bluuebunny/crossref_metadata_2025 huggingface dataset:
Evasion of apoptosis by DNA viruses
Authors: CUFF SIMONE , RUBY JANET
Published: June 2007

Apoptosis is a form of cell death distinct from necrosis which plays an important role in processes such as homoeostasis and the elimination of damaged cells. It can be triggered by a variety of stimuli including DNA damage and cytotoxic T lymphocyte activity,1 both of which may be induced in the course of a viral infection. Initially, induction of apoptosis may occur through pathways which have also been shown to be activated on disturbance of the cell cycle or damage to cellular DNA.2 At later time points during the course of infection, apoptosis can also be triggered by cytokines and immune effector cells.1 Apoptosis of the host cell before the completion of the viral replication cycle may limit the number of progeny and the spread of infection. The importance of apoptosis as an antiviral defence is illustrated by the presence of multiple pathways for apoptosis induction and inhibition in both the host and virus. In this review, the inhibition of apoptosis is described in adenovirus and poxvirus infection. These examples illustrate two of the divergent paths by which viruses may avoid the apoptotic response.
Regulation of host cell function by glycosylphosphatidylinositols of the parasitic protozoa
Authors: SCHOFIELD LOUIS , TACHADO SOUVENIR D
Published: June 2007

Antigenic variation, antigenic drift, molecular mimicry, intracellular localization and sequestration in privileged sites are important mechanisms of immune evasion by infectious organisms. Added to this however is the phenomenon by which pathogens deliberately regulate host cell function by the production of glycolipids with agonistic or antagonistic signal transduction capacity. Such pro‐active glycolipids are often pathogenicity factors, but they also serve as immunomodulators and immunosuppressants, and these activities may serve as mechanisms of immune evasion. Here we review glycosylphosphatidylinositols and related structures, a novel class of glycolipid common to eukaryotic parasites and their hosts, which recent studies suggest may play a role in immune evasion and immunosuppression by regulating host cell function via the activation or suppression of endogenous host signalling pathways.
Resonance energy transfer from a fluorescent dye molecule to plasmon and electron-hole excitations of a metal nanoparticle
Authors: Swathi R. S. , Sebastian K. L.
Published: June 2007

The authors study the distance dependence of the rate of electronic excitation energy transfer from a dye molecule to a metal nanoparticle. Using the spherical jellium model, they evaluate the rates corresponding to the excitation of l=1, 2, and 3 modes of the nanoparticle. The calculation takes into account both the electron-hole pair and the plasmon excitations of the nanoparticle. The rate follows conventional R−6 dependence at large distances while small deviations from this behavior are observed at shorter distances. Within the framework of the jellium model, it is not possible to attribute the experimentally observed d−4 dependence of the rate to energy transfer to plasmons or electron-hole pair excitations.
Quasi-incoherent propagation in waveguide arrays
Authors: Szameit Alexander , Dreisow Felix , Hartung Holger , Nolte Stefan , Tünnermann Andreas , Lederer Falk
Published: June 2007

In this letter a “quasi-incoherent” propagation in waveguide arrays is theoretically derived and experimentally verified. Depending on the initial light distribution the propagation in a waveguide array after multiwaveguide excitation exhibits an interference pattern or not. For the experimental verification the waveguide array is realized in OH rich fused silica by femtosecond laser direct writing. The light propagation within the array is directly visible due to the fluorescence of the created color centers. A precise excitation of different waveguides is achieved using a phase grating.
An ab initio study of the CH3I photodissociation. I. Potential energy surfaces
Authors: Alekseyev Aleksey B. , Liebermann Heinz-Peter , Buenker Robert J. , Yurchenko Sergei N.
Published: June 2007

The multireference spin-orbit (SO) configuration interaction (CI) method in its Λ-S contracted SO-CI version is employed to calculate two-dimensional potential energy surfaces for the ground and low-lying excited states of CH3I relevant to the photodissociation process in its A absorption band. The computed equilibrium geometry for the X̃A1 ground state, as well as vibrational frequencies for the ν2 umbrella and ν3 symmetric stretch modes, are found to be in good agreement with available experimental data. The Q0+3 state converging to the excited I(P1∕2o2) limit is found to possess a shallow minimum of 850cm−1 strongly shifted to larger internuclear distances (RC–I≈6.5a0) relative to the ground state. This makes a commonly employed single-exponent approximation for analysis of the CH3I fragmentation dynamics unsuitable. The 4E(A13) state dissociating to the same atomic limit is calculated to lie too high in the Franck-Condon region to have any significant impact on the A-band absorption. The computed vertical excitation energies for the Q13, Q0+3, and Q1 states indicate that the A-band spectrum must lie approximately between 33 000 and 44300cm−1, i.e., between 225 and 300nm. This result is in very good agreement with the experimental findings. The lowest Rydberg states are computed to lie at ⩾49000cm−1 and correspond to the …a12n3a1(6sI) leading configuration. They are responsible for the vacuum ultraviolet absorption lines found experimentally beyond the A-band spectrum at 201.1nm (49722cm−1) and higher.
An ab initio study of the CH3I photodissociation. II. Transition moments and vibrational state control of the I* quantum yields
Authors: Alekseyev Aleksey B. , Liebermann Heinz-Peter , Buenker Robert J.
Published: June 2007

