bluuebunny/crossref_metadata_2025 huggingface dataset:
Meteor observations using the Davis mesosphere‐stratosphere‐troposphere radar
Authors: Reid Iain M. , Holdsworth David A. , Morris Ray J. , Murphy Damian J. , Vincent Robert A.
Published: May 2006

The Davis mesosphere‐stratosphere‐troposphere (MST) radar (69°S, 78°E) was installed in February 2003. Although the primary interest is the observation of polar mesosphere summer echoes, external transmit and receive antennas were installed to allow all‐sky interferometric meteor radar observations. This paper presents the first results from the meteor observations. The annual count rate variation shows good agreement with previous high‐latitude observations, peaking in midsummer and minimizing in early spring. The height distribution shows significant annual variation, with minimum (maximum) peak heights and maximum (minimum) widths observed in early spring (midsummer). Radiant mapping has been used to identify the Southern delta‐Aquarid Sagittariid and July Phoenicid meteor showers, and to investigate sources of sporadic meteors. Winds and temperatures derived from the meteor observations are also presented, showing good agreement with independent colocated measurements. There is some indication that the winds below the peak height of the meteor height distribution are smeared to lower heights, which may be indicative of a previously undocumented bias in meteor wind estimates.
Assessment of model uncertainty for soil moisture through ensemble verification
Authors: De Lannoy Gabriëlle J. M. , Houser Paul R. , Pauwels Valentijn R. N. , Verhoest Niko E. C.
Published: May 2006

The Community Land Model (CLM2.0) has been used to simulate land surface processes in a small corn field. The subdivision of grid cells into patches in the CLM2.0 was explored for the generation of Monte Carlo simulations for use in calibration and ensemble generation. A distributed multiobjective calibration was developed for the optimal estimation of parameters and initial state variables for 36 soil moisture profiles. Since the resulting parameter and initial state values did not lead to perfect simulations for soil moisture, and in order to better understand the forecast uncertainty, ensemble runs were generated. The ensembles generated by CLM2.0 have been verified by several methods that are commonly used in meteorology. It was shown that the perfect model approach cannot be applied for bounded hydrological applications and that perturbation of parameters is a necessity to obtain a realistic assessment of the forecast error. Perturbation of forcings only captures more of the model uncertainty than perturbation of initial conditions only, but also causes a too limited spread in the ensembles. The generation of ensemble members through perturbation of the parameter set, found through calibration, does not necessarily result in ensembles that surround the calibrated deterministic control run for soil moisture. This is partially due the nonlinearity of the model in the parameters. It may also indicate that some parameter sets are not robust and not appropriate to perturb for ensemble generation. Consequently, the resulting ensemble mean may not represent the best forecast or a priori state estimation. During periods of extreme drought or precipitation, the ensemble probability density function (pdf) deviates far from normality and the model behaves very nonlinearly. For state estimation, methods like the ensemble Kalman filter are best suited for the propagation of the first moments to account for the nonlinear dynamics during crucial events for hydrological simulations. However, the a posteriori estimate for this technique will only be optimal in the limited class of linear filters, since the underlying pdfs cannot be assumed to be Gaussian.
Response of vegetation and net ecosystem carbon dioxide exchange at different peatland microforms following water table drawdown
Authors: Strack M. , Waddington J. M. , Rochefort L. , Tuittila E.‐S.
Published: May 2006

Northern peatlands are significant stocks of terrestrial soil carbon, and it has been predicted that warmer temperatures and lower water tables resulting from climate change will convert these ecosystems into sources for atmospheric carbon dioxide (CO2). However, these predictions do not consider the potential for hydrologically induced ecological succession or the spatial variability of carbon accumulation rates between different microforms in peatlands. To address these issues, the vegetation community was described, and the rates of gross ecosystem photosynthesis (GEP), ecosystem respiration (Rtot) and net ecosystem CO2 exchange were determined along poor fen microtopographic gradients at a control site and at a site which experienced a water table drawdown of ∼20 cm 8 years prior to the study (drained). Sampling plots within these sites were classified as microforms of hummocks, lawns, or hollows. The coverage of Sphagnum moss declined on drained hummocks, drained lawns were invaded by sedges, and hollows shifted from open water plots at the control site to Sphagnum‐dominated plots with sparse vascular plant cover at the drained site. As a result, Rtot was significantly greater at the drained site at all microforms while maximum rates of GEP declined at drained hummocks and were enhanced at drained lawns and hollows compared to similar control microforms. These results suggest that predictions about the response of northern peatland carbon exchange to climate change must consider the interaction between ecology and hydrology and the differential responses of microforms related to their initial ecohydrological conditions.
High‐latitude forcing of interior ocean δ13C
Authors: Rutberg Randye L. , Peacock Synte L.
Published: May 2006

