bluuebunny/crossref_metadata_2025 huggingface dataset:
Type II radio bursts and energetic solar eruptions
Authors: Gopalswamy N. , Aguilar‐Rodriguez E. , Yashiro S. , Nunes S. , Kaiser M. L. , Howard R. A.
Published: October 2005

We report on a study of type II radio bursts from the Wind/WAVES experiment in conjunction with white‐light coronal mass ejections (CME) from the Solar and Heliospheric Observatory (SOHO). The type II bursts considered here have emission components in all the spectral domains: metric, decameter‐hectometric (DH) and kilometric (km), so we refer to them as m‐to‐km type II bursts. CMEs associated with the m‐to‐km type II bursts were more energetic than those associated with bursts in any single wavelength regime. CMEs associated with type II bursts confined to the metric domain were more energetic (wider and faster) than the general population of CMEs but less energetic than CMEs associated with DH type II bursts. Thus the CME kinetic energy seems to organize the life time of the type II bursts. Contrary to previous results, the starting frequency of metric type II bursts with interplanetary counterparts seems to be no different from that of type II bursts without interplanetary counterparts. We also verified this by showing that the average CME height at the onset time of the type II bursts is the same for the two metric populations. The majority (78%) of the m‐to‐km type II bursts were associated with solar energetic particle (SEP) events. The solar sources of the small fraction of m‐to‐km type II bursts without SEP association were poorly connected to the observer near Earth. Finally, we found that the m‐to‐km type II bursts were associated with bigger flares compared to the purely metric type II bursts.
General circulation of the western subtropical North Atlantic observed using profiling floats
Authors: Kwon Young‐Oh , Riser Stephen C.
Published: October 2005

The general circulation of the subtropical western North Atlantic is described using hydrography and subsurface velocity measured simultaneously by 71 profiling floats during the period July 1997 to December 2002. Subsurface trajectories of the floats revealed a strong topographic influence and depth‐dependence of the Gulf Stream, its recirculation gyres, and the North Atlantic Current. We discuss eddy‐like and nonsteady flows in several subregions, especially near the major topographic features. The seasonal cycle of volume transport, estimated using the absolute geostrophic velocity in the upper 900 m, was shown to be a maximum in winter and minimum in summer. The eddy kinetic energy and eddy diffusivity, derived from the float data and mapped over the subtopical gyre, show seasonal variability in the vicinity of the Gulf Stream with a maximum in spring and minimum in winter for both quantities.
Seasonal variability of turbulence parameters at 2 to 21 km from MST radar measurements at Vandenberg Air Force Base, California
Authors: Nastrom G. D. , Eaton F. D.
Published: October 2005

Seasonal profiles of the turbulent kinetic energy, eddy dissipation rate, inner scale of turbulence, and vertical eddy diffusivity are presented from observations using the VHF Doppler profiling radar at Vandenberg (VBG) Air Force Base, California, over 4 calendar years from 2 to 21 km. Results are displayed seasonally both as a function of distance above the surface and relative to the tropopause. The VBG radar is located in the littoral region of southern California with a pronounced marine boundary layer; results are compared to those derived from other radars with similar performance located in different climatic regimes and terrain conditions. Turbulent kinetic energy values at VBG are between the higher values found at White Sands Missile Range (WSMR), New Mexico, which is located in a semiarid valley, and the site at Gadanki, India, except under Indian monsoon conditions. The same trend in general is found for the eddy dissipation rate for the same three sites although differences between the two U.S. sites are small. Inner scale profiles show the largest values at Gadanki and the smallest at WSMR with VBG estimates in the middle. Eddy diffusivity values at WSMR and VBG are in general slightly smaller than those found with the MU radar near Kyoto, Japan, but are greater than the values found in the stratosphere in Gadanki, India. All turbulence parameters show significant correlations with wind speed.
A New Pixel-Oriented Visualization Technique Through Color Image
Authors: Blanchard Frédéric , Herbin Michel , Lucas Laurent
Published: October 2005

Color image is often considered as a fundamental perceptual unit of visualization. In this paper, we suggest using this medium (color image) to summarize multidimensional data and thus to turn a data set into a meaningful insight. The methodology we use is based on the theory of Keim for designing pixel-oriented visualization techniques. The technique we propose consists in a three-step pipeline. The first one is devoted to dimensionality reduction by projecting multidimensional data into a three-dimensional space. In this work, we use the classical principal component analysis (PCA) to reduce the dimension to three. The second step, called color mapping, is based on the reverse color information transformation defined by Ohta et al. This stage is the main novelty of this work in addition to the pipeline itself. The third step consists in a pixel-oriented method to display large data sets with an image using space-filling curve techniques. The combination of these steps (first, dimensionality reduction with PCA, second, color mapping with color information of Ohta et al., and third, space-filling curve with Peano–Hilbert curve) allows us to obtain a new unsupervised visualization technique through color images. This blind (i.e. unsupervised) technique using a color image gives a previsualization that can be used before exploring the data set or choosing more effective colors. Some applications are proposed in the field of multicomponent image visualization.
Image Fusion Based on Topographic Mappings Using the Hyperbolic Space
Authors: Saalbach Axel , Ontrup Jörg , Ritter Helge , Nattkemper Tim W.
Published: October 2005

