bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy landscape view of nonideality in binary mixtures
Authors: Abraham Sneha Elizabeth , Chakrabarti Dwaipayan , Bagchi Biman
Published: February 2007

Positive and negative deviations from the prediction of Raoult’s Law on the composition dependence of a property of binary mixtures are often explained in terms of structure formation and structure breakage, respectively, upon mixing. However, a detailed theoretical description of these ideas seems to be lacking in the literature. Here we present the energy landscape view of nonideality of the viscosity of the binary mixture using two different models, one for structure former and the other for structure breaker. For both the models, the average inherent structure energy shows an inverse correlation with the viscosity. The inherent structures of the structure former indicate that there is a considerable enhancement of short range order due to stronger attractive interaction between the two constituent species. On the other hand, for the structure breaker, there is no such enhancement of short range order due to weaker interaction between the two constituent species. We find the inherent structures of the structure breaker to be phase separated in many cases where the parent phase is homogeneous. When the configurational entropy of the parent liquid is computed for the two model systems, we find that the configurational entropy also shows an inverse correlation with the viscosity in both the cases.
Gain and saturation energy characteristics in transversely excited N2 lasers
Authors: Hariri A. , Ghoreyshi S. , Rahimian K.
Published: February 2007

Measurements for laser parameters (i.e., small signal gain, g0, and saturation energy density, Es) have been carried out in a transversely excited N2 laser with a variable electrode gap separation, using an arrangement based on an oscillator-amplifier laser system. Our measurements indicate that the measured g0 and Es parameters depend on the electrode gap separation, and thereby the relevant characteristic curves showing this dependency, and consequently the g0 and Es dependencies on the E∕p value or electron temperature in the laser amplifier are introduced. It was also found experimentally that in the present system with the corona preionization, the product of the optimum N2 gas pressure and the gap separation is a constant value of 54Torrcm, where it is valid only for a system operating in a rather small range of electrode gap separation where the laser output power is maximized. Therefore, we show that the pd product is playing an important role for optimized performances of transversely excited N2 lasers. At last, the g0 and Es measurements across the amplifier discharge width have shown that the g0 parameter is not uniformly distributed within the discharge electrode gap separation, while the Es parameter has a minimum at the gap center with a symmetrical distribution of the output energy density.
Tunneling magnetoresistance observed in La0.67Sr0.33MnO3/organic molecule/Co junctions
Authors: Xu W. , Szulczewski G. J. , LeClair P. , Navarrete I. , Schad R. , Miao G. , Guo H. , Gupta A.
Published: February 2007

Tunneling magnetoresistance has been observed in organic based spintronic devices using the organic semiconductors tetraphenyl porphyrin (TPP) and aluminum tris(8-hyroxyquinoline) (Alq3) as the spacer layer between La0.67Sr0.33MnO3 (LSMO) and Co films. The evidence for tunneling is twofold: (1) nonlinear current and conductance versus voltage curves and (2) an increasing junction resistance with decreasing temperature. In general, the magnetoresistance is found to decrease with increasing bias voltage and increasing temperature in both Alq3 and TPP junctions. These results demonstrate that organic molecules can form tunnel barriers that perform as well as most inorganic barrier materials on LSMO.
Chern-Simons matrix models and Stieltjes-Wigert polynomials
Authors: Dolivet Yacine , Tierz Miguel
Published: February 2007

Employing the random matrix formulation of Chern-Simons theory on Seifert manifolds, we show how the Stieltjes-Wigert orthogonal polynomials are useful in exact computations in Chern-Simons matrix models. We construct a biorthogonal extension of the Stieltjes-Wigert polynomials, not available in the literature, necessary to study Chern-Simons matrix models when the geometry is a lens space. We also study the relationship between Stieltjes-Wigert and Rogers-Szegö polynomials and the corresponding equivalence with a unitary matrix model. Finally, we give a detailed proof of a result that relates quantum dimensions with averages of Schur polynomials in the Stieltjes-Wigert ensemble.
Transition metal NMR chemical shifts from optimized effective potentials
Authors: Teale Andrew M. , Cohen Aron J. , Tozer David J.
Published: February 2007

Metal shielding constants and chemical shifts are determined for nine transition metal complexes using an uncoupled formalism with orbitals and eigenvalues determined using the Yang-Wu implementation [W. Yang and Q. Wu, Phys. Rev. Lett. 89, 143002 (2002)] of the optimized effective potential approach in density functional theory. Preliminary calculations using generalized gradient approximation functionals quantify the influence of the variables in the optimized effective potential implementation. In particular, a flexible potential expansion is necessary for a precise calculation of these quantities. Hybrid functionals are then considered. Expanding the potential in the primary orbital basis yields chemical shifts that are a notable improvement over conventional hybrid values, and which are a marginal improvement over those obtained using a high-quality generalized gradient approximation. Similar shifts are obtained using a more flexible potential expansion, although care is required to avoid unphysical structure in the exchange-correlation potential.
A hybrid method for calorimetry with subnanoliter samples using Schottky junctions
Authors: Hakala T. K. , Toppari J. J. , Törmä P.
Published: February 2007

