bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting rupture arrests, rupture jumps and cascading earthquakes
Authors: Finzi Y. , Langer S.
Published: October 2012

The devastation inflicted by recent earthquakes demonstrates the danger of under‐predicting the size of earthquakes. Unfortunately, earthquakes may rupture fault‐sections larger than previously observed, making it essential to develop predictive rupture models. We present numerical models based on earthquake physics and fault zone data, that determine whether a rupture on a segmented fault could cascade and grow into a devastating, multisegment earthquake. We demonstrate that weakened (damaged) fault zones and bi‐material interfaces promote rupture propagation and greatly increase the risk of cascading ruptures and triggered seismicity. This result provides a feasible explanation for the outstanding observation of a very large (10 km) rupture jump documented in theMW7.8 2001 Kunlun, China earthquake. However, enhanced inter‐seismic deformation and energy dissipation at fault tips suppress rupture propagation and may turn even small discontinuities into effective earthquake barriers. By assessing fault stability, identifying rupture barriers and foreseeing multisegment earthquakes, we provide a tool to improve earthquake prediction and hazard analysis.
Variability of the Denmark Strait overflow: Moored time series from 1996–2011
Authors: Jochumsen Kerstin , Quadfasel Detlef , Valdimarsson Heðinn , Jónsson Steingrímur
Published: October 2012

The Denmark Strait overflow provides about half of the total dense water overflow from the Nordic Seas into the North Atlantic Ocean. The velocity of the overflow has been monitored in the Strait with two moored Acoustic Doppler Current Profilers since 1996 with several interruptions due to mooring losses or instrument failure. So far, overflow transports were only calculated when data from both moorings were available. In this work, we introduce a linear model to fill gaps in the time series when data from only one instrument is available. The mean overflow transport is 3.4 Sv and exhibits a variance of 2.0 Sv2. No significant trend was detected in the time series. The highest variability in the transport is associated with the passage of mesoscale eddies with time scales of 2–10 days (associated with a variance of 1.5 Sv2). Seasonal variability is weak and explains less than 5% of the variance in all time series, which is in contrast to the strong seasonal cycle found in high resolution model simulations. Interannual variability is on the order of 10% of the mean. A relation to atmospheric forcing such as the local wind stress curl, as well as to larger scale phenomena, e.g. the North Atlantic Oscillation, is not detected. Since 2005 data from moored temperature, conductivity and pressure recorders have been available as well, monitoring the hydrographic variability at the bottom of Denmark Strait. In recent years the temperature time series of the Denmark Strait overflow revealed a cooling, while the salinity stayed nearly constant.
Feedback attribution of the El Niño–Southern Oscillation–related atmospheric and surface temperature anomalies
Authors: Park Tae‐Won , Deng Yi , Cai Ming
Published: October 2012

A feedback attribution analysis is conducted for the ENSO‐related atmospheric and surface temperature anomalies in boreal winter. Local temperature anomalies are decomposed into partial temperature changes due to changes in oceanic dynamics/heat storage, water vapor, clouds, atmospheric dynamics, ozone, and surface albedo. It is shown that atmospheric dynamics plays distinctly different roles in establishing the tropical and extratropical temperature response to El Niño. The atmospheric dynamics serves as a primary negative feedback to the tropical (tropospheric) warming by transporting out of the tropics excessive energy production associated with oceanic dynamical forcing. In the northern extratropics, it is the main forcing of atmospheric temperature changes and also modulates surface temperatures via longwave radiative heating and cooling. This provides an alternative view of the “atmospheric bridge” mechanism from the perspective of local energetics and temperature feedback attribution. Substantial tropospheric cooling over the eastern North Pacific is found to be collectively contributed by water vapor, cloud, and atmospheric dynamical feedbacks, driven at least partly by the equatorward shift of the Pacific storm track during El Niño. Polar stratospheric warming (cooling), largely due to atmospheric dynamics, is seen over the Eurasian‐Pacific (Atlantic) sector, with ozone feedback contributing significantly to the midstratospheric cooling over the Atlantic sector. Water vapor (atmospheric dynamical) feedback has an overall warming (cooling) effect throughout the tropical troposphere, and cloud feedback cools (warms) the tropical lower to middle (upper) troposphere. Atmospheric dynamics induces stratospheric warming over the entire northern extratropics and drives over northern midlatitudes (high latitudes) a tropospheric cooling (warming) that generally intensifies with altitude.
Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) north polar springtime recession mapping: First 3 Mars years of observations
Authors: Brown Adrian J. , Calvin Wendy M. , Murchie Scott L.
Published: October 2012

We report on mapping of the north polar region of Mars using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument. We have observed 3 Mars years (28–30) of late winter and spring recessions (Ls = 304°–92°). Our investigations have led to the following observations. (1) We classify the retreat of the north polar seasonal cap into “presublimation,” “early spring,” “asymmetric” and “stable” periods according to the prevalent H2O ice grain size distributions. (2) During the early spring, the signatures of CO2 ice at the edge of the cap are obscured by H2O ice, which increases the apparent size of the H2O ice annulus around the seasonal CO2 cap at this time. At around Ls = 25°, this process changes into an asymmetrical distribution of H2O deposition, covering CO2 signatures more rapidly in the longitude range from 90 to 210°E. (3) We detect signatures of “pure” CO2 ice in extremely limited locations (in Lomonosov Crater) even in midwinter. H2O ice signatures appear everywhere in the retreating CO2 seasonal cap, in contrast with the south polar seasonal cap. (4) We find that average H2O ice grain sizes continuously increase from northern midwinter to the end of springtime; this is the inverse of the behavior of CO2 ice grain sizes in the southern springtime.
Highly porous metal–organic framework sustained with 12-connected nanoscopic octahedra
Authors: Lu Weigang , Yuan Daqiang , Makal Tegan A. , Wei Zhangwen , Li Jian-Rong , Zhou Hong-Cai
Published: October 2012

