bluuebunny/crossref_metadata_2025 huggingface dataset:
Light input and processing in the circadian clock of Neurospora
Authors: Schafmeier Tobias , Diernfellner Axel C.R.
Published: April 2011

Circadian clocks are endogenous oscillators that use zeitgebers as environmental cues to synchronise with the exogenous day–night cycle. The role of light as a zeitgeber has been investigated intensively to date. In Neurospora crassa the transcription factor White Collar Complex (WCC) is directly activated by light, which resets the clock. In addition, a hierarchical cascade of transcription factors activates the light‐induced expression of hundreds of genes. Disturbance of the clock during the day through changes in light intensity should be prevented to ensure efficient synchronisation. This can be achieved by desensitisation to the ambient light (photoadaptation). Photoadaptation in Neurospora is dependent on the blue light receptor Vivid (VVD), which accumulates immediately after light activation and rapidly silences the expression of WCC‐dependent genes. Recent studies have elucidated the molecular mechanism of VVD‐mediated photoadaptation. Here we review the increasing knowledge about light‐dependent gene expression and photoadaptation in Neurospora and discuss their relevance for synchronisation of the circadian clock.
Prediction of body mass index in mice using dense molecular markers and a regularized neural network
Authors: OKUT HAYRETTIN , GIANOLA DANIEL , ROSA GUILHERME J. M. , WEIGEL KENT A.
Published: April 2011

Bayesian regularization of artificial neural networks (BRANNs) were used to predict body mass index (BMI) in mice using single nucleotide polymorphism (SNP) markers. Data from 1896 animals with both phenotypic and genotypic (12 320 loci) information were used for the analysis. Missing genotypes were imputed based on estimated allelic frequencies, with no attempt to reconstruct haplotypes based on family information or linkage disequilibrium between markers. A feed-forward multilayer perceptron network consisting of a single output layer and one hidden layer was used. Training of the neural network was done using the Bayesian regularized backpropagation algorithm. When the number of neurons in the hidden layer was increased, the number of effective parameters, γ, increased up to a point and stabilized thereafter. A model with five neurons in the hidden layer produced a value of γ that saturated the data. In terms of predictive ability, a network with five neurons in the hidden layer attained the smallest error and highest correlation in the test data although differences among networks were negligible. Using inherent weight information of BRANN with different number of neurons in the hidden layer, it was observed that 17 SNPs had a larger impact on the network, indicating their possible relevance in prediction of BMI. It is concluded that BRANN may be at least as useful as other methods for high-dimensional genome-enabled prediction, with the advantage of its potential ability of capturing non-linear relationships, which may be useful in the study of quantitative traits under complex gene action.
ℤd-actions with prescribed topological and ergodic properties
Authors: LIMA YURI
Published: April 2011

We extend constructions of Hahn and Katznelson [On the entropy of uniquely ergodic transformations. Trans. Amer. Math. Soc.126 (1967), 335–360] and Pavlov [Some counterexamples in topological dynamics. Ergod. Th. & Dynam. Sys.28 (2008), 1291–1322] to ℤd-actions on symbolic dynamical spaces with prescribed topological and ergodic properties. More specifically, we describe a method to build ℤd-actions which are (totally) minimal, (totally) strictly ergodic and have positive topological entropy.
What should psychiatric trainees in years 1–3 gain from CBT training? Implications from a Royal College Divisional Workshop
Authors: Moorhead Steve , Lloyd Adrian , Holmes John
Published: April 2011

Competencies for psychiatric training have been developed that reflect what psychiatrists have to be able to do in order to function in their role. Although the need for a formally delivered psychotherapy experience is assumed and associated competencies are represented in the curriculum, it is not clear which competencies thereby achieved can be translated into generic practice. This paper reports the outcomes of a workshop held at an academic regional meeting of the Royal College of Psychiatrists. Potential competencies to be achieved following training and experience in CBT were presented. Small group review of the frameworks and subsequent feedback demonstrated broad support for requirements of CBT knowledge and attitudinal competencies that could inform day-to-day practice, within a generic psychotherapeutic skills framework. New competencies that were related to CBT and considered meaningful in daily psychiatric practice emerged. Further development of these ideas from the workshop in this paper leads to a set of coherent competencies that would be helpful in non-CBT specialist practice and are congruent with the context of generic psychiatric practice. These enable models of training other than the delivery of a single ‘brief’ psychotherapy case to be considered.
Two modes of lytic granule fusion during degranulation by natural killer cells
Authors: Liu Dongfang , Martina Jose A , Wu Xufeng S , Hammer John A , Long Eric O
Published: April 2011

Lytic granules in cytotoxic lymphocytes, which include T cells and natural killer (NK) cells, are secretory lysosomes that release their content upon fusion with the plasma membrane (PM), a process known as degranulation. Although vesicle exocytosis has been extensively studied in endocrine and neuronal cells, much less is known about the fusion of lytic granules in cytotoxic lymphocytes. Here, we used total internal reflection fluorescence microscopy to examine lytic granules labeled with fluorescently tagged Fas ligand (FasL) in the NK cell line NKL stimulated with phorbol ester and ionomycin and in primary NK cells activated by physiological receptor–ligand interactions. Two fusion modes were observed: complete fusion, characterized by loss of granule content and rapid diffusion of FasL at the PM; and incomplete fusion, characterized by transient fusion pore opening and retention of FasL at the fusion site. The pH‐sensitive green fluorescence protein (pHluorin) fused to the lumenal domain of FasL was used to visualize fusion pore opening with a time resolution of 30 ms. Upon incomplete fusion, pHluorin emission lasted several seconds in the absence of noticeable diffusion. Thus, we conclude that lytic granules in NK cells undergo both complete and incomplete fusion with the PM, and propose that incomplete fusion may promote efficient recycling of lytic granule membrane after the release of cytotoxic effector molecules.
Chirality from Dynamic Kinetic Resolution
Authors: Pellissier Helene
Published: April 2011

