bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural basis for the interaction between human milk oligosaccharides and the bacterial lectin PA-IIL of Pseudomonas aeruginosa
Authors: Perret Stéphanie , Sabin Charles , Dumon Claire , Pokorná Martina , Gautier Catherine , Galanina Oxana , Ilia Shahov , Bovin Nicolai , Nicaise Magali , Desmadril Michel , Gilboa-Garber Nechama , Wimmerov´ Michaela , Mitchell Edward P. , Imberty Anne
Published: July 2005

One of the mechanisms contributing to the protection by breast-feeding of the newborn against enteric diseases is related to the ability of human milk oligosaccharides to prevent the attachment of pathogenic bacteria to the duodenual epithelium. Indeed, a variety of fucosylated oligosaccharides, specific to human milk, form part of the innate immune system. In the present study, we demonstrate the specific blocking of PA-IIL, a fucose-binding lectin of the human pathogen Pseudomonas aeruginosa, by milk oligosaccharides. Two fucosylated epitopes, Lewis a and 3-fucosyl-lactose (Lewis x glucose analogue) bind to the lectin with dissociation constants of 2.2×10−7 M and 3.6×10−7 M respectively. Thermodynamic studies indicate that these interactions are dominated by enthalpy. The entropy contribution is slightly favourable when binding to fucose and to the highest-affinity ligand, Lewis a. The high-resolution X-ray structures of two complexes of PA-IIL with milk oligosaccharides allow the precise determination of the conformation of a trisaccharide and a pentasaccharide. The different types of interaction between the oligosaccharides and the protein involve not only hydrogen bonding, but also calcium- and water-bridged contacts, allowing a rationalization of the thermodynamic data. This study provides important structural information about compounds that could be of general application in new therapeutic strategies against bacterial infections.
Structural characterization of the feline-immunodeficiency-virus envelope glycoprotein 36 ectodomain for the development of new antivirals
Authors: Desmaris Florestan , Lemaire David , Ricard-Blum Sylvie , Chatrenet Benoît , Forest Eric
Published: July 2005

In the fight against the human HIV, new targets are being explored, such as the proteins involved in the process of fusion of the virus with the host cell. Recently, the first generation of fusion inhibitors (enfuvirtide), targeting gp41 (virus envelope glycoprotein 41), has become commercially available. However, this promising class of drugs has to be improved in respect of their efficacy and bioavailability. Considering the strong homologies between HIV and FIV (feline immunodeficiency virus), as well as the highly conserved structure of the transmembrane envelope protein among species, FIV represents a relevant model of pre-screening studies for HIV. Taking into account (i) sequence homologies between the ectodomain of HIV gp41 and FIV gp36 (envelope glycoprotein 36), (ii) structural data available for gp41 and (iii) the fact that synthetic peptides derived from gp36 are effective inhibitors of FIV infection, we designed several peptides derived from gp36 sequence. We checked that these peptides had the same structural features as the corresponding peptides from gp41 HIV by CD, analytical ultracentrifugation and 1H–2H (hydrogen–deuterium) exchange combined with MS. By combining this latter technique with surface-plasmon-resonance assays, we identified the amino acid residues of the C-terminal region of the ectodomain of gp36 that are critical for interaction with the N-terminal region. This gave clues for therapy and vaccines against FIV, thus providing helpful data for treatments against HIV.
In vivo characterization of the first acyl-CoA Δ6-desaturase from a member of the plant kingdom, the microalga Ostreococcus tauri
Authors: Domergue Frédéric , Abbadi Amine , Zähringer Ulrich , Moreau Hervé , Heinz Ernst
Published: July 2005

Genomic DNA of Ostreococcus tauri, a fully sequenced marine unicellular alga from the phytoplankton, was used to amplify a gene coding for a typical front-end desaturase involved in polyunsaturated fatty acid biosynthesis. Heterologous expression in Saccharomyces cerevisiae revealed very high desaturation activity with Δ6-regioselectivity. Short-time kinetic experiments showed that the desaturase product was detected in the acyl-CoA pool 5 min after addition of the exogenous substrate to the yeast medium and long before its appearance in the total fatty acids. When this desaturase was co-expressed with the acyl-CoA Δ6-elongase from Physcomitrella patens and the lipid-linked Δ5-desaturase from Phaeodactylum tricornutum, high proportions of arachidonic or eicosapentaenoic acid were obtained, because nearly all of the Δ6-desaturated products were elongated. Furthermore, the product/educt ratios calculated in each glycerolipid for the Δ6-desaturase or for the acyl-CoA Δ6-elongase were in about the same range, whereas this ratio showed a very uneven profile in the case of the lipid-linked Δ5-desaturase. Finally, a sequence-based comparison of all the functionally characterized Δ6-desaturases showed that this enzyme was not related to any previously described sequence. Altogether, our data suggest that this desaturase from O. tauri is an acyl-CoA Δ6-desaturase, the first one cloned from a photosynthetically active organism.
Binding of microtubule-associated protein 1B to LIS1 affects the interaction between dynein and LIS1
Authors: JiméNez-Mateos Eva M. , Wandosell Francisco , Reiner Orly , Avila Jesús , González-Billault Christian
Published: July 2005

