bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric response of concentrated colloidal suspensions
Authors: Carrique F. , Arroyo F. J. , Jiménez M. L. , Delgado A. V.
Published: January 2003

The determination of the low-frequency (typically 0–1 MHz) dielectric dispersion of colloidal suspensions may become an electrokinetic tool of wider use if the accuracy of experimental data can be improved and if trustable theories, available for a wide range of situations, are made available. In the present work, we focus on the latter aspect: Since the dielectric constant of the suspensions is in fact a collective property, its determination could be most useful in concentrated suspensions. This is our aim in this paper. Using the classical electrokinetic equations and a cell model accounting for particle–particle interactions, we present calculations of the dielectric spectra of concentrated (volume fractions up to 50%) suspensions of spheres. Most of our results cannot be thought of as any sort of extrapolation of those corresponding to dilute suspensions (the reverse is true), and in fact the notion of a dilute colloidal system is itself not free of uncertainties, as no “critical volume fraction” can be identified separating the dilute and concentrated ranges. According to the calculations described, increasing the particle concentration by a sufficient amount can lead to a decrease of the dielectric constant of the whole system that can be well below that of the dispersion medium, even for high zeta potentials, ζ. The latter quantity affects (and this is also true if φ → 0) considerably both the dielectric constant εr′ and the relaxation frequency, frel: When ζ is increased, both the low-frequency value, εr′(0), of εr′, and frel increase at all particle concentrations. We also analyze the effect of the product κa, where a is the particle radius and κ is the reciprocal Debye length: higher κa values correspond to larger εr′(0) and lower frel. Finally, the model is compared to previously reported experimental data: it is found that the qualitative agreement is excellent both concerning εr′(0) and frel. Possible improvements of the theory, particularly the inclusion of a dynamic Stern layer, are suggested.
Chain-length-dependent change in the structure of self-assembled monolayers of n-alkanethiols on Au(111) probed by broad-bandwidth sum frequency generation spectroscopy
Authors: Nishi Naoya , Hobara Daisuke , Yamamoto Masahiro , Kakiuchi Takashi
Published: January 2003

The structure of the self-assembled monolayers (SAMs) of n-alkanethiols [CH3(CH2)nSH, n=3–11, 13–15, 17] on Au(111) has been studied using broad-bandwidth sum frequency generation spectroscopy. Sum-frequency vibrational spectra show three pronounced CH3 vibrational modes for all alkanethiol investigated, indicating that the commonly accepted picture that the alkyl chain for the long-chain alkanethiol SAMs has the all-trans conformation applies even to the short chain SAMs. The chain-length dependence of the ratio of the intensity for the CH3 symmetric vibrational mode to that for the CH3 asymmetric mode clearly shows the odd–even effect due to the difference in the direction of methyl group for SAMs with odd and even n, also supporting that the alkyl chain of SAMs has the all-trans conformation. An analysis of the vibrational intensities with respect to the angle between the main axis of the methyl group and the surface normal reveals that the structure of the alkanethiol SAMs gradually changes with n.
Solvated electron in (H2O)20− and (H2O)21− clusters: A theoretical study
Authors: Khan Arshad
Published: January 2003

The dodecahedral (H2O)20− and (H2O)21− clusters are studied by applying the Becke-3-parameter density functional theory and Lee–Yang–Parr correlation functional. The geometry optimizations are carried out with 6-31G* basis set followed by single-point calculations for energy and charge distribution values with 6-311++G** basis set. While the structures of these clusters are very similar to their neutral counterparts, the charge distributions are significantly different. In the dodecahedral (H2O)20− cluster with an empty cavity, the −1 charge is distributed almost evenly among the half of the water molecules (10) on the cage surface. However, in a filled dodecahedral (H2O)21− cluster, the −1 charge is almost entirely localized unto the water molecule in the cavity. The calculated electron binding energies for the (H2O)20− and (H2O)21− clusters are 0.805 and 1.12 eV, respectively, and the stabilization energies relative to monomers and separated electron are 202 and 214 kcal/mol, respectively.
Usefulness of the Colle–Salvetti model for the treatment of the nondynamic correlation
Authors: Sancho-Garcı́a J. C. , Moscardó F.
Published: January 2003

In this work, the behavior of the Colle–Salvetti correlation functional is examined for strongly correlated systems with non-negligible nondynamic effects. Used with an appropriate multideterminantal wave function, it is able to reproduce accurately previous multireference coupled-cluster results for the problem of the automerization of cyclobutadiene, as well as to provide the correct energetical profiles for diatomic molecules under dissociation. The results confirm the current quality of the functional for complicated chemical problems, in spite of the fact that the functional does not satisfy some known exact properties.
Change in the temperature dependence of segmental dynamics in deeply supercooled polycarbonate
Authors: Thurau Courtney T. , Ediger M. D.
Published: January 2003

The equilibrium and nonequilibrium segmental dynamics of bisphenol-A-polycarbonate (PC) have been investigated near the glass transition by studying the rotational and translational diffusion of probe molecules in the polymer matrix. The temperature dependence of equilibrium dynamics was studied from 149 to 124 °C. We report a change in the temperature dependence of equilibrium molecular motion near 134 °C. Below this temperature, the activation energy of both the translational diffusion coefficient DT and the rotational correlation time τc decreases by nearly a factor of 3. This change is not caused by the transition to the nonequilibrium glassy state, but occurs in equilibrium. Additionally, we present evidence that the equilibrium dynamics of PC are spatially heterogeneous. Translational diffusion of rubrene shows an enhancement of 2.5 decades over what would be expected in a homogeneous system at Tg and the mean-square displacement of tetracene translation is not linear with time at low temperatures. In the nonequilibrium glassy state, differences in the physical aging behavior of rotational and translational observables suggest that physical aging dynamics are spatially heterogeneous. During isothermal aging, regions of faster mobility initially age towards equilibrium faster than regions of slower mobility.
Equation of state for hard Gaussian overlap fluids
Authors: de Miguel Enrique , Martı́n del Rı́o Elvira
Published: January 2003

