bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared absorption of CH3OSO and CD3OSO radicals produced upon photolysis of CH3OS(O)Cl and CD3OS(O)Cl in p-H2 matrices
Authors: Lee Yu-Fang , Kong Lin-Jun , Lee Yuan-Pern
Published: March 2012

Irradiation at 239 ± 20 nm of a p-H2 matrix containing methoxysulfinyl chloride, CH3OS(O)Cl, at 3.2 K with filtered light from a medium-pressure mercury lamp produced infrared (IR) absorption lines at 3028.4 (attributable to ν1, CH2 antisymmetric stretching), 2999.5 (ν2, CH3 antisymmetric stretching), 2950.4 (ν3, CH3 symmetric stretching), 1465.2 (ν4, CH2 scissoring), 1452.0 (ν5, CH3 deformation), 1417.8 (ν6, CH3 umbrella), 1165.2 (ν7, CH3 wagging), 1152.1 (ν8, S=O stretching mixed with CH3 rocking), 1147.8 (ν9, S=O stretching mixed with CH3 wagging), 989.7 (ν10, C−O stretching), and 714.5 cm−1 (ν11, S−O stretching) modes of syn-CH3OSO. When CD3OS(O)Cl in a p-H2 matrix was used, lines at 2275.9 (ν1), 2251.9 (ν2), 2083.3 (ν3), 1070.3 (ν4), 1056.0 (ν5), 1085.5 (ν6), 1159.7 (ν7), 920.1 (ν8), 889.0 (ν9), 976.9 (ν10), and 688.9 (ν11) cm−1 appeared and are assigned to syn-CD3OSO; the mode numbers correspond to those used for syn-CH3OSO. The assignments are based on the photolytic behavior and a comparison of observed vibrational wavenumbers, infrared intensities, and deuterium isotopic shifts with those predicted with the B3P86/aug-cc-pVTZ method. Our results extend the previously reported four transient IR absorption bands of gaseous syn-CH3OSO near 2991, 2956, 1152, and 994 cm−1 to 11 lines, including those associated with C−O, O−S, and S=O stretching modes. Vibrational wavenumbers of syn-CD3OSO are new. These results demonstrate the advantage of a diminished cage effect of solid p-H2 such that the Cl atom, produced via UV photodissociation of CH3OS(O)Cl in situ, might escape from the original cage to yield isolated CH3OSO radicals.
Spectral methods for the equations of classical density-functional theory: Relaxation dynamics of microscopic films
Authors: Yatsyshin Petr , Savva Nikos , Kalliadasis Serafim
Published: March 2012

We propose a numerical scheme based on the Chebyshev pseudo-spectral collocation method for solving the integral and integro-differential equations of the density-functional theory and its dynamic extension. We demonstrate the exponential convergence of our scheme, which typically requires much fewer discretization points to achieve the same accuracy compared to conventional methods. This discretization scheme can also incorporate the asymptotic behavior of the density, which can be of interest in the investigation of open systems. Our scheme is complemented with a numerical continuation algorithm and an appropriate time stepping algorithm, thus constituting a complete tool for an efficient and accurate calculation of phase diagrams and dynamic phenomena. To illustrate the numerical methodology, we consider an argon-like fluid adsorbed on a Lennard-Jones planar wall. First, we obtain a set of phase diagrams corresponding to the equilibrium adsorption and compare our results obtained from different approximations to the hard sphere part of the free energy functional. Using principles from the theory of sub-critical dynamic phase field models, we formulate the time-dependent equations which describe the evolution of the adsorbed film. Through dynamic considerations we interpret the phase diagrams in terms of their stability. Simulations of various wetting and drying scenarios allow us to rationalize the dynamic behavior of the system and its relation to the equilibrium properties of wetting and drying.
Determining the dissociation threshold of ammonia trimers from action spectroscopy of small clusters
Authors: Case Amanda S. , Heid Cornelia G. , Western Colin M. , Crim F. Fleming
Published: March 2012

Infrared-action spectroscopy of small ammonia clusters obtained by detecting ammonia fragments from vibrational predissociation provides an estimate of the dissociation energy of the trimer. The product detection uses resonance enhanced multiphoton ionization (REMPI) of individual rovibrational states of ammonia identified by simulations using a consistent set of ground-electronic-state spectroscopic constants in the PGOPHER program. Comparison of the infrared-action spectra to a less congested spectrum measured in He droplets [M. N. Slipchenko, B. G. Sartakov, A. F. Vilesov, and S. S. Xantheas, J. Phys. Chem. A 111, 7460 (2007)]10.1021/jp071279+ identifies the contributions from the dimer and the trimer. The relative intensities of the dimer and trimer features in the infrared-action spectra depend on the amount of energy available for breaking the hydrogen bonds in the cluster, a quantity that depends on the energy content of the detected fragment. Infrared-action spectra for ammonia fragments with large amounts of internal energy have almost no trimer component because there is not enough energy available to break two bonds in the cyclic trimer. By contrast, infrared-action spectra for fragments with low amounts of internal energy have a substantial trimer component. Analyzing the trimer contribution quantitatively shows that fragmentation of the trimer into a monomer and dimer requires an energy of 1700 to 1800 cm−1, a range that is consistent with several theoretical estimates.
Effects of out-of-plane shear flows on fast reconnection in a two-dimensional Hall magnetohydrodynamics model
Authors: Wang Jiaqi , Xiao Chijie , Wang Xiaogang
Published: March 2012

