bluuebunny/crossref_metadata_2025 huggingface dataset:
Si delta doping in a GaN barrier layer of InGaN∕GaN multiquantum well for an efficient ultraviolet light-emitting diode
Authors: Kwon Min-Ki , Park Il-Kyu , Baek Sung-Ho , Kim Ja-Yeon , Park Seong-Ju
Published: May 2005

The effect of Si delta doping of the GaN barrier on the optical and electrical properties of an InGaN∕GaN ultraviolet light-emitting diode (UV LED) was studied. The photoluminescence (PL) intensity of the multiquantum well (MQW) and the output power of UV LED with an emission wavelength of 385 nm were greatly improved as the result of introducing a Si delta-doping layer in GaN barrier of an InGaN∕GaN MQW. A temperature-dependent PL study showed that the integrated intensity of the PL of a MQW with a Si delta-doping layer was slowly quenched with increasing temperature compared to that of a MQW without a Si delta-doping layer. The improvement in thermal stability and optical power of the UV MQW and LED is attributed to an increase in the injection of electrons from the Si delta-doped GaN barrier layer into the InGaN quantum well layer and an increase in hole accumulation due to the higher valance band offset of a Si delta-doped GaN barrier layer in a MQW structure.
Carrier density and mobility modifications of the two-dimensional electron gas due to an embedded AlN potential barrier layer in AlxGa1−xN∕GaN heterostructures
Authors: Kim T. W. , Choo D. C. , Yoo K. H. , Jung M. H. , Cho Y. H. , Lee Jae-Hoon , Lee Jung-Hee
Published: May 2005

The variations in the electronic properties of the two-dimensional electron gas (2DEG) in AlxGa1−xN∕GaN heterostructures due to an AlN embedded spacer layer were investigated by using Shubnikov–de Haas (SdH) measurements. The carrier densities of the 2DEGs in the Al0.4Ga0.6N∕AlN∕GaN and the Al0.4Ga0.6N∕GaN heterostructures, determined from the SdH data, were 8.75×1012 and 8.66×1012cm−2, respectively. The electron carrier density and the mobility of the 2DEG in the AlxGa1−xN∕GaN heterostructure with an AlN spacer layer were larger than those in the AlxGa1−xN∕GaN heterostructure. The electronic subband energies, the wave functions, and the Fermi energies in the Al0.4Ga0.6N∕AlN∕GaN and Al0.4Ga0.6N∕GaN heterostructures were calculated by using a self-consistent method taking into account spontaneous and piezoelectric polarizations. These present results indicate that the electronic parameters of the 2DEG occupying an AlxGa1−xN∕GaN heterostructure are significantly affected by an AlN spacer layer, and they can help to improve the understanding of the applications of AlxGa1−xN∕GaN heterostructures with AlN spacer layers in high-speed and high-power electronic devices.
The role of ferroelectric-ferromagnetic layers on the properties of superlattice-based multiferroics
Authors: Murugavel P. , Singh M. P. , Prellier W. , Mercey B. , Simon Ch. , Raveau B.
Published: May 2005

A series of superlattices and trilayers composed of ferromagnetic and ferroelectric or paraelectric layers were grown on (100) SrTiO3 by the pulsed-laser deposition technique. Their structural and magnetoelectric properties were examined. The superlattices made of ferromagnetic Pr0.85Ca0.15MnO3 (PCMO) and a ferroelectric, namely, Ba0.6Sr0.4TiO3 (BST) or BaTiO3, showed enhanced magnetoresistance (MR) at high applied magnetic field, whereas such enhancement was absent in Pr0.85Ca0.15MnO3∕SrTiO3 superlattices, which clearly demonstrates the preponderant role of the ferroelectric layers in this enhanced MR. Furthermore, the absence of enhanced MR in trilayers of PCMO∕BST indicates that the magnetoelectric coupling which is responsible for MR in these systems is stronger in multilayers than in their trilayer counterparts.
VSI
i
space–times and the ϵ-property
Authors: Pelavas N. , Coley A. , Milson R. , Pravda V. , Pravdová A.
Published: May 2005

We investigate Lorentzian space–times where all zeroth and first order curvature invariants vanish and discuss how this class differs from the one where all curvature invariants vanish (VSI). We show that for VSI space–times all components of the Riemann tensor and its derivatives up to some fixed order can be made arbitrarily small. We discuss this in more detail by way of examples.
The Maurer–Cartan structure of BRST differentials
Authors: Gao Jining
Published: May 2005

In this paper, we construct a sequence of generators of the BRST complex and reformulate the BRST differential so that it acts on elements of the complex much like the Maurer–Cartan differential acts on left-invariant forms. Thus our BRST differential is formally analogous to the differential defined on the BRST formulation of the Chevalley–Eilenberg cochain complex of a Lie algebra. Moreover, for an important class of physical theories, we show that in fact the differential is a Chevalley–Eilenberg differential. As one of the applications of our formalism, we show that the BRST differential provides a mechanism which permits us to extend a nonintegrable system of vector fields on a manifold to an integrable system on an extended manifold.
Electrostriction of lead zirconate titanate/polyurethane composites
Authors: Lam K. S. , Zhou Y. , Wong Y. W. , Shin F. G.
Published: May 2005

