bluuebunny/crossref_metadata_2025 huggingface dataset:
Sub‐kilometer dynamical downscaling of near‐surface winds in complex terrain using WRF and MM5 mesoscale models
Authors: Horvath Kristian , Koracin Darko , Vellore Ramesh , Jiang Jinhua , Belu Radian
Published: May 2012

Sub‐kilometer dynamical downscaling was performed using the Weather Research and Forecasting (WRF) and Mesoscale Model Version 5 (MM5) models. The models were configured with horizontal grid spacing ranging from 27 km in the outermost telescoping to 333 m in the innermost domains and verified with observations collected at four 50‐m towers in west‐central Nevada during July and December 2007. Moment‐based and spectral verification metrics showed that the performance of WRF was superior to MM5. The modeling results were more accurate at 50 m than at 10 m AGL. Both models accurately simulated the mean near‐surface wind shear; however, WRF (MM5) generally overestimated (underestimated) mean wind speeds at these levels. The dispersion errors were the dominant component of the root‐mean square errors. The major weakness of WRF was the overestimation of the intensity and frequency of strong nocturnal thermally driven flows and their sub‐diurnal scale variability, while the main weaknesses of MM5 were larger biases, underestimation of the frequency of stronger daytime winds in the mixed layer and underestimation of the observed spectral kinetic energy of the major energy‐containing motions. Neither of the verification metrics showed systematic improvement in the models' accuracy with increasing the horizontal resolution and the share of dispersion errors increased with increased resolution. However, a profound improvement in the moment‐based accuracy was found for the mean vertical wind shear and the temporal variability of wind speed, in particular for summer daytime simulations of the thermally driven flows. The most prominent spectral accuracy improvement among the primary energy‐containing frequency bands was found for both models in the summertime diurnal periods. Also, the improvement for WRF (MM5) was more (less) apparent for longer‐than‐diurnal than for sub‐diurnal periods. Finally, the study shows that at least near‐kilometer horizontal grid spacing is necessary for dynamical downscaling of near‐surface wind speed climate over complex terrain; however, some of the physics options might be less appropriate for grid spacing nearing the scales of the energy‐containing turbulent eddies, i.e., resolutions of several hundred meters. In addition to the effects of the lower boundary, the accuracy of the lateral boundary conditions of the parent domains also controls the onset and evolution of the thermally driven flows.
Relationship of Soluble RAGE and RAGE Ligands HMGB1 and EN-RAGE to Endothelial Dysfunction in Type 1 and Type 2 Diabetes Mellitus
Authors: Škrha Jr J. , Kalousová M. , Švarcová J. , Muravská A. , Kvasnička J. , Landová L. , Zima T. , Škrha J.
Published: May 2012

Receptor for advanced glycation endproducts (RAGE) plays the essential role in the pathogenesis of diabetic vascular complications. The aim of the study was to compare concentration of soluble RAGE and its ligands (EN-RAGE and HMGB1) with different biochemical parameters in Type 1 (T1DM) and Type 2 (T2DM) diabetes mellitus.

Total number of 154 persons (45 T1DM, 68 T2DM, 41 controls) was examined and concentrations of sRAGE, EN-RAGE and HMGB1 were measured and compared to diabetes control, albuminuria, cell adhesion molecules and metalloproteinases (MMPs).

Mean serum sRAGE concentration was higher in T1DM as compared to controls (1137±532 ng/l vs. 824±309 ng/l, p<0.01). Similarly, EN-RAGE was significantly higher in both diabetic groups (p<0.001) and HMGB1 concentrations were elevated in T2DM patients (p<0.01). Significant relationship was found between MMP9 and HMGB1 and EN-RAGE in diabetic patients. Inverse relationship was observed between MMP2 and MMP9 in both types of diabetic patients (r= − 0.602, p<0.002 and r= − 0.771, p<0.001). Significant positive correlation was found between sRAGE and ICAM-1, VCAM-1 or vWF (p<0.01 to p<0.001).

We conclude that serum sRAGE and RAGE ligands concentrations reflect endothelial dysfunction developing in diabetes.
59-jähriger Patient mit Augen- und Hautveränderungen sowie Diabetes mellitus
Authors: Ewald N. , Bretzel R.
Published: May 2012

Der 59-jähriger Patient stellte sich aufgrund eines neuaufgetretenen Diabetes
mellitus (HbA1c 6,8 %, Nüchtern-Glukose 129 mg/dl), Veränderungen
der Augen und unklarer Hautveränderung im Bereich der unteren Extremitäten
erstmalig in der Sprechstunde vor.

Die Untersuchung ergab zwei pathologische Befunde.
Bariatrischer Eingriff bei einem Patienten mit
Adipositas permagna und nicht beherrschbarer
Insulinresistenz
Authors: Haak T. , Horbach T.
Published: May 2012

Anamnese und klinischer Befund: Bei einem 58-jährigen Mann bestand seit 21 Jahren ein Typ 2 Diabetes mellitus mit zahlreichen Folgeschäden. Es lag eine Adipositas Grad III mit einem Body-Mass-Index von 42,7 kg/m2 (190 cm, 154 kg) vor, der Bauchumfang betrug 141 cm. Nach Erschöpfung der leitlinienkonformen ambulanten konservativen Behandlung im Rahmen des Disease Management Programmes Diabetes erfolgte die Vorstellung im Fachkrankenhaus.