For neuronal migration to occur, the cell must undergo morphological changes that require modifications of the cytoskeleton. Several different MAPs (microtubule-associated proteins) or actin-binding proteins are proposed to be involved in the migration of neurons. Therefore we have specifically analysed how two members of the MAP family, MAP1B and LIS1 (lissencephaly-related protein 1), interact with one another and participate in neuronal migration. Our results indicate that, in hippocampal neurons, MAP1B and LIS1 co-localize, associate and interact with each another. The interaction between these two MAPs is regulated by the phosphorylation of MAP1B. Furthermore, this interaction interferes with the association between LIS1 and the microtubule-dependent molecular motor, dynein. Clearly, the differential binding of these cytoskeletal proteins could regulate the functions attributed to the LIS1–dynein complex, including those related to extension of the neural processes necessary for neuronal migration.
Doxorubicin activates nuclear factor of activated T-lymphocytes and Fas ligand transcription: role of mitochondrial reactive oxygen species and calcium
Authors: Kalivendi Shasi V. , Konorev Eugene A. , Cunningham Sonya , Vanamala Sravan K. , Kaji Eugene H. , Joseph Joy , Kalyanaraman B.
Published: July 2005

Doxorubicin (DOX), a widely used antitumour drug, causes dose-dependent cardiotoxicity. Cardiac mitochondria represent a critical target organelle of toxicity during DOX chemotherapy. Proposed mechanisms include generation of ROS (reactive oxygen species) and disturbances in mitochondrial calcium homoeostasis. In the present study, we probed the mechanistic link between mitochondrial ROS and calcium in the embryonic rat heart-derived H9c2 cell line and in adult rat cardiomyocytes. The results show that DOX stimulates calcium/calcineurin-dependent activation of the transcription factor NFAT (nuclear factor of activated T-lymphocytes). Pre-treatment of cells with an intracellular calcium chelator abrogated DOX-induced nuclear NFAT translocation, Fas L (Fas ligand) expression and caspase activation, as did pre-treatment of cells with a mitochondria-targeted antioxidant, Mito-Q (a mitochondria-targeted antioxidant consisting of a mixture of mitoquinol and mitoquinone), or with adenoviral-over-expressed antioxidant enzymes. Treatment with GPx-1 (glutathione peroxidase 1), MnSOD (manganese superoxide dismutase) or a peptide inhibitor of NFAT also inhibited DOX-induced nuclear NFAT translocation. Pre-treatment of cells with a Fas L neutralizing antibody abrogated DOX-induced caspase-8- and -3-like activities during the initial stages of apoptosis. We conclude that mitochondria-derived ROS and calcium play a key role in stimulating DOX-induced ‘intrinsic and extrinsic forms’ of apoptosis in cardiac cells with Fas L expression via the NFAT signalling mechanism. Implications of ROS- and calcium-dependent NFAT signalling in DOX-induced apoptosis are discussed.
The Ins(1,3,4)P3 5/6-kinase/Ins(3,4,5,6)P4 1-kinase is not a protein kinase
Authors: Qian Xun , Mitchell Jennifer , Wei Sung-Jen , Williams Jason , Petrovich Robert M. , Shears Stephen B.
Published: July 2005

Among inositol phosphate kinases, Ins(3,4,5,6)P4 1-kinase has been considered to be an outsider with disparate sequence, a proclaimed capacity to also phosphorylate proteins and apparent 1-phosphatase activity. Such multifunctionality, coupled with ignorance of its operational domains, complicates any mechanistic rationale behind literature reports that Ins(3,4,5,6)P4 1-kinase regulates apoptosis, salt and fluid secretion, and transcription. We have expressed poly(His)-tagged human Ins(3,4,5,6)P4 1-kinase in Sf9 insect cells and purified the enzyme using Ni–agarose chromatography. Protein kinase activity was eluted from the Ni–agarose column, but this did not co-elute with the Ins(3,4,5,6)P4 1-kinase, indicating that the protein kinase and inositol kinase activities belong to separate proteins. To pursue this conclusion, we prepared catalytically inactive mutants of the Ins(3,4,5,6)P4 1-kinase by identifying and targeting the ATP-binding site. Our strategy was based on sequence alignments suggesting homology of the Ins(3,4,5,6)P4 1-kinase with ATP-grasp metabolic enzymes. Individual mutation of four candidate MgATP-binding participants, Lys157, Asp281, Asp295 and Asn297, severely compromised Ins(3,4,5,6)P4 1-kinase activity. Yet, these mutations did not affect the protein kinase activity. We conclude that the Ins(3,4,5,6)P4 1-kinase is not a protein kinase, contrary to earlier reports [e.g. Wilson, Sun, Cao and Majerus (2001) J. Biol. Chem. 276, 40998–41004]. Elimination of protein kinase activity from the enzyme's repertoire and recognition of its ATP-grasp homology together indicate that structural, functional and catalytic relationships between Ins(3,4,5,6)P4 1-kinase and other inositol phosphate kinases are closer than previously thought [Gonzalez, Schell, Letcher, Veprintsev, Irvine and Williams (2004) Mol. Cell 15, 689–701].
Multidimensional vibrational spectroscopy for tunneling processes in a dissipative environment
Authors: Ishizaki Akihito , Tanimura Yoshitaka
Published: July 2005