The analysis of multivariate image data is a field of research that is becoming increasingly important in a broad range of applications from remote sensing to medical imaging. While traditional scientific visualization techniques are often not suitable for the analysis of this kind of data, methods of image fusion have evolved as a promising approach for synergistic data integration. In this paper, a new approach for the analysis of multivariate image data by means of image fusion is presented, which employs topographic mapping techniques based on non-Euclidean geometry. The hyperbolic self-organizing map (HSOM) facilitates the exploration of high-dimensional data and provides an interface in the tradition of distortion-oriented presentation techniques. For the analysis of hidden patterns and spatial relationships, the HSOM gives rise to an intuitive and efficient framework for the dynamic visualization of multivariate image data by means of color. In an application, the hyperbolic data explorer (HyDE) is employed for the visualization of image data from dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Using 12 image sequences from breast cancer research, the method is introduced by different visual representations of the data and is also quantitatively analyzed. The HSOM is compared to different standard classifiers and evaluated with respect to topology preservation.
Correlated one-particle method: Numerical results
Authors: Beste Ariana , Bartlett Rodney J.
Published: October 2005

In a previous paper a correlated one-particle method was formulated, where the effective Hamiltonian was composed of the Fock operator and a correlation potential. The objective was to define a correlated one-particle theory that would give all properties that can be obtained from a one-particle theory. The Fock-space coupled-cluster method was used to construct the infinite-order correlation potential, which yields correct ionization potentials (IP’s) and electron affinities (EA’s) as the negative of the eigenvalues. The model, however, was largely independent of orbital choice. To exploit the degree of freedom of improving the orbitals, the Brillouin-Brueckner condition is imposed, which leads to an effective Brueckner Hamiltonian. To assess its numerical properties, the effective Brueckner Hamiltonian is approximated through second order in perturbation. Its eigenvalues are the negative of IP’s and EA’s correct through second order, and its eigenfunctions are second-order Brueckner orbitals. We also give expressions for its energy and density matrix. Different partitioning schemes of the Hamiltonian are used and the intruder state problem is discussed. The results for ionization potentials, electron affinities, dipole moments, energies, and potential curves are given for some sample molecules.
Improving the calculation of rovibrational spectra of five-atom molecules with three identical atoms by using a C3υ(G6) symmetry-adapted grid: Applied to CH3D and CHD3
Authors: Wang Xiao-Gang , Carrington Tucker
Published: October 2005

In this paper we report two improvements on the approach we have used to compute rovibrational levels of methane and apply the new ideas to calculate rovibrational levels of two methane isotopomers CH3D and CHD3. Both improvements make the bend calculation better. The first improvement is a G6-invariant (or C3υ-invariant) grid which is designed such that each point on the grid is mapped to another point on the grid by any of the G6 operations. The second improvement is the use of fast Fourier transform (FFT) to compute the bend potential matrix-vector products. The FFT matrix-vector product is about three and ten times faster than the previous sequential summation method for the J=0 and J>0 cases, respectively. The calculated J=1 rovibrational levels of CH3D and CHD3 on the Schwenke and Partridge [Spectrochim. Acta, Part A 57, 887 (2001)] ab initio potential are in good agreement (within 6cm−1 for the levels up to 3000cm−1) with the experimental data. The agreement is even better (within 0.1cm−1 for the levels up to 6000cm−1) if the associated J=0 energies are subtracted.
Continuity bounds on the quantum relative entropy
Authors: Audenaert Koenraad M. R. , Eisert Jens
Published: October 2005

The quantum relative entropy is frequently used as a distance, or distinguishability measure between two quantum states. In this article we study the relation between this measure and a number of other measures used for that purpose, including the trace norm distance. More specifically, we derive lower and upper bounds on the relative entropy in terms of various distance measures for the difference of the states based on unitarily invariant norms. The upper bounds can be considered as statements of continuity of the relative entropy distance in the sense of Fannes. We employ methods from optimisation theory to obtain bounds that are as sharp as possible.
A field theoretic derivation of the Max Born hypothesis
Authors: Ali Abdulmuhsen H.
Published: October 2005

It is shown in this article that the statistical character of the nonrelativistic, one particle quantum probabilities can be inferred from the function which results from the Wigner transformation on the field operator ψ̂†(x⃗) which, in turn, must be expressed in the occupation number representation. The function which results from the Wigner transformation is shown to be the state function of a single particle which is defined in the conventional quantum mechanics. The integral of the norm squared of that function is proven to be unity which is the step that proves the Max Born hypothesis. The compatibility of the expression for the field amplitude, obtained here, with the measurability of the Bosonic and the Fermionic fields is explained.
Transient cavities and the excess chemical potentials of hard-spheroid solutes in dipolar hard-sphere solvents
Authors: Camp Philip J.
Published: October 2005

Monte Carlo computer simulations are used to study transient cavities and the solvation of hard-spheroid solutes in dipolar hard-sphere solvents. The probability distribution of spheroidal cavities in the solvent is shown to be well described by a Gaussian function, and the variations of fit parameters with cavity elongation and solvent properties are analyzed. The excess chemical potentials of hard-spheroid solutes with aspect ratios x in the range of 1∕5⩽x⩽5, and with volumes between 1 and 20 times that of a solvent molecule, are presented. It is shown that for a given molecular volume and solvent dipole moment (or temperature) a spherical solute has the lowest excess chemical potential and hence the highest solubility, while a prolate solute with aspect ratio x should be more soluble than an oblate solute with aspect ratio 1∕x. For a given solute molecule, the excess chemical potential increases with increasing temperature; this same trend can be observed in hydrophobic solvation. A scaled-particle theory based on the solvent equation of state and a fitted solute-solvent interfacial tension shows excellent agreement with the simulation results over the whole range of solute elongations and volumes considered. An information-theoretic model based on the solvent density and radial distribution function is less successful, being accurate only for small solute volumes and low solvent densities.
High tunnel magnetoresistance in spin-polarized scanning tunneling microscopy of Co nanoparticles on Pt(111)
Authors: Rusponi S. , Weiss N. , Cren T. , Epple M. , Brune H.
Published: October 2005

