bluuebunny/crossref_metadata_2025 huggingface dataset:
General approach to the magnetostatic force and interaction between cylindrically shaped nanoparticles
Authors: Morales-Concha C. , Ossandón M. , Pereira A. , Altbir D. , Escrig J.
Published: March 2012

In this paper we obtain analytical expressions for the magnetostatic interaction between cylindrical particles based on the assumption of a fixed uniform magnetization. Magnetostatic forces between the particles are established by these interactions. These general expressions allow the investigation of the magnetostatic interactions and forces between cylindrically shaped particles with different geometrical parameters like barcode-type magnetic nanostructures, multilayer nanotubes and nanowires, nanoparticles with modulated diameter, the ordering of nanoparticles on fluids, and others.
Microstructure evaluation for Dy-free Nd-Fe-B sintered magnets with high coercivity
Authors: Goto R. , Matsuura M. , Sugimoto S. , Tezuka N. , Une Y. , Sagawa M.
Published: March 2012

Nd-Fe-B sintered magnets are used for motors of hybrid or electric vehicles due to their high energy products. Dy is added to Nd-Fe-B sintered magnets to work in a high temperature environment. Although the addition of Dy decreases the magnetization of Nd-Fe-B magnets, it increases coercivity; a decrease in the amount of Dy is strongly required. Recently, Nd-Fe-B sintered magnets with a grain size of 1 μm achieved high coercivity of ∼20 kOe without the addition of Dy or other heavy rare earth elements. In this paper, the microstructure of their magnets was observed and compared to magnets with a grain size of ∼3 μm. The coercivity of magnets consisting of larger particles was 17 kOe. Microstructures were observed by the scanning electron microscope and the shapes of grains and the distribution of the Nd-rich phase were evaluated. The observation was promoted in two directions. One direction is the plane perpendicular to the magnetically aligned direction (c plane side) and the other is the side parallel to the magnetically aligned direction (c axis side). For magnets consisting of smaller particles, the shapes of grains are isotropic for the c plane side and elongated for the c axis side. The angle of minor axis prefers to be parallel to magnetically aligned direction. The distribution of the Nd-rich phase for magnets was also evaluated for both magnets. The distribution of the Nd-rich phase at triple junctions for the magnets with smaller particles becomes homogeneous compared to that for magnets with larger particles. It is considered that Dy-free magnets with high coercivity were realized by the achievement of homogeneous distribution of Nd-rich phase besides decreasing grain size.
Size effect on the structural, magnetic, and magnetotransport properties of electron doped manganite La0.15Ca0.85MnO3
Authors: Thomas Rini , Das Gangadhar , Mondal Rajib , Pradheesh R. , Mahato R. N. , Geetha Kumary T. , Nirmala R. , Morozkin A. V. , Lamsal J. , Yelon W. B. , Nigam A. K. , Malik S. K.
Published: March 2012

Nanocrystalline La0.15Ca0.85MnO3 samples of various grain sizes ranging from ∼17 to 42 nm have been prepared by sol-gel technique. Phase purity and composition were verified by room temperature x-ray diffraction and SEM-EDAX analysis. The bulk La0.15Ca0.85MnO3 is known to order antiferromagnetically around 170 K and to undergo a simultaneous crystal structural transition. DC magnetization measurements on 17 nm size La0.15Ca0.85MnO3 show a peak at ∼130 K (TN) in zero-field-cooled (ZFC) state. Field-cooled magnetization bifurcates from ZFC data around 200 K hinting a weak ferromagnetic component near room temperature due to surface moments of the nanoparticle sample. Low temperature powder neutron diffraction experiments reveal that the incomplete structural transition from room temperature orthorhombic to low temperature orthorhombic-monoclinic state also occurs in the nanoparticle sample as in the bulk. Magnetization in the ordered state decreases as particle size increases, thus indicating the reduction of the competing ferromagnetic surface moments.
Polarization mechanism and quasi-electric-double-layer modeling for indium-tin-oxide electric-double-layer thin-film-transistors
Authors: Dai Mingzhi , Xu Wangying
Published: March 2012

The polarization mechanism of oxide-based electric-double-layer (EDL) thin-film transistors (TFTs) is not well understood. In this letter, a frequency-dependent circuit model for the oxide-based EDL TFTs is given. In addition, a quasi-EDL model is proposed to explain the conduction mechanism of this kind of EDL TFTs quantitatively. According to this model, in order to ensure an equivalent field-effect mobility up to 1.0 cm2/V · s, the minimum ITO channel thickness is ∼8.5 nm for the self-assembled indium-tin-oxide (ITO)-based EDL TFTs. With the circuit model and the quasi-EDL model, our results may contribute to improved control of oxide-based TFTs.
Spin transport calculation for the branch-shaped zigzag graphene nano-ribbon
Authors: Lee Hsin-Han , Chang Ching-Ray
Published: March 2012

The zigzag graphene nano-ribbon (ZGNR) has a novel physical property called the quantum spin Hall effect (QSHE). In this paper, we use the Landauer method to calculate the current and polarization on two types of branching ZGNR (fork-shaped and H-shaped). Our results indicate that the branch-shape graphene device will enhance the spin polarizing current.
A technique for contactless measurement of water temperature using Stokes and anti-Stokes comparative Raman spectroscopy
Authors: Nikitin S. P. , Manka C. , Grun J. , Bowles J.
Published: March 2012