Simulating tunneling processes as well as their observation are challenging problems for many areas. In this study, we consider a double-well potential system coupled to a heat bath with a linear-linear (LL) and square-linear (SL) system-bath interactions. The LL interaction leads to longitudinal (T1) and transversal (T2) homogeneous relaxations, whereas the SL interaction leads to the inhomogeneous dephasing (T2*) relaxation in the white noise limit with a rotating wave approximation. We discuss the dynamics of the double-well system under infrared (IR) laser excitations from a Gaussian–Markovian quantum Fokker–Planck equation approach, which was developed by generalizing Kubo’s stochastic Liouville equation. Analytical expression of the Green function is obtained for a case of two-state-jump modulation by performing the Fourier–Laplace transformation. We then calculate a two-dimensional infrared signal, which is defined by the four-body correlation function of optical dipole, for various noise correlation time, system-bath coupling parameters, and temperatures. It is shown that the bath-induced vibrational excitation and relaxation dynamics between the tunneling splitting levels can be detected as the isolated off-diagonal peaks in the third-order two-dimensional infrared (2D-IR) spectroscopy for a specific phase matching condition. Furthermore, this spectroscopy also allows us to directly evaluate the rate constants for tunneling reactions, which relates to the coherence between the splitting levels; it can be regarded as a novel technique for measuring chemical reaction rates. We depict the change of reaction rates as a function of system-bath coupling strength and a temperature through the 2D-IR signal.
Electrical characterization of 5 keV phosphorous implants in silicon
Authors: Ruffell S. , Simpson P. J. , Mitchell I. V.
Published: July 2005

Si(100) wafers were implanted with 5-keV phosphorous (fluences of 1×1014–1×1016cm−2) and then annealed at 600–1000 °C, for 30 s or for 5 mins, to study shallow junction formation. Carrier densities were obtained by Van de Pauw Hall measurements, and carrier concentrations were depth profiled via a native-oxide stripping, differential Hall technique. For implanted fluences ⩾5×1014cm−2, an amorphous silicon surface layer is created. This results in solid-phase epitaxial growth at low annealing temperatures (600 °C), with reverse annealing upon dissolution of end-of-range interstitial clusters at higher temperatures (>700°C). Sheet resistances as low as 20Ω∕sq with electrical activation approaching 100% were achieved after annealing at 1000 °C.
Multiple states and hysteresis for type I superconductors
Authors: Du Y. , Pan X. B.
Published: July 2005

For type I superconductors with penetration parameter λ below a certain critical value, the existence of multiple local minimizers of the energy functional is shown. The behavior of these minimizers is examined when the Ginzburg–Landau parameter is small, and a hysteresis phenomenon is demonstrated. In contrast to the case investigated by X. B. Pan [J. Math. Phys. 44, 2639 (2003)] where λ is above the critical value, the results presented in this paper show that type I superconductors with λ below the critical value have higher critical magnetic field Hc, and exhibit more complicated superconducting behavior.
Cavity ring-down spectroscopy and vibronic activity of benzo[ghi]perylene
Authors: Tan Xiaofeng , Salama Farid
Published: July 2005

Gas-phase cavity ring-down spectroscopy of jet-cooled benzo[ghi]perylene (C22H12) in the 26950–28600-cm−1 spectral range is reported for the first time. This study is part of our extensive laboratory astrophysics program for the study of interstellar polycyclic aromatic hydrocarbons. The observed spectrum shows an intermediate level structure and significant broadening and is associated with the vibronically coupled S1(A11)←S0(A11) and S2(B11)←S0(A11) electronic transitions. Time-dependent density-functional calculations were performed to calculate the energetics, vibrational frequencies, and normal coordinates of the S1 and S2 states. A simple vibronic model was employed to account for the vibronic interaction between the vibronic levels of the S1 and S2 states. The calculated vibronic spectrum is found to be in good agreement with the experimental spectrum.
Dynamics and rheology of immiscible polymer-liquid-crystal systems
Authors: Yu Wei , Zhou Chixing
Published: July 2005

The morphology evolution in immiscible polymer-liquid-crystal systems is quite different from flexible polymer–polymer mixtures due to the anisotropic properties of liquid crystals. The dynamics and rheology of such system are discussed. A theoretical model is proposed to describe the dynamics of liquid-crystal droplets in a flow field and the rheological properties of immiscible liquid-crystal/polymer mixtures. The deformation of liquid-crystal droplet is found to be greatly dependent on the interfacial properties of polymer-liquid crystal. The scaling relationships of interfacial contribution to the stresses are found to be quite different from the isotropic mixtures with droplet morphology.
Implementation of the locally renormalized CCSD(T) approaches for arbitrary reference function
Authors: Kowalski Karol
Published: July 2005

Several new variants of the locally-renormalized coupled-cluster (CC) approaches that account for the effect of triples (LR-CCSD(T)) have been formulated and implemented for arbitrary reference states using the TENSOR CONTRACTION ENGINE functionality, enabling the automatic generation of an efficient parallel code. Deeply rooted in the recently derived numerator–denominator-connected (NDC) expansion for the ground-state energy [K. Kowalski and P. Piecuch, J. Chem. Phys. 122, 074107 (2005)], LR-CCSD(T) approximations use, in analogy to the completely renormalized CCSD(T) (CR-CCSD(T)) approach, the three-body moments in constructing the noniterative corrections to the energies obtained in CC calculations with singles and doubles (CCSD). In contrast to the CR-CCSD(T) method, the LR-CCSD(T) approaches discussed in this paper employ local denominators, which assure the additive separability of the energies in the noninteracting system limit when the localized occupied spin-orbitals are employed in the CCSD and LR-CCSD(T) calculations. As clearly demonstrated on several challenging examples, including breaking the bonds of the F2, N2, and CN molecules, the LR-CCSD(T) approaches are capable of providing a highly accurate description of the entire potential-energy surface (PES), while maintaining the characteristic N7scaling of the ubiquitous CCSD(T) approach. Moreover, as illustrated numerically for the ozone molecule, the LR-CCSD(T) approaches yield highly competitive values for a number of equilibrium properties including bond lengths, angles, and harmonic frequencies.
Interface traps and dangling-bond defects in (100)Ge∕HfO2
Authors: Afanas’ev V. V. , Fedorenko Y. G. , Stesmans A.
Published: July 2005