The last 15 years have witnessed significant developments in the efficiency and scope of the application of DKR. These now offer a serious alternative to conventional methods for asymmetric synthesis. Indeed, impressive examples using new enzymes and major progress in the DKR of racemates have taken place over the past few years. The powerful combination of enzymes and metals has also been the subject of spectacular development. In addition, a new type of DKR, involving organocatalysts, has recently appeared. Although asymmetric catalysis has undergone development during the last two decades, the most common industrial process used to obtain enantiomerically pure compounds is still via resolution of racemic mixtures. This is despite the major disadvantage that only a maximum of 50% product yield can be obtained. It is not surprising that DKR, which solves the problem of the limitation in yield, has attracted an increasing amount of interest from both the industrial and the academic perspective. This book provides an up-date on the principle methods employed to obtain dynamic kinetic resolution (DKR) by either enzymatic or non-enzymatic methods. It also illustrates the diversity of useful chiral products that can be obtained through this powerful concept. Divided into three sections, the book deals successively with non-enzymatic methods, enzymatic methods, and the use of transition metals and enzymes in tandem.
A label-free fluorescent turn-on enzymatic amplification assay for DNA detection using ligand-responsive G-quadruplex formation
Authors: Zhao Chuanqi , Wu Li , Ren Jinsong , Qu Xiaogang
Published: April 2011

A facile and general label-free assay based on enzyme amplification and ligand-responsive quadruplex formation for sensitive and selective DNA detection.
CIO: Concept is Over
Authors: King John Leslie
Published: April 2011

In the last 20 years the 1990 joke that CIO is starting to mean ‘Career Is Over’ has been buried under the proliferation of CIOs, but the concept behind the CIO – the idea of the C-level executive – probably is over. The C-level fad is waning as the title ‘chief is debased, but more important the very sensibility of the idea of the chief is embodied and entombed in a managerial orthodoxy of 20th century industrial administration that simply cannot hold together much longer. It is time for management educators, starting with people in the information systems field, to look beyond orthodoxy to a risky but engaging new world in which the M-Form organization and all that went with it is seen as a way station en route to a new kind of human enterprise.
Plasmonic coupling of SiO2–Ag “post-cap” nanostructures and silver film for surface enhanced Raman scattering
Authors: Wu Hsin-Yu , Cunningham Brian T.
Published: April 2011

We demonstrate a surface enhanced Raman scattering (SERS) substrate consisting of SiO2–Ag “post-cap” nanostructures with an underlying silver film fabricated by the glancing angle deposition technique. Electromagnetic simulations predict that SERS enhancement is strongly polarization-dependent, consistent with experimental measurements. Optimized coupling between Ag cap nanoparticles and the underlying silver film can be achieved by controlling the thickness of SiO2 post sandwiched between them to significantly enhance local electric-field intensity and to increase the density of electromagnetic hot spots. A maximum SERS enhancement factor of 2.38×109 within the hot spot region is demonstrated, providing sufficient sensitivity for many important applications.
Combined dynamic scanning tunneling microscopy and frequency modulation atomic force microscopy investigations on polythiophene chains on graphite with a tuning fork sensor
Authors: Polesel-Maris Jérôme , Lubin Christophe , Thoyer François , Cousty Jacques
Published: April 2011

Polythiophene molecules adsorbed on a highly oriented pyrolytic graphite surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM) with a quartz tuning fork sensor operating in Qplus mode and equipped with a Pt/Ir tip. Upon completing a careful sub-angström oscillation amplitude calibration of the probe, experiments were conducted in an ultra high vacuum at room temperature. By selecting the tip/surface distance regulation parameter, one can select the type of simultaneous information obtained in an area. For distance regulation based on the mean tunneling current, dynamic STM images together with maps of tip/surface force gradient were obtained. FM-AFM images with maps of the tunneling current were also acquired when the distance regulation was based on the frequency shift. Comparison between these images reveals interesting features. For example the tip which operates in STM mode with ultra low current (<10 pA) generates different interaction forces above molecules or graphite. Changes in energy dissipation processes as small as tens of millielectronvolts per cycle were recorded when the tip oscillates above the polymer or on the graphite surface. Hence data demonstrates that a stiff piezoelectric tuning fork of several kilonewtons/meters working as an AFM/STM probe with sub-angström amplitude can characterize weakly adsorbed molecules.
Columnar structure in porous silicon: influence of etching time on pore dynamics and ordering.
Authors: Nikulin A. Y. , Pelliccia D. , Starkov V. V. , Sakata O.
Published: April 2011

Applications of porous silicon are ranging from drug delivery vehicles to micro fuel cells. The size of the pores and their distribution plays critical role in the final properties of the devices manufactured on their base. We performed nondestructive quantitative experimental studies of selected porous silicon samples with gradient porosity. We were able to determine the average size of the pores and its dynamics as a function of the etching time. We also were able to determine the statistical parameters of the pore formation.
Energetic deposition of carbon in a cathodic vacuum arc with a biased mesh
Authors: Moafi A. , Lau D. W. M. , Sadek A. Z. , Partridge J. G. , McKenzie D. R. , McCulloch D. G.
Published: April 2011

