bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluctuation-driven magnetic fields in the Madison Dynamo Experiment
Authors: Spence E. J. , Nornberg M. D. , Bayliss R. A. , Kendrick R. D. , Forest C. B.
Published: April 2008

Turbulent fluctuations in the velocity and magnetic fields of electrically conducting fluids have been experimentally shown to be capable of inducing large-scale magnetic fields. Here, simulations of the Madison Dynamo Experiment are used to qualitatively reproduce these experimental results. Due to the high magnetic Prandtl number of the simulations, Pm=0.08 vs Pm∼10−5 for liquid sodium, the simulations do not identically reproduce the fluctuation levels of the experiment’s magnetic and velocity fields. Nonetheless, the simulations reproduce the qualitative behavior of the fluctuation-induced large-scale magnetic field as a function of applied field magnitude and magnetic Reynolds number. The scaling of the induced dipole moment as a function of Reynolds number is also presented, demonstrating that the nature of the fluctuations in the simulations changes after a critical value of the Reynolds number is crossed, resulting in a change in the direction of the induced dipole moment. Experimental conditions using corotating impellers are presented, demonstrating that the induced dipole moment may be dependent on the shear layer present in the counter-rotating case. Measurements of velocity field fluctuations are examined to determine the possibility of an inhomogeneous turbulent resistivity.
Numerical simulation of a flow with a magnetic field in an induction furnace of various materials
Authors: Im Kichang , Bae Myung-whan
Published: April 2008

The material effects of an induction furnace on a flow and magnetic field are numerically investigated by two parameters, the Reynolds and magnetic Prandtl numbers. These parameters are obtained from the nondimensional governing equations containing the motion effects in Maxwell’s equations. Under the assumption of an axisymmetric field, vorticity-stream function formulation is used in conjunction with Maxwell’s equations in a boundary-fitted coordinate system. “No slip on the wall” and “no shear stress tensor on the free surface” are used as the boundary conditions of a velocity field, and the boundary conditions of a magnetic field are obtained considering the insulated interface and the magnetic field induced by external coils. Presented are streamlines, magnetic streamlines, and the variation of the axial velocity component with Reynolds and magnetic Prandtl numbers. It is found that the flow field varies remarkably with the Reynolds number but slightly with the magnetic Prandtl number except one of the high viscous liquid.
A switched supply tunable red-green-blue light emitting diode driver
Authors: Feng Weifeng , Shi Frank G. , He Yongzhi , Zhao Bin
Published: April 2008

This paper presents a new switched supply tunable red-green-blue (RGB) light emitting diode (LED) driver. The RGB LEDs act not only as light emitting devices but also as rectifying diodes in the presented driver circuit. The RGB LED color control is realized by controlling the switched supply voltage amplitude, frequency, and duty cycle. The driver efficiency is high since the only loss in the driver circuit is the switch and can be further reduced by direct alternate current supply.
Optically controlled resonance energy transfer: Mechanism and configuration for all-optical switching
Authors: Bradshaw David S. , Andrews David L.
Published: April 2008

In a molecular system of energy donors and acceptors, resonance energy transfer is the primary mechanism by means of which electronic energy is redistributed between molecules, following the excitation of a donor. Given a suitable geometric configuration it is possible to completely inhibit this energy transfer in such a way that it can only be activated by application of an off-resonant laser beam: this is the principle of optically controlled resonance energy transfer, the basis for an all-optical switch. This paper begins with an investigation of optically controlled energy transfer between a single donor and acceptor molecule, identifying the symmetry and structural constraints and analyzing in detail the dependence on molecular energy level positioning. Spatially correlated donor and acceptor arrays with linear, square, and hexagonally structured arrangements are then assessed as potential configurations for all-optical switching. Built on quantum electrodynamical principles the concept of transfer fidelity, a parameter quantifying the efficiency of energy transportation, is introduced and defined. Results are explored by employing numerical simulations and graphical analysis. Finally, a discussion focuses on the advantages of such energy transfer based processes over all-optical switching of other proposed forms.
Axisymmetric instabilities of fast electron beams in dense plasmas
Authors: Shafiq-ur-Rehman  , Wang Xiaogang , Liu Yue
Published: April 2008

Axisymmetric radial modes of fast electron beams propagating through dense background plasmas with a return current are studied in a two electron-fluid model. The linear growth rate is obtained by numerically solving the self-consistent electron fluids system. The dispersion relation is also calculated for certain parameters. It is found that various radial modes are excited over the entire range of axial wavelengths, as the long-wavelength regime is dominated by hollowinglike modes characterized by an azimuthal number of m=0 and radial numbers of n=2 and n=3, and the short-wavelength regime is dominated by electromagnetic beam-plasma instabilities with higher radial mode numbers. Also, it is found that the finite beam-plasma temperatures, collisional effects and strongly asymmetric density conditions, with density of the beam being much less than the plasma density, can significantly reduce the growth rate of the instabilities.
Structural and optical properties of ZnO thin films by rf magnetron sputtering with rapid thermal annealing
Authors: Suvorova N. A. , Usov I. O. , Stan L. , DePaula R. F. , Dattelbaum A. M. , Jia Q. X. , Suvorova A. A.
Published: April 2008

