bluuebunny/crossref_metadata_2025 huggingface dataset:
Endocytosis of the Viral Chemokine Receptor US28 Does Not Require Beta‐Arrestins But Is Dependent on the Clathrin‐Mediated Pathway
Authors: Fraile‐Ramos Alberto , Kohout Trudy A. , Waldhoer Maria , Marsh Mark
Published: August 2009

Arrestins bind phosphorylated G‐protein coupled‐receptors (GPCR) and inhibit agonist‐induced signal transduction by uncoupling the receptors from their cognate G‐proteins. β‐arrestins also act as adaptors that target GPCR to endocytic clathrin‐coated vesicles. Unlike cellular GPCRs, the human cytomegalovirus GPCRs and chemokine receptor, US28, shows constitutive signal transduction activity and undergoes constitutive endocytosis. To determine the role of β‐arrestins in US28 trafficking, we used embryonic fibroblasts derived from β‐arrestin knockout mice. In these cells, the internalization of transfected β2‐adrenergic receptor and of the cellular chemokine receptor CCR5 was impaired. By contrast, US28 distribution was unaffected, and US28‐mediated RANTES internalization was similar in normal and knockout cell lines. To investigate whether a clathrin‐mediated pathway is involved in US28 endocytosis, we developed small interfering RNA against the μ2‐adaptin subunit of the AP‐2 adaptor complex. In cells transfected with μ2 small interfering RNA transferrin endocytosis was severely inhibited. Antibody‐feeding experiments and biochemical analysis showed that US28 internalization was also inhibited. Together, these data indicate that US28 endocytosis occurs via a clathrin‐mediated mechanism but is independent of β‐arrestins.
Differential Distribution of Low‐Density Lipoprotein‐Receptor‐Related Protein (LRP) and Megalin in Polarized Epithelial Cells is Determined by Their Cytoplasmic Domains
Authors: Marzolo María‐Paz , Yuseff María Isabel , Retamal Claudio , Donoso Maribel , Ezquer Fernando , Farfán Pamela , Li Yonghe , Bu Guojun
Published: August 2009

Megalin and the low‐density lipoprotein (LDL) receptor‐related protein (LRP) are two large members of the LDL receptor family that bind and endocytose multiple ligands. The molecular and cellular determinants that dictate the sorting behavior of these receptors in polarized epithelial cells are largely unknown. Megalin is found apically distributed, whereas the limited information on LRP indicates its polarity. We show here that in Madin‐Darby canine kidney cells, both endogenous LRP and a minireceptor containing the fourth ligand‐binding, transmembrane and LRP cytosolic domains were basolaterally sorted. In contrast, minireceptors that either lacked the cytoplasmic domain or had the tyrosine in the NPTY motif mutated to alanine showed a preferential apical distribution. In LLC‐PK1 cells, endogenous megalin was found exclusively in the apical membrane. Studies were also done using chimeric proteins harboring the cytosolic tail of megalin, one with the fourth ligand‐binding domain of LRP and the other two containing the green fluorescent protein as the ectodomain and transmembrane domains of either megalin or LRP. Findings from these experiments showed that the cytosolic domain of megalin is sufficient for apical sorting, and that the megalin transmembrane domain promotes association with lipid rafts. In conclusion, we show that LRP and megalin both contain sorting information in their cytosolic domains that directs opposite polarity, basolateral for LRP and apical for megalin. Additionally, we show that the NPTY motif in LRP is important for basolateral sorting and the megalin transmembrane domain directs association with lipid rafts.
Phosphoinositide Recognition Domains
Authors: Lemmon Mark A.
Published: August 2009

Domains or modules known to bind phosphoinositides have increased dramatically in number over the past few years, and are found in proteins involved in intracellular trafficking, cellular signaling, and cytoskeletal remodeling. Analysis of lipid binding by these domains and its structural basis has provided significant insight into the mechanism of membrane recruitment by the different cellular phosphoinositides. Domains that target only the rare (3‐phosphorylated) phosphoinositides must bind with very high affinity, and with exquisite specificity. This is achieved solely by headgroup interactions in the case of certain pleckstrin homology (PH) domains [which bind PtdIns(3,4,5)P3 and/or PtdIns(3,4)P2], but requires an additional membrane‐insertion and/or oligomerization component in the case of the PtdIns(3)P‐targeting phox homology (PX) and FYVE domains. Domains that target PtdIns(4,5)P2, which is more abundant by some 25‐fold, do not require the same stringent affinity and specificity characteristics, and tend to be more diverse in structure. The mode of phosphoinositide binding by different domains also appears to reflect their distinct functions. For example, pleckstrin homology domains that serve as simple targeting domains recognize only phosphoinositide headgroups. By contrast, certain other domains, notably the epsin ENTH domain, appear to promote bilayer curvature by inserting into the membrane upon binding.
Modeling cardiac rhythm and heart rate using BFO and DOLCE
Authors: Temal Lynda , Rosier Arnaud , Dameron Olivier , Burgun Anita
Published: August 2009

This paper presents an application ontology for modeling cardiac rhythm and its anomalies such as tachycardia and bradycardia. We use BFO and DOLCE as ontological reference framework in order to compare their impact on ontology design.
Intensification of Turbulence by Chemical Heat Release
Authors: Eschenroeder Alan Q.
Published: August 2009

