bluuebunny/crossref_metadata_2025 huggingface dataset:
On the failure of the quasicylindrical approximation and the connection to vortex breakdown in turbulent swirling flow
Authors: Gyllenram W. , Nilsson H. , Davidson L.
Published: April 2007

This paper analyzes the properties of viscous swirling flow in a pipe. The analysis is based on the time-averaged quasicylindrical Navier-Stokes equations and is applicable to steady, unsteady, and turbulent swirling flow. A method is developed to determine the critical level of swirl (vortex breakdown) for an arbitrary vortex. The method can also be used for an estimation of the radial velocity profile if the other components are given or measured along a single radial line. The quasicylindrical equations are rearranged to yield a single ordinary differential equation for the radial distribution of the radial velocity component. The equation is singular for certain levels of swirl. It is shown that the lowest swirl level at which the equation is singular corresponds exactly to the sufficient condition for axisymmetric vortex breakdown as derived by Wang and Rusak [J. Fluid Mech. 340, 177 (1997)] and Rusak et al. [AIAA J. 36, 1848 (1998)]. In narrow regions around the critical levels of swirl, the solution violates the quasicylindrical assumptions and the flow must undergo a drastic change of structure. The critical swirl level is determined by the sign change of the smallest eigenvalue of the discrete linear operator which relates the radial velocities to effects of viscosity and turbulence. It is shown that neither viscosity nor turbulence directly alters the critical level of swirl.
Electrical properties of the Sm2Ti2O7 thin films for metal-insulator-metal capacitor applications
Authors: Jeong Y. H. , Kim J. C. , Lim J. B. , Hong K. P. , Nahm S. , Sun H. J. , Ghong T. H. , Kim Y. D. , Lee H. J.
Published: April 2007

A homogeneous crystalline Sm2Ti2O7 (ST) phase was formed in films grown at temperatures ranging between 100 and 200 °C and subsequently annealed at 900 °C. The ST film had a large dielectric constant of 58, which is similar to that of ST ceramics. The leakage current density of the ST film was low and the Poole-Frenkel emission was suggested as being the leakage current mechanism. The ST film had a negative quadratic voltage coefficient of capacitance (VCC), possibly due to the dipolar relaxation. The 100-nm-thick ST film had a high capacitance density of 5.2 fF∕μm2 with a low leakage current density of 1.34 nA∕cm2 at 2 V. Its quadratic and linear VCCs were −99.5 ppm∕V2 and 11 ppm/V, respectively, with a low temperature coefficient of capacitance of 135 ppm∕°C at 100 kHz. These results confirmed the potential for the ST film to be used as a high performance metal-insulator-metal capacitor.
Numerical calculations of the intrinsic electrostatic resonances of artificial dielectric heterostructures
Authors: Mejdoubi Abdelilah , Brosseau Christian
Published: April 2007

In order to study the intrinsic electrostatic resonances (ERs) of artificial dielectric heterostructures, we develop an efficient effective-medium-based method for modeling the effective permittivity, with careful attention paid to several key factors controlling ERs. Our method relies on finite element modeling and is applicable to inclusions with complex boundaries, e.g., fractal inclusion. A series of isolated and square arrays of several types of negative-permittivity media is considered. The inclusion shapes investigated can be considered as cross sections of infinite three-dimensional objects, where the properties and characteristics are invariant along the perpendicular cross-sectional plane. The continuum model used in this work is accurate only if the homogeneous representation of the composite structure makes sense, i.e., quasistatic approximation. It is found, among the conclusions of the article, that the effective permittivity of the composite (lossless) structures versus surface fraction curves presents a sharp peak, which occurs precisely at ER. For lossy inclusions, the primary signature of the ER is seen in the peak in the imaginary part of the complex permittivity or as an inflexion in the curve of the real part of the complex permittivity. The focus in this effort is on the analysis of intrinsic ER as a function of the shape and permittivity of the inclusion. The variations in the effective permittivity related to the iteration number show the following hierarchy for Sierpinski’s square and triangle: the higher the iteration number of the inclusion the smaller value of ϕ2 corresponding to the ER. In the vicinity of the ER peak, field enhancement is observed, which consists of enormous changes in the local electric field. Differences between the ER characteristics for aperiodic and periodic orders through the introduction of localized voids in the structure are also noteworthy. In addition, our approach performs well for fractal-shaped inclusions, e.g., Siepinski square, for which we show that the ERs satisfy a similarity transformation. These calculations can aid in the discovery of new materials with optimized magnetoelectric structures whose ER may be manipulated by electromagnetic fields.
Conducting atomic force microscopy studies of InN nanocomposite layers having conducting and nonconducting phases
Authors: Mann Ajay Kumar , Varandani Deepak , Mehta Bodh Raj , Malhotra Lalit Kumar
Published: April 2007

Conducting atomic force microscopy of InN layers grown by activated reactive evaporation method reveals that they are composed of conducting and nonconducting phases distributed at nanoscale. Deposition at higher substrate temperature or postdeposition annealing in nitrogen plasma results in an increase of the volume fraction of conducting phase, improved crystallinity of InN crystallites, shift in the absorption edge from 1.6to1.9eV, and increase in the carrier concentration of InN nanocomposite layers. The nanocomposite nature of the InN layers and variation of parameters such as percent of high conducting phase and its distribution with process parameters explain the lack of direct relationship between the “measured” value of carrier concentration and shift in absorption edge, normally observed in poly/nanocrystalline InN layers.
Dynamical properties of liquid water from ab initio molecular dynamics performed in the complete basis set limit
Authors: Lee Hee-Seung , Tuckerman Mark E.
Published: April 2007