Two dicopper(ii)-paddlewheel-based metal–organic frameworks (PCN-81 and -82) have been synthesized by using tetratopic ligands featured with 90°-carbazole–dicarboxylate moieties.
The transcription factor AtDOF4.2 regulates shoot branching and seed coat formation in Arabidopsis
Authors: Zou Hong-Feng , Zhang Yu-Qin , Wei Wei , Chen Hao-Wei , Song Qing-Xin , Liu Yun-Feng , Zhao Ming-Yu , Wang Fang , Zhang Bao-Cai , Lin Qing , Zhang Wan-Ke , Ma Biao , Zhou Yi-Hua , Zhang Jin-Song , Chen Shou-Yi
Published: October 2012

Plant-specific DOF (DNA-binding with one finger)-type transcription factors regulate various biological processes. In the present study we characterized a silique-abundant gene AtDOF (Arabidopsis thaliana DOF) 4.2 for its functions in Arabidopsis. AtDOF4.2 is localized in the nuclear region and has transcriptional activation activity in both yeast and plant protoplast assays. The T-M-D motif in AtDOF4.2 is essential for its activation. AtDOF4.2-overexpressing plants exhibit an increased branching phenotype and mutation of the T-M-D motif in AtDOF4.2 significantly reduces branching in transgenic plants. AtDOF4.2 may achieve this function through the up-regulation of three branching-related genes, AtSTM (A. thaliana SHOOT MERISTEMLESS), AtTFL1 (A. thaliana TERMINAL FLOWER1) and AtCYP83B1 (A. thaliana CYTOCHROME P450 83B1). The seeds of an AtDOF4.2-overexpressing plant show a collapse-like morphology in the epidermal cells of the seed coat. The mucilage contents and the concentration and composition of mucilage monosaccharides are significantly changed in the seed coat of transgenic plants. AtDOF4.2 may exert its effects on the seed epidermis through the direct binding and activation of the cell wall loosening-related gene AtEXPA9 (A. thaliana EXPANSIN-A9). The dof4.2 mutant did not exhibit changes in branching or its seed coat; however, the silique length and seed yield were increased. AtDOF4.4, which is a close homologue of AtDOF4.2, also promotes shoot branching and affects silique size and seed yield. Manipulation of these genes should have a practical use in the improvement of agronomic traits in important crops.
Comment on “Elastic incoherent neutron scattering operating by varying instrumental energy resolution: Principle, simulations, and experiments of the resolution elastic neutron scattering (RENS)” [Rev. Sci. Instrum. 82, 105115 (2011)]
Authors: Wuttke Joachim
Published: October 2012

In a recent contribution to this journal, Magazù, Migliardo, and Benedetto suggest to determine relaxation times from inflection points in the elastic neutron scattering intensity as function of (1) resolution time or (2) temperature. Method (1) can be generalized into a scaling law. Method (2) is only approximately valid; its application to protein data does not back a wavenumber-independent dynamic transition.
Oblique electron-cyclotron-emission radial and phase detector of rotating magnetic islands applied to alignment and modulation of electron-cyclotron-current-drive for neoclassical tearing mode stabilization
Authors: Volpe F. , Austin M. E. , Campbell G. , Deterly T.
Published: October 2012

A two channel oblique electron cyclotron emission (ECE) radiometer was installed on the DIII-D tokamak and interfaced to four gyrotrons. Oblique ECE was used to toroidally and radially localize rotating magnetic islands and so assist their electron cyclotron current drive (ECCD) stabilization. In particular, after manipulations operated by the interfacing analogue circuit, the oblique ECE signals directly modulated the current drive in synch with the island rotation and in phase with the island O-point, for a more efficient stabilization. Apart from the different toroidal location, the diagnostic view is identical to the ECCD launch direction, which greatly simplified the real-time use of the signals. In fact, a simple toroidal extrapolation was sufficient to lock the modulation to the O-point phase. This was accomplished by a specially designed phase shifter of nearly flat response over the 1–7 kHz range. Moreover, correlation analysis of two channels slightly above and below the ECCD frequency allowed checking the radial alignment to the island, based on the fact that for satisfactory alignment the two signals are out of phase.
Effect of ion temperature on ion-acoustic solitary waves in a plasma with a q-nonextensive electron velocity distribution
Authors: Roy Kaushik , Saha Taraknath , Chatterjee Prasanta
Published: October 2012

The effect of ion temperature on the existence of arbitrary amplitude ion-acoustic solitary waves is studied in a two component plasma in presence of a q-nonextensive velocity distributed electrons by using Sagdeev's pseudo potential technique. The range of relevent parameters for which solitons may exist is discussed. It is observed that both q, the nonextensive parameter and the ion temperature σ, play significant roles in the formation and existence of solitons.
Thermal decomposition of CH3CHO studied by matrix infrared spectroscopy and photoionization mass spectroscopy
Authors: Vasiliou AnGayle K. , Piech Krzysztof M. , Reed Beth , Zhang Xu , Nimlos Mark R. , Ahmed Musahid , Golan Amir , Kostko Oleg , Osborn David L. , David Donald E. , Urness Kimberly N. , Daily John W. , Stanton John F. , Ellison G. Barney
Published: October 2012