A μm-scale calorimeter realized by using Schottky junctions as a thermometer is presented. Combined with a hybrid experimental method, it enables simultaneous time-resolved measurements of variations in both the energy and the heat capacity of subnanoliter samples.
Neoclassical toroidal viscosity for an axisymmetric toroidal equilibrium with multiple trapping of particles
Authors: Shaing K. C. , Sabbagh S. A. , Peng M.
Published: February 2007

A method is illustrated on how to apply existing formulas to the neoclassical toroidal plasma viscosity for an axisymmetric toroidal equilibrium with an arbitrary aspect ratio that has multiple trapping states. The effect of the energy scattering on the viscosity in the ν regime is presented using an approximate collision operator. Here, ν is the collision frequency. The explicit expressions for the steady state toroidal flow speed resulting from the neoclassical toroidal flow damping in both the 1∕ν and the ν regime are also presented. The physics origin of the toroidal viscous force is the broken toroidal symmetry induced by the error fields and the amplification of these fields by stable or unstable resistive wall modes, or other asymmetric magnetic field perturbations.
Poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene) conjugated polymer domains in a thermoplastic polyurethane matrix
Authors: Patrício Patrícia S. O. , Silva Glaura G. , de Oliveira Flávio A. C. , Righi Ariete , Neves Bernardo R. A. , Cury Luiz A.
Published: February 2007

Self-sustained and spin-casting films formed from blends of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) conjugated polymer and thermoplastic poly-urethane (TPU) at different concentrations have been investigated. Scanning electron microscopy images of self-sustained films show the formation of circularlike domains of MEH-PPV in the TPU matrix, characterizing the blend material as heterogeneous. The circularlike domains in the spin-casting films were also observed by electric force microscopy (EFM) and by atomic force microscopy. The EFM, in particular, has allowed the differentiation of the MEH-PPV domains from the TPU matrix due to the electrical properties of the conjugated polymer. The MEH-PPV domains in the spin-casting films are much smaller in size than in the case of self-sustained films. The glass transition temperatures for the TPU and for the self-sustained blended films were obtained by temperature modulated differential scanning calorimetry. A very small variation in the glass transition temperature (Tg) has been observed for the blends. This fact further corroborates that MEH-PPV and TPU form immiscible blends. Intermolecular interactions between the MEH-PPV and the TPU materials were proposed to occur at the interfaces of the domains. These interfacial interactions have not affected the Raman modes, which pointed out that they are relatively weak interactions. The formation of small conjugation segments of the MEH-PPV molecules due to these interfacial interactions with the TPU molecules at the interfaces of the domains was assigned to be responsible by the appearance of a large tail and clear shoulders to the high energy side of the photoluminescence (PL) spectra of self-sustained samples. This was also assigned to be responsible by the blueshift observed in the PL spectra of spin-casting films. The redshift of the pure electronic transition peak and the first vibronic band (which presents an inhomogeneous broadening) were observed in the self-sustained blended films and were related, respectively, to the increase of the internal intermolecular and intramolecular interactions due to the conformational disorder of the MEH-PPV molecules imposed by the casting spread technique.
Effect of hydrogen on Ni∕Ti multilayer neutron monochromator performance
Authors: Ju Hyunsu , Heuser Brent J.
Published: February 2007

Ni ∕ Ti multilayers with and without hydrogen added to the Ti layers have been prepared by dc-magnetron sputtering to investigate the effect of hydrogen on neutron monochromator performance. The addition of hydrogen further reduces the negative scattering length density of Ti, thereby increasing the contrast with the Ni. Increases in the first order peak reflectivity by factors of 2–3 have been observed in neutron reflectivity measurements. The improved performance is attributed to a larger neutron scattering length density contrast and to a sharpening of the interfaces.
Slow periodic oscillations in time domain dynamics of NO2
Authors: Sanrey Michaël , Joyeux Marc
Published: February 2007

The authors investigated the time domain nonadiabatic dynamics of NO2 on the coupled XA12 and AB22 electronic states by launching wave packets on the excited electronic state and focused on the evolution at long times (t>200fs), which has received little attention up to now. The authors showed that the initial fast spreading of the wave packets is followed at all energies by slow periodic intramolecular vibronic energy redistribution (IVER) with periods in the range of 0.3 to several tens of picoseconds. These energy transfers lead to oscillations with the same periods in the population of each electronic state. Propagation of wave packets indicates that IVER frequencies also dominate the fluctuations of the squared modulus of the autocorrelation function ∣A(t)∣2 at energies not too high above the bottom of the conical intersection, but this is no longer the case at higher energies. For example, for initial wave packets prepared by almost vertical excitation of the vibrational ground state of the ground electronic surface, the oscillations of ∣A(t)∣2 essentially reflect the detuning from 1:2 resonance between the frequency of the bend and that of the symmetric stretch in the excited electronic state. These theoretical results were used to discuss the possible origin of the low-frequency oscillations which were recently observed in time domain experimental spectra of NO2.
Investigation of interface magnetic moment of Fe∕Ge multilayer: A neutron reflectivity study
Authors: Singh Surendra , Basu Saibal , Gupta Mukul , Vedpathakz Mahesh , Kodama R. H.
Published: February 2007