We employ variable-temperature spin-polarized scanning tunneling microscopy in constant current mode to read the magnetic state of monodomain cobalt nanoparticles on Pt(111). In order to avoid stray fields we use in situ prepared antiferromagnetically (Cr) coated W tips. The contrast in apparent height between nanoparticles with opposite magnetization is typically Δz=0.20±0.05Å, but can reach up to 1.1Å, indicating 80% spin-polarization of the nanoparticles and 850% magnetoresistance of the tip-sample tunnel junction with tip and sample at 300K and 160K, respectively. There is no zero-bias anomaly. These results suggest state-selective tunneling which is expected to lead to very high magnetoresistance values.
Imaging hydrogenous materials with a neutron microscope
Authors: Cremer J. T. , Piestrup M. A. , Park H. , Gary C. K. , Pantell R. H. , Glinka C. J. , Barker J. G.
Published: October 2005

Magnified images of materials containing hydrogen, for which the main contrast mechanism for neutrons is incoherent scattering, have been obtained using a microscope employing a neutron compound refractive lens (CRL). The CRL was composed of 100 MgF2 biconcave lenses that produced magnified (22.5×) images of polyethylene and polypropylene (hydrogen-rich) grids and biological specimens using 8.5Å cold neutrons with a 10% bandwidth. For hydrogenous materials, 98%–99% of the attenuation is by incoherent scattering and 1%–2% from neutron absorption by the hydrogen nuclei. The small angle of acceptance of the CRL discriminates against scattered neutrons from the hydrogenous object, thereby producing the needed contrast for imaging.
In situ hole doping of wide-gap semiconductors by dual-target simultaneous laser ablation: GaN and SiC epitaxial films
Authors: Muto Hachizo , Asano Takashi , Wang Rong-Ping , Kusumori Takeshi
Published: October 2005

Apparatus for dual-target simultaneous laser ablation deposition and in situ doping techniques have been developed to achieve p-type doping during epitaxial growth of wide-band-gap semiconductors. The apparatus has two target holders with a target-rotation mechanism and a rotation-axis adjusting mechanism to obtain homogeneously doped films. Mg-doped GaN films have been fabricated on 6H–SiC(0001) and Si(111) substrates in NH3 ambient by simultaneous ablation of GaN and Mg-metal targets using two lasers. Junctions of the films with n-type substrates show a diode curve characteristic of p-n junctions, but not for junction with p-Si, indicating hole doping without further procedures. In situ p-type doping to SiC was also achieved by using SiC and Al4C3 targets.
Imaging of vortex states in mesoscopic superconductors
Authors: Karapetrov Goran , Fedor Jan , Iavarone Maria , Marshall M. T. , Divan R.
Published: October 2005

Enhanced vortex pinning in nanoscale-engineered superconductors increases the superconducting critical currents by orders of magnitude. Spatial imaging of vortices in these systems at high magnetic fields would provide further insight into the pinning mechanisms and enable development of high-pinning-strength materials. We have developed a novel method of fabricating atomically flat superconductor surfaces containing periodic array of normal metal pinning centers. Using scanning tunneling microscopy and spectroscopy, we map the local density of states in this heterostructure showing the vortex distribution at different applied magnetic fields. By increasing the applied magnetic field, the normal metal pinning centers accommodate several vortices per center until reaching the saturation point, beyond which new vortices get accommodated in the interstitial superconducting regions. The arrangement and pinning of the interstitial vortices is determined by the periodic pinning potential, and repulsive vortex-vortex interaction.
Photonic crystal waveguides with acute bending angles
Authors: Malkova Natalia , Ning C. Z.
Published: October 2005

We propose and study photonic crystal waveguides with bending angles smaller than 90°. The waveguide is formed by coupled defect cavities. To achieve a reflectionless transmission through an acute angle, we surround the defects in the bends with distorted cells having a prescribed symmetry. Detailed analysis and numerical simulation confirm that the transmission through the acute bend can be increased by two orders of magnitude to 100%.
Thermoelastic effect induced by ferroelastic domain switching
Authors: Cho Yong Chan , Park Sang Eon , Cho Chae-Ryong , Jeong Se-Young
Published: October 2005

Temperature changes induced by externally applied mechanical stress were observed in the Pb3(PO4)2 ferroelastic crystal. These characteristic features can be explained by the thermoelastic effect as in other thermoelastic martensitic materials. In this study, the mechanical stress dependence of the thermoelastic effect was studied using a modified thermomechanical analysis system. The thermoelastic effect strongly depended on the mechanical stress and was enhanced by ferroelastic domain switching, responsible for the pseudoelastic behavior of ferroelastic materials. The ∂T∕∂σsin, the change of sample temperature with varying stress enhanced by pseudoelasticity, was ∼9.5×10−2°C∕MPa at 159 °C, ferroelastic temperature region under 1.2 MPa sinusoidal stress. This value is eight to nine times higher than the values obtained under bias stress. This result can be explained by a thermoelastic equation which includes the effective thermal expansion coefficient in the ferroelastic phase.
Semiconductor gas sensor based on tin oxide nanorods prepared by plasma-enhanced chemical vapor deposition with postplasma treatment
Authors: Huang Hui , Tan O. K. , Lee Y. C. , Tran T. D. , Tse M. S. , Yao X.
Published: October 2005