Transit time distribution probability density functions (TTDs) are used to investigate the possible role of changing boundary conditions in driving the δ13C signal in the interior of a steady state ocean. We use idealized examples to investigate the general question of how a conservative tracer propagates from the surface ocean to interior ocean and to illustrate how a given tracer boundary signal will be “filtered” with increasing distance from its source region. We show that tracers in the deep southeast Atlantic Ocean will respond much more strongly to changes in the surface Southern Ocean than to changes in the high‐latitude North Atlantic, while the opposite is true for waters at intermediate depths. The impact of a change in the Southern Ocean surface δ13C on a profile from the western South Atlantic is estimated using model‐derived transit time distributions, and it is shown that significant deep ocean δ13C variations can be expected on glacial‐interglacial timescales, even under a steady state circulation regime. Records of δ13C from the high‐latitude North Atlantic and Southern Ocean are used as a proxy for glacial‐interglacial changes in the surface ocean boundary condition in regions of deepwater formation. By convolving these high‐latitude boundary conditions with model‐derived TTDs, we are able to explain a significant part of the observed variability in benthic δ13C records spanning the last glacial cycle(s) from locations as diverse as the equatorial Atlantic Ocean, the Cape Basin, and the equatorial Pacific. This suggests that changing boundary conditions may be driving a significant fraction of benthic δ13C variability previously attributed to changes in ocean circulation. Furthermore, we show that our results predict a slightly higher δ13C than observed in high‐productivity regions, consistent with the concept of a productivity‐induced low‐δ13C overprint.
Flow resistance dynamics in step‐pool channels: 2. Partitioning between grain, spill, and woody debris resistance
Authors: Wilcox Andrew C. , Nelson Jonathan M. , Wohl Ellen E.
Published: May 2006

In step‐pool stream channels, flow resistance is created primarily by bed sediments, spill over step‐pool bed forms, and large woody debris (LWD). In order to measure resistance partitioning between grains, steps, and LWD in step‐pool channels we completed laboratory flume runs in which total resistance was measured with and without grains and steps, with various LWD configurations, and at multiple slopes and discharges. Tests of additive approaches to resistance partitioning found that partitioning estimates are highly sensitive to the order in which components are calculated and that such approaches inflate the values of difficult‐to‐measure components that are calculated by subtraction from measured components. This effect is especially significant where interactions between roughness features create synergistic increases in resistance such that total resistance measured for combinations of resistance components greatly exceeds the sum of those components measured separately. LWD contributes large proportions of total resistance by creating form drag on individual pieces and by increasing the spill resistance effect of steps. The combined effect of LWD and spill over steps was found to dominate total resistance, whereas grain roughness on step treads was a small component of total resistance. The relative contributions of grain, spill, and woody debris resistance were strongly influenced by discharge and to a lesser extent by LWD density. Grain resistance values based on published formulas and debris resistance values calculated using a cylinder drag approach typically underestimated analogous flume‐derived values, further illustrating sources of error in partitioning methods and the importance of accounting for interaction effects between resistance components.
Mechanism of action of novel NO‐releasing furoxan derivatives of aspirin in human platelets
Authors: Turnbull Catriona M , Cena Clara , Fruttero Roberta , Gasco Alberto , Rossi Adriano G , Megson Ian L
Published: May 2006

Incorporation of a nitric oxide (NO)‐releasing moiety in aspirin can overcome its gastric side effects.

We investigated the NO‐release patterns and antiplatelet effects of novel furoxan derivatives of aspirin (B8 and B7) in comparison to existing antiplatelet agents.

Cyclooxygenase (COX) activity was investigated in purified enzyme using an electron paramagnetic resonance‐based technique. Concentration–response curves for antiplatelet agents±the soluble guanylate cyclase inhibitor, ODQ (50 μM) were generated in platelet‐rich plasma (PRP) and washed platelets (WP) activated with collagen using turbidometric aggregometry. NO was detected using an isolated NO electrode.

The furoxan derivatives of aspirin (B8, B7) and their NO‐free furazan equivalents (B16, B15; all 100 μM) significantly inhibited COX activity (P<0.01; n=6) in vitro and caused aspirin‐independent, cGMP‐dependent inhibition of collagen‐induced platelet aggregation in WP. B8 was more potent than B7 (PRP IC50=0.62±0.1 μM for B8; 400±89 μM for B7; P<0.0001. WP IC50s=0.6±0.1 and 62±10 μM, respectively). The NO‐free furazan counterparts were less potent antiplatelet agents (WP IC50s=54±3 μM and 62±10 μM, respectively; P<0.0001, B8 vs B16). Of the hybrids investigated, only B8 retained antiplatelet activity in PRP.

NO release from furoxan–aspirin hybrids was undetectable in buffer alone, but was accelerated in the presence of either plasma or plasma components, albumin (4%), glutathione (GSH; 3 μM) and ascorbate (50 μM), the effects of which were additive for B7 but not B8. NO generation from furoxans was greatly enhanced by platelet extract, an effect that could largely be explained by the synergistic effect of intracellular concentrations of GSH (3 mM) and ascorbate (1 mM).

We conclude that the decomposition of furoxan–aspirin hybrids to generate biologically active NO is catalysed by endogenous agents which may instil a potential for primarily intracellular delivery of NO. The blunting of the aspirin effects of furoxan hybrids is likely to be due to loss of the acetyl moiety in plasma; the observed antiplatelet effects are thereby primarily mediated via NO release. Compounds of this class might represent a novel means of inhibiting platelet aggregation by a combination of NO generation and COX inhibition.

British Journal of Pharmacology (2006) 148, 517–526. doi:10.1038/sj.bjp.0706743
Interaction between cyclodextrin and neuronal membrane results in modulation of GABAA receptor conformational transitions
Authors: Pytel Maria , Mercik Katarzyna , Mozrzymas Jerzy W
Published: May 2006

Cyclodextrins (CDs) are nanostructures widely applied in biotechnology and chemistry. Owing to partially hydrophobic character, CDs interact with biological membranes. While the mechanisms of CDs interactions with lipids were widely studied, their effects on proteins are less understood. In the present study we investigated the effects of beta cyclodextrin (βCD) on GABAA receptor (GABAAR) gating.