Fe ∕ Ge multilayer sample was grown on Si(100) substrate by rf sputtering. X-ray diffraction shows that the Fe layers are polycrystalline whereas the Ge layers are amorphous in this sample. X-ray reflectometry and unpolarized neutron reflectometry techniques have been used to determine the structural parameters viz. individual layer thickness, interface roughness, and the density of the layers. Polarized neutron reflectometry has given magnetic moment depth profile for the multilayer thin film. There is a large reduction in magnetic moment for Fe atom on an average in the Fe layers. Magnetic moments of Fe at the interfaces are lower compared to the regions away from the interfaces. There is an asymmetry between magnetic moments at Fe on Ge interfaces and Ge on Fe interfaces as well. Superconducting quantum interference device measurement indicates that the sample is ferromagnetic at room temperature with a lower magnetic moment compared to bulk iron.
Effect of electronic excited states on transport in magnetized hydrogen plasma
Authors: Bruno D. , Laricchiuta A. , Capitelli M. , Catalfamo C.
Published: February 2007

Multicomponent diffusion coefficients for magnetized, equilibrium hydrogen plasma have been calculated. The equilibrium composition of the plasma is determined by taking consistently into account the number of allowed atomic electronic excited states (EES) as determined by the average interparticle distance. The coefficients are shown to depend on the inclusion of realistic cross sections for the interactions with EES. The effect of an applied magnetic field on the diffusion coefficients and on derived quantities like the electrical conductivity and the internal and reactive thermal conductivity is studied and explained.
Electronic structure and transport properties of doped CoSi single crystal
Authors: Pan Z. J. , Zhang L. T. , Wu J. S.
Published: February 2007

The lattice parameter and electronic structures of CoSi and CoSi1−xYx (Y=Al and P, x=0.03125 and 0.125) were calculated using the full-potential linear augmented plane wave approach based on density functional theory. The calculated lattice parameter of binary CoSi is about 0.27% smaller than the experimental value. Calculated electronic structures show that CoSi is a semimetal and its density of states is very small at the Fermi level. Doping with Y on the Si site can tune the Fermi level and the effective masses as well as the density of the hole carriers or electron ones in the electronic structure of CoSi, which is a valuable way to modulate the transport properties of this compound. Based on the calculated electronic structures and our experimental results on CoSi, the intrinsic relations between the electronic structures and transport properties of doped and undoped CoSi are discussed in detail.
Drag force on an absorbing body in highly collisional plasmas
Authors: Khrapak S. A. , Zhdanov S. K. , Ivlev A. V. , Morfill G. E.
Published: February 2007

The force acting on a small absorbing body embedded in a highly collisional plasma with drifting ions is calculated using the linear response formalism. It is shown that the absorption introduces physical effects leading to a drastic reduction of the force. The importance of this result is discussed, mostly in the context of complex (dusty) plasma research, but it can be relevant to many other situations, ranging from astrophysics, thunderclouds, dust in fusion devices, colloidal suspensions, biological systems, etc.
Enhancement in the efficiency of light emission from silicon by a thin Al2O3 surface-passivating layer grown by atomic layer deposition at low temperature
Authors: Chen M. J. , Shih Y. T. , Wu M. K. , Tsai F. Y.
Published: February 2007

Thin Al2O3 surface-passivating layers grown by atomic layer deposition at 100°C were demonstrated to be instrumental in producing efficient light emission from silicon. External quantum efficiency up to 1.3×10−4 was observed from silicon metal-insulator-semiconductor light-emitting diodes with a 5nm Al2O3 surface-passivating layer as the insulator, which is more than tenfold that from similar devices with a 5nm SiO2 insulator layer thermally oxidized at 1000°C. Anomalous temperature dependences of the photoluminescence intensities and spectra at low temperatures indicate the presence of bound excitonic traps at the Al2O3∕Si interface. The enhanced light emission may be attributed to the temporary capture of excitons by the interfacial bound excitonic traps, which effectively reduces nonradiative recombination.
A molecular dynamics investigation of fluorocarbon based layer-by-layer etching of silicon and SiO2
Authors: Rauf S. , Sparks T. , Ventzek P. L. G. , Smirnov V. V. , Stengach A. V. , Gaynullin K. G. , Pavlovsky V. A.
Published: February 2007

A molecular dynamics model is used to understand the layer-by-layer etching of Si and SiO2 using fluorocarbon and Ar+ ions. In these two-step etch processes, a nanometer-scale fluorocarbon passivation layer is grown on the material’s surface using low energy CFx+ ions or radicals. The top layers of the material are then reactive ion etched by Ar+ ions utilizing the fluorocarbon already present on the material surface. By repeating these two steps, Si or SiO2 can be etched with nanometer-scale precision and the etch rate is considerably faster than what traditional atomic layer etching techniques provide. The modeling results show that fluorocarbon passivation films can be grown in a self-limiting manner on both Si and SiO2 using low energy CF2+ and CF3+ ions. The fluorocarbon passivation layer is a few angstroms thick, and its thickness increases with the fluorocarbon ion’s energy. Increasing the ion energy, however, amorphizes the top atomic layers of the material. In addition, the fluorocarbon film becomes F rich with increasing ion energy. Simulations of fluorocarbon passivated SiO2 surface show that Ar+ ions with energy below 50eV etch Si (within SiO2) in a self-limiting manner. Si etching stops once F in the fluorocarbon passivation layer is exhausted or is pushed too deep into the substrate. Oxygen within SiO2 is more easily sputtered from the material surface than Si, and the top layers of SiO2 are expected to become O deficient during Ar+ ion bombardment. Ar+ ion etching of fluorocarbon passivated Si also appears to be self-limiting below 30eV ion energy, and etching stops once F on the material surface is either consumed or becomes inaccessible.
Analysis of the multireflection effects in compensated liquid crystal devices
Authors: Jang Yong-Kyu , Bos Philip
Published: February 2007

