bluuebunny/crossref_metadata_2025 huggingface dataset:
Coriolis forces influence the secondary circulation of gravity currents flowing in large‐scale sinuous submarine channel systems
Authors: Cossu Remo , Wells Mathew G.
Published: September 2010

A combination of centrifugal and Coriolis forces drive the secondary circulation of turbidity currents in sinuous channels, and hence determine where erosion and deposition of sediment occur. Using laboratory experiments we show that when centrifugal forces dominate, the density interface shows a superelevation at the outside of a channel bend. However when Coriolis forces dominate, the interface is always deflected to the right (in the Northern Hemisphere) for both left and right turning bends. The relative importance of either centrifugal or Coriolis forces can be described in terms of a Rossby number defined as Ro = U/fR, where U is the mean downstream velocity, f the Coriolis parameter and R the radius of curvature of the channel bend. Channels with larger bends at high latitudes have ∣Ro∣ < 1 and are dominated by Coriolis forces, whereas smaller, tighter bends at low latitudes have ∣Ro∣ ≫ 1 and are dominated by centrifugal forces.
BRG1 helps RNA polymerase II to overcome a nucleosomal barrier during elongation, in vivo
Authors: Subtil‐Rodríguez Alicia , Reyes José C
Published: September 2010

RNA polymerase II (RNAPII) transcribes genes in a chromatin context. We have designed a system to investigate the role of chromatin remodelling during elongation in vivo, which involves inserting a strong nucleosome‐positioning sequence between a promoter and a reporter gene. Our data indicate that a nucleosome positioned in the body of a transcription unit impairs RNAPII progression, provokes RNAPII accumulation upstream to the positioned nucleosome and reduces transcription. By using this system, we show that BRG1, the enzymatic motor of the SWI–SNF chromatin‐remodelling complex, is recruited to the positioned nucleosome in a transcription elongation‐dependent manner and facilitates traversal of the nucleosome by RNAPII.
Catalysis
Authors: Ai Mamoru , Raje Ajoy , Davis Burtron H , Eguchi Koichi , Horanyi Gyorgy , Ishihara Tatsumi , Takita Yusaku , Mandai Shigemi , Matsuhisa Toshio , Seehra Mohindar , Ibrahim M , Vayenas Constantinos , Neophytides Stylianos
Published: September 2010

There is an increasing challenge for chemical industry and research institutions to find cost-efficient and environmentally sound methods of converting natural resources into fuels chemicals and energy. Catalysts are essential to these processes and the Catalysis Specialist Periodical Report series serves to highlight major developments in this area. This series provides systematic and detailed reviews of topics of interest to scientists and engineers in the catalysis field. The coverage includes all major areas of heterogeneous and homogeneous catalysis and also specific applications of catalysis such as NOx control kinetics and experimental techniques such as microcalorimetry. Each chapter is compiled by recognised experts within their specialist fields and provides a summary of the current literature. This series will be of interest to all those in academia and industry who need an up-to-date critical analysis and summary of catalysis research and applications. Catalysis will be of interest to anyone working in academia and industry that needs an up-to-date critical analysis and summary of catalysis research and applications. Specialist Periodical Reports provide systematic and detailed review coverage in major areas of chemical research. Compiled by teams of leading experts in their specialist fields, this series is designed to help the chemistry community keep current with the latest developments in their field. Each volume in the series is published either annually or biennially and is a superb reference point for researchers. www.rsc.org/spr
Baroreflex sensitivity is higher during acute psychological stress in healthy subjects under β-adrenergic blockade
Authors: Truijen Jasper , Davis Shyrin C.A.T. , Stok Wim J. , Kim Yu-Sok , van Westerloo David J. , Levi Marcel , van der Poll Tom , Westerhof Berend E. , Karemaker John M. , van Lieshout Johannes J.
Published: September 2010

Acute psychological stress challenges the cardiovascular system with an increase in BP (blood pressure), HR (heart rate) and reduced BRS (baroreflex sensitivity). β-adrenergic blockade enhances BRS during rest, but its effect on BRS during acute psychological stress is unknown. This study tested the hypothesis that BRS is higher during acute psychological stress in healthy subjects under β-adrenergic blockade. Twenty healthy novice male bungee jumpers were randomized and studied with (PROP, n=10) or without (CTRL, n=10) propranolol. BP and HR responses and BRS [cross-correlation time-domain (BRSTD) and cross-spectral frequency-domain (BRSFD) analysis] were evaluated from 30 min prior up to 2 h after the jump. HR, cardiac output and pulse pressure were lower in the PROP group throughout the study. Prior to the bungee jump, BRS was higher in the PROP group compared with the CTRL group [BRSTD: 28 (24–42) compared with 17 (16–28) ms·mmHg−1, P<0.05; BRSFD: 27 (20–34) compared with 14 (9–19) ms·mmHg−1, P<0.05; values are medians (interquartile range)]. BP declined after the jump in both groups, and post-jump BRS did not differ between the groups. In conclusion, during acute psychological stress, BRS is higher in healthy subjects treated with non-selective β-adrenergic blockade with significantly lower HR but comparable BP.
Variable Binned Scatter Plots
Authors: Hao Ming C. , Dayal Umeshwar , Sharma Ratnesh K. , Keim Daniel A. , Janetzko Halldór
Published: September 2010