Dynamical properties of liquid water were studied using Car-Parrinello [Phys. Rev. Lett. 55, 2471 (1985)] ab initio molecular dynamics (AIMD) simulations within the Kohn-Sham (KS) density functional theory employing the Becke-Lee-Yang-Parr exchange-correlation functional for the electronic structure. The KS orbitals were expanded in a discrete variable representation basis set, wherein the complete basis set limit can be easily reached and which, therefore, provides complete convergence of ionic forces. In order to minimize possible nonergodic behavior of the simulated water system in a constant energy (NVE) ensemble, a long equilibration run (30ps) preceded a 60ps long production run. The temperature drift during the entire 60ps trajectory was found to be minimal. The diffusion coefficient [0.055Å2∕ps] obtained from the present work for 32 D2O molecules is a factor of 4 smaller than the most up to date experimental value, but significantly larger than those of other recent AIMD studies. Adjusting the experimental result so as to match the finite-sized system used in the present study brings the comparison between theory and experiment to within a factor of 3. More importantly, the system is not observed to become “glassy” as has been reported in previous AIMD studies. The computed infrared spectrum is in good agreement with experimental data, especially in the low frequency regime where the translational and librational motions of water are manifested. The long simulation length also made it possible to perform detailed studies of hydrogen bond dynamics. The relaxation dynamics of hydrogen bonds observed in the present AIMD simulation is slower than those of popular force fields, such as the TIP4P potential, but comparable to that of the TIP5P potential.
Above-threshold drain current model including band tail states in nanocrystalline silicon thin-film transistors for circuit implementation
Authors: Pappas I. , Dimitriadis C. A. , Templier F. , Oudwan M. , Kamarinos G.
Published: April 2007

A simple analytical expression for the above threshold voltage drain current is derived in nanocrystalline silicon thin-film transistors (TFTs), based on an exponential energy distribution of band tail states. When the characteristic temperature distribution of the band tails is equal to 1.5 times the lattice temperature, the derived expression leads to the basic “quadratic” metal-oxide-semiconductor current expression. By including the impact ionization effect and using the same trap distribution parameters, the model describes adequately the output characteristics of TFTs with different channel dimensions, making the proposed model suitable for the design of circuits with nc-Si TFTs.
Charge states of strongly correlated 3d oxides: from typical insulator to unconventional electron–hole Bose liquid
Authors: Moskvin A. S.
Published: April 2007

We present a model approach to describe charge fluctuations and different charge phases in strongly correlated 3d oxides. As a generic model system we consider that of centers each with three possible valence states M0,± described in the framework of an S=1 pseudospin (isospin) formalism by an effective anisotropic non-Heisenberg Hamiltonian which includes two types of single-particle correlated hopping and also the two-particle hopping. Simple uniform mean-field phases include an insulating monovalent M0 phase, mixed-valence binary (disproportionated) M± phase, and a mixed-valence ternary (“under-disproportionated”) M0,± phase. We consider the first two phases in more detail, focusing on the problem of electron–hole states and different types of excitons in the M0 phase and the formation of electron–hole Bose liquid in the M± phase. The pseudospin formalism provides a useful framework for revealing and describing different topological charge fluctuations, such as, in particular, domain walls or bubble domains in antiferromagnets. Electron–lattice polarization effects are shown to be crucial for the stabilization of either phase. All the insulating systems such as M0 phase are subdivided to two classes: stable and unstable ones with respect to the formation of self-trapped charge transfer (CT) excitons. The latter systems appear to be unstable with respect to the formation of CT exciton clusters, or droplets of the electron–hole Bose liquid. The model approach suggested is believed to apply to the description of the physics of strongly correlated oxides such as cuprates, manganites, bismuthates, and other systems with charge transfer excitonic instability and/or mixed valence. We briefly discuss an unconventional scenario of the essential physics of cuprates which implies their instability with respect to the self-trapping of charge-transfer excitons and the formation of electron–hole Bose liquid.
Electrophysical properties of bromine-intercalated low-dimensional carbon structures
Authors: Buryakov T. I. , Romanenko A. I. , Anikeeva O. B. , Okotrub A. V. , Yudanov N. F. , Kotosonov A. S.
Published: April 2007

The temperature dependence of the resistivity ρ of a brominated material containing multiwall carbon nanotubes, and also that of brominated crystalline and pyrolytic graphites, are measured in the temperature interval 4.2–700K. The temperature dependence of the resistivity is investigated at different rates of heating and cooling in two gaseous media — air and helium. A comparison of ρ(T) for the initial and brominated materials is made. For the brominated materials unusual behavior of ρ(T) at temperatures above 390K is revealed. A conjecture is put forth which describes the behavior found.
On the relation between secondary and modulational instabilities
Authors: Strintzi D. , Jenko F.
Published: April 2007

The nonlinear saturation of microinstabilities in toroidal magnetoplasmas is sometimes discussed in the framework of secondary instability theory. At the same time, it has been proposed that the nonlinear generation of zonal flows—which are often responsible for turbulence control—can be explained in terms of modulational instabilities. The question of how these two approaches are connected to each other is addressed.
Non-Hamiltonian molecular dynamics implementation of the Gibbs ensemble method. I. Algorithm
Authors: Bratschi Christoph , Huber Hanspeter
Published: April 2007