Untersuchungen: Die Durchbrechung der Insulinresistenz gelang auch mit differenzierten Maßnahmen nicht, letztlich war eine Blutzuckerkontrolle nur mit Insulinpumpentherapie und zusätzlicher Insulingabe zu den Mahlzeiten möglich, mit mittleren Tagesinsulinmengen von über 500 IE. Die Lebensqualität und die Möglichkeiten zu körperlicher Bewegung waren bei dem Patienten stark eingeschränkt. Im interdisziplinären Dialog wurde zusammen mit dem Patienten die Indikation entsprechend der S3-Leitlinie Adipositaschirurgie zu einer Magenbypass-Anlage gestellt.

Therapie: Zwei Wochen nach der komplikationslosen minimal invasiven Operation war der Insulinbedarf bereits auf ca. 100 IE pro Tag fraktioniert zu den Mahlzeiten zurückgegangen. Nach Rückverlegung in die Diabetesfachklinik konnte die weitere Therapieoptimierung durchgeführt werden. Drei Monate nach der Operation fand sich im Rahmen der strukturierten Nachsorge nach Magenbypass noch ein BMI von 34,3 kg/m2. Der Eingriff führte zu einer besseren Stoffwechselkontrolle sowie zu einer besseren Lebensqualität und nicht zuletzt zu einer erheblichen Kosteneinsparung in der Therapie.

Schlussfolgerung: Die Operation ist eine Ergänzung zur konservativen Behandlungsmöglichkeiten. Die Zusammenarbeit zwischen diabetologischer Schwerpunktpraxis, Fachklinik und Zentrum für metabolische Chirurgie ist sowohl für Indikationsstellung als auch Nachbehandlung essenziell.
Novel Association of Thymic Carcinoid with a Germline Mutation in a Kindred with Multiple Endocrine Neoplasia 1 (MEN1)
Authors: Khoo J. , Bee Y. , Giraud S. , Chen R.Y. , Rajasoorya C. , Teh B.-T.
Published: May 2012

Multiple endocrine neoplasia 1 (MEN1) is an autosomal dominant syndrome characterized by a triad of endocrine (parathyroid, enteropancreatic and pituitary) tumors. Familial MEN1 is defined by one first-degree relative having at least one of these 3 main tumors, and is associated with germline mutations in the MEN1 gene on 11q13 in a large proportion of cases. MEN1 patients may also develop non-endocrine tumors, notably thymic carcinoid. These are rare tumors found predominantly in men, and are a major cause of death in MEN1 due to their insidious nature, lack of effective treatment and unpredictable recurrence. Prophylactic thymectomy has been advocated for prevention but continued surveillance for recurrence is necessary. Although genotype-phenotype correlation in MEN1-related thymic carcinoid is inconsistent, there is a high prevalence of truncating mutations in this condition. We describe a father and son with MEN1, associated with thymic carcinoid (father) and the truncating mutation R29X (son), which was not previously reported in MEN1-related thymic carcinoid, and review the literature about thymic carcinoids in MEN1. Our cases illustrate the importance of a high index of suspicion for early diagnosis and lifelong surveillance in MEN1, and the utility of genetic analysis in defining surveillance for MEN1-related thymic carcinoid.
High efficiency warm-white organic light emitting diodes from a single emitter in graded-doping device architecture
Authors: Bhansali Unnat S. , Jia Huiping , Oswald Iain W. H. , Omary Mohammad A. , Gnade Bruce E.
Published: May 2012

We report high efficiency single-emitter white organic light emitting diodes (SWOLEDs) from a phosphorescent platinum-pyridyltriazolate complex. We have demonstrated good control of the recombination zone and its impact on device performance by adjusting the number of emissive layers, their thicknesses and relative positions in the device stack. Device optimization has resulted in SWOLEDs with a peak power efficiency (PE) = 30.4 ± 1.3 lm/W, external quantum efficiency = 17.0% ± 0.1%, and correlated color temperature = 3450 K, within acceptable warm-white range despite the color rendering index being only 62. The devices exhibit negligible performance roll-off at 500–1000 cd/m2.
Vibrational modes of hydrogens in the proton ordered phase XI of ice: Raman spectra above 400 cm−1
Authors: Shigenari Takeshi , Abe Kohji
Published: May 2012

Polarized Raman spectra of the proton ordered phase of ice Ih, i.e., ice XI, were measured above 400 cm−1 in the range of librational, bending, and stretching vibrations. Vibrational modes in ice XI, of which symmetry is \documentclass[12pt]{minimal}\begin{document}${\rm C}_{2v}^{12}$\end{document}C2v12(Cmc21), were discussed from the group theoretical point of view. In the librational mode spectra below 1200 cm−1, several new peaks and clear polarization dependencies were observed. Assignments of the librational modes agree reasonably well with the recent MD calculations by Iwano et al. (J. Phys. Soc. Jpn. 79, 063601 (2010)10.1143/JPSJ.79.063601). In contrast, the spectra for bands above 1200 cm−1 show no distinct polarization dependencies and the spectra resemble those in ice Ih. In ice XI, however, fine structure composed of several weak peaks appear on the broad bending and the combination band. No direct evidence of the LO-TO splitting of the ν3 anti-symmetric stretching mode was obtained. It is contrary to the case of the translational modes Abe and Shigenari (J. Chem. Phys. 134, 104506 (2011)10.1063/1.3551620). Present results suggest that the influence of the proton ordering in ice XI is weaker than the effect of inter- and intra-molecular couplings in the stretching vibrations of ice Ih.
Doubly hybrid density functional xDH-PBE0 from a parameter-free global hybrid model PBE0
Authors: Zhang Igor Ying , Su Neil Qiang , Brémond Éric A. G. , Adamo Carlo , Xu Xin
Published: May 2012