To reliably resolve the kinetics of conformational transitions, currents were elicited by ultrafast gamma‐aminobutyric acid (GABA) applications to outside‐out patches from rat cultured hippocampal neurons. βCD increased the amplitude of responses to saturating GABA concentration ([GABA]) in a dose‐dependent manner and this effect was accompanied by profound alterations in the current kinetics.

Current deactivation was slowed down by βCD but this effect was biphasic with a maximum at around 0.5 mM βCD. While the fast deactivation time constant was monotonically slowed down within considered βCD concentration range, the slow component first increased and then, at millimolar βCD concentration, decreased.

The rate and extent of desensitization was decreased by βCD in a dose‐dependent manner.

The analysis of current responses to nonsaturating [GABA] indicated that βCD affected the GABAAR agonist binding site by slowing down the unbinding rate.

Modulation of GABAAR desensitization and binding showed different concentration‐dependence suggesting different modualtory sites with higher affinity of the latter one.

All the βCD effects were fully reversible indicating that cholesterol uptake into βCD was not the primary mechanism.

We conclude that βCD is a strong modulator of GABAAR conformational transitions.

British Journal of Pharmacology (2006) 148, 413–422. doi:10.1038/sj.bjp.0706747
Radiative shocks: An opportunity to study laboratory astrophysics
Authors: Koenig M. , Vinci T. , Benuzzi-Mounaix A. , Ozaki N. , Ravasio A. , Rabec le Glohaec M. , Boireau L. , Michaut C. , Bouquet S. , Atzeni S. , Schiavi A. , Peyrusse O. , Batani D.
Published: May 2006

In this paper, experimental results on radiative shocks generated by a high power laser in a xenon gas cell are presented. Two sets of experiments have been performed at the Laser pour l'Utilisation des Lasers Intenses (LULI) laboratory. Several shock parameters were simultaneously measured: shock temperature and velocities, the precursor two-dimensional (2D) time evolution, its electron density, density gradient, and temperature. Data were obtained varying initial conditions for different laser intensities and gas pressures. Comparisons with 1D and 2D radiative hydrodynamic simulations are shown for all measured parameters (shock velocity, shape, radial expansion, and temperature as well as precursor velocity and electron density).
Governing factors for production of photoemission-modulated electron beams
Authors: Harris J. R. , Neumann J. G. , O’Shea P. G.
Published: May 2006

Charged particle beams normally contain a complicated pulse shape structure when created. This structure is created by particular equipment and techniques such as high bandwidth laser systems driving photocathodes, and may drive effects that degrade beam quality or produce coherent electromagnetic radiation. While often encountered, such structure is generally poorly diagnosed and difficult to control. To study the effects of pulse shape structure in intense beams, we have developed a system using combined thermionic emission and photoemission to produce carefully tailored pulse shapes in an electron beam. In this paper, we discuss the performance of this system and derive limiting curves to explain the range of electron beam pulse shapes measured with it. Suggestions for improved design of future photomodulation systems are also made.
Elimination of translational and rotational motions in nuclear orbital plus molecular orbital theory: Application of Møller-Plesset perturbation theory
Authors: Hoshino Minoru , Nakai Hiromi
Published: May 2006

The translation- and rotation-free nuclear orbital plus molecular orbital (TRF-NOMO) theory was developed to determine the nonadiabatic nuclear and electronic wave functions. This study presents a formulation of TRF-NOMO second-order Møller-Plesset (MP2) perturbation and Epstein-Nesbet (EN) theory with the use of the TRF Hamiltonian. Numerical assessment of the TRF-NOMO/MP2 and EN is performed for several molecules. We confirm the importance of the elimination of translational and rotational motions in the many-body calculations.
Measured Davydov splitting in oligothiophene crystals
Authors: Tavazzi S. , Campione M. , Laicini M. , Raimondo L. , Borghesi A. , Spearman P.
Published: May 2006

The polarized absorption spectra of single crystals of oligothiophenes in a wide spectral range are reported. The experimental procedure is discussed, underlying several details which are relevant to obtain reliable spectra particularly for samples of increasing thickness. On the basis of these considerations, it has been possible to fully detect the transition to the upper Davydov exciton originating from the first molecular state. The position and shape of the main exciton peak in these materials are compared and discussed, taking into consideration the molecular arrangement and the longitudinal contribution which depends on the transition moment orientation. The Davydov splitting values as deduced from the experimental data at room temperature are also reported either for the first vibronic replica or for the electronic transition as a whole. The difference between the purely transverse and the measured Davydov splitting is discussed.
Optical coherence and theoretical study of the excitation dynamics of a highly symmetric cyclophane-linked oligophenylenevinylene dimer
Authors: Moran Andrew M. , Maddox Jeremy B. , Hong Janice W. , Kim Jeongho , Nome Rene A. , Bazan Guillermo C. , Mukamel Shaul , Scherer Norbert F.
Published: May 2006

