bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural, thermal, optical, and photoacoustic study of nanocrystalline Bi2Te3 produced by mechanical alloying
Authors: Souza S. M. , Trichês D. M. , Poffo C. M. , de Lima J. C. , Grandi T. A. , de Biasi R. S.
Published: January 2011

Nanocrystalline Bi2Te3 was produced by mechanical alloying and its properties were investigated by differential scanning calorimetry (DSC) x-ray diffraction (XRD), Raman spectroscopy (RS), and photoacoustic spectroscopy (PAS). Combining the XRD and RS results, the volume fraction of the interfacial component in as-milled and annealed samples was estimated. The PAS results suggest that the contribution of the interfacial component to the thermal diffusivity of nanostructured Bi2Te3 is very significant.
Widely tuning optical properties of nanoporous gold-titania core-shells
Authors: Qian Lihua , Shen Bo , Qin Gaowu W. , Das Biswajit
Published: January 2011

Widely shifting localized surface plasmon resonance (LSPR) bands of nanoporous metals is essential for light manipulation within small volumes. In this work, nanoporous gold-titania core-shells fabricated by atomic layer deposition exhibit tunable LSPR of gold skeletons in comparison with nanoporous gold-alumina developed before. Extremely large red-shift of LSPR band in nanoporous gold-titania from 537 to 751 nm results from high refractive index of titania and its dielectric medium dependence of LSPR, and the well-controlled thickness of titania shell at the nanometer scale will benefit to integrate optical nanodevices with supreme performances.
Copper coverage effect on tungsten crystallites texture development in W/Cu nanocomposite thin films
Authors: Girault B. , Eyidi D. , Chauveau T. , Babonneau D. , Renault P.-O. , Le Bourhis E. , Goudeau P.
Published: January 2011

Morphological and crystallographic structures of multilayered W/Cu nanocomposite thin films elaborated by physical vapor deposition were studied by varying copper and tungsten thicknesses. Sample examinations were performed by x-ray diffraction (XRD), grazing incidence small-angle x-ray scattering and transmission electron microscopy (TEM). Samples were found to be composed of copper nanoparticles, homogeneously dispersed in planes parallel to the film-substrate interface and periodically separated by tungsten layers along the growth direction. Our observations revealed an original texture development of the tungsten matrix from a mixture of unexpected α-W⟨111⟩ and α-W⟨110⟩ components to unique α-W⟨110⟩ component as the copper coverage passes a thickness threshold of 0.6 nm. Local TEM texture stereology investigations revealed simultaneous columnar growth of both preferential orientations posterior to polycrystalline development while XRD reveals strong compressive residual stresses in both texture components. Physical origins of the preferential crystallographic orientation evolution are discussed. Copper mono layers adsorption on W surfaces promotes surface energy anisotropy and diminution which is effective over the threshold. Below, the presence of a W(Cu) solid solution which does not affect substantially the texture is revealed by the stress-free lattice parameter value extracted from XRD.
Metamaterial tunnel barrier gives broadband microwave transmission
Authors: Butler Celia A. M. , Hooper Ian R. , Hibbins Alastair P. , Sambles J. Roy , Hobson Peter A.
Published: January 2011

A simple structure comprising a metal mesh, symmetrically surrounded by subwavelength thickness dielectric layers, is shown to give near total microwave transmission over a broad frequency range. The mesh may be considered to be a tunnel barrier since it behaves as an ideal plasmonic metamaterial with a negative effective permittivity and no loss. The introduction of the mesh into the dielectric cavity imposes a finite gradient on the electromagnetic fields at the two mesh-dielectric interfaces. This defines a finite wavelength of the zeroth order Fabry-Pérot-type mode, which would otherwise be infinite. Suitable choice of the mesh parameters yields a broad band of near total transmission associated with the overlap of this zeroth order mode with that of the first order half-wavelength Fabry-Pérot-type resonance.
Shock compression response of alumina-THV composites
Authors: Neel Christopher , Thadhani Naresh N.
Published: January 2011

The shock compression response of several THV-alumina particle composites (where THV is a terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinyldiene fluoride) was investigated based on experiments performed in the pressure range of 2–6 GPa. The composites, composed of 25% by volume of either 1, 10, or 100 μm Al2O3, had varying degrees of porosity. The high level of porosity, particularly in the 1 μm Al2O3 composite, obscured determination of any particle size effects. In general, the composites displayed a stiffer shock response than expected, based on the known response of the constituent materials, with the 10 μm Al2O3 composite being slightly stiffer than the 100 μm composite. It is argued that a possible way to describe the stiffer shock compression response is by assigning a higher value for the “effective” Grüneisen parameter γ to the composites. The higher value is consistent with arguments made in the literature that γ for polymers is much higher (by as much as an order of magnitude) than the often reported values (generally ∼1 or less for polymers). The particle size effect can, however, possibly explain the difference in the stiffness between 10 and 100 μm Al2O3 composites, which is consistent with results reported in the literature.
Improved reliability of Au/Si3N4/Ti resistive switching memory cells due to a hydrogen postannealing treatment
Authors: Kim Hee-Dong , An Ho-Myoung , Kim Tae Geun
Published: January 2011