Epitaxial ZnO thin films were grown on c-plane sapphire substrates by rf magnetron sputtering at room temperature followed by a rapid thermal annealing process. We found that crystallinity of the films was strongly affected by the partial oxygen pressure during deposition. Both x-ray diffraction and transmission electron microscopy studies revealed that the ZnO films grow epitaxially predominantly with aligned ZnO domains. An unresolved excitonic resonance was observed in the optical absorption spectrum. Nevertheless, refractive index and absorption edge of the ZnO films are similar to that of single crystal ZnO.
Disk-shaped Bose–Einstein condensates in the presence of an harmonic trap and an optical lattice
Authors: Kapitula Todd , Kevrekidis Panayotis G. , Frantzeskakis D. J.
Published: April 2008

We study the existence and stability of solutions of the two-dimensional nonlinear Schrödinger equation in the combined presence of a parabolic and a periodic potential. The motivating physical example consists of Bose–Einstein condensates confined in an harmonic (e.g., magnetic) trap and an optical lattice. By connecting the nonlinear problem with the underlying linear spectrum, we examine the bifurcation of nonlinear modes out of the linear ones for both focusing and defocusing nonlinearities. In particular, we find real-valued solutions (such as multipoles) and complex-valued ones (such as vortices). A primary motivation of the present work is to develop “rules of thumb” about what waveforms to expect emerging in the nonlinear problem and about the stability of those modes. As a case example of the latter, we find that among the real-valued solutions, the one with larger norm for a fixed value of the chemical potential is expected to be unstable.
Dependency of the apparent contact angle on nonisothermal conditions
Authors: Krahl Rolf , Gerstmann Jens , Behruzi Philipp , Bänsch Eberhard , Dreyer Michael E.
Published: April 2008

The dynamic behavior of liquids in partly filled containers is influenced to a large extend by the angle between the gas-liquid phase boundary and the solid container wall at the contact line. This contact angle in turn is influenced by nonisothermal conditions. In the case of a cold liquid meniscus spreading over a hot solid wall, the contact angle apparently becomes significantly larger. In this paper we want to establish a quantitative equation for this enlargement, both from experimental and numerical data. Our findings can be used to build a subgrid model for computations, where the resolution is not sufficient to resolve the boundary layers. This might be the case for large containers which are exposed to low accelerations and where the contact angle boundary condition determines the position of the free surface. These types of computation are performed, for example, to solve propellant management problems in launcher and satellite tanks. In this application, the knowledge of the position of the free surface is very important for the withdrawal of liquid and the calculation of heat and mass transfer.
Photoresponses and memory effects in organic thin film transistors incorporating poly(3-hexylthiophene)/CdSe quantum dots
Authors: Chen Chen-Chia , Chiu Mao-Yuan , Sheu Jeng-Tzong , Wei Kung-Hwa
Published: April 2008

This paper describes the optical responses and memory effects of poly(3-hexylthiophene) (P3HT)/CdSe quantum dot (QD) thin-film transistors (TFTs). TFTs incorporating P3HT/CdSe QD blends as the active layer exhibited higher photocurrents than did the corresponding P3HT-only devices because the heterojunction between P3HT and the CdSe QDs enhanced the separation of excitons. Moreover, the CdSe QDs served as trap centers so that the memory effect was maintained for several hours, even when the device was operated without a gating voltage. Here, we demonstrate the potential applicability of such P3HT/CdSe QD TFTs through repeated optical programming and electrical erasing.
Buckling analysis of carbon nanotubes modeled using nonlocal continuum theories
Authors: Kumar Devesh , Heinrich Christian , Waas Anthony M.
Published: April 2008

In this paper, the buckling of carbon nanotubes, modeled as nonlocal one dimensional continua within the framework of Euler–Bernoulli beams, is considered. Both a stress gradient and a strain gradient approach are considered and a variational approach is adopted to obtain the variationally consistent boundary conditions. The dependence of the buckling load on the nonlocal parameter has been determined using the boundary conditions obtained from the variational analysis. Results indicate significant dependence of nonlocal parameter on buckling load for particular types of boundary conditions. These findings are important in mechanical design considerations of devices that use carbon nanotubes.
Boltzmann transport study of bulk and interfacial spin depolarization effects in spin valves
Authors: Ma M. J. , Jalil M. B. A. , Tan S. G. , Han G. C.
Published: April 2008

A theoretical model is proposed to analyze both bulk and interfacial spin depolarization effects on the magnetoresistance (MR) of nanoscale spin valves (SVs). The model is based on the spin coupled Boltzmann transport equations where the momentum spin relaxation arising from spin flip and non-spin-flip scattering are considered. In the boundary conditions we include the parameter q which denotes the interfacial spin flip probability, while bulk spin depolarization is characterized by the ratio r of spin flip to non-spin-flip scattering times. We consider a typical Fe∕Cr∕Fe pseudo-SV trilayer, and calculate the current for parallel and antiparallel alignments, to deduce the MR. A decreasing trend in MR is observed with an increase in either r or q, with the dependence on q being more pronounced. We also studied the combined effect of interfacial diffusive scattering (described by parameters Ns and D↑) and spin flip scattering. We found that although diffusive scattering generally results in an improvement in MR, this is more than offset by the MR suppression effect arising from spin flip scattering.
Conical tips inside cone-jet electrosprays
Authors: Marín Álvaro G. , Loscertales Ignacio G. , Barrero A.
Published: April 2008