SnO 2 thin films were deposited by radio-frequency inductively coupled plasma-enhanced chemical vapor deposition. Postplasma treatments were used to modify the microstructure of the as-deposited SnO2 thin films. Uniform nanorods with dimension of ∅7×100nm were observed in the plasma-treated films. After plasma treatments, the optimal operating temperature of the plasma-treated SnO2 thin films decreased by 80 °C, while the gas sensitivity increased eightfold. The enhanced gas sensing properties of the plasma-treated SnO2 thin film were believed to result from the large surface-to-volume ratio of the nanorods’ tiny grain size in the scale comparable to the space-charge length and its unique microstructure of SnO2 nanorods rooted in SnO2 thin films.
Effect of side shields on neighbor-induced transition shift in perpendicular magnetic recording
Authors: Kapoor Manish , Yoseph Sissay G. , Victora R. H.
Published: October 2005

The use of side shields is considered for the purpose of countering the neighbor-induced transition shift (NITS) in perpendicular magnetic recording. Two kinds of shield geometries are incorporated in the micromagnetic model. It is shown that, while the shields are ineffective against the worst case scenario, one shield design is highly effective in a less restrictive situation. It is further shown that the benefits (∼65% reduction of NITS) only occur over a restricted range of shield saturation magnetization (Ms). Optimal shield Ms is found to be in the range of 500–800emu∕cc.
Semimetal-semiconductor rectifiers for sensitive room-temperature microwave detectors
Authors: Young A. C. , Zimmerman J. D. , Brown E. R. , Gossard A. C.
Published: October 2005

In contrast to traditional metal-semiconductor (i.e., Schottky) junctions, ErAs:InAlGaAs heterojunctions have recently been shown to provide highly “engineerable” electrical rectification characteristics through the tuning of the Schottky barrier height and differential resistance, while maintaining the very low specific capacitance for which Schottky diodes are famous. We demonstrate that these new rectifiers can operate effectively at zero bias and can be extremely sensitive at microwave frequencies. We report a tangential sensitivity of −63dBm at 3.1 GHz in an 8.0 KHz bandwidth, corresponding to a noise-equivalent power (NEP) of 8.9×10−13W∕Hz1∕2. We attribute this noise performance to the high rf-to-dc current responsivity (∼8A∕W), zero bias operation, and noise source reduction. The new diodes are found to be ∼19dB more sensitive than the best available Hewlett–Packard zero-bias diodes at comparable frequencies.
Different cell surface oligomeric states of B7-1 and B7-2: Implications for signaling
Authors: Bhatia Sumeena , Edidin Michael , Almo Steven C. , Nathenson Stanley G.
Published: October 2005

The costimulatory ligands B7-1 and B7-2 are expressed on the surface of antigen-presenting cells and interact with the costimulatory receptors CD28 and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) expressed on T cells. Although B7-1 and B7-2 are homologous ligands having common receptors, they exhibit distinct biochemical features and roles in immune regulation. Several biochemical and structural studies have indicated differences in the oligomeric state of B7-1 and B7-2. However, the organization of B7 ligands on the cell surface has not been examined. By using photobleaching-based FRET (pbFRET), we demonstrate that B7-1 and B7-2 adopt different oligomeric states on the cell surface. Our study shows that B7-2 exists as a monomer on the cell surface whereas B7-1 exists predominantly as dimers on the cell surface. A series of mutations in B7-1 result in the expression of a predominantly monomeric species on the cell surface and validate the dimer interface proposed by prior crystallographic analysis. The difference in the oligomeric states of B7-1 and B7-2 provides insight into the geometric organization of the costimulatory receptor–ligand complexes in the immunological synapse and suggests constraints on signal transduction mechanisms involved in T cell activation.
Single-molecule Förster resonance energy transfer study of protein dynamics under denaturing conditions
Authors: Kuzmenkina Elza V. , Heyes Colin D. , Nienhaus G. Ulrich
Published: October 2005

Proteins are highly complex systems, exhibiting a substantial degree of structural variability in their folded state. In the presence of denaturants, the heterogeneity is greatly enhanced, and fluctuations among vast numbers of folded and unfolded conformations occur via many different pathways. Here, we have studied the structure and dynamics of the small enzyme ribonuclease HI (RNase H) in the presence of the chemical denaturant guanidinium chloride (GdmCl) using single-molecule fluorescence microscopy, with a particular focus on the characterization of the unfolded-state ensemble. A dye pair was specifically attached to the enzyme to measure structural changes through Förster resonance energy transfer (FRET). Enzyme immobilization on star-polymer surfaces that were specially developed for negligible interaction with folded and unfolded proteins enabled us to monitor conformational changes of individual proteins for several hundred seconds. FRET efficiency histograms were calculated from confocal scan images. They showed an expansion of the unfolded proteins with increasing GdmCl concentration. Cross-correlation analysis of donor and acceptor fluorescence intensity time traces from single molecules revealed reconfiguration of the polypeptide chain on a timescale of ≈20 μs at 1.7 M GdmCl. Slow conformational dynamics gave rise to characteristic, stepwise FRET efficiency changes. Transitions between folded and unfolded enzyme molecules occurred on the 100-s timescale, in excellent agreement with bulk denaturation experiments. Transitions between unfolded conformations were more frequent, with characteristic times of ≈2 s. These data were analyzed to obtain information on the free energy landscape of RNase H in the presence of chemical denaturants.
Partner Choice during Meiosis Is Regulated by Hop1-promoted Dimerization of Mek1
Authors: Niu Hengyao , Wan Lihong , Baumgartner Bridget , Schaefer Dana , Loidl Josef , Hollingsworth Nancy M.
Published: October 2005