Multireference spin-orbit configuration interaction calculations of transition moments from the X̃A1 ground state to the 3Q0+, Q13, and Q1 excited states responsible for the A absorption band of CH3I are reported and employed for an analysis of the photofragmentation in this system. Contrary to what is usually assumed, the Q0+3(A1), Q13(E), and Q1(E)←X̃A1 transition moments are found to be strongly dependent on the C–I fragmentation coordinate. The sign of this dependence is opposite for the parallel and perpendicular transitions, which opens an opportunity for vibrational state control of the photodissociation product yields. The computed absorption intensity distribution and the I* quantum yield as a function of excitation energy are analyzed in comparison with existing experimental data, and good agreement between theory and experiment is found. It is predicted that significantly higher I* quantum yield values (>0.9) may be achieved when vibrationally hot CH3I molecules are excited in the appropriate spectral range. It is shown that vibrational state control of the I*∕I branching ratio in the alkyl (hydrogen) iodide photodissociation has an electronic rather than a dynamic nature: Due to a different electron density distribution at various molecular geometries, one achieves a more efficient excitation of a particular fragmentation channel rather than influences the dynamics of the decay process.
Gas diffusion in glasses via a probabilistic molecular dynamics
Authors: Willmore Frank T. , Wang Xiao-Yan , Sanchez Isaac C.
Published: June 2007

A probabilistic protocol which makes possible the calculation of the diffusivity of light gases in amorphous materials from limited Monte Carlo and molecular dynamics data is presented. Diffusion coefficients are calculated for helium and methane in polystyrene, and for helium, neon, and methane in three pairs of polysulfone isomers. Results include diffusion coefficients as small as 10−9cm2∕s and are in good agreement with results obtained from traditional molecular dynamics and with available experimental data.
Long-range surface plasmon-polariton waveguides and devices in lithium niobate
Authors: Berini Pierre , Charbonneau Robert , Jetté-Charbonneau Stéphanie , Lahoud Nancy , Mattiussi Greg
Published: June 2007

Long-range surface plasmon-polariton waveguides and devices based on a thin narrow Au stripe buried in z-cut LiNbO3 claddings and designed for operation at free-space optical wavelengths near 1550nm are described and discussed. Parallel or antiparallel crystal orientations for the claddings lead to phase modulation or intensity modulation via mode cutoff, respectively. Theoretical results are given for straight waveguides, curved waveguides, and Bragg gratings in symmetric claddings, and for straight waveguides in electro-optically induced asymmetric claddings. The main theoretical findings are that 1dB∕mm of attenuation (or less) is achievable using Au stripes of reasonable dimensions (0.5–1μm wide, 20–40nm thick), that low overlap losses (<1dB) to large and small modes are achievable for the same stripe thickness, that radii of curvature in the range of 10–30mm are required for stripes having a moderate (10−3) confinement, that first order gratings having a reflectance of 0.9 and a bandwidth of 0.75nm are achievable and that they are electro-optically tunable over a 2.9nm range, and that an electro-optically induced index asymmetry of about 4×10−4 is sufficient to cut off weakly (10−4) confined modes. Structures were fabricated by direct wafer bonding and thinning to form the lithium niobate claddings. The measured optical insertion loss of 2mm long waveguides varied from 10to17dB, which are somewhat higher than theoretical expectations. Low frequency electro-optic mode cutoff measurements produced extinction ratios near 12dB and a linear transfer characteristic, thus demonstrating intensity modulation via this mechanism. The results suggest that bulk values for the optical and electro-optic properties of the LiNbO3 claddings have been retained.
Spectral analysis of synthesized nanocrystalline aggregates of Er3+:Y2O3
Authors: Gruber John B. , Sardar Dhiraj K. , Nash Kelly L. , Yow Raylon M. , Gorski Waldemar , Zhang Maogen
Published: June 2007

The absorption and fluorescence spectra of nanocrystalline aggregates of Y2O3 doped with Er3+ are reported between 8K and room temperature. The nanocrystalline particles were synthesized from a homogenous solution of the metal ions and urea at elevated temperatures in order to control the precipitation of the mixed hydroxides by a slow uniform reaction throughout the solution. The morphology of the calcinated materials revealed uniformly spherical aggregates 200nm or less depending on the ratio of the metal ions in the initial solution. Spectra obtained from these particles were analyzed in detail for the crystal-field splitting of the LJ2S+1 multiplet manifolds of Er3+(4f11) including the ground-state manifold I15∕24, and excited manifolds I9∕24, F9∕24, S3∕24, H11∕22, F7∕24, F5∕24, and F3∕24. Fluorescence lifetimes and results from an analysis of the intensities of manifold-to-manifold transitions are also reported. The sharp-line absorption and emission spectra are comparable to spectra reported earlier for Er3+:Y2O3 grown as large single crystals by a flame fusion method. The results described in the present study suggest that the simple, inexpensive method of preparation that is reported will lead to further investigation of these nanocrystals for their optical properties, especially in the near infrared region of the spectrum.
Autocorrelation functions of a fluid of molecules interacting through steeply repulsive and attractive forces
Authors: Rickayzen G. , Heyes D. M.
Published: June 2007