In coaxial jet electrosprays inside liquid baths, a conductive liquid forms a cone-jet electrospray within a bath containing a dielectric liquid. An additional dielectric liquid is injected inside the Taylor cone, forming a liquid meniscus. The motion of the conductive liquid that flows toward the vertex cone deforms the inner dielectric meniscus until a liquid jet is issued from its tip. Both the conductive and inner dielectric liquid jets flow coaxially and, further downstream, they will eventually be broken up by capillary instabilities. Coaxial jet electrosprays inside liquid baths is a useful technique to generate fine simple or double emulsions. However, in certain circumstances, we have observed that the dielectric menisci present extremely sharp tips that can be stabilized and made completely steady without mass emission. In this paper, we will first explore the parametrical range of liquid properties, mainly viscosities and surface tensions, under which these sharp tips take place. In addition, a simplified analytical model of the very complex electrohydrodynamical flow is presented for a more complete approach to the phenomena.
A nearly ideal phosphor-converted white light-emitting diode
Authors: Allen Steven C. , Steckl Andrew J.
Published: April 2008

A phosphor-converted light-emitting diode was obtained with nearly ideal blue-to-white conversion loss of only 1%. This is achieved using internal reflection to steer phosphor emission away from lossy surfaces, a reflector material with high reflectivity, and a remotely located organic phosphor having (1) unity quantum efficiency (ηq), (2) homogeneous refractive index to minimize scattering, and (3) refractive index-matched to the encapsulation to eliminate total internal reflection. An inorganic composite phosphor is also reported with a nearly homogeneous refractive index to minimize diffuse scattering of emitted light, thereby maximizing the effective phosphor ηq and light extraction.
Electronic and photoconductive properties of ultrathin InGaN photodetectors
Authors: Lebedev V. , Polyakov V. M. , Hauguth-Frank S. , Cimalla V. , Wang Ch. Y. , Ecke G. , Schwierz F. , Schober A. , Lozano J. G. , Morales F. M. , González D. , Ambacher O.
Published: April 2008

We report on the compositional dependencies of electron transport and photoconductive properties for ultrathin metal-semiconductor-metal photodetectors based on In-rich InxGa1−xN alloys. For a In0.64Ga0.36N∕GaN structure, the rise time close to the RC constant at low fields has been measured along with a transparency of ∼77% and an absorbance of ∼0.2 at a wavelength of 632nm. The electron density profiles and low-field mobilities for different compositions of InGaN have been calculated by numerically solving the Schrödinger and Poisson equations and applying the ensemble Monte Carlo method, respectively. It was demonstrated that in ultrathin InxGa1−xN∕GaN (0.5<x<1) heterostructures, in contrast to bulk InN exhibiting a strong surface electron accumulation, free electrons mostly tend to accumulate at the buried InGaN∕GaN interface. We have also found that the low-field mobility in the InGaN∕GaN heterostructures is strongly limited by the buried interface roughness which causes more than 95% of all scattering events occurred by two-dimensional electron transport under low electric field conditions.
Analysis of the axisymmetric indentation of a semi-infinite piezoelectric material: The evaluation of the contact stiffness and the effective piezoelectric constant
Authors: Yang Fuqian
Published: April 2008

A general solution of the axisymmetric indentation is obtained in the closed form for a semi-infinite, transverse isotropic piezoelectric material by a rigid-conducting indenter of arbitrary-axisymmetric profile. Explicit relationships are derived for dependences of the indentation depth and the indentation-induced charge on indentation force and applied electrical potential. Simple formulas are obtained for contact stiffness and effective piezoelectric constant, which can be used in indentation test and piezoresponse force microscopy to analyze the elastic and piezoelectric responses of piezoelectric materials. Depending on the direction of electric field (the potential difference), the electric field can either increase or suppress indentation deformation. The corresponding results are given for cylindrical, conical, and paraboloidal indenters.
Reduction of spacer layer thickness of InAs quantum dots using GaNAs strain compensation layer
Authors: Suzuki Ryoichiro , Miyamoto Tomoyuki , Sengoku Tomoyuki , Koyama Fumio
Published: April 2008

Emission and shape characteristics of the InGaAs covered InAs quantum dots with GaNAs strain compensation layers (SCLs) are investigated, focusing on the reduction of the spacer thickness for device applications. Using the GaNAs SCL, the suppression of inhomogeneous emission broadening induced by the compressive strain from lower dot layers was confirmed with the suppression of increase in the dot size of upper dot layers. This result is effective for the suppression of the spacer thickness.
A novel surface shear viscometer
Authors: Bánó Mikuláš , Pudlák Michal , Tomori Zoltán , Demjén Erna , Hrmo Igor , Bothová Hedviga
Published: April 2008

A novel rotary viscometer—developed for the determination of rheologic properties of liquid/air interface layers—is presented. The instrument can be used to measure the shear viscosity and the shear elasticity of liquid surfaces. It contains a rotor floating on the liquid surface which is rotated by means of an electromagnetic torque. A torsion filament is used to calibrate the applied torque. The viscosity data are obtained on the basis of the Navier–Stokes equation solved for the rotation of a cylinder touching the surface of water and submerged into the water. The time behavior of the surface viscosity of films gradually formed from solutions of some proteins as well as their activation energy is presented.
Thermally induced adjacent track erasure in exchange spring media
Authors: Dean J. , Bashir M. A. , Goncharov A. , Hrkac G. , Bance S. , Schrefl T. , Cazacu A. , Gubbins M. , Lamberton R. W. , Suess D.
Published: April 2008