Optoelectronic properties of a polyphenylenevinylene-based oligomer and its paracylophane-linked dimer are studied using a variety of experimental and theoretical techniques. Despite the symmetrical structure and redshifted absorption of the dimer versus the monomer, an exciton picture is not the most appropriate. Electronic structure calculations establish changes in charge density upon optical excitation and show localized excitations that cannot be accounted for by a simple Frenkel exciton model. Visible frequency pump-probe anisotropy measurements suggest that the dimer should be considered as a three-level system with a fast, ∼130fs, internal conversion from the higher to lower energy excited electronic state. Signatures of nuclear relaxation processes are compared for electric field-resolved transient grating and two-dimensional photon echo spectra. These measurements reveal that nuclear relaxation occurs on similar time scales for the monomer and dimer. The connection between the spectral phase of four-wave mixing signals and the time dependent width of a nuclear wave packet is discussed. Semiempirical electronic structure and metropolis Monte Carlo calculations show that the dominant line broadening mechanisms for the monomer and dimer are associated with inter-ring torsional coordinates. Together, the theoretical calculations and electric field-resolved four-wave mixing experiments suggest that while the structure of dimer is more rigid than that of monomer, the difference in their rigidities is not sufficient to slow down excited state relaxation of dimer with respect to the monomer.
Electromigration resistance in a short three-contact interconnect tree
Authors: Chang C. W. , Choi Z.-S. , Thompson C. V. , Gan C. L. , Pey K. L. , Choi W. K. , Hwang N.
Published: May 2006

Electromigration has been characterized in via-terminated interconnect lines with additional vias in the middle, creating two adjacent segments that can be stressed independently. The mortality of a segment was found to depend on the direction and magnitude of the current in the adjacent segment, confirming that there is not a fixed value of the product of the current density and segment length, jL, that defines immortality in individual segments that are part of a multisegment interconnect tree. Instead, it is found that the probability of failure of a multisegment tree increases with the increasing value of an effective jL product defined in earlier work. However, contrary to expectations, the failures were still observed when (jL)eff was less than the critical jL product for which lines were found to be immortal in single-segment test structures. It is argued that this is due to reservoir effects associated with unstressed segments or due to liner failure at the central via. Multisegment test structures are therefore shown to reveal more types of failure mechanisms and mortality conditions that are not found in tests with single-segment structures.
Measurement of the current in water discharge using magneto-optical Faraday effect
Authors: Sarkisov G. S. , Woodworth J. R.
Published: May 2006

The observation of magnetooptical Faraday effects in water in experiments with electrical breakdown is presented. After high-voltage breakdown, the ionized channel with ∼4kA current was generated. The magnetic field from the current channel induces a circular birefringence which results in rotation of the polarization plane of a probing laser (200ps, 532nm). In spite of fast opposite radius drop of the magnetic field in radial direction, the Faraday rotation effect drops very slowly. The rotation of the polarization plane was ∼0.65°±5%. The optical measurements are in good agreement within ∼7% with the electrical measurements of the current.
Molecular dynamic simulations and atomic structures of amorphous materials
Authors: Chen G. L. , Liu X. J. , Hui X. D. , Hou H. Y. , Yao K. F. , Liu C. T. , Wadsworth J.
Published: May 2006

A long-standing issue of using molecular dynamics (MD) to simulate local atomic structures in nonequilibrium metals and alloys is the huge difference in cooling rates used in experimental studies and theoretical calculations. In this study, a unique approach was introduced to correct the fast time steps involved in the MD calculations. This approach has demonstrated various medium-range ordered zones with imperfect ordered packing, which are verified experimentally by high-resolution transmission electron microscopy and its selected simulation imaging of Zr2Ni glass.
Forward flux sampling-type schemes for simulating rare events: Efficiency analysis
Authors: Allen Rosalind J. , Frenkel Daan , ten Wolde Pieter Rein
Published: May 2006

We analyze the efficiency of several simulation methods which we have recently proposed for calculating rate constants for rare events in stochastic dynamical systems in or out of equilibrium. We derive analytical expressions for the computational cost of using these methods and for the statistical error in the final estimate of the rate constant for a given computational cost. These expressions can be used to determine which method to use for a given problem, to optimize the choice of parameters, and to evaluate the significance of the results obtained. We apply the expressions to the two-dimensional nonequilibrium rare event problem proposed by Maier and Stein [Phys. Rev. E 48, 931 (1993)]. For this problem, our analysis gives accurate quantitative predictions for the computational efficiency of the three methods.
Reducing probe dependent drift in atomic force microscope with symmetrically supported torsion levers
Authors: Beyder Arthur , Spagnoli Chiara , Sachs Frederick
Published: May 2006

Drift and thermal instability present significant limitations to atomic force microscopy and other cantilever-based sensor measurements. Most drift has been attributed to the asymmetric geometry of the cantilever, which acts as a chemical and thermal bimorphs. For example, cantilevers drift hundreds of nanometers upon immersion in water. The time course of drift is roughly exponential with a time constant of ∼70min. Symmetrically supported torsion cantilevers significantly reduce this drift. Prototypical torsion levers have long-term drift of 1.0±0.36Å∕min, more than an order of magnitude smaller than commercial cantilevers. These torsion levers also have extraordinarily high thermal stability. In response to a 20°C change in bath temperature, they move an average of 15±11nm, whereas traditional levers deflect by >1μm.
Soft landing of silicon nanocrystals in plasma enhanced chemical vapor deposition
Authors: Chaâbane Nihed , Suendo Veinardi , Vach Holger , Roca i Cabarrocas Pere
Published: May 2006

