sphere increased the drag of the sphere without martially affecting the value of the Reynolds Number(sub crith); 3) great disturbances of the boundary layer of the sphere likewise change R.N.(sub crith); 4) turbulence of the approaching air stream lowers critical R.N.
Ni, Aiguo; Wu, Ming Jing; Chavala, Sai H
2014-12-15
Somatic cells can be reprogrammed to induced pluripotent stem (iPS) cells by defined sets of transcription factors. We previously described reprogramming of monolayer-cultured adult mouse ciliary body epithelial (CE) cells by Oct4 and Klf4, but not with Oct4 alone. In this study, we report that Oct4 alone is sufficient to reprogram CE cells to iPS cells through sphere formation. Furthermore, we demonstrate that sphere formation induces a partial reprogramming state characterized by expression of retinal progenitor markers, upregulation of reprogramming transcription factors, such as Sall4 and Nanog, demethylation in the promoter regions of pluripotency associated genes, and mesenchymal to epithelial transition. The Oct4-iPS cells maintained normal karyotypes, expressed markers for pluripotent stem cells, and were capable of differentiating into derivatives of all three embryonic germ layers in vivo and in vitro. These findings suggest that sphere formation may render somatic cells more susceptible to reprogramming.
Clustering and gelation of hard spheres induced by the Pickering effect
NASA Astrophysics Data System (ADS)
Fortini, Andrea
2012-04-01
A mixture of hard-sphere particles and model emulsion droplets is studied with a Brownian dynamics simulation. We find that the addition of nonwetting emulsion droplets to a suspension of pure hard spheres can lead to both gas-liquid and fluid-solid phase separations. Furthermore, we find a stable fluid of hard-sphere clusters. The stability is due to the saturation of the attraction that occurs when the surface of the droplets is completely covered with colloidal particles. At larger emulsion droplet densities a percolation transition is observed. The resulting networks of colloidal particles show dynamical and mechanical properties typical of a colloidal gel. The results of the model are in good qualitative agreement with recent experimental findings [E. Koos and N. Willenbacher, ScienceSCIEAS0036-807510.1126/science.1199243 331, 897 (2011)] in a mixture of colloidal particles and two immiscible fluids.
Equilibrium and nonequilibrium dynamics of soft sphere fluids.
Ding, Yajun; Mittal, Jeetain
2015-07-14
We use computer simulations to test the freezing-point scaling relationship between equilibrium transport coefficients (self-diffusivity, viscosity) and thermodynamic parameters for soft sphere fluids. The fluid particles interact via the inverse-power potential (IPP), and the particle softness is changed by modifying the exponent of the distance-dependent potential term. In the case of IPP fluids, density and temperature are not independent variables and can be combined to obtain a coupling parameter to define the thermodynamic state of the system. We find that the rescaled coupling parameter, based on its value at the freezing point, can approximately collapse the diffusivity and viscosity data for IPP fluids over a wide range of particle softness. Even though the collapse is far from perfect, the freezing-point scaling relationship provides a convenient and effective way to compare the structure and dynamics of fluid systems with different particle softness. We further show that an alternate scaling relationship based on two-body excess entropy can provide an almost perfect collapse of the diffusivity and viscosity data below the freezing transition. Next, we perform nonequilibrium molecular dynamics simulations to calculate the shear-dependent viscosity and to identify the distinct role of particle softness in underlying structural changes associated with rheological properties. Qualitatively, we find a similar shear-thinning behavior for IPP fluids with different particle softness, though softer particles exhibit stronger shear-thinning tendency. By investigating the distance and angle-dependent pair correlation functions in these systems, we find different structural features in the case of IPP fluids with hard-sphere like and softer particle interactions. Interestingly, shear-thinning in hard-sphere like fluids is accompanied by enhanced translational order, whereas softer fluids exhibit loss of order with shear. Our results provide a systematic evaluation
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.
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
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.
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.
Temperature dependent cubic and hexagonal close packing in micellar structures.
Wolff, Nicole; Gerth, Stefan; Gutfreund, Philipp; Wolff, Max
2014-11-14
The interfacial structure and phase diagram of a micellar solution formed by the three block copolymer (EO20-PO70-EO20) also known as P123 solved in deuterated water close to a solid boundary is investigated with respect to temperature. We find a hysteretic behavior of the d-spacing of the micellar crystal and a spontaneous change in the lateral correlation length going hand in hand with a structural reorganization between cubic and hexagonal. The phase transitions may be initiated by a change in the shape of the micelles from spherical to elongated together with a minimization of the polymer water interface. PMID:25212786
Cubic and hexagonal liquid crystals as drug delivery systems.
Chen, Yulin; Ma, Ping; Gui, Shuangying
2014-01-01
Lipids have been widely used as main constituents in various drug delivery systems, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers, and lipid-based lyotropic liquid crystals. Among them, lipid-based lyotropic liquid crystals have highly ordered, thermodynamically stable internal nanostructure, thereby offering the potential as a sustained drug release matrix. The intricate nanostructures of the cubic phase and hexagonal phase have been shown to provide diffusion controlled release of active pharmaceutical ingredients with a wide range of molecular weights and polarities. In addition, the biodegradable and biocompatible nature of lipids demonstrates the minimum toxicity and thus they are used for various routes of administration. Therefore, the research on lipid-based lyotropic liquid crystalline phases has attracted a lot of attention in recent years. This review will provide an overview of the lipids used to prepare cubic phase and hexagonal phase at physiological temperature, as well as the influencing factors on the phase transition of liquid crystals. In particular, the most current research progresses on cubic and hexagonal phases as drug delivery systems will be discussed. PMID:24995330
Cubic and Hexagonal Liquid Crystals as Drug Delivery Systems
Chen, Yulin; Ma, Ping; Gui, Shuangying
2014-01-01
Lipids have been widely used as main constituents in various drug delivery systems, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers, and lipid-based lyotropic liquid crystals. Among them, lipid-based lyotropic liquid crystals have highly ordered, thermodynamically stable internal nanostructure, thereby offering the potential as a sustained drug release matrix. The intricate nanostructures of the cubic phase and hexagonal phase have been shown to provide diffusion controlled release of active pharmaceutical ingredients with a wide range of molecular weights and polarities. In addition, the biodegradable and biocompatible nature of lipids demonstrates the minimum toxicity and thus they are used for various routes of administration. Therefore, the research on lipid-based lyotropic liquid crystalline phases has attracted a lot of attention in recent years. This review will provide an overview of the lipids used to prepare cubic phase and hexagonal phase at physiological temperature, as well as the influencing factors on the phase transition of liquid crystals. In particular, the most current research progresses on cubic and hexagonal phases as drug delivery systems will be discussed. PMID:24995330
NASA Astrophysics Data System (ADS)
Rakhimov, Abdulla; Askerzade, Iman N.
2014-09-01
We have shown that the critical temperature of a Bose-Einstein condensate to a normal phase transition of noninteracting bosons in cubic optical lattices has a linear dependence on the filling factor, especially at large densities. The condensed fraction exhibits a linear power law dependence on temperature in contrast to the case of ideal homogeneous Bose gases.
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.
The flow past a freely rotating sphere
NASA Astrophysics Data System (ADS)
Fabre, David; Tchoufag, Joël; Citro, Vincenzo; Giannetti, Flavio; Luchini, Paolo
2016-08-01
We consider the flow past a sphere held at a fixed position in a uniform incoming flow but free to rotate around a transverse axis. A steady pitchfork bifurcation is reported to take place at a threshold Re^OS=206 leading to a state with zero torque but nonzero lift. Numerical simulations allow to characterize this state up to Re≈ 270 and confirm that it substantially differs from the steady-state solution which exists in the wake of a fixed, non-rotating sphere beyond the threshold Re^SS=212 . A weakly nonlinear analysis is carried out and is shown to successfully reproduce the results and to give substantial improvement over a previous analysis (Fabre et al. in J Fluid Mech 707:24-36, 2012). The connection between the present problem and that of a sphere in free fall following an oblique, steady (OS) path is also discussed.
Unveiling the scattering behavior of small spheres
NASA Astrophysics Data System (ADS)
Tzarouchis, Dimitrios C.; Ylä-Oijala, Pasi; Sihvola, Ari
2016-10-01
A classical way for exploring the scattering behavior of a small sphere is to approximate Mie coefficients with a Taylor series expansion. This ansatz delivered a plethora of insightful results, mostly for small spheres supporting electric localized plasmonic resonances. However, many scattering aspects are still uncharted, especially with regards to magnetic resonances. Here, an alternative system ansatz is proposed based on the Padé approximants for the Mie coefficients. The results reveal the existence of a self-regulating radiative damping mechanism for the first magnetic resonance and general resonating aspects for the higher order multipoles. Hence, a systematic way of exploring the scattering response is introduced, sharpening our understanding of the sphere's scattering behavior and its emergent functionalities.
Negative thermal expansion materials related to cubic zirconium tungstate
NASA Astrophysics Data System (ADS)
Lind, Cora
2001-12-01
A non-hydrolytic sol-gel method for the preparation of ZrW2O 8 was developed. A new trigonal polymorph was discovered, which is structurally related to trigonal ZrMO2O8 and MnRe2O 8 as evidenced by powder x-ray diffraction and EXAFS studies. Seeding of the starting mixtures with cubic ZrW2O8 promoted crystallization of the cubic phase instead of trigonal material. Dehydration of ZrW2O7(OH)2·2H 2O gave cubic ZrW2O8 at 650°C, and a modification of this route led to the discovery of the new NTE materials cubic ZrMo 2O8 and HfMo2O8. These compounds crystallize in the same temperature range as the more stable trigonal AMo2O 8 polymorphs. To facilitate preparation of phase pure cubic molybdates, the influence of precursor chemistry on the crystallization behavior was investigated. The synthesis was extended to the solid solution system ZrxHf 1-xMoyW2-yO8 (0 ≤ x ≤ 1, 0 ≤ y ≤ 2). All compounds showed negative thermal expansion between 77 and 573 K. High-pressure in situ diffraction experiments were conducted on several AM2O8 polymorphs. With the exception of monoclinic ZrMo2O8, all materials underwent at least one pressure induced phase transition. Quasi-hydrostatic experiments on cubic AMo 2O8 led to a reversible transition to a new high-pressure structure, while low-pressure amorphization was observed under non-hydrostatic conditions. Isothermal kinetic studies of the cubic to trigonal transformation for ZrMo2O8 were carried out on four samples. Apparent activation energies of 170--290 kJ/mol were obtained using an Avrami model in combination with an Arrhenius analysis. This corresponds to 5% conversion levels after one year at temperatures between 220 and 315°C. Ex situ studies showed that the conversion at lower temperatures was considerably slower than what would be expected from extrapolation of the kinetic data. Drop solution calorimetry was carried out on several polymorphs of ZrMo 2O8, HfMo2O8 and ZrW2O 8. Only monoclinic ZrMo2O8 was enthalpically
Possible significance of cubic water-ice, H2O-Ic, in the atmospheric water cycle of Mars
NASA Technical Reports Server (NTRS)
Gooding, James L.
1988-01-01
The possible formation and potential significance of the cubic ice polymorph on Mars is discussed. When water-ice crystallizes on Earth, the ambient conditions of temperature and pressure result in the formation of the hexagonal ice polymorph; however, on Mars, the much lower termperature and pressures may permit the crystallization of the cubic polymorph. Cubic ice has two properties of possible importance on Mars: it is an excellant nucleator of other volatiles (such as CO2), and it undergoes an exothermic transition to hexagonal ice at temperatures above 170 K. These properties may have significant implications for both martian cloud formation and the development of the seasonal polar caps.
Mesoporous hollow spheres from soap bubbling.
Yu, Xianglin; Liang, Fuxin; Liu, Jiguang; Lu, Yunfeng; Yang, Zhenzhong
2012-02-01
The smaller and more stable bubbles can be generated from the large parent bubbles by rupture. In the presence of a bubble blowing agent, hollow spheres can be prepared by bubbling a silica sol. Herein, the trapped gas inside the bubble acts as a template. When the porogen, i.e., other surfactant, is introduced, a mesostructured shell forms by the co-assembly with the silica sol during sol-gel process. Morphological evolution emphasizes the prerequisite of an intermediate interior gas flow rate and high exterior gas flow rate for hollow spheres. The method is valid for many compositions from inorganic, polymer to their composites. PMID:22078340
Mesoporous hollow spheres from soap bubbling.
Yu, Xianglin; Liang, Fuxin; Liu, Jiguang; Lu, Yunfeng; Yang, Zhenzhong
2012-02-01
The smaller and more stable bubbles can be generated from the large parent bubbles by rupture. In the presence of a bubble blowing agent, hollow spheres can be prepared by bubbling a silica sol. Herein, the trapped gas inside the bubble acts as a template. When the porogen, i.e., other surfactant, is introduced, a mesostructured shell forms by the co-assembly with the silica sol during sol-gel process. Morphological evolution emphasizes the prerequisite of an intermediate interior gas flow rate and high exterior gas flow rate for hollow spheres. The method is valid for many compositions from inorganic, polymer to their composites.
Vakarelski, Ivan U; Chan, Derek Y C; Thoroddsen, Sigurdur T
2014-08-21
We investigate the dynamic effects of a Leidenfrost vapour layer sustained on the surface of heated steel spheres during free fall in water. We find that a stable vapour layer sustained on the textured superhydrophobic surface of spheres falling through 95 °C water can reduce the hydrodynamic drag by up to 75% and stabilize the sphere trajectory for the Reynolds number between 10(4) and 10(6), spanning the drag crisis in the absence of the vapour layer. For hydrophilic spheres under the same conditions, the transition to drag reduction and trajectory stability occurs abruptly at a temperature different from the static Leidenfrost point. The observed drag reduction effects are attributed to the disruption of the viscous boundary layer by the vapour layer whose thickness depends on the water temperature. Both the drag reduction and the trajectory stabilization effects are expected to have significant implications for development of sustainable vapour layer based technologies.
Negative Magnus Effect on a Rotating Sphere at around the Critical Reynolds Number
NASA Astrophysics Data System (ADS)
Muto, Masaya; Watanabe, Hiroaki; Tsubokura, Makoto; Oshima, Nobuyuki
2011-12-01
Negative Magnus lift acting on a sphere rotating about the axis perpendicular to an incoming flow is investigated using large-eddy simulation at three Reynolds numbers of 1.0× 104, 2.0 × 105, and 1.14 × 106. The numerical methods adopted are first validated on a non-rotating sphere and the spatial resolution around the sphere is determined so as to reproduce the laminar separation, reattachment, and turbulent transition of the boundary layer observed at around the critical Reynolds number. In the rotating sphere, positive or negative Magnus effect is observed depending on the Reynolds number and the rotating speed imposed. At the Reynolds number in the subcritical or supercritical region, the direction of the lift force follows the Magnus effect to be independent of the rotational speed tested here. In contrast, negative lift is observed at the Reynolds number at the critical region when particular rotating speeds are imposed. The negative Magnus effect is discussed in the context of the suppression or promotion of boundary layer transition around the separation point.
Negative Magnus lift on a rotating sphere at around the critical Reynolds number
NASA Astrophysics Data System (ADS)
Muto, Masaya; Tsubokura, Makoto; Oshima, Nobuyuki
2012-01-01
Negative Magnus lift acting on a sphere rotating about the axis perpendicular to an incoming flow was investigated using large-eddy simulation at three Reynolds numbers of 1.0 × 104, 2.0 × 105, and 1.14 × 106. The numerical methods used were first validated on a non-rotating sphere, and the spatial resolution around the sphere was determined so as to reproduce the laminar separation, reattachment, and turbulent transition of the boundary layer observed in the vicinity of the critical Reynolds number. The rotating sphere exhibited a positive or negative Magnus effect depending on the Reynolds number and the imposed rotating speed. At Reynolds numbers in the subcritical or supercritical regimes, the direction of the Magnus lift force was independent of the rotational speed. In contrast, the lift force was negative in the critical regime when particular rotating speeds were imposed. This negative Magnus effect was investigated in the context of suppression or promotion of boundary layer transition around the separation point.
Shen, Laifa; Yu, Le; Wu, Hao Bin; Yu, Xin-Yao; Zhang, Xiaogang; Lou, Xiong Wen David
2015-03-23
While the synthesis of hollow structures of transition metal oxides is well established, it is extremely challenging to fabricate complex hollow structures for mixed transition metal sulfides. Here we report an anion exchange method to synthesize a complex ternary metal sulfides hollow structure, namely nickel cobalt sulfide ball-in-ball hollow spheres. Uniform nickel cobalt glycerate solid spheres are first synthesized as the precursor and subsequently chemically transformed into nickel cobalt sulfide ball-in-ball hollow spheres. When used as electrode materials for electrochemical capacitors, these nickel cobalt sulfide hollow spheres deliver a specific capacitance of 1,036 F g(-1) at a current density of 1.0 A g(-1). An asymmetric supercapacitor based on these ball-in-ball structures shows long-term cycling performance with a high energy density of 42.3 Wh kg(-1) at a power density of 476 W kg(-1), suggesting their potential application in high-performance electrochemical capacitors.
Shen, Laifa; Yu, Le; Wu, Hao Bin; Yu, Xin-Yao; Zhang, Xiaogang; Lou, Xiong Wen David
2015-01-01
While the synthesis of hollow structures of transition metal oxides is well established, it is extremely challenging to fabricate complex hollow structures for mixed transition metal sulfides. Here we report an anion exchange method to synthesize a complex ternary metal sulfides hollow structure, namely nickel cobalt sulfide ball-in-ball hollow spheres. Uniform nickel cobalt glycerate solid spheres are first synthesized as the precursor and subsequently chemically transformed into nickel cobalt sulfide ball-in-ball hollow spheres. When used as electrode materials for electrochemical capacitors, these nickel cobalt sulfide hollow spheres deliver a specific capacitance of 1,036 F g(-1) at a current density of 1.0 A g(-1). An asymmetric supercapacitor based on these ball-in-ball structures shows long-term cycling performance with a high energy density of 42.3 Wh kg(-1) at a power density of 476 W kg(-1), suggesting their potential application in high-performance electrochemical capacitors. PMID:25798849
Barauskas, Justas; Anderberg, Hanna; Svendsen, Allan; Nylander, Tommy
2016-01-01
In this study well-ordered glycerol monooleate (GMO)-based cubic liquid crystalline nanoparticles (LCNPs) have been used as substrates for Thermomyces lanuginosus lipase in order to establish the relation between the catalytic activity, measured by pH-stat titration, and the change in morphology and nanostructure determined by cryogenic transmission electron microscopy and synchrotron small angle X-ray diffraction. The initial lipase catalyzed LCNP hydrolysis rate is approximately 25% higher for large 350nm nanoparticles compared to the small 190nm particles, which is attributed to the increased number of structural defects on the particle surface. At pH 8.0 and 8.4 bicontinuous Im3m cubic LCNPs transform into "sponge"-like assemblies and disordered multilamellar onion-like structures upon exposure to lipase. At pH 6.5 and 7.5 lipolysis induced phase transitions of the inner core of the particles, following the sequence Im3m cubic → reversed hexagonal → reversed micellar Fd3m cubic → reversed micelles. These transitions to the liquid crystalline phases with higher negative curvature of the lipid/water interface were found to trigger protonation of the oleic acid produced during lipase catalyzed reaction. The increase curvature of the reversed discrete micellar cubic phase was suggested to cause an increase in the oleic acid pKa to a larger value observed by pH-stat titration.
An optimized cubic interpolator for image resampling
NASA Technical Reports Server (NTRS)
Schowengerdt, R. A.; Gray, R. T.; Park, S. K.
1984-01-01
It is noted that the cubic resampling function is only one member of a family of functions, defined by the single parameter of the slope of the cubic function at its first zero crossing, whose other members are in some cases superior to the standard cubic. This superiority is especially noteworthy with respect to the extent of gray level overshoot induced by the resampling process at high contrast edges. It is shown that there is an optimum member of this 'parametric cubic convolution' family which minimizes the mean-squared radiometric error arising from interpolation. This interpolator requires no additional computation time over the conventional cubic one. These conclusions are supported and illustrated by resampling simulations with both a high resolution digitized aerial image and a Landsat Multispectral Scanner image.
Dependence on sphere size of the phase behavior of mixtures of rods and spheres
NASA Astrophysics Data System (ADS)
Urakami, Naohito; Imai, Masayuki
2003-07-01
By the addition of chondroitin sulfate (Chs) to the aqueous suspension of tobacco mosaic virus (TMV), the aggregation of TMV occurs at very dilute TMV concentration compared with the addition of polyethylene oxide (PEO). The difference of physical behavior between Chs and PEO is the chain conformation in solution. The Chs chain has a semirigid nature, whereas the PEO chain has a flexible nature. In this study, the Chs and PEO chains are simplified to spherical particles having different size, and we use the spherocylinder model for TMV particle. The effect of the sphere size on the phase behaviors in the mixtures of rods and spheres is investigated by Monte Carlo simulations. By the addition of small spheres, the system transforms from the miscible isotropic phase to the miscible nematic phase. On the other hand, by the addition of large spheres, the system changes from the miscible isotropic phase to the immiscible nematic phase through the immiscible isotropic phase. The different phase behaviors between the small and the large spheres originate from the difference of overlapping volume of the depletion zone. In addition, we perform the Monte Carlo simulations in the case that semirigid chains are used as the Chs chain models. The same phase behaviors are observed as the mixtures of rods and large spheres. Thus the sphere model captures the phase behaviors of rod and polymer mixture systems.
The "Reverse Commute": Adult Students and the Transition from Professional to Academic Literacy
ERIC Educational Resources Information Center
Michaud, Michael J.
2011-01-01
The notion of "transporting literacy" across spheres or cultures is a useful way to imagine the transition many of today's adult students make as writers from the literate sphere of the workplace to that of the school--a transition the author refers to in this article as the "reverse commute." By the time such students reach (or rereach) the…
Intrinsic nonlinearities in the mechanics of hard sphere suspensions.
Kumar, Mansi A; Ewoldt, Randy H; Zukoski, Charles F
2016-09-28
The onset of nonlinear responses in near hard sphere suspensions is characterized as a function of oscillatory frequency and strain amplitude. At low frequencies where the viscous behavior dominates, the onset of nonlinearities is driven by increases in rate of strain. At high deformation frequency, where suspension mechanics is dominated by an elastic response, the nonlinear responses occur when deformation exceeds a characteristic strain. This strain is associated with the transient confinement of particles by nearest neighbors and its volume fraction dependence is through cage parameters derived from the high frequency elastic modulus. The onset of nonlinear responses takes on a universal behavior when deformation frequency is normalized by the characteristic time governing the shift from viscous to elastic behavior indicating that this transition is associated with transient particle localization and is expected to be observed for all volume fractions where pair interactions are important. PMID:27530863
Replica exchange Monte Carlo applied to hard spheres.
Odriozola, Gerardo
2009-10-14
In this work a replica exchange Monte Carlo scheme which considers an extended isobaric-isothermal ensemble with respect to pressure is applied to study hard spheres (HSs). The idea behind the proposal is expanding volume instead of increasing temperature to let crowded systems characterized by dominant repulsive interactions to unblock, and so, to produce sampling from disjoint configurations. The method produces, in a single parallel run, the complete HS equation of state. Thus, the first order fluid-solid transition is captured. The obtained results well agree with previous calculations. This approach seems particularly useful to treat purely entropy-driven systems such as hard body and nonadditive hard mixtures, where temperature plays a trivial role.
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.
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.…
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.
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.
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.
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.
Properties of a Two-Sphere Singularity
NASA Astrophysics Data System (ADS)
Konkowski, Deborah A.; Helliwell, Thomas M.
2015-01-01
Recently Böhmer and Lobo have shown that a metric due to Florides can be extended to reveal a classical singularity that has the form of a two-sphere. Here we discuss and expand on the classical singularity properties and then show the classical singularity is not healed by a quantum analysis.
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.
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.
He II heat transfer through random packed spheres
NASA Astrophysics Data System (ADS)
Vanderlaan, Mark
Superfluid helium (He II) contained in porous media is examined. In particular, heat transfer experiments were performed on He II contained in random packs of uniform size polyethylene spheres. Measured results include the steady state temperature and pressure drops across packs of spheres (35 micron, 49 micron, and 98 micron diameter) and the associated steady, step, and pulse heat inputs. Bath temperatures range from 1.6 K to 2.1 K to help grasp the superfluid effects. Laminar, turbulent, and transitional fluid flow regimes are examined. Turbulent results are fitted to an empirically derived turbulent He II heat flow in a channel equation with an added tortuosity (extra length traveled) term that accounts for the porous media. An average tortuosity of 1.33 +/- 0.07 was obtained, which is in good agreement with the values of 1.36 - 1.41 concluded from published work on classical fluid pressure drop across random packed spheres. Laminar permeability and shape factor results are compared to past studies of He II in porous media and in channel flows. The average critical heat flux, which describes the onset of turbulence, is predicted to be 0.19 W cm-2. The onset of turbulence is determined through a critical heat flux from which a critical Reynolds number is formulated, but does not describe He II turbulence in the normal fluid component. Other proposed He II "Reynolds numbers" are examined. The addition of the laminar and turbulent heat flow equations into a unifying prediction fits the transition regime data within 25 %. Transient temperatures compare favorably to a one-dimensional numerical solution that considers a variable Gorter-Mellink exponent and a piece-wise determination of the heat flux. Turbulent pressure drop results are fitted with empirically derived friction factors. The laminar permeability and equivalent channel shape factor derived from the pressure drop are compared the permeability and shape factor obtained from the temperature drop. Results
An Automatic Phase-Change Detection Technique for Colloidal Hard Sphere Suspensions
NASA Technical Reports Server (NTRS)
McDowell, Mark; Gray, Elizabeth; Rogers, Richard B.
2005-01-01
Colloidal suspensions of monodisperse spheres are used as physical models of thermodynamic phase transitions and as precursors to photonic band gap materials. However, current image analysis techniques are not able to distinguish between densely packed phases within conventional microscope images, which are mainly characterized by degrees of randomness or order with similar grayscale value properties. Current techniques for identifying the phase boundaries involve manually identifying the phase transitions, which is very tedious and time consuming. We have developed an intelligent machine vision technique that automatically identifies colloidal phase boundaries. The algorithm utilizes intelligent image processing techniques that accurately identify and track phase changes vertically or horizontally for a sequence of colloidal hard sphere suspension images. This technique is readily adaptable to any imaging application where regions of interest are distinguished from the background by differing patterns of motion over time.
Domain-wall supergravities from sphere reduction
NASA Astrophysics Data System (ADS)
Cvetič , M.; Liu, James T.; Lü, H.; Pope, C. N.
1999-10-01
Kaluza-Klein sphere reductions of supergravities that admit Ads × Sphere vacuum solutions are believed to be consistent. The examples include the S4 and S7 reductions of eleven-dimensional supergravity, and the S5 reduction of ten-dimensional type IIB supergravity . In this paper we provide evidence that sphere reductions of supergravities that admit instead Domain-wallxSphere vacuum solutions are also consistent, where the background can be viewed as the near-horizon structure of a dilatonic p-brane of the theory. The resulting lower-dimensional theory is a gauged supergravity that admits a domain wall, rather than AdS, as a vacuum solution. We illustrate this consistency by taking the singular limits of certain modulus parameters, for which the original Sn compactifying spheres ( n = 4, 5 or 7) becomes Sp × Rq, with p = n - q < n. The consistency of the S4, S7 reductions then implies the consistency of the S p reductions of the lower-dimensional supergravities. In particular, we obtain explicit non-linear ansätze for the S3 reduction of type IIA and heterotic supergravities, restricting to the U(1) 2 subgroup of the SO(4) gauge group of S3. We also study the black-hole solutions in the lower-dimensional gauged supergravities with domain-wall backgrounds. We find new domain-wall black holes which are not the singular-modulus limits of the AdS black holes of the original theories, and we obtain their Killing spinors.
Falconer, J.W.; Nazarov, W. ); Horsfield, C.J.; Sutton, D.W.; Rothman, S.D.; Freeman, N.J. )
1994-09-01
Hollow cylindrical fusion targets of 200--300 [mu]m diam and 500--600 [mu]m length, were fabricated and fitted at one end with a metallic ablator plate. The cylinders were then filled with a solution of polyfunctional acrylate monomer, which was subsequently polymerized to a gel using ultraviolet initiated polymerization. Either one or two aluminum spheres of diameter between 10 and 30 [mu]m were placed in the gel at defined locations, before the gel was precipitated to give, on drying by critical point dryer, a foam of the required density (about 100 mg cm[sup [minus]3]). The final targets had the sphere or spheres embedded in the foam at specified locations. Several techniques for placing the spheres were examined and the relative merits of the techniques are discussed.
Transient Temperature Behavior of a Sphere Heated by Microwaves
NASA Technical Reports Server (NTRS)
Jackson, H. W.; Barmatz, M.; Wagner, P.
1993-01-01
We have developed a model for microwave heating of a sphere in a rectangular resonant cavity. The model calculates transient temperature distributions within a sphere during the approach to steady state conditions or on the path to thermal runaway.