Volumetric chemical energy release is studied as a mechanism for enhancing the isotropic turbulent motion of a compressible fluid medium. Both the vortical and dilatational components are examined to determine the influence of irreversible heat addition from exothermic reactions. To a first-order approximation, the density fluctuations caused by eddy production and destruction are shown to be insensitive to the behavior of internal degrees of freedom in the gas (including chemistry). Based on this finding, the pressure fluctuations are determined from a linearized analysis of the combined chemical and gasdynamic response to density fluctuations. The results for amplitudes and phase relationship between pressure and density fluctuations are used to obtain an estimate of the power delivered. The leading contribution to the work integral is of second order in fluctuation amplitudes. A generalized rate model for a highly dissociated gas relaxing toward equilibrium is retained through-out the analysis. Limiting cases are examined by the use of the resulting general expression. The power delivered is proportional (in all cases) to the product of the mean reaction rate and the fourth power of turbulence Mach number (fluctuation velocity divided by local frozen acoustic velocity). For eddy lifetimes shorter than chemical relaxation times, it is shown that the power delivered is essentially independent of frequency.
Variable Viscosity Effects on the Flow and Stability of Flow in Channels and Pipes
Authors: Joseph Daniel D.
Published: August 2009

Variable viscosity and frictionally heated channel and pipe flows are investigated. The solutions are bounded and improved estimates of the critical stress (beyond which there are no steady solutions) developed. The stress first increases, then decreases, with increasing maximum temperature. At this stress maximum there is a neutral solution and neighboring unstable solutions to an associated stability problem. Points of inflection in the velocity profile can develop in Poiseuille flows and must develop in Couette flows. The Poiseuille profiles which develop are inviscidly unstable in channels but stable in pipes.
Distribution of Density in an Ion-Exosphere of a Nonrotating Planet
Authors: Eviatar Aharon , Lenchek Allen M. , Singer S. Fred
Published: August 2009

A model of an ion-exosphere is set up and an expression is derived for the variation of density with altitude. The ions are considered to be under the control of superimposed gravitational and static, centered-dipole magnetic fields and to have mirror points in the barosphere. Collisions are ignored and the particles are assumed to be trapped in the dipole field.

By use of the first adiabatic invariant and Liouville's theorem, the density is found to fall off faster with height in the exomagnetosphere than in either a neutral exosphere or an ionized barosphere.
Model Fokker-Planck Equation for a Plasma and Its Solution
Authors: Dougherty J. P.
Published: August 2009

A model Fokker-Planck equation for a single species of particles in a plasma is discussed. This equation has several properties in common with the real equation, and ascribes an approximately correct behavior to most of the particles, though incorrect for the high-energy tail in the thermal distribution. It is shown that the equation can be solved completely, for the small perturbations of a uniform plasma by electric fields harmonic in space and time, in an external magnetic field. Applications to ionospheric radar scattering are briefly discussed; it is shown that in certain circumstances, ion-ion collisions can have a profound effect on the scattering even though the collision frequency is much smaller than the ion gyrofrequency, and this appears to agree with observation.
Resonant Wave—Wave Scattering of Plasma Oscillations
Authors: Aamodt R. E. , Drummond W. E.
Published: August 2009

The effect of resonant wave—wave scattering of plasma oscillations on the energy spectrum in a turbulent plasma is derived. The problem of a small bump instability in an infinite external magnetic field is discussed as an example.
Density Fluctuations in the Etude Stellarator
Authors: Bol K.
Published: August 2009

Density fluctuations of the Ohmically heated plasma of the Étude stellarator can be resolved into azimuthally propagating waves by means of narrow-band correlation measurements. At frequencies below roughly 100 kHz, propagation velocities are comparable to macroscopic plasma velocities, but increase with frequency and azimuthal mode number. Kink or field degeneracy modes, such as those found on B-1, dominate the spectrum of azimuthal modes at appropriate plasma currents. At frequencies above 100 kHz, the wave propagation velocity tends to become constant at a value nearly an order of magnitude larger than either the ion diamagnetic drift or the mean column rotation velocity, but remains in the same direction.
Excellent low field magnetoresistance properties of the La0.7Sr0.3Mn1+dO3-manganese oxide composites
Authors: Kang Young-Min , Kim Hyo-Jin , Yoo Sang-Im
Published: August 2009

Excellent low field magnetoresistance (LFMR) properties could be achieved from the La0.7Sr0.3Mn1+dO3 (LSMO)-manganese oxide polycrystalline composites. While the improvement of LFMR properties in the perovskite maganite-oxide composites is commonly accompanied with a significant increase in their electrical resistivities, optimally processed LSMO-manganese composite in this study exhibits greatly enhanced LFMR of 1.7% at 0.5 kOe and unprecedentedly high maximum dMR/dH value of 28.3% kOe−1 at 300 K without an appreciable increase in its resistivity, which is attributable to the formation of sharp grain boundaries between neighboring LSMO ferromagnetic grains, acting as very effective spin-dependent scattering center.
Microsolvation of methyl hydrogen peroxide: Ab initio quantum chemical approach
Authors: Kulkarni Anant D. , Rai Dhurba , Bartolotti Libero J. , Pathak Rajeev K.
Published: August 2009