A new method is presented for an extension of Enskog’s approximation for the evaluation of the autocorrelation functions of a fluid, and this approach is used to evaluate these functions when the interaction between the molecules includes both steeply repulsive and steeply attractive forces. Consequently the correlation functions depend upon the temperature in a nontrivial way. As an example, the method is applied to calculate the velocity and force autocorrelation functions of a fluid when the molecules interact through the specific potential, V(r)=4ε[(σ∕r)2n−(σ∕r)n] when the parameter n is large. There is a relationship between this model and the “sticky sphere” one which is exploited in the theoretical computations. The results obtained from the theory are compared with molecular dynamics simulation for n=72 and 144 and for a range of temperatures from T=ε∕kB down to ε∕3kB. The two approaches agree very well for a range of state points, especially at short times. At later times the theory predicts a more oscillatory behavior than the simulation especially at very low reduced temperatures.
Berry phase approach to longitudinal dipole moments of infinite chains in electronic-structure methods with local basis sets
Authors: Kudin Konstantin N. , Car Roberto , Resta Raffaele
Published: June 2007

The authors provide a reformulation of the modern theory of polarization for one-dimensional stereoregular polymers, at the level of the single determinant Hartree-Fock and Kohn-Sham methods within a basis set of local orbitals. By starting with localization of one-electron orbitals, their approach naturally arrives to the Berry phases of Bloch orbitals. Then they describe a novel numerical algorithm for evaluation of longitudinal dipole moments, computationally more convenient than those presently implemented within the local basis periodic codes. This method is based on the straightforward evaluation of the usual direct space dipole matrix elements between local orbitals, as well as overlap matrices between wave functions at two neighboring k points of the reciprocal space mesh. The practical behavior of the algorithm and its convergence properties with respect to the k-point mesh density are illustrated in benchmark calculations for water chains and fluorinated trans-polyacetylene.
Simulation of electromechanical responses of ferroelectric ceramics driven by combined alternating electrical and mechanical loadings
Authors: Lo Veng-cheong , Chung Winnie Wing-yee , Chow Simon Ching-kin
Published: June 2007

The experimental result on dielectric and mechanical properties of PbZrxTi1−xO3 driven by combined alternating electrical and mechanical loadings in various phase differences has been obtained by Zhou et al. [J. Appl. Phys. 96, 6634 (2004)]. This paper presents the numerical simulation of this result using a two-dimensional four state Potts model. In this model, there are four different dipole orientations to reflect the coexistence of 90° and 180° domain walls. The coupling between the electrical and mechanical responses is implemented by the presence of two different ferroelastic strain states which are associated to the four different dipole orientations. The interactions of these dipoles and strains together with the mechanical energy density are incorporated into the system Hamiltonian. The enhanced and reduced electromechanical responses when the electric field and the compressive stress are out of phase and in phase, respectively, are reproduced by our model.
The influence of fluorosurfactants on the flexoelectro-optic properties of a chiral nematic liquid crystal
Authors: Morris S. M. , Cho Y. , Pivnenko M. N. , Coles H. J.
Published: June 2007

In this paper, we demonstrate an increase in the flexoelectro-optic response of a hypertwisted chiral nematic liquid crystal with the addition of a low concentration (0.7wt%) of a fluorosurfactant so as to reduce the anchoring energy at the liquid crystal∕substrate boundary. Specifically, the results show that the tilt angle per unit of applied electric field is increased by approximately 20% whereas the response time is decreased by approximately 30%. An increase in the concentration of the fluorosurfactant agent does not appear to greatly affect the magnitude of the tilt angle for a given field strength but does result in a further reduction of the response time.
Method for solution of the interaction between superconductor and permanent magnet
Authors: Yang Yong , Zheng Xiaojing
Published: June 2007

A method for calculating the interaction between a superconductor and a permanent magnet for various initial cooling conditions is proposed. The exact solutions are obtained for the point magnetic dipole over a flat nonideal type-II superconductor. The distinction of the method from the frozen-image method is in the using of the vertical and horizontal movement images that create the same magnetic field distribution outside the superconductor as the trapped fluxes do when the permanent magnet moves vertically and horizontally, respectively. The vertical and lateral forces that are obtained by the method agree with the previous measurements qualitatively. Comparing with the frozen-image method, the method can give the lateral force in zero field cooling and the hysteresis in the vertical and lateral forces. The two characteristics cannot be obtained by the frozen-image method. In this case, the vertical stiffness during vertical traverses and the lateral and cross stiffnesses during lateral traverses are obtained by the analytic expressions of vertical and lateral forces. Those stiffness expressions can reflect the effect of cooling conditions and movement history.
Periodic unit cell reconstruction of porous media: Application to open-cell aluminum foams
Authors: Perrot Camille , Panneton Raymond , Olny Xavier
Published: June 2007

In this article, the issue of reconstructing an idealized periodic unit cell (PUC) to represent a porous medium is examined by means of microcomputed tomography (μCT). Using μCT, three-dimensional images of open-cell foam are collected and used to characterize the representative parameters of its cellular morphology. These parameters are used in order to reconstruct the porous medium by means of an idealized PUC: a tetrakaidecahedron with ligaments of triangular cross sections, whose characteristic dimensions have been measured on the μCT images. The proposed reconstruction of the idealized PUC is applied to four aluminum foams. The averaged macroscopic properties of the foams (open porosity and thermal characteristic length) are deduced from their respective PUC model and compared to experimental measurements and literature data. Good correlations are obtained. For each of the foams, this provides a parameterized idealized periodic unit cell on which the partial differential equations governing sound dissipation and propagation in foams can be solved with a view to studying the microphysical basis of the acoustical macrobehavior.
Anisotropic optical phonon scattering of holes in cubic semiconductors
Authors: Dolguikh M. V. , Peale R. E.
Published: June 2007

