bluuebunny/crossref_metadata_2025 huggingface dataset:
Tectonically controlled subglacial lakes on the flanks of the Gamburtsev Subglacial Mountains, East Antarctica
Authors: Bell Robin E. , Studinger Michael , Fahnestock Mark A. , Shuman Christopher A.
Published: January 2006

The morphology of surface lakes strongly influences their ecology and limnology (Wetzel, 2001). This morphology is a result of both the geologic processes that produce topographic basins and the regional climatic and local hydrologic processes that control water depth and sediment infilling (Carroll and Bohacs, 1999). Although basin forming processes range from glacial scour to meteorite impacts (Cohen, 2003), the deepest, oldest surface lakes are tectonically controlled (Meybeck, 1995) and contain diverse exotic ecosystems (Rossiterm and Kawanabe, 2000). Subglacial lakes are also thought to be ancient systems that may contain exotic biota (Bulat et al., 2004; Karl et al., 1999; Priscu et al., 1999). Here we present evidence for the scale and configuration of 2 large subglacial lakes in East Antarctica that together with Lake Vostok define a province of major lakes on the flanks of the Gamburtsev Subglacial Mountains. Spatially‐defined in the new Moderate Resolution Imaging Spectroradiometer (MODIS) imagery of Antarctica (T. Scambos et al., A MODIS‐based mosaic of Antarctica: MOA, submitted to Remote Sensing of Environment, 2005, hereinafter referred to as Scambos et al., submitted manuscript, 2005), these lakes are aligned parallel to Lake Vostok. Other data shows that they are distinguished by distinct gravity lows, flat ice surface slopes and have estimated water depths of at least 900 m. Surface elevation data indicates that large deep subglacial lakes have a profound influence on the regional ice sheet topography and probably ice sheet flow. These deep subglacial lakes with elongate, rectilinear morphology are tectonically controlled features. Unlike the shallow lakes in West Antarctica and beneath Dome Concordia, these deep subglacial lakes remained stable environments through many glacial cycles since their origin 10–35 Ma enabling the development of novel ecosystems.
Dynamic deformation of the accretionary prism excites very low frequency earthquakes
Authors: Ito Yoshihiro , Obara Kazushige
Published: January 2006

We have detected anomalous very‐low‐frequency earthquakes within the accretionary prism along the Nankai Trough, southwestern Japan. Centroid moment tensor inversion analysis reveals that the earthquake hypocenters are distributed at ∼10 km depth above the upper surface of the subducting Philippine Sea Plate, and within 50–70 km landward of the trough axis. The focal mechanisms indicate reverse faulting. Their hypocenters are distributed beneath a deformation zone of an accretionary prism in sea‐floor topography. These observations suggest that the occurrence of very‐low‐frequency earthquakes is related to numerous reverse fault systems within the accretionary prism, and that the earthquakes reflect the dynamics of deformation within this accretionary prism.
Interspecies pharmacokinetics and in vitro metabolism of SQ109
Authors: Jia Lee , Noker Patricia E , Coward Lori , Gorman Gregory S , Protopopova Marina , Tomaszewski Joseph E
Published: January 2006

This study aimed at characterizing the interspecies absorption, distribution, metabolism and elimination (ADME) profile of N‐geranyl‐N′‐(2‐adamantyl)ethane‐1,2‐diamine (SQ109), a new diamine‐based antitubercular drug.

Single doses of SQ109 were administered (intravenously (i.v.) and per os (p.o.)) to rodents and dogs and blood samples were analyzed by liquid chromatography tandem mass spectrometry (LC/MS/MS). Based on i.v. equivalent body surface area dose, the terminal half‐life (t1/2) of SQ109 in dogs was longer than that in rodents, reflected by a larger volume of distribution (Vss) and a higher clearance rate of SQ109 in dogs, compared to that in rodents. The oral bioavailability of SQ109 in dogs, rats and mice were 2.4–5, 12 and 3.8%, respectively.

After oral administration of [14C]SQ109 to rats, the highest level of radioactivity was in the liver, followed by the lung, spleen and kidney. Tissue‐to‐blood ratios of [14C]SQ109 were greater than 1. Fecal elimination of [14C]SQ109 accounted for 22.2% of the total dose of [14C]SQ109, while urinary excretion accounted for only 5.6%. The binding of [14C]SQ109 (0.1–2.5 μg ml−1) to plasma proteins varied from 6 to 23% depending on the species (human, mouse, rat and dog).

SQ109 was metabolized by rat, mouse, dog and human liver microsomes, resulting in 22.8, 48.4, 50.8 or 58.3%, respectively, of SQ109 remaining after a 10‐min incubation at 37°C. The predominant metabolites in the human liver microsomes gave intense ion signals at 195, 347 and 363m/z, suggesting the oxidation, epoxidation and N‐dealkylation of SQ109. P450 reaction phenotyping using recombinant cDNA‐expressed human CYPs in conjunction with specific CYP inhibitors indicated that CYP2D6 and CYP2C19 were the predominant CYPs involved in SQ109 metabolism.

British Journal of Pharmacology (2006) 147, 476–485. doi:10.1038/sj.bjp.0706650
Cu2+(1,10 phenanthroline)3is an open‐channel blocker of the human skeletal muscle sodium channel
Authors: Popa Mariana Oana , Lerche Holger
Published: January 2006

The formation of disulfide bridges is a classical approach used to study the mobility, proximity and distances of residues in a variety of proteins, including ligand‐ and voltage‐gated ion channels. We performed patch‐clamp studies to investigate the interaction of a pair of cysteines introduced into the human skeletal muscle voltage‐gated Na+channel (hNav1.4) using the oxidation catalyst, Cu2+(1,10‐phenanthroline)3(CuPhen).