Meiotic recombination differs from mitotic recombination in that DSBs are repaired using homologous chromosomes, rather than sister chromatids. This change in partner choice is due in part to a barrier to sister chromatid repair (BSCR) created by the meiosis-specific kinase, Mek1, in a complex with two other meiosis-specific proteins, Hop1 and Red1. HOP1 contains two functional domains, called the N and C domains. Analysis of a point mutation that specifically inactivates the C domain (hop1-K593A) reveals that the N domain is sufficient for Hop1 localization to chromosomes and for Red1 and Hop1 interactions. The C domain is needed for spore viability, for chromosome synapsis, and for preventing DMC1-independent DSB repair, indicating it plays a role in the BSCR. All of the hop1-K593A phenotypes can be bypassed by fusion of ectopic dimerization domains to Mek1, suggesting that the function of the C domain is to promote Mek1 dimerization. Hop1 is a DSB-dependent phosphoprotein, whose phosphorylation requires the presence of the C domain, but is independent of MEK1. These results suggest a model in which Hop1 phosphorylation in response to DSBs triggers dimerization of Mek1 via the Hop1 C domain, thereby enabling Mek1 to phosphorylate target proteins that prevent repair of DSBs by sister chromatids.
Phosphatidylinositol 4,5-Bisphosphate Anchors Cytosolic Group IVA Phospholipase A2to Perinuclear Membranes and Decreases Its Calcium Requirement for Translocation in Live Cells
Authors: Casas Javier , Gijón Miguel A. , Vigo Ana G. , Crespo Mariano Sánchez , Balsinde Jesús , Balboa María A.
Published: October 2005

The eicosanoids are centrally involved in the onset and resolution of inflammatory processes. A key enzyme in eicosanoid biosynthesis during inflammation is group IVA phospholipase A2(also known as cytosolic phospholipase A2α, cPLA2α). This enzyme is responsible for generating free arachidonic acid from membrane phospholipids. cPLA2α translocates to perinuclear membranes shortly after cell activation, in a process that is governed by the increased availability of intracellular Ca2+. However, cPLA2α also catalyzes membrane phospholipid hydrolysis in response to agonists that do not mobilize intracellular Ca2+. How cPLA2α interacts with membranes under these conditions is a major, still unresolved issue. Here, we report that phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] promotes translocation of cPLA2α to perinuclear membranes of intact cells in a manner that is independent of rises in the intracellular Ca2+concentration. PtdIns(4,5)P2anchors the enzyme to perinuclear membranes and allows for a proper interaction with its phospholipid substrate to release arachidonic acid.
The Nuclear RNA-binding Protein Sam68 Translocates to the Cytoplasm and Associates with the Polysomes in Mouse Spermatocytes
Authors: Paronetto Maria Paola , Zalfa Francesca , Botti Flavia , Geremia Raffaele , Bagni Claudia , Sette Claudio
Published: October 2005

Translational control plays a crucial role during gametogenesis in organisms as different as worms and mammals. Mouse knockout models have highlighted the essential function of many RNA-binding proteins during spermatogenesis. Herein we have investigated the expression and function during mammalian male meiosis of Sam68, an RNA-binding protein implicated in several aspects of RNA metabolism. Sam68 expression and localization within the cells is stage specific: it is expressed in the nucleus of spermatogonia, it disappears at the onset of meiosis (leptotene/zygotene stages), and it accumulates again in the nucleus of pachytene spermatocytes and round spermatids. During the meiotic divisions, Sam68 translocates to the cytoplasm where it is found associated with the polysomes. Translocation correlates with serine/threonine phosphorylation and it is blocked by inhibitors of the mitogen activated protein kinases ERK1/2 and of the maturation promoting factor cyclinB-cdc2 complex. Both kinases associate with Sam68 in pachytene spermatocytes and phosphorylate the regulatory regions upstream and downstream of the Sam68 RNA-binding motif. Molecular cloning of the mRNAs associated with Sam68 in mouse spermatocytes reveals a subset of genes that might be posttranscriptionally regulated by this RNA-binding protein during spermatogenesis. We also demonstrate that Sam68 shuttles between the nucleus and the cytoplasm in secondary spermatocytes, suggesting that it may promote translation of specific RNA targets during the meiotic divisions.
UXT Is a Novel Centrosomal Protein Essential for Cell Viability
Authors: Zhao Huiwu , Wang Qiang , Zhang Hongtao , Liu Qingdu , Du Xiulian , Richter Mark , Greene Mark I.
Published: October 2005