The formula for the nonpolar optical phonon scattering rate of holes in cubic semiconductors is obtained in the case of strong valence band anisotropy. The deformation potential approximation is used. A three-band, 6×6, k∙p Luttinger-Kohn representation includes states belonging to the heavy, light, and split-off bands. Mixing with the latter causes strong anisotropy in the transition matrix elements as well as in the density of final states. The derived formula is recommended for silicon, where inter- and intravalence-band scattering rates are much more strongly anisotropic and have significantly different values than those estimated from the usual two-band 4×4, “warped spheres” approximation that neglects the split-off band. Results for the more isotropic case of germanium are presented for comparison.
White organic light-emitting devices with mixed interfaces between light emitting layers
Authors: Lee Young Gu , Kee In Seo , Shim Hong Shik , Ko Ick Hwan , Lee Soonil , Koh Ken Ha
Published: June 2007

White organic light-emitting devices with mixed interfaces between emitting layers (MI-EML WOLEDs) showed luminance and efficiency as large as 26213cd∕m2 and 9.85cd∕A. Efficiencies of MI-EML WOLEDs were about 1.5 times better than those of conventional three-EML WOLEDs for luminance of 1000–5000cd∕m2, and their half-decay lifetime showed 3.1 times improvement. Note that if the authors operate typical active-matrix mobile-phone displays based on combination of WOLED and color filters to produce standard white emission for high definition televisions and illumination sources, MI-EML WOLEDs will have advantages of 25% less power consumption and 2.8 times longer lifetime over conventional three-EML WOLEDs.
Two color, low intensity photocurrent feedback for local photocurrent spectroscopy
Authors: Brezna W. , Strasser G. , Smoliner J.
Published: June 2007

In this work, we introduce a two color, low intensity photocurrent feedback method for photocurrent spectroscopy utilizing an atomic force microscope (AFM). In most applications, measurements with weak optical excitations are not feasible with an AFM because the powerful AFM feedback laser severely disturbs the measurements. Therefore, we have developed a feedback system based on the pressure dependent Schottky barrier height at the tip-sample interface. The versatility of the new feedback system is demonstrated by recording high resolution photocurrent spectra on GaAs∕InAs heterostructures.
Resistance maps for a submicron Hall electrosensor in the diffusive regime
Authors: Papp G. , Peeters F. M.
Published: June 2007

The response of a mesoscopic Hall cross to a local potential barrier is calculated from which we derive two-dimensional resistance maps. At zero magnetic field a double butterfly Hall resistance pattern arises in the Hall cross that is attributed to barrier-induced inhomogeneous current flow. Small, i.e., nonquantizing magnetic fields smoothen out the two wings of the butterfly into a single elongated feature. The longitudinal resistance pattern shows the strongest changes in the current leads leading to two well separated (by the cross area) bumps. Symmetry properties are found for the resistance maps (Hall and longitudinal) with respect to the position of the local introduced potential barrier.
Radially distributed Ni and Co nanowire arrays
Authors: Sanz R. , Vazquez M. , Pirota K. R. , Hernández-Velez M.
Published: June 2007

Ni and Co nanowire arrays are prepared by electroplating filling of self-assembled radial nanopores in cylindrical anodic alumina, and their magnetic behavior is compared with that of nanowire arrays with the same geometry parameters in a planar configuration. Diameter and length of radially oriented nanowires are 35nm and 2μm, respectively. They are arranged in hexagonal symmetry with lattice constant of 105nm within a 5μm thick porous microtubular alumina shell with an outer diameter of 100μm. The magnetic response of such arrays has been investigated for magnetic field applied along parallel and perpendicular directions. The azimuthal distribution of radial nanowires in the cylindrical configuration grants a different magnetic response in comparison with that of arrays in conventional planar configuration. The study of hysteresis loops reveals a clear radial anisotropy for Ni nanowire arrays owing to the shape anisotropy of individual nanowires. However, for Co nanowire arrays a nearly isotropic behavior is observed, which is ascribed to the near balance between circular magnetocrystalline anisotropy and radial shape anisotropy of individual nanowires.
A time-resolved microwave conductivity study of the optoelectronic processes in TiO2∣In2S3∣CuInS2 heterojunctions
Authors: Savenije Tom J. , Nanu Marian , Schoonman Joop , Goossens Albert
Published: June 2007

Photoinduced interfacial charge carrier generation, separation, trapping, and recombination in TiO2∣In2S3∣CuInS2 cells have been studied with time-resolved microwave conductivity (TRMC). Single layer, double layer, and complete triple layer configurations have been studied. Selective electronic excitation in one of the components is accomplished by using monochromatic pulsed laser excitation. In bare CuInS2 films and in TiO2∣CuInS2 double layers, photoinduced charge carriers recombine on a subnanosecond time scale. This fast recombination slows down significantly when an In2S3 buffer layer is applied between TiO2 and CuInS2. In that case, the charge separation lifetime increases by more than one order of magnitude. A superlinear dependence of the TRMC signals on the incident laser intensity is observed for the triple layer configuration, which indicates saturation of electron traps in In2S3 or hole traps in CuInS2. Furthermore, TRMC signals from TiO2∣In2S3∣CuInS2 triple junctions and those from In2S3∣CuInS2 double layers are identical, which shows that charge carrier separation exclusively takes place at the In2S3∣CuInS2 interface.
Impact of free-surface passivation on silicon on insulator buried interface properties by pseudotransistor characterization
Authors: Hamaide G. , Allibert F. , Hovel H. , Cristoloveanu S.
Published: June 2007

