bluuebunny/crossref_metadata_2025 huggingface dataset:
A site-selective in situ study of CO adsorption and desorption on Pt(355)
Authors: Tränkenschuh B. , Fritsche N. , Fuhrmann T. , Papp C. , Zhu J. F. , Denecke R. , Steinrück H.-P.
Published: February 2006

Using time-dependent high-resolution x-ray photoelectron spectroscopy at BESSY II, the adsorption and desorption processes of CO on stepped Pt(355)=Pt[5(111)×(111)] were investigated. From a quantitative analysis of C 1s data, the distribution of CO on the various adsorption sites can be determined continuously during adsorption and desorption. These unique data show that the terrace sites are only occupied when the step sites are almost saturated, even at temperatures as low as 130K. The coverage-dependent occupation of on-top and bridge adsorption sites on the (111) terraces of Pt(355) is found to differ from that on Pt(111), which is attributed to the finite width of the terraces and changes in adsorbate-adsorbate interactions. In particular, no long-range order of the adsorbate layer could be observed by low-energy electron diffraction. Further details are derived from sticking coefficient measurements using the method devised by King and Wells [Proc. R. Soc. London, Ser. A 339, 245 (1974)] and temperature-programmed desorption. The CO saturation coverage is found to be slightly smaller on the stepped surface as compared to that on Pt(111). The initial sticking coefficient has the same high value of 0.91 for both surfaces.
The role of temperature and density on the glass-transition dynamics of glass formers
Authors: Floudas G. , Mpoukouvalas K. , Papadopoulos P.
Published: February 2006

A correlation between the monomeric volume and the dynamic quantity EV*∕H*, used to provide a quantitative measure of the role of temperature and density on the dynamics, is demonstrated for a series of polymers and glass-forming liquids. We show that monomeric volume and local packing play a key role in controlling the value of this ratio and thus the dynamics associated with the glass temperature.
Theoretical study of properties of H bonds and intermolecular interactions in linear cis-,trans-cyclotriazane clusters (n=2–8)
Authors: Song Hua-Jie , Xiao He-Ming , Dong Hai-Shan
Published: February 2006

Our calculations based upon Becke’s three-parameter functional of density-functional theory (DFT) with the correlation of Lee, Yang, and Parr (B3LYP), natural bond orbital, and atoms in molecule indicate that in drastic contrast to most H-bonded systems, the anticooperative and cooperative effects coexist in the linear H-bonded cis-,trans (c,t)-cyclotriazane clusters (n=2–8). As cluster size increases, the properties along the H-bonded chains at trans-positions take on the unexpectedly anticooperative changes which are reflected in elongation of the N⋯H hydrogen bonds, frequency blueshift in the N–H stretching vibrations, decay in the n(N)→σ*(N–H) charge transfers, and weakening of strengths of the N⋯H bonds. And the cooperative changes in the corresponding properties for the cis- H-bonded chains are observed to be concurrent with the anticooperativities. The rise and fall in the n(N)→σ*(N–H) interactions cause increment and decrement in capacities of the clusters to concentrate electrons at the bond critical points of the N⋯H bonds, and thereby leading to the cooperative and the anticooperative changes especially in the N⋯H lengths and the N–H stretching frequencies. In terms of three-body symmetry-adapted perturbation theory (three-body SAPT), the first exchange nonadditivity plays a more important role in stabilizing trimer than the nonadditive induction. However, the dominance of the first exchange nonadditivity in three-body interaction unexpectedly triggers the anticooperative effect that counteracts the concurrent cooperative effect. According to the SAPT(DFT), which is a combination of SAPT with asymptotically corrected DFT, DFT/B3LYP is able to succeed in describing the electrostatic, exchange, and induction components, but fails to yield satisfactory interaction energies due to the fact that about 40% of short-range dispersion energy is neglected by the DFT, which is different from many H-bonded described well by the DFT. A quantum cluster equilibrium model illustrates that the c,t-cyclotriazane liquid phase exhibits a weak cooperative effect.
Photoinduced electron transfer from N,N-dimethylaniline to 7-amino Coumarins in protein-surfactant complex: Slowing down of electron transfer dynamics compared to micelles
Authors: Chakraborty Anjan , Seth Debabrata , Setua Palash , Sarkar Nilmoni
Published: February 2006

Photoinduced electron transfer from N,N-dimethylaniline to different Coumarin dyes has been investigated in dodecyl trimethyl ammonium bromide (DTAB) micelles and in Bovine serum albumin (BSA)-DTAB protein-surfactant complex using steady-state and picosecond time-resolved fluorescence spectroscopy. We observed a slower fluorescence quenching rate in the DTAB micelles and in the protein-surfactant complex as compared to that in pure acetonitrile solution. Moreover, the observed fluorescence quenching in BSA-DTAB complex was found to be slower than that in DTAB micelles. In the correlation of free-energy change with the fluorescence quenching constant we observed a deviation in the fluorescence quenching electron transfer rate for Coumarin 151 (C-151) from the normal Marcus curve. This observation is ascribed to the stronger interaction of C-151 with the surfactant molecules present in the micelles. This is evident from the slower translation diffusion (DL) of Coumarin 151 compared to other probe molecules.
Contrast improvement of organic light-emitting devices with Sm:Ag cathode
Authors: Lau K. C. , Xie W. F. , Sun H. Y. , Lee C. S. , Lee S. T.
Published: February 2006