The effect of multiple internal reflections on the extinction ratio of perfectly compensated liquid crystal devices is studied. We find the previously unexplained wavelength dependence of light leakage in an ideally compensated device is caused by the interference of the internally reflected ordinary and extraordinary waves. While these effects have not been previously made clear, they can place a limit on the performance of liquid crystal devices used as displays, optical switches, and optical attenuators.
Ferroelectric domain structures of epitaxial (001) BiFeO3 thin films
Authors: Chen Y. B. , Katz M. B. , Pan X. Q. , Das R. R. , Kim D. M. , Baek S. H. , Eom C. B.
Published: February 2007

Ferroelectric domain structures of epitaxial BiFeO3 thin films on miscut (001) SrTiO3 substrates have been studied by transmission electron microscopy. BiFeO3 on 0.8° miscut substrates are composed of both 109° and 71° domains; in contrast, only 71° stripe domains are observed in BiFeO3 on 4° miscut (001) SrTiO3 substrates. The domain width in BiFeO3 on 4° miscut substrates increases as film thickness increases due to a reduction in domain wall energy. The domain configurations of BiFeO3 thin films affect their ferroelectric switching behavior due to the pinning at the junctions between 109° and 71° domain walls.
Nucleation and growth of TiSi2 thin films deposited on glass by atmospheric pressure chemical vapor deposition
Authors: Du Jun , Du Piyi , Xu Ming , Hao Peng , Huang Yanfei , Han Gaorong , Song Chenlu , Weng Wenjian , Wang Jianxun , Shen Ge
Published: February 2007

Titanium silicide (TiSi2) thin films were prepared on glass substrate by atmospheric pressure chemical vapor deposition using SiH4 and TiCl4 as the precursors. The phase structure of the thin films was identified by x-ray diffractometry. The surface morphology and thickness of the thin films were observed by field emission scannig electron microscopy and the sheet resistance of the thin films was measured using the four point probe method. The results show that the TiSi2 thin films are formed in a face-centered orthorhombic structure. Due to the influence of the amorphous glass substrate, an amorphous layer is initially formed on the substrate and the TiSi2 crystalline phase grows on top of it. As the thickness and content of TiSi2 crystalline phase increase with deposition time, the resistivity of the thin film decreases. Besides, the growth rate and thus the size of TiSi2 crystalline phase increase as the deposition temperature increases. The stack density decreases when the deposition temperature increases above 700°C because the rapid growth at the higher temperatures causes more irregular shape of crystalline particles. The maximal stack density of the crystalline phase and thus the minimum resistivity of the thin films are obtained at the deposition temperature of 700°C. The expressions of the stack density of crystalline phase and the resistivity of the thin films as functions of the deposition conditions are theoretically deduced which are well consistent with the experimental results.
Analytical conductivity model for doped organic semiconductors
Authors: Li Ling , Meller Gregor , Kosina Hans
Published: February 2007

Charge transport in doped organic semiconductors is investigated, and an analytical conductivity model is proposed based on the variable range hopping theory. The model can well explain the superlinear increase of the conductivity with doping, as well as the change in the conductivity of an organic semiconductor upon the doping ratio. The model demonstrates that the exponent of an empirical power law for the conductivity is actually temperature-dependent. Calculation results coincide well with experimental observations.
A dynamical equation for the distribution of a scalar advected by turbulence
Authors: Venaille Antoine , Sommeria Joel
Published: February 2007

A phenomenological model for the dissipation of scalar fluctuations due to the straining by the fluid motion is proposed in this Brief Communication. An explicit equation is obtained for the time evolution of the probability distribution function of a coarse-grained scalar concentration. The model relies on a self-convolution process. We first present this model in the Batchelor regime and then extend empirically our result to the turbulent case. This approach is finally compared with other models.
Utilization of high-energy neutrons for the detection of fissionable materials
Authors: Thompson S. J. , Kinlaw M. T. , Harmon J. F. , Wells D. P. , Farfan E. B. , Hunt A. W.
Published: February 2007

The detection of high-energy prompt fission neutrons was investigated as a method of fissionable material detection. Neutron energy spectra of U238 and several nonfissionable materials were measured using a neutron time of flight spectrometer. The photonuclear reactions were induced in the targets using a pulsed bremsstrahlung beam for several endpoint energies between 8 and 15MeV. While fission neutrons can have energies in excess of 10MeV, neutrons emitted from nonfissionable materials have distinct energy limits that depend upon binding and incident particle energies. Hence the presence of high-energy neutrons can be used to discriminate fissionable from most nonfissionable materials.
Electronic rule for formation of glassy alloys
Authors: Fukuhara Mikio , Takahashi Masae , Kawazoe Yoshiyuki , Inoue Akihisa
Published: February 2007