It has been reported previously [N. Bresson et al., Proceedings of the ECS Seventh International Symposium on Silicon-on-Insulator Technology and Devices, 2005 (unpublished), pp. 317–324; F Allibert et al., Proceedings of the IEEE International SOI Conference, Honolulu, HI, 2002 (unpublished)] that the film thickness strongly impacts the parameters extracted using the pseudo metal oxide semiconductor field effect transistor (pseudo-MOSFET) with the usual FET equations [S. Cristoloveanu and S. S. Li, Electrical Characterization of SOI Materials and Devices (Kluwer, Boston, MA, 1995)]. In this paper, we investigate the influence of top free-surface states on the pseudo-MOSFET characteristics by comparing passivated versus nonpassivated samples. The parameters of concern, investigated here, are carrier mobility, density of interface states, threshold (VT), and flatband (VFB) voltages. Based on systematic measurements and existing models [H. J. Hovel, Solid-State Electron. 47, 1311 (2003)] for VT, VFB, and subthreshold slope, we show how the free-surface impact increases as the film thickness is reduced. Comparison of extracted results with simulated curves demonstrates that, in state-of-the-art ultrathin silicon on insulator structures, the preparation and properties of the free surface are no longer negligible.
Domain wall release in “hard” piezoelectric under continuous large amplitude ac excitation
Authors: Gao Yongkang , Uchino Kenji , Viehland Dwight
Published: June 2007

Systematic investigation of large amplitude ac excitation effects on the polarization–electric-field (P-E) and strain–electric-field (ε-E) characteristics of both “hard” and “soft” Pb(Zr,Ti)O3 ceramics was performed. Upon ac excitation, a gradual disappearance of the shift on P-E response along the E axis (Eint) was observed for the hard piezoelectric; however, no such change was observed for the soft one. With increasing ac excitation cycle number, for a hard piezoelectric the internal dipolar field and mechanical quality factor Qm decrease by following an exponential time law, whereas the electromechanical and dielectric properties increase with significant deviation from the time law. It is proposed that additional domain release mechanism may exist for hard piezoelectric, besides the decrease of internal dipolar field upon continuous ac excitation.
Improved electrical properties in AlGaN∕GaN heterostructures using AlN∕GaN superlattice as a quasi-AlGaN barrier
Authors: Kawakami Y. , Nakajima A. , Shen X. Q. , Piao G. , Shimizu M. , Okumura H.
Published: June 2007

The authors report the electrical properties of two-dimensional electron gas (2DEG) in AlGaN∕GaN heterostructures using AlN∕GaN superlattices working as a quasi-AlGaN barrier layer. It is found that the electrical properties (2DEG mobility and sheet carrier density) in the quasi-AlGaN∕GaN heterostructure are greatly improved compared to those in the conventional alloy-AlGaN∕GaN one at the high Al composition more than 0.35. The improved 2DEG properties result in the reduction of the sheet resistance to as low as 172Ω∕□, which is extremely important for the high power and high frequency device application. Theoretical calculations clearly indicate that the quasi-AlGaN barrier plays an important role in enhancing the confinement of the carrier at the quasi-AlGaN∕GaN interface.
Correlation of nitrogen related traps in InGaAsN with solar cell properties
Authors: Khan Aurangzeb , Kurtz Sarah R. , Prasad S. , Johnston S. W. , Gou Jihua
Published: June 2007

The thermal annealing of nitrogen related traps in p-type InGaAsN and GaAsN is investigated by deep level transient spectroscopy (DLTS). Upon annealing, an apparent recovery of the photovoltaic properties correlates with changes in the DLTS data observed for InGaAsN and GaAsN diodes and solar cells, revealing that a nitrogen related E1 (EC−0.20eV) center has an important role in governing the solar cell performance. The large electron capture cross section (∼8.9×10−15cm2) of this center indicates that this defect may act as an efficient recombination center. Therefore, its complete removal by annealing or by some other process is essential for the high performance of GaInAsN solar cells. The internal quantum efficiency data were modeled to quantify the change in material properties associated with this improvement upon annealing. Annealed cells with indium impurity (InGaAsN) show a slightly higher photoresponse, which could be due to low scattering caused by In–N pair formation after annealing.
Strained single-crystal Al2O3 grown layer by layer on Nb (110) thin films
Authors: Welander Paul B. , Eckstein James N.
Published: June 2007