A heated SiC microtubular reactor has been used to decompose acetaldehyde and its isotopomers (CH3CDO, CD3CHO, and CD3CDO). The pyrolysis experiments are carried out by passing a dilute mixture of acetaldehyde (roughly 0.1%–1%) entrained in a stream of a buffer gas (either He or Ar) through a heated SiC reactor that is 2–3 cm long and 1 mm in diameter. Typical pressures in the reactor are 50–200 Torr with the SiC tube wall temperature in the range 1200–1900 K. Characteristic residence times in the reactor are 50–200 μs after which the gas mixture emerges as a skimmed molecular beam at a pressure of approximately 10 μTorr. The reactor has been modified so that both pulsed and continuous modes can be studied, and results from both flow regimes are presented. Using various detection methods (Fourier transform infrared spectroscopy and both fixed wavelength and tunable synchrotron radiation photoionization mass spectrometry), a number of products formed at early pyrolysis times (roughly 100–200 μs) are identified: H, H2, CH3, CO, CH2=CHOH, HC≡CH, H2O, and CH2=C=O; trace quantities of other species are also observed in some of the experiments. Pyrolysis of rare isotopomers of acetaldehyde produces characteristic isotopic signatures in the reaction products, which offers insight into reaction mechanisms that occur in the reactor. In particular, while the principal unimolecular processes appear to be radical decomposition CH3CHO (+M) → CH3 + H + CO and isomerization of acetaldehyde to vinyl alcohol, it appears that the CH2CO and HCCH are formed (perhaps exclusively) by bimolecular reactions, especially those involving hydrogen atom attacks.
Harnessing the meta-generalized gradient approximation for time-dependent density functional theory
Authors: Bates Jefferson E. , Furche Filipp
Published: October 2012

Density functionals within the meta-generalized gradient approximation (MGGA) are widely used for ground-state electronic structure calculations. However, the gauge variance of the kinetic energy density τ confounds applications of MGGAs to time-dependent systems, excited states, magnetic properties, and states with strong spin-orbit coupling. Becke and Tao used the paramagnetic current density to construct a gauge invariant generalized kinetic energy density \documentclass[12pt]{minimal}\begin{document}$\hat{\tau }$\end{document}τ̂. We show that \documentclass[12pt]{minimal}\begin{document}$\tau _W \le \hat{\tau }$\end{document}τW≤τ̂, where τW is the von Weizsäcker kinetic energy density of a one-electron system. Thus, replacing τ by \documentclass[12pt]{minimal}\begin{document}$\hat{\tau }$\end{document}τ̂ leads to current-dependent MGGAs (cMGGAs) that are not only gauge invariant but also restore the accuracy of MGGAs in iso-orbital regions for time-dependent and current-carrying states. The current dependence of cMGGAs produces a vector exchange-correlation (XC) potential in the time-dependent adiabatic Kohn-Sham (KS) equations. While MGGA response properties of current-free ground states become manifestly gauge-variant to second order, linear response properties are affected by a new XC kernel appearing in the cMGGA magnetic orbital rotation Hessian. This kernel reflects the first-order coupling of KS orbitals due to changes in the paramagnetic current density and has apparently been ignored in previous MGGA response implementations. Inclusion of the current dependence increases total computation times by less than 50%. Benchmark applications to 109 adiabatic excitation energies using the Tao-Perdew-Staroverov-Scuseria (TPSS) MGGA and its hybrid version TPSSh show that cMGGA excitation energies are slightly lower than the MGGA ones on average, but exhibit fewer outliers. Similarly, the optical rotations of 13 small organic molecules show a small but systematic improvement upon inclusion of the magnetic XC kernel. We conclude that cMGGAs should replace MGGAs in all applications involving time-dependent or current-carrying states.
A one-parameter quantum cluster equilibrium approach
Authors: Brüssel Marc , Perlt Eva , von Domaros Michael , Brehm Martin , Kirchner Barbara
Published: October 2012

The established quantum cluster equilibrium approach is further developed in this work. The equations are reformulated to result in a one-parameter expression, i.e., with one of two empirical parameters eliminated. Instead of a parametrized constant mean field interaction we present two further approaches using temperature dependent mean field functions. The suggested functions are assessed by means of two test systems, namely hydrogen fluoride and water which are investigated concerning their liquid phase properties as well as the phenomenon of evaporation. The obtained thermodynamic data are compared with each other for the different mean field functions including the conventional approach as well as to experimental data.
Large eddy simulation models for incompressible magnetohydrodynamics derived from the variational multiscale formulation
Authors: Sondak David , Oberai Assad A.
Published: October 2012

Novel large eddy simulation (LES) models are developed for incompressible magnetohydrodynamics (MHD). These models include the application of the variational multiscale formulation of LES to the equations of incompressible MHD. Additionally, a new residual-based eddy viscosity model is introduced for MHD. A mixed LES model that combines the strengths of both of these models is also derived. The new models result in a consistent numerical method that is relatively simple to implement. The need for a dynamic procedure in determining model coefficients is no longer required. The new LES models are tested on a decaying Taylor-Green vortex generalized to MHD and benchmarked against classical LES turbulence models. The LES simulations are run in a periodic box of size [−π, π]3 with 32 modes in each direction and are compared to a direct numerical simulation (DNS) with 512 modes in each direction. The new models are able to account for the essential MHD physics which is demonstrated via comparisons of energy spectra. We also compare the performance of our models to a DNS simulation by Pouquet et al. [“The dynamics of unforced turbulence at high Reynolds number for Taylor–Green vortices generalized to MHD,” Geophys. Astrophys. Fluid Dyn. 104, 115–134 (2010)], for which the ratio of DNS modes to LES modes is 262:144.
Superior magnetic softness at elevated temperature of Si-rich Fe-based nanocrystalline alloy
Authors: Shi Rui-min , Wang Zhi , Jia Yun-yun , Wen Zhuan-ping , Wang Bo-wen , Zhang Tao
Published: October 2012