Plasma-generated silicon nanocrystals have been selectively trapped on a cooled substrate to yield nanocrystalline films. We here present experimental evidence that the contribution of positively charged nanocrystals largely dominates the film deposition. As a direct application, we illustrate how the use of a simple substrate bias voltage allows us to “toggle switch” between 100% nanocrystalline and 100% amorphous layers. Moreover, we demonstrate that the applied bias voltage can be used to “tune” the photoluminescence of the nanocrystals between 630 and 730nm.
Neutron diffraction investigation of hysteresis reduction and increase in linearity in the stress-strain response of superelastic NiTi
Authors: Rathod C. R. , Clausen B. , Bourke M. A. M. , Vaidyanathan R.
Published: May 2006

In situ neutron diffraction measurements during loading have been performed on plastically deformed superelastic NiTi samples. The measurements observed retained B19′ phase in the unloaded state as a result of the plastic deformation in otherwise completely B2 phase samples. A reversible stress-induced B2–B19′ transformation on application and removal of stress occurred in the presence of this retained B19′ phase. The amount and orientation of this retained B19′ phase changed with cycling. Such direct atomic scale observations in the bulk are used here for the first time to qualitatively elucidate the macroscopic stress-strain response in plastically deformed superelastic NiTi.
Optical monitoring of nonequilibrium carrier lifetime in freestanding GaN by time-resolved four-wave mixing and photoluminescence techniques
Authors: Malinauskas T. , Jarašiūnas K. , Miasojedovas S. , Juršėnas S. , Beaumont B. , Gibart P.
Published: May 2006

Optical monitoring of nonequilibrium carrier dynamics was performed in freestanding GaN. Four-wave mixing kinetics directly provided carrier lifetime of 5.4ns in the layer, while complementary measurements by photoluminescence technique revealed the fast transients with subnanosecond decay time. Numerical modeling of photoluminescence decay taking into account the carrier spatial-temporal dynamics allowed us to attribute an origin of the fast photoluminescence transients to carrier diffusion to the bulk and to reabsorption of the backward emission. The studies demonstrated carrier diffusion limited applicability of the time-resolved photoluminescence technique for carrier lifetime measurements in a high quality thick III-nitride layers.
Branched Ta nanocolumns grown by glancing angle deposition
Authors: Zhou C. M. , Gall D.
Published: May 2006

Periodic arrays of Ta nanocolumns, 200nm wide and 600nm tall, were grown by glancing angle sputter deposition onto self-assembled close-packed arrays of 260-nm-diameter silica spheres. Each sphere leads to the development of a single Ta column. As growth progresses, roughening of the column top surfaces causes branching of some columns into subcolumns. The measured fraction of branched columns fb decreases with increasing growth temperature, from 30% at 200°C to 4% at 700°C. This is attributed to the increased adatom mobility at elevated temperatures, leading to a larger average separation of growth mounds and, in turn, lower nucleation probabilities for subcolumns. Branching into 3 and 4 subcolumns exhibits probabilities proportional to fb2 and fb3, respectively. A fit of the data with a simple nucleation model provides an effective activation energy for Ta surface diffusion of 2.0eV.
Quasi-one-dimensional quantum well on Si(100) surface crafted by using scanning tunneling microscopy tip
Authors: Sagisaka Keisuke , Fujita Daisuke
Published: May 2006

We fabricated quasi-one-dimensional (1D) quantum wells on the Si(100) surface by using a scanning tunneling microscopy (STM) tip. Electron waves were confined to a single silicon dimer row by two tungsten nanodots that were separated by several nanometers. The tungsten dots were deposited by point contact between the STM tip and the sample. The size of the dots we created on the Si(100) surface was as small as the width of a single dimer. Differential conductance mapping and scanning tunneling spectroscopy detected different quantum states confined to the quasi-1D quantum well as changing bias voltage.
Microfluidic mixing through electrowetting-induced droplet oscillations
Authors: Mugele F. , Baret J.-C. , Steinhauser D.
Published: May 2006

We used electrowetting to trigger self-excited oscillations of millimeter-sized sessile droplets of water-glycerol mixtures in a viscosity range from 1to65mPas. During the oscillations the contact angle of the droplets varied periodically between ≈130° and 80° with a frequency between 10 and 125s−1, depending on the viscosity and the drop size. By initially staining drops partially with fluorescent dye, we found that the liquid within the drop is completely mixed within 100–2000 oscillation cycles for low and high viscosities, respectively. Compared to pure diffusion, droplet oscillations accelerated mixing by approximately two orders of magnitude for millimeter-sized droplets.
High charge carrier densities and conductance maxima in single-crystal organic field-effect transistors with a polymer electrolyte gate dielectric
Authors: Panzer Matthew J. , Frisbie C. Daniel
Published: May 2006

High charge carrier densities have been realized in organic field-effect transistors based on single crystals of the organic semiconductors rubrene and tetracene using a high capacitance polymer electrolyte gate dielectric. The source-drain current was modulated by five orders of magnitude in a rubrene single-crystal organic field-effect transistor (SC-OFET) with gate voltages ranging from 0to−3V. A peak in the field-effect conductance was also observed in SC-OFETs at induced carrier densities of ∼1015charges∕cm2. Key to successful device fabrication was the introduction of a thin, insulating spacer layer between the organic single crystal (OSC) and the polymer electrolyte gate dielectric. Further improvement of the device fabrication procedure may eliminate suspected solvent-related degradation effects and raise mobility values in these SC-OFETs, opening the door to a wide spectrum of experiments on OSCs at high charge carrier densities.
In-line aligned and bottom-up Ag nanorods for surface-enhanced Raman spectroscopy
Authors: Suzuki Motofumi , Maekita Wataru , Wada Yoshinori , Nakajima Kaoru , Kimura Kenji , Fukuoka Takao , Mori Yasushige
Published: May 2006