Contactless measurements of water temperature are utilized in a number of sciences, such as oceanography, climatology, and biology. Previously reported Raman spectroscopy techniques exploited the changes in the shapes of water Raman bands. Interpretation of these changes is difficult since these bands are composed of multiple lines, each influenced not only by temperature but also by pressure and salinity. This paper presents a proof-of-principal demonstration of a contactless technique which determines water temperature from the ratio of Stokes and anti-Stokes intensities of the water 180 cm−1 Raman band. This ratio is not sensitive to pressure and salinity, allowing reliable determination of water temperature.
Investigation of cation distribution in single crystalline Fe3−xMnxO4 microspheres based on Mössbauer spectroscopy
Authors: Hui Li Yong , Kouh Taejoon , Shim In-Bo , Sung Kim Chul
Published: March 2012

Monodispersed Fe3−xMnxO4 (x = 0, 0.25, 0.5, 0.75, and 1.0) microspheres were prepared by a solvothermal reaction method. Field emission scanning electronmicroscope (FESEM) and high resolution transmission electron microscope (HRTEM) measurements showed that the size of the monodispersed particles was around 200 ∼ 400 nm, with single crystalline spots in the selected-area electron diffraction (SAED) patterns. From the detailed Rietveld refinement analysis, the crystal structure was determined to be cubic spinel with lattice constant a0, linearly increasing from 8.3956 to 8.4319 Å with the Mn concentration. Also, with Mn concentration, saturation magnetization decreased from 76.9 to 60.3 emu/g at 295 K and 99.5 to 78.4 emu/g at 4.2 K, while coercivity decreased from 66 to 36 Oe at 295 K and 271 to 185 Oe at 4.2 K. We have analyzed the recorded Mössbauer spectra as 3 sets with six lines of tetrahedral A site and octahedral B1 and B2 sites at 295 K and 4.2 K. From the isomer shift values, the valence state of the A and B1 site was determined to be ferric, while the B2 site was ferrous. The corresponding area ratio of the A site increased from 40 to 50%, while that of the B site decreased from 60 to 50% as the Mn concentration changed from x = 0 to 1.0. Here, the changes in the area ratios of A and B sites are due to the changes in the cation distributions at the A and B sites, originating from the randomly substituted Mn ions in Fe3−xMnxO4 microspheres.
Fabrication of FePt networks by porous anodic aluminum oxide
Authors: Huang Yen-Chun , Hsiao Ju-Cheng , Liu I-Yun , Wang Liang-Wei , Liao Jung-Wei , Lai Chih-Huang
Published: March 2012

It is demonstrated that the large-area FePt network nanostructures with strong perpendicular anisotropy can be obtained by growing the mask of porous anodic aluminum oxide (AAO) directly on the L10-FePt films and subsequent plasma etching. The aspect ratio of the AAO mask is critical to achieve well-organized FePt networks. The out-of-plane coercivity of FePt networks is enhanced by 20% compared to that of the FePt film, due to the domain wall pinning effects imposed by the presence of pores.
Exciton coherence lifetimes from electronic structure
Authors: Parkhill John A. , Tempel David G. , Aspuru-Guzik Alan
Published: March 2012

We model the coherent energy transfer of an electronic excitation within covalently linked aromatic homodimers from first-principles. Our results shed light on whether commonly used models of the bath calculated via detailed electronic structure calculations can reproduce the key dynamics. For the systems we model, the time scales of coherent transport are experimentally known from time-dependent polarization anisotropy measurements, and so we can directly assess whether current techniques are predictive for modeling coherent transport. The coupling of the electronic degrees of freedom to the nuclear degrees of freedom is calculated from first-principles rather than assumed, and the fluorescence anisotropy decay is directly reproduced. Surprisingly, we find that although time-dependent density functional theory absolute energies are routinely in error by orders of magnitude more than the coupling energy between monomers, the coherent transport properties of these dimers can be semi-quantitatively reproduced from these calculations. Future directions which must be pursued to yield predictive and reliable models of coherent transport are suggested.
Soliton propagation in a moving electron-positron pair plasma having negatively charged dust grains
Authors: Malik Rakhee , Malik Hitendra K. , Kaushik Subhash C.
Published: March 2012

We consider an electron-positron pair plasma that has negatively charged dust grains. Being the same mass of the electrons and positrons, both of these species contribute to the wave excitation in the plasma. Since the frequency of oscillations is high, the dust grains are considered to be fixed and they only provide the restoring force for the wave excitation. For the sake of completeness, we include the finite temperatures of the electrons and positrons species and derive the expressions for the phase velocities. Two types of modes propagating in opposite directions occur in this pair plasma model. Based on Korteweg-de Vries (KdV) equation, it is realized that these modes evolve only into compressive solitons. However, usual KdV approach fails when both the species carry the same temperatures and also drift with the same velocity. Under this situation, modified KdV (mKdV) equation is derived that shows the occurrence of rarefactive solitons also, which carry the same amplitudes as the compressive solitons attain corresponding to mKdV equation. In addition to the expressions of peak amplitude and width of the solitons, we calculate soliton energy for examining their propagation characteristics in detail under the effect of positron to electron temperature ratio σ, their drift velocities (ve0 and vp0), dust concentration nd0, and dust charge valency Zd. The issue of nonvanishing coefficient of nonlinearity is also discussed in greater detail.
Nonlocality of microwave-induced variations in the intensity of the visible continuum from a medium-pressure cesium-xenon dc discharge
Authors: Gitlin M. S. , Fedotov A. E. , Stukachev S. E. , Tsvetkov A. I.
Published: March 2012