Our experiments resulted in a surprising finding, a reversible current inhibition of the mutant I1160C/L1482C containing two cysteines in the D3/and D4/S4–S5 loops, subjected to oxidative cross‐linking in the presence of CuPhen.

We report here that CuPhen is an open channel blocker of both mutant and wild‐type (WT) hNav1.4 channels, however, for WT channels a more than 10‐fold higher concentration was needed to induce the same effect. Moreover, 1,10‐phenanthroline was capable of blocking Na+channels in the absence of Cu2+ions. Our results indicate a use‐ and voltage‐dependent binding and unbinding of CuPhen, reminiscent of the lidocaine quaternary derivative QX‐314 and the neurotoxin batrachotoxin.

Care should be taken when using CuPhen as an oxidizing reagent in cross‐linking experiments, since it may directly affect channel activity. Our results identify CuPhen (and phenantroline) as a novel use‐dependent inhibitor of Na+channels, a mechanism that is shared by drugs widely used in the treatment of epilepsy, neuropathic pain, cardiac arrhythmia and myotonia. We hypothesize that I1160C in D3/S4–S5 and the corresponding L1482C mutation in D4/S4–S5 could allosterically affect a binding site located in the inner pore region of the channel.

British Journal of Pharmacology(2006)147, 808–814. doi:10.1038/sj.bjp.0706667
Suppression of current fluctuations in a crossed E×B field system for low-voltage plasma immersion treatment
Authors: Levchenko I. , Keidar M. , Ostrikov K. , Yu M. Y.
Published: January 2006

Plasma transport in a hybrid dc vacuum arc plasma source for ion deposition and plasma immersion treatment is considered. It is found that external crossed electric and magnetic fields near the substrate can significantly reduce the relative amplitude of ion current fluctuations I¯f at the substrate surface. In particular, I¯f decreases with the applied magnetic field when the bias voltage exceeds 300V, thus allowing one to reduce the deviations from the rated process parameters. This phenomenon can be attributed to an interaction between the metal-plasma jet from the arc source and the discharge plasma in the crossed fields.
Graphical analysis for gel morphology. III. Gel size and temperature effects on the volume phase transition of gels
Authors: Hashimoto Chihiro , Ushiki Hideharu
Published: January 2006

Just after poly(N-isopropylacrylamide) (PNIPA) gels are immersed into hot water over the critical temperature, they undergo a two- or three-step shrinking accompanied with the whitening. The size of gels and the destination temperature were changed and their effects on the shrinking process of PNIPA gels were studied. The following important knowledge in the volume phase transition process of PNIPA gels was obtained. The first is the fact that the fraction of first shrinking is determined by the shrinking rate in the first shrinking stage. The second is the fact that PNIPA gels are divided into small parts by the pinning of density fluctuation in the final stage of the first shrinking and that the shrinking process of each small part undergoes in the secondary shrinking stage. The volume phase transition process of PNIPA gels is briefly discussed from the viewpoint of the scaling theory.
Three homeotropically aligned nematic liquid crystals: Comparison of ultrafast to slow time-scale dynamics
Authors: Li Jie , Wang Irene , Fayer M. D.
Published: January 2006

The dynamics of two nematic liquid crystals, 4-(trans-4′-n-octylcyclohexyl)isothiocyanatobenzene and 4-(4-pentyl-cyclohexyl)-benzonitrile, are investigated as a function of temperature both in the homeotropically aligned nematic phase and in the isotropic phase using optical heterodyne-detected optical Kerr effect experiments, which measures the time derivative of the polarizability–polarizability-correlation function (orientational relaxation). Data are presented over a time range of 500fs−70μs for the nematic phase and 500fs to a few hundred nanoseconds for the isotropic phase. The nematic dynamics are compared with a previously studied liquid crystal in the nematic phase. All three liquid crystals have very similar dynamics in the nematic phase that are very different from the isotropic phase. On the slowest time scale (20ns–70μs), a temperature-independent power law, the final power law, t−f with f∼0.5, is observed. On short time scales (∼3psto∼1ns), a temperature-dependent intermediate power law is observed with an exponent that displays a linear dependence on the nematic order parameter. Between the intermediate power law and the final power law, there is a crossover region that has an inflection point. For times that are short compared to the intermediate power law (≲2ps), the data decay much faster, and can be described as a third power law, although this functional form is not definitive. The isotopic phase data have the same features as found in previous studies of nematogens in the isotropic phase, i.e., the temperature-independent intermediate power law and von Schweidler power law at short to intermediate times, and a highly temperature-dependent long time exponential decay that is well described by the Landau-de Gennes theory. The results show that liquid-crystal dynamics in the nematic phase exhibit universal behavior.
Pulsed plasma polymerized dichlorotetramethyldisiloxane high-k gate dielectrics for polymer field-effect transistors
Authors: Xu Yifan , Berger Paul R. , Cho Jai , Timmons Richard B.
Published: January 2006