The effect of hydrogen-postannealing on the endurance and data retention characteristics of an Au/Si3N4/Ti resistance memory cell is investigated. Compared to the as-deposited sample, the set and reset currents of the Au/Si3N4/Ti sample annealed at 250 °C for 30 min in a N2–H2 ambient gas, are reduced from 10 mA to 1.5 mA and from 3 mA to 5 μA, respectively, whereas the current ratio increases from ∼0.5×101 to ∼103. In addition, its reliability features, including its endurance (>103 cycles) and retention time (>ten years), have been improved due to the reduction in the interface trap.
Investigation of the drain current shift in ZnO thin film transistors
Authors: Abdel-Motaleb Ibrahim , Shetty Neeraj , Leedy Kevin , Cortez Rebecca
Published: January 2011

A ZnO thin film transistor (TFT), with barium strontium titanate (BST) as a gate oxide, has been fabricated and characterized. The ZnO and the BST layers were deposited using pulsed laser deposition. The I-V characteristics were measured, and an upward shift in the drain current was observed when the voltage sweeping was repeated. The reasons for this shift were investigated and it was found that the shift could be attributed to the combination effect of the reduction in the built-in potential of the grain boundaries, the population and depopulation of trap centers in the channel, and the existence of mobile charges in the gate oxide layer.
Experimental characterization of efficient second harmonic generation of Lamb wave modes in a nonlinear elastic isotropic plate
Authors: Matlack Kathryn H. , Kim Jin-Yeon , Jacobs Laurence J. , Qu Jianmin
Published: January 2011

This research experimentally characterizes the efficiency of Lamb wave mode pairs to generate the cumulative second harmonic in an undamaged aluminum plate. Previous research developed the theoretical framework for the characteristics of second harmonic generation of Lamb waves in nonlinear elastic plates, and identified five mode types where the amplitude of the measured second harmonic should increase linearly with ultrasonic wave propagation distance. The current research considers one of these five mode types, Lamb wave mode pairs at the longitudinal velocity, and experimentally confirms the theoretically predicted ratios of the rate of accumulation of the second harmonic amplitude versus propagation distance for two different Lamb wave mode pairs. By comparing these rates of accumulation, these experimental results are used to characterize the measurement efficiency of the mode pairs under consideration.
Communication: Heavy atom quantum diffraction by scattering from surfaces
Authors: Moix Jeremy M. , Pollak Eli
Published: January 2011

Typically one expects that when a heavy particle collides with a surface, the scattered angular distribution will follow classical mechanics. The heavy mass usually assures that the coherence length of the incident particle in the direction of the propagation of the particle (the parallel direction) will be much shorter than the characteristic lattice length of the surface, thus leading to a classical description. Recent work on molecular interferometry has shown that extreme collimation of the beam creates a perpendicular coherence length which is sufficiently long so as to observe interference of very heavy species passing through a grating. Here we show, using quantum mechanical simulations, that the same effect will lead to quantum diffraction of heavy particles colliding with a surface. The effect is robust with respect to the incident energy, the angle of incidence, and the mass of the particle.
Thin film colossal dielectric constant oxide La2−xSrxNiO4: Synthesis, dielectric relaxation measurements, and electrode effects
Authors: Podpirka Adrian , Ramanathan Shriram
Published: January 2011

We have successfully synthesized the colossal dielectric constant oxide La2−xSrxNiO4 in thin film form by reactive cosputtering from metallic targets and careful annealing protocols. Composition and phase purity was determined through energy dispersive spectra and x-ray diffraction, respectively. The dielectric constant exceeds values of over 20 000 up to 1 kHz and the activation energy for the frequency-independent conductivity plateau was extracted to be approximately 155 meV from 300 to 473 K, both in agreement with measurements conducted on bulk single crystals. However, unlike in single crystals, we observe early onset of relaxation in thin films indicating the crucial role of grain boundaries in influencing the dielectric response. ac conductivity at varying temperatures is analyzed within the framework of the universal dielectric law leading to an exponent of approximately 0.3, dependent on the electrode material. Impedance spectroscopy with electrodes of different work function (Pt, Pd, and Ag) was further carried out as a function of temperature and applied bias to provide mechanistic insights into the nature of the dielectric response.
Spin injection from epitaxial Fe3O4 films to ZnO films
Authors: Li P. , Guo B. L. , Bai H. L.
Published: January 2011

The fully epitaxial Fe3O4/ZnO heterostructures were fabricated by reactive dc sputtering (Fe3O4) and rf sputtering (ZnO) on c-Al2O3 substrates. The epitaxial relationship is verified to be Fe3O4(111)⟨11¯0⟩∥ZnO(0002)⟨112¯0⟩ by φ scans. The nonlinear and rectifying properties of I-V curves were observed in the heterostructures. The transport mechanism across the interface between Fe3O4 and ZnO is thermal emission and the Schottky barrier is calculated to be 0.51 eV. The magnetoresistance of the heterostructures is symmetric and depends on current. The spin polarization of the transport electrons from Fe3O4 into ZnO is determined to be 28.5% at 30 K.
Advanced mechanical properties of graphene paper
Authors: Ranjbartoreh Ali R. , Wang Bei , Shen Xiaoping , Wang Guoxiu
Published: January 2011

Graphene paper (GP) has been prepared by flow-directed assembly of graphene nanosheets. The mechanical properties of as-prepared GPs were investigated by tensile, indentation, and bending tests. Heat treated GPs demonstrate superior hardness, ten times that of synthetic graphite, and two times that of carbon steel; besides, their yielding strength is significantly higher than that of carbon steel. GPs show extremely high modulus of elasticity during bending test; in the range of a few terapascal. The high strength and stiffness of GP is ascribed to the interlocking-tile microstructure of individual graphene nanosheets in the paper. These outstanding mechanical properties of GPs could lead to a wide range of engineering applications.
Instability regimes in flowing suspensions of swimming micro-organisms
Authors: Pahlavan Amir Alizadeh , Saintillan David
Published: January 2011

