bluuebunny/crossref_metadata_2025 huggingface dataset:
Shape‐free inference of hyporheic traveltime distributions from synthetic conservative and “smart” tracer tests in streams
Authors: Liao Zijie , Cirpka Olaf A.
Published: July 2011

The hyporheic zone has been identified as important for river ecology, natural biogeochemical turnover, filtration of particles, degradation of dissolved pollutants—and thus for the self‐cleaning capacity of streams, and for groundwater quality. Good estimation of the traveltime distribution in the hyporheic zone is required to achieve a better understanding of transport in the river system. The transient‐storage model has been accepted as an appropriate tool for reach‐scale transport in rivers undergoing hyporheic exchange, but the choice of the best parametric function for the hyporheic traveltime distribution has remained unclear. We present an approach to obtaining hyporheic traveltime distributions from synchronous conservative and “smart” tracer experiments that does not rely on a particular functional form of the hyporheic traveltime distribution, but treats the latter as a continuous function. Nonnegativity of the hyporheic traveltime distribution is enforced by the application of Lagrange multipliers. A smoothness parameter, needed for regularization, and uncertainty bounds are obtained by the expectation‐maximization method relying on conditional realizations. The shape‐free inference provides the opportunity for capturing unconventional shapes, e.g., multiple peaks, in the estimation. We test the approach by applying it to a virtual test case with a bimodal hyporheic traveltime distribution, which is recaptured in the inversion of noisy data.
Cortical Substrate Oxidation during Hyperketonemia in the Fasted Anesthetized Rat in Vivo
Authors: Jiang Lihong , Mason Graeme F , Rothman Douglas L , de Graaf Robin A , Behar Kevin L
Published: July 2011

Ketone bodies are important alternate brain fuels, but their capacity to replace glucose and support neural function is unclear. In this study, the contributions of ketone bodies and glucose to cerebral cortical metabolism were measured in vivo in halothane-anesthetized rats fasted for 36 hours ( n=6) and receiving intravenous [2,4-13C2]-d- β-hydroxybutyrate (BHB). Time courses of 13C-enriched brain amino acids (glutamate-C4, glutamine-C4, and glutamate and glutamine-C3) were measured at 9.4 Tesla using spatially localized 1H-[13C]-nuclear magnetic resonance spectroscopy. Metabolic rates were estimated by fitting a constrained, two-compartment (neuron–astrocyte) metabolic model to the 13C time-course data. We found that ketone body oxidation was substantial, accounting for 40% of total substrate oxidation (glucose plus ketone bodies) by neurons and astrocytes. d- β-Hydroxybutyrate was oxidized to a greater extent in neurons than in astrocytes (∼70:30), and followed a pattern closely similar to the metabolism of [1-13C]glucose reported in previous studies. Total neuronal tricarboxylic acid cycle (TCA) flux in hyperketonemic rats was similar to values reported for normal (nonketotic) anesthetized rats infused with [1-13C]glucose, but neuronal glucose oxidation was 40% to 50% lower, indicating that ketone bodies had compensated for the reduction in glucose use.
Heterogeneity in the penumbra
Authors: del Zoppo Gregory J , Sharp Frank R , Heiss Wolf-Dieter , Albers Gregory W
Published: July 2011

Original experimental studies in nonhuman primate models of focal ischemia showed flow-related changes in evoked potentials that suggested a circumferential zone of low regional cerebral blood flow with normal K+ homeostasis, around a core of permanent injury in the striatum or the cortex. This became the basis for the definition of the ischemic penumbra. Imaging techniques of the time suggested a homogeneous core of injury, while positing a surrounding ‘penumbral’ region that could be salvaged. However, both molecular studies and observations of vascular integrity indicate a more complex and dynamic situation in the ischemic core that also changes with time. The microvascular, cellular, and molecular events in the acute setting are compatible with heterogeneity of the injury within the injury center, which at early time points can be described as multiple ‘mini-cores' associated with multiple ‘mini-penumbras’. These observations suggest the progression of injury from many small foci to a homogeneous defect over time after the onset of ischemia. Recent observations with updated imaging techniques and data processing support these dynamic changes within the core and the penumbra in humans following focal ischemia.
Screening Of Antibiotic Producing Microorganism From Rhizoshphere Soil, Their Antibiotic Production And Characterization
Authors: Bhandare Vishwambhar , Chavre Sandip Mahadev
Published: July 2011

Rhizosphere soil samples were preferred as it contains most of the prospective antibiotic producers. In an attempt to screen out new potent antibiotic producers from soil, the Rhizobium species was isolated. Antibiotic produced by shake flask culture is found to be effective against both gram positive and gram negative organisms. This product was found to be a very promising antibiotic when assayed biologically. UV treatment showed positive effect on antibiotic production. The molecular structure of the antibiotic was identified by using advanced analytical techniques like UV Visible spectroscopy, FTIR, GCMS, NMR spectroscopy.
l(2)01810 is a novel type of glutamate transporter that is responsible for megamitochondrial formation
Authors: Shim Myoung Sup , Kim Jin Young , Lee Kwang Hee , Jung Hee Kyoung , Carlson Bradley A. , Xu Xue-Ming , Hatfield Dolph L. , Lee Byeong Jae
Published: July 2011