The thermodynamic properties of hard Gaussian overlap fluids have been studied by computer simulation using constant-pressure Monte Carlo techniques for various molecular elongations κ in the range 3⩽κ⩽15. The work reported here concentrates on the equation of state and the Helmholtz free energy for the isotropic and nematic phases. Several theoretical approaches, based on the decoupling approximation, are considered and their predictions are compared with the simulation results. According to our results, none of these approximations yields a fully satisfactory description of the isotropic phase. In the nematic phase, the simple Parsons–Lee approximation is the only approach that yields results in quantitative agreement with simulation data for all elongations.
Stokes–Einstein relations and the fluctuation-dissipation theorem in a supercooled colloidal fluid
Authors: Bonn Daniel , Kegel Willem K.
Published: January 2003

The Stokes–Einstein (SE) relation is a form of the fluctuation-dissipation theorem (FDT), and relates the diffusion coefficient of colloidal particles to the viscosity via the thermal energy kBT. We study the diffusion coefficient and viscosity of concentrated hard-sphere colloidal model systems in the frequency domain. We show that for these metastable fluid systems strong deviations from the SE relation occur, contrary to predictions of mode coupling theory. Using the FDT, these deviations can be quantified by an effective temperature, Teff. The deviation Teff/T−1 exhibits power-law behavior over several decades in frequency.
AlN/diamond heterojunction diodes
Authors: Miskys C. R. , Garrido J. A. , Nebel C. E. , Hermann M. , Ambacher O. , Eickhoff M. , Stutzmann M.
Published: January 2003

An aluminum nitride/diamond p–n heterojunction has been realized by plasma-induced molecular-beam epitaxy growth of AlN on (100) diamond. The epitaxial nature of this heterojunction has been confirmed by high-resolution x-ray diffraction. The silicon-doped AlN film (n-type) on the natural boron-doped (p-type) diamond substrate formed a heterobipolar diode with good rectifying properties and surprisingly efficient light emission in the spectral range from 2.7 to 4.8 eV under forward bias. Results concerning the structural, electrical, and optical characterization of the AlN/diamond heterojunction are reported in this letter.
Breaking of rotational symmetry in a swirling jet experiment
Authors: Loiseleux Thomas , Chomaz Jean-Marc
Published: January 2003

In this experimental investigation, the dynamics of symmetry-breaking instabilities in swirling jets is analyzed for swirl parameters S in the pre-breakdown range 0⩽S⩽Sc, where Sc=1.3 is the critical swirl value for the appearance of vortex breakdown determined by Billant, Chomaz, and Huerre [J. Fluid Mech. 376, 183 (1998)]. As S is increased, three distinct dynamical regimes have been identified in the streamwise region extending to the end of the potential core. In the low swirl range S<0.6, the evolution is governed by the same instability mechanisms as in a nonswirling jet. The shear in axial direction generates axisymmetric vortex rings at a Strouhal number independent of the swirl S. As S increases, the amplitude of the axisymmetric mode decreases in magnitude. Concurrently, co-rotating streamwise vortices form in the braids connecting the rings due to a secondary instability mechanism. The advection by the mean rotation of these secondary structures generates an azimuthal wave propagating cyclonically when compared to the imposed rotation, at a phase velocity proportional to swirl. When swirl reaches the transitional swirl level S∼0.6, no azimuthal or standing wave is observed, and the swirling jet is completely dominated by the development of the axisymmetric mode into ring vortices. In the intermediate swirl range 0.6<S⩽1, vortex rings form concurrently with several interacting helical cyclonic waves of azimuthal wave number 2. The mean phase velocity of the resulting propagating wave increases at a constant rate with swirl, and much more rapidly than in the low swirl regime. In this swirl range, azimuthal and axisymmetric deformations are of comparable high levels. In the high swirl range 1<S<1.3, another step toward complexity is reached, and there is a strong interaction between the azimuthal waves and the ringlike structures. The most striking feature of this flow regime is the emergence of a bending mode m=1 propagating with a high negative phase velocity.
Thermal convection below a conducting lid of variable extent: Heat flow scalings and two-dimensional, infinite Prandtl number numerical simulations
Authors: Lenardic A. , Moresi L.
Published: January 2003

Theoretical heat flow scalings are presented for free thermal convection occurring below a conducting lid. Cases in which the lid covers the full extent of the convecting fluid and in which the lid has a variable lateral extent are treated. The scaling predictions are tested against a suite of two-dimensional numerical simulations that solve the full mathematical equations describing infinite Prandtl number thermal convection occurring below a conducting lid. The scaling predictions and simulation results show reasonably good agreement for Rayleigh numbers greater than 107. The scaling predictions are also tested against previous numerical simulations of finite Prandtl number thermal convection below a laterally uniform lid. Scaling predictions and simulations results again show reasonable agreement.
Random spin–orbit coupling and spin relaxation in symmetric quantum wells
Authors: Sherman E. Ya.
Published: January 2003