The effects of an external shear flow on the dynamics and pattern formation in a dilute suspension of swimming micro-organisms are investigated using a linear stability analysis and three-dimensional numerical simulations, based on the kinetic model previously developed by [D. Saintillan and M. J. Shelley, Phys. Fluids 20, 123304 (2008)]. The external shear flow is found to damp the instabilities that occur in these suspensions by controlling the orientation of the particles. We demonstrate in our simulations that the rate of damping is direction-dependent: it is fastest in the flow direction, but slowest in the direction perpendicular to the shear plane. As a result, transitions from three- to two- to one-dimensional instabilities are observed to occur as shear rate increases, and above a certain shear rate the instabilities altogether disappear. The density patterns and complex flows that arise at long time in the suspensions are also analyzed from the numerical simulations using standard techniques from the literature on turbulent flows. The imposed shear flow is found to have an effect on both density patterns and flow structures, which typically align with the extensional axis of the external flow. The disturbance flows in the simulations are shown to exhibit similarities with turbulent flows, and in particular two of the seemingly universal characteristics of turbulent flows also occur, namely: (i) the bias of Q-R plots toward the second and fourth quadrants, corresponding to stable focus/stretching and unstable node/saddle/saddle flow topologies, respectively, and (ii) the alignment of the vorticity vector with the intermediate strain-rate eigenvector. However, the flows described herein also significantly differ from turbulent flows owing to the strong predominance of large scales, as exemplified by the very rapid decay of the kinetic energy spectrum, an effect further enhanced after the transitions to two- and one-dimensional instabilities.
Efficiency measurement of GaN-based quantum well and light-emitting diode structures grown on silicon substrates
Authors: Zhu Dandan , McAleese Clifford , Häberlen Maik , Salcianu Carmen , Thrush Ted , Kappers Menno , Phillips Andrew , Lane Penelope , Kane Michael , Wallis David , Martin Trevor , Astles Mike , Hylton Nicolas , Dawson Phil , Humphreys Colin
Published: January 2011

The optical efficiency of GaN-based multiple quantum well (MQW) and light emitting diode (LED) structures grown on Si(111) substrates by metal-organic vapor phase epitaxy was measured and compared with equivalent structures on sapphire. The crystalline quality of the LED structures was comprehensively characterized using x-ray diffraction, atomic force microscopy, and plan-view transmission electron microscopy. A room temperature photoluminescence (PL) internal quantum efficiency (IQE) as high as 58% has been achieved in an InGaN/GaN MQW on Si, emitting at 460 nm. This is the highest reported PL-IQE of a c-plane GaN-based MQW on Si, and the radiative efficiency of this sample compares well with similar structures grown on sapphire. Processed LED devices on Si also show good electroluminescence (EL) performance, including a forward bias voltage of ∼3.5 V at 20 mA and a light output power of 1 mW at 45 mA from a 500×500 μm2 planar device without the use of any additional techniques to enhance the output coupling. The extraction efficiency of the LED devices was calculated, and the EL-IQE was then estimated to have a maximum value of 33% at a current density of 4 A cm−2, dropping to 30% at a current density of 40 A cm−2 for a planar LED device on Si emitting at 455 nm. The EL-IQE was clearly observed to increase as the structural quality of the material increased for devices on both sapphire and Si substrates.
High order symmetry interference lithography based nanoimprint
Authors: Letailleur Alban A. , Nomenyo Komla , Mc Murtry Stefan , Barthel Etienne , Søndergård Elin , Lérondel Gilles
Published: January 2011

We report on soft nanoimprint lithography using masters obtained by high order symmetry interference lithography. The use of high order symmetry leads to the formation of three-dimensional structures with features smaller than 40 nm. Masters were realized in silicon in a two-step process without transfer layer. Pure silicon masters allow mechanical stability and potential surface functionalization. We further demonstrate the ability of these masters as mold for nanoimprint lithography. High fidelity replication in hybrid sol-gel and pure silica with conservation of both minute features and long distance organization is observed over large areas.
Electromagnetically driven oscillatory shallow layer flow
Authors: Figueroa Aldo , Cuevas Sergio , Ramos Eduardo
Published: January 2011

We report experimental observations of the laminar flow in a thin horizontal layer of electrolyte, generated by a time-periodic Lorentz force produced by an alternate, unidirectional electric current and the field of a small permanent magnet. The force drives a periodically oscillating dipolar vortex which displays some spatial and temporal symmetries. The attention is focused on the motion of the oscillatory layer in vertical planes perpendicular to both the bottom wall and the injected current. For different frequencies of the injected current, velocity fields were obtained using particle image velocimetry in the zone of more intense magnetic field as well as close to the edges of the magnet where the inhomogeneity of the field is more pronounced. Velocity profiles as functions of the normal coordinate are determined in characteristic points at different phases and oscillation frequencies. Experimental results are compared with a simple analytical solution and a full three-dimensional numerical simulation that reproduces satisfactorily the experimental observations. Under the explored conditions and available experimental resolution, results indicate that except in the zone above of the lateral edges of the magnet, no recirculating flows appear and vertical velocity components are negligible.
Analysis of the resolution of split-ring metamaterial lenses with application in parallel magnetic resonance imaging
Authors: Algarin Jose M. , Freire Manuel J. , Lopez Marcos A. , Lapine Mikhail , Jakob Peter M. , Behr Volker C. , Marqués Ricardo
Published: January 2011