Electrostriction of a ferroelectric inclusion/nonferroelectric matrix composite system was studied. The samples were prepared by blending the lead zirconate titanate (PZT) particles with the thermoplastic polyurethane through extrusion and subsequently by hot pressing. Quasistatic cyclic electric fields were applied across the samples while strains and currents were monitored simultaneously. It was found that the electrostriction of the composites depended on the applied electric field in a hysteretic manner. In particular at the high-field regime, the samples exhibited a reversal in the electrostrictive strain. This switching effect occurred at a critical field which was inversely proportional to the PZT content. An associated increase in the displacement current with the critical field was also observed. It indicates that the switching in strain of the composites was mainly due to the flipping of the PZT dipoles in the nonferroelectric polymer matrix. A model was developed for describing the electrostriction behavior of this composite system and the calculated results are comparable to the experimental curves. The success of this theoretical model encourages its application further to the ferroelectric–ferroelectric composite systems.
Charge-state-resolved ion energy distributions of aluminum vacuum arcs in the absence and presence of a magnetic field
Authors: Rosén Johanna , Anders André , Mráz Stanislav , Schneider Jochen M.
Published: May 2005

The charge-state-resolved ion energy distributions (IEDs) of aluminum vacuum arc plasma species were measured and analyzed for different geometric and magnetic field configurations. The IEDs were fitted by shifted Maxwellian distributions. Plasma expansion in the absence of a magnetic field showed higher ion energies for higher charge states. The introduction of a magnetic field (independent of geometric configuration) resulted in a broader distribution and increased average ion energies. The energy gain was approximately proportional to the charge state, which may be due to the presence of electric fields in the magnetized plasma. The evolution of ion energy distributions is relevant to thin-film growth, and it is shown that the IEDs can be modified by suitable magnetic field configurations.
Autocorrelation analysis and statistical consideration for the determination of velocity fluctuations in fusion plasmas
Authors: Bencze A. , Zoletnik S.
Published: May 2005

A new statistical method is proposed and investigated to detect modulation in the poloidal flow velocity via the motion of turbulent eddies. The technique needs a single-point measurement only, and investigates modulation of the autocorrelation function. In order to evaluate the sensitivity of the method an analytical expression is derived for the relative scatter of the autocorrelation function when the fluctuating signal is composed of random events with a given event rate. Detailed formulas are obtained for the case of identical Gaussian pulses. The result of the calculation allows estimation of the scatter of the autocorrelation function due to both event statistical and detector noise.
Stability of dust voids
Authors: Vladimirov S. V. , Tsytovich V. N. , Morfill G. E.
Published: May 2005

Dust voids are frequently observed as dust-free regions in a dusty plasma. Experiments demonstrate a variety of dust void structures such as stable or unstable voids, global “heatbeat” modes of oscillations of voids, dust voids in the center of the chamber or near its walls. Theory shows that a dust void generally results from the balance of the electrostatic and the plasma (such as the ion drag) forces acting on a dust particle. Here, the stability theory of a void is developed and the void behavior is modeled. It is shown that sequences of stable and unstable void sizes can exist. The dynamics of dust in a plasma follows these stability characteristics leading to various stable and/or unstable dust void structures.
Effect of oxygen addition to methane on growth of vertically oriented carbon nanotubes by radio-frequency plasma-enhanced chemical-vapor deposition
Authors: Ikuno Takashi , Honda Shin-ichi , Kamada Kazunori , Oura Kenjiro , Katayama Mitsuhiro
Published: May 2005

We have investigated the effect of oxygen addition to methane on the growth of vertically oriented carbon nanotubes (VCNTs) by radio-frequency plasma-enhanced chemical-vapor deposition (RFCVD). By adding moderate concentrations of oxygen to methane during RFCVD, highly crystalline VCNTs were densely grown at 430°C. With increasing oxygen concentration, the length of the VCNTs was increased and the linearity was degraded, whereas when excess oxygen was added to methane, no VCNTs were grown. Plasma states were investigated by optical emission spectroscopy during RFCVD. In the case of RFCVD with oxygen added to methane, peaks due to CO and OH radicals were dominant. The CO species appear to be one of the key factors in the growth of well-crystallized VCNTs. Moreover, VCNTs were grown at temperatures as low as 350°C with the addition of moderate amounts of oxygen to methane in RFCVD.
Structural and electrical properties of Ge nanocrystals embedded in SiO2 by ion implantation and annealing
Authors: Duguay S. , Grob J. J. , Slaoui A. , Le Gall Y. , Amann-Liess M.
Published: May 2005

Silicon dioxide (SiO2) on Si layers with embedded germanium nanocrystals (Ge-ncs) were fabricated using Ge+ implantation and subsequent annealing. Transmission electron microscopy and Rutherford backscattering spectrometry have been used to study the Ge redistribution in the SiO2 films as a function of annealing temperature. A monolayer of Ge-ncs near the Si∕SiO2 interface was formed under specific annealing conditions. This layer, with a nc density and mean size measured to be, respectively, 1.1×1012∕cm2 and 5nm, is located at approximately 4nm from the Si∕SiO2 interface. Capacitance–voltage measurements were performed on metal-oxide-semiconductor structures containing such implanted SiO2 layers in order to study their electrical properties. The results indicate a strong memory effect at relatively low programming voltages (<5V) due to the presence of Ge-ncs near the Si∕SiO2 interface.
The phase-modulated logistic map
Authors: Nandi Amitabha , Dutta Debabrata , Bhattacharjee Jayanta K. , Ramaswamy Ramakrishna
Published: May 2005