In this paper (paper I) and the following paper (paper II) [C. Bratschi, H. Huber, and D. J. Searles, J. Chem. Phys. 126, 164105 (2007)], a new molecular dynamics algorithm implementing the Gibbs ensemble will be presented and then on applied to the liquid-vapor coexistence curve for two ab initio CO2 potentials. In paper I, the Gibbs ensemble molecular dynamics algorithm using non-Hamiltonian molecular dynamics techniques is introduced. It is shown that states of the correct probability density function are sampled and the correct exchange probability is generated. The extended system Nosé-Hoover formalism is used to generate a constant temperature ensemble with equal pressures in the subsystems, combined with single particle transfers between the subsystems, over several time steps, to get equal chemical potentials.
Energy harvesting using martensite variant reorientation mechanism in a NiMnGa magnetic shape memory alloy
Authors: Karaman I. , Basaran B. , Karaca H. E. , Karsilayan A. I. , Chumlyakov Y. I.
Published: April 2007

Magnetic shape memory alloys demonstrate significant potential for harvesting waste mechanical energy utilizing the Villari effect. In this study, a few milliwatts of power output are achieved taking advantage of martensite variant reorientation mechanism in Ni51.1Mn24Ga24.9 single crystals under slowly fluctuating loads (10Hz) without optimization in the power conversion unit. Effects of applied strain range, bias magnetic field, and loading frequency on the voltage output are revealed. Anticipated power outputs under moderate frequencies are predicted showing that the power outputs higher than 1W are feasible.
Multiphoton femtosecond phase-coherent two-dimensional electronic spectroscopy
Authors: Li Chunqiang , Wagner Wolfgang , Ciocca Maria , Warren Warren S.
Published: April 2007

In this paper the authors compare 400nm one-photon and 800nm two-photon two-dimensional Fourier transform electronic spectra of the organic laser dye Coumarin 102 in methanol using collinear optical pulse sequences and phase cycling. Results from the two different experiments show differences in the photon echo peak positions and shapes, reflecting differences in the two-photon and one-photon selection rules.
Thermal and electrical properties of porphyrin derivatives and their relevance for molecule interferometry
Authors: Deachapunya Sarayut , Stefanov André , Berninger Martin , Ulbricht Hendrik , Reiger Elisabeth , Doltsinis Nikos L. , Arndt Markus
Published: April 2007

The authors present new measurements of thermal and electrical properties for two porphyrin derivatives. They determine their sublimation enthalpy from the temperature dependence of the effusive beam intensity. The authors study H2TPP and Fe(TPP)Cl in matter-wave interferometry. Both molecules have nearly equal de Broglie wavelengths but different internal characteristics: only Fe(TPP)Cl exhibits an electric dipole moment of about 2.7D and the authors discuss its influence on the molecular interference pattern. The authors add an external electric force field to the interferometer and use it to measure the scalar polarizability. They compare their experimental values α(H2TPP)=105±4±6Å3 and α(Fe(TPP)Cl)=102±9±6Å3 to ab initio calculations and they discuss the influence of thermal excitations on the polarizability.
Scanning magnetic microscope system utilizing a magneto-impedance sensor for a nondestructive diagnostic tool of geological samples
Authors: Uehara Minoru , Nakamura Norihiro
Published: April 2007

We have developed a scanning magneto-impedance (MI) magnetic microscope to image surface stray magnetic fields of room-temperature geological samples with submillimeter resolution. The instrument consists of a small, 30 μm diameter, 5 mm length amorphous wire-based magneto- impedance (MI) sensor without any cooling mechanisms. The spacing between the sensor head and the sample was less than 300 μm. The length of the amorphous wire and sample-to-wire distance limits the spatial resolution. We have achieved a spatial resolution of 400 μm with a magnetic resolution of 10 nT. This instrument enables us to map a two-dimensional out-of-page component of a stray magnetic field of a natural remanent magnetization over a millimeter-thick slab of a primitive ordinary chondrite meteorite, documenting dipolelike features. A comparison of element mapping images with the stray field of the meteorites reveals what individual metals carry the dipolar remanences in the meteorites. These results suggest that the scanning MI microscope offers a room-temperature operable, small, low-maintenance alternative to the scanning SQUID microscope, and can aid in the interpretation of the magnetic remanence acquisition process of a meteorite.
Water-gas-shift reaction on metal nanoparticles and surfaces
Authors: Liu Ping , Rodriguez José A.
Published: April 2007

Density functional theory was employed to investigate the water-gas-shift reaction (WGS, CO+H2O→H2+CO2) on Au29 and Cu29 nanoparticles seen with scanning tunneling microscopy in model Au∕CeO2(111) and Cu∕CeO2(111) catalysts. Au(100) and Cu(100) surfaces were also included for comparison. According to the calculations of the authors, the WGS on these systems operate via either redox or associative carboxyl mechanism, while the rate-limiting step is the same, water dissociation. The WGS activity decreases in a sequence: Cu29>Cu(100)>Au29>Au(100), which agrees well with the experimental observations. Both nanoparticles are more active than their parent bulk surfaces. The nanoscale promotion on the WGS activity is associated with the low-coordinated corner and the edge sites as well as the fluxionality of the particles, which makes the nanoparticles more active than the flat surfaces for breaking the O–H bond. In addition, the role of the oxide support during the WGS was addressed by comparing the activity seen in the calculations of the authors for the Au29 and Cu29 nanoparticles and activity reported for X∕CeO2(111) and X∕ZnO(000ı¯)(X=Cu or Au) surfaces.
Twist viscoelastic coefficient of novel thiol terminated alkoxy-cyanobiphenyl nematic liquid crystals
Authors: Agarwal Amit K. , Suresh K. A. , Pal Santanu K. , Kumar Sandeep
Published: April 2007