We have demonstrated surface-enhanced Raman spectroscopy on arrays of Ag nanorods aligned in line by a dynamic oblique deposition technique. For the light polarized along the major axis of the nanorods, the plasma resonance of the Ag nanorods has been tuned to a wavelength suitable for Raman spectroscopy. The average width and the length-to-width ratio of the resulting nanorods are 56nm and 3.5, respectively, and the nanorods align in line with small gaps of a few 10nm. The Raman scattering for the polarized light along the nanorods is enhanced significantly as compared with that perpendicular to the nanorods. This polarization dependent Raman enhancement is attributed to the local field concentration at the ends of the nanorods. Since the preparation process is physical and completely bottom up, it is robust in its selection of the materials and is useful in providing the surface-enhanced Raman scattering sensors at low cost.
Radiation-induced differential optical absorption of metal nanoparticles
Authors: Plaksin Oleg , Takeda Yoshihiko , Amekura Hiroshi , Kishimoto Naoki
Published: May 2006

A method of measuring the temperature of metal nanoparticles under ion bombardment is proposed. Optical absorption in the range of the surface plasmon resonance of metal nanoparticles was measured during implantation of 3MeV Cu2+ ions into silica glass to derive a difference in optical absorption between beam on and off regimes. The radiation-induced differential (RD) spectra were similar to the spectra of thermomodulation (TM) and quite different from the spectra of nonlinear optical response measured by the pump-probe method. Increasing amplitude of RD and TM spectra was assigned to an increase of lattice temperature of Cu nanoparticles.
Visible light diffraction studies on periodically aligned arrays of carbon nanotubes: Experimental and theoretical comparison
Authors: Rybczynski J. , Kempa K. , Wang Y. , Ren Z. F. , Carlson J. B. , Kimball B. R. , Benham G.
Published: May 2006

We have investigated visible light diffraction on honeycomb arrays of aligned carbon nanotubes grown on nickel nanoparticles prepared using the nanosphere lithography. A monolayer of 980nm polystyrene spheres was used as the mask for the deposition of nickel nanoparticles from which carbon nanotubes of 100nm in diameter and up to a couple of microns in length were grown. We show that a standard theory of diffraction from point scatterers explains all the observed diffraction features including Bragg’s law and the strong enhancement of the second and fifth order diffraction spots.
Spin-polarized transport in hybrid (Zn,Cr)Te∕Al2O3∕Co magnetic tunnel junctions
Authors: Wang W. G. , Ni C. , Moriyama T. , Wan J. , Nowak E. , Xiao John Q.
Published: May 2006

Tunnel magnetoresistance (TMR) of 21% is observed at low temperature in hybrid magnetic tunnel junctions (MTJs) composed of a magnetic semiconductor (Zn,Cr)Te and Co electrodes separated by an alumina barrier. The TMR is observed up to 250K, which is a considerable improvement over previous work on MTJs with semiconductor electrodes. The temperature and bias dependence of the TMR are consistent with a transport model involving spin-polarized tunneling and spin-independent hopping through impurity states.
External cavity quantum-cascade laser tunable from 8.2to10.4μm using a gain element with a heterogeneous cascade
Authors: Maulini Richard , Mohan Arun , Giovannini Marcella , Faist Jérôme , Gini Emilio
Published: May 2006

A heterogeneous quantum-cascade structure based on two bound-to-continuum designs emitting at 9.6 and 8.4μm is presented. Its spontaneous emission spectrum at room temperature has a full width at half maximum of 350cm−1 and shows a variation of intensity of less than 20% over more than 200cm−1. External cavity lasers using a grating in Littrow configuration and antireflection coated chips with this active region could be tuned over 265cm−1 from 8.2to10.4μm, that is, over 24% of the center wavelength.
Synthesis and laser annealing of embedded CdSe-nanoparticles in SiO2 by pulsed excimer laser radiation
Authors: Huber P. , Karl H. , Stritzker B.
Published: May 2006

CdSe-semiconductor nanocrystals embedded in SiO2 on silicon have been synthesized by ion implantation of Cd+ and Se+ followed by pulsed excimer laser annealing at room temperature. Transmission electron microscopy and x-ray diffraction-analysis results suggest that wurzite-type embedded CdSe nanocrystals have been formed. Since laser annealing can be applied locally this opens a route towards spatially selective annealing. In a second type of experiment pulsed laser annealing was performed on embedded CdSe nanoparticles synthesized by standard thermal annealing resulting in oriented ellipsoidal deformation and morphological changes of the larger precipitates. Computer simulation results suggest a size-selective temperature increase of the CdSe nanocrystals as the underlying mechanism.
Effect of strain on structure and charge order transitions in epitaxial Bi0.4Ca0.6MnO3 films on perovskite (001) and (011) substrates
Authors: Kim Dae Ho , Christen Hans M. , Varela Maria , Lee Ho Nyung , Lowndes Douglas H.
Published: May 2006

