bluuebunny/crossref_metadata_2025 huggingface dataset:
A French Perspective on Hospital Ethics Committees
Authors: MINO JEAN-CHRISTOPHE , COPEL LAURE , ZUCKER JEAN-MICHEL
Published: May 2008

In this article we highlight the main points of the development of bioethics and ethics committees in France. We argue that the French cultural context of medicine and its current political transformations favor new models of hospital ethics committee and we provide an example of such a model developed at Paris's Institut Curie, the oldest French cancer treatment and research centre.
Public Moralities Concerning Donation and Disposition of Organs: Results from a Cross-European Study
Authors: SCHWEDA MARK , SCHICKTANZ SILKE
Published: May 2008

There are not many international consensuses in the governance of biomedicine. One that exists concerns a general reluctance toward a commercialization of organ procurement. However, with reference to the problem of “organ scarcity,” there is an increasingly louder call in ethical and legal discourse to “give urgent consideration to any option that may make up the shortfall,” and to establish a debate on financial incentives “without any taboos.” Other ethicists and jurists criticize this development, and warn of injustice, exploitation of the poor, and a commodification of the human body.
Immortal Fetuses
Authors: CUTAŞ DANIELA
Published: May 2008

“Dissecting Bioethics,” edited by Tuija Takala and Matti Häyry, welcomes contributions on the conceptual and theoretical dimensions of bioethics.

The section is dedicated to the idea that words defined by bioethicists and others should not be allowed to imprison people's actual concerns, emotions, and thoughts. Papers that expose the many meanings of a concept, describe the different readings of a moral doctrine, or provide an alternative angle to seemingly self-evident issues are therefore particularly appreciated.

The themes covered in the section so far include dignity, naturalness, public interest, community, disability, autonomy, parity of reasoning, symbolic appeals, and toleration.

All submitted papers are peer reviewed. To submit a paper or to discuss a suitable topic, contact Tuija Takala at tuija.takala@helsinki.fi.
From the Editors
Authors: Heilig Steve
Published: May 2008

At a large bioethics conference in the early 1990s, the International Bioethics Institute presented a panel discussion on the newly-hot issue of “medical futility.” Erudite experts held forth from various perspectives, with convincing if conflicting arguments. During the question-and-answer session that followed, however, one attendee gently offered the one remark most recalled from that session. He was, if memory serves, a Latino physician working near the Mexico/USA border. “Thank you for your presentations,” he said, apparently with great sincerity. “I learned a lot. But on behalf of my own patients, I would ask that before you give them the right to say ‘no’ to medical treatment, we first give them the option of saying ‘yes’.”
Vegetation data, Walnut Gulch Experimental Watershed, Arizona, United States
Authors: Skirvin Susan , Kidwell Mary , Biedenbender Sharon , Henley J. P. , King Donna , Collins Chandra Holifield , Moran Susan , Weltz Mark
Published: May 2008

The U.S. Department of Agriculture Agricultural Research Service Southwest Watershed Research Center Walnut Gulch Experimental Watershed (WGEW) is an outdoor laboratory located in southeastern Arizona to study water and soil conservation in semiarid lands. Permanent vegetation transects were established adjacent to 55 rain gauges within WGEW in 1967 to quantify vegetation. Some sites were subsequently added or dropped. Detailed vegetation data were collected in 1967, 1994–2000, and 2005, including repeat photography of transects. Ground cover data were collected after 1967. A vegetation map was developed in 2002. The transect sites, vegetation map, data collection methods, and current data availability are described. Data are available at http://www.tucson.ars.ag.gov/dap/.
Correlation of atmospheric UV transient events with lunar phase
Authors: Garipov G. K. , Khrenov B. A. , Panasyuk M. I.
Published: May 2008

The near UV detector onboard the Moscow State University micro satellite “Universitetsky‐Tatiana” observed the atmosphere in the 300–400 nm wavelength range. Data shows a correlation between the transient UV event rates and brightness with the Earth's lunar phase. The observed UV transient events are found to be concentrated in the equatorial region and may be correlated with water vapor concentration. A possible interpretation of these observational results is discussed.
Continuum modeling of coupled oscillator arrays with coupling delay
Authors: Pogorzelski Ronald J.
Published: May 2008

The previously published linearized continuum model of a linear (one‐dimensional) array of mutually injection locked oscillators is generalized to include the effects of time delay in the interoscillator coupling. This generalization is motivated by a desire for causal solutions describing the dynamics of the phase distribution in the aperture of a phase array antenna driven by such an array of oscillators. The solutions for the phase dynamics will, in general, be noncausal unless the coupling delay is taken into account. In the present formulation the coupling delay is represented by an exponential factor introduced in the Laplace transform of the partial differential equation arising in the continuum model. As a result of this, the transform of the phase distribution exhibits an infinite set of branch points in the complex frequency plane and the inverse transform is computed as the sum of the integrals around the branch cuts.
Understanding uncertainty in distributed flash flood forecasting for semiarid regions
Authors: Yatheendradas Soni , Wagener Thorsten , Gupta Hoshin , Unkrich Carl , Goodrich David , Schaffner Mike , Stewart Anne
Published: May 2008

