bluuebunny/crossref_metadata_2025 huggingface dataset:
Ten years of Hubble Space Telescope observations of the variation of the Jovian satellites' auroral footprint brightness
Authors: Wannawichian S. , Clarke J. T. , Nichols J. D.
Published: February 2010

During the past decade, FUV imaging of Jupiter's auroral region by the Hubble Space Telescope (HST) using two instruments, the Space Telescope Imaging Spectrograph (STIS) and the Advanced Camera for Surveys (ACS), has provided detailed information on the electrodynamic interaction between Io's, Ganymede's, and Europa's atmospheres and plasma in Jupiter's magnetosphere. This interaction is responsible for the satellites' auroral footprints in Jupiter's atmosphere connected via magnetic flux tubes to the satellites' interaction regions. The observed brightness of each auroral footprint is considered to be one main observable quantity to characterize the interaction environment at the satellites. Previous observations of Io's magnetic footprints using HST STIS images showed that the footprint emission appears brightest when Io is centered in the plasma torus. With the much larger data set obtained from the 2007 HST campaigns, we find the same variation observed by Serio and Clarke (2008), but with significantly better statistics over a time period of 10 years. These results confirm that Io's footprint brightness varies mainly with the satellite's location in Jupiter's plasma torus over a long time scale. Additional observations of the downstream emissions and their variations were presented by Bonfond et al. (2007). In Ganymede's case, the relation between the footprint brightness and the satellite's position in Jupiter's magnetosphere shows some evidence for the same general trend, although the data are noisier than the data for Io. Ganymede's footprint brightness appears to be less consistent over time than Io's. The variation of Ganymede's footprints over short time periods was studied by Grodent et al. (2009). Europa's fainter footprint brightness makes it difficult to see any systematic trend.
Effect of tidal flat on seawater temperature variation in the southwest coast of Korea
Authors: Kim Tae‐Wan , Cho Yang‐Ki , You Kwang‐Woo , Jung Kyung Tae
Published: February 2010

The seawater temperature observed near macrotidal flats demonstrates distinguished semidiurnal variations. The range of seawater temperature variations was approximately 2–4°C during a clear day in spring. The seawater temperature increased during flood tides but decreased during ebb tides in spring and summer, while the opposite occurred in autumn and winter. A model was developed to evaluate the effect of the tidal flat on changes in the seawater temperature. The seawater temperature, calculated using this model, was verified with observed seawater temperatures. The heat of seawater in shallow zones changed more than 581 J m−3 s−1 (0.5°C h−1) because of heat content exchange with the tidal flat, regardless of season. The maximum heat gain (835 W m−2) of seawater from the tidal flat and heat loss (588W m−2) of seawater from the tidal flat occurred in June 2004, whereas the minimum heat gain (554 W m−2) from the tidal flat occurred in March 2004 and heat loss (316W m−2) to the tidal flat occurred in February 2004.
Potent anti‐tumor responses to immunization with dendritic cells loaded with tumor tissue and an NKT cell ligand
Authors: Petersen Troels R , Sika‐Paotonu Dianne , Knight Deborah A , Dickgreber Nina , Farrand Kathryn J , Ronchese Franca , Hermans Ian F
Published: February 2010

Cancer immunotherapy is well tolerated and specific, but its efficacy remains variable. To enhance anti‐tumor CD8+ T‐cell responses induced by immunization with antigen‐loaded dendritic cells (DCs), we explored the impact of eliciting a potent source of T‐cell help from activated invariant natural killer (NK)‐like T cells (iNKT cells) using the specific glycolipid ligand α‐galactosylceramide (α‐GalCer). As cytokines released by iNKT cells may drive proliferation of CD4+CD25+ regulatory T cells (Tregs), we assessed this immunization strategy in animals treated with anti‐CD25 antibody to inactivate Treg function. Combining DC immunization with iNKT cell activation was found to significantly enhance anti‐tumor activity, which was improved further by the prior inactivation of Tregs. The improved anti‐tumor activity with Treg inactivation was associated with a prolonged proliferative burst of responding CD8+ T cells. We could find no evidence that inclusion of α‐GalCer in the vaccine enhanced Treg numbers, or that the ‘helper’ function of iNKT cells was improved in the absence of Treg activity. Rather, the two activities appeared to act independently to improve the tumor‐specific T‐cell response. Inactivating regulatory T cells and eliciting iNKT cell activation are therefore two useful strategies that can be used in combination to improve anti‐tumor immunization with antigen‐loaded DCs.
First beams from the new electron cyclotron resonance source LEGIS (LEGnaro ecrIS) at INFN-LNL
Authors: Galatà A. , Kulevoy T. , Sattin M. , Scarpa F. , Facco A.
Published: February 2010