The scatter plot is a well-known method of visualizing pairs of two continuous variables. Scatter plots are intuitive and easy-to-use, but often have a high degree of overlap which may occlude a significant portion of the data. To analyze a dense non-uniform data set, a recursive drill-down is required for detailed analysis. In this article, we propose variable binned scatter plots to allow the visualization of large amounts of data without overlapping. The basic idea is to use a non-uniform (variable) binning of the x and y dimensions and to plot all data points that are located within each bin into the corresponding squares. In the visualization, each data point is then represented by a small cell (pixel). Users are able to interact with individual data points for record level information. To analyze an interesting area of the scatter plot, the variable binned scatter plots with a refined scale for the subarea can be generated recursively as needed. Furthermore, we map a third attribute to color to obtain a visual clustering. We have applied variable binned scatter plots to solve real-world problems in the areas of credit card fraud and data center energy consumption to visualize their data distributions and cause-effect relationships among multiple attributes. A comparison of our methods with two recent scatter plot variants is included.
Local probing of ionic diffusion by electrochemical strain microscopy: Spatial resolution and signal formation mechanisms
Authors: Morozovska A. N. , Eliseev E. A. , Balke N. , Kalinin S. V.
Published: September 2010

Electrochemical insertion-deintercalation reactions are typically associated with significant change in molar volume of the host compound. This strong coupling between ionic currents and strains underpins image formation mechanisms in electrochemical strain microscopy (ESM), and allows exploring the tip-induced electrochemical processes locally. Here we analyze the signal formation mechanism in ESM, and develop the analytical description of operation in frequency and time domains. The ESM spectroscopic modes are compared to classical electrochemical methods including potentiostatic and galvanostatic intermittent titration, and electrochemical impedance spectroscopy. This analysis illustrates the feasibility of spatially resolved studies of Li-ion dynamics on the sub-10-nm level using electromechanical detection.
A comparative evaluation of elasticity in pentaerythritol tetranitrate using Brillouin scattering and resonant ultrasound spectroscopy
Authors: Stevens Lewis L. , Hooks Daniel E. , Migliori Albert
Published: September 2010

Elastic tensors for organic molecular crystals vary significantly among different measurements. To understand better the origin of these differences, Brillouin scattering and resonant ultrasound spectroscopy measurements were made on the same specimen for single crystal pentaerythritol tetranitrate. The results differ significantly despite mitigation of sample-dependent contributions to errors. The frequency dependence and vibrational modes probed for both measurements are discussed in relation to the observed tensor variance.
High aspect ratio silicon etch: A review
Authors: Wu Banqiu , Kumar Ajay , Pamarthy Sharma
Published: September 2010

High aspect ratio (HAR) silicon etch is reviewed, including commonly used terms, history, main applications, different technological methods, critical challenges, and main theories of the technologies. Chronologically, HAR silicon etch has been conducted using wet etch in solution, reactive ion etch (RIE) in low density plasma, single-step etch at cryogenic conditions in inductively coupled plasma (ICP) combined with RIE, time-multiplexed deep silicon etch in ICP-RIE configuration reactor, and single-step etch in high density plasma at room or near room temperature. Key specifications are HAR, high etch rate, good trench sidewall profile with smooth surface, low aspect ratio dependent etch, and low etch loading effects. Till now, time-multiplexed etch process is a popular industrial practice but the intrinsic scalloped profile of a time-multiplexed etch process, resulting from alternating between passivation and etch, poses a challenge. Previously, HAR silicon etch was an application associated primarily with microelectromechanical systems. In recent years, through-silicon-via (TSV) etch applications for three-dimensional integrated circuit stacking technology has spurred research and development of this enabling technology. This potential large scale application requires HAR etch with high and stable throughput, controllable profile and surface properties, and low costs.
Runaway-loss induced negative and positive loop voltage spikes in the Aditya Tokamak
Authors: Paradkar Bhooshan , Ghosh J. , Chattopadhyay P. K. , Tanna R. L. , Raju D. , Bhatt S. B. , Rao C. V. S. , Joisa Sankar , Banerjee Santanu , Manchanda R. , Gupta C. N. , Saxena Y. C. ,   Aditya Team
Published: September 2010

Negative spikes followed by positive ones in the loop voltage signal during the discharge are observed in the Aditya Tokamak [S. B. Bhatt et al., Indian J. Pure Appl. Phys. 27, 710 (1989)]. These spikes are always accompanied by hard x-ray bursts caused by sudden loss of runaway electrons. The observed growth of m=3 mode seemed responsible for the losses of localized beams of runaway electrons (Eγ∼1–5 MeV) from the plasma region around q=3 magnetic surface. The movement of these runaway electrons during their extraction from inside the plasma induces both positive and negative electric fields at those locations. In this paper, a one-dimensional toroidal electric field diffusion model is used to estimate the induced electric field at the plasma boundary, which matches quite well with the observed spikes in loop voltage in both magnitude as well as its temporal evolution.
Rung 3.5 density functionals
Authors: Janesko Benjamin G.
Published: September 2010