The authors report on the growth of single-crystal Al2O3 thin films on Nb (110) surfaces. Niobium is grown on α-Al2O3 (112¯0), followed by the evaporation of Al in an O2 background. Initially, Al2O3 grows layer by layer with hexagonal symmetry indicating either α-Al2O3 (0001) or γ-Al2O3 (111). Diffraction measurements show that the Al2O3 initially grows clamped to the Nb with tensile strain near 10%. This strain relaxes with further deposition and beyond about 50Å, the authors observe island growth. Despite the asymmetric misfit between Al2O3 and Nb, the strain is surprisingly isotropic. Josephson junctions employing epitaxial Al2O3 show low effective tunnel barriers and high leakage currents.
Optical nanometer-scale sensing of mechanical vibrations with a planar glass at critical angle
Authors: Micheletto Ruggero , Kawakami Yoichi , Hamamoto Katsumi
Published: June 2007

The authors have devised an optical multireflection system to detect nanometer-scale mechanical vibrations in a very simple and cost effective manner. The system is based on a planar glass, reflecting laser light internally a number of times in near critical angular conditions. Any small angular displacement results in an abrupt change of reflectivity. Monitoring the light at the exit of the device results in extremely high sensitivity to small mechanical vibrations. Calibrated tiny vibrations of 2.4nm were resolved corresponding to an angular shift of about 2×10−7rad.
Mode switching and beam steering in photonic crystal heterostructures implemented with vertical-cavity surface-emitting lasers
Authors: Lundeberg L. D. A. , Kapon E.
Published: June 2007

The authors demonstrate electrically controlled mode switching and beam steering in separate-contact photonic crystal heterostructures implemented with two-dimensional arrays of coupled vertical-cavity surface-emitting lasers. Two weakly coupled, lasing photonic crystal domains are switched in and out of mutual coherence by controlling the injected currents. Switching of the transverse lasing mode is accompanied by corresponding variations in the far-field pattern and the emission wavelength. Proper adjustment of the driving currents also allows steering of the beam of the ensemble of coupled lasers.
HgCdTe negative luminescence devices with high internal and external efficiencies in the midinfrared
Authors: Lindle J. R. , Bewley W. W. , Vurgaftman I. , Meyer J. R. , Thomas M. L. , Piquette E. C. , Edwall D. D. , Tennant W. E.
Published: June 2007

The authors report the fabrication and characterization of mid-IR HgCdTe negative luminescence (NL) devices grown on silicon substrates. Sensitive optical modulation measurements of the 5mm square array with ∼5.4μm cutoff and single-layer antireflection (AR) coating yield an internal NL efficiency of 98% at room temperature. This is the highest ever reported, and represents a factor-of-50 suppression of the blackbody emission. The corresponding external NL efficiency of 86% is consistent with the internal efficiency and the spectrally weighted reflectivity of 15%, which could be improved substantially through the incorporation of a state-of-the-art multilayer AR coating.
Vectorial electric field measurement using isotropic electro-optic crystals
Authors: Gaborit G. , Coutaz J.-L. , Duvillaret L.
Published: June 2007

The authors present a two-component electric field measurement using a single electro-optic crystal and a single laser probe beam. This vectorial electric field measurement based on polarization state modulation is possible using isotropic electro-optic crystals for which directions of the eigendielectric axes are directly linked to the direction of the applied electric field. The proposed method can be used either for continuous wave or single shot measurements as the two electric field components are measured simultaneously.
Observation of electric current induced by optically injected spin current
Authors: Cui Xiao-Dong , Shen Shun-Qing , Li Jian , Ji Yang , Ge Weikun , Zhang Fu-Chun
Published: June 2007

Linearly polarized light at normal incidence injects a spin current into a strip of two-dimensional electron gas with Rashba spin-orbit coupling. The authors report observation of an electric current when such light is shed on the vincinity of the junction in a crossbar-shaped InGaAs∕InAlAs quantum well Rashba system. The polarization dependence of this electric current was experimentally observed to be the same as that of the spin current. The authors attribute the observed electric current to the scattering of the optically injected spin current at the crossing.
Theoretical phase diagram of ultrathin films of incipient ferroelectrics
Authors: Akbarzadeh A. R. , Bellaiche L. , Íñiguez Jorge , Vanderbilt David
Published: June 2007

A first-principles-based scheme is used to compute the temperature-versus-misfit strain “Pertsev” phase diagram of ultrathin films of incipient ferroelectric KTaO3. The results suggest that, at variance with the bulk material, KTaO3 ultrathin films cannot be described as quantum paraelectrics. Rather, the behavior of the films is largely determined by surface/interface effects that favor ferroelectricity and the imperfect screening of the depolarizing fields. This leads to Pertsev phase diagrams that are qualitatively similar to those of normal ferroelectrics such as BaTiO3.
Anisotropic spin splitting of the electron ground state in InAs quantum dots
Authors: Aubry E. , Testelin C. , Bernardot F. , Chamarro M. , Lemaître A.
Published: June 2007

Photoinduced circular dichroism experiments in an oblique magnetic field allow measurements of Larmor precession frequencies, and so give a precise determination of the electron Landé g factor and its anisotropy in self-assembled InAs∕GaAs quantum dots emitting at 1.32eV. In good agreement with recent theoretical results, the authors measure ∣g⊥∣=0.397±0.003 and ∣g‖∣=0.18±0.02.
Rice-based mucosal vaccine as a global strategy for cold-chain- and needle-free vaccination
Authors: Nochi Tomonori , Takagi Hidenori , Yuki Yoshikazu , Yang Lijun , Masumura Takehiro , Mejima Mio , Nakanishi Ushio , Matsumura Akiko , Uozumi Akihiro , Hiroi Takachika , Morita Shigeto , Tanaka Kunisuke , Takaiwa Fumio , Kiyono Hiroshi
Published: June 2007