l(2)01810 causes glutamine-dependent megamitochondrial formation when it is overexpressed in Drosophila cells. In the present study, we elucidated the function of l(2)01810 during megamitochondrial formation. The overexpression of l(2)01810 and the inhibition of glutamine synthesis showed that l(2)01810 is involved in the accumulation of glutamate. l(2)01810 was predicted to contain transmembrane domains and was found to be localized to the plasma membrane. By using 14C-labelled glutamate, l(2)01810 was confirmed to uptake glutamate into Drosophila cells with high affinity (Km=69.4 μM). Also, l(2)01810 uptakes glutamate in a Na+-independent manner. Interestingly, however, this uptake was not inhibited by cystine, which is a competitive inhibitor of Na+-independent glutamate transporters, but by aspartate. A signal peptide consisting of 34 amino acid residues targeting to endoplasmic reticulum was predicted at the N-terminus of l(2)01810 and this signal peptide is essential for the protein's localization to the plasma membrane. In addition, l(2)01810 has a conserved functional domain of a vesicular-type glutamate transporter, and Arg146 in this domain was found to play a key role in glutamate transport and megamitochondrial formation. These results indicate that l(2)01810 is a novel type of glutamate transporter and that glutamate uptake is a rate-limiting step for megamitochondrial formation.
Glycaemic variability affects ischaemia-induced angiogenesis in diabetic mice
Authors: Biscetti Federico , Pitocco Dario , Straface Giuseppe , Zaccardi Francesco , de Cristofaro Raimondo , Rizzo Paola , Lancellotti Stefano , Arena Vincenzo , Stigliano Egidio , Musella Tittania , Ghirlanda Giovanni , Flex Andrea
Published: July 2011

The aim of the present study was to investigate the role of GV (glycaemic variability) in diabetic vascular complications and to explore the molecular pathways modulated by glycaemic ‘swings’. We developed a murine model. A total of 30 diabetic mice received once daily basal insulin administration plus two oral boluses of glucose solution (GV group, named ‘V’) and 30 diabetic mice received once daily basal insulin plus two oral boluses of saline solution (stable hyperglycaemia group, named ‘S’) for a period of 30 days. Glycaemia was measured eight times daily to detect GV. Finally, postischaemic vascularization, induced by hindlimb ischaemia 30 days after diabetes onset, was evaluated. We found that GV was significantly different between S and V groups, whereas no significant difference in the mean glycaemic values was detected. Laser Doppler perfusion imaging and histological analyses revealed that the ischaemia-induced angiogenesis was significantly impaired in V mice compared with S group, after ischaemic injury. In addition, immunostaining and Western blot analyses revealed that impaired angiogenic response in V mice occurred in association with reduced VEGF (vascular endothelial growth factor) production and decreased eNOS (endothelial nitric oxide synthase) and Akt (also called protein kinase B) phosphorylation. In conclusion, we describe a murine model of GV. GV causes an impairment of ischaemia-induced angiogenesis in diabetes, likely to be independent of changes in average blood glucose levels, and this impaired collateral vessel formation is associated with an alteration of the VEGF pathway.
Speaking Rate Effects on Normal Aspects of Articulation: Outcomes and Issues
Authors: Berry Jeff
Published: July 2011

The articulatory effects of speaking rate have been a point of focus for a substantial literature in speech science. The normal aspects of speaking rate variation have influenced theories and models of speech production and perception in the literature pertaining to both normal and disordered speech. While the body of literature pertaining to the articulatory effects of speaking rate change is reasonably large, few speaker-general outcomes have emerged. The purpose of this paper is to review outcomes of the existing literature and address problems related to the study of speaking rate that may be germane to the recurring theme that speaking rate effects are largely idiosyncratic.
Lessons From the Neural Bases of Speech and Voice
Authors: Ludlow Christy L.
Published: July 2011

The premise of this article is that increased understanding of the brain bases for normal speech and voice behavior will provide a sound foundation for developing therapeutic approaches to establish or re-establish these functions. The neural substrates involved in speech/voice behaviors, the types of muscle patterning for speech and voice, the brain networks involved and their regulation, and how they can be externally modulated for improving function will be addressed.
Ambulatory Monitoring of Daily Voice Use
Authors: Hillman Robert E. , Mehta Daryush D.
Published: July 2011

Many common voice disorders are chronic or recurring conditions likely to result from faulty and/or abusive patterns of vocal behavior. Such behaviorally based disorders can be difficult to assess accurately in the clinical setting and potentially could be much better characterized by long-term ambulatory monitoring of vocal function as individuals engage in their typical daily activities. Ambulatory monitoring also could provide new insight into the actual role of voice use in common disorders and missing quantitative data on what constitutes normal levels of daily voice use for different groups of individuals, activities, and occupations. This report describes the motivation, previous development efforts, current state-of-the-art technology, and future directions in ambulatory monitoring of voice use.
Green Voice Project: Preserving the Healthy Voice in Teachers
Authors: Chan Karen M. K. , Yiu Edwin M.-L.
Published: July 2011

This article reviews five recent studies on preventing voice problems in vocally healthy student teachers and teachers. The differences in research design are discussed and suggestions for future studies are provided. A prevention study carried out at The University of Hong Kong also is reported. Preliminary results suggest that voice care information may be useful in preventing voice problems in teachers.
Voice Disorders in Teachers
Authors: Roy Nelson
Published: July 2011