This work proposes a new term on the “Jacob’s ladder” of approximate exchange-correlation functionals in Kohn–Sham density functional theory. In these Rung 3.5 functionals, the exchange-correlation energy density at a point depends linearly (rather than quadratically) on the nonlocal Kohn–Sham one-particle density matrix in a finite neighborhood around the point. These functionals are intermediate in complexity between the semilocal approximations of Rungs 1–3, and fully nonlocal Rung 4 approximations such as global hybrids. Rung 3.5 functionals built on the model for exchange in [B. G. Janesko, J. Chem. Phys. 131, 234111 (2009)] predict molecular thermochemistry and kinetics with accuracy intermediate between their “parent” semilocal functional and the corresponding global hybrid. The best Rung 3.5 functional presented here gives mean absolute errors of 5.7 kcal/mol for G3/99 thermochemistry, 5.2 kcal/mol for HTBH38/04 hydrogen-transfer reaction barriers, and 5.7 kcal/mol for NHTBH38/04 nonhydrogen-transfer reaction barriers, while incorporating only two empirical parameters.
Magnetic-field-orientation dependent magnetization reversal and spin waves in elongated permalloy nanorings
Authors: Ma F. S. , Zhang V. L. , Wang Z. K. , Lim H. S. , Ng S. C. , Kuok M. H. , Ren Y. , Adeyeye A. O.
Published: September 2010

The field-orientation dependence of magnetization reversal and spin wave modes in nanorings has been investigated by focused magneto-optical Kerr effect spectroscopy, Brillouin spectroscopy, and micromagnetic simulations. The samples studied are periodic arrays of 150 nm wide Ni80Fe20 rings with long axes of 850, 1200, and 1500 nm, and respective short axes of 550, 700, and 900 nm. For the smallest ring, the onion-to-vortex transition is observed for both the applied magnetic field directed along, and 5° from its magnetization easy axis. In contrast for the two larger rings, this transition is not observed for the field in the latter orientation. Splitting of spin wave modes is observed for the transition from the onion to vortex state. Micromagnetic simulations of magnetization reversal and spin waves are in good agreement with experiments. The simulated temporal recording of magnetization distributions during transition reveals that different switching mechanisms result from different applied magnetic field orientations.
Visualization and quantification of four steps in magnetic field induced two-dimensional ordering of superparamagnetic submicron particles
Authors: Gajula Gnana Prakash , Neves-Petersen Maria Teresa , Petersen Steffen B.
Published: September 2010

We hereby report a methodology that permits a quantitative investigation of the temporal self-organization of submicron sized superparamagnetic composite particles in the presence of an external magnetic field. The kinetics of field-induced self-organization into linear chains, time-dependent chain-size distribution, resolved growth steps (condensation, polarization, colinearity, and concatenation), the average chain growth rate, and interparticle interaction length were calculated in the presence of a 120 G external magnetic field using optical microscopy and “in-house” developed image analysis software. The measurements are in good agreement with theoretical assumptions.
Analysis of current-driven motion of morphologically stable voids in metallic thin films: Steady and time-periodic states
Authors: Cho Jaeseol , Gungor M. Rauf , Maroudas Dimitrios
Published: September 2010

We report results of self-consistent numerical simulations of current-induced migration of morphologically stable voids in metallic thin films accounting rigorously for current crowding, surface curvature, and surface diffusional anisotropy effects. In a previous study, we demonstrated that as the morphological stability limit is approached, the migration speed of a morphologically stable steady void deviates substantially from being inversely proportional to the void size. We also derived a scaling relationship for the void migration speed, rescaled properly with a shape factor, as a function of the void size as described by Cho et al. [Appl. Phys. Lett. 85, 2214 (2004)]. In this study, we calculate accurately shape factors for stable steady void morphologies, as well as for stable time-periodic void morphologies with surface waves propagating on the voids. We predict the effects of surface diffusional anisotropy strength on the migration of stable steady voids, as well as the effects of void size on void migration speed for both steady and time-periodic states. The results validate fully our scaling theory for the current-driven migration of morphologically stable voids and establish its universality. This theory provides an enabling tool for better design of interconnects in integrated circuits toward optimal reliability under conditions that render void migration an important source of metallic thin-film failure.
Electron-electron scattering in a double quantum dot: Effective mass approach
Authors: Kruchinin S. Yu. , Fedorov A. V. , Baranov A. V. , Perova T. S. , Berwick K.
Published: September 2010

We present a theoretical description of the first-order scattering of interacting electrons and holes in a double quantum dot. Assuming infinitely high walls, strong confinement, and a two-band approximation, we derive general expressions for the two-particle matrix elements of the screened Coulomb potential. We also determine the selection rules for different scattering channels and consider special cases where the corresponding matrix elements can be represented by simple analytical expressions. Numerical calculations of the matrix elements and an analysis of their dependence on the geometrical and material parameters of the double quantum dot have also been performed.
Communication: Simple self-correlation corrections to the Ragot–Cortona model of local correlation energy
Authors: Ragot Sébastien
Published: September 2010

The Ragot–Cortona or RC model of local correlation energy [J. Chem. Phys. 121, 7671 (2004)] improves the standard local approximation in various respects. This letter aims at illustrating the origin of this improvement. To that aim, simple self-interaction corrected versions of the RC model are implemented, which involve local energy differences only. Several correlation functionals are selected for direct comparison using Hartree–Fock charge densities of atomic ions (H− to Ar). One of the self-interaction corrected versions of the RC model shows surprising improvements over the initial RC model. First, it dramatically improves the atomic correlation energies of atomic ions. Second, the impact on the contribution of the correlation energy to ionization potentials or electron affinities is still more convincing. In both cases, the accuracy achieved is close to or better than a selection of gradient-level functionals.
Finite-dimensional attractors for the Kirchhoff models
Authors: Zhijian Yang
Published: September 2010