Effects of out-of-plane shear flows on fast magnetic reconnection in Hall magnetohydrodynamics approximation are studied in a slab model with an initial Harris sheet equilibrium. It is found that the out-of-plane shear flows can also generate a series of out-of-plane magnetic perturbations that significantly modify the out-of-plane quadrupolar magnetic perturbation induced by the Hall effect in magnetic reconnection. The modification to out-of-plane magnetic perturbations then considerably affects the magnetic reconnection process. Particularly, flows along the X-line can either enhance or reduce the reconnection rate, even altering the X-point to an O-point and resulting in a secondary island. The impact on satellite observations is also discussed.
Kinetic transition in the growth of Al nanocrystals in Al-Sm alloys
Authors: Imhoff S. D. , Ilavsky J. , Zhang F. , Jemian P. , Evans P. G. , Perepezko J. H.
Published: March 2012

The formation of Al nanocrystals from an amorphous Al92Sm8 alloy involves kinetic phenomena with very different characteristic length and timescales, including initial nucleation and later growth and coarsening. Insight into these processes can be derived from the evolution of the sizes of nanocrystals as a function of time. Synchrotron small angle x-ray scattering (SAXS) experiments provide information about the evolution of the nanocrystal size distribution, particularly at times after nucleation has reached saturation. Accurately interpreting the distribution of intensity measured using SAXS requires a nanoparticle model consisting of nanocrystalline core of pure Al surrounded by a shell enriched in Sm. With this approach, statistical parameters derived from SAXS are independent of detailed assumptions regarding the distribution of Sm around the nanocrystals and allow the maximum radius of nanocrystals within the distribution to be determined unambiguously. Sizes determined independently using transmission electron microcopy are in excellent agreement with the SAXS results. The maximum radius obtained from SAXS is proportional to the cube root of time at large sizes and long times, consistent with a coarsening model. The diffusivity of Al within the Al-Sm alloy is obtained from a quantitative analysis of the coarsening process. Further analysis with this diffusivity and a particle growth model provides a satisfactory account for the particle size evolution at early times before the kinetic transition to coarsening.
Emissivity measurements with an atomic force microscope
Authors: van Zwol P. J. , Ranno L. , Chevrier J.
Published: March 2012

We show that functionalized micromechanical bilayer levers can be used as sensitive probes to accurately measure radiative heat flux in vacuum between two materials at the micro scale. By means of calibration to one material these measurements can be made quantitative for radiative heat flux or for either temperature or material emissivity. We discuss issues and opportunities for our method and provide ample technical details regarding its implementation and demonstrate good correspondence with the Stefan Boltzmann law. We use this system to probe the phase transition of VO2 and find that radiative heat transfer in farfield between VO2 and glass can be reversibly modulated by a factor of 5.
Explicitly correlated Wn theory: W1-F12 and W2-F12
Authors: Karton Amir , Martin Jan M. L.
Published: March 2012

In an attempt to extend the applicability of the W1 and W2 ab initio computational thermochemistry methods, we propose explicitly correlated versions thereof, denoted W1-F12 and W2-F12. In W2-F12, we can “save” one cardinal number (viz., angular momentum) in the basis set sequences without loss in accuracy; in W1-F12, we can do so for first-row compounds but not for second-row compounds. At a root mean square deviation (RMSD) = 0.19 kcal/mol for the first-row molecules in the W4-11 benchmark dataset, W1-F12 is in fact superior to ordinary W1 theory. For the entire W4-11 set, W2-F12 yields a RMSD = 0.20 kcal/mol, comparable to 0.19 kcal/mol from ordinary W2 theory. The extended applicability ranges of W1-F12 and W2-F12 are not just due to the lower computational cost but also to greatly reduced memory and especially storage requirements. They are illustrated through applications to nucleic acids and to polyacenes (with up to four rings), for which the following revised gas-phase heats of formation are found: \documentclass[12pt]{minimal}\begin{document}$\Delta _fH^\circ _{298}$\end{document}ΔfH298∘ = 19.6 (benzene), 34.94 (naphthalene), 53.9, (anthracene), 73.9 (naphthacene/tetracene), 54.9 (adenine), −16.3 (cytosine), 5.1 (guanine), −80.6 (thymine), and −71.6 (uracil) kcal/mol. Our theoretical values for the DNA/RNA bases largely confirm recent predictions based on much lower-level calculations. The W1-F12 theoretical values for benzene, naphthalene, and anthracene are in very good to reasonable agreement with experiment. However, both W1-F12 and other computational estimates show that the accepted experimental value for naphthacene cannot be reconciled with those for the lower acenes: we suggest that \documentclass[12pt]{minimal}\begin{document}$\Delta _f H^\circ _{298}$\end{document}ΔfH298∘[naphthacene(g)] = 74.25 ± 1 kcal/mol is a more realistic estimate.
Coupled Monte Carlo-Poisson method for the simulation of particle-particle effects in dielectrophoretic devices
Authors: La Magna A. , Camarda M. , Deretzis I. , Fisicaro G. , Coffa S.
Published: March 2012

Simulations can aid to bridge the gap between the proof-of-concept stage and the engineering of dielectrophoretic devices. We present a simulation method overcoming the limits of fluid-flow based approaches. In our Monte-Carlo-Poisson simulator, the colloidal system is described at the particle resolution. This characteristic allows for taking into account volume forces and particle-particle interactions usually neglected in the continuum approximation. In turn, large number of particles and large systems can be simulated to meet the device design needs. In an experimentally verifiable case study, we discuss the role of the multi-particle interaction in high and moderate density regimes.
Origin of de-swelling and dynamics of dense ionic microgel suspensions
Authors: Romeo Giovanni , Imperiali Luna , Kim Jin-Woong , Fernández-Nieves Alberto , Weitz David A.
Published: March 2012