The effective “spin–orbit” field acting upon spins of carriers in two-dimensional electronic structures (the Rashba field) arises due to the spatial asymmetry of the system. It will be shown in this letter that even in quantum wells with perfectly symmetric environment, a random Rashba field arises due to fluctuations of concentration of dopant ions. The magnitude of the field, its correlation function, and electron spin relaxation rate in this field are presented.
Interaction between Ekman pumping and the centrifugal instability in Taylor–Couette flow
Authors: Czarny Olivier , Serre Eric , Bontoux Patrick , Lueptow Richard M.
Published: January 2003

The endwalls in a Taylor–Couette cell introduce adjacent boundary layers that interact with the centrifugal instability. We investigate the interaction between the endwall Ekman layers and the Taylor vortices near transition from nonvortical to vortical flow via direct numerical simulation using a spectral method. We consider a radius ratio of η=0.75 in a short annulus having a length-to-gap ratio of Γ=6. To analyze the nature of the interaction between the vortices and the endwall layers, three endwall boundary conditions were considered: fixed endwalls, endwalls rotating with the inner cylinder, and stress-free endwalls. Below the critical Taylor number, endwall vortices for rotating endwalls are more than twice the strength of the vortices for fixed endwalls. This trend continues well above the transition to vortical flow, consistent with a simple force balance analysis near the endwalls. Stress-free endwalls result in endwall vortices that are similar in strength to those for rotating endwalls above the critical Taylor number. The endwall conditions significantly change the bifurcation diagram based on the radial velocity near the center of the annulus. For stress-free endwall conditions, the bifurcation is quite sharp, although only one fork of the bifurcation results unless the initial conditions are specifically set to favor the other fork. For rotating and fixed endwalls, there is a continuous transition from a featureless flow to a vortical flow due to the endwall vortices.
Surface acoustic wave applications of lithium niobate thin films
Authors: Lee T.-C. , Lee J.-T. , Robert M. A. , Wang S. , Rabson T. A.
Published: January 2003

A technique combining metalorganic decomposition and rf sputtering is used to grow lithium niobate (LiNbO3) thin films on diamond/silicon substrates, and surface acoustic wave (SAW) filters are fabricated by depositing interdigital transducers onto the multilayer LiNbO3/diamond/silicon structures. Microwave characterization is achieved by using a network analyzer. Evidence is found for SAW propagation in these structures. These experimental findings agree with theoretical predictions.
Nearly total spin polarization in La2/3Sr1/3MnO3 from tunneling experiments
Authors: Bowen M. , Bibes M. , Barthélémy A. , Contour J.-P. , Anane A. , Lemaı̂tre Y. , Fert A.
Published: January 2003

We have performed magnetotransport measurements on La2/3Sr1/3MnO3/SrTiO3/La2/3Sr1/3MnO3 magnetic tunnel junctions. A magnetoresistance ratio of more than 1800% is obtained at 4 K, from which we infer an electrode spin polarization of at least 95%. This result strongly underscores the half-metallic nature of mixed-valence manganites and demonstrates their capability as a spin analyzer. The magnetoresistance extends up to temperatures of more than 270 K. We argue that these improvements over most previous works may result from optimizing the patterning process for oxide heterostructures.
Controlling the surface enhanced Raman effect via the nanoshell geometry
Authors: Jackson J. B. , Westcott S. L. , Hirsch L. R. , West J. L. , Halas N. J.
Published: January 2003

Systematic variation of the internal geometry of a dielectric core-metal shell nanoparticle allows the local electromagnetic field at the nanoparticle surface to be precisely controlled. The strength of the field as a function of core and shell dimension is measured by monitoring the surface enhanced Raman scattering (SERS) response of nonresonant molecular adsorbates (para-mercaptoaniline) bound to the nanoparticle surface. The SERS enhancement appears to be directly and exclusively due to nanoparticle geometry. Effective SERS enhancements of 106 are observable in aqueous solution, which correspond to absolute enhancements of 1012 when reabsorption of Raman emission by nearby nanoparticles is taken into account.
Inverted top-emitting organic light-emitting diodes using sputter-deposited anodes
Authors: Dobbertin T. , Kroeger M. , Heithecker D. , Schneider D. , Metzdorf D. , Neuner H. , Becker E. , Johannes H.-H. , Kowalsky W.
Published: January 2003

We demonstrate vacuum-sublimed topside-emitting inverted organic light-emitting diodes (IOLEDs) employing low-power radio-frequency magnetron sputter-deposited indium tin oxide (ITO) anodes. The device introduces a two-step sputtering sequence to reduce damage incurred by the sputtering process, paired with a buffer- and hole-transporting material Pentacene. Systematic optimization of the organic growth sequence focused on device performance characterized by current and luminous efficiencies, suggest the incorporation of rather thick Pentacene layers. The optimized thickness is obtained as a trade-off between light absorption and protective properties of Pentacene. The optically and electrically undoped organic multilayer devices capped with 90-nm ITO exhibit high current efficiencies of 3.9 cd/A at a raised luminance level of 1.500 cd/m2, combined with luminous efficiencies of 0.7 lm/W. The inverted configuration allows for integration of organic light-emitting diodes (OLEDs) with preferentially used n-channel field-effect transistors for driver backplanes in active matrix OLED displays.
Transmission electron microscopy measurements of the injection distances in nanocrystal-based memories
Authors: Assayag G. Ben , Bonafos C. , Carrada M. , Claverie A. , Normand P. , Tsoukalas D.
Published: January 2003