The paper studies the existence of the finite-dimensional global attractor and exponential attractor for the dynamical system associated with the Kirchhoff models arising in elasto-plastic flow utt−div{|∇u|m−1∇u}−Δut+Δ2u+h(ut)+g(u)=f(x). By using the method of ℓ-trajectories and the operator technique, it proves that under subcritical case, 1≤m<N+2(N−2)+, the above-mentioned dynamical system possesses in different phase spaces a finite-dimensional (weak) global attractor and a weak exponential attractor, respectively. For application, the fact shows that for the concerned elasto-plastic flow the permanent regime (global attractor) can be observed when the excitation starts from any bounded set in phase space, and the fractal dimension of the attractor, that is, the number of degree of freedom of the turbulent phenomenon and thus the level of complexity concerning the flow, is finite.
Mechanism for the abiotic synthesis of uracil via UV-induced oxidation of pyrimidine in pure H2O ices under astrophysical conditions
Authors: Bera Partha P. , Nuevo Michel , Milam Stefanie N. , Sandford Scott A. , Lee Timothy J.
Published: September 2010

The UV photoirradiation of pyrimidine in pure H2O ices has been explored using second-order Møller–Plesset perturbation theory and density functional theory methods, and compared with experimental results. Mechanisms studied include those starting with neutral pyrimidine or cationic pyrimidine radicals, and reacting with OH radical. The ab initio calculations reveal that the formation of some key species, including the nucleobase uracil, is energetically favored over others. The presence of one or several water molecules is necessary in order to abstract a proton which leads to the final products. Formation of many of the photoproducts in UV-irradiated H2O:pyrimidine=20:1 ice mixtures was established in a previous experimental study. Among all the products, uracil is predicted by quantum chemical calculations to be the most favored, and has been identified in experimental samples by two independent chromatography techniques. The results of the present study strongly support the scenario in which prebiotic molecules, such as the nucleobase uracil, can be formed under abiotic processes in astrophysically relevant environments, namely in condensed phase on the surface of icy, cold grains before being delivered to the telluric planets, like Earth.
Magic and hot giant fullerenes formed inside ion irradiated weakly bound C60 clusters
Authors: Zettergren H. , Johansson H. A. B. , Schmidt H. T. , Jensen J. , Hvelplund P. , Tomita S. , Wang Y. , Martín F. , Alcamí M. , Manil B. , Maunoury L. , Huber B. A. , Cederquist H.
Published: September 2010

We find that the most stable fullerene isomers, C70–C94, form efficiently in close-to central collisions between keV atomic ions and weakly bound clusters of more than 15 C60-molecules. We observe extraordinarily high yields of C70 and marked preferences for C78 and C84. Larger even-size carbon molecules, C96–C180, follow a smooth log-normal (statistical) intensity distribution. Measurements of kinetic energies indicate that C70–C94 mainly are formed by coalescence reactions between small carbon molecules and C60, while Cn with n≥96 are due to self-assembly (of small molecules) and shrinking hot giant fullerenes.
Mathematical model of flux relaxation phenomenon
Authors: Ma Rongchao
Published: September 2010

The investigations on the flux relaxation phenomenon of a type-II superconductor are important because they provide the information about the flux pinning ability and current-carrying ability of the superconductor. However, a unified theory of flux relaxation is currently unavailable. Here, I present a general mathematical model of the flux relaxation. In this model, I proposed a series expansion to the activation energy and derived a general formula for the current decay behavior. In the light of these formulas, I can analyze the experimental data on the current decay behavior and then calculate the activation energy of a vortex system without subjecting to any special conditions. The results are accurate for the current decay measurements from a Bi2Sr2CaCu2O8+x superconductor.
Extrinsic ferromagnetism in epitaxial Co-doped CeO2 pulsed laser deposited films
Authors: Colis S. , Bouaine A. , Moubah R. , Schmerber G. , Ulhaq-Bouillet C. , Dinia A. , Dahéron L. , Petersen J. , Becker C.
Published: September 2010

We report on the structural and magnetic properties of 5 at. % Co-doped CeO2 films grown on LaAlO3(001) substrates by pulsed laser deposition. A series of epitaxially grown samples made under different oxygen partial pressures ranging from 10−4 to 10−1 mbar showed a ferromagnetic signal at room temperature. This signal is independent on the oxygen partial pressure during deposition. X-ray photoelectron spectroscopy showed an increasing concentration of defects as the oxygen pressure during deposition decreases. Although x-ray diffraction and transmission electron microscopy observations could not prove the existence of spurious phases, the temperature dependent variation in the magnetization suggests the existence of small magnetic Co clusters with a large distribution of blocking temperatures.
Pressure-volume-temperature equation of state of tungsten carbide to 32 GPa and 1673 K
Authors: Litasov Konstantin D. , Shatskiy Anton , Fei Yingwei , Suzuki Akio , Ohtani Eiji , Funakoshi Kenichi
Published: September 2010