A direct consequence of the finite compressibility of a swollen microgel is that it can shrink and deform in response to an external perturbation. As a result, concentrated suspensions of these particles exhibit relaxation dynamics and rheological properties which can be very different with respect to those of a hard sphere suspension or an emulsion. We study the reduction in size of ionic microgels in response to increasing number of particles to show that particle shrinkage originates primarily from steric compression, and that the effect of ion-induced de-swelling of the polymer network is negligible. With increasing particle concentration, the single particle dynamics switch from those typical of a liquid to those of a super-cooled liquid and finally to those of a glass. However, the transitions occur at volume fractions much higher than those characterizing a hard sphere system. In the super-cooled state, the distribution of displacements is non-Gaussian and the dependence of the structural relaxation time on volume fraction is describable by a Volger-Fulcher-Tammann function.
How to accelerate protein search on DNA: Location and dissociation
Authors: Kolomeisky Anatoly B. , Veksler Alex
Published: March 2012

One of the most important features of biological systems that controls their functioning is the ability of protein molecules to find and recognize quickly specific target sites on DNA. Although these phenomena have been studied extensively, detailed mechanisms of protein-DNA interactions during the search are still not well understood. Experiments suggest that proteins typically find their targets fast by combining three-dimensional and one-dimensional motions, and most of the searching time proteins are non-specifically bound to DNA. However these observations are surprising since proteins diffuse very slowly on DNA, and it seems that the observed fast search cannot be achieved under these conditions for single proteins. Here we propose two simple mechanisms that might explain some of these controversial observations. Using first-passage time analysis, it is shown explicitly that the search can be accelerated by changing the location of the target and by effectively irreversible dissociations of proteins. Our theoretical predictions are supported by Monte Carlo computer simulations.
Nanostructures and phase diagrams of ABC star triblock copolymers in pore geometries
Authors: Li Shiben , Qiu Wenjuan , Zhang Linxi , Liang Haojun
Published: March 2012

The nanostructures and phase diagrams of ABC star triblock copolymers in pore geometries are investigated using the real-space self-consistent field theory in two-dimensional space. Two types of pores with neutral surfaces, namely, pores with small and large diameters, are considered. A rich variety of nanostructures are exhibited by the ABC star triblock copolymers in these two types of pores, which differ from those observed in bulk and in other confinements. These structures include perpendicular undulating lamellae, concentric core-shell cylinders, polygonal tiling with cylindrical arrangements, and other complex structures. Triangular phase diagrams for the ABC star triblock copolymers are constructed. The small pores clearly affect the corner and central space of the phase diagrams by distorting the bulk structures into concentric arrangements. Meanwhile, the large pores induce the transformation of bulk structures into concentric structures in most of the phase space, but slightly affect the structures at the center of the phase diagrams. Furthermore, the order–order and order–disorder phase transitions, as well as the stable and metastable phases, in the triangular phase diagrams are examined by analyzing their free energies. These observations on the ABC star triblock copolymers in the pore geometries provide a deeper insight into the behavior of macromolecules in a confined system.
Note: Interionic potentials of mean force for Ca2+-Cl− in polarizable water
Authors: Dang Liem X. , Truong Tai Ba , Ginovska-Pangovska Bojana
Published: March 2012

We describe our molecular dynamics simulation studies of the inter-ionic potentials of mean force (PMF) for the Ca2+-Cl− ion pair in water. Ion-water and ion-ion polarizable potential models were constructed to reproduce experimental ion-hydration enthalpies as well as the electronic-structure calculations of the minimum energy for the Ca2+-Cl− interactions. Our study predicted a PMF with no contact ion pair state and a shallow solvent-separated ion-pair state. In addition, our computed radial distribution function, gCa-Cl, for a 1-M CaCl2 electrolyte solution indicated that there is no contact ion pair but, instead, showed a maximum near 5 Å. This observation is consistent with our PMF calculation. These new results are discussed and compared to the recent classical and ab initio PMF calculations on the same system reported by Timko et al. [J. Chem. Phys. 134, 204510 (2011)]10.1063/1.3595261.
No fragile-to-strong crossover in LiCl-H2O solution
Authors: Nakanishi Masahiro , Griffin Philip , Mamontov Eugene , Sokolov Alexei P.
Published: March 2012

Dynamics of water, especially in the temperature range of the “no man's land”, remain a mystery. We present detailed study of dynamics in aqueous LiCl solution that is often considered as a model for bulk water. We employ broadband dielectric and light scattering spectroscopy in a broad frequency and temperature range. Our analysis reveals no sign of the fragile-to-strong crossover (FSC) neither in structural relaxation nor in translational motions. Our experimental results combined with a large selection of literature data lead to the clear conclusion–there is no FSC in dynamics of aqueous solutions at T ∼ 200–230 K. Instead, our analysis reveals appearance of the so-called excess wing at the high frequency tail of the structural relaxation peak. We discuss the localized nature of the relaxation process that contributes to the excess wing.
Approaching chemical accuracy with quantum Monte Carlo
Authors: Petruzielo F. R. , Toulouse Julien , Umrigar C. J.
Published: March 2012