Following the XYG3 model which uses orbitals and density from B3LYP, an empirical doubly hybrid (DH) functional is developed by using inputs from PBE0. This new functional, named xDH-PBE0, has been tested on a number of different molecular properties, including atomization energies, bond dissociation enthalpies, reaction barrier heights, and nonbonded interactions. From the results obtained, xDH-PBE0 not only displays a significant improvement with respect to the parent PBE0, but also shows a performance that is comparable to XYG3. Arguably, while PBE0 is a parameter-free global hybrid (GH) functional, the B3LYP GH functional contains eight fit parameters. From a more general point of view, the present work points out that reliable and general-purpose DHs can be obtained with a limited number of fit parameters.
Long range excitonic transport in a biomimetic system inspired by the bacterial light-harvesting apparatus
Authors: Harel Elad
Published: May 2012

Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. Recently, the organization of light-harvesting LH2 complexes and dimeric reaction center-light-harvesting I-PufX core complexes in membranes of purple non-sulfur bacteria was revealed by atomic force microscopy [S. Bahatyrova et al., Nature (London) 430, 1058 (2004)]. Here, we discuss optimal exciton transfer in a biomimetic system closely modeled on the structure of LH2 and its organization within the membrane using a Markovian quantum model with dissipation and trapping added phenomenologically. In a deliberate manner, we neglect the high level detail of the bacterial light-harvesting complex and its interaction with the phonon bath in order to elucidate a set of design principles that may be incorporated in artificial pigment-scaffold constructs in a supramolecular assembly. We show that our scheme reproduces many of the most salient features found in their natural counterpart and may be largely explained by simple electrostatic considerations. Most importantly, we show that quantum effects act primarily to enforce robustness with respect to spatial and spectral disorder between and within complexes. The implications of such an arrangement are discussed in the context of biomimetic photosynthetic analogs capable of transferring energy efficiently across tens to hundreds of nanometers.
Equation-of-motion coupled-cluster method for ionized states with spin-orbit coupling
Authors: Tu Zheyan , Wang Fan , Li Xiangyuan
Published: May 2012

We report implementation of the equation of motion coupled-cluster approach for ionized states (EOMIP-CC) with spin-orbit coupling (SOC) using closed-shell state as reference in this work. Ionization potentials (IPs) are calculated in the ionized 1h and 2h1p space with EOM at the CC singles (CCS) as well as the CC singles and doubles levels (CCSD). In this EOMIP-CC approach, SOC is included either in both the CC and EOM steps or only in the EOM step. It should be noted that IPs provided by the EOMIP-CC approach with SOC included only in the EOM step are not size-intensive. Time-reversal symmetry and spatial symmetry are exploited for D2h and its subgroups to reduce computational effort. All these approaches have been shown to be able to afford acceptable estimates for SOC splittings. The EOMIP-CCSD with SOC included only in the EOM step can provide reasonable IPs for systems containing up to 5th row elements. On the other hand, the EOMIP-CCS approach with SOC included in both CC and EOM steps could not predict a bounded 2∑g+ state for I2+ and should be used with care.
Torsion-wagging tunneling and vibrational states in hydrazine determined from its ab initio potential energy surface
Authors: Łodyga Wiesław , Makarewicz Jan
Published: May 2012

Geometries, anharmonic vibrations, and torsion-wagging (TW) multiplets of hydrazine and its deuterated species are studied using high-level ab initio methods employing the second-order Møller-Plesset perturbation theory (MP2) as well as the coupled cluster singles and doubles model including connected triple corrections, CCSD(T), in conjunction with extended basis sets containing diffuse and core functions. To describe the splitting patterns caused by tunneling in TW states, the 3D potential energy surface (PES) for the large-amplitude TW modes is constructed. Stationary points in the 3D PES, including equivalent local minima and saddle points are characterized. Using this 3D PES, a flexible Hamiltonian is built numerically and then employed to solve the vibrational problem for TW coupled motion. The calculated ground state rav structure is expected to be more reliable than the experimental one that has been determined using a simplified structural model. The calculated fundamental frequencies allowed resolution of the assignment problems discussed earlier in the literature. The determined energy barriers, including the contributions from the small-amplitude vibrations, to the tunneling of the symmetric and antisymmetric wagging mode of 1997 cm−1 and 3454 cm−1, respectively, are in reasonable agreement with the empirical estimates of 2072 cm−1 and 3312 cm−1, respectively [W. Łodyga et al. J. Mol. Spectrosc. 183, 374 (1997)10.1006/jmsp.1997.7271]. However, the empirical torsion barrier of 934 cm−1 appears to be overestimated. The ab initio calculations yield two torsion barriers: cis and trans of 744 cm−1 and 2706 cm−1, respectively. The multiplets of the excited torsion states are predicted from the refined 3D PES.
Convergence of the multipole expansions of the polarization and dispersion interactions for atoms under confinement
Authors: Zhang Yong-Hui , Tang Li-Yan , Zhang Xian-Zhou , Jiang Jun , Mitroy J.
Published: May 2012

The multipole expansion of the polarization interaction between a charged particle and an electrically neutral object has long been known to be asymptotic in nature, i.e., the multiple expansion diverges at any finite distance from the atom. However, the multipole expansion of the polarization potential of a confined hydrogen atom is shown to be absolutely convergent at a distance outside the confinement radius, R0, of the atom. The multipole expansion of the dispersion potential between two confined hydrogen atoms is also shown to be absolutely convergent provided the two atoms satisfy R > 2R0, where R is the inter-nuclear separation. These results were established analytically using oscillator strength sum rules and verified numerically using a B-spline description of the hydrogen ground state and its excitation spectrum.
Medium decoupling of dynamics at temperatures ∼100 K above glass-transition temperature: A case study with (acetamide + lithium bromide/nitrate) melts
Authors: Guchhait Biswajit , Daschakraborty Snehasis , Biswas Ranjit
Published: May 2012