Sm:Ag, easily fabricated via simple thermal evaporation, was investigated as a single-layer light-absorbing cathode to increase the contrast ratio of organic light-emitting devices (OLEDs). The performance of OLEDs with Sm:Ag cathode was found to be comparable to that of the traditional OLEDs with Mg:Ag cathode in terms of brightness, electroluminescence (EL) efficiency, and turn-on voltage. The maximum EL efficiency of the device with Sm:Ag black cathode is 2.72cd∕A at 15V, while the contrast ratio reaches 390:1 at 10V under 140 lx of ambient light, which is 8 times better than that of the traditional device. The lower EL efficiency and enhanced contrast are due to the reduced optical reflectance of Sm:Ag black cathode, which was calculated to be about 0.15.
Controlled surface-plasmon coupling in SiO2-coated gold nanochains for tunable nonlinear optical properties
Authors: Yang Yong , Nogami Masayuki , Shi Jianlin , Chen Hangrong , Ma Guohong , Tang Singhai
Published: February 2006

Linear chains of SiO2-coated Au nanoparticles, exhibiting large third-order nonlinearity at multiple wavelengths ranging from visible to near infrared, were successfully synthesized and self-assembled on glass substrates using a reduction of HAuCl4 and chemical surfactant modification. The optical absorption spectra peaking at 530, 620, 715, 830, and 1100nm wavelengths were measured to the transverse and longitudinal surface plasmon resonance modes of 2, 3, 4, and 5 Au particles, respectively. Greatly enhanced third-order nonlinear optical responses have been observed at multiple wavelengths.
Collective excitations in an ionic liquid
Authors: Urahata Sérgio M. , Ribeiro Mauro C. C.
Published: February 2006

Collective dynamics in a representative model of ionic liquids, namely, 1-butyl-3-methylimidazolium chloride, have been revealed by molecular dynamics simulation. Dispersion of energy excitation, ω versus k, of longitudinal acoustic (LA) and transverse acoustic (TA) modes was obtained in the wave vector range 0.17<k<1.40Å−1, which encompasses the main peak of the static structure factor S(k). Linear dispersion of acoustic modes is observed up to k∼0.7Å−1. Due to mixing between LA and TA modes, LA spectra display transverselike component, and vice versa. Due to anisotropy in short-time ionic dynamics, acoustic modes achieve distinct limiting ω values at high k when the cation displacement is projected either along the plane or perpendicular to the plane of the imidazolium ring. In charge current spectra, branch with negative dispersion of ω versus k is a signature of optic modes in the simulated ionic liquid. Conductivity κ estimated by using ionic diffusion coefficients in the Nernst-Einstein equation is higher than the actual κ calculated by integrating the charge current correlation function. From TA spectra, a wave vector dependent viscosity η(k) has been evaluated, whose low-k limit gives η in reasonable agreement with experimental data.
Ionic dimers in He droplets: Interaction potentials for Li2+–He,Na2+–He, and K2+–He and stability of the smaller clusters
Authors: Bodo E. , Yurtsever E. , Yurtsever M. , Gianturco F. A.
Published: February 2006

We present post Hartree-Fock calculations of the potential energy surfaces (PESs) for the ground electronic states of the three alkali dimer ions Li2+,Na2+, and K2+ interacting with neutral helium. The calculations were carried out for the frozen molecular equilibrium geometries and for an extensive range of the remaining two Jacobi coordinates, R and θ, for which a total of about 1000 points is generated for each surface. The corresponding raw data were then fitted numerically to produce analytic expressions for the three PESs, which were in turn employed to evaluate the bound states of the three trimers for their J=0 configurations: The final spatial features of such bound states are also discussed in detail. The possible behavior of additional systems with more helium atoms surrounding the ionic dopants is gleaned from further calculations on the structural stability of aggregates with up to six He atoms. The validity of a sum-of-potential approximation to yield realistic total energies of the smaller cluster is briefly discussed vis-a-vis the results from many-body calculations.
Hyper-Rayleigh scattering and hyper-Raman scattering of dye-adsorbed silver nanoparticles induced by a focused continuous-wave near-infrared laser
Authors: Itoh Tamitake , Ozaki Yukihiro , Yoshikawa Hiroyuki , Ihama Takashi , Masuhara Hiroshi
Published: February 2006

We report that hyper-Rayleigh scattering, surface-enhanced hyper-Raman scattering, and two-photon excited luminescence occur intermittently by focusing a continuous-wave near-infrared (cw-NIR) laser into a colloidal silver solution including rhodamine 6G (R6G) and sodium chloride (NaCl). On the other hand, continuous hyper-Rayleigh scattering is observed from colloidal silver free from R6G and NaCl, demonstrating that hyper-Raman scattering and two-photon excited luminescence are attributed to R6G and their intermittent features are dependent on the colloidal dispersion. These results suggest that the cw-NIR laser has three roles; the source of the nonlinear response, optical trapping of nanoparticles, and making nanoparticle aggregates possessing the high activity for the nonlinear response.
The spin-orbit and rotational constants for the N2 C″Πui5(v=3) state
Authors: Field Robert W. , Pirali Olivier , Tokaryk Dennis W.
Published: February 2006

The spin-orbit (A=−16.4cm−1) and rotational (B=1.017cm−1) constants for the N2 C″Πui5(v=3) level are determined by a fit to rotational lines in the C″Πu5−A′Σg+5(3-1) band that terminate in JΩ′′=33, 43, 32, and 42 levels of the C″ state. The C″-state spin-orbit constant is consistent with semi-empirical estimates, based on spin-orbit constants observed in several other electronic states of N2 and the atomic spin-orbit coupling constant, ζ(N2p). The C″–A′ bands exhibit the unusual feature of oppositely degraded sub-band heads, Ω′=3 (red) and Ω′=1, 0, and −1 (blue). The unusually wide range of BΩeff values, from 0.85cm−1 (Ω=3) to 1.28cm−1 (Ω=−1) for C″Π5(v=3) should be diagnostically useful for Ω′-assignments. The C″Π5(v=3) level lies 14257.17 and 90599cm−1 above A′Σg+5(v=1) and XΣg+1(v=0), respectively, and Re(C″Π5)=1.50Å.
Relativistic molecular orbital study of the optical and magnetic properties of hexachloro protactinate (IV): PaCl62−
Authors: Arratia-Pérez Ramiro , Malli Gulzari L.
Published: February 2006