The characteristics of nonvolatile memories making use of Si nanocrystals as charge storage elements buried in the gate oxide of regular metal–oxide–semiconductor transistors strongly depend on the distances between the nanocrystals and two electrodes, the channel and the gate. In this letter, we compare two transmission electron microscopy methods that can be used to extract such distances. We demonstrate by using image simulations that conventional electron microscopy under out-of-Bragg and strongly underfocused conditions is the fastest and most efficient technique to be used for routine measurements at a subnanometer resolution. Finally, we show that the injection oxide thickness of nanocrystal devices obtained by low-energy Si implantation into thin SiO2 layers and subsequent annealing can be precisely tuned from 8 to 5 nm by adjusting the implantation energy from 0.65 to 2 keV.
High-efficiency screen-printed silicon ribbon solar cells by effective defect passivation and rapid thermal processing
Authors: Rohatgi Ajeet , Jeong Ji-Weon
Published: January 2003

A conversion efficiency of 15.9% has been achieved on low-cost edge-defined film-fed grown silicon ribbon solar cells. This represents an improvement over the previously reported efficiencies for silicon ribbon solar cells with manufacturable screen-printed contacts and single layer silicon nitride (SiNx) antireflection coating. Two separate rapid thermal processing cycles with fast ramp-up and cooling rates contributed to the enhancement in cell efficiency. The fast ramp-up rate improved the quality of back surface field and contacts; and a short firing time with a fast cooling rate improved contacts and the SiNx-induced hydrogen passivation of defects, resulting in bulk lifetime enhancement from ∼2 to ∼50 μs.
Interface properties of thermally oxidized n-GaN metal–oxide–semiconductor capacitors
Authors: Nakano Yoshitaka , Jimbo Takashi
Published: January 2003

We report on the interface properties of thermally oxidized n-GaN metal–oxide–semiconductor capacitors fabricated on sapphire substrates. 100-nm-thick β-Ga2O3 was grown by dry oxidation at 880 °C for 5 h. From secondary ion mass spectrometry measurements, an intermediate Ga oxynitride layer with graded compositions is clearly observed at the β-Ga2O3/GaN interface. Capacitance–voltage measurements show a deep depletion feature and a low interface state density of ∼5.5×1010 eV−1 cm−2. Additionally, no discrete interface traps can be detected by deep-level transient spectroscopic measurements. These results indicate that the surface Fermi level is unpinned at the β-Ga2O3/GaN interface, which may be associated with the presence of the interfacial Ga oxynitride layer.
Optimization of cubic GaN growth by metalorganic chemical vapor deposition based on residual strain relaxation
Authors: Feng Z. H. , Yang H. , Zheng X. H. , Fu Y. , Sun Y. P. , Shen X. M. , Wang Y. T.
Published: January 2003

The reduction of residual strain in cubic GaN growth by inserting a thermoannealing process is investigated. It is found that the epilayer with smaller tensile strain is subject to a wider optimal “growth window.” Based on this process, we obtain the high-quality GaN film of pure cubic phase with the thickness of 4 μm by metalorganic chemical vapor deposition. The photoluminescence spectrum at room temperature shows the thick GaN layer has a near-band emission peak with a full width at half maximum of 42 meV which confirms its high crystal quality, further supported by the x-ray (002) diffraction measurement. A simplified model is demonstrated to interpret this strain effect on the growth process.
Increased efficiency in vertically segregated thin-film conjugated polymer blends for light-emitting diodes
Authors: Corcoran N. , Arias A. C. , Kim J. S. , MacKenzie J. D. , Friend R. H.
Published: January 2003

The effect of film morphology on the performance of conjugated polymer-blend light-emitting diodes (LEDs) has been investigated. Vertically segregated structures have been fabricated by varying the spinning conditions and solvents used so that phase separation normal to the substrate is induced. External quantum efficiencies show that LEDs made with vertically segregated structures are between 25% and 100% more efficient than laterally segregated LEDs, depending on the scale of lateral phase separation.
Capillary pinch-off in inviscid fluids
Authors: Leppinen David , Lister John R.
Published: January 2003

The axisymmetric pinch-off of an inviscid drop of density ρ1 immersed in an ambient inviscid fluid of density ρ2 is examined over a range of the density ratio D=ρ2/ρ1. For moderate values of D, time-dependent simulations based on a boundary-integral representation show that inviscid pinch-off is asymptotically self-similar with both radial and axial length scales decreasing like τ2/3 and velocities increasing like τ−1/3, where τ is the time to pinch-off. The similarity form is independent of initial conditions for a given value of D. The similarity equations are solved directly using a modified Newton’s method and continuation on D to obtain a branch of similarity solutions for 0⩽D⩽11.8. All solutions have a double-cone interfacial shape with one of the cones folding back over the other in such a way that its internal angle is greater than 90°. Bernoulli suction due to a rapid internal jet from the narrow cone into the folded-back cone plays a significant role near pinching. The similarity solutions are linearly stable for 0⩽D⩽6.2 and unstable to an oscillatory instability for D⩾6.2. Oscillatory behavior is also seen in the approach to self-similarity in the time-dependent calculations. Further instabilities are found as D increases and the steady solution branch is lost at a stationary bifurcation at D=11.8.
Giant anisotropic magnetostriction in Pr0.5Sr0.5MnO3
Authors: Mahendiran R. , R. Ibarra M. , Marquina C. , Garcia-Landa B. , Morellon L. , Maignan A. , Raveau B. , Arulraj A. , Rao C. N. R.
Published: January 2003

