bluuebunny/crossref_metadata_2025 huggingface dataset:
Field observations of basal forces and fluid pore pressure in a debris flow
Authors: McArdell Brian W. , Bartelt Perry , Kowalski Julia
Published: April 2007

Using results from an 8 m2 instrumented force plate we describe field measurements of normal and shear stresses, and fluid pore pressure for a debris flow. The flow depth increased from 0.1 to 1 m within the first 12 s of flow front arrival, remained relatively constant until 100 s, and then gradually decreased to 0.5 m by 600 s. Normal and shear stresses and pore fluid pressure varied in‐phase with the flow depth. Calculated bulk densities are ρb = 2000–2250 kg m−3 for the bulk flow and ρf = 1600–1750 kg m−3 for the fluid phase. The ratio of effective normal stress to shear stress yields a Coulomb basal friction angle of ϕ = 26° at the flow front. We did not find a strong correlation between the degree of agitation in the flow, estimated using the signal from a geophone on the force plate, and an assumed dynamic pore fluid pressure. Our data support the idea that excess pore‐fluid pressures are long lived in debris flows and therefore contribute to their unusual mobility.
North Atlantic–Arctic Mediterranean exchanges in an ensemble hindcast experiment
Authors: Olsen Steffen Malskær , Schmith Torben
Published: April 2007

An ensemble‐hindcast approach is designed to simulate North Atlantic circulation changes during the period 1948–2005 using the Max Plank Institute Ocean Model forced by atmospheric reanalysis data. The experiment seeks to isolate oceanic changes related to the atmospheric forcing history by evaluating the role of initial conditions and masking internal model variability in the ensemble mean results. Characteristics of the complete North Atlantic–Arctic Mediterranean exchange system is described at key sections by time series of exchanges of volume, ice, heat, and liquid freshwater. Volume transports are divided into water masses by properties, and the constructed climatology of exchanges is shown to compare well with available observational estimates of individual branches. In response to the atmospheric forcing history, we find a modest but robust decline of the Atlantic meridional overturning circulation of 0.4 Sv/decade, in total 2–2.5 Sv since 1948. In contrast, overturning exchanges with the North Atlantic and Nordic Seas and with the Nordic Seas and Arctic Ocean show no sign of cessation. A marked increase in the freshwater storage of the Nordic Seas and in particular of the subpolar Atlantic accompany the model decline in Atlantic overturning. The characteristics of the modeled freshening bears similarities with observed patterns of change since the 1950s, but whereas the origin of observed freshening is uncertain, freshening in the model predominantly results from dynamic changes linked to prominent changes in atmospheric circulation. Moreover, documented increase in the drainage of major Arctic‐rivers is found to have a negligible effect on the oceanic changes.
B/Ca in planktonic foraminifera as a proxy for surface seawater pH
Authors: Yu Jimin , Elderfield Henry , Hönisch Bärbel
Published: April 2007

Boron isotope systematics indicate that boron incorporation into foraminiferal CaCO3 is determined by the partition coefficient, KD (= ), and [B(OH)4−/HCO3−]seawater, providing, in principle, a method to estimate seawater pH and PCO2. We have measured B/Ca ratios in Globigerina bulloides and Globorotaliainflata for a series of core tops from the North Atlantic and the Southern Ocean and in Globigerinoides ruber (white) from Ocean Drilling Program (ODP) site 668B on the Sierra Leone Rise in the eastern equatorial Atlantic. B/Ca ratios in these species of planktonic foraminifera seem unaffected by dissolution on the seafloor. KD shows a strong species‐specific dependence on calcification temperature, which can be corrected for using the Mg/Ca temperature proxy. A preliminary study of G. inflata from Southern Ocean sediment core CHAT 16K suggests that temperature‐corrected B/Ca was ∼30% higher during the last glacial. Correspondingly, pH was 0.15 units higher and aqueous PCO2 was 95 μatm lower at this site at the Last Glacial Maximum. The covariation between reconstructed PCO2 and the atmospheric pCO2 from the Vostok ice core demonstrates the feasibility of using B/Ca in planktonic foraminifera for reconstructing past variations in pH and PCO2.
Hydrometeorological application of a microwave link: 1. Evaporation
Authors: Leijnse H. , Uijlenhoet R. , Stricker J. N. M.
Published: April 2007

A method to estimate areal evaporation using a microwave link (radio wave scintillometer) in combination with an energy budget constraint is proposed. This radio wave scintillometry‐energy budget method (RWS‐EBM) is evaluated for its applicability in different meteorological conditions and for its sensitivity to various variables (the structure parameter of the refractive index of air Cn2, the total available energy Rn − G, the wind velocity u, the effective average vegetation height h0, and the correlation coefficient between the temperature and humidity fluctuations rTQ). The method is shown to be best suited for use in wet to moderately dry conditions, where the latent heat flux is at least a third of the total available energy (i.e., Bowen ratio ≤2). It is important to accurately measure the total available energy and the wind velocity as the RWS‐EBM is most sensitive to these variables. The Flevoland field experiment has provided the data, obtained with a 27‐GHz radio wave scintillometer (over 2.2 km), a large‐aperture scintillometer (also 2.2 km), and four eddy covariance systems, which are used to test the RWS‐EBM. Comparing 92 daytime measurements (30‐min intervals) of the evaporation estimated using the RWS‐EBM to that determined in alternative manners (eddy covariance and two‐wavelength scintillometry) leads to the conclusion that the method provides consistent estimates (coefficient of determination r2 = 0.85 in both cases) under relatively wet conditions.
Transient Cooling during Early Reperfusion Attenuates Delayed Edema and Infarct Progression in the Spontaneously Hypertensive Rat. Distribution and Time Course of Regional Brain Temperature Change in a Model of Postischemic Hypothermic Protection
Authors: Kurasako Toshiaki , Zhao Liang , Pulsinelli William A , Nowak Thaddeus S
Published: April 2007