Our ab initio all-electron Dirac-Fock and the corresponding nonrelativistic limit calculations performed at four Pa–Cl bond distances yield for octahedral PaCl62− the optimized Pa–Cl bond distances of 2.758 and 2.771Å, respectively. Dirac scattered wave and its nonrelativistic limit calculations are performed at the optimized Pa–Cl bond distances using a first-order perturbation procedure to obtain the molecular g and hyperfine tensors for the octahedral anion PaCl62−. The calculated Zeeman and Pa231 hyperfine interactions are in fairly good agreement with the electron paramagnetic resonance and electron nuclear double resonance values of the Pa4+ impurity site in the octahedral Cs2ZrCl6 lattice. The calculated relativistic transition energies of the 5f→5f and 5f→6d absorption bands are also in good agreement with the experimental results.
Effects of excitonic diffusion on stimulated emission in nanocrystalline ZnO
Authors: Tobin Ger , McGlynn Enda , Henry Martin O. , Mosnier Jean-Paul , de Posada Eduardo , Lunney James G.
Published: February 2006

We present optically pumped emission data for ZnO, showing that high excitation effects and stimulated emission/lasing are observed in nanocrystalline ZnO thin films at room temperature, although such effects are not seen in bulk material of better optical quality. A simple model of exciton density profiles is developed which explains our results and those of other authors. Inhibition of exciton diffusion in nanocrystalline samples compared to bulk significantly increases exciton densities in the former, leading—via the nonlinear dependence of emission in the exciton bands on the pump intensity—to large increases in emission and to stimulated emission.
1∕
f
noise in all-epitaxial metal-semiconductor diodes
Authors: Young A. C. , Zimmerman J. D. , Brown E. R. , Gossard A. C.
Published: February 2006

In contrast to traditional metal-semiconductor (i.e., Schottky) junctions, molecular beam epitaxy (MBE)-grown ErAs:InAlGaAs heterojunctions have recently been shown to provide highly “engineerable” electrical rectification characteristics through the tuning of the Schottky barrier height, while maintaining the very low specific capacitance. This letter reports an approximate 10× improvement in the low-frequency noise performance by using MBE-grown ErAs as the Schottky contact instead of evaporated aluminum. The low-frequency noise power spectrum of ErAs devices has been observed to have a 1∕f1.0 frequency dependence. Constant-current bias-dependent measurements have shown a 1.8 power law dependence of the noise spectral density on dc current.
Lifetime of organic thin-film transistors with organic passivation layers
Authors: Han Seung Hoon , Kim Jun Hee , Jang Jin , Cho Sang Mi , Oh Myung Hwan , Lee Sun Hee , Choo Dong Joon
Published: February 2006

We fabricated a high-performance pentacene organic thin-film transistor (OTFT) on plastic and passivated it with polyvinylalcohol and photosensitive acryl layers. The pentacene was grown on the thin-film transistor area using a self-organized process. The OTFT after the passivation exhibited the field-effect mobility of 0.80cm2∕Vs, threshold voltage of −9.2V, and on/off current ratio of 108. The field-effect mobility and threshold voltage change exponentially with time in air. The lifetime, defined as the time required to decrease the on current by one-half, was found to be ∼11000h in ambient air. The absolute value of threshold voltage of the unpassivated OTFT increases with time in air, but it decreases with time in the passivated OTFT. This indicates that the origins for the degradation in the performances of the two OTFTs are different. H2O in unpassivated and O2 in passivated OTFT appear to be the major origin for the degradation.
Electronic characterization and effects of light-induced degradation on hydrogenated nanocrystalline silicon
Authors: Halverson Adam F. , Gutierrez James J. , Cohen J. David , Yan Baojie , Yang Jeffrey , Guha Subhendu
Published: February 2006

Hydrogenated nanocrystalline silicon was characterized using the transient photocapacitance (TPC) method. The TPC spectra show these materials to have a mixed-phase nature. At low temperatures, the spectra appeared very microcrystalline, whereas at moderate temperatures they appeared very similar to those for hydrogenated amorphous silicon. These differences are shown to result from the temperature dependence of the minority carrier collection from the nanocrystalline component. The effects of light-induced degradation were also studied. This caused a substantial decrease in minority carrier collection, similar to lowering the temperature of the undegraded sample. However, no concomitant increase in dangling bond defect density was observed.
Single-electron tunneling in a silicon-on-insulator layer embedding an artificial dislocation network
Authors: Ishikawa Yasuhiko , Yamamoto Chihiro , Tabe Michiharu
Published: February 2006

A two-dimensional dislocation network artificially embedded in a silicon-on-insulator (SOI) layer was examined as the source of lattice strain to generate a periodic potential. A screw dislocation network with the period of 20nm was formed in an SOI layer using a twist bonding of two SOI wafers. n-channel metal-oxide-semiconductor field-effect transistors using the dislocation-embedded SOI layer showed an oscillation of drain current with the gate voltage at the temperatures below 40K. This oscillation is ascribed to the single-electron tunneling through the spatially modulated potential. The results suggest that the dislocation network works as the strain source to form the potential array.
Simultaneous determination of size and refractive index of red blood cells by light scattering measurements
Authors: Ghosh N. , Buddhiwant P. , Uppal A. , Majumder S. K. , Patel H. S. , Gupta P. K.
Published: February 2006