A quantum Monte Carlo study of the atomization energies for the G2 set of molecules is presented. Basis size dependence of diffusion Monte Carlo atomization energies is studied with a single determinant Slater-Jastrow trial wavefunction formed from Hartree-Fock orbitals. With the largest basis set, the mean absolute deviation from experimental atomization energies for the G2 set is 3.0 kcal/mol. Optimizing the orbitals within variational Monte Carlo improves the agreement between diffusion Monte Carlo and experiment, reducing the mean absolute deviation to 2.1 kcal/mol. Moving beyond a single determinant Slater-Jastrow trial wavefunction, diffusion Monte Carlo with a small complete active space Slater-Jastrow trial wavefunction results in near chemical accuracy. In this case, the mean absolute deviation from experimental atomization energies is 1.2 kcal/mol. It is shown from calculations on systems containing phosphorus that the accuracy can be further improved by employing a larger active space.
Agglomeration of magnetic nanoparticles
Authors: Chuan Lim Eldin Wee , Feng Ruili
Published: March 2012

The formation of agglomerates by salt-induced double layer compression of magnetic nanoparticles in the absence and presence of an external magnetic field was investigated experimentally as well as computationally in this study. The structures of the agglomerates were analyzed through scanning electron microscopy and proved to be highly porous and composed of large spaces among the branches of a convoluted network. In the absence of an external magnetic field, the branches of such a network were observed to be oriented in no particular direction. In contrast, when the agglomeration process was allowed to occur in the presence of an external magnetic field, these branches appeared to be oriented predominantly in one direction. A modified Discrete Element Method was applied to simulate the agglomeration process of magnetic nanoparticles both in the absence and presence of an external magnetic field. The simulations show that agglomeration occurred by the formation of random clusters of nanoparticles which then joined to form a network. In the presence of anisotropic magnetic forces, these clusters were rotated to align along the direction of the magnetic field and the final network formed consisted largely of elongated branches of magnetic nanoparticles.
Polarization anisotropic luminescence of tunable single lateral quantum dot molecules
Authors: Hermannstädter C. , Witzany M. , Heldmaier M. , Hafenbrak R. , Jöns K. D. , Beirne G. J. , Michler P.
Published: March 2012

We investigate the photoluminescence polarization anisotropy of self-assembled individual lateral InGaAs/GaAs quantum dot molecules. In contrast to similarly grown single quantum dots, the dot molecules exhibit a remarkable degree of linear polarization, which remains almost unchanged when a lateral electric field is applied to tune the exciton wave function and, thus, the luminescence spectral properties. We discuss the nature of this polarization anisotropy and suggest possible causes based on the system’s symmetry and heterostructure alloy composition.
1-nm-capacitance-equivalent-thickness HfO2/Al2O3/InGaAs metal-oxide-semiconductor structure with low interface trap density and low gate leakage current density
Authors: Suzuki R. , Taoka N. , Yokoyama M. , Lee S. , Kim S. H. , Hoshii T. , Yasuda T. , Jevasuwan W. , Maeda T. , Ichikawa O. , Fukuhara N. , Hata M. , Takenaka M. , Takagi S.
Published: March 2012

We have studied the impact of the Al2O3 inter-layer on interface properties of HfO2/InGaAs metal-oxide-semiconductor (MOS) interfaces. We have found that the insertion of the ultrathin Al2O3 inter-layer (2 cycle: 0.2 nm) can effectively improve the HfO2/InGaAs interface properties. The frequency dispersion and the stretch-out of C-V characteristics are improved, and the interface trap density (Dit) value is significantly decreased by the 2 cycle Al2O3 inter-layer. Finally, we have demonstrated the 1-nm-thick capacitance equivalent thickness in the HfO2/Al2O3/InGaAs MOS capacitors with good interface properties and low gate leakage of 2.4 × 10−2 A/cm2.
Second and higher harmonics generation with memristive systems
Authors: Cohen Guy Z. , Pershin Yuriy V. , Di Ventra Massimiliano
Published: March 2012

We show that memristive systems can be used very efficiently to generate passively both double and higher frequency harmonics. A technique for maximizing the power conversion efficiency into any given harmonic is developed and applied to a single memristive system and memristive bridge circuits. We find much higher rates of power conversion compared to the standard diode bridge, with the memristive bridge more efficient for second and higher harmonics generation compared to the single memristive system. The memristive bridge circuit optimized for second harmonic generation behaves as a two-quarter-wave rectifier.
Strain effect on the surface potential and nanoscale switching characteristics of multiferroic BiFeO3 thin films
Authors: Yan F. , Miao S. , Zhu T. J. , Lai M. O. , Lu L.
Published: March 2012

The BiFeO3 films were deposited on the SrTiO3 (001) substrates via tuning the thickness of the SrRuO3 (SRO) bottom electrode by pulsed laser deposition. The macroscopic ferroelectric and dielectric properties were dramatically impacted by the various nanoscale domain structures for both films due to the tunable SRO thickness. The nanoscale domain switching behaviors for both films were investigated via piezoresponse force microscopy, and results suggest that the domain structure could be changed by tuning the strain state. The surface potential investigation indicates that strain helps increase data storage density and stability.
Infinite symmetry on the boundary of SL(3)/SO(3)
Authors: Arponen Heikki
Published: March 2012

Asymptotic symmetries of the five-dimensional noncompact symmetric space \documentclass[12pt]{minimal}\begin{document}$SL(3,\mathbb {R})/SO(3,\mathbb {R})$\end{document}SL(3,R)/SO(3,R) are found to form an infinite-dimensional Lie algebra, analogously to the asymptotic symmetries of anti-de Sitter/hyperbolic spaces in two and three dimensions. Possible generalizations of the AdS/CFT correspondence and gauge/gravity dualities to such a space is discussed.
A characterization of causal automorphisms by wave equations
Authors: Kim Do-Hyung
Published: March 2012