Polymerized dichlorotetramethyldisiloxane (DCTMDS) films deposited by radio-frequency pulsed plasma polymerization (PPP) demonstrated very high dielectric constants for a polymer-based system, in the range of 7–10. The high dielectric constants of PPP DCTMDS films are due to the high polarizability of the DCTMDS monomer. The pulsed plasma duty cycle (on/off) resulted in slightly higher dielectric constant DCTMDS films for higher duty cycles. The variation of dielectric constants does not show any trend with varying film thicknesses, indicating that the thickness of the deposited films is not significant for controlling permittivity. Postdeposition annealing in a certain temperature range improves the electrical integrity of PPP DCTMDS films, but temperatures that are too high induce even higher leakage than the samples with no heat treatment. An optimal annealing temperature was identified to be in the range of 150–200 °C. Samples annealed within this temperature window have low leakage current densities below 0.1pA∕μm2 at 10 V for film thicknesses about 100 nm. Poly(3-hexythiophene) polymer field-effect transistors (PFETs) using PPP DCTMDS gate dielectric films were fabricated and tested. Due to the high dielectric constants of PPP DCTMDS, these PFETs possess high gate capacitance and operate at low voltage.
Optical spectroscopy of Yb3+-doped Ca3Sc2Ge3O12 garnet crystal
Authors: Ramírez M. O. , Bausá L. E. , Cavalli E. , Bovero E.
Published: January 2006

Good quality Ca3Sc2Ge3O12 garnet crystals activated with Yb3+ have been grown by means of the flux growth method and characterized using optical spectroscopy techniques. The low-temperature absorption and emission spectra give evidence of the presence of nonequivalent optical centers, as a consequence of the distribution of the Yb3+ ions in different lattice sites. The effect of codoping with Na+ or Mg2+ on the Yb3+ site distribution has been investigated. The energy-level schemes of the most important centers have been determined on the basis of site-selective spectroscopy experiments. Cooperative luminescence has also been observed and reliably compared with the self-convolution of the NIR luminescence.
Nanoscale defect formation on InP (111) surfaces after MeV Sb implantation
Authors: Paramanik Dipak , Pradhan Asima , Varma Shikha
Published: January 2006

We have studied the surface modifications as well as the surface roughness of the InP(111) surfaces after 1.5 MeV Sb ion implantations. A scanning probe microscope has been utilized to investigate the ion-implanted InP(111) surfaces. We observe the formation of nanoscale defect structures on the InP surface. The density, height, and size of the nanostructures have been investigated here as a function of ion fluence. The rms surface roughness, of the ion implanted InP surfaces, has also been investigated. Raman-scattering results demonstrate that at the critical fluence, where the decrease in surface roughness occurs, the InP lattice becomes amorphous.
Residual impurities and native defects in 6H-SiC bulk crystals grown by halide chemical-vapor deposition
Authors: Huh S. W. , Chung H. J. , Nigam S. , Polyakov A. Y. , Li Q. , Skowronski M. , Glaser E. R. , Carlos W. E. , Shanabrook B. V. , Fanton M. A. , Smirnov N. B.
Published: January 2006

A variety of defect-sensitive techniques have been employed to detect, identify, and quantify the residual impurities and native defects in high-purity (undoped) 6H-SiC crystals grown by halide chemical-vapor deposition technique. The incorporation efficiencies of N and B are determined by the site-competition effect. Most notably, material with low residual N levels (∼1014cm−3) can be produced. In addition, the nitrogen concentrations obtained from Hall-effect measurements and low-temperature photoluminescence are systematically lower than those determined from secondary-ion-mass spectrometry. The difference is ascribed to nitrogen forming complexes with native defects. The energy level of this complex is approximately 0.27eV below the conduction band. Four major electron traps with activation energies of 0.4, 0.5, 0.65, and 1eV and five hole traps with activation energies of 0.3, 0.4, 0.55, 0.65, and 0.85eV were observed by deep-level transient spectroscopy. The concentration of all traps decreased strongly with increasing C∕Si ratio during growth. Increasing the C∕Si flow ratio also led to increased resistivity of the crystals and change of conductivity from conductive n type to high-resistivity p type. The Fermi level in p-type material is pinned either to highly compensated shallow B acceptors or to deep B-related center at 0.6eV above the valence band. Electron paramagnetic resonance shows the presence of positively charged carbon vacancies in such high-resistivity material.
Electro-optical effect in ZnO:Mn thin films prepared by Xe sputtering
Authors: Ashida Atsushi , Nagata Takahiro , Fujimura Norifumi
Published: January 2006

ZnO thin films were epitaxially deposited on platinum∕c-sapphire epitaxial layer using a radio frequency magnetron sputtering method. Xe, rather than Ar, was used as the sputtering gas. The leakage current as well as dielectric loss was suppressed upon use of Xe. Moreover, the full width at half maximum ω scan and surface morphology were improved by using Xe. These improvements are attributed to the fact that damage to the films during deposition using Xe is less than that upon the use of Ar. The electro-optical (EO) effect was evaluated by reflection configuration. ZnO films prepared with Ar showed no EO response. However, films prepared with Xe show a linear response of change in the birefringence with the electric field. The EO coefficient (rc) was evaluated as 0.2pm∕V. In order to reduce the leakage current and further improve the EO property, Mn was doped to the ZnO films prepared with Xe. As a result, the leakage current was eight orders of magnitude less than that of the undoped film. The dielectric loss was also reduced. Additionally, the frequency dispersion of dielectric loss was suppressed. Therefore, the space charge in the films is thought to be reduced by using Xe and doping with Mn. As a result of suppression of space charges, an rc of 2.2pm∕V was achieved. This value is close to that of the single crystal.
Reduction of switching field in spin-flop switching for high-density magnetic random access memory
Authors: Kim K. S. , Shin K. H. , Lim S. H.
Published: January 2006