We present a fast and accurate approach for simultaneous determination of both the mean diameter and refractive index of a collection of red blood cells (RBCs). The approach uses the peak frequency of the power spectrum and the corresponding phase angle obtained by performing Fourier transform on the measured angular distribution of scattered light to determine these parameters. Results on the measurement of two important clinical parameters, the mean cell volume and mean cell hemoglobin concentration of a collection of RBCs, are presented.
Thermoacoustically driven refrigerator with double thermoacoustic-Stirling cycles
Authors: Luo Ercang , Dai Wei , Zhang Yong , Ling Hong
Published: February 2006

Recently, considerable research efforts have been made to search substitution technologies for chlorofluorocarbon-based vapor compression cycles due to the concern over environmental issues. This letter introduces a helium-based thermoacoustic refrigeration system, which is a thermoacoustic-Stirling refrigerator driven by a thermoacoustic-Stirling heat engine, for domestic refrigeration purpose. In the regenerators of both the refrigerator and the prime mover, helium gas experiences near to reversible high efficiency Stirling process. At the operating point with 3.0MPa mean pressure, 57.7Hz frequency, and 2.2kW heat input, the experimental cooler provides a lowest temperature of −64.4°C and 250W cooling power at −22.1°C. These results show good potential of the system to be an alternative in near future for domestic refrigeration with advantages of environment-friendliness, no moving parts, and heat driven mechanism.
A technique for uniform generation of very-high-frequency plasma suited to large-area thin-film deposition
Authors: Yamakoshi H. , Satake K. , Takeuchi Y. , Mashima H. , Aoi T.
Published: February 2006

Two very-high-frequency powers between which the phase difference is varying in split of time are supplied to a ladder-shaped electrode through multiple feeding points located at symmetrical positions of the electrode to generate a large-area uniform plasma. Theoretical calculations of the voltage distribution at several phase difference show good agreement with experiments. Plasma emission uniformity within ±15% is demonstrated at 60MHz for the substrate size of 1.4×1.1m, with nitrogen gas of 10Pa.
Motion control of single F1-ATPase rotary biomolecular motor using microfabricated local heating devices
Authors: Arata Hideyuki F. , Noji Hiroyuki , Fujita Hiroyuki
Published: February 2006

Biomolecular motors are major targets in single-molecule studies, which reveal molecular behaviors usually hidden in the emsemble- and time-averaging of bulk experiments. Methods for rapid experimental condition control during single-biomolecule observation are a key technology to elucidate the molecular mechanisms of proteins. One of the most promising methods is real-time rapid temperature alternation. A microheater and a microthermosensor were integrated on the glass plate for controlling the temperature locally; the maximum response speeds were 71.5 and 56.9K∕s for temperature rise and fall, respectively. Rapid temperature alternation with microfabricated thermodevice allowed rapid and reversible angular velocity control of a single F1-ATPase, a rotary biomolecular motor. The rapid control of the temperature enabled us to perform rotation assay at temperatures higher than that would “normally” denature them. This revealed that the torque of F1-ATPase seems to increase at higher temperatures with the increasing rate of 4% per 10°C. This method and knowledge for controlling the biomolecular motor can also be applied to future hybrid organic-inorganic nanosystems, which use biomolecular motors as nanoactuators.
Nonlinear current-voltage characteristics of bismuth nanodot structures
Authors: Chiu Pit Ho Patrio , Shih Ishiang
Published: February 2006

Bismuth (Bi) nanodot structures have been fabricated using the proximity effects of electron-beam writing technique. Bi nanodots, each 100nm in diameter, were fabricated on an oxidized silicon substrate with a 200nm thick silicon oxide layer. Current-voltage (I-V) measurements were performed under low vacuum condition at temperatures from 77 to 300K. The measurement results showed significant nonlinearities with symmetric resistance peaks, indicating the existence of energy level spacing within the nanodot structures. The successful observation of energy level spacing in such a large nanodot is due to the small effective mass of Bi material, which leads to measurable energy level spacing.
Experimental study of LO phonons and excitons in ZnO nanoparticles produced by room-temperature organometallic synthesis
Authors: Demangeot F. , Paillard V. , Chassaing P. M. , Pagès C. , Kahn M. L. , Maisonnat A. , Chaudret B.
Published: February 2006

We report here the study by optical microspectroscopy of crystalline ZnO nanoparticles produced by room-temperature organometallic synthesis. We present resonant Raman scattering spectrum obtained from different sized nanostructures from which the longitudinal-optical (LO) phonon frequency has been found to be very weakly dependent on their size. Low-temperature photoluminescence measurements reveal that (i) the band-edge PL of ZnO nanoparticles is dominated by weakly bound localized exciton, and that (ii) its energy does not exhibit any spatial confinement effect. These results enlighten the need for surface passivation of the nanoparticles to improve their UV emission potential.
Continuous polymer nanofibers by extrusion into a viscous medium: A modified wet-spinning technique
Authors: Gorantla M. , Boone S. E. , El-Ashry M. , Young D.
Published: February 2006

We present a wet-spinning technique capable of producing continuous polymer nanofibers. This method involves injecting a solvated polymer into a highly viscous moving medium through a microaperture. The extruded fiber moves in a predictable spiral path and is collected around a spinning mandrel which also serves to pull the extruded fiber away from the aperture. Semicontinuous, solid nanofibers of polyvinyl butyral were produced with diameters ranging from 10μmto400nm. Electron microscopy indicates that submicron fibers exhibit a ribbonlike morphology. The effect of different processing parameters on the fiber size and shape is discussed.
Ab initio calculated binodal and spinodal of cubic Ti1−xAlxN
Authors: Mayrhofer P. H. , Music D. , Schneider J. M.
Published: February 2006