A violation of the local relation between the visible continuum (VC) emissivity and the millimeter wave (MMW) intensity was observed in the experiments on imaging of MMW beams with subcentimeter width using the VC from a slab of the positive column (PC) of a medium-pressure cesium-xenon (Cs-Xe) dc discharge. The spatial distribution of the microwave-induced variation in the VC emissivity of the plasma slab was modeled. For this, perturbations of the electron temperature and density in a slab of the PC of a Cs-Xe discharge affected by an MMW beam were calculated. The relation between the spatial distributions of the VC brightness perturbation and the MMW intensity has been obtained. Good agreement between the results of the experiments and the modeling is demonstrated. The line spread function of a two-dimensional (2D) plasma sensor for MMWs is found, and its width is shown to be equal to 2 mm. We proved that the nonlocality of microwave-induced variations in the intensity of the VC from the PC, as well as the spatial resolution of the plasma technique of MMW imaging, are primarily determined by the influence of the electron heat conduction. Along with the electron heat conduction, the nonlocality of the electron temperature variation is caused by the influence of the hydrodynamic flux of electron enthalpy, diffusion and thermodiffusion fluxes of electrons, and also spatial inhomogeneity of the electron heating by a dc electric field, which results from a microwave-induced variation in plasma conductivity. These factors are responsible for the axial asymmetry of the images of the axisymmetric MMW beams.
Thermocapillary-assisted pulling of contact-free liquid films
Authors: Scheid Benoit , van Nierop Ernst A. , Stone Howard A.
Published: March 2012

We study the formation of a free liquid film that is pulled out of a bath at constant speed and stabilized by the action of thermocapillary stresses prescribed at the free surfaces. The basic concept was introduced recently by Scheid et al. [“Thermocapillary-assisted pulling of thin films: Application to molten metals,” Appl. Phys. Lett. 97, 171906 (2010)]10.1063/1.3505523. The theory suggests that very thin ribbons of molten material can be drawn out of a melt by adequately tuning the temperature gradient along the dynamic meniscus that connects the static meniscus at the melting bath to the region of the drawn flat film. In the present paper, we extend our original analysis by investigating the roles of inertia and gravity on the film thickness, and show how the results depend on heat transfer/conduction properties. Furthermore, we analyze the one-dimensional transverse stability of the free film with respect to the long-wave thermocapillary instability.
A molecular “phase ordering” phase transition leading to a modulated aperiodic composite in n-heptane/urea
Authors: Mariette C. , Huard M. , Rabiller P. , Nichols Shane M. , Ecolivet C. , Janssen Ted , Alquist Keith E. , Hollingsworth Mark D. , Toudic B.
Published: March 2012

n-Heptane/urea is an aperiodic inclusion compound in which the ratio of host and guest repeats along the channel axis is very close to unity and is found to have a constant value (0.981) from 280 K to 90 K. Below 280 K, two phase transitions are observed. The first (Tc1 = 145 K) is a ferroelastic phase transition that generates superstructure reflections for the host while leaving the guest with 1D order. The second (Tc2 = 130 K) is a “phase ordering” transition to a four-dimensional structure (P2111(0βγ)) with pronounced host-guest intermodulation and a temperature dependent phase shift between guests in adjacent channels.
Temperature dependent droplet impact dynamics on flat and textured surfaces
Authors: Alizadeh Azar , Bahadur Vaibhav , Zhong Sheng , Shang Wen , Li Ri , Ruud James , Yamada Masako , Ge Liehui , Dhinojwala Ali , Sohal Manohar
Published: March 2012

Droplet impact dynamics determines the performance of surfaces used in many applications such as anti-icing, condensation, boiling, and heat transfer. We study impact dynamics of water droplets on surfaces with chemistry/texture ranging from hydrophilic to superhydrophobic and across a temperature range spanning below freezing to near boiling conditions. Droplet retraction shows very strong temperature dependence especially on hydrophilic surfaces; it is seen that lower substrate temperatures lead to lesser retraction. Physics-based analyses show that the increased viscosity associated with lower temperatures combined with an increased work of adhesion can explain the decreased retraction. The present findings serve as a starting point to guide further studies of dynamic fluid-surface interaction at various temperatures.
Photoelectron spectroscopy and density functional calculations of CuSin− (n = 4–18) clusters
Authors: Xu Hong-Guang , Wu Miao Miao , Zhang Zeng-Guang , Yuan Jinyun , Sun Qiang , Zheng Weijun
Published: March 2012