From April 2008 the PIAVE injector for the ALPI booster was involved in the upgrade of the high voltage platform housing an electron cyclotron resonance (ECR) source. A 14.5 GHz SUPERNANOGAN type ECR replaced the existing source ALICE; at the same time, the whole platform beam line was redesigned and beam shaping and diagnostic system were installed. The source and the platform were ready to be put into operation in January 2009. PIAVE’s commissioning was started from late March and completed in May 2009 using an argon beam. A description of the upgrade will be given in the following; beam quality leading to an improved transmission through the injector will be shown. Results on first gaseous and metallic beams produced will also be given.
Spallation neutron source saddle antenna H− ion source project
Authors: Dudnikov Vadim , Johnson Rolland P. , Dudnikova Galina , Stockli Martin , Welton Robert
Published: February 2010

In this project we are developing an H− source which will synthesize the most important developments in the field of negative ion sources to provide high current, high brightness, good lifetime, high reliability, and high power efficiency. We describe two planned modifications to the present spallation neutron source external antenna source in order to increase the plasma density near the output aperture: (1) replacing the present 2 MHz plasma-forming solenoid antenna with a 13 MHz saddle-type antenna and (2) replacing the permanent multicusp magnetic system with a weaker electromagnet.
Thermal stability of microstructural and optical modifications induced in sapphire by ultrafast laser filamentation
Authors: Benayas A. , Jaque D. , McMillen Ben , Chen K. P.
Published: February 2010

We report on the thermal stability of both structural and optical micromodifications created by ultrafast laser written filaments in sapphire crystals. By using the Cr3+ traces as optical probes, we have concluded that the filaments are constituted by both reversible and nonreversible defects with very different spatial locations. The strain field measured from the analysis of R lines has been found to be erased at the same time when the reversible centers are recombined (∼1100 °C). This fact seems to indicate that these defects act as pinning centers for the induced stress. Furthermore, we have found that the waveguide generated in the proximity of the filament disappear for annealing temperatures above 1100 °C. This clearly supports the assumption that waveguiding is produced by the strain stress induced refractive index increment based on the dominant electronic polarizability enhancement.
Identification of extremely radiative nature of AlN by time-resolved photoluminescence
Authors: Onuma T. , Hazu K. , Uedono A. , Sota T. , Chichibu S. F.
Published: February 2010

Extremely radiative nature of high-quality AlN single crystalline epilayers was identified by means of far ultraviolet time-resolved photoluminescence using a frequency-quadrupled femtosecond Al2O3:Ti laser. The gross radiative lifetimes of a free excitonic polariton emission as short as 10 ps at 7 K and 180 ps at 300 K were revealed, which are the shortest ever reported for bulk semiconductor materials.
Influence of multiple magnetic phases on the extrinsic damping of FeCo–SiO2 soft magnetic films
Authors: Liu Bailin , Yang Yi , Tang Dongming , Chen Jiangwei , Lu Huaixian , Lu Mu , Shi Yi
Published: February 2010

In order to investigate the high-frequency damping properties of the ferromagnetic film for the electromagnetic shielding applications, a series of (FeCo)2x/(Fe)x/(SiO2)1−3x nanogranular films with various volume fractions (x) were fabricated by alternate triple-target magnetron sputtering. The (FeCo)0.50/Fe0.25/(SiO2)0.25 film shows excellent soft magnetic properties (4πMs∼1.48T,Hce∼4.3Oe,ρ∼4.3μΩ m). In both ferromagnetic resonance (FMR) and frequency-dependent permeability spectra measurements, two resonance peaks of the permeability for this film are obtained, which can be attributed to the complicated magnetic structure of FeCo and Fe phases in the film. This multiphase system makes an additional contribution to the extrinsic damping. As a result, the higher natural resonance frequency f for the film is up to 2.75 GHz with full width at half maximum of about 2.5 GHz for the imaginary part μ∥; meanwhile, the real part μ/ is as high as 650 while f<1.3 GHz. These films could be novel candidates for the electromagnetic shielding applications.
Interaction of vacuum ultraviolet excimer laser radiation with fused silica. III. Negative ion formation
Authors: George Sharon R. , Langford S. C. , Dickinson J. T.
Published: February 2010