Mechanism for direct graphite-to-diamond phase transition
Xie, Hongxian; Yin, Fuxing; Yu, Tao; Wang, Jian-Tao; Liang, Chunyong
2014-01-01
Using classical molecular dynamics with a more reliable reactive LCBOPII potential, we have performed a detailed study on the direct graphite-to-diamond phase transition. Our results reveal a new so-called “wave-like buckling and slipping” mechanism, which controls the transformation from hexagonal graphite to cubic diamond. Based on this mechanism, we have explained how polycrystalline cubic diamond is converted from hexagonal graphite, and demonstrated that the initial interlayer distance of compressed hexagonal graphite play a key role to determine the grain size of cubic diamond. These results can broaden our understanding of the high pressure graphite-to-diamond phase transition. PMID:25088720
Mechanism for direct graphite-to-diamond phase transition.
Xie, Hongxian; Yin, Fuxing; Yu, Tao; Wang, Jian-Tao; Liang, Chunyong
2014-08-04
Using classical molecular dynamics with a more reliable reactive LCBOPII potential, we have performed a detailed study on the direct graphite-to-diamond phase transition. Our results reveal a new so-called "wave-like buckling and slipping" mechanism, which controls the transformation from hexagonal graphite to cubic diamond. Based on this mechanism, we have explained how polycrystalline cubic diamond is converted from hexagonal graphite, and demonstrated that the initial interlayer distance of compressed hexagonal graphite play a key role to determine the grain size of cubic diamond. These results can broaden our understanding of the high pressure graphite-to-diamond phase transition.
Synthesis of cubic silicon nitride
NASA Astrophysics Data System (ADS)
Zerr, Andreas; Miehe, Gerhard; Serghiou, George; Schwarz, Marcus; Kroke, Edwin; Riedel, Ralf; Fueß, Hartmut; Kroll, Peter; Boehler, Reinhard
1999-07-01
Silicon nitride (Si3N4) is used in a variety of important technological applications. The high fracture toughness, hardness and wear resistance of Si3N4-based ceramics are exploited in cutting tools and anti-friction bearings; in electronic applications, Si3N4 is used as an insulating, masking and passivating material. Two polymorphs of silicon nitride are known, both of hexagonal structure: α- and β-Si3N4. Here we report the synthesis of a third polymorph of silicon nitride, which has a cubic spinel structure. This new phase, c-Si3N4, is formed at pressures above 15GPa and temperatures exceeding 2,000K, yet persists metastably in air at ambient pressure to at least 700K. First-principles calculations of the properties of this phase suggest that the hardness of c-Si3N4 should be comparable to that of the hardest known oxide (stishovite, a high-pressure phase of SiO2), and significantly greater than the hardness of the two hexagonal polymorphs.
Pressure-driven orbital reorientations and coordination-sphere reconstructions in [CuF2(H2O)2(pyz)
Prescimone, A.; Morien, C.; Allan, D.; Schlueter, J.; Tozer, S.; Manson, J. L.; Parsons, S.; Brechin, E. K.; Hill, S.
2012-07-23
Successive reorientations of the Jahn-Teller axes associated with the Cu{sup II} ions accompany a series of pronounced structural transitions in the title compound, as is shown by X-ray crystallography and high-frequency EPR measurements. The second transition forces a dimerization involving two thirds of the Cu{sup II} sites due to ejection of one of the water molecules from the coordination sphere
Cubic phases and cubic phase dispersions in a phospholipid-based system.
Johnsson, Markus; Barauskas, Justas; Tiberg, Fredrik
2005-02-01
A cubic liquid crystalline phase forming system based on the phospholipid dioleoylphosphatidylethanolamine (DOPE) which is fortified with small amounts of PEGylated (poly(ethylene) glycol) glycerol monooleate (PEG(660)-GMO) is characterized. The cubic phase formed by the DOPE/PEG(660)-GMO/water system coexists with water in the dilute part of the phase diagram and can be fragmented into colloidal size particles with retained cubic phase structure.
Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography.
Demurtas, Davide; Guichard, Paul; Martiel, Isabelle; Mezzenga, Raffaele; Hébert, Cécile; Sagalowicz, Laurent
2015-01-01
Bulk and dispersed cubic liquid crystalline phases (cubosomes), present in the body and in living cell membranes, are believed to play an essential role in biological phenomena. Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications. Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures. It is demonstrated that the interior is constituted of a perfect bicontinuous cubic phase, while the outside shows interlamellar attachments, which represent a transition state between the liquid crystalline interior phase and the outside vesicular structure. Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase. This is crucial to understand and enhance controlled release of target molecules and calls for a revision of postulated transport mechanisms from cubosomes to the aqueous phase. PMID:26573367
Effect of pressure on itinerant magnetism and spin disorder in cubic FeGe.
Pulikkotil, J J; Auluck, S; Rout, P K; Budhani, R C
2012-03-01
The results of ab initio calculations of the pressure dependence of Fe magnetism in cubic FeGe are presented. We find that when the pressure-volume scale is set by means of generalized gradient approximation total energies and magnetism is described by means of the local density approximation, the critical pressure at which the magnetic phase transition occurs is estimated at ≈18 GPa, which is in good agreement with experiments. Using the disordered local moment method we find a localized to itinerant model cross-over of Fe magnetism in cubic FeGe, as a function of volume. Moreover, our calculations also suggest subtle signatures of longitudinal spin fluctuations in cubic FeGe, and that the stiffness parameter softens with increasing pressure. We associate the retention of metallicity in FeGe under pressure with the spin-disorder scattering. The effect of spin-orbit coupling on the electronic structure is also discussed.
Direct visualization of dispersed lipid bicontinuous cubic phases by cryo-electron tomography
NASA Astrophysics Data System (ADS)
Demurtas, Davide; Guichard, Paul; Martiel, Isabelle; Mezzenga, Raffaele; Hébert, Cécile; Sagalowicz, Laurent
2015-11-01
Bulk and dispersed cubic liquid crystalline phases (cubosomes), present in the body and in living cell membranes, are believed to play an essential role in biological phenomena. Moreover, their biocompatibility is attractive for nutrient or drug delivery system applications. Here the three-dimensional organization of dispersed cubic lipid self-assembled phases is fully revealed by cryo-electron tomography and compared with simulated structures. It is demonstrated that the interior is constituted of a perfect bicontinuous cubic phase, while the outside shows interlamellar attachments, which represent a transition state between the liquid crystalline interior phase and the outside vesicular structure. Therefore, compositional gradients within cubosomes are inferred, with a lipid bilayer separating at least one water channel set from the external aqueous phase. This is crucial to understand and enhance controlled release of target molecules and calls for a revision of postulated transport mechanisms from cubosomes to the aqueous phase.
Black carbon measurements using an integrating sphere
NASA Astrophysics Data System (ADS)
Hitzenberger, R.; Dusek, U.; Berner, A.
1996-08-01
An integrating sphere was used to determine the black carbon (BC) content of aerosol filter samples dissolved in chloroform (method originally described by Heintzenberg [1982]). The specific absorption coefficient Ba (equal to absorption per mass) of the samples was also measured using the sphere as an integrating detector for transmitted light. Comparing the Ba of ambient samples taken in Vienna, Austria, to the BC concentrations measured on the dissolved filters, a value of approximately 6 m2/g was found to be a reasonable value for the Ba of the black carbon found at the site. The size dependence of Ba of a nebulized suspension of soot was measured using a rotating impactor, and a reasonable agreement between measured and calculated values was found.
Chirality and Dirac Operator on Noncommutative Sphere
NASA Astrophysics Data System (ADS)
Carow-Watamura, Ursula; Watamura, Satoshi
1997-01-01
We give a derivation of the Dirac operator on the noncommutative 2-sphere within the framework of the bosonic fuzzy sphere and define Connes' triple. It turns out that there are two different types of spectra of the Dirac operator and correspondingly there are two classes of quantized algebras. As a result we obtain a new restriction on the Planck constant in Berezin's quantization. The map to the local frame in noncommutative geometry is also discussed. Acknowledgement. The authors benefited from discussions with M. Bordemann, O. Grandjean and M. Pillin. S.W. would like to thank K. Osterwalder for his hospitality during the stay in ETH where this work began. He also thanks the Canon Foundation in Europe for supporting that stay. U.C. would like to acknowledge the Japan Society for Promotion of Science for financial support.-->
Criticality of a {sup 237}Np Sphere
Sanchez, Rene G.; Hayes, David K.; Cappiello, Charlene C.; Myers, William L.; Jaegers, Peter J.; Clement, Steven D.; Butterfield, Kenneth B.
2003-07-22
A critical mass experiment using a 6-kg {sup 237}Np sphere has been performed. The purpose of the experiment is to get a better estimate of the critical mass of {sup 237}Np. To attain criticality, the {sup 237}Np sphere was surrounded with 93 wt % {sup 235}U shells. A 1/M as a function of uranium mass was performed. An MCNP neutron transport code was used to model the experiment. The MCNP code yielded a k{sub eff} of 0.99089 {+-} 0.0003 compared with a k{sub eff} 1.0026 for the experiment. Based on these results, it is estimated that the critical mass of {sup 237}Np ranges from kilogram weights in the high fifties to low sixties.
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.
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.
Kimura, Keiji; Takehiro, Shin-ichi; Yamada, Michio
2014-08-15
We investigate properties of convective solutions of the Boussinesq thermal convection in a moderately rotating spherical shell allowing the respective rotation of the inner and outer spheres due to the viscous torque of the fluid. The ratio of the inner and outer radii of the spheres, the Prandtl number, and the Taylor number are fixed to 0.4, 1, and 500{sup 2}, respectively. The Rayleigh number is varied from 2.6 × 10{sup 4} to 3.4 × 10{sup 4}. In this parameter range, the behaviours of obtained asymptotic convective solutions are almost similar to those in the system whose inner and outer spheres are restricted to rotate with the same constant angular velocity, although the difference is found in the transition process to chaotic solutions. The convective solution changes from an equatorially symmetric quasi-periodic one to an equatorially symmetric chaotic one, and further to an equatorially asymmetric chaotic one, as the Rayleigh number is increased. This is in contrast to the transition in the system whose inner and outer spheres are assumed to rotate with the same constant angular velocity, where the convective solution changes from an equatorially symmetric quasi-periodic one, to an equatorially asymmetric quasi-periodic one, and to equatorially asymmetric chaotic one. The inner sphere rotates in the retrograde direction on average in the parameter range; however, it sometimes undergoes the prograde rotation when the convective solution becomes chaotic.
Viscosities and sintering rates of composite packings of spheres
Jagota, A.; Scherer, G.W.
1995-03-01
The effective sintering rates and viscosities of three-dimensional composite packings have been studied using a discrete numerical model. The packings consist of random mixtures of hard and soft spheres of the same size. With increasing substitution of hard particles for soft particles in the packing, the viscosity increases and the sintering rate decreases. This is particularly abrupt at well-defined rigidity thresholds where there is a transition from softlike to hardlike behavior. The site fraction of hard particles at which the transition occurs depends on the nature of the interaction between hard particles. When the contact between hard particles resists all six relative degrees of freedom (relative velocities and spins). the bonded case, the rigidity threshold coincides with the percolation threshold (site fraction {approx}0.32). When the contact between hard particles resists only interpenetration. the sliding case, the threshold occurs at a site fraction of hard particles very close to unity. Results for the variation of effective properties with site fraction of hard particles are presented for these and other cases. These results can also be applied to the study of elastic percolating networks.
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
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.
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.
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.
Planetary Education and Outreach Using the NOAA Science on a Sphere
NASA Technical Reports Server (NTRS)
Simon-Miller, A. A.; Williams, D. R.; Smith, S. M.; Friedlander, J. S.; Mayo, L. A.; Clark, P. E.; Henderson, M. A.
2011-01-01
animated at frame rates up to 30 frames per second. Transitions, special effects, and other computer graphics techniques can be added to a sequence through the use of off-the-shelf software, like Final Cut Pro. However, one drawback is that the Sphere cannot be used in the same manner as a flat movie screen; images cannot be pushed to a "side", a highlighted area must be viewable to all sides of the room simultaneously, and some transitions do not work as well as others. We discuss these issues and workarounds in our poster.
Fully-resolved slumping of a pile of spheres in a fluid
NASA Astrophysics Data System (ADS)
Wang, Yayun; Sierakowski, Adam; Prosperetti, Andrea
2015-11-01
Turbidity currents form when a particle-laden fluid propagates into the lighter clear fluid in a predominantly horizontal direction. This work studies some microscopic aspects of the phenomenon by simulating numerically the evolution of a block of several hundred spheres released from an initial roughly cubic pile resting on the bottom of a liquid pool. The motion of the particles as well as the liquid flow are fully resolved by the Physalis method. The process undergoes several stages starting with an initial inertia-dominated one and ending with viscosity-dominated flow. The effects of the particle mass on the evolution of the kinetic energy of the particles and of the fluid, on the viscous energy dissipation and on the velocity of the front of the turbidity current will be analyzed. The study of the pair distribution function and of particle triads and tetrads sheds light on the evolution of the mutual particle arrangement. Supported by NSF award No CBET 1335965.
Ultrahard nanotwinned cubic boron nitride.
Tian, Yongjun; Xu, Bo; Yu, Dongli; Ma, Yanming; Wang, Yanbin; Jiang, Yingbing; Hu, Wentao; Tang, Chengchun; Gao, Yufei; Luo, Kun; Zhao, Zhisheng; Wang, Li-Min; Wen, Bin; He, Julong; Liu, Zhongyuan
2013-01-17
Cubic boron nitride (cBN) is a well known superhard material that has a wide range of industrial applications. Nanostructuring of cBN is an effective way to improve its hardness by virtue of the Hall-Petch effect--the tendency for hardness to increase with decreasing grain size. Polycrystalline cBN materials are often synthesized by using the martensitic transformation of a graphite-like BN precursor, in which high pressures and temperatures lead to puckering of the BN layers. Such approaches have led to synthetic polycrystalline cBN having grain sizes as small as ∼14 nm (refs 1, 2, 4, 5). Here we report the formation of cBN with a nanostructure dominated by fine twin domains of average thickness ∼3.8 nm. This nanotwinned cBN was synthesized from specially prepared BN precursor nanoparticles possessing onion-like nested structures with intrinsically puckered BN layers and numerous stacking faults. The resulting nanotwinned cBN bulk samples are optically transparent with a striking combination of physical properties: an extremely high Vickers hardness (exceeding 100 GPa, the optimal hardness of synthetic diamond), a high oxidization temperature (∼1,294 °C) and a large fracture toughness (>12 MPa m(1/2), well beyond the toughness of commercial cemented tungsten carbide, ∼10 MPa m(1/2)). We show that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall-Petch effect below a critical grain size or the twin thickness of ∼10-15 nm found in metals and alloys.
Analytical solution for the lubrication force between two spheres in a bi-viscous fluid
NASA Astrophysics Data System (ADS)
Vázquez-Quesada, A.; Ellero, M.
2016-07-01
An analytical solution for the calculation of the normal lubrication force acting between two moving spheres embedded in a shear-thinning fluid represented by a bi-viscous model is provided. The resulting force between the suspended spheres exhibits a consistent transition between the Newtonian constant-viscosity limits and it reduces to the well-known standard Newtonian lubrication theory for viscosity-ratio approaching one. Effects of several physical parameters of the theory are analyzed under relevant physical conditions, i.e., for a prototypical case of two non-colloidal spheres immersed in a non-Newtonian fluid with rheology parameterized by a bi-viscosity model. Topological results for high/low-viscosity regions in the gap between spheres are also analyzed in detail showing a rich phenomenology. The presented model enables the extension of lubrication dynamics for suspensions interacting with non-Newtonian matrices and provides a clean theoretical framework for new numerical computations of flow of dense complex particulate systems.
Stability of a cubic fixed point in three dimensions: Critical exponents for generic N
NASA Astrophysics Data System (ADS)
Varnashev, K. B.
2000-06-01
The detailed analysis of the global structure of the renormalization-group (RG) flow diagram for a model with isotropic and cubic interactions is carried out in the framework of the massive field theory directly in three dimensions (3D) within an assumption of isotropic exchange. Perturbative expansions for RG functions are calculated for arbitrary N up to four-loop order and resummed by means of the generalized Padé-Borel-Leroy technique. Coordinates and stability matrix eigenvalues for the cubic fixed point are found under the optimal value of the transformation parameter. Critical dimensionality of the model is proved to be equal to Nc=2.89+/-0.02 that agrees well with the estimate obtained on the basis of the five-loop ɛ expansion [H. Kleinert and V. Schulte-Frohlinde, Phys. Lett. B 342, 284 (1995)] resummed by the above method. As a consequence, the cubic fixed point should be stable in 3D for N>=3, and the critical exponents controlling phase transitions in three-dimensional magnets should belong to the cubic universality class. The critical behavior of the random Ising model being the nontrivial particular case of the cubic model when N=0 is also investigated. For all physical quantities of interest the most accurate numerical estimates with their error bounds are obtained. The results achieved in the work are discussed along with the predictions given by other theoretical approaches and experimental data.
Statistical equilibria of the coupled barotropic flow and shallow water flow on a rotating sphere
NASA Astrophysics Data System (ADS)
Ding, Xueru
The motivation of this research is to build equilibrium statistical models that can apply to explain two enigmatic phenomena in the atmospheres of the solar system's planets: (1) the super-rotation of the atmospheres of slowly-rotating terrestrial planets---namely Venus and Titan, and (2) the persistent anticyclonic large vortex storms on the gas giants, such as the Great Red Spot (GRS) on Jupiter. My thesis is composed of two main parts: the first part focuses on the statistical equilibrium of the coupled barotropic vorticity flow (non-divergent) on a rotating sphere; the other one has to do with the divergent shallow water flow rotating sphere system. The statistical equilibria of these two systems are simulated in a wide range of parameter space by Monte Carlo methods based on recent energy-relative enstrophy theory and extended energy-relative enstrophy theory. These kind of models remove the low temperatures defect in the old classical doubly canonical energy-enstrophy theory which cannot support any phase transitions. The other big difference of our research from previous work is that we work on the coupled fluid-sphere system, which consists of a rotating high density rigid sphere, enveloped by a thin shell of fluid. The sphere is considered to have infinite mass and angular momentum; therefore, it can serve as a reservoir of angular momentum. Unlike the fluid sphere system itself, the coupled fluid sphere system allows for the exchange of angular momentum between the atmosphere and the solid planet. This exchange is the key point in any model that is expected to capture coherent structures such as the super-rotation and GRS-like vortices problems in planetary atmospheres. We discovered that slowly-rotating planets can have super-rotation at high energy state. All known slowly-rotating cases in the solar system---Venus and Titan---have super-rotation. Moreover, we showed that the anticyclonicity in the GRS-like structures is closely associated with the
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
Fabrication and calibration of sensitively photoelastic biocompatible gelatin spheres
NASA Astrophysics Data System (ADS)
Fu, Henry; Ceniceros, Ericson; McCormick, Zephyr
2013-11-01
Photoelastic gelatin can be used to measure forces generated by organisms in complex environments. We describe manufacturing, storage, and calibration techniques for sensitive photoelastic gelatin spheres to be used in aqueous environments. Calibration yields a correlation between photoelastic signal and applied force to be used in future studies. Images for calibration were collected with a digital camera attached to a linear polariscope. The images were then processed in Matlab to determine the photoelastic response of each sphere. The effect of composition, gelatin concentration, glycerol concentration, sphere size, and temperature were all examined for their effect on signal response. The minimum detectable force and the repeatability of our calibration technique were evaluated for the same sphere, different spheres from the same fabrication batch, and spheres from different batches. The minimum force detectable is 10 μN or less depending on sphere size. Factors which significantly contribute to errors in the calibration were explored in detail and minimized.
NASA Astrophysics Data System (ADS)
Liu, R.; Bayram, C.
2016-07-01
Hexagonal and cubic GaN—integrated on on-axis Si(100) substrate by metalorganic chemical vapor deposition via selective epitaxy and hexagonal-to-cubic-phase transition, respectively—are studied by temperature- and injection-intensity-dependent cathodoluminescence to explore the origins of their respective luminescence centers. In hexagonal (cubic) GaN integrated on Si, we identify at room temperature the near band edge luminescence at 3.43 eV (3.22 eV), and a defect peak at 2.21 eV (2.72 eV). At low temperature, we report additional hexagonal (cubic) GaN bound exciton transition at 3.49 eV (3.28 eV), and a donor-to-acceptor transition at 3.31 eV (3.18 eV and 2.95 eV). In cubic GaN, two defect-related acceptor energies are identified as 110 and 360 meV. For hexagonal (cubic) GaN (using Debye Temperature ( β ) of 600 K), Varshni coefficients of α = 7.37 ± 0.13 × 10 - 4 ( 6.83 ± 0.22 × 10 - 4 ) eV / K and E 0 = 3.51 ± 0.01 ( 3.31 ± 0.01 ) eV are extracted. Hexagonal and cubic GaN integrated on CMOS compatible on-axis Si(100) are shown to be promising materials for next generation devices.
Equation of state for fluid mixtures of hard spheres and linear homonuclear fused hard spheres
NASA Astrophysics Data System (ADS)
Largo, J.; Solana, J. R.
1998-08-01
This paper develops a theoretically based equation of state for fluid mixtures consisting of hard spheres and linear homonuclear fused hard spheres. The procedure is based on the equation of state previously developed for monocomponent athermal fluids. The equation of state only requires two parameters, namely the averaged effective molecular volume of the molecules in the mixture and the corresponding effective nonsphericity parameter. These parameters can be obtained from the geometry of the molecules forming the mixture. The results are in excellent agreement with simulation data and compare favorably with those obtained from other theories for athermal fluid mixtures.
Eggs and milk: Spinning spheres partially immersed in a liquid bath
NASA Astrophysics Data System (ADS)
Langley, Kenneth R.; Maynes, Daniel; Truscott, Tadd T.
2015-03-01
When a hard-boiled egg spins through a pool of milk on the kitchen counter, the milk rises up the sides of the egg and droplets are ejected. This phenomenon occurs when any partially submerged object whose radius increases upward from the fluid surface (e.g., spheres, inverted cones, and rings) spins in a liquid bath. The fluid ejects from the surface near the maximum radius in one of three ejection modes: jets, sheets, or sheet breakup. Additionally, a surprisingly large flow rate is induced by the spinning object. In this study, we used spheres to determine the effects of experimental parameters on the induced flow rate. We characterized the modes of ejection and measured the sheet breakup distance using high-speed imaging. The basis of our closed form analytical model utilizes an integral momentum boundary layer analysis both beneath the free surface and in the thin film attached to the sphere. We present criteria defining the transitions between ejection modes and the radius where liquid sheets break up in the sheet ejection regime. Criteria defining the transitions between ejection modes and the radius where liquid sheets break up in the sheet ejection regime shows good agreement with experiments.
A density functional model for the binary crystal of hard spheres with vacancies.
Singh, Sunil P; Das, Shankar P
2007-02-14
We study the stability of a binary mixture of hard spheres in the crystalline state in which a small fraction of lattice sites in the solid structure are vacant. The optimum vacancy concentration is obtained by minimizing the free energy of the inhomogeneous solid state. We use the modified weighted density functional approximation to compute the free energy. The necessary input for the theory is the thermodynamic properties of the homogeneous state of the mixture and is obtained from the solutions of the corresponding Percus-Yevick integral equations for the binary system. We compute the free energy for the crystal having two kinds of ordered structures in which (i) both the species lie in a disordered manner on a single face-centered-cubic lattice and (ii) each of the two species lie on a separate cubic lattice. Our theoretical model obtains equilibrium vacancy fraction of O(10(-5)) near the freezing point in both cases. The vacancy concentration decreases with the increase of density in both cases.
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
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.
Fear not the tectosphere (and other -spheres)
NASA Astrophysics Data System (ADS)
Lee, C. A.
2004-12-01
Based on a highly unrepresentative sampling of the community, not unlike Fox news polls, it has been recognized that the use of words having the suffix "-sphere" is confused and often abused. Such words include lithosphere, asthenosphere, perisphere, tectosphere, and mesosphere. In addition, there appears to be equal confusion in the use of the related terms: mechanical boundary layer, thermal boundary layer, chemical boundary layer, low velocity zone, low viscosity zone, effective elastic thickness, etc. This confusion is not confined to beginning students of the Earth sciences but is also manifest in seasoned Earth scientists (including myself), that is, it is not uncommon to find a geochemist and a geophysicist with completely different definitions of "lithosphere" and "tectosphere", for example. In this poster, an attempt will be made to illustrate the concepts behind some of these terms using visual and verbal aids. One of the focuses, could be the concept of a tectosphere, which may go something like this: A Wise maN once said to me; That cOntinents float because they are light; Then said my dog - DiorITE; Oceans sInk because they are heavy; And so I ask, why miGht this be?; With a Laugh and a Bark, she says the oceans are cOld; And to test if she's rigHT; I stick a tHermometer in the continent's core; To my surprise coNtinents are cold, if not more; So something does not Jive; A parAdox has come alive; Perhaps you surMise that the story is not coMplete; Indeed, you may be right; BecausE under the contiNents lie Green rocks - PerIdotite!; InFertile as Hell and fortuitouslY light; Together they fOrm the TecToSphere; And this is why we are here; Fear not the TecToSphere.
Diagnosis of a Poorly Performing Liquid Hydrogen Bulk Storage Sphere
NASA Technical Reports Server (NTRS)
Krenn, Angela G.
2011-01-01
There are two 850,000 gallon Liquid Hydrogen (LH2) storage spheres used to support the Space Shuttle Program; one residing at Launch Pad A and the other at Launch Pad B. The LH2 Sphere at Pad B has had a high boiloff rate since being brought into service in the 1960's. The daily commodity loss was estimated to be approximately double that of the Pad A sphere, and well above the minimum required by the sphere's specification. Additionally, after being re-painted in the late 1990's a "cold spot" appeared on the outer sphere which resulted in a poor paint bond, 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 Space Shuttle program service which provided a unique opportunity to diagnose the sphere's poor performance. The sphere was drained and inerted, and then opened from the annular relief device on the top where a series of boroscoping operations were accomplished. Boroscoping revealed a large Perlite insulation void in the region of the sphere where the cold spot was apparent. Perlite was then trucked in and off-loaded into the annular void region until the annulus was full. The sphere has not yet been brought back into service.
Hydrodynamics of linked sphere model swimmers.
Alexander, G P; Pooley, C M; Yeomans, J M
2009-05-20
We describe in detail the hydrodynamics of a simple model of linked sphere swimmers. We calculate the asymptotic form of both the time averaged flow field generated by a single swimmer and the interactions between swimmers in a dilute suspension, showing how each depends on the parameters describing the swimmer and its swimming stroke. We emphasize the importance of time reversal symmetry in determining the far field flow around a swimmer and show that the interactions between swimmers are highly dependent on the relative phase of their swimming strokes. PMID:21825517
Hydrodynamics of linked sphere model swimmers
NASA Astrophysics Data System (ADS)
Alexander, G. P.; Pooley, C. M.; Yeomans, J. M.
2009-05-01
We describe in detail the hydrodynamics of a simple model of linked sphere swimmers. We calculate the asymptotic form of both the time averaged flow field generated by a single swimmer and the interactions between swimmers in a dilute suspension, showing how each depends on the parameters describing the swimmer and its swimming stroke. We emphasize the importance of time reversal symmetry in determining the far field flow around a swimmer and show that the interactions between swimmers are highly dependent on the relative phase of their swimming strokes.
Random packing of spheres in Menger sponge.
Cieśla, Michał; Barbasz, Jakub
2013-06-01
Random packing of spheres inside fractal collectors of dimension 2 < d < 3 is studied numerically using Random Sequential Adsorption (RSA) algorithm. The paper focuses mainly on the measurement of random packing saturation limit. Additionally, scaling properties of density autocorrelations in the obtained packing are analyzed. The RSA kinetics coefficients are also measured. Obtained results allow to test phenomenological relation between random packing saturation density and collector dimension. Additionally, performed simulations together with previously obtained results confirm that, in general, the known dimensional relations are obeyed by systems having non-integer dimension, at least for d < 3.
Further Investigations of NIST Water Sphere Discrepancies
Broadhead, B.L.
2001-01-11
Measurements have been performed on a family of water spheres at the National Institute of Standards and Technology (NIST) facilities. These measurements are important for criticality safety studies in that, frequently, difficulties have arisen in predicting the reactivity of individually subcritical components assembled in a critical array. It has been postulated that errors in the neutron leakage from individual elements in the array could be responsible for these problems. In these NIST measurements, an accurate determination of the leakage from a fission spectrum, modified by water scattering, is available. Previously, results for 3-, 4-, and 5-in. diam. water-filled spheres, both with and without cadmium covers over the fission chambers, were presented for four fissionable materials: {sup 235}U, {sup 238}U, {sup 237}Np, and {sup 239}Pu. Results were also given for ''dry'' systems, in which the water spheres were drained of water, with the results corresponding to essentially measurements of unmoderated {sup 252}Cf spontaneous-fission neutrons. The calculated-to-experimental (C/E) values ranged from 0.94 to 1.01 for the dry systems and 0.93 to 1.05 for the wet systems, with experimental uncertainties ranging from 1.5 to 1.9%. These results indicated discrepancies that were clearly outside of the experimental uncertainties, and further investigation was suggested. This work updates the previous calculations with a comparison of the predicted C/E values with ENDF/B-V and ENDF/B-VI transport cross sections. Variations in the predicted C/E values that arise from the use of ENDF/B-V, ENDF/B-VI, ENDL92, and LLLDOS for the response fission cross sections are also tabulated. The use of both a 45-group NIST fission spectrum and a continuous-energy fission spectrum for {sup 252}Cf are evaluated. The use of the generalized-linear-least-squares (GLLSM) procedures to investigate the reported discrepancies in the water sphere results for {sup 235}U, {sup 238}U, {sup 239}Pu
Nonlinear sequential laminates reproducing hollow sphere assemblages
NASA Astrophysics Data System (ADS)
Idiart, Martín I.