We conducted a combined anion photoelectron spectroscopy and density functional theory study on the structural evolution of copper-doped silicon clusters, CuSin− (n = 4–18). Based on the comparison between the experiments and theoretical calculations, CuSi12− is suggested to be the smallest fully endohedral cluster. The low-lying isomers of CuSin− with n ≥ 12 are dominated by endohedral structures, those of CuSin− with n < 12 are dominated by exohedral structures. The most stable structure of CuSi12− is a double-chair endohedral structure with the copper atom sandwiched between two chair-style Si6 rings or, in another word, encapsulated in a distorted Si12 hexagonal prism cage. CuSi14− has an interesting C3h symmetry structure, in which the Si14 cage is composed by three four-membered rings and six five-membered rings.
Employing a cylindrical single crystal in gas-surface dynamics
Authors: Hahn Christine , Shan Junjun , Liu Ying , Berg Otto , Kleijn Aart W. , Juurlink Ludo B. F.
Published: March 2012

We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based low energy electron diffraction/retarding field Auger electron spectrometer (AES) apparatus identifies surface structures present on the outer surface of the cylinder, while a separate double pass cylindrical mirror analyzer AES verifies surface cleanliness. A supersonic molecular beam, skimmed by a rectangular slot, impinges molecules on a narrow longitudinal strip of the surface. Here, we use the King and Wells technique to demonstrate how surface structure influences the dissociation probability of deuterium at various kinetic energies. Finally, we introduce spatially-resolved temperature programmed desorption from areas exposed to the supersonic molecular beam to show how surface structures influence desorption features.
Examination of argon metastable atom velocity distribution function close to a conducting wall
Authors: Claire N. , Mazouffre S. , Rebont C. , Doveil F.
Published: March 2012

The spatial evolution of the 1s5 metastable argon atom velocity distribution function is recorded in the sheath and pre-sheath regions of a metallic wall using laser induced fluorescence (LIF) spectroscopy. Metastable argon atom temperature and fluid velocity are computed from measured data. Owing to the loss of metastable argon atom after a collision with the surface, the atom temperature seemingly decreases and the velocity increases when approaching the wall. These artifacts are carefully examined and explained in terms of changes in the metastable argon atom distribution function. In addition, the atom nonelastic reflection coefficient is computed from the ratio of outward to inward atom flux to the surface. This study indicates less than 1% of metastable atoms survive a collision with the metallic wall.
From protein denaturant to protectant: Comparative molecular dynamics study of alcohol/protein interactions
Authors: Shao Qiang , Fan Yubo , Yang Lijiang , Qin Gao Yi
Published: March 2012

It is well known that alcohols can have strong effects on protein structures. For example, monohydric methanol and ethanol normally denature, whereas polyhydric glycol and glycerol protect, protein structures. In a recent combined theoretical and NMR experimental study, we showed that molecular dynamics simulations can be effectively used to understand the molecular mechanism of methanol denaturing protein. In this study, we used molecular dynamics simulations to investigate how alcohols with varied hydrophobicity and different numbers of hydrophilic groups (hydroxyl groups) exert effects on the structure of the model polypeptide, BBA5. First, we showed that methanol and trifluoroethanol (TFE) but not glycol or glycerol disrupt hydrophobic interactions. The latter two alcohols instead protect the assembly of the α- and β-domains of the polypeptide. Second, all four alcohols were shown to generally increase the stability of secondary structures, as revealed by the increased number of backbone hydrogen bonds formed in alcohol/water solutions compared to that in pure water, although individual hydrogen bonds can be weakened by certain alcohols, such as TFE. The two monohydric alcohols, methanol and TFE, display apparently different sequence-dependence in affecting the backbone hydrogen bond stability: methanol tends to enhance the stability of backbone hydrogen bonds of which the carbonyl groups are from polar residues, whereas TFE tends to stabilize those involving non-polar residues. These results demonstrated that subtle differences in the solution environment could have distinct consequences on protein structures.
A photoelectron spectroscopy and ab initio study of B21−: Negatively charged boron clusters continue to be planar at 21
Authors: Piazza Zachary A. , Li Wei-Li , Romanescu Constantin , Sergeeva Alina P. , Wang Lai-Sheng , Boldyrev Alexander I.
Published: March 2012

The structures and chemical bonding of the B21− cluster have been investigated by a combined photoelectron spectroscopy and ab initio study. The photoelectron spectrum at 193 nm revealed a very high adiabatic electron binding energy of 4.38 eV for B21− and a congested spectral pattern. Extensive global minimum searches were conducted using two different methods, followed by high-level calculations of the low-lying isomers. The global minimum of B21− was found to be a quasiplanar structure with the next low-lying planar isomer only 1.9 kcal/mol higher in energy at the CCSD(T)/6-311-G* level of theory. The calculated vertical detachment energies for the two isomers were found to be in good agreement with the experimental spectrum, suggesting that they were both present experimentally and contributed to the observed spectrum. Chemical bonding analyses showed that both isomers consist of a 14-atom periphery, which is bonded by classical two-center two-electron bonds, and seven interior atoms in the planar structures. A localized two-center two-electron bond is found in the interior of the two planar isomers, in addition to delocalized multi-center σ and π bonds. The structures and the delocalized bonding of the two lowest lying isomers of B21− were found to be similar to those in the two lowest energy isomers in B19−.
Argon plasma modeling with detailed fine-structure cross sections
Authors: Gangwar R. K. , Sharma L. , Srivastava R. , Stauffer A. D.
Published: March 2012