We have obtained pressure-volume-temperature (P-V-T) equation of state for hexagonal tungsten carbide (α-WC) up to 32 GPa and 1673 K using synchrotron x-ray diffraction in a multianvil apparatus at the SPring-8 facility. MgO and Au were used as pressure calibrants. A least-squares fit of the P-V-T-data to a high-temperature Birch–Murnaghan equation of state yielded V0=20.750±0.002 Å3, KT=384±4 GPa, K′=4.65±0.32, temperature derivative of the bulk modulus (∂KT/∂T)P=−0.014±0.002 GPa/K, and thermal expansion α=a0+a1T with a0=0.96(±0.05)×10−5 K−1 and a1=0.48(±0.05)×10−8 K−2. The data showed an anisotropic nature of compressibility, with the a-axis (KTa=341±6 GPa) more compressible than the c-the axis (KTc=506±12 GPa) as well as an anisotropic temperature dependence of KT. The estimated thermal Grüneisen parameters are 1.44–1.64 and the Debye temperature is calculated to be 1220 K, which is different from previous estimates.
Dynamic free energies, cage escape trajectories, and glassy relaxation in dense fluids of uniaxial hard particles
Authors: Zhang Rui , Schweizer Kenneth S.
Published: September 2010

We extend the naïve mode coupling theory and nonlinear Langevin equation theory of coupled translational-rotational activated dynamics in dense fluids of uniaxial hard particles to more anisotropic rods, and mechanistically analyze in depth the dynamic free-energy surface, hopping process, kinetic vitrification, and fragility. Universal behavior is predicted for the transient center-of-mass (CM) localization length and angle based on a differential volume fraction that quantifies the distance from the dynamic crossover and proper geometric nondimensionalization of the localization quantities. The thermally activated real space cage escape process is increasingly controlled by the CM translation relative to the rotational motion as the particle aspect ratio grows. The mean first passage or structural relaxation time grows faster than exponentially with volume fraction, and is a nonmonotonic function of aspect ratio. The latter results in a kinetic vitrification volume fraction and dynamic fragility that vary nonmonotonically with shape anisotropy. The barrier hopping time based on the simplified CM theory where particle rotation is dynamically frozen is massively reduced by ∼2–3.5 orders of magnitude if the cooperative rotation-translation paths are exploited to escape local cage constraints.
Annealing induced nanostructure and photoluminescence property evolution in solution-processed Mg-alloyed ZnO nanowires
Authors: Shimpi Paresh , Ding Yong , Suarez Ernesto , Ayers John , Gao Pu-Xian
Published: September 2010

Solution-processed Mg-alloyed ZnO nanowire arrays have been achieved recently without using high temperature annealing process. By introducing thermal annealing processes in oxygen-rich ambient condition, the UV near-band-edge (NBE) emission was surprisingly mitigated until disappeared with annealing temperature increasing from 400 to 900 °C. As the annealing temperature increased, intensity of UV peak decreased while intensity of visible peak (490–520 nm) increased. The structure evolution upon thermal annealing was revealed to be responsible for these abnormal photoluminescence property variations, where unusual (Zn,Mg)1.7SiO4 epitaxially evolved on ZnMgO nanowires surface and contributed to the quenching of UV NBE emission. The structure evolution induced UV-NBE quenching and nanoscale localized alloying in semiconductor ZnMgO nanowires could bring up opportunities in catalysis, optoelectronics, spintronics, and sensors.
Tuning ferromagnetism in MgxZn1−xO thin films by band gap and defect engineering
Authors: Li Yongfeng , Deng Rui , Yao Bin , Xing Guozhong , Wang Dandan , Wu Tom
Published: September 2010

We investigate the room temperature ferromagnetism in band gap tunable MgxZn1−xO (x≤0.22) alloy thin films and find that ferromagnetism is significantly enhanced in p-type MgxZn1−xO (x≥0.17) compared with the n-type counterparts (x≤0.15). Temperature-dependent photoluminescence measurements reveal the correlation between the p-type behavior, enhanced ferromagnetism, and zinc vacancies. First-principle calculations demonstrate that the formation energy of zinc vacancies decreases with the increasing Mg content and the zinc vacancies in MgxZn1−xO alloys stabilize the ferromagnetic coupling. Our results suggest a viable route to tune the magnetic properties of oxides through band gap and defect engineering.
Redox-based resistive switching in ferroelectric perovskite nanotubes
Authors: Nonnenmann Stephen S. , Gallo Eric M. , Spanier Jonathan E.
Published: September 2010

Hysteresis in current and ferroelectric piezoelectric phase were collected across the walls of individual, electrically interfaced lead zirconate titanate (PZT) nanotubes. The nanotubes exhibit average on/off current ratios of ∼10 and ∼1000 in static local probe and top-electroded configurations, respectively. Reversibility in conduction state of an individual nanotube following different stages of an O2-rich/O2-deficient/O2-rich anneal cycle provide evidence of an oxygen vacancy concentration-based conduction mechanism.
Lateral signals in piezoresponse force microscopy at domain boundaries of ferroelectric crystals
Authors: Johann Florian , Jungk Tobias , Lilienblum Martin , Hoffmann Ákos , Soergel Elisabeth
Published: September 2010

In piezoresponse force microscopy a lateral signal at the domain boundaries is occasionally observed. In recent years, a couple of experiments have been reported and varying explanations for the origin of this lateral signal have been proposed. Additionally, elaborated theoretical modeling for this particular issue has been carried out. Here we present experimental data obtained on different crystallographic cuts of LiNbO3, BaTiO3, and KTiOPO4 single crystals. We could thereby rule out some of the explanations proposed so far, introduce another possible mechanism, and quantitatively compare our results to the existing modeling.
A low-temperature crystallization path for device-quality ferroelectric films
Authors: Li Jinwang , Kameda Hiroyuki , Trinh Bui Nguyen Quoc , Miyasako Takaaki , Tue Phan Trong , Tokumitsu Eisuke , Mitani Tadaoki , Shimoda Tatsuya
Published: September 2010