The glass transition temperature Tg of 100 kinds of glassy alloys can be expressed as a function of their valence electron concentration (VEC): Tg=131VEC+57 for metal/metal bonding type and Tg=−236VEC+2375 for metal/metalloid bonding one. The electron valences of the constituent elements of the glassy alloys are somewhat larger than those predicted by crystalline metallic valence bond theory, suggesting a valence electron contribution associated with spd or spf hybridization for glass formation. Ab initio molecular orbital calculations of the optimized structures for Mg monoanion clusters warranted application of the valence electron rule.
Germanium nanowire transistors with ethylene glycol treated poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) contacts
Authors: Yoo Byungwook , Dodabalapur Ananth , Lee Doh C. , Hanrath Tobias , Korgel Brian A.
Published: February 2007

Germanium nanowires (Ge NWs) were synthesized via the supercritical fluid-liquid-solid (SFLS) process, followed by surface passivation with isoprene. The Ge NWs were then drop cast from ethanol suspension onto SiO2∕Si substrates. Conductivity-enhanced poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) with ethylene glycol treatment was employed as the source-drain electrodes. The field-effect mobility of Ge nanowire field-effect transistors was as high as 7.0cm2∕Vs, with a p-type response similar to Pt-electrode devices previously reported for SFLS-grown Ge NWs. The organic based contacts provide a potential platform for inexpensive production of flexible nanowire devices.
Optical tuning and switching of photonic defect modes in cholestericliquid crystals
Authors: Yoshida Hiroyuki , Lee Chee Heng , Miura Yusuke , Fujii Akihiko , Ozaki Masanori
Published: February 2007

Optical tuning of photonic defect modes in cholesteric liquid crystals is demonstrated based on a contrast in the pitch length. Two-photon laser lithography was performed in a cholesteric helix to leave an unpolymerized region in the center to act as a structural defect. The unpolymerized region was then substituted by an azobenzene dye-doped cholesteric liquid crystal which exhibits a pitch shortening upon ultraviolet exposure. Reversible shifting or on-off switching of the defect mode was realized as a result of selectively inducing a pitch shortening of the cholesteric liquid crystal at the defect and changing the contrast in the pitch length between the bulk and defect.
Resonant energy transfer within a colloidal nanocrystal polymer host system
Authors: Kaufmann Stefan , Stöferle Thilo , Moll Nikolaj , Mahrt Rainer F. , Scherf Ulli , Tsami Argiri , Talapin Dmitri V. , Murray Christopher B.
Published: February 2007

The authors report on resonant energy transfer of nonequilibrium excitons in an amorphous polyfluorene donor CdSe∕ZnS core-shell nanocrystal acceptor system. By time-resolved photoluminescence (PL) spectroscopy, they have investigated the PL decay behavior of the primarily excited polyfluorene in dependence of the concentration of the nanocrystals. The authors are able to demonstrate that the finite rise time of the PL transient monitored at the spectral position of the acceptor PL directly reflects the PL decay of the donor.
Cooling-rate induced softening in a Zr50Cu50 bulk metallic glass
Authors: Liu Y. , Bei H. , Liu C. T. , George E. P.
Published: February 2007

Contrary to the cooling-rate induced hardening observed in crystalline metals, the authors report here an unexpected surface softening in rapidly solidified Zr50Cu50 bulk metallic glass. A soft layer ∼500μm thick was detected near the surface with both hardness and elastic modulus increasing from the surface to the interior. To understand the reason for this, a correlation between cooling rate and defect concentration was derived. Defect concentration was found to increase as the cooling rate increased, suggesting that surface softening may be the result of freezing-in of excess defects, induced by a faster cooling rate near the surface compared to the interior.
Intersubband absorption in CdSe∕ZnxCdyMg1−x−ySe self-assembled quantum dot multilayers
Authors: Shen A. , Lu H. , Charles W. , Yokomizo I. , Tamargo M. C. , Franz K. J. , Gmachl C. , Zhang S. K. , Zhou X. , Alfano R. R. , Liu H. C.
Published: February 2007

The authors report the observation of intersubband absorption in multilayers of CdSe∕ZnxCdyMg1−x−ySe self-assembled quantum dots. The samples were grown by molecular beam epitaxy on InP substrates. For samples with the CdSe dot layers doped with Cl and with the deposited CdSe equivalent layer thickness between 5.2 and 6.9 ML, peak absorption between 2.5 and 3.5μm was observed. These materials are promising for intersubband devices operating in the mid- and near-infrared ranges.
Shock compression response of nanoiron powder compact
Authors: Dai Chengda , Eakins Daniel , Thadhani Naresh , Liu J. Ping
Published: February 2007

The shock compression response of nano-Fe powder (∼25nm) pressed to ∼35% theoretical maximum density was determined based on shock stress and wave velocity measurements using piezoelectric stress gauges. The obtained data show a discontinuity in shock wave velocity plotted against particle velocity and an inflexion in specific volume from compression to expansion with increasing shock stress. It is found that the Hugoniot of 25nm Fe powder cannot be fully described using analytical models that are otherwise capable of predicting the Hugoniot of micron-sized powder or highly porous materials.
Electrohydrogenation of MgH2-thin films
Authors: Borgschulte A. , Rector J. H. , Schreuders H. , Dam B. , Griessen R.
Published: February 2007