Semiarid flash floods pose a significant danger for life and property in many dry regions around the world. One effective way to mitigate flood risk lies in implementing a real‐time forecast and warning system based on a rainfall‐runoff model. This study used a semiarid, physics‐based, and spatially distributed watershed model driven by high‐resolution radar rainfall input to evaluate such a system. The predictive utility of the model and dominant sources of uncertainty were investigated for several runoff events within the U.S. Department of Agriculture Agricultural Research Service Walnut Gulch Experimental Watershed located in the southwestern United States. Sources of uncertainty considered were rainfall estimates, watershed model parameters, and initial soil moisture conditions. Results derived through a variance‐based comprehensive global sensitivity analysis indicated that the high predictive uncertainty in the modeled response was heavily dominated by biases in the radar rainfall depth estimates. Key model parameters and initial model states were identified, and we generally found that modeled hillslope characteristics are more influential than channel characteristics in small semiarid basins. We also observed an inconsistency in the parameter sets identified as behavioral for different events, which suggests that model calibration to historical data is unlikely to consistently improve predictive performance for different events and that real‐time parameter updating may be preferable.
FORCinel: An improved algorithm for calculating first‐order reversal curve distributions using locally weighted regression smoothing
Authors: Harrison Richard J. , Feinberg Joshua M.
Published: May 2008

We describe a modification to existing algorithms for the calculation of first‐order reversal curve (FORC) diagrams using locally weighted regression smoothing (often referred to as “LOESS” smoothing). The new algorithm offers several advantages over current methods: (1) it allows the FORC distribution to be calculated using a constant smoothing factor all the way to the Hc = 0 axis; (2) noninteger values of the smoothing factor can be specified, enabling finer control over the degree of smoothing and the development of a graphical method for automated selection of the optimum smoothing factor; (3) it performs automated extrapolation across gaps or undefined regions of FORC space. This has two applications: first, bad curves or outlying data points caused by instrumental instabilities can be removed from the data, eliminating artifacts from the final FORC diagram; second, specific regions of interest in the FORC measurement can be masked out in order to investigate their contribution to the final FORC diagram. The new algorithm forms the basis of FORCinel, a new user‐friendly suite of FORC analysis tools with graphical user interface.
Bridging the gap between seismically and geodetically detected slow earthquakes
Authors: Ide Satoshi , Imanishi Kazutoshi , Yoshida Yasuhiro , Beroza Gregory C. , Shelly David R.
Published: May 2008

Recently observed unusual seismic events: deep low frequency earthquakes and tremor, very low frequency earthquakes, and slow slip events form a family of slow earthquakes that are governed by a scaling law different from ordinary earthquakes. Guided by this scaling law, we have observed previously unknown events, with source duration of 20–200 s and moment magnitude of 3–4, under the Kii Peninsula in western Japan. These events radiate seismic energy in the 2–8 Hz band in direct proportion to their seismic moment‐rate, though the constant of proportionality is 4–5 orders of magnitude smaller than for ordinary earthquakes. Slow earthquakes in this region may be comprised of numerous shear slip events, which in aggregate are manifest seismically as tremor or isolated longer events up to 200 s and geodetically as slow slip events.
Structural assignment of adenine aggregates in CDCl3
Authors: Biemann Lars , Häber Thomas , Maydt Daniela , Schaper Klaus , Kleinermanns Karl
Published: May 2008

We reinvestigated the self-association of 9-substituted adenine derivatives in CDCl3 solutions and present the infrared spectra of 9-ethyladenine and N-methyl-9-ethyladenine and its aggregates in the spectral regions between 1500 and 1800cm−1 and between 2700 and 3600cm−1. Wavelength dependent absolute extinction coefficients of the monomer and dimers are presented on the basis of a simple deconvolution method. Comparison of the deconvoluted dimer spectra with quantum chemical calculations allows for a structural assignment of the two dimer structures that coexist in 9-ethyladenine/CDCl3 solutions. In contrast, the dimer spectrum of N-methyl-9-ethyladenine is dominated by a single isomer.
Projective-anticipating, projective, and projective-lag synchronization of time-delayed chaotic systems on random networks
Authors: Feng Cun-Fang , Xu Xin-Jian , Wang Sheng-Jun , Wang Ying-Hai
Published: May 2008

We study projective-anticipating, projective, and projective-lag synchronization of time-delayed chaotic systems on random networks. We relax some limitations of previous work, where projective-anticipating and projective-lag synchronization can be achieved only on two coupled chaotic systems. In this paper, we realize projective-anticipating and projective-lag synchronization on complex dynamical networks composed of a large number of interconnected components. At the same time, although previous work studied projective synchronization on complex dynamical networks, the dynamics of the nodes are coupled partially linear chaotic systems. In this paper, the dynamics of the nodes of the complex networks are time-delayed chaotic systems without the limitation of the partial linearity. Based on the Lyapunov stability theory, we suggest a generic method to achieve the projective-anticipating, projective, and projective-lag synchronization of time-delayed chaotic systems on random dynamical networks, and we find both its existence and sufficient stability conditions. The validity of the proposed method is demonstrated and verified by examining specific examples using Ikeda and Mackey–Glass systems on Erdös–Rényi networks.
Localized electrostatic excitations in a Thomas–Fermi plasma containing degenerate electrons
Authors: Abdelsalam U. M. , Moslem W. M. , Shukla P. K.
Published: May 2008