Capable of inducing antigen-specific immune responses in both systemic and mucosal compartments without the use of syringe and needle, mucosal vaccination is considered ideal for the global control of infectious diseases. In this study, we developed a rice-based oral vaccine expressing cholera toxin B subunit (CTB) under the control of the endosperm-specific expression promoter 2.3-kb glutelin
GluB-1
with codon usage optimization for expression in rice seed. An average of 30 μg of CTB per seed was stored in the protein bodies, which are storage organelles in rice. When mucosally fed, rice seeds expressing CTB were taken up by the M cells covering the Peyer's patches and induced CTB-specific serum IgG and mucosal IgA antibodies with neutralizing activity. When expressed in rice, CTB was protected from pepsin digestion
in vitro
. Rice-expressed CTB also remained stable and thus maintained immunogenicity at room temperature for >1.5 years, meaning that antigen-specific mucosal immune responses were induced at much lower doses than were necessary with purified recombinant CTB. Because they require neither refrigeration (cold-chain management) nor a needle, these rice-based mucosal vaccines offer a highly practical and cost-effective strategy for orally vaccinating large populations against mucosal infections, including those that may result from an act of bioterrorism.
Processes of
de novo
duplication of human α-globin genes
Authors: Lam Kwan-Wood G. , Jeffreys Alec J.
Published: June 2007

Ectopic recombination between repeated but nonallelic DNA sequences plays a major role in genome evolution, creating gene families and generating copy number variation and pathological rearrangements in human chromosomes. Previous studies on the α2- and α1-globin genes have shown that
de novo
deletions common in α
+
-thalassemics can be directly accessed in human DNA and provide an informative system for studying deletion dynamics and processes. However, nothing is known about the reciprocal products of ectopic recombination, namely gene duplications. We now show that molecules carrying three α-globin genes can be detected in human DNA by using physical enrichment plus an inverse PCR strategy. These
de novo
duplications are common in blood and sperm and appear to arise by two distinct mechanisms: meiotic exchanges between homologous chromosomes that generate a minority of sperm duplications, plus mitotic ectopic exchanges that occur in the soma and germ line and can show erratic fluctuations in frequency most likely caused by mutational mosaicism. The dynamics and processes of duplication are very similar to those of deletion, particularly for meiotic exchanges. This result suggests rearrangement pathways dominated by fully reciprocal ectopic exchange, with nonreciprocal pathways such as intramolecular recombination and single-strand annealing playing at best only a minor role in the generation of deletions. Finally, the high level of instability at the α-globin locus contrasts with the rarity in most populations of chromosomes carrying duplications or deletions, pointing to strong selective constraints that maintain α-globin gene copy number in human populations.
Different modes of stop codon restriction by the
Stylonychia
and
Paramecium
eRF1 translation termination factors
Authors: Lekomtsev Sergey , Kolosov Petr , Bidou Laure , Frolova Ludmila , Rousset Jean-Pierre , Kisselev Lev
Published: June 2007

In universal-code eukaryotes, a single-translation termination factor, eukaryote class-1 polypeptide release factor (eRF1), decodes the three stop codons: UAA, UAG, and UGA. In some ciliates, like
Stylonychia
and
Paramecium
, eRF1s exhibit UGA-only decoding specificity, whereas UAG and UAA are reassigned as sense codons. Because variant-code ciliates may have evolved from universal-code ancestor(s), structural features should exist in ciliate eRF1s that restrict their stop codon recognition. In omnipotent eRF1s, stop codon recognition is associated with the N-terminal domain of the protein. Using both
in vitro
and
in vivo
assays, we show here that chimeric molecules composed of the N-terminal domain of
Stylonychia
eRF1 fused to the core domain (MC domain) of human eRF1 retained specificity toward UGA; this unambiguously associates eRF1 stop codon specificity to the nature of its N-terminal domain. Functional analysis of eRF1 chimeras constructed by swapping ciliate N-terminal domain sequences with the matching ones from the human protein highlighted the crucial role of the tripeptide QFM in restricting
Stylonychia
eRF1 specificity toward UGA. Using the site-directed mutagenesis, we show that
Paramecium
eRF1 specificity toward UGA resides within the NIKS (amino acids 61–64) and YxCxxxF (amino acids 124–131) motifs. Thus, we establish that eRF1 from two different ciliates relies on different molecular mechanisms to achieve specificity toward the UGA stop codon. This finding suggests that eRF1 restriction of specificity to only UGA might have been an early event occurring in independent instances in ciliate evolutionary history, possibly facilitating the reassignment of UAG and UAA to sense codons.
Chimeric
Saccharomyces cerevisiae
Msh6 protein with an Msh3 mispair-binding domain combines properties of both proteins
Authors: Shell Scarlet S. , Putnam Christopher D. , Kolodner Richard D.
Published: June 2007