Time-resolved fluorescence Stokes shift and anisotropy measurements using a solvation probe in [0.78CH3CONH2 + 0.22{f LiBr + (1-f) LiNO3}] melts reveal a strong decoupling of medium dynamics from viscosity. Interestingly, this decoupling has been found to occur at temperatures ∼50–100 K above the glass transition temperatures of the above melt at various anion concentrations (fLiBr). The decoupling is reflected via the following fractional viscosity dependence (η) of the measured average solvation and rotation times (⟨τs⟩ and ⟨τr⟩, respectively): ⟨τx⟩ ∝ (η/T)p (x being solvation or rotation), with p covering the range, 0.20 < p < 0.70. Although this is very similar to what is known for deeply supercooled liquids, it is very surprising because of the temperature range at which the above decoupling occurs for these molten mixtures. The kinship to the supercooled liquids is further exhibited via p which is always larger for ⟨τr⟩ than for ⟨τs⟩, indicating a sort of translation-rotation decoupling. Multiple probes have been used in steady state fluorescence measurements to explore the extent of static heterogeneity. Estimated experimental dynamic Stokes shift for coumarin 153 in these mixtures lies in the range, 1000 < Δνt/cm−1 < 1700, and is in semi-quantitative agreement with predictions from our semi-molecular theory. The participation of the fluctuating density modes at various length-scales to the observed solvation times has also been investigated.
Non-relativistic Lee model in two-dimensional Riemannian manifolds
Authors: Erman Fatih , Turgut O. Teoman
Published: May 2012

This work is a continuation of our previous work [F. Erman and O. T. Turgut, J. Math. Phys. 48, 122103 (2007)10.1063/1.2813026], where we constructed the non-relativistic Lee model in three-dimensional Riemannian manifolds. Here we renormalize the two-dimensional version by using the same methods and the results are shortly given since the calculations are basically the same as in the three-dimensional model. We also show that the ground state energy is bounded from below due to the upper bound of the heat kernel for compact and Cartan-Hadamard manifolds. In contrast to the construction of the model and the proof of the lower bound of the ground state energy, the mean field approximation to the two-dimensional model is not similar to the one in three dimensions and it requires a deeper analysis, which is the main result of this paper.
Defect chemistry of Ti-doped antiferroelectric Bi0.85Nd0.15FeO3
Authors: Reaney Ian M. , MacLaren Ian , Wang Liqiu , Schaffer Bernhard , Craven Alan , Kalantari Kambiz , Sterianou Iasmi , Miao Shu , Karimi Sarah , Sinclair Derek C.
Published: May 2012

Aberration corrected scanning transmission electron microscopy revealed that Bi0.85Nd0.15Fe0.9Ti0.1O3 ceramics contain coherent Nd-rich precipitates distributed throughout the perovskite lattice, implying charge compensation is obtained by the creation of VNd/// and not VBi///. At low concentrations, therefore, Ti4+ replace Fe2+ with the creation of 2/3VNd///, and at higher concentrations (when Fe2+ have been eliminated and the conductivity suppressed), Fe3+ with the creation of 1/3VNd///. The switch in ionic compensation mechanism from 2/3VNd/// at low Ti concentrations (∼1%) to 1/3VNd/// at higher concentrations (>1%) results in a decrease in the magnitude of ΔTC/Δx, as the disruption of long range anti-polar coupling declines.
A wall-free climate unit for acoustic levitators
Authors: Schlegel M. C. , Wenzel K.-J. , Sarfraz A. , Panne U. , Emmerling F.
Published: May 2012

Acoustic levitation represents the physical background of trapping a sample in a standing acoustic wave with no contact to the wave generating device. For the last three decades, sample holders based on this effect have been commonly used for contact free handling of samples coupled with a number of analytical techniques. In this study, a wall-free climate unit is presented, which allows the control of the environmental conditions of suspended samples. The insulation is based on a continuous cold/hot gas flow around the sample and thus does not require any additional isolation material. This provides a direct access to the levitated sample and circumvents any influence of the climate unit material to the running analyses.
Local structure of titania decorated double-walled carbon nanotube characterized by scanning transmission X-ray microscopy
Authors: Zhang Hongbo , Wang Jian , Pan Xiulian , Hu Yongfeng , Bao Xinhe
Published: May 2012

Scanning transmission X-ray microscopy was demonstrated to deliver detailed local structure and chemical composition of a complicated system with titania nanoparticles dispersed inside and outside the double-walled carbon nanotube (DWNT) channels. Areas with inhomogeneous distribution of titania and the associated water were particularly investigated at the C K-edge, Ti L-edge, and O K-edge. The results show that titania nanoparticles located inside DWNTs are present as amorphous, while those unsuccessfully introduced into the channels behave more like bulk materials in forms of anatase and rutile. Strong interaction was detected between the confined titania and DWNTs, as evidenced by up to 0.6 eV energy shift at the Ti L-edge. Strong hydration was observed for the as-prepared samples. Functionalization due to reduction and oxidation between titania and carbon layer is observed upon heat-treatment. This detailed structural information of specific areas cannot be provided by other techniques such as HRTEM, XRD, and XANES.
Mimicking trimeric interactions in the aromatic side chains of the proteins: A gas phase study of indole…(pyrrole)2 heterotrimer
Authors: Kumar Sumit , Das Aloke
Published: May 2012