Voice disorders are a common occupational hazard of teaching school. This article provides an overview of recent epidemiological research surrounding this high-risk occupation, identifies possible mechanisms contributing to voice disorder development including vibration overdose, summarizes recent clinical trials research evaluating treatments for teachers with voice disorders, and discusses primary prevention and the relative inadequacy of “education only” approaches.
Spatial imaging of individual vibronic states in the interior of single molecules
Authors: Huan Q. , Jiang Y. , Zhang Y. Y. , Ham U. , Ho W.
Published: July 2011

Selective excitations of specific vibronic modes in position space are realized in single naphthalocyanine molecules adsorbed on an ultrathin alumina film by a scanning tunneling microscope at low temperature. Distinct spatial distributions are imaged for the different vibronic modes, which are in accordance with spectra recorded over different points of the molecule and its orbital structure. These distinct vibronic images, together with the differential conductance images and calculated molecular orbitals, lead to vibrational excitations that are associated with the doubly degenerate lowest unoccupied molecular orbitals (LUMO) – LUMO-α and LUMO-β. These results reveal the presence of different molecular conformations on the surface and the nature of the electron-vibrational coupling.
Effect of thermal properties on self-propagating fronts in reactive nanolaminates
Authors: Alawieh Leen , Knio Omar M. , Weihs Timothy P.
Published: July 2011

The effects of thermal diffusion on flame front dynamics in a (1:1) Ni/Al multilayered system are computationally investigated. A systematic refinement of the thermal conductivity model is performed, namely by incorporating the effects of concentration, direction, and temperature dependence. The resulting thermal conductivity models are incoporated into the reduced reaction formalism developed by Salloum and Knio [Combust. Flame 157(6),1154 (2010]). Computations using constant and variable conductivity models are contrasted with each other, for axial and normal front propagation. Notable differences between the predictions of the various conductivity models are observed, particularly concerning the thermal and reaction widths. Differences in the average front propagation velocity are, unexpectedly, less pronounced. Brief computational experiments are finally conducted for 3D front propagation using constant and variable thermal conductivity models. The 3D variable-conductivity computations reveal the occurrence of transient, spinlike reactions that appear to be consistent with recent experimental observations, whereas stable front behavior is observed when a constant-conductivity model is used. Thus, the present experiences suggest that thermo-diffusive instabilities are likely to play a role in the onset and manifestation of some of the experimentally-observed transient front propagation regimes.
InxGa1-xSb channel p-metal-oxide-semiconductor field effect transistors: Effect of strain and heterostructure design
Authors: Nainani Aneesh , Yuan Ze , Krishnamohan Tejas , Bennett Brian R. , Boos J. Brad , Reason Matthew , Ancona Mario G. , Nishi Yoshio , Saraswat Krishna C.
Published: July 2011

InxGa1-xSb is an attractive candidate for high performance III-V p-metal-oxide-semiconductor field effect transistors (pMOSFETs) due to its high bulk hole mobility that can be further enhanced with the use of strain. We fabricate and study InxGa1−xSb-channel pMOSFETs with atomic layer deposition Al2O3 dielectric and self-aligned source/drain formed by ion implantation. The effects of strain and heterostructure design for enhancing transistor performance are studied systematically. Different amounts of biaxial compression are introduced during MBE growth, and the effect of uniaxial strain is studied using wafer-bending experiments. Both surface and buried channel MOSFET designs are investigated. Buried (surface) channel InxGa1−xSb pMOSFETs with peak hole mobility of 910 (620) cm2/Vs and subthreshold swing of 120 mV/decade are demonstrated. Pulsed I-V measurements and low-temperature I-V measurements are used to investigate the physics in transistor characteristics.
Sparse one-dimensional discrete Dirac operators II: Spectral properties
Authors: Carvalho S. L. , de Oliveira C. R. , Prado R. A.
Published: July 2011

We study spectral properties of some discrete Dirac operators with nonzero potential only at some sparse and suitably randomly distributed positions. As observed in the corresponding Schrödinger operators, we determine the Hausdorff dimension of its spectral measure and identify a sharp spectral transition from point to singular continuous.
Magnetic field-induced metamagnetic transitions of Pr0.5Ca0.5Mn0.97Ga0.03O3
Authors: Wu Y. Y. , Li H. N. , Xia Z. C. , Huang Y. , Ouyang Z. W. , Li L. , Xiao L. X. , Peng L. P. , Huang J. W. , Zuo H. K.
Published: July 2011

Measurements of isothermal magnetization and electrical transport on Pr0.5Ca0.5Mn0.97Ga0.03O3 have been performed in a magnetic field up to 15 T. Two distinct metamagnetic transitions, which may relate to the collapse of the pseudo-CE-type and CE-type antiferromagnetic phases (CE, a composite antiferromagnetic structure composed of a chequeboard of alternating C and E type), have been observed in the temperature region of 2.5–140 K. Different from the traditional magnetization steps, the two metamagnetic transitions are not dependent on the field sweep rate. These peculiar features are sensitive to the microstructure of the sample. A temperature-field phase diagram has been constructed and found to exhibit a minimum critical field, similar to other phase-separated systems.
Formalism of thermal waves applied to the characterization of materials thermal effusivity
Authors: Chauchois Alexis , Antczak Emmanuel , Defer Didier , Carpentier Olivier
Published: July 2011