During annealing, metastable NaCl-structured (c) Ti1−xAlxN films initially exhibit spinodal decomposition which results in age hardening. Based on ab initio calculations, we show that the chemical requirement for spinodal decomposition in the quasibinary c-TiN–c-AlN system is fulfilled over a wide composition and temperature range. The enthalpy change for the decomposition of c-Ti0.34Al0.66N is ∼26.4kJmol−1, which is in good agreement with previously reported experiments. The obtained results enable materials design of Ti1−xAlxN-based coating systems for high-temperature applications.
Strain relaxation and surface migration effects in InGaAlAs and InGaAsP selective-area-grown ridge waveguides
Authors: Sirenko A. A. , Kazimirov A. , Ougazzaden A. , O’Malley S. M. , Bilderback D. H. , Cai Z.-H. , Lai B. , Huang R. , Gupta V. K. , Chien M. , Chu S. N. G.
Published: February 2006

Surface migration of the group-III precursors and strain relaxation at the ridge sidewalls are compared for 2.5μm wide waveguides based on InGaAsP and InGaAlAs multiple-quantum-well (MQW) structures. The cross-sectional thickness and strain variations have been measured using synchrotron radiation-based x-ray diffraction with an angular resolution of 2arcs and a beam size of (0.24×0.35)μm2. Indium-rich overgrowth has been observed for the InGaAsP-based waveguides, while InGaAlAs-based waveguides demonstrate thickness uniformity of the MQW active region with a strain relief of 0.4%∕μm at the sidewalls.
Plasma-free hydrogenation of ultralow-temperature polycrystalline silicon thin-film transistors with SiNx:H as interlayer dielectric
Authors: Chung Choong-Heui , Kim Yong-Hae , Moon Jaehyun , Lee Myung-Hee , Lim Jung Wook , Yun Sun Jin , Park Dong-Jin , Kim Dae-Won , Lee Jin Ho
Published: February 2006

Plasma-free defect passivation is achieved on polycrystalline silicon thin-film transistors fabricated below 150°C by annealing and extracting H from SiNx:H interlayer dielectric. By annealing at 250°C without a plasma application, VT and μFE were improved from 11.5Vto3.5V and from 86cm2∕Vsto212cm2∕Vs, respectively. Improvement in performance is attributed to defect passivation by H diffusing out from SiNx:H. Dangling bonds and strained bonds can be acceptably passivated around 170°C, and 205°C, respectively. The activation energy for the diffusion of H into polycrystalline silicon was estimated to be 0.87eV.
Small dc magnetic field response of magnetoelectric laminate composites
Authors: Dong Shuxiang , Zhai Junyi , Li JieFang , Viehland D.
Published: February 2006

We have found that small long-type magnetoelectric (ME) laminate composites of magnetostrictive Tb1−xDyxFe2−y and piezoelectric Pb(Zr,Ti)O3 are quite sensitive to small dc magnetic field (Hdc) variations, when driven by a constant ac magnetic field. The sensitivity limit is Hdc<10−3Oe (10−7Tesla) using a constant amplitude low frequencies drive, and Hdc<10−4Oe (10−8Tesla) under resonant drive. In addition, an unusual ME switching effect—a 180° phase shift—was observed, in response to changes in the sign of a small Hdc.
Anther wall development and structure in wild tomatoes (Solanum sect. Lycopersicon): functional inferences
Authors: García Carolina Carrizo , Barboza Gloria E.
Published: February 2006

Development of the anther wall and its structure at maturity in wild tomatoes (Solanum sect. Lycopersicon) are described, and the features are discussed in relation to anther dehiscence and the buzz-pollination mechanism. The anther wall formation follows two different patterns in the same microsporangia and a high number of cells divisions may occur. The number of layers formed varies across the ventral, dorsal and lateral surfaces of each theca. Large epidermal cells develop, lining the stomium, and they could possibly be involved in stomium opening. Cells with thickenings are formed in the apical fifth of the anther, where the tissues seem to degenerate after the stomium opening, forming a wider aperture through which the pollen can be shed. The multilayered dorsal wall remains swollen and could act as an attractant to pollinators and as mechanical support. The apparently disordered anther wall development sets up different structures across and along the anther, which can be interpreted as histological adaptations to the buzz-pollination mechanism.
The TasFACE climate-change impacts experiment: design and performance of combined elevated CO2 and temperature enhancement in a native Tasmanian grassland
Authors: Hovenden M. J. , Miglietta F. , Zaldei A. , Vander Schoor J. K. , Wills K. E. , Newton P. C. D.
Published: February 2006

The potential impacts of climate change on both natural and managed ecosystems are far-reaching and are only beginning to be understood. Here we describe a new experiment that aims to determine the impacts of elevated concentration of CO2 ([CO2]) and elevated temperature on a native Themeda–Austrodanthonia-dominated grassland ecosystem in south-eastern Tasmania. The experimental site contains 60 vascular plant species. The experiment combines the latest developments in free-air CO2 enrichment (FACE) technology with the use of infrared (IR) heaters to mimic environmental conditions expected to exist in the year 2050. The CO2 concentration in the FACE treatments is reliably maintained at 550 µmol mol–1 and leaf temperature is elevated by an average of 2.1°C by the IR treatment, with 1-cm soil temperature being elevated by 0.8°C. Measurements being made in the experiment cover plant ecophysiological responses, plant population dynamics and community interactions. Soil processes and ecosystem effects, including nutrient cycling and plant animal interactions, are also being investigated. Collaborations are invited from interested parties.
Specific pollinators reveal a cryptic taxon in the bird orchid, Chiloglottis valida sensu lato (Orchidaceae) in south-eastern Australia
Authors: Bower Colin C.
Published: February 2006