In this work, we experimentally determine the resolution of split-ring metamaterials lenses with emphasis in magnetic resonance imaging applications. Two small sources are used to determine the minimal resolution of the lens, which is compared with previous theoretical predictions. Taking into account this minimal resolution, a second experiment is designed in order to study the ability of a split-ring lens to improve the localization of the field produced by two closely spaced coils. This ability could find application in parallel magnetic resonance imaging, which take advantage of the distinct coil sensitivities in order to reduce the image acquisition time.
Real-time probing of ultrafast residual charge dynamics
Authors: Li Junjie , Wang Xuan , Chen Zhaoyang , Zhou Jun , Mao Samuel S. , Cao Jianming
Published: January 2011

The temporal evolution of residual charges during laser ablation of metal and dielectric materials was investigated by measuring the correlated transient electric field using femtosecond electron shadow imaging and deflectometry. The results indicate that residual charges in metals can redistribute themselves almost instantly, abiding by the boundary conditions and Maxwell equations in the same way as they would at electrostatic equilibrium condition, but residual charges in dielectrics are confined within the excited area for hundreds of picoseconds and beyond. These observations provide an experimental support to the alleged Coulomb explosion phenomenon in previous studies as well as a reference for modeling residual charge dynamics.
A numerical and experimental study on the nonlinear evolution of long-crested irregular waves
Authors: Goullet Arnaud , Choi Wooyoung
Published: January 2011

The spatial evolution of nonlinear long-crested irregular waves characterized by the JONSWAP spectrum is studied numerically using a nonlinear wave model based on a pseudospectral (PS) method and the modified nonlinear Schrödinger (MNLS) equation. In addition, new laboratory experiments with two different spectral bandwidths are carried out and a number of wave probe measurements are made to validate these two wave models. Strongly nonlinear wave groups are observed experimentally and their propagation and interaction are studied in detail. For the comparison with experimental measurements, the two models need to be initialized with care and the initialization procedures are described. The MNLS equation is found to approximate reasonably well for the wave fields with a relatively smaller Benjamin–Feir index, but the phase error increases as the propagation distance increases. The PS model with different orders of nonlinear approximation is solved numerically, and it is shown that the fifth-order model agrees well with our measurements prior to wave breaking for both spectral bandwidths.
High-performance metal-insulator-metal capacitor with Ge-stabilized tetragonal ZrO2/amorphous La-doped ZrO2 dielectric
Authors: Wu Yung-Hsien , Lin Chia-Chun , Chen Lun-Lun , Hu Yao-Chung , Wu Jia-Rong , Wu Min-Lin
Published: January 2011

A Ge-stabilized tetragonal ZrO2 dielectric with a permittivity (κ) value of 36.5 has been obtained by annealing a ZrO2/Ge/ZrO2 laminate at 500 °C and it is a more reliable approach toward stabilizing a tetragonal ZrO2 film. However, metal-insulator-metal (MIM) capacitors with the sole tetragonal ZrO2 film as an insulator achieve a high capacitance density of 27.8 fF/μm2 at the price of a degraded quadratic voltage coefficient of capacitance (VCC) of 81 129 ppm/V2 and unacceptably high leakage current. By capping an amorphous La-doped ZrO2 layer with a κ value of 26.3 to block grain boundaries-induced leakage paths of the crystalline ZrO2 dielectric, high-performance MIM capacitors in terms of a capacitance density of 19.8 fF/μm2, a VCC of 3135 ppm/V2, leakage current of 6.5×10−8 A/cm2 at −1 V, as well as a satisfactory capacitance change of 1.21% after ten-year operation can be realized.
Confinement and flow dynamics in thin polymer films for nanoimprint lithography
Authors: Teisseire Jérémie , Revaux Amélie , Foresti Maud , Barthel Etienne
Published: January 2011

In nanoimprint lithography (NIL) viscous flow in polymeric thin films is the primary mechanism for the generation and the relaxation of the structures. Here we quantify the impact of confinement on the flow rate. Pattern relaxation experiments were carried out above the glass transition temperature as a function of film thickness. The results are adequately fitted by a simple expression for the flow rate valid at all confinements. This expression, based on Newtonian viscosity, should be of use in NIL process design and for the measurement of the rheological properties of confined polymers.
A silicon nanowire ion-sensitive field-effect transistor with elementary charge sensitivity
Authors: Clément N. , Nishiguchi K. , Dufreche J. F. , Guerin D. , Fujiwara A. , Vuillaume D.
Published: January 2011

We investigate the mechanisms responsible for the low-frequency noise in liquid-gated nanoscale silicon nanowire field-effect transistors (SiNW-FETs) and show that the charge-noise level is lower than elementary charge. Our measurements also show that ionic strength of the surrounding electrolyte has a minimal effect on the overall noise. Dielectric polarization noise seems to be at the origin of the 1/f noise in our devices. The estimated spectral density of charge noise Sq=1.6×10−2 e/Hz1/2 at 10 Hz opens the door to metrological studies with these SiNW-FETs for the electrical detection of a small number of molecules.
Comparison of spin signals in silicon between nonlocal four-terminal and three-terminal methods
Authors: Sasaki Tomoyuki , Oikawa Tohru , Shiraishi Masashi , Suzuki Yoshishige , Noguchi Kiyoshi
Published: January 2011