We report our studies on the refractive indices and twist viscoelastic coefficient of novel thiol terminated alkoxy-cyanobiphenyl nematic liquid crystals. Dynamic light scattering (DLS) was employed to measure the twist viscoelastic coefficient as a function of temperature and the length of alkoxy chain. Our studies show that the twist viscoelastic coefficient is about three times smaller than that of the ordinary alkoxy-cyanobiphenyl nematic liquid crystals. DLS experiments carried out on this system with applied electric field show that the director relaxation frequency increases. These measurements yield the ratio of dielectric anisotropy to twist viscosity. We have also estimated the activation energy corresponding to twist viscosity.
3-mercaptopropyltrimethoxysilane as insulating coating and surface for protein immobilization for piezoelectric microcantilever sensors
Authors: Capobianco Joseph A. , Shih Wan Y. , Shih Wei-Heng
Published: April 2007

We have examined coating (PbMg1∕3Nb2∕3O3)0.63–(PbTiO3)0.37 (PMN-PT)/tin and lead zirconate titanate (PZT)/glass piezoelectric microcantilever sensor (PEMS) with 3-mercaptopropyl-trimethoxysilane (MPS) by a simple solution method to electrically insulate the PEMS for in-water applications. In contrast to earlier methytrimethoxysilane insulation coating, the MPS coating also facilitated receptor immobilization on the sensor surface via bonding of its sulhydryl group to a bifunctional linker, sulfosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate. We showed that a MPS coating of 21nm in thickness is sufficient to electrically insulate and provide immobilization surface to the PEMS for in-liquid electrical self-excitation and self-sensing. The in-phosphate buffered saline solution resonance spectra were stable with Q values ranging from 41 to 55. The mass detection sensitivities were determined to be 5×10−11 and 8×10−12g∕Hz for the MPS-insulated PZT-glass and PMN-PT/tin PEMSs, respectively.
First-principles theoretical investigation of the electronic couplings in single crystals of phenanthroline-based organic semiconductors
Authors: Li Hong , Brédas Jean-Luc , Lennartz Christian
Published: April 2007

The electronic couplings between adjacent molecules in the phenanthroline-based bathocuproine (BCP) and bathophenanthroline (Bphen) crystals have been studied using density functional theory on model dimers. Within the frame of the “two-state model” of charge-transfer theory, a generalized definition of the “effective transfer integral” is proposed. This definition addresses the issue arising when the lowest unoccupied molecular orbital (LUMO) [highest occupied molecular orbital (HOMO)] and LUMO+1 (HOMO−1) of the single molecules both have significant contributions to the dimer LUMO (HOMO) level. Charge-transfer integrals based on the new definition are compared with those from previous models; significant differences are found. The authors’ results indicate that, within a simple Marcus theory approach, the charge-transport parameters of the BCP and Bphen crystals are expected to be similar.
Ultrafast transient photoinduced absorption in silicon nanocrystals: Coupling of oxygen-related states to quantized sublevels
Authors: Lioudakis Emmanouil , Othonos Andreas , Nassiopoulou A. G.
Published: April 2007

The authors have studied transient photoinduced absorption in single monolayers of oxidized silicon nanocrystals. Transient photoinduced absorption measurements along with optical absorption and photoluminescence (PL) emission reveal that the light-absorption process takes place in defects related to strong PL emission, suggesting that the photoexcited carriers are in oxygen-related interface states. They have time-resolved ultrafast relaxation paths in oxygen-related states and quantized sublevels, which have important implications in the understanding of fundamental optical properties for this system.
Enhanced pyroelectric effect in self-supported films of BaTiO3 with polycrystalline macrodomains
Authors: Ivry Yachin , Lyahovitskaya Vera , Zon Ilya , Lubomirsky Igor , Wachtel Ellen , Roytburd Alexander L.
Published: April 2007

Self-supported films of nanocrystalline BaTiO3 exhibit a two orders of magnitude enhancement of the pyroelectric coefficient (≈1μC∕cm2K) with respect to the value measured for a single BaTiO3 crystal. The enhancement strongly depends on film geometry and appears only in buckled films where ferroelectric grains undergo self-organization into polycrystalline macrodomains. The authors posit that the enhancement of the pyroelectric effect is related to 90° polarization switching and is, therefore, similar in nature to an “extrinsic” piezoelectric effect.
Magnetization rotation and rearrangement of martensite variants in ferromagnetic shape memory alloys
Authors: Ma Y. F. , Li J. Y.
Published: April 2007

It is widely recognized that the rearrangement of martensite variants in a ferromagnetic shape memory alloy (FSMA) can lead to much higher strain than conventional magnetostriction. In this letter, the authors show that magnetization rotation can reduce ferromagnetic shape memory effect substantially when motion of the interface is severely hindered under a relatively large applied stress. This limits the energy density of FSMA actuators and suggests that hard magnetic anisotropy is necessary to achieve large actuation force. The analysis agrees well with experiments.
Enhanced neutron production from pyroelectric fusion
Authors: Geuther Jeffrey A. , Danon Yaron
Published: April 2007