2007-07-01
A special class of nonlinear porous materials with isotropic 'sequentially laminated' microstructures is found to reproduce exactly the hydrostatic behavior of 'hollow sphere assemblages'. It is then argued that this result supports the conjecture that Gurson's approximate criterion for plastic porous materials, and its viscoplastic extension of Leblond et al. (1994), may actually yield rigorous upper bounds for the hydrostatic flow stress of porous materials containing an isotropic, but otherwise arbitrary, distribution of porosity. To cite this article: M.I. Idiart, C. R. Mecanique 335 (2007).
Free vibration of layered magnetoelectroelastic spheres.
Heyliger, P R; Pan, E
2016-08-01
A discrete-layer model is presented and applied to the free vibration of layered anisotropic spheres with coupling among the elastic, electric, and magnetic fields. Through-thickness approximations in the radial direction are pre-integrated and combined with independent approximations in the azimuthal and circumferential directions to provide estimates of the natural frequencies for a variety of representative geometries. Results are in excellent agreement with existing analytical studies and additional results are presented for higher-order spheroidal modes. Predictions of the level of influence of magnetoelectric coupling are also given. PMID:27586731
Interplay between lattice dynamics and the low-pressure phase of simple cubic polonium
NASA Astrophysics Data System (ADS)
Zaoui, A.; Belabbes, A.; Ahuja, R.; Ferhat, M.
2011-04-01
Low-pressure structural properties of simple cubic polonium are explored through first-principles density-functional theory based relativistic total energy calculations using pseudopotentials and plane-wave basis set, as well as linear-response theory. We have found that Po undergoes structural phase transition at low pressure near 2 GPa, where the element transforms from simple cubic to a mixture of two trigonal phases namely, hR1 (α=86°) and hR2 (α=97.9°) structures. The lattice dynamics calculations provide strong support for the observed phase transition, and show the dynamical stability (instability) of the hR2 (hR1) phase.
Roughening and Preroughening of Diamond-Cubic {l_brace}111{r_brace} Surfaces
Woodraska, D.L.; Jaszczak, J.A.
1997-01-01
A solid-on-solid model for {l_brace}111{r_brace} surfaces of diamond-cubic materials that correctly takes into account the diamond-cubic crystal structure has been developed for Monte Carlo simulation. In addition to a roughening transition at temperature T{sub R}, a distinct preroughening transition at T{sub PR}{approx}0.43T{sub R} is indicated by divergences in the surface specific heat and order-parameter susceptibility. Preroughening appears to arise naturally in our nearest-neighbor bond model from the entropic freedom available in the nontrivial crystal structure. Preroughening is shown to dramatically lower the nucleation barrier for growth and etching at low driving forces. {copyright} {ital 1997} {ital The American Physical Society}
Scaling collapse at the jamming transition.
Kallus, Yoav
2016-01-01
The jamming transition of particles with finite-range interactions is characterized by a variety of critical phenomena, including power-law distributions of marginal contacts. We numerically study a recently proposed simple model of jamming, which is conjectured to lie in the same universality class as the jamming of spheres in all dimensions. We extract numerical estimates of the critical exponents, θ=0.451±0.006 and γ=0.404±0.004, that match the exponents observed in sphere packing systems. We analyze finite-size scaling effects that manifest in a subcritical cutoff regime and size-independent but protocol-dependent scaling curves. Our results support the conjectured link with sphere jamming, provide more precise measurements of the critical exponents than previously reported, and shed light on the finite-size scaling behavior of continuous constraint satisfiability transitions. PMID:26871138
Physics of Hard Spheres Experiment (PhaSE) or "Making Jello in Space"
NASA Technical Reports Server (NTRS)
Ling, Jerri S.; Doherty, Michael P.
1998-01-01
The Physics of Hard Spheres Experiment (PHaSE) is a highly successful experiment that flew aboard two shuttle missions to study the transitions involved in the formation of jellolike colloidal crystals in a microgravity environment. A colloidal suspension, or colloid, consists of fine particles, often having complex interactions, suspended in a liquid. Paint, ink, and milk are examples of colloids found in everyday life. In low Earth orbit, the effective force of gravity is thousands of times less than at the Earth's surface. This provides researchers a way to conduct experiments that cannot be adequately performed in an Earth-gravity environment. In microgravity, colloidal particles freely interact without the complications of settling that occur in normal gravity on Earth. If the particle interactions within these colloidal suspensions could be predicted and accurately modeled, they could provide the key to understanding fundamental problems in condensed matter physics and could help make possible the development of wonderful new "designer" materials. Industries that make semiconductors, electro-optics, ceramics, and composites are just a few that may benefit from this knowledge. Atomic interactions determine the physical properties (e.g., weight, color, and hardness) of ordinary matter. PHaSE uses colloidal suspensions of microscopic solid plastic spheres to model the behavior of atomic interactions. When uniformly sized hard spheres suspended in a fluid reach a certain concentration (volume fraction), the particle-fluid mixture changes from a disordered fluid state, in which the spheres are randomly organized, to an ordered "crystalline" state, in which they are structured periodically. The thermal energy of the spheres causes them to form ordered arrays, analogous to crystals. Seven of the eight PHaSE samples ranged in volume fraction from 0.483 to 0.624 to cover the range of interest, while one sample, having a concentration of 0.019, was included for
López de Haro, Mariano; Tejero, Carlos F; Santos, Andrés
2013-04-28
The problem of demixing in a binary fluid mixture of highly asymmetric additive hard spheres is revisited. A comparison is presented between the results derived previously using truncated virial expansions for three finite size ratios with those that one obtains with the same approach in the extreme case in which one of the components consists of point particles. Since this latter system is known not to exhibit fluid-fluid segregation, the similarity observed for the behavior of the critical constants arising in the truncated series in all instances, while not being conclusive, may cast serious doubts as to the actual existence of a demixing fluid-fluid transition in disparate-sized binary additive hard-sphere mixtures.
Superhard BC(3) in cubic diamond structure.
Zhang, Miao; Liu, Hanyu; Li, Quan; Gao, Bo; Wang, Yanchao; Li, Hongdong; Chen, Changfeng; Ma, Yanming
2015-01-01
We solve the crystal structure of recently synthesized cubic BC(3) using an unbiased swarm structure search, which identifies a highly symmetric BC(3) phase in the cubic diamond structure (d-BC(3)) that contains a distinct B-B bonding network along the body diagonals of a large 64-atom unit cell. Simulated x-ray diffraction and Raman peaks of d-BC(3) are in excellent agreement with experimental data. Calculated stress-strain relations of d-BC(3) demonstrate its intrinsic superhard nature and reveal intriguing sequential bond-breaking modes that produce superior ductility and extended elasticity, which are unique among superhard solids. The present results establish the first boron carbide in the cubic diamond structure with remarkable properties, and these new findings also provide insights for exploring other covalent solids with complex bonding configurations.
Movements of a Sphere Moving Over Smooth and Rough Inclines
NASA Astrophysics Data System (ADS)
Jan, Chyan-Deng
1992-01-01
The steady movements of a sphere over a rough incline in air, and over smooth and rough inclines in a liquid were studied theoretically and experimentally. The principle of energy conservation was used to analyze the translation velocities, rolling resistances, and drag coefficients of a sphere moving over the inclines. The rolling resistance to the movement of a sphere from the rough incline was presumed to be caused by collisions and frictional slidings. A varnished wooden board was placed on the bottom of an experimental tilting flume to form a smooth incline and a layer of spheres identical to the sphere moving over them was placed on the smooth wooden board to form a rough incline. Spheres used in the experiments were glass spheres, steel spheres, and golf balls. Experiments show that a sphere moving over a rough incline with negligible fluid drag in air can reach a constant translation velocity. This constant velocity was found to be proportional to the bed inclination (between 11 ^circ and 21^circ) and the square root of the sphere's diameter, but seemingly independent of the sphere's specific gravity. Two empirical coefficients in the theoretical expression of the sphere's translation velocity were determined by experiments. The collision and friction parts of the shear stress exerted on the interface between the moving sphere and rough incline were determined. The ratio of collision to friction parts appears to increase with increase in the bed inclination. These two parts seem to be of the same order of magnitude. The rolling resistances and the relations between the drag coefficient and Reynolds number for a sphere moving over smooth and rough inclines in a liquid, such as water or salad oil, were determined by a regression analysis based on experimental data. It was found that the drag coefficient for a sphere over the rough incline is larger than that for a sphere over the smooth incline, and both of which are much larger than that for a sphere in free
Zhang, Cuimiao; Huo, Shuying; Shen, Shigang; Jia, Guang; Sun, Jing
2013-06-01
A series of uniform and well-dispersed TiO2 spheres have been successfully synthesized through a controlled hydrolysis route by using different titanium alkoxides as reactants. The types of titanium alkoxides and stirring time have an effect on the uniformity and dispersion of the TiO2 spherical particles. The addition of a small amount of salt also plays a crucial role for the formation of the monodisperse TiO2 spheres. Under ultraviolet excitation, the as-obtained Eu(3+)-doped TiO2 spheres exhibit red emission corresponding to the electric-dipole allowed 5D0-7F2 transition of Eu3+ ions, which is induced by the lack of inversion symmetry at the Eu3+ ions site. The Eu(3+)-doped TiO2 phosphors might find potential applications in the fields such as optical displays, photoelectric devices, and light-emitting diodes (LEDs).
Ulfat Jafri, A D; Lakhtakia, Akhlesh
2014-01-01
An exact transition matrix was formulated for electromagnetic scattering by an orthorhombic dielectric-magnetic sphere whose permeability dyadic is a scalar multiple of its permittivity dyadic. Calculations were made for plane waves incident on the sphere. As the size parameter increases, the role of anisotropy evolves; multiple lobes appear in the plots of the differential scattering efficiency in any scattering plane; the total scattering, extinction, and forward-scattering efficiencies exhibit a prominent maximum each; and the absorption efficiency generally increases with weak undulations. Certain orientations of the sphere with respect to the directions of propagation and the electric field of the incident plane wave make it highly susceptible to detection in a monostatic configuration, whereas other orientations make it much less vulnerable to detection. Impedance match to the ambient free space decreases backscattering efficiency significantly, although anisotropy prevents null backscattering. PMID:24561944
Ulfat Jafri, A D; Lakhtakia, Akhlesh
2014-01-01
An exact transition matrix was formulated for electromagnetic scattering by an orthorhombic dielectric-magnetic sphere whose permeability dyadic is a scalar multiple of its permittivity dyadic. Calculations were made for plane waves incident on the sphere. As the size parameter increases, the role of anisotropy evolves; multiple lobes appear in the plots of the differential scattering efficiency in any scattering plane; the total scattering, extinction, and forward-scattering efficiencies exhibit a prominent maximum each; and the absorption efficiency generally increases with weak undulations. Certain orientations of the sphere with respect to the directions of propagation and the electric field of the incident plane wave make it highly susceptible to detection in a monostatic configuration, whereas other orientations make it much less vulnerable to detection. Impedance match to the ambient free space decreases backscattering efficiency significantly, although anisotropy prevents null backscattering.
Geometric aspects of shear jamming induced by deformation of frictionless sphere packings
NASA Astrophysics Data System (ADS)
Vinutha, H. A.; Sastry, Srikanth
2016-09-01
It has recently been demonstrated that shear deformation of frictionless sphere packings leads to structures that will undergo jamming in the presence of friction, at densities well below the isotropic jamming point {φj}≈ 0.64 , and at high enough strains. Here, we show that the geometric features induced by strain are robust with respect to finite size effects, and include the feature of hyperuniformity, previously studied in the context of jamming, and more recently in driven systems. We study the approach to jamming as strain is increased, by evolving frictionless sheared configurations through frictional dynamics, and thereby identify a critical, or jamming, strain for each density, for a chosen value of the coefficient of friction. In the presence of friction above a certain strain value the sheared frictionless packings begin to develop finite stresses, which marks the onset of shear jamming. At a higher strain value, the shear stress reaches a saturation value after rising rapidly above the onset of shear jamming, which permits identification of the shear jamming transition. The onset of shear jamming and shear jamming are found to occur when the coordination number Z reaches values of Z = 3 and Z = 4 respectively. By considering percolation probabilities for the contact network, clusters of four coordinated and six coordinated spheres, we show that the percolation of four coordinated spheres corresponds to the onset of shear jamming behaviour, whereas the percolation of six coordinated spheres corresponds to shear jamming, for the chosen friction coefficients. At the onset of shear jamming, the force distribution begins to develop a peak at finite value and the force network is anisotropic and heterogeneous. And at the shear jamming transition, the force distribution has a well defined peak close to < f> and the force network is less anisotropic and homogeneous. We briefly discuss mechanical aspects of the jamming behaviour by
Characterizing HR 3549 B using SPHERE
NASA Astrophysics Data System (ADS)
Mesa, D.; Vigan, A.; D'Orazi, V.; Ginski, C.; Desidera, S.; Bonnefoy, M.; Gratton, R.; Langlois, M.; Marzari, F.; Messina, S.; Antichi, J.; Biller, B.; Bonavita, M.; Cascone, E.; Chauvin, G.; Claudi, R. U.; Curtis, I.; Fantinel, D.; Feldt, M.; Garufi, A.; Galicher, R.; Henning, Th.; Incorvaia, S.; Lagrange, A.-M.; Millward, M.; Perrot, C.; Salasnich, B.; Scuderi, S.; Sissa, E.; Wahhaj, Z.; Zurlo, A.
2016-10-01
Aims: In this work, we characterize the low-mass companion of the A0 field star HR 3549. Methods: We observed HR 3549B in imaging mode with the near-infrared branch (IFS and IRDIS) of SPHERE at the VLT, with IFS in YJ mode and IRDIS in the H band. We also acquired a medium-resolution spectrum with the IRDIS long-slit spectroscopy mode. The data were reduced using the dedicated SPHERE GTO pipeline, which is custom-designed for this instrument. We employed algorithms such as PCA and TLOCI to reduce the speckle noise. Results: The companion was clearly visible with both IRDIS and IFS. We obtained photometry in four different bands and also the astrometric position for the companion. Based on our astrometry, we confirm that it is a bound object and set constraints on its orbit. Although several uncertainties still remain, we estimate an age of ~100-150 Myr for this system, yielding a most probable mass for the companion of 40-50 MJup and Teff ~ 2300-2400 K. Compared with template spectra, this points to a spectral type between M9 and L0 for the companion, commensurate with its position on the color-magnitude diagram.
Global warming in the public sphere.
Corfee-Morlot, Jan; Maslin, Mark; Burgess, Jacquelin
2007-11-15
Although the science of global warming has been in place for several decades if not more, only in the last decade and a half has the issue moved clearly into the public sphere as a public policy issue and a political priority. To understand how and why this has occurred, it is essential to consider the history of the scientific theory of the greenhouse effect, the evidence that supports it and the mechanisms through which science interacts with lay publics and other elite actors, such as politicians, policymakers and business decision makers. This article reviews why and how climate change has moved from the bottom to the top of the international political agenda. It traces the scientific discovery of global warming, political and institutional developments to manage it as well as other socially mediated pathways for understanding and promoting global warming as an issue in the public sphere. The article also places this historical overview of global warming as a public issue into a conceptual framework for understanding relationships between society and nature with emphasis on the co-construction of knowledge.
Mie scattering by a uniaxial anisotropic sphere
Geng Youlin; Wu Xinbao; Li Lewei; Guan Boran
2004-11-01
The field solution to the electromagnetic scattering of a plane wave by a uniaxial anisotropic sphere is obtained in terms of a spherical vector wave function expansion form. Using the source-free Maxwell's equations for uniaxial anisotropic media and making the Fourier transform of the field quantities, the electromagnetic fields in the spectral domain in uniaxial anisotropic media are assumed to have a form similar to the plane wave expanded also in terms of the spherical vector wave functions. Applying the continuous boundary conditions of electromagnetic fields on the surface between the air region and uniaxial anisotropic sphere, the coefficients of transmitted fields and the scattered fields in uniaxial anisotropic media can be obtained analytically in the expansion form of vector wave eigenfunctions. Numerical results for some special cases are obtained and compared with those of the classical Lorenz-Mie theory and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach. We also present some new numerical results for the more general uniaxial dielectric material media.
Mie scattering by a uniaxial anisotropic sphere.
Geng, You-Lin; Wu, Xin-Bao; Li, Le-Wei; Guan, Bo-Ran
2004-11-01
The field solution to the electromagnetic scattering of a plane wave by a uniaxial anisotropic sphere is obtained in terms of a spherical vector wave function expansion form. Using the source-free Maxwell's equations for uniaxial anisotropic media and making the Fourier transform of the field quantities, the electromagnetic fields in the spectral domain in uniaxial anisotropic media are assumed to have a form similar to the plane wave expanded also in terms of the spherical vector wave functions. Applying the continuous boundary conditions of electromagnetic fields on the surface between the air region and uniaxial anisotropic sphere, the coefficients of transmitted fields and the scattered fields in uniaxial anisotropic media can be obtained analytically in the expansion form of vector wave eigenfunctions. Numerical results for some special cases are obtained and compared with those of the classical Lorenz-Mie theory and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach. We also present some new numerical results for the more general uniaxial dielectric material media.
The hydrodynamics of an oscillating porous sphere
NASA Astrophysics Data System (ADS)
Looker, Jason R.; Carnie, Steven L.
2004-01-01
We determine the hydrodynamics of a rigid, weakly permeable sphere undergoing translational oscillations in an incompressible Newtonian fluid. We check using homogenization and scaling arguments that the flow inside the sphere may be modeled by Darcy's law and that the Beavers-Joseph-Saffman (BJS) boundary condition still applies for oscillatory flows, provided the frequency of oscillation is not too high. The BJS boundary condition introduces a slip velocity and to leading order in ɛ=√k /a, where k is the particle permeability and a is the radius, the particle may be regarded as impermeable with a slip length independent of frequency. Under these circumstances we solve for the flow field, pressure distribution and drag explicitly and show their behavior for 0⩽ɛ⩽0.05 and frequencies relevant to electroacoustics (1-10 MHz). From the drag we find the leading order corrections due to particle permeability of the pseudo-steady drag, Basset force and added mass.
An evaluation of temperature profiles from falling sphere soundings
NASA Technical Reports Server (NTRS)
Quiroz, R. S.; Gelman, M. E.
1976-01-01
An evaluation of 30 pairs of high-altitude inflatable falling spheres and independent thermistor soundings with a mean rocket-launch-time separation of 27 min shows average temperature differences within 6 C at 32-70 km, except for an average difference of 10 C at 68 km near Mach 1 in the sphere descent curve. The mean difference is exhibited as a negative bias (sphere temperature colder) for which various explanations are considered. The rms temperature differences are greatest near 50 km (7 C) and 68 km (11 C). From 70 to approximately 87.5 km, confidence in the reliability of the sphere temperature soundings is based on the 'repeatability' of pairs of sphere soundings taken within 20 min, temperature differences generally being less than 10 C. Illustrations of large atmospheric variations measured by the sphere soundings are given along with verification from independent measurements.
Analysis of rainbow scattering by a chiral sphere.
Shang, Qing-Chao; Wu, Zhen-Sen; Qu, Tan; Li, Zheng-Jun; Bai, Lu; Gong, Lei
2013-09-23
Based on the scattering theory of a chiral sphere, rainbow phenomenon of a chiral sphere is numerically analyzed in this paper. For chiral spheres illuminated by a linearly polarized wave, there are three first-order rainbows, with whose rainbow angles varying with the chirality parameter. The spectrum of each rainbow structure is presented and the ripple frequencies are found associated with the size and refractive indices of the chiral sphere. Only two rainbow structures remain when the chiral sphere is illuminated by a circularly polarized plane wave. Finally, the rainbows of chiral spheres with slight chirality parameters are found appearing alternately in E-plane and H-plane with the variation of the chirality.
Photoelastic gelatin spheres for investigation of locomotion in granular media
NASA Astrophysics Data System (ADS)
Mirbagheri, Seyed Amir; Ceniceros, Ericson; Jabbarzadeh, Mehdi; McCormick, Zephyr; Fu, Henry
2014-11-01
We describe a force measurement method in granular media which uses highly-sensitive photoelastic gelatin spheres and its application to measuring forces exerted as animals burrow through granular media. The method is applicable to both freshwater and marine organisms. We fabricate sensitively photoelastic gelatin spheres and describe a calibration method which relates forces applied to gelatin spheres with photoelastic signal. We show that photoelastic gelatin spheres can detect forces as small as 1 microNewton, and quantitatively measure forces with up to 60 microNewton precision, a two order of magnitude improvement compared to methods using plastic disks. Gelatin spheres can be fabricated with a range of sizes to investigate a variety of granular media. Finally, we used the calibrated gelatin spheres in a proof-of-principle experiment to measure forces during earthworm locomotion.
The physics of anisotropic spheres in general relativity
NASA Astrophysics Data System (ADS)
Dev, Krsna
2001-11-01
We study the effects of anisotropic pressure on the properties of spherically symmetric, gravitationally bound spheres. We consider the full general-relativistic and Newtonian treatment of this problem and obtain exact solutions for various forms of the equation of state connecting the radial and tangential pressures. It is shown that pressure anisotropy can have significant effects on the structure and properties of both Newtonian and general relativistic spheres. We show that it is possible for Newtonian spheres to have an infinite core pressure without requiring the radius to be infinite and that there exists stable anisotropic spheres with adiabatic exponents less than 4/3. For general relativistic spheres we demonstrate that the maximum value of 2M/R can approach unity (2M/R < 8/9 for isotropic spheres) and the surface redshift can be arbitrarily large.
Analysis of rainbow scattering by a chiral sphere.
Shang, Qing-Chao; Wu, Zhen-Sen; Qu, Tan; Li, Zheng-Jun; Bai, Lu; Gong, Lei
2013-09-23
Based on the scattering theory of a chiral sphere, rainbow phenomenon of a chiral sphere is numerically analyzed in this paper. For chiral spheres illuminated by a linearly polarized wave, there are three first-order rainbows, with whose rainbow angles varying with the chirality parameter. The spectrum of each rainbow structure is presented and the ripple frequencies are found associated with the size and refractive indices of the chiral sphere. Only two rainbow structures remain when the chiral sphere is illuminated by a circularly polarized plane wave. Finally, the rainbows of chiral spheres with slight chirality parameters are found appearing alternately in E-plane and H-plane with the variation of the chirality. PMID:24104080
Quadratic-Like Dynamics of Cubic Polynomials
NASA Astrophysics Data System (ADS)
Blokh, Alexander; Oversteegen, Lex; Ptacek, Ross; Timorin, Vladlen
2016-02-01
A small perturbation of a quadratic polynomial f with a non-repelling fixed point gives a polynomial g with an attracting fixed point and a Jordan curve Julia set, on which g acts like angle doubling. However, there are cubic polynomials with a non-repelling fixed point, for which no perturbation results into a polynomial with Jordan curve Julia set. Motivated by the study of the closure of the Cubic Principal Hyperbolic Domain, we describe such polynomials in terms of their quadratic-like restrictions.
Purely cubic action for string field theory
NASA Technical Reports Server (NTRS)
Horowitz, G. T.; Lykken, J.; Rohm, R.; Strominger, A.
1986-01-01
It is shown that Witten's (1986) open-bosonic-string field-theory action and a closed-string analog can be written as a purely cubic interaction term. The conventional form of the action arises by expansion around particular solutions of the classical equations of motion. The explicit background dependence of the conventional action via the Becchi-Rouet-Stora-Tyutin operator is eliminated in the cubic formulation. A closed-form expression is found for the full nonlinear gauge-transformation law.
NASA Astrophysics Data System (ADS)
Zhang, Zhi-Hua; He, Ming; Duan, Xiao-Feng
2009-06-01
Optical properties of hexagonal and cubic ZnS nanoribbons are studied by using valence electron energy loss spectroscopy (VEELS) and ab initio band structure calculations. The peaks in VEELS are assigned to interband transitions by comparing the interband transition strengths with the calculated densities of states. The optical properties are deduced from the experimental VEELS, and the theoretical calculations give consistent results. This combination of experimental and theoretical approaches provides a comprehensive understanding of the optical properties of polytype ZnS.
Three-sphere magnetic swimmer in a shear flow
NASA Astrophysics Data System (ADS)
Taghiloo, Maryam; Miri, MirFaez
2013-08-01
We consider a low-Reynolds-number swimmer made from three spheres linked by two slender arms, and explore its motion in a shear flow. This rodlike three-sphere swimmer finally follows the direction dictated by the shear flow. To overcome this shortcoming, we propose a model in which the two outer spheres have permanent magnetic moments along the arms. This magnetic swimmer can be navigated to a desired direction by applying an external static and uniform magnetic field.
Cubic Phases in Phosphatidylcholine-Cholesterol Mixtures: Cholesterol as Membrane 'Fusogen'
Tenchov, Boris G.; MacDonald, Robert C.; Siegel, David P.
2010-01-18
X-ray diffraction reveals that mixtures of some unsaturated phosphatidylcholines (PCs) with cholesterol (Chol) readily form inverted bicontinuous cubic phases that are stable under physiological conditions. This effect was studied in most detail for dioleoyl PC/Chol mixtures with molar ratios of 1:1 and 3:7. Facile formation of Im3m and Pn3m phases with lattice constants of 30-50nm and 25-30nm, respectively, took place in phosphate-buffered saline, in sucrose solution, and in water near the temperature of the L{alpha}HII transition of the mixtures, as well as during cooling of the HII phase. Once formed, the cubic phases displayed an ability to supercool and replace the initial L{sub {alpha}} phase over a broad range of physiological temperatures. Conversion into stable cubic phases was also observed for mixtures of Chol with dilinoleoyl PC but not for mixtures with palmitoyl-linoleoyl PC or palmitoyl-oleoyl PC, for which only transient cubic traces were recorded at elevated temperatures. A saturated, branched-chain PC, diphytanoyl PC, also displayed a cubic phase in mixture with Chol. Unlike the PEs, the membrane PCs are intrinsically nonfusogenic lipids: in excess water they only form lamellar phases and not any of the inverted phases on their own. Thus, the finding that Chol induces cubic phases in mixtures with unsaturated PCs may have important implications for its role in fusion. In ternary mixtures, saturated PCs and sphingomyelin are known to separate into liquid-ordered domains along with Chol. Our results thus suggest that unsaturated PCs, which are excluded from these domains, could form fusogenic domains with Chol. Such a dual role of Chol may explain the seemingly paradoxical ability of cell membranes to simultaneously form rigid, low-curvature raft-like patches while still being able to undergo facile membrane fusion.
Wurtzite ZnO (001) films grown on cubic MgO (001) with bulk-like opto-electronic properties
Zhou Hua; Wang Huiqiong; Chen Xiaohang; Zhan Huahan; Kang Junyong; Wu Lijun; Zhu Yimei; Zhang Lihua; Kisslinger, Kim
2011-10-03
We report the growth of ZnO (001) wurtzite thin films with bulk-like opto-electronic properties on MgO (001) cubic substrates using plasma-assisted molecular beam epitaxy. In situ reflection high-energy electron diffraction patterns and ex situ high resolution transmission electron microscopy images indicate that the structure transition from the cubic MgO substrates to the hexagonal films involves 6 ZnO variants that have the same structure but different orientations. This work demonstrates the possibility of integrating wurtzite ZnO films and functional cubic substrates while maintaining their bulk-like properties.
Method and apparatus for producing small hollow spheres
Hendricks, Charles D.
1979-01-01
Method and apparatus 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.gtoreq.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.
Swelling of cross-linked polystyrene spheres in toluene vapor
Zhang, R.; Graf, K.; Berger, R.
2006-11-27
The swelling behavior of individual micron-sized polystyrene (PS) spheres in toluene vapor was studied via mass loading by means of micromechanical cantilever sensors. For 4%-8% cross-linked PS a mass increase of 180% in saturated toluene vapor was measured. The mass of the swollen PS sphere decreases with increasing exposure time to ultraviolet light. In addition, the swelling response is significantly different between the first and the second exposure to toluene vapor. This is attributed to the formation of a cross-linked shell at the surface of the PS spheres. Shape persistent parts were observed for locally irradiated PS spheres.
ISS Update: SPHERES with Telerobotics Project Manager Terry Fong
NASA Public Affairs Officer Brandi Dean talks with Terry Fong, Telerobotics Project Manager, about how the Synchronized Position, Hold, Engage and Reorient Experimental Satellites, or SPHERES, are ...
Orbital dynamics of two electrically charged conducting spheres
NASA Astrophysics Data System (ADS)
Hoffmeister, Brent K.; Meyer, Deseree A.; Atkins, Brad M.; Franks, Gavin A.; Fuchs, Joshua T.; Li, Lulu; Sliger, Chase W.; Thompson, Jennifer E.
2010-10-01
The similar forms of Coulomb's law of electrostatics and Newton's law of gravitation suggest that two oppositely charged spheres can orbit each other by means of the electrostatic force. We demonstrate electrostatic binary orbits using two oppositely charged graphite coated Styrofoam® spheres. The experiment was conducted on the NASA aircraft Weightless Wonder which simulates weightless conditions. Videos of 23 orbital attempts were analyzed to investigate the dynamics and orbital stability of the two sphere system. The results support predictions of a recently developed theory that establishes criteria for stable orbits between two conducting, electrically charged spheres.