The three-terminal (3T) measurement is a method of detecting spin accumulation at a ferromagnetic/semiconductor interface. Spin polarization (P) at the injector with an electric field (Pinjector) and that at the detector without an electric field (Pdetector) were measured separately by using the nonlocal (NL)-Hanle and 3T measurements, and Pinjector and Pdetector exhibited the same behavior with increasing temperature. We also found that the spin lifetime (τsp) in highly doped silicon measured by using the 3T method coincides with that estimated by the NL-Hanle measurement, which shows that the localized state does not exist at the interface.
Experimental investigation into segregating granular flows down chutes
Authors: Wiederseiner Sébastien , Andreini Nicolas , Épely-Chauvin Gaël , Moser Gaudenz , Monnereau Mathieu , Gray J. M. N. T. , Ancey Christophe
Published: January 2011

We experimentally investigated how a binary granular mixture made up of spherical glass beads (size ratio of 2) behaved when flowing down a chute. Initially, the mixture was normally graded, with all the small particles on top of the coarse grains. Segregation led to a grading inversion, in which the smallest particles percolated to the bottom of the flow, while the largest rose toward the top. Because of diffusive remixing, there was no sharp separation between the small-particle and large-particle layers, but a continuous transition. Processing images taken at the sidewall, we were able to measure the evolution of the concentration and velocity profiles. These experimental profiles were used to test a recent theory developed by Gray and Chugunov [J. Fluid Mech. 569, 365 (2006)], who derived a nonlinear advection diffusion equation that describes segregation and remixing in dense granular flows of binary mixtures. We found that this theory was able to provide a consistent description of the segregation/remixing process under steady uniform flow conditions. To obtain the correct depth-averaged concentration far downstream, it was very important to use an accurate approximation to the downstream velocity profile through the avalanche depth. The S-shaped concentration profile in the far field provided a useful way of determining what we refer to as the Péclet number for segregation, a dimensionless number that quantifies how large the segregation is compared to diffusive remixing. While the theory was able to closely match the final fully developed concentration profile far downstream, there were some discrepancies in the inversion region (i.e., the region in which the mixing occurs). The reasons for this are not clear. The difficulty to set up the experiment with both well controlled initial conditions and a steady uniform bulk flow field is one of the most plausible explanations. Another interesting lead is that the flux of segregating particles, which was assumed to be a quadratic function of the concentration in small beads, takes a more complicated form.
Organic vapor jet printing at micrometer resolution using microfluidic nozzle arrays
Authors: McGraw Gregory J. , Peters Diane L. , Forrest Stephen R.
Published: January 2011

Organic vapor jet printing with a print head comprised of a microfluidic Si nozzle array is used to deposit parallel lines of an organic semiconductor thin film with a line width of 16 μm and edge resolution of 4 μm. Line width and feature size are functions of process conditions, depending strongly on nozzle-to-substrate separation distance. Experimental results are accurately characterized by a direct simulation Monte Carlo model. The model suggests that feature sizes of <1.5 μm are attainable by this printing process. The ability of the print head to codeposit doped films is demonstrated by growing the emissive layer of a green phosphorescent organic light emitting diode sandwiched between hole and electron transport layers deposited by vacuum thermal evaporation. This device had an external quantum efficiency of 8.8±1.3%, comparable to a similar device entirely grown by vacuum thermal evaporation.
Low temperature epitaxial growth of Ge quantum dot on Si(100)-(2×1) by femtosecond laser excitation
Authors: Er Ali Oguz , Ren Wei , Elsayed-Ali Hani E.
Published: January 2011

Low temperature epitaxy of Ge quantum dots on Si(100)-(2×1) by femtosecond pulsed laser deposition under femtosecond laser excitation was investigated. Reflection high-energy electron diffraction and atomic force microscopy were used to analyze the growth mode and morphology. Epitaxial growth was achieved at ∼70 °C by using femtosecond laser excitation of the substrate. A purely electronic mechanism of enhanced surface diffusion of the Ge adatoms is proposed.
Strain engineering of epitaxially transferred, ultrathin layers of III-V semiconductor on insulator
Authors: Fang Hui , Madsen Morten , Carraro Carlo , Takei Kuniharu , Kim Ha Sul , Plis Elena , Chen Szu-Ying , Krishna Sanjay , Chueh Yu-Lun , Maboudian Roya , Javey Ali
Published: January 2011

Strain state of ultrathin InAs-on-insulator layers obtained from an epitaxial transfer process is studied. The as-grown InAs epilayer (10–20 nm thick) on the GaSb/AlGaSb source wafer has the expected ∼0.62% tensile strain. The strain is found to fully release during the epitaxial transfer of the InAs layer onto a Si/SiO2 substrate. In order to engineer the strain of the transferred InAs layers, a ZrOx cap was used during the transfer process to effectively preserve the strain. The work presents an important advance toward the control of materials properties of III-V on insulator layers.
Characteristics of field-effect transistors using the one-dimensional extended hydrocarbon [7]phenacene
Authors: Sugawara Yasuyuki , Kaji Yumiko , Ogawa Keiko , Eguchi Ritsuko , Oikawa Shohei , Gohda Hiroyuki , Fujiwara Akihiko , Kubozono Yoshihiro
Published: January 2011

Field-effect transistors (FETs) with solid gate dielectrics are fabricated with thin films of the one-dimensional (1D) extended hydrocarbon [7]phenacene, which contains seven benzene rings. p-channel FET characteristics are observed for these FETs, with a mobility of 0.75 cm2 V−1 s−1 at 100 Torr of O2. The O2 gas-sensing effect is examined for the [7]phenacene FET and for the 1D hydrocarbon picene FET. These FETs’ trap density and contact resistance are investigated with the multiple shallow trap and release model and the transfer line method. Unlike picene FETs, [7]phenacene FETs have few charge traps and are therefore air-stable.
Strong room temperature magnetism in highly resistive strained thin films of BiFe0.5Mn0.5O3
Authors: Choi E.-M. , Patnaik S. , Weal E. , Sahonta S.-L. , Wang H. , Bi Z. , Xiong J. , Blamire M. G. , Jia Q. X. , MacManus-Driscoll J. L.
Published: January 2011