We show that the polycrystalline perovskite antiferromagnet Pr0.5Sr0.5MnO3 exhibits a giant anisotropic magnetostriction (λt=1.5×10−3 at T=25 K and H=14.2 T) contrary to much smaller λt (<0.1×10−3) found in most other three-dimensional manganites. The value of λt decreases rapidly as the Néel temperature is approached from below, but an unusually high value of λt is also found below the ferromagnetic Curie temperature. We suggest that the magnetic-field-induced antiferromagnetic-to-ferromagnetic transition is accompanied by a structural transition from orthorhombic to tetragonal symmetry and attribute the giant anisotropic effect to the preferential growth of the orbital disordered tetragonal (ferromagnetic) domains along the field direction in the eg-dx2−y2 orbital ordered orthorhombic (antiferromagnetic) matrix.
Emission of an intense electron beam from a ceramic honeycomb
Authors: Friedman M. , Myers M. , Hegeler F. , Swanekamp S. B. , Sethian J. D. , Ludeking L.
Published: January 2003

Inserting a slab of honeycomb ceramic in front of the emitting surface of a large-area cathode improves the electron beam emission uniformity, decreases the beam current rise and fall times, and maintains a more constant diode impedance. Moreover, changing the cathode material from velvet to carbon fiber achieved a more robust cathode that starts to emit at a higher electric field without a degradation in beam uniformity. In addition, an 80% reduction in the postshot diode pressure was also observed when gamma alumina was deposited on the ceramic. A possible explanation is that reabsorption and recycling of adsorbed gases takes place.
Formation mechanism of TiO2 nanotubes
Authors: Yao B. D. , Chan Y. F. , Zhang X. Y. , Zhang W. F. , Yang Z. Y. , Wang N.
Published: January 2003

Transmission electron microscopic observation showed that TiO2 nanotubes synthesized via a simple hydrothermal chemical process formed a crystalline structure with open-ended and multiwall morphologies. Unlike multiwalled carbon nanotubes, the TiO2 nanotube walls were not seamless. During alkali treatment, crystalline TiO2 raw material underwent delamination in the alkali solution to produce single-layer TiO2 sheets. TiO2 nanotubes were formed by rolling up the single-layer TiO2 sheets with a rolling-up vector of [001] and attracting other sheets to surround the tubes.
Spin-exchange optical pumping of high-density xenon-129
Authors: Mortuza Muhammad G. , Anala Satyanarayana , Pavlovskaya Galina E. , Dieken Todd J. , Meersmann Thomas
Published: January 2003

Gas mixtures with high xenon densities are explored for continuous flow spin-exchange optical pumping. It is shown that the Xe-NMR129 signal increases significantly with increasing xenon partial pressures up to about 200 kPa, despite a decreasing spin-polarization. Comparison of the rubidium infrared D2 emission with the xenon polarization demonstrates that radiation quenching by molecular nitrogen is of no substantial benefit for the pumping process at xenon pressures above 100 kPa. This reflects a diminished importance of spin-depolarization by radiation trapping due to the increased significance of spin-relaxation by rubidium-xenon collisions at high xenon densities. A quantitative expression for this effect is provided.
Phonon dispersion curves in KOD-doped ice observed by neutron scattering
Authors: Fukazawa Hiroshi , Ikeda Susumu , Oguro Mitsugu , Bennington Stephen M. , Mae Shinji
Published: January 2003

We measured the inelastic neutron scattering (INS) of a single crystal of KOD-doped D2O ice, and investigated the dispersion curves in a proton-ordered phase of ice Ih (ice XI) and ice Ih. The intensity maps of the INS show that ice XI and ice Ih have two phonon dispersion curves in 50–65 and 72–90 meV, which assigned to the librational vibrations of water molecules. The results indicate that the phonon dispersion curves caused by the collective motions of protons exist in ice, and that ice Ih has small domains with proton-ordered arrangements.
Arrhenius viscosity in fragile liquids due to non-Newtonian effects
Authors: Lacks Daniel J.
Published: January 2003

Nonequilibrium molecular dynamics simulations are carried out for a liquid undergoing shear flow. Upon cooling at constant shear rate, the temperature dependence of the viscosity changes from faster-than-Arrhenius to Arrhenius: this change is analogous to a fragile-to-strong transition. An energy landscape analysis shows that this change in the temperature dependence of the viscosity occurs because the region of the energy landscape visited by the system becomes nearly temperature-independent.
Pharmacokinetic and pharmacodynamic interaction between grapefruit juice and halofantrine
Authors: Charbit Beny , Becquemont Laurent , Lepère Bénédicte , Peytavin Gilles , Funck‐Brentano Christian
Published: January 2003

Background

Halofantrine, an antimalarial drug that prolongs the QT interval, is metabolized into N‐debutyl‐halofantrine by cytochrome P450 (CYP) 3A4. Grapefruit juice increases the bioavailability of several orally administered CYP3A4 substrates by inhibiting CYP3A4 at the enterocyte level and could therefore increase the risk of halofantrine‐induced QT interval prolongation. We studied the effect of grapefruit juice on halofantrine bioavailability and on QT interval prolongation associated with its oral administration.

Methods

Twelve healthy male and female volunteers received 500 mg of halofantrine with 250 mL of water, orange juice, or grapefruit juice (250 mL once a day of regular strength for 3 days and once at 12 hours before halofantrine administration), in a random order, during a crossover study. Plasma pharmacokinetics of halofantrine and N‐debutyl‐halofantrine and QTc interval duration were studied during the following 168 hours.