Our recently reported fully relativistic distorted-wave electron-impact cross sections from the ground and metastable states of argon to various excited fine-structure levels are incorporated in a collisional-radiative model to obtain the population densities for the 3p54s and 3p54p (1s and 2p) fine-structure manifolds for low temperature argon plasmas. Excitation cross sections from the two 3p54s J = 1 resonance levels, 1s2 and 1s4, to the higher lying 2p fine-structure manifold as well as for transitions among individual levels of the 1s and 2p manifolds are also calculated and included in the present model which were not fully considered in any earlier model. Our results for the population densities of the 1s and 2p levels show good agreement with recent measurements. The variation of population densities of all the 1s and 2p levels with electron temperature and density are presented. We have also calculated and compared the intensities for the 750.38 nm (2p1 → 1s2) and 696.54 nm (2p2 → 1s5) lines with recently reported experimental results. The present work suggests that the inclusion of a complete fine-structure description of the electronic processes occurring in the plasma is important for a collisional radiative model, which includes separate 1s and 2p levels.
Perpendicular exchange bias of [Pt/Co]n/CoO multilayer on ordered nanosphere arrays
Authors: Zhang Y. J. , Li W. , Li J. , Zhang Y. M. , Wang Y. X. , Yang S. Y. , Liu S. S. , Wu L. C. , Beach Geoffrey S. D. , Yang J. H.
Published: March 2012

Polystyrene nanosphere arrays are used as the substrate for [Pt/Co]nCoO multilayer deposition. The effects of nanosphere size and CoO thicknesses on the magnetic properties of [Pt/Co]nCoO multilayer nanocaps are investigated. With decreasing nanosphere diameter, the nanocaps exhibit systematic variations of coercivity, exchange bias field, and switching field distribution. The switching field distribution is broadened and the coercivity is enhanced when the nanosphere sizes decrease, which are ascribed to the magnetic dipole-dipole interaction of the isolated nanocaps when the thickness of multilayer is far below the nanosphere radius. The mixture formation and the anisotropy direction changes of Co and CoO interface play an important role in the variation of the exchange bias field when the multilayer film is deposited on the nanosphere with diameter of 60 nm.
The transition to turbulence in slowly diverging subsonic submerged jets
Authors: Landa P. S. , McClintock P. V. E.
Published: March 2012

We address the problem of how turbulence is created in a submerged plane jet, near to the nozzle from which it issues. We do so by making use of a WKB-like asymptotic expansion for approximate solution of a complex, linear, fourth-order differential equation describing small deviations from the steady-state stream function. The result is used as a generating solution for application of the asymptotic Krylov–Bogolyubov method, enabling us to find the spatial and temporal spectra of the turbulence in the first approximation. We have thus been able to find the complex eigenvalues and eigenfunctions, i.e., the natural waves. We show that, for any given set of parameters, there is a continuum of frequencies and, for each frequency, a continuum of phase velocities. Correspondingly, there is an infinite number of wavelengths. It follows that there is no unique dispersion law and, because of perturbations (however, small they may be), a regular temporal spectrum does not exist even in cases where the spatial spectrum is regular.
Electron shielding current in neutral beam current drive in general tokamak equilibria and arbitrary collisionality regime
Authors: Hu Y. J. , Hu Y. M. , Lin-Liu Y. R.
Published: March 2012

A formula based on the solutions to the drift kinetic equation is proposed for modeling the trapped electron correction to the electron shielding current in neutral beam current drive in general tokamak equilibria and arbitrary collisionality regime.
Casimir amplitudes and capillary condensation of near-critical fluids between parallel plates: Renormalized local functional theory
Authors: Okamoto Ryuichi , Onuki Akira
Published: March 2012

We investigate the critical behavior of a near-critical fluid confined between two parallel plates in contact with a reservoir by calculating the order parameter profile and the Casimir amplitudes (for the force density and for the grand potential). Our results are applicable to one-component fluids and binary mixtures. We assume that the walls absorb one of the fluid components selectively for binary mixtures. We propose a renormalized local functional theory accounting for the fluctuation effects. Analysis is performed in the plane of the temperature T and the order parameter in the reservoir ψ∞. Our theory is universal if the physical quantities are scaled appropriately. If the component favored by the walls is slightly poor in the reservoir, there appears a line of first-order phase transition of capillary condensation outside the bulk coexistence curve. The excess adsorption changes discontinuously between condensed and noncondensed states at the transition. With increasing T, the transition line ends at a capillary critical point \documentclass[12pt]{minimal}\begin{document}$T=T_c^{\rm ca}$\end{document}T=Tc ca slightly lower than the bulk critical temperature Tc for the upper critical solution temperature. The Casimir amplitudes are larger than their critical point values by 10–100 times at off-critical compositions near the capillary condensation line.
Random walk of magnetic field lines in dynamical turbulence: A field line tracing method. II. Two-dimensional turbulence
Authors: Guest B. , Shalchi A.
Published: March 2012