Repeated writing causes adjacent track erasure. During multiple write cycles, the grains of neighboring tracks are exposed to the write field, which will lower the energy barrier. Grains in an adjacent track are likely to reverse their magnetization when the cumulated field expose time exceeds the transition time. The energy barrier of a grain subject to the write field is computed as a function of distance from the track center. For the same perpendicular writer and the same intergranular exchange field, the number of passes before erasure is orders of magnitudes higher in exchange spring media than in single phase media.
Simple active method for reducing magnetic interference in a thermoelectrically cooled photomultiplier tube
Authors: Kärhä Petri , Jaakkola Teemu
Published: April 2008

We present a simple modification for thermoelectrically cooled photomultiplier tube (PMT) assemblies that eliminates the magnetic interference between the peltier element and the PMT. An active compensation is accomplished by forming current loops of the wires of the peltier element and placing them in such a way that they eliminate the interfering magnetic field. It is demonstrated that the improved system reduces measurement errors of the order of 1% to statistical noise at the level of 0.07%.
Suppression of near-edge optical absorption band in sputter deposited HfO2–Al2O3 nanolaminates containing nonmonoclinic HfO2
Authors: Hoppe E. E. , Aita C. R.
Published: April 2008

Nanolaminates of polycrystalline (tetragonal+orthorhombic) HfO2 and amorphous Al2O3 are sputter deposited on unheated fused SiO2, air annealed at 573–1273K, and analyzed by x-ray diffraction and spectrophometry. Significant O 2p→Hf 5d interband absorption occurs in all films at energy E⩾6.2eV. For E<6.2eV, films annealed below 1273K retain a featureless optical absorption edge despite further crystallization. A band with a 5.65eV onset concurrently develops with m-HfO2 crystallization after a 1273K anneal, indicating this phase and not nanocrystallinity per se is responsible for increased absorption.
Infrared quantum cutting in Tb3+,Yb3+ codoped transparent glass ceramics containing CaF2 nanocrystals
Authors: Ye Song , Zhu Bin , Chen Jingxin , Luo Jin , Qiu Jian Rong
Published: April 2008

Tb 3 + – Yb 3 + codoped transparent oxyfluoride glass ceramics containing CaF2 nanocrystals were synthesized. The formation of CaF2 nanocrystals in the glass ceramics was confirmed by x-ray diffraction and high resolution transmission electron microscopy. The incorporation of Tb3+ and Yb3+ into CaF2 nanocrystal lattice was confirmed by energy dispersive spectroscopy. Infrared quantum cutting involving Yb3+ 950–1100nm (F5∕22→F7∕22) emission was achieved upon the excitation of D45 energy level of Tb3+ at 484nm. The photoluminescence properties have been studied for these glass ceramics. Yb3+ concentration dependent quantum efficiency was calculated, and the maximum efficiency approaches 155% before reaching concentration quenching threshold.
Nanotomography with enhanced resolution using bimodal atomic force microscopy
Authors: Dietz C. , Zerson M. , Riesch C. , Gigler A. M. , Stark R. W. , Rehse N. , Magerle R.
Published: April 2008

High resolution volume images of semicrystalline polypropylene were obtained by stepwise wet-chemical etching followed by atomic force microscopy of the specimen. Enhanced signal-to-noise ratio and spatial resolution were achieved by using the second flexural eigenmode of the cantilever for phase imaging while the amplitude of the first mode was used as feedback signal. The energy dissipated between the tip and the sample revealed characteristic differences between the crystalline and the amorphous regions of the polypropylene after etching, indicating the presence of a thin (<10nm thick) amorphous layer on top of crystalline regions.
Frequency response characteristic of single-walled carbon nanotubes as supercapacitor electrode material
Authors: Liu C. G. , Liu M. , Li F. , Cheng H. M.
Published: April 2008

Impedance analysis was employed to study the frequency response characteristics of supercapacitors utilizing single-walled carbon nanotubes (SWNTs) as electrode material. The knee frequency is around 631Hz for the electrochemically oxidized SWNT supercapacitor, much higher than that of the as-prepared one (around 316Hz) and the common activated carbon supercapacitor (<1Hz). The good frequency response observed in this work is due to the introduction of nanosized mesopores and oxygen-containing groups formed during the electrochemical oxidization of SWNTs. The capacitance of electrochemically oxidized SWNT supercapacitor is 113F∕g, which is much higher than the value of the as-prepared one (20F∕g).
Role of substrate on the electrical properties of SnO2–La0.7Sr0.3MnO3 bilayers
Authors: Mona J. , Kale S. N. , Choudhary R. J. , Phase D. M.
Published: April 2008