A magnetization switching method for magnetic random access memory (MRAM), recently proposed by Savtchenko et al. [U.S. Patent No. 6,545,906 (2003)], is known to have an important advantage of a wide window for bit writing over the conventional method based on the asteroid curve, but it has a serious problem of high switching fields. In an effort to solve this problem, the effects of the thickness asymmetry and antiferromagnetic exchange coupling of the synthetic antiferromagnetic free-layer structure on the switching field have been investigated by micromagnetic computer simulation. At conditions relevant to high-density MRAM, magnetization switching in the direct write mode occurs at reasonably low values of word- and bit-line fields (below 100Oe), combined with a substantially wide window for bit writing. A much wider window is observed in the toggle mode, but the required switching fields are too high, being over 150Oe.
Stability of the quasicubic phase in the initial stage of the growth of bismuth films on Si(111)-7×7
Authors: Sadowski J. T. , Nagao T. , Yaginuma S. , Fujikawa Y. , Sakurai T. , Oreshkin A. , Saito M. , Ohno T.
Published: January 2006

We discuss the results of the scanning tunneling microscopy (STM) investigations and ab initio calculations of the structure and stability of the quasicubic Bi{012} film formed in the initial stage of the bismuth deposition on the Si(111)-7×7 surface at room temperature. Results of our STM experiments show that paired-layer Bi{012} film grows on top of the initially formed wetting layer, with the Si 7×7 lattice preserved underneath. The pairing of the layers in the {012} film leads to the substantial stabilization of the film when it consists of an even number of layers and only even-number layered Bi{012} islands are observed to be stable. The buckling of the atoms in the topmost paired layer induced by the relaxation of the film is evidenced by the high-resolution STM images.
Transient response during resistance switching in Ag∕Pr0.7Ca0.3MnO3∕Pt thin films
Authors: Odagawa Akihiro , Kanno Tsutomu , Adachi Hideaki
Published: January 2006

The transient response during resistance switching in Ag∕Pr0.7Ca0.3MnO3∕Pt thin films is investigated by measurements using pulsed voltage biases. Semiconducting Pr0.7Ca0.3MnO3 (PCMO) films sandwiched by Ag and Pt electrodes show nonvolatile resistance switching (two orders of magnitude) as a result of applying pulsed voltage biases, even at room temperature. The transient responses of the voltage across the PCMO for a set (positive) and a reset (negative) pulse application are consistent with the resistance-switching behavior and show quite fast switching (3–100 ns) for the set pulse application, compared with 60–135 ns for the reset pulse application. The large resistance-switching ratio is saturated after a finite transient time, indicating that the carrier filling of the trap sites into PCMO is completed within quite a short time.
Top-emitting polymer light-emitting diodes with environmentally stable cathodes
Authors: Deng X. Y. , Ho M. K. , Wong K. Y.
Published: January 2006

We report the demonstration of polymer-based top-emitting diodes that employed environmentally stable cathode materials. The device employed an emissive polymer blend that we reported previously [Deng et al. Appl. Phys. Lett. 84, 3522 (2004)]. By constructing a semitransparent cathode using the stable metals Al and Ag, bright light emission through the top cathode was achieved. An index-matching overlayer deposited by spin coating was shown to enhance the transmission efficiency through the top electrode. Microcavity effects were observed for the device by replacing the indium tin oxide anode with Au, resulting in wavelength tunability of the device.
Biological properties of titanium implants covered with hydroxyapatite and zirconia layers by pulsed laser: In vitro study
Authors: Seydlova Michaela , Teuberova Zuzana , Dostalova Tatjana , Dvorankova Barbora , Smetana Karel , Jelinek Miroslav , Kocourek Tomas , Mroz Waldemar
Published: January 2006

The biological and physical properties of dental implants coated by the sandwich technique with a thin layer of hydroxyapatite and an interlayer of zirconia were evaluated. The implant samples were covered by pulsed laser deposition. The aim of our study is to evaluate the cytotoxicity and the surface characteristics of the titanium targets modified with zirconia and hydroxyapatite. The titanium substrates were analyzed physically by x-ray diffraction and scanning electron microscopy. We used a direct test of cytotoxicity to compare the prepared samples with other reference materials. No changes in the morphology or the proliferation rate of the cells used were found in the presence of the modified titanium targets. The adhesion, proliferation, and fibronectin expressions of human fibroblasts were also evaluated on the surface of the modified titanium targets. The results show that the modified titanium samples are at least as attractive as the tissue grade polystyrene in promoting fibroblasts’ adhesion and proliferation. The results show adhesion and cell proliferation, which in turn implies that the studied material is not cytotoxic and is suitable for cell colonization. Titanium modified with zirconia and hydroxyapatite can be beneficially employed in oral bone surgery.
Some mathematical properties of Maxwell’s equations for macroscopic dielectrics
Authors: Tip A.
Published: January 2006

We consider a number of mathematical properties of Maxwell’s equations for linear dispersive and absorptive dielectric media using the auxiliary field method developed earlier by the author [A. Tip, Phys. Rev. A 57, 4818 (1998)]. Here the fields are interpreted as square integrable functions of x∊R3. In case the susceptibility χ(x,t) is piecewise constant in x, we show rigorously that a decomposition into independent equations for longitudinal and transverse fields can be made. We point out its relevance for the study of spectral properties of photonic crystals. Again, for the piecewise constant case we discuss the usual boundary conditions at interfaces and discuss the different nature of those for the longitudinal and transverse fields. Then we consider energy conservation for dispersive, nonabsorptive, media. We show that additional contributions to the free field energy density, as given in the literature, are associated with the energy stored in the auxiliary field modes. Finally, we show that also for nonlinear dielectrics it is possible to obtain a conserved energy by introducing auxiliary fields.
Piezoelectric resonance of lead zirconate titanate ceramics excited by a stepwise electric field
Authors: Jin Li , Yao Xi , Wei Xiaoyong
Published: January 2006