Results

Compared with water, grapefruit juice increased halofantrine area under the plasma concentration versus time curve (AUC) and peak plasma concentration by 2.8‐fold ± 1.5‐fold (P < .0001) and 3.2‐fold ± 1.3‐fold (P < .0001), respectively. There was a concomitant 2.4‐fold ± 1.6‐fold decrease in N‐debutyl‐halofantrine AUC (P < .01) but no significant change in halofantrine elimination half‐life. Maximum QTc interval prolongation increased from 17 ± 6 ms when halofantrine was administered with water to 31 ± 12 ms when it was administered with grapefruit juice (P < .0005). Multiple regression analysis showed that QTc interval prolongation was better correlated with halofantrine (partial r = 0.432; P < .0001) than with N‐debutyl‐halofantrine (partial r = 0.117; P < .01) concentrations. There was no significant difference between the water and orange juice study periods.

Conclusions

Grapefruit juice increases halofantrine bioavailability and halofantrine‐induced QT interval prolongation. Grapefruit juice should be contraindicated during administration of halofantrine.

Clinical Pharmacology & Therapeutics (2002) 72, 514–523; doi: 10.1067/mcp.2002.128148
Bidirectional synaptic plasticity in the cerebellum-like mammalian dorsal cochlear nucleus
Authors: Fujino Kiyohiro , Oertel Donata
Published: January 2003

The dorsal cochlear nucleus integrates acoustic with multimodal sensory inputs from widespread areas of the brain. Multimodal inputs are brought to spiny dendrites of fusiform and cartwheel cells in the molecular layer by parallel fibers through synapses that are subject to long-term potentiation and long-term depression. Acoustic cues are brought to smooth dendrites of fusiform cells in the deep layer by auditory nerve fibers through synapses that do not show plasticity. Plasticity requires Ca
2+
-induced Ca
2+
release; its sensitivity to antagonists of
N
-methyl-
d
-aspartate and metabotropic glutamate receptors differs in fusiform and cartwheel cells.
Store-operated calcium channel regulates the chemotactic behavior of ascidian sperm
Authors: Yoshida Manabu , Ishikawa Makiko , Izumi Hiroko , De Santis Rosaria , Morisawa Masaaki
Published: January 2003

The sperm-activating and -attracting factor released from the eggs of the ascidians
Ciona intestinalis
and
Ciona savignyi
requires extracellular Ca
2+
for activating sperm motility and eliciting chemotactic behavior of the activated sperm toward the egg. Here, we show that modulators of the store-operated Ca
2+
channel, SK&F96365, Ni
2+
, 2-aminoethoxydiphenylborane, and thapsigargin inhibit the chemotactic behavior of the ascidian sperm; on the other hand, blockers of voltage-dependent Ca
2+
channels did not inhibit the chemotaxis, even though they inhibited the sperm activation operated by voltage-dependent Ca
2+
channels. The blockers of store-operated Ca
2+
channels also inhibited the asymmetrical flagellar beating and turning movements of the ascidian sperm, which are typical signs of sperm chemotaxis. Depletion of internal Ca
2+
stores by thapsigargin induced capacitative Ca
2+
entry into the sperm, which was blocked by SK&F96365. These results suggest that the intracellular Ca
2+
concentration increase through the store-operated Ca
2+
channels induces asymmetrical flagellar movements to establish the chemotactic behavior of the sperm.
Genetically engineered stem rust resistance in barley using the
Rpg1
gene
Authors: Horvath Henriette , Rostoks Nils , Brueggeman Robert , Steffenson Brian , von Wettstein Diter , Kleinhofs Andris
Published: January 2003

The stem-rust-susceptible barley cv. Golden Promise was transformed by
Agrobacterium
-mediated transformation of immature zygotic embryos with the
Rpg1
genomic clone of cv. Morex containing a 520-bp 5′ promoter region, 4,919-bp gene region, and 547-bp 3′ nontranscribed sequence. Representatives of 42 transgenic barley lines obtained were characterized for their seedling infection response to pathotype Pgt-MCC of the stem rust fungus
Puccinia graminis
f. sp.
tritici
. Golden Promise was converted from a highly susceptible cultivar into a highly resistant one by transformation with the dominant
Rpg1
gene. A single copy of the gene was sufficient to confer resistance against stem rust, and progenies from several transformants segregated in a 3:1 ratio for resistance/susceptibility as expected for Mendelian inheritance. These results unequivocally demonstrate that the DNA segment isolated by map-based cloning is the functional
Rpg1
gene for stem rust, resistance. One of the remarkable aspects about the transformants is that they exhibit a higher level of resistance than the original sources of
Rpg1
(cvs. Chevron and Peatland). In most cases, the Golden Promise transformants exhibited a highly resistant reaction where no visible sign of infection was evident. Hypersensitive necrotic “fleck” reactions were also observed, but less frequently. With both infection types, pathogen sporulation was prevented. Southern blot and RT-PCR analysis revealed that neither
Rpg1
gene copy number nor expression levels could account for the increased resistance observed in Golden Promise transformants. Nevertheless, this research demonstrates that stem-rust-susceptible barley can be made resistant by transformation with the cloned
Rpg1
gene.
Formation and character of an ancient 19-m ice cover and underlying trapped brine in an “ice-sealed” east Antarctic lake
Authors: Doran Peter T. , Fritsen Christian H. , McKay Christopher P. , Priscu John C. , Adams Edward E.
Published: January 2003