Ubiquitously expressed transcript (UXT) is a prefoldinlike protein that has been suggested to be involved in human tumorigenesis. Here, we have found that UXT is overexpressed in a number of human tumor tissues but not in the matching normal tissues. We demonstrate that UXT is located in human centrosomes and is associated with γ-tubulin. In addition, overexpression of UXT disrupts centrosome structure. Furthermore, abrogation of UXT protein expression by small interfering RNA knockdown leads to cell death. Together, our findings suggest that UXT is a component of centrosome and is essential for cell viability. We propose that UXT may facilitate transformation by corrupting regulated centrosome functions.
FIVE YEARS OF SINGLE EUROPEAN MONETARY POLICY IN PRACTICE: IS THE ECB RULE‐BASED?
Authors: FENDEL RALF M. , FRENKEL MICHAEL R.
Published: October 2005

The article discusses the conduct of monetary policy of the ECB during its first five years. The authors estimate different versions of the forward‐looking policy rule proposed by Clarida et al. (1998, 2000). The results suggest that the ECB applied indeed a Taylor‐type rule to its monetary policy. The implied inflation targets that are extracted from the regressions are close to the range of the target that the ECB announced. (JEL E52,E58,F4)
THE EFFECTS OF STATUTORY RAPE LAWS ON NONMARITAL TEENAGE CHILDBEARING
Authors: JEPSEN CHRISTOPHER A. , JEPSEN LISA K.
Published: October 2005

Many policy makers view the enforcement of statutory rape laws as a way to reduce teenage childbirths. This article considers whether unmarried teenage girls covered by a state statutory rape law are less likely to give birth than girls who are not covered by a statutory rape law. The presence of statutory rape laws is negatively correlated with nonmarital birthrates for white females but is not a significant predictor for black or Hispanic females. In contrast, the enforcement of statutory rape laws has a deterrent effect on teen childbearing for blacks and Hispanics but not for whites. (JEL J13,K14)
Optimum Microstructure of Transformation‐Toughened Ceramics for Enhanced Wear Performance
Authors: Thomsen Niels B. , Karihaloo Bhushan L.
Published: October 2005

The poor rolling/sliding wear performance of transformation‐toughened ceramics such as partially stabilized zirconia (PSZ) is believed to be a result of the phase transformation of precipitates located immediately beneath the contacting surface. These very precipitates, on the other hand, enhance the toughness of the ceramic by preventing the growth of surface cracks. In order to find a compromise solution, an optimization problem is formulated for an idealized model consisting of an edge crack normal to the contacting surface and a periodic distribution of transformable grains in the layer immediately beneath this surface. The objective is to maximize the crack tip shielding by varying the volume fraction and size of the layer without exceeding a prescribed allowable surface uplift. It is shown that maximum volume fraction is attained at a certain depth below the surface but that its magnitude is considerably smaller than that pertaining in peak‐aged PSZ.
X‐ray Diffraction and Chemical Characterization of the Plastic Colloid Fraction of Chinastone
Authors: Lehman Richard L. , Greenhut Victor A. , Gao Lingxiang
Published: October 2005

The fine particle size fraction from a South China china‐stone material used in porcelains and renowned for its plasticity was characterized to determine the chemical and crystallographic structure of the <2 μm fraction. Chemical analysis suggested the presence of a chloritic material in the fine fraction, a premise which was supported by X‐ray diffraction and thermal analysis. The chinastone has a well‐defined 1.4‐nm basal spacing which did not expand when subjected to ethylene glycol. However, the (001) reflections produced an anomalous broadening and decrease in spacing to 1.28 nm when heated to 700°C. The X‐ray patterns and chemical composition are similar to those at an aluminum‐treated montmorillonite which contains condensed gibbsite interlayered between montmorillonite units. Chemical analysis of individual particles plus X‐ray and thermal analysis leads to the conclusion that the fine fraction of the chinastone is an alumina‐rich chlorite with unusually low iron and magnesium levels.
Kinetics and Mechanisms for Nitridation of Floating Aluminum Powder
Authors: Chang An‐jae , Rhee Shi‐Woo , Baik Sunggi
Published: October 2005

Aluminum powder entrained by ammonia‐containing nitrogen gas was reacted at various temperatures and time to form aluminum nitride powder. The kinetics of nitride formation were determined by a quantitative X‐ray analysis and compared with those determined by a nitrogen analysis of the product. The conversion to aluminum nitride increased with the reaction time following a sigmoidal rate law. The reaction time for full conversion decreased as the temperature increased in the range 1050°–1300°C. The reaction rate constant at a given temperature was evaluated using the Avrami equation. The activation energy for the reaction was 1054 ± 91 kJ/mol in the temperature range of 1050°–1200°C, and decreased to 322 ± 70 kJ/mol above 1200°C. Comparative analysis of powders formed below and above 1200°C suggested strongly that the rate‐controlling step changed from chemical reaction to mass transport above 1200°C.
Powder Processing for the Fabrication of Si3N4 Ceramics: I, Influence of Spray‐Dried Granule Strength on Pore Size Distribution in Green Compacts
Authors: Kamiya Hidehiro , Isomura Kenji , Jimbo Genji , Jun‐ichiro Tsubaki
Published: October 2005

The effect of spray‐dried granule strength on the micro‐structure of green compacts obtained by isostatic pressing was quantitatively analyzed. The fracture strength of single granules of Si3N4 powder made with ultrafine A12O3 and Y2O3 powders was measured directly by diametral compression. It was found that fracture strength increased notably with the increasing relative density of the granule and the decreasing size of agglomerates in suspension before spray‐drying. Even when green bodies were prepared at an isostatic pressure of 200 MPa, intergranular pores, which negatively affected densification of the sintered bodies, occurred between unfractured granules. The volume and size of these pores in the green compacts increased with the increasing fracture strength of the granules. In the case of closely packed granules, an isostatic pressure of 800 MPa was required to completely collapse the intergranular pores. A simple equation was derived to calculate the isostatic pressure necessary for complete collapse of intergranular pores in the green compacts, and it was determined that granule strength must be kept as low as possible to obtain uniform green compacts.
Coating of Carbon Fibers—The Strength of the Fibers
Authors: Helmer Thomas , Peterlik Herwig , Kromp Karl
Published: October 2005