We study the logistic mapping with the nonlinearity parameter varied through a delayed feedback mechanism. This history dependent modulation through a phaselike variable offers an enhanced possibility for stabilization of periodic dynamics. Study of the system as a function of nonlinearity and modulation parameters reveals new phenomena: In addition to period-doubling and tangent bifurcations, there can be bifurcations where the period increases by unity. These are extensions of crises that arise in nonlinear dynamical systems. Periodic orbits in this system can be systematized via the kneading theory, which in the present case extends the analysis of Metropolis, Stein, and Stein for unimodal maps.
Edge-localized modes and edge transport in spherical tokamaks
Authors: Kleva Robert G. , Guzdar Parvez N.
Published: May 2005

Turbulent energy transport in numerical simulations of the edge region of spherical tokamaks with small toroidal aspect ratio A=1.5 is directly compared to that in conventional tokamaks with larger aspect ratio A=3. Depending upon the aspect ratio of the torus, the energy flux can vary greatly. While a tokamak plasma with aspect ratio A=3 is in the high (H) mode where the transport rate is small, an otherwise identical tokamak plasma with small aspect ratio A=1.5 exhibits extremely poor confinement. The magnitude of the energy flux in these two cases differs by a multiplicative factor larger than 50. However, good H mode confinement in small aspect ratio spherical tokamaks can be obtained by a further increase in the edge density gradient. Confinement is then dominated by bursts of ballooning modes which periodically transport energy to large major radius. The periodic bursts in the numerical simulations are similar to the periodic radiation bursts that characterize edge-localized modes in tokamaks.
Lubrication flow between a cavity and a flexible wall
Authors: Yin Xiuyan , Kumar Satish
Published: May 2005

Lubrication flows near deformable solid boundaries occur in a diverse range of settings including coating and printing processes, biological systems, and suspensions. In order to examine the effect of surface topography on the elastohydrodynamic interactions that arise in these flows, the flow between a rigid cavity and a flexible wall is studied. Reynolds equation for the fluid is coupled to a model for the wall which is backed by a series of springs and/or held by a uniform tension force. The resulting nonlinear ordinary differential equations are then solved numerically to obtain pressure profiles and wall positions. When the wall modulus or tension is large relative to viscous forces, the wall hardly deforms and both a pressure mountain and valley are observed due to the gap change produced by the cavity topography. When the wall modulus and tension are small relative to viscous forces, the wall easily deforms and assumes a shape similar to that of the cavity. The pressure profiles are also dramatically altered and in some cases show only a valley without a mountain. Cavity shape is found to have a significant influence on both the pressure profiles and the wall deformation. The results suggest that surface topography may significantly modify the elastohydrodynamic interactions that arise in lubrication flows near deformable solid boundaries.
Leakage current characteristics of Pt∕Bi3.25La0.75Ti3O12∕Pt thin-film capacitors
Authors: Wu Di , Li Aidong , Ming Naiben
Published: May 2005

Leakage current characteristics of Pt∕Bi3.25La0.75Ti3O12(BLaT)∕Pt ferroelectric thin-film capacitors were studied as a function of temperature (30∼220°C). Schottky emission dominated the leakage current above the ohmic conduction regime. The Schottky barrier height of BLaT∕Pt junction was calculated to be 0.84 eV. At low temperatures (⩽70°C), the breakdown voltage was observed to increase with increasing temperature, which indicates avalanche breakdown. Above this temperature, no apparent dielectric breakdown was observed. The high-temperature high-voltage leakage current showed a linear logJ–V relation and was interpreted as ionic hopping conduction of thermally activated oxygen vacancies.
Meanders and reconnection–collision sequences in the standard nontwist map
Authors: Wurm A. , Apte A. , Fuchss K. , Morrison P. J.
Published: May 2005

New global periodic orbit collision and separatrix reconnection scenarios exhibited by the standard nontwist map are described in detail, including exact methods for determining reconnection thresholds, methods that are implemented numerically. Results are compared to a parameter space breakup diagram for shearless invariant curves. The existence of meanders, invariant tori that are not graphs, is demonstrated numerically for both odd and even period reconnection for certain regions in parameter space. Implications for transport are discussed.
Public-key encryption based on generalized synchronization of coupled map lattices
Authors: Wang Xingang , Gong Xiaofeng , Zhan Meng , Lai Choy Heng
Published: May 2005

Currently used public-key cryptosystems are based on difficulties in solving certain numeric theoretic problems, in which the way to predict the private key from the knowledge of the public key is computationally infeasible. Here we propose a method of constructing public-key cryptosystems by generalized synchronization of coupled map lattices, in which the difficulty in predicting the synchronous function is used as the trap-door function to deduce the private key from the public key. In specific, we implement this idea on the method of “Merkle’s puzzles,” and find that, incorporated with the chaotic dynamics, this traditional method is equipped with some new features and can be practical in certain situations.
Hot-core characterization of direct-drive spherical cryogenic D2 target implosion
Authors: Smalyuk V. A. , Delettrez J. A. , Dumanis S. B. , Epstein R. , Glebov V. Yu. , Meyerhofer D. D. , Radha P. B. , Regan S. P. , Sangster T. C. , Stoeckl C. , Toscano N. C. , Frenje J. A. , Li C. K. , Petrasso R. D. , Séguin F. H. , Koch J. A.
Published: May 2005