An excellent high-temperature magnetic softness was observed in a Si-rich nanocrystalline Fe74.5Cu1Nb2Si17.5B5 alloy. The Curie temperatures of amorphous and crystal phases, TCA* and TCcry, for this alloy were detected to be 365 °C and 580 °C, respectively. For the 480 °C-annealed alloy, the initial permeability μi drops to nearly zero just above TCA*; however, for the 540 °C-annealed alloy, the μi of about 10 000 at f = 10 kHz has no perceivable decline in this temperature range and can hold up to more than 400 °C. Such a magnetic softness at elevated temperature is superior to that of Finemet-type Fe-based nanocrystalline alloys ever reported. The origin of the high temperature magnetic softness was interpreted by the enhancement effect of Curie temperature in residual amorphous matrix.
Comparison of gate geometries for tunable, local barriers in InAs nanowires
Authors: Dahl Nissen Peter , Sand Jespersen Thomas , Grove-Rasmussen Kasper , Márton Attila , Upadhyay Shivendra , Hannibal Madsen Morten , Csonka Szabolcs , Nygård Jesper
Published: October 2012

We report measurements and analysis of gate-induced electrostatic barriers for electron transport in InAs nanowires. Three types of local gates are analyzed; narrow gates (50−100 nm) located on top of or below the nanowire, and wide gates overlapping the interfaces between nanowire and source and drain electrodes. We find that applying negative potentials to the local gate electrodes induces tunable barriers of up to 0.25 eV and that transport through the wire can be blocked at neutral and slightly positive potentials on the nanowire-contact gates, indicating that built-in barriers can exist at the nanowire-contact interface. The contact gates can be biased to remove the unwanted interface barriers occasionally formed during processing. From the temperature dependence of the conductance, the barrier height is extracted and mapped as a function of gate voltage. Top and bottom gates are similar to each other in terms of electrostatic couplings (lever arms ∼0.1−0.2 eV/ V) and threshold voltages for barrier induction (Vg∼−1 to −2 V), but low temperature gate sweeps suggest that device stability could be affected by the differences in device processing for the two gate geometries.
Cylindrical coordinate representation for multiband Hamiltonians
Authors: Takhtamirov Eduard
Published: October 2012

Rotationally invariant combinations of the Brillouin zone-center Bloch functions are used as basis function to express in cylindrical coordinates the valence-band and Kane envelope-function Hamiltonians for wurtzite and zinc-blende semiconductor heterostructures. For cylindrically symmetric systems, this basis allows to treat the envelope functions as eigenstates of the operator of projection of total angular momentum on the symmetry axis, with the operator's eigenvalue conventionally entering the Hamiltonians as a parameter. Complementing the Hamiltonians with boundary conditions for the envelope functions on the symmetry axis, we present for the first time a complete formalism for efficient modeling and description of multiband electron states in low-dimensional semiconductor structures with cylindrical symmetry. To demonstrate the potency of the cylindrical symmetry approximation and establish a criterion of its applicability for actual structures, we map the ground and several excited valence-band states in an isolated wurtzite GaN quantum wire of a hexagonal cross-section to the states in an equivalent quantum wire of a circular cross-section.
Local current mapping of single vertically aligned multi-walled carbon nanotube in a polymer matrix
Authors: Villeneuve C. , Pacchini S. , Boulanger P. , Brouzes A. , Roussel F. , Pinault M. , Mayne-L’Hermite M. , Plana R.
Published: October 2012

This paper reports our work on the development of thin composite films based on aligned multi-walled carbon nanotubes (CNTs) forest embedded in epoxy polymer matrix dedicated for 3D-interconnection in flexible substrate. To reach this goal, information about local CNT properties is strongly needed. In this study, aligned multi-walled carbon nanotube carpets were prepared by aerosol Assisted catalytical chemical vapor deposition (AA-CCVD) process. Such carpets were then embedded in a polymer matrix, subsequently thinned by chemical mechanical polishing (CMP) process and finally treated by plasma process. Then, to determine local conducting properties of CNT, the surface of the composite film is studied by conductive AFM (C-AFM) and scanning spreading resistance microscopy. These methods are discussed and compared. C-AFM appears to be the most efficient method to obtain high resolution current maps. For the first time, a local electrical property mapping and current versus applied voltage characteristics over single carbon nanotube in vertical arrangement are obtained. These results show metallic behavior for nanotubes and emphasize that the electrical conduction is mainly driven by the external walls.
Modeling the effect of orientation on the shock response of a damageable composite material
Authors: Lukyanov Alexander A.
Published: October 2012