A characterization of causal automorphisms on Minkowski spacetime is given by use of wave equations.
Ge/SiGe heterostructures as emitters of polarized electrons
Authors: Bottegoni F. , Ferrari A. , Isella G. , Cecchi S. , Marcon M. , Chrastina D. , Trezzi G. , Ciccacci F.
Published: March 2012

The spin polarization of electrons photoemitted from Ge-on-Si and strained Ge epilayers is measured by means of Mott polarimetry. Our results indicate that efficient electron spin polarization can be obtained using SiGe heterostructures deposited on Si(001). Mismatch strain is seen to increase spin polarization above the 50% bulk limit by removing the heavy-hole/light-hole degeneracy in the valence band.
Fresnel-reflection-based fiber sensor for high-temperature measurement
Authors: Pan Jingshun , Huang Xuguang , He Yuming , Huang Binjie
Published: March 2012

A fiber sensor system was developed to measure high temperatures. The system consists of a diode laser as the light source, three optical couplers, two sensing fiber ends, and two photodetectors. The measurement is based on the relative Fresnel reflection intensity and the thermo-optic effect of the fiber. The application of this relative technique can operatively eliminate the errors resulting from light source fluctuations and the effect of the environment. The stability of the system for long-duration measurements can also be effectively improved.
Design of a vector magnet for the measurements of anisotropic magnetoresistance and rotational magneto-optic Kerr effect
Authors: Li J. , Jin E. , Son H. , Tan A. , Cao W. N. , Hwang Chanyong , Qiu Z. Q.
Published: March 2012

A vector magnet is designed and assembled with two electromagnets to produce a rotational magnetic field in any direction within a plane. This design allows a rotation of the magnetic field without a mechanical rotation of the magnets. The fast speed of the field rotation (∼10 s for a complete 360° rotation) and the stability against mechanical vibration easily overcome the slow drifting effect in anisotropic magnetoresistance (AMR) and rotational magneto-optic Kerr effect (ROTMOKE) measurements. As an example we applied this vector magnet to carry out AMR and ROTMOKE measurements on epitaxial growth of Fe(10 nm)/MgO(001) films. The result demonstrates the stability and high quality of the vector magnet in determining the magnetic anisotropy of magnetic thin films using AMR and ROTMOKE techniques.
Growth stress in SiO2 during oxidation of SiC fibers
Authors: Hay R. S.
Published: March 2012

A method to calculate growth stress in SiO2 scales formed during SiC fiber oxidation was developed. Calculations were done for Hi-NicalonTM-S SiC fibers using previously measured Deal-Grove oxidation kinetics parameters. Initial compressive stresses in SiO2 of ∼25 GPa from the 2.2× oxidation volume expansion are rapidly relaxed to lower levels by flow of silica with a shear-stress dependent viscosity. At >1200°, viscous flow of silica relaxes stress to negligible levels. At 700° – 900 °C, compressive axial and hoop stress at the GPa level persist, but radial stresses are much smaller. The decrease in growth stress with increase in temperature is a consequence of larger activation energy for silica viscosity than for oxidation kinetics. Radial expansion of the outer scale eventually causes hoop stress to become tensile in the outer scale, and axial stress becomes tensile from the Poisson effect. Tensile hoop stresses can be >1 GPa for thick scales formed at <1000 °C. Approximate analytical expressions for growth stress for some limiting cases are discussed. Growth stresses were also calculated for crystallized SiO2 scales; these were qualitatively consistent with microstructural evidence of stress. Assumptions and limitations of the calculation method are discussed, along with the possible effects of growth stress on SiC oxidation kinetics and on SiC fiber strength.
Oxygen-diffusion limited metal combustions in Zr, Ti, and Fe foils: Time- and angle-resolved x-ray diffraction studies
Authors: Wei Haoyan , Yoo Choong-Shik , Chen Jing-Yin , Shen Guoyin
Published: March 2012

The transient phase and chemical transformations of diffusion controlled metal combustions in bulk Zr, Ti, and Fe foils have been investigated, in situ, using novel time- and angle-resolved x-ray diffraction (TARXD). The TARXD employs monochromatic synchrotron x-rays and a fast-rotating diffracted beam chopper resolving the diffraction image temporally in time-resolution of ∼45 μs along the azimuth on a 2D pixel array detector. The metal foil strips (10–25 μm in thickness) are ignited using a pulsed electrical heating with a typical heating rate of ∼106 K/s. The x-ray results indicate that the combustion occurs in molten metals, producing a wide range of stoichiometric solid oxides. It reflects an enhanced oxygen solubility and mobility of molten metals with respect to those of solid metals. However, the initial oxides formed are mainly oxygen-deficient metal oxides of ZrO, TiO, and FeO/Fe3O4 —the lowest suboxides stable at these high temperatures. These transition metal monoxides further react with unreacted molten metals, yielding the secondary products of Zr3O, Ti3O, and Ti2O — but not in FeO/Fe3O4. On the other hand, the higher stoichiometric oxides of ZrO2 and TiO2 are formed in the later time only on the metal surface. These results clearly indicate that the combustion process of metal strips is diffusion limited and strongly depends on the solubility and diffusivity of oxygen into molten metals. The time-resolved diffraction data reveals no evidence for metal oxidation in solids, but a series of temperature-induced polymorphic phase transitions. The dynamic thermal expansibility of Fe measured in the present fast heating experiments is similar to those in static conditions (3.3*10−5/K vs 3.5*10−5/K for α-Fe and 6.5*10−5/K versus 7.0*10−5/K for γ-Fe).
Tunable magnetocaloric effect near room temperature in La0.7-xPrxSr0.3MnO3 (0.02 ≤ x ≤ 0.30) manganites
Authors: Zhang YingDe , Lampen Paula J. , Phan The-Long , Yu Seong-Cho , Srikanth Hariharan , Phan Manh-Huong
Published: March 2012