The temperature threshold for protection by brief postischemic cooling was evaluated in a model of transient focal ischemia in the Spontaneously Hypertensive Rat, using an array of epidural probes to monitor regional brain temperatures. Rats were subjected to 90 mins tandem occlusion of the right middle cerebral artery (MCA) and common carotid artery. Systemic cooling to 32°C was initiated 5 mins before recirculation, with simultaneous brain cooling to temperatures ranging from 28°C to 32°C within the MCA territory by means of a temperature-controlled saline drip. Rewarming was initiated at 2 h recirculation and was complete within 30 mins. Tissue damage and edema volume showed clear temperature-dependent reductions when evaluated at 3 days survival, with no protection evident in the group at 32°C but progressive effects on both parameters after deeper cooling. A particularly striking effect was the essentially complete elimination of edema progression between 1 and 3 days. Temperature at distal sites within the MCA territory better predicted reductions in lesion volume, indicating that protection required effective cooling of the penumbral regions destined to be spared. These results show that even brief cooling can be highly protective when initiated at the time of recirculation after focal ischemia, but indicate a substantially lower temperature threshold for hypothermic protection than has been reported for other strains, occlusion methods, and cooling durations.
Three-dimensional modeling of the sawtooth instability in a small tokamak
Authors: Breslau J. A. , Jardin S. C. , Park W.
Published: April 2007

The sawtooth instability is one of the most fundamental dynamics of an inductive tokamak discharge such as will occur in ITER [R. Aymar et al., Plasma Phys. Controlled Fusion 44, 519 (2002)]. Sawtooth behavior is complex and remains incompletely explained. The Center for Extended MHD Modeling (CEMM) SciDAC project has undertaken an ambitious campaign to model this periodic motion in a small tokamak as accurately as possible using the extended MHD model. Both M3D [W. Park et al., Phys. Plasmas 6, 1796 (1999)] and NIMROD [C. R. Sovinec et al., Phys. Plasmas 10, 1727 (2003)] have been applied to this problem. Preliminary nonlinear MHD results show pronounced stochasticity in the magnetic field following the sawtooth crash but are not yet fully converged. Compared to the MHD model, extended MHD predicts plasma rotation, faster reconnection, and reduced field line stochasticity in the crash aftermath. The multiple time and space scales associated with the reconnection layer and growth time make this an extremely challenging computational problem. However, these calculations are providing useful guidelines to the numerical and physical requirements for more rigorous future studies.
80% tunneling magnetoresistance at room temperature for thin Al–O barrier magnetic tunnel junction with CoFeB as free and reference layers
Authors: Wei H. X. , Qin Q. H. , Ma M. , Sharif R. , Han X. F.
Published: April 2007

Magnetic tunnel junctions (MTJs) with structures of Ta(5)∕Cu(10)∕Ta(5)∕Ir21Mn79(10)∕Co75Fe25(2)∕Ru(0.75)∕Co40Fe40B20(3)∕Al(0.6)–O∕Co40Fe40B20(2.5)∕Ta(3)∕Ru(7) (units in nanometers) were deposited via ultrahigh vacuum magnetron sputtering (ULVAC). Microscale ring-type magnetic tunnel junctions (RMTJs) with an outer radius of 2μm and an inner radius of 1μm were patterned using standard UV lithography combined with ion milling. Both reference and free layers were Co40Fe40B20 and a very thin Al–O (0.6nm) barrier layer was used. Tunneling magnetoresistances (TMRs) of up to 81% at room temperature and 107% at 4.2K were observed. These RMTJs with high TMR and low coercivity, of about 26Oe, combined with the ring-type geometry, which greatly reduces stray magnetic field, are ideal for certain magnetic field sensor applications.
Effect of magnetic nanoparticles to NMR and nuclear spin relaxation in liquid and solid hosts
Authors: Noginova N. , Weaver T. , King M. , Bourlinos A. B. , Giannelis E. P. , Atsarkin V. A.
Published: April 2007

The H1 NMR spectra and spin dynamics of the host system in liquid and solid suspensions of γ-Fe2O3 nanoparticles are reported. Significant line broadening of H1 NMR spectra and growing relaxation rates were observed with increased concentration of nanoparticles in liquid systems, with the relation T1∕T2 depending on the particular host. Solid systems demonstrate inhomogeneous broadening of the spectra depending on the nanoparticle concentration and practically no dependence of T1 upon the nanoparticle concentration. In variable temperature experiments, significant increase in the relaxation rates was observed in the liquid systems. The experimental results are explained in terms of the self-diffusion as a predominating source of the spin-lattice relaxation. The effective radius of relaxation in the systems in study is estimated.
Ab initio calculation of the electronic structures of the Φ3 ground and Φ5 excited states of CoH
Authors: Tomonari Mutsumi , Okuda Rei , Nagashima Umpei , Tanaka Kiyoshi , Hirano Tsuneo
Published: April 2007