Transient current of ferroelectric ceramics has been intensively studied using a stepwise electric field. Abnormal oscillations were observed in the transient current when a stepwise electric field was applied onto modified lead zirconate titanate (PZT) ceramic samples in a very short time (less than 100ns) in the present study. Compared to the frequency spectrum of those samples, it is found that those frequencies of oscillations correspond to that of piezoelectric resonance. Four samples of PZT ceramics were cut into different dimensions according to the requirement of five different electromechanical coupling modes. Experimental results demonstrate that those five piezoelectric resonance modes of the ferroelectric samples could be excited by a stepwise electric field, and different resonance modes of a sample could be excited simultaneously. The authors also found that whether piezoelectric resonance could be excited depends on the parameters of test circuit.
Defects and electrical behavior in 1MeV Si+-ion-irradiated 4H–SiC Schottky diodes
Authors: Roccaforte F. , Libertino S. , Raineri V. , Ruggiero A. , Massimino V. , Calcagno L.
Published: January 2006

In this paper, the formation and evolution of defects induced by ion irradiation with 1MeV Si+ ions in Ni2Si∕4H–SiC Schottky diodes were studied and correlated with the electrical properties of the contacts. The current-voltage characteristics of the contacts monitored before and after irradiation showed an increase of the Schottky barrier height, of the series resistance, and of the leakage current with increasing irradiation fluence. The changes in the barrier height and in the series resistance values could be attributed to the dopant deactivation in the near-interface region, while the increase of the leakage current was associated with the formation of irradiation-induced defects. These defects showed an evolution with increasing irradiation fluence. Moreover, a combination of deep-level transient spectroscopy and current-voltage measurements of the diodes allowed us to demonstrate that the Z1∕Z2 center of 4H–SiC has the major influence on the increase of the diodes leakage current in the irradiated material.
Limitations on standard procedure of determining internal loss and efficiency in quantum dot lasers
Authors: Asryan Levon V.
Published: January 2006

Limitations are discussed on the use in quantum dot (QD) lasers of the conventional method of determining internal loss coefficient αint and internal quantum efficiency ηint from a measured plot of the reciprocal slope efficiency versus the cavity length L. The limitations are imposed by the L-dependence of αint and ηint themselves. The effect of internal loss is quantitatively analyzed, which originates from the dependence of αint on the carrier density, with the latter being L-dependent. In short cavities, a plot of the reciprocal slope efficiency versus L can significantly deviate from a straight line, thus limiting the practicality of the standard procedure. For L longer than several hundred μm, the limitations are strong in a single-QD-layer laser and moderate in a multiple-QD-layer laser.
Formation of nickel nanodots on GaN
Authors: Aurongzeb D. , Ram K. Bhargava , Holtz M. , Basavaraj M. , Kipshidze G. , Yavich B. , Nikishin S. A. , Temkin H.
Published: January 2006

We examine the annealing-induced formation of nickel nanodots on GaN substrates. The initial Ni layer thickness is 2 nm. Annealing temperatures range from 550 to 930 °C. The islands are well defined at the highest temperatures. Island formation kinetics provide an activation energy of 0.34±0.07eV. Time dependence of the nanodot island areas, annealed at 750 °C, is consistent with a t2∕3. These observations are indicative of diffusion-limited ripening as the primary formation mechanism. X-ray diffraction results show that nickel gallides form at anneal temperatures 750 °C and above.
Raman study of phonon modes and disorder effects in Pb1−xSrxSe alloys grown by molecular beam epitaxy
Authors: Chen J. , Shen W. Z.
Published: January 2006

We report phonon modes and alloy disorder effects of Pb1−xSrxSe alloys (x⩽0.3) grown on BaF2 (111) substrates by Raman spectroscopy measurements. On the basis of phonon modes in binary PbSe and SrSe, first-, second-, and high-order Raman scattering phonon frequencies of ternary Pb1−xSrxSe are observed, together with the deduction of the disorder activated modes due to the breakdown of the selection rule. The alloy disorder is found to play a more important role than the strain effect in Pb1−xSrxSe, and has been further investigated by employing the special correlation model. The PbSe-like second-order features are also shown to broaden slightly and diminish in intensity with increasing Sr concentration, which has been attributed to a weak breakdown in the long-range order.
Neutral gas temperature measurements of high-power-density fluorocarbon plasmas by fitting swan bands of C2 molecules
Authors: Bai Bo , Sawin Herbert H. , Cruden Brett A.
Published: January 2006