Weighted Circle Actions on the Heegaard Quantum Sphere
NASA Astrophysics Data System (ADS)
Brzeziński, Tomasz; Fairfax, Simon A.
2013-11-01
Weighted circle actions on the quantum Heeqaard 3-sphere are considered. The fixed point algebras, termed quantum weighted Heegaard spheres, and their representations are classified and described on algebraic and topological levels. On the algebraic side, coordinate algebras of quantum weighted Heegaard spheres are interpreted as generalised Weyl algebras, quantum principal circle bundles and Fredholm modules over them are constructed, and the associated line bundles are shown to be non-trivial by an explicit calculation of their Chern numbers. On the topological side, the C*-algebras of continuous functions on quantum weighted Heegaard spheres are described and their K-groups are calculated.
GRADIENT INDEX SPHERES BY THE SEQUENTIAL ACCRETION OF GLASS POWDERS
MARIANO VELEZ
2008-06-15
The Department of Energy is seeking a method for fabricating mm-scale spheres having a refractive index that varies smoothly and continuously from the center to its surface [1]. The fabrication procedure must allow the creation of a range of index profiles. The spheres are to be optically transparent and have a refractive index differential greater than 0.2. The sphere materials can be either organic or inorganic and the fabrication technique must be capable of scaling to low cost production. Mo-Sci Corporation proposed to develop optical quality gradient refractive index (GRIN) glass spheres of millimeter scale (1 to 2 mm diameter) by the sequential accretion and consolidation of glass powders. Other techniques were also tested to make GRIN spheres as the powder-accretion method produced non-concentric layers and poor optical quality glass spheres. Potential ways to make the GRIN spheres were (1) by "coating" glass spheres (1 to 2 mm diameter) with molten glass in a two step process; and (2) by coating glass spheres with polymer layers.
Anomalous absorption, plasmonic resonances, and invisibility of radially anisotropic spheres
NASA Astrophysics Data System (ADS)
Wallén, Henrik; Kettunen, Henrik; Sihvola, Ari
2015-01-01
This article analyzes the response of a sphere with radially anisotropic permittivity dyadic (RA sphere), in both the electrostatic and full electrodynamic settings. Depending on the values and signs of the permittivity components, the quasistatic polarizability of the RA sphere exhibits several very different interesting properties, including invisibility, field concentration, resonant singularities, and emergent losses. Special attention is given to the anomalous losses that appear in the case of certain hyperbolic anisotropy values. We show that their validity can be justified in a limiting sense by puncturing the sphere at the origin and adding a small imaginary part into the permittivity components. A hyperbolic RA sphere with very small intrinsic losses can thus have significant effective losses making it an effective absorber. With different choices of permittivities, the RA sphere could also perform as a cloak or a sensor. The Mie scattering results by an RA sphere are used to justify the quasistatic calculations. It is shown that in the small parameter limit the absorption efficiency of an RA sphere is nonzero for certain lossless hyperbolic anisotropies. The absorption and scattering efficiencies agree with the quasistatic calculations fairly well for spheres with size parameters up to 1/3.
Patrinoiu, Greta; Calderón-Moreno, Jose Maria; Culita, Daniela C.; Birjega, Ruxandra; Ene, Ramona; Carp, Oana
2013-06-15
A green template route for the synthesis of mesoscale solid ZnO spheres was ascertained. The protocol involves a double coating of the carbonaceous spheres with successive layers of zinc-containing species by alternating a non-ultrasound and ultrasound-assisted deposition, followed by calcination treatments. The composites were characterized by FTIR spectroscopy, thermal analysis, scanning electron microscopy while the obtained ZnO spheres by X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, N{sub 2} adsorption–desorption isotherms and photoluminescence investigations. A growth mechanism of the solid spheres is advanced based on these results. While the spheres' diameters and the mean size values of ZnO are independent on deposition order, the surface area and the external porosity are fairly dependent. The photoluminescence measurements showed interesting emission features, with emission bands in the violet to orange region. The spheres present high photocatalytical activity towards the degradation of phenol under UV irradiation, the main reaction being its mineralization. - Graphical abstract: A novel and eco-friendly methodology for the synthesis of mesoscale solid ZnO spheres was developed. The protocol involves a double coating of the starch-derived carbonaceous spheres with successive layers of zinc-containing species by alternating a non-ultrasound and ultrasound-assisted deposition, followed by calcination treatments. - Highlights: • ZnO solid spheres are obtained via a template route using carbonaceous spheres. • Two-step coatings of interchangeable order are used as deposition procedure. • The coating procedure influences the porosity and surface area. • ZnO spheres exhibited interesting visible photoluminescence properties. • Solid spheres showed photocatalytical activity in degradation of phenol.
Cubic Polynomials with Rational Roots and Critical Points
ERIC Educational Resources Information Center
Gupta, Shiv K.; Szymanski, Waclaw
2010-01-01
If you want your students to graph a cubic polynomial, it is best to give them one with rational roots and critical points. In this paper, we describe completely all such cubics and explain how to generate them.
Use of Pom Pons to Illustrate Cubic Crystal Structures.
ERIC Educational Resources Information Center
Cady, Susan G.
1997-01-01
Describes a method that uses olefin pom pons to illustrate cubic crystal structure. Facilitates hands-on examination of different packing arrangements such as hexagonal close-packed and cubic close-packed structures. (JRH)
A monotonicity conjecture for real cubic maps
Dawson, S.P.; Galeeva, R.; Milnor, J.; Tresser, C.
1993-12-01
This will be an outline of work in progress. We study the conjecture that the topological entropy of a real cubic map depends ``monotonely`` on its parameters, in the sense that each locus of constant entropy in parameter space is a connected set. This material will be presented in more detail in a later paper.
NASA Astrophysics Data System (ADS)
Landeau, Maylis; Aubert, Julien
2011-04-01
The convective instability in a rapidly rotating, self-graviting sphere sets up in the form of equatorially symmetric, non-axisymmetric columnar vortices aligned with the rotation axis, carrying heat away in the cylindrical radial direction. In this study, we present numerical simulations of thermal convection and dynamo action driven by internal heating (intended to model a planetary core subject to uniform secular cooling) in a rotating sphere where, from the classical columnar convection regime, we find a spontaneous transition towards an unexpected and previously unobserved flow regime in which an equatorially antisymmetric, axisymmetric (EAA) mode strongly influences the flow. This EAA mode carries heat away along the rotation axis and is the nonlinear manifestation of the first linearly unstable axisymmetric mode. When the amplitude of the EAA mode reaches high enough values, we obtain hemispherical dynamos with one single hemisphere bearing more than 75% of the total magnetic energy at the surface of the rotating sphere. We perform the linear analysis of the involved convective modes and the nonlinear study of this hydrodynamic transition, with and without dynamo action, to obtain scaling laws for the regime boundaries. As secular cooling in a full sphere (i.e. without inner core) is a configuration which has probably been widespread in the early solar system in planetary cores, including the core of Mars, we discuss the possible implications of our results for the past martian dynamo.
A Bonner Sphere Spectrometer for pulsed fields.
Aza, E; Dinar, N; Manessi, G P; Silari, M
2016-02-01
The use of conventional Bonner Sphere Spectrometers (BSS) in pulsed neutron fields (PNF) is limited by the fact that proportional counters, usually employed as the thermal neutron detectors, suffer from dead time losses and show severe underestimation of the neutron interaction rate, which leads to strong distortion of the calculated spectrum. In order to avoid these limitations, an innovative BSS, called BSS-LUPIN, has been developed for measuring in PNF. This paper describes the physical characteristics of the device and its working principle, together with the results of Monte Carlo simulations of its response matrix. The BSS-LUPIN has been tested in the stray neutron field at the CERN Proton Synchrotron, by comparing the spectra obtained with the new device, the conventional CERN BSS and via Monte Carlo simulations.
Aging dynamics of colloidal hard sphere glasses.
Martinez, V A; Bryant, G; van Megen, W
2010-09-21
We report the results of dynamic light scattering measurements of the coherent intermediate scattering function (ISF) of glasses of colloidal hard spheres for several volume fractions and a range of scattering vectors around the primary peak of the static structure factor. The ISF shows a clear crossover from an initial fast decay to a slower nonstationary decay. Aging is quantified in several different ways. However, regardless of the method chosen, the perfect "aged" glass is approached in a power law fashion. In particular the coupling between the fast and slow decays, as measured by the degree of stretching of the ISF at the crossover, also decreases algebraically with waiting time. The nonstationarity of this coupling implies that even the fastest detectable processes are themselves nonstationary. PMID:20866156
Unit quaternions and the Bloch sphere
NASA Astrophysics Data System (ADS)
Wharton, K. B.; Koch, D.
2015-06-01
The spinor representation of spin-1/2 states can equally well be mapped to a single unit quaternion, yielding a new perspective despite the equivalent mathematics. This paper first demonstrates a useable map that allows Bloch-sphere rotations to be represented as quaternionic multiplications, simplifying the form of the dynamical equations. Left-multiplications generally correspond to non-unitary transformations, providing a simpler (essentially classical) analysis of time-reversal. But the quaternion viewpoint also reveals a surprisingly large broken symmetry, as well as a potential way to restore it, via a natural expansion of the state space that has parallels to second order fermions. This expansion to ‘second order qubits’ would imply either a larger gauge freedom or a natural space of hidden variables.
Carbon adsorption system protects LPG storage sphere
Gothenquist, C.A.; Rooker, K.M.
1996-07-01
Chevron U.S.A. Products Co. installed a carbon adsorption system to protect an LPG storage sphere at its refinery in Richmond, Calif. Vessel damage can result when amine contamination leads to emulsion formation and consequent amine carry-over, thus promoting wet-H{sub 2}S cracking. In Chevron`s No. 5 H{sub 2}S recovery plant, a mixture of butane and propane containing H{sub 2}S is contacted with diethanolamine (DEA) in a liquid-liquid absorber. The absorber is a countercurrent contactor with three packed beds. Because the sweetening system did not include a carbon adsorption unit for amine purification, contaminants were building up in the DEA. The contaminants comprised: treatment chemicals, hydrocarbons, foam inhibitors, and amine degradation products. The paper describes the solution to this problem.
Preliminary Tests in the Supersonic Sphere
NASA Technical Reports Server (NTRS)
Baker, John E.
1947-01-01
This report presents preliminary data obtained in the Langley supersonic sphere. The supersonic sphere is essentially a whirling mechanism enclosed in a steel shell which can be filled with either air or Freon gas. The test models for two-dimensional study are of propeller form having the same plan form and diameter but varying only in the airfoil shape and thickness ratio. Torque coefficients for the 16-006, 65-110, and the 15 percent thick ellipse models are presented, as well as pressure distributions on a circular-arc supersonic airfoil section having a maximum thickness of 10 percent chord at the 1/3-chord position. Torque coefficients were measured in both Freon and air on the 15 percent thick ellipse, and the data obtained in air and Freon are found to be in close agreement. The torque coefficients for the three previously mentioned models showed large differences in magnitude at tip Mach numbers above 1, the model with the thickest airfoil section having the largest torque coefficient. Pressure distribution on the previously mentioned circular-arc airfoil section are presented at Mach numbers of 0.69, 1.26, and 1.42. At Mach numbers of 1.26 and 1.42 the test section is in the mixed flow region where both subsonic and supersonic speeds occur on the airfoil. No adequate theory has been developed for this condition of mixed flow, but the experimental data have been compared with values of pressure based on Ackeret's theory. The experimental data obtained at a Mach number of 1.26 on the rear portion of the airfoil section agree fairly well with the values calculated by Ackeret's theory. At a Mach number of 1.42 a larger percentage of the airfoil is in supersonic flow, and the experimental data for the entire airfoil agree fairly well with the values obtained using Ackeret's theory.
Parametric forms and the inductive response of a permeable conducting sphere
Smith, J. Torquil; Morrison, H. Frank; Becker, Alex
2003-12-11
At early time, the time derivative of the response of isolated conductive bodies to step function excitation decays as t-1/2 (under a quasi-static approximation). One simple parametric form for the response with correct early time behavior is k'(1 + t1/2/a1/2)-beta e-t/gamma. For a conducting magnetic sphere, parameter values are determined from the high and low frequency limit responses, together with two time scales taken from the form of the analytic solution. Parameters alpha and gamma correspond to transition times, for transition from an early time t-1/2 derivative response, and to late time exponential decay. For conducting spheres with high permeability, increasing the permeability moves the transition from early time behavior earlier in inverse proportion to the relative permeability mu r, and increases the time constant of the late time decay in proportion to mu r. Magnitude parameter k' corresponds to the difference between high frequency and low frequency limit responses.
Helledi, L S; Schubert, L
2001-11-01
Acyclovir is a widely used agent in the treatment of herpes virus infections of the skin, but owing to its poor physicochemical properties in terms of bioavailability and suboptimal formulations, the treatment is far from optimal. The liquid crystalline cubic phase system has been reported to act as a bioadhesive drug delivery system. In the present study, acyclovir was suspended in a cubic phase of glycerol monooleate (GMO) and water 65%:35% w/w, and the phase behavior and release kinetics were examined. X-ray diffraction and differential scanning calorimetry (DSC) measurements demonstrated that the cubic phase containing 1%-10% (w/w) acyclovir retains its phase condition in the temperature range investigated (20 degrees C-70 degrees C). Acyclovir can be incorporated in high amounts (approximately 40% w/w) without causing phase transition, as is shown in polarized light. This is probably because of its low solubility (approximately 0.11% w/w) in the cubic phase. The release characteristics of acyclovir incorporated as a suspension (1%-5% w/w) into a cubic phase were investigated using Franz diffusion cells. Acyclovir was quantified by high-performance liquid chromatography (HPLC). The drug was readily released from the system, and the release increased with the initial drug load concentration. About 25%-50% was released after 24 h. The release is dependent on the square root of time, and the kinetics can be described by the Higuchi theory. The rate-limiting step in the release process is most likely diffusion. The suggested theory is further supported by identical release data obtained for micronized and nonmicronized acyclovir. The fluxes for 1% and 5% w/w were 380 and 900 microg/h(1/2), respectively. Comparison of the release rates of acyclovir delivered from a cubic phase and from the commercial product, Zovir cream, showed the rate to be six times faster from the cubic phase. The results indicate that the cubic phase is a promising drug delivery system for
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 and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An...
21 CFR 886.3320 - Eye sphere implant.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Eye sphere implant. 886.3320 Section 886.3320 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An...
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 and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An...
21 CFR 886.3320 - Eye sphere implant.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Eye sphere implant. 886.3320 Section 886.3320 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An...
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 and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3320 Eye sphere implant. (a) Identification. An...
Social Justice and Education in the Public and Private Spheres
ERIC Educational Resources Information Center
Power, Sally; Taylor, Chris
2013-01-01
This paper explores the complex relationship between social justice and education in the public and private spheres. The politics of education is often presented as a battle between left and right, the state and the market. In this representation, the public and the private spheres are neatly aligned on either side of the line of battle, and…
Equations of state for fused-hard-sphere fluids
NASA Astrophysics Data System (ADS)
Maeso, M. J.; Solana, J. R.
1993-09-01
Analytical equations of state for fused-hard-sphere fluids are developed from a generalization of the Carnahan-Starling method for obtaining the equation of state of the hard-sphere fluid. The results are in good agreement with existing simulation data.
Torsional oscillations of a sphere in a Stokes flow
NASA Astrophysics Data System (ADS)
Box, F.; Thompson, A. B.; Mullin, T.
2015-12-01
The results of an experimental investigation into a sphere performing torsional oscillations in a Stokes flow are presented. A novel experimental set-up was developed, which enabled the motion of the sphere to be remotely controlled through application of an oscillatory magnetic field. The response of the sphere to the applied field was characterised in terms of the viscous, magnetic and gravitational torques acting on the sphere. A mathematical model of the system was developed, and good agreement was found between experimental, numerical and theoretical results. The flow resulting from the motion of the sphere was measured, and the fluid velocity was found to have an inverse square dependence on radial distance from the sphere. The good agreement between measurements and the analytical solutions for both fluid velocity and angular displacement of the sphere indicates that the flow may be considered Stokesian, thus providing an excellent basis for experimental and theoretical characterisation of hydrodynamic interactions between multiple oscillating spheres at low Reynolds number.
Dual-Purpose Millikan Experiment with Polystyrene Spheres
ERIC Educational Resources Information Center
Wall, C. N.; Christensen, F. E.
1975-01-01
This procedure, using polystyrene spheres of specified diameter, renders the Millikan oil drop experiment more accurate than the conventional procedure of the polystyrene spheres, eliminates size estimation error, and removes the guesswork involved in assigning proper index integers to the observed charges. (MLH)
Mesoscale assembly of NiO nanosheets into spheres
Zhang Meng; Yan Guojin; Hou Yonggai; Wang Chunhua
2009-05-15
NiO solid/hollow spheres with diameters about 100 nm have been successfully synthesized through thermal decomposition of nickel acetate in ethylene glycol at 200 deg. C. These spheres are composed of nanosheets about 3-5 nm thick. Introducing poly(vinyl pyrrolidone) (PVP) surfactant to reaction system can effectively control the products' morphology. By adjusting the quantity of PVP, we accomplish surface areas-tunable NiO assembled spheres from {approx}70 to {approx}200 m{sup 2} g{sup -1}. Electrochemical tests show that NiO hollow spheres deliver a large discharge capacity of 823 mA h g{sup -1}. Furthermore, these hollow spheres also display a slow capacity-fading rate. A series of contrastive experiments demonstrate that the surface area of NiO assembled spheres has a noticeable influence on their discharge capacity. - Graphical abstract: The mesoscale assembly of NiO nanosheets into spheres have been achieved by a solvothermal method. N{sub 2} adsorption/desorption isotherms show the S{sub BET} of NiO is tunable. NiO spheres show large discharge capacity and slow capacity-fading rate.
Segregation of Fluidized Binary Hard-Sphere Systems Under Gravity
NASA Astrophysics Data System (ADS)
Kim, Soon-Chul
We have derived an analytic expression for the contact value of the local density of binary hard-sphere systems under gravity. We have obtained the crossover conditions for the Brazil-nut type segregation of binary hard-sphere mixtures and binary hard-sphere chain mixtures from the segregation criterion, where the segregation occurs when the density (or the pressure) of the small spheres at the bottom is higher than that of the large spheres, or vice versa. For the binary hard-sphere chain mixtures, the crossover condition for the segregation depends on the number of monomers composed of hard-sphere chains as well as the mass and the diameter of each species. The fundamental-measure theories (FMTs) and local density approximation (LDA) are employed to examine the crossover condition for the segregation of the gravity-induced hard-sphere mixtures. The calculated results show that the LDA does not explain the density oscillation near the bottom, whereas the modified fundamental-measure theory (MFMT) compares with molecular dynamics simulations.
Orbital Motion of Electrically Charged Spheres in Microgravity
ERIC Educational Resources Information Center
Banerjee, Shubho; Andring, Kevin; Campbell, Desmond; Janeski, John; Keedy, Daniel; Quinn, Sean; Hoffmeister, Brent
2008-01-01
The similar mathematical forms of Coulomb's law and Newton's law of gravitation suggest that two uniformly charged spheres should be able to orbit each other just as two uniform spheres of mass are known to do. In this paper we describe an experiment that we performed to demonstrate such an orbit. This is the first published account of a…
Experimental Visualization of Flows in Packed Beds of Spheres
NASA Technical Reports Server (NTRS)
Hendricks, R. C.; Lattime, S.; Braun, M. J.; Athavale, M. M.
1997-01-01
The flow experiment consisted of an oil tunnel, 76 x 76 mm in cross-section, packed with lucite spheres. The index of refraction of the working fluid and the spheres were matched such that the physical spheres invisible to the eye and camera. By seeding the oil and illuminating the packed bed with planar laser light sheet, aligned in the direction of the bulk flow, the system fluid dynamics becomes visible and the 2-D projection was recorded at right angles to the bulk flow. The planar light sheet was traversed from one side of the tunnel to the other providing a simulated 3-D image of the entire flow field. The boundary interface between the working fluid and the sphere rendered the sphere black permitting visualization of the exact locations of the circular interfaces in both the axial and transverse directions with direct visualization of the complex interstitial spaces between the spheres within the bed. Flows were observed near the surfaces of a plane and set of spheres as well as minor circles that appear with great circles and not always uniformly ordered. In addition to visualizing a very complex flow field, it was observed that flow channeling in the direction of the bulk flow occurs between sets of adjacent spheres. Still photographs and video recordings illustrating the flow phenomena will be presented.
Comparing standard Bonner spheres and high-sensitivity Bonner cylinders.
Lee, Kuo-Wei; Yuan, Ming-Chen; Jiang, Shiang-Huei; Sheu, Rong-Jiun
2014-10-01
Standard Bonner spheres and proposed high-sensitivity Bonner cylinders were calibrated in a neutron calibration room, using a (252)Cf source. The Bonner sphere system consists of 11 polyethylene (PE) spheres of various diameters and 4 extended spheres that comprise embedded metal shells. Similar to the design of Bonner spheres, a set of Bonner cylinders was assembled using a large cylindrical (3)He tube as the central probe, which was wrapped using various thicknesses of PE. A layer of lead was employed inside one of the PE cylinders to increase the detection efficiency of high-energy neutrons. The central neutron probe used in the Bonner cylinders exhibited an efficiency of ∼17.9 times higher than that of the Bonner spheres. However, compared with the Bonner spheres, the Bonner cylinders are not fully symmetric in their geometry, exhibiting angular dependence in their responses to incoming neutrons. Using a series of calculations and measurements, this study presents a systematic comparison between Bonner spheres and cylinders in terms of their response functions, detection efficiencies, angular dependences and spectrum unfolding.
Computational Analysis of Wake Field Flow between Multiple Identical Spheres
NASA Astrophysics Data System (ADS)
Brand, Wesley; Greenslit, Morton; Klassen, Zach; Hastings, Jay; Matson, William
2014-11-01
It is well understood both that objects moving through a fluid perturb the motion of nearby objects in the same fluid and that some configurations of objects moving through a fluid have little inter-object perturbation, such as a flock of birds flying in a V-formation. However, there is presently no known method for predicting what configurations of objects will be stable while moving through a fluid. Previous work has failed to find such stable configurations because of the computational complexity of finding individual solutions. In this research, the motions of two spheres in water were simulated and combinations of those simulations were used to extrapolate the motions of multiple spheres and to find configurations where the lateral forces on each sphere were negligible and the vertical forces on each sphere were equivalent. Two and three sphere arrangements were simulated in COMSOL Multiphysics and Mathematica was used both to demonstrate that combinations of two sphere cases are identical to three sphere cases and to identify stable configurations of three or more spheres. This new approach is expected to simplify optimization of aerodynamic configurations and applications such as naval and aerospace architecture and racecar driving. Advisor.
Seeded Synthesis of Monodisperse Core-Shell and Hollow Carbon Spheres.
Gil-Herrera, Luz Karime; Blanco, Álvaro; Juárez, Beatriz H; López, Cefe
2016-08-01
Monodisperse carbon spheres between 500 and 900 nm are hydrothermally synthesized from glucose on polystyrene seeds. Control over temperature, time, glucose concentration, and seed size yields hybrid spheres without aggregation and no additional spheres population. Pyrolysis transforms the hybrid into hollow carbon spheres preserving monodispersity. This approach provides a basis for functional carbon spheres applicable in photonics and energy storage. PMID:27337299
Seeded Synthesis of Monodisperse Core-Shell and Hollow Carbon Spheres.
Gil-Herrera, Luz Karime; Blanco, Álvaro; Juárez, Beatriz H; López, Cefe
2016-08-01
Monodisperse carbon spheres between 500 and 900 nm are hydrothermally synthesized from glucose on polystyrene seeds. Control over temperature, time, glucose concentration, and seed size yields hybrid spheres without aggregation and no additional spheres population. Pyrolysis transforms the hybrid into hollow carbon spheres preserving monodispersity. This approach provides a basis for functional carbon spheres applicable in photonics and energy storage.
Tuning emission in violet, blue, green and red in cubic GaN/InGaN/GaN quantum wells
NASA Astrophysics Data System (ADS)
Orozco Hinostroza, I. E.; Avalos-Borja, M.; Compeán García, V. D.; Zamora, C. Cuellar; Rodríguez, A. G.; López Luna, E.; Vidal, M. A.
2016-02-01
Light emission in the three primary colors was achieved in cubic GaN/InGaN/GaN heterostructures grown by molecular beam epitaxy on MgO substrates in a single growth process. A heterostructure with four quantum wells with a width of 10 nm was grown; this quantum wells width decrease the segregation effect of In. Photoluminescence emission produced four different emission signals: violet, blue, green-yellow and red. Thus, we were able to tune energy transitions in the visible spectrum modifying the In concentration in cubic InxGa1-xN ternary alloy.
NASA Astrophysics Data System (ADS)
Song, T.; Ma, Q.; Sun, X. W.; Liu, Z. J.; Fu, Z. J.; Wei, X. P.; Wang, T.; Tian, J. H.
2016-09-01
The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model.
Equilibrium Sampling of Hard Spheres up to the Jamming Density and Beyond
NASA Astrophysics Data System (ADS)
Berthier, Ludovic; Coslovich, Daniele; Ninarello, Andrea; Ozawa, Misaki
2016-06-01
We implement and optimize a particle-swap Monte Carlo algorithm that allows us to thermalize a polydisperse system of hard spheres up to unprecedentedly large volume fractions, where previous algorithms and experiments fail to equilibrate. We show that no glass singularity intervenes before the jamming density, which we independently determine through two distinct nonequilibrium protocols. We demonstrate that equilibrium fluid and nonequilibrium jammed states can have the same density, showing that the jamming transition cannot be the end point of the fluid branch.
Equilibrium Sampling of Hard Spheres up to the Jamming Density and Beyond.
Berthier, Ludovic; Coslovich, Daniele; Ninarello, Andrea; Ozawa, Misaki
2016-06-10
We implement and optimize a particle-swap Monte Carlo algorithm that allows us to thermalize a polydisperse system of hard spheres up to unprecedentedly large volume fractions, where previous algorithms and experiments fail to equilibrate. We show that no glass singularity intervenes before the jamming density, which we independently determine through two distinct nonequilibrium protocols. We demonstrate that equilibrium fluid and nonequilibrium jammed states can have the same density, showing that the jamming transition cannot be the end point of the fluid branch. PMID:27341260
Mapping a hard-sphere fluid mixture onto a single component hard-sphere fluid
NASA Astrophysics Data System (ADS)
Barrio, C.; Solana, J. R.
2005-06-01
The possibility of obtaining the thermodynamic and structural properties of a binary additive hard-sphere fluid mixture on the basis of the corresponding properties of a suitable single-component hard-sphere fluid is analyzed. To this end, Monte Carlo simulations have been performed for binary mixtures of hard spheres for different densities, compositions and diameter ratios in order to obtain the compressibility factor Z and the partial radial distribution functions gij(r) for pairs ij of the mixtures. These data are used to test the reliability of different proposals available in the literature for mapping the thermodynamic and structural properties of conformal mixtures onto those of a single-component fluid. It is found that, while the averaged radial distribution function and the equation of state of the mixture can be reasonably well reproduced by means of those of an equivalent single-component fluid, the partial radial distribution functions cannot be obtained with enough accuracy from the radial distribution function of the equivalent fluid. A possible explanation for this fact is suggested.
ERIC Educational Resources Information Center
Statfeld, Jenna L.
2011-01-01
Post-school transition is the movement of a child with disabilities from school to activities that occur after the completion of school. This paper provides information about: (1) post-school transition; (2) transition plan; (3) transition services; (4) transition planning; (5) vocational rehabilitation services; (6) services that are available…
Pool boiling from rotating and stationary spheres in liquid nitrogen
NASA Technical Reports Server (NTRS)
Cuan, Winston M.; Schwartz, Sidney H.
1988-01-01
Results are presented for a preliminary experiment involving saturated pool boiling at 1 atm from rotating 2 and 3 in. diameter spheres which were immersed in liquid nitrogen (LN2). Additional results are presented for a stationary, 2 inch diameter sphere, quenched in LN2, which were obtained utilizing a more versatile and complete experimental apparatus that will eventually be used for additional rotating sphere experiments. The speed for the rotational tests was varied from 0 to 10,000 rpm. The stationary experiments parametrically varied pressure and subcooling levels from 0 to 600 psig and from 0 to 50 F, respectively. During the rotational tests, a high speed photographic analysis was undertaken to measure the thickness of the vapor film surrounding the sphere. The average Nusselt number over the cooling period was plotted against the rotational Reynolds number. Stationary sphere results included local boiling heat transfer coefficients at different latitudinal locations, for various pressure and subcooling levels.
Flow past a porous sphere at small Reynolds number
NASA Astrophysics Data System (ADS)
Srivastava, A. C.; Srivastava, Neetu
2005-09-01
low of an incompressible viscous fluid past a porous sphere has been discussed. The flow has been divided in three regions. The Region-I is the region inside the porous sphere in which the flow is governed by Brinkman equation with the effective viscosity different from that of the clear fluid. In Regions II and III clear fluid flows and Stokes and Oseen solutions are respectively valid. In all the three regions Stokes stream function is expressed in powers of Reynolds number. Stream function of Region II is matched with that of Region I at the surface of the sphere by the conditions suggested by Ochao-Tapia and Whitaker and it is matched with that of Oseen’s solutions far away from the sphere. It is found that the drag on the sphere reduces significantly when it is porous and it decreases with the increase of permeability of the medium.