The electronic structures and the spectroscopic constants of the electronic ground Φ3 and low-lying Φ5 electronic excited states of the CoH molecule were studied by multireference single and double excitation configuration interaction (MR-SDCI)+Davidson’s correction (Q) calculations and size-consistent multireference coupled pair approximation (MRCPA) calculations. Calculations were performed under C∞v symmetry using Slater-type basis functions. The electronic ground state was confirmed to be the Φ3 state. It was found that at least four reference configurations were needed to describe the ground Φ3 state correctly at the MR-SDCI+Q level, while the Φ5 state can be described well by one reference configuration, namely, the Hartree-Fock configuration. Larger dynamical electron correlation for the low-spin Φ3 state than that for the high-spin Φ5 state is discussed. Spectroscopic constants, i.e., equilibrium bond lengths (re), harmonic frequency (ωe), and excitation energy, obtained by the MR-SDCI+Q method showed good correspondence with experimental values. MRCPA calculations gave a slightly shorter value for re than experimental values, but improved ωe and the excitation energy bringing them very close to experimental values.
Thermodynamical calculation of metal heating in nanosecond exploding wire and foil experiments
Authors: Sarkisov G. S. , Rosenthal S. E. , Struve K. W.
Published: April 2007

A method of thermodynamical calculation of thin metal wire heating during its electrical explosion is discussed. The technique is based on a calculation of Joule energy deposition taking into account the current wave form and the temperature dependence of the resistivity and heat capacity of the metal. Comparing the calculation to a set of exploding tungsten wire experiments demonstrates good agreement up to the time of melting. Good agreement is also demonstrated with resistive magnetohydrodynamics simulation. A similar thermodynamical calculation for Mo, Ti, Ni, Fe, Al, and Cu shows good agreement with experimental data. The thermodynamical technique is useful for verification of the voltage measurements in exploding wire experiments. This technique also shows good agreement with an exploding W foil experiment.
Spin-forbidden cΣ1+3←XΣ+1 band system of YF
Authors: Nagarajan Ramya , Morse Michael D.
Published: April 2007

Optical spectra of jet-cooled diatomic YF have been recorded using resonant two-photon ionization spectroscopy. A vibrational progression corresponding to the cΣ1+3←XΣ+1 system has been identified. The vibrational frequency ωe′ and anharmonicity ωe′xe′ of the cΣ+3 state are 546.70 and 2.45cm−1, respectively. The 0-0, 1-0, and 2-0 bands of the cΣ1+3←XΣ+1 system were rotationally resolved and analyzed, allowing the v′=0, 1, and 2 levels of the cΣ1+3 substate to be characterized. From these studies, Be′=0.26981(3)cm−1, αe′=0.00172(3)cm−1, and re′=1.9979(1)Å were obtained (1σ error limits). For these levels the spin-spin coupling constant λv is identical within experimental error, as λ=−22.5cm−1. The spin-forbidden cΣ1+3←XΣ+1 transition is made allowed by spin-orbit interaction between the cΣ1+3 and the BΠ1 states. Excited state lifetimes of the cΣ1+3 and the BΠ1 states have been measured as 7.11(41) and 0.133(15)μs, respectively. A spin-orbit analysis shows that the cΣ1+3 state is contaminated with 2% BΠ1 character, which is approximately sufficient to explain the 7μs lifetime of the cΣ1+3 state.
The formation of self-assembled InAs∕GaAs quantum dots emitting at 1.3μm followed by photoreflectance spectroscopy
Authors: Rudno-Rudziński W. , Sęk G. , Misiewicz J. , Lamas T. E. , Quivy A. A.
Published: April 2007

Photoreflectance (PR) modulation spectroscopy, supported by photoluminescence (PL) and atomic force microscopy, was applied to the study of the optical properties of InAs∕GaAs structures at the transition from the typical two-dimensional epitaxial growth to three-dimensional Stranski-Krastanov mode of InAs self-assembled quantum dot (QD) formation. Room temperature photoreflectance was measured on several molecular-beam epitaxy (MBE) grown structures, with growth conditions optimized for the 1.3μm emission (an important window for telecommunication applications), differing in the nominal thickness of InAs layer from 1 to 2.5 ML (monolayer). The evolution of optical transitions connected with energy levels confined in a very thin InAs∕GaAs quantum well was observed. For a small InAs nominal layer thickness (up to the critical thickness for the formation of three-dimensional islands), the heavy (light)-hole level to electron level transitions shift towards lower energy, indicating the increase in the quantum well width. When the nominal InAs layer thickness exceeds the critical value, the transition energies remain constant. It implies the formation of the so-called wetting layer, whose thickness is independent of the amount of deposited InAs material (fully driven by the strain). Its energy level structure was calculated (exploiting the effective mass approximation, with strain effects) in order to determine the actual wetting layer thickness, which was found to be approximately 1.6 ML. The features connected with the transitions between levels confined in QDs appear in PR and PL spectra for the amount of InAs material exceeding this number. The energies of the QD transitions shift to the red when the InAs layer nominal thickness is increased from 1.7 to 2 ML (indicating the increase in the average dot sizes) but remain constant for thicker layers, which is the evidence that the additional InAs material increases the density of QDs, but not their sizes. It points out at the existence of size limitation effect in the MBE growth of self-assembled QDs.
Room temperature magneto-resistance and temperature coefficient of resistance in La0.7Ca0.3−xAgxMnO3 thin films
Authors: Siwach P. K. , Awana V. P. S. , Kishan H. , Prasad R. , Singh H. K. , Balamurugan S. , Takayama-Muromachi E. , Srivastava O. N.
Published: April 2007