Combined electrical and electron spin resonance analysis reveals dramatic differences in the interface defect properties of the (100)Ge∕GeOxNy∕HfO2 and (100)Ge∕GeO2 interfaces from the seemingly similar interfaces of (100)Si with the HfO2 and SiO2. No dangling bond centers associated with Ge crystal surface atoms are detected. Only paramagnetic defects in the near-interfacial Ge oxide or Ge (oxy)nitride layers are observed. In contrast to the amphoteric traps related to the dangling bonds (Pb-type centers) commonly observed at the silicon/insulator interfaces, the major component of the Ge/insulator interface trap spectrum comes from slow acceptor states which show no correlation with paramagnetic centers and are resistant to passivation by hydrogen.
Dielectric response of graded composites having general power-law-graded cylindrical inclusions
Authors: Wei En-Bo , Poon Y. M.
Published: July 2005

The dielectric response of graded composites having general power-law-graded cylindrical inclusions under a uniform applied electric field is investigated. The dielectric profile of the cylindrical inclusions is modeled by the equation εi(r)=c(b+r)k (where r is the radius of the cylindrical inclusions and c,b and k are parameters). Analytical solutions for the local electrical potentials are derived in terms of hypergeometric functions and the effective dielectric response of the graded composites is predicted in the dilute limit. Moreover, for a simple power-law dielectric profile εi(r)=crk and a linear dielectric profile εi(r)=c(b+r), analytical expressions of the electrical potentials and the effective dielectric response are derived exactly from our results by taking the limits b→0 and k→1, respectively. For a higher concentration of inclusions, the effective dielectric response is estimated by an effective-medium approximation. In addition, we have discussed the effective response of graded cylindrical composites with a more complex dielectric profile of inclusion, εi(r)=c(b+r)keβr.
The role of higher silanes in silane-discharge particle growth
Authors: Bano Gregory , Horvath Peter , Rozsa Karoly , Gallagher Alan
Published: July 2005

A small concentration of stable higher silanes (HS) build up in an (initially) pure-silane discharge. Here it is shown that these HS cause a major increase in particle growth rates but have no effect on film growth rates. This explains the observed increase of growth rate during the first seconds of a transient discharge, as the HS build up toward a steady-state concentration of several percent. A rapid increase in particle versus film growth rate also occurs at larger values of discharge power and pressure, and the HS also appear to cause this. Possible reasons for this extreme sensitivity of particles, but not of films, to the HS are evaluated.
Sub-Tg dynamics in polycarbonate by neutron scattering and its relation with secondary γ relaxation
Authors: Arrese-Igor S. , Arbe A. , Alegría A. , Colmenero J. , Frick B.
Published: July 2005

We have investigated the dynamics of phenylene rings in glassy bisphenol-A (BPA) polycarbonate (PC) by means of quasielastic neutron scattering. Taking advantage of selective deuteration of the samples, we have studied the incoherent scattering of hydrogens in phenylene rings on the one hand, and on the other hand the coherent quasielastic scattering of all the atoms in the sample. Two different types of neutron spectrometers, time of flight and backscattering, were used in order to cover a wide dynamic range, which extends from microscopic (∼10−13s) to mesoscopic (∼10−9s) times. Moreover, neutron-diffraction experiments with polarization analysis were carried out in order to characterize the structural features, and the relative coherent and incoherent contributions of the samples investigated. In contrast with previous studies of phenylene ring dynamics in BPA polysulfone performed by us also by neutron scattering, phenylene rings in BPA PC exhibit an “extra” motion in addition to those found for BPA polysulfone’s phenylene rings. This extra motion of the rings in PC perfectly correlates with the main carbonate group motion followed by dielectric spectroscopy and allows us to (i) consistently interprete the PC’s γ relaxation in terms of two different motions; and (ii) experimentally confirm the relation between the motion of phenylene rings and carbonate groups within BPA PC formerly predicted by computational methods.
A global investigation of phase equilibria using the perturbed-chain statistical-associating-fluid-theory approach
Authors: Yelash Leonid , Müller Marcus , Paul Wolfgang , Binder Kurt
Published: July 2005