A carbon fiber-epoxy composite (CFEC) shock response in the through thickness orientation and in one of the fiber directions is significantly different. The hydrostatic pressure inside anisotropic materials depends on deviatoric strain components as well as volumetric strain. Non-linear effects, such as shock effects, can be incorporated through the volumetric straining in the material. Thus, a new basis is required to couple the anisotropic material stiffness and strength with anisotropic shock effects, associated energy dependence, and damage softening process. This article presents these constitutive equations for shock wave modeling of a damageable carbon fiber-epoxy composite. Modeling the effect of fiber orientation on the shock response of a CFEC has been performed using a generalized decomposition of the stress tensor [A. A. Lukyanov, Int. J. Plast. 24, 140 (2008)] and Mie-Grüneisen's extrapolation of high-pressure shock Hugoniot states to other thermodynamics states for shocked CFEC materials. The three-wave structure (non-linear anisotropic, fracture, and isotropic elastic waves) that accompanies damage softening process is also proposed in this work for describing CFEC behavior under shock loading which allows to remove any discontinuities observed in the linear case for relation between shock velocities and particle velocities [A. A. Lukyanov, Eur. Phys. J. B 74, 35 (2010)]. Different Hugoniot stress levels are obtained when the material is impacted in different directions; their good agreement with the experiment demonstrates that the anisotropic equation of state, strength, and damage model are adequate for the simulation of shock wave propagation within damageable CFEC material. Remarkably, in the through thickness orientation, the material behaves similar to a simple polymer whereas in the fiber direction, the proposed in this paper model explains an initial ramp, before at sufficiently high stresses, and a much faster rising shock above it. The numerical results for shock wave modeling using proposed constitutive equations are presented, discussed, and future studies are outlined.
High temperature thermoelectric properties of p-type skutterudites BaxYbyCo4-zFezSb12
Authors: Dong Y. , Puneet P. , Tritt T. M. , Martin J. , Nolas G. S.
Published: October 2012

Several polycrystalline p-type skutterudites with compositions BaxYbyCo4−zFezSb12, with varying filler concentrations x and y, and z = 1 to 2, were synthesized by reacting the constituents and subsequent solid state annealing, followed by densification by hot-pressing. Their thermoelectric properties were evaluated from 300 to 820 K. The Yb filling fraction increased with Fe content while the amount of Fe substitution had little influence on the Ba filling fraction. High purity specimens were obtained when the Fe content was low. Bipolar conduction contributed to the thermal conductivity at elevated temperatures. A maximum ZT value of 0.7 was obtained at 750 K for the specimen with the highest Fe content and filling fraction. The potential for thermoelectric applications is also discussed.
Magnetocaloric effect and nature of magnetic transition in nanoscale Pr0.5Ca0.5MnO3
Authors: Narayana Jammalamadaka S. , Rao S. S. , Bhat S. V. , Vanacken J. , Moshchalkov V. V.
Published: October 2012

Systematic measurements pertinent to the magnetocaloric effect and nature of magnetic transition around the transition temperature are performed in the 10 nm Pr0.5Ca0.5MnO3 nanoparticles (PCMO10). Maxwell's relation is employed to estimate the change in magnetic entropy. At Curie temperature (TC) ∼ 83.5 K, the change in magnetic entropy (−ΔSM) discloses a typical variation with a value 0.57 J/kg K, and is found to be magnetic field dependent. From the area under the curve (ΔS vs T), the refrigeration capacity is calculated at TC ∼ 83.5 K and it is found to be 7.01 J/kg. Arrott plots infer that due to the competition between the ferromagnetic and anti-ferromagnetic interactions, the magnetic phase transition in PCMO10 is broadly spread over both in temperature as well as magnetic field coordinates. Upon tuning the particle size, size distribution, morphology, and relative fraction of magnetic phases, it may be possible to enhance the magnetocalorific effect further in PCMO10.
Effect of relative humidity on crack propagation in barrier films for flexible electronics
Authors: Vellinga W. P. , De Hosson J. Th. M. , Bouten P. C. P.
Published: October 2012

A set of propagating cracks in a SiN barrier film on poly ethylene naphthalate (PEN) were subjected to differing levels of relative humidity. It was observed that the propagation speed of the cracks increased for increasing levels of relative humidity. This was shown using two independent, simultaneous techniques. One of the techniques (a resistance measurement) gives a qualitative measure of the averaged crack tip speed and the other (a microscopic technique) a quantitative measure. An attempt is made to quantify the resistance measurements in terms of crack tip speed. The effects that humidity may have on the crack driving force through differences in hygroscopic expansion are discussed, using independent determination of the diffusion constant of water into PEN. It is concluded that hygroscopic expansion alone cannot account for the observations.
Structures and magnetism of multinuclear vanadium-pentacene sandwich clusters and their 1D molecular wires
Authors: Zhang Tingting , Zhu Liyan , Wu Qisheng , Yang Shuo-Wang , Wang Jinlan
Published: October 2012

Two types of multinuclear sandwich clusters, (V3)nPenn+1, (V4)nPenn+1 (Pen = Pentacene; n = 1, 2), and their corresponding infinite one-dimensional (1D) molecular wires ([V3Pen]∞, [V4Pen]∞) are investigated theoretically, especially on their magnetic coupling mechanism. These sandwich clusters and molecular wires are found to be of high stability and exhibit intriguing magnetic properties. The intra-layered V atoms in (V3)nPenn+1 clusters prefer antiferromagnetic (AFM) coupling, while they can be either ferromagnetic (FM) or AFM coupling in (V4)nPenn+1 depending on the intra-layered V-V distances via direct exchange or superexchange mechanism. The inter-layered V atoms favor FM coupling in (V3)2Pen3, whereas they are AFM coupled in (V4)2Pen3. Such magnetic behaviors are the consequence of the competition between direct exchange and superexchange interactions among inter-layered V atoms. In contrast, the 1D molecular wires, [V3Pen]∞ and [V4Pen]∞, appear to be FM metallic with ultra high magnetic moments of 6.8 and 4.0 μB per unit cell respectively, suggesting that they can be served as good candidates for molecular magnets.
Dynamics of the reactions of O(1D) with CD3OH and CH3OD studied with time-resolved Fourier-transform IR spectroscopy
Authors: Huang Chong-Kai , Xu Zhen-Feng , Nakajima Masakazu , Nguyen Hue M. T. , Lin M. C. , Tsuchiya Soji , Lee Yuan-Pern
Published: October 2012