We report highly resistive strongly ferromagnetic strained thin (∼30 nm) films of BiFe0.5Mn0.5O3 (BFMO) grown on (001) SrTiO3 substrates using pulsed laser deposition. The films are tetragonal with high epitaxial quality and phase-purity. The magnetic moment and coercivity values at room temperature are 90 emu/cc (0.58μB/B-site ion) at H=3 kOe and 274 Oe, respectively. The magnetic transition temperature is strongly enhanced up to ∼600 K, which is ∼500 K higher than for pure bulk BiMnO3. Strained BFMO is a potential room temperature spin filter material for magnetic tunnel devices.
Intraflagellar transport protein 122 antagonizes Sonic Hedgehog signaling and controls ciliary localization of pathway components
Authors: Qin Jian , Lin Yulian , Norman Ryan X. , Ko Hyuk W. , Eggenschwiler Jonathan T.
Published: January 2011

Primary cilia are required for proper Sonic Hedgehog (Shh) signaling in mammals. However, their role in the signal transduction process remains unclear. We have identified
sister of open brain
(
sopb
), a null allele of mouse
Intraflagellar transport protein 122
(
Ift122
). IFT122 negatively regulates the Shh pathway in the cilium at a step downstream of the Shh ligand and the transmembrane protein Smoothened, but upstream of the Gli2 transcription factor.

Ift122
sopb

mutants generate primary cilia, but they show features of defective retrograde intraflagellar transport. IFT122 controls the ciliary localization of Shh pathway regulators in different ways. Disruption of IFT122 leads to accumulation of Gli2 and Gli3 at cilia tips while blocking the ciliary localization of the antagonist TULP3. Suppressor of Fused and Smoothened localize to the cilium through an IFT122-independent mechanism. We propose that the balance between positive and negative regulators of the Shh pathway at the cilium tip controls the output of the pathway and that Shh signaling regulates this balance through intraflagellar transport.
Structural and mechanistic insight into covalent substrate binding by
Escherichia coli
dihydroxyacetone kinase
Authors: Shi Rong , McDonald Laura , Cui Qizhi , Matte Allan , Cygler Miroslaw , Ekiel Irena
Published: January 2011

The
Escherichia coli
dihydroxyacetone (Dha) kinase is an unusual kinase because (
i
) it uses the phosphoenolpyruvate carbohydrate: phosphotransferase system (PTS) as the source of high-energy phosphate, (
ii
) the active site is formed by two subunits, and (
iii
) the substrate is covalently bound to His218
K
*
of the DhaK subunit. The PTS transfers phosphate to DhaM, which in turn phosphorylates the permanently bound ADP coenzyme of DhaL. This phosphoryl group is subsequently transferred to the Dha substrate bound to DhaK. Here we report the crystal structure of the
E. coli
Dha kinase complex, DhaK–DhaL. The structure of the complex reveals that DhaK undergoes significant conformational changes to accommodate binding of DhaL. Combined mutagenesis and enzymatic activity studies of kinase mutants allow us to propose a catalytic mechanism for covalent Dha binding, phosphorylation, and release of the Dha-phosphate product. Our results show that His56
K
is involved in formation of the covalent hemiaminal bond with Dha. The structure of H56N
K
with noncovalently bound substrate reveals a somewhat different positioning of Dha in the binding pocket as compared to covalently bound Dha, showing that the covalent attachment to His218
K
orients the substrate optimally for phosphoryl transfer. Asp109
K
is critical for activity, likely acting as a general base activating the γ-OH of Dha. Our results provide a comprehensive picture of the roles of the highly conserved active site residues of dihydroxyacetone kinases.
Prediction of a hexagonal SiO
2
phase affecting stabilities of MgSiO
3
and CaSiO
3
at multimegabar pressures
Authors: Tsuchiya Taku , Tsuchiya Jun
Published: January 2011

Ultrahigh-pressure phase relationship of SiO
2
silica in multimegabar pressure condition is still quite unclear. Here, we report a theoretical prediction on a previously uncharacterized stable structure of silica with an unexpected hexagonal Fe
2
P-type form. This phase, more stable than the cotunnite-type structure, a previously postulated postpyrite phase, was discovered to stabilize at 640 GPa through a careful structure search by means of ab initio density functional computations over various structure models. This is the first evidential result of the pressure-induced phase transition to the Fe
2
P-type structure among all dioxide compounds. The crystal structure consists of closely packed, fairly regular SiO
9
tricapped trigonal prisms with a significantly compact lattice. Additional investigation further elucidates large effects of this phase change in SiO
2
on the stability of MgSiO
3
and CaSiO
3
at multimegabar pressures. A postperovskite phase of MgSiO
3
breaks down at 1.04 TPa along an assumed adiabat of super-Earths and yields Fe
2
P-type SiO
2
and CsCl (B2)-type MgO. CaSiO
3
perovskite, on the other hand, directly dissociates into SiO
2
and metallic CaO, skipping a postperovskite polymorph. Predicted ultrahigh-pressure and temperature phase diagrams of SiO
2
, MgSiO
3
, and CaSiO
3
indicate that the Fe
2
P-type SiO
2
could be one of the dominant components in the deep mantles of terrestrial exoplanets and the cores of gas giants.
Role of the ubiquitin-like protein Urm1 as a noncanonical lysine-directed protein modifier
Authors: Van der Veen Annemarthe G. , Schorpp Kenji , Schlieker Christian , Buti Ludovico , Damon Jadyn R. , Spooner Eric , Ploegh Hidde L. , Jentsch Stefan
Published: January 2011