We investigate the magnetotransport properties of La0.7Ca0.3−xAgxMnO3 (0⩽x⩽0.3) polycrystalline films prepared by spray pyrolysis. The virgin La0.7Ca0.3MnO3 (LCMO) (x=0.0) film shows paramagnetic-ferromagnetic [insulator-metal (IM)] transition at TC∼260K (TIM∼245K). Ag doping induces appreciable enhancement in TC∕TIM and interestingly TIM of Ag doped films is higher than the corresponding TC value. In the 30% Ag doped film IM transition occurs at ∼325K which is ∼10K higher than its TC∼315K. Strong irreversibility is observed in zero field cooled–field cooled magnetization of all the films and the irreversibility temperature Tirr>TC increases with Ag doping. This suggests the formation of magnetic clusters above TC. The pure LCMO film exhibits small magnetoresistance (MR) ∼20% and rather poor temperature coefficient of resistance (TCR) in the vicinity of the room temperature. In contrast, around room temperature the Ag doped films show large MR which is ∼60% for x=0.15 and decreases to ∼30% for the pure Ag doped film. Ag doped films also have good TCR ∼4%∕K in the vicinity of room temperature.
Local linear viscoelasticity of confined fluids
Authors: Hansen J. S. , Daivis P. J. , Todd B. D.
Published: April 2007

In this paper the authors propose a novel method to study the local linear viscoelasticity of fluids confined between two walls. The method is based on the linear constitutive equation and provides details about the real and imaginary parts of the local complex viscosity. They apply the method to a simple atomic fluid undergoing zero mean oscillatory flow using nonequilibrium molecular dynamics simulations. The method shows that the viscoelastic properties of the fluid exhibit dramatic spatial changes near the wall-fluid boundary due to the high density in this region. It is also shown that the real part of the viscosity converges to the frequency dependent local shear viscosity sufficiently far away from the wall. This also provides valuable information about the transport properties in the fluid, in general. The viscosity is compared with predictions from the local average density model. The two methods disagree in that the local average density model predicts larger viscosity variations near the wall-fluid boundary than what is observed through the method presented here.
Gaussian and finite-element Coulomb method for the fast evaluation of Coulomb integrals
Authors: Kurashige Yuki , Nakajima Takahito , Hirao Kimihiko
Published: April 2007

The authors propose a new linear-scaling method for the fast evaluation of Coulomb integrals with Gaussian basis functions called the Gaussian and finite-element Coulomb (GFC) method. In this method, the Coulomb potential is expanded in a basis of mixed Gaussian and finite-element auxiliary functions that express the core and smooth Coulomb potentials, respectively. Coulomb integrals can be evaluated by three-center one-electron overlap integrals among two Gaussian basis functions and one mixed auxiliary function. Thus, the computational cost and scaling for large molecules are drastically reduced. Several applications to molecular systems show that the GFC method is more efficient than the analytical integration approach that requires four-center two-electron repulsion integrals. The GFC method realizes a near linear scaling for both one-dimensional alanine α-helix chains and three-dimensional diamond pieces.
The theory of ion beam induced charge in metal-oxide-semiconductor structures
Authors: Vizkelethy G. , Brice D. K. , Doyle B. L.
Published: April 2007

Silicon-on-insulator circuits have been considered less sensitive to single event effects than devices made using bulk technology. However, model experiments have indicated that charge collection occurs not only from the active layer above the buried oxide (BOX) but also from the substrate below the BOX, contrary to the earlier belief. In this paper we will present an analytical model based on the Gunn theorem to describe ion induced charge collection in metal-oxide-semiconductor devices.
Ultrahigh-temperature microwave annealing of Al+- and P+-implanted 4H-SiC
Authors: Sundaresan Siddarth G. , Rao Mulpuri V. , Tian Yong-lai , Ridgway Mark C. , Schreifels John A. , Kopanski Joseph J.
Published: April 2007

In this work, an ultrafast solid-state microwave annealing has been performed, in the temperature range of 1700–2120°C on Al+- and P+-implanted 4H-SiC. The solid-state microwave system used in this study is capable of raising the SiC sample temperatures to extremely high values, at heating rates of ∼600°C∕s. The samples were annealed for 5–60s in a pure nitrogen ambient. Atomic force microscopy performed on the annealed samples indicated a smooth surface with a rms roughness of 1.4nm for 5×5μm2 scans even for microwave annealing at 2050°C for 30s. Auger sputter profiling revealed a <7nm thick surface layer composed primarily of silicon, oxygen, and nitrogen for the samples annealed in N2, at annealing temperatures up to 2100°C. X-ray photoelectron spectroscopy revealed that this surface layer is mainly composed of silicon oxide and silicon nitride. Secondary ion mass spectrometry depth profiling confirmed almost no dopant in diffusion after microwave annealing at 2100°C for 15s. However, a sublimation of ∼100nm of the surface SiC layer was observed for 15s annealing at 2100°C. Rutherford backscattering spectra revealed a lattice damage-free SiC material after microwave annealing at 2050°C for 15s, with scattering yields near the virgin SiC material. Van der Pauw–Hall measurements have revealed sheet resistance values as low as 2.4kΩ∕◻ for Al+-implanted material annealed at 2100°C for 15s and 14Ω∕◻ for the P+-implanted material annealed at 1950°C for 30s. The highest electron and hole mobilities measured in this work were 100 and 6.8cm2∕Vs, respectively, for the P+- and Al+-implanted materials.
Order-disorder phase transformation in ion-irradiated rare earth sesquioxides
Authors: Tang M. , Valdez J. A. , Sickafus K. E. , Lu P.
Published: April 2007