We have fabricated a SnO2–La0.7Sr0.3MnO3 (LSMO) bilayer on different substrates: Si (001), Al2O3 (0001), and LaAlO3 (LAO) (001), using a pulsed laser deposition system. X-Ray diffraction analysis shows a polycrystalline growth of both layers on Si and Al2O3, while an oriented growth of LSMO on LAO. Transport characteristics on Si are nonlinear, while on Al2O3 it is linear. A sample on LAO shows a steplike voltage response to low current values. The transport seen on Si has been envisaged in terms of Si-LSMO rectifying characteristics with SnO2 as buffer.
Indium distribution at the interfaces of (Ga,In)(N,As)∕GaAs quantum wells
Authors: Luna E. , Ishikawa F. , Batista P. D. , Trampert A.
Published: April 2008

The indium distribution across (Ga,In)(N,As) quantum wells is determined by using transmission electron microscopy techniques. Inside the quantum well, the indium distribution is well described by Muraki’s segregation model; however, it fails in reflecting the concentration at the interfaces. To describe them, we propose a sigmoidal law which defines the smooth variation of the indium concentration with the position and provides a systematic and quantitative characterization of the interfaces. The thermal stability of the interfaces and their interplay with segregation effects are discussed. A connection between the high thermal robustness of the interfaces and the inherent thermodynamic miscibility gap of the alloy is suggested.
Wireless resonant magnetic microactuator for untethered mobile microrobots
Authors: Vollmers Karl , Frutiger Dominic R. , Kratochvil Bradley E. , Nelson Bradley J.
Published: April 2008

Power and propulsion are primary challenges in building untethered submillimeter robots. We present a class of actuators utilizing wireless resonant magnetic actuation which accomplishes both tasks with a high degree of control. The actuator harvests magnetic energy from the environment and transforms it to impact-driven mechanical force. It can be powered and controlled with oscillating fields in the kilohertz range and strengths as low as 2mT. The wireless resonant magnetic microactuator was incorporated in microrobots, which measure 300×300×70μm3, that are capable of moving forward, backward, and turning in place while reaching speeds in excess of 12.5mm∕s.
Low vacuum process for polymer solar cells: Effect of TiOx interlayer
Authors: Yoon Sang Jun , Park Jong Hyeok , Lee Hang Ken , Park O. Ok
Published: April 2008

Here, the effect of integration of a TiOx interlayer on low vacuum-processible organic-based solar cells is reported. Devices with an Al electrode prepared at a low vacuum condition shows lower efficiency compared to those with an Al electrode prepared at a high vacuum condition because the interface between the active layer and Al electrode is too rough. When a TiOx layer is inserted between the active layer and Al electrode of the device, the cell efficiency is regained and much less dependent on the level of vacuum during Al deposition so that it may be possible to develop low cost process.
Two-step exciton dissociation in poly(3-hexylthiophene)/fullerene heterojunctions
Authors: Lloyd Matthew T. , Lim Yee-Fun , Malliaras George G.
Published: April 2008

Charge and energy transfer are competing processes in photoexcited organic donor/acceptor systems. By inserting a thin interlayer of a wide band gap organic semiconductor in a poly(3-hexylthiophene)/fullerene heterojunction, we were able to selectively suppress electron transfer. External quantum efficiency measurements show that device performance is unaffected by the presence of the interlayer. These results can be explained by two-step exciton dissociation where energy transfer of excitons from the donor to the acceptor is followed by hole transfer to the donor. The same interlayer was shown to decrease the photocurrent in a heterojunction where this energy transfer pathway is forbidden.
Strain effect on coercive field of epitaxial barium titanate thin films
Authors: Choudhury S. , Li Y. L. , Chen L. Q. , Jia Q. X.
Published: April 2008

Strain is generally known to increase the coercive field of a ferroelectric thin film as compared to a stress-free single crystal or a strain-relaxed film. We studied the coercive fields and remanent polarizations of (001)-oriented epitaxial barium titanate thin films using the phase-field approach. It is demonstrated, while the remanent polarization decreases as in-plane strain changes from being compressive to tensile, the variation of coercive field with strain is complicated. We noted more than two times drop in coercive field with a reduction of compressive strain of only ∼0.05%, which we attribute to the existence of multiple ferroelectric phases.
Near-infrared third-order nonlinearity of PbO–GeO2 films containing Cu and Cu2O nanoparticles
Authors: Gómez Luis A. , dos Santos F. E. P. , Gomes A. S. L. , de Araújo Cid B. , Kassab Luciana R. P. , Hora Windson G.
Published: April 2008

We report measurements of the nonlinear (NL) refractive index n2 of lead-germanium films (LGFs) containing Cu and Cu2O nanoparticles (NPs). The thermally managed eclipse Z-scan technique with 150fs pulses from a laser operating at 800nm was used. The NL refractive index measured, n2=6.3×10−12cm2∕W has electronic origin and the NL absorption coefficient α2 is smaller than 660cm∕GW. The figure of merit n2∕λα2 is enhanced by more than two orders of magnitude in comparison with the result for the LGFs without the copper based NPs.
Direct high-resolution transmission electron microscopy observation of tetragonal nanotwins within the monoclinic MC phase of Pb(Mg1∕3Nb2∕3)O3-0.35PbTiO3 crystals
Authors: Bhattacharyya Somnath , Jinschek J. R. , Cao Hu , Wang Yu U. , Li Jiefang , Viehland D.
Published: April 2008