A novel model to infer the hot-core temperature–density profiles in cryogenic deuterium capsule implosions is presented. The profiles are consistent with the measured primary deuterium–deuterium and secondary deuterium–tritium yields, the neutron-averaged ion temperature, and the x-ray image at peak neutron production. The electron pressure and the areal density of a neutron-producing region were inferred to be 2.7±0.4Gbar and ∼10mg∕cm2, respectively. This new model introduces a more accurate hot-core characterization from previous techniques.
Improved upper critical field in bulk-form magnesium diboride by mechanical alloying with carbon
Authors: Senkowicz B. J. , Giencke J. E. , Patnaik S. , Eom C. B. , Hellstrom E. E. , Larbalestier D. C.
Published: May 2005

High-energy milling of magnesium diboride (MgB2) prereacted powder renders the material largely amorphous through extreme mechanical deformation and is suitable for mechanically alloying MgB2 with dopants including carbon. Bulk samples of milled carbon and MgB2 powders subjected to hot isostatic pressing and Mg vapor annealing have achieved upper critical fields in excess of 32T and critical current density approaching 106A∕cm2.
On-demand single-photon source for 1.3μm telecom fiber
Authors: Ward M. B. , Karimov O. Z. , Unitt D. C. , Yuan Z. L. , See P. , Gevaux D. G. , Shields A. J. , Atkinson P. , Ritchie D. A.
Published: May 2005

We demonstrate an on-demand single-photon source that is compatible with standard telecom optical fiber. Through careful control of the critical strains of InAs∕GaAs self-assembled quantum dots, we produce a microcavity sample with a low density of large dots emitting into the fiber-optic transmission band at 1.3μm. The second-order correlation function of the source reveals a strong suppression in the rate of multiphoton pulses at both 5K and above 30K. The source may be useful for fiber-optic-based single-photon applications, such as quantum metrology, quantum communications, and distributed quantum computing.
Dynamic anisotropy of thin Permalloy films measured by use of angle-resolved pulsed inductive microwave magnetometry
Authors: Schneider M. L. , Kos A. B. , Silva T. J.
Published: May 2005

In this study, angle-resolved pulsed inductive microwave magnetometry is used to investigate the symmetry of the dynamic anisotropy of thin Permalloy films. We measured the dynamic anisotropy field as a function of angle between the easy axis and the applied bias field. We found that, in addition to the expected uniaxial anisotropy, there is a rotatable component of anisotropy. This component of the anisotropy is present only during the dynamics measurements and is attributed to surface effects in the thin films. However, the native oxide layer is not the cause of the rotatable anisotropy components in these films.
Cross-sectional ballistic electron emission microscopy for Schottky barrier height profiling on heterostructures
Authors: Rakoczy D. , Strasser G. , Smoliner J.
Published: May 2005

In this work, cross-sectional ballistic electron emission microscopy is introduced to determine a Schottky barrier height profile of a GaAs–AlGaAs multiheterostructure in cross-sectional geometry. Ballistic electron spectra measured across the heterostructure with nanometer resolution indicate that the measured Schottky barrier height profile is smeared out compared to the conduction band profile calculated from the sample growth parameters. We attribute this behavior to lateral band bending effects along the heterojunction. In addition, we have evidence that the barrier height profile is influenced by single impurities in the AlGaAs layers.
A self-similar array model of single-walled carbon nanotubes
Authors: Sun C. H. , Li F. , Liu C. G. , Lu G. Q. , Cheng H. M. , Sun C. H. , Lu G. Q.
Published: May 2005

To describe single-walled carbon nanotube (SWNT) arrays, we propose a self-similar array model. For isolated SWNT bundles, the self-similar array model is consistent with the classical triangular array model; for SWNT bundle arrays, it can present hierarchy structures and specify different array configurations. Based on this self-similar array model, we calculated the energetics of SWNT arrays, investigated the driving force for the formation of macroscopic SWNT arrays, and briefly discussed the hierarchy structures in real macroscopic SWNT arrays.
Single-piece polycrystalline silicon accumulation/depletion/inversion model with implicit/explicit surface-potential solutions
Authors: Chiah S. B. , Zhou X. , Chandrasekaran K. , Shangguan W. Z. , See G. H. , Pandey S. M.
Published: May 2005

A single-piece analytical equation for the surface potential at the polycrystalline-silicon (poly-Si) gate of a metal-oxide-semiconductor field-effect transistor is presented, which accounts for the poly-accumulation, poly-depletion, and poly-inversion effects. It is shown that the model accurately describes the physical behavior of the surface potentials, gate charge, and capacitance, with smooth transitions, which has been verified with iterative, explicit, and numerical solutions. The proposed model can be used in implicit or explicit surface-potential-based formulations.
Super-small energy gaps of single-walled carbon nanotube strands
Authors: Zhu Hongwei , Zhao Guang-Lin , Masarapu Charan , Young David P. , Wei Bingqing
Published: May 2005

The temperature dependence of the resistance measured on long single-walled carbon nanotube (SWNT) strands has been investigated. By applying a simple model to the detailed analysis of our experimental results, we discovered a super-small energy gap of 1–3meV, which is an intrinsic property of the “metallic” SWNT bundles in long SWNT strands.
Strain-assisted tunneling current through TbMnO3∕Nb-1 wt %-doped SrTiO3 p–n junctions
Authors: Cui Y. M. , Zhang L. W. , Wang C. C. , Xie G. L. , Chen C. P. , Cao B. S.
Published: May 2005