The 6k carbon fiber Torayca T800H was coated with pyrolytic carbon by a CVD process. Fiber bundles were tested and evaluated. By this procedure, the whole distribution of the failure probability with respect to the fiber strength is obtained in a single experiment. The 50% strength of the fiber bundle, i.e., the strength at which 50% of the fibers in the bundle are broken, is inversely proportional to the square root of the thickness of the coating. By relating the strength to the defect size according to linear‐elastic fracture mechanics (LEFM), the probability density function of the defects was derived. It is Weibull‐shaped for the uncoated fiber and shows an increasing bimodal shape for the increasing coating thicknesses.
Nucleation and Growth of Inversion Domains in AIN: Part I, Study of Fundamental Processes
Authors: Berger Axel
Published: October 2005

Inversion domains (IDs) are frequently observed in sintered AIN ceramics. In the present study, different stages of ID formation and growth were analyzed by transmission electron microscopy. A model was derived to describe the mechanisms of ID nucleation, growth, and interaction with dislocations. Accordingly, IDs are nucleated by wide inverted dislocation dissociations. Preexisting dislocations interact with moving ID boundaries (IDBs) by a mechanism of dissociation and integration into the IDE. The defect structures at IDBs are characterized by the inversion, a translation R = 1/3(1100) corresponding to Shockley partials, and a translation R = w·[0001] perpendicular to the basal plane. The results are fundamental for further experiments of artificial generation or annihilation of IDs.
Processing and Properties of Particulate Composites from Coated Powders
Authors: Mitchell Tyrone D. , De Jonghe Lutgard C.
Published: October 2005

A method is described for sintering of highly loaded (≤20 vol%) alumina matrix/silicon carbide whisker or platelet composites to closed porosity. The method uses controlled heterogeneous precipitation in a suspension of whiskers or platelets. The suspension‐coated particles are calcined to produce a free‐flowing composite powder which can be hot‐pressed or free‐sintered to high density. The results of consolidation and mechanical property testing are reported.
Fabrication of Polycrystal line, Transparent YAG Ceramics by a Solid‐State Reaction Method
Authors: Ikesue Akio , Furusato Isao , Kamata Kiichiro
Published: October 2005

Polycrystalline, transparent YAG (Y3AI5O12) ceramics were fabricated by a solid‐state reaction method using high‐purity Al2O3 and Y2O3 powders. The mixed powder compacts were sintered at 1600° to 1850°C for 5 h under vacuum. Optical transmittance in the region between the ultraviolet and infrared wavelengths for YAG ceramics (1 mm thick) sintered at 1800°C was similar to that for a YAG single crystal.
Effect of Tungsten and Molybdenum Doping on the Semiconductor–Metallic Transition in Vanadium Dioxide Produced by Evaporative Decomposition of Solutions and Hydrogen Reduction
Authors: Lawton Stanley A. , Theby Edward A.
Published: October 2005

V1–xWxO2 and V1–xMoxO2, 0 < x < 0.03, powders have been produced by the evaporative decomposition of solutions of vanadyl sulfate hydrate with tungsten dioxide dichloride or molybdenum dioxide dichloride in a hydrogen/nitrogen atmosphere. The powders consist primarily of hollow, porous, spherical shells. Differential scanning calorimetric analysis of the powders indicates that the 67°C mono‐clinic‐tetragonal phase transition in VO2 shifts to lower temperatures by 23°C/(at.% tungsten) and 6.3°C/(at.% molybdenum).
Use of Succinic Acid to Test the Stability of PTCR Barium Titanate Ceramics under Reducing Conditions
Authors: Sinclair Derek C. , West Anthony R.
Published: October 2005

On heating positive temperature coefficient of resistance (PTCR) BaTiO3 ceramics at 350°C in succinic acid powder, a reducing atmosphere is created as the succinic acid pyrolyzes. Grain boundary resistances, which may give a PTCR effect, are reduced by this treatment, whereas surface layer resistances, which may also give a PTCR effect, are much less affected.
Preparation of Porous Ceramics with Calcium Metaphosphate Fiber Skeleton for Biomedical Use
Authors: Kasuga Ihiro , Inoue Tatsuya , Tsuji Kenji , Ota Yoshio , Abe Yoshihiro
Published: October 2005

High‐strength calcium metaphosphate fibers for biomedical applications are extracted from crystallized products of calcium ultraphosphate glasses by aqueous leaching. In the present work, new types of porous ceramics with a skeleton composed of the crystalline fibers are prepared by heating the fibrous products extracted. The fibers in the ceramic are interlinked to each other by glassy phases formed during the heating. This porous material has a large porosity of >60%. The surface of the skeleton can be successfully converted into new calcium phosphate phases such as apatite by heating the porous material treated with a molten salt mixture of CaCl2‐Ca(NO3)2.
Oxidation and Temperature Effects on the Interfacial Shear Strength in SCS‐6 Fiber‐Reinforced Reaction‐Bonded Silicon Nitride
Authors: Guermazi Mohamed
Published: October 2005