Aromatic trimeric interactions are extremely significant in the stabilization of the specific structures of the proteins as well as protein-protein, and protein-ligand interactions. Here we have reported a direct evidence of the observation of a cyclic asymmetric structure of indole…(pyrrole)2 trimer bound by three N–H…π hydrogen bonding interactions in a supersonic jet. The experiment has been performed by using resonant two-photon ionization (R2PI), IR-UV, and UV-UV double resonance spectroscopic techniques. Density functional theory (DFT) calculations nicely corroborate the experimental results showing one weakly allowed IR-active band due to symmetric stretch of the N–H bonds and two strongly allowed IR-active bands due to two types of asymmetric stretches of the N–H bonds in the trimer. The present spectroscopic investigation demonstrates that the strength of the three N–H…π bound intermolecular interactions in the cyclic asymmetric trimer is quite different unlike the corresponding interactions of similar strength in a cyclic symmetric trimer.
Electronic spectroscopy of I2–Xe complexes in solid Krypton
Authors: Hulkko Eero , Ahokas Jussi , Lindgren Johan , Myllyperkiö Pasi , Pettersson Mika
Published: May 2012

In the present work, we have studied ion-pair states of matrix-isolated I2 with vacuum-UV absorption and UV-vis-NIR emission, where the matrix environment is systematically changed by mixing Kr with Xe, from pure Kr to a more polarizable Xe host. Particular emphasis is put on low doping levels of Xe that yield a binary complex I2–Xe, as verified by coherent anti-Stokes Raman scattering (CARS) measurements. Associated with interaction of I2 with Xe we can observe strong new absorption in vacuum-UV, redshifted 2400 cm−1 from the X → D transition of I2. Observed redshift can be explained by symmetry breaking of ion-pair states within the I2–Xe complex. Systematic Xe doping of Kr matrices shows that at low doping levels, positions of I2 ion-pair emissions are not significantly affected by complexation with Xe, but simultaneous increase of emissions from doubly spin-excited states indicates non-radiative relaxation to valence states. At intermediate doping levels ion-pair emissions shift systematically to red due to change in the average polarizability of the environment. We have conducted spectrally resolved ultrafast pump-probe ion-pair emission studies with pure and Xe doped Kr matrices, in order to reveal the influence of Xe to I2 dynamics in solid Kr. Strikingly, relaxed emission from the ion-pair states shows no indication of complex presence. It further indicates that the complex escapes detection due to a non-radiative relaxation.
Magnetization configurations of a tri-layer nanopillar ferromagnet/nonmagnetic spacer/ferromagnet
Authors: Sukhostavets Oksana V. , Aranda Gloria R. , Guslienko Konstantin Y.
Published: May 2012

The equilibrium magnetization configurations of tri-layer circular nanopillar are calculated within micromagnetic approach. Nanopillar is assumed to be a vertical stack of ferromagnetic/nonmagnetic/ferromagnetic layers. The regions of geometrical parameters of nanopillar (radius and thickness), where the magnetic vortices and single domain states appear in the ground state, are calculated analytically and checked by micromagnetic simulations. The interlayer magnetostatic coupling affects essentially the formation of vortices or single domain states in both ferromagnetic layers. A considerable influence of the thicknesses of the ferromagnetic layers and spacer on the stability of vortex states is found. The results can be applied to interpret experiments on spin torque induced magnetization dynamics in nanopillars and tunnel junctions and also to estimate the nanopillar ground states.
Spectroscopic ellipsometry model for optical constant of NiSi formed on silicon-on-insulator substrates
Authors: Vellei A. , Fallica R. , Sangalli D. , Lamperti A.
Published: May 2012

Nickel silicide is considered the best candidate material to achieve the lowest contact resistance in sub 45 nm CMOS devices. NiSi films with thickness 20–60 nm were prepared by rapid thermal annealing of Ni (temperature 230 °C–780 °C) on top of thin 230 nm silicon-on-insulator substrates, with a constant formation ratio. Based on film independent characterizations, a novel model for the interpretation of spectroscopic ellipsometry data, featuring a combination of two Lorentzian oscillators and one Drude dispersion model, is proposed, and its goodness is checked in comparison to other known models. This new approach is proved to deliver more accurate estimation of the film thickness and resistivity.
Cascaded plasmon resonant field enhancement in nanoparticle dimers in the point dipole limit
Authors: Toroghi Seyfollah , Kik Pieter G.
Published: May 2012

Cascaded field enhancement in silver dimer nanostructures is investigated using a dipole-dipole interaction model. Field enhancement spectra are evaluated as a function of the particle size difference and inter-particle spacing. We observe three distinct regimes of cascaded field enhancement: hindered cascading, multiplicative cascading, and the ultimate cascading limit, depending on the dimer interaction strength. Multiplicative cascading at small inter-particle spacing leads to analytic expressions for the ultimate internal and external field enhancement factors. For silver dimers in a host with index 1.5, we obtain a maximum internal field enhancement of 2.9 × 103, a factor of 75 larger than that of an isolated silver nanoparticle.
Optimizing transition states via kernel-based machine learning
Authors: Pozun Zachary D. , Hansen Katja , Sheppard Daniel , Rupp Matthias , Müller Klaus-Robert , Henkelman Graeme
Published: May 2012