Simple oxide heterostructures have been fabricated by growing multiferroic TbMnO3 thin film on Nb-1 wt %-doped SrTiO3 substrate. In addition to the beneficial rectifying characteristics in a temperature range from 350 to 30 K, the intriguing observation is that at constant reverse bias the current increases with decreasing temperature below 275 K. By analyzing the band diagram, the anomalous increasing current with decreasing temperature was ascribed to the strain-assisted tunneling current through TbMnO3∕Nb-doped p–n junctions.
Photonic band gaps and localization in the Thue–Morse structures
Authors: Jiang Xunya , Zhang Yonggang , Feng Songlin , Huang Kerwyn C. , Yi Yasha , Joannopoulos J. D.
Published: May 2005

Both theoretically and experimentally, we demonstrate that the photonic band gaps in Thue–Morse aperiodic systems can be separated into two flavors, the fractal gaps and the traditional gaps, distinguished by the presence or absence of fractal structure, respectively. The origin of two kind gaps is explained by the different interface correlations. This explanation is confirmed by the gap width behaviors. In addition, the eigenstates near the fractal gaps have a cluster-periodic form, while those near the traditional gaps have the Bloch wavelike form. Our detailed study of these differences is essential for understanding the spectra and light localization in aperiodic systems.
Self-assembled monolayer-enhanced hydrogen sensing with ultrathin palladium films
Authors: Xu T. , Zach M. P. , Xiao Z. L. , Rosenmann D. , Welp U. , Kwok W. K. , Crabtree G. W.
Published: May 2005

Resistive-type palladium structures for hydrogen sensing remains as a research focus for their simplicity in device construction. We demonstrate that a siloxane self-assembled monolayer placed between a substrate and an evaporated ultrathin Pd film promotes the formation of small Pd nanoclusters and reduces the stiction between the palladium and the substrate. The resulting Pd nanocluster film can detect 2%H2 with a rapid response time of ∼70ms and is sensitive to 25 ppm hydrogen, detectable by a 2% increase in conductance due to the hydrogen-induced palladium lattice expansion.
Spectroscopic ellipsometry study of wurtzite InN epitaxial films on Si(111) with varied carrier concentrations
Authors: Ahn H. , Shen C.-H. , Wu C. -L. , Gwo S.
Published: May 2005

Spectroscopic ellipsometry (SE) has been performed to determine the optical properties of the InN epitaxial films grown by nitrogen-plasma-assisted molecular-beam epitaxy on Si(111) substrates using a double-buffer technique. In addition to SE, cross-sectional transmission electron microscopy and x-ray diffraction reveal that epitaxially grown InN epilayer is homogeneous with high crystalline quality and does not include any metallic In. SE results analyzed by the Adachi’s model for the dielectric function of InN show that the optical absorption edge of InN varies in the range of 0.76–0.83 eV depending on the carrier concentration, which is determined by the thickness of the AlN buffer layer.
Fabrication and characterization of 1.1GHz blade nanoelectromechanical resonator
Authors: Agache V. , Legrand B. , Collard D. , Buchaillot L. , Fujita H.
Published: May 2005

An electromechanical resonator based on a blade geometry is proposed in this letter. This particular geometry allows self-alignment of the mechanical resonator structure to its lateral electrodes while achieving high eigenfrequencies in the GHz range. This letter reports both the fabrication process of the device and measurements in order to extract its mechanical response according to a lateral flexural solicitation. A mixing setup characterization is performed in order to suppress direct capacitive coupling feedthrough from the output current measurement and enable the effective quality factor extraction.
Mechanical properties of ZnO epitaxial layers grown on a- and c-axis sapphire
Authors: Coleman V. A. , Bradby J. E. , Jagadish C. , Munroe P. , Heo Y. W. , Pearton S. J. , Norton D. P. , Inoue M. , Yano M.
Published: May 2005

The mechanical properties of zinc oxide epitaxial layers grown on a- and c-axis sapphire have been studied by spherical nanoindentation and cross-sectional transmission electron microscopy. As-grown threading dislocations, which are characteristic of epitaxial material, combined with the presence of the much harder, underlying substrate are found to have a significant effect on the mechanical behavior of ZnO epilayers as compared to bulk material. Epilayer material is found to be significantly harder than its bulk counterpart. For a-axis epilayers, analysis of load–unload data yields a hardness of 6.6±1.2GPa, and 5.75±0.8GPa for c-axis layers. We attribute this increased hardness to strain compensation via the presence of as-grown defects. These defects inhibit the slip mechanism responsible for relative softness of bulk single crystals. The absence of pop-in events from analyzed continuous-load nanoindentation data is further evidence for strain compensation by native defects within the epilayers. Large variations in the spread of collected data are indicative of inhomegenity in the epilayers.
Operation and high-frequency performance of nanoscale unipolar rectifying diodes
Authors: Mateos J. , Vasallo B. G. , Pardo D. , González T.
Published: May 2005