We have systematically investigated the compositional dependence of the magnetic and magnetocaloric properties of La0.7-xPrxSr0.3MnO3 (LPSMO). Polycrystalline samples of LPSMO with 0.02 ≤ x ≤ 0.30 were prepared by a standard solid-state reaction method with phase purity and structure confirmed using x-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order ferromagnetic transitions in each sample with Curie temperature decreasing progressively with increasing Pr content from ∼350 K for x = 0.02 to ∼295 K for x = 0.30. Magnetic entropy change (ΔSM) was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field dependent magnetization curves. In the sample with x = 0.30, the maximum value of −ΔSM reaches ∼2.08 J/kg K at 295 K for a field change of 1.5 T. Reduced Pr content corresponds to larger values of entropy change, reaching −ΔSM ∼2.79 J/kg K for the x = 0.02 doping. The refrigeration capacity for each composition reached sizable values of 33–48 J/kg for a small applied field of 1.5 T.
Monte Carlo simulation for the electron cascade due to gamma rays in semiconductor radiation detectors
Authors: Narayan Raman D. , Miranda Ryan , Rez Peter
Published: March 2012

A Monte Carlo code was developed for simulating the electron cascade in radiation detector materials. The electron differential scattering cross sections were derived from measured electron energy-loss and optical spectra, making the method applicable for a wide range of materials. The detector resolution in a simplified model system shows dependence on the bandgap, the plasmon strength and energy, and the valence band width. In principle, these parameters could be optimized to improve detector performance. The intrinsic energy resolution was calculated for three semiconductors: silicon (Si), gallium arsenide (GaAs), and zinc telluride (ZnTe). Setting the ionization thresholds for electrons and holes is identified as a critical issue, as this strongly affects both the average electron-hole pair energy w and the Fano factor F. Using an ionization threshold from impact ionization calculations as an effective bandgap yields pair energies that are well matched to measured values. Fano factors of 0.091 (Si), 0.100 (GaAs), and 0.075 (ZnTe) were calculated. The Fano factor calculated for silicon using this model was lower than some results from past simulations and experiments. This difference could be attributed to problems in simulating inter-band transitions and the scattering of low-energy electrons.
Effect of temperature on turbulent and laminar flow efficacy analysis of nanofluids
Authors: Tesfai Waka , Singh Pawan K. , Masharqa Salim J. S. , Chiesa Matteo , Shatilla Youssef
Published: March 2012

The present study investigates the temperature-dependent efficacy analysis of nanofluids for both laminar and turbulent flow applications. Characterizations for the thermo-physical properties of nanofluids are carried out at different temperatures for the viability analysis. Thermal conductivity of yttria nanofluids shows strong temperature dependence compared to copper nanofluids with an increase of 7.5% to 21% for a temperature range of 25 °C to 85 °C. Moreover, the effective viscosity of yttria nanofluids is found to decrease gradually with temperatures in spite of copper nanofluid insensitivity. A theoretical study is carried out to compute the efficacy of yttria and copper nanofluids for laminar and turbulent flow regimes over a range of temperatures with the help of their thermo-physical properties. Yttria nanofluids are found viable for both laminar and turbulent flow for temperatures above 37 °C and 45 °C, respectively. On the other hand, copper nanofluids are found applicable only in laminar flow condition for temperatures above 75 °C. The stability and superior figure of merit for yttria nanofluids with temperature make it a potential coolant for higher-temperature convective cooling systems working on both laminar and turbulent flows.
Determination of the spin polarization of RFe2 (R = Dy, Er, Y) by point contact Andreev reflection
Authors: Morrison C. , Wang D. , Bowden G. J. , Ward R. C. C. , Groot P. A. J. de
Published: March 2012

Epitaxially grown intermetallic RFe2 (R = Dy, Er, Y) thin films have been studied by point contact Andreev reflection. Spin polarization values were extracted by fitting normalized conductance curves for mechanical Nb/RFe2 point contacts, using a modified Blonder-Tinkham-Klapwijk model. Good agreement is found between this model and the experimentally obtained data. Extracted values of spin polarization, which are close to the spin polarization of Fe, reveal no variation with the rare earth component for the measured intermetallic compounds. This suggests that using this technique we probe the Fe sub-lattice, and that this lattice drives spintronic effects in these compounds.
Combined experimental and theoretical study of the low temperature dielectric and magnetic properties of trivalent Eu ion doped SrTiO3 ceramics
Authors: Yu Jiangzhou , Fang Liang , Cai Tianyi , Ju Sheng , Dong Wen , Zheng Fengang , Shen Mingrong
Published: March 2012

Single-phase Sr1–3x/2EuxTiO3 (SETOx) (x = 0–0.075) ceramics were prepared to study the effects of Eu substitution on their crystal structure, low temperature dielectric, and magnetic behaviors. Rietveld refinement of X-ray diffraction data yields direct evidence that the Eu ion substitutes Sr site at the perovskite. The measured dielectric properties can be well explained by the mean-field model. It has been found that the anomaly dielectric enhancement behavior exists in the SETOx = 0.005 sample, while more stable quantum paraelectric states are obtained in other doped samples. On the other hand, all the Eu doped samples exhibit doping concentration dependence of paramagnetism. Developing the linear response model, we conclude that a molecular field is acting on Eu ions possibly via the spin polarized Eu-O-Ti hybridization.
Microcrystalline silicon solar cells deposited using a plasma process excited by tailored voltage waveforms
Authors: Johnson E. V. , Delattre P. A. , Booth J. P.
Published: March 2012