The recently developed perturbed-chain statistical-associating-fluid theory (PC-SAFT) is investigated for a wide range of model parameters including the parameter m representing the chain length and the thermodynamic temperature T and pressure p. This approach is based upon the first-order thermodynamic perturbation theory for chain molecules developed by Wertheim [M. S. Wertheim, J. Stat. Phys. 35, 19 (1984); ibid. 42, 459 (1986)] and Chapman et al. [G. Jackson, W. G. Chapman, and K. E. Gubbins, Mol. Phys. 65, 1 (1988); W. G. Chapman, G. Jackson, and K. E. Gubbins, ibid.  65, 1057 (1988)] and includes dispersion interactions via the second-order perturbation theory of Barker and Henderson [J. A. Barker and D. Henderson, J. Chem. Phys. 47, 4714 (1967)]. We systematically study a hierarchy of models which are based on the PC-SAFT approach using analytical model calculations and Monte Carlo simulations. For one-component systems we find that the analytical model in contrast with the simulation results exhibits two phase-separation regions in addition to the common gas-liquid coexistence region: One phase separation occurs at high density and low temperature. The second demixing takes place at low density and high temperature where usually the ideal-gas phase is expected in the phase diagram. These phenomena, which are referred to as “liquid-liquid” and “gas-gas” equilibria, give rise to multiple critical points in one-component systems, as well as to critical end points and equilibria of three fluid phases, which can usually be found in multicomponent mixtures only. Furthermore, it is shown that the liquid-liquid demixing in this model is not a consequence of a “softened” repulsive interaction as assumed in the theoretical derivation of the model. Experimental data for the melt density of polybutadiene with molecular mass Mw=45000g∕mol are correlated here using the PC-SAFT equation. It is shown that the discrepancies in modeling the polymer density at ambient temperature and high pressure can be traced back to the liquid-liquid phase separation predicted by the equation of state at low temperatures. This investigation provides a basis for understanding possible inaccuracies or even unexpected phase behavior which can occur in engineering applications of the PC-SAFT model aiming at predicting properties of macromolecular substances.
On the temperature and pressure dependences of cavities in the dielectric continuum picture
Authors: Manjari Swati R. , Kim Hyung J.
Published: July 2005

Cavity size at equilibrium and its variations with thermodynamic conditions are studied in the dielectric continuum framework of solvents. By employing Gibbs’ theory of dividing surfaces, the fluctuating cavity description of Kim [H.J. Kim, J. Chem. Phys. 105, 6818 (1996)] is extended to include effects related to the local solvent density inhomogeneity near the cavity. The resulting theory is applied to study cavity size variations with temperature and pressure in dipolar and nondipolar solvents. Model calculations show that the cavity size tends to increase with temperature along an isobar and decrease with pressure along an isotherm.
Dispersed fluorescence spectroscopy of jet-cooled HCF and DCF: Vibrational structure of the X̃A′1 state
Authors: Fan Haiyan , Mukarakate Calvin , Deselnicu Mihaela , Tao Chong , Reid Scott A.
Published: July 2005

We recorded dispersed fluorescence (DF) spectra following excitation of the pure bending levels 20n and the combination states 10120n and 20n301 in the ÃA″1←X̃A′1 system of HCF and DCF. Spectra were measured with a 0.3m spectrograph equipped with a gated intensified charge coupled device (CCD) detector and obtained under jet-cooled conditions using a pulsed discharge source. The DF spectra reveal rich detail concerning the vibrational structure of the X̃ state up to 10000cm−1. For HCF, resonances among the nearly degenerate levels 112n, 2n+131, and 2n+2 produce a polyadlike structure in the spectrum, and the usual effective spectroscopic Hamiltonian (Dunham expansion) poorly reproduces the experimental term energies. In contrast, this Hamiltonian works well for the term energies of DCF. Density functional calculations of the ground state vibrational frequencies were performed; the results are in excellent agreement with the experimentally derived vibrational parameters. The search for perturbations involving the low-lying ãA″3 state is described.
Light extinction in metallic powder beds: Correlation with powder structure
Authors: Rombouts M. , Froyen L. , Gusarov A. V. , Bentefour E. H. , Glorieux C.
Published: July 2005

A theoretical correlation between the effective extinction coefficient, the specific surface area, and the chord length distribution of powder beds is verified experimentally. The investigated powder beds consist of metallic particles of several tens of microns. The effective extinction coefficients are measured by a light-transmission technique at a wavelength of 540nm. The powder structure is characterized by a quantitative image analysis of powder bed cross sections resulting in two-point correlation functions and chord length distributions. The specific surface area of the powders is estimated by laser-diffraction particle-size analysis and by the two-point correlation function. The theoretically predicted tendency of increasing extinction coefficient with specific surface area per unit void volume is confirmed by the experiments. However, a significant quantitative discrepancy is found for several powders. No clear correlation of the extinction coefficient with the powder material and particle size, and morphology is revealed, which is in line with the assumption of geometrical optics.
Dielectric phase-transition and polarization studies in stepped and compositionally graded lead magnesium niobate–lead titanate relaxor thin films
Authors: Ranjith R. , Sarkar Asis , Laha Apurba , Krupanidhi S. B. , Balamurugan A. K. , Rajagoplan S. , Tyagi A. K.
Published: July 2005

Ferroelectric properties of chemically heterogeneous multilayers and graded composition thin films of (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3, a well-known relaxor, were prepared using a multitarget pulsed laser ablation system. Target materials with different values of x (0.0, 0.1, 0.2, and 0.3) were used for ablation growth. Films with sharp interfaces and graded interfaces were prepared and were characterized for their electrical properties. The stepped films were found to have a phase-transition behavior dominated by the individual layer behavior with their corresponding local dielectric maxima. The graded films showed an overall averaged effect of the system. The graded films showed an enhanced diffusiveness in the phase transition and the γ value was found to be 2.43, which is a measure of diffusivity. The tunability of these graded films was found to be high around 60% and was twice that of any of the film of homogeneous composition films. The room-temperature polarization hysteresis curves exhibited slim loop characteristics with a saturation polarization of about 40μC∕cm2 in the case of both stepped and graded films.
Measuring carrier density in parallel conduction layers of quantum Hall systems
Authors: Grayson M. , Fischer F.
Published: July 2005