By means of the microscopic transport description supplied by a semiclassical two-dimensional Monte Carlo simulator, we provide an in depth explanation of the operation (based on electrostatic effects) of the nanoscale unipolar rectifying diode, so called self-switching diode, recently proposed in A. M. Song, M. Missous, P. Omling, A. R. Peaker, L. Samuelson, and W. Seifert, Appl. Phys. Lett. 83, 1881 (2003). The simple downscaling of this device and the intrinsically high electron velocity of InGaAs channels allows one to envisaging the fabrication of structures working in the THz range. We analyze the high-frequency performance of the diodes and provide design considerations for the optimization of the downscaling process.
Near-field optical photolithography for high-aspect-ratio patterning using bilayer resist
Authors: Naya M. , Tsuruma I. , Tani T. , Mukai A. , Sakaguchi S. , Yasunami S.
Published: May 2005

We attempted to achieve a sufficiently large high-aspect-ratio patterning in near-field optical photolithography employing a bilayer resist process. In this experiment, we formed a resist pattern with a linewidth of 130nm and a depth of 550nm. This suggests that a practical method of near-field optical photolithography should become available. We also studied the dependency of an optical pattern on resist film thickness by the three-dimentional finite-difference time-domain method. The calculation results suggest that the resist film thickness affects the distribution of light in the resist.
Tuning negative differential resistance in a molecular film
Authors: Grobis M. , Wachowiak A. , Yamachika R. , Crommie M. F.
Published: May 2005

We have observed variable negative differential resistance (NDR) in scanning tunneling spectroscopy measurements of a double layer of C60 molecules on a metallic surface. Minimum to maximum current ratios in the NDR region are tuned by changing the tunneling barrier width. The multilayer geometry is critical, as NDR is not observed when tunneling into a C60 monolayer. Using a simple model, we show that the observed NDR behavior is explained by voltage-dependent changes in the tunneling barrier height.
Origin of the 370-nm luminescence in Si oxide nanostructures
Authors: Yang X. , Wu X. L. , Li S. H. , Li H. , Qiu T. , Yang Y. M. , Chu P. K. , Siu G. G.
Published: May 2005

The nature of the ∼370-nm (3.35-eV) photoluminescence (PL) in Si oxide and nanostructures, which has a PL excitation band at ∼260nm, is studied experimentally and theoretically. It is revealed that the PL occurs at the interface between Si structure and its oxide and is closely associated with a characteristic infrared absorption band at ∼1250cm−1. Spectral analyses suggest that the ∼370-nm PL originates in the –SiO3 group, which bonds to Si structural surface. The density functional theory calculations are consistent with our experiments. This work clarifies some controversies regarding the ∼370-nm PL mechanisms in a number of Si oxide and nanostructures.
NO and NO2 production in pulsed low pressure dc discharge
Authors: Rousseau Antoine , Gatilova Lina V. , Röpcke Jürgen , Meshchanov Alexander V. , Ionikh Yury Z.
Published: May 2005

Simultaneous measurements of both NO and NO2 are performed downstream a pulsed low pressure dc discharge in flowing air using tunable diode laser absorption spectroscopy in the infrared region. Pulse duration and repetition rate range from 20 μs to 5 ms and from 50 to 1000 Hz, respectively. The gas pressure is 4 mbar and the peak current is 80 mA. Experimental results show that NO and NO2 production depends only on the duty cycle ratio, that is, on the average power at a given current. A numerical computation of a simplified kinetics agrees well with experiment results.
Brain response to putative pheromones in homosexual men
Authors: Savic Ivanka , Berglund Hans , Lindström Per
Published: May 2005

The testosterone derivative 4,16-androstadien-3-one (AND) and the estrogen-like steroid estra-1,3,5(10),16-tetraen-3-ol (EST) are candidate compounds for human pheromones. AND is detected primarily in male sweat, whereas EST has been found in female urine. In a previous positron emission tomography study, we found that smelling AND and EST activated regions covering sexually dimorphic nuclei of the anterior hypothalamus, and that this activation was differentiated with respect to sex and compound. In the present study, the pattern of activation induced by AND and EST was compared among homosexual men, heterosexual men, and heterosexual women. In contrast to heterosexual men, and in congruence with heterosexual women, homosexual men displayed hypothalamic activation in response to AND. Maximal activation was observed in the medial preoptic area/anterior hypothalamus, which, according to animal studies, is highly involved in sexual behavior. As opposed to putative pheromones, common odors were processed similarly in all three groups of subjects and engaged only the olfactory brain (amygdala, piriform, orbitofrontal, and insular cortex). These findings show that our brain reacts differently to the two putative pheromones compared with common odors, and suggest a link between sexual orientation and hypothalamic neuronal processes.
Alternative
Gnas
gene products have opposite effects on glucose and lipid metabolism
Authors: Chen Min , Gavrilova Oksana , Liu Jie , Xie Tao , Deng Chuxia , Nguyen Annie T. , Nackers Lisa M. , Lorenzo Javier , Shen Laura , Weinstein Lee S.
Published: May 2005