We report mass- and time-resolved measurements of negative ions produced by exposing fused silica to 157 nm radiation at fluences below the threshold for optical breakdown. The principal observed negative ions are O−, Si−, and SiO−, in order of decreasing intensity. The peak in the negative ion time-of-flight signals occurs after the peak in the positive ion signal and before the peak in the corresponding neutral atom or molecule signal. The negative ion intensities are strong functions of the degree of overlap between the positive ion and neutral atom densities. We propose that O−, Si−, and SiO− are created after the laser pulse, by electron attachment to these neutral particles and that the electrons participating in attachment events are trapped in the electrostatic potential of the positive ions.
Microwave permeability of flake-shaped FeCuNbSiB particle composite with rotational orientation
Authors: Yang Weifeng , Qiao Liang , Wei Jianqiang , Zhang Zhaoqi , Wang Tao , Li Fashen
Published: February 2010

Flake-shaped FeCuNbSiB particles were fabricated by ball milling the annealed ribbons. The composites of flake particles/paraffin wax were prepared with and without rotational orientation in an applied magnetic field. The complex permeability of the composites was measured in the frequency range of 0.1–18 GHz. The oriented composite showed higher permeability and resonance frequency compared with the unoriented one, while its value of (μ0−1)fr reached 128.9 GHz and exceeded the Snoek’s limit. Considering random and uniform distribution of the flake planes of the particles in the unoriented and oriented composites, respectively, the real part and imaginary part of the complex permeability of the composites were calculated using the Landau–Lifshitz–Gilbert equation and Bruggeman’s effective medium theory. The calculated results were basically in agreement with the experimental data.
Tailoring absorption and emission of light in dielectric polymer nanofluids of reinforced poly(vinylidene fluoride) with silver nanoparticles
Authors: Phule A. D. , Ram S. , Tyagi A. K.
Published: February 2010

Polymer nanofluids of poly(vinylidene fluoride) (PVF2) containing 0–5 wt % Ag nanoparticles (Ag NPs) are synthesized via a simple in situ caloric Ag+→Ag reaction in liquid N,N-dimethyl formamide by sonication in hot conditions. An upright dielectric field on formation of a percolation network over the electron donor Ag NPs and electron acceptor CF2 from an ordered β-PVF2 tailors light absorption 250–550 nm and green emission 520–620 nm of variable intensities, with a small percolation threshold of 0.1 wt % Ag NPs. On higher Ag contents, the intensity drops rapidly in both the absorption and emission roughly by an order of magnitude, following the percolation theory of a hybrid dielectric composite. Results open scope of developing newer materials for optical sensors, barcodes, energy transfer pairs, or light emitters.
Semiconducting Sn3O4 nanobelts: Growth and electronic structure
Authors: Berengue O. M. , Simon R. A. , Chiquito A. J. , Dalmaschio C. J. , Leite E. R. , Guerreiro H. A. , Guimarães F. E. G.
Published: February 2010

The study of structures based on nonstoichiometric SnO2−x compounds, besides experimentally observed, is a challenging task taking into account their instabilities. In this paper, we report on single crystal Sn3O4 nanobelts, which were successfully grown by a carbothermal evaporation process of SnO2 powder in association with the well known vapor-solid mechanism. By combining the structural data and transport properties, the samples were investigated. The results showed a triclinic semiconductor structure with a fundamental gap of 2.9 eV. The semiconductor behavior was confirmed by the electron transport data, which pointed to the variable range hopping process as the main conduction mechanism, thus giving consistent support to the mechanisms underlying the observed semiconducting character.
Effect of liquid environment on laser-induced backside wet etching of fused silica
Authors: Lee Taehwa , Jang Deoksuk , Ahn Daehwan , Kim Dongsik
Published: February 2010