The effect of epitaxial strain on the charge order (CO) transition in Bi0.4Ca0.6MnO3 films was studied by varying the strain’s strength and symmetry via the use of SrTiO3 and LaAlO3 substrates having different crystallographic orientations. The film on pseudocubic (001) LaAlO3, under symmetric compressive strain, exhibits a clear CO transition. In the film on a (001) SrTiO3 substrate, under symmetric tensile strain, highly segregated line-shaped features in the Bi distribution are seen in Z-contrast scanning transmission microscopy, accompanied by a strongly broadened CO transition. The asymmetric tensile stress on (011) SrTiO3 results in an apparent compressive strain state with a deviation from tetragonality (i.e., γ≠90°), accompanied by the sharpest CO transition. These comparisons illustrate the importance of considering both the strength and symmetry of epitaxial strain.
Spin transfer by nonuniform current injection into a nanomagnet
Authors: Ozatay O. , Emley N. C. , Braganca P. M. , Garcia A. G. F. , Fuchs G. D. , Krivorotov I. N. , Buhrman R. A. , Ralph D. C.
Published: May 2006

We have used nanofabrication techniques to incorporate an ∼20–30nm diameter nanoaperture within a 150×250nm2 elliptical magnetic multilayer to enable the localized injection of spin-polarized currents into a thin film nanomagnet. This results in very low spin transfer currents being required for at least partial nanomagnet reversal as well as for onset of dynamic precession. Micromagnetic simulations using Landau-Liftshitz-Gilbert equation with a spin-torque term indicate that reversal occurs via domain nucleation at the injection site followed by domain wall propagation away from the aperture, with the nanomagnet ending in one of several different states depending upon the current amplitude.
Hooge’s constant for carbon nanotube field effect transistors
Authors: Ishigami Masa , Chen J. H. , Williams E. D. , Tobias David , Chen Y. F. , Fuhrer M. S.
Published: May 2006

The 1∕f noise in individual semiconducting carbon nanotubes (s-CNT) in a field effect transistor configuration has been measured in ultrahigh vacuum and following exposure to air. The amplitude of the normalized current spectral noise density is independent of source-drain current and inversely proportional to gate voltage, to channel length, and therefore to carrier number, indicating that the noise is due to mobility rather than number fluctuations. Hooge’s constant for s-CNT is found to be (9.3±0.4)×10−3 The magnitude of the 1∕f noise is substantially decreased by exposing the devices to air.
Subgap structure in resistively shunted superconducting atomic point contacts
Authors: Dai Zhenting , Marchenkov Alexei
Published: May 2006

We report the transport properties of superconducting atomic-size contacts in different resistive environments. Embedding resistive shunts close to a junction affects the spectrum of multiple Andreev reflections. In particular, the subgap structure in current-voltage characteristics shifts to lower voltages. Experiments were performed in a special-purpose circuit that enables both voltage-biased and phase-biased measurements on the same contact configuration. Methods developed for full characterization of superconducting point contacts can be directly applied in this layout.
Piezoelectric waves near an imperfectly bonded interface between two half-spaces
Authors: Fan Hui , Yang Jiashi , Xu Limei
Published: May 2006

We show the existence of certain waves propagating near an imperfectly bonded interface between two half-spaces of different piezoelectric ceramics. Some of the waves reduce to known waves when perfect bonding is assumed. There are also waves that rely on the imperfection of the interface bonding and they do not remain as interface waves when the bonding is perfect. In particular, it is shown that interface imperfection causes dispersion in general, although there does not explicitly exist a geometric characteristic length of the two-half-space structure. The theoretical results obtained can also be used to design experiments for measuring interface properties.
Resistant starch and starch pasting properties of a starch synthase IIa-deficient wheat with apparent high amylose
Authors: Yamamori M. , Kato M. , Yui M. , Kawasaki M.
Published: May 2006

The bread wheat (Triticum aestivum L.) analysed in this study has been produced by genetically eliminating the starch synthase IIa and shows apparent high amylose (HA) in the flour starch. Some starch properties of the HA wheat were analysed. The HA wheat contained 2.8–3.6% resistant starch (RS), much more than the normal (control) wheat, which contained almost no RS. Autoclaving the HA and normal wheat starches increased RS. The former contained 10.5% RS and the latter 5.9 or 6.8% RS. Swelling of the HA wheat starch and its pasting properties using Rapid ViscoAnalyzer (RVA) were investigated. Swelling power (g/g) of the HA wheat in 0.1% AgNO3 and swelling volume (mL/g) in urea solution were significantly less than those of the normal wheat. The RVA profile of the HA wholemeal and starch also differed from the normal. The peak viscosity, minimum viscosity, and final viscosity of HA were low, and breakdown (peak minus minimum viscosity) was very small. These findings show that amount of resistant starch and pasting properties are unique in the HA wheat starch, probably caused by lack of starch synthase IIa.
The capacity of dryland lucerne for groundwater uptake
Authors: Ward P. R. , Micin S. F.
Published: May 2006

Lucerne is being widely promoted as a means of salinity prevention, due to its ability to grow roots deeper into the soil and use more water than annual crops or pastures. This helps to reduce groundwater recharge. Direct groundwater use would also help to lower water tables, but lucerne’s role in this regard is poorly understood. In this research, lucerne plants growing in 2 landscape positions (one position with access to moderately saline groundwater, and one without access to groundwater) at similar plant densities were compared in terms of their pre-dawn leaf water potentials and evapotranspiration (ET) rates during summer. Soil analysis (pH, EC, texture, and water content) indicated that soil water content below a depth of 0.9 m was the only major difference between the 2 landscape positions. Plants with access to groundwater were larger (55 v. 13 kg dry matter/ha), less stressed (–0.71 v. –1.16 MPa pre-dawn leaf water potential), and exhibited 2–3 times higher ET rates early in the morning than plants without access to groundwater. ET rates in the afternoon were similar. Total ET from plants in both landscape positions was very low relative to potential ET. We conclude that lucerne plants with access to groundwater are able to use the water to maintain lower stress levels, but not for active growth under conditions of dry topsoil and high vapour pressure deficit. Direct groundwater uptake by lucerne is likely to be low, but may be significant for salinity control in the longer term.
The kinetics and mechanisms of the acid-catalysed hydrolysis of t-butyl formate in aqueous solution.
Authors: Fredlein RA , Lauder I
Published: May 2006