Carbon films were deposited in a filtered cathodic vacuum arc with a bias potential applied to a conducting mesh mounted in the plasma stream between the source and the substrate. We determined the stress and microstructural properties of the resulting carbon films and compared the results with those obtained using direct substrate bias with no mesh. Since the relationship between deposition energy and the stress, sp2 fraction and density of carbon are well known, measuring these film properties enabled us to investigate the effect of the mesh on the energy and composition of the depositing flux. When a mesh was used, the film stress showed a monotonic decrease for negative mesh bias voltages greater than 400V, even though the floating potential of the substrate did not vary. We explain this result by the neutralization of some ions when they are near to or passing through the negatively biased mesh. The microstructure of the films showed a change from amorphous to glassy carbonlike with increasing bias. Potential applications for this method include the deposition of carbon films with controlled stress on low conductivity substrates to form rectifying or ohmic contacts.
Thermo-optic microring resonator switching elements made of dielectric-loaded plasmonic waveguides
Authors: Tsilipakos Odysseas , Kriezis Emmanouil E. , Bozhevolnyi Sergey I.
Published: April 2011

Thermo-optic switching elements made of dielectric-loaded plasmonic (DLSPP) waveguides are theoretically investigated by utilizing the three-dimensional vector finite element method. The configurations considered employ microring resonators, whose resonant frequency is varied by means of thermal tuning. First, a classic add-drop filter with parallel access waveguides is examined. Such a component features very poor drop port extinction ratio (ER). We therefore extend the analysis to add-drop filters with perpendicular access waveguides, which are found to exhibit superior drop port ERs, due to interference effects associated with the drop port transmission. In the process, the performance of a DLSPP waveguide crossing is also assessed, since it is a building block of those filters whose bus waveguides intersect. An elliptic tapering scheme is proposed for minimizing cross talk and its effect on the filter performance is explored. The dual-resonator add-drop filter with perpendicular bus waveguides and an untreated waveguide crossing of Sec. V can act as an efficient 2×2 switching element (the single-resonator variant can only act as a 1×2 switch due to structure asymmetry), possessing two equivalent input ports and featuring high ERs for both output ports over a broad wavelength range. Specifically, an extinction ratio of at least 8 dB can be attained for both output ports over a wavelength range of 3.2 nm, accommodating four 100-GHz-spaced channels. Switching times are in the order of a few microseconds, rendering the aforementioned structure capable of handling real-world routing scenarios.
Exchange interaction in L1-ordered FePt and CoPt from first-principles
Authors: Liu X. B. , Altounian Z.
Published: April 2011

The exchange interactions have been studied from a first-principles density functional calculation in FePt and CoPt with the tetragonal L10-type structure. For FePt, the effective exchange parameters of Fe at the sites 1a and 1c, JFe1a and JFe1c, have the same negative value (−1.40 mRy) while that between Fe (1a) and Fe (1c), JFe1a-1c, have a large positive value (8.29 mRy) and JFe-Pt also has a positive value (1.20 mRy). Similarly, for CoPt, the exchange parameters are JCo1a = JCo1c = −0.86 mRy, JCo1a-1c = 8.47 mRy and JCo-Pt = 1.30 mRy. The estimated mean fields TC are about 802 K and 870 K for FePt and CoPt, respectively, in good agreement with the experiments. TC shows peak value at c/a = 1 in FePt and CoPt, respectively, resulting from the interplay between negative and positive exchange interactions.
Magnetic properties and thermal stability of MnBi/NdFeB hybrid bonded magnets
Authors: Cao S. , Yue M. , Yang Y. X. , Zhang D. T. , Liu W. Q. , Zhang J. X. , Guo Z. H. , Li W.
Published: April 2011

Magnetic properties and thermal stability were investigated for the MnBi/NdFeB (MnBi = 0, 20, 40, 60, 80, and 100 wt.%) bonded hybrid magnets prepared by spark plasma sintering (SPS) technique. Effect of MnBi content on the magnetic properties of the hybrid magnets was studied. With increasing MnBi content, the coercivity of the MnBi/NdFeB hybrid magnets increases rapidly, while the remanence and maximum energy product drops simultaneously. Thermal stability measurement on MnBi magnet, NdFeB magnet, and the hybrid magnet with 20 wt.% MnBi indicates that both the NdFeB magnet and the MnBi/NdFeB hybrid magnet have a negative temperature coefficient of coercivity, while the MnBi magnet has a positive one. The (BH)max of the MnBi/NdFeB magnet (MnBi = 20 wt.%) is 5.71 MGOe at 423 K, which is much higher than 3.67 MGOe of the NdFeB magnet, indicating a remarkable improvement of thermal stability.
A comparative analysis of Ag and Cu heat sink layers in L1-FePt films for heat-assisted magnetic recording
Authors: Fernandez Robert , Teweldebrhan Desalegne , Zhang Chen , Balandin Alexander , Khizroev Sakhrat
Published: April 2011