The neutral gas temperature of fluorocarbon plasmas in a remote toroidal transformer-coupled source was measured to be greater than 5000K, under the conditions of a power density greater than 15W∕cm3 and pressures above 2torr. The rovibrational bands of C2 molecules (swan bands, dΠg3→aΠu3) were fitted to obtain the rotational temperature that was assumed to equal the translational temperature. This rotational-translational temperature equilibrium assumption was supported by the comparison with the rotational temperature of second positive system of added N2. For the same gas mixture, the neutral gas temperature is nearly a linear function of plasma power, since the conduction to chamber wall and convection are the major energy-loss processes, and they are both proportional to neutral gas temperature. The dependence of the neutral gas temperature on O2 flow rate and pressure can be well represented through the power dependence, under the condition of constant current operation. An Arrhenius type of dependence between the etching rate of oxide film and the neutral gas temperature is observed, maybe indicating the importance of the pyrolytic dissociation in the plasma formation process when the temperature is above 5000K.
Influence of Cu content on electronic transport and shunting behavior of Cu(In,Ga)Se2 solar cells
Authors: Virtuani A. , Lotter E. , Powalla M. , Rau U. , Werner J. H. , Acciarri M.
Published: January 2006

The paper presents the structural and electrical characterizations of Cu(In,Ga)Se2 thin films and thin-film solar cells realized with different Cu contents in the absorber material. It is shown that the bulk resistivity of the Cu(In,Ga)Se2 thin films (measured in coplanar geometry) dramatically increases with decreasing Cu content. Simultaneously, the shunt resistance Rp of the Cu(In,Ga)Se2 solar cells increases with decreasing Cu content in the absorber material. For a wide range of Cu contents, the resistivity of the thin films is directly proportional to Rp of the solar cell made from the same absorber material. We propose that Rp in Cu(In,Ga)Se2 solar cells originates from highly localized shunt regions in the absorber material. The higher Rp of cells made from Cu-poor material is then due to the high resistivity of the embedding Cu-poor material resistively suppressing extensive current flow towards these shunt regions. Further, we observe an increase of the film resistivity by two orders of magnitude if the Cu(In,Ga)Se2 absorbers are produced using a Na blocking layer on the glass substrate. However, the high resistivity of these Na-free samples does not go along with an increase of Rp in the corresponding solar cells, indicating that the high resistivity of Na-free Cu(In,Ga)Se2 results from electrostatic barriers at the grain boundaries and is not a bulk property.
Unusual glassy states in LaMn0.5Fe0.5O3: Evidence of two distinct dynamical freezing processes
Authors: De K. , Thakur M. , Manna A. , Giri S.
Published: January 2006

An interesting scenario of unusual glassy states is observed from the dc and ac susceptibility measurements in LaMn0.5Fe0.5O3. The dc measurements at 5mT exhibit two distinct peaks at ∼20(Tg) and ∼255K(Tp). The large field-cooled effect and frequency-dependent results indicate a glassy state between Tg and Tp, while the relaxation dynamics does not show cooperative relaxation without aging, suggesting the existence of noninteracting clusters of frozen spin. On the other hand, the glassy state with clear evidence of a cooperative relaxation process is noticed below Tg, which has been characterized from the field- and frequency-dependent results associated with the evidence of aging. The nature of the cooperative glassy state does not meet the glassy features of classical spin-glass compounds.
Dielectric relaxation in SrFe1∕2Nb1∕2O3
Authors: Saha Sonali , Sinha T. P.
Published: January 2006

The strontium iron niobate SrFe1∕2Nb1∕2O3 ceramic is synthesized by a solid-state reaction technique. The x-ray diffraction of the sample at room temperature shows a monoclinic phase. The dielectric permittivity and the loss tangent of the sample are measured in a frequency range from 50Hzto2MHz and in a temperature range from 143to473K. The frequency dependence of the loss peak is found to obey an Arrhenius law with an activation energy of 0.272eV. An analysis of the loss factor with frequency is performed by using the scaling behavior of the dielectric loss spectra. The scaling behavior of the dielectric loss spectra shows its temperature-independent nature. The relaxation mechanism is discussed in the framework of conductivity and impedance spectroscopy. The variation of dielectric constant with temperature is explained considering the space-charge polarization.
Low gain threshold of the cavity mode close to the cutoff wavelength in a three-slab asymmetric conjugated polymer-based waveguide structure
Authors: Li Feng , Solomesch Olga , Mackie Philip R. , Cupertino Domenico , Tessler Nir
Published: January 2006

The emission mode close to the cutoff wavelength in a three-slab asymmetric (glass/polymer/air) conjugated polymer-based waveguide structure is characterized and found to be largely affected by microcavity effects. The spectral profiles of the emission as a function of viewing angle suggest that the peak emission is due to a cavity effect between the fully reflecting polymer-air interface and the highly reflecting polymer-glass interface. A low gain threshold (<190Wcm−2) is found using conjugated benzothiadiazole-arylamine copolymer as the gain medium. The exceptionally low threshold is attributed to cavity enhancement effects.
Polarization-dependent measurement of the near-field distribution of a waveguide with subwavelength aperture
Authors: Ctistis G. , Schimek O. , Fumagalli P. , Paggel J. J.
Published: January 2006

The understanding of the near field is essential for scanning near-field optical microscopy. We present here a simple model experiment to examine the polarization of the near field in the proximity of a subwavelength aperture. We make use of microwaves, a fast diode, and different apertures. This allows us to model a polarization-sensitive scanning near-field optical microscope by mapping the field intensity around the aperture in the near-field region.
Band-gap energies and structural properties of doped Ba0.5Sr0.5TiO3 thin films
Authors: Zheng Y. B. , Wang S. J. , Huan A. C. H. , Tripathy S. , Chai J. W. , Kong L. B. , Ong C. K.
Published: January 2006