Methyl hydrogen peroxide (MHP), one of the simplest organic hydroperoxides, is a strong oxidant, with enhanced activity in aqueous ambience. The present study investigates, at the molecular level, the role of hydrogen bonding that is conducive to cluster formation of MHP with water molecules from its peroxide end, with the methyl group remaining hydrophobic for up to five water molecules. Ab initio quantum chemical computations on MHP⋯(H2O)n, [n=1–5] are performed at second order Møller–Plesset (MP2) perturbation theory employing the basis sets 6-31G(d,p) and 6-311++G(2d,2p) to study the cluster formation of MHP with water molecules from its peroxide end and hydrophobic hydration due to the methyl group. Successive addition of water molecules alters the hydrogen bonding pattern, which leads to changes in overall cluster geometry and in turn to IR vibrational frequency shifts. Molecular co-operativity in these clusters is gauged directly through a detailed many-body interaction energy analysis. Molecular electrostatic potential maps are shown to have a bearing on predicting further growth of these clusters, which is duly corroborated through sample calculations for MHP⋯(H2O)8. Further, a continuum solvation model calculation for energetically stable clusters suggests that this study should serve as a precursor for pathways to aqueous solvation of MHP.
Dynamics of microbubble generation and trapping by self-focused femtosecond laser pulses
Authors: Yang Kun , Zhou Yun , Ren Qiushi , Ye Jing Yong , Deng Cheri X.
Published: August 2009

Different from conventional optical tweezers used for trapping high refractive index micron-sized particles, bubble generation and trapping by femtosecond laser offer a unique strategy to manipulate microbubbles. Using high frequency ultrasound imaging and fast-frame optical video microscopy, we obtained results revealing the spatiotemporal characteristics of bubble generation and trapping by self-focused femtosecond laser pulses at multiple locations along the laser beam. We detected distinct acoustic signals associated with the laser focus and measured the trapping force by using acoustic radiation force to detrap the bubble from the laser beam.
Desorption of hydroxyl radicals in the vacuum ultraviolet photolysis of amorphous solid water at 90 K
Authors: Hama Tetsuya , Yabushita Akihiro , Yokoyama Masaaki , Kawasaki Masahiro , Andersson Stefan
Published: August 2009

We have studied the desorption dynamics of OH radicals from the 157 nm photodissociation of amorphous solid water (ASW) as well as H2O2 deposited on an ASW surface at 90 K. The translational and internal energy distributions of OH were measured using resonance-enhanced multiphoton ionization methods. These distributions are compared to reported molecular dynamics calculations for the condensed phase photodissociation of water ice and also reported results for the gas phase photodissociation of H2O at 157 nm. We have confirmed that OH radicals are produced from two different mechanisms: one from primary photolysis of surface H2O of ASW, and the other being secondary photolysis of H2O2 photoproducts on the ASW surface after prolonged irradiation at 157 nm.
Fast degenerate correlation-corrected vibrational self-consistent field calculations of the vibrational spectrum of 4-mercaptopyridine
Authors: Respondek Inga , Benoit David M.
Published: August 2009

We introduce a fast degeneracy-corrected vibrational second-order Møller–Plesset (fast-DCVMP2) method to compute anharmonic vibrational spectra of large molecules where the computational cost of the full potential energy surface is high. We examine the suitability of the non-self-consistent Harris functional as a robust prescreening technique to replace the semiempirical PM3 model used in our previous studies. We analyze the mode-mode coupling strength statistically and present a scheme that provides a more flexible determination of the threshold used to identify strong couplings. Our methodology is validated on the methanol molecule and applied to mercaptomethane and pyridine, where we compare our results with experimental frequencies. We show that a standard perturbative correction of the vibrational self-consistent field energy can lead to unreliable results even for systems where degeneracies are not expected to play an important role. Our fast technique leads to results close to those obtained with standard DCVMP2 calculations, but with substantial time savings. Using this new technique, we compute the vibrational frequencies of 4-mercaptopyridine, an interesting compound for molecular-electronic applications, and compare our results with experimental values.
Random copolymer adsorption: Morita approximation compared to exact numerical simulations
Authors: Polotsky Alexey , Degenhard Andreas , Schmid Friederike
Published: August 2009

We study the adsorption of ideal random lattice copolymers with correlations in the sequences on homogeneous substrates with two different methods: An analytical solution of the problem based on the constrained annealed approximation introduced by Morita in 1964 and the generating function technique, and direct numerical simulations of lattice chains averaged over many realizations of random sequences. Both methods allow to calculate the free energy and different conformational characteristics of the adsorbed chain. The comparison of the results for random copolymers with different degree of correlations and different types of nonadsorbing monomers (neutral or repelling from the surface) shows not only qualitative but a very good quantitative agreement, especially in the cases of Bernoullian and quasialternating random sequences.
Nonadiabatic reactive scattering in atom+triatom systems: Nascent rovibronic distributions in F+H2O→HF+OH
Authors: Ziemkiewicz Michael , Nesbitt David J.
Published: August 2009