We show a path for low-temperature crystallization of device-quality solution-processed lead zirconate titanate films. The essential aspect of the path is to circumvent pyrochlore formation at around 300 °C during temperature increase up to 400 °C. By maintaining enough carbon via pyrolysis at 210 °C, well below the temperature for pyrochlore formation, Pb2+ can be reduced to Pb0. This leads to the lack of Pb2+ in the film to suppress the development of pyrochlore, which accounts for the usual high-temperature conversion to perovskite. Films on metal, metal/oxide hybrid, and oxide bottom electrodes were successfully crystallized at 400–450 °C.
Imaging biological tissues with electrical conductivity contrast below 1 S m−1 by means of magnetoacoustic tomography with magnetic induction
Authors: Hu Gang , Li Xu , He Bin
Published: September 2010

Magnetoacoustic tomography with magnetic induction (MAT-MI) is a recently introduced imaging modality for noninvasive electrical impedance imaging, with ultrasound imaging resolution and a contrast reflecting the electrical conductivity properties of tissues. However, previous MAT-MI systems can only image samples that are much more conductive than real human or animal tissues. To image real biological tissue samples, a large-current-carrying coil that can give stronger magnetic stimulations and stronger MAT-MI acoustic signals is employed in this study. The conductivity values of all the tissue samples employed in this study are also directly measured using a well calibrated four-electrode system. The experimental results demonstrated the feasibility to image biological tissues with electrical conductivity contrast below 1.0 S/m using the MAT-MI technique with safe level of electromagnetic energy applied to tissue samples.
Vertical polyelectrolyte-gated organic field-effect transistors
Authors: Liu J. , Herlogsson L. , Sawatdee A. , Favia P. , Sandberg M. , Crispin X. , Engquist I. , Berggren M.
Published: September 2010

Short-channel, vertically structured organic transistors with a polyelectrolyte as gate insulator are demonstrated. The devices are fabricated using low-resolution, self-aligned, and mask-free photolithography. Owing to the use of a polyelectrolyte, our vertical electrolyte-gated organic field-effect transistors (VEGOFETs), with channel lengths of 2.2 and 0.7 μm, operate at voltages below one volt. The VEGOFETs show clear saturation and switch on and off in 200 μs. A vertical geometry to achieve short-transistor channels and the use of an electrolyte makes these transistors promising candidates for printed logics and drivers with low operating voltage.
Transverse-microcavity modulation of photoluminescence from GaN nanowires
Authors: Long J. P. , Flynn R. A. , Vurgaftman I. , Simpkins B. S. , Mäkinen A. J. , Mastro M. A. , Pehrsson P. E.
Published: September 2010

Spatially resolved photoluminescence (PL) spectra from tapered GaN nanowires (NWs) with triangular cross section exhibit marked intensity modulations along the NW length. The modulation periodicity is attributed to previously unrecognized, leaky transverse standing-waves that occur when the PL wavelength matches path length criteria. These Fabry–Perot modes can affect optical measurements in transparent nanostructures even for dimensions less than ∼λ/2n, where λ is the free-space wavelength and n is the index of refraction.
An L-band coaxial relativistic backward wave oscillator with mechanical frequency tunability
Authors: Ge Xingjun , Zhong Huihuang , Qian Baoliang , Zhang Jun , Gao Liang , Jin Zhenxing , Fan Yuwei , Yang Jianhua
Published: September 2010

The initial experimental results of an L-band coaxial relativistic backward wave oscillator with mechanical frequency tunability are presented. The key effects of the inner-conductor contributing to the mechanical frequency tunability are investigated theoretically and experimentally. In the experiments, the L-band microwave with frequency of 1.58 GHz is radiated when the inner-conductor radius is 1.5 cm. Meanwhile, the S-band microwave with frequency of 2.31 GHz is generated after removing the inner-conductor. In addition, the frequency tuning within 4% is realized by mechanically altering the radius of the inner-conductor at a half power level.
Basis set dependence of the doubly hybrid XYG3 functional
Authors: Zhang Igor Ying , Luo Yi , Xu Xin
Published: September 2010

In the present study, we investigated the basis set dependence of XYG3, a newly developed doubly hybrid functional [Y. Zhang, X. Xu, and W. A. Goddard III, Proc. Natl. Acad. Sci. U.S.A. 106, 4963 (2009)], in prediction of (1) heats of formation (HOFs), (2) bond dissociation enthalpies (BDEs), (3) reaction barrier heights (RBHs), and (4) nonbonded interactions (NBIs). We used basis sets of triple-zeta quality starting from 6-311+G(d,p) with increasing completeness of the polarization functions to the largest Pople-type basis set 6-311++G(3df,3pd) and found that there was a continued improvement with larger basis sets. We showed that while HOF predictions were prone to basis set deficiencies, the basis set dependences in calculating BDEs, RBHs, and NBIs were mild. All of them converged fast with the increase of basis set size. We extended XYG3 to propose the XYG3o functional which was specifically optimized for a particular basis set in order to enhance its performance when using basis set of moderate size. With the 6-311+G(2df,p) basis set, XYG3o led to MADs of 2.56 kcal/mol for HOFs of the G3/99 set, 1.17 kcal/mol for BDEs of the BDE92/07 set, 1.11 kcal/mol for RBHs of the NHTBH38/04 and HTBH38/04 sets, and 0.40 kcal/mol for NBIs of the NCIE31/05 set, being comparable to those obtained by using XYG3/6-311++G(3df,3pd).
Remote sensing and control of phase qubits
Authors: Li Dale , da Silva Fabio C. S. , Braje Danielle A. , Simmonds Raymond W. , Pappas David P.
Published: September 2010