The pyroelectric effect has been utilized as a means of producing x rays, electrons, positive ions, and neutrons. Pyroelectric sources have advantages over conventional sources, in that they are low cost, only consume a few watts of power, and are smaller than most sources. While pyroelectric x ray sources are already mature enough to be sold as commercial devices, the current generation of pyroelectric neutron sources is too low in intensity to be useful for commercial applications. This report demonstrates techniques which increase neutron production by a factor of 5.6 over previously published data.
Microfabricated tuning fork temperature and infrared sensor
Authors: Tsow Francis , Tao Nongjian
Published: April 2007

The authors demonstrated a microfabricated tuning fork temperature/infrared sensor with noise equivalent temperature difference (NETD) of 0.5mK at 20°C and with a thermal limited noise level of 5μ°C. The sensor raw material can cost less than 10 cents each and has a time constant of approximately 50ms. The sensitivity of infrared signal can potentially be further improved and optimized by selecting polymer materials with a proper thermal response.
Effect of depolarization and coercivity on actuation strains due to domain switching in barium titanate
Authors: Shu Y. C. , Yen J. H. , Shieh J. , Yeh J. H.
Published: April 2007

Large electrostrictive actuation in ferroelectric single crystals can be achieved through non-180° domain switching using various biasing fields and loads. The theoretical maximum actuation strain such as 1.1% for barium titanate crystals, however, has not been observed yet. In this letter, the authors propose a possible mechanism accounting for the depolarization effect to explain the significant strain reduction observed in their recent experiment. They find that a low-energy path requires the switching of 90° domains together with that of in-plane alternating layers of 180° domains formed to reduce the depolarization energy. Therefore, reduction in strain is significant for crystals with large 180° coercivities. The result is consistent with their recent experimental observations.
Nonadiabatic photodissociation dynamics in (HI)2 induced by intracluster collisions
Authors: López-López S. , Prosmiti R. , García-Vela A.
Published: April 2007

The sequential photodissociation dynamics of (HI)2 is studied by means of a nonadiabatic wave packet treatment starting from the I*−HI complex. The model reproduces the main experimental findings for photolysis with 266nm radiation. The results confirm that some of the H atoms dissociated from the I*−HI complex deactivate the I* atom through a H∕I* intracluster collision which induces an I*→I electronically nonadiabatic transition. As a consequence, these H fragments become very fast by acquiring nearly all the I* excitation energy, equivalent to the I*∕I spin-orbit splitting. A most interesting result is the high production of bound I2 fragments in highly excited rovibrational states in the photolysis, indicating that the H dissociation is mainly direct.
Sn
O
2
:
Eu
3
+
nanoparticles dispersed in TiO2 matrix: Improved energy transfer between semiconductor host and Eu3+ ions for the low temperature synthesized samples
Authors: Ningthoujam R. S. , Sudarsan V. , Godbole S. V. , Kienle L. , Kulshreshtha S. K. , Tyagi A. K.
Published: April 2007

Sn O 2 : Eu 3 + nanoparticles uniformly dispersed in TiO2 matrix were prepared at 185°C in ethylene glycol. Unlike in SnO2:Eu3+, significant improvement in the exciton mediated energy transfer between SnO2 and Eu3+ ions was observed when SnO2:Eu3+ nanoparticles are dispersed in TiO2 matrix, and this is attributed to effective shielding of surface Eu3+ ions present in SnO2:Eu3+ nanoparticles from the vibrations of stabilizing ligand by TiO2 matrix. Annealing the samples at high temperatures leads to formation of Sn1−xTixO2, without significantly affecting the energy transfer process between Eu3+ ions and semiconductor host.
Dropwise condensation on superhydrophobic surfaces with two-tier roughness
Authors: Chen Chuan-Hua , Cai Qingjun , Tsai Chialun , Chen Chung-Lung , Xiong Guangyong , Yu Ying , Ren Zhifeng
Published: April 2007

Dropwise condensation can enhance heat transfer by an order of magnitude compared to film condensation. Superhydrophobicity appears ideal to promote continued dropwise condensation which requires rapid removal of condensate drops; however, such promotion has not been reported on engineered surfaces. This letter reports continuous dropwise condensation on a superhydrophobic surface with short carbon nanotubes deposited on micromachined posts, a two-tier texture mimicking lotus leaves. On such micro-/nanostructured surfaces, the condensate drops prefer the Cassie state which is thermodynamically more stable than the Wenzel state. With a hexadecanethiol coating, superhydrophobicity is retained during and after condensation and rapid drop removal is enabled.
Topotaxial growth of Ti2AlN by solid state reaction in AlN∕Ti(0001) multilayer thin films
Authors: Höglund C. , Beckers M. , Schell N. , Borany J. v. , Birch J. , Hultman L.
Published: April 2007

The formation of Ti2AlN by solid state reaction between layers of wurtzite-AlN and α-Ti was characterized by in situ x-ray scattering. The sequential deposition of these layers by dual magnetron sputtering onto Al2O3(0001) at 200°C yielded smooth, heteroepitaxial (0001) oriented films, with abrupt AlN∕Ti interfaces as shown by x-ray reflectivity and Rutherford backscattering spectroscopy. Annealing at 400°C led to AlN decomposition and diffusion of released Al and N into the Ti layers, with formation of Ti3AlN. Further annealing at 500°C resulted in a phase transformation into Ti2AlN(0001) after only 5min.
Universal Toffoli gate in ballistic nanowires
Authors: Sarkar Angik , Bhattacharyya T. K.
Published: April 2007