Gnas
is an imprinted gene with multiple gene products resulting from alternative splicing of different first exons onto a common exon 2. These products include stimulatory G protein α-subunit (G
s
α), the G protein required for receptor-stimulated cAMP production; extralarge G
s
α (XLαs), a paternally expressed G
s
α isoform; and neuroendocrine-specific protein (NESP55), a maternally expressed chromogranin-like protein. G
s
α undergoes tissue-specific imprinting, being expressed primarily from the maternal allele in certain tissues. Heterozygous mutation of exon 2 on the maternal (E2
m-/+
) or paternal (E2
+/p-
) allele results in opposite effects on energy metabolism. E2
m-/+
mice are obese and hypometabolic, whereas E2
+/p-
mice are lean and hypermetabolic. We now studied the effects of G
s
α deficiency without disrupting other
Gnas
gene products by deleting G
s
α exon 1 (E1). E1
+/p-
mice lacked the E2
+/p-
phenotype and developed obesity and insulin resistance. The lean, hypermetabolic, and insulin-sensitive E2
+/p-
phenotype appears to result from XLαs deficiency, whereas loss of paternal-specific G
s
α expression in E1
+/p-
mice leads to an opposite metabolic phenotype. Thus, alternative
Gnas
gene products have opposing effects on glucose and lipid metabolism. Like E2
m-/+
mice, E1
m-/+
mice had s.c. edema at birth, presumably due to loss of maternal G
s
α expression. However, E1
m-/+
mice differed from E2
m-/+
mice in other respects, raising the possibility for the presence of other maternal-specific gene products. E1
m-/+
mice had more severe obesity and insulin resistance and lower metabolic rate relative to E1
+/p-
mice. Differences between E1
m-/+
and E1
+/p-
mice presumably result from differential effects on G
s
α expression in tissues where G
s
α is normally imprinted.
Cellulose utilization by
Clostridium thermocellum
: Bioenergetics and hydrolysis product assimilation
Authors: Zhang Yi-Heng Percival , Lynd Lee R.
Published: May 2005

The bioenergetics of cellulose utilization by
Clostridium thermocellum
was investigated. Cell yield and maintenance parameters,

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\begin{equation*}Y_{X/{\mathrm{ATP}}}^{{\mathrm{True}}}=16.44\end{equation*}\end{document}

g cell/mol ATP and
m
= 3.27 mmol ATP/g cell per hour, were obtained from cellobiose-grown chemostats, and it was shown that one ATP is required per glucan transported. Experimentally determined values for

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\begin{equation*}G_{{\mathrm{ATP}}}^{P-T}\end{equation*}\end{document}

(ATP from phosphorolytic β-glucan cleavage minus ATP for substrate transport, mol ATP/mol hexose) from chemostats fed β-glucans with degree of polymerization (DP) 2-6 agreed well with the predicted value of (
n
-1)/
n
(
n
= mean cellodextrin DP assimilated). A mean

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value of 0.52 ± 0.06 was calculated for cellulose-grown chemostat cultures, corresponding to
n
= 4.20 ± 0.46. Determination of intracellular β-glucan radioactivity resulting from
14
C-labeled substrates showed that uptake is different for cellulose and cellobiose (G2). For
14
C-cellobiose, radioactivity was greatest for G2; substantially smaller but measurable for G1, G3, and G4; undetectable for G5 and G6; and
n
was ≈2. For
14
C-cellulose, radioactivity was greatest for G5; lower but substantial for G6, G2, and G1; very low for G3 and G4; and
n
was ≈4. These results indicate that: (
i
)
C. thermocellum
hydrolyzes cellulose by a different mode of action from the classical mechanism involving solubilization by cellobiohydrolase; (
ii
) bioenergetic benefits specific to growth on cellulose are realized, resulting from the efficiency of oligosaccharide uptake combined with intracellular phosphorolytic cleavage of β-glucosidic bonds; and (
iii
) these benefits exceed the bioenergetic cost of cellulase synthesis, supporting the feasibility of anaerobic biotechnological processing of cellulosic biomass without added saccharolytic enzymes.
Dissecting human cytomegalovirus gene function and capsid maturation by ribozyme targeting and electron cryomicroscopy
Authors: Yu Xuekui , Trang Phong , Shah Sanket , Atanasov Ivo , Kim Yong-Hwan , Bai Yong , Zhou Z. Hong , Liu Fenyong
Published: May 2005

Human CMV (HCMV) is the leading viral cause of birth defects and causes one of the most common opportunistic infections among transplant recipients and AIDS patients. Cleavage of internal scaffolding proteins by the viral protease (Pr) occurs during HCMV capsid assembly. To gain insight into the mechanism of HCMV capsid maturation and the roles of the Pr in viral replication, an RNase P ribozyme was engineered to target the Pr mRNA and down-regulate its expression by >99%, generating premature Pr-minus capsids. Furthermore, scaffolding protein processing and DNA encapsidation were inhibited by 99%, and viral growth was reduced by 10,000-fold. 3D structural comparison of the Pr-minus and wild-type B capsids by electron cryomicroscopy, at an unprecedented 12.5-Å resolution, unexpectedly revealed that the structures are identical in their overall shape and organization. However, the Pr-minus capsid contains tenuous connections between the scaffold and the capsid shell, whereas the wild-type B capsid has extra densities in its core that may represent the viral Pr. Our findings indicate that cleavage of the scaffolding protein is not associated with the morphological changes that occur during capsid maturation. Instead, the protease appears to be required for DNA encapsidation and the subsequent maturation steps leading to infectious progeny. These results therefore provide key insights into an essential step of HCMV infection using an RNase P ribozyme-based inhibition strategy.
Functional organization of human occipital-callosal fiber tracts
Authors: Dougherty Robert F. , Ben-Shachar Michal , Bammer Roland , Brewer Alyssa A. , Wandell Brian A.
Published: May 2005