Crossed supersonic jet studies of F+H2O→HF+OH(Π23/2,Π21/2) have been performed under low density, single collision conditions at Ecom=6(2) kcal/mol, yielding rotational, vibrational, and spin-orbit state distributions in the nascent OH product by laser induced fluorescence methods. The lowest reaction barriers on the ground and first excited electronic surfaces are ΔE≈4 kcal/mol and ΔE≈25 kcal/mol, correlating with OH(Π23/2) and OH(Π21/2), respectively. Although only reactions on the ground state potential are Born–Oppenheimer allowed at the experimental collision energies, both ground and excited spin-orbit OH products are observed in a Π23/2:Π21/2=69(1)%:31(1)% branching ratio. This indicates the presence of strong nonadiabatic surface hopping interactions, in agreement with previous results for the F+D2O→DF+OD reaction. Despite clear differences in the rotational distributions between F+H2O and F+D2O isotopic reactions, the overall electronic branching into spin-orbit manifolds is nearly identical for both OH and OD products. Furthermore, when plotted versus total electronic+rotational energy, the nascent OH and OD populations each lie on single curves, with pronounced kinks in the Boltzmann plots suggestive of microscopic branching in the reaction dynamics. Such an equivalence of electronic and rotational energy release in the OH/OD products is consistent with predominantly nonadiabatic processes taking place in the immediate post-transition state region rather than asymptotically in the exit channel.
Ferromagnetic shape memory alloys for positioning with nanometric resolution
Authors: Feuchtwanger Jorge , Asua Estibalitz , García-Arribas Alfredo , Etxebarria Victor , Barandiaran Jose M.
Published: August 2009

Ferromagnetic shape memory alloys are promising active elements for actuators. Our work centered on achieving and maintaining an intermediate fixed deformation so that they can be used as precision positioning actuators. For this purpose, a custom actuator was built using a single crystal of NiMnGa. The results show that these alloys can be controlled within less than 5 nm for both precision and accuracy, a result comparable to piezoelectric ceramics. Interestingly, the defect structure plays a fundamental role in achieving such performance. The stochastically distributed defects determine a progressive diminution of the magnetic field strength required to achieve the control.
Energetics and diffusion of intrinsic surface and subsurface defects on anatase TiO2(101)
Authors: Cheng Hongzhi , Selloni Annabella
Published: August 2009

We report on density functional theory (DFT) calculations of the formation energies and diffusion pathways of oxygen vacancies and Ti interstitials at and near the (101) surface and in the bulk of the anatase polymorph of TiO2. At the generalized gradient approximation level, both defects are found to be energetically more stable by ∼0.5 eV or more at bulk and subsurface sites than on the surface. Moreover, the energy barriers to diffuse from the surface to the bulk are rather low, while the opposite is true for the barriers to diffuse from the bulk to the surface. This indicates that similar to Ti interstitials, also oxygen vacancies should preferentially occur at subsurface rather than at surface sites. To substantiate these findings, additional DFT+U calculations have been performed using different values of U in the range 2.5≤U≤4.5 eV. These show small differences in the relative stabilities of surface and subsurface oxygen vacancies with subsurface vacancies being more stable at low U values and a crossover in stability taking place around U∼3 eV. Analogous calculations for the TiO2(110) surface of rutile show that surface bridging oxygen vacancies are largely favored with respect to subsurface vacancies for all values of U. Altogether, our results provide evidence of important differences between reduced anatase and rutile surfaces in agreement with recent experimental observations.
Study of absorption spectra and (hyper)polarizabilities of SiCn and SinC (n=2–6) clusters using density functional response approach
Authors: Lan You-Zhao , Feng Yun-Long
Published: August 2009

We theoretically investigate the absorption spectra, dipole polarizabilities, and first-order hyperpolarizabilities of SiCn and SinC (n=2–6) clusters using the density functional response approach. Similar to other semiconductor clusters such as Si and gallium arsenide (GaAs) clusters, the absorption spectra of the SiCn and SinC clusters show long absorption tails in the low-transition-energy region and strong absorption peaks in the high-transition-energy region (>4.0 eV). For the same n, the absorption spectrum of the SinC cluster is blueshifted with respect to that of the SiCn cluster, which may be related to the larger highest occupied molecular orbital-lowest unoccupied molecular orbital gap in the former. The isotropic (⟨α⟩) dipole polarizabilities of the SiCn and SinC clusters are larger than the bulk polarizability of 3C-SiC and lie between the dipole polarizabilities of Si and C. The SiCn clusters have lower dipole polarizabilities and larger first-order hyperpolarizabilities than the SinC clusters. The size dependence of the first-order hyperpolarizabilities of the SiCn clusters, which have approximate Si-terminated linear chain geometry, is similar to that observed in π-conjugated organic molecules.
Enhancement in interface robustness regarding thermal oxidation in nanostructured Al2O3 deposited on 4H-SiC
Authors: Corrêa S. A. , Marmitt G. G. , Bom N. M. , da Rosa A. T. , Stedile F. C. , Radtke C. , Soares G. V. , Baumvol I. J. R. , Krug C. , Gobbi A. L.
Published: August 2009