Lake Vida, one of the largest lakes in the McMurdo Dry Valleys of Antarctica, was previously believed to be shallow (<10 m) and frozen to its bed year-round. New ice-core analysis and temperature data show that beneath 19 m of ice is a water column composed of a NaCl brine with a salinity seven times that of seawater that remains liquid below −10°C. The ice cover thickens at both its base and surface, sealing concentrated brine beneath. The ice cover is stabilized by a negative feedback between ice growth and the freezing-point depression of the brine. The ice cover contains frozen microbial mats throughout that are viable after thawing and has a history that extends to at least 2,800
14
C years B.P., suggesting that the brine has been isolated from the atmosphere for as long. To our knowledge, Lake Vida has the thickest subaerial lake ice cover recorded and may represent a previously undiscovered end-member lacustrine ecosystem on Earth.
Amyloid β-protein (Aβ) assembly: Aβ40 and Aβ42 oligomerize through distinct pathways
Authors: Bitan Gal , Kirkitadze Marina D. , Lomakin Aleksey , Vollers Sabrina S. , Benedek George B. , Teplow David B.
Published: January 2003

Amyloid β-protein (Aβ) is linked to neuronal injury and death in Alzheimer's disease (AD). Of particular relevance for elucidating the role of Aβ in AD is new evidence that oligomeric forms of Aβ are potent neurotoxins that play a major role in neurodegeneration and the strong association of the 42-residue form of Aβ, Aβ42, with the disease. Detailed knowledge of the structure and assembly dynamics of Aβ thus is important for the development of properly targeted AD therapeutics. Recently, we have shown that Aβ oligomers can be cross-linked efficiently, and their relative abundances quantified, by using the technique of photo-induced cross-linking of unmodified proteins (PICUP). Here, PICUP, size-exclusion chromatography, dynamic light scattering, circular dichroism spectroscopy, and electron microscopy have been combined to elucidate fundamental features of the early assembly of Aβ40 and Aβ42. Carefully prepared aggregate-free Aβ40 existed as monomers, dimers, trimers, and tetramers, in rapid equilibrium. In contrast, Aβ42 preferentially formed pentamer/hexamer units (paranuclei) that assembled further to form beaded superstructures similar to early protofibrils. Addition of Ile-41 to Aβ40 was sufficient to induce formation of paranuclei, but the presence of Ala-42 was required for their further association. These data demonstrate that Aβ42 assembly involves formation of several distinct transient structures that gradually rearrange into protofibrils. The strong etiologic association of Aβ42 with AD may thus be a result of assemblies formed at the earliest stages of peptide oligomerization.
Inhibiting HIV-1 infection in human T cells by lentiviral-mediated delivery of small interfering RNA against CCR5
Authors: Qin Xiao-Feng , An Dong Sung , Chen Irvin S. Y. , Baltimore David
Published: January 2003

Double-stranded RNAs ≈21 nucleotides long [small interfering RNA (siRNA)] are recognized as powerful reagents to reduce the expression of specific genes. To use them as reagents to protect cells against viral infection, effective methods for introducing siRNAs into primary cells are required. Here, we describe success in constructing a lentivirus-based vector to introduce siRNAs against the HIV-1 coreceptor, CCR5, into human peripheral blood T lymphocytes. With high-titer vector stocks, >40% of the peripheral blood T lymphocytes could be transduced, and the expression of a potent CCR5-siRNA resulted in up to 10-fold inhibition of CCR5 expression on the cell surface over a period of 2 weeks in the absence of selection. In contrast, the expression of another major HIV-1 coreceptor, CXCR4, was not affected. Importantly, blocking CCR5 expression by siRNAs provided a substantial protection for the lymphocyte populations from CCR5-tropic HIV-1 virus infection, dropping infected cells by 3- to 7-fold; only a minimal effect on infection by a CXCR4-tropic virus was observed. Thus, our studies demonstrate the feasibility and potential of lentiviral vector-mediated delivery of siRNAs as a general means of intracellular immunization for the treatment of HIV-1 and other viral diseases.
Flexibility and molecular recognition in the immune system
Authors: Jimenez Ralph , Salazar Georgina , Baldridge Kim K. , Romesberg Floyd E.
Published: January 2003

Photon echo spectroscopy has been used to measure the response of three antibody-binding sites to perturbation from electronic excitation of a bound antigen, fluorescein. The three antibodies show motions that range in time scale from tens of femtoseconds to nanoseconds. Relative to the others, one antibody, 4-4-20, possesses a rigid binding site that likely results from a short and inflexible heavy chain complementarity-determining region 3 (HCDR3) loop and a critical Tyr that acts as a “molecular splint,” rigidifying the antigen across its most flexible internal degree of freedom. The remaining two antibodies, 34F10 and 40G4, despite being generated against the same antigen, possess binding sites that are considerably more flexible. The more flexible combining sites likely result from longer HCDR3 loops and a deletion in the light chain complementarity-determining region 1 (LCDR1) that removes the critical Tyr residue. The binding site flexibilities may result in varying mechanisms of antigen recognition including lock-and-key, induced-fit, and conformational selection.
UDP-Glc:glycoprotein glucosyltransferase recognizes structured and solvent accessible hydrophobic patches in molten globule-like folding intermediates
Authors: Caramelo Julio J. , Castro Olga A. , Alonso Leonardo G. , de Prat-Gay Gonzalo , Parodi Armando J.
Published: January 2003