In laser-induced backside wet etching (LIBWE), the liquid absorbent indirectly heats the transparent material, causing explosive phase change and cavitation. Accordingly, the hydrodynamics of the absorbing liquid, including the size of the liquid chamber, is strongly related to the ablation process. Because the hydrodynamics is dependent on the elastic deformation of the sample, the sample thickness also affects the performance of LIBWE. In this work, experimental analyses were performed to elucidate the hydrodynamics in LIBWE and the effect on the etch rate by varying the liquid chamber size and sample thickness. A KrF excimer laser was used to ablate fused silica samples in toluene and the etch rate was quantified using a scanning profilometer. Laser flash shadowgraphy and photodeflection probing techniques were employed for in situ measurement of the laser-induced hydrodynamics and displacement of the sample, respectively, with a time resolution of approximately nanoseconds. To directly observe the effect of increased liquid pressure on LIBWE, the liquid pressure on the etching spot was locally increased by an external shock wave and the etch results are examined. This study confirms that the photomechanical effects from the laser-induced bubble plays a key role in the LIBWE process, revealing a linear relationship between the etch rate the applied recoil momentum. However, the dependence of the etch rate on the chamber size and sample thickness could not be explained by the change in recoil momentum, i.e., by the bubble pressure. Instead, transient deformation of the sample by the pressure impact was estimated to be mainly responsible for the dependence.
Strain effects on basal-plane hydrogenation of graphene: A first-principles study
Authors: Xue Kun , Xu Zhiping
Published: February 2010

In this letter we discuss basal-plane hydrogenation of graphene, in the extent of intercoupling between strain and electronic structure. Our first-principles calculations reveal that the atomic structures, binding energies, mechanical and electronic properties of graphene are significantly modified by applying strain. At a biaxial strain of 10%, binding energies of hydrogen on graphene can be improved by 53.89% and 23.56% in the symmetric and antisymmetric phase. In symmetric phase, carbon-hydrogen binding is unstable in compression. In antisymmetric phase, binding of hydrogen atoms reduces the sp2 characteristic of graphene, which is partially recovered at finite tensile strain.
Protein solvation from theory and simulation: Exact treatment of Coulomb interactions in three-dimensional theories
Authors: Perkyns John S. , Lynch Gillian C. , Howard Jesse J. , Pettitt B. Montgomery
Published: February 2010

Solvation forces dominate protein structure and dynamics. Integral equation theories allow a rapid and accurate evaluation of the effect of solvent around a complex solute, without the sampling issues associated with simulations of explicit solvent molecules. Advances in integral equation theories make it possible to calculate the angle dependent average solvent structure around an irregular molecular solution. We consider two methodological problems here: the treatment of long-ranged forces without the use of artificial periodicity or truncations and the effect of closures. We derive a method for calculating the long-ranged Coulomb interaction contributions to three-dimensional distribution functions involving only a rewriting of the system of integral equations and introducing no new formal approximations. We show the comparison of the exact forms with those implied by the supercell method. The supercell method is shown to be a good approximation for neutral solutes whereas the new method does not exhibit the known problems of the supercell method for charged solutes. Our method appears more numerically stable with respect to thermodynamic starting state. We also compare closures including the Kovalenko–Hirata closure, the hypernetted-chain (HNC) and an approximate three-dimensional bridge function combined with the HNC closure. Comparisons to molecular dynamics results are made for water as well as for the protein solute bovine pancreatic trypsin inhibitor. The proposed equations have less severe approximations and often provide results which compare favorably to molecular dynamics simulation where other methods fail.
Alfvén continuum deformation by kinetic geodesic effect in rotating tokamak plasmas
Authors: Elfimov A. G.
Published: February 2010

Using a quasitoroidal set of coordinates with coaxial circular magnetic surfaces, Vlasov equation is solved for collisionless plasmas in drift approach and a perpendicular dielectric tensor is found for large aspect ratio tokamaks in a low frequency band. Taking into account plasma rotation and charge separation parallel electric field, it is found that an ion geodesic effect deform Alfvén wave continuum producing continuum minimum at the rational magnetic surfaces, which depends on the plasma rotation and poloidal mode numbers. In kinetic approach, the ion thermal motion defines the geodesic effect but the mode frequency also depends on electron temperature. A geodesic ion Alfvén mode predicted below the continuum minimum has a small Landau damping in plasmas with Maxwell distribution but the plasma rotation may drive instability.
Position dependent mass Schrödinger equation and isospectral potentials: Intertwining operator approach
Authors: Midya Bikashkali , Roy B. , Roychoudhury R.
Published: February 2010