We report on the direct observation of tetragonal nanodomains within an average monoclinic MC phase of Pb(Mg1∕3Nb2∕3)O3-0.35PbTiO3 single crystals by high-resolution transmission electron microscopy. These nanodomains are geometrically arranged in alternating layers of twins. The findings are consistent with the fundamental underlying assumptions of the ferroelectric adaptive phase theory [Y. M. Jin et al., Phys. Rev. Lett. 91, 197601 (2003)].
Differences in spontaneous mutation frequencies as a function of environmental stress in soil fungi at “Evolution Canyon,” Israel
Authors: Lamb Bernard C. , Mandaokar Snehal , Bahsoun Basma , Grishkan Isabella , Nevo Eviatar
Published: April 2008

When various wild strains of
Penicillium lanosum
and
Aspergillus niger
were placed in the same mild laboratory environment, their frequencies of new spontaneous mutations were clearly related to whether they had been isolated from a region of high or low microclimatic stress. In the mild environment, the total frequencies of conidial color and morphological mutations in
P. lanosum
, summed over all relevant loci, ranged from 0.29% to 2.4% for six strains from the north-facing, less stressful “European” slope (ES/NFS) of “Evolution Canyon” I, compared with 6.5–11.6% for five strains from the south-facing “African” slope (AS/SFS), which is a much more stressful environment, being harsher, drier, more fluctuating in temperature, and receiving up to eight times more UV radiation than the opposite slope. The corresponding figures for
A. niger
were 0.42–1.50% for three strains from the ES/NFS and 2.3–4.9% for six strains from the AS/SFS. The more mutagenic environment of the AS/SFS than of the ES/NFS means that, in Evolution Canyon, the mutation frequency differences between the very stressful environment and the less stressful environment are probably even larger than the 4- and 6-fold differences found here in a mild laboratory environment. The evidence from these two filamentous fungi, which have no sexual cycle, is that there are inherited differences in spontaneous mutation rates according to the levels of stress in the environment, and this feature may well be adaptive. Evolution Canyon I is at Nahal Oren, Mount Carmel, Israel.
A Novel Group of Glutaredoxins in thecis-Golgi Critical for Oxidative Stress Resistance
Authors: Mesecke Nikola , Spang Anne , Deponte Marcel , Herrmann Johannes M.
Published: April 2008

Glutaredoxins represent a ubiquitous family of proteins that catalyze the reduction of disulfide bonds in their substrate proteins by use of reduced glutathione. In an attempt to identify the full complement of glutaredoxins in baker's yeast, we found three so-far uncharacterized glutaredoxin-like proteins that we named Grx6, Grx7, and Grx8. Grx6 and Grx7 represent closely related monothiol glutaredoxins that are synthesized with N-terminal signal sequences. Both proteins are located in the cis-Golgi, thereby representing the first glutaredoxins found in a compartment of the secretory pathway. In contrast to formerly described monothiol glutaredoxins, Grx6 and Grx7, showed a high glutaredoxin activity in vitro. Grx6 and Grx7 overlap in their activity and deletion mutants lacking both proteins show growth defects and a strongly increased sensitivity toward oxidizing agents such as hydrogen peroxide or diamide. Our observations suggest that Grx6 and Grx7 do not play a general role in the oxidative folding of proteins in the early secretory pathway but rather counteract the oxidation of specific thiol groups in substrate proteins.
Mitochondrial Protein Import Motor: Differential Role of Tim44 in the Recruitment of Pam17 and J-Complex to the Presequence Translocase
Authors: Hutu Dana P. , Guiard Bernard , Chacinska Agnieszka , Becker Dorothea , Pfanner Nikolaus , Rehling Peter , van der Laan Martin
Published: April 2008

The presequence translocase of the mitochondrial inner membrane (TIM23 complex) mediates the import of preproteins with amino-terminal presequences. To drive matrix translocation the TIM23 complex recruits the presequence translocase-associated motor (PAM) with the matrix heat shock protein 70 (mtHsp70) as central subunit. Activity and localization of mtHsp70 are regulated by four membrane-associated cochaperones: the adaptor protein Tim44, the stimulatory J-complex Pam18/Pam16, and Pam17. It has been proposed that Tim44 serves as molecular platform to localize mtHsp70 and the J-complex at the TIM23 complex, but it is unknown how Pam17 interacts with the translocase. We generated conditional tim44 yeast mutants and selected a mutant allele, which differentially affects the association of PAM modules with TIM23. In tim44-804 mitochondria, the interaction of the J-complex with the TIM23 complex is impaired, whereas unexpectedly the binding of Pam17 is increased. Pam17 interacts with the channel protein Tim23, revealing a new interaction site between TIM23 and PAM. Thus, the motor PAM is composed of functional modules that bind to different sites of the translocase. We suggest that Tim44 is not simply a scaffold for binding of motor subunits but plays a differential role in the recruitment of PAM modules to the inner membrane translocase.
Species detection using environmental DNA from water samples
Authors: Ficetola Gentile Francesco , Miaud Claude , Pompanon François , Taberlet Pierre
Published: April 2008