Thermal characterization of materials, especially civil engineering materials, in the way of non-destructive methods, are more and more widespread. In this article, we show an original point of view to describe the used method, the thermal waves, to obtain the thermal impedance of the studied system, using a specific sensor – a fluxmeter. The identification technique, based on a frequential approach, is optimized by applying a random input to the system. This kind of random heating is shown to provide a frequency range where the thermal effusivity is able to be identified and not correlated to another parameter. The strength of the method is also the determination of the contact resistance of the system, that allows to validate the identification process. Experimental results obtained from a sample with well-known thermal properties (polyvinyl chloride) are used to validate the proposed method.
Gyrokinetic large eddy simulations
Authors: Morel P. , Navarro A. Bañón , Albrecht-Marc M. , Carati D. , Merz F. , Görler T. , Jenko F.
Published: July 2011

The large eddy simulation approach is adapted to the study of plasma microturbulence in a fully three-dimensional gyrokinetic system. Ion temperature gradient driven turbulence is studied with the GENE code for both a standard resolution and a reduced resolution with a model for the sub-grid scale turbulence. A simple dissipative model for representing the effect of the sub-grid scales on the resolved scales is proposed and tested. Once calibrated, the model appears to be able to reproduce most of the features of the free energy spectra for various values of the ion temperature gradient.
Analysis on wetting and local dynamic properties of single water droplet on a polarized solid surface: A molecular dynamics study
Authors: Surblys D. , Yamaguchi Y. , Kuroda K. , Nakajima T. , Fujimura H.
Published: July 2011

Molecular dynamics simulations of single water droplets on a solid surface were carried out in order to investigate the effects that the Coulomb interaction between liquid and solid molecules has on wetting behavior by appending vertical electric polarization on a solid surface. The water droplet became more wettable both on upward and downward polarized surfaces, although structures of the adsorption layer appearing near the solid surface were clearly different, and the relation between droplet contact angle and surface polarization was also different for upward and downward polarization directions. The probability density distribution of molecular orientation around the adsorption layer indicated that preferable water molecule orientations varied largely by the surface polarization, and the rotational mobility around the preferable orientations was also affected. The dynamic property due to this rotational mobility was clearly captured by means of distribution of rotational diffusion coefficient, which potentially corresponded to local viscosity distribution.
Fluctuation theory of molecular association and conformational equilibria
Authors: Jiao Yuanfang , Smith Paul E.
Published: July 2011

General expressions relating the effects of pressure, temperature, and composition on solute association and conformational equilibria using the fluctuation theory of solutions are provided. The expressions are exact and can be used to interpret experimental or computer simulation data for any multicomponent mixture involving molecules of any size and character at any composition. The relationships involve particle-particle, particle-energy, and energy-energy correlations within local regions in the vicinity of each species involved in the equilibrium. In particular, it is demonstrated that the results can be used to study peptide and protein association or aggregation, protein denaturation, and protein-ligand binding. Exactly how the relevant fluctuating properties may be obtained from experimental or computer simulation data are also outlined. It is shown that the enthalpy, heat capacity, and compressibility differences associated with the equilibrium process can, in principle, be obtained from a single simulation. Fluctuation based expressions for partial molar heat capacities, thermal expansions, and isothermal compressibilities are also provided.
Thermal annealing effect on spin coherence in ZnO single crystals
Authors: Yang Z. , Li Y. , Look D. C. , Zhou H. M. , Chen W. V. , Kawakami R. K. , Yu P. K. L. , Liu J. L.
Published: July 2011

The spin coherence time (T2*) in ZnO single crystals at 8.5 K decreases significantly from ∼11.2 ns to ∼2.3 ns after annealing at 500 °C, as indicated by time-resolved Kerr-rotation pump-probe magneto-optical spectroscopy. The annealing-induced spin coherence degradation in ZnO arises neither from crystallinity degradation during the annealing process, as confirmed by x-ray rocking curves; nor from reflection variations of the probe laser beam induced by surface roughness changes during the annealing process, as confirmed by atomic force microscopy. Temperature-dependent Hall-effect studies indicate that decreased mobility and increased shallow-donor concentration in the annealing-induced surface conducting layer on top of the bulk ZnO are most likely to be the reasons for the spin coherence degradation in ZnO during the annealing process.
The binding energies of NO–Rg (Rg = He, Ne, Ar) determined by velocity map imaging
Authors: Holmes-Ross Heather L. , Lawrance Warren D.
Published: July 2011

We report velocity map imaging measurements of the binding energies, D0, of NO–Rg (Rg = He, Ne, Ar) complexes. The $\tilde X$X̃ state binding energies determined are 3.0 ± 1.8, 28.6 ± 1.7, and 93.5 ± 0.9 cm−1 for NO–He, –Ne, and –Ar, respectively. These values compare reasonably well with ab initio calculations. Because the $\tilde A$Ã–$\tilde X$X̃ transitions were unable to be observed for NO–He and NO–Ne, values for the binding energies in the $\tilde A$Ã state of these complexes have not been determined. Based on our $\tilde X$X̃ state value and the reported $\tilde A$Ã–$\tilde X$X̃ origin band position, the $\tilde A$Ã state binding energy for NO–Ar was determined to be 50.6 ± 0.9 cm−1.
Secondary electron emission in extreme-UV detectors: Application to diamond based devices
Authors: Ciancaglioni I. , Marinelli Marco , Milani E. , Prestopino G. , Verona C. , Verona-Rinati G. , Angelone M. , Pillon M.
Published: July 2011