We present a method for optimizing transition state theory dividing surfaces with support vector machines. The resulting dividing surfaces require no a priori information or intuition about reaction mechanisms. To generate optimal dividing surfaces, we apply a cycle of machine-learning and refinement of the surface by molecular dynamics sampling. We demonstrate that the machine-learned surfaces contain the relevant low-energy saddle points. The mechanisms of reactions may be extracted from the machine-learned surfaces in order to identify unexpected chemically relevant processes. Furthermore, we show that the machine-learned surfaces significantly increase the transmission coefficient for an adatom exchange involving many coupled degrees of freedom on a (100) surface when compared to a distance-based dividing surface.
How does water-nanotube interaction influence water flow through the nanochannel?
Authors: Li Xiaoyi , Shi Yanchao , Yang Yuling , Du Huailiang , Zhou Ruhong , Zhao Yuliang
Published: May 2012

Water permeation across various nitrogen-doped double-walled carbon nanotubes (N-DWCNT) has been studied with molecular dynamics simulations to better understand the influence of water-nanopore interaction on the water permeation rate. There exists a threshold interaction energy at around –34.1 kJ/mol. Over the threshold energy, the water flow through N-DWCNT decreases monotonically with the strengthening of the water-nanotube interaction. The effect on the water flow across the channel is found to be negligible when the interaction energy is weaker than the threshold. The water-nanotube interaction energy can be controlled by doping nitrogen atoms into the nanotube walls. Although the van der Waals interaction energy is much stronger than the electrostatic interaction energy, it is less sensitive to the proportion of doped nitrogen atoms. On the other hand, the electrostatic interaction energy weakens after the initial strengthening when the percentage of doped nitrogen atoms increases to ∼25%. The doped nitrogen atoms make less influence on the overall electrostatic interaction energy when the proportion is over 25%, due to the repulsions among themselves. Thus, the monotonous strengthening of the van der Waals interaction energy seems to dominate the overall trend of the total interaction energy, whereas the change of the long-range electrostatic interaction energy characterizes the shape of the correlation curve, as the percentage of doped nitrogen atoms increases.
Contactless electroreflectance studies of Fermi level position on c-plane GaN surface grown by molecular beam epitaxy and metalorganic vapor phase epitaxy
Authors: Kudrawiec R. , Gladysiewicz M. , Janicki L. , Misiewicz J. , Cywinski G. , Chèze C. , Wolny P. , Prystawko P. , Skierbiszewski C.
Published: May 2012

Contactless electroreflectance (CER) has been applied to study the Fermi-level position on c-plane GaN surface in Van Hoof structures grown by molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE). A clear CER resonance followed by strong Franz-Keldysh oscillation (FKO) of various periods was clearly observed for the series of samples of different thicknesses (30, 50, and 70 nm) of undoped GaN layer. The built-in electric field in this layer has been determined from the period of GaN-related FKO. A good agreement between the calculated and measured electric fields has been found for the Fermi-level located ∼0.4 and ∼0.3 eV below the conduction band for the MBE and MOVPE samples, respectively.
Application of double-hybrid density functionals to charge transfer in N-substituted pentacenequinones
Authors: Sancho-García J. C.
Published: May 2012

A set of N-heteroquinones, deriving from oligoacenes, have been recently proposed as n-type organic semiconductors with high electron mobilities in thin-film transistors. Generally speaking, this class of compounds self-assembles in neighboring π-stacks linked by weak hydrogen bonds. We aim at theoretically characterizing here the sequential charge transport (hopping) process expected to take place across these arrays of molecules. To do so, we need to accurately address the preferred packing of these materials simultaneously to single-molecule properties related to charge-transfer events, carefully employing dispersion-corrected density functional theory methods to accurately extract the key molecular parameters governing this phenomenon at the nanoscale. This study confirms the great deal of interest around these compounds, since controlled functionalization of model molecules (i.e., pentacene) allows to efficiently tune the corresponding charge mobilities, and the capacity of modern quantum-chemical methods to predict it after rationalizing the underlying structure-property relationships.
Determination of the solid-fluid coexistence of the n − 6 Lennard-Jones system from free energy calculations
Authors: Sousa J. M. G. , Ferreira A. L. , Barroso M. A.
Published: May 2012

The solid-fluid coexistence properties of the n − 6 Lennard-Jones system, n from 7 to 12, are reported. The procedure relies on determining Helmholtz free energy curves as a function of volume for each phase independently, from several NVT simulations, and then connecting it to points of known absolute free energy. For n = 12 this requires connecting the simulated points to states of very low densities on the liquid phase, and to a harmonic crystal for the solid phase, which involves many extra simulations for each temperature. For the reference points of the remaining systems, however, the free energy at a given density and temperature can be calculated relative to the n = 12 system. The method presented here involves a generalization of the multiple histogram method to combine simulations performed with different potentials, provided they visit overlapping regions of the phase space, and allows for a precise calculation of relative free energies. The densities, free energies, average potential energies, pressure, and chemical potential at coexistence are presented for up to T* = 5.0 and new estimations of the triple points are given for the n − 6 Lennard-Jones system.
State-dependent photoionization cross-sections of 3d transition metal atoms
Authors: Zheng Xianfeng , Chen Xiaohu , Chen Yangyang , Dong Bingling , Zhang Ke , Yao Guanxin , Cui Zhifeng
Published: May 2012

Using the saturation method, we measured the absolute photoionization cross-sections of several excited states of titanium, vanadium, chromium, iron, and cobalt. These results are reported for the first time in this paper. The measured values range from 0.4 ± 0.1 Mb to 6.9 ± 2.0 Mb. The results show that the photoionization cross-section depends on the atomic state and not just on the electronic configuration.
Raman spectra of vibrational and librational modes in methane clathrate hydrates using density functional theory
Authors: Ramya K. R. , Pavan Kumar G. V. , Venkatnathan Arun
Published: May 2012