The ubiquitin (Ub)-related modifier Urm1 functions as a sulfur carrier in tRNA thiolation by means of a mechanism that requires the formation of a thiocarboxylate at the C-terminal glycine residue of Urm1. However, whether Urm1 plays an additional role as a Ub-like protein modifier remains unclear. Here, we show that Urm1 is conjugated to lysine residues of target proteins and that oxidative stress enhances protein urmylation in both
Saccharomyces cerevisiae
and mammalian cells. Similar to ubiquitylation, urmylation involves a thioester intermediate and results in the formation of a covalent peptide bond between Urm1 and its substrates. In contrast to modification by canonical Ub-like modifiers, however, conjugation of Urm1 involves a C-terminal thiocarboxylate of the modifier. We have confirmed that the peroxiredoxin Ahp1 is such a substrate in
S. cerevisiae
and found that Urm1 targets a specific lysine residue of Ahp1 in vivo. In addition, we have identified several unique substrates in mammalian cells and show that Urm1 targets at least two pathways on oxidant treatment. First, Urm1 is appended to lysine residues of three components that function in its own pathway (i.e., MOCS3, ATPBD3, and CTU2). Second, Urm1 is conjugated to the nucleocytoplasmic shuttling factor cellular apoptosis susceptibility protein. Thus, Urm1 has a conserved dual role by integrating the functions of prokaryotic sulfur carriers with those of eukaryotic protein modifiers of the Ub family.
Therapeutic enzyme deimmunization by combinatorial T-cell epitope removal using neutral drift
Authors: Cantor Jason R. , Yoo Tae Hyeon , Dixit Aakanksha , Iverson Brent L. , Forsthuber Thomas G. , Georgiou George
Published: January 2011

A number of heterologous enzymes have been investigated for cancer treatment and other therapeutic applications; however, immunogenicity issues have limited their clinical utility. Here, a new approach has been created for heterologous enzyme deimmunization whereby combinatorial saturation mutagenesis is coupled with a screening strategy that capitalizes on the evolutionary biology concept of neutral drift, and combined with iterative computational prediction of T-cell epitopes to achieve extensive reengineering of a protein sequence for reduced MHC-II binding propensity without affecting catalytic and pharmacological properties.Escherichia coliL-asparaginase II (EcAII), the only nonhuman enzyme approved for repeated administration, is critical in treatment of childhood acute lymphoblastic leukemia (ALL), but elicits adverse antibody responses in a significant fraction of patients. The neutral drift screening of combinatorial saturation mutagenesis libraries at a total of 12 positions was used to isolate an EcAII variant containing eight amino acid substitutions within computationally predicted T-cell epitopes—of which four were nonconservative—while still exhibitingkcat/KM = 106 M-1 s-1for L-Asn hydrolysis. Further, immunization of HLA-transgenic mice expressing the ALL-associated DRB1*0401 allele with the engineered variant resulted in significantly reduced T-cell responses and a 10-fold reduction in anti-EcAII IgG titers relative to the existing therapeutic. This significant reduction in the immunogenicity of EcAII may be clinically relevant for ALL treatment and illustrates the potential of employing neutral drift screens to achieve large jumps in sequence space as may be required for the deimmunization of heterologous proteins.
Embryonic day 9 yolk sac and intra-embryonic hemogenic endothelium independently generate a B-1 and marginal zone progenitor lacking B-2 potential
Authors: Yoshimoto Momoko , Montecino-Rodriguez Encarnacion , Ferkowicz Michael J. , Porayette Prashanth , Shelley W. Christopher , Conway Simon J. , Dorshkind Kenneth , Yoder Mervin C.
Published: January 2011

The majority of B lymphocytes in the adult mouse are generated in the bone marrow from hematopoietic stem cells (HSCs) that first appear in the aorta-gonado-mesonephros region of the fetus on embryonic day (E) 10.5–11. Comparatively less is known about B-cell development during embryogenesis. For example, which specific embryonic tissues participate in B lymphopoiesis and whether hematopoietic differentiation is skewed toward specific B-cell subsets in the embryo are unanswered questions, because the systemic circulation is initiated early during embryogenesis, resulting in an admixture of cells potentially originating from multiple sites. We demonstrate, usingNcx1−/−mice that lack systemic blood circulation, that the E9 yolk sac (YS) and the intra-embryonic para-aortic splanchnopleura (P-Sp) tissues independently give rise to AA4.1+CD19+B220lo-negB progenitor cells that preferentially differentiate into innate type B-1 and marginal zone (MZ) B cells but not into B-2 cells upon transplantation. We have further demonstrated that these B-1 progenitor cells arise directly from YS and P-Sp hemogenic endothelium. These results document the initial wave of innate B lymphopoietic progenitor cells available for seeding the fetal liver at E11. The results of these studies expand our knowledge of hemogenic endothelial sites specifying distinct B-1 and MZ cell fates apart from B-2 cells and independent of an HSC origin during development.
Ca
2
+
-dependent structural rearrangements within Na
+
–Ca
2+
exchanger dimers
Authors: John Scott A. , Ribalet Bernard , Weiss James N. , Philipson Kenneth D. , Ottolia Michela
Published: January 2011