Thin film solar cells in a p-i-n structure with an absorbing layer of intrinsic hydrogenated microcrystalline silicon (μc-Si:H) deposited through plasma enhanced chemical vapour deposition excited by tailored voltage waveforms have been prepared. The use of an asymmetric voltage waveform decouples the ion-bombardment energy at the growth surface from the injected power and allows the growth of good quality μc-Si:H at reasonable deposition rates (3 Å/s) using low pressure, powder-free conditions. Unoptimized photovoltaic devices with an efficiency of 6.1% are demonstrated using an i-layer deposited at 1.3 Å/s and a process pressure of 500 mTorr.
Structural investigations of interfaces in Fe90Sc10 nanoglasses using high-energy x-ray diffraction
Authors: Ghafari M. , Kohara S. , Hahn H. , Gleiter H. , Feng T. , Witte R. , Kamali S.
Published: March 2012

High-resolution diffraction experiments of Fe90Sc10 nanoglasses and rapidly quenched metallic glasses as reference materials have been performed using high-energy x-rays with a wavelength of 0.21 Å from a synchrotron radiation source. Nanoglasses are amorphous alloys with a significant fraction of interfaces on the nanometer scale. The short- and intermediate-range orders of a nanoglass are different from the well known amorphous materials produced by rapid quenching from the melt. These structural modifications have significant influence on the physical properties. In this paper, the short- and intermediate-range orders of the nanoglass Fe90Sc10 and the reference metallic glass Fe90Sc10 alloy prepared by rapid quenching are discussed.
Communication: Engineered tunable decay rate and controllable dissipative dynamics
Authors: Lü Zhiguo , Zheng Hang
Published: March 2012

We investigate the steering dissipative dynamics of a two-level system (qubit) by means of the modulation of an assisted tunneling degree of freedom which is described by a quantum-oscillator spin-boson model. Our results reveal that the decoherence rate of the qubit can be significantly suppressed and simultaneously its quality factor is enhanced. Moreover, the modulated dynamical susceptibility exhibits a multi-peak feature which is indicative of the underlying structure and measurable in experiment. Our findings demonstrate that the interplay between the combined degrees of freedom and the qubit is crucial for reducing the dissipation of qubit and expanding the coherent regime of quantum operation much large. The strategy might be used to fight against deterioration of quantum coherence in quantum information processing.
Enhancement and quenching of photoluminescence from silicon quantum dots by silver nanoparticles in a totally integrated configuration
Authors: Benami A. , López-Suárez A. , Rodríguez-Fernández L. , Crespo-Sosa A. , Cheang-Wong J. C. , Reyes-Esqueda J. A. , Oliver A.
Published: March 2012

In this study, Si QDs were formed inside silica matrix by implantation and annealing. Subsequent implantations with Ag+2 ions at different energies were performed in order to vary the distance between the previously formed Si QDs and newly aggregated Ag NPs. The coupling between them was observed through the PL energy and intensity from Si QDs. A PL enhancement is well evidenced at the lowest implantation energy (1 MeV), but at higher energies, a decrease in intensity (2 MeV) and a quenching (3 MeV) are observed.
Solving real time evolution problems by constructing excitation operators
Authors: Wang Pei
Published: March 2012

In this paper we study the time evolution of an observable in the interacting fermion systems driven out of equilibrium. We present a method for solving the Heisenberg equations of motion by constructing excitation operators which are defined as the operators \documentclass[12pt]{minimal}\begin{document}$\hat{A}$\end{document}Â satisfying \documentclass[12pt]{minimal}\begin{document}$[\hat{H},\hat{A}]=\lambda \hat{A}$\end{document}[Ĥ,Â]=λÂ. It is demonstrated how an excitation operator and its excitation energy λ can be calculated. By an appropriate supposition of the form of \documentclass[12pt]{minimal}\begin{document}$\hat{A}$\end{document}Â we turn the problem into the one of diagonalizing a series of matrices whose dimension depends linearly on the size of the system. We perform this method to calculate the evolution of the creation operator in a toy model Hamiltonian which is inspired by the Hubbard model and the nonequilibrium current through the single impurity Anderson model. This method is beyond the traditional perturbation theory in Keldysh-Green's function formalism, because the excitation energy λ is modified by the interaction and it will appear in the exponent in the function of time.
Small angle electron diffraction and deflection
Authors: Koyama T. , Takayanagi K. , Togawa Y. , Mori S. , Harada K.
Published: March 2012

Electron optical system is constructed in order to obtain small angle diffraction and Lorentz deflection of electrons at the order of down to 10-6 radian in the reciprocal space. Long-distance camera length up to 3000 m is achieved in a conventional transmission electron microscope with LaB6 thermal emission type. The diffraction pattern at 5 × 10-6 radian is presented in a carbon replica grating with 500 nm lattice spacing while the magnetic deflection pattern at 2 × 10-5 radian is exhibited in Permalloy elements. A simultaneous recording of electron diffraction and Lorentz deflection is also demonstrated in 180 degree striped magnetic domains of La0.825Sr0.175MnO3.
Evidence that hyperprolactinaemia is associated with ovarian acyclicity in female zoo African elephants
Authors: Dow T. L. , Brown J. L.
Published: March 2012