Here, we have studied first- and second-order intertwining approaches to generate isospectral partner potentials of position dependent (effective) mass Schrödinger equation. The second-order intertwiner is constructed directly by taking it as second-order linear differential operator with position dependent coefficients, and the system of equations arising from the intertwining relationship is solved for the coefficients by taking an ansatz. A complete scheme for obtaining general solution is obtained, which is valid for any arbitrary potential and mass function. The proposed technique allows us to generate isospectral potentials with the following spectral modifications: (i) to add new bound state(s), (ii) to remove bound state(s), and (iii) to leave the spectrum unaffected. To explain our findings with the help of an illustration, we have used point canonical transformation to obtain the general solution of the position dependent mass Schrodinger equation corresponding to a potential and mass function. It is shown that our results are consistent with the formulation of type A N-fold supersymmetry [T. Tanaka, J. Phys. A 39, 219 (2006); A. Gonzalez-Lopez and T. Tanaka, J. Phys. A 39, 3715 (2006)] for the particular cases N=1 and N=2, respectively.
Whittaker modules for the twisted Heisenberg–Virasoro algebra
Authors: Liu Dong , Wu Yuezhu , Zhu Linsheng
Published: February 2010

We define Whittaker modules for the twisted Heisenberg–Virasoro algebra and obtain several results from the classical setting, including a classification of simple Whittaker modules by central characters.
Efficiency droop in 245–247 nm AlGaN light-emitting diodes with continuous wave 2 mW output power
Authors: Sun W. , Shatalov M. , Deng J. , Hu X. , Yang J. , Lunev A. , Bilenko Y. , Shur M. , Gaska R.
Published: February 2010

We report on 245–247 nm AlGaN-based deep ultraviolet (DUV) light-emitting diodes with continuous wave output power up to 2 mW. DUV diodes with peak emission wavelength of 245 and 247 nm exhibit turn-on voltage less than 10 V. At room temperature and cw operation the maximum external quantum efficiency was close to 0.18%, which is the highest value published to date for devices with peak emission wavelength shorter than 250 nm. A large external efficiency droop observed at current densities above 100 A/cm2 is attributed to self-heating, carrier spillover from the QWs into the barrier layers or the p-type cladding layer, and/or Auger recombination. A semiempirical equation was proposed to describe the efficiency droop in DUV diodes at a high current injection.
Highly tensile-strained, type-II, Ga1−xInxAs/GaSb quantum wells
Authors: Taliercio T. , Gassenq A. , Luna E. , Trampert A. , Tournié E.
Published: February 2010

We have investigated the properties of highly tensile-strained (Ga,In)As layers in a GaSb matrix. In situ observations of the growth mode suggest the formation of (Ga,In)As quantum dots. In contrast, ex situ transmission electron microscopy evidences the formation of perfect quantum wells with the presence of a (Ga,In)Sb interfacial layer. This is analyzed taking into account the surfactant behavior of Sb and stabilization of the system by reduction of the overall strain. Photoluminescence is observed up to 3.0 μm at room temperature, in good agreement with calculations assuming a type-II band alignment and including the (Ga,In)Sb interfacial layer.
Effect of Mg doping on enhancement of terahertz emission from InN with different lattice polarities
Authors: Wang X. Q. , Zhao G. Z. , Zhang Q. , Ishitani Y. , Yoshikawa A. , Shen B.
Published: February 2010

Effect of Mg doping on terahertz (THz) emission from InN with different lattice polarities was studied. Strong enhancement of THz emission was observed from InN with appropriate Mg-concentrations (1018 cm−3), which is independent of lattice polarity. The buried p-type layers show stronger THz emission than the n-type ones. The dominant mechanism for THz emission was found to be photo-Dember effect and the emission intensity was inversely proportional to the conductivity, which is beneficial to investigate THz emission from InN since the conductivity can be more accurately measured than the carrier concentration and mobility due to the electron accumulation on surface.
First-principles investigations of the dielectric properties of crystalline and amorphous Si3N4 thin films
Authors: Pham T. Anh , Li Tianshu , Shankar Sadasivan , Gygi Francois , Galli Giulia
Published: February 2010