Diffusion tensor imaging (DTI) and fiber tracking (FT) were used to measure the occipital lobe fiber tracts connecting the two hemispheres in individual human subjects. These tracts are important for normal vision. Also, damage to portions of these tracts is associated with alexia. To assess the reliability of the DTI-FT measurements, occipital-callosal projections were estimated from each subject's left and right hemispheres independently. The left and right estimates converged onto the same positions within the splenium. We further characterized the properties of the estimated occipital-callosal fiber tracts by combining them with functional MRI. We used functional MRI to identify visual field maps in cortex and labeled fibers by the cortical functional response at the fiber endpoint. This labeling reveals a regular organization of the fibers within the splenium. The dorsal visual maps (dorsal V3, V3A, V3B, V7) send projections through a large band in the middle of the splenium, whereas ventral visual maps (ventral V3, V4) send projections through the inferior-anterior corner of the splenium. The agreement between the independent left/right estimates, further supported by previous descriptions of homologous tracts in macaque, validates the DTI-FT methods. However, a principal limitation of these methods is low sensitivity: a large number of fiber tracts that connect homotopic regions of ventral and lateral visual cortex were undetected. We conclude that most of the estimated tracts are real and can be localized with a precision of 1-2 mm, but many tracts are missed because of data and algorithm limitations.
Insights into TOR function and rapamycin response: Chemical genomic profiling by using a high-density cell array method
Authors: Xie Michael W. , Jin Fulai , Hwang Heejun , Hwang Seungmin , Anand Vikram , Duncan Mara C. , Huang Jing
Published: May 2005

With the advent of complete genome sequences, large-scale functional analyses are generating new excitement in biology and medicine. To facilitate genomewide functional analyses, we developed a high-density cell array with quantitative and automated readout of cell fitness. Able to print at >×10 higher density on a standard microtiter plate area than currently possible, our cell array allows single-plate screening of the complete set of
Saccharomyces cerevisiae
gene-deletion library and significantly reduces the amount of small molecules and other materials needed for the study. We used this method to map the relation between genes and cell fitness in response to rapamycin, a medically important natural product that targets the eukaryotic kinase Tor. We discuss the implications for pharmacogenomics and the uncharted complexity in genotype-dependent drug response in molecularly targeted therapies. Our analysis leads to several basic findings, including a class of gene deletions that confer better fitness in the presence of rapamycin. This result provides insights into possible therapeutic uses of rapamycin/CCI-779 in the treatment of neurodegenerative diseases (including Alzheimer's, Parkinson's, and Huntington's diseases), and cautions the possible existence of similar rapamycin-enhanceable mutations in cancer. It is well established in yeast that although TOR2 has a unique rapamycin-insensitive function, TOR1 and TOR2 are interchangeable in the rapamycin-sensitive functions. We show that even the rapamycin-sensitive functions are distinct between TOR1 and TOR2 and map the functional difference to a ≈120-aa region at the N termini of the proteins. Finally, we discuss using cell-based genomic pattern recognition in designing electronic or optical biosensors.
Detecting remotely related proteins by their interactions and sequence similarity
Authors: Espadaler Jordi , Aragüés Ramón , Eswar Narayanan , Marti-Renom Marc A. , Querol Enrique , Avilés Francesc X. , Sali Andrej , Oliva Baldomero
Published: May 2005

The function of an uncharacterized protein is usually inferred either from its homology to, or its interactions with, characterized proteins. Here, we use both sequence similarity and protein interactions to identify relationships between remotely related protein sequences. We rely on the fact that homologous sequences share similar interactions, and, therefore, the set of interacting partners of the partners of a given protein is enriched by its homologs. The approach was benchmarked by assigning the fold and functional family to test sequences of known structure. Specifically, we relied on 1,434 proteins with known folds, as defined in the Structural Classification of Proteins (SCOP) database, and with known interacting partners, as defined in the Database of Interacting Proteins (DIP). For this subset, the specificity of fold assignment was increased from 54% for position-specific iterative
blast
to 75% for our approach, with a concomitant increase in sensitivity for a few percentage points. Similarly, the specificity of family assignment at the
e
-value threshold of 10
-8
was increased from 70% to 87%. The proposed method would be a useful tool for large-scale automated discovery of remote relationships between protein sequences, given its unique reliance on sequence similarity and protein-protein interactions.
Patellamide A and C biosynthesis by a microcin-like pathway inProchloron didemni, the cyanobacterial symbiont ofLissoclinum patella
Authors: Schmidt Eric W. , Nelson James T. , Rasko David A. , Sudek Sebastian , Eisen Jonathan A. , Haygood Margo G. , Ravel Jacques
Published: May 2005

Prochloronspp. are obligate cyanobacterial symbionts of many didemnid family ascidians. It has been proposed that the cyclic peptides of the patellamide class found in didemnid extracts are synthesized byProchloronspp., but studies in which host and symbiont cells are separated and chemically analyzed to identify the biosynthetic source have yielded inconclusive results. As part of theProchloron didemnisequencing project, we identified patellamide biosynthetic genes and confirmed their function by heterologous expression of the whole pathway inEscherichia coli. The primary sequence of patellamides A and C is encoded on a single ORF that resembles a precursor peptide. We propose that this prepatellamide is heterocyclized to form thiazole and oxazoline rings, and the peptide is cleaved to yield the two cyclic patellamides, A and C. This work represents the full sequencing and functional expression of a marine natural-product pathway from an obligate symbiont. In addition, a related cluster was identified inTrichodesmium erythraeumIMS101, an important bloom-forming cyanobacterium.