We investigated the reactivity of O(1D) towards two types of hydrogen atoms in CH3OH. The reaction was initiated on irradiation of a flowing mixture of O3 and CD3OH or CH3OD at 248 nm. Relative vibration-rotational populations of OH and OD (1 ≤ v ≤ 4) states were determined from their infrared emission recorded with a step-scan time-resolved Fourier-transform spectrometer. In O(1D) + CD3OH, the rotational distribution of OD is nearly Boltzmann, whereas that of OH is bimodal; the product ratio [OH]/[OD] is 1.56 ± 0.36. In O(1D) + CH3OD, the rotational distribution of OH is nearly Boltzmann, whereas that of OD is bimodal; the product ratio [OH]/[OD] is 0.59 ± 0.14. Quantum-chemical calculations of the potential energy and microcanonical rate coefficients of various channels indicate that the abstraction channels are unimportant and O(1D) inserts into the C−H and O−H bonds of CH3OH to form HOCH2OH and CH3OOH, respectively. The observed three channels of OH are consistent with those produced via decomposition of the newly formed OH or the original OH moiety in HOCH2OH or decomposition of CH3OOH. The former decomposition channel of HOCH2OH produces vibrationally more excited OH because of incomplete intramolecular vibrational relaxation, and decomposition of CH3COOH produces OH with greater rotational excitation, likely due to a large torque angle during dissociation. The predicted [OH]/[OD] ratios are 1.31 and 0.61 for O(1D) + CD3OH and CH3OD, respectively, at collision energy of 26 kJ mol−1, in satisfactory agreement with the experimental results. These predicted product ratios vary weakly with collision energy.
Image reconstruction based on L1 regularization and projection methods for electrical impedance tomography
Authors: Wang Qi , Wang Huaxiang , Zhang Ronghua , Wang Jinhai , Zheng Yu , Cui Ziqiang , Yang Chengyi
Published: October 2012

Electrical impedance tomography (EIT) is a technique for reconstructing the conductivity distribution by injecting currents at the boundary of a subject and measuring the resulting changes in voltage. Image reconstruction in EIT is a nonlinear and ill-posed inverse problem. The Tikhonov method with L2 regularization is always used to solve the EIT problem. However, the L2 method always smoothes the sharp changes or discontinue areas of the reconstruction. Image reconstruction using the L1 regularization allows addressing this difficulty. In this paper, a sum of absolute values is substituted for the sum of squares used in the L2 regularization to form the L1 regularization, the solution is obtained by the barrier method. However, the L1 method often involves repeatedly solving large-dimensional matrix equations, which are computationally expensive. In this paper, the projection method is combined with the L1 regularization method to reduce the computational cost. The L1 problem is mainly solved in the coarse subspace. This paper also discusses the strategies of choosing parameters. Both simulation and experimental results of the L1 regularization method were compared with the L2 regularization method, indicating that the L1 regularization method can improve the quality of image reconstruction and tolerate a relatively high level of noise in the measured voltages. Furthermore, the projected L1 method can also effectively reduce the computational time without affecting the quality of reconstructed images.
Measurement of parameters in Indus-2 synchrotron radiation source
Authors: Ghodke A. D. , Husain Riyasat , Kumar Pradeep , Yadav Surendra , Puntambekar T. A.
Published: October 2012

The paper presents the measurement of optics parameters in Indus-2 synchrotron radiation source, which include betatron tune, beta function, dispersion function, natural chromaticity, corrected chromaticity, central RF frequency, momentum compaction factor, and linear betatron coupling. Two methods were used for beta function measurement; a conventional quadrupole scan method and a method using the fitting of the orbit response matrix. A robust Levenberg-Marquardt algorithm was used for nonlinear least square fitting of the orbit response matrix. In this paper, detailed methods for the parameter measurements are described. The measured results are discussed and compared with the theoretical values obtained using accelerator simulation code Accelerator Toolbox in MATLAB.
Modulated structure in the martensite phase of Ni1.8Pt0.2MnGa: A neutron diffraction study
Authors: Singh Sanjay , Ziebeck K. R. A. , Suard E. , Rajput P. , Bhardwaj S. , Awasthi A. M. , Barman S. R.
Published: October 2012

7M orthorhombic modulated structure in the martensite phase of Ni1.8Pt0.2MnGa is reported by powder neutron diffraction study, which indicates that it is likely to exhibit magnetic field induced strain. The change in the unit cell volume is less than 0.5% between the austenite and the martensite phases, as expected for a volume conserving martensite transformation. The magnetic structure analysis shows that the magnetic moment in the martensite phase is higher compared to Ni2MnGa, which is in good agreement with magnetization measurement.
Probing the structural and electronic properties of small vanadium dioxide clusters by density functional theory and comparison with experimental photoelectron spectroscopy
Authors: Wang Huai-Qian , Li Hui-Fang
Published: October 2012