The wandering of magnetic field lines is an important topic in theoretical plasma physics and astrophysics. Previous analytical work, as well as computer simulations, is based on magnetostatic models to warrant mathematical and numerical tractability. Recently, we have studied the first time field line random walk in dynamical turbulence by using a field line tracing method. These calculations were performed for a slab model of the turbulence. It is the purpose of the present paper to use the latter method to compute the field line diffusion coefficient for dynamical two-dimensional turbulence. Two models for the dynamical correlation function are used, namely the damping model of dynamical turbulence and the nonlinear anisotropic dynamical turbulence model. It is shown that the largest scales of the turbulence and the choice of the dynamical turbulence model have a strong influence on the diffusivity of the field lines and the absolute value of the diffusion coefficient.
Effects of molecular architectures and solvophobic additives on the aggregative properties of polymeric surfactants
Authors: Lin Yung-Lung , Wu Ming-Zher , Sheng Yu-Jane , Tsao Heng-Kwong
Published: March 2012

The aggregative behavior of the polymeric surfactants with various molecular architectures in dilute solutions is studied by dissipative particle dynamics. The effects of the solvophobic/solvophilic length, polymeric architecture (linear, star, dendritic, and cyclic type), chain rigidity, and solvophobic additives on the critical micelle concentration (CMC) and the aggregative patterns are systematically investigated. It is found that molecular architectures have a noteworthy impact on the aggregative properties. For linear diblock copolymers, the CMC declines with increasing solvophobic length but rises with increasing solvophilic length. Nonetheless, the solvophobic group has comparatively greater influence on the CMC. Imposition of the star, dendritic, or cyclic structures onto the solvophobic or solvophilic parts of the polymeric surfactant leads to an increase in the CMC. On the contrary, polymers imposed with the greater degree of the rigidity on the solvophobic or solvophilic block have lower CMC. The addition of solvophobic additives results in a decrease of CMC as well. The effects of the concentration and length of the additives on the aggregative behaviors of polymer surfactants were investigated. Interesting supramolecular structures such as caterpillar and worm-like micelles were observed.
Optimal configurations of bistable piezo-composites for energy harvesting
Authors: Betts D. N. , Kim H. A. , Bowen C. R. , Inman D. J.
Published: March 2012

This paper presents an arrangement of bistable composites combined with piezoelectrics for broadband energy harvesting of ambient vibrations. These non-linear devices have improved power generation over conventional resonant systems and can be designed to occupy smaller volumes than magnetic cantilever systems. This paper presents results based on optimization of bistable composites that enables improved electrical power generation by discovering the optimal configurations for harvesting based on the statics of the device. The optimal device aspect ratio, thickness, stacking sequence, and piezoelectric area are considered. Increased electrical output is found for geometries and piezoelectric configurations, which have not been considered previously.
Time-dependent dielectric breakdown of plasma-exposed porous organosilicate glass
Authors: Nichols M. T. , Sinha H. , Wiltbank C. A. , Antonelli G. A. , Nishi Y. , Shohet J. L.
Published: March 2012

Time-dependent dielectric breakdown (TDDB) is a major concern for low-k organosilicate dielectrics. To examine the effect of plasma exposure on TDDB degradation, time-to-breakdown measurements were made on porous SiCOH before and after exposure to plasma. A capillary-array window was used to separate charged particle and vacuum ultraviolet (VUV) photon bombardment. Samples exposed to VUV photons, and a combination of VUV photons and ion bombardment exhibited significant degradation in breakdown time. The samples exposed to VUV photons and ion bombardment showed more degradation in breakdown time in comparison to samples exposed to VUV photons alone.
Transition dipole moments between the low-lying Ωg,u(+/−) states of the Rb2 and Cs2 molecules
Authors: Allouche Abdul-Rahman , Aubert-Frécon Monique
Published: March 2012

For the Rb2 and Cs2 molecules, the adiabatic potential-energy curves and the transition dipole moments of the 43 Ω(+/−)g,u low-lying states dissociating adiabatically to the limits up to ns+(n−1)d (n = 5,6 for Rb2 and Cs2, respectively), have been computed as a function of the internuclear distance R for a large and dense grid. Each molecule was treated as a two-electron system. We used an ab initio approach involving a relativistic non-empirical pseudo-potential for Rb and Cs cores, core-valence polarization potentials, and full valence configuration interaction calculations for the two valence electrons. Spin-orbit effects were taken into account through semi-empirical spin-orbit pseudopotentials. Equilibrium distances, transition energies, rotational constants, and harmonic frequencies as well as depths of wells and heights of barriers are reported for all the molecular states investigated in Hund's cases (a) and (c). Extensive tables of energy values and transition dipole moments are given in an auxiliary (EPAPS) files as a database for future studies on Rb2 and Cs2.
Refraction-type sonic crystal junction diode
Authors: Cicek Ahmet , Adem Kaya Olgun , Ulug Bulent
Published: March 2012

Unidirectional sound transmission across a junction of two square sonic crystals with different orientations and lattice constants is numerically investigated. Re-scaling and rotating the wave vectors through refractions across the air-first sonic crystal interface and the junction, respectively, facilitate coupling into the spatial modes of the second crystal. Unidirectional transmission, demonstrated through finite element method simulations, is accomplished between 10.4 kHz and 12.8 kHz. Transmission values to the right and left are greater than 60% and less than 1.0%, respectively, between 11.0 kHz and 12.4 kHz, resulting in a contrast ratio greater than 0.9.
Tuneable electromechanical comb generation
Authors: Mahboob I. , Wilmart Q. , Nishiguchi K. , Fujiwara A. , Yamaguchi H.
Published: March 2012