The assessment of species distribution is a first critical phase of biodiversity studies and is necessary to many disciplines such as biogeography, conservation biology and ecology. However, several species are difficult to detect, especially during particular time periods or developmental stages, potentially biasing study outcomes. Here we present a novel approach, based on the limited persistence of DNA in the environment, to detect the presence of a species in fresh water. We used specific primers that amplify short mitochondrial DNA sequences to track the presence of a frog (
Rana catesbeiana
) in controlled environments and natural wetlands. A multi-sampling approach allowed for species detection in all environments where it was present, even at low densities. The reliability of the results was demonstrated by the identification of amplified DNA fragments, using traditional sequencing and parallel pyrosequencing techniques. As the environment can retain the molecular imprint of inhabiting species, our approach allows the reliable detection of secretive organisms in wetlands without direct observation. Combined with massive sequencing and the development of DNA barcodes that enable species identification, this approach opens new perspectives for the assessment of current biodiversity from environmental samples.
Waves in lattices with imperfect junctions and localized defect modes
Authors: Zalipaev V.V , Movchan A.B , Jones I.S
Published: April 2008

A correspondence between continuum periodic structures and discrete lattices is well known in the theory of elasticity. Frequently, lattice models are the result of the discretization of continuous mechanical problems. In this paper, we discuss the discretization of two-dimensional square thin-walled structures. We consider the case when thin-walled bridges have defects in the vicinity of junctions. At these points, the displacement satisfies an effective Robin-type boundary condition. We study a defect vibration mode localized in the neighbourhood of the damaged junction. We analyse dispersion diagrams that show the existence of standing waves in a structure with periodically distributed defects.
Morphometric analysis of Epidendrum secundum (Orchidaceae) in southeastern Brazil
Authors: Pinheiro F. , De Barros F.
Published: April 2008

One of the largest genera of Orchidaceae with about 1125 species, Epidendrum L. presents several taxonomic problems, mainly due to the great variability of some of its species. The present study aims at evaluating the influence of different environments on the morphology of individuals from Epidendrum secundum, using morphometry to compare plants under cultivation and plants collected directly from the field. Eighty specimens maintained in cultivation at the Institute of Botany of São Paulo (Brazil) and 146 individuals originating from three natural populations, totaling 226 specimens, were analyzed with multivariate methods (PCA, CVA, DA). The fact that plants growing in rocky outcrops and plants from the Atlantic rainforest showed the largest morphological differentiation among themselves, indicates that phenotypes are strongly influenced by the habitat. Because plants collected from both habitats, maintained under cultivation for at least 20 years maintained their differentiation, such differentiation may have a genetic component. Because individuals collected in such environments present the largest morphological dimensions, new habitats generated by human activity, such as highway margins, seem to be quite favorable for these plants.
A numerical taxonomy of the pan species of Crinum based on morphological characters
Authors: Kwembeya Ezekeil G. , Stedje Brita
Published: April 2008

Fourteen characters of 64 specimens from five taxa; Crinum rautanenianum Schinz, C. paludosum Verdoorn, C. carolo‐schmidtii Dinter and C. lugardiae N. E. Brown, previously described within the complex and the more widespread C. macowanii Baker, were subjected to multivariate and univariate statistical analyses in order to circumscribe morphological species as objectively as possible. Results of the clustering and ordination analyses confirm the existence of five distinct phenetic species in the group. The most useful characters that provide taxonomic clarity are identified whilst previously used diagnostic features are discussed. A new key to the species based on examined specimens is provided. Distribution maps of members of this species complex are also presented.
Reproductive success of Dactylorhiza incarnata ssp. incarnata (Orchidaceae): the effects of population size and plant visibility
Authors: Vallius Elisa , Lammi Antti , Kuitunen Markku
Published: April 2008

Reproduction of plants pollinated solely by flower‐visiting animals depends on the ability of the population and each of its flowering member to attract pollinators. Factors affecting the pollination of nectarless species differ somewhat from those affecting the pollination of rewarding species due to the avoidance behaviour of pollinators after visiting empty flowers.

We studied a non‐mimic food‐deceptive orchid, Dactylorhiza incarnata ssp. incarnata, in 16 populations in central Finland to examine if population properties and plant size affected reproductive success of plants.

We found that the number of flowering plants increased total pollinia removal and seed production of the population, but had no effect on reproduction of individual plants. Dactylorhiza incarnata occurred in open mires with virtually no rewarding species in the neighbourhood, but the distance from the forest edge did not have any effect on reproduction. However, increased variation in the number of flowers among within‐population plants enhanced plant reproductive success. The increased variation probably hampered the learning process of flower visitors. Plant size affected reproductive success only in populations with a high general reproductive success indicating that in the rarely visited populations, pollination of individual plants is mainly affected by random effects.
Pollen morphology of Croton sect. Lamprocroton (Müll. Arg.) Pax (Euphorbiaceae) and its taxonomic implications
Authors: Ribes de Lima Letícia , Amélia Vitorino da Cruz‐Barros Maria , Rubens Pirani José , Maria da Silva Corrêa Angela
Published: April 2008

A palynological analysis of 22 taxa of Croton sect. Lamprocroton (Müll. Arg.) Pax was accomplished in order to obtain evidence for a good interspecific delimitation and phylogenetic characterization of this group. Samples of 22 taxa (from which approximately 90% of the species belonged to this section) were obtained from herbarium specimens; moreover, pollen grains were analyzed with light and scanning electron microscopy. Characters observed from pollen grain diameter and from exine ornamentation were registered and compared. Pollen grains were found to be spherical, apolar, inaperturate and with a diameter ranging from 49.32±0.94 μm in C. ehrenbergii Schltdl. to 86.42±1.33 μm in C. muellerianus L. R. Lima. Pollen morphology of three recently described species of Croton was analyzed for the first time herein. In addition the results of this study confirm the distinctness of these species but do not support a recently proposed new variety of C. pallidulus Baill.
Remarkable desmids (Desmidiaceae, Charophyta) from Sardinia, Italy
Authors: Coesel Peter F. M. , Alfinito Silvia
Published: April 2008

A number of benthic microfauna samples collected in Sardinia in the 1970s, and screened for the occurrence of microalgae in the 1990s, revealed some remarkable desmid species. Most of these species could not be found in a series of samples collected in 2006. Eleven desmid taxa are discussed in detail, two of which are described as new to science; Cosmarium majaeforme sp. nov. and Xanthidiumsardiniense sp. nov. The specific composition of the Sardinian desmid flora is discussed both in relation to the prevailing environmental conditions and to its geographic position close to the African continent.
Chromosome numbers and mode of reproduction in Picrishieracioides s.l. (Asteraceae), with notes on some other Picristaxa
Authors: Slovák Marek , Šingliarová Barbora , Mráz Patrik
Published: April 2008

Chromosome numbers for 88 plants of Picris hieracioides s.l. originating from 32 localities from Austria, Andorra, Croatia, France, Germany, Hungary, Italy, Slovakia and Spain are reported. All analysed plants were diploid, with 2n=2x=10. In addition to P. hieracioides s.l., we also found diploidy (2n=2x=10) in P. nuristanica from Kirgizia and P. japonica from Japan. Our data confirmed previously published results in the literature. We also studied the mode of reproduction in all three taxa. Picrisnuristanica and P. japonica s.l. were able to produce some seeds by selfing, and this is the first record of autogamy in this genus. In P. hieracioides s.l. only strict allogamy was found, demonstrating the presence of a self‐incompatibility system in this species. Because apomixis, namely apospory, has previously been reported in P. hieracioides, castration experiments were performed in order to confirm or reject this report. However, no evidence of apomictic seed formation was found within this species. In the light of our results, P. hieracioides should be considered a strictly sexual taxon.
Feasibility of prophylaxis and immune tolerance induction regimens in haemophilic children using fully implantable central venous catheters
Authors: Mancuso Maria Elisa , Mannucci Pier Mannuccio , Sartori Angelo , Agliardi Andrea , Santagostino Elena
Published: April 2008

Venous access represents the major barrier to the feasibility of prophylaxis and immune tolerance induction (ITI) in haemophilic children. Ports improve treatment feasibility, but their duration is limited by infectious complications. This study aimed at evaluating whether or not ports allow haemophilic children to maintain the treatment regimen in the long term. Children were prospectively followed‐up and underwent port removal either for complications or transition to peripheral veins. Of 27 ports (17 used for prophylaxis and 10 for ITI), 25 were removed after a median of 3·3 years. Inhibitor children showed a younger age at port insertion (P = 0·02), an earlier occurrence of infections (P = 0·006) at a higher rate (P = 0·00001) and an earlier removal for infection (P = 0·05) than non‐inhibitor patients. Daily port use was associated with earlier infections at a higher rate compared to less frequent use (P = 0·02). Port removal after a median of 0·8 years prevented ITI completion in 50% of children, while it hampered the maintenance of prophylaxis in 27% of patients. This study showed that ports improved the feasibility of prophylaxis in the majority of non‐inhibitor children, while they were not suitable for inhibitor children who require a prolonged ITI regimen with daily infusions.
Farnesyltransferase inhibitors and their potential role in therapy for myelodysplastic syndromes and acute myeloid leukaemia
Authors: Braun Thorsten , Fenaux Pierre
Published: April 2008

Novel strategies are required for treatment of acute myeloid leukaemia (AML) and higher risk myelodysplastic syndrome (MDS) patients who are not eligible for intensive chemotherapy and/or allogenic stem cell transplantation. As activating RAS mutations are frequent in these diseases, one novel approach, consisting of interfering with isoprenylation of RAS proteins by farnesyltransferase inhibitors (FTIs), has been proposed. Clinical phase II studies with the oral FTIs tipifarnib and lonafarnib in previously untreated AML, MDS and chronic myelomonocytic leukaemia yielded rather encouraging results while results in relapsed and/or refractory AML were disappointing. Results of a phase III trial in untreated AML in the elderly with tipifarnib were also disappointing. Clinical responses were not related to RAS mutations, suggesting additional actions of FTIs on other molecular targets. The combination of existing FTIs with other treatments, such as chemotherapy (in AML) and hypomethylating agents (in MDS and AML), is under investigation. Ongoing studies will also determine if gene profiling analysis may help to identify patients that will respond to FTIs.
The use of intravenous iron in patients with cancer‐related anaemia
Authors: Littlewood T. J. , Alikhan R.
Published: April 2008

Intravenous iron has become the standard of care in patients with renal failure receiving treatment with erythropoiesis stimulating agents (ESAs) to treat true and functional iron deficiency and to prevent its development in haemodialysis patients. In cancer‐related anaemia, several recently published, randomised studies suggested that intravenous iron improved haemoglobin response rates in ESA‐treated patients compared to those treated with oral iron or placebo. The data supporting the efficacy of intravenous iron instead of oral iron in this setting are increasingly persuasive but larger randomised trials are needed before definitive recommendations are made.