Implementation of the universal Toffoli gate in a ballistic nanowire based structure has been discussed in this letter. The gate operation is dependent on spin manipulation in nanowires. Spin injection into the Toffoli gate can be done using a similar intertwined ballistic nanowire based setup. The device inputs are digital voltages and the output is obtained by spin readout. Realization of NAND gate, fan out, and half-adder based on the Toffoli gate has also been presented.
Competitive adsorption and two-site occupation effects in metal-organic chemical vapor deposition of ZnO
Authors: Ye J. D. , Gu S. L. , Liu W. , Zhu S. M. , Zhang R. , Shi Y. , Zheng Y. D. , Sun X. W. , Lo G. Q. , Kwong D. L.
Published: April 2007

The growth dynamics of ZnO epilayers by metal-organic chemical vapor deposition have been investigated by a comprehensive modeling of the competitive adsorption and two-site occupation effects. The established model, based on Langmuir-Hinshelwood mechanism, well explains the abnormal growth rate dependence on the VI/II ratio for different growth regimes. It is found that, for surface reaction and mass-transport limited growth, the competitive adsorption and two-site occupation effects dominate the surface adsorption process, respectively. The proposed dynamics model quantitatively well matched a wide range of experiments, providing a new insight into the general MOCVD growth mechanism for binary compound materials.
Self-organized tantalum oxide nanopyramidal arrays for antireflective structure
Authors: Wu Chia-Tien , Ko Fu-Hsiang , Lin Chun-Hung
Published: April 2007

A self-organized tantalum oxide nanopyramidal structure without tedious semiconductor processing is proposed in this letter. Construction of pyramid arrays with a close-packed periodicity of 200nm and a height of 200nm was achieved by the anodic alumina template method directly on the substrate. The tantalum oxide nanopyramidal structure was formed as the underlying tantalum film oxidized and localized precisely by the pore of alumina. The reflectance from the spectroscopic measurement suggests that the nanopyramidal array structures have more broadband antireflection (<2%) than the nanodot arrays and thin film structures.
Single-crystalline polymeric nitrogen
Authors: Eremets M. I. , Gavriliuk A. G. , Trojan I. A.
Published: April 2007

The authors synthesized polymeric nitrogen at pressures above 110GPa with laser heating above 2000K. To prove its cubic gauche (cg) structure, the authors have grown single crystals which produced strong reflections at large diffraction angles. The authors found nine peaks in the 2Θ=35° range with a special diamond anvil cell. All of the peaks agree with the cg-N structure. The authors checked various combinations of gasket materials and heaters to study possible contamination of the polymeric nitrogen by products of the reaction of the hot nitrogen with these materials or diamond anvils, and found that this is not the case.
Correlation of bonding of grain boundary and fracture mode with local electronic structure in steels by electron energy loss spectroscopy
Authors: Zhang X. , Yang W. G. , Zhang L. N. , Qi J. J. , Yuan J.
Published: April 2007

Electron energy loss spectroscopy (EELS) was used to study bonding of grain boundaries (GBs) in various types of commercial steels. It is found that if the GB has a higher occupancy of 3d states of iron than that of the grain, the sample tends to fracture intergranularly. Otherwise if the GB has a lower occupancy of 3d state of iron than the grain, the sample would have a strong GB bonding and tends to fracture transgranularly. It is proposed that EELS can estimate the GB cohesion and its impact on the fracture mode of commercial steels.
First-principles calculation of N:H codoping effect on energy gap narrowing of TiO2
Authors: Mi Lan , Xu Peng , Shen Hong , Wang Pei-Nan , Shen Weidian
Published: April 2007

The energy band structures and density of states for N-doped and N:H-doped anatase TiO2 are calculated based on the first-principles density-functional theory. For N-doped TiO2, there appear two isolated states above the top of the valence band and the band gap narrowing is very small. With the same nitrogen dopant concentration, N:H doping yields a significant band gap narrowing. The calculated results support our experimental data that N:H-doped TiO2 exhibited higher visible-light photocatalytic efficiency than the N-doped one.
Transport and quantum scattering time in field-effect transistors
Authors: Sakowicz M. , Łusakowski J. , Karpierz K. , Grynberg M. , Majkusiak B.
Published: April 2007

A modulated magnetoresistance method was applied to measure the transport (τt) and quantum (τq) scattering times for electrons in Si metal-oxide-semiconductor field-effect transistors. Both τt and τq were determined by self-consistent fitting the derivative of the low-field magnetoresistance and the derivative of Shubnikov–de Haas oscillations. The ratio τt∕τq allows to estimate a distance of the electron gas to the plane containing scattering centers to be equal to about 2nm. This agrees with a mean distance of the electron density to the interface given by self-consistent calculations of the electrostatic potential. Application of the method for nanotransistors is discussed.
Multiple wavelength InGaAs quantum dot lasers using selective area epitaxy
Authors: Mokkapati S. , Tan H. H. , Jagadish C.
Published: April 2007