African elephants of reproductive age in zoos are experiencing high rates of ovarian cycle problems (>40%) and low reproductive success. Previously, our laboratory found that 1/3 of acyclic females exhibit hyperprolactinaemia, a likely cause of ovarian dysfunction. This follow-up study re-examined hyperprolactinaemia in African elephants and found the problem has increased significantly to 71% of acyclic females. Circulating serum progestagens and prolactin were analysed in 31 normal cycling, 13 irregular cycling and 31 acyclic elephants for 12 months. In acyclic females, overall mean prolactin concentrations differed from cycling females (P < 0.05), with concentrations being either higher (n = 22; 54.90 ± 13.31 ng mL–1) or lower (n = 9; 6.47 ± 1.73 ng mL–1) than normal. No temporal patterns of prolactin secretion were evident in elephants that lacked progestagen cycles. In cycling females, prolactin was secreted in a cyclical manner, with higher concentrations observed during nonluteal (34.38 ± 1.77 and 32.75 ± 2.61 ng mL–1) than luteal (10.51 ± 0.30 and 9.67 ± 0.42 ng mL–1) phases for normal and irregular females, respectively. Of most concern was that over two-thirds of acyclic females now are hyperprolactinemic, a dramatic increase over that observed 7 years earlier. Furthermore, females of reproductive age constituted 45% of elephants with hyperprolactinaemia. Until the cause of this problem is identified and a treatment is developed, reproductive rates will remain suboptimal and the population nonsustaining.
Rectal self-sampling in non-clinical venues for detection of sexually transmissible infections among behaviourally bisexual men
Authors: Dodge Brian , Van Der Pol Barbara , Reece Michael , Malebranche David , Martinez Omar , Goncalves Gabriel , Schnarrs Phillip , Nix Ryan , Fortenberry J. Dennis
Published: March 2012

Rectal sexually transmissible infections are a common health concern for men who have sex with men but little is known about these infections among men who have sex with both men and women. Self-obtained rectal specimens were collected from a diverse sample of behaviourally bisexual men. From a total sample of 75 bisexual men, 58 collected specimens. A relatively high prevalence of rectal Chlamydia trachomatis infection was found. Participants who collected specimens reported overall acceptability and comfort with self-sampling. Future efforts are needed focusing on increasing awareness of and options for rectal sexually transmissible infection testing among bisexual men.
Use of alcohol, nicotine and other drugs in the Western Australian HIV Cohort study
Authors: Herrmann Susan E. , McKinnon Elizabeth J. , Williams Leah J. , John Mina , Mallal Simon , Lucas Michaela , Nolan David A.
Published: March 2012

Self-report questionnaires on alcohol, nicotine and other drugs were administered to assess the current prevalence of alcohol, drug and nicotine use in our tertiary HIV service and inform the establishment of effective interventions. Many respondents reported use of alcohol over the preceding month (111 out of 152, 73%), and recent drug use (48 out of 137, 35%) and frequently both. Sessional alcohol consumption was prevalent among drinkers (52 out of 111, 47%), and correlated with both early treatment phase (P = 0.009) and non-adherence (P = 0.03). Encouraged by a notable proportion of patients expressing interest in clinic-based smoking cessation counselling, we recommend a targeted education strategy to motivate patients in health-seeking behaviours.
Missed opportunities for chlamydia screening by community pharmacists
Authors: Dabrera Gavin , Pinson David , Whiteman Steve
Published: March 2012

Provision of Emergency Hormonal Contraception (EHC) is an ideal opportunity for offering Chlamydia screening (CS) to sexually active young women. We audited 3 months of CS activity in community pharmacies. This identified low rates of offers and uptake of CS in community pharmacies providing EHC to young women. This highlights the potential for significant improvement in CS uptake among this at-risk group in the pharmacy setting.
Deficiency in DNA methylation increases meiotic crossover rates in euchromatic but not in heterochromatic regions in Arabidopsis
Authors: Melamed-Bessudo Cathy , Levy Avraham A.
Published: March 2012

Meiotic recombination is tightly regulated by
cis
- and
trans
-acting factors. Although DNA methylation and chromatin remodeling affect chromosome structure, their impact on meiotic recombination is not well understood. To study the effect of DNA methylation on the landscape of chromosomal recombination, we analyzed meiotic recombination in the
decreased DNA methylation 1
(
ddm1
) mutant. DDM1 is a SWI2/SNF2-like chromatin-remodeling protein necessary for DNA methylation and heterochromatin maintenance in
Arabidopsis thaliana
. The rate of meiotic recombination between markers located in euchromatic regions was significantly higher in both heterozygous (
DDM1
/
ddm1)
and homozygous (
ddm1/ddm1)
backgrounds than in WT plants. The effect on recombination was similar for both male and female meiocytes. Contrary to expectations,
ddm1
had no effect on the number of crossovers between markers in heterochromatic pericentric regions that underwent demethylation. These results are surprising, because the pericentromeric regions are hypermethylated and were expected to be the regions most affected by demethylation. Thus,
DDM1
loss of function may trigger changes that enhance meiotic recombination in euchromatin regions but are not sufficient to induce the same events in heterochromatic segments. This work uncovers the repressive role of methylation on meiotic recombination in euchromatic regions and suggests that additional factors may have a role in controlling the suppression of recombination in heterochromatin.
Land-use legacy effects of cultivation on ecological processes.
Authors: Morris L. R.
Published: March 2012

In this chapter, the anthropogenic disturbances associated with cultivation, different from natural ones, how these exotic disturbances create land-use legacies through alteration of biotic and abiotic processes, and what managers might do to help repair these processes are discussed.