A study on the effect of secondary electron emission, which strongly affects the detection of extreme-UV radiation, was performed on diamond detectors. Two different structures were compared: interdigitated contacts and a transverse Schottky diode configuration. Both devices were electrically characterized by I-V measurements and their responsivity was measured in the extreme UV spectral region (20–120 nm) by using He-Ne gas discharge radiation sources and a toroidal grating vacuum monochromator. Through an ad-hoc measurement configuration, the contributions of the internal photocurrent and of the photoemission current have been analyzed and separately evaluated. The results showed that secondary electron emission, which clearly depends on the experimental conditions (e.g., external electric field, pressure, etc.), is one of the most relevant processes affecting the spectral responsivity in the extreme UV band. In particular, for interdigitated devices, extreme care must be taken in order to obtain an absolute value of their responsivity, while detectors in the transverse configuration can be shielded in such a way to avoid secondary electron current contribution and therefore provide a more correct and reliable response.
Interaction of He with Cu, V, and Ta in bcc Fe: A first-principles study
Authors: Yan J. X. , Tian Z. X. , Xiao W. , Geng W. T.
Published: July 2011

Precipitates often play key roles in improving the mechanical performance of structural materials. Using first-principles density functional theory method, we have calculated the geometry and energetics of small Xn and XnHe (X = Cu, V, and Ta) clusters in bcc Fe matrix to investigate the effect of He on X precipitation on the initial stage in neutron-irradiated Fe alloys. Both substitutional and interstitial He attract solute atoms. The attraction of a substitutional He and a Cu atom is as strong as 0.30 eV (nearest neighbor) or 0.25 eV (next-nearest neighbor), even stronger than the vacancy-Cu pair. Such an attraction facilitates the clustering of Cu atoms. By comparison, the attraction of He to V (0.02 eV) or Ta (0.22 eV) is weaker than that of a vacancy. We find that one He can bind up to four Ta atoms to form a tetrahedron, despite the fact that in the absence of He, Ta atoms prefer to stay away from each other. The effect of He on the solute-solute and solute-matrix interactions can be understood from the facts that He behaves both as a free-volume filler and as a bonding insulator.
Magnetic quartz crystal microbalance: Magneto-acoustic parameters
Authors: Vavra Kevin C. , Yu George , Josowicz Mira , Janata Jií
Published: July 2011

Magnetic quartz crystal microbalance is a new instrument that allows determination of magneto-acoustic parameters of thin magnetic films. The analysis in this paper is based on simple Butterworth-van-Dyke oscillator model. To demonstrate the use of the new instrument, CuNi magnetic alloy has been electroplated on a gold electrode of a quartz crystal microbalance substrate. The magneto-acoustic admittance and magneto-acoustic capacitance of the alloy film were measured in the static magnetic field between 0 and 10.00 kG, at room temperature.
Effect of aging on the magnetic characteristics of nickel nanowires embedded in polycarbonate
Authors: Maaz K. , Ishrat S. , Karim S. , Kim Gil-Ho
Published: July 2011

Single crystalline Ni nanowires (with a controlled diameter of ∼14 nm) have been fabricated by electrochemical deposition in etched ion-track polycarbonate templates. The exchange bias effect in these nanowires has been studied at 10 K under a cooling field of 10 kOe applied parallel to the wire axis for different time intervals starting from the as-fabricated to ∼2 yr old samples. A continuous drop in the saturation magnetization has been observed with time due the formation of an antiferromagnetic oxide layer at the periphery of nanowires. A model for the drop of magnetization has been used to calculate the thickness of the oxide layer in nickel nanowires. The observed variation in exchange bias and saturation magnetization has been explained by taking into account the exchange interactions at the Ni-NiO interface and the development of antiferromagnetic NiO at the expense of metallic Ni.
Dielectric function and optical properties of quaternary AlInGaN alloys
Authors: Sakalauskas E. , Reuters B. , Khoshroo L. Rahimzadeh , Kalisch H. , Heuken M. , Vescan A. , Röppischer M. , Cobet C. , Gobsch G. , Goldhahn R.
Published: July 2011

The optical properties of quaternary AlxInyGa1-x-yN alloy films with 0.16<x<0.64 and 0.02<y<0.13 are presented. The (0001)-oriented AlInGaN layers were grown by metal-organic vapor phase epitaxy on thick GaN/sapphire templates. High-resolution x-ray diffraction measurements revealed the pseudomorphic growth of the AlInGaN films on the GaN buffer. Rutherford backscattering and wavelength-dispersive x-ray spectroscopy analysis were used in order to determine the composition of the alloys. The ordinary dielectric function (DF) of the AlInGaN samples was determined in the range of 1–10 eV by spectroscopic ellipsometry (SE) at room temperature (synchrotron radiation: BESSY II). The sharp onset of the imaginary part of the DF defines the direct absorption edge of the alloys. At higher photon energies, pronounced peaks are observed in the DF indicating a promising optical quality of the material. These features are correlated to the critical points of the band structure (van Hove singularities). An analytical model, which permits us to accurately describe the dielectric function (or optical constants) in the range of 1–10 eV, is also presented. The band-gap and high-energy interband transition values are obtained by fitting the experimental DF with the analytical model. The strain influence on the bandgap is evaluated by using the k×p formalism. Furthermore, an empirical expression is proposed which allows us to calculate the AlInGaN band-gap and high-energy inter-band transitions in the whole compositional range (x, y). The band-gap values obtained from the empirical expression are in good agreement with both the calculated ab initio and the experimental values determined by SE.
The effect of humidity on nano-scaled domain switching in LiNbO3 single crystal
Authors: Sun X. , Su Y. J. , Gao K. W. , Guo L. Q. , Qiao L. J. , Chu W. Y.
Published: July 2011