The authors demonstrate multiple wavelength lasers fabricated from InGaAs quantum dots. Selective area epitaxy is used to grow the active region, consisting of five layer stack of InGaAs quantum dots with different band gap energies in selected regions of the substrate, for fabrication of the lasers. The mechanism responsible for engineering of the band gap of quantum dots is discussed. The performance of the selectively grown lasers is compared to the lasers fabricated from structures grown in a standard, nonselective area growth process.
Characteristics of dilute-nitride GaAsSbN∕InP strained multiple quantum wells
Authors: Xu D. P. , Huang J. Y. T. , Park J. H. , Mawst L. J. , Kuech T. F. , Vurgaftman I. , Meyer J. R.
Published: April 2007

Ga As Sb N ∕ In P strained layer superlattice (SL) structures have been grown using low-temperature metal organic chemical vapor deposition with N composition varying from 0.6% to 1.6%. High-resolution x-ray diffraction measurements indicate that GaAsSbN∕InP SLs with defect-free layers and abrupt interfaces were achieved. Low-temperature photoluminescence measurements reveal that nitrogen incorporation into the GaAsSbN layers extends the emission wavelength, increases the conduction band offset, and dramatically changes the As∕Sb ratio. In parallel with the experimental efforts, simulation studies using a ten-band k∙p model are carried out to correlate the emission properties of these SL structures with experiment. Photoluminescence measurements indicate an emission wavelength redshift with respect to the simulated values.
Koalas continue to occupy their previous home-ranges after selective logging in Callitris - Eucalyptus forest
Authors: Kavanagh Rodney P. , Stanton Matthew A. , Brassil Traecey E.
Published: April 2007

The koala (Phascolarctos cinereus) is a charismatic, high-profile species whose conservation needs are commonly perceived to be incompatible with logging. However, koala biology and the results of chronosequence studies elsewhere suggest that this species may tolerate a degree of habitat alteration caused by logging. In this study, 30 koalas, five in each of six areas available for logging within a mixed white cypress pine (Callitris glaucophylla)–Eucalyptus forest in north-western New South Wales, were radio-tracked for one year during 1997–1998 to determine their movements, home-range sizes and tree preferences. Five months after the study began, three of these areas were logged selectively for sawlogs and thinnings of the white cypress pine, a tree that is important to koalas for daytime shelter. This removed about one-quarter of the stand basal area, but the eucalypt component was unaffected. The remaining three areas were left undisturbed as controls. Radio-tracking continued in all six areas for another seven months. Koalas continued to occupy all or part of their previous home-ranges after selective logging, and home-range sizes remained similar between logged and unlogged areas. Home-ranges for both sexes overlapped and were ~12 ha for males and 9 ha for females. Koala survival and the proportions of breeding females were similar in logged and unlogged areas. The principal food trees of the koala were red gums, mainly Eucalyptus blakelyi and E. chloroclada, and the pilliga box (E. pilligaensis), none of which were logged in this study. These results suggest that selective logging for white cypress pine does not appear to adversely affect koala populations and that koalas may not be as sensitive to logging as previously thought. Further work is required to determine thresholds in the level of retention of koala food trees in logging operations.
Aerial baiting for wild dogs has no observable impact on spotted-tailed quolls (Dasyurus maculatus) in a rainshadow woodland
Authors: Claridge Andrew W. , Mills Douglas J.
Published: April 2007

The short-term impact of 1080 aerial baiting for wild dogs (Canis lupus dingo, Canis lupus familiaris and hybrids of the two) on spotted-tailed quolls (Dasyurus maculatus) was investigated at a rainshadow woodland site in southern New South Wales, Australia. Sixteen quolls were trapped and fitted with radio-transmitters containing mortality sensors. Three feral cats were also opportunistically trapped and radio-collared. One week after trapping ceased, meat baits nominally containing 6 mg of 1080 poison and 50 mg of the biomarker rhodamine B were deployed aerially over a 10-km transect across the study area. Following bait deployment, collared quolls and cats were monitored daily over four weeks for evidence of mortality. During this time, one quoll and two cats died. The quoll did not die from 1080 but both cats showed clear signs of poisoning. Whisker samples were obtained from trapped quolls 5–8 weeks after baiting to determine whether they had been exposed to baits. Of the 15 remaining collared quolls, 12 were retrapped. Four of these tested positive for rhodamine B. Three individuals originally collared were not retrapped but confirmed alive at least seven weeks after bait deployment. A further six non-collared quolls were also trapped, with two of these positive for rhodamine B. Of the 19 quolls from which whisker samples were tested for rhodamine B then, 13 (68%) were negative and six (32%) were positive. Aerial baiting had no observable impact on the local radio-collared quoll population, a finding consistent with results from a similar study recently conducted in northern New South Wales.
Physical interaction between the serotonin transporter and neuronal nitric oxide synthase underlies reciprocal modulation of their activity
Authors: Chanrion B. , Mannoury la Cour C. , Bertaso F. , Lerner-Natoli M. , Freissmuth M. , Millan M. J. , Bockaert J. , Marin P.
Published: April 2007