An experimental analysis for two parallel conducting layers determines the full resistivity tensor of the parallel layer, at magnetic fields where the other layer is in the quantum Hall regime. In heterostructures which exhibit parallel conduction in the modulation-doped layer, this analysis quantitatively determines the charge density in the doping layer and can be used to estimate the mobility. To illustrate one application, experimental data show magnetic freeze-out of parallel conduction in a modulation-doped heterojunction. As another example, the carrier density of a minimally populated second subband in a two-subband quantum well is determined. A simple formula is derived that can estimate the carrier density in a highly resistive parallel layer from a single Hall measurement of the total system.
Influence of voltmeter impedance on quantum Hall measurements
Authors: Fischer F. , Grayson M.
Published: July 2005

We report the influence of voltmeters on measurements of the longitudinal resistance Rxx in the quantum Hall-effect regime. We show that for input resistances typical of standard digital lock-in amplifiers, Rxx can show a nonzero minimum which might be mistaken for a parallel conduction in the doping layer. This residual impedance at the Rxx minima can be calculated with Zres=Rxy2∕Rin+jωCRxy2, where Rin is the input resistance of the voltmeter, C is the measurement capacitance, and Rxy=h/νe2 is the Hall resistance. In contrast to a real parallel conduction, the effect disappears when either the current source and ground contact are swapped or the polarity of the magnetic field is changed; examples with data are shown. We discuss how proper phasing of a lock-in amplifier is necessary to eliminate false residual minima which arise from stray capacitances.
Transport coefficients and dynamic properties of hydrogen sulfide from molecular simulation
Authors: Nieto-Draghi Carlos , Mackie Allan D. , Bonet Avalos Josep
Published: July 2005

Molecular-dynamics simulation results on thermodynamic and transport properties of pure H2S under conditions of practical interest are presented. Our data are in very good quantitative agreement with the scarce experimental data and estimates on thermophysical properties of this substance. Our results serve as a test of the validity of the intermolecular potential used in the simulations as well as the consistency of the existing data in the studied range. New simulation data on thermal conductivity at low temperature as well as in supercritical states are also reported. Furthermore, we present a comparative analysis between the local order in the liquid phase of pure hydrogen sulfide and water, due to the molecular analogies between both substances, and its relation with the formation of HS bonds. Our results indicate that under the same corresponding thermodynamic states, H2S is a much less structured substance, with a first solvation shell with a dodecahedral order instead of the tetrahedral order observed in water.
Temperature dependence of the double-layer capacitance for the restricted primitive model: The effect of chemical association between unlike ions
Authors: Reszko-Zygmunt J. , Sokolowski S. , Pizio O.
Published: July 2005

A version of the density-functional theory, which takes into account the association between unlike ions is applied to calculate the temperature dependence of the capacitance of an electric double layer. The results are compared with those obtained for the model without association.
Field-enhancement factor for carbon nanotube array
Authors: Wang M. , Li Z. H. , Shang X. F. , Wang X. Q. , Xu Y. B.
Published: July 2005

To estimate the apex field-enhancement factor associated with an array of carbon nanotubes (CNTs) on a planar cathode surface, the model of the floating spheres between parallel anode and cathode plates was proposed. An approximate formula for the enhancement factor was derived showing that the intertube distance of a CNT array critically affects the field emission. When the intertube distance is less than the height of the tube, the enhancement factor decreases rapidly with decreasing distance in qualitative agreement with the numerical simulation. Considering the field-emission current density, the field emission can be optimized when the intertube distance is comparable with the tube height, in accordance with the results from the experiments. Finally, the influence of the anode-cathode distance on the enhancement factor was also discussed, showing that the anode-cathode distance has little effect on the field emission from a CNT array. Thus, we can reduce the theshold voltage to some extent by decreasing the anode-cathode distance.
Titanium diffusion and residual stress of platinum thin films on Ti∕SiO2∕Si substrate
Authors: Wang Kai , Yao Kui , Chua Soo Jin
Published: July 2005

The residual stresses of Pt thin films deposited on Ti∕SiO2∕Si substrate and annealed at different temperatures in air were quantified by x-ray-diffraction method. A grazing-incidence x-ray-diffraction technique was applied to effectively investigate the diffusion and oxidation of Ti. The surface morphology of the Pt film was examined with field-emission scanning electron microscopy. TiO2 phase was detected on the surface of the Pt thin film after the annealing process, indicating strong diffusion and oxidation of Ti through the Pt layer. The dependence of the residual stress on annealing temperature was strongly related to the diffusion and oxidation of Ti, which generally increased the compressive stress, probably due to the associated volume expansion. However, stress release happened when the stress reached a certain high level. The diffusion and oxidation of Ti also resulted in serious hillock formation on the surface of the Pt film. The effects of Pt deposition temperature on the residual stress and Ti diffusion are also discussed.
Determination of strain-induced valence-band splitting in GaAsN thin films from circularly polarized photoluminescence
Authors: Egorov A. Yu. , Kalevich V. K. , Afanasiev M. M. , Shiryaev A. Yu. , Ustinov V. M. , Ikezawa M. , Masumoto Y.
Published: July 2005