This paper deals with the influence of relative humidity on nano-scaled domain switching caused by the electric field of atomic force microscopy (AFM) in a LiNbO3 single crystal. Experimental results show that the switched domain size under AFM tip does not increase monotonously with relative humidity. The domain radius increases slightly in lower relative humidity conditions (< 40%), and decreases dramatically in higher relative humidity conditions (40–99%). The domain is not created under a relative humidity of 99%. Experiments on the AFM force-distance curve prove that there is a water bridge between the tip and the sample surface, whose size increases with the rise of humidity. The influence of water bridges on the effective electric field acting on the domain switching in the sample is discussed.
Ohmic contacts to n-GaAs nanowires
Authors: Gutsche C. , Lysov A. , Regolin I. , Brodt A. , Liborius L. , Frohleiks J. , Prost W. , Tegude F.-J.
Published: July 2011

We report on the technology and the electrical properties of two different contact systems on n-GaAs nanowires. Annealed Ge/Ni/Ge/Au and Pd/Ge/Au multilayer metallization were investigated. Rapid thermal annealing at temperatures common for identical contact systems on n-GaAs layers is found to be crucial due to an enhanced out-diffusion of the Ga component into the Au contact layer. The maximum annealing temperatures ensuring intact nanowires are 320 °C for Ge/Ni/Ge/Au and 280 °C for Pd/Ge/Au. The fabricated Pd/Ge/Au contacts reveal a specific contacts resistance of 2.77 × 10−7 Ωcm2, which is about one order of magnitude lower compared to the values of Ge/Ni/Ge/Au and also lower than Pd/Ge/Au contacts on bulk material (1.2 × 10−6 Ωcm2).
Ultra-low voltage ferroelectric electron emission from lead zirconate titanate thin films with nanostructured top electrodes
Authors: Becherer J. , Mieth O. , Vidyarthi V. S. , Gerlach G. , Eng L. M.
Published: July 2011

Electron emission from thin ferroelectric Pb(Zr0.4Ti0.6)O3 films is demonstrated reaching emission current densities of up to 3×10-8 A cm-2 for pulsed excitation voltages of 60 V. Nevertheless, the emission process sets in at voltages as low as 10 V. Thin lead zirconate titanate (PZT) films were prepared with a structured top electrode, which exhibits nanometer-sized regularly arranged apertures. The emission current was measured under UHV conditions by both a single electron detector for small emission currents and an amperemeter for larger currents. The voltage dependent polarization state within the emission apertures was imaged using piezoresponse force microscopy and revealed that an increased fraction of the free surface area is switched by an increased applied voltage. This shows that the emission process is strongly correlated to the switching of ferroelectric polarization. Moreover, with the help of a metal grid in front of the detector, the maximum kinetic energy of emitted electrons was investigated and found to be limited by the excitation voltage, only.
Silicon doping effect on SF6/O2 plasma chemical texturing
Authors: Dilonardo Elena , Valerio Bianco Giuseppe , Michela Giangregorio Maria , Losurdo Maria , Capezzuto Pio , Bruno Giovanni
Published: July 2011

A SF6/O2 plasma chemical etching is proposed as a process to texture n- and p-doped c-Si (100) by chemical reactivity of active fluorine species, under conditions avoiding ion bombardment and sputtering. Under this chemical etching regime, we found a strong impact of silicon doping on texturing characteristics and effectiveness. Specifically, an anisotropic square-based hillock-like texturing with 6% reflectivity is obtained for n-type Si. Conversely, for p-type Si, H2 plasma pretreatments are necessary to activate the silicon etching and obtain a nanotextured surface with a reflectivity of 16%. Reflectance from textured silicon surfaces is investigated and correlated to the morphology, surface roughness, and dimension of features.
A rheological model of the dynamic behavior of magnetorheological elastomers
Authors: Chen Lin , Jerrams Steve
Published: July 2011

A rheological model is described that was developed to simulate the dynamic behavior of magnetorheological elastomers (MREs). The viscoelasticity of the polymer composite, magnetic field-induced properties and interfacial slippage between the matrix and particles were modeled by analogy with a standard linear solid model, a stiffness variable spring, and a spring-Coulomb friction slider, respectively. The loading history and rate dependent constitutive relationships for MREs were derived from the rheological model. The hysteresis loop from shear strain-shear stress plots, which determines the shear modulus and loss factor, were obtained from substituting cyclic loading into these constitutive relationships. The dynamic behavior of MREs was simulated by changing parameters in the rheological model to influence MREs’ performance. The simulation results verified the effectiveness of the model.
Simple orbital theory for the molecular electrician
Authors: Ernzerhof Matthias
Published: July 2011