Orchid species belonging to the sexual-deception pollination syndrome exhibit highly specific, usually one-to-one, relationships with their pollinators. This specificity is mediated by the orchid’s mimicry of the sex-attractant pheromones emitted by females of the pollinator species. Chiloglottis valida D.Jones sensu lato is a widespread, sexually deceptive, terrestrial orchid found in south-eastern New South Wales, and eastern and southern Victoria from sea level to at least 1600 m in the Australian Alps. Flowers from 38 C. valida s.l. populations from throughout this area were compared in field choice experiments for the specificity of attracted pollinator species. Four potential pollinator wasps in the thynnine genus Neozeleboria Rohwer were attracted. The data demonstrate the existence of two attractant odour types among C. valida s.l. and its pollinators, and support the recognition of two partially sympatric cryptic species in the orchid, each with two potential pollinators. The copheromone pollinator pairs replace each other on the altitudinal gradient, albeit with some overlap. In alpine areas the pollinators of the two cryptic orchid species are themselves sibling species within Neozeleboria monticola Turner s.l. The results indicate that C. aff. valida, the sister species of C. valida s.s., has two geographically replacing pollinators.
AMPA receptor downscaling at the onset of Alzheimer’s disease pathology in double knockin mice
Authors: Chang Eric H. , Savage Mary J. , Flood Dorothy G. , Thomas Justin M. , Levy Robert B. , Mahadomrongkul Veeravan , Shirao Tomoaki , Aoki Chiye , Huerta Patricio T.
Published: February 2006

It is widely thought that Alzheimer’s disease (AD) begins as a malfunction of synapses, eventually leading to cognitive impairment and dementia. Homeostatic synaptic scaling is a mechanism that could be crucial at the onset of AD but has not been examined experimentally. In this process, the synaptic strength of a neuron is modified so that the overall excitability of the cell is maintained. Here, we investigate whether synaptic scaling mediated by
l
-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) contributes to pathology in double knockin (2×KI) mice carrying human mutations in the genes for amyloid precursor protein and presenilin-1. By using whole-cell recordings, we show that 2×KI mice exhibit age-related downscaling of AMPAR-mediated evoked currents and spontaneous, miniature currents. Electron microscopic analysis further corroborates the synaptic AMPAR decrease. Additionally, 2×KI mice show age-related deficits in bidirectional plasticity (long-term potentiation and long-term depression) and memory flexibility. These results suggest that AMPARs are important synaptic targets for AD and provide evidence that cognitive impairment may involve downscaling of postsynaptic AMPAR function.
Mdm4 and Mdm2 cooperate to inhibit p53 activity in proliferating and quiescent cells
in vivo
Authors: Francoz Sarah , Froment Pascal , Bogaerts Sven , De Clercq Sarah , Maetens Marion , Doumont Gilles , Bellefroid Eric , Marine Jean-Christophe
Published: February 2006

The Mdm2 and Mdm4 oncoproteins are key negative regulators of the p53 tumor suppressor. However, their physiological contributions to the regulation of p53 stability and activity remain highly controversial. Here, we combined a
p53
knock-in allele, in which
p53
is silenced by a transcriptional stop element flanked by loxP sites, with the
mdm2
- and
mdm4
-null alleles. This approach allows Cre-mediated conditional p53 expression in tissues
in vivo
and cells
in vitro
lacking Mdm2, Mdm4, or both. Using this strategy, we show that Mdm2 and Mdm4 are essential in a nonredundant manner for preventing p53 activity in the same cell type, irrespective of the proliferation/differentiation status of the cells. Although Mdm2 prevents accumulation of the p53 protein, Mdm4 contributes to the overall inhibition of p53 activity independent of Mdm2. We propose a model in which Mdm2 is critical for the regulation of p53 levels and Mdm4 is critical for the fine-tuning of p53 transcriptional activity, both proteins acting synergistically to keep p53 in check.
Ecological divergence exhibits consistently positive associations with reproductive isolation across disparate taxa
Authors: Funk Daniel J. , Nosil Patrik , Etges William J.
Published: February 2006

To what degree is the divergent adaptation responsible for life’s phenotypic variety also responsible for generating the millions of species that manifest this variation? Theory predicts that ecological divergence among populations should promote reproductive isolation, and recent empirical studies provide support for this hypothesis in a limited number of specific taxa. However, the essential question of whether ecology plays a truly general role in speciation has yet to be systematically evaluated. Here we address this integral issue using an approach that adds an ecological dimension to comparative studies investigating the relationship between reproductive isolation and divergence time. Specifically, we quantify ecological divergence for >500 species pairs from eight plant, invertebrate, and vertebrate taxa and statistically isolate its association with reproductive isolation. This approach demonstrates a highly consistent and significant positive association between ecological divergence and reproductive isolation across taxa. This relationship was also observed across different aspects of ecological divergence and components of reproductive isolation. These findings are highly consistent with the hypothesis that ecological adaptation plays a fundamental and taxonomically general role in promoting reproductive isolation and speciation.
Structure and mechanism of mouse cysteine dioxygenase
Authors: McCoy Jason G. , Bailey Lucas J. , Bitto Eduard , Bingman Craig A. , Aceti David J. , Fox Brian G. , Phillips George N.
Published: February 2006