An order-to-disorder (OD) transformation induced by ion irradiation in rare earth (RE) sesquioxides, Dy2O3, Er2O3, and Lu2O3, was studied using grazing incidence x-ray diffraction and transmission electron microscopy. These sesquioxides are characterized by a cubic C-type RE structure known as bixbyite. They were irradiated with heavy Kr++ ions (300keV) and light Ne+ ions (150keV) at cryogenic temperature (∼120K). In each oxide, following a relatively low ion irradiation dose of ∼2.5 displacements per atom, the ordered bixbyite structure was transformed to a disordered, anion-deficient fluorite structure. This OD transformation was found in all three RE sesquioxides (RE=Dy, Er, and Lu) regardless of the ion type used in the irradiation. The authors discuss the irradiation-induced OD transformation process in terms of anion disordering, i.e., destruction of the oxygen order associated with the bixbyite structure.
Conveyor-belt method for assembling microparticles into large-scale structures using electric fields
Authors: Kumar Anil , Acrivos Andreas , Khusid Boris , James Conrad D. , Jacqmin David
Published: April 2007

The authors propose and experimentally demonstrate a conveyor-belt method appropriate for building large-scale microparticle structures by sequentially energizing electrodes to aggregate the particles into predetermined locations and then to translate them collectively to a work area for final assembly. This approach employs collective phenomena in a negatively polarized suspension exposed to a high-gradient strong ac electric field.
Deformation mechanisms of face-centered-cubic metal nanowires with twin boundaries
Authors: Cao A. J. , Wei Y. G. , Mao Scott X.
Published: April 2007

This letter addresses the issue of deformation mechanisms and mechanical tensile behavior of the twinned metal nanowires using atomistic simulations. Free surfaces are always the preferential dislocation nucleation sites in the initial inelastic deformation stage, while with further plastic deformation, twin boundary interfaces will act as sources of dislocations with the assistance of the newly formed defects. The smaller the twin boundary spacing, the higher the yielding stresses of the twinned nanowires. Twin boundaries, which serve both as obstacles to dislocation motion and dislocation sources, can lead to hardening effects and contribute to the tensile ductility. This work illustrates that the mechanical properties of metal nanowires could be controlled by tailoring internal growth twin structures.
Magnetic-field-induced fourfold azimuthal angle dependence in the terahertz radiation power of (100) InAs
Authors: Estacio Elmer , Sumikura Hisashi , Murakami Hidetoshi , Tani Masahiko , Sarukura Nobuhiko , Hangyo Masanori , Ponseca Carlito , Pobre Romeric , Quiroga Reuben , Ono Shingo
Published: April 2007

The azimuthal angle dependence in the terahertz radiation power of (100) InAs under 1T magnetic field is presented. Results show that although the dominant radiation mechanism is surge current, azimuthal-angle-dependent radiation due to the nonlinear effect is also observed. The twofold symmetry of the p-polarized terahertz radiation power was modified to a fourfold symmetry with the transverse magnetic field. Moreover, results exhibited fourfold symmetry for the s-polarized terahertz power even with no applied field. The anisotropic intervalley scattering of photocarriers is tentatively proposed as the origin of quadrupole response and the fourfold emission symmetry.
MnBi nanostructures: Size dependence of magnetostructural transition and matrix templating
Authors: Kang Kyongha , Moodenbaugh A. R. , Lewis L. H.
Published: April 2007

Rapidly solidified MnxBi(1−x) (x=0.05 Mn5, x=0.10 Mn10) alloys form as NiAs-type low-temperature phase MnBi nanoparticles in a Bi matrix. Microstructural differences underlie diverse magnetic behavior: Mn5 has well-separated nanorods along the basal plane axial directions of Bi, while Mn10 consists of MnBi nanorods and submicron-sized MnBi grains. The Curie transition of Mn10 is TC=630K with a second-order thermodynamic character, while Mn5 nanorods exhibit a reduced and hysteretic TC=520K. Magnetic field annealing fosters (00n) alignment of the MnBi phase. Mn10 also shows alignment of the Bi matrix by a proposed templating mechanism.
Polarity inversion in aluminum nitride thin films under high sputtering power
Authors: Akiyama Morito , Kamohara Toshihiro , Ueno Naohiro , Sakamoto Michiru , Kano Kazuhiko , Teshigahara Akihiko , Kawahara Nobuaki
Published: April 2007

The authors have investigated the influence of sputtering power on the piezoelectric response of aluminum nitride (AlN) thin films prepared on titanium nitride bottom electrodes. The piezoelectric response strongly depends on the sputtering power. The polar inversion was found by piezoresponse force microscopy. The polarity gradually changes from the N polarity to Al polarity with increasing sputtering power. The piezoelectric response of the films changes from −2.7to+4.3pC∕N with increasing sputtering power from 100to500W. Furthermore, the polarity inversion from the N polarity to Al polarity is observed by increasing sputtering power during growth.
Extreme anisotropy of graphite and single-walled carbon nanotube bundles
Authors: Wang Li-Feng , Zheng Quan-Shui
Published: April 2007

The anisotropic elastic properties of hexagonal crystals are examined in this letter. It is found that graphite possesses extreme properties with the highest anisotropy degree and the lowest shear modulus to Young’s modulus ratio compared with all other known hexagonal crystals. Further, single-walled carbon nanotube (SWNT) bundles, as a kind of hexagonal material, have higher anisotropy degree and lower modulus ratio than those of graphite. These extreme mechanical properties of graphite and SWNT bundles promise great application potentials in composites, sensors, and functional materials.
Top-emitting 230dots∕in. active-matrix polymer light-emitting diode displays on flexible metal foil substrates
Authors: Chuang Ta-Ko , Troccoli Matias , Kuo Po-Chin , Jamshidi-Roudbari Abbas , Hatalis Miltiadis K. , Biaggio Ivan , Voutsas Apostolos T.
Published: April 2007