Experimental evidences of enhanced stability of Al2O3/SiC structures following thermal annealing are presented. 5- and 40-nm-thick Al2O3 films evaporated on the Si- and C-terminated faces of 4H-SiC were annealed up to 1000 °C in different atmospheres, leading to crystallization and densification of Al2O3, with an increase in the band gap. Exposure to O2 at high temperatures produced SiO2 and AlSixOy at the Al2O3/SiC interface, with less silicate on the Si-terminated face. Annealing in N2 before exposure to O2 hindered oxygen diffusion and exchange, leading to more stable thin film structures from the point of view of atomic transport.
Full-dimensional, ab initio potential energy and dipole moment surfaces for water
Authors: Wang Yimin , Shepler Benjamin C. , Braams Bastiaan J. , Bowman Joel M.
Published: August 2009

We report full-dimensional, ab initio potential energy (PES) and dipole moment surfaces (DMS) for water. The PES is a sum of one-, two- and three-body terms. The three-body potential is a fit, reported here, to roughly 30,000 intrinsic three-body energies obtained with second-order Møller–Plesset perturbation theory (MP2) and using the aug-cc-pVTZ basis set (avtz). The one- and two-body potentials are from an ab initio water dimer potential [Shank et al., J. Chem. Phys. 130, 144314 (2009)]. The predictive accuracy of the PES is demonstrated for the water trimer, tetramer, and hexamer by comparing the energies and harmonic frequencies obtained from the PES and new high level ab initio calculations at the respective global minima. The DMS is constructed from one- and two-body dipole moments, based on fits to MP2/avtz dipole moments. It is shown to be very accurate for the hexamer by comparison with direct calculations of the hexamer dipole. To illustrate the anharmonic character of the PES one-mode calculations of the 18 monomer fundamentals of the hexamer are reported in normal coordinates.
Excited state intramolecular charge transfer reaction in nonaqueous electrolyte solutions: Temperature dependence
Authors: Pradhan Tuhin , Gazi Harun Al Rasid , Biswas Ranjit
Published: August 2009

Temperature dependence of the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in ethyl acetate (EA), acetonitrile (ACN), and ethanol at several concentrations of lithium perchlorate (LiClO4) has been investigated by using the steady state and time resolved fluorescence spectroscopic techniques. The temperature range considered is 267–343 K. The temperature dependent spectral peak shifts and reaction driving force (−ΔGr) in electrolyte solutions of these solvents can be explained qualitatively in terms of interaction between the reactant molecule and ion-atmosphere. Time resolved studies indicate that the decay kinetics of P4C is biexponential, regardless of solvents, LiClO4 concentrations, and temperatures considered. Except at higher electrolyte concentrations in EA, reaction rates in solutions follow the Arrhenius-type temperature dependence where the estimated activation energy exhibits substantial electrolyte concentration dependence. The average of the experimentally measured activation energies in these three neat solvents is found to be in very good agreement with the predicted value based on data in room temperature solvents. While the rate constant in EA shows a electrolyte concentration induced parabolic dependence on reaction driving force (−ΔGr), the former in ethanol and ACN increases only linearly with the increase in driving force (−ΔGr). The data presented here also indicate that the step-wise increase in solvent reorganization energy via sequential addition of electrolyte induces the ICT reaction in weakly polar solvents to crossover from the Marcus inverted region to the normal region.
Multiscaled density-functional theory for helical polymers
Authors: Xu Xiaofei , Cao Dapeng
Published: August 2009

We propose a density-functional theory (DFT) for helical polymers by introducing the orientational potential of a molecule. A multiscaled finite element approach is incorporated to reduce the time consumption of the computation efficiently. The multiscaled finite element approach proposed here can be easily applied to the calculations of different versions of DFTs. The agreements of the calculated results and Monte Carlo data in studying flexible and rodlike polymers confirm that our approach does lead to correct predictions. By using the proposed theory, we explore the self-assembly of helical polymers on a hydrophobic surface. The dependences of density profiles and orientational distributions on the helical conformation and the attractive strength of the surface are also investigated. It is found that a homeotropic monolayer would be formed on the surface directly as the ratio between helical radii (R) and height (H) is less than 0.5. At the range of 0.5≤R/H<1, a planar homogeneous monolayer would be first formed at low attractive strength and then transmitted to a homeotropic monolayer at high attractive strength. For the case of R/H≥1, the helical polymers only assemble into the planar homogeneous monolayer with no transition to the homeotropic monolayer. Finally, we studied the effect of the helical conformation on the self-assembly by changing the helix angle from 75° to 0°. It is found that the helical conformation makes the polymers more difficult for the self-assembly compared to the noncoiled structures.
Solid-liquid interface free energy in binary systems: Theory and atomistic calculations for the (110) Cu–Ag interface
Authors: Frolov T. , Mishin Y.
Published: August 2009