The paper studies the circularly polarized photoluminescence (PL) from dilute GaAsN alloys with nitrogen content of 1%–3.4%, grown on GaAs substrates. The room-temperature PL is found to consist of two bands whose splitting grows with increasing nitrogen content. The analysis of the PL circular polarization has shown that the PL bands originate from the splitting of light- and heavy-hole subbands, induced by an elastic strain in GaAsN layer. The dependence of the energy gap of unstrained GaAsN on the nitrogen content has been calculated using the measured light- and heavy-hole splittings.
Effect of current crowding and Joule heating on electromigration-induced failure in flip chip composite solder joints tested at room temperature
Authors: Nah J. W. , Suh J. O. , Tu K. N.
Published: July 2005

The electromigration of flip chip solder joints consisting of 97Pb–3Sn and 37Pb–63Sn composite solders was studied under high current densities at room temperature. The mean time to failure and failure modes were found to be strongly dependent on the change in current density. The composite solder joints did not fail after 1month stressed at 4.07×104A∕cm2, but failed after just 10h of current stressing at 4.58×104A∕cm2. At a slightly higher current stressing of 5.00×104A∕cm2, the composite solder joints failed after only 0.6h due to melting. Precipitation and growth of Cu6Sn5 at the cathode caused the Cu under bump metallurgy to be quickly consumed and resulted in void formation at the contact area. The void reduced the contact area and displaced the electrical path, affecting the current crowding and Joule heating inside the solder bump. Significant Joule heating inside solder bumps can cause melting of the solder and quick failure. The effect of void propagation on current crowding and Joule heating was confirmed by simulation.
Giant magnetoimpedance effect in ultrasoft FeAlSiBCuNb nanocomposites for sensor applications
Authors: Phan Manh-Huong , Peng Hua-Xin , Wisnom Michael R. , Yu Seong-Cho
Published: July 2005

Fe 73 − x Al x Si 14 B 8.5 Cu 1 Nb 3.5  (x=0,2) nanocomposite materials consisting of a nanocrystalline phase in an amorphous matrix were obtained by annealing their precursor amorphous ribbons, which were prepared by the melt-spinning technique, at different temperatures ranging between 350 and 650°C for 45min in vacuum. Investigation on their magnetic and magnetoimpedance properties indicates that the Al-containing sample (x=2) possesses superior magnetic softness and giant magnetoimpedance (GMI) effect over the Al-free counterpart. This can be likely ascribed to the increased magnetic permeability, decreased coercive force, and decreased resistivity. The increased magnetic permeability results from a reduction in magnetocrystalline anisotropy and saturation magnetostriction. The correlations between magnetic softness, electrical properties, and GMI behavior are discussed in the light of the skin effect model. These results indicate that the Al-containing Fe-based nanocomposite material can be ideally used for high-performance GMI sensor applications.
Doping effects of dimethyl-tin-dichloride on material properties of CdS films and on formation of CdS∕CdTe heterostructures
Authors: Toyama Toshihiko , Oda Hiroyuki , Matsune Kengo , Okamoto Hiroaki , Kudriavysevand Yuriy , Asomoza René , Kubo Motoki , Tsutsumi Yasuo
Published: July 2005

A series of systematic investigations has been conducted to examine the doping effects of dimethyl-tin-dichloride (DMTC) on the structural, electrical, and optical properties of CdS films used for photovoltaic applications. After the DMTC doping, Sn and Cl concentrations in CdS are found to increase to 6×1017 and 4.5×1018atoms∕cm3, respectively; the CdS grain size also tends to increase. A slight increase in the electrical conductivity is discussed in conjunction with the increase in the grain size and the Cl donor concentration. In addition, the optical-absorption spectra reveal almost no change in the band gap of CdS due to the doping, while the spectra indicate a deterioration of the crystallinity of the heavily doped CdS. The influence of the DMTC doping into the CdS films on the formation of the CdS∕CdTe heterostructure is also discussed. With an increase in the grain size of the CdS underlayer due to the DMTC doping, the degree of the (111) preferential orientation of CdTe increases, which generally corresponds to an improvement in the photovoltaic performance. On the other hand, a fairly small reduction is observed in the sulfur fraction in the CdTe1−xSx mixed-crystal interlayer, which indicates no marked deterioration at the CdS∕CdTe interface. The DMTC doping is also effective in reducing the optical reflectance in almost the entire active spectral region of the CdS∕CdTe solar cell.
Hydrogen interaction with platinum and palladium metal–insulator–semiconductor devices
Authors: Salomonsson Anette , Eriksson Mats , Dannetun Helen
Published: July 2005

Hydrogen-sensitive Pd–SiO2–Si and Pt–SiO2–Si metal–insulator–semiconductor (MIS) devices have been studied in ultrahigh vacuum in the temperature range of 223–523K. Adsorption/absorption of hydrogen occurs at the metal surface, in the metal bulk, and at the metal–insulator interface. The sensor signal, caused by hydrogen adsorption at the interface, shows a logarithmic dependence on the applied hydrogen pressure. The Pt-MIS device, which is fully functional at atmospheric pressures, is sensitive to changes in hydrogen pressure down to the 10−12-Torr scale. We propose that the interface adsorption follows a so-called Temkin isotherm with an interface heat of adsorption that varies with hydrogen coverage as ΔHi0(1−aθ). The initial heat of adsorption ΔHi0 is determined to 0.78eV∕hydrogen atom. The adsorption potential at the external Pt surface is found to be 0.45eV∕hydrogen atom. These values were obtained by modeling the hydrogen interaction with the MIS devices and fitting the model to a number of experimental results. Also studies of Pd-based devices were performed and compared with Pt. The hydrogen adsorption on the metal surface, previously treated as a first-order process on Pd, is shown to follow a second-order process. Qualitatively the results from the Pd- and Pt-MIS devices agree. Quantitatively there are differences. The hydrogen sensitivity of the Pt-MIS device is only approximately one-third compared to that of the Pd-MIS structure. This agrees with the result that the concentration of available hydrogen adsorption sites at the Pt–SiO2 interface is approximately 7×1017m−2 whereas the concentrations of sites at the Pd–SiO2 interface is roughly three times larger (2×1018m−2). An estimate of the size of the dipole moments (0.6–0.7D) implies that the interface hydrogen atoms are strongly polarized. Differences are also observed in the microstructure of the metal films. Atomic force microscopy results show that the Pd surface reconstructs during H2–O2 exposures, while the Pt surface shows no such change at these temperatures.
Effects of electron irradiation on the ferroelectric properties of Langmuir-Blodgett copolymer films
Authors: Othon C. M. , Bateman F. B. , Ducharme Stephen
Published: July 2005