The structural evolution and bonding of a series of early transition-metal dioxide clusters, ${\rm V_n O}_2^{\rm q} $VnO2q(n = 3–9, q = 0, −1), have been investigated using density functional theory (DFT) calculations and the results are compared with experimental literature data. For each vanadium dioxide cluster, many low-lying isomers are generated using the Saunders “Kick” global minimum stochastic search method. Theoretical electron detachment energies (both vertical and adiabatic) were compared with the experimental measurements to verify the ground states of the vanadium dioxide clusters obtained from the DFT calculations. Five kinds of dissociative adsorption configurations of ground-state structure of ${\rm V_n O}_2^{\rm q} $VnO2q are identified. The dissociative adsorption of O2 on Vn−1, 0 is more favorable than O2 molecular adsorption. Furthermore, the adsorption energy of O2 is higher than that of a single atom on the bare Vn−1, 0 clusters, but less than twice the adsorption energy for an atom, indicating that O2 being adsorbed on vanadium clusters are more difficult than single O atom adsorbed on vanadium clusters.
Annular solid-immersion lenslet array super-resolution optical microscopy
Authors: Liau Z. L.
Published: October 2012

We describe a novel solid-immersion lenslet array, micro-fabricated in a chip form in the high-index (3.45) gallium phosphide. The innovatively designed lenslet features an annular aperture with appropriately patterned light absorbers and antireflection coatings. The array chip is easy to handle and enables the direct deposition of the specimen of interest onto its back-plane for tight adhesion and good optical coupling. The ensuing diffraction from the near field can yield supercritical rays inside the high-index lenslet and can, therefore, overcome the refraction and critical-angle limitations. This model showed agreement with the experimental observation of the solid-immersion fluorescence microscopy imaging, in which the refracted rays were completely blocked by the annular aperture. A large longitudinal (depth) magnification effect was also predicted and showed agreement with experiment. The annular lenslet's additional advantages of improved resolution and contrast were also discussed. Resolution of nested-L patterns with grating pitch as small as 100 nm was experimentally demonstrated. The demonstrated annular solid-immersion lenslet array concept is promising for a wider use in super-resolution optical microscopy.
Brownian dynamics simulations with hard-body interactions: Spherical particles
Authors: Behringer Hans , Eichhorn Ralf
Published: October 2012

A novel approach to account for hard-body interactions in (overdamped) Brownian dynamics simulations is proposed for systems with non-vanishing force fields. The scheme exploits the analytically known transition probability for a Brownian particle on a one-dimensional half-line. The motion of a Brownian particle is decomposed into a component that is affected by hard-body interactions and into components that are unaffected. The hard-body interactions are incorporated by replacing the “affected” component of motion by the evolution on a half-line. It is discussed under which circumstances this approach is justified. In particular, the algorithm is developed and formulated for systems with space-fixed obstacles and for systems comprising spherical particles. The validity and justification of the algorithm is investigated numerically by looking at exemplary model systems of soft matter, namely at colloids in flow fields and at protein interactions. Furthermore, a thorough discussion of properties of other heuristic algorithms is carried out.
Laser schlieren deflectometry for temperature analysis of filamentary non-thermal atmospheric pressure plasma
Authors: Schäfer J. , Foest R. , Reuter S. , Kewitz T. , Šperka J. , Weltmann K.-D.
Published: October 2012

The heat convection generated by micro filaments of a self-organized non-thermal atmospheric pressure plasma jet in Ar is characterized by employing laser schlieren deflectometry (LSD). It is demonstrated as a proof of principle, that the spatial and temporal changes of the refractive index n in the optical beam path related to the neutral gas temperature of the plasma jet can be monitored and evaluated simultaneously. The refraction of a laser beam in a high gradient field of n(r) with cylindrical symmetry is given for a general real refraction index profile. However, the usually applied Abel approach represents an ill-posed problem and in particular for this plasma configuration. A simple analytical model is proposed in order to minimize the statistical error. Based on that, the temperature profile, specifically the absolute temperature in the filament core, the FWHM, and the frequencies of the collective filament dynamics are obtained for non-stationary conditions. For a gas temperature of 700 K inside the filament, the presented model predicts maximum deflection angles of the laser beam of 0.3 mrad which is in accordance to the experimental results obtained with LSD. Furthermore, the experimentally obtained FWHM of the temperature profile produced by the filament at the end of capillary is (1.5 ± 0.2) mm, which is about 10 times wider than the visual radius of the filament. The obtained maximum temperature in the effluent is (450 ± 30) K and is in consistence with results of other techniques. The study demonstrates that LSD represents a useful low-cost method for monitoring the spatiotemporal behaviour of microdischarges and allows to uncover their dynamic characteristics, e.g., the temperature profile even for challenging diagnostic conditions such as moving thin discharge filaments. The method is not restricted to the miniaturized and self-organized plasma studied here. Instead, it can be readily applied to other configurations that produce measurable gradients of refractive index by local gas heating and opens new diagnostics prospects particularly for microplasmas.
Design, modeling, and performance evaluation of a novel dye cell for a high repetition rate dye laser
Authors: Singh Nageshwar , Patel Hemant K. , Dixit S. K. , Vora H. S.
Published: October 2012