By using the Thomas–Fermi electron density distribution for quantum degenerate electrons, the hydrodynamic equations for ions, and the Poisson equation, planar and nonplanar ion-acoustic solitary waves in an unmagnetized collisionless plasma are investigated. The reductive perturbation method is used to derive cylindrical and spherical Korteweg–de Vries equations. Numerical solutions of the latter are presented. The present results can be useful in understanding the features of small but finite amplitude localized ion-acoustic solitary pulses in a degenerate plasma.
On the stability of a dc-driven oxygen discharge in cylindrical geometry
Authors: Bruhn B. , Richter A. , May B.
Published: May 2008

Starting from the hydrodynamic equations describing the positive column of glow discharges in oxygen, the stability of the homogeneous state is investigated. The model contains electrons, positive and negative ions as well as the metastable molecule O2(a1Δg) as a detachment partner. It is shown that the transition from the H-mode to the T-mode of a dc-driven oxygen discharge is caused by an attachment-induced ionization instability. The stability boundaries are calculated for selected values of the plasma parameters. The comparison of experimental data and theoretical predictions shows satisfactory agreement.
Ion drag force on a small grain in highly collisional weakly anisotropic plasma: Effect of plasma production and loss mechanisms
Authors: Chaudhuri M. , Khrapak S. A. , Morfill G. E.
Published: May 2008

The ion drag force acting on a small absorbing grain has been calculated in highly collisional plasma with slowly drifting ions taking into account plasma production and loss processes in the vicinity of the grain. It is shown that the strength of the plasma production and loss mechanisms not only affects the magnitude of the ion drag force, but also determines the direction of the force. The parameter regimes for the “positive” and “negative” ion drag forces have been identified. In addition, the qualitative features of the electric potential distribution around the grain in isotropic conditions (in the absence of the ion drift) are investigated.
Critical electron binding to linear electric quadrupole systems
Authors: Garrett W. R.
Published: May 2008

Results for critical quadrupolar moments for electron binding to fixed, point-charge systems are normalized, extended, and displayed in graphical forms. The influence of rotational degrees of freedom on critical binding to quadrupolar systems is examined through calculations of critical moments for electron binding to linear electric quadrupolar rotors. The results are presented for rotors covering useful ranges of size and inertial parameters. The effect of rotational degrees of freedom on critical binding is found to be less important for quadrupolar as compared to dipolar rotors.
Laterally coupled self-assembled InAs quantum dots embedded in resonant tunnel diode with multigate electrodes
Authors: Amaha S. , Hatano T. , Teraoka S. , Shibatomi A. , Tarucha S. , Nakata Y. , Miyazawa T. , Oshima T. , Usuki T. , Yokoyama N.
Published: May 2008

We study the electronic properties of submicron vertical resonant tunneling structures containing several self-assembled InAs quantum dots (SADs) surrounded by four gate electrodes. The four gates are designed not only to squeeze the conductive channel containing a few SADs but also to differently modulate the electrochemical potential of each SAD. We measure the stability diagram and distinguish the features of lateral interdot coupling, such as the type of coupling (quantum mechanical or capacitive), the number of coupled dots, and the relative coupled dot position. This technique will be useful in characterizing the electronic properties of coupled SAD systems.
Parallel implementation of electronic structure energy, gradient, and Hessian calculations
Authors: Lotrich V. , Flocke N. , Ponton M. , Yau A. D. , Perera A. , Deumens E. , Bartlett R. J.
Published: May 2008

ACES III is a newly written program in which the computationally demanding components of the computational chemistry code ACES II [J. F. Stanton et al., Int. J. Quantum Chem. 526, 879 (1992); [ACES II program system, University of Florida, 1994] have been redesigned and implemented in parallel. The high-level algorithms include Hartree–Fock (HF) self-consistent field (SCF), second-order many-body perturbation theory [MBPT(2)] energy, gradient, and Hessian, and coupled cluster singles, doubles, and perturbative triples [CCSD(T)] energy and gradient. For SCF, MBPT(2), and CCSD(T), both restricted HF and unrestricted HF reference wave functions are available. For MBPT(2) gradients and Hessians, a restricted open-shell HF reference is also supported. The methods are programed in a special language designed for the parallelization project. The language is called super instruction assembly language (SIAL). The design uses an extreme form of object-oriented programing. All compute intensive operations, such as tensor contractions and diagonalizations, all communication operations, and all input-output operations are handled by a parallel program written in C and FORTRAN 77. This parallel program, called the super instruction processor (SIP), interprets and executes the SIAL program. By separating the algorithmic complexity (in SIAL) from the complexities of execution on computer hardware (in SIP), a software system is created that allows for very effective optimization and tuning on different hardware architectures with quite manageable effort.
Computational investigation and experimental considerations for the classical implementation of a full adder on SO2 by optical pump-probe schemes
Authors: Bomble L. , Lavorel B. , Remacle F. , Desouter-Lecomte M.
Published: May 2008