Protein folding in the cell involves the action of different molecular chaperones and folding-facilitating enzymes. In the endoplasmic reticulum (ER), the folding status of glycoproteins is stringently controlled by a glucosyltranferase enzyme (GT) that creates monoglucosylated structures recognized by ER resident lectins (calnexin/calreticulin, CNX/CRT). GT serves as a folding sensor because it only glucosylates misfolded or partly folded glycoproteins. Nevertheless, the molecular mechanism behind this recognition process remains largely unknown. In this paper we explore the structural determinants for GT recognition by using a single domain model protein. For this purpose we used a family of chemically glycosylated proteins derived from chymotrypsin inhibitor-2 as GT substrates. Structural characterization of species showing higher glucose acceptor capacity suggests that GT recognizes solvent accessible hydrophobic patches in molten globule-like conformers mimicking intermediate folding stages of nascent glycoproteins. It was further confirmed that BiP (binding protein, a chaperone of the heat shock protein 70 family) preferentially recognized neoglycoproteins displaying extended conformations, thus providing a molecular rationale for the sequential BiP-CNX/CRT interaction with folding glycoproteins observed
in vivo
.
Hepatoblastomas in Mice in the US National Toxicology Program (NTP) Studies
Authors: Turusov Vladimir S. , Tor Mikinori , Sills Robert C. , Willson Gabrielle A. , Herbert Ronald A. , Hailey James R. , Haseman Joseph K. , Boorman Gary A.
Published: January 2003

Over the last 8 years, a 5-fold increase in the incidence of mice with spontaneous hepatoblastomas and a moderate increase in the incidence of chemically induced hepatoblastomas in B6C3F1 mice occurred in 2-year NTP studies compared to the previous 7 years. There was a positive association between an increased incidence of mice with hepatoblastoma and an increased incidence of mice with hepatocellular tumors in the treated mice. The rate of pulmonary metastases for hepatoblastoma was similar to that of pulmonary metastasis for hepatocellular carcinomas. Although a variety of chemicals caused an increased incidence of mice with hepatoblastoma, there was no apparent association between a specificchemical structure or a biological class of compounds and their capacity to induce hepatoblastomas. Hepatoblastomas frequently arose within hepatocellular carcinomas or adenoma s and were induced by the same compound s that induced hepatocellular neoplasms. Therefore, it seems reasonable to combine the incidence of mice with hepatoblastomas and the incidence of mice with hepatocellular carcinomas in hazard identification studies.
Music education in Taiwan: the dynamics and dilemmas of globalization, localization and sinophilia
Authors: Ho Wai‐Chung , Law Wing‐Wah
Published: January 2003

The article examines the complicated interplay of globalization, localization and sinophilia that, along with associated social changes, determines reforms in Taiwanese music education today. Students are expected not only to be tri‐lingual, in so far as they are obliged to learn English, Mandarin and a local language, such as Southern Fujianese, Hakka or an aboriginal dialect, but they must also become tri‐cultural with respect to western classical music, traditional Chinese music and indigenous Taiwanese music. The findings of our questionnaires suggest that the processes of globalization, localization and sinophilia are unequal determinants in the transformation of Taiwanese music education. The survey, which was conducted among 2596 primary and secondary school students (1309 from Tainan and 1287 from Taipei) between May and November 2000, shows that schools are less inclined than the Taiwanese government to promote local music. Students in the survey much prefer western classical and popular music to local Taiwanese and traditional Chinese styles. They show little interest in promoting Chinese culture or in singing Taiwan's national anthem. By examining the major concerns of music education from the perspective of the complex dynamics of globalization, this study illuminates the tensions and dilemmas facing the music curriculum of Taiwan today.
Differential expression and upregulation of interleukin‐1α, interleukin‐1β and interleukin‐6 by freshly isolated human small intestinal epithelial cells
Authors: Madrigal-Estebas Laura , Doherty Derek G. , O′Donoghue Diarmuid P. , Feighery Conleth , O′Farrelly Cliona
Published: January 2003

Background: Small intestinal epithelial cells (SIEC) may contribute to local immune regulation.

Aim: To examine production of interleukin (IL)‐1α , IL‐1β and IL‐6 by freshly isolated human SIEC.

Methods: IL‐1α and IL‐1β mRNA in epithelial layers (EL) prepared from small intestine and in intestinal epithelial cell (EC) lines were examined by reverse transcription‐polymerase chain reaction. IL‐1α, IL‐1β and IL‐6 protein expression by SIEC was examined by flow cytometry before and after activation with lipopolysaccharide and epithelial growth factor.

Results: IL‐1α and IL‐1β mRNA was detected in EL and EC lines. Background expression of IL‐1α and IL‐1β protein by SIEC was observed, which did not increase even following activation. IL‐6 protein was expressed by SIEC, in a proportion that increased in two out of three samples following activation.

Conclusions: IL‐6 expression and the presence of IL‐1α and IL‐1β mRNA suggest a role for SIEC in the regulation of local inflammation.
Ten‐Year Follow‐Up of a Patient with Metastatic Ewing′s Sarcomaof the Pelvis
Authors: Ashford Robert U. , McCloskey Eugene V. , Purohit O. Prakash , Ingram Christine E. , Grimer Robert J. , Coleman Robert E.
Published: January 2003

Patient: We report a 32‐year‐old women with a pelvic Ewing′s sarcoma, who developed skeletal metastases within 20 months
of diagnosis but following treatment remains disease‐free at 10 years.

Discussion: Ewing′s sarcoma is a highly malignant tumour of bone. Presentation of a pelvic tumour over the age of 30 years
is extremely rare and associated with a poor prognosis. Early recurrence is also associated with an extremely grave prognosis.
In our patient there was little or no response to salvage chemotherapy, but, against the odds, remission was induced
with pamidronate and palliative radiotherapy to some but not all sites of disease.This remission has been maintained without
additional therapy for a further 5 years.