We demonstrate a remote sensing design of phase qubits by separating the control and readout circuits from the qubit loop. This design improves measurement reliability because the control readout chip can be fabricated using more robust materials and can be reused to test different qubit chips. Typical qubit measurements such as Rabi oscillations, spectroscopy, and excited-state energy relaxation are presented.
Whispering gallery mode lasing in electrically driven quantum dot micropillars
Authors: Albert F. , Braun T. , Heindel T. , Schneider C. , Reitzenstein S. , Höfling S. , Worschech L. , Forchel A.
Published: September 2010

We report on whispering gallery mode lasing in electrically driven quantum dot micropillar cavities. The high quality microcavity structures feature whispering gallery mode emission with Q-factors up to 40 000 and laser threshold currents below 10 μA for devices with diameters between 2.6 and 5.6 μm. For large diameter micropillars a coexistence of lasing from two whispering gallery modes is realized which could be the basis for efficient terahertz generation via difference frequency generation.
Improved n-type bottom-contact organic transistors by introducing a poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) coating on the source/drain electrodes
Authors: Hong Kipyo , Kim Se Hyun , Yang Chanwoo , Jang Jaeyoung , Cha Hyojung , Park Chan Eon
Published: September 2010

We improved the device performance of N,N′-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) n-type field-effect transistors, increasing electron-mobility from 0.003 to 0.101 cm2/V s, by applying a coating of poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) to gold source/drain (S/D) electrodes, thereby reducing contact resistance in the devices. Crystallinity and electronic structure studies suggested that the improved device performance resulted from higher crystallinity of PTCDI-C13 on the PEDOT:PSS-coated S/D electrodes at the interface between the electrode and the channel.
Mechanically and electronically controlled molecular switch behavior in a compound molecular device
Authors: Ren Yun , Chen Ke-Qiu , He Jun , Tang Li-Ming , Pan Anlian , Zou B. S. , Zhang Yan
Published: September 2010

A compound molecular device constructed by carbon nanotube, organic molecule, and metal electrode is proposed, and their electronic transport properties are calculated by using nonequilibrium Green’s functions method in combination with the density-functional theory. The results show that mechanically controlled molecular switch, and electrically induced molecular switch behavior based on negative differential resistance can be observed in such molecular devices. The mechanism for the switch behavior is suggested.
Low gap amorphous GaN1−xAsx alloys grown on glass substrate
Authors: Yu K. M. , Novikov S. V. , Broesler R. , Liliental-Weber Z. , Levander A. X. , Kao V. M. , Dubon O. D. , Wu J. , Walukiewicz W. , Foxon C. T.
Published: September 2010

Amorphous GaN1−xAsx layers with As content in the range of x=0.1 to 0.6 were grown by molecular beam epitaxy on Pyrex glass substrate. These alloys exhibit a wide range of band gap values from 2.2 to 1.3 eV. We found that the density of the amorphous films is ∼0.8–0.85 of their corresponding crystalline value. These amorphous films have smooth morphology, homogeneous composition, and sharp well defined optical absorption edges. The measured band gap values for the crystalline and amorphous GaN1−xAsx alloys are in excellent agreement with the predictions of the band anticrossing model. The high absorption coefficient of ∼105 cm−1 for the amorphous GaN1−xAsx films suggests that relatively thin films (on the order of 1 μm) are necessary for photovoltaic application.
Interface layer thickness effect on the photocurrent of Pt sandwiched polycrystalline ferroelectric Pb(Zr,Ti)O3 films
Authors: Cao Dawei , Zhang Hui , Fang Liang , Dong Wen , Zheng Fengang , Shen Mingrong
Published: September 2010

Based on the analysis of the photocurrent behavior of Pt sandwiched Pb(Zr0.2Ti0.8)O3 (PZT) films, the experimental evidence of top Pt/PZT interface layer thickness effect on the photocurrent is reported. It was well established before that the photocurrent of metal/ferroelectric film is attributed to the height of Schottky contact barrier. However, our results suggest that the photocurrent of Pt/PZT interface contact is determined not only by the barrier height but also by the interface layer thickness, namely, by the built-in electrical field at the interface layer. The mechanism behind such photocurrent phenomenon is proposed.
Exploring challenges in rational enzyme design by simulating the catalysis in artificial kemp eliminase
Authors: Frushicheva Maria P. , Cao Jie , Chu Zhen T. , Warshel Arieh
Published: September 2010

One of the fundamental challenges in biotechnology and in biochemistry is the ability to design effective enzymes. Doing so would be a convincing manifestation of a full understanding of the origin of enzyme catalysis. Despite an impressive progress, most of the advances on this front have been made by placing the reacting fragments in the proper places, rather than by optimizing the environment preorganization, which is the key factor in enzyme catalysis. Rational improvement of the preorganization would require approaches capable of evaluating reliably the actual catalytic effect. This work takes apreviously designed kemp eliminases as a benchmark for a computer aided enzyme design, using the empirical valence bond as the main screening tool. The observed absolute catalytic effect and the effect of directed evolution are reproduced and analyzed (assuming that the substrate is in the designed site). It is found that, in the case of kemp eliminases, the transition state charge distribution makes it hard to exploit the active site polarity, even with the ability to quantify the effect of different mutations. Unexpectedly, it is found that the directed evolution mutants lead to the reduction of solvation of the reactant state by water molecules rather that to the more common mode of transition state stabilization used by naturally evolved enzymes. Finally it is pointed out that our difficulties in improving Kemp eliminase are not due to overlooking exotic effect, but to the challenge in designing a preorganized environment that would exploit the small change it charge distribution during the formation of the transition state.
Effects of compliance currents on the formation and rupture of conducting filaments in unipolar resistive switching of CoO film
Authors: Wang Z Q , Li X H , Xu H Y , Wang W , Yu H , Zhang X T , Liu Y X , Liu Y C
Published: September 2010