Following the scheme recently proposed by Remacle and Levine [Phys. Rev. A 73, 033820 (2006)], we investigate the concrete implementation of a classical full adder on two electronic states (X̃A11 and C̃B21) of the SO2 molecule by optical pump-probe laser pulses using intuitive and counterintuitive (stimulated Raman adiabatic passage) excitation schemes. The resources needed for providing the inputs and reading out are discussed, as well as the conditions for achieving robustness in both the intuitive and counterintuitive pump-dump sequences. The fidelity of the scheme is analyzed with respect to experimental noise and two kinds of perturbations: The coupling to the neighboring rovibrational states and a finite rotational temperature that leads to a mixture for the initial state. It is shown that the logic processing of a full addition cycle can be realistically experimentally implemented on a picosecond time scale while the readout takes a few nanoseconds.
Ultrafast optical nonlinearities and figures of merit in acceptor-substituted 3,4,5-trimethoxy chalcone derivatives: Structure-property relationships
Authors: Gu Bing , Ji Wei , Patil P. S. , Dharmaprakash S. M.
Published: May 2008

By performing both Z-scan and transient transmission measurements with 130 fs laser pulses in the near infrared region, we investigated structure-property relationships for χ(3) in acceptor-substituted 3,4,5-trimethoxy chalcone derivatives. We determined all nonlinear parameters, including two-photon absorption (2PA) cross section, 2PA-induced excited-state absorption (ESA) cross section, microscopic second-order hyperpolarizability, and lifetime of the excited state in these molecules. We found that the microscopic second-order hyperpolarizability γR and 2PA cross section σ2PA in chalcone derivatives increase as the acceptor strength of the molecules increases, which demonstrates an enhancement in optical nonlinearities by simple structural variations. We evaluated the one-photon, two-photon, and effective three-photon figures of merit for acetone solutions of chalcone derivatives at irradiance of 100 GW/cm2. Furthermore, we observed optical limiting behavior in these compounds, which result from both 2PA and 2PA-assisted ESA. These results indicated that chalcone derivatives are a promising candidate for applications on nonlinear photonic devices.
Optical emission from erbium-doped silica nanowires
Authors: Elliman R. G. , Wilkinson A. R. , Kim T.-H. , Sekhar P. K. , Bhansali S.
Published: May 2008

Infrared optical emission from erbium-doped silica nanowires is shown to have property characteristic of the material nanostructure and to provide the basis for the fabrication of integrated photonic devices and biosensors. Silica nanowires of approximately 150 nm diameter were grown on a silicon wafer by metal-induced growth using a thin (20 nm) sputter-deposited palladium layer as a catalyst. The resulting wires were then ion implanted with 110 keV ErO− ions and annealed at 900 °C to optically activate the erbium. These wires exhibited photoluminescence emission at 1.54 μm, characteristic of the I415/2−I413/2 transition in erbium; however, comparison to similarly implanted fused silica layers revealed stronger thermal quenching and longer luminescence lifetimes in the nanowire samples. The former is attributed to an increase in defect-induced quenching partly due to the large surface-volume ratio of the nanowires, while the latter is attributed to a reduction in the optical density of states associated with the nanostructure morphology. Details of this behavior are discussed together with the implications for potential device applications.
Properties of light-emitting porous silicon formed by stain etching in HF∕KIO3 solution under light illumination
Authors: Xu Yan Kai , Adachi Sadao
Published: May 2008

The structural and optical properties of stain-etched porous silicon are investigated using optical microscopy, scanning electron microscopy, ex situ atomic force microscopy (AFM), photoluminescence (PL), and Fourier transform infrared (FTIR) spectroscopy. The stained layers were formed in a 50% HF solution with the addition of an oxidizing agent of KIO3 on n-type silicon substrates with and without light illumination of λ=532nm. Strong yellowish emission is observed only when porous silicon is formed under light illumination and in the limited KIO3 concentrations. Surprisingly enough, no PL emission is observed on stained surfaces formed without light illumination. The surface morphology as characterized by AFM reveals that light illumination can produce microscopic roughnesses on the stained surfaces. No specific chemical species on the stained surfaces can be identified by FTIR spectroscopy. The origin of the yellowish luminescence is hypothesized to be due to the quantum-size effect that enables the nondirect optical transitions via a momentum conservation relaxation.
Shallow level trap formation in SiO2 induced by high field and thermal stresses
Authors: Lin Hao-Peng , Hwu Jenn-Gwo
Published: May 2008

This work studies the effects of high electric field stress and thermal stress, separately or simultaneously, on the gate injection current of metal-oxide-semiconductor (MOS) capacitors with ultrathin SiO2 (2.5nm). After applying either Fowler–Nordheim stress (FNS) or thermal stress (TS), a slight increase in gate injection current of MOS(P) is occasionally observed. However, a more abrupt increase in gate injection current with higher occurrence probability is measured if both FNS and TS (FNTS) are applied together. Some percolation path might be formed among the oxide defects and cause the abrupt current rise. Interestingly, it is found that the soft breakdown time of FNTS devices is prolonged after being treated with subsequent de-ionized (DI) water immersion. Furthermore, the gate current density is recovered due to DI water immersion treatment. A shallow trap level of 0.168eV in SiO2 for FNTS devices is extracted according to Poole–Frenkel conduction model analysis. This shallow trap level induced by FNTS may vanish after water immersion. It is supposed that these shallow traps are responsible for the occurrence of the abrupt increase in gate current observed in FNTS devices.
Optical properties of simple hexagonal and rhombohedral few-layer graphenes in an electric field
Authors: Chang C. P. , Wang J. , Lu C. L. , Huang Y. C. , Lin M. F. , Chen R. B.
Published: May 2008