Critical levitation loci for spheres on cryogenic fluids.
NASA Technical Reports Server (NTRS)
Hendricks, R. C.; Ohm, S. A.
1972-01-01
The conditions which allow a fluid to support a sphere having a higher specific gravity than its own are investigated. Three basic parameters which together define the maximum floating conditions are considered, including the Bond number, the wetting angle of the interface, and the ratio of solid-liquid specific gravities. The Bond number represents the ratio of buoyancy to surface tension forces. An analysis of the forces at the sphere-liquid interface is conducted to determine the optimum levitation loci, that is, the conditions permitting flotation of a maximum density sphere. Data for glycerine, carbon tetrachloride, and water spheres floating on a liquid nitrogen surface appear to be in good agreement with the analysis. Data for Teflon spheres on water also appear to be in agreement with the analytical results.
Sampling theorems and compressive sensing on the sphere
NASA Astrophysics Data System (ADS)
McEwen, Jason D.; Puy, Gilles; Thiran, Jean-Philippe; Vandergheynst, Pierre; Van De Ville, Dimitri; Wiaux, Yves
2011-09-01
We discuss a novel sampling theorem on the sphere developed by McEwen & Wiaux recently through an association between the sphere and the torus. To represent a band-limited signal exactly, this new sampling theorem requires less than half the number of samples of other equiangular sampling theorems on the sphere, such as the canonical Driscoll & Healy sampling theorem. A reduction in the number of samples required to represent a band-limited signal on the sphere has important implications for compressive sensing, both in terms of the dimensionality and sparsity of signals. We illustrate the impact of this property with an inpainting problem on the sphere, where we show superior reconstruction performance when adopting the new sampling theorem.
Surface roughness measurement of tooling spheres for laser measurements
NASA Astrophysics Data System (ADS)
Sarr, Dennis P.; Reed, Paul W.
2001-02-01
The usage of chrome or highly polished precision tooling (reference) spheres is common in the calibration and operational characterization of measurement systems such as a Coordinate Measurement Machine (CMM). The usage of a three-dimensional, (3D) laser triangulation, non-contact measurement system on CMMs and other scanning systems pose several obstacles. The highly specular mirror finish on the tooling sphere provides an accurate mechanical entity that has adverse results with laser sensors. The development of tooling spheres with a diffuse surface would benefit laser based measurement systems. The surface roughness and reflectivity properties have an effect on the laser measurements' accuracy. Efforts to develop spheres and establish meaningful measurements of spheres with modified surface finishes are investigated.
Debye series for light scattering by a multilayered sphere.
Li, Renxian; Han, Xiange; Jiang, Huifen; Ren, Kuan Fang
2006-02-20
We have derived the formula for the Debye-series decomposition for light scattering by a multilayered sphere. This formulism permits the mechanism of light scattering to be studied. An efficient algorithm is introduced that permits stable calculation for a large sphere with many layers. The formation of triple first-order rainbows by a three-layered sphere and single-order rainbows and the interference of different-order rainbows by a sphere with a gradient refractive index, are then studied by use of the Debye model and Mie calculation. The possibility of taking only one single mode or several modes for each layer is shown to be useful in the study of the scattering characteristics of a multilayered sphere and in the measurement of the sizes and refractive indices of particles. PMID:16523791
The Physics of Hard Spheres Experiment on MSL-1: Required Measurements and Instrument Performance
NASA Technical Reports Server (NTRS)
Doherty, Michael P.; Lant, Christian T.; Ling, Jerri S.
1998-01-01
The Physics of HArd Spheres Experiment (PHaSE), one of NASA Lewis Research Center's first major light scattering experiments for microgravity research on complex fluids, flew on board the Space Shuttle's Microgravity Science Laboratory (MSL-1) in 1997. Using colloidal systems of various concentrations of micron-sized plastic spheres in a refractive index-matching fluid as test samples, illuminated by laser light during and after crystallization, investigations were conducted to measure the nucleation and growth rate of colloidal crystals as well as the structure, rheology, and dynamics of the equilibrium crystal. Together, these measurements support an enhanced understanding of the nature of the liquid-to-solid transition. Achievement of the science objectives required an accurate experimental determination of eight fundamental properties for the hard sphere colloidal samples. The instrument design met almost all of the original measurement requirements, but with compromise on the number of samples on which data were taken. The instrument performs 2-D Bragg and low angle scattering from 0.4 deg. to 60 deg., dynamic and single-channel static scattering from 10 deg. to 170 deg., rheology using fiber optics, and white light imaging of the sample. As a result, PHaSE provided a timely microgravity demonstration of critical light scattering measurement techniques and hardware concepts, while generating data already showing promise of interesting new scientific findings in the field of condensed matter physics.
Simple effective rule to estimate the jamming packing fraction of polydisperse hard spheres.
Santos, Andrés; Yuste, Santos B; López de Haro, Mariano; Odriozola, Gerardo; Ogarko, Vitaliy
2014-04-01
A recent proposal in which the equation of state of a polydisperse hard-sphere mixture is mapped onto that of the one-component fluid is extrapolated beyond the freezing point to estimate the jamming packing fraction ϕJ of the polydisperse system as a simple function of M1M3/M22, where Mk is the kth moment of the size distribution. An analysis of experimental and simulation data of ϕJ for a large number of different mixtures shows a remarkable general agreement with the theoretical estimate. To give extra support to the procedure, simulation data for seventeen mixtures in the high-density region are used to infer the equation of state of the pure hard-sphere system in the metastable region. An excellent collapse of the inferred curves up to the glass transition and a significant narrowing of the different out-of-equilibrium glass branches all the way to jamming are observed. Thus, the present approach provides an extremely simple criterion to unify in a common framework and to give coherence to data coming from very different polydisperse hard-sphere mixtures.
Simple effective rule to estimate the jamming packing fraction of polydisperse hard spheres
NASA Astrophysics Data System (ADS)
Santos, Andrés; Yuste, Santos B.; López de Haro, Mariano; Odriozola, Gerardo; Ogarko, Vitaliy
2014-04-01
A recent proposal in which the equation of state of a polydisperse hard-sphere mixture is mapped onto that of the one-component fluid is extrapolated beyond the freezing point to estimate the jamming packing fraction ϕJ of the polydisperse system as a simple function of M1M3/M22, where Mk is the kth moment of the size distribution. An analysis of experimental and simulation data of ϕJ for a large number of different mixtures shows a remarkable general agreement with the theoretical estimate. To give extra support to the procedure, simulation data for seventeen mixtures in the high-density region are used to infer the equation of state of the pure hard-sphere system in the metastable region. An excellent collapse of the inferred curves up to the glass transition and a significant narrowing of the different out-of-equilibrium glass branches all the way to jamming are observed. Thus, the present approach provides an extremely simple criterion to unify in a common framework and to give coherence to data coming from very different polydisperse hard-sphere mixtures.
Liquid water in the domain of cubic crystalline ice Ic
NASA Astrophysics Data System (ADS)
Jenniskens, P.; Banham, S. F.; Blake, D. F.; McCoustra, M. R. S.
1997-07-01
Vapor-deposited amorphous water ice, when warmed above the glass transition temperature (120-140 K), is a viscous liquid which exhibits a viscosity vs temperature relationship different from that of liquid water at room temperature. New studies of thin water ice films now demonstrate that viscous liquid water persists in the temperature range 140-210 K, where it coexists with cubic crystalline ice. The liquid character of amorphous water above the glass transition is demonstrated by (1) changes in the morphology of water ice films on a nonwetting surface observed in transmission electron microscopy (TEM) at around 175 K during slow warming, (2) changes in the binding energy of water molecules measured in temperature programmed desorption (TPD) studies, and (3) changes in the shape of the 3.07 μm absorption band observed in grazing angle reflection-absorption infrared spectroscopy (RAIRS) during annealing at high temperature, whereby the decreased roughness of the water surface is thought to cause changes in the selection rules for the excitation of O-H stretch vibrations. Because it is present over such a wide range of temperatures, we propose that this form of liquid water is a common material in nature, where it is expected to exist in the subsurface layers of comets and on the surfaces of some planets and satellites.
Transition metal catalysis in confined spaces.
Leenders, Stefan H A M; Gramage-Doria, Rafael; de Bruin, Bas; Reek, Joost N H
2015-01-21
Transition metal catalysis plays an important role in both industry and in academia where selectivity, activity and stability are crucial parameters to control. Next to changing the structure of the ligand, introducing a confined space as a second coordination sphere around a metal catalyst has recently been shown to be a viable method to induce new selectivity and activity in transition metal catalysis. In this review we focus on supramolecular strategies to encapsulate transition metal complexes with the aim of controlling the selectivity via the second coordination sphere. As we will discuss, catalyst confinement can result in selective processes that are impossible or difficult to achieve by traditional methods. We will describe the template-ligand approach as well as the host-guest approach to arrive at such supramolecular systems and discuss how the performance of the catalyst is enhanced by confining it in a molecular container.
Shape-dependent electrocatalysis: formic acid electrooxidation on cubic Pd nanoparticles.
Vidal-Iglesias, Francisco J; Arán-Ais, Rosa M; Solla-Gullón, José; Garnier, Emmanuel; Herrero, Enrique; Aldaz, Antonio; Feliu, Juan M
2012-08-01
The electrocatalytic properties of palladium nanocubes towards the electrochemical oxidation of formic acid were studied in H(2)SO(4) and HClO(4) solutions and compared with those of spherical Pd nanoparticles. The spherical and cubic Pd nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The intrinsic electrocatalytic properties of both nanoparticles were shown to be strongly dependent on the amount of metal deposited on the gold substrate. Thus, to properly compare the activity of both systems (spheres and nanocubes), the amount of sample has to be optimized to avoid problems due to a lower diffusion flux of reactants in the internal parts of the catalyst layer resulting in a lower apparent activity. Under the optimized conditions, the activity of the spheres and nanocubes was very similar between 0.1 and 0.35 V. From this potential value, the activity of the Pd nanocubes was remarkably higher. This enhanced electrocatalytic activity was attributed to the prevalence of Pd(100) facets in agreement with previous studies with Pd single crystal electrodes. The effect of HSO(4)(-)/SO(4)(2-) desorption-adsorption was also evaluated. The activity found in HClO(4) was significantly higher than that obtained in H(2)SO(4) in the whole potential range. PMID:22722609
Experimental study on combustion of a methane hydrate sphere
NASA Astrophysics Data System (ADS)
Yoshioka, Tomoki; Yamamoto, Yuji; Yokomori, Takeshi; Ohmura, Ryo; Ueda, Toshihisa
2015-10-01
The combustion behavior of a methane hydrate sphere under normal gravity is experimentally investigated. The initial diameter of the sphere is 20 mm. Variation in temperature at the center of the sphere ( T c) is measured with a K-type thermocouple at ignition temperatures ( T c,i) from 193 to 253 K at 20 K intervals. Variation in the near-surface temperature of the sphere ( T s) is measured at ignition temperatures ( T s,i) from 233 to 263 K at 10 K intervals. Two combustion phases are observed. When the hydrate is ignited, a stable flame envelope is formed around the sphere (phase 1). In phase 1, the surface of the sphere is dry. After a few seconds, water formed by dissociation of the methane hydrate appears on the surface and methane bubbles are formed by methane ejected from inside the sphere (phase 2), thus destabilizing the flame and causing local extinction. Methane bubbles move down along the surface and merge into a large methane bubble at the bottom of the sphere. This bubble bursts, releasing methane to form a temporary flame, and the water drops from the hydrate sphere. Water on the surface is cooled by the hydrate inside, and an ice shell confines the methane gas that dissociated inside the sphere. Because the dissociation occurs continuously inside the hydrate, the inner pressure gradually increases and at some instant, the ice cracks and methane gas is ejected from the cracks, which results in a micro-explosion with a flame. In phase 1, the surface temperature is below the freezing point of water, and so the surface remains dry and a stable flame envelope is formed; in phase 2, the surface temperature is above the freezing point, and so water appears on the surface. When the temperature at the center of the sphere is lower (193, 213, or 233 K), some methane hydrate remains even after flame extinction because heat transfer from the flame decreases in phase 2 as a result of local extinction. The diameter of the sphere decreases during combustion in
Deterministic implementation of weak quantum cubic nonlinearity
Marek, Petr; Filip, Radim; Furusawa, Akira
2011-11-15
We propose a deterministic implementation of weak cubic nonlinearity, which is a basic building block of a full-scale continuous-variable quantum computation. Our proposal relies on preparation of a specific ancillary state and transferring its nonlinear properties onto the desired target by means of deterministic Gaussian operations and feed forward. We show that, despite the imperfections arising from the deterministic nature of the operation, the weak quantum nonlinearity can be implemented and verified with the current level of technology.
NASA Astrophysics Data System (ADS)
Hu, Xiaotang; Xu, Zongwei; Li, Kang; Fang, Fengzhou; Wang, Liyang
2015-11-01
Methods for fabricating three-dimensional nanofeature arrays for surface-enhanced Raman spectroscopy (SERS) substrates were explored by combining the self-assembly of nanoscale polystyrene (PS) spheres with subsequent Au film ion sputter coating modulation. The substrate's nanoscale hot-spot features were controlled using the Au coating film thickness regulation and focused ion beam (FIB) nano-patterning regulation methods. Scanning electron microscopy and Raman spectroscopy were employed to analyze the substrate morphology and the enhancement mechanism of the three-dimensional SERS substrate. PS microspheres with diameters of 151 nm and 360 nm were coated with Au layers of different thicknesses ranging from 10 nm to 270 nm. The configuration of the Au-PS spheres can be regulated to hexagonal close packing with nanoscale V-shaped slits with a 10-20 nm gap pattern. Nanoscale Au particles and clusters with a clear outline covered the surface of the PS spheres, in which the multiple-scale structures increase the specific surface area of the SERS-active substrate. Nanoscale cracks formed on the smaller Au-PS spheres with a diameter of 151 nm, which also exhibited strong SERS activity. The substrate surface temperature regularly increased after Au coating, and the thermal expansion coefficient difference and PS glass transition properties were studied to explain the Au-PS spheres nanofeature configuration development. The fabricated Au-PS spheres SERS feature is a type of three-dimensional and highly ordered array, which can show Raman scattering characteristics by providing a SERS enhancement factor of greater than 107.
C{sub 60}: Sphere or polyhedron?
Haddon, R.C.
1997-02-19
In the original publication on the subject, C{sub 60} was depicted with the aid of a soccer ball, but this representation soon gave way to the familiar line drawing of chemical bonds between nucleii. To a large extent the dichotomy in the representation of the fullerenes remains today, and it is the purpose of this paper to pose and address the question that appears in the title. Of course, in reality the answer is well-known, and neither the sphere nor the polyhedron represent C{sub 60}, which like other molecules exists as a collection of nuclei with an associated distribution of electron density. Nevertheless, it is of interest to consider which of these conventional representations is most relevant for the fullerenes and in particular the language most appropriate to the description of the shape of these molecules and the geometry of the carbon atoms. The analysis presented here shows that topology of the molecule is paramount, and hence, C{sub 60} (and the fullerenes) are best modeled as polyhedra. 16 refs., 3 figs.
Consistent Kaluza-Klein sphere reductions
NASA Astrophysics Data System (ADS)
Cvetič, M.; Lü, H.; Pope, C. N.
2000-09-01
We study the circumstances under which a Kaluza-Klein reduction on an n-sphere, with a massless truncation that includes all the Yang-Mills fields of SO(n+1), can be consistent at the full non-linear level. We take as the starting point a theory comprising a p-form field strength and (possibly) a dilaton, coupled to gravity in the higher dimension D. We show that aside from the previously studied cases with (D,p)=(11,4) and (10,5) (associated with the S4 and S7 reductions of D=11 supergravity, and the S5 reduction of type IIB supergravity), the only other possibilities that allow consistent reductions are for p=2, reduced on S2, and for p=3, reduced on S3 or SD-3. We construct the fully non-linear Kaluza-Klein Ansätze in all these cases. In particular, we obtain D=3, N=8, SO(8) and D=7, N=2, SO(4) gauged supergravities from S7 and S3 reductions of N=1 supergravity in D=10.
Collective excitations in soft-sphere fluids.
Bryk, Taras; Gorelli, Federico; Ruocco, Giancarlo; Santoro, Mario; Scopigno, Tullio
2014-10-01
Despite that the thermodynamic distinction between a liquid and the corresponding gas ceases to exist at the critical point, it has been recently shown that reminiscence of gaslike and liquidlike behavior can be identified in the supercritical fluid region, encoded in the behavior of hypersonic waves dispersion. By using a combination of molecular dynamics simulations and calculations within the approach of generalized collective modes, we provide an accurate determination of the dispersion of longitudinal and transverse collective excitations in soft-sphere fluids. Specifically, we address the decreasing rigidity upon density reduction along an isothermal line, showing that the positive sound dispersion, an excess of sound velocity over the hydrodynamic limit typical for dense liquids, displays a nonmonotonic density dependence strictly correlated to that of thermal diffusivity and kinematic viscosity. This allows rationalizing recent observation parting the supercritical state based on the Widom line, i.e., the extension of the coexistence line. Remarkably, we show here that the extremals of transport properties such as thermal diffusivity and kinematic viscosity provide a robust definition for the boundary between liquidlike and gaslike regions, even in those systems without a liquid-gas binodal line. Finally, we discuss these findings in comparison with recent results for Lennard-Jones model fluid and with the notion of the "rigid-nonrigid" fluid separation lines.
Radar Imaging of Spheres in 3D using MUSIC
Chambers, D H; Berryman, J G
2003-01-21
We have shown that multiple spheres can be imaged by linear and planar EM arrays using only one component of polarization. The imaging approach involves calculating the SVD of the scattering response matrix, selecting a subset of singular values that represents noise, and evaluating the MUSIC functional. The noise threshold applied to the spectrum of singular values for optimal performance is typically around 1%. The resulting signal subspace includes more than one singular value per sphere. The presence of reflections from the ground improves height localization, even for a linear array parallel to the ground. However, the interference between direct and reflected energy modulates the field, creating periodic nulls that can obscure targets in typical images. These nulls are largely eliminated by normalizing the MUSIC functional with the broadside beam pattern of the array. The resulting images show excellent localization for 1 and 2 spheres. The performance for the 3 sphere configurations are complicated by shadowing effects and the greater range of the 3rd sphere in case 2. Two of the three spheres are easily located by MUSIC but the third is difficult to distinguish from other local maxima of the complex imaging functional. Improvement is seen when the linear array is replace with a planar array, which increases the effective aperture height. Further analysis of the singular values and their relationship to modes of scattering from the spheres, as well as better ways to exploit polarization, should improve performance. Work along these lines is currently being pursued by the authors.
Public sphere as assemblage: the cultural politics of roadside memorialization.
Campbell, Elaine
2013-09-01
This paper investigates contemporary academic accounts of the public sphere. In particular, it takes stock of post-Habermasian public sphere scholarship, and acknowledges a lively and variegated debate concerning the multiple ways in which individuals engage in contemporary political affairs. A critical eye is cast over a range of key insights which have come to establish the parameters of what 'counts' as a/the public sphere, who can be involved, and where and how communicative networks are established. This opens up the conceptual space for re-imagining a/the public sphere as an assemblage. Making use of recent developments in Deleuzian-inspired assemblage theory - most especially drawn from DeLanda's (2006) 'new philosophy of society' - the paper sets out an alternative perspective on the notion of the public sphere, and regards it as a space of connectivity brought into being through a contingent and heterogeneous assemblage of discursive, visual and performative practices. This is mapped out with reference to the cultural politics of roadside memorialization. However, a/the public sphere as an assemblage is not simply a 'social construction' brought into being through a logic of connectivity, but is an emergent and ephemeral space which reflexively nurtures and assembles the cultural politics (and political cultures) of which it is an integral part. The discussion concludes, then, with a consideration of the contribution of assemblage theory to public sphere studies. (Also see Campbell 2009a).
Extrinsic Calibration of Camera Networks Using a Sphere
Guan, Junzhi; Deboeverie, Francis; Slembrouck, Maarten; van Haerenborgh, Dirk; van Cauwelaert, Dimitri; Veelaert, Peter; Philips, Wilfried
2015-01-01
In this paper, we propose a novel extrinsic calibration method for camera networks using a sphere as the calibration object. First of all, we propose an easy and accurate method to estimate the 3D positions of the sphere center w.r.t. the local camera coordinate system. Then, we propose to use orthogonal procrustes analysis to pairwise estimate the initial camera relative extrinsic parameters based on the aforementioned estimation of 3D positions. Finally, an optimization routine is applied to jointly refine the extrinsic parameters for all cameras. Compared to existing sphere-based 3D position estimators which need to trace and analyse the outline of the sphere projection in the image, the proposed method requires only very simple image processing: estimating the area and the center of mass of the sphere projection. Our results demonstrate that we can get a more accurate estimate of the extrinsic parameters compared to other sphere-based methods. While existing state-of-the-art calibration methods use point like features and epipolar geometry, the proposed method uses the sphere-based 3D position estimate. This results in simpler computations and a more flexible and accurate calibration method. Experimental results show that the proposed approach is accurate, robust, flexible and easy to use. PMID:26247950
Cross section for absorption of partly shielded dielectric sphere
NASA Astrophysics Data System (ADS)
Vinogradov, S. S.; Sulima, A. V.
1984-05-01
The effect of an ideally conducting spherical metal cup, as a shield, on the microwave absorption characteristics of a dielectric sphere is evaluated on the basis of the known solution to the diffraction problem for a plane electromagnetic wave propagating along the axis of cup and sphere. The Debye electric and magnetic potentials are calculated for the shielded segment of the sphere and for the unshielded remainder of the dielectric sphere, the cup lying either on the front surface or the back surface of the sphere. The problem reduces to two coupled systems of linear algebraic equations of the second kind. The cross section for absorption, equal to the difference between total incident energy flux and scattered energy flux in accordance with power balance or conservation of diffraction energy, has been calculated as a function of kb (k- wave number in free space, b- radius of cup base circle). Numerical results indicate that within the resonance range (b- wavelength of incident radiation) correction must be made to include quasi-natural modes of the shield. A narrow shield behind the sphere increases the overall absorption level in the latter, while a narrow shield before the sphere has almost no effect on the absorption.
Synthesis and characterization of oil-chitosan composite spheres.
Huang, Keng-Shiang; Wang, Chih-Yu; Yang, Chih-Hui; Grumezescu, Alexandru Mihai; Lin, Yung-Sheng; Kung, Chao-Pin; Lin, I-Yin; Chang, Yi-Ching; Weng, Wei-Jie; Wang, Wei-Ting
2013-05-16
Oil-chitosan composite spheres were synthesized by encapsulation of sunflower seed oil in chitosan droplets, dropping into NaOH solution and in situ solidification. Hydrophilic materials (i.e., iron oxide nanoparticles) and lipophilic materials (i.e., rhodamine B or epirubicin) could be encapsulated simultaneously in the spheres in a one step process. The diameters of the prepared spheres were 2.48 ± 0.11 mm (pure chitosan spheres), 2.31 ± 0.08 mm (oil-chitosan composites), 1.49 ± 0.15 mm (iron-oxide embedded oil-chitosan composites), and 1.69 ± 0.1 mm (epirubicin and iron oxide encapsulated oil-chitosan composites), respectively. Due to their superparamagnetic properties, the iron-oxide embedded oil-chitosan composites could be guided by a magnet. A lipophilic drug (epirubicin) could be loaded in the spheres with encapsulation rate measured to be 72.25%. The lipophilic fluorescent dye rhodamine B was also loadable in the spheres with red fluorescence being observed under a fluorescence microscope. We have developed a novel approach to an in situ process for fabricating oil-chitosan composite spheres with dual encapsulation properties, which are potential multifunctional drug carriers.
Forming MOFs into spheres by use of molecular gastronomy methods.
Spjelkavik, Aud I; Aarti; Divekar, Swapnil; Didriksen, Terje; Blom, Richard
2014-07-14
A novel method utilizing hydrocolloids to prepare nicely shaped spheres of metal-organic frameworks (MOFs) has been developed. Microcrystalline CPO-27-Ni particles are dispersed in either alginate or chitosan solutions, which are added dropwise to solutions containing, respectively, either divalent group 2 cations or base that act as gelling agents. Well-shaped spheres are immediately formed, which can be dried into spheres containing mainly MOF (>95 wt %). The spheronizing procedures have been optimized with respect to maximum specific surface area, shape, and particle density of the final sphere. At optimal conditions, well-shaped 2.5-3.5 mm diameter CPO-27-Ni spheres with weight-specific surface areas <10 % lower than the nonformulated CPO-27-Ni precursor, and having sphere densities in the range 0.8 to 0.9 g cm(-3) and particle crushing strengths above 20 N, can be obtained. The spheres are well suited for use in fixed-bed catalytic or adsorption processes.
Alternative approach of cell encapsulation by Volvox spheres.
Teong, Benjamin; Manousakas, Ioannis; Chang, Shwu Jen; Huang, Han Hsiang; Ju, Kuen-Cheng; Kuo, Shyh Ming
2015-10-01
Volvox sphere is a bio-mimicking concept of a biomaterial structure design able to encapsulate chemicals, drugs and/or cells. The aim of this study was to prepare Volvox spheres encapsulating AML12 liver cells and mesenchymal stem cells (MSCs) via a high voltage electrostatic field system. The results demonstrated that AML12 liver cells and MSCs could be successfully encapsulated into the inner spheres and the outer sphere of the Volvox spheres. The improved cell viability of MSCs was achieved by the addition of collagen and polyethylene glycol into the preparation components of the Volvox spheres. Collagen material potentially provides extracellular matrix-like structure for cell adhesion while polyethylene glycol provides a void/loose space for permeability of metabolites. The encapsulated MSCs were able to differentiate into hepatocytes or hepatocyte-like cells and express liver cell markers including albumin, alpha feto-protein and cytokeratin 18. The encapsulated cells secreted albumin to about 140 ng on day 14. Based on these observations, we conclude that Volvox spheres can be used as an alternative approach to encapsulate multiple types of cells, here AML12 hepatocyte cell line and MSCs. Nevertheless, efforts are still needed to improve the viability of the encapsulated cells and increase the differentiation of MSCs into functional liver cells. PMID:26117741
Synthesis and characterization of oil-chitosan composite spheres.
Huang, Keng-Shiang; Wang, Chih-Yu; Yang, Chih-Hui; Grumezescu, Alexandru Mihai; Lin, Yung-Sheng; Kung, Chao-Pin; Lin, I-Yin; Chang, Yi-Ching; Weng, Wei-Jie; Wang, Wei-Ting
2013-01-01
Oil-chitosan composite spheres were synthesized by encapsulation of sunflower seed oil in chitosan droplets, dropping into NaOH solution and in situ solidification. Hydrophilic materials (i.e., iron oxide nanoparticles) and lipophilic materials (i.e., rhodamine B or epirubicin) could be encapsulated simultaneously in the spheres in a one step process. The diameters of the prepared spheres were 2.48 ± 0.11 mm (pure chitosan spheres), 2.31 ± 0.08 mm (oil-chitosan composites), 1.49 ± 0.15 mm (iron-oxide embedded oil-chitosan composites), and 1.69 ± 0.1 mm (epirubicin and iron oxide encapsulated oil-chitosan composites), respectively. Due to their superparamagnetic properties, the iron-oxide embedded oil-chitosan composites could be guided by a magnet. A lipophilic drug (epirubicin) could be loaded in the spheres with encapsulation rate measured to be 72.25%. The lipophilic fluorescent dye rhodamine B was also loadable in the spheres with red fluorescence being observed under a fluorescence microscope. We have developed a novel approach to an in situ process for fabricating oil-chitosan composite spheres with dual encapsulation properties, which are potential multifunctional drug carriers. PMID:23681059
Extrinsic Calibration of Camera Networks Using a Sphere.
Guan, Junzhi; Deboeverie, Francis; Slembrouck, Maarten; van Haerenborgh, Dirk; van Cauwelaert, Dimitri; Veelaert, Peter; Philips, Wilfried
2015-08-04
In this paper, we propose a novel extrinsic calibration method for camera networks using a sphere as the calibration object. First of all, we propose an easy and accurate method to estimate the 3D positions of the sphere center w.r.t. the local camera coordinate system. Then, we propose to use orthogonal procrustes analysis to pairwise estimate the initial camera relative extrinsic parameters based on the aforementioned estimation of 3D positions. Finally, an optimization routine is applied to jointly refine the extrinsic parameters for all cameras. Compared to existing sphere-based 3D position estimators which need to trace and analyse the outline of the sphere projection in the image, the proposed method requires only very simple image processing: estimating the area and the center of mass of the sphere projection. Our results demonstrate that we can get a more accurate estimate of the extrinsic parameters compared to other sphere-based methods. While existing state-of-the-art calibration methods use point like features and epipolar geometry, the proposed method uses the sphere-based 3D position estimate. This results in simpler computations and a more flexible and accurate calibration method. Experimental results show that the proposed approach is accurate, robust, flexible and easy to use.
Self-assembled clusters of spheres related to spherical codes.