Cysteine dioxygenase (CDO) catalyzes the oxidation of
l
-cysteine to cysteine sulfinic acid. Deficiencies in this enzyme have been linked to autoimmune diseases and neurological disorders. The x-ray crystal structure of CDO from
Mus musculus
was solved to a nominal resolution of 1.75 Å. The sequence is 91% identical to that of a human homolog. The structure reveals that CDO adopts the typical β-barrel fold of the cupin superfamily. The NE2 atoms of His-86, -88, and -140 provide the metal binding site. The structure further revealed a covalent linkage between the side chains of Cys-93 and Tyr-157, the cysteine of which is conserved only in eukaryotic proteins. Metal analysis showed that the recombinant enzyme contained a mixture of iron, nickel, and zinc, with increased iron content associated with increased catalytic activity. Details of the predicted active site are used to present and discuss a plausible mechanism of action for the enzyme.
The Vif and Vpr accessory proteins independently cause HIV-1-induced T cell cytopathicity and cell cycle arrest
Authors: Sakai Keiko , Dimas Joseph , Lenardo Michael J.
Published: February 2006

HIV type I (HIV-1) can cause G2cell cycle arrest and death of CD4+T lymphocytesin vitroand inexorable depletion of these cellsin vivo. However, the molecular mechanism of viral cytopathicity has not been satisfactorily elucidated. Previously, we showed that HIV-1 kills T cells by a necrotic form of cell death that requires high level expression of an integrated provirus but not theenvornefgenes. To determine which viral protein(s) are required for cell death, we systematically mutated, alone and in combination, the ORFs of the NL4-3 strain of HIV-1. We found that the elimination of the viral functions encoded bygag-polandvpu,tat, andrevdid not mitigate cytopathicity. However, elimination of thevifandvpraccessory genes together, but not individually, renders the virus incapable of causing cell death and G2cell cycle blockade. We thus identifyvifandvpras necessary for T cell cytopathic effects induced by HIV-1. These findings may provide an important insight into the molecular mechanism of viral pathogenesis in AIDS.
Spatial heterogeneity, predator cognition, and the evolution of color polymorphism in virtual prey
Authors: Bond Alan B. , Kamil Alan C.
Published: February 2006

Cryptically colored prey species are often polymorphic, occurring in multiple distinctive pattern variants. Visual predators promote such phenotypic variation through apostatic selection, in which they attack more abundant prey types disproportionately often. In heterogeneous environments, disruptive selection to match the coloration of disparate habitat patches could also produce polymorphism, but how apostatic and disruptive selection interact in these circumstances is unknown. Here we report the first controlled selection experiment on the evolution of prey coloration on heterogeneous backgrounds, in which blue jays (
Cyanocitta cristata
) searched for digital moths on mixtures of dark and light patches at three different scales of heterogeneity. As predicted by ecological theory, coarse-grained backgrounds produced a functional dimorphism of specialists on the two patch types; fine-grained backgrounds produced generalists. The searching strategies of the jays also varied with the habitat configuration, however. Complex backgrounds with many moth-like features elicited a slow, serial search that depended heavily on selective attention. The result was increased apostatic selection, producing a broad range of moth phenotypes. Backgrounds with larger, more uniform patches allowed the birds to focus on the currently most rewarding patch type and to search entire patches rapidly in parallel. The result was less apostatic selection and lower phenotypic variability. The evolution of polymorphism in camouflaged prey depends on a complex interaction between habitat structure and predator cognition.
TNFα induces ABCA1 through NF-κB in macrophages and in phagocytes ingesting apoptotic cells
Authors: Gerbod-Giannone Marie-Christine , Li Yankun , Holleboom Adriaan , Han Seongah , Hsu Li-Chung , Tabas Ira , Tall Alan R.
Published: February 2006

Recent evidence suggests that tumor necrosis factor α (TNFα) signaling in vascular cells can have antiatherogenic consequences, but the mechanisms are poorly understood. TNFα is released by free cholesterol-loaded apoptotic macrophages, and the clearance of these cells by phagocytic macrophages may help to limit plaque development. Macrophage cholesterol uptake induces ATP-binding cassette (ABC) transporter ABCA1 promoting cholesterol efflux to apolipoprotein A-I and reducing atherosclerosis. We show that TNFα induces ABCA1 mRNA and protein in control and cholesterol-loaded macrophages and enhances cholesterol efflux to apolipoprotein A-I. The induction of ABCA1 by TNFα is reduced by 65% in IκB kinase β-deficient macrophages and by 30% in p38α-deficient macrophages, but not in jun kinase 1 (JNK1)- or JNK2-deficient macrophages. To evaluate the potential pathophysiological significance of these observations, we fed TNFα-secreting free cholesterol-loaded apoptotic macrophages to a healthy macrophage monolayer (phagocytes). ABCA1 mRNA and protein were markedly induced in the phagocytes, a response that was mediated both by TNFα signaling and by liver X receptor activation. Thus, TNFα signals primarily through NF-κB to induce ABCA1 expression in macrophages. In atherosclerotic plaques, this process may help phagocytic macrophages to efflux excess lipids derived from the ingestion of cholesterol-rich apoptotic corpses.
Proteomic analysis of adaptor protein 1A coats selectively assembled on liposomes
Authors: Baust Thorsten , Czupalla Cornelia , Krause Eberhard , Bourel-Bonnet Line , Hoflack Bernard
Published: February 2006