The influence of a perpendicular electric field (F) on the optical properties of simple hexagonal and rhombohedral few-layer graphenes is studied through the tight-binding model. The electric-field-modulated absorption spectra depend on the stacking sequence. The low-energy absorption spectra of simple hexagonal few-layer graphenes exhibit the jumping structures in the absence or presence of an electric field. On the other hand, absorption spectra of rhombohedral few-layer graphenes show discontinuities and sharp peaks at F=0. Besides, the application of F affects the absorption spectra, generates new peaks, and changes peak position and peak height. The frequency of the peak is predicted to be closely associated with the stacking sequences and the field strength. Above all, the predicted absorption spectra could be verified by optical measurements.
Barrier breakdown in multiple quantum well structure
Authors: Gomez Aurore , Berger Vincent , Péré-Laperne Nicolas , De Vaulchier Louis-Anne
Published: May 2008

We explore a regime of unipolar electronic transport in a multiple quantum well structure with very large current discontinuities—up to five orders of magnitude. Magnetotransport experiments reveal different transport regimes. Quantum well impact ionization shifts the structure from a resistive “down” state, where the current flows through interwell quantum tunneling, to a highly conductive “up” state. In the latter regime, the current leaks through a barrier suddenly broken down because of an efficient ionization of the first quantum well. This mechanism might open the way to original devices based on unipolar impact ionization.
Fractional actionlike variational problems
Authors: El-Nabulsi Rami Ahmad , Torres Delfim F. M.
Published: May 2008

Fractional actionlike variational problems have recently gained importance in studying dynamics of nonconservative systems. In this note we address multidimensional fractional actionlike problems of the calculus of variations.
Three-electrode gas switches with electrodynamical acceleration of a discharge channel
Authors: Kovalchuk B. M. , Kim A. A. , Kharlov A. V. , Kumpyak E. V. , Tsoy N. V. , Vizir V. V. , Zorin V. B.
Published: May 2008

High voltage, high current, and high Coulomb transfer closing switches are required for many high power pulsed systems. There are a few alternatives for closing switches, for example, ignitrons, vacuum switches, solid-state switches, high pressure gas switches (spark gaps), and some others. The most popular closing switches up to date are spark gaps due to relatively simple design, robustness, easily field maintenance, and repair. Main drawback of spark gaps is limited lifetime, which is related directly or indirectly to erosion of the electrodes. Multichannel switches and switches with moving arc have been proposed to prevent the electrodes erosion. This study investigates switches, where a spark channel is initiated in a three-electrode layout and then the spark accelerates due to electrodynamic force and moves along the extended electrodes. At a given current amplitude, the diameter of the extended electrodes allows to control the spark velocity and hence, the erosion of the electrodes providing the required lifetime. The first switch is designed for 24kV charging voltage and ∼4C total charge transfer. This spark gap was tested at 25kA peak current in 40 000 shots in a single polarity discharge and in 20 000 shots in bipolar discharge. Second spark gap is designed for 24kV charging voltage and ∼70C total charge transfer. It was tested in 22 000 shots, at a current of 250kA with a pulse length of 360μs. In this paper, we present design of these spark gaps and trigger generator, describe the test bed, and present the results of the tests.
Broadband single-shot electron spectrometer for GeV-class laser-plasma-based accelerators
Authors: Nakamura K. , Wan W. , Ybarrolaza N. , Syversrud D. , Wallig J. , Leemans W. P.
Published: May 2008

Laser-plasma-based accelerators can provide electrons over a broad energy range and/or with large momentum spread. The electron beam energy distribution can be controlled via accurate control of laser and plasma properties, and beams with energies ranging from ≃0.5to1000MeV have been observed. Measuring these energy distributions in a single shot requires the use of a diagnostic with large momentum acceptance and, ideally, sufficient resolution to accurately measure narrow energy spread beams. Such a broadband single-shot electron magnetic spectrometer for GeV-class laser-plasma-based accelerators has been developed at Lawrence Berkeley National Laboratory. Detailed descriptions of the design concept and hardware are presented, as well as a performance evaluation of the spectrometer. The spectrometer covered electron beam energies raging from 0.01to1.1GeV in a single shot, and enabled the simultaneous measurement of the laser properties at the exit of the accelerator through the use of a sufficiently large pole gap. Based on measured field maps and third-order transport analysis, a few percent-level resolution and determination of the absolute energy were achieved over the entire energy range. Laser-plasma-based accelerator experiments demonstrated the capability of the spectrometer as a diagnostic and its suitability for measuring broadband electron sources.
Planar nanowire arrays formed by atomic-terrace low-angle shadowing
Authors: Cuccureddu F. , Usov V. , Murphy S. , Coileain C. O. , Shvets I. V.
Published: May 2008

A relatively simple method for preparation of planar nanowire arrays on vicinal substrates by molecular beam epitaxy is presented. The atomic step-and-terrace morphology of vicinal substrates is used to produce a shadowing effect on a highly collimated molecular beam at an oblique incidence to the substrate. The collimation is achieved by placing the evaporation source at a large working distance (40–100cm) from the substrate. The method’s capabilities have been demonstrated by preparation of arrays of Ag and Au nanowires on vicinal Si(111) and α-Al2O3 (0001) substrates. Nanowires with a width of down to 10–15nm and a thickness of 1.5nm have been readily achieved.
The enhancement of the spin polarization of Co2MnSn by Fe doping
Authors: Rajanikanth A. , Takahashi Y. K. , Hono K.
Published: May 2008