We have investigated the dielectric properties of silicon nitride thin films with thickness below 6 nm, by using density functional theory calculations. We find a substantial decrease in the static dielectric constant of crystalline films, as their size is reduced. The variation in the response in proximity of the surface plays a key role in the observed decrease. In addition, amorphization of the films may bring further reduction of both the static and optical dielectric constants.
Determination of the microstructure of Eu-treated ZnO nanowires by x-ray absorption
Authors: Huang W. L. , Labis J. , Ray S. C. , Liang Y. R. , Pao C. W. , Tsai H. M. , Du C. H. , Pong W. F. , Chiou J. W. , Tsai M.-H. , Lin H. J. , Lee J. F. , Chou Y. T. , Shen J. L. , Chen C. W. , Chi G. C.
Published: February 2010

X-ray absorption near-edge structure (XANES), extended x-ray absorption fine structures (EXAFS), and photoluminescence measurements were used to elucidate the microstructural and photoluminescence properties of ZnO nanowires (ZnO-NWs) that had been treated with Eu by thermal diffusion. The O K- and Eu L3-edge XANES and EXAFS spectra at the Zn K- and Eu L3-edge verified the formation of Eu2O3-like layer on the surface of ZnO-NWs. X-ray diffraction, XANES and EXAFS measurements consistently suggest the lack of substitutional doping of Eu ions at the Zn ion sites in the interior of ZnO-NWs. The clear sharp and intense emission bands in the range 610–630 nm of Eu-treated ZnO-NWs originated from the intra-4f transition of Eu ions in the Eu2O3-like surface layer.
Cleavage pattern of DNA caused by endonuclease: Theoretical modeling and experimental verification
Authors: Inagaki Shio , Liu Li , Takinoue Masahiro , Yoshikawa Kenichi
Published: February 2010

In apoptotic cells, genomic DNA molecules are fragmented into multiple fragments with lengths that are integer multiples of approximately 180–200 base pairs (bp), i.e., the size of a single nucleosome. Here we propose a simple mathematical model for interpreting this cleavage pattern of DNA. Under the condition of a purely stochastic cleavage process, we derive a time evolution of the probability distribution of the fragment length by a Poisson distribution. We examine the applicability of our model by analyzing experimental results with apoptotic cells. Our model enables us to satisfactorily interpret the experimental trends. Interestingly, this theoretical fitting of the experimental data provides kinetic information for the cleavage reaction.
Continuously tunable, phase-locked, continuous-wave terahertz generator based on photomixing of two continuous-wave lasers locked to two independent optical combs
Authors: Yasui Takeshi , Takahashi Hisanari , Iwamoto Yutaka , Inaba Hajime , Minoshima Kaoru
Published: February 2010

A continuously tunable, phase-locked, single-frequency, continuous-wave (cw) terahertz generator has been demonstrated around 120 GHz, corresponding to the spectral bandwidth of the F-band unitraveling-carrier photodiode (UTC-PD) used as a photomixer in this study. This cw-terahertz generator is based on photomixing of an accurately tunable cw laser and a tightly fixed cw laser in the optical frequency region, phase locked to two independent optical combs. The continuous tuning range of the presented method was three orders of magnitude around 0.1 THz and two orders around 1 THz broader than that of a previous photomixing method in which two cw lasers are phase locked to a single optical comb, and fully covered the available spectral bandwidth of the F-band UTC-PD. The spectral behavior of the tight locking and continuous tuning of 120 GHz cw-terahertz radiation was confirmed in real time by use of a terahertz-comb-referenced spectrum analyzer. This cw-terahertz generator shows promise as a terahertz clock and synthesizer for terahertz frequency metrology.
Density functional theory study of the optical and electronic properties of oligomers based on phenyl-ethynyl units linked to triazole, thiadiazole, and oxadiazole rings to be used in molecular electronics
Authors: Garzón Andrés , Granadino-Roldán José M. , Moral Mónica , García Gregorio , Fernández-Liencres M. Paz , Navarro Amparo , Peña-Ruiz Tomás , Fernández-Gómez Manuel
Published: February 2010