We analyze thermodynamics of solid-liquid interfaces in binary systems when the solid is in a nonhydrostatic state of stress. The difficulty lies in the fact that chemical potential of at least one of the chemical components in a nonhydrostatic solid is an undefined quantity. We show, nevertheless, that the interface free energy γ can be defined as excess of an appropriate thermodynamic potential that depends on the chemical potentials in the liquid phase. We derive different forms of the adsorption equation for solid-liquid interfaces, with differential coefficients representing excesses of extensive properties. This leads, in particular, to the formulation of interface stress τij as an appropriate excess over nonhydrostatic bulk stresses. The interface stress is not unique unless the solid is in a hydrostatic state of stress. We also derive Gibbs–Helmholtz type equations that can be applied for thermodynamic integration of γ. All thermodynamic relations derived here are presented in forms suitable for atomistic simulations. In particular, the excess quantities can be computed without constructing interface profiles. As an application, we perform semigrand canonical Monte Carlo simulations of the (110) solid-liquid interface in the Cu–Ag system. We show that γ computed by thermodynamic integration along a coexistence path decreases with increasing composition difference between the phases. At the same time, τij remains negative (i.e., the interface is in a state of compression), drastically increases in magnitude, and becomes highly anisotropic. Some of the interface excess properties are computed by different methods and demonstrate accurate agreement with each other, confirming the correctness of our analysis.
Conduction band intersubband transitions in Ge/SiGe quantum wells
Authors: De Seta M. , Capellini G. , Busby Y. , Evangelisti F. , Ortolani M. , Virgilio M. , Grosso G. , Pizzi G. , Nucara A. , Lupi S.
Published: August 2009

In this letter we present the experimental evidence of intersubband absorption in the conduction band of compressively strained germanium quantum wells bounded by Ge-rich SiGe barriers. The measured absorption energies are in the terahertz range and are interpreted by means of tight binding calculations which include self-consistent band-bending and depolarization effects. From the comparison of experimental and numerical results a conduction band offset along the L line of about 120 meV has been estimated for the studied heterostructures.
Femtosecond stimulated Raman scattering for polyatomics with harmonic potentials: Application to rhodamine 6G
Authors: Niu Kai , Cong Shulin , Lee Soo-Y.
Published: August 2009

The perturbation theory of stimulated Raman scattering (SRS), with Raman pump on minus pump off and heterodyne detection along the probe direction, is reviewed. It has four third-order polarization terms, labeled as SRS or inverse Raman scattering (IRS): SRS(I), SRS(II), IRS(I), and IRS(II). These four polarizations have a wave packet interpretation. The polarizations, with homogenous and inhomogeneous broadening included, can be written as integrals over four-time correlation functions, and analytic formulas are derived for the latter for multidimensional harmonic potential surfaces with Franck–Condon displacements in the modes which facilitates the calculation of the SRS cross sections. The theory is applied to understand recent experimental results on the femtosecond SRS (FSRS) of a fluorescent dye, rhodamine 6G (R6G), where the Raman pump pulse is about 1 ps long, and the probe pulse is about 10 fs. The calculations compared very well with the R6G experimental results for off-resonance and resonance FSRS spectra spanning both Stokes and anti-Stokes bands, and for negative and positive pump-probe delay times on resonance.
High quality AlN for deep UV photodetectors
Authors: Nikishin S. , Borisov B. , Pandikunta M. , Dahal R. , Lin J. Y. , Jiang H. X. , Harris H. , Holtz M.
Published: August 2009

We have prepared large-area, 0.50×0.55mm2, metal-semiconductor-metal photodetectors based on AlN layers with different density of inversion domains (IDs). AlN layers were grown on (0001) sapphire substrates using gas source molecular beam epitaxy. The introduction of AlN∕GaN short period superlattices after growth of AlN nucleation layer yields significant reduction in the ID density. Photodetectors with ID density of 106cm−2 exhibit a very low dark current of 0.5fA at zero bias, which remains below 50fA up to a bias of ±30V. The peak responsivity of 0.08A∕W was obtained at a wavelength of ∼202nm.
Photoluminescence study of single ZnO nanostructures: Size effect
Authors: Feng L. , Cheng C. , Yao B. D. , Wang N. , Loy M. M. T.
Published: August 2009

Spatially resolved photoluminescence (PL) investigations were carried out on ZnO single nanowires, tetrapods, and nanocrystals. The fractional intensity for bound exciton (BX) transitions was shown to be correlated with the size in all these ZnO nanostructures. This size dependency is attributed to the inhomogeneous density distribution of the defects as binding sites for BX in the ZnO nanostructures, in good agreement with a simple model calculation.
Ferromagnetic resonance and damping in granular Co–Cr films with perpendicular anisotropy
Authors: Krivosik Pavol , Kalarickal Sangita S. , Mo Nan , Wu Stella , Patton Carl E.
Published: August 2009

The 17.3 GHz ferromagnetic resonance field (HFMR) and linewidth (ΔH) have been measured as a function of the angle (θH) between the external magnetic field and film normal for a 16 nm thick Co–Cr granular film with uniaxial perpendicular anisotropy. The HFMR(θH) response is significantly different from the uniform rotation prediction. The ΔH(θH) dependence shows major deviations from the Gilbert phenomenological damping model. Both dependences can be modeled simultaneously through a combination of two-magnon scattering processes, inhomogeneity line broadening, and an intrinsic damping from magnon-electron scattering processes, with a Gilbert damping α-value of 0.004.
High-pressure Raman spectroscopy of carbon onions and nanocapsules
Authors: Guo J. J. , Liu G. H. , Wang X. M. , Fujita T. , Xu B. S. , Chen M. W.
Published: August 2009