A top-emitting 230dots∕in. monochrome active-matrix polymer light-emitting diode (PLED) display having the VGA format and fabricated on a flexible steel foil utilizing the polycrystalline silicon thin-film transistor (TFT) technology is reported. The pixel circuitry architecture consists of the conventional two TFT circuitries made of two p-channel metal-oxide-semiconductor (PMOS) transistors and one storage capacitor. The average field-effect hole mobility and threshold voltage of the PMOS polysilicon TFTs fabricated on the metal foil are 37(±4)cm2∕Vs and −1.9(±0.6)V, respectively. The light turn-on voltage of the PLED is 4.0V.
High-power, continuous-operation intersubband laser for wavelengths greater than 10μm
Authors: Slivken S. , Evans A. , Zhang W. , Razeghi M.
Published: April 2007

In this letter, high-power continuous-wave emission (>100mW) and high temperature operation (358K) at a wavelength of 10.6μm is demonstrated using an individual diode laser. This wavelength is advantageous for many medium-power applications previously reserved for the carbon dioxide laser. Improved performance was accomplished using industry-standard InP-based materials and by careful attention to design, growth, and fabrication limitations specific to long-wave infrared semiconductor lasers. The main problem areas are explored with regard to laser performance, and general steps are outlined to minimize their impact.
Room temperature laser action from multiple bands in photoexcited GaN grown on a silicon substrate
Authors: Al-Ajmi F. S. , Kolbas R. M. , Roberts J. C. , Rajagopal P. , Cook J. W. , Piner E. L. , Linthicum K. J.
Published: April 2007

Room temperature stimulated emission and laser action with well developed longitudinal optical modes from high-quality GaN films grown on silicon substrates by metal-organic chemical-vapor deposition are presented. Laser action with well developed Fabry-Pérot modes involving the A, B, and C bands was observed. Stimulated emission one exciton below the A band and the B band and one longitudinal optical phonon below the B band was also observed. The effective index of refraction during laser operation was measured to be 2.9.
Group delay measurements on photonic crystal resonators
Authors: Sünner T. , Gellner M. , Löffler A. , Kamp M. , Forchel A.
Published: April 2007

The authors have investigated the group delay of light propagating through photonic crystal resonators fabricated in GaAs membranes. The group delay was measured by detecting the phase shift of a microwave signal which was modulated onto the light. The group delay was found to increase linearly with the quality factor of the resonator. A maximum group delay of 132ps was observed for a resonator with a quality factor of 82 000.
Cubic HfO2 doped with Y2O3 epitaxial films on GaAs (001) of enhanced dielectric constant
Authors: Yang Z. K. , Lee W. C. , Lee Y. J. , Chang P. , Huang M. L. , Hong M. , Hsu C.-H. , Kwo J.
Published: April 2007

Nanometer thick cubic HfO2 doped with 19at.% Y2O3 (YDH) epitaxial films were grown on GaAs (001) using molecular beam epitaxy. Structural studies determined the epitaxial orientation relationships between the cubic YDH films and GaAs to be (001)GaAs∕∕(001)YDH and [100]GaAs∕∕[100]YDH. The YDH structure is strain relaxed with a lattice constant of 0.5122nm with a small mosaic spread of 0.023° and a twist angle of 2.9°. The YDH/GaAs interface is atomically abrupt without evidence of reacted interfacial layers. From C-V and I-V measurements a 7.7nm thick YDH film has an enhanced dielectric constant κ∼32, an equivalent oxide thickness of ∼0.94nm, an interfacial state density Dit∼7×1012cm−2eV−1, and a low leakage current density of 6×10−5A∕cm2 at 1V gate bias.
Gorilla-like anatomy onAustralopithecus afarensismandibles suggestsAu. afarensislink to robust australopiths
Authors: Rak Yoel , Ginzburg Avishag , Geffen Eli
Published: April 2007

Mandibular ramus morphology on a recently discovered specimen ofAustralopithecus afarensisclosely matches that of gorillas. This finding was unexpected given that chimpanzees are the closest living relatives of humans. Because modern humans, chimpanzees, orangutans, and many other primates share a ramal morphology that differs from that of gorillas, the gorilla anatomy must represent a unique condition, and its appearance in fossil hominins must represent an independently derived morphology. This particular morphology appears also inAustralopithecus robustus. The presence of the morphology in both the latter andAu. afarensisand its absence in modern humans cast doubt on the role ofAu. afarensisas a modern human ancestor. The ramal anatomy of the earlierArdipithecus ramidusis virtually that of a chimpanzee, corroborating the proposed phylogenetic scenario.
β-Arrestin is a necessary component of Wnt/β-catenin signaling
in vitro
and
in vivo
Authors: Bryja Vítězslav , Gradl Dietmar , Schambony Alexandra , Arenas Ernest , Schulte Gunnar
Published: April 2007