Theories of molecular electronic devices (MEDs) are quite involved in general. However, various prominent features of MEDs can be understood drawing only on elementary quantum theory. To support this point of view, we provide a two component orbital theory that enables one to reproduce various important features of MEDs. In this theory, the device orbitals are divided into two components, each of which is obtained from simple rules. To illustrate our two-component model, we apply it to explain, among other things, the conductance suppression in cross-conjugated systems and the dependence of the conductance on the contact position in aromatic systems.
Integrable hierarchies related to the Kuper-CH spectral problem
Authors: Zhang Ling , Zuo Dafeng
Published: July 2011

In this paper, from a given Kuper-CH spectral problem, we propose two kinds of super integrable hierarchies. One is the Kuper-CH hierarchy, the other is the generalized Kuper-Harry-Dym hierarchy. Moreover, we construct their zero curvature representations and super-bi-Hamiltonian structures.
A frequency shifting liquid metal antenna with pressure responsiveness
Authors: Rashed Khan Mohammad , Hayes Gerard J. , So Ju-Hee , Lazzi Gianluca , Dickey Michael D.
Published: July 2011

This letter describes the fabrication and characterization of a shape shifting antenna that changes electrical length and therefore, frequency, in a controlled and rapid response to pressure. The antenna is composed of a liquid metal alloy (eutectic gallium indium) injected into microfluidic channels that feature rows of posts that separate adjacent segments of the metal. The initial shape of the antenna is stabilized mechanically by a thin oxide skin that forms on the liquid metal. Rupturing the skin merges distinct segments of the metal, which rapidly changes the length, and therefore frequency, of the antenna. A high speed camera elucidates the mechanism of merging and simulations model accurately the spectral properties of the antennas.
Investigation of multiple roots of the resistive wall mode dispersion relation, including kinetic effects
Authors: Berkery J. W. , Betti R. , Sabbagh S. A.
Published: July 2011

The resistive wall mode instability in tokamak plasmas has a complex frequency which can be determined by a dispersion relation that is cubic, in general, leading to three distinct roots. A simplified model of the dispersion relation, including kinetic effects, is presented and used to explore the behavior of these roots. By changing the plasma rotation frequency, it is shown that one root has a slow mode rotation frequency (less than the inverse wall time) while the other two rotate more quickly, one leading and one lagging the plasma rotation frequency. When realistic experimental parameters from the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40, 557 (2000)] are used, however, only one slow rotating, near-marginal stability root is found, consistent with present experiments and more detailed calculations with the MISK code [B. Hu et al., Phys. Plasmas 12, 057301 (2005)]. Electron collisionality acts to stabilize one of the rotating roots, while ion collisionality can stabilize the other. In devices with low rotation and low collisionality, these two rotating roots may manifest themselves, but they are likely to remain stable.
Condensed phase molecular dynamics using interpolated potential energy surfaces with application to the resolvation process of coumarin 153
Authors: Park Jae Woo , Kim Hyun Woo , Song Chang-ik , Rhee Young Min
Published: July 2011

Interpolated potential energy surfaces (PESs) have been used for performing reliable molecular dynamics (MD) simulations of small molecular reactions. In this article, we extend this method to MD simulations in condensed phase and show that the same scheme can also be feasibly used when it is supplemented with additional terms for describing intermolecular interactions. We then apply the approach for studying the resolvation process of coumarin 153 in a number of polar solvents. We find that the interpolated surface actually reproduces experimentally found features much better than the conventional force field based potential especially in terms of both dynamics Stokes shift in the short time limit and solute vibrational decoherence. This shows that the solute vibrational effect is important to some degree along the resolvation and should be modeled properly for accurate description of the related dynamics. The stability issue of trajectories on the interpolated PESs is also discussed, in regard to the goal of reliably performing long time simulations. Operational limitations of the present scheme are also discussed.
An enhanced splined saddle method
Authors: Ghasemi S. Alireza , Goedecker Stefan
Published: July 2011

We present modifications for the method recently developed by Granot and Baer [J. Chem. Phys. 128, 184111 (2008)]10.1063/1.2916716. These modifications significantly enhance the efficiency and reliability of the method. In addition, we discuss some specific features of this method. These features provide important flexibilities which are crucial for a double-ended saddle point search method in order to be applicable to complex reaction mechanisms. Furthermore, it is discussed under what circumstances this methods might fail to find the transition state and remedies to avoid such situations are provided. We demonstrate the performance of the enhanced splined saddle method on several examples with increasing complexity, isomerization of ammonia, ethane and cyclopropane molecules, tautomerization of cytosine, the ring opening of cyclobutene, the Stone-Wales transformation of the C60 fullerene, and finally rolling a small NaCl cube on NaCl(001) surface. All of these calculations are based on density functional theory. The efficiency of the method is remarkable in regard to the reduction of the total computational time.
The perpendicular anisotropy of Co40Fe40B20 sandwiched between Ta and MgO layers and its application in CoFeB/MgO/CoFeB tunnel junction
Authors: Wang W. X. , Yang Y. , Naganuma H. , Ando Y. , Yu R. C. , Han X. F.
Published: July 2011