The sI type methane clathrate hydrate lattice is formed during the process of nucleation where methane gas molecules are encapsulated in the form of dodecahedron (512CH4) and tetrakaidecahedron (51262CH4) water cages. The characterization of change in the vibrational modes which occur on the encapsulation of CH4 in these cages plays a key role in understanding the formation of these cages and subsequent growth to form the hydrate lattice. In this present work, we have chosen the density functional theory (DFT) using the dispersion corrected B97-D functional to characterize the Raman frequency vibrational modes of CH4 and surrounding water molecules in these cages. The symmetric and asymmetric C–H stretch in the 512CH4 cage is found to shift to higher frequency due to dispersion interaction of the encapsulated CH4 molecule with the water molecules of the cages. However, the symmetric and asymmetric O–H stretch of water molecules in 512CH4 and 51262CH4 cages are shifted towards lower frequency due to hydrogen bonding, and interactions with the encapsulated CH4 molecules. The CH4 bending modes in the 512CH4 and 51262CH4 cages are blueshifted, though the magnitude of the shifts is lower compared to modes in the high frequency region which suggests bending modes are less affected on encapsulation of CH4. The low frequency librational modes which are collective motion of the water molecules and CH4 in these cages show a broad range of frequencies which suggests that these modes largely contribute to the formation of the hydrate lattice.
Time-resolved mirage method: A three-dimensional theory and experiments
Authors: Astrath N. G. C. , Malacarne L. C. , Bernabe H. S. , Baesso M. L. , Jacinto C.
Published: May 2012

A general time-resolved three-dimensional theory of the photothermal beam deflection for the measurement of thermal properties of opaque materials is presented. We derive the analytical solutions for the laser induced temperature profiles in the sample and in the fluid above the sample assuming flux discontinuity at the interface sample/fluid. We compare the analytical solutions with all numerical modeling using finite element analysis. The photothermal deflection signal is calculated and an expression is provided for the transverse photothermal signal at a position-sensing detector. We use the model and the experimental method to investigate opaque plastic and metals, and the results for the thermal properties of the samples are in an excellent agreement in the literature values.
Xenon doping of glow discharge polymer by ion implantation
Authors: Shin Swanee J. , Kucheyev Sergei O. , Orme Christine A. , Youngblood Kelly P. , Nikroo Abbas , Moreno Kari A. , Chen Bryan , Hamza Alex V.
Published: May 2012

We demonstrate controlled doping of a glow discharge polymer by implantation with 500 keV Xe ions at room temperature. The Xe retention exhibits a threshold behavior, with a threshold dose of ∼2 × 1014 cm−2. Doping is accompanied by irradiation-induced changes in the polymer composition, including gradual H loss and a more complex non-monotonic behavior of the O concentration. The matrix composition saturates at C0.77H0.22O0.01 for Xe doses above ∼5 × 1014 cm−2 and up to the maximum dose studied (5 × 1015 cm−2). The retention mechanism is attributed to the modification of the polymer from a chain-like to clustered ring structure. The dopant profile and the elemental composition of the implanted polymer exhibit good stability upon thermal annealing up to 305 °C.
An atomic beam source for fast loading of a magneto-optical trap under high vacuum
Authors: McDowall Peter D. , Grünzweig Tzahi , Hilliard Andrew , Andersen Mikkel F.
Published: May 2012

We report on a directional atomic beam created using an alkali metal dispenser and a nozzle. By applying a high current (15 A) pulse to the dispenser at room temperature we can rapidly heat it to a temperature at which it starts dispensing, avoiding the need for preheating. The atomic beam produced is capable of loading 90% of a magneto-optical trap (MOT) in less than 7 s while maintaining a low vacuum pressure of <10−11 Torr. The transverse velocity components of the atomic beam are measured to be within typical capture velocities of a rubidium MOT. Finally, we show that the atomic beam can be turned off within 1.8 s.
A furnace with rotating load frame for in situ high temperature deformation and creep experiments in a neutron diffraction beam line
Authors: Reiche H. M. , Vogel S. C. , Mosbrucker P. , Larson E. J. , Daymond M. R.
Published: May 2012

A resistive furnace combined with a load frame was built that allows for in situ neutron diffraction studies of high temperature deformation, in particular, creep. A maximum force of 2700 N can be applied at temperatures up to 1000 °C. A load control mode permits studies of, e.g., creep or phase transformations under applied uni-axial stress. In position control, a range of high temperature deformation experiments can be achieved. The examined specimen can be rotated up to 80° around the vertical compression axis allowing texture measurements in the neutron time-of-flight diffractometer HIPPO (High Pressure – Preferred Orientation). We present results from the successful commissioning, deforming a Zr-2.5 wt.% Nb cylinder at 975 °C. The device is now available for the user program of the HIPPO diffractometer at the LANSCE (Los Alamos Neutron Science Center) user facility.
Cometary flow equation with a self-consistent electromagnetic field
Authors: Chen Zili , Zhang Xianwen
Published: May 2012