The magnetic properties, structural properties, and thermal conductivity of FePt films deposited on Ag and Cu heat sink layers designed for use in heat-assisted magnetic recording (HAMR) were investigated. It has been found that FePt films grown on Cu have a well-defined L10-FePt (001) texture while the FePt films grown on Ag appear to be more isotropic. As the thickness of the heat sink layer increases from 15 to 120 nm the coercivity of the FePt films decreases from 1.7 to 1.5 T for Cu and from 1.3 to 1.0 T for Ag. The thermal conductivity measurements, carried out with the “laser-flash” technique, revealed that the overall thermal resistance of the examined structures is dominated by the thermal boundary resistance and the interface effects. The increase in the thickness of Ag and Cu heat sink layers does not lead to the higher effective thermal conductivity of the layered structure in the cross-plane direction. The obtained results are important for optimization of the FePt-based structures for HAMR.
Coexistence of tunneling magnetoresistance and electroresistance at room temperature in La0.7Sr0.3MnO3/(Ba, Sr)TiO3/La0.7Sr0.3MnO3 multiferroic tunnel junctions
Authors: Yin Y. W. , Raju M. , Hu W. J. , Weng X. J. , Li X. G. , Li Q.
Published: April 2011

Tunnel junctions composed of two ferromagnetic electrodes separated by a ferroelectric barrier were fabricated from epitaxial La0.7Sr0.3MnO3/Ba0.95Sr0.05TiO3/La0.7Sr0.3MnO3 trilayers. Typical R−H curves with sharp-switched resistance states (magnetic parallel and antiparallel) of magnetic tunnel junctions have been observed up to room temperature. After applying a poling voltage, which reverses the barrier polarization, both the parallel and antiparallel resistance states will switch to different values. Clear tunneling magnetoresistance and tunneling electroresistance, hence the four resistance states have been observed at room temperature.
Surface structures and magnetic anisotropies of a Fe/Pt (001) surface: An ab initio study
Authors: Lee Eung-Kwan , Choi Heechae , Hwang Yubin , Chung Yong-Chae
Published: April 2011

Using ab initio calculations, we obtained the surface phase diagram of a Fe/Pt(001) surface and the magnetic anisotropy energies of the equilibrium Fe/Pt(001) surface structures. From the obtained surface phase diagram, Fe-rich L12 B and perpendicular L10 B were found to be the most stable Fe–Pt surface phases. The calculated magnetic anisotropy energies of the Fe-rich L12 B and perpendicular L10 B Fe/Pt(001) structures revealed that the magnetic easy axes of the surface structures prefer to align in the [001] direction. Through systematic calculations, we showed that the magnetic anisotropy reduction in Fe/Pt(001) originates from the changed electron filling in the 3dz2 orbital of Fe atoms due to the surface formation.
High performance bonded neo magnets using high density compaction
Authors: Herchenroeder J. , Miller D. , Sheth N. K. , Foo M. C. , Nagarathnam K.
Published: April 2011

This paper presents a manufacturing method called Combustion Driven Compaction (CDC) for the manufacture of isotropic bonded NdFeB magnets (bonded Neo). Magnets produced by the CDC method have density up to 6.5 g/cm3 which is 7–10% higher compared to commercially available bonded Neo magnets of the same shape. The performance of an actual seat motor with a representative CDC ring magnet is presented and compared with the seat motor performance with both commercial isotropic bonded Neo and anisotropic NdFeB rings of the same geometry. The comparisons are made at both room and elevated temperatures. The airgap flux for the magnet produced by the proposed method is 6% more compared to the commercial isotropic bonded Neo magnet. After exposure to high temperature due to the superior thermal aging stability of isotropic NdFeB powders the motor performance with this material is comparable to the motor performance with an anisotropic NdFeB magnet.
Inverse giant magnetoresistance in CoFe/Tb multilayer with perpendicular magnetic anisotropy
Authors: Son Yoonkook , Lee Seungkyo , Lee Kisu , Cho B. K.
Published: April 2011

We detected inverse giant magnetoresistance (GMR) in a multilayer of Ta (4 nm)/[Tb (1.6 nm)/CoFe (1.2 nm)]5/Cu (3 nm)/[CoFe (1.2 nm)/Tb (0.6 nm)]5/Ta (4 nm); both the bottom [Tb (1.6 nm)/CoFe (1.2 nm)]5 and top [CoFe (1.2 nm)/Tb (0.6 nm)]5 layers revealed a perpendicular magnetic anisotropy. Furthermore, depending on the Tb layer thickness, we confirmed the magnetization of the bottom CoFe layer to be either parallel or antiparallel to the applied field. Hence, the GMR behavior could be controlled by tuning the perpendicular magnetic anisotropy, i.e., it was switchable from inverse to normal GMR or from normal to inverse. Changes in GMR occurred at a compensation composition of CoFe and Tb for which no magnetization was observed due to antiferromagnetic cancellation of the Tb and CoFe moments.
Microstructures and perpendicular magnetic properties of Co/Pd multilayers on various metal/MgO seed-layers
Authors: Kim Sanghoon , Lee Sangho , Kim Joonyong , Kang Jaeyong , Hong Jongill
Published: April 2011