We report high-pressure Raman spectra of carbon onions and nanocapsules investigated by diamond anvil cell experiments. The pressure coefficient and elastic behavior of carbon onions and nanocapsules are found to be very similar to those of multiwall carbon nanotubes. Additionally, detectable structure changes, particularly the collapse of the concentric graphite structure, cannot been seen at pressures as high as ∼20 GPa, demonstrating that carbon onions and nanocapsules have significant hardness and can sustain very high pressures.
Designing periodic arrays of metal nanoparticles for light-trapping applications in solar cells
Authors: Mokkapati S. , Beck F. J. , Polman A. , Catchpole K. R.
Published: August 2009

We present criteria for optimizing the light-trapping efficiency of periodic arrays of metal nanoparticles for Si solar cell applications. The scattering cross section of the nanoparticles and the diffraction efficiency of the grating should be maximized in the long wavelength range. The grating pitch should be chosen to allow higher order diffraction modes for long wavelengths while maintaining the highest possible fill factor. These conditions place strong constraints on the optimal parameters (particle size of ∼200 nm and pitch of ∼400 nm) for periodic arrays of metal nanoparticles, in contrast to dielectric gratings, where a relatively wide range of periods and feature sizes can be used for efficient light trapping.
Fabry–Pérot nanocavities in multilayered plasmonic crystals for enhanced biosensing
Authors: Artar Alp , Yanik Ahmet Ali , Altug Hatice
Published: August 2009

We have demonstrated extraordinary light transmission effect through Fabry–Pérot cavities in multilayered plasmonic crystals formed by coupling two physically separated metallic nanohole and nanodisk array layers. Superior field-medium overlap is observed with Fabry–Pérot resonances as a result of stronger electromagnetic field confinement in the dielectric region far from the metallic surfaces. We show that these cavity resonances are highly sensitive to refractive index changes. The large field-material overlap combined with simple fabrication scheme used here makes these structures an ideal candidate for biosensing applications.
Charge trap memory characteristics of AlOx shell-Al core nanoparticles embedded in HfO2 gate oxide matrix
Authors: Lee Jun Seok , Yang Jung Yup , Hong Jin Pyo
Published: August 2009

The memory behavior of natively oxidized AlOx shell-Al nanoparticles (NPs) in a metal oxide semiconductor (MOS) structure was investigated. Transmission electron microscopy images clearly demonstrate the formation of an AlOx shell (thicknesses of 1–1.5 nm), surrounding Al (sizes of 5–7 nm) core NPs in the MOS structure. Electrical measurements exhibited a memory window of 3.6 V, together with a promising charge retention time of about 10 years. A possible band model needed for enhanced retention characteristics was given by considering the electron/hole barrier width and the additional interface states through the AlOx shell as a method of tunneling barrier engineering.
Breakdown of anomalous channeling with ion energy for accurate strain determination in GaN-based heterostructures
Authors: Redondo-Cubero A. , Lorenz K. , Gago R. , Franco N. , Fernández-Garrido S. , Smulders P. J. M. , Muñoz E. , Calleja E. , Watson I. M. , Alves E.
Published: August 2009

The influence of the beam energy on the determination of strain state with ion channeling in GaN-based heterostructures (HSs) is addressed. Experimental results show that anomalous channeling may hinder an accurate analysis due to the steering effects at the HS interface, which are more intense at lower ion energies. The experimental angular scans have been well reproduced by Monte Carlo simulations, correlating the steering effects with the close encounter probability at the interface. Consequently, limitations in the determination of the strain state by ion channeling can be overcome by selecting the adequate beam energy.
Diffusion of linear polymer melts in shear and extensional flows
Authors: Hunt Thomas A. , Todd B. D.
Published: August 2009

We present results from molecular dynamics simulations for the anisotropic self-diffusion tensor and the velocity autocorrelation functions of monodisperse systems of dense linear chain molecules under flow. Two molecular models are used in these simulations: The finitely extensible nonlinear elastic chain and the freely jointed tangent sphere chain. Nonequilibrium molecular dynamics is used to simulate these systems under planar Couette flow and planar extensional flow. Under planar extensional flow, results presented here are the first, from simulation, for diffusion and velocity autocorrelation functions of molecules, while for planar Couette flow, we compare the broadest range of conditions. An explicit derivation is provided of the Green–Kubo expression for the diffusion tensor. This expression is then used to derive the relation involving the mean-squared displacement—an often used alternative method to calculate diffusion coefficients. Velocity autocorrelation functions have been used, in combination with results on the alignment of molecules from a previous paper, to provide some details of the molecular scale dynamics that influence diffusive transport under flow.
Compact expressions for spherically averaged position and momentum densities
Authors: Crittenden Deborah L. , Bernard Yves A.
Published: August 2009