Phillips, Carolyn L; Jankowski, Eric; Marval, Michelle; Glotzer, Sharon C
2012-10-01
We consider the thermodynamically driven self-assembly of spheres onto the surface of a central sphere. This assembly process forms self-limiting, or terminal, anisotropic clusters (N-clusters) with well-defined structures. We use Brownian dynamics to model the assembly of N-clusters varying in size from two to twelve outer spheres and free energy calculations to predict the expected cluster sizes and shapes as a function of temperature and inner particle diameter. We show that the arrangements of outer spheres at finite temperatures are related to spherical codes, an ideal mathematical sequence of points corresponding to the densest possible sphere packings. We demonstrate that temperature and the ratio of the diameters of the inner and outer spheres dictate cluster morphology. We present a surprising result for the equilibrium structure of a 5-cluster, for which the square pyramid arrangement is preferred over a more symmetric structure. We show this result using Brownian dynamics, a Monte Carlo simulation, and a free energy approximation. Our results suggest a promising way to assemble anisotropic building blocks from constituent colloidal spheres. PMID:23214546
Magnetic properties of cubic FeCo nanoparticles with anisotropic long chain structure
NASA Astrophysics Data System (ADS)
Liu, Jinming; Wu, Kai; Wang, Jian-Ping
2016-05-01
Cubic FeCo alloy nanoparticles (NPs) with body-centered cubic (bcc) phase were prepared using sputter based gas-condensation method. When the NPs formed long chain assemblies, the magnetic properties were quite different from that of well-dispersed NPs. Most of the well-dispersed NPs were superparamagnetic at room temperature while the long chain NP assemblies were ferromagnetic with coercivities around 765 Oe, which displayed quite different magnetic properties. The ferromagnetism of long chain NPs was from the exchange coupling between NPs, which eventually led to the transition from superparamagnetism (SPM) to superferromagetism (SFM). Zero-field-cooled (ZFC) and field-cooled (FC) curves were obtained and long chain NP assemblies displayed ferromagnetism at the temperature ranging from 10 K to 400 K. Time-dependent remanent magnetic moment curves also indicated that the long chain structure had better thermal stability due to the strong exchange coupling.
Curie temperatures of cubic (Ga, Mn)N diluted magnetic semiconductors from the RKKY spin model.
Zhu, Li-Fang; Liu, Bang-Gui
2009-11-01
We explore how much the RKKY spin interaction can contribute to the high-temperature ferromagnetism in cubic (Ga, Mn)N diluted magnetic semiconductors. The usual coupling constant is used and effective carriers are considered independent of doped magnetic atoms, as is shown experimentally. Our Monte Carlo simulated results show that maximal Curie temperature is reached at the optimal carrier concentration for a given Mn concentration, equaling 373 K for 5% Mn and 703 K for 8% Mn. Because such a Monte Carlo method does not overestimate transition temperatures, these calculations indicate that the RKKY spin interaction alone can yield high-enough Curie temperatures in cubic (Ga, Mn)N under optimized conditions.
Zhang, Youjin Yao, Chengpeng; Fan, Yun; Zhou, Maozhong
2014-11-15
Highlights: • Orthorhombic PrCrO{sub 3} cubic particles were prepared by a simple and facile one-step hydrothermal method. • The possible formation mechanism of PrCrO{sub 3} cubic particles was proposed. • The as-synthesized PrCrO{sub 3} exhibited behaviors of magnetic transition and negative magnetization. - Abstract: Orthorhombic PrCrO{sub 3} cubic particles were synthesized by a simple and facile one-step hydrothermal method of processing temperature 280 °C for 7 days. The products prepared in this paper have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and field-emission scanning electron microscopy (FESEM). The magnetic properties of the final sample are also studied. The XRD pattern shows the pure orthorhombic phase for PrCrO{sub 3} particles, the XPS and FTIR results further demonstrate the purity and composition of the product. FESEM images show cubic morphology for the PrCrO{sub 3} particles. The possible growth mechanism for PrCrO{sub 3} cubic particles is proposed. Through the investigation of magnetic properties, it can be seen that the orthorhombic PrCrO{sub 3} cubic particles exhibit behaviors of magnetic transition and negative magnetization. The Néel temperature is about 232 K and the magnetic hysteresis loop under 4 K shows that the coercivity (H{sub C}) and remanence (M{sub r}) is about 1728 Oe and 4.88 emu/g, respectively.
From Ewald sphere to Ewald shell in nonlinear optics
NASA Astrophysics Data System (ADS)
Huang, Huang; Huang, Cheng-Ping; Zhang, Chao; Hong, Xu-Hao; Zhang, Xue-Jin; Qin, Yi-Qiang; Zhu, Yong-Yuan
2016-07-01
Ewald sphere is a simple vector scheme to depict the X-ray Bragg diffraction in a crystal. A similar method, known as the nonlinear Ewald sphere, was employed to illustrate optical frequency conversion processes. We extend the nonlinear Ewald sphere to the Ewald shell construction. With the Ewald shell, a variety of quasi-phase-matching (QPM) effects, such as the collective envelope effect associated with multiple QPM resonances, the enhanced second- harmonic generation due to multiple reciprocal vectors etc., are suggested theoretically and verified experimentally. By rotating the nonlinear photonic crystal sample, the dynamic evolution of these QPM effects has also been observed, which agreed well with the Ewald shell model.
Hollow carbon spheres in microwaves: Bio inspired absorbing coating
NASA Astrophysics Data System (ADS)
Bychanok, D.; Li, S.; Sanchez-Sanchez, A.; Gorokhov, G.; Kuzhir, P.; Ogrin, F. Y.; Pasc, A.; Ballweg, T.; Mandel, K.; Szczurek, A.; Fierro, V.; Celzard, A.
2016-01-01
The electromagnetic response of a heterostructure based on a monolayer of hollow glassy carbon spheres packed in 2D was experimentally surveyed with respect to its response to microwaves, namely, the Ka-band (26-37 GHz) frequency range. Such an ordered monolayer of spheres mimics the well-known "moth-eye"-like coating structures, which are widely used for designing anti-reflective surfaces, and was modelled with the long-wave approximation. Based on the experimental and modelling results, we demonstrate that carbon hollow spheres may be used for building an extremely lightweight, almost perfectly absorbing, coating for Ka-band applications.
Potential Polymeric Sphere Construction Materials for a Spacecraft Electrostatic Shield
NASA Technical Reports Server (NTRS)
Smith, Joseph G., Jr.; Smith, Trent; Williams, Martha; Youngquist, Robert; Mendell, Wendell
2006-01-01
An electrostatic shielding concept for spacecraft radiation protection under NASA s Exploration Systems Research and Technology Program was evaluated for its effectiveness and feasibility. The proposed shield design is reminiscent of a classic quadrupole with positively and negatively charged spheres surrounding the spacecraft. The project addressed materials, shield configuration, power supply, and compared its effectiveness to that of a passive shield. The report herein concerns the identification of commercially available materials that could be used in sphere fabrication. It was found that several materials were needed to potentially construct the spheres for an electrostatic shield operating at 300 MV.
Submicrometer-sized hollow nickel spheres synthesized by autocatalytic reduction
Deng Yida . E-mail: denyda@sjtu.edu.cn; Zhao Ling; Liu Lei; Shen Bin; Hu Wenbin
2005-10-06
A facile method to fabricate submicrometer-sized hollow nickel spheres by autocatalyzing the redox reaction around a sacrificial colloidal particle surface is presented in this paper. The size distribution of these spheres can be controlled by regulating the concentration of the alkali solution. The hollow nickel particles were characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray powder diffraction. The hollow spheres produced by this process may have potential applications in many fields, including chemistry, biotechnology and materials science.
Spherical interferometry for the characterization of precision spheres
NASA Astrophysics Data System (ADS)
Nicolaus, R. A.; Bartl, G.
2016-09-01
Interferometry with spherical wavefronts is usually used for characterizing precise optics. A special spherical interferometer was set up to measure the volume of high precision spheres used for the new definition of the SI unit kilogram, for which a fundamental constant, such as Planck’s constant h or Avogadro’s constant N A, was to be determined. Furthermore with this type of interferometer and with a special evaluating algorithm, absolute form deviations of spheres can be determined. With this knowledge, a sphere can be processed further to reach unrivaled small sphericity deviations.
Preparation of nuclear fuel spheres by flotation-internal gelation
Haas, Paul A.; Fowler, Victor L.; Lloyd, Milton H.
1987-01-01
A simplified internal gelation process for the preparation of gel spheres of nuclear fuels. The process utilizes perchloroethylene as a gelation medium. Gelation is accomplished by directing droplets of a nuclear fuel broth into a moving volume of hot perchloroethylene (about 85.degree. C.) in a trough. Gelation takes place as the droplets float on the surface of the perchloroethylene and the resultant gel spheres are carried directly into an ager column which is attached to the trough. The aged spheres are disengaged from the perchloroethylene on a moving screen and are deposited in an aqueous wash column.
Cubic ice and large humidity with respect to ice in cold cirrus clouds
NASA Astrophysics Data System (ADS)
Bogdan, A.; Loerting, T.
2009-04-01
Recently several studies have reported about the possible formation of cubic ice in upper-tropospheric cirrus ice clouds and its role in the observed elevated relative humidity with respect to hexagonal ice, RHi, within the clouds. Since cubic ice is metastable with respect to stable hexagonal ice, its vapour pressure is higher. A key issue in determining the ratio of vapour pressures of cubic ice Pc and hexagonal ice Ph is the enthalpy of transformation from cubic to hexagonal ice Hcâh. By dividing the two integrated forms of the Clausius-Clapeyron equation for cubic ice and hexagonal ice, one obtains the relationship (1): ln Pc-- ln P*c-=--(Hcâh--) Ph P*h R 1T-- 1T* (1) from which the importance of Hcâh is evident. In many literature studies the approximation (2) is used: ln Pc-= Hc-âh. Ph RT (2) Using this approximated form one can predict the ratio of vapour pressures by measuring Hcâh. Unfortunately, the measurement of Hcâh is difficult. First, the enthalpy difference is very small, and the transition takes place over a broad temperature range, e.g., between 230 K and 260 K in some of our calorimetry experiments. Second, cubic ice (by contrast to hexagonal ice) can not be produced as a pure crystal. It always contains hexagonal stacking faults, which are evidenced by the (111)-hexagonal Bragg peak in the powder diffractogram. If the number of hexagonal stacking faults in cubic ice is high, then one could even consider this material as hexagonal ice with cubic stacking faults. Using the largest literature value of the change of enthalpy of transformation from cubic to hexagonal ice, Hcâh ? 160 J/mol, Murphy and Koop (2005) calculated that Pc would be ~10% higher than that of hexagonal ice Phat 180 K - 190 K, which agrees with the measurements obtained later by Shilling et al. (2006). Based on this result Shilling et al. concluded that "the formation of cubic ice at T < 202 K may significantly contribute to the persistent in
"Outer-sphere to inner-sphere" redox cycling for ultrasensitive immunosensors.
Akanda, Md Rajibul; Choe, Yu-Lim; Yang, Haesik
2012-01-17
This paper reports chemical-chemical (CC) and electrochemical-chemical-chemical (ECC) redox cycling, for use in ultrasensitive biosensor applications. A triple chemical amplification approach using an enzymatic reaction, CC redox cycling, and ECC redox cycling is applied toward electrochemical immunosensors of cardiac troponin I. An enzymatic reaction, in which alkaline phosphatase converts 4-aminophenyl phosphate to 4-aminophenol (AP), triggers CC redox cycling in the presence of an oxidant and a reductant, and electrochemical signals are measured with ECC redox cycling after an incubation period of time in an air-saturated solution. To obtain high, selective, and reproducible redox cycling without using redox enzymes, two redox reactions [the reaction between AP and the oxidant and the reaction between the oxidized form of AP (4-quinone imine, QI) and the reductant] should be fast, but an unwanted reaction between the oxidant and reductant should be very slow. Because species that undergo outer-sphere reactions (OSR-philic species) react slowly with species that undergo inner-sphere reactions (ISR-philic species), highly OSR-philic Ru(NH(3))(6)(3+) and highly ISR-philic tris(2-carboxyethyl)phosphine (TCEP) are chosen as the oxidant and reductant, respectively. The OSR- and ISR-philic QI/AP couple allows fast redox reactions with both the OSR-philic Ru(NH(3))(6)(3+) and the ISR-philic TCEP. Highly OSR-philic indium-tin oxide (ITO) electrodes minimize unwanted electrochemical reactions with highly ISR-philic species. Although the formal potential of the Ru(NH(3))(6)(3+)/Ru(NH(3))(6)(2+) couple is lower than that of the QI/AP couple, the endergonic reaction between Ru(NH(3))(6)(3+) and AP is driven by the highly exergonic reaction between TCEP and QI (via a coupled reaction mechanism). Overall, the "outer-sphere to inner-sphere" redox cycling in the order of highly OSR-philic ITO, highly OSR-philic Ru(NH(3))(6)(3+)/Ru(NH(3))(6)(2+) couple, OSR- and ISR-philic QI
Direct measurement of the free energy of aging hard sphere colloidal glasses.
Zargar, Rojman; Nienhuis, Bernard; Schall, Peter; Bonn, Daniel
2013-06-21
The nature of the glass transition is one of the most important unsolved problems in condensed matter physics. The difference between glasses and liquids is believed to be caused by very large free energy barriers for particle rearrangements; however, so far it has not been possible to confirm this experimentally. We provide the first quantitative determination of the free energy for an aging hard sphere colloidal glass. The determination of the free energy allows for a number of new insights in the glass transition, notably the quantification of the strong spatial and temporal heterogeneity in the free energy. A study of the local minima of the free energy reveals that the observed variations are directly related to the rearrangements of the particles. Our main finding is that the probability of particle rearrangements shows a power law dependence on the free energy changes associated with the rearrangements similar to the Gutenberg-Richter law in seismology. PMID:23829762
Correspondence between sonic points of ideal photon gas accretion and photon spheres
NASA Astrophysics Data System (ADS)
Koga, Yasutaka; Harada, Tomohiro
2016-08-01
In the accretion flow of a fluid, its velocity may transit from subsonic to supersonic. The point at which such a transition occurs is called the sonic point and is often mathematically special. We consider the steady-state and spherically symmetric accretion problem of an ideal photon gas in general static spherically symmetric spacetimes, neglecting backreaction. Our main result is that the equation of state (EOS) of an ideal photon gas leads to a correspondence between its sonic point and the photon sphere of the spacetime in general situations. Moreover, we also show that in spite of the dependence of the EOS on the dimension of spacetime, this correspondence holds for spacetimes of arbitrary dimensions.
Intracellular Degradable Hydrogel Cubes and Spheres for Anti-Cancer Drug Delivery.
Xue, Bing; Kozlovskaya, Veronika; Liu, Fei; Chen, Jun; Williams, J Fox; Campos-Gomez, Javier; Saeed, Mohammad; Kharlampieva, Eugenia
2015-06-24
Shape and responsiveness of nanoengineered delivery carriers are crucial characteristics for rapid and efficient delivery of therapeutics. We report on a novel type of micrometer-sized hydrogel particles of controlled shape with dual pH- and redox-sensitivity for intracellular delivery of anticancer drugs. The cubical and spherical poly(methacrylic acid) (PMAA) networks with disulfide links are obtained by cross-linking PMAA with cystamine within hydrogen-bonded multilayers of PMAA/poly(vinylpyrrolidone) (PMAA/PVPON) on sacrificial mesoporous templates. The pH-triggered hydrogel swelling/shrinkage not only affords effective doxorubicin entrapment but also efficient endosomal/lysosomal escape, and redox-triggered degradation provides drug release into the cytosolic space. The hydrogels degrade rapidly to low molecular weight chains in the presence of the typical intracellular concentration of glutathione, which should ensure a rapid renal clearance in vivo. Particle shape is found to affect internalization at the initial step of cell-particle interactions. Drug-loaded spherical particles are found to be 12% more cytotoxic than the corresponding cubes within the first 10 h of cell incubation suggesting more rapid internalization of spheres. Both doxorubicin-loaded hydrogel cubes and spheres demonstrate 50% and 90% cytotoxicity when incubated with HeLa cancer cells for 24 and 48 h, respectively. The presented approach integrates the advantages of pH-sensitivity, enzymatic degradation, and shape-regulated internalization for novel types of "intelligent" three-dimensional networks with programmable behavior for use in controlled delivery of therapeutics.
NASA Astrophysics Data System (ADS)
Haswell, Carole A.
2010-07-01
1. Our solar system from afar; 2. Exoplanet discoveries by the transit method; 3. What the transit lightcurve tells us; 4. The transiting exoplanet population; 5. Transmission spectroscopy and Rossiter-McLaughlin effect; 6. Secondary eclipses and phase variations; 7. Transit timing variations and orbital dynamics; 8. Brave new worlds: the future; Index.
Cubic membranes: a structure-based design for DNA uptake.
Almsherqi, Zakaria; Hyde, Stephen; Ramachandran, Malarmathy; Deng, Yuru
2008-09-01
Cubic membranes are soft three-dimensional crystals found within cell organelles in a variety of living systems, despite the aphorism of Fedorov: 'crystallization is death'. They consist of multi-bilayer lipid-protein stacks, folded onto anticlastic surfaces that resemble triply periodic minimal surfaces, forming highly swollen crystalline sponges. Although cubic membranes have been observed in numerous cell types and under different pathophysiological conditions, knowledge about the formation and potential function(s) of non-lamellar, cubic structures in biological systems is scarce. We report that mitochondria with this cubic membrane organization isolated from starved amoeba Chaos carolinense interact sufficiently with short segments of phosphorothioate oligonucleotides (PS-ODNs) to give significant ODNs uptake. ODNs condensed within the convoluted channels of cubic membrane by an unknown passive targeting mechanism. Moreover, the interaction between ODNs and cubic membrane is sufficient to retard electrophoretic mobility of the ODN component in the gel matrix. These ODN-cubic membrane complexes are readily internalized within the cytoplasm of cultured mammalian cells. Transmission electron microscopic analysis confirms ODNs uptake by cubic membranes and internalization of ODN-cubic membrane complexes into the culture cells. Cubic membranes thus may offer a new, potentially benign medium for gene transfection. PMID:18270148
A colloidal model system with an interaction tunable from hard sphere to soft and dipolar.
Yethiraj, Anand; van Blaaderen, Alfons
2003-01-30
Monodisperse colloidal suspensions of micrometre-sized spheres are playing an increasingly important role as model systems to study, in real space, a variety of phenomena in condensed matter physics--such as glass transitions and crystal nucleation. But to date, no quantitative real-space studies have been performed on crystal melting, or have investigated systems with long-range repulsive potentials. Here we demonstrate a charge- and sterically stabilized colloidal suspension--poly(methyl methacrylate) spheres in a mixture of cycloheptyl (or cyclohexyl) bromide and decalin--where both the repulsive range and the anisotropy of the interparticle interaction potential can be controlled. This combination of two independent tuning parameters gives rise to a rich phase behaviour, with several unusual colloidal (liquid) crystalline phases, which we explore in real space by confocal microscopy. The softness of the interaction is tuned in this colloidal suspension by varying the solvent salt concentration; the anisotropic (dipolar) contribution to the interaction potential can be independently controlled with an external electric field ranging from a small perturbation to the point where it completely determines the phase behaviour. We also demonstrate that the electric field can be used as a pseudo-thermodynamic temperature switch to enable real-space studies of melting transitions. We expect studies of this colloidal model system to contribute to our understanding of, for example, electro- and magneto-rheological fluids.
Hydrothermal vents and methane seeps: Rethinking the sphere of influence
Levin, Lisa A.; Baco, Amy; Bowden, David; Colaco, Ana; Cordes, Erik E.; Cunha, Marina; Demopoulos, Amanda; Gobin, Judith; Grupe, Ben; Le, Jennifer; Metaxas, Anna; Netburn, Amanda; Rouse, Greg; Thurber, Andrew; Tunnicliffe, Verena; Van Dover, Cindy L.; Vanreusel, Ann; Watling, Les
2016-01-01
regional oceanography and biodiversity. Many ecosystem services are associated with the interactions and transitions between chemosynthetic and background ecosystems, for example carbon cycling and sequestration, fisheries production, and a host of non-market and cultural services. The quantification of the sphere of influence of vents and seeps could be beneficial to better management of deep-sea environments in the face of growing industrialization.
Tidally Driven Dynamos in a Rotating Sphere
NASA Astrophysics Data System (ADS)
Cébron, D.; Hollerbach, R.
2014-07-01
Large-scale planetary or stellar magnetic fields generated by a dynamo effect are mostly attributed to flows forced by buoyancy forces in electrically conducting fluid layers. However, these large-scale fields may also be controlled by tides, as previously suggested for the star τ-boo, Mars, or the early Moon. By simulating a small local patch of a rotating fluid, Barker & Lithwick have recently shown that tides can drive small-scale dynamos by exciting a hydrodynamic instability, the so-called elliptical (or tidal) instability. By performing global magnetohydrodynamic simulations of a rotating spherical fluid body, we investigate if this instability can also drive the observed large-scale magnetic fields. We are thus interested in the dynamo threshold and the generated magnetic field in order to test if such a mechanism is relevant for planets and stars. Rather than solving the problem in a geometry deformed by tides, we consider a spherical fluid body and add a body force to mimic the tidal deformation in the bulk of the fluid. This allows us to use an efficient spectral code to solve the magnetohydrodynamic problem. We first compare the hydrodynamic results with theoretical asymptotic results and numerical results obtained in a truly deformed ellipsoid, which confirms the presence of elliptical instability. We then perform magnetohydrodynamic simulations and investigate the dynamo capability of the flow. Kinematic and self-consistent dynamos are finally simulated, showing that the elliptical instability is capable of generating a dipole-dominated large-scale magnetic field in global simulations of a fluid rotating sphere.
TIDALLY DRIVEN DYNAMOS IN A ROTATING SPHERE
Cébron, D.; Hollerbach, R. E-mail: r.hollerbach@leeds.ac.uk
2014-07-01
Large-scale planetary or stellar magnetic fields generated by a dynamo effect are mostly attributed to flows forced by buoyancy forces in electrically conducting fluid layers. However, these large-scale fields may also be controlled by tides, as previously suggested for the star τ-boo, Mars, or the early Moon. By simulating a small local patch of a rotating fluid, Barker and Lithwick have recently shown that tides can drive small-scale dynamos by exciting a hydrodynamic instability, the so-called elliptical (or tidal) instability. By performing global magnetohydrodynamic simulations of a rotating spherical fluid body, we investigate if this instability can also drive the observed large-scale magnetic fields. We are thus interested in the dynamo threshold and the generated magnetic field in order to test if such a mechanism is relevant for planets and stars. Rather than solving the problem in a geometry deformed by tides, we consider a spherical fluid body and add a body force to mimic the tidal deformation in the bulk of the fluid. This allows us to use an efficient spectral code to solve the magnetohydrodynamic problem. We first compare the hydrodynamic results with theoretical asymptotic results and numerical results obtained in a truly deformed ellipsoid, which confirms the presence of elliptical instability. We then perform magnetohydrodynamic simulations and investigate the dynamo capability of the flow. Kinematic and self-consistent dynamos are finally simulated, showing that the elliptical instability is capable of generating a dipole-dominated large-scale magnetic field in global simulations of a fluid rotating sphere.
Turbulent mixing in a precessing sphere
Goto, Susumu Shimizu, Masaki; Kawahara, Genta
2014-11-15
By numerically simulating turbulent flows at high Reynolds numbers in a precessing sphere, we propose a method to enhance the mixing of a fluid confined within a smooth cavity by its rotational motion alone. To precisely evaluate the mixing efficiency, we extend the quantification method proposed by Danckwerts [“The definition and measurement of some characteristics of mixtures,” Appl. Sci. Res. A 3, 279–296 (1952)] to the case in which only a finite number of fluid particle trajectories can be known. Our accurate numerical tracking of fluid particles in the flow, which is controlled by the Reynolds number (an indicator of the spin rate) and the Poincaré number (the precession rate), shows the following results. First, the mixing process on the time scale normalized by the spin period is independent of the Reynolds number as long as it is high enough for the flow to be developed turbulence. Second, fastest mixing is achieved under weak precession (Poincaré number ≈0.1); in such cases, perfect mixing requires only 10–15 spins of the container. Third, the power to sustain turbulence is a weakly increasing function of the Poincaré number, and the energy efficiency of the mixing is also maximized when the Poincaré number is about 0.1. Fourth, efficient mixing driven by the weak precession arises from the effective cooperation of complex large-scale flow and small-scale turbulence, which itself is sustained by the large-scale flow.
Unusual thermodynamics on the fuzzy 2-sphere
NASA Astrophysics Data System (ADS)
Digal, Sanatan; Padmanabhan, Pramod
2010-10-01
Higher spin Dirac operators on both the continuum sphere( S 2) and its fuzzy analog( S {F/2}) come paired with anticommuting chirality operators. A consequence of this is seen in the fermion-like spectrum of these operators which is especially true even for the case of integer-spin Dirac operators. Motivated by this feature of the spectrum of a spin 1 Dirac operator on S {F/2}, we assume the spin 1 particles obey Fermi-Dirac statistics. This choice is inspite of the lack of a well defined spin-statistics relation on a compact surface such as S 2. The specific heats are computed in the cases of the spin 1/2 and spin 1 Dirac operators. Remarkably the specific heat for a system of spin 1/2 particles is more than that of the spin 1 case, though the number of degrees of freedom is more in the case of spin 1 particles. The reason for this is inferred through a study of the spectrums of the Dirac operators in both the cases. The zero modes of the spin 1 Dirac operator is studied as a function of the cut-off angular momentum L and is found to follow a simple power law. This number is such that the number of states with positive energy for the spin 1 and spin 1/2 system become comparable. Remarks are made about the spectrums of higher spin Dirac operators as well through a study of their zero-modes and the variation of their spectrum with degeneracy. The mean energy as a function of temperature is studied in both the spin 1/2 and spin 1 cases. They are found to deviate from the standard ideal gas law in 2+ 1 dimensions.
3. VIEW NORTHWEST OF VACUUM SPHERES 168 AND 146 ...
3. VIEW NORTHWEST OF VACUUM SPHERES 168 AND 146 - Naval Surface Warfare Center, Supersonic Wind Tunnel Building, Bounded by Clara Barton Parkway & McArthur Boulevard, Silver Spring, Montgomery County, MD
2. VIEW SOUTHEAST OF VACUUM SPHERES 146 AND 168 ...
2. VIEW SOUTHEAST OF VACUUM SPHERES 146 AND 168 - Naval Surface Warfare Center, Supersonic Wind Tunnel Building, Bounded by Clara Barton Parkway & McArthur Boulevard, Silver Spring, Montgomery County, MD
Numerical Flow Visualization in Basic- and Hyper-Cluster Spheres
NASA Technical Reports Server (NTRS)
Hendricks, R. C.; Athavale, M. M.; Braun, M. J.; Lattime, S.
1997-01-01
Packed spherical particle beds have wide applications throughout the process industry and are usually analyzed using an appropriate combination of laminar and turbulent flows with empirically derived coefficients of which the Ergun (1952) relation is probably the best known. The 3-D complexity of the void distribution within the beds has precluded detailed studies of sphere clusters. Numerical modeling and flow vector visualization for the basic tetra- and hexa-sphere clusters and two hyper-sphere clusters are presented at two Reynolds numbers, 400 and 1200. Cutting planes are used to enable visualization of the complex flows generated within the sphere clusters and are discussed herein. The boundary conditions and flow fields for the simple clusters are also compared to the hyper-clusters with larger variations found for hexa-clusters.
Liquid trampolines: droplets and spheres bouncing off soap films
NASA Astrophysics Data System (ADS)
Courbin, Laurent; Dubail, Jerome; Crotiere, Suzie; Quere, David
2005-11-01
We report on the impact of rigid spheres and liquid droplets on soap films. These systems exhibit a rich variety of dynamics including bouncing and adhesion. In the case of drop impact, at low speeds the drops bounce, while for intermediate speeds the drops can pass through the film without the film breaking. The bouncing can be analyzed using mechanical models. In the case of the impact of rigid spheres, by tuning the physical property of the surface of the impacting sphere, which may or may not be surrounded by a skin of oil, we experimentally observe two distinct regimes: the solid sphere can bounce off of the fluid film or get entrapped. In all cases the film can be considered an absorber of kinetic energy. Finally, the possibility of tuning the bounce of an object will be presented.
Analysis of integrating sphere performance for IR enhanced DT layering
Stephens, R.B.,; Collins, G.W.
1997-06-01
Absorbed IR energy can supplement the beta decay energy from DT ice to improve the driving force toward uniform layers. A significant problem with this approach has been to deliver the added IR energy with sufficient uniformity to enhance rather than destroy the uniformity of the ice layers. Computer modeling has indicated that one can achieve {approximately}1% uniformity in the angular variation of the absorbed power using an integrating sphere containing holes large enough to allow external inspection of the ice layer uniformity. The power required depends on the integrating sphere size, a 25 mm diameter sphere requires {approximately}35 mW of IR to deposit as much energy in the ice as the 50 mW/cm{sup 3}(35 pW total) received from tritium decay in DT. Power absorbed in the plastic can cause unacceptable ice-layer non-uniformities for the integrating sphere design considered here.
The Volume of a Sphere: A Chinese Derivation.
ERIC Educational Resources Information Center
Swetz, Frank J.