A study on the unipolar resistive switching of a CoO thin film shows that the compliance current (CC) has strong effects on the local structure of conducting filaments (CFs). Lower CCs produce CFs with simple connectivity and good controllability, resulting in a narrow distribution of switching voltages (SVs) and a high ratio of high-to-low resistance states. In contrast, the stronger net-like CFs are formed at higher CCs, and their complete rupture is difficult. Thus, the lower high-resistance states and a wide distribution of SVs appear in the reversible switching processes. Our results suggest that the generation of CFs with simple local structures is as important as the rupture process.
Optical nonlinearity in lead sulfide microtowers
Authors: Tamilselvan V , Sridharan Kishore , Narasimha Rao K , Philip Reji
Published: September 2010

Lead sulfide (PbS) microtowers on silicon substrates, having the physical properties of bulk PbS, have been synthesized. Optical nonlinearity studies using the open aperture z-scan technique employing 5 ns and 100 fs laser pulses reveal effective two-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (βeff) are in the order of 10−11 m W−1, two orders of magnitude less than the values reported for quantum confined PbS nanocrystals. For femtosecond excitation βeff is of the order of 10−14 m W−1. These results obtained in bulk PbS experimentally confirm the importance of quantum confinement in the enhancement of optical nonlinearities in semiconductor materials.
Collinear Velocity-map Photoelectron Imaging Spectrometer for Cluster Anions
Authors: Wu Xia , Qin Zheng-bo , Xie Hua , Wu Xiao-hu , Cong Ran , Tang Zi-chao
Published: September 2010

We describe a collinear velocity-map photoelectron imaging spectrometer, which combines a Wiley-McLaren time-of-flight mass analyzer with a dual-valve laser vaporization source for investigating size-selected cluster and reaction intermediate anions. To generate the reaction anions conveniently, two pulsed valves and a reaction channel are employed instead of premixing carrier gas. The collinear photoelectron imaging spectrometer adopts modified velocity-map electrostatic lens, and provides kinetic energy resolution better than 3%. The performance of the instrument is demonstrated on the photodetachment of Si4− at 532 and 355 nm, and Si3C− at 532 nm, respectively. In both cases, photoelectron spectra and anisotropy parameters are obtained from the images. For Si4−, the spectra show two well-resolved vibrational progressions which correspond to the ground state and the first excited state of the neutral Si4 with peak spacing of 330 and 312 cm−1, respectively. Preliminary results suggest that the apparatus is a powerful tool for characterizing the electronic structure and photodetachment dynamics of cluster anions.
DFT Study of Benzofuroxan Synthesis Mechanism from 2-Nitroaniline via Sodium Hypochlorite
Authors: Hou Chun-yuan , Chen Xiao-fang , Liu Jian-yong , Lai Wei-peng , Wang Bo-zhou
Published: September 2010

The oxidative cyclization reaction of 2-nitroaniline via sodium hypochlorite to yield benzofuroxan is investigated by the hybrid density functional theory B3LYP/6–31G(d,p) method. Solvent effects are estimated with the polarizable continuum model to optimize structures. The title reaction is predicted to undergo two pathways, each of which is a stepwise process. Path A includes four steps, namely oxidization, H-attack, hydrolysis, and cyclization. Path B involves the nucleophilic attack of OH− to the H atom of the N-H bond and the proton transfer to the N atom of amino group leading to the cleavage of the N-H single bond in the amino group. The calculated results indicate that path A is favored mechanism for the title reaction. Furthermore, it is rational for one water molecule serving as a bridge to assist in the hydrolysis step of Path A and our calculations exhibit that this process is the rate-determining step.
First Principle Study on the Magnetic and Electric Properties of Wurtzite Cr-phosphides and Cr-sulphides: Several Half-metallic Ferromagnets
Authors: Liu Jun , Chen Pei-da , Chen Li , Dong Hui-ning , Zheng Rui-lun
Published: September 2010

The geometrical structures of wurtzite CrX (X = As, Sb, O, Se, and Te) were optimized, then their electric and magnetic properties were investigated by the first-principle calculations within the generalized gradient approximation for the exchange-correlation functional based on the density functional theory. These Cr-phosphides and Cr-sulphides were predicted to be half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely 100%. The molecular magnetic moments of Cr-phosphides and Cr-sulphides are 3.00 and 4.00 μB, which arise mainly from Cr-ions, respectively. There is ferromagnetic coupling in both Cr-phosphides and Cr-sulphides. The Curie temperatures of Cr-sulphides and Cr-phosphides are high. The electronic structures of Cr-ions are a21g↑↓t41u↑↓t11u↑e2g↑ in Cr-phosphides and a21g↑↓t41u↑↓t11u↑t32g↑ in Cr-sulphides, respectively.