The effect of irradiation on the ferroelectric properties of Langmuir-Blodgett films of the copolymer poly(vinylidene fluoride-trifluoroethylene) was investigated using 1-MeV electrons for doses from 0.16to1.10MGy, where 1Gray(Gy)=100rad. Irradiation causes a systematic decrease in the phase-transition temperature, crystallinity, and spontaneous polarization of the films. The crystallinity and spontaneous polarization of the films decreased by amounts proportional to the dose, both tending toward zero near a dose of 1.30MGy. The ferroelectric-paraelectric phase-transition temperature, however, was only reduced by about 12%, indicating that the primary effect of irradiation was to convert a crystalline ferroelectric material to a noncrystalline dielectric.
Ion-beam texturing of uniaxially textured Ni films
Authors: Park S. J. , Norton D. P. , Selvamanickam Venkat
Published: July 2005

The formation of biaxial texture in uniaxially textured Ni thin films via Ar-ion irradiation is reported. The ion-beam irradiation was not simultaneous with deposition. Instead, the ion beam irradiates the uniaxially textured film surface with no impinging deposition flux, which differs from conventional ion-beam-assisted deposition. The uniaxial texture is established via a nonion beam process, with the in-plane texture imposed on the uniaxial film via ion beam bombardment. Within this sequential ion beam texturing method, grain alignment is driven by selective etching and grain overgrowth.
Integration of massive states as contractions of nonlinear σ models
Authors: Andrianopoli L. , Ferrara S. , Lledó M. A. , Maciá O.
Published: July 2005

We consider the contraction of some nonlinear σ models which appear in effective supergravity theories. In particular we consider the contractions of maximally symmetric spaces corresponding to N=1 and N=2 theories, as they appear in certain low energy effective supergravity actions with mass deformations. The contraction procedure is shown to describe the integrating out of massive modes in the presence of interactions, as it happens in many supergravity models after spontaneous supersymmetry breaking.
Batchelor versus Stewartson flow structures in a rotor-stator cavity with throughflow
Authors: Poncet Sebastien , Chauve Marie-Pierre , Schiestel Roland
Published: July 2005

The present work considers the turbulent flow inside a high-speed rotor-stator cavity with or without superimposed throughflow. New extensive measurements made at IRPHE by a two-component laser Doppler anemometer technique and by pressure transducers are compared to numerical predictions based on one-point statistical modeling using a low-Reynolds-number second-order full stress transport closure (Reynolds stress model). The advanced second-order model provides good predictions for the mean flow as well as for the turbulent field and so is the adequate level of closure to describe such complex flows. A better insight into the dynamics of such flows is also gained from this study. Indeed the transition between a Batchelor type of flow with two boundary layers separated by a central rotating core and a Stewartson type of flow with only one boundary layer on the rotating disk is characterized in the (r*,Ro) plane, where r* is the dimensionless radial location and Ro a modified Rossby number. The 5∕7 power-law of Poncet et al. [“Turbulent rotating disk with inward throughflow,” J. Fluid Mech. 522, 253 (2005)] describing the mean centripetal flow in a rotor-stator system is extended to different aspect ratios and to the case of centrifugal Batchelor type of flows.
Large-eddy simulation of Rayleigh-Taylor turbulence with compressible miscible fluids
Authors: Mellado J. P. , Sarkar S. , Zhou Y.
Published: July 2005

Turbulence developed from Rayleigh-Taylor instability between two compressible miscible fluids in an unbounded domain is addressed in this paper. It is demonstrated that the turbulent Mach number in the turbulent core has an upper bound, independent of the density ratio under a broad range of initial mean configurations. The initial thermodynamic state of the system determines the amount of potential energy per unit mass involved in the turbulent mixing stage, and thus the characteristic level of turbulent fluctuations that is achievable is linked to the characteristic speed of sound such that the turbulent Mach number is limited. For the particular case of an ideal gas, this bound on the turbulent Mach number is found to be between 0.25 and 0.6, depending on the particular initial thermodynamic state. Hence, intrinsic compressibility effects (those owing to large Mach number) are likely to be limited in the turbulent stage of a pure Rayleigh-Taylor problem. This result is confirmed by large-eddy simulations (LES) of systems with density jumps at the interface of 3:1, a density ratio for which there is extensive data available in the literature. The LES predictions of the mixing depth growth and overall mixing agree with results previously obtained in incompressible configurations with a negligibly small Mach number, and the data fully describing the Reynolds stresses and the budget of the (resolved) turbulent kinetic energy equation are provided.