1995-01-01
Examines how ancient Chinese mathematicians attempted to correct an error concerning the volume of a sphere in the Nine Chapters on the Mathematical Art, a compendium of the mathematics known and used in China in ancient times. (MKR)
Method for producing dustless graphite spheres from waste graphite fines
Pappano, Peter J; Rogers, Michael R
2012-05-08
A method for producing graphite spheres from graphite fines by charging a quantity of spherical media into a rotatable cylindrical overcoater, charging a quantity of graphite fines into the overcoater thereby forming a first mixture of spherical media and graphite fines, rotating the overcoater at a speed such that the first mixture climbs the wall of the overcoater before rolling back down to the bottom thereby forming a second mixture of spherical media, graphite fines, and graphite spheres, removing the second mixture from the overcoater, sieving the second mixture to separate graphite spheres, charging the first mixture back into the overcoater, charging an additional quantity of graphite fines into the overcoater, adjusting processing parameters like overcoater dimensions, graphite fines charge, overcoater rotation speed, overcoater angle of rotation, and overcoater time of rotation, before repeating the steps until graphite fines are converted to graphite spheres.
Prototype sphere-on-sphere silica particles for the separation of large biomolecules.
Fekete, Szabolcs; Rodriguez-Aller, Marta; Cusumano, Alessandra; Hayes, Richard; Zhang, Haifei; Edge, Tony; Veuthey, Jean-Luc; Guillarme, Davy
2016-01-29
The goal of this study was to evaluate the possibilities offered by a prototype HPLC column packed with ∼2.5μm narrow size distribution sphere-on-sphere (SOS) silica particles bonded with C4 alkyl chains, for the analytical characterization of large biomolecules. The kinetic performance of this material was evaluated in both isocratic and gradient modes using various model analytes. The data were compared to those obtained on other widepore state-of-the-art fully core-shell and fully porous materials commonly employed to separate proteins moreover to a reference 5μm wide pore material that is still often used in QC labs. In isocratic mode, minimum reduced plate height values of hmin=2.6, 3.3 and 3.3 were observed on butylparaben, decapeptide and glucagon, respectively. In gradient elution mode, the SOS column performs very high efficiency when working with fast gradients. This prototype column was also comparable (and sometimes superior) to other widepore stationary phases, whatever the gradient time and flow rate, when analyzing the largest model protein, namely BSA. These benefits may be attributed to the SOS particle morphology, minimizing the intra-particle mass transfer resistance. Finally, the SOS column was also applied for the analytical characterization of commercial monoclonal antibody (mAb) and antibody-drug conjugate (ADC) samples. With these classes of proteins, the performance of SOS column was similar to the best widepore stationary phases available on the market.
Prototype sphere-on-sphere silica particles for the separation of large biomolecules.
Fekete, Szabolcs; Rodriguez-Aller, Marta; Cusumano, Alessandra; Hayes, Richard; Zhang, Haifei; Edge, Tony; Veuthey, Jean-Luc; Guillarme, Davy
2016-01-29
The goal of this study was to evaluate the possibilities offered by a prototype HPLC column packed with ∼2.5μm narrow size distribution sphere-on-sphere (SOS) silica particles bonded with C4 alkyl chains, for the analytical characterization of large biomolecules. The kinetic performance of this material was evaluated in both isocratic and gradient modes using various model analytes. The data were compared to those obtained on other widepore state-of-the-art fully core-shell and fully porous materials commonly employed to separate proteins moreover to a reference 5μm wide pore material that is still often used in QC labs. In isocratic mode, minimum reduced plate height values of hmin=2.6, 3.3 and 3.3 were observed on butylparaben, decapeptide and glucagon, respectively. In gradient elution mode, the SOS column performs very high efficiency when working with fast gradients. This prototype column was also comparable (and sometimes superior) to other widepore stationary phases, whatever the gradient time and flow rate, when analyzing the largest model protein, namely BSA. These benefits may be attributed to the SOS particle morphology, minimizing the intra-particle mass transfer resistance. Finally, the SOS column was also applied for the analytical characterization of commercial monoclonal antibody (mAb) and antibody-drug conjugate (ADC) samples. With these classes of proteins, the performance of SOS column was similar to the best widepore stationary phases available on the market. PMID:26755414
Silica hollow spheres with nano-macroholes like diatomaceous earth.
Fujiwara, Masahiro; Shiokawa, Kumi; Sakakura, Ikuko; Nakahara, Yoshiko
2006-12-01
Artificial synthesis of hollow cell walls of diatoms is an ultimate target of nanomaterial science. The addition of some water-soluble polymers such as sodium polymethacrylate to a solution of water/oil/water emulsion system, which is an essential step of the simple synthetic procedure of silica hollow spheres (microcapsules), led to the formation of silica hollow spheres with nano-macroholes (>100 nm) in their shell walls, the morphologies of which are analogous to those of diatom earth.
Integrating sphere transmissometer for field measurement of leaf transmittance
NASA Astrophysics Data System (ADS)
Vanderbilt, V. C.; Dewitt, D. P.; Robinson, B. F.
1987-12-01
A simple field-rated transmissometer is described for rapidly determining the normal hemispherical transmittance T(0 deg, 2 pi) of leaves measured in situ in the four Landsat wavelength bands. The transmissometer requires direct solar illumination of the leaf sample. It collects the transmitted light with an integrating sphere and measures the collected light using a commercially available radiometer. The transmittances determined by the transmissometer are comparable with those measured by a labortory spectrophotometer with an integrating sphere attachment.
Microwave characterization of submicrometer-sized nickel hollow sphere composites
NASA Astrophysics Data System (ADS)
Deng, Yida; Zhao, Ling; Shen, Bin; Liu, Lei; Hu, Wenbin
2006-07-01
In this work, we report on the microwave properties of the nickel hollow spheres (NHSs) synthesized by a facile autocatalytic reduction method. The resonance characterization of the NHS-polyvinyl butyral composite, due to the skin effect, is observed in the microwave frequency. It is shown that the resonant and the matching frequencies of the composite largely depend on the particle size of the spheres.
Economic dependency and divorce: implications for the private sphere.
Clark, R
1990-01-01
"This paper asserts a connection between economic dependency and divorce. It argues that, because dependency deprives women of equal access to the public sphere and because it confines them, through normative definition, to the private sphere, it reduces their likelihood of seeking divorce. The paper also argues, contrary to recent findings, that socioeconomic development should be linearly and positively associated with divorce. Data from 51 nations are examined and multiple regression analysis [suggests] considerable support for these arguments." PMID:12283805
Low Velocity Sphere Impact of a Soda Lime Silicate Glass
Wereszczak, Andrew A; Fox, Ethan E; Morrissey, Timothy G; Vuono, Daniel J
2011-10-01
This report summarizes TARDEC-sponsored work at Oak Ridge National Laboratory (ORNL) during the FY11 involving low velocity (< 30 m/s or < 65 mph) ball impact testing of Starphire soda lime silicate glass. The intent was to better understand low velocity impact response in the Starphire for sphere densities that bracketed that of rock. Five sphere materials were used: borosilicate glass, soda-lime silicate glass, steel, silicon nitride, and alumina. A gas gun was fabricated to produce controlled velocity delivery of the spheres against Starphire tile targets. Minimum impact velocities to initiate fracture in the Starphire were measured and interpreted in context to the kinetic energy of impact and the elastic property mismatch between the any of the five sphere-Starphire-target combinations. The primary observations from this low velocity (< 30 m/s or < 65 mph) testing were: (1) Frictional effects contribute to fracture initiation. (2) Spheres with a lower elastic modulus require less force to initiate fracture in the Starphire than spheres with a higher elastic modulus. (3) Contact-induced fracture did not initiate in the Starphire SLS for impact kinetic energies < 150 mJ. Fracture sometimes initiated or kinetic energies between {approx} 150-1100 mJ; however, it tended to occur when lower elastic modulus spheres were impacting it. Contact-induced fracture would always occur for impact energies > 1100 mJ. (4) The force necessary to initiate contact-induced fracture is higher under dynamic or impact conditions than it is under quasi-static indentation conditions. (5) Among the five used sphere materials, silicon nitride was the closest match to 'rock' in terms of both density and (probably) elastic modulus.
Intensive drying and the related microstructure features in agglomerate spheres
NASA Astrophysics Data System (ADS)
Kudlyk, Rostyslav
Most metal ore concentrates are fine particulates with a wide particle-size distribution. Industrially they are pelletized by tumbling in balling discs or drums into spheres, an operation which requires the addition of typically up to 10% by weight of water. Further processing of these agglomerates involves first drying and then induration by heating up to 1250°C. The main objective of this thesis was the study of the interrelationship between the microstructure of the agglomerates with, on the one hand, the mechanical and physical properties of the pellets and their behaviour during intensive drying, on the other. The previously developed model of the drying process identified the loss of capillarity, resulting from the vapour lock, to be a critical component of the mechanism of intense as opposed to 'classical' drying. It was shown that the absence of the constant-rate drying period is a natural consequence of this effect. Several significant shortcomings of the previous model have been identified. This model treats the period of transition between surface- and shrinking-core drying as an instantaneous event. The new extended model, which overcomes the original model limitations, was developed in this project. In its formalism, the new model includes the pore-size distribution and thus simulates a gradual surface/shrinking-core transition. It was shown that the nature of the transition between the surface- and shrinking-core drying regimes during intensive drying is fundamentally different from that of classical drying, i.e. carried out at mild temperatures. In the latter case, liquid is being delivered to the surface through the network of interconnected small pores reaching the surface. The transition occurs when the larger pores, also reaching the surface, are being drained. On the other hand, under intense-drying conditions, the rate-limiting factor is the vapour lock. The latter phenomenon will occur in the smaller pores first, as they have smaller liquid
Squeeze flow of a Carreau fluid during sphere impact
NASA Astrophysics Data System (ADS)
Uddin, J.; Marston, J. O.; Thoroddsen, S. T.
2012-07-01
We present results from a combined numerical and experimental investigation into the squeeze flow induced when a solid sphere impacts onto a thin, ultra-viscous film of non-Newtonian fluid. We examine both the sphere motion through the liquid as well as the fluid flow field in the region directly beneath the sphere during approach to a solid plate. In the experiments we use silicone oil as the model fluid, which is well-described by the Carreau model. We use high-speed imaging and particle tracking to achieve flow visualisation within the film itself and derive the corresponding velocity fields. We show that the radial velocity either diverges as the gap between the sphere and the wall diminishes (Ztip → 0) or that it reaches a maximum value and then decays rapidly to zero as the sphere comes to rest at a non-zero distance (Ztip = Zmin) away from the wall. The horizontal shear rate is calculated and is responsible for significant viscosity reduction during the approach of the sphere. Our model of this flow, based on lubrication theory, is solved numerically and compared to experimental trials. We show that our model is able to correctly describe the physical features of the flow observed in the experiments.
A new method for visualizing data on a sphere
NASA Technical Reports Server (NTRS)
Hon, David
1991-01-01
A method for visualizing data on a globe or unit sphere is described. Information that is distributed over a sphere - global oceanographic or geographic measurements, all-sky astronomy observations, or any quantities that are best represented in spherical coordinates - can benefit from this technique. Retaining a better sense of the geometry and information content of the data, 3D graphics can provide an unobstructed view of the entire sphere, without undue deformation of its surface area. A 'parameterized ray trace' produces look-up tables (LUTs) that can be used for all visualizations. The ray-trace result shows one or more spheres with the data as a texture map and three reflecting rectangles that 'mirror' the far sides of the sphere(s) into view. The LUTs need only be created once. No special purpose hardware is required beyond a PC or workstation that supports color. Examples from astronomical and geophysical datasets, which are commonly displayed with an area deforming (2D) projection, are presented.
Solvation Sphere of I- and Br- in Water
Not Available
2011-06-22
The solvation sphere of halides in water has been investigated using a combination of extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) analysis techniques. The results have indicated that I- and Br- both have an asymmetric, 8 water molecule primary solvation spheres. These spheres are identical, with the Br{sup -} sphere about .3 {angstrom} smaller than the I{sup -} sphere. This study utilized near-edge analysis to supplement EXAFS analysis which suffers from signal dampening/broadening due to thermal noise. This paper has reported on the solvation first sphere of I{sup -} and Br{sup -} in water. Using EXAFS and XANES analysis, strong models which describe the geometric configuration of water molecules coordinated to a central anion have been developed. The combination of these techniques has provided us with a more substantiated argument than relying solely on one or the other. An important finding of this study is that the size of the anion plays a smaller role than previously assumed in determining the number of coordinating water molecules Further experimental and theoretical investigation is required to understand why the size of the anion plays a minor role in determining the number of water molecules bound.
Investigating hard sphere interactions through spin echo scattering angle measurement
NASA Astrophysics Data System (ADS)
Washington, Adam
Spin Echo Scattering Angle Measurement (SESAME) allows neutron scattering instruments to perform real space measurements on large micron scale samples by encoding the scattering angle into the neutron's spin state via Larmor precession. I have built a SESAME instrument at the Low Energy Neutron Source. I have also assisted in the construction of a modular SESAME instrument on the ASTERIX beamline at Los Alamos National lab. The ability to tune these instruments has been proved mathematically and optimized and automated experimentally. Practical limits of the SESAME technique with respect to polarization analyzers, neutron spectra, Larmor elements, and data analysis were investigated. The SESAME technique was used to examine the interaction of hard spheres under depletion. Poly(methyl methacrylate) spheres suspended in decalin had previously been studied as a hard sphere solution. The interparticle correlations between the spheres were found to match the Percus-Yevick closure, as had been previously seen in dynamical light scattering experiments. To expand beyond pure hard spheres, 900kDa polystyrene was added to the solution in concentrations of less than 1% by mass. The steric effects of the polystyrene were expected to produce a short-range, attractive, "sticky" potential. Experiment showed, however, that the "sticky" potential was not a stable state and that the spheres would eventually form long range aggregates.
STRENGTH OF A C-SPHERE FLEXURE SPECIMEN
Wereszczak, Andrew A; Wang, Wei; Jadaan, Osama M.; Lance, Michael J; Lin, Hua-Tay
2007-01-01
A 'C-Sphere' flexure strength specimen geometry was conceived and developed to measure a relevant strength of bearing-grade Si{sub 3}N{sub 4} balls and to relate that to surface-located strength-limiting flaws and to ultimately link those flaw populations to rolling contact fatigue performance. A slot was machined into the balls to a set depth to produce the C-sphere geometry. C-sphere specimens were then diametrally compressed to produce a monotonically increasing flexure or hoop tensile stress at their surface that caused their fracture. The strength was determined using the combination of failure load, C-sphere geometry, and FEA, and the stress field was used to determine C-sphere effective areas and effective volumes as a function of Weibull modulus. A description of the specimen and the aforementioned analysis are provided and a comparison of C-sphere flexure strength distributions of two bearing grade Si{sub 3}N{sub 4} materials (NBD200 and SN101C) is given.
Global Calibration of Multiple Cameras Based on Sphere Targets
Sun, Junhua; He, Huabin; Zeng, Debing
2016-01-01
Global calibration methods for multi-camera system are critical to the accuracy of vision measurement. Proposed in this paper is such a method based on several groups of sphere targets and a precision auxiliary camera. Each camera to be calibrated observes a group of spheres (at least three), while the auxiliary camera observes all the spheres. The global calibration can be achieved after each camera reconstructs the sphere centers in its field of view. In the process of reconstructing a sphere center, a parameter equation is used to describe the sphere projection model. Theoretical analysis and computer simulation are carried out to analyze the factors that affect the calibration accuracy. Simulation results show that the parameter equation can largely improve the reconstruction accuracy. In the experiments, a two-camera system calibrated by our method is used to measure a distance about 578 mm, and the root mean squared error is within 0.14 mm. Furthermore, the experiments indicate that the method has simple operation and good flexibility, especially for the onsite multiple cameras without common field of view. PMID:26761007
Cherenkov and Scintillation Properties of Cubic Zirconium
NASA Technical Reports Server (NTRS)
Christl, M.J.; Adams, J.H.; Parnell, T.A.; Kuznetsov, E.N.
2008-01-01
Cubic zirconium (CZ) is a high index of refraction (n =2.17) material that we have investigated for Cherenkov counter applications. Laboratory and proton accelerator tests of an 18cc sample of CZ show that the expected fast Cherenkov response is accompanied by a longer scintillation component that can be separated by pulse shaping. This presents the possibility of novel particle spectrometers which exploits both properties of CZ. Other high index materials being examined for Cherenkov applications will be discussed. Results from laboratory tests and an accelerator exposure will be presented and a potential application in solar energetic particle instruments will be discussed
Entropy-driven structural transition and kinetic trapping in formamidinium lead iodide perovskite
Chen, Tianran; Foley, Benjamin J.; Park, Changwon; Brown, Craig M.; Harriger, Leland W.; Lee, Jooseop; Ruff, Jacob; Yoon, Mina; Choi, Joshua J.; Lee, Seung-Hun
2016-01-01
A challenge of hybrid perovskite solar cells is device instability, which calls for an understanding of the perovskite structural stability and phase transitions. Using neutron diffraction and first-principles calculations on formamidinium lead iodide (FAPbI3), we show that the entropy contribution to the Gibbs free energy caused by isotropic rotations of the FA+ cation plays a crucial role in the cubic-to-hexagonal structural phase transition. Furthermore, we observe that the cubic-to-hexagonal phase transition exhibits a large thermal hysteresis. Our first-principles calculations confirm the existence of a potential barrier between the cubic and hexagonal structures, which provides an explanation for the observed thermal hysteresis. By exploiting the potential barrier, we demonstrate kinetic trapping of the cubic phase, desirable for solar cells, even at 8.2 K by thermal quenching.
Li, Xufan; Chi, Miaofang; Mahurin, Shannon Mark; Liu, Rui; Chuang, Yen -Jun; Dai, Sheng; Pan, Zhengwei
2016-01-18
Hard-sphere-templating method has been widely used to synthesize hollow carbon spheres (HCSs), in which the spheres were firstly coated with a carbon precursor, followed by carbonization and core removal. The obtained HCSs are generally amorphous or weakly graphitized (with the help of graphitization catalysts). In this work, we report on the fabrication of graphitized HCSs and yolk–shell Au@HCS nanostructures using a modified templating method, in which smooth, uniform graphene layers were grown on SiO2 spheres or Au@SiO2 nanoparticles via metal-catalyst-free chemical vapor deposition (CVD) of methane. Furthermore, our work not only provides a new method to fabricate high-quality, graphitized HCSsmore » but also demonstrates a reliable approach to grow quality graphene on oxide surfaces using CVD without the presence of metal catalysts.« less
Low pressure growth of cubic boron nitride films
NASA Technical Reports Server (NTRS)
Ong, Tiong P. (Inventor); Shing, Yuh-Han (Inventor)
1997-01-01
A method for forming thin films of cubic boron nitride on substrates at low pressures and temperatures. A substrate is first coated with polycrystalline diamond to provide a uniform surface upon which cubic boron nitride can be deposited by chemical vapor deposition. The cubic boron nitride film is useful as a substitute for diamond coatings for a variety of applications in which diamond is not suitable. any tetragonal or hexagonal boron nitride. The cubic boron nitride produced in accordance with the preceding example is particularly well-suited for use as a coating for ultra hard tool bits and abrasives, especially those intended to use in cutting or otherwise fabricating iron.
Examining the T Tauri system with SPHERE
NASA Astrophysics Data System (ADS)
Csépány, Gergely; van den Ancker, Mario; Ábrahám, Péter; Brandner, Wolfgang; Hormuth, Felix
2015-06-01
Context. The prototypical low-mass young stellar object, T Tauri, is a well-studied multiple system with at least three components. Aims: We aim to explore the T Tau system with the highest spatial resolution, study the time evolution of the known components, and re-determine the orbital parameters of the stars. Methods: Near-infrared classical imaging and integral field spectrograph observations were obtained during the Science Verification of SPHERE, the new high-contrast imaging facility at the VLT. The obtained FWHM of the primary star varies between 0.050'' and 0.059'', making these the highest spatial resolution near-infrared images of the T Tauri system obtained to date. Results: Our near-infrared images confirm the presence of extended emission south of T Tau Sa, reported in the literature. New narrow-band images show, for the first time, that this feature shows strong emission in both the Br-γ and H2 1-0 S(1) lines. Broadband imaging at 2.27 μm shows that T Tau Sa is 0.92 mag brighter than T Tau Sb, which is in contrast to observations from Jan. 2014 (when T Tau Sa was fainter than Sb), and demonstrates that T Tau Sa has entered a new period of high variability. The newly obtained astrometric positions of T Tau Sa and Sb agree with orbital fits from previous works. The orbit of T Tau S (the centre of gravity of Sa and Sb) around T Tau N is poorly constrained by the available observations and can be fit with a range of orbits ranging from a nearly circular orbit with a period of 475 years to highly eccentric orbits with periods up to 2.7 × 104 years. We also detected a feature south of T Tau N, at a distance of 144 ± 3 mas, which shows the properties of a new companion. Based on observations made at the La Silla Paranal Observatory under programme ID 60.A-9363(A) and 60.A-9364(A).Figures 3-5 are available in electronic form at http://www.aanda.org
Critical Masses for Unreflected Metal Spheres
Westfall, Robert Michael; Wright, Richard Q
2009-01-01
Calculated critical masses of bare metal spheres for 28 actinide isotopes, using the SCALE/XSDRNPM one-dimensional, discrete-ordinates system, are presented. ENDF/B-VI, ENDF/B-VII, and JENDL-3.3 cross sections were used in the calculations. Results are given for isotopes of uranium, neptunium, plutonium, americium, curium, californium, and for one isotope of einsteinium. Calculated k values for these same nuclides are also given. We show that, for non-threshold or low-threshold fission nuclides, a good approximation for the nuclide k is the value of nubar at 1 MeV. A plot of the critical mass versus k values is given for 19 nuclides with A-numbers between 232 and 250. The peaks in the critical mass curve (for seven nuclides) correspond to dips in the k curve. For the seven cases with the largest critical mass, six are even-even nuclides. Neptunium-237, with a critical mass of about 62.7 kg (ENDF/B-VI calculation), has an odd number of protons and an even number of neutrons. However, two cases with quite small critical masses, 232U and 236Pu, are also even-even. These two nuclides do not exhibit threshold fission behavior like most other even-even nuclides. The largest critical mass is 208.8 kg for 243Am and the smallest is 2.44 kg for 251Cf. The calculated k values vary from 1.5022 for 234U to 4.4767 for 251Cf. A correlation between the calculated critical mass (kg) and the fission spectrum averaged value of is given for the elements U, Np, Pu, Am, Cm, and Cf. For each of the five elements, a fit to the data for that element is provided. In each case the fit employs a negative exponential of the form mass = exp(A + B ~ ln( ) The values of A and B are element dependent and vary slightly for each of the five elements. The method described here is mainly applicable for non-threshold fission nuclides (15 of the 28 nuclides considered in this paper). There are three exceptions, 238Pu, 244Cm, and 250Cf, which all exhibit threshold fission behavior.
Mechanical properties for irradiated face-centred cubic nanocrystalline metals
Xiao, X. Z.; Song, D. K.; Chu, H. J.; Xue, J. M.; Duan, H. L.
2015-01-01
In this paper, a self-consistent plasticity theory is proposed to model the mechanical behaviours of irradiated face-centred cubic nanocrystalline metals. At the grain level, a tensorial crystal model with both irradiation and grain size effects is applied for the grain interior (GI), whereas both grain boundary (GB) sliding with irradiation effect and GB diffusion are considered in modelling the behaviours of GBs. The elastic-viscoplastic self-consistent method with considering grain size distribution is developed to transit the microscopic behaviour of individual grains to the macroscopic properties of nanocrystals (NCs). The proposed theory is applied to model the mechanical properties of irradiated NC copper, and the feasibility and efficiency have been validated by comparing with experimental data. Numerical results show that: (i) irradiation-induced defects can lead to irradiation hardening in the GIs, but the hardening effect decreases with the grain size due to the increasing absorption of defects by GBs. Meanwhile, the absorbed defects would make the GBs softer than the unirradiated case. (ii) There exists a critical grain size for irradiated NC metals, which separates the grain size into the irradiation hardening dominant region (above the critical size) and irradiation softening dominant region (below the critical size). (iii) The distribution of grain size has a significant influence on the mechanical behaviours of both irradiated and unirradiated NCs. The proposed model can offer a valid theoretical foundation to study the irradiation effect on NC materials. PMID:27547091
NASA Astrophysics Data System (ADS)
Sazegaran, Hamid; Kiani-Rashid, Ali-Reza; Khaki, Jalil Vahdati
2016-06-01
The effects of sphere size on the microstructural and mechanical properties of ductile iron-steel hollow sphere (DI-SHS) syntactic foams were investigated in this study. The SHSs were manufactured by fluidized-bed coating via the Fe-based commercial powder-binder suspension onto expanded polystyrene spheres (EPSs). Afterwards, the DI-SHS syntactic foams were produced via a sand-mold casting process. The microstructures of specimens were investigated by optical microscopy, scanning electron microscopy (SEM), and energy- dispersive X-ray spectroscopy (EDS). The microscopic evaluations of specimens reveal distinct regions composed of the DI matrix, SHS shells, and compatible interface. As a result, the microstructures and graphite morphologies of the DI matrix depend on sphere size. When the sphere size decreases, the area fractions of cementite and graphite phases are observed to increase and decrease, respectively. Compression tests were subsequently conducted at ambient temperature on the DI-SHS syntactic foams. The results reveal that the compression behavior of the syntactic foams is enhanced with increasing sphere size. Furthermore, the compressed specimens demonstrate that microcracks start and grow from the interface region.
The capillary bridge between two spheres: New closed-form equations in a two century old problem.
Lian, Guoping; Seville, Jonathan
2016-01-01
We discuss progress in obtaining explicit equations for the capillary force between nano and micron sized solid spheres. Early approaches to this two-century old problem adopted approximations to the geometry. With the toroidal approximation, the meridian profile is approximated by an arc, and the approach leads to the capillary force being dependent on the location at which the force is evaluated. The Derjaguin approximation further assumes that the meridian radius is orders of magnitude smaller than the azimuth radius. An explicit expression for the capillary force is obtained, but the equation is limited to sufficiently small liquid volumes and separation distances. Significant progress has been made in recent years in using numerical solutions to derive analytical expressions for capillary bridges. Early numerical investigation established that the maximum separation for stable capillary bridges before rupture scales to the cubic root of the liquid volume. We report new progress in using numerical solutions to obtain more accurate and more general closed-form expressions for capillary bridges. Simple explicit algebraic equations have been observed to fit the numerical results well, leading to a closed-form solution applicable to capillary bridges between equal and unequal spheres and with zero or finite solid-liquid contact angles. The newly derived closed-form equation is more accurate and reduces to the Derjaguin equation when the liquid volume (or half-filling angle) and separation distance are both sufficiently small.
NASA Astrophysics Data System (ADS)
Fischer, Lukas P.; Peter, Toni; Holm, Christian; de Graaf, Joost
2015-08-01
The so-called "raspberry" model refers to the hybrid lattice-Boltzmann and Langevin molecular dynamics scheme for simulating the dynamics of suspensions of colloidal particles, originally developed by Lobaskin and Dünweg [New J. Phys. 6, 54 (2004)], wherein discrete surface points are used to achieve fluid-particle coupling. This technique has been used in many simulation studies on the behavior of colloids. However, there are fundamental questions with regards to the use of this model. In this paper, we examine the accuracy with which the raspberry method is able to reproduce Stokes-level hydrodynamic interactions when compared to analytic expressions for solid spheres in simple-cubic crystals. To this end, we consider the quality of numerical experiments that are traditionally used to establish these properties and we discuss their shortcomings. We show that there is a discrepancy between the translational and rotational mobility reproduced by the simple raspberry model and present a way to numerically remedy this problem by adding internal coupling points. Finally, we examine a non-convex shape, namely, a colloidal dumbbell, and show that the filled raspberry model replicates the desired hydrodynamic behavior in bulk for this more complicated shape. Our investigation is continued in de Graaf et al. [J. Chem. Phys. 143, 084108 (2015)], wherein we consider the raspberry model in the confining geometry of two parallel plates.