We have investigated the effect of Ti and Mg dopants on the structural properties and band-gap energies of Ba0.5Sr0.5TiO3 (BST) thin films grown on LaAlO3 substrates. The transmission spectra of these BST thin films measured by ultraviolet-visible spectrophotometer show that the band-gap energies are strongly dependent on the dopant concentration. Based on the structural analyses and theoretical calculation, the variation of the band-gap energies can be attributed to the combined effects of stress, grain size, and phase transformation in Ti- and Mg-doped BST thin films.
Transient response of piezoelectric thin-film vibration sensor under pulse excitation
Authors: Yang Zhaochun , Wang Qing-Ming
Published: January 2006

We present an analytical model to describe the transient response of a piezoelectric thin-film vibration sensor under pulse excitation. The structure of the thin-film vibration sensor consists of four suspended flexural piezoelectric lead zirconate titanate-on-silicon beam transducers and a central seismic mass. The model takes into account the effect of device geometry and materials properties of the piezoelectric thin film. The relationships between the dynamic behavior and voltage sensitivity with the device’s structure are established. It is found that with the increase of initial vibration magnitude U0 and reciprocal time constant α(α=1∕τ) of the excitation, the maximum voltage sensitivity increases, and the maximum output voltage decreases with the increase of the resonance frequency. When damping is taken into account, the output voltage of the device under pulse excitation is simply an exponentially decaying function of time. The results can be readily applied for design and fabrication of the on-chip vibration sensor or accelerometer.
Minimal field requirement in precessional magnetization switching
Authors: Xiao Di , Tsoi M. , Niu Qian
Published: January 2006

We investigate the minimal field strength in precessional magnetization switching using the Landau-Lifshitz-Gilbert equation in undercritically damped systems. It is shown that precessional switching occurs when localized trajectories in phase space become unlocalized upon application of field pulses. By studying the evolution of the phase space, we obtain the analytical expression of the critical switching field in the limit of small damping for a magnetic object with biaxial anisotropy in both the easy and hard plane. We also calculate the switching times for the zero damping situation by numerical means. We show that applying the field along the medium axis is good for both small field and fast switching times.
Characterization of the X̃A12, ÃB12, and X̃Π2 electronic states of the Ga2H molecule and the X̃A′2 and ÃA″2 isomerization transition states connecting the three minima
Authors: Wang Hongyan , Wang Suyun , Yan Ge , Yamaguchi Yukio , Schaefer Henry F.
Published: January 2006

A wide range of highly correlated ab initio methods has been used to predict the geometrical parameters of the linear (X̃Π2) and H-bridged (X̃A12 and ÃB12) Ga2H isomers and two isomerization transition states (X̃A′2 and ÃA″2) connecting the three minima. Dipole moments and vibrational frequencies are also obtained. The global minimum X̃A12 ground state of the H-bridged GaHGa isomer is predicted to lie only 1.6 [1.9 with the zero-point vibrational energy (ZPVE) corrections] kcalmol−1 below the ÃB12 state. The X̃A12 state lies 5.4kcalmol−1 below the X̃Π2 ground state of the linear GaGaH isomer at the coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] level of theory with the augmented correlation-consistent polarized valence quadruple-zeta (aug-cc-pVQZ) basis set. The full triples coupled-cluster method is found to alter these CCSD(T) predictions by as much as 0.3kcalmol−1. The forward isomerization barriers from the linear ground state to the X̃A′2 and ÃA″2 transition states are determined to be 3.3 and 5.3kcalmol−1, respectively. The reverse isomerization barrier between the X̃A12 GaHGa structure and the X̃Π2 GaGaH structure is predicted to be 8.6 (8.2 with the ZPVE corrections) kcalmol−1 at the aug-cc-pVQZ CCSD(T) level of theory.
Electric-field-coupled resonators for negative permittivity metamaterials
Authors: Schurig D. , Mock J. J. , Smith D. R.
Published: January 2006

A lithographically patterned inductive-capacitive resonator is described that has a strong electric response. This resonator can be used to construct metamaterials with desired positive or negative permittivity. Such materials provide an alternative to wire media, and have the benefit of not requiring continuous current paths between unit cells. A planar medium composed of these resonators was simulated, fabricated, and measured in the microwave frequency range.
10
V
programmable Josephson voltage standard circuits using NbN∕TiNx∕NbN∕TiNx∕NbN double-junction stacks
Authors: Yamamori H. , Ishizaki M. , Shoji A. , Dresselhaus P. D. , Benz S. P.
Published: January 2006

Using NbN∕TiNx∕NbN∕TiNx∕NbN double-junction stack technology we have demonstrated a programmable Josephson voltage standard chip that operates up to 10.16V output voltage cooled with a two-stage Gifford–McMahon cryocooler. The circuit uses double-junction stacks, where two junctions are fabricated in each stack, in order to integrate 327 680 junctions into a 15.3mm×15.3mm chip. A 1-to-32 microwave distribution circuit is also integrated on the chip. The chip is divided into 22 cells, which perform as an 11-bit digital-to-analog converter. The 21 working cells include 307 200 junctions biased with 16GHz microwaves at 10.2K that generated flat voltage steps with current margins greater than 1mA, which indicates good uniformity of the stacked junctions.
Enhanced low-temperature impact toughness of nanostructured Ti
Authors: Stolyarov V. V. , Valiev R. Z. , Zhu Y. T.
Published: January 2006