In this paper, a new dye cell for transverse pumping was designed, modeled, and its performance in a narrow spectral width dispersive resonator, pumped by a high repetition rate copper vapor laser, was investigated. The scheme essentially involves the profiling of the cubical glass and stainless steel cylindrical surface such that convex-plano contour be present near the optical pumping region. The design is an amalgamation of straight and curved periphery to enhance the dye solution flow stabilities near the dye laser axis. A computational fluid dynamics analysis of the liquid flow through this dye cell has been carried out. The dye laser outputs such as optical average power, spectral width and wavelength stability, tuning range, pulse shape, through this new dye cell was evaluated. The dye laser average power about 30 mW was fairly steady over the observation period of more than an hour. The dye laser short-term (1 min) spectral width was within 0.824 ± 0.075 GHz, while, in a long-term, more than an hour, drifted by about 180 MHz. The dye laser wavelength in short-term fluctuates within ±0.0065 nm whereas in a long-term, more than an hour, drifted by about 0.0105 nm. The dye laser tuning range was 10 nm with a sub GHz spectral width operation. The pulse shape of the dye laser follows the pump laser pulse profile. Thus, the dye laser has demonstrated fairly long-term stability, without the use of either low expansion material or close loop control on the output.
Evidence of Eu2+ 4f electrons in the valence band spectra of EuTiO3 and EuZrO3
Authors: Kolodiazhnyi T. , Valant M. , Williams J. R. , Bugnet M. , Botton G. A. , Ohashi N. , Sakka Y.
Published: October 2012

We report on optical band gap and valence electronic structure of two Eu2+-based perovskites, EuTiO3 and EuZrO3 as revealed by diffuse optical scattering, electron energy loss spectroscopy, and valence-band x-ray photoelectron spectroscopy. The data show good agreement with the first-principles studies in which the top of the valence band structure is formed by the narrow Eu 4f7 electron band. The O 2p band shows the features similar to those of the Ba(Sr)TiO3 perovskites except that it is shifted to higher binding energies. Appearance of the Eu2+ 4f7 band is a reason for narrowing of the optical band gap in the title compounds as compared to their Sr-based analogues.
Single photon emission from impurity centers in AlGaAs epilayers on Ge and Si substrates
Authors: Minari S. , Cavigli L. , Sarti F. , Abbarchi M. , Accanto N. , Muñoz Matutano G. , Bietti S. , Sanguinetti S. , Vinattieri A. , Gurioli M.
Published: October 2012

We show that the epitaxial growth of thin layers of AlGaAs on Ge and Si substrates allows to obtain single photon sources by exploiting the sparse and unintentional contamination with acceptors of the AlGaAs. Very bright and sharp single photoluminescence lines are observed in confocal microscopy. These lines behave very much as single excitons in quantum dots, but their implementation is by far much easier, since it does not require 3D nucleation. The photon antibunching is demonstrated by time resolved Hanbury Brown and Twiss measurements.
Electronic structures and magnetism of diluted magnetic semiconductors Sn1−xGdxTe: A density functional theory study
Authors: Wang Yong , Zhan Yongzhong , Pang Mingjun
Published: October 2012

The structural, energy stability, and magnetic properties of the diluted magnetic semiconductors Sn1−xGdxTe (x = 3.125 at. %, 6.25 at. %, and 12.5 at. %) were investigated based on density functional theory. The calculated lattice parameters of the Sn1−xGdxTe compounds at zero pressure and zero temperature are in very good agreement with the existing experimental data. The energy stability of different configurations was also investigated, and the results show that Gd atoms prefer to occupy the nearest neighbor positions to the next nearest. It is hopeful to obtain ferromagnetic actual samples with Gd concentration around 6.25 at. %. It also confirms that there is presence of a small ferromagnetic interaction, competitive with the main antiferromagnetic interaction. However, this ferromagnetic interaction is too weak to show global magnetic moment.
Magnetically and thermally induced switching processes in hard magnets
Authors: Behler Christian , Neu Volker , Schultz Ludwig , Fähler Sebastian
Published: October 2012

Magnetic switching can occur under the influence of external magnetic fields and/or thermal activation. To separate the role of both effects, here we examplarily analyse an epitaxial FePt film with a mesoscopic grain size by angular and time dependent magnetization measurements. On one hand, the switching field exhibits a minimum as predicted by the coherent rotation model. On the other hand, viscosity measurements reveal that the switching volume is below the grain volume, indicating an incoherent nucleation process. Our analysis shows that the reduced switching of 7.6 T compared to the effective anisotropy field of 10.8 T can be attributed to two facts, both connected with incoherent reversal processes caused by mesoscopic grain size and non-ellipsoidal grain shape: (1) a decrease in the non-thermally activated switching field and (2) a strong reduction of the zero-field energy barrier, which makes thermally activated reversal processes noticeable also for high anisotropic materials.
Uncoupled optical phonons in core/shell GaAs/GaP nanowires: Strain effects
Authors: Santiago-Pérez Darío G. , Trallero-Giner C. , Pérez-Álvarez R. , Chico L. , Baquero R. , Marques G. E.
Published: October 2012

A detailed analysis of the uncoupled polar optical-phonon modes with cylindrical symmetry and translational invariance along the wire in core/shell semiconductor nanowires is presented, within the framework of a phenomenological continuum model. The effects of strain on confined longitudinal optical (LO) and transverse optical (TO) core-like and shell-like phonon modes in GaAs/GaP quantum wire are considered. The reported TO splitting together with LO confined modes may be used to extract information on the core and shell nanostructures, by comparison to Raman and infrared spectroscopy techniques. Employing recently reported experimental results on GaAsP/GaP core-shell nanowires, the ratio of the LO and TO Grüneisen mode parameters is determined.