Fischer, Lukas P; Peter, Toni; Holm, Christian; de Graaf, Joost
2015-08-28
The so-called "raspberry" model refers to the hybrid lattice-Boltzmann and Langevin molecular dynamics scheme for simulating the dynamics of suspensions of colloidal particles, originally developed by Lobaskin and Dünweg [New J. Phys. 6, 54 (2004)], wherein discrete surface points are used to achieve fluid-particle coupling. This technique has been used in many simulation studies on the behavior of colloids. However, there are fundamental questions with regards to the use of this model. In this paper, we examine the accuracy with which the raspberry method is able to reproduce Stokes-level hydrodynamic interactions when compared to analytic expressions for solid spheres in simple-cubic crystals. To this end, we consider the quality of numerical experiments that are traditionally used to establish these properties and we discuss their shortcomings. We show that there is a discrepancy between the translational and rotational mobility reproduced by the simple raspberry model and present a way to numerically remedy this problem by adding internal coupling points. Finally, we examine a non-convex shape, namely, a colloidal dumbbell, and show that the filled raspberry model replicates the desired hydrodynamic behavior in bulk for this more complicated shape. Our investigation is continued in de Graaf et al. [J. Chem. Phys. 143, 084108 (2015)], wherein we consider the raspberry model in the confining geometry of two parallel plates. PMID:26328818
Assembly of vorticity-aligned hard-sphere colloidal strings in a simple shear flow
Cheng, Xiang; Xu, Xinliang; Rice, Stuart A.; Dinner, Aaron R.; Cohen, Itai
2012-01-01
Colloidal suspensions self-assemble into equilibrium structures ranging from face- and body-centered cubic crystals to binary ionic crystals, and even kagome lattices. When driven out of equilibrium by hydrodynamic interactions, even more diverse structures can be accessed. However, mechanisms underlying out-of-equilibrium assembly are much less understood, though such processes are clearly relevant in many natural and industrial systems. Even in the simple case of hard-sphere colloidal particles under shear, there are conflicting predictions about whether particles link up into string-like structures along the shear flow direction. Here, using confocal microscopy, we measure the shear-induced suspension structure. Surprisingly, rather than flow-aligned strings, we observe log-rolling strings of particles normal to the plane of shear. By employing Stokesian dynamics simulations, we address the mechanism leading to this out-of-equilibrium structure and show that it emerges from a delicate balance between hydrodynamic and interparticle interactions. These results demonstrate a method for assembling large-scale particle structures using shear flows. PMID:22198839
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.
Role of quadratic and cubic spectral phases in ladder climbing with ultrashort pulses
Chatel, Beatrice; Degert, Jerome; Girard, Bertrand
2004-11-01
Two-photon excitation of a quantum ladder system by an ultrashort chirped pulse leads to interferences in the excited-state population, between direct and sequential paths. Experimental results have been obtained in atomic sodium vapor. The presence of several intermediate and final states leads to new phenomena. The interplay between the two sequential paths leads to strongly contrasted oscillations and a large enhancement of the transition probability for precise values of the chirp. A cubic spectral phase modifies significantly the behavior of the quantum interferences and can be used to enhance the two-photon absorption rate.
NASA Astrophysics Data System (ADS)
Borghi, F.; Sogne, E.; Lenardi, C.; Podestà, A.; Merlini, M.; Ducati, C.; Milani, P.
2016-08-01
Nanostructured zirconium dioxide (zirconia) films are very promising for catalysis and biotechnological applications: a precise control of the interfacial properties of the material at different length scales and, in particular, at the nanoscale, is therefore necessary. Here, we present the characterization of cluster-assembled zirconia films produced by supersonic cluster beam deposition possessing cubic structure at room temperature and controlled nanoscale morphology. We characterized the effect of thermal annealing in reducing and oxidizing conditions on the crystalline structure, grain dimensions, and topography. We highlight the mechanisms of film growth and phase transitions, which determine the observed interfacial morphological properties and their resilience against thermal treatments.
In Situ Synthesis of Uranium Carbide and its High Temperature Cubic Phase
Reiche, Helmut Matthias; Vogel, Sven C.
2015-03-25
New in situ data for the U-C system are presented, with the goal of improving knowledge of the phase diagram to enable production of new ceramic fuels. The none quenchable, cubic, δ-phase, which in turn is fundamental to computational methods, was identified. Rich datasets of the formation synthesis of uranium carbide yield kinetics data which allow the benchmarking of modeling, thermodynamic parameters etc. The order-disorder transition (carbon sublattice melting) was observed due to equal sensitivity of neutrons to both elements. This dynamic has not been accurately described in some recent simulation-based publications.
Pronounced negative thermal expansion from a simple structure : Cubic ScF{sub 3}.
Greve, B. K.; Martin, K. L.; Lee, P. L.; Chupas, P. J.; Chapman, K. W.; Wilkinson, A. P.; X-Ray Science Division; Georgia Inst. of Tech.
2010-10-19
Scandium trifluoride maintains a cubic ReO{sub 3} type structure down to at least 10 K, although the pressure at which its cubic to rhombohedral phase transition occurs drops from >0.5 GPa at {approx}300 K to 0.1-0.2 GPa at 50 K. At low temperatures it shows strong negative thermal expansion (NTE) (60-110 K, {alpha}{sub l} {approx} -14 ppm K{sup -1}). On heating, its coefficient of thermal expansion (CTE) smoothly increases, leading to a room temperature CTE that is similar to that of ZrW{sub 2}O{sub 8} and positive thermal expansion above {approx}1100 K. While the cubic ReO{sub 3} structure type is often used as a simple illustration of how negative thermal expansion can arise from the thermally induced rocking of rigid structural units, ScF{sub 3} is the first material with this structure to provide a clear experimental illustration of this mechanism for NTE.
First-principles investigation of cubic BaRuO3: A Hund's metal
NASA Astrophysics Data System (ADS)
Dasari, Nagamalleswararao; Yamijala, S. R. K. C. Sharma; Jain, Manish; Dasgupta, T. Saha; Moreno, Juana; Jarrell, Mark; Vidhyadhiraja, N. S.
2016-08-01
A first-principles investigation of cubic BaRuO3, by combining density functional theory with dynamical mean-field theory and a hybridization expansion continuous time quantum Monte Carlo solver, has been carried out. Nonmagnetic calculations with appropriately chosen on-site Coulomb repulsion U and Hund's exchange J for single-particle dynamics and static susceptibility show that cubic BaRuO3 is in a spin-frozen state at temperatures above the ferromagnetic transition point. A strong redshift with increasing J of the peak in the real frequency dynamical susceptibility indicates a dramatic suppression of the Fermi liquid coherence scale as compared to the bare parameters in cubic BaRuO3. The self-energy also shows clear deviation from Fermi liquid behavior that manifests in the single-particle spectrum. Such a clean separation of energy scales in this system provides scope for an incoherent spin-frozen (SF) phase that extends over a wide temperature range, to manifest in non-Fermi liquid behavior and to be the precursor for the magnetically ordered ground state.
Structure and optical properties of cubic gallium oxynitride synthesized by solvothermal route
Oberländer, Andreas; Kinski, Isabel; Zhu, Wenliang; Pezzotti, Giuseppe; Michaelis, Alexander
2013-04-15
Cubic gallium oxynitride was synthesized using a solvothermal processing route. Crystal structure, chemical composition, optical properties and the influence of heat treatment in either reactive or inert atmospheres have been investigated. Despite a strongly distorted lattice revealed using X-ray diffraction, the Raman active modes of a cubic gallium oxynitride structure could be observed. With diffusive reflectance UV–Vis spectroscopy a band gap at around 4.8 eV has been observed. Additionally, cathodoluminescence spectroscopy exhibited observable luminescence caused by defect-related transitions within the optical gap. Cathodoluminescence and photoluminescence spectra collected after heat treatments showed significant changes in the defect structure. In particular, for annealing in ammonia the main spectral modifications were related to the substitution of oxygen by nitrogen on anion sites. - Graphical abstract: CL spectra of gallium oxynitride: As-prepared and heat-treated at temperatures of 500 °C in different atmospheres. Highlights: ► Raman spectrum of cubic gallium oxynitride. ► Experimental determination of optical band gap. ► Shift of band gap energy due to heat treatment. ► Nitrogen incorporation leads to deep level acceptor states. ► Red shifted luminescence spectrum.
Combustion of a Polymer (PMMA) Sphere in Microgravity
NASA Technical Reports Server (NTRS)
Yang, Jiann C.; Hamins, Anthony; Donnelly, Michelle K.
1999-01-01
A series of low gravity, aircraft-based, experiments was conducted to investigate the combustion of supported thermoplastic polymer spheres under varying ambient conditions. The three types of thermoplastic investigated were polymethylmethacrylate (PMMA), polypropylene (PP). and polystyrene (PS). Spheres with diameters ranging from 2 mm to 6.35 mm were tested. The total initial pressure varied from 0.05 MPa to 0. 15 MPa whereas the ambient oxygen concentration varied from 19 % to 30 % (by volume). The ignition system consisted of a pair of retractable energized coils. Two CCD cameras recorded the burning histories of the spheres. The video sequences revealed a number of dynamic events including bubbling and sputtering, as well as soot shell formation and break-up during combustion of the spheres at reduced gravity. The ejection of combusting material from the burning spheres represents a fire hazard that must be considered at reduced gravity. The ejection process was found to be sensitive to polymer type. All average burning rates were measured to increase with initial sphere diameter and oxygen concentration, whereas the initial pressure had little effect. The three thermoplastic types exhibited different burning characteristics. For the same initial conditions, the burning rate of PP was slower than PMMA, whereas the burning rate of PS was comparable to PMMA. The transient diameter of the burning thermoplastic exhibited two distinct periods: an initial period (enduring approximately half of the total burn duration) when the diameter remained approximately constant, and a final period when the square of the diameter linearly decreased with time. A simple homogeneous two-phase model was developed to understand the changing diameter of the burning sphere. Its value is based on a competition between diameter reduction due to mass loss from burning and sputtering, and diameter expansion due to the processes of swelling (density decrease with heating) and bubble growth
Characterization of maximally random jammed sphere packings: Voronoi correlation functions
NASA Astrophysics Data System (ADS)
Klatt, Michael A.; Torquato, Salvatore
2014-11-01
We characterize the structure of maximally random jammed (MRJ) sphere packings by computing the Minkowski functionals (volume, surface area, and integrated mean curvature) of their associated Voronoi cells. The probability distribution functions of these functionals of Voronoi cells in MRJ sphere packings are qualitatively similar to those of an equilibrium hard-sphere liquid and partly even to the uncorrelated Poisson point process, implying that such local statistics are relatively structurally insensitive. This is not surprising because the Minkowski functionals of a single Voronoi cell incorporate only local information and are insensitive to global structural information. To improve upon this, we introduce descriptors that incorporate nonlocal information via the correlation functions of the Minkowski functionals of two cells at a given distance as well as certain cell-cell probability density functions. We evaluate these higher-order functions for our MRJ packings as well as equilibrium hard spheres and the Poisson point process. It is shown that these Minkowski correlation and density functions contain visibly more information than the corresponding standard pair-correlation functions. We find strong anticorrelations in the Voronoi volumes for the hyperuniform MRJ packings, consistent with previous findings for other pair correlations [A. Donev et al., Phys. Rev. Lett. 95, 090604 (2005), 10.1103/PhysRevLett.95.090604], indicating that large-scale volume fluctuations are suppressed by accompanying large Voronoi cells with small cells, and vice versa. In contrast to the aforementioned local Voronoi statistics, the correlation functions of the Voronoi cells qualitatively distinguish the structure of MRJ sphere packings (prototypical glasses) from that of not only the Poisson point process but also the correlated equilibrium hard-sphere liquids. Moreover, while we did not find any perfect icosahedra (the locally densest possible structure in which a central
Tin-wall hollow ceramic spheres from slurries. Final report
Chapman, A.T.; Cochran, J.K.
1992-12-31
The overall objective of this effort was to develop a process for economically fabricating thin-wall hollow ceramic spheres from conventional ceramic powders using dispersions. This process resulted in successful production of monosized spheres in the mm size range which were point contact bonded into foams. Thin-wall hollow ceramic spheres of small (one to five millimeter) diameter have novel applications as high-temperature insulation and light structural materials when bonded into monolithic foams. During Phase 1 of this program the objective as to develop a process for fabricating thin-wall hollow spheres from powder slurries using the coaxial nozzle fabrication method. Based on the success during Phase 1, Phase 2 was revised to emphasize the assessment of the potential structural and insulation applications for the spheres and modeling of the sphere formation process was initiated. As more understanding developed, it was clear that to achieve successful structural application, the spheres had to be bonded into monolithic foams and the effort was further expanded to include both bonding into structures and finite element mechanical modeling which became the basis of Phase 3. Successful bonding techniques and mechanical modeling resulted but thermal conductivities were higher than desired for insulating activities. In addition, considerable interest had been express by industry for the technology. Thus the final Phase 4 concentrated on methods to reduce thermal conductivity by a variety of techniques and technology transfer through individualized visits. This program resulted in three Ph.D. theses and 10 M.S. theses and they are listed in the appropriate technical sections.
Outer Sphere Adsorption of Pb(II)EDTA on Goethite
Bargar, John R
1999-07-16
FTIR and EXAFS spectroscopic measurements were performed on Pb(II)EDTA adsorbed on goethite as functions of pH (4-6), Pb(II)EDTA concentration (0.11 {micro}M - 72 {micro}M), and ionic strength (16 {micro}M - 0.5M). FTIR measurements show no evidence for carboxylate-Fe(III) bonding or protonation of EDTA at Pb:EDTA = 1:1. Both FTIR and EXAFS measurements suggest that EDTA acts as a hexadentate ligand, with all four of its carboxylate and both amine groups bonded to Pb(II). No evidence was observed for inner-sphere Pb(II)-goethite bonding at Pb:EDTA = 1:1. Hence, the adsorbed complexes should have composition Pb(II)EDTA{sup 2{minus}}. Since substantial uptake of PbEDTA(II){sup 2{minus}} occurred in the samples, we infer that Pb(II)EDTA{sup 2{minus}} adsorbed as outer-sphere complexes and/or as complexes that lose part of their solvation shells and hydrogen bond directly to goethite surface sites. We propose the term ''hydration-sphere'' for the latter type of complexes because they should occupy space in the primary hydration spheres of goethite surface functional groups, and to distinguish this mode of sorption from common structural definitions of inner- and outer-sphere complexes. The similarity of Pb(II) uptake isotherms to those of other divalent metal ions complexed by EDTA suggests that they too adsorb by these mechanisms. The lack of evidence for inner-sphere EDTA-Fe(III) bonding suggests that previously proposed metal-ligand - promoted dissolution mechanisms should be modified, specifically to account for the presence of outer-sphere precursor species.
Phase behavior of mixtures of colloidal rods and spheres
NASA Astrophysics Data System (ADS)
Adams, Marie Elizabeth
In this thesis we study entropy driven order in mixtures of rods and spheres. Systems of rod-like particles, as pure systems, exhibit rich liquid crystalline phase behavior. We chose to work with aqueous suspensions of either TMV or fd virus particles, both rod-like lyotropic systems. We complicate the phase behavior by adding a second component, colloidal spheres (PEG/PEO, BSA, polystyrene latex, or Dextran). Our first paper explores the phase behavior of TMV mixed with BSA or PEO, mapping out a phase diagram based on optical microscopy observations. We found our qualitative observations of TMV mixtures to be consistent with theoretical models of the depletion force. The second paper extends our study of phase behavior to mixtures of fd virus and polystyrene latex spheres. We qualitatively observe bulk demixing for very small diameter added spheres and for very large diameter added spheres. In addition, we observed microphase separation morphologies, such as lamellar and columnar structures, which formed for fd mixed with polystyrene latex spheres 0.1 microns in diameter. All of these microphase samples were viewed with differential interference microscopy (a few samples were further investigated using electron microscopy). Both our data and theoretical calculations illustrated that 0.1 micron diameter spheres have a stabilizing effect on the smectic phase. Our final work focused on fd virus mixed with Dextran. The purpose of these experiments was to examine the effect of added polymer on the isotropic-cholesteric co-existence region. I-Ch samples were prepared and fd and Dextran concentrations were measured using a spectrophotometer. Several conditions were explored, including two different molecular weights of Dextran and a range of ionic strengths. In agreement with theoretical predictions, the I-Ch coexistence region widens with added Dextran with the polymer preferentially partioned into the isotropic phase.
Muñoz, F F; Acuña, L M; Albornoz, C A; Leyva, A G; Baker, R T; Fuentes, R O
2015-01-01
In this work, nanostructured LnxCe(1-x)O2-δ (Ln: Gd and Pr; x = 0.1 and 0.2) spheres were synthesized by microwave assisted hydrothermal homogeneous co-precipitation and their properties were characterized by synchrotron radiation XRD, X-ray absorption near-edge spectroscopy (XANES) and scanning and high-resolution electron microscopy (SEM and HRTEM). In situ XRD and XANES experiments were carried out under reducing and oxidizing conditions in order to investigate the redox behaviour of these materials. The nanostructured mixed oxide spheres were found to have a cubic crystal structure (Fm3m space group). The spheres were composed of nanoparticles with an average crystallite size of about 10 nm. The Ln(0.1)Ce(0.9)O2-δ compositions exhibited the highest specific surface area (∼ 60 m(2) g(-1)). In situ XRD experiments showed an increase in lattice parameters upon reduction, which was attributed to the reduction of Ce(4+) and Pr(4+) cations to Ce(3+) and Pr(3+), which have larger radii, and to the associated increase in VO concentration. This increase in lattice parameters was considerably more pronounced for PrDC than GDC, and was explained by the considerably larger change in ionic radius for Pr upon reduction. XANES absorption experiments at the Ce and Pr L3-edge showed that the changes observed upon reduction of the Pr-containing samples resulted mostly from the formation of Pr(3+) rather than Ce(3+), and supported the previously reported proposal that Pr(3+) has a stabilizing effect on Ce(4+).
Bai, Da-Chang; Yu, Fei-Le; Wang, Wan-Ying; Chen, Di; Li, Hao; Liu, Qing-Rong; Ding, Chang-Hua; Chen, Bo; Hou, Xue-Long
2016-01-01
The palladium-catalysed allylic substitution reaction is one of the most important reactions in transition-metal catalysis and has been well-studied in the past decades. Most of the reactions proceed through an outer-sphere mechanism, affording linear products when monosubstituted allyl reagents are used. Here, we report an efficient Palladium-catalysed protocol for reactions of β-substituted ketones with monosubstituted allyl substrates, simply by using N-heterocyclic carbene as ligand, leading to branched products with up to three contiguous stereocentres in a (syn, anti)-mode with excellent regio and diastereoselectivities. The scope of the protocol in organic synthesis has been examined preliminarily. Mechanistic studies by both experiments and density functional theory (DFT) calculations reveal that the reaction proceeds via an inner-sphere mechanism—nucleophilic attack of enolate oxygen on Palladium followed by C–C bond-forming [3,3']-reductive elimination. PMID:27283477
NASA Astrophysics Data System (ADS)
Yoshimura, Yukio; Kojima, Akira; Yoshioka, Tadahiko; Kawakatsu, Yasuhiro; Tozaki, Ken-ichi; Iwasaki, Hiroshi
2001-04-01
A convenient method has been developed to measure displacement currents along three crystallographic directions with a heat flux sensor on a fine temperature scale at the phase transition in solids. An example of the measurements is shown for the cubic-tetragonal phase transition in BaTiO3, revealing a complicated feature of the current flow at the transition point.
del Moral, A.; Arnaudas, J.I. ); Gehring, P.M. ); Salamon, M.B. ); Ritter, C. ); Joven, E. ); Cullen, J. (Magnetics Group, Naval Surface Warfare Center, 10901 New Hampshire Avenue, White Oak, Silver Spring, Maryland 20903-5000 (United State
1993-04-01
The low-temperature ([ital T]=0 K) first-order phase transition, predicted to drive systems with both weak random and uniform cubic anisotropy from a correlated spin glass to a ferromagnet, has been observed. At higher temperatures the transition is to a quasi- or random ferromagnet. The transition occurs at a concentration [ital x][sub [ital t
Locating responsibility: the Sphere Humanitarian Charter and its rationale.
Darcy, James
2004-06-01
Criticised by some as a technical initiative that neglects core principles, Sphere was seen by its originators precisely as an articulation of principle. The Humanitarian Charter was the main vehicle through which this was expressed, but its relationship to the Minimum Standards has remained a matter of uncertainty. Specifically, it was unclear in the original (1999) edition of Sphere how the concept of rights informed the Minimum Standards. The revised (2004) edition goes some way to clarifying this in the way the standards are framed, yet the link between the standards and the charter remains unclear. The concern with the quality and accountability of humanitarian assistance, which motivated the attempt to establish system-wide standards through the Sphere Project, was accompanied by a desire to establish such actions in a wider framework of legal and political responsibility. In part, this reflects the conditional nature of the undertaking that agencies make when they adopt Sphere. This aspect of the charter has been neglected, but it is fundamental to an understanding of the standards and their application. This paper considers the rationale of the Sphere Humanitarian Charter and the conceptual model that underpins it. It discusses the relationship between the charter and the Minimum Standards, and the sense in which the latter are properly called "rights-based" (explored further in a related paper herein by Young and Taylor). The author was closely involved in the conception and drafting of the charter, and this paper attempts to convey some of the thinking that lay behind it.
Hydrothermal synthesis and photocatalytic activity of zinc oxide hollow spheres.
Yu, Jiaguo; Yu, Xiaoxiao
2008-07-01
ZnO hollow spheres with porous crystalline shells were one-pot fabricated by hydrothermal treatment of glucose/ZnCl2 mixtures at 180 degrees C for 24 h, and then calcined at different temperatures for 4 h. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption isotherms. The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic decolorization of Rhodamine B aqueous solution at ambient temperature. The results indicated that the average crystallite size, shell thickness, specific surface areas, pore structures, and photocatalytic activity of ZnO hollow spheres could be controlled by varying the molar ratio of glucose to zinc ions (R). With increasing R, the photocatalytic activity increases and reaches a maximum value at R = 15, which can be attributed to the combined effects of several factors such as specific surface area, the porous structure and the crystallite size. Further results show that hollow spheres can be more readily separated from the slurry system by filtration or sedimentation after photocatalytic reaction and reused than conventional powder photocatalyst. After many recycles for the photodegradation of RhB, the catalyst does not exhibit any great loss in activity, confirming ZnO hollow spheres is stability and not photocorroded. The prepared ZnO hollow spheres are also of great interest in solar cell, catalysis, separation technology, biomedical engineering, and nanotechnology.
ORSPHERE: CRITICAL, BARE, HEU(93.2)-METAL SPHERE
Margaret A. Marshall
2013-09-01
In the early 1970’s Dr. John T. Mihalczo (team leader), J.J. Lynn, and J.R. Taylor performed experiments at the Oak Ridge Critical Experiments Facility (ORCEF) with highly enriched uranium (HEU) metal (called Oak Ridge Alloy or ORALLOY) in an attempt to recreate GODIVA I results with greater accuracy than those performed at Los Alamos National Laboratory in the 1950’s (HEU-MET-FAST-001). The purpose of the Oak Ridge ORALLOY Sphere (ORSphere) experiments was to estimate the unreflected and unmoderated critical mass of an idealized sphere of uranium metal corrected to a density, purity, and enrichment such that it could be compared with the GODIVA I experiments. “The very accurate description of this sphere, as assembled, establishes it as an ideal benchmark for calculational methods and cross-section data files.” (Reference 1) While performing the ORSphere experiments care was taken to accurately document component dimensions (±0. 0001 in. for non-spherical parts), masses (±0.01 g), and material data The experiment was also set up to minimize the amount of structural material in the sphere proximity. A three part sphere was initially assembled with an average radius of 3.4665 in. and was then machined down to an average radius of 3.4420 in. (3.4425 in. nominal). These two spherical configurations were evaluated and judged to be acceptable benchmark experiments; however, the two experiments are highly correlated.
Experimental determination of the dynamics of an acoustically levitated sphere
NASA Astrophysics Data System (ADS)
Pérez, Nicolás; Andrade, Marco A. B.; Canetti, Rafael; Adamowski, Julio C.
2014-11-01
Levitation of solids and liquids by ultrasonic standing waves is a promising technique to manipulate materials without contact. When a small particle is introduced in certain areas of a standing wave field, the acoustic radiation force pushes the particle to the pressure node. This movement is followed by oscillations of the levitated particle. Aiming to investigate the particle oscillations in acoustic levitation, this paper presents the experimental and numerical characterization of the dynamic behavior of a levitated sphere. To obtain the experimental response, a small sphere is lifted by the acoustic radiation force. After the sphere lift, it presents a damped oscillatory behavior, which is recorded by a high speed camera. To model this behavior, a mass-spring-damper system is proposed. In this model, the acoustic radiation force that acts on the sphere is theoretically predicted by the Gor'kov theory and the viscous forces are modeled by two damping terms, one term proportional to the square of the velocity and another term proportional to the particle velocity. The proposed model was experimentally verified by using different values of sound pressure amplitude. The comparison between numerical and experimental results shows that the model can accurately describe the oscillatory behavior of the sphere in an acoustic levitator.
Grid-Sphere Electrodes for Contact with Ionospheric Plasma
NASA Technical Reports Server (NTRS)
Stone, Nobie H.; Poe, Garrett D.
2010-01-01
Grid-sphere electrodes have been proposed for use on the positively biased end of electrodynamic space tethers. A grid-sphere electrode is fabricated by embedding a wire mesh in a thin film from which a spherical balloon is formed. The grid-sphere electrode would be deployed from compact stowage by inflating the balloon in space. The thin-film material used to inflate the balloon is formulated to vaporize when exposed to the space environment. This would leave the bare metallic spherical grid electrode attached to the tether, which would present a small cross-sectional area (essentially, the geometric wire shadow area only) to incident neutral atoms and molecules. Most of the neutral particles, which produce dynamic drag when they impact a surface, would pass unimpeded through the open grid spaces. However, partly as a result of buildup of a space charge inside the grid-sphere, and partially, the result of magnetic field effects, the electrode would act almost like a solid surface with respect to the flux of electrons. The net result would be that grid-sphere electrodes would introduce minimal aerodynamic drag, yet have effective electrical-contact surface areas large enough to collect multiampere currents from the ionospheric plasma that are needed for operation of electrodynamic tethers. The vaporizable-balloon concept could also be applied to the deployment of large radio antennas in outer space.
Fuel Fabrication for Surrogate Sphere-Pac Rodlet
Del Cul, G.D.
2005-07-19
Sphere-pac fuel consists of a blend of spheres of two or three different size fractions contained in a fuel rod. The smear density of the sphere-pac fuel column can be adjusted to the values obtained for light-water reactor (LWR) pellets (91-95%) by using three size fractions, and to values typical of the fast-reactor oxide fuel column ({approx}85%) by using two size fractions. For optimum binary packing, the diameters of the two sphere fractions must differ by at least a factor of 7 (ref. 3). Blending of spheres with smaller-diameter ratios results in difficult blending, nonuniform loading, and lower packing fractions. A mixture of about 70 vol% coarse spheres and 30 vol% fine spheres is needed to obtain high packing fractions. The limiting smear density for binary packing is 86%, with about 82% achieved in practice. Ternary packing provides greater smear densities, with theoretical values ranging from 93 to 95%. Sphere-pac technology was developed in the 1960-1990 period for thermal and fast spectrum reactors of nearly all types (U-Th and U-Pu fuel cycles, oxide and carbide fuels), but development of this technology was most strongly motivated by the need for remote fabrication in the thorium fuel cycle. The application to LWR fuels as part of the DOE Fuel Performance Improvement Program did not result in commercial deployment for a number of reasons, but the relatively low production cost of existing UO{sub 2} pellet fuel is probably the most important factor. In the case of transmutation fuels, however, sphere-pac technology has the potential to be a lower-cost alternative while also offering great flexibility in tailoring the fuel elements to match the exact requirements of any particular reactor core at any given time in the cycle. In fact, the blend of spheres can be adjusted to offer a different composition for each fuel pin or group of pins in a given fuel element. Moreover, it can even provide a vertical gradient of composition in a single fuel pin. For
Hydrothermal Syntheses of Colloidal Carbon Spheres from Cyclodextrins
Shin, Yongsoon; Wang, Li Q.; Bae, In-Tae; Arey, Bruce W.; Exarhos, Gregory J.
2008-09-18
Colloidal carbon spheres have been prepared from aqueous alpha-, beta-, and gamma-cyclodextrin (CD) solutions in closed systems under hydrothermal conditions at 160 oC. Both liquid and solid-state 13C NMR spectra taken for samples at different reaction times have been used to monitor the dehydration and carbonization pathways. CD slowly hydrolyzes to glucose and forms 5-hydroxymethyl furfural (HMF) followed by carbonization into colloidal carbon spheres. The isolated carbon spheres are 70-150 nm in diameter, exhibit a core-shell structure, and are comprised of a condensed core (C=C) peppered with resident chemical functionalities including carboxylate and hydroxyl groups. Evidence from 13C solid-state NMR and FT-IR spectra reveal that the evolving carbon spheres show a gradual increase in the amount of aromatic carbon as a function of reaction time and that the carbon spheres generated from gamma-CD contain significantly higher aromatic carbon than those derived from alpha- and beta-CD.
Experimental determination of the dynamics of an acoustically levitated sphere
Pérez, Nicolás; Andrade, Marco A. B.; Canetti, Rafael; Adamowski, Julio C.
2014-11-14
Levitation of solids and liquids by ultrasonic standing waves is a promising technique to manipulate materials without contact. When a small particle is introduced in certain areas of a standing wave field, the acoustic radiation force pushes the particle to the pressure node. This movement is followed by oscillations of the levitated particle. Aiming to investigate the particle oscillations in acoustic levitation, this paper presents the experimental and numerical characterization of the dynamic behavior of a levitated sphere. To obtain the experimental response, a small sphere is lifted by the acoustic radiation force. After the sphere lift, it presents a damped oscillatory behavior, which is recorded by a high speed camera. To model this behavior, a mass-spring-damper system is proposed. In this model, the acoustic radiation force that acts on the sphere is theoretically predicted by the Gor'kov theory and the viscous forces are modeled by two damping terms, one term proportional to the square of the velocity and another term proportional to the particle velocity. The proposed model was experimentally verified by using different values of sound pressure amplitude. The comparison between numerical and experimental results shows that the model can accurately describe the oscillatory behavior of the sphere in an acoustic levitator.