We study the Cauchy problem of a three-dimensional cometary flow equation with a self-consistent electromagnetic field. This kinetic model comes from the theory of astrophysical plasmas and can be viewed as a perturbation by a wave-particle collision operator of the classical Vlasov-Maxwell system. The main result is a global existence theorem of a non-negative weak solution for initial data meeting the physical significance, namely, for initial data having finite mass and total energy and verifying some compatibility conditions.
Field dependence of the E1′ and M3′ electron traps in inductively coupled Ar plasma treated n-Gallium Arsenide
Authors: Venter A. , Nyamhere C. , Botha J. R. , Auret F. D. , Coelho S. M. M. , Meyer W. E.
Published: May 2012

Inductively coupled Ar plasma etching of n-type (Si doped) Gallium Arsenide (GaAs) introduces several electron traps, Ec – 0.04 eV (labelled E1′), Ec – 0.19 eV, Ec – 0.31 eV, Ec – 0.53 eV, and Ec – 0.61 eV (behaving like the well documented M3 and labelled M3′ in this study), of which the metastable defects Ec – 0.04 eV (E1′), and Ec – 0.07 eV are novel. Furthermore, E1′ and M3′ exhibit strong field enhanced carrier emission. Double-correlation deep level transient spectroscopy was used to investigate the field dependent emission behaviour of these two defects. It is shown that for both traps, the observed enhanced emission is due to phonon assisted tunnelling. The latter observation is contrary to the literature reports suggesting that enhanced carrier emission for M3 occurs via the Poole-Frenkel mechanism.
Suppress temperature instability of InGaZnO thin film transistors by N2O plasma treatment, including thermal-induced hole trapping phenomenon under gate bias stress
Authors: Chang Geng-Wei , Chang Ting-Chang , Jhu Jhe-Ciou , Tsai Tsung-Ming , Syu Yong-En , Chang Kuan-Chang , Tai Ya-Hsiang , Jian Fu-Yen , Hung Ya-Chi
Published: May 2012

An abnormal subthreshold leakage current is observed at high temperature, which causes a notable stretch-out phenomenon in amorphous InGaZnO thin film transistors (a-IGZO TFTs). This is due to trap-induced thermal-generated holes accumulating at the source region, which leads to barrier lowering on the source side and causes an apparent subthreshold leakage current. In order to obtain superior thermal stability performance of a-IGZO TFTs, conducting N2O plasma treatment on active layer was expected to avert defects generation during SiO2 deposition process. Reducing defects generation not only suppresses subthreshold current stretch-out phenomenon but also significantly improves the bias stress stability in a-IGZO TFTs at high temperature.
Dynamics of freely swimming flexible foils
Authors: Alben Silas , Witt Charles , Baker T. Vernon , Anderson Erik , Lauder George V.
Published: May 2012

We use modeling and simulations guided by initial experiments to study thin foils which are oscillated at the leading edge and are free to move unidirectionally under the resulting fluid forces. We find resonant-like peaks in the swimming speed as a function of foil length and rigidity. We find good agreement between the inviscid model and the experiment in the foil motions (particularly the wavelengths of their shapes), the dependences of their swimming speeds on foil length and rigidity, and the corresponding flows. The model predicts that the foil speed is proportional to foil length to the −1/3 power and foil rigidity to the 2/15 power. These scalings give a good collapse of the experimental data.
Influence of the number of detectors by laser scattering method for estimation of particle size
Authors: Igushi Tatsuo , Yoshida Hideto
Published: May 2012

Effect of the number of detectors on an inversion problem of a scattering pattern by laser scattering method based on Mie scattering model has been investigated. The influence of the number of detectors is obtained by comparing a given size distribution and a calculated size distribution by computer simulation and experimental method. An observing range of scattering angles is from 0.0007 to 2.5 rad. A non-linear iteration method is used for calculating particle size distribution. The number of detectors is changed from 6 to 81 elements by the computer simulation. The algorithm of the inversion problem is applied with mean diameters of log-normal distribution in a range from 0.546 to 214 μm at standard deviation of 0.27 and 0.68. Experimental results of certified mono-disperse polystyrene latex standards and a poly-disperse aluminum sample are obtained with 21, 41, and 81 elements detector, respectively. All tests are performed under conditions at diluted aqueous suspensions. Narrow size distribution is influenced by the number of detectors compared with wide size distribution. Not the number of physical detectors but the number of useful detectors affects the algorithm of the inversion problem. When the detector elements are over 20, the influence of the number of detectors is decreased.
Micro-reactors for characterization of nanostructure-based sensors
Authors: Savu R. , Silveira J. V. , Flacker A. , Vaz A. R. , Joanni E. , Pinto A. C. , Gobbi A. L. , Santos T. E. A. , Rotondaro A. L. P. , Moshkalev S. A.
Published: May 2012

Fabrication and testing of micro-reactors for the characterization of nanosensors is presented in this work. The reactors have a small volume (100 μl) and are equipped with gas input/output channels. They were machined from a single piece of kovar in order to avoid leaks in the system due to additional welding. The contact pins were electrically insulated from the body of the reactor using a borosilicate sealing glass and the reactor was hermetically sealed using a lid and an elastomeric o-ring. One of the advantages of the reactor lies in its simple assembly and ease of use with any vacuum/gas system, allowing the connection of more than one device. Moreover, the lid can be modified in order to fit a window for in situ optical characterization. In order to prove its versatility, carbon nanotube-based sensors were tested using this micro-reactor. The devices were fabricated by depositing carbon nanotubes over 1 μm thick gold electrodes patterned onto Si/SiO2 substrates. The sensors were tested using oxygen and nitrogen atmospheres, in the pressure range between 10−5 and 10−1 mbar. The small chamber volume allowed the measurement of fast sensor characteristic times, with the sensors showing good sensitivity towards gas and pressure as well as high reproducibility.