Mg-metal hydride systems are potential hydrogen storage media and might be used in hydrogen switchable mirrors. However, absorption kinetics are too slow even with appropriate catalysts. The authors demonstrate the enhancement of the formation of MgH2 by an electric current, thus enabling the hydrogenation of Mg without an external heat source. The effect is explained by the local heating of the Mg together with an electromigration of H− ions. The electrically supported hydrogen uptake might also be a possibility to enhance the hydrogen uptake rate of complex hydrides due to a similar electronic structure.
Annealing of InGaAsN quantum wells in hydrogen
Authors: Geelhaar L. , Galluppi M. , Averbeck R. , Jaschke G. , Riechert H.
Published: February 2007

In 0.37 Ga 0.63 As 0.983 N 0.017 quantum wells grown by molecular beam epitaxy at different temperatures were annealed under a comprehensive variety of conditions either in Ar or in H2. A significantly higher luminescence efficiency (i.e., room temperature photoluminescence intensity) can be obtained for annealing in H2. Thus, there is an additional chemical effect beyond the mere thermal effect of annealing. At the same time, band gap and localization of charge carriers are not influenced. Hence, the electronic structure is not affected by the H2 treatment. Indirect experiments suggest that hydrogen is reversibly incorporated into the samples and can be removed by mild annealing in Ar.
Role of buffer in organic solar cells using C60 as an acceptor
Authors: Song Q. L. , Li C. M. , Wang M. L. , Sun X. Y. , Hou X. Y.
Published: February 2007

A thin buffer layer is indispensable for a high power conversion efficiency in an organic solar cell with fullerene (C60) as the acceptor. In present work, the authors proposed that the role of the buffer layer in an organic solar cell is to prohibit the electron transfer from metal to C60, and thus a desired built-in electric field can promote the free carrier collection. The built-in electric field in different organic solar cells with and without the thin C60 layer was studied by the transient photovoltage technique. The experimental results supported our proposal and indicated that the exciton blocking effect reported in the literature might not be the role of the buffer layer.
Generation of high-power arbitrary-wave-form modulated inductively coupled plasmas for materials processing
Authors: Tanaka Yasunori , Morishita Yu , Fushie Shunsuke , Okunaga Kyota , Uesugi Yoshihiko
Published: February 2007

An arbitrary-wave-form modulated induction thermal plasma (AMITP) system was developed using a high-power semiconductor high-frequency power supply. The modulated high-power plasma is a breakthrough technique for controlling the temperature and the radical density in high-density plasmas. The arbitrary-wave-form modulation of the coil current enables more detailed control of the temperature of the high-density plasmas than the pulse-amplitude modulation that has already been developed. The Ar AMITP with intentionally modulated coil current could be generated at a power of 10–15kW. Results showed that the Ar excitation temperature between the specified excitation levels was changed intentionally according to the modulation control signal.
Photodissociation of hydrogen halide molecules on free ice nanoparticles
Authors: Poterya Viktoriya , Fárník Michal , Slavíček Petr , Buck Udo , Kresin Vitaly V.
Published: February 2007

Photodissociation of water clusters doped with HX(X=Br,Cl), molecules has been studied in a molecular beam experiment. The HX(H2O)n clusters are dissociated with 193nm laser pulses, and the H fragments are ionized at 243.07nm and their time-of-flight distributions are measured. Experiments with deuterated species DBr(H2O)n and HBr(D2O)n suggest that the photodissociation signal originates from the presence of the HX molecule on the water cluster, but does not come directly from a photolysis of the HX molecule. The H fragment is proposed to originate from the hydronium molecule H3O. Possible mechanisms of the H3O production are discussed. Experimental evidence suggests that acidic dissociation takes place in the cluster, but the H3O+ ion remains rather immobile.
Observation of the “missing” polar OCS dimer
Authors: Afshari Mahin , Dehghani M. , Abusara Z. , Moazzen-Ahmadi N. , McKellar A. R. W.
Published: February 2007

A new infrared band at 2069.3cm−1 is observed and assigned to the long-anticipated polar isomer of the OCS dimer, helping to explain apparent discrepancies among earlier studies. The data reported here should enable direct observation of the microwave spectrum of polar (OCS)2 and motivate new theoretical works on the energetics of OCS dimer isomers and interconversion energy barriers.
Patterns of abundance and size of Dictyoceratid sponges among neighbouring islands in central Torres Strait, Australia
Authors: Duckworth Alan R. , Wolff Carsten W.
Published: February 2007

Distribution and size frequency patterns of sessile organisms such as sponges may vary among and within neighbouring reefs. In the present study, we examined small-scale variation of dictyoceratid sponges (class Demospongiae), commonly found on coral reefs, by surveying six neighbouring islands in central Torres Strait. Each island had four study sites, at least 1 km apart, with each site consisting of three shallow (4 to 6 m) and three deep (10 to 15 m) 20 m2 transects. For each transect, we recorded the number of each species and measured the size of the more common dictyoceratid sponges. Seven species of dictyoceratid were recorded in central Torres Strait, with only three species, Coscinoderma sp., Dysidea herbacea and Hyrtios erecta, common to all six islands. Abundance patterns generally varied greatly among islands or sites within islands, perhaps resulting from a combination of physical, biological and stochastic factors. More dictyoceratids were found in deeper water; however, abundance across depth for some species varied among islands or sites. Size-frequency distribution patterns also varied greatly among islands and dictyoceratid species, indicating that factors that may promote growth for one species may not necessarily promote growth for a related species. This study shows that patterns of abundance and size of dictyoceratids can vary greatly over small spatial scales, and that patterns are species-specific.
Critical role of dipeptidyl peptidase I in neutrophil recruitment during the development of experimental abdominal aortic aneurysms
Authors: Pagano Monica B. , Bartoli Michel A. , Ennis Terri L. , Mao Dongli , Simmons Pamela M. , Thompson Robert W. , Pham Christine T. N.
Published: February 2007