We studied the effects of metal/MgO seeds (metal = Ta, Ru, or Pd) on the crystalline structure and perpendicular magnetic properties of Co/Pd multilayers to investigate the possibility of developing a (100) texture with sufficiently high perpendicular anisotropy and small switching field distributions for applications such as patterned media and perpendicular magnetic random access memories. The Pd/MgO or the MgO seed successfully promoted a (100) texture of Co/Pd multilayers. In particular, the Pd/MgO seed developed a strong (100) texture in the Co/Pd multilayer and resulted in perpendicular magnetic anisotropies ∼2 × 106 erg/cm3. On the other hand, the Co/Pd multilayer with the Ta/MgO or the Ru/MgO seed showed a strong (111) texture, inducing a perpendicular magnetic anisotropy higher than that of the (100) textured films. The coercive fields of Co/Pd multilayers with the (111) texture were over 4 kOe and higher than those with the (100) texture, which were ∼2 kOe when they were patterned into 2 × 2 μm2 islands. The switching field distributions of the Co/Pd multilayers with the (100) texture were smaller than those of the Co/Pd multilayers with the (111) texture. Our findings suggest that the Pd/MgO or the MgO seed can be a template suitable for device applications.
Reduction of hysteresis losses in the magnetic refrigerant La0.8Ce0.2Fe11.4Si1.6 by the addition of boron
Authors: Shamba P. , Debnath J. C. , Zeng R. , Wang J. L. , Campbell S. J. , Kennedy S. J. , Dou S. X.
Published: April 2011

In an effort to improve the magnetocaloric effects of the NaZn13-type La0.8Ce0.2Fe11.4Si1.6 compound, the effect of boron doping on the magnetic properties and magnetocaloric properties has been investigated. The magnetic entropy change (ΔSM) for the La0.8Ce0.2Fe11.4Si1.6 compound, obtained for a field change of 0–5 T using the Maxwell relation exhibits a spike and appears to be overestimated and is thus corrected by using the Clausius-Clapeyron equation (CC). The ΔSM determined from the CC equation is estimated to be 19.6 J kg−1K−1. However, large hysteretic losses which are detrimental to the magnetic refrigeration efficiency occur in the same temperature range. In this work, we report a significant reduction in hysteretic losses by doping the La0.8Ce0.2Fe11.4Si1.6 compound with a small amount of boron to obtain La0.8Ce0.2Fe11.4Si1.6Bx compounds. The hysteresis loss decreases from 131.5 to 8.1 J kg −1 when x increases from 0 to 0.3, while ΔSM, obtained for a field change of 0–5 T, varies from 19.6 to 15.9 J kg−1K−1. This also simultaneously shifts the TC from 174 to 184 K and significantly improves the effective refrigerant capacity (RCeff) of the material from 164 to 305 J kg−1.
Effect of the exchange bias coupling strength on the magnetoimpedance of IrMn/NiFe films
Authors: García C. , Florez J. M. , Vargas P. , Ross C. A.
Published: April 2011

The asymmetrical magnetoimpedance (MI) response has been analyzed in thin multilayer strips of exchange-coupled [NiFe (t nm)/IrMn (35 nm)] × n(t), where t and n take values of 20, 30, 40, and 60 nm and n = 15, 10, 8, and 5, respectively. The antiferromagnetic layer creates an exchange bias that shifts both the hysteresis loop and the MI response, and the magnitude of this shift depends on the ferromagnetic (FM) layer thickness. The MI peak positions are also shifted to a higher magnetic field as the probe frequency increases, and the MI ratio increases with increasing thickness of the FM layer. The impedance of a sandwich-like layered system was modeled based on an exchange coupled Stoner–Wohlfarth energy density. The model reproduces the principal features of the experimental results, describing the effect of the strength of the exchange bias on the MI ratio.
Electron back scattered diffraction characterization of Sm(CoFeCuZr)z magnets
Authors: Yonamine T. , Fukuhara M. , Archanjo B. S. , Missell F. P.
Published: April 2011

In permanent magnets based on the Sm2Co17 phase, the high coercivity depends on the presence of a complex microstructure, consisting of a Sm2(Co,Fe)17 cell phase, a cell boundary phase Sm(Co,Cu)5, and a Zr-rich platelet or lamellae phase. The aim of this work is to use electron back scatter diffraction (EBSD) in order to identify the different phases present in the isotropic magnets produced from cast alloys with the composition of Sm(CobalFe0.2Cu0.1Zrx)8, where x = 0, 0.02, or 0.06, and correlate them with the different phases observed in scanning electron microscopy (SEM) images. Due to the combination of careful surface preparation and high resolution microscopy, it was possible to observe the cellular structure characteristic of the 2:17 magnets in the SEM images. Until now, only transmission electron microscopy (TEM) had been used. Composition maps, energy dispersive spectroscopy (EDS), and EBSD measurements were used for doing the phase identification.
AC field dependence of cluster disruption in magnetic fluids
Authors: Xiang Qing , Zhong Jing , Zhou Ming , Cesar Paulo , Liu Wenzhong
Published: April 2011

This paper attempts to explore the effects of the different external fields on the inverse susceptibility-temperature curve. The superlinear property found in the inverse susceptibility-temperature curve of magnetic nanoparticle colloid solutions is assumed to be related to dimer disruption. The ac magnetic field accelerates cluster disruption, whereas the critical transition temperature decreases with an increase of frequency. Higher frequency of the applied field raises the slope of susceptibility when the temperature of the magnetic fluid is below the transition temperature.
Influence of milled α-Fe powders on structure and magnetic properties of Sm(Co,Zr)7/α-(Fe,Co) nanocomposite magnets made by mechanical alloying
Authors: Liu Z. , Chen R. J. , Lee D. , Yan A. R.
Published: April 2011