The Wnt/β-catenin signaling pathway is crucial for proper embryonic development and tissue homeostasis. The phosphoprotein dishevelled (Dvl) is an integral part of Wnt signaling and has recently been shown to interact with the multifunctional scaffolding protein β-arrestin. Using Dvl deletion constructs, we found that β-arrestin binds a region N-terminal of the PDZ domain of Dvl, which contains casein kinase 1 (CK1) phosphorylation sites. Inhibition of Wnt signaling by CK1 inhibitors reduced the binding of β-arrestin to Dvl. Moreover, mouse embryonic fibroblasts lacking β-arrestins were able to phosphorylate LRP6 in response to Wnt-3a but decreased the activation of Dvl and blocked β-catenin signaling. In addition, we found that β-arrestin can bind axin and forms a trimeric complex with axin and Dvl. Furthermore, treatment of
Xenopus laevis
embryos with β-arrestin morpholinos reduced the activation of endogenous β-catenin, decreased the expression of the β-catenin target gene, Xnr3, and blocked axis duplication induced by X-Wnt-8, CK1ε, or DshΔDEP, but not by β-catenin. Thus, our results identify β-arrestin as a necessary component for Wnt/β-catenin signaling, linking Dvl and axin, and open a vast array of signaling avenues and possibilities for cross-talk with other β-arrestin-dependent signaling pathways.
Genomic resources for songbird research and their use in characterizing gene expression during brain development
Authors: Li XiaoChing , Wang Xiu-Jie , Tannenhauser Jonathan , Podell Sheila , Mukherjee Piali , Hertel Moritz , Biane Jeremy , Masuda Shoko , Nottebohm Fernando , Gaasterland Terry
Published: April 2007

Vocal learning and neuronal replacement have been studied extensively in songbirds, but until recently, few molecular and genomic tools for songbird research existed. Here we describe new molecular/genomic resources developed in our laboratory. We made cDNA libraries from zebra finch (
Taeniopygia guttata
) brains at different developmental stages. A total of 11,000 cDNA clones from these libraries, representing 5,866 unique gene transcripts, were randomly picked and sequenced from the 3′ ends. A web-based database was established for clone tracking, sequence analysis, and functional annotations. Our cDNA libraries were not normalized. Sequencing ESTs without normalization produced many developmental stage-specific sequences, yielding insights into patterns of gene expression at different stages of brain development. In particular, the cDNA library made from brains at posthatching day 30–50, corresponding to the period of rapid song system development and song learning, has the most diverse and richest set of genes expressed. We also identified five microRNAs whose sequences are highly conserved between zebra finch and other species. We printed cDNA microarrays and profiled gene expression in the high vocal center of both adult male zebra finches and canaries (
Serinus canaria
). Genes differentially expressed in the high vocal center were identified from the microarray hybridization results. Selected genes were validated by
in situ
hybridization. Networks among the regulated genes were also identified. These resources provide songbird biologists with tools for genome annotation, comparative genomics, and microarray gene expression analysis.
Lack of
Spem1
causes aberrant cytoplasm removal, sperm deformation, and male infertility
Authors: Zheng Huili , Stratton Clifford J. , Morozumi Kazuto , Jin Jingling , Yanagimachi Ryuzo , Yan Wei
Published: April 2007

We identified a previously uncharacterized gene, spermatid maturation 1 (
Spem1
), encoding a protein exclusively expressed in the cytoplasm of steps 14–16 elongated spermatids in the mouse testis. This protein contains no known functional domains and is highly conserved across mammalian species. Male mice deficient in
Spem1
were completely infertile because of deformed sperm characterized by a bent head wrapped around by the neck and the middle piece of the tail. We show that lack of
Spem1
causes failure of the cytoplasm to become loose and detach from the head and the neck region of the developing spermatozoa. Retained cytoplasmic components mechanically obstruct the straightening of the sperm head and the stretching of the growing tail, leading to the bending of the head in the neck, followed by the wrapping of the head by the neck or the middle piece of the sperm tail. Our study reveals that proper cytoplasm removal is a genetically regulated process requiring the participation of
Spem1
and that lack of
Spem1
causes sperm deformation and male infertility.
Vesicle formation from the nuclear membrane is induced by coexpression of two conserved herpesvirus proteins
Authors: Klupp Barbara G. , Granzow Harald , Fuchs Walter , Keil Günther M. , Finke Stefan , Mettenleiter Thomas C.
Published: April 2007

Although the nuclear envelope is a dynamic structure that disassembles and reforms during mitosis, the formation of membranous vesicles derived from the nuclear envelope has not yet been described in noninfected cells. However, during herpesvirus maturation, intranuclear capsids initiate transit to the cytosol for final maturation by budding at the inner nuclear membrane. Two conserved herpesvirus proteins are required for this primary envelopment, designated in the alphaherpesviruses as pUL31 and pUL34. Here, we show that simultaneous expression of pUL31 and pUL34 of the alphaherpesvirus pseudorabies virus in stably transfected rabbit kidney cells resulted in the formation of vesicles in the perinuclear space that resemble primary envelopes without a nucleocapsid. They contain pUL31 and pUL34 as shown by immunolabeling and are derived from the nuclear envelope. Thus, coexpression of only two conserved herpesvirus proteins without any other viral factor is sufficient to induce the formation of vesicles from the nuclear membrane. This argues for the contribution of cellular factors in this process either recruited from their natural cytoplasmic location or not yet identified as components of the nuclear compartment.
Differential P
1
arginine and lysine recognition in the prototypical proprotein convertase Kex2
Authors: Wheatley Joshua L. , Holyoak Todd
Published: April 2007