The fiber/matrix interfacial shear strength of Textron SCS‐6 SiC‐fiber‐reinforced reaction‐bonded Si3N4 (RBSN) was studied as a function of temperature after oxidation for 24 h at 600°C. Fiber push‐out experiments were conducted using a diamond indenter in a high‐temperature micro‐hardness tester under vacuum. The interfacial shear strength increased with temperature because of the relief of residual tensile stresses arising from the difference in thermal expansion coefficients between the fiber and the matrix. Most of sublayer 2 of the fiber outer coating, which mainly consisted of carbon in the form of BSU (basic structure unit) aggregates, had disappeared after the heat treatment of the composite. Oxidation resulted in severe changes in the fiber outer coating and caused a lower interfacial shear strength with respect to that of the unoxidized composite.
Structure of Zirconia Prepared by Homogeneous Precipitation
Authors: Déchamps Michel , Djuriçić Boro , Pickering Stephen
Published: October 2005

The structure of pure zirconia powders prepared by homogeneous precipitation was examined by electron microscopy. Some of these powders consisted of metastable tetragonal zirconia in the form of spherical aggregates up to 1 μm in diameter. The size of single crystals within these particles exceeded 100 nm, which is much larger than usually reported for metastable zirconia. We conclude that the existence of these large teragonal monocrystals is due principally to the very fine internal porosity within the domains, which gave rise to a surface area/volume ratio sufficient to stabilize tetragonal zirconia by the same mechanism as in nanocrystalline powders.
Scanning Acoustic Microscopy of Indentation Damage in Y2O3‐Stabilized Tetragonal Zirconia
Authors: Suganuma Motohiro
Published: October 2005

Scanning acoustic microscopy (SAM) has been applied to investigate Vickers indentation‐induced damage in Y2O3‐stabilized tetragonal zirconia polycrystal (Y‐TZP). The leaky Rayleigh wave velocity, vR, around the indentation is determined from the V(Z) curve technique. A considerable anisotropy in vR is observed within the elastic/plastic zone which results from the indentation‐induced residual stresses. In contreast, an isotropic reduction in vR is found within the indentation core, implying the presence of microcracks. Furthermore, the SAM observations reveal that the elasic/plastic boundary is axisymmetric with respect to the loading axis and that its radius is 1.2 times as large as the indentation half‐diagonal. These results are discussed in terms of an analysis based on the pressurized‐sphericalcavity model.
Wetting in an Electronic Packaging Ceramic System: II, Wetting of Alumina by a Silicate Glass Melt under Controlled pO2 Conditions
Authors: Weirauch Douglas A. , Lazaroff Jerold E. , Ownby P. Darrell
Published: October 2005

The wetting of polycrystalline alumina by a colored, calciamagnesia aluminosilicae glass was found to be dependent on temperatutre between 1300° and 1500°C, but independent of gas atmosphere effects. Neither the oxygen partial pressure, oveer the range of 10‐6 to 10‐10 Pa, the gas buffer system (Co/CO2 or H2/H2O), nor pre‐equilibration of the substrate surface with the atmosphere at tge exoperimental temperature before solid‐liuid interface formation affected the stable contact angle. An initial drop in contact angle the stable contact angle. An initial drop in contact angle occurring within the first hour is attributed to repaid dissolution of alumina and the formation of a stable glass/alumina interface. The contact angle after an 8‐h isothermal hold decreased from 1300° to 1500°C. The solid‐liquid interfacial energy, μMS1, controls the wetting behavior. Changes in μMs1 are attributed to he breakup of the silica network as temperature increases.
27Al and 29Si MAS NMR Study of Kaolinite Thermal Decomposition by Controlled Rate Thermal Analysis
Authors: Massiot Dominique , Dion Pascal , Alcover Jean Fran¸ois , Bergaya Faiza
Published: October 2005

The processing of kaolinite under controlled rate thermal analysis conditions (CRTA) provides homogeneously transformed samples at defined dehydroxylation rates. The kaolinite‐to‐metakaolinite transformation has been monitored by solid‐state NMR and X‐ray diffraction. The metakaolinite product is an amorphous material with no resolved XRD pattern and is based on a disordered polymerized silicon/aluminum network in which aluminum preferably occupies four‐ and five‐fold structural positions in the ratio 60% AlVI, 30% AlV, and 10% AlVI. This complex dehydroxylation process has been viewed at different scales, with the aluminum NMR tracing a site‐by‐site destructon of the octahedral sheet and the silicon NMR and XRD following a more rapid destruction of the longrange order.
Overview of Fine‐Scale Piezoelectric Ceramic/Polymer Composite Processing
Authors: Janas Victor F. , Safari Ahmad
Published: October 2005

In the past two decades, piezoelectric ceramic/polymer composites with different connectivities have been developed for transducer applications such as hydrophones, biomedical imaging, nondestructive testing, and air imaging. Recently, much attention has been given to fine‐scale piezoelectric ceramic/polymer composites. These composites allow higher operating frequencies, and thus increased resolution, in medical imaging transducers. In this review, methods for processing fine‐scale piezoelectric ceramic/polymer composites are discussed. The current capabilities, strengths, and weaknesses of each method are compared. The importance of spatial scale in composite performance is also reviewed. Several of the processing methods have demonstrated composites with fine‐scale ceramic phases (<50 μm), and others have potential to form composites with a ceramic scale of under 20 μm.