We have investigated the effect of Fe doping on the spin polarization of Co2Mn1−xFexSn (x=0.0, 0.05, 0.1, and 0.2) Heusler alloys by using the point contact Andreev reflection method. The spin polarization increased from 0.6 for x=0.0 to 0.65 for x=0.05. This is attributed to the increase in the spin up states near the Fermi level since Fe is a high valent element compared to Mn. However, with further increase in Fe content, the spin polarization decreased to 0.63 and 0.58 for x=0.1 and 0.2, respectively. Hence, the alloy Co2Mn0.95Fe0.05Sn with low Fe doping (1.25 at. % Fe) could be a potential material for spintronics applications.
High-efficiency voltage oscillation in VO2 planer-type junctions with infinite negative differential resistance
Authors: Sakai Joe
Published: May 2008

A vanadium dioxide (VO2) thin film planer-type junction fabricated on an Al2O3 (0001) substrate, possessing an infinite negative-differential-resistance region in their current-voltage characteristics, acts as an oscillator of high efficiency. A voltage application to the pair of a VO2 junction and a load resistor drives an oscillation of the junction voltage only when the combination of the source voltage and the load resistance satisfies certain conditions. On the basis of the experimental results, with the source voltage and the load resistance systematically varied, the mechanism of the oscillation was revealed to be the alternate occurrence of an electric-field-induced resistance switching in the VO2 junction and a rapid dielectric relaxation in the load resistor.
Multifunction Gd2O3:Eu nanocrystals produced by solution combustion synthesis: Structural, luminescent, and magnetic characterization
Authors: Jacobsohn L. G. , Bennett B. L. , Muenchausen R. E. , Tornga S. C. , Thompson J. D. , Ugurlu O. , Cooke D. W. , Lima Sharma A. L.
Published: May 2008

The synthesis, structural, luminescent, and magnetic properties of multifunction 8 at. % Eu-doped Gd2O3 nanocrystals were investigated. The material was synthesized by the solution combustion technique and characterized by x-ray diffraction (XRD), transmission electron microscopy, and photoluminescence and magnetization measurements. The as-prepared material presents predominant base-centered monoclinic structure with average crystallite size of 35 nm. Isothermal annealing at 1000 °C for up to 152 h induced gradual structural transition toward the body-centered cubic structure. Debye–Scherrer analysis of XRD results showed that annealing did not induce grain growth of monoclinic nanocrystals, while cubic nanocrystals reached 47 nm after annealing for 152 h. The luminescent behavior was monitored as a function of annealing time and related to the structural transformation. In particular, an inversion of the predominant photoluminescence emission line from 621.4 to 609.5 nm was observed and related to changes in the crystalline field resultant to phase transformation from cubic to monoclinic. Magnetic measurements revealed the paramagnetic nature of the material, much insensitive to the crystallographic structure.
Experimental characterization of a metal-oxide-semiconductor field-effect transistor-based Coulter counter
Authors: Sridhar Manoj , Xu Dongyan , Kang Yuejun , Hmelo Anthony B. , Feldman Leonard C. , Li Dongqing , Li Deyu
Published: May 2008

We report the detailed characterization of an ultrasensitive microfluidic device used to detect the translocation of small particles through a sensing microchannel. The device connects a fluidic circuit to the gate of a metal-oxide-semiconductor field-effect transistor (MOSFET) and detects particles by monitoring the MOSFET drain current modulation instead of the modulation in the ionic current through the sensing channel. The minimum volume ratio of the particle to the sensing channel detected is 0.006%, which is about ten times smaller than the lowest detected volume ratio previously reported in the literature. This volume ratio is detected at a noise level of about 0.6% of the baseline MOSFET drain current, clearly showing the amplification effects from the fluidic circuits and the MOSFETs. We characterize the device sensitivity as a function of the MOSFET gate potential and show that its sensitivity is higher when the MOSFET is operating below its threshold gate voltage than when it is operating above the threshold voltage. In addition, we demonstrate that the device sensitivity linearly increases with the applied electrical bias across the fluidic circuit. Finally, we show that polystyrene beads and glass beads with similar sizes can be distinguished from each other based on their different translocation times, and the size distribution of microbeads can be obtained with accuracy comparable to that of direct scanning electron microscopy measurements.
Optical properties and ultrafast optical nonlinearity of Yb3+ doped sodium borate and bismuthate glasses
Authors: Karthikeyan B. , Suchand Sandeep C. S. , Cha Jaemine , Takebe Hiromichi , Philip Reji , Mohan S.
Published: May 2008