Impact toughness is one of the major mechanical properties for structural materials. It is generally observed that in coarse-grained materials the impact toughness decreases with decreasing testing temperature. Here, we report that the impact toughness of nanostructured Ti processed by severe plastic deformation is enhanced at low temperatures of −70°C and −196°C, a unique phenomenon that contradicts the observations in coarse-grained materials. The enhanced impact toughness is attributed to the increased strength and ductility of nanostructured Ti as well as smaller fracture dimples at lower temperatures. This result demonstrates the advantage of using nanostructured Ti in low-temperature applications.
Band gap renormalization and carrier localization effects in InGaN∕GaN quantum-wells light emitting diodes with Si doped barriers
Authors: Wang Y. J. , Xu S. J. , Li Q. , Zhao D. G. , Yang H.
Published: January 2006

The optical properties of two kinds of InGaN∕GaN quantum-wells light emitting diodes, one of which was doped with Si in barriers while the other was not, are comparatively investigated using time-integrated photoluminescence and time-resolved photoluminescence techniques. The results clearly demonstrate the coexistence of the band gap renormalization and phase-space filling effect in the structures with Si doped barriers. It is surprisingly found that photogenerated carriers in the intentionally undoped structures decay nonexponentially, whereas carriers in the Si doped ones exhibit a well exponential time evolution. A new model developed by O. Rubel, S. D. Baranovskii, K. Hantke, J. D. Heber, J. Koch, P. Thomas, J. M. Marshall, W. Stolz, and W. H. Rühle [J. Optoelectron. Adv. Mater. 7, 115 (2005)] was used to simulate the decay curves of the photogenerated carriers in both structures, which enables us to determine the localization length of the photogenerated carriers in the structures. It is found that the Si doping in the barriers not only leads to remarkable many-body effects but also significantly affects the carrier recombination dynamics in InGaN∕GaN layered heterostructures.
Large redshift in photoluminescence of p-doped InP nanowires induced by Fermi-level pinning
Authors: van Weert M. H. M. , Wunnicke O. , Roest A. L. , Eijkemans T. J. , Yu Silov A. , Haverkort J. E. M. , ’t Hooft G. W. , Bakkers E. P. A. M.
Published: January 2006

We have studied the effect of impurity doping on the optical properties of indium phosphide (InP) nanowires. Photoluminescence measurements have been performed on individual nanowires at low temperatures (5–70 K) and at low excitation intensities (0.5–10W∕cm2). We show that the observed redshift (200 meV) and the linewidth (70 meV) of the emission of p-type InP wires are a result of a built-in electric field in the nanowires. This bandbending is induced by Fermi-level pinning at the nanowire surface. Upon increasing the excitation intensity, the typical emission from these p-InP wires blueshifts with 70meV∕decade, due to a reduction of the bandbending induced by an increase in the carrier concentration. For intrinsic and n-type nanowires, we found several impurity-related emission lines.
Armadillo-related proteins promote lateral root development in Arabidopsis
Authors: Coates Juliet C. , Laplaze Laurent , Haseloff Jim
Published: January 2006

Armadillo/β-catenin and related proteins have important functions during animal and
Dictyostelium
development, regulating cell differentiation, proliferation, and adhesion. Armadillo-repeatcontaining proteins also exist in plants, but the majority have unknown roles. The
Arabidopsis
genes that show greatest sequence homology to Armadillo/β-catenin are called ARABIDILLO-1 and -2. Here, we demonstrate that ARABIDILLO-1 and -2 promote lateral root development.
arabidillo-1
/-
2
mutants form fewer lateral roots, and ARABIDILLO-1-overexpressing lines produce more lateral roots than wild-type seedlings. ARABIDILLO-yellow fluorescent protein fusions are nuclear. ARABIDILLO proteins contain an F-box motif, and thus may target other proteins for proteasomal degradation. Overexpression of ARABIDILLO-1 protein fragments, including F-box fragments, in wild-type seedlings reduces lateral root formation to the level of the
arabidillo-1
/-
2
mutant. We have shown that plant β-catenin-related proteins regulate root development. We suggest that ARABIDILLO proteins may target an inhibitor of lateral root development for degradation and propose that
Arabidopsis
β-catenin-related proteins define a previously uncharacterized pathway that promotes root branching.
Zonula Occludens-1 Function in the Assembly of Tight Junctions in Madin-Darby Canine Kidney Epithelial Cells
Authors: McNeil Elizabeth , Capaldo Christopher T. , Macara Ian G.
Published: January 2006

Zonula occludens (ZO)-1 was the first tight junction protein to be cloned and has been implicated as an important scaffold protein. It contains multiple domains that bind a diverse set of junction proteins. However, the molecular functions of ZO-1 and related proteins such as ZO-2 and ZO-3 have remained unclear. We now show that gene silencing of ZO-1 causes a delay of ∼3 h in tight junction formation in Madin-Darby canine kidney (MDCK) epithelial cells, but mature junctions seem functionally normal even in the continuing absence of ZO-1. Depletion of ZO-2, cingulin, or occludin, proteins that can interact with ZO-1, had no discernible effects on tight junctions. Rescue of junction assembly using murine ZO-1 mutants demonstrated that the ZO-1 C terminus is neither necessary nor sufficient for normal assembly. Moreover, mutation of the PDZ1 domain did not block rescue. However, point mutations in the Src homology 3 (SH3) domain almost completely prevented rescue. Surprisingly, the isolated SH3 domain of ZO-1 could also rescue junction assembly. These data reveal an unexpected function for the SH3 domain of ZO-1 in regulating tight junction assembly in epithelial cells and show that cingulin, occludin, or ZO-2 are not limiting for junction assembly in MDCK monolayers.