Dipeptidyl peptidase I (DPPI) is a lysosomal cysteine protease critical for the activation of granule-associated serine proteases, including neutrophil elastase, cathepsin G, and proteinase 3. DPPI and granule-associated serine proteases have been shown to play a key role in regulating neutrophil recruitment at sites of inflammation. It has recently been suggested that neutrophils and neutrophil-associated proteases may also be important in the development and progression of abdominal aortic aneurysms (AAAs), a common vascular disease associated with chronic inflammation and destructive remodeling of aortic wall connective tissue. Here we show that mice with a loss-of-function mutation in DPPI are resistant to the development of elastase-induced experimental AAAs. This is in part because of diminished recruitment of neutrophils to the elastase-injured aortic wall and impaired local production of CXC-chemokine ligand (CXCL) 2. Furthermore, adoptive transfer of wild-type neutrophils is sufficient to restore susceptibility to AAAs in DPPI-deficient mice, as well as aortic wall expression of CXCL2. In addition,
in vivo
blockade of CXCL2 by using neutralizing antibodies directed against its cognate receptor leads to a significant reduction in aortic dilatation. These findings suggest that DPPI and/or granule-associated serine proteases are necessary for neutrophil recruitment into the diseased aorta and that these proteases act to amplify vascular wall inflammation that leads to AAAs.
Glucocorticoid-stimulated preadipocyte differentiation is mediated through acetylation of C/EBPβ by GCN5
Authors: Wiper-Bergeron Nadine , Salem Houssein Abdou , Tomlinson Julianna J. , Wu Dongmei , Haché Robert J. G.
Published: February 2007

Preadipocyte differentiation in culture is driven by an insulin and cAMP dependant transcriptional cascade which induces the bzip transcription factors C/EBPβ and C/EBPδ. We have previously shown that glucocorticoid treatment, which strongly potentiates this differentiation pathway, stimulates the titration of the corepressor histone deacetylase 1 (HDAC1) from C/EBPβ. This results in a dramatic enhancement of C/EBPβ-dependent transcription from the C/EBPα promoter, concomitant with potentiation of preadipocyte differentiation. Here, we show that C/EBPβ is acetylated by GCN5 and PCAF within a cluster of lysine residues between amino acids 98–102 and that this acetylation is strongly induced by glucocorticoid treatment. Arginine substitution of the lysine residues within the acetylation motif of C/EBPβ prevented acetylation and blocked the ability of glucocorticoids to enhance C/EBPβ-directed transcription and to potentiate C/EBPβ-dependent preadipocyte differentiation. Moreover, acetylation of C/EBPβ appeared to directly interfere with the interaction of HDAC1 with C/EBPβ, suggesting that PCAF/GCN5-dependent acetylation of C/EBPβ serves as an important molecular switch in determining the transcriptional regulatory potential of this transcription factor.
Cholesterol-dependent actin remodeling via RhoA and Rac1 activation by theStreptococcus pneumoniaetoxin pneumolysin
Authors: Iliev Asparouh I. , Djannatian Jasmin Roya , Nau Roland , Mitchell Timothy J. , Wouters Fred S.
Published: February 2007

TheStreptococcus pneumoniaetoxin pneumolysin belongs to the group of cholesterol-dependent cytolysins. It produces rapid cell lysis at higher concentrations or apoptosis at lower concentrations. In cell membranes, it forms prepores and pores. Here, we show that sublytic concentrations of pneumolysin produce rapid activation of Rho and Rac GTPases and formation of actin stress fibers, filopodia, and lamellipodia. That Rac1-specific and Rho-associated kinase (ROCK)-specific inhibitors reverted the formation of lamellipodia and stress fibers, respectively, identifies RhoA and Rac1 as key toxin effectors. Live imaging excluded macropore formation (as judged by membrane impermeability toward calcein) but indicated very early membrane depolarization [as judged by bis-(1,3-dibutylbarbituric acid)trimethine oxanol staining], indicative of formation of micropores with ion channel properties. That Rac1-dependent lamellipodia formation was reverted by the voltage-gated calcium channel inhibitor SKF96365 and by toxin exposure in calcium-free medium suggests a role for calcium influx via endogenous calcium channels in the Rac1 activation. Cellular cholesterol depletion by methyl-β-cyclodextrin or incubation of the toxin with cholesterol before cell treatment eliminated its membrane binding and the subsequent GTPase activation. Thus, that our experiments show small GTPase activation by a cholesterol-dependent cytolysin suggests a membrane cholesterol-dependent activation mechanism.
Cleavage of p65/RelA of the NF-κB pathway by
Chlamydia
Authors: Lad Sonya P. , Li Jiali , da Silva Correia Jean , Pan Qilin , Gadwal Shilpa , Ulevitch Richard J. , Li Erguang
Published: February 2007