In this paper, we report the optical and ultrafast nonlinear optical properties of Yb3+ doped sodium borate and bismuthate glasses. The glasses have been prepared through the melt quench technique. Optical absorption measurements show compositional dependent absorption spectrum of Yb3+, which is due to the higher crystal field induced by Bi3+ ions. Local structure of the glasses has been identified by using Fourier transform infrared and Raman studies. From open aperture z-scan measurements done by using 100 fs laser pulses, the ultrafast optical nonlinearity in these materials is calculated at the nonresonant excitation wavelength of 800 nm. The measured three-photon absorption originates from the glass host, with contributions from the nonbridging oxygens and the nonlinear electronic polarization of the Bi3+ ions.
Near-resonance electro-optic activity enhancement and improved modulation performance for polymer based Fabry–Pérot interferometers
Authors: Gan Haiyong , Greenlee Charles , Sheng Chuanxiang , Norwood Robert A. , Fallahi Mahmoud , Wang Shuangxi , Lin Weiping , Yamamoto Michiharu , Mohanalingam Kathaperumal , Peyghambarian Nasser
Published: May 2008

Fabry–Pérot interferometers (FPIs) are designed to work near and off the absorption resonance of an electro-optic (EO) polymer. The near-resonance EO activity (EO coefficient r13∼25.4pm∕V at ∼1086nm) is enhanced over that off resonance (r13∼9.0pm∕V at ∼1526nm). The full width at half maximum of the FPI transmission band is ∼16nm near resonance compared to ∼22nm off resonance. The modulation performance can, therefore, be improved with a modulation ratio increased to ∼78% near resonance (at 1064nm) from ∼19% off resonance (at 1520nm). The modulation speed is approximately megahertz and can be increased to greater than gigahertz with improved circuit design.
Heavily doped and fully compensated Ge single-crystalline films on GaAs
Authors: Mitin V. F.
Published: May 2008

Heavily doped and fully compensated Ge single-crystalline thin (∼0.1μm) films were epitaxially grown in vacuum on semi-insulating GaAs substrates. Such films have high resistivity (up to 140Ω∕cm), conductance activation energy as high as half the band gap of Ge, low free charge carrier mobility (∼50cm2∕V⋅s) and concentration (∼1014cm−3). The transport properties of the films were studied and explained involving the theory of two-dimensional potential fluctuations and percolation.
Repetitive ultrafast melting of InSb as an x-ray timing diagnostic
Authors: Navirian H. , Enquist H. , Hansen T. N. , Mikkelsen A. , Sondhauss P. , Srivastava A. , Zakharov A. A. , Larsson J.
Published: May 2008

We have demonstrated the possibility of using repetitive ultrafast melting of InSb as a timing diagnostic in connection with visible-light pump∕x-ray probe measurements at high-repetition-rate x-ray facilities. Although the sample was molten and regrown approximately 1×106 times, a distinct reduction in time-resolved x-ray reflectivity could be observed using a streak camera with a time resolution of 2.5ps. The time-resolved x-ray reflectivity displayed this distinct decrease despite the fact that the average reflectivity of the sample had fallen to approximately 50% of its original value due to accumulated damage from the prolonged laser exposure. The topography of the laser-exposed sample was mapped using an optical microscope, a stylus profilometer, photoelectron microscopy, and a scanning tunneling microscope. Although the surface of the sample is not flat following prolonged exposure at laser fluences above 15mJ∕cm2, the atomic scale structure regrows, and thus, regenerates the sample on a nanosecond timescale. In the fluence range between 15 and 25mJ∕cm2, the laser power is sufficient to melt the sample, while regrowth occurs with a sufficiently good structure to allow the extraction of timing information via ultrafast time-resolved x-ray measurements. This can be applied for timing purposes at synchrotron radiation and x-ray free-electron laser facilities. It is also noteworthy that we were able to reproduce the fluence dependencies of melting depth and disordering time previously obtained in single-shot, nonthermal melting experiments with higher temporal resolution.
The timing and nature of floristic and structural changes during secondary succession in wet forests
Authors: Serong Merrilyn , Lill Alan
Published: May 2008

The timing and nature of floristic and structural changes to vegetation were documented during secondary succession in wet forests in the Victorian Central Highlands from 3 to > 100 years after severe disturbance by timber-harvesting or wildfire. A chronosequence of five forest age-classes was employed. Vegetation surveys were conducted in two 15 × 50 m sampling quadrats in each of 12 replicate sites in each forest age-class between April 2000 and June 2001. Frequencies of occurrence of 67 floristic variables (plant taxa, other vegetation elements and litter components) were used to distinguish among plant communities in the different forest age-classes. Structural comparisons were made among the age-classes using species richness, floristic variability (i.e. spatial heterogeneity), trunk diameter and stem density of Mountain Ash Eucalyptus regnans F.Muell. and heights of forest strata. Most patterns of change showed a clear unidirectional trend from the youngest to the oldest age-class. Much of the floristic change occurred within a few decades of disturbance, but some of the structural changes continued throughout succession. Vegetation changes were generally attributable to natural succession, but a few differences between young forests that regenerated after timber-harvesting and older forests that originated after wildfire were likely to be due to the different disturbance histories. The pattern of vegetation change during secondary succession in forests after severe disturbance can influence the pattern of forest use by birds. The findings of this study thus formed the foundation of an examination of the community and behavioural responses of diurnal birds to secondary succession.
Nitrogen use efficiency: does a trade-off exist between the N productivity and the mean residence time within species?
Authors: Yuan Zhi Y. , Chen Han Y. H. , Li Ling H.
Published: May 2008