Cytoplasmic Ca
2+
is known to regulate Na
+
–Ca
2+
exchanger (NCX) activity by binding to two adjacent Ca
2+
-binding domains (CBD1 and CBD2) located in the large intracellular loop between transmembrane segments 5 and 6. We investigated Ca
2+
-dependent movements as changes in FRET between exchanger proteins tagged with CFP or YFP at position 266 within the large cytoplasmic loop. Data indicate that the exchanger assembles as a dimer in the plasma membrane. Addition of Ca
2+
decreases the distance between the cytoplasmic loops of NCX pairs. The Ca
2+
-dependent movements detected between paired NCXs were abolished by mutating the Ca
2+
coordination sites in CBD1 (D421A, E451A, and D500V), whereas disruption of the primary Ca
2+
coordination site in CBD2 (E516L) had no effect. Thus, the Ca
2+
-induced conformational changes of NCX dimers arise from the movement of CBD1. FRET studies of CBD1, CBD2, and CBD1–CBD2 peptides displayed Ca
2+
-dependent movements with different apparent affinities. CBD1–CBD2 showed a Ca
2+
-dependent phenotype mirroring full-length NCX but distinct from both CBD1 and CBD2.
Archaeal 3′-phosphate RNA splicing ligase characterization identifies the missing component in tRNA maturation
Authors: Englert Markus , Sheppard Kelly , Aslanian Aaron , Yates John R. , Söll Dieter
Published: January 2011

Intron removal from tRNA precursors involves cleavage by a tRNA splicing endonuclease to yield tRNA 3′-halves beginning with a 5′-hydroxyl, and 5′-halves ending in a 2′,3′-cyclic phosphate. A tRNA ligase then incorporates this phosphate into the internucleotide bond that joins the two halves. Although this 3′-P RNA splicing ligase activity was detected almost three decades ago in extracts from animal and later archaeal cells, the protein responsible was not yet identified. Here we report the purification of this ligase from
Methanopyrus kandleri
cells, and its assignment to the still uncharacterized RtcB protein family. Studies with recombinant
Pyrobaculum aerophilum
RtcB showed that the enzyme is able to join spliced tRNA halves to mature-sized tRNAs where the joining phosphodiester linkage contains the phosphate originally present in the 2′,3′-cyclic phosphate. The data confirm RtcB as the archaeal RNA 3′-P ligase. Structural genomics efforts previously yielded a crystal structure of the
Pyrococcus horikoshii
RtcB protein containing a new protein fold and a conserved putative Zn
2+
binding cleft. This structure guided our mutational analysis of the
P. aerophilum
enzyme. Mutations of highly conserved residues in the cleft (C100A, H205A, H236A) rendered the enzyme inactive suggesting these residues to be part of the active site of the
P. aerophilum
ligase. There is no significant sequence similarity between the active sites of
P. aerophilum
ligase and that of T4 RNA ligase, nor ligases from plants and fungi. RtcB sequence conservation in archaea and in eukaryotes implicates eukaryotic RtcB as the long-sought animal 3′-P RNA ligase.
TNF-α promotes fracture repair by augmenting the recruitment and differentiation of muscle-derived stromal cells
Authors: Glass Graeme E. , Chan James K. , Freidin Andrew , Feldmann Marc , Horwood Nicole J. , Nanchahal Jagdeep
Published: January 2011

With an aging population, skeletal fractures are increasing in incidence, including the typical closed and the less common open fractures in normal bone, as well as fragility fractures in patients with osteoporosis. For the older age group, there is an urgent unmet need to induce predictable bone formation as well as improve implant fixation in situations such as hip joint replacement. Using a murine model of slow-healing fractures, we have previously shown that coverage of the fracture with muscle accelerated fracture healing and increased union strength. Here, we show that cells from muscle harvested after 3 d of exposure to an adjacent fracture differentiate into osteoblasts and form bone nodules in vitro. The osteogenic potential of these cells exceeds that of adipose and skin-derived stromal cells and is equivalent to bone marrow stromal cells. Supernatants from human fractured tibial bone fragments promote osteogenesis and migration of muscle-derived stromal cells (MDSC) in vitro. The main factor responsible for this is TNF-α, which promotes first MDSC migration, then osteogenic differentiation at low concentrations. However, TNF-α is inhibitory at high concentrations. In our murine model, addition of TNF-α at 1 ng/mL at the fracture site accelerated healing. These data indicate that manipulating the local inflammatory environment to recruit, then differentiate adjacent MDSC, may be a simple yet effective way to enhance bone formation and accelerate fracture repair. Our findings are based on a combination of human specimens and an in vivo murine model and may, therefore, translate to clinical care.
Y a-t-il un "sens" à une dégradation? A propos de Boivin de Provins
Authors: Bianciotto Gabriel
Published: January 2011

Résumé Le fabliau de Boivin de Provins, que distinguent sa qualité littérare et la truculence du récit, a été souvent retenu pour illustrer
le genre dans les anthologies. J. Rychner le premier a attiré l'attention sur les divergences textuelles entre les manuscrits existants, où
l'on doit voir deux versions différentes du même récit, et il a retenu l'exemple de Boivin pour caractériser le phénomène de remaniement
dans le développement d'une tradition manuscrite, désignant la leçon de A comme la plus proche de l'original. A sa suite, la "lecture" du
fabliau s'est faite constamment en partant de A, pour analyser P comme le témoin d'une réécriture assimilable à une corruption du conte
primitif. Un nouvel examen des deux leçons semble permettre d'aboutir à des conclusions radicalement opposées.