The hydrolysis of t-butyl
formate in aqueous acid solution has been studied over the range 35-83�. At low
concentrations of catalysing acid, specific hydronium-ion
catalysis is enhanced by the formic acid produced during the reaction. A series
of oxygen-18 tracer experiments was performed, taking into account the
formation of isobutylene, which is a by-product of hydrolysis by alkyl-oxygen
fission. ��� The percentage alkyl-oxygen fission varies
from 3 at 35� to 40 at 76�. Catalytic rate constants for reactions by the AAL1
and the AAC2 mechanisms are expressed respectively by the equations

���������������� k?1 = 1016.6exp(-28000/RT)�� 1. mole-1 sec-1���������������� k?2 = 107.8exp(-13600/RT)�� 1. mole-1 sec-1�����������������

The rate constants found for
the BAL1 mechanism are of order-of- magnitude significance only.
A thermal technique for studying moderately fast reactions in solution
Authors: Fredlein RA , Lauder I
Published: May 2006

A thermal technique is described
for studying reactions with half-life periods from 2 to 100 sec. The method has
been used to study the acidic hydrolysis of t-butyl formate at 65.6� and also
the hydrolysis of acetic anhydride at 64.8�, both in aqueous solution.
Dithiolium and diselenolium compounds of the transition metals
Authors: Martin RL , Stewart IM
Published: May 2006

The preparations are
reported of an extended series of compounds of the type ML2X4
where M is Mn, Fe, Co, or Ni; X is Cl or Br; and L is analytically identical
with dithioacetylacetone. ��� Electronic, infrared, and Mossbauer spectra
together with the temperature dependence of the magnetism (80-300�K) of these
compounds establish-contrary to previous suggestions in the literature-that
they should be properly formulated as tetrahalometallate salts of the 3,5-
dimethyl-1,2-dithiolium cation. Simple salts of this cation (such as the
iodide) have also been isolated. ��� During the course of this work salts (I-
and [CoCl4]2-) of the hitherto unknown
3,5-dimethyl-1,2-diselenolium ion were synthesized and characterized for the
first time.
Magnetism, electronic spectra, and structure of transition metal alkaloids. VII. Iron(III) halo alkaloids
Authors: Kakos GA , Winter G
Published: May 2006

The compounds Fe4X6(OMe)6,4MeOH (I), Fe4X3(OMe)9 (II) (X = Cl,
Br), and FeCl(OMe)2
have been prepared. From their magnetic behaviour it is proposed that in the
compounds (I) the iron atoms are situated at the corners of a rhombus, that in
compounds (II) they are at the corners of a tetrahedron, and that in FeCl(OMe)2 the iron
atoms are at the corners of an isosceles triangle.
Studies in chrome mordanting. III. The oxidation of wool by chromium(VI)
Authors: Hartley FR
Published: May 2006

The effect of boiling wool
in a chromium(VI) solution on the groups present in wool has been investigated.
At low pH the disulphide bonds were oxidized directly, whereasat high pH the
hydrolysis products of the disulphide bonds, such as hydrogen sulphide, rather
than the disulphide bonds themselves were oxidized. In addition, tyrosine was
oxidized throughout the pH range investigated (pH 2-9) and lysine was oxidized
at high pH (pH 7-9), though not at low pH. The maximum chromium(III) uptake by
the wool, for a given concentration of chromium(VI) in the bath, occurred at pH
4.
Kinetics of hydrolysis of n-hexyl bromide, n-heptyl bromide, and n-octyl bromide in alkaline and neutral media
Authors: Singh B , Behari K , Krishna B
Published: May 2006

Data obtained in the
kinetic study of the hydrolysis of n-hexyl, n-heptyl, and n-octyl bromide in
alkaline and neutral media at different temperatures and in varying
ethanol-water mixtures are reported. The rate constants for the three reactions
(bimolecular and unimolecular substitution, and bimolecular elimination) which
occur simultaneously have been calculated for each compound.
Synthesis of pyridocarbazoles for anti-tumour studies
Authors: Dalton LK , Demerac S , Teitei T
Published: May 2006

Cyclodehydration in
orthophosphoric acid of the azomethines of 3- formyl-carbazoles and
aminoacetals has yielded 5-methyl- (IId), 3,5,11-
trimethyl-(11b), 3,5,9,11-tetramethyl-(IIc), and
5,7,10,11-tetramethyl- 6H-pyrido[4,3-b]carbazoles (IIa).
In the same way γ-carboline and 6,9- dimethyl-γ-carboline were
obtained from the azomethines of 3-formyl- and 3-formyl-4,7-dimethyl-indole. A Doebner reaction with 3-amino-2- methylcarbazole, acetaldehyde,
and pyruvic acid yielded 1-carboxy-3,5- dimethyl-7H-pyrido[2,3-c]carbazole (VIIIb) from which was derived the methyl ester (VIIIc) and 3,5-dimethyl-7H-pyrido [2,3-c]carbazole (VIIIa).