Msh2–Msh3 and Msh2–Msh6 are two partially redundant mispair-recognition complexes that initiate mismatch repair in eukaryotes. Crystal structures of the prokaryotic homolog MutS suggest the mechanism by which Msh6 interacts with mispairs because key mispair-contacting residues are conserved in these two proteins. Because Msh3 lacks these conserved residues, we constructed a series of mutants to investigate the requirements for mispair interaction by Msh3. We found that a chimeric protein in which the mispair-binding domain (MBD) of Msh6 was replaced by the equivalent domain of Msh3 was functional for mismatch repair. This chimera possessed the mispair-binding specificity of Msh3 and revealed that communication between the MBD and the ATPase domain is conserved between Msh2–Msh3 and Msh2–Msh6. Further, the chimeric protein retained Msh6-like properties with respect to genetic interactions with the MutL homologs and an Msh2 MBD deletion mutant, indicating that Msh3-like behaviors beyond mispair specificity are not features controlled by the MBD.
Fish diversity in the upper Paraná River basin: habitats, fisheries, management and conservation
Authors: Agostinho A. A. , Pelicice F. M. , Petry A. C. , Gomes L. C. , Júlio H. F.
Published: June 2007

The Paraná River is the second longest river in South America and the tenth largest river in the world in water discharge. The upper stretches are characterized by high human occupation and intense anthropogenic activities, and few areas are still in pristine conditions. Despite this, fish diversity is remarkably high in the upper Paraná River basin, and the existence of different habitats greatly influences fish biodiversity. Although most species are sedentary, migratory species are considered the most important, since they have historically sustained commercial and recreational fisheries. Recently, stocks of migratory species have diminished in many rivers due to overfishing and habitat modifications caused by dams. Impoundments have a long history in the basin and constitute the main source of impacts for both sedentary and migratory fish species. Government agencies have implemented management actions to mitigate the effects of damming on fish populations, which included fish stocking (using native and non-native species), the construction of transposition mechanisms and fishery control. However, their efficacy for conservation has been severely questioned and, in many instances, these actions have produced negative outcomes to biodiversity. The lack of studies and monitoring programs contributed to the uncritical adoption of some dubious management actions. Inevitably, management plans directed to conserve fish biodiversity in the basin need urgent revision.
Freshwater fishes of the Amazon River basin: their biodiversity, fisheries, and habitats
Authors: Junk Wolfgang J. , Soares Maria Gercilia Mota , Bayley Peter B.
Published: June 2007

Stretching more than seven million square kilometers, the Amazon River basin is the largest river basin in the world and discharges about one-sixth of all freshwater from the continents to the oceans of the world. The age of this ecosystem, its position near the equator and the enormous diversity of its aquatic habitats, have produced the most diverse fish fauna on the planet. About 2,500 fish species have already been described and it is estimated that more than 1,000 new species remain to be discovered. Knowledge concerning this multitude of fish species is still insufficient, which makes their management and protection difficult. About 50% of the species are thought to occur in the large rivers and connected floodplains and another 50% in headwater streams. Inland fisheries give rise to 450,000 t of fish each year and thus contribute substantially to the protein supply of local populations. However, despite their economic importance, these fisheries receive little attention from the respective governments. The fisheries are highly selective and several stocks of large species with high market value have been over fished. Fish culture is still in its infancy but its development is expected to provide high-quality species during periods of low supply. Over large areas, aquatic habitats are still in near-natural conditions because of the low densities of resident human populations. Nonetheless, over the last few decades, the pressure on aquatic ecosystems and habitats has steadily increased, mainly due to large-scale destruction of natural vegetation cover by agro-industries in the savanna belt (cerrado), small-scale agriculture in the Andean hill slopes, and logging in rain forests. These activities have placed aquatic biodiversity, including fishes, at serious risk. Many headwater species have restricted distributions and are therefore particularly vulnerable to large-scale environmental degradation. Moreover, the construction of large reservoirs for hydroelectric power generation has serious consequences for fish fauna. Currently, about 16.4% of the Amazon River basin is protected, and another 15.2% is under partial protection in indigenous reserves in Brazil. Another 9.1% will be implemented as reserves in the next 10 years in the Brazilian part of the basin. The formulation by the Amazonian countries of a coherent policy that integrates long-term management of the river basin with sustainable management of aquatic and wetland habitats, including their fauna and flora, is urgently needed.
Freshwater fishes of the Altiplano
Authors: Vila Irma , Pardo Rodrigo , Scott Sergio
Published: June 2007

Fisheries of the Altiplano, dating from 1500 to 2000 BC, are active in the Andean inter-montane plateau that extends from Ancash, Perú, to Antofagasta, Chile, at altitudes above 3600 m. The ancient and remote nature of these systems has merited the inclusion of many areas as National Parks and RAMSAR sites.

Among 58 native fish species, 45 belong to the killifish complex Orestias and the rest to the catfish complex Trichomycterus. The main fishery resources consist of “ispi”, Orestias ispi, with 32 175 (64.5%) metric tons and “karachi”, Orestias of the group agassii, with 455 metric tons (0.9%). The introduced fishes “silversides”, Odontesthes bonariensis, and “trouts”, Oncorhynchus mykiss, contribute 16 900 metric tons (33.9%) and 324 metric tons (0.7%) respectively.

Hydro-acoustic evaluations show a permanent diminution of the endemic Orestias. Lake species such as O. pentlandii “boga” and O. cuvieri “humanto” were important for their biogeographic relationships and were highly endemic. Native fishes are nowadays threatened by the salmonids, Oncorhynchus mykiss, Salvelinus namaycush, Salvelinus fontinalis and Salmo trutta, introduced since 1939. Later, the silverside Odontesthes bonariensis was introduced during 1955–1956.