Sm(Co,Zr)7/α-(Fe,Co) nanocomposite magnets were produced by extensive milling of the mixture of crushed as-cast SmCo6.8Zr0.2 powders and 10 wt. % iron powders followed by annealing. The iron powders were added either with 600 min premilling or without premilling. The phase structures are studied by XRD patterns and thermomagnetic curves (M−T). According to the results of XRD patterns, the structures of the Sm(Co,Zr)7/α-(Fe,Co) nanocomposite magnets made with the premilled Fe powders consist of SmCo7 phase and α-(Co,Fe) phase. However, the composite of Sm (Co,Zr)7/α-Fe nanocomposite made from Fe powders without premilling consists of SmCo7, α-(Co,Fe) and SmCo5 phases. The α-(Co,Fe) phase is further studied by XRD and thermomagnetic measurements. It indicates that different composition of α-(Co,Fe) phase was obtained in two Sm(Co,Zr)7/α-(Fe,Co) nanocomposite magnets made with the premilled α-Fe powders and without premilled α-Fe powders. The magnetic properties of the soft phase can be tailored. The intergrain exchange coupling strength of the Sm(Co,Zr)7/α-(Fe,Co) nanocomposite magnets is found to be influenced by the soft-phase grain size and properties.
Fabrication and characterization of parylene-bonded Nd–Fe–B powder micromagnets
Authors: Yang Tzu-Shun , Wang Naigang , Arnold David P.
Published: April 2011

This paper presents the fabrication and characterization of parylene-bonded isotropic Nd–Fe–B powder micromagnets with dimensions in the range of 100–1000 μm. The batch fabrication process involves dry-pressing of magnetic powders into microstructured cavities in a substrate followed by conformal vapor deposition of parylene C. The parylene coating penetrates the gaps between the magnetic particles and mechanically bonds the powder. Additionally, by mixing magnetic powders with different particle sizes, higher fill factors are achieved, thereby increasing the magnetic moment and energy product. An intrinsic coercivity of 720 kA/m, a remanence of 0.36 T, and a maximum energy product of 22 kJ/m3 are demonstrated for magnets with dimensions 700 × 700 × 220 μm. The room-temperature processing steps and chemically stable parylene coating facilitate the integration of these magnets with other microfabrication processing steps.
Direct exchange interaction of localized spins associated with unpaired sp electrons in Be-doped low-temperature-grown GaAs layers
Authors: Bae K. W. , Mohamed Mohd Ambri , Jung D. W. , Otsuka N.
Published: April 2011

Beryllium-doped GaAs layers grown at low temperatures by molecular-beam epitaxy contain localized spins associated with unpaired sp electrons of AsGa+ ions. Interactions of these localized spins are investigated by measuring the magnetization with a superconducting quantum interference device and the peak-to-peak width of electron paramagnetic resonance (EPR) spectra for samples with different spin concentrations ranging from 3 × 1018 to 2.0 × 1019 cm−3. The results show that localized spins in this material antiferromagnetically interact on each other via direct exchange. From the analysis of the temperature dependence and field dependence of the magnetization on the basis of the Curie–Weiss law and the molecular-field approximation, exchange energy of each sample was derived. The dependence of the exchange energy on the concentration of localized spins is reasonably explained by a model of direct exchange, which results from the overlapping of wave functions of unpaired electrons at AsGa+ ions. The peak-to-peak width of EPR spectra increases with an increase in the spin concentration at low temperatures, whereas it decreases with an increase in the temperature for samples with high spin concentrations. These EPR results also show that significant exchange interactions indeed occur between localized spins in this material. These effects of direct exchange interactions between localized spins can clearly be observed at their average distances of around 4 nm, which implies a considerably large spatial extension of the wave function of an unpaired sp electron around an AsGa+ ion.
A distribution-based method to resolve single-molecule Förster resonance energy transfer observations
Authors: Backović Mihailo , Price E. Shane , Johnson Carey K. , Ralston John P.
Published: April 2011

We introduce a new approach to analyze single-molecule Förster resonance energy transfer (FRET) data. The method recognizes that FRET efficiencies assumed by traditional ensemble methods are unobservable for single molecules. We propose instead a method to predict distributions of FRET parameters obtained directly from the data. Distributions of FRET rates, given the data, are precisely defined using Bayesian methods and increase the information derived from the data. Benchmark comparisons find that the response time of the new method outperforms traditional methods of averaging. Our approach makes no assumption about the number or distribution of underlying FRET states. The new method also yields information about joint parameter distributions going beyond the standard framework of FRET analysis. For example, the running distribution of FRET means contains more information than any conceivable single measure of FRET efficiency. The method is tested against simulated data and then applied to a pilot-study sample of calmodulin molecules immobilized in lipid vesicles, revealing evidence for multiple dynamical states.
Gate- and drain-lag effects in (Mg,Zn)O-based metal-semiconductor field-effect transistors
Authors: Klüpfel F. J. , Lajn A. , Frenzel H. , von Wenckstern H. , Grundmann M.
Published: April 2011

The dynamic properties of (Mg,Zn)O-based metal-semiconductor field-effect transistors (MESFETs) with the gate materials AgxO, PtOy, and Au were investigated. The AgxO-gated FETs exhibit the best static properties but are limited in their switching speed, probably due to Ag atoms present in the channel after diffusion during the transistor fabrication. Devices with PtOy and Au gates did not exhibit any significant delay in frequency-dependent gate lag measurements in the studied frequency range up to 1 MHz.
Production of atmospheric pressure diffuse nanosecond pulsed dielectric barrier discharge using the array needles-plate electrode in air
Authors: Yang De-zheng , Wang Wen-chun , Jia Li , Nie Dong-xia , Shi Heng-chao
Published: April 2011