In the present work, we have studied from a theoretical perspective the geometry and electronic properties of the series of related compounds 2,5-bis(phenylethynyl)-1,3,4-thiadiazole, 2,5-bis(phenylethynyl)-1,3,4-oxadiazole, and 2,5-bis(phenylethynyl)-1,2,4-triazole as candidates for electron-conducting polymers and compounds with desirable (opto)electronic properties. The effect of the ethynyl group (CC) on the structure and electronic properties was also studied. The influence of planarity on electrical conductivity has been studied by a natural-bond-orbital analysis. The (opto)electronic properties and conducting capability were investigated through the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, excitation energy, bond length alternation, LUMO energy, electron affinities, and intramolecular reorganization energy. Finally, the evolution of some properties such as optical bandgap and electron affinity with the increase of the number of repeat units in the oligomer chain has been checked.
Observation of shallow-donor muonium in Ga2O3: Evidence for hydrogen-induced conductivity
Authors: King P. D. C. , McKenzie I. , Veal T. D.
Published: February 2010

The electrical nature of muonium in the transparent conducting oxide material Ga2O3 is investigated via muon-spin rotation and relaxation spectroscopy. It is found to be a shallow donor, with an effective donor depth of 15≤ED≤30 meV and a hyperfine splitting of 0.13±0.01 MHz. This is in contrast to the deep level observed in the majority of semiconductors but supports the recent suggestion that muonium should be a shallow donor across the class of transparent conducting oxides. These observations suggest that hydrogen will also be a shallow donor in Ga2O3, with important implications both for unintentional conductivity and deliberate n-type doping of this material.
On the origin of leakage current reduction in TiO2 passivated porosus silicon Schottky-barrier diode
Authors: Hwang J. D. , Chou C. H.
Published: February 2010

Significant reduction by 40 times was achieved in the leakage current of TiO2 passivated porous silicon (PS) Schottky-barrier diode, compared to that of as-grown PS one. It was found that the imperfect native oxide, nonstoichiometric Si-suboxide (SiOx) and Si-O bond with nonbridging oxygen, and highly chemically reactive Si–H2 species are the issues of leakage current. These issues can be drastically suppressed and replaced by a stable stoichiometric SiO2 and Si–OH bond on the TiO2 passivated PS surface. The enriched OH formation will favor the growth of TiO2 and passivate the surface states of PS, hence reducing the leakage current.
The influence of Ni additions on the relative stability of η and η′ Cu6Sn5
Authors: Schwingenschlögl U. , Di Paola C. , Nogita K. , Gourlay C. M.
Published: February 2010

We investigate how 5 at. % Ni influences the relative stability of η and η′ Cu6Sn5. Synchrotron x-ray diffraction shows that, while Cu6Sn5 exists as η′ at 25 and 150 °C and transforms to η on heating to 200 °C, Cu5.5Ni0.5Sn5 is best fit to η throughout 25–200 °C. Our first principles calculations predict that η′ is stable at T=0 K in both Cu6Sn5 and Cu5.5Ni0.5Sn5, but that the energy difference is substantially reduced from 1.21 to 0.90 eV per 22 atom cell by the Ni addition. This effect is attributed to Ni developing distinct bonding to both Cu and Sn in the η phase.
Breakdown probability of neon under the influence of field electron emission and surface charges on the cathode surface
Authors: Marković V. Lj. , Gocić S. R. , Stamenković S. N.
Published: February 2010

Improved relations are suggested to determine of the breakdown probability in neon under the influence of field electron emission and surface charges on the gold plated cathode surfaces. The influence of field electron emission from a vacuum deposited gold layer is confirmed by the Fowler–Nordheim plot based on an analysis of the breakdown time delay dependence on the voltage td¯(U). Surface regions with a reduced conductivity on a hard galvanic layer of gold caused by diffusion of nickel atoms from a nickel sublayer are confirmed by scanning electron microscopy and energy dispersive x-ray spectrum.
Modeling of leakage currents in high-κ dielectrics: Three-dimensional approach via kinetic Monte Carlo
Authors: Jegert Gunther , Kersch Alfred , Weinreich Wenke , Schröder Uwe , Lugli Paolo
Published: February 2010

We report on a simulation algorithm, based on kinetic Monte Carlo techniques, that allows us to investigate transport through high-permittivity dielectrics. In the example of TiN/ZrO2/TiN capacitor structures, using best-estimate physical parameters, we have identified the dominant transport mechanisms. Comparison with experimental data reveals the transport to be dominated by Poole–Frenkel emission from donorlike trap