Magnetic anisotropy of Co40Fe40B20 thin films sandwiched between Ta and MgO layers was investigated. Magnetic properties of CoFeB layers deposited on top and bottom of MgO layer are different. The thickness of the CoFeB layer and annealing temperature are the critical parameters to achieve and keep the perpendicular magnetic anisotropy. The phase diagram of perpendicular anisotropic strength of CoFeB layers on annealing temperatures and thicknesses of CoFeB layers is observed. According to phase diagrams, perpendicular CoFeB/MgO/CoFeB tunnel junctions were fabricated, and tunneling magnetoresistance (TMR) ratio was higher than 30% at low temperatures.
Self-navigation of a scanning tunneling microscope tip toward a micron-sized graphene sample
Authors: Li Guohong , Luican Adina , Andrei Eva Y.
Published: July 2011

We demonstrate a simple capacitance-based method to quickly and efficiently locate micron-sized conductive samples, such as graphene flakes, on insulating substrates in a scanning tunneling microscope (STM). By using edge recognition, the method is designed to locate and to identify small features when the STM tip is far above the surface, allowing for crash-free search and navigation. The method can be implemented in any STM environment, even at low temperatures and in strong magnetic field, with minimal or no hardware modifications.
Dynamics of collapsed polymers under the simultaneous influence of elongational and shear flows
Authors: Sing Charles E. , Alexander-Katz Alfredo
Published: July 2011

Collapsed polymers in solution represent an oft-overlooked area of polymer physics, however recent studies of biopolymers in the bloodstream have suggested that the physics of polymer globules are not only relevant but could potentially lead to powerful new ways to manipulate single molecules using fluid flows. In the present article, we investigate the behavior of a collapsed polymer globule under the influence of linear combinations of shear and elongational flows. We generalize the theory of globule-stretch transitions that has been developed for the specific case of simple shear and elongational flows to account for behavior in arbitrary flow fields. In particular, we find that the behavior of a globule in flow is well represented by a two-state model wherein the critical parameters are the transition probabilities to go from a collapsed to a stretched state Pg − s and vice versa Ps − g. The collapsed globule to stretch transition is described using a nucleation protrusion mechanism, and the reverse transition is described using either a tumbling or a relaxation mechanism. The magnitudes of Pg − s and Ps − g govern the state in which the polymer resides; for Pg − s ≈ 0 and Ps − g ≈ 1 the polymer is always collapsed, for Pg − s ≈ 0 and Ps − g ≈ 0 the polymer is stuck in either the collapsed or stretched state, for Pg − s ≈ 1 and Ps − g ≈ 0 the polymer is always stretched, and for Pg − s ≈ 1 and Ps − g ≈ 1 the polymer undergoes tumbling behavior. These transition probabilities are functions of the flow geometry, and we demonstrate that our theory quantitatively predicts globular polymer conformation in the case of mixed two-dimensional flows, regardless of orientation and representation, by comparing theoretical results to Brownian dynamics simulations. Generalization of the theory to arbitrary three-dimensional flows is discussed as is the incorporation of this theory into rheological equations.
Self-assembly behavior of ABA coil-rod-coil triblock copolymers: A Brownian dynamics simulation approach
Authors: Li Yongliang , Lin Shaoliang , He Xiaohua , Lin Jiaping , Jiang Tao
Published: July 2011

The self-assembly behavior of ABA coil-rod-coil triblock copolymers in a selective solvent was studied by a Brownian molecular dynamics simulation method. It was found that the rod midblock plays an important role in the self-assembly of the copolymers. With a decrease in the segregation strength, ɛRR, of rod pairs, the aggregate structure first varies from a smecticlike disk shape to a long twisted string micelle and then to small aggregates. The influence of the block length and the asymmetry of the triblock copolymer on the phase behavior were studied and the corresponding phase diagrams were mapped. It was revealed that the variation of these parameters has a profound effect on microstructure. The simulation results are consistent with experimental results. Compared to rod-coil diblock copolymers, the coil-rod-coil triblock copolymers has a larger entropy penalty associated with the interfacial grafting density of the aggregate, leading to a higher ɛRR value for structural transitions.
Electronic properties of twisted armchair graphene nanoribbons
Authors: Sadrzadeh Arta , Hua Ming , Yakobson Boris I.
Published: July 2011

We study the effect of twist on the electronic structure of H-terminated armchair graphene nanoribbons, for both relaxed and unrelaxed unit cell size. We investigate the band gap change as a function of the twist angle for different ribbon widths. In the case of unrelaxed unit cell size, the band gap closes for smaller twist angles as opposed to relaxed unit cell size. We calculate strain energy as a function of twist angle and show its direct correlation with the reduction of the band gap. Furthermore, the conductance is calculated at arbitrary degree of torsion.
Damping phenomena in Co90Fe10/Ni multilayers and alloys
Authors: Shaw Justin M. , Nembach Hans T. , Silva T. J.
Published: July 2011

We used perpendicular ferromagnetic resonance to measure the damping parameter in Co90Fe10/Ni multilayers over a wide range of layer thicknesses. The magnetic anisotropy within this range varied from in-plane to out-of-plane. We measured (Co90Fe10)xNi1−x alloys of identical thicknesses over the same compositional range of Co90Fe10 and Ni in order to isolate the influence of the multilayer structure. The damping parameter varied from 0.004 to 0.030 and depended only on the relative amounts of Co90Fe10 and Ni and was independent of the magnetic anisotropy and layer structure.