In this paper, a bidirectional high pulse voltage with 20 ns rising time is employed to generate an atmospheric pressure diffuse dielectric barrier discharge using the array needles-plate electrode configuration. Both double needle and multiple needle electrode configurations nanosecond pulsed dielectric barrier discharges are investigated. It is found that a diffuse discharge plasma with low gas temperature can be obtained, and the plasma volume increases with the increase of the pulse peak voltage, but remains almost constant with the increase of the pulse repetition rate. In addition to showing the potential application on a topographically nonuniform surface treatment of the discharge, the multiple needle-plate electrode configuration with different needle-plate electrode gaps are also employed to generate diffuse discharge plasma.
Self-consistent model of unipolar transport in organic semiconductor diodes: Accounting for a realistic density-of-states distribution
Authors: Yampolskii S. V. , Genenko Yu. A. , Melzer C. , von Seggern H.
Published: April 2011

A self-consistent, mean-field model of charge-carrier injection and unipolar transport in an organic semiconductor diode is developed utilizing the effective transport energy concept and taking into account a realistic density-of-states distribution as well as the presence of trap states in an organic material. The consequences resulting from the model are exemplarily discussed on the basis of an indium tin oxide/organic semiconductor/metallic conductor structure. A comparison of the theory to experimental data of a unipolar indium tin oxide/poly-3-hexyl-thiophene/Al device is presented.
On the continuous limits and integrability of a new coupled semidiscrete mKdV system
Authors: Zhu Zuo-nong , Zhao Hai-qiong , Wu Xiao-nan
Published: April 2011

In this paper, we aim to get more insight on the relation between semidiscrete coupled mKdV system (where “semidiscrete” means that the system is discrete in the space variable and continuous in time) and the coupled mKdV equations; to this purpose, we propose a new coupled semidiscrete mKdV system. The Lax pairs, the Darboux transformation, soliton solutions and conservation laws for the coupled semidiscrete mKdV system are given. The coupled mKdV theory including the Lax pairs, the Darboux transformation, soliton solutions, and conservation laws is recovered through the continuous limits of corresponding theory for the new semidiscrete mKdV system.
Onset of three-dimensionality in electromagnetically driven thin-layer flows
Authors: Kelley Douglas H. , Ouellette Nicholas T.
Published: April 2011

Two-dimensional fluid flow is often approximated in the laboratory with thin electromagnetically forced fluid layers. The faithfulness of such an experimental model must be considered carefully, however, because the physical world is inherently three-dimensional. By adapting an analysis technique developed for oceanographic data, we divide velocity measurements from a thin-layer flow into two components: one that is purely two-dimensional and another that accounts for all out-of-plane flow. We examine the two- and three-dimensional components separately, finding that motion in thin-layer flows is nearly two-dimensional at low Reynolds numbers, but that out-of-plane flow grows quickly above a critical Reynolds number. This onset is likely due to a shear instability.
Preparing polymer films doped with magnetic nanoparticles by spin-coating and melt-processing can induce an in-plane magnetic anisotropy
Authors: Wouters Jelle , Lebedev Oleg I. , Van Tendeloo Gustaaf , Yamada Hitoshi , Sato Norio , Vanacken Johan , Moshchalkov Victor V. , Verbiest Thierry , Valev Ventsislav K.
Published: April 2011

Faraday rotation has been used to investigate a series of polymer films doped with magnetic iron oxide nanoparticles. The films have been prepared by spin-coating and melt-processing. In each case, upon varying the angle of optical incidence on the films, an in-plane magnetic anisotropy is observed. The effect of such an anisotropy on the Faraday rotation as a function of the angle of optical incidence is verified by comparison with magnetically poled films. These results demonstrate that care should be taken upon analyzing the magnetic behavior of such films on account of the sample preparation techniques themselves being able to affect the magnetization.
Physics and modeling of an end-Hall (gridless) ion source
Authors: Oudini N. , Hagelaar G. J. M. , Boeuf J.-P. , Garrrigues L.
Published: April 2011

In an end-Hall source, an ion beam is extracted from a magnetized plasma and accelerated by the plasma electric field without grids. The principle of end-Hall sources is similar to that of Hall effect thrusters (or closed-drift thrusters), but their design is optimized for processing applications (ion beam assisted deposition or substrate cleaning) rather than propulsion. The beam divergence is larger in end-Hall ion sources, and these sources can operate at low ion energies. Although end-Hall sources are commonly used in the surface processing industry, no detailed modeling of these sources is available, and their operation is quite empirical. In this paper, a self-consistent, two-dimensional, quasineutral model of an end-Hall ion source is developed and used in order to improve the understanding of the basic physics of these plasma sources and to quantify the parameters controlling the properties of the extracted ion beam.
A compact repetitive high-voltage nanosecond pulse generator for the application of gas discharge
Authors: Pang Lei , Zhang Qiaogen , Ren Baozhong , He Kun
Published: April 2011

Uniform and stable discharge plasma requires very short duration pulses with fast rise times. A repetitive high-voltage nanosecond pulse generator for the application of gas discharge is presented in this paper. It is constructed with all solid-state components. Two-stage magnetic compression is used to generate a short duration pulse. Unlike in some reported studies, common commercial fast recovery diodes instead of a semiconductor opening switch (SOS) are used in our experiment that plays the role of SOS. The SOS-like effects of four different kinds of diodes are studied experimentally to optimize the output performance. It is found that the output pulse voltage is higher with a shorter reverse recovery time, and the rise time of pulse becomes faster when the falling time of reverse recovery current is shorter. The SOS-like effect of the diodes can be adjusted by changing the external circuit parameters. Through optimization the pulse generator can provide a pulsed voltage of 40 kV with a 40 ns duration, 10 ns rise time, and pulse repetition frequency of up to 5 kHz. Diffuse plasma can be formed in air at standard atmospheric pressure using the developed pulse generator. With a light weight and small packaging the pulse generator is suitable for gas discharge application.
High-responsivity terahertz detection by on-chip InGaAs/GaAs field-effect-transistor array
Authors: Popov V. V. , Ermolaev D. M. , Maremyanin K. V. , Maleev N. A. , Zemlyakov V. E. , Gavrilenko V. I. , Shapoval S. Yu.
Published: April 2011

Terahertz detection by a one-dimensional dense array of field-effect transistors (FETs) is studied experimentally. Such terahertz detector demonstrates greatly enhanced responsivity without using supplementary antenna elements because a short-period grating formed by metal contact fingers of densely ordered transistors in the array serves as an effective antenna coupling incident terahertz radiation to the transistor channels. Asymmetrical position of the gate contact in each FET in the array enables strong photovoltaic response.
Monoclinic crystal structure of polycrystalline Na0.5Bi0.5TiO3
Authors: Aksel Elena , Forrester Jennifer S. , Jones Jacob L. , Thomas Pam A. , Page Katharine , Suchomel Matthew R.
Published: April 2011

Bismuth-based ferroelectric ceramics are currently under intense investigation for their potential as Pb-free alternatives to lead zirconate titanate-based piezoelectrics. Na0.5Bi0.5TiO3 (NBT), one of the widely studied compositions, has been assumed thus far to exhibit the rhombohedral space group R3c at room temperature. High-resolution powder x-ray diffraction patterns, however, reveal peak splitting in the room temperature phase that evidence the true structure as monoclinic with space group Cc. This peak splitting and Cc space group is only revealed in sintered powders; calcined powders are equally fit to an R3c model because microstructural contributions to peak broadening obscure the peak splitting.
Note: A high performance pulse energy detector for Q-switched laser based on photoacoustic effect
Authors: Huang Xiao-Chun , Guo Xiao-Zhi , Weng Yu-Xiang
Published: April 2011

A high performance pulse energy detector is developed based on photoacoustic effect. Different from the detectors reported before which also utilized photoacoustic effect, our detector can measure the energy of each pulse output from a Q-switched laser and monitor the pulse energy fluctuation in real time owing to the signal processing circuit designed. By comparing with a commercial laser energy meter, our detector is proved to be of high sensitivity and accuracy. We test the detector under illumination of different pulse energy at varied wavelengths, and the results demonstrate that the detector has a broad spectral response and a dynamical energy range. Besides, the measurements of this detector will not be affected by the background light according to the principle of photoacoustic effect.
Magnetic circular dichroism in real-time time-dependent density functional theory
Authors: Lee K.-M. , Yabana K. , Bertsch G. F.
Published: April 2011

We apply the adiabatic time-dependent density functional theory to magnetic circular dichroism (MCD) spectra using the real-space, real-time computational method. The standard formulas for the MCD response and its ${\cal A}$A and ${\cal B}$B terms are derived from the observables in the time-dependent wave function. We find real-time method is well suited for calculating the overall spectrum, particularly at higher excitation energies where individual excited states are numerous and overlapping. The MCD sum rules are derived and intepreted in the real-time formalism; we find that they are very useful for normalization purposes and assessing the accuracy of the theory. The method is applied to MCD spectrum of C60 using the adiabatic energy functional from the local density approximation. The theory correctly predicts the signs of the ${\cal A}$A and ${\cal B}$B terms for the lowest allowed excitations. However, the magnitudes of the terms only show qualitative agreement with experiment.
Gap-dependent transitions of atmospheric microplasma in open air
Authors: Chu Hong-Yu , Huang Bo-Shiun
Published: April 2011

We report on the gap dependence of the planar atmospheric microplasma in air. We investigate the transitions of the dielectric barrier discharge in open air, including the random walk filaments (plasma columns), localized filaments, stochastic filaments, and diffuse discharge. A star-shaped filamentary discharge pattern is observed after the formation of the localized filaments. The liquid drops found on the dielectric surface further become a confining pattern for star-shaped discharge. We also demonstrate the applications of the insulating pattern for the use of the plasma display in open air by the handwritten characters with UV adhesive.
Anisotropy induced wave birefringence in bounded supercritical plasma confined in a multicusp magnetic field
Authors: Dey Indranuj , Bhattacharjee Sudeep
Published: April 2011

Laboratory observation of rotation of the polarization axis (θc∼20°–40° with respect to vacuum) of a penetrating electromagnetic wave through a bounded supercritical plasma (plasma frequency ωp>wave frequency ω), confined in a multicusp magnetic field is reported. Birefringence of the radial and polar wave electric field components (Er and Eθ) has been identified as the cause for the rotation, similar to a magneto-optic medium, however, with distinct differences owing to the presence of wave induced resonances. Numerical simulation results obtained by solving the Maxwell’s equations by incorporating the plasma and magnetostatic field inhomogeneities within a conducting boundary shows a reasonable agreement with the experimental results.