Compact expressions for spherically averaged position and momentum density integrals are given in terms of spherical Bessel functions (jn) and modified spherical Bessel functions (in), respectively. All integrals required for ab initio calculations involving s, p, d, and f-type Gaussian functions are tabulated, highlighting a neat isomorphism between position and momentum space formulae. Spherically averaged position and momentum densities are calculated for a set of molecules comprising the ten-electron isoelectronic series (Ne–CH4) and the eighteen-electron series (Ar–SiH4, F2–C2H6).
Temporal evolution of double layers in pulsed helicon plasmas
Authors: Biloiu Ioana A. , Scime Earl E.
Published: August 2009

Delays of the order of tens of milliseconds in the appearance of the fast argon ion population in the expansion region of a pulsed helicon plasma are observed in time-resolved, laser induced fluorescence measurements. The fast ion population is a proxy for the presence of a double layer. The magnitude of the time delay depends strongly on the length of the interval between plasma pulses; the shorter the time between pulses, the shorter the time delay. The time delay approaches zero for inter-pulse intervals smaller than 30 ms. The double layer strength is not affected by plasma source modulation frequency.
Ontology and the Conservation of Built Heritage
Authors: Tait Malcolm , While Aidan
Published: August 2009

The ontological status of historic buildings has until recently been little explored, particularly in relation to their conservation. This is curious, for the assumed status and existence of buildings have critical impacts upon our attempts to conserve them. Conventional conservation thought has conceived buildings as solid objects constructed under the gaze of a single architect and retaining exemplar properties worth preserving. This paper offers an alternative and novel conceptualisation of buildings in time and space, drawing on the naturalistic ontology of Jubien and combining this with actor-network theory to explore how buildings might be conceived as multiple things with variant but persisting properties (some of which may be worthy of conservation). Using the moment of post-1945 reconstruction, we explore conservation of the architecture and spaces of Exeter (UK) to consider three objects, their nature, persistence, properties, and formation. Doing so reveals the multiplicity of material and social objects that may become entwined in attempts to conserve these buildings. Things such as ‘views’ become reconsidered as multiply constructed, with variant nonessential parts. The paper concludes that conservation practice requires a more heterogeneous understanding of these objects, how they are formed, and the potential for their social and material hybridity.
Parkour, the City, the Event
Authors: Mould Oli
Published: August 2009

Parkour, or l'art du déplacement, has become widely practised in recent years, with most of its participants (or traceurs) conducting it in urban environments. Studying parkour and those who practise it provides urban geographers with a new and fascinating way in which movement is perceived in the city. Using the theoretical idioms of ‘smooth and striated space’ (Deleuze and Guattari, 1987, A Thousand Plateaus Continuum, London) and ‘the event’ (Badiou, 2005, Being and Event Continum, London), this paper will position parkour as an alternate way of theorising the city as an arena for capitalist versus subversive practices. Moving away from the idea of smooth space incorporating a ‘war machine’, the Badiouian event is a more appropriate lens through which to theorise parkour and its participants’ relationship with the city, in that it embraces a serene ethos of urban rediscovery.
Auschwitz, Ethics, and Testimony: Exposure to the Disaster
Authors: Carter-White Richard
Published: August 2009

Witness testimonies provide a singular challenge to historians of Auschwitz. Survivor accounts offer a privileged perspective on the world of the camp, yet as recent conceptual work has shown the performative structure of these texts exceeds and eludes this representational duty. The challenge for historians is that, given their privileged, ‘insider’ status, any equivocality regarding the content of witness testimonies provides space for Holocaust denial. This paper offers a critical reading of one historical strategy for meeting this challenge: Exposing witness accounts to an uncompromising criteria of evidentiality and plausibility, designed to test their representational quality as a means of preempting negationist attempts to manipulate ‘faulty’ accounts. Drawing on Lyotard, I argue that, even as this strategy succeeds in refuting individual cases of denial, by refusing to enter into dialogue with the language game of testimony, and, more importantly, by invalidating any attempt to do so, this strategy actually reiterates the tactics of those deniers it is designed to oppose, thus undermining its own important work. Rather than rejecting this historical approach, I argue that it is compromised only by an historiographical insistence on imposing this ‘evidential’ language game as universal and representational; if we conversely recognise its performative, nonrepresentational status, it is more equipped to refute denial and without making of testimony a collateral damage.
Poststructuralism and GIS: Is There a ‘Disconnect’?
Authors: Leszczynski Agnieszka
Published: August 2009

Human geography critiques of GIS are operationalized under a unique interpretation of ontology and epistemology. Internal to poststructuralism, this metaphysics collapses the traditional separation between ontology and epistemology, reducing ontological questions to epistemological constructs. Although critiques have moved beyond an initial fixation upon positivism, critical/cultural assessments of GIS tendered within the last ten years continue to motivate epistemology as a basis for its deconstruction. The epistemological reductionism of such a reading of the technology inappropriately abstracts GIS from its ontic basis in computing, giving rise to a fundamental ‘disconnect’ of poststructuralist metaphysics to the technology. This disconnect is identified in terms of (1) the epistemic fallacy, which, underwritten by (2) an ‘undoing’ of the metaphysics of presence, culminates in (3) an effective ‘deontologization’ of an immediately ontic entity. This does not negate the poststructuralist critique of GIS, but it necessitates that critical engagements of the technology accord a material ontological ground to the objects of critique.