An array of equally spaced oscillations or a comb is created within the bandwidth of the fundamental mode of an electromechanical resonator. This phenomenon utilises 2 continuous-wave (CW) pump excitations that piezoelectrically modulate the tension in the mechanical element and is seeded by a CW harmonic excitation of the first mode i.e., the signal. The resultant comb can be dynamically manipulated via the pumps and signal where the teeth separation can be tuned over 3 orders of magnitude and the comb density can be increased from just 2 teeth to nearly 102.
Hydrogen fluoride adsorption and reaction on the α-Al2O3(0001) surface: A density functional theory study
Authors: Quan Jie-Li , Teng Bo-Tao , Wen Xiao-Dong , Zhao Yue , Liu Rui , Luo Meng-Fei
Published: March 2012

The adsorption and reaction behaviors of HF on the α-Al2O3(0001) surface are systematically investigated using density functional theory method. By increasing the number of HF molecules in a p(2 × 1) α-Al2O3(0001) slab, we find that HF is chemically dissociated at low coverage; while both physical and dissociative adsorption occurs at a 3/2 monolayer (ML) coverage. At the same coverage (1.0 ML), diverse configurations of the dissociated HF are obtained in the p(2 × 1) model; while only one is observed in the p(1 × 1) slab due to its smaller surface area compared with the former one. Preliminary fluorination reaction study suggests that the total energy of two dissociated HF in the p(2 × 1) slab increases by 1.00 and 0.72 eV for the formation and desorption of water intermediate, respectively. The coadsorption behaviors of HF and H2O indicate that the pre-adsorbed water is unfavorable for the fluorination of Al2O3, which is well consistent with the experimental results. The calculated density of states show that the peak of σH–F disappears, while the peaks of σH–O and σAl–F are observed at −8.4 and −5 to −3 eV for the dissociated HF. Charge density difference analysis indicates that the dissociated F atom attracts electrons, while no obvious changes on electrons are observed for the surface Al atoms.
Physical origins of nonlinearity in InP double heterojunction bipolar transistors
Authors: Xu H. , Iverson E. W. , (Donald) Cheng K. Y. , Feng M.
Published: March 2012

Two tone inter-modulation distortion measurements were performed at 18 GHz to characterize the nonlinearity of Type-I InP/InGaAs/InP and Type-I/II AlInP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs). Two-dimensional hydrodynamic (HD) simulations were also performed, showing that the base push-out and charge accumulation effects are the dominant physical origins of nonlinearity for the Type-I DHBT at high current densities. Comparatively, the Type-I/II DHBT exhibits no such effects. Hence, we conclude that DHBTs having a Type-I/II energy band alignment will have an inherent linearity advantage compared to DHBTs with the Type-I energy band alignment.
Visualizing charge movement near organic heterojunctions with ultrafast time resolution via an induced Stark shift
Authors: Wiederrecht Gary P. , Giebink Noel C. , Hranisavljevic Jasmina , Rosenmann Daniel , Martinson Alex B. F. , Schaller Richard D. , Wasielewski Michael R.
Published: March 2012

We introduce a method to monitor photoinduced charge separation processes in organic donor-acceptor heterostructures. This approach utilizes a transient Stark shift of the exciton band of a molecular J-aggregate, deposited as a thin probe layer adjacent to the organic heterojunction. The high temporal dynamic range of this approach, from 100 femtoseconds to nanoseconds and longer, enables the entire charge separation process to be followed in both space and time. More broadly, this method can be applied to characterize photoinduced charge injection and separation processes in different materials and architectures, where sub-picosecond time resolution is needed at high spatial resolution.
Note: High-speed optical tracking of a flying insect
Authors: Sakakibara Jun , Kita Junichiro , Osato Naoyuki
Published: March 2012

We developed a video recording system with the capability of tracking moving objects and used it to track the flight of an insect. The system consists of two galvano mirrors, which redirect the light coming from the object in two orthogonal directions toward a high-speed camera to capture the image. An additional high-speed camera, which views the same object through a beam splitter placed between one of the galvano mirrors and the observation camera, detects the position of the object. The mirror angle is controlled to maintain the position of the object at the center of the view, allowing the object to be tracked. In order to validate this system, images of a live fly in flight were recorded along a flight path that was much longer than the field of view of the stationary camera. A high-resolution video image of a rapidly moving live fly was successfully captured.
A comprehensive analytical model for threshold voltage calculation in GaN based metal-oxide-semiconductor high-electron-mobility transistors
Authors: Ťapajna M. , Kuzmík J.
Published: March 2012

An analytical model for threshold voltage calculation for metal-oxide-semiconductor GaN based high electron mobility transistors is proposed. This model includes polarization induced charges at each heterostructure interface/surface, surface donors, oxide/barrier interface traps charge, and interfacial and bulk fixed oxide charge. Applicability of the model is demonstrated on GaN/AlGaN/GaN MOS heterostructure capacitors with Al2O3 and HfO2 gate dielectrics grown by atomic layer deposition with different barrier surface treatment and Al2O3 thicknesse.
Systematically controlling Kapitza conductance via chemical etching
Authors: Duda John C. , Hopkins Patrick E.
Published: March 2012