The spatiotemporal regulation of neurotransmitter transporters involves proteins that interact with their intracellular domains. Using a proteomic approach, we identified several proteins that interact with the C terminus of the serotonin transporter (SERT). These included neuronal nitric oxide synthase (nNOS), a PSD-95/Disc large/ZO-1 (PDZ) domain-containing protein recruited by the atypical PDZ binding motif of SERT. Coexpression of nNOS with SERT in HEK293 cells decreased SERT cell surface localization and 5-hydroxytryptamine (5-HT) uptake. These effects were absent in cells transfected with SERT mutated in its PDZ motif to prevent physical association with nNOS, and 5-HT uptake was unaffected by activation or inhibition of nNOS enzymatic activity. 5-HT uptake into brain synaptosomes was increased in both nNOS-deficient and wild-type mice i.v. injected with a membrane-permeant peptidyl mimetic of SERT C terminus, which disrupted interaction between SERT and nNOS, suggesting that nNOS reduces SERT activityin vivo. Furthermore, treating cultured mesencephalic neurons with the mimetic peptide similarly increased 5-HT uptake. Reciprocally, indicating that 5-HT uptake stimulates nNOS activity, NO production was enhanced on exposure of cells cotransfected with nNOS and SERT to 5-HT. This effect was abolished by 5-HT uptake inhibitors and absent in cells expressing SERT mutated in its PDZ motif. In conclusion, physical association between nNOS and SERT provides a molecular substrate for their reciprocal functional modulation. In addition to showing that nNOS controls cell surface localization of SERT, these findings provide evidence for regulation of cellular signaling (NO production) by a substrate-carrying transporter.
Nonrandom variations in human cancer ESTs indicate that mRNA heterogeneity increases during carcinogenesis
Authors: Brulliard Marie , Lorphelin Dalia , Collignon Olivier , Lorphelin Walter , Thouvenot Benoit , Gothié Emmanuel , Jacquenet Sandrine , Ogier Virginie , Roitel Olivier , Monnez Jean-Marie , Vallois Pierre , Yen Frances T. , Poch Olivier , Guenneugues Marc , Karcher Gilles , Oudet Pierre , Bihain Bernard E.
Published: April 2007

Virtually all cancer biological attributes are heterogeneous. Because of this, it is currently difficult to reconcile results of cancer transcriptome and proteome experiments. It is also established that cancer somatic mutations arise at rates higher than suspected, but yet are insufficient to explain all cancer cell heterogeneity. We have analyzed sequence variations of 17 abundantly expressed genes in a large set of human ESTs originating from either normal or cancer samples. We show that cancer ESTs have greater variations than normal ESTs for >70% of the tested genes. These variations cannot be explained by known and putative SNPs. Furthermore, cancer EST variations were not random, but were determined by the composition of the substituted base (b0) as well as that of the bases located upstream (up to b − 4) and downstream (up to b + 3) of the substitution event. The replacement base was also not randomly selected but corresponded in most cases (73%) to a repetition of b − 1 or of b + 1. Base substitutions follow a specific pattern of affected bases: A and T substitutions were preferentially observed in cancer ESTs. In contrast, cancer somatic mutations [Sjoblom T,
et al.
(2006)
Science
314:268–274] and SNPs identified in the genes of the current study occurred preferentially with C and G. On the basis of these observations, we developed a working hypothesis that cancer EST heterogeneity results primarily from increased transcription infidelity.
βKlotho is required for metabolic activity of fibroblast growth factor 21
Authors: Ogawa Yasushi , Kurosu Hiroshi , Yamamoto Masaya , Nandi Animesh , Rosenblatt Kevin P. , Goetz Regina , Eliseenkova Anna V. , Mohammadi Moosa , Kuro-o Makoto
Published: April 2007

Fibroblast growth factor 21 (FGF21) is a liver-derived endocrine factor that stimulates glucose uptake in adipocytes. Here, we show that FGF21 activity depends on βKlotho, a single-pass transmembrane protein whose expression is induced during differentiation from preadipocytes to adipocytes. βKlotho physically interacts with FGF receptors 1c and 4, thereby increasing the ability of these FGF receptors to bind FGF21 and activate the MAP kinase cascade. Knockdown of βKlotho expression by siRNA in adipocytes diminishes glucose uptake induced by FGF21. Importantly, administration of FGF21 into mice induces MAP kinase phosphorylation in white adipose tissue and not in tissues without βKlotho expression. Thus, βKlotho functions as a cofactor essential for FGF21 activity.
Bradykinin B1 and B2 receptors both have protective roles in renal ischemia/reperfusion injury
Authors: Kakoki Masao , McGarrah Robert W. , Kim Hyung-Suk , Smithies Oliver
Published: April 2007

To explore the role of the kallikrein–kinin system in relation to ischemia/reperfusion injury in the kidney, we generated mice lacking both the bradykinin B1 and B2 receptor genes (B1RB2R-null,
Bdkrb1
−/−
/
Bdkrb2
−/−
) by deleting the genomic region encoding the two receptors. In 4-month-old mice, blood pressures were not significantly different among B1RB2R-null, B2R-null (
Bdkrb2
−/−
), and WT mice. After 30 min of bilateral renal artery occlusion and 24 h of reperfusion, mortality rates, renal histological and functional changes, 8-hydroxy-2′-deoxyguanosine levels in total DNA, mtDNA deletions, and the number of TUNEL-positive cells in the kidneys increased progressively in the following order (from lowest to highest): WT, B2R-null, and B1RB2R-null mice. Increases in mRNA levels of TGF-β1, connective tissue growth factor, and endothelin-1 after ischemia/reperfusion injury were also exaggerated in the same order (from lowest to highest): WT, B2R-null, and B1RB2R-null. Thus, both the B1 and B2 bradykinin receptors play an important role in reducing DNA damage, apoptosis, morphological and functional kidney changes, and mortality during renal ischemia/reperfusion injury.