Chlamydia trachomatis
is a bacterial pathogen that infects the eyes and urogenital tract. Ocular infection by this organism is the leading cause of preventable blindness worldwide. The infection is also a leading cause of sexually transmitted disease in the United States. As obligate intracellular pathogens, chlamydiae have evolved sophisticated, yet undefined, mechanisms to maintain a favorable habitat for intracellular growth while avoiding harm to the host. We show here that chlamydiae have the ability to interfere with the NF-κB pathway of host inflammatory response. We found that
Chlamydia
infection did not promote IκBα degradation, a prerequisite for NF-κB nuclear translocation/activation, nor induce p65/RelA nuclear redistribution. Instead, it caused p65 cleavage into an N terminus-derived p40 fragment and a p22 of the C terminus. The activity was specific because no protein cleavage or degradation of NF-κB pathway components was detected. Moreover, murine p65 protein was resistant to cleavage by both human and mouse biovars. The chlamydial protein that selectively cleaved p65 was identified as a tail-specific protease (CT441). Importantly, expression of either this protease or the p40 cleavage product could block NF-κB activation. A hallmark of chlamydial STD is its asymptomatic nature, although inflammatory cellular response and chronic inflammation are among the underlying mechanisms. The data presented here demonstrate that chlamydiae have the ability to convert a regulatory molecule of host inflammatory response to a dominant negative inhibitor of the same pathway potentially to minimize inflammation.
Cannabinoid action in the olfactory epithelium
Authors: Czesnik Dirk , Schild Detlev , Kuduz Josko , Manzini Ivan
Published: February 2007

The perception of odors is influenced by a variety of neuromodulators, and there is growing evidence that modulation already takes place in the olfactory epithelium. Here we report on cannabinergic actions in the olfactory epithelium of
Xenopus laevis
tadpoles. First we show that CB1 receptor-specific antagonists AM251, AM281, and LY320135 modulate odor-evoked calcium changes in olfactory receptor neurons. Second, we localize CB1-like immunoreactivity on dendrites of olfactory receptor neurons. Finally, we describe the cannabinergic influence on odor-induced spike-associated currents in individual olfactory receptor neurons. Here we demonstrate that the cannabinergic system has a profound impact on peripheral odor processing and discuss its possible function.
Biotin uptake in prokaryotes by solute transporters with an optional ATP-binding cassette-containing module
Authors: Hebbeln Peter , Rodionov Dmitry A. , Alfandega Anja , Eitinger Thomas
Published: February 2007

BioMNY proteins are considered to constitute tripartite biotin transporters in prokaryotes. Recent comparative genomic and experimental analyses pointed to the similarity of BioMN to homologous modules of prokaryotic transporters mediating uptake of metals, amino acids, and vitamins. These systems resemble ATP-binding cassette-containing transporters and include typical ATPases (e.g., BioM). Absence of extracytoplasmic solute-binding proteins among the members of this group, however, is a distinctive feature. Genome context analyses uncovered that only one-third of the widespread
bioY
genes are linked to
bioMN
. Many
bioY
genes are located at loci encoding biotin biosynthesis, and others are unlinked to biotin metabolic or transport genes. Heterologous expression of the
bioMNY
operon and of the single
bioY
of the α-proteobacterium
Rhodobacter capsulatus
conferred biotin-transport activity on recombinant
Escherichia coli
cells. Kinetic analyses identified BioY as a high-capacity transporter that was converted into a high-affinity system in the presence of BioMN. BioMNY-mediated biotin uptake was severely impaired by replacement of the Walker A lysine residue in BioM, demonstrating dependency of high-affinity transport on a functional ATPase. Biochemical assays revealed that BioM, BioN, and BioY proteins form stable complexes in membranes of the heterologous host. Expression of truncated
bio
transport operons, each with one gene deleted, resulted in stable BioMN complexes but revealed only low amounts of BioMY and BioNY aggregates in the absence of the respective third partner. The results substantiate our earlier suggestion of a mechanistically novel group of membrane transporters.
Tissue-driven hypothesis of genomic evolution and sequence-expression correlations
Authors: Gu Xun , Su Zhixi
Published: February 2007

To maintain normal physiological functions, different tissues may have different developmental constraints on expressed genes. Consequently, the evolutionary tolerance for genomic evolution varies among tissues. Here, we formulate this argument as a “tissue-driven hypothesis” based on the stabilizing selection model. Moreover, several predicted genomic correlations are tested by the human–mouse microarray data. Our results are as follows. First, between the human and mouse, we have elaborated the among-tissue covariation between tissue expression distance (
E
ti
) and tissue sequence distance (
D
ti
). This highly significant
E
ti
−
D
ti
correlation emerges when the expression divergence and protein sequence divergence are under the same tissue constraints. Second, the tissue-driven hypothesis further explains the observed significant correlation between the tissue expression distance (between the human and mouse) and the duplicate tissue distance (
T
dup
) between human (or mouse) paralogous genes. In other words, between-duplicate and interspecies expression divergences covary among tissues. Third, for genes with the same expression broadness, we found that genes expressed in more stringent tissues (e.g., neurorelated) generally tend to evolve more slowly than those in more relaxed tissues (e.g., hormone-related). We conclude that tissue factors should be considered as an important component in shaping the pattern of genomic evolution and correlations.