We measure the thermal interface conductance between thin aluminum films and silicon substrates via time-domain thermoreflectance from 100 to 300 K. The substrates are chemically etched prior to aluminum deposition, thereby offering a means of controlling interface roughness. We find that conductance can be systematically varied by manipulating roughness. In addition, transmission electron microscopy confirms the presence of a conformal oxide for all roughnesses, which is then taken into account via a thermal resistor network. This etching process provides a robust technique for tuning the efficiency of thermal transport while alleviating the need for laborious materials growth and/or processing.
Misfit dislocations in multimetallic core-shelled nanoparticles
Authors: Ding Yong , Sun Xiaolian , Lin Wang Zhong , Sun Shouheng
Published: March 2012

Core-shelled multimetallic nanoparticles have unique catalytic properties compared to their single-element counterparts. Due to the different lattice parameters of the core and shell, the strain field is built up at the interface between the two phases. As for thin films, a formation of misfit and threading dislocations is an approach to release interface strain. However, for two-phase nanoparticles especially when their sizes are at nanometer scale, their dislocation formation in the volume remains to be investigated owing to the large surface-to-volume ratio. Here, we confirmed the existence of dislocations in the Au-FePt core-shelled nanoparticles of sizes less than 10 nm. It is suggested that the different atom sizes of the core and the shell materials are likely to be a key factor to generate and lock dislocations inside the nanoparticles.
Regulatory architecture determines optimal regulation of gene expression in metabolic pathways
Authors: Chubukov Victor , Zuleta Ignacio A. , Li Hao
Published: March 2012

In response to environmental changes, the connections (“arrows”) in gene regulatory networks determine which genes modulate their expression, but the quantitative parameters of the network (“the numbers on the arrows”) are equally important in determining the resulting phenotype. What are the objectives and constraints by which evolution determines these parameters? We explore these issues by analyzing gene expression changes in a number of yeast metabolic pathways in response to nutrient depletion. We find that a striking pattern emerges that couples the regulatory architecture of the pathway to the gene expression response. In particular, we find that pathways controlled by the intermediate metabolite activation (IMA) architecture, in which an intermediate metabolite activates transcription of pathway genes, exhibit the following response: the enzyme immediately downstream of the regulatory metabolite is under the strongest transcriptional control, whereas the induction of the enzymes upstream of the regulatory intermediate is relatively weak. This pattern of responses is absent in pathways not controlled by an IMA architecture. The observation can be explained by the constraint imposed by the fundamental feedback structure of the network, which places downstream enzymes under a negative feedback loop and upstream ones under a positive feedback loop. This general design principle for transcriptional control of a metabolic pathway can be derived from a simple cost/benefit model of gene expression, in which the observed pattern is an optimal solution. Our results suggest that the parameters regulating metabolic enzyme expression are optimized by evolution, under the strong constraint of the underlying regulatory architecture.
Structure of the heterodimer of human NONO and paraspeckle protein component 1 and analysis of its role in subnuclear body formation
Authors: Passon Daniel M. , Lee Mihwa , Rackham Oliver , Stanley Will A. , Sadowska Agata , Filipovska Aleksandra , Fox Archa H. , Bond Charles S.
Published: March 2012

Proteins of the
Drosophila
behavior/human splicing (DBHS) family include mammalian SFPQ (PSF), NONO (p54nrb), PSPC1, and invertebrate NONA and Hrp65. DBHS proteins are predominately nuclear, and are involved in transcriptional and posttranscriptional gene regulatory functions as well as DNA repair. DBHS proteins influence a wide gamut of biological processes, including the regulation of circadian rhythm, carcinogenesis, and progression of cancer. Additionally, mammalian DBHS proteins associate with the architectural long noncoding RNA
NEAT1 (Men
ε/β) to form paraspeckles, subnuclear bodies that alter gene expression via the nuclear retention of RNA. Here we describe the crystal structure of the heterodimer of the multidomain conserved region of the DBHS proteins, PSPC1 and NONO. These proteins form an extensively intertwined dimer, consistent with the observation that the different DBHS proteins are typically copurified from mammalian cells, and suggesting that they act as obligate heterodimers. The PSPC1/NONO heterodimer has a right-handed antiparallel coiled-coil that positions two of four RNA recognition motif domains in an unprecedented arrangement on either side of a 20-Å channel. This configuration is supported by a protein:protein interaction involving the NONA/paraspeckle domain, which is characteristic of the DBHS family. By examining various mutants and truncations in cell culture, we find that DBHS proteins require an additional antiparallel coiled-coil emanating from either end of the dimer for paraspeckle subnuclear body formation. These results suggest that paraspeckles may potentially form through self-association of DBHS dimers into higher-order structures.
Scaling behaviour of a-IGZO TFTs with transparent a-IZO source/drain electrodes
Authors: Jeong Jaewook , Lee Gwang Jun , Kim Joonwoo , Choi Byeongdae
Published: March 2012

We analysed the scaling behaviour of amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) with amorphous indium zinc oxide (a-IZO) transparent source/drain (S/D) electrodes. Due to the sputtering damage of the back-channel region during the a-IZO deposition process, the output characteristics show early saturation behaviour and the field-effect mobility in the saturation region is severely decreased in comparison with that in the linear region, especially when the channel length is decreased. Based on the transmission line method, we found that a long gate overlap distance is required due to the long current transfer length. Therefore, optimizing the parasitic resistance is required for the scaling down of a-IGZO TFTs with transparent a-IZO S/D electrodes.