Nitrogen use efficiency (NUE) can be divided into two components, i.e. N productivity (A) and the mean residence time (MRT). Controlled experiments indicate that there is not a trade-off between A and MRT within species, but this theory has not been well tested in field conditions. Here, we studied the A, MRT and NUE of Stipa krylovii Roshev. in a grassland over 4 years of N fertilisation experimentation. The three parameters (A, MRT and NUE) were significantly related to soil N supply and there was a negative relationship between A and MRT within this species (r = –0.775, P < 0.05), i.e. plants with higher A had lower MRT. Our results showed a trade-off between A and MRT within this Stipa species and this observed trade-off was attributed to different responses of A and MRT to soil fertility.
Cotyledon areoles in subtribe Kennediinae (Leguminosae: Phaseoleae)
Authors: Lackey James A.
Published: May 2008

Cotyledon areoles are reported for the first time in Phaseoleae subtribe Kennediinae. All three genera, Kennedia, Hardenbergia and Vandasina, have cotyledon areoles in mature dormant seeds. The remarkably uniform seeds also consistently have an adaxial palisade layer in cotyledons and a greatly expanded middle endosperm layer, which appears to consist primarily of normal legume cell-wall galactomannan.
Swapping metals in Fe- and Mn-dependent dioxygenases: Evidence for oxygen activation without a change in metal redox state
Authors: Emerson Joseph P. , Kovaleva Elena G. , Farquhar Erik R. , Lipscomb John D. , Que Lawrence
Published: May 2008

Biological O
2
activation often occurs after binding to a reduced metal [e.g., M(II)] in an enzyme active site. Subsequent M(II)-to-O
2
electron transfer results in a reactive M(III)-superoxo species. For the extradiol aromatic ring-cleaving dioxygenases, we have proposed a different model where an electron is transferred from substrate to O
2
via the M(II) center to which they are both bound, thereby obviating the need for an integral change in metal redox state. This model is tested by using homoprotocatechuate 2,3-dioxygenases from
Brevibacterium fuscum
(Fe-HPCD) and
Arthrobacter globiformis
(Mn-MndD) that share high sequence identity and very similar structures. Despite these similarities, Fe-HPCD binds Fe(II) whereas Mn-MndD incorporates Mn(II). Methods are described to incorporate the nonphysiological metal into each enzyme (Mn-HPCD and Fe-MndD). The x-ray crystal structure of Mn-HPCD at 1.7 Å is found to be indistinguishable from that of Fe-HPCD, while EPR studies show that the Mn(II) sites of Mn-MndD and Mn-HPCD, and the Fe(II) sites of the NO complexes of Fe-HPCD and Fe-MndD, are very similar. The uniform metal site structures of these enzymes suggest that extradiol dioxygenases cannot differentially compensate for the 0.7-V gap in the redox potentials of free iron and manganese. Nonetheless, all four enzymes exhibit nearly the same
K
M
and
V
max
values. These enzymes constitute an unusual pair of metallo-oxygenases that remain fully active after a metal swap, implicating a different way by which metals are used to promote oxygen activation without an integral change in metal redox state.
Identification and functional analysis of genes controlling biosynthesis of 2-methylisoborneol
Authors: Komatsu Mamoru , Tsuda Muneya , Ōmura Satoshi , Oikawa Hideaki , Ikeda Haruo
Published: May 2008

To identify the genes for biosynthesis of the off-flavor terpenoid alcohol, 2-methylisoborneol (2-MIB), the key genes encoding monoterpene cyclase were located in bacterial genome databases by using a combination of hidden Markov models, protein–family search, and the sequence alignment of their gene products. Predicted terpene cyclases were classified into three groups: sesquiterpene, diterpene, and other terpene cyclases. Genes of the terpene cyclase group that form an operon with a gene encoding
S
-adenosyl-
l
-methionine (SAM)-dependent methyltransferase were found in genome data of seven microorganisms belonging to actinomycetes,
Streptomyces ambofaciens
ISP5053,
Streptomyces coelicolor
A3(
2
),
Streptomyces griseus
IFO13350,
Streptomyces lasaliensis
NRRL3382R,
Streptomyces scabies
87.22,
Saccharopolyspora erythraea
NRRL2338, and
Micromonospora olivasterospora
KY11048. Among six microorganisms tested,
S. ambofaciens
,
S. coelicolor
A3(
2
),
S. griseus
, and
S. lasaliensis
produced 2-MIB but
M. olivasterospora
produced 2-methylenebornane (2-MB) instead. The regions containing monoterpene cyclase and methyltransferase genes were amplified by PCR from
S. ambofaciens
,
S. lasaliensis
, and
Saccharopolyspora erythraea
, respectively, and their genes were heterologously expressed in
Streptomyces avermitilis
, which was naturally deficient of 2-MIB biosynthesis by insertion and deletion. All exoconjugants of
S. avermitilis
produced 2-MIB. Full-length recombinant proteins, monoterpene cyclase and methyltransferase of
S. lasaliensis
were expressed at high level in
Escherichia coli
. The recombinant methyltransferase catalyzed methylation at the C2 position of geranyl diphosphate (GPP) in the presence of SAM. 2-MIB was generated by incubation with GPP, SAM, recombinant methyltransferase, and terpene cyclase. We concluded that the biosynthetic pathway involves the methylation of GPP by GPP methyltransferase and its subsequent cyclization by monoterpene cyclase to 2-MIB.