The high-resolution crystal structure of kexin (Kex2) in complex with a peptidyl-chloromethylketone inhibitor containing a noncognate lysine at the P
1
position provides the structural basis for the differential lysine/arginine selectivity that defines the prohormone (proprotein) convertase (PC) family. By comparison with the previous structures of Kex2 and furin, this structure of the acylated enzyme provides a basis for the observed decrease in the acylation rate with substrates containing a lysine at P
1
and the absence of an effect on the deacylation rate without involving mobility of the S
1
lid. The structure of the complex shows that a secondary subsite in the S
1
pocket is present, and that this site recognizes and binds the P
1
lysine in a more shallow fashion than arginine. This results in a displacement of the bound peptide away from the S385 nucleophile relative to substrates containing a P
1
arginine. It is concluded that this alternate binding site and resultant displacement of the scissile bond in the active site results in the observed decrease in the acylation rate. Studies of the inactivation kinetics of Kex2 by two peptidyl chloromethylketone inhibitors demonstrates that the selectivity between lysine and arginine at the P
1
position arises at the acylation step, consistent with what was observed with peptidyl substrates [Rockwell NC, Fuller RS (2001)
J Biol Chem
276:38394–38399].
Loss of Cell Adhesion Causes Hydrocephalus in Nonmuscle Myosin II-B–ablated and Mutated Mice
Authors: Ma Xuefei , Bao Jianjun , Adelstein Robert S.
Published: April 2007

Ablation of nonmuscle myosin (NM) II-B in mice during embryonic development leads to marked enlargement of the cerebral ventricles and destruction of brain tissue, due to hydrocephalus. We have identified a transient mesh-like structure present at the apical border of cells lining the spinal canal of mice during development. This structure, which only contains the II-B isoform of NM, also contains β-catenin and N-cadherin, consistent with a role in cell adhesion. Ablation of NM II-B or replacement of NM II-B with decreased amounts of a mutant (R709C), motor-impaired NM II-B in mice results in collapse of the mesh-like structure and loss of cell adhesion. This permits the underlying neuroepithelial cells to invade the spinal canal and obstruct cerebral spinal fluid flow. These defects in the CNS of NM II-B–ablated mice seem to be the cause of hydrocephalus. Interestingly, the mesh-like structure and patency of the spinal canal can be restored by increasing expression of the motor-impaired NM II-B, which also rescues hydrocephalus. However, the mutant isoform cannot completely rescue neuronal cell migration. These studies show that the scaffolding properties of NM II-B play an important role in cell adhesion, thereby preventing hydrocephalus during mouse brain development.
Cytokinin-mediated leaf manipulation by a leafminer caterpillar
Authors: Giron David , Kaiser Wilfried , Imbault Nadine , Casas Jérôme
Published: April 2007

A large number of hypotheses have been proposed to explain the adaptive significance and evolution of the endophagous-feeding mode, nutritional benefits being considered to be one of the main advantages. Leaf-mining insects should feed on most nutritional tissues and avoid tissues with high structural and/or biochemical plant defences. This selective feeding behaviour could furthermore be reinforced by manipulating the plant physiology, as suggested by the autumnal formation of ‘green islands’ around mining caterpillars in yellow leaves. The question we address here is how such metabolic manipulation occurs and what the nutritional consequences for the insect are. We report a large accumulation of cytokinins in the mined tissues which is responsible for the preservation of functional nutrient-rich green tissues at a time when leaves are otherwise turning yellow. The analogy with other plant manipulating organisms, in particular galling insects, is striking.
Food-specific spatial memory biases in an omnivorous bird
Authors: Sulikowski Danielle , Burke Darren
Published: April 2007

The tendency of nectarivorous birds to perform better on tasks requiring them to avoid previously rewarding locations (to win–shift) than to return to them (win–stay) has been explained as an adaptation to the depleting nature of nectar. This interpretation relies on the previously untested assumption that the win–shift tendency is not associated with food types possessing a different distribution. To test this assumption, we examined the specificity of this bias to different food types in an omnivorous honeyeater, the noisy miner (
Manorina melanocephala
). As predicted, we found that the win–shift bias was sensitive to foraging context, manifesting only in association with foraging for nectar, not with foraging for invertebrates.
Patterns of antigenic diversity and the mechanisms that maintain them
Authors: Lipsitch Marc , O'Hagan Justin J
Published: April 2007

Many of the remaining challenges in infectious disease control involve pathogens that fail to elicit long-lasting immunity in their hosts. Antigenic variation is a common reason for this failure and a contributor to the complexity of vaccine design. Diversifying selection by the host immune system is commonly, and often correctly, invoked to explain antigenic variability in pathogens. However, there is a wide variety of patterns of antigenic variation across space and time, and within and between hosts, and we do not yet understand the determinants of these different patterns. This review describes five such patterns, taking as examples two bacteria (Streptococcus pneumoniaeandNeisseria meningitidis), two viruses (influenza A and HIV-1), as well as the pathogens (taken as a group) for which antigenic variation is negligible. Pathogen-specific explanations for these patterns of diversity are critically evaluated, and the patterns are compared against predictions of theoretical models for antigenic diversity. Major remaining challenges are highlighted, including the identification of key protective antigens in bacteria, the design of vaccines to combat antigenic variability for viruses and the development of more systematic explanations for patterns of antigenic variation.
Predator perception and the interrelation between different forms of protective coloration
Authors: Stevens Martin
Published: April 2007

Animals possess a range of defensive markings to reduce the risk of predation, including warning colours, camouflage, eyespots and mimicry. These different strategies are frequently considered independently, and with little regard towards predator vision, even though they may be linked in various ways and can be fully understood only in terms of predator perception. For example, camouflage and warning coloration need not be mutually exclusive, and may frequently exploit similar features of visual perception. This paper outlines how different forms of protective markings can be understood from predator perception and illustrates how this is fundamental in determining the mechanisms underlying, and the interrelation between, different strategies. Suggestions are made for future work, and potential mechanisms discussed in relation to various forms of defensive coloration, including disruptive coloration, eyespots, dazzle markings, motion camouflage, aposematism and mimicry.