Coat components localize to specific membrane domains, where they sort selected transmembrane proteins. To study how clathrin coats are stabilized on such domains and to identify the protein networks involved, we combined proteomic screens and
in vitro
liposome-based assays that recapitulate the fidelity of protein sorting
in vivo
. Our study identifying ≈40 proteins on AP-1A-coated liposomes revealed that AP-1A coat assembly triggers the concomitant recruitment of Rac1, its effectors, and the Wave/Scar complex as well as that of Rab11 and Rab14. The coordinated recruitment of these different machineries requires a mosaic of membrane components comprising the GTPase ADP-ribosylation factor 1, sorting signals in selected transmembrane proteins, and phosphatidylinositol 4-phosphate. These results demonstrate that the combinatorial use of low-affinity binding sites present on the same membrane domain accounts not only for a selective coat assembly but also for the coordinated assembly of selected machineries required for actin polymerization and subsequent membrane fusion.
The HIV lipidome: A raft with an unusual composition
Authors: Brügger Britta , Glass Bärbel , Haberkant Per , Leibrecht Iris , Wieland Felix T. , Kräusslich Hans-Georg
Published: February 2006

The lipids of enveloped viruses play critical roles in viral morphogenesis and infectivity. They are derived from the host membranes from which virus budding occurs, but the precise lipid composition has not been determined for any virus. Employing mass spectrometry, this study provides a quantitative analysis of the lipid constituents of HIV and a comprehensive comparison with its host membranes. Both a substantial enrichment of the unusual sphingolipid dihydrosphingomyelin and a loss of viral infectivity upon inhibition of sphingolipid biosynthesis in host cells are reported, establishing a critical role for this lipid class in the HIV replication cycle. Intriguingly, the overall lipid composition of native HIV membranes resembles detergent-resistant membrane microdomains and is strikingly different from that of host cell membranes. With this composition, the HIV lipidome provides strong evidence for the existence of lipid rafts in living cells.
Memory T and memory B cells share a transcriptional program of self-renewal with long-term hematopoietic stem cells
Authors: Luckey Chance John , Bhattacharya Deepta , Goldrath Ananda W. , Weissman Irving L. , Benoist Christophe , Mathis Diane
Published: February 2006

The only cells of the hematopoietic system that undergo self-renewal for the lifetime of the organism are long-term hematopoietic stem cells and memory T and B cells. To determine whether there is a shared transcriptional program among these self-renewing populations, we first compared the gene-expression profiles of naïve, effector and memory CD8
+
T cells with those of long-term hematopoietic stem cells, short-term hematopoietic stem cells, and lineage-committed progenitors. Transcripts augmented in memory CD8
+
T cells relative to naïve and effector T cells were selectively enriched in long-term hematopoietic stem cells and were progressively lost in their short-term and lineage-committed counterparts. Furthermore, transcripts selectively decreased in memory CD8
+
T cells were selectively down-regulated in long-term hematopoietic stem cells and progressively increased with differentiation. To confirm that this pattern was a general property of immunologic memory, we turned to independently generated gene expression profiles of memory, naïve, germinal center, and plasma B cells. Once again, memory-enriched and -depleted transcripts were also appropriately augmented and diminished in long-term hematopoietic stem cells, and their expression correlated with progressive loss of self-renewal function. Thus, there appears to be a common signature of both up- and down-regulated transcripts shared between memory T cells, memory B cells, and long-term hematopoietic stem cells. This signature was not consistently enriched in neural or embryonic stem cell populations and, therefore, appears to be restricted to the hematopoeitic system. These observations provide evidence that the shared phenotype of self-renewal in the hematopoietic system is linked at the molecular level.
Aminoacyl-transferases and the N-end rule pathway of prokaryotic/eukaryotic specificity in a human pathogen
Authors: Graciet Emmanuelle , Hu Rong-Gui , Piatkov Konstantin , Rhee Joon Haeng , Schwarz Erich M. , Varshavsky Alexander
Published: February 2006

The N-end rule relates the
in vivo
half-life of a protein to the identity of its N-terminal residue. Primary destabilizing N-terminal residues (Nd
p
) are recognized directly by the targeting machinery. The recognition of secondary destabilizing N-terminal residues (Nd
s
) is preceded by conjugation of an Nd
p
residue to Nd
s
of a polypeptide substrate. In eukaryotes,
ATE1
-encoded arginyl-transferases (R
D,E,C*
-transferases) conjugate Arg (R), an Nd
p
residue, to Nd
s
residues Asp (D), Glu (E), or oxidized Cys residue (C*). Ubiquitin ligases recognize the N-terminal Arg of a substrate and target the (ubiquitylated) substrate to the proteasome. In prokaryotes such as
Escherichia coli
, Nd
p
residues Leu (L) or Phe (F) are conjugated, by the
aat
-encoded Leu/Phe-transferase (L/F
K,R
-transferase), to N-terminal Arg or Lys, which are Nd
s
in prokaryotes but Nd
p
in eukaryotes. In prokaryotes, substrates bearing the Nd
p
residues Leu, Phe, Trp, or Tyr are degraded by the proteasome-like ClpAP protease. Despite enzymological similarities between eukaryotic R
D,E,C*
-transferases and prokaryotic L/F
K,R
-transferases, there is no significant sequelogy (sequence similarity) between them. We identified an aminoacyl-transferase, termed Bpt, in the human pathogen
Vibrio vulnificus
. Although it is a sequelog of eukaryotic R
D,E,C*
-transferases, this prokaryotic transferase exhibits a “hybrid” specificity, conjugating Nd
p
Leu to Nd
s
Asp or Glu. Another aminoacyl-transferase, termed ATEL1, of the eukaryotic pathogen
Plasmodium falciparum
, is a sequelog of prokaryotic L/F
K,R
-transferases (Aat), but has the specificity of eukaryotic R
D,E,C*
-transferases (ATE1). Phylogenetic analysis suggests that the substrate specificity of R-transferases arose by two distinct routes during the evolution of eukaryotes.