bluuebunny/crossref_metadata_2025 huggingface dataset:
Cloning and characterization of dominant negative splice variants of the human histamine H4 receptor
Authors: van Rijn Richard M. , van Marle André , Chazot Paul L. , Langemeijer Ellen , Qin Yongjun , Shenton Fiona C. , Lim Herman D. , Zuiderveld Obbe P. , Sansuk Kamonchanok , Dy Michel , Smit Martine J. , Tensen Cornelis P. , Bakker Remko A. , Leurs Rob
Published: May 2008

The H4R (histamine H4 receptor) is the latest identified member of the histamine receptor subfamily of GPCRs (G-protein-coupled receptors) with potential functional implications in inflammatory diseases and cancer. The H4R is primarily expressed in eosinophils and mast cells and has the highest homology with the H3R. The occurrence of at least twenty different hH3R (human H3R) isoforms led us to investigate the possible existence of H4R splice variants. In the present paper, we report on the cloning of the first two alternatively spliced H4R isoforms from CD34+ cord blood-cell-derived eosinophils and mast cells. These H4R splice variants are localized predominantly intracellularly when expressed recombinantly in mammalian cells. We failed to detect any ligand binding, H4R–ligand induced signalling or constitutive activity for these H4R splice variants. However, when co-expressed with full-length H4R [H4R(390) (H4R isoform of 390 amino acids)], the H4R splice variants have a dominant negative effect on the surface expression of H4R(390). We detected H4R(390)–H4R splice varianthetero-oligomers by employing both biochemical (immunoprecipitation and cell-surface labelling) and biophysical [time-resolved FRET (fluorescence resonance energy transfer)] techniques. mRNAs encoding the H4R splice variants were detected in various cell types and expressed at similar levels to the full-length H4R(390) mRNA in, for example, pre-monocytes. We conclude that the H4R splice variants described here have a dominant negative effect on H4R(390) functionality, as they are able to retain H4R(390) intracellularly and inactivate a population of H4R(390), presumably via hetero-oligomerization.
Endosomal compartment contributes to the propagation of CD95/Fas-mediated signals in type II cells
Authors: Matarrese Paola , Manganelli Valeria , Garofalo Tina , Tinari Antonella , Gambardella Lucrezia , Ndebele Kenneth , Khosravi-Far Roya , Sorice Maurizio , Esposti Mauro Degli , Malorni Walter
Published: May 2008

Participation of diverse organelles in the intracellular signalling that follows CD95/Fas receptor ligation encompasses a series of subcellular changes that are mandatory for, or even bolster, the apoptotic cascade. In the present study, we analysed the role of endocytosis in the propagation of cell death signalling after CD95/Fas engagement in type II cells (CEM cells). We show that this receptor–ligand interaction triggers endocytosis independently of any caspase activation. This FasL (Fas ligand)-induced endocytosis also leads to an early and directional ‘movement’ of endocytic vesicles towards the mitochondrial compartment. In turn, this cross-talk between endosomal and mitochondrial compartments was followed by the loss of the mitochondrial membrane potential and apoptosis execution. This cell remodelling was absent in receptor-independent cell death, such as that induced by the mitochondriotropic drug staurosporine, and in a CEM cell line selected for its multidrug resistance (CEM VBL100). In these cells a reduced FasL (Fas ligand)-induced endocytosis and a reduced organelle cross-talk corresponded to a reduced apoptosis. Altogether, these findings suggest a key role of endocytosis in the propagation and amplification of the CD95/Fas-activated signalling leading to type II cell demise.
Topology mapping of the vacuolar Vcx1p Ca2+/H+ exchanger from Saccharomyces cerevisiae
Authors: Segarra Verónica A. , Thomas Lise
Published: May 2008

Saccharomyces cerevisiae uses vacuolar storage to dynamically control the cytoplasmic calcium concentration. Vcx1p, a Ca2+/H+ antiporter and a member of the CAX (Ca2+/anion exchanger) family of exchangers, is one of the proteins that sequesters calcium into the vacuole. Although the biological importance of Vcx1p is clear, the molecular mechanism by which Vcx1p and its family members mediate Ca2+/H+ exchange activity remains poorly understood. To provide a basic structural framework for understanding functional studies of the CAX proteins, we have mapped Vcx1p's topology using three biochemical assays: C-terminal reporter localization, glycosylation mapping and proteolysis. We have found that the protein has an odd number of TM (transmembrane) domains and that its termini are located on opposite sides of the membrane, with the N-terminus in the cytoplasm. Our results indicate that loops 1, 3, 7 and 9 are luminal, while loops 6 and 8 are cytosolic. Our experimentally-based topology model for Vcx1p is in agreement with models derived from topology algorithms and with biochemical data reported by other groups. In addition, our studies suggest that the calcium domain, a nine-residue domain found to be critical for function in CAX proteins from plants, is not essential to Vcx1p activity.
Identification of an iron–hepcidin complex
Authors: Farnaud Sébastien , Rapisarda Chiara , Bui Tam , Drake Alex , Cammack Richard , Evans Robert W.
Published: May 2008

Following its identification as a liver-expressed antimicrobial peptide, the hepcidin peptide was later shown to be a key player in iron homoeostasis. It is now proposed to be the ‘iron hormone’ which, by interacting with the iron transporter ferroportin, prevents further iron import into the circulatory system. This conclusion was reached using the corresponding synthetic peptide, emphasizing the functional importance of the mature 25-mer peptide, but omitting the possible functionality of its maturation. From urine-purified native hepcidin, we recently demonstrated that a proportion of the purified hepcidin had formed iron–hepcidin complexes. This interaction was investigated further by computer modelling and, based on the sequence similarity of hepcidin with metallothionein, a three-dimensional model of hepcidin, containing one atom of iron, was constructed. To characterize these complexes further, the interaction with iron was analysed using different spectroscopic methods. Monoferric hepcidin was identified by MS, as were possibly other complexes containing two and three atoms of iron respectively, although these were present only in minor amounts. UV/visible absorbance and CD studies identified the iron-binding events which were facilitated at a physiological pH. EPR spectroscopy identified the ferric state of the bound metal, and indicated that the iron–hepcidin complex shares some similarities with the rubredoxin iron–sulfur complex, suggesting the presence of Fe3+ in a tetrahedral sulfur co-ordination. The potential roles of iron binding for hepcidin are discussed, and we propose either a regulatory function in the maturation of pro-hepcidin into active hepcidin or as the necessary link in the interaction between hepcidin and ferroportin.
Hypothiocyanous acid is a more potent inducer of apoptosis and protein thiol depletion in murine macrophage cells than hypochlorous acid or hypobromous acid
Authors: Lloyd Mitchell M. , van Reyk David M. , Davies Michael J. , Hawkins Clare L.
Published: May 2008

Hypohalous acids are generated by activated leucocytes, via the formation of H2O2 and the release of peroxidase enzymes (myeloperoxidase and eosinophil peroxidase). These species are important bactericidal agents, but HOCl (hypochlorous acid) and HOBr (hypobromous acid) have also been implicated in tissue damage in a number of inflammatory diseases. HOSCN (hypothiocyanous acid; cyanosulfenic acid) is a milder, more thiol-specific, oxidant than HOCl or HOBr and as such may be a more potent inducer of cellular dysfunction due to selective targeting of critical thiol residues on proteins. In the present study, HOCl and HOBr are shown to react rapidly with macrophage (J774A.1) cells, resulting in a greater extent of cell lysis compared with HOSCN. However, HOSCN induces apoptosis and necrosis with greater efficacy, and at lower concentrations, than HOCl or HOBr. Apoptosis occurs in conjunction with an increased release of cytochrome c into the cytosol, but no associated increase in caspase activity. Similarly, apoptosis is observed on treating the cells in the presence of a caspase inhibitor, suggesting that it is mediated by a caspase-independent pathway. HOSCN oxidized protein thiols more efficiently than either HOCl or HOBr. The greater efficacy of HOSCN in inducing apoptosis is attributed to selective damage to critical mitochondrial membrane protein thiol groups, resulting in increased permeability and subsequent leakage of cytochrome c into the cytosol. This induction of damage by HOSCN may be of critical importance in people with elevated levels of SCN− (thiocyanate ions) arising from cigarette smoking, and plays a role in the pathologies associated with this biological insult.
Variants of the tetrahaem cytochrome c quinol dehydrogenase NrfH characterize the menaquinol-binding site, the haem c-binding motifs and the transmembrane segment
Authors: Kern Melanie , Einsle Oliver , Simon Jörg
Published: May 2008

Members of the NapC/NrfH family are multihaem c-type cytochromes that exchange electrons with oxidoreductases situated at the outside of the cytoplasmic membrane or in the periplasmic space of many proteobacteria. They form a group of membrane-bound quinol dehydrogenases that are essential components of several electron transport chains, for example those of periplasmic nitrate respiration and respiratory nitrite ammonification. Knowledge of the structure–function relationships of NapC/NrfH proteins is scarce and only one high-resolution structure (Desulfovibrio vulgaris NrfH) is available. In the present study, several Wolinella succinogenes mutants that produce variants of NrfH, the membrane anchor of the cytochrome c nitrite reductase complex, were constructed and characterized in order to improve the understanding of the putative menaquinol-binding site, the maturation and function of the four covalently bound haem c groups and the importance of the N-terminal transmembrane segment. Based on amino acid sequence alignments, a homology model for W. succinogenes NrfH was constructed that underlines the overall conservation of tertiary structure in spite of a low sequence homology. The results support the proposed architecture of the menaquinol-binding site in D. vulgaris NrfH, demonstrate that each histidine residue arranged in one of the four CX2CH haem c-binding motifs is essential for NrfH maturation in W. succinogenes, and indicate a limited flexibility towards the length and structure of the transmembrane region.
Mutations of β-arrestin 2 that limit self-association also interfere with interactions with the β2-adrenoceptor and the ERK1/2 MAPKs: implications for β2-adrenoceptor signalling via the ERK1/2 MAPKs
Authors: Xu Tian-Rui , Baillie George S. , Bhari Narinder , Houslay Thomas M. , Pitt Andrew M. , Adams David R. , Kolch Walter , Houslay Miles D. , Milligan Graeme
Published: May 2008

FRET (fluorescence resonance energy transfer) and co-immunoprecipitation studies confirmed the capacity of β-arrestin 2 to self-associate. Amino acids potentially involved in direct protein–protein interaction were identified via combinations of spot-immobilized peptide arrays and mapping of surface exposure. Among potential key amino acids, Lys285, Arg286 and Lys295 are part of a continuous surface epitope located in the polar core between the N- and C-terminal domains. Introduction of K285A/R286A mutations into β-arrestin 2–eCFP (where eCFP is enhanced cyan fluorescent protein) and β-arrestin 2–eYFP (where eYFP is enhanced yellow fluorescent protein) constructs substantially reduced FRET, whereas introduction of a K295A mutation had a more limited effect. Neither of these mutants was able to promote β2-adrenoceptor-mediated phosphorylation of the ERK1/2 (extracellular-signal-regulated kinase 1/2) MAPKs (mitogen-activated protein kinases). Both β-arrestin 2 mutants displayed limited capacity to co-immunoprecipitate ERK1/2 and further spot-immobilized peptide arrays indicated each of Lys285, Arg286 and particularly Lys295 to be important for this interaction. Direct interactions between β-arrestin 2 and the β2-adrenoceptor were also compromised by both K285A/R286A and K295A mutations of β-arrestin 2. These were not non-specific effects linked to improper folding of β-arrestin 2 as limited proteolysis was unable to distinguish the K285A/R286A or K295A mutants from wild-type β-arrestin 2, and the interaction of β-arrestin 2 with JNK3 (c-Jun N-terminal kinase 3) was unaffected by the K285A/R286A or L295A mutations. These results suggest that amino acids important for self-association of β-arrestin 2 also play an important role in the interaction with both the β2-adrenoceptor and the ERK1/2 MAPKs. Regulation of β-arrestin 2 self-association may therefore control β-arrestin 2-mediated β2-adrenoceptor-ERK1/2 MAPK signalling.
Laser-driven shock wave stability in Al through Au and determination of the TPa hugoniot point in Au
Authors: Shu Hua , Fu Si-zu , Huang Xiu-guang , Ma Min-xun , Wu Jiang , Ye Jun-jian , He Ju-hua , Gu Yuan , Luo Pin-qin , Long Tao
Published: May 2008

High-quality shock waves were produced using the ninth laser beam (converted to 2ω) of Shenguang-II laser facility and the beam smoothing technology of a lens array. The spatial uniformity of the shock wave was estimated by measurements of the self-emission from the target rear surface. An Al–Au four-step target with 30μm Al base and four Au steps was fabricated and used to investigate the temporal steadiness of the shock wave in the Al–Au two-layer target. The Al–Au four-step target experiment indicated that the shock wave steadily propagated in the Au material with thickness range <11μm. A modified Al–Au impedance-match target was designed, which could simultaneously measure shock-wave stability and Au Hugoniot data in one shot. The experiment results indicated that the shock wave steadily propagated in the Al target with thickness of about 30–47μm under a power density of ∼1.0×1014W∕cm2.
Continuous wave operation of injectorless quantum cascade lasers at low temperatures
Authors: Katz Simeon , Friedrich Andrea , Boehm Gerhard , Amann Markus-Christian
Published: May 2008

A continuous wave operating quantum-cascade-laser without injector is presented. The core design was taken from a low-threshold pulsed staircase laser. The active zone of one sample was optimized for low threshold current densities, using 60 periods and a low doping of 2.4×1010cm−2∕period. The second sample consists of 50 periods and a high doping of 6.3×1010cm−2∕period. For the first (second) sample, the threshold current density at 77K for continuous operation was measured with 0.13 (0.24)kA∕cm2 and maximum output power of 16.2 (22.7)mW was observed. Continuous operation was maintained up to 140K for both lasers.
Formation mechanism of Ohmic contacts on AlGaN∕GaN heterostructure: Electrical and microstructural characterizations
Authors: Wang Liang , Mohammed Fitih M. , Adesida Ilesanmi
Published: May 2008

The electrical characteristics and interfacial reactions of Ti∕Al∕Mo∕Au metallization on AlGaN∕GaN heterostructures at various annealing temperatures ranging from 400to950°C have been investigated in an effort to elucidate the Ohmic contact formation mechanism. A transition from Schottky to Ohmic electrical behavior occurred at ∼500°C. This transition was engendered by the formation of a thin epitaxial TiN layer on the AlGaN. Binary and ternary intermetallic compound formations were observed to have formed as a result of intermixing and reactions among the metals. The Mo layer remained continuous until 700°C, where it disintegrated into particles embedded in the metallic matrix. An optimal contact performance was obtained for Ti∕Al∕Mo∕Au on AlGaN∕GaN at 850°C; this was correlated to TiN island formation along dislocations penetrating into the heterostructure beyond the plane of the two-dimensional electron gas. Overannealing degradation mechanism at 950°C is also explained based on structural characterization.
Rayleigh scattering from argon clusters in a planar expansion
Authors: DeArmond F. M. , Suelzer J. , Masters M. F.
Published: May 2008

Rayleigh scattering is presented as evidence for the presence of large argon clusters formed in a planar expansion. Based on the observed scattering signal, the dependence of mean cluster size on stagnation pressure is ⟨N⟩∝P03.38. This is in contrast to the dependence of the mean cluster size on stagnation pressure for a symmetric expansion of ⟨N⟩∝P02.29.
Polymer-dispersed liquid crystal devices using highly conducting polymers as electrodes
Authors: Kim Jin-Yeol , Woo Hak-Yong , Baek Ji-Woong , Kim Tae-Wook , Song Eun-Ah , Park Su-Cheol , Ihm Dae-Woo
Published: May 2008

Flexible all-organic polymer-dispersed liquid crystal (PDLC) devices were fabricated by using highly transparent and conductive poly(3,4-ethylenedioxy thiophene): p-toluene sulfonate (PEDOT:PTS) films, as electrode layers. These conductive PEDOT:PTS films have a high transparency up to 80%, and possess a very low sheet resistance of 100Ωsq−1 at 100nm thickness. We report on the fabrication and characterization of a PDLC device using a highly conductive PEDOT:PTS for the electrodes and demonstrate its superior performance relative to that of a similar device using the indium tin oxide layer as the electrodes.
Active control of internal transport barrier formation due to off-axis electron-cyclotron heating in GAMMA 10 experiments
Authors: Cho T. , Pastukhov V. P. , Horton W. , Numakura T. , Hirata M. , Kohagura J. , Chudin N. V. , Pratt J.
Published: May 2008

The controlled formation of an internal transport barrier (ITB) is observed in GAMMA 10 [T. Cho et al., Nucl. Fusion 45, 1650 (2005)]. The barrier is localized within a layer of a strongly sheared Er×B plasma rotation (5.5<rc⩽10cm). This high-vorticity layer is formed and maintained by off-axis electron-cyclotron heating, which generates a cylindrical layer (4<rc<7cm) with a high-energy electron population that modifies the initial Gaussian radial potential profile into a nonmonotonic one with a hump structure. The local gradients of Ti and Te are appreciably enhanced in the ITB layer, similarly to those of the ITB in tokamaks and stellarators. Reductions in the effective ion and electron thermal diffusivities are obtained in the barrier layer. A reduction of the observed low-frequency turbulence in the ITB layer and a partial decoupling of the turbulent structures localized on either side of the layer are demonstrated by two-dimensional x-ray diagnostics.
Photocurrent spectroscopy of low-k dielectric materials: Barrier heights and trap densities
Authors: Atkin J. M. , Song D. , Shaw T. M. , Cartier E. , Laibowitz R. B. , Heinz T. F.
Published: May 2008

Measurements of photoinduced current have been performed on thin films of porous low-k dielectric materials comprised of carbon-doped oxides. The dielectric films were deposited on silicon surfaces and prepared with a thin gold counterelectrode. From the spectral dependence of the photoinduced current, barrier heights for the dielectric∕silicon and dielectric∕gold interface were deduced. Transient currents were also found to flow after the photoexcitation was abruptly stopped. An estimate of the density of shallow electron traps within the low-k material was obtained from the measurement of the net charge transported from this detrapping current. A density of traps in the range of 6×1016traps∕cm3 was inferred for the low-k films, far exceeding that observed by the same technique for reference dielectric films of pure SiO2. This behavior was also compatible with photocurrent I-V measurements on the low-k dielectric films and SiO2 reference sample.
Ga kinetics in plasma-assisted molecular-beam epitaxy of GaN(112¯2): Effect on the structural and optical properties
Authors: Lahourcade L. , Renard J. , Gayral B. , Monroy E. , Chauvat M. P. , Ruterana P.
Published: May 2008

GaN directly deposited on m-sapphire by plasma-assisted molecular-beam epitaxy settles into two main crystalline orientation domains: GaN(112¯2) and GaN{101¯3}. The dominant phase is GaN(112¯2) with ⟨112¯3¯⟩GaN∥⟨0001⟩sapphire and ⟨11¯00⟩GaN∥⟨112¯0⟩sapphire in-plane epitaxial relationships. Deposition of GaN on top of an AlN(112¯2) buffer layer and growth under slightly Ga-rich conditions reduce GaN{101¯3} precipitates below the detection limits. Studies of Ga adsorption demonstrate that it is possible to stabilize up to one Ga monolayer on the GaN(112¯2) surface. The presence of this monolayer of Ga excess on the growth front reduces the (112¯2) surface energy and hence minimizes the surface roughness. Photoluminescence from two-dimensional GaN(112¯2) layers is dominated by a near-band-edge emission, which is assigned to excitons bound to stacking faults, present with a density around 3×105cm−1.
Data assimilation as a nonlinear dynamical systems problem: Stability and convergence of the prediction-assimilation system
Authors: Carrassi Alberto , Ghil Michael , Trevisan Anna , Uboldi Francesco
Published: May 2008

We study prediction-assimilation systems, which have become routine in meteorology and oceanography and are rapidly spreading to other areas of the geosciences and of continuum physics. The long-term, nonlinear stability of such a system leads to the uniqueness of its sequentially estimated solutions and is required for the convergence of these solutions to the system’s true, chaotic evolution. The key ideas of our approach are illustrated for a linearized Lorenz system. Stability of two nonlinear prediction-assimilation systems from dynamic meteorology is studied next via the complete spectrum of their Lyapunov exponents; these two systems are governed by a large set of ordinary and of partial differential equations, respectively. The degree of data-induced stabilization is crucial for the performance of such a system. This degree, in turn, depends on two key ingredients: (i) the observational network, either fixed or data-adaptive, and (ii) the assimilation method.
Activation energy of surface diffusion and terrace width dynamics during the growth of In(4×3) on Si(100)-(2×1) by femtosecond pulsed laser deposition
Authors: Hafez M. A. , Elsayed-Ali H. E.
Published: May 2008

The nucleation and growth of indium on a vicinal Si(100)-(2×1) surface at high temperature by femtosecond pulsed laser deposition was investigated by in situ reflection high energy electron diffraction (RHEED). RHEED intensity relaxation was observed for the first ∼2 ML during the growth of In(4×3) by step flow. From the temperature dependence of the rate of relaxation, an activation energy of 1.4±0.2 eV of surface diffusion was determined. The results indicate that indium small clusters diffused to terrace step edges with a diffusion frequency constant of (1.0±0.1)×1011 s−1. The RHEED specular beam split peak spacing, which is characteristic of a vicinal surface, was analyzed with the growth temperature to obtain the average terrace width. Gradual reduction in the terrace width during growth of In(4×3) was observed with In coverage and is attributed to the detachment of In atoms from terrace edges. At a substrate temperature of 405 °C, the average terrace width decreased from 61±10 Å, which corresponds to the vicinal Si(100) surface, to an equilibrium value of 45±7 Å after deposition of ∼23 ML. Further In coverage showed a transition of the RHEED pattern from (4×3) to (1×1) and the growth of rounded In islands (average height of ∼1 nm and width of ∼25 nm), as examined by ex situ atomic force microscopy.
Excitation of atomic force microscope cantilever vibrations by a Schottky barrier
Authors: Schwarz K. , Rabe U. , Hirsekorn S. , Arnold W.
Published: May 2008

We have developed a method to excite cantilever vibrations for dynamic force microscopy. A n-doped silicon cantilever is coated by platinum. At the interface, a Schottky barrier forms whose depletion layer couples to the elastic strain mainly by Maxwell stress and by electrostriction. If a sinusoidal voltage is applied to the Schottky barrier, the cantilever is excited to periodic vibrations due to the transverse strain generated parallel to the length axis of the cantilever. In atomic force acoustic microscopy contact-resonance spectroscopy, this technique delivers clean resonance spectra devoid of spurious signals.
1
∕
f
spectrum and memory function analysis of solvation dynamics in a room-temperature ionic liquid
Authors: Jeong Daun , Choi M. Y. , Jung YounJoon , Kim Hyung J.
Published: May 2008

To understand the nonexponential relaxation associated with solvation dynamics in the ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate, we study power spectra of the fluctuating Franck–Condon energy gap of a diatomic probe solute via molecular dynamics simulations. Results show 1∕f dependence in a wide frequency range over 2–3 decades, indicating distributed relaxation times. We analyze the memory function and solvation time in the framework of the generalized Langevin equation using a simple model description for the power spectrum. It is found that the crossover frequency toward the white-noise plateau is directly related to the time scale for the memory function and thus the solvation time. Specifically, the low crossover frequency observed in the ionic liquid leads to a slowly decaying tail in its memory function and long solvation time. By contrast, acetonitrile characterized by a high crossover frequency and (near) absence of 1∕f behavior in its power spectra shows fast relaxation of the memory function and single exponential decay of solvation dynamics in the long-time regime.
Formation mechanism of nanotrenches induced by mobile catalytic nanoparticles
Authors: Chan S. K. , Lok S. K. , Wang G. , Cai Y. , Wang Y. J. , Wang N. , Sou I. K.
Published: May 2008

⟨110⟩ oriented nanotrenches were generated by thermally annealing an ultrathin Au layer deposited on ZnSe surfaces of different orientations. Results from a number of structural and chemical analyses indicate that they were induced by the migration of Au-alloy droplets through a catalytic reaction with ZnSe. Highly aligned nanotrenches can be achieved on (100)-oriented substrates, which can potentially serve as templates for the fabrication of one-dimensional nanostructures of various materials.
Decoherence rates for Galilean covariant dynamics
Authors: Clark Jeremy
Published: May 2008

We introduce a measure of decoherence for a class of density operators. For Gaussian density operators in dimension one, it coincides with an index used by Morikawa [“Quantum decoherence and classical correlation in quantum mechanics,” Phys. Rev. D 42, 2929–2931 (1990)]. Spatial decoherence rates are derived for three large classes of the Galilean covariant quantum semigroups introduced by Holevo [“On conservativity of covariant dynamical semigroups,” Rep. Math. Phys. 33, 95–110 (1993)]. We also characterize the relaxation to a Gaussian state for these dynamics and give a theorem for the convergence of the Wigner function to the probability distribution of the classical analog of the process.
Laser beam-profile impression and target thickness impact on laser-accelerated protons
Authors: Schollmeier M. , Harres K. , Nürnberg F. , Blažević A. , Audebert P. , Brambrink E. , Fernández J. C. , Flippo K. A. , Gautier D. C. , Geißel M. , Hegelich B. M. , Schreiber J. , Roth M.
Published: May 2008

Experimental results on the influence of the laser focal spot shape onto the beam profile of laser-accelerated protons from gold foils are reported. The targets’ microgrooved rear side, together with a stack of radiochromic films, allowed us to deduce the energy-dependent proton source-shape and size, respectively. The experiments show, that shape and size of the proton source depend only weakly on target thickness as well as shape of the laser focus, although they strongly influence the proton’s intensity distribution. It was shown that the laser creates an electron beam that closely follows the laser beam topology, which is maintained during the propagation through the target. Protons are then accelerated from the rear side with an electron created electric field of a similar shape. Simulations with the Sheath-Accelerated Beam Ray-tracing for IoN Analysis code SABRINA, which calculates the proton distribution in the detector for a given laser-beam profile, show that the electron distribution during the transport through a thick target (50μm Au) is only modified due to multiple small angle scattering. Thin targets (10μm) show large source sizes of over 100μm diameter for 5MeV protons, which cannot be explained by multiple scattering only and are most likely the result of refluxing electrons.
Au
/
n
-ZnO
rectifying contact fabricated with hydrogen peroxide pretreatment
Authors: Gu Q. L. , Cheung C. K. , Ling C. C. , Ng A. M. C. , Djurišić A. B. , Lu L. W. , Chen X. D. , Fung S. , Beling C. D. , Ong H. C.
Published: May 2008

Au contacts were deposited on n-type ZnO single crystals with and without hydrogen peroxide pretreatment for the ZnO substrate. The Au/ZnO contacts fabricated on substrates without H2O2 pretreatment were Ohmic and those with H2O2 pretreatment were rectifying. With an aim of fabricating a good quality Schottky contact, the rectifying property of the Au/ZnO contact was systemically investigated by varying the treatment temperature and duration. The best performing Schottky contact was found to have an ideality factor of 1.15 and a leakage current of ∼10−7 A cm−2. A multispectroscopic study, including scanning electron microscopy, positron annihilation spectroscopy, deep level transient spectroscopy, x-ray photoelectron spectroscopy, and photoluminescence, showed that the H2O2 treatment removed the OH impurity and created Zn-vacancy related defects hence decreasing the conductivity of the ZnO surface layer, a condition favorable for forming good Schottky contact. However, the H2O2 treatment also resulted in a deterioration of the surface morphology, leading to an increase in the Schottky contact ideality factor and leakage current in the case of nonoptimal treatment time and temperature.
Surface charge induced variation in the electrical conductivity of nanoporous gold
Authors: Mishra A. K. , Bansal C. , Hahn H.
Published: May 2008

The electrical conductivity of nanoporous gold was measured in situ during the charging and decharging of the surface of the metal. The nanoporous gold samples were prepared by the process of selective dealloying of Ag from Au–Ag alloy. Charge was induced on the surface by making the sample a working electrode in an electrochemical cell. The conductivity was observed to vary reversibly with the induced surface charge.
Structural and dielectric characterizations of relaxor/ferroelectric superlattice films Pb(Sc1/2Nb1/2)O3/PbTiO3 fabricated on a single-lattice scale
Authors: Asanuma Shutaro , Uesu Yoshiaki , Malibert Charlotte , Kiat Jean-Michel
Published: May 2008

Relaxor/ferroelectric superlattice (SL) films Pb(Sc1/2Nb1/2)O3(PSN)/PbTiO3(PT) with nine different PT concentrations x are fabricated by a pulsed laser deposition method, which keeps the total film thickness at 100 nm. The structure of the SL films is examined by out-of-plane and in-plane x-ray diffractions. All films are epitaxial and their SL structures are coherent over the whole sample. SL reflections up to the fourth order are observed. Lattice constants of the PT and PSN layers in the SL are determined, and the PT lattice constant exhibits a marked increase at xm=32%. At this PT concentration, this phenomenon is due to a polarization reorientation from the a-axis oriented to the c-axis oriented domain. The complex dielectric constants of all samples are measured in the frequency region from 1 to 106 Hz, and the intrinsic dielectric constant ε of the SL is derived by an analysis using the equivalent electric circuit model. ε takes the maximum at xm. The possible origin of this peculiar phenomenon is discussed.
N
-type carbon nanotube by alkaline-earth metal Sr doping
Authors: Kim Byung Hoon , Park Tae Hoi , Baek Seung Jae , Lee Dong Su , Park Seung Joo , Kim Jun Sung , Park Yung Woo
Published: May 2008

Alkaline-earth metal, Sr, was doped on multiwalled carbon nanotubes (MWNTs) by vapor phase reaction method. The tunneling electron microscopy, energy dispersive x ray, and Raman spectroscopy were studied for verifying the Sr doping on MWNT. The temperature-dependent resistivity [ρ(T)] and thermoelectric power [S(T)] were also performed for both pristine MWNT and Sr-doped MWNT (Sr-MWNT). ρ(T) of Sr-MWNT did not significantly change compared to pristine MWNT. However, S(T) of Sr-MWNT considerably changes, i.e., it shows n-type behavior in contrast to pristine MWNT.
Effect of orientation on the thermal stability in advanced metal particulate tapes
Authors: Nishio Hiroaki
Published: May 2008

The effects of the degree of particle orientation on the normalized magnetization decay and activation volume (Vact) were investigated for advanced data recording tapes prepared from ultrafine metal particulate (MP) composite. In this study, the mean volume of particles (Vphy) for advanced MP tapes varied between 1.7 and 5.3×10−18cm3, inclusive of a surface oxide layer. In MP tape with a larger Vphy (=5.3×10−18cm3), increasing the orientation ratio (OR) for improved recording characteristics was found to decrease the normalized magnetization decay. However, the OR values had little effect on the normalized magnetization decay of MP tape with a smaller Vphy (=1.7×10−18cm3). This may be attributed to the existence of a few particles approaching the theoretical superparamagnetic limit of 0.7×10−18cm3. In order to decrease the normalized magnetization decay, it is particularly important to increase Hc, which improves the anisotropy constant and the distribution of anisotropy field (HA) for advanced data recording tapes with very small Vphy. The value of Vact in the low reverse field, which is a major factor affecting media noise, decreased as OR increased regardless of Vphy. Also, Vact of both tapes decreased as the reverse field decreased in the range of 1.2kOe or less. Vact of an assembly of ultrafine particles was dependent on the distributions of HA and volume of particles, also the value of rotational hysteresis integral that related to the deterioration in the mechanism of magnetization reversal giving rise to an incoherent rotation.
Amorphous versus crystalline state for ultrathin Al2O3 overgrowths on Al substrates
Authors: Reichel F. , Jeurgens L. P. H. , Richter G. , Mittemeijer E. J.
Published: May 2008

The thermodynamic and kinetic background of the stability of ultrathin (<3nm) amorphous Al2O3 overgrowths on Al{111}, Al{100}, and Al{110} substrates was investigated by thermal oxidation of the bare substrates in pure oxygen gas for oxidation times up to 6000s in the temperature range of T=350–650K. The microstructural evolutions of the developing oxide films were analyzed by angle-resolved x-ray photoelectron spectroscopy, low energy electron diffraction, and high-resolution transmission electron microscopy. For sufficiently small thicknesses, stable amorphous Al2O3 films form on all substrates. The critical thickness values beyond which a crystalline state for the Al2O3 film is thermodynamically preferred can be reliably calculated provided that a layer-by-layer mode of oxide-film growth occurs. With increasing temperature, a transition from a layer by layer to an island-by-layer type of oxide growth mode occurs and, consequently (tensile), growth strain in a crystalline Al2O3 overgrowth can be more relaxed by lateral extension of the oxide islands, which results in a reduction of the critical thickness for the amorphous-to-crystalline transition. Oxygen incorporation in the metal substrate at the onset of oxidation, in particular, at higher temperatures and for the less densely packed surfaces of the metal substrate, can provide a mechanism for easy nucleation of crystallization at the metal/oxide interface of the amorphous oxide film of thickness larger than the critical thickness.
A new magic titanium-doped gold cluster and orientation dependent cluster-cluster interaction
Authors: Chen Ming-Xing , Yan X. H.
Published: May 2008

The stability and structures of titanium-doped gold clusters AunTi (n=2–16) are studied by the relativistic all-electron density-functional calculations. The most stable structures for AunTi clusters with n=2–7 are found to be planar. A structural transition of AunTi clusters from two-dimensional to three-dimensional geometry occurs at n=8, while the AunTi (n=12–16) prefer a gold cage structure with Ti atom locating at the center. Binding energy and second-order energy differences indicate that the Au14Ti has a significantly higher stability than its neighbors. A high ionization potential, low electron affinity, and large energy gap being the typical characters of a magic cluster are found for the Au14Ti. For cluster-cluster interaction between magic transition-metal-doped gold clusters, calculations were performed for cluster dimers, in which the clusters have an icosahedral or nonicosahedral structure. It is concluded that both electronic shell effect and relative orientation of clusters are responsible for the cluster-cluster interaction.
Terahertz-wave absorption in liquids measured using the evanescent field of a silicon waveguide
Authors: Cheng Li , Hayashi Shin’ichiro , Dobroiu Adrian , Otani Chiko , Kawase Kodo , Miyazawa Teruo , Ogawa Yuichi
Published: May 2008

A technique is presented for the measurement of the absorption properties of liquids in the terahertz wave range, based on the interaction between the liquid and the evanescent wave covering the surface of a cylindrical waveguide made of high-resistivity silicon. The terahertz wave propagates inside the waveguide as the fundamental EH11 mode. The presence of a medium around the silicon rod has a measurable effect on the overall end-to-end transmission of the waveguide. As demonstration, we report the measurements of a D-glucose aqueous solution with a concentration ranging from 0% to 45%, using a backward-wave oscillator as the terahertz wave source.
Hyperbolic Hubbard–Stratonovich transformation made rigorous
Authors: Fyodorov Y. V. , Wei Y. , Zirnbauer M. R.
Published: May 2008

We revisit a long standing issue in the theory of disordered electron systems and their effective description by a nonlinear sigma model: the hyperbolic Hubbard–Stratonovich (HS) transformation in the bosonic sector. For time-reversal invariant systems without spin, this sector is known to have a noncompact orthogonal symmetry Op,q. There exists an old proposal by Pruisken and Schäfer how to perform the HS transformation in an Op,q-invariant way [Nucl. Phys. B. 200, 20 (1982)]. Giving a precise formulation of this proposal, we show that the HS integral is a sign-alternating sum of integrals over disjoint domains.
Applications of continuity and discontinuity of a fractional derivative of the wave functions to fractional quantum mechanics
Authors: Dong Jianping , Xu Mingyu
Published: May 2008

The space fractional Schrödinger equation with a finite square potential, periodic potential, and delta-function potential is studied in this paper. We find that the continuity or discontinuity condition of a fractional derivative of the wave functions should be considered to solve the fractional Schrödinger equation in fractional quantum mechanics. More parity states than those given by standard quantum mechanics for the finite square potential well are obtained. The corresponding energy equations are derived and then solved by graphical methods. We show the validity of Bloch’s theorem and reveal the energy band structure for the periodic potential. The jump (discontinuity) condition for the fractional derivative of the wave function of the delta-function potential is given. With the help of the jump condition, we study some delta-function potential fields. For the delta-function potential well, an alternate expression of the wave function (the H function form of it was given by Dong and Xu [J. Math. Phys. 48, 072105 (2007)]) is obtained. The problems of a particle penetrating through a delta-function potential barrier and the fractional probability current density of the particle are also discussed. We study the Dirac comb and show the energy band structure at the end of the paper.
A versatile all-optical Bose–Einstein condensates apparatus
Authors: Wenas Y. C. , Hoogerland M. D.
Published: May 2008

We report on the construction of an all-optical Bose–Einstein condensate apparatus by using a CO2 laser trap. We also report on measurements of the trap frequency by applying a periodic perturbation to the trap potential. The derived trap parameters agree well with the design parameters.
Annealing-induced transition from a (311)A-oriented Ga0.98Mn0.02As alloy to a GaMnAs/MnAs hybrid structure studied by angle-dependent magnetotransport
Authors: Elm M. T. , Klar P. J. , Heimbrodt W. , Wurstbauer U. , Reinwald M. , Wegscheider W.
Published: May 2008

The angle-dependent behavior of the magneto-resistance of a series of low-temperature molecular beam epitaxy grown Ga0.98Mn0.02As samples on (311)A-GaAs-substrates is studied. The samples are annealed at different temperatures in a range from 300 °C to 500 °C, which leads to a redistribution of the manganese in the sample and finally to the formation of MnAs clusters. As a consequence, the angle-dependence of the magneto-resistance changes with increasing annealing temperature and vanishes finally at an annealing temperature of 400 °C. The observed anisotropy of the magneto-resistance can be correlated with the magnetic anisotropy of the magnetization. The parameters describing this magnetic anisotropy and their changes due to annealing are extracted from the experimental magneto-resistance data by a fitting procedure. The magnetocrystalline anisotropy of the samples can be described by the sum of cubic and uniaxial contributions. The former are not affected by the annealing whereas the latter change considerably.
Achievement of sensing single spin with the aid of Kondo resonance in quantum dot connected to ferromagnetic electrodes
Authors: Chen Jiang , Hu Yibin , Xia Ke , Ma Zhongshui
Published: May 2008

We theoretically propose the detection of spin states of magnetic atom or molecule in proximity to a quantum dot by the Kondo effect with ferromagnetic electrodes, which can be switched in parallel or antiparallel alignments. The relative orientation of spin to the magnetization of electrode can be evidentially tracked from the spin splitting in Kondo peak of differential conductance. The experimental realization is discussed.
Antiferromagnetic interlayer exchange coupling between Fe3O4 layers across a nonmagnetic MgO dielectric layer
Authors: Wu Han-Chun , Arora S. K. , Mryasov O. N. , Shvets I. V.
Published: May 2008

We have investigated the interlayer exchange coupling between the epitaxial spinel Fe3O4 layers across an insulating nonmagnetic MgO spacer. The epitaxial structure used for these investigations was Fe3O4 (10nm)∕MgO (0.8–3nm)∕Fe3O4 (10nm)∕NiO (15nm) multilayers grown on MgO (100) substrates. We find that the two Fe3O4 layers are antiferromagnetic coupled through the MgO spacer when the MgO thickness is less than 1.5nm. Furthermore, ab initio calculation of IEC for Fe∕MgO∕Fe indicates the importance of electrode states, in particular, partial oxidation of the ferromagnetic electrodes.
Giant strain in lead-free (Bi0.5Na0.5)TiO3-based single crystals
Authors: Teranishi Shunsuke , Suzuki Muneyasu , Noguchi Yuji , Miyayama Masaru , Moriyoshi Chikako , Kuroiwa Yoshihiro , Tawa Katsunori , Mori Shigeo
Published: May 2008

A giant electric-field-induced strain of 0.87% is reported for tetragonal (Bi0.5Na0.5)TiO3-(Bi0.5K0.5)TiO3-BaTiO3 single crystals along the [100]cubic direction, which is six times as large as that of Pb(Zr0.52Ti0.48)O3 ceramics. In situ x-ray diffraction measurements and transmission electron microscope observations show that the giant strain mainly originates from switching of nanosized 90° domains. Strain measurements indicate that the strain caused by the 90° domain switching is reversible for both unipolar and bipolar electric-field applications. The reversibility of the 90° domain switching can be explained by the interaction between the spontaneous polarization and the defect dipole composed of A-site vacancy and oxygen vacancy.
Room temperature giant dielectric tunability effect in bulk LuFe2O4
Authors: Li Chang-Hui , Zhang Xiang-Qun , Cheng Zhao-Hua , Sun Young
Published: May 2008

We report the extreme sensitivity of dielectric permittivity to applied dc bias electric field in bulk LuFe2O4. A small bias field of 50V∕cm can greatly reduce the dielectric permittivity in the vicinity of room temperature, which is in strong contrast to conventional ferroelectric materials where a large electric field of the order of tens of kV/cm is required. This giant dielectric tunability effect within a broad temperature interval around room temperature is very promising for tunable device applications. The possible origins of this giant effect are discussed.
Magnetocontrollable photonic crystals based on colloidal ferrofluids
Authors: Fan C. Z. , Wang G. , Huang J. P.
Published: May 2008

We theoretically exploit a class of one-dimensional double-layer photonic crystals based on colloidal ferrofluids, which are made of ferromagnetic nanoparticles suspended in a carrier liquid. Depending on the magnetic-field-induced anisotropic property of the ferrofluid, precise controllability of the band gaps is demonstrated to be possible by applying an appropriate external magnetic field.
An easy mechanical way to create ferromagnetic defective ZnO
Authors: Potzger K. , Zhou Shengqiang , Grenzer J. , Helm M. , Fassbender J.
Published: May 2008

We present an experiment for the creation of unconventional ferromagnetism in pure ZnO powder by application of mechanical force. The ferromagnetism is related to flakelike structures in planar compressed pieces of the powder with easy axis in the plane. It is associated with defect creation and disappears upon annealing in oxygen. Besides cluster formation, such defects might be one of the nonintrinsic origins of ferromagnetism in transition metal doped ZnO.
Laser action from Yb3+ ions in the ferroelectric and paraelectric phases of strontium barium niobate
Authors: Martín Rodríguez E. , Jaque D. , García Solé J. , Pankrath R.
Published: May 2008

We report on continuous wave laser oscillation of trivalent ytterbium ions in the frequency converter Yb3+:Sr0.6Ba0.4Nb2O6 ferroelectric laser crystal. Pump induced thermal loading has been used to drive the crystal from its ferroelectric to paraelectric phase. Stable laser radiation at 1070nm was found in both phases while a bistable laser output is observed through phase transition. In addition, diffuse green (535nm) radiation was generated by self-frequency doubling of the fundamental laser radiation because of the random distribution of microferroelectric domains existing in the ferroelectric as grown crystal.