bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and thermodynamics of metal-loaded transferrins: transferrin receptor 1 interactions
Authors: Ha-Duong Nguyêt-Thanh , Hémadi Miryana , Chikh Zohra , Chahine Jean-Michel El Hage
Published: December 2008

Transferrin receptor 1 (R) and human serum transferrin (T) are the two main actors in iron acquisition by the cell. R binds TFe2 (iron-loaded transferrin), which allows its internalization in the cytoplasm by endocytosis. T also forms complexes with metals other than iron. In order to follow the iron-acquisition pathway, these metals should obey at least two essential rules: (i) formation of a strong complex with T; and (ii) interaction of this complex with R. In the present paper, we propose a general mechanism for the interaction of five metal-loaded Ts [Fe(III), Al(III), Bi(III), Ga(III) and Co(III)] with R and we discuss their potential incorporation by the iron-acquisition pathway. With iron- and cobalt-loaded Ts, the interaction of R takes place in two steps: the first is detected by the T-jump technique and occurs in the 100 μs range, whereas the second is slow and occurs in the hour range. Bi(III)- and Ga(III)-loaded Ts interact with R in a single fast kinetic step, which occurs in the 100–500 μs range. No interaction is detected between R and aluminium-saturated T. The fast steps are ascribed to the interaction of the C-lobe of metal-loaded T with the helical domain of R: dissociation constant, K′1, of 0.50±0.07, 0.82±0.25, 4±0.4 and 1.10±0.12 μM for Fe(III), Co(III), Bi(III) and Ga(III) respectively. The second slow steps are ascribed to changes in the conformation of the protein–protein adducts which increase the stability to achieve, at thermodynamic equilibrium, an overall dissociation constant, K1, of 2.3 and 25 nM for Fe(III) and Co(III) respectively. This last step occurs over several hours, whereas endocytosis takes place in several minutes. This implies that metal-loaded Ts are internalized with only the C-lobe interacting with R. This suggests that, despite a lower affinity for R when compared with TFe2, some metal-loaded Ts can compete kinetically with TFe2 for the interaction with R and thus follow the iron-acquisition pathway.
Residual dipolar couplings as a tool to study molecular recognition of ubiquitin
Authors: Lakomek Nils-Alexander , Lange Oliver F. , Walter Korvin F.A. , Farès Christophe , Egger Dalia , Lunkenheimer Peter , Meiler Jens , Grubmüller Helmut , Becker Stefan , de Groot Bert L. , Griesinger Christian
Published: December 2008

RDCs (residual dipolar couplings) in NMR spectroscopy provide information about protein dynamics complementary to NMR relaxation methods, especially in the previously inaccessible time window between the protein correlation time τc and 50 μs. For ubiquitin, new modes of motion of the protein backbone could be detected using RDC-based techniques. An ensemble of ubiquitin based on these RDC values is found to comprise all different conformations that ubiquitin adopts upon binding to different recognition proteins. These conformations in protein–protein complexes had been derived from 46 X-ray structures. Thus, for ubiquitin recognition by other proteins, conformational selection rather than induced fit seems to be the dominant mechanism.
iPEP: peptides designed and selected for interfering with protein interaction and function
Authors: Mason Jody M. , M. Müller Kristian , Arndt Katja M.
Published: December 2008

Semi-rational design is combined with PCAs (protein-fragment complementation assays) and phage-display screening techniques to generate a range of iPEPs (interfering peptides) that target therapeutically relevant proteins with much higher interaction stability than their native complexes. PCA selection has been improved to impose a competitive and negative design initiative on the library screen, thus simultaneously improving the specificity of assay ‘winners’. The folding pathways of designed pairs imply that early events are dominated by hydrophobic collapse and helix formation, whereas later events account for the consolidation of more intricate intermolecular electrostatic interactions.
Lectin–glycoconjugate interactions in health and disease
Authors: Kilpatrick David C.
Published: December 2008

It is increasingly being acknowledged that complex carbohydrates mediate a huge variety of cellular interactions, permitting and regulating recognition and signalling events. This is achieved by the enormous range and complexity of branched structures in glycoconjugates and the ability of carbohydrate-binding proteins (lectins) to decipher this ‘glycocode’. Approx. 120 participants attended the 23rd International Lectin Meeting (Interlec-23) held at the Universities of Edinburgh (2 days) and Stirling (4 days) between 11 and 16 July 2008. These ‘Interlecs’ are truly international multi-disciplinary symposia, providing opportunities for scientists from different backgrounds, but with a common interest in some aspect of protein–carbohydrate interactions, to present their work in an informal and stimulating atmosphere. A major aim is always to induce cross-fertilization of ideas and concepts, and Interlec-23 was intended to have some bias towards lectins (galectins, collectins, selectins, siglecs etc.) and their ligands in human health and disease. Delegates from over 30 countries attended this meeting which was divided into seven oral sessions opened by a keynote speaker. This issue of Biochemical Society Transactions contains papers based on the keynote lectures and is therefore representative of the main themes of Interlec-23.
Lectins: past, present and future1
Authors: Sharon Nathan
Published: December 2008

Lectins, a class of sugar-binding and cell-agglutinating proteins, are ubiquitous in Nature, being found in all kinds of organisms, from viruses to humans. This review describes how plant lectins were developed as widely used reagents for the study of glycoconjugates in solution and on cells, and for cell characterization and separation. A summary is then given of the discoveries that demonstrated the role of lectins as cell recognition molecules of micro-organisms and of animal cells. The specialized functions of these lectins are discussed, as well as the potential medical applications of the knowledge gained. The review ends with speculations about future developments in lectin research and applications.
C-type lectins on dendritic cells: key modulators for the induction of immune responses
Authors: van Kooyk Yvette
Published: December 2008

DCs (dendritic cells) are specialized in the recognition of pathogens and play a pivotal role in the control of immune responses. DCs are also important for homoeostatic control, recognizing self-antigens and tolerizing the tissue environment. The nature of the antigen recognized tilts the balance towards immunity or tolerance. CLRs (C-type lectin receptors) expressed by DC are involved in the recognition and capture of many glycosylated self-antigens and pathogens. It is now becoming clear that these CLRs may not only serve as antigen receptors allowing internalization and antigen presentation, but also function in the recognition of glycosylated self-antigens, and as adhesion and/or signalling molecules. The expression of C-type lectins is very sensitive to maturation stimuli, leading to down-regulation as DCs mature. CLRs such as DC-SIGN (DC-specific intracellular adhesion molecule-3 grabbing non-integrin) recognizes high-mannose-containing structures and Lewis antigens (Lex, Ley, Leb and Lea), whereas the CLR MGL (macrophage galactose/N-acetylgalactosamine-specific C-type lectin) recognizes GalNAc. Lex, Ley and GalNAc glycan structures are often expressed on tumours. We have demonstrated that glycan modification of antigen can strongly enhance MHC class I responses and the induction of antigen-specific cytotoxic T-lymphocytes, indicating that glycosylated antigen targets C-type lectin to enhance antigen-specific T-cell responses. Moreover, these CLRs induce signalling processes in DCs and specific cytokine responses in combination with TLR (Toll-like receptor) triggering. This implies that specific C-type lectin-targeted antigens can regulate T-cell polarization. Understanding the diversity of C-type lectins being expressed on DCs as well as their carbohydrate-specific recognition profiles should promote understanding of pathogen recognition in many diseases, as well as the regulation of cellular interactions of DCs that are essential in the control of immunity.
Glycans: bioactive signals decoded by lectins
Authors: Gabius Hans-Joachim
Published: December 2008

The glycan part of cellular glycoconjugates affords a versatile means to build biochemical signals. These oligosaccharides have an exceptional talent in this respect. They surpass any other class of biomolecule in coding capacity within an oligomer (code word). Four structural factors account for this property: the potential for variability of linkage points, anomeric position and ring size as well as the aptitude for branching (first and second dimensions of the sugar code). Specific intermolecular recognition is favoured by abundant potential for hydrogen/co-ordination bonds and for C–H/π-interactions. Fittingly, an array of protein folds has developed in evolution with the ability to select certain glycans from the natural diversity. The thermodynamics of this reaction profits from the occurrence of these ligands in only a few energetically favoured conformers, comparing favourably with highly flexible peptides (third dimension of the sugar code). Sequence, shape and local aspects of glycan presentation (e.g. multivalency) are key factors to regulate the avidity of lectin binding. At the level of cells, distinct glycan determinants, a result of enzymatic synthesis and dynamic remodelling, are being defined as biomarkers. Their presence gains a functional perspective by co-regulation of the cognate lectin as effector, for example in growth regulation. The way to tie sugar signal and lectin together is illustrated herein for two tumour model systems. In this sense, orchestration of glycan and lectin expression is an efficient means, with far-reaching relevance, to exploit the coding potential of oligosaccharides physiologically and medically.
Bifurcated equilibria in centrifugally confined plasma
Authors: Shamim I. , Teodorescu C. , Guzdar P. N. , Hassam A. B. , Clary R. , Ellis R. , Lunsford R.
Published: December 2008

A bifurcation theory and associated computational model are developed to account for abrupt transitions observed recently on the Maryland Centrifugal eXperiment (MCX) [R. F. Ellis et al. Phys. Plasmas 8, 2057 (2001)], a supersonically rotating magnetized plasma that relies on centrifugal forces to prevent thermal expansion of plasma along the magnetic field. The observed transitions are from a well-confined, high-rotation state (HR-mode) to a lower-rotation, lesser-confined state (O-mode). A two-dimensional time-dependent magnetohydrodynamics code is used to simulate the dynamical equilibrium states of the MCX configuration. In addition to the expected viscous drag on the core plasma rotation, a momentum loss term is added that models the friction of plasma on the enhanced level of neutrals expected in the vicinity of the insulators at the throats of the magnetic mirror geometry. At small values of the external rotation drive, the plasma is not well-centrifugally confined and hence experiences the drag from near the insulators. Beyond a critical value of the external drive, the system makes an abrupt transition to a well-centrifugally confined state in which the plasma has pulled away from the end insulator plates; more effective centrifugal confinement lowers the plasma mass near the insulators allowing runaway increases in the rotation speed. The well-confined steady state is reached when the external drive is balanced by only the viscosity of the core plasma. A clear hysteresis phenomenon is shown.
Biosensors and tools for surface functionalization from the macro- to the nanoscale: The way forward
Authors: Nicu Liviu , Leïchlé Thierry
Published: December 2008

Most of review articles or even books dedicated to biosensing issues are organized by the generally admitted scheme of a biosensor. Subsequently, biological receptors, modified surfaces (and ways to specifically modify those surfaces using established biological and/or chemical recipes), and transduction techniques are thoroughly addressed in this precise order. In this review, we deliberately decided to break the conventional way of providing biosensing review by uniquely addressing biomolecules’ immobilization methods onto a solid surface and biosensing-related transduction techniques. The aim of this review is to provide a contemporary snapshot of the biosensing landscape without neglecting the seminal references or products where needed. The main guiding line of the review is the downscaling (from the macro- to the nanoscale) of biosensors and their respective most known applications. To conclude, a brief overview of the most popularized nanodevices applied to biology is given before attempting to comment on biosensors’ comparison criteria in terms of targeted applications.
Study of trap states in polyspirobifluorene based devices: Influence of chromophore addition
Authors: Renaud Cédric , Nguyen Thien-Phap
Published: December 2008

The defect states in spiro copolymer based light emitting diodes were investigated by charge based deep level transient spectroscopy (Q-DLTS). Two types of polymers have been studied: blue emitting spiro copolymer and white emitting spiro blend polymer. The white emitting spiro polymer was obtained by adding green and red chromophores into the host blue copolymer. The devices are composed of indium-tin oxide–polyethylene dioxythiophene:polystyrene sulfonate-spiro copolymer-Ba–Al. Q-DLTS measurements were performed on these diodes with various conditions of charging time, charging voltage, and temperature aiming at determining the role of chromophores in the defect formation process. Analysis of the Q-DLTS spectra obtained in both devices revealed at least five trap levels. The mean activation energies of traps are distributed in the range 0.17–0.85 eV within the band gap of the copolymers with capture cross sections of the order of 10−16–10−20 cm2. The trap densities are in the range of 1015–1016 cm−3. The results show that incorporation of dyes into the copolymer resulted in creation of an additional electron trap level and an increase in the density of the existing trap levels, indicating a more disordered state of the emitting material containing chromophores
Coplanar waveguide resonators for circuit quantum electrodynamics
Authors: Göppl M. , Fragner A. , Baur M. , Bianchetti R. , Filipp S. , Fink J. M. , Leek P. J. , Puebla G. , Steffen L. , Wallraff A.
Published: December 2008

High quality on-chip microwave resonators have recently found prominent new applications in quantum optics and quantum information processing experiments with superconducting electronic circuits, a field now known as circuit quantum electrodynamics (QED). They are also used as single photon detectors and parametric amplifiers. Here we analyze the physical properties of coplanar waveguide resonators and their relation to the materials properties for use in circuit QED. We have designed and fabricated resonators with fundamental frequencies from 2 to 9 GHz and quality factors ranging from a few hundreds to a several hundred thousands controlled by appropriately designed input and output coupling capacitors. The microwave transmission spectra measured at temperatures of 20 mK are shown to be in good agreement with theoretical lumped element and distributed element transmission matrix models. In particular, the experimentally determined resonance frequencies, quality factors, and insertion losses are fully and consistently explained by the two models for all measured devices. The high level of control and flexibility in design renders these resonators ideal for storing and manipulating quantum electromagnetic fields in integrated superconducting electronic circuits.
Internal field effects on the lasing characteristics of InGaN/GaN quantum well lasers
Authors: Dialynas G. E. , Deligeorgis G. , Zervos M. , Pelekanos N. T.
Published: December 2008

A theoretical investigation of InxGa1−xN/GaN single quantum well lasers with x in the range 0.05⩽x⩽0.3 is carried out via self-consistent Schrödinger–Poisson calculations in the effective mass approximation in order to quantify the adverse effects of the internal electric field on the lasing characteristics of these heterostructures. We find a nonzero optimum internal field value that minimizes the threshold current density Jth, and whose amplitude depends on the quantum well width, In content, and cavity losses. We demonstrate that the complete elimination of the internal field in In0.2Ga0.8N/GaN blue laser diodes with typical cavity losses should result in a decrease in Jth by as much as a factor of 4. Furthermore, for a wide range of In contents and cavity losses, we find that the optimum well width that minimizes Jth ranges between 2.5 and 4 nm. Finally, we show that the longest lasing wavelength that can be achieved from an InGaN/GaN quantum well laser is in the range of 480–500 nm depending on cavity losses.
Characterization of miniaturized metamaterial resonators coupled to planar transmission lines through parameter extraction
Authors: Aznar F. , Gil M. , Bonache J. , Jelinek L. , Baena J. D. , Marqués R. , Martín F.
Published: December 2008

In this paper, a method for obtaining the electrical characteristics of metamaterial resonators coupled to planar transmission lines is proposed. This parameter extraction technique is based on the comparison between the measured (or full wave electromagnetic simulated) transmission and reflection characteristics of a host line loaded with such resonators and those obtained from its lumped element equivalent circuit model (previously reported by some of the authors). The resonant particles considered in this study are split ring resonators, spiral resonators, and other electrically small resonant particles based on two metal levels. The interest in this technique lies in the lack of analytical models providing the electrical parameters of several of the considered ultrasmall resonator topologies (due to their complexity). From the extracted parameters, it is concluded that the circuit models predict very accurately the frequency responses of the considered structures for the different resonators under study. There is an increasing interest in the synthesis of metamaterial transmission lines with extremely small unit cell size. In order to achieve dimensions close to (or even below) λg/100, it is imperative to use complex resonator topologies that combine broadside coupling and extremely elongated metallic strips (etched in different metal levels connected through vias). This justifies the proposed technique. Thus, this work is useful in aiding the synthesis of microwave components based on resonant type metamaterial transmission lines.
Anisotropy of Snoek relaxation in a highly textured Ti–Nb–O β-Ti alloy
Authors: Yin Fuxing , Yu Liming , Ping Dehai , Iwasaki Satoshi
Published: December 2008

Snoek relaxation behavior of a Ti–25.2Nb–0.6O at. % alloy, which is processed to have an intensified normal plane∥{112} texture, is investigated on three specimens with specific crystalline orientations along the flexure vibration stressing direction. In the case of rolling direction specimen, the Snoek relaxation peak temperature is 473.5 K, the activation energy is 1.51 eV, and the peak broadness parameter r2(β) is 1.96. While all those factors show only slight variation with the change in specimen orientation, the deduced relaxation strength, QP−1/f2(0,β) changes linearly with the average orientation parameter Γ of the specimens. Considering that the observed Snoek relaxation peak can be modeled by a continuous spectrum, we get a dipole shape factor of 0.42 for the alloy with the average orientation parameters calculated by the optimized sampling grain approximation method.
Thermal stresses analysis in adhesive/solder bonded bimaterial assemblies
Authors: Wang Jialai , Zeng Shixin
Published: December 2008

An analytical model is developed to predict thermal stresses in adhesive/solder bonded bimaterial assemblies. This model simulates the adhesive layer as a “three-parameter” elastic foundation. It eliminates the shortcoming in the existing analytical models and satisfies the zero-shear stress boundary condition at the free edge. It predicts a tensile peeling stress along the interface between the layer with a smaller coefficient of thermal expansion and the adhesive. For comparison, the existing solutions give the same peeling stresses along two interfaces. The accuracy of this model is verified by finite element analysis. Parametric study has been conducted to shed light on thermal stress concentration in adhesive/solder bonded beams. The results of this study are very helpful in the analysis and physical design of bimaterial assemblies in electronic and photonic packagings.
Relativistic laser pulse focusing and self-compression in stratified plasma-vacuum systems
Authors: Karle Ch. , Spatschek K. H.
Published: December 2008

Laser pulse compression in plasma-vacuum systems is investigated in the weakly relativistic regime. First, within one-dimensional hydrodynamic models, the basic features of propagation in plasmas, like width and amplitude changes, are demonstrated. The numerical findings can be interpreted, in part, a by simplified model based on the variation of action method. Since transverse effects like filamentation do play a significant role, the numerical evaluations are then generalized to two-dimensional situations. An approximate analytical criterion for the dominating transverse wave number during laser propagation in plasmas is presented. Finite plasma-vacuum systems show in addition to the filamentation instability the so-called plasma lens effect. The latter is first demonstrated for a single plasma layer. It is then discussed how (i) longitudinal and transversal self-compression in plasmas, (ii) focusing by a plasma layer, and (iii) cleaning of unstable modes compete with each other in layered plasma-vacuum systems. Depending on the available parameters, optimized plasma-vacuum systems are proposed for pulse compression. Such systems can be used as a substitute for hollow fibers which are in use to shorten a pulse. Pulse lengths of one or two cycles can be reached by optimized plasma-vacuum systems, while attaining ultrarelativistic intensities in the focal spot behind the system of layers.
Atom abstraction and gas phase dissociation in the interaction of XeF2 with Si(100)
Authors: Hefty R. C. , Holt J. R. , Tate M. R. , Ceyer S. T.
Published: December 2008

Xenon difluoride reacts with Si(100)2×1 by single atom abstraction whereby a dangling bond abstracts a F atom from XeF2, scattering the complementary XeF product molecule into the gas phase, as observed in a molecular beam surface scattering experiment. Partitioning of the available reaction energy produces sufficient rovibrational excitation in XeF for dissociation of most of the XeF to occur. The resulting F and Xe atoms are shown to arise from the dissociation of gas phase XeF by demonstrating that the angle-resolved velocity distributions of F, Xe, and XeF conserve momentum, energy, and mass. Dissociation occurs within 2 Å of the surface and within a vibrational period of the excited XeF molecule. Approximately an equal amount of the incident XeF2 is observed to react by two atom abstraction, resulting in adsorption of a second F atom and scattering of a gas phase Xe atom. Two atom abstraction occurs for those XeF product molecules whose bond axes at the transition state are oriented within ±60° of the normal and with the F end pointed toward the surface.
Escape dynamics of a few electrons in a single-electron ratchet using silicon nanowire metal-oxide-semiconductor field-effect transistor
Authors: Miyamoto Satoru , Nishiguchi Katsuhiko , Ono Yukinori , Itoh Kohei M. , Fujiwara Akira
Published: December 2008

Transport dynamics of a few electrons in a quantum dot are investigated in a single-electron ratchet using silicon nanowire metal-oxide-semiconductor field-effect transistors. Time-resolved measurements in a nanosecond regime are carried out to determine the escape times of the first, second, and third electrons from the quantum dot originally containing three electrons. The escape time strongly depends on the number of electrons due to the single-electron charging effect in the quantum dot, which makes it possible to achieve selective ejection of a desired number of electrons.
Simulation and analysis of solenoidal ion sources
Authors: Alderwick A. R. , Jardine A. P. , Hedgeland H. , MacLaren D. A. , Allison W. , Ellis J.
Published: December 2008

We present a detailed analysis and simulation of solenoidal, magnetically confined electron bombardment ion sources, aimed at molecular beam detection. The aim is to achieve high efficiency for singly ionized species while minimizing multiple ionization. Electron space charge plays a major role and we apply combined ray tracing and finite element simulations to determine the properties of a realistic geometry. The factors controlling electron injection and ion extraction are discussed. The results from simulations are benchmarked against experimental measurements on a prototype source.
Fabrication of gravity-driven microfluidic device
Authors: Yamada H. , Yoshida Y. , Terada N. , Hagihara S. , Komatsu T. , Terasawa A.
Published: December 2008

We have studied the micro total analysis system as a blood test. A microfluidic device with a three-pronged microchannel and artificial capillary vessels was fabricated. The microchannel is to transport blood, focus blood cells, and line them up. The vessels are to observe red blood cell deformation. An excimer laser was used to form grooves and so on. Numbers of thermosetting resin film and fluororesin were piled up on a cover glass. A laser fabricated part of the channel at the each film every lamination, and then a three-dimensional structure microchannel was fabricated. The channel sizes have widths of 50–150 μm and depths of 45 μm. Through holes used as artificial capillary vessels are made in the fluororesin having a minimum diameter of 5 μm and a length of 100 μm. As blood and a physiological saline are injected into the microchannel, the device stands upward facing the channel, and blood cells go into the vessels by the force of gravity and sheath flow of the saline. By gravity various groove patterns were made changing the width and length for measurement of blood focusing. Moreover, the red blood cell deformation was observed in the vessels with a microscope.
Radio-frequency reflectometry on large gated two-dimensional systems
Authors: Taskinen L. J. , Starrett R. P. , Martin T. P. , Micolich A. P. , Hamilton A. R. , Simmons M. Y. , Ritchie D. A. , Pepper M.
Published: December 2008

We have embedded an AlGaAs/GaAs based, gated two-dimensional (2D) hole system (2DHS) into an impedance transformer LC circuit and show that by using radio-frequency reflectometry it is possible to perform sensitive, large bandwidth, electrical resistance measurements of 2D systems at millikelvin temperatures. We construct a simple lumped element model where the gated 2DHS is described as a resistive transmission line. The model gives a qualitative understanding of the experimental results. As an example, we use our method to map out the Landau level evolution in a 2DHS as a function of magnetic field and gate voltage.
Improvement of temporal resolution for three-dimensional continuous-wave electron paramagnetic resonance imaging
Authors: Sato-Akaba Hideo , Fujii Hirotada , Hirata Hiroshi
Published: December 2008

This paper describes improved temporal resolution for three-dimensional (3D) continuous-wave electron paramagnetic resonance (EPR) imaging. To improve temporal resolution, the duration of magnetic filed scanning that is used to obtain an EPR spectrum for each projection was reduced to 40 ms. The Helmholtz coil pair for field scanning was driven by triangular waves. The uniform distribution of projections was also used to reduce the number of projections for 3D image reconstruction. The reduction reaction of 4-hydroxy-2,2,6,6-tetramethyl-piperidinooxy with ascorbic acid was visualized by improved 3D EPR imaging techniques with a temporal resolution of 5.8 s.
A frequency-stabilized difference frequency generation laser spectrometer for precise line profile studies in the midinfrared
Authors: Deng Wen-Ping , Gao Bo , Cheng Cun-Feng , Cheng Guo-Sheng , Hu Shui-Ming , Zhu Qing-Shi
Published: December 2008

A midinfrared laser spectrometer is built up based on the difference frequency generation (DFG) of a Nd:YAG (yttrium aluminum garnet) laser and a tunable Ti:sapphire (Ti:Sa) laser. Tuning the Ti:Sa laser and operating properly with the periodically poled lithium niobate crystal, the DFG emission is tunable in the spectral range of 2.3–5.0 μm. The 1064 nm Nd:YAG laser frequency is stabilized to the 10−6 cm−1 level on a Doppler-broadened I2 absorption line at 532 nm. As a result, the DFG emission frequency is stabilized within 1×10−4 cm−1. The measurement of an absorption line of CH4 near 3 μm demonstrates that the DFG spectrometer is very suitable for the molecular absorption line profile studies in the midinfrared region.
Thermal behavior of the interlayer coupling in a spin-valve Co/Pt multilayer with perpendicular anisotropy
Authors: Liu Z. Y. , Zhang F. , Li N. , Xu B. , Yu D. L. , He J. L. , Tian Y. J.
Published: December 2008

In the spin-valve Co(4 Å)/Pt(36 Å)/[Co(4 Å)/Pt(6 Å)]2 multilayer with perpendicular anisotropy, with the decrease in temperature from 300 to 20 K, our investigations have revealed one transition of the interlayer coupling from antiferromagnetic to ferromagnetic through the Pt spacer at the temperature close to 80 K. Above 80 K, the obtained positive minor-loop shift displays a nonmonotonic variation with temperature, while below 80 K, the obtained negative minor-loop shift demonstrates a fast decrease in magnitude with temperature until a square hysteresis major loop is observed at 20 K. This observed unusual temperature behavior of the interlayer coupling can be attributed to the thermal variations in the magnetization of the bottom Co single layer and the polarization of the Pt spacer with temperature.
Dust-acoustic wave modulation in the presence of superthermal ions
Authors: Saini N. S. , Kourakis I.
Published: December 2008

A study is presented of the nonlinear self-modulation of low-frequency electrostatic (dust acoustic) waves propagating in a dusty plasma, in the presence of a superthermal ion (and Maxwellian electron) background. A kappa-type superthermal distribution is assumed for the ion component, accounting for an arbitrary deviation from Maxwellian equilibrium, parametrized via a real parameter κ. The ordinary Maxwellian-background case is recovered for κ→∞. By employing a multiple scales technique, a nonlinear Schrödinger-type equation (NLSE) is derived for the electric potential wave amplitude. Both dispersion and nonlinearity coefficients of the NLSE are explicit functions of the carrier wavenumber and of relevant physical parameters (background species density and temperature, as well as nonthermality, via κ). The influence of plasma background superthermality on the growth rate of the modulational instability is discussed. The superthermal feature appears to control the occurrence of modulational instability, since the instability window is strongly modified. Localized wavepackets in the form of either bright-or dark-type envelope solitons, modeling envelope pulses or electric potential holes (voids), respectively, may occur. A parametric investigation indicates that the structural characteristics of these envelope excitations (width, amplitude) are affected by superthermality, as well as by relevant plasma parameters (dust concentration, ion temperature).
Stress gradients induced in Cu films by capping layers
Authors: Murray Conal E. , Besser Paul R. , Witt Christian , Jordan-Sweet Jean L.
Published: December 2008

The presence of capping layers deposited on copper films can create strain gradients through the Cu film thickness. Grazing-incidence and conventional x-ray diffraction measurements determined the in-plane stress of the Cu films as a function of depth. Cu films possessing a SiCxNyHz capping layer exhibited greater tensile stress near the cap than in the bulk, whereas Cu films possessing a CoWP film did not show a gradient. The constraint imposed by the SiCxNyHz cap during the cooling process from the cap deposition temperature (350 °C) leads to an increase in the in-plane stress of 180 MPa from the bulk value.
Enhanced linearly polarized lasing emission from nanoimprinted surface-emitting distributed feedback laser based on polymeric liquid crystals
Authors: Jeong Soon Moon , Ha Na Young , Chee Mu Guen , Araoka Fumito , Ishikawa Ken , Takezoe Hideo , Nishimura Suzushi , Suzaki Goro
Published: December 2008

The authors have demonstrated the enhancement of linearly polarized lasing emission intensity using a structure made by a simple fabrication process. The enhanced lasing is achieved using a nanoimprinted distributed feedback structure together with spin-coated polymeric liquid crystals. The backward linearly TE-polarized lasing emission is transformed to left-handed circularly polarized light (L-CPL) by employing a dye-doped polymeric nematic liquid crystal (PNLC) film as a (−1/4)λ[=(3/4)λ] plate. The L-CPL is effectively reflected by a L-polymeric cholesteric liquid crystal film as a reflector and transformed back to TE-polarized light by the PNLC film; as a result one-directional emission intensity is enhanced.
Demonstration of enhanced absorption in thin film Si solar cells with textured photonic crystal back reflector
Authors: Zeng L. , Bermel P. , Yi Y. , Alamariu B. A. , Broderick K. A. , Liu J. , Hong C. , Duan X. , Joannopoulos J. , Kimerling L. C.
Published: December 2008

Herein the authors report the experimental application of a powerful light trapping scheme, the textured photonic crystal (TPC) backside reflector, to thin film Si solar cells. TPC combines a one-dimensional photonic crystal as a distributed Bragg reflector with a diffraction grating. Light absorption is strongly enhanced by high reflectivity and large angle diffraction, as designed with scattering matrix analysis. 5 μm thick monocrystalline thin film Si solar cells integrated with TPC were fabricated through an active layer transfer technique. Measured short circuit current density Jsc was increased by 19%, compared to a theoretical prediction of 28%.
Microdischarge propagation and expansion in a surface dielectric barrier discharge
Authors: Hoskinson A. R. , Oksuz L. , Hershkowitz N.
Published: December 2008

We have recorded light emission from a surface dielectric barrier discharge with one exposed and one insulated electrode using an intensified digital camera. The discharge was operated in atmospheric pressure air. When the voltage to the exposed electrode is increasing, streamers form and propagate away from the exposed electrode in tens of nanoseconds. When the voltage is decreasing, more diffuse microdischarges form in a few nanoseconds. The qualitative behaviors of the plasma agree well with two-dimensional fluid simulations. Expansion in the average length of microdischarges as the applied voltage changes in both half-cycles of the waveform is also observed.
Improved endurance behavior of resistive switching in (Ba,Sr)TiO3 thin films with W top electrode
Authors: Shen Wan , Dittmann Regina , Breuer Uwe , Waser Rainer
Published: December 2008

We compared the resistive switching performance of barium strontium titanate (BST) thin films with tungsten (W) and platinum (Pt) top electrodes, respectively. The yield, endurance, and reliability were strongly improved for the samples with W top electrode. Whereas the samples with Pt top electrode show a fast drop in the resistance for both high and low resistance states, the devices with W top electrode can be switched for 104 times without any obvious degradation. We attribute the improved switching performance to a reversible oxidation and reduction in a WOx layer at the W-BST interface, which was detected by time-of-flight secondary-ion-mass spectroscopy measurements.
Electron doping of small-diameter carbon nanotubes with exohedral fullerenes
Authors: Pradhan Basudev , Kohlmeyer Ryan R. , Setyowati Kristina , Chen Jian
Published: December 2008

The interaction between carbon nanotubes (CNTs) and exohedral fullerenes, which represent two types of carbon allotropes with extraordinary properties, has received little attention so far. The effect of exohedral fullerenes on CNTs’ electronic properties is essentially unknown. We report the electron doping of small-diameter semiconducting single-walled CNTs (SWNTs) with fullerenes such as 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 ([60]PCBM). The resulting [60]PCBM-doped SWNTs demonstrate significantly enhanced electrical conductivity while still retaining characteristics of semiconducting nanotubes. Polymer nanocomposites based on air-stable, n-doped SWNTs show a (15–22)-fold enhancement in electrical conductivity compared with nanocomposites based on undoped SWNTs at the same nanotube loading level.
Structure of chemically derived mono- and few-atomic-layer boron nitride sheets
Authors: Han Wei-Qiang , Wu Lijun , Zhu Yimei , Watanabe Kenji , Taniguchi Takashi
Published: December 2008

We prepared mono- and few-layer hexagonal boron nitride sheets by a chemical-solution-derived method starting from single-crystalline hexagonal boron nitride. Using high-resolution transmission electron microscopy and electron-energy-loss spectrometry, we characterized the microstructure, composition, and near-edge fine structure of the boron nitride sheets. We conclude that the fringe contrast in the edge and the moiré patterns are feasible criteria for determining the number of layers and their stacking orientation in the sheets. These criteria are also useful for other mono- and few-layer materials, such as graphene sheets.
The 2008 Nobel Chemistry Prize honors the development of a fluorescent tag for bioscience
Authors: Levi Barbara Goss
Published: December 2008

Researchers can now program cells to make their own dyes, which illuminate the activities of proteins within a cell.
Japan aims to internationalize its science enterprise
Authors: Feder Toni
Published: December 2008

Money and bows to other cultures, such as merit-based salaries and English in the lab, are cultivating good science and attracting leading scientists to spend time in Japan.
Could ‘green gasoline’ displace ethanol as the biofuel of choice?
Authors: Kramer David
Published: December 2008

Researchers report advances in making renewable fuels that are compatible with the US petroleum infrastructure.
Italy’s students protest government attack on universities
Authors: Feder Toni
Published: December 2008

Researchers in Italy say basing both hiring and budget cuts on merit is the most they can hope for to minimize a new law’s damage to universities.
Obama is urged to quickly appoint science adviser
Authors: Kramer David
Published: December 2008

As the transition of power begins, groups seek restoration of the status that science advising held in the White House before the Bush administration.
Web watch
Authors: Day Charles
Published: December 2008

The suggest topics or sites for Web Watch, please visit http://www.physicstoday.org/suggestwebwatch.html. Compiled and edited by Charles Day.
A physicist’s tour of the upper atmosphere
Authors: Emmert John T.
Published: December 2008

The character of Earth’s upper atmosphere is shaped not only by internal processes but also by energy received from deep space above and Earth’s surface below.
Seasonal variations in soil respiration and temperature sensitivity under three land-use types in hilly areas of the Sichuan Basin
Authors: Wang XiaoGuo , Zhu Bo , Gao MeiRong , Wang YanQiang , Zheng XunHua
Published: December 2008

CO2 emissions from soils were measured under 3 land-use types at the adjacent plots of forest plantation, grassland, and cropland from January 2005 to December 2006. Mean soil CO2 efflux rates measured during the 2-year study varied from 59 to 527 mg CO2/m2.h in forest plantation, 37 to 498 mg CO2/m2.h in grassland, and 32 to 397 mg CO2/m2.h in cropland. Soil respiration in the 3 types of land-use showed a similar seasonal pattern in variation during both years, in which the single-peaked curve occurred in early summer and the minimum in winter. In particular, the date of maximum soil CO2 efflux rate in cropland occurred about 30 days earlier than in forest and grassland in both 2005 and 2006. The relationship of soil respiration rate (R) with soil temperature (T ) and soil moisture (W ) fitted well to the equation R = β0eβ1TW β2 (a, b, c were constants) than other univariate models which consider soil water content or soil temperature alone. Soil temperature and soil moisture together explained 69–92% of the temporal variation in soil respiration in the 3 land-use types. Temperature sensitivity of soil respiration (Q10) was affected positively by soil moisture of top 0.1 m layer and negatively by soil temperature at 0.05 m depth. The relationship between Q10 values and soil temperature (T ) or soil moisture (W ) indicated that a 1°C increase in soil temperature at 0.05 m depth will reduce the Q10 value by 0.07, 0.05, and 0.06 in forest, grassland, and cropland, respectively. Similarly, a 1% decrease in soil moisture of the top 0.1 m layer will reduce the Q10 value by 0.10, 0.09, and 0.11 in forest, grassland, and cropland.
Organic amendment addition enhances phosphate fertiliser uptake and wheat growth in an acid soil
Authors: Schefe C. R. , Patti A. F. , Clune T. S. , Jackson W. R.
Published: December 2008

The effect of 2 organic amendments (lignite and compost) on wheat growth and phosphate fertiliser efficiency (triple superphosphate, TSP; di-ammonium phosphate, DAP) in an acid soil was investigated in a glasshouse experiment. Organic amendments were incorporated into the top 40 mm of soil at rates resulting in a 1% and 2.5% increase in soil C, and fertilisers were banded within the seed row at rates equivalent to 5, 10, and 25 kg P/ha. When no P was applied, addition of both organic amendments increased shoot height, with greatest growth recorded in the compost-amended treatments. Addition of organic amendments and P fertiliser resulted in additive effects, with increased shoot height, tiller number, and shoot dry matter (DM) in both the lignite- and compost-amended soils with fertiliser addition. The addition of 1% C resulted in plant growth equal to that measured at a higher rate of addition (2.5% C), resulting in a higher relative efficiency of application. Tissue P uptake was significantly increased when soil amendment was combined with 25 kg P/ha DAP addition. Significant differences in nutrient uptake were also measured for other important plant nutrients. As the addition of organic amendments resulted in increased DM compared with untreated soil per unit of P fertiliser applied, it is feasible that this growth response may translate into increased yield. However, further study is required to define the agronomic and economic feasibility of broad-scale application of such amendments for production gains.
Soil and landscape attributes interpret subsurface drainage clusters
Authors: Bakhsh A. , Kanwar R. S.
Published: December 2008

Water in excess of evapotranspiration follows topographically defined flow paths and can affect spatial subsurface drainage patterns. This 1993–2003 field study was conducted near Nashua, Iowa, to delineate the subsurface drainage clusters and identify the landscape and hydrologic variables that contributed significantly in discriminating these clusters. A digital elevation model was developed using 6695 elevation data measurements collected with GPS navigation system across 36 field plots (0.4 ha in size each). A spherical model was used to interpolate the elevation data within a Spatial Analyst tool of ArcGIS software. Plot-scale average topographic attributes of elevation, slope, aspect, and curvature were derived using the Zonal function in the Spatial Analyst tool. Hydrologic attributes of flow direction, flow length, and flow accumulation were derived using the Hydrology module of Spatial Analyst tool after performing Fill function for the sink areas. Annual normalised subsurface drainage data and plot-scale derived soil and topographic attributes were used in the cluster and discriminant analysis, respectively, to investigate their relationships. Stepwise discriminant analysis identified elevation and flow accumulation as the variables that discriminated the subsurface drainage clusters of low, medium, and high categories significantly (P = 0.01). The role of elevation and flow accumulation was verified using discriminant functions that predicted all members of the high drainage cluster accurately with zero error rates. GIS data layer of subsurface drainage clusters also showed that high drainage clusters were located at the lower elevation levels and were in close agreement with the elevation and flow accumulation data layers. The results of this study indicate that elevation and flow accumulation GIS data layers can be used as a guideline to minimise nutrient losses through subsurface drainage water.
Modern and palaeogeographic trends in the salinisation of the Western Australian wheatbelt: a review
Authors: George Richard , Clarke Jonathan , English Pauline
Published: December 2008

The Western Australian wheatbelt contains vast areas of agricultural land underlayed by saline and deeply weathered regolith derived from Archaean rocks and recent sediments. The region has been geologically stable since the late Permian, although the Archaean basement sustained some movement during the break-up of Gondwanaland and the northward drift of Australia from Antarctica. During the Early Cretaceous, Eocene and more recently, the wheatbelt region’s weathered mantle has been successively eroded by rivers. The palaeovalleys have been infilled with terrestrial and marine sediments, and subjected to ongoing deep weathering. During the Pliocene and Quaternary the region experienced alternating arid and wetter climates. These cyclic episodes influenced regolith development, affected vegetation species and catchment water balances, and also promoted the accumulation of massive volumes of salt. In more recent times, these salt stores have interacted with vegetation, soils, surface water bodies, and groundwater systems and left a distinctive and pervasive legacy in the landscape. Salinisation was manifest in the wheatbelt from as long ago as 2.8 Ma, concentrating in valley floors as arid and wetter cycles prevailed and while the continent migrated northwards. Today, agricultural development has altered the water balance on 20 Mha of cleared farmland. As a result, salinity is spreading, further degrading 300 000 ha of variably saline landscape that existed before the arrival of Europeans, and affecting an additional 1.1 Mha of formerly arable land. Unchecked by reduced rainfall or human-induced changes to the water balance, salinity may expand even further, potentially affecting 1.7–3.4 Mha of the wheatbelt’s agricultural land and its unique natural resources. This paper reviews the palaeogeography and palaeoclimates of the region and its hydrogeology and examines the nature of its susceptibility to salinisation. It poses questions about the relationship between palaeo-salinity and contemporary salinity, seeking geomorphic evidence to indicate whether salinity is likely to expand beyond extant palaeo-salinity markers. Finally, it considers the likely timeframes involved in salinisation and whether clearing-induced salinity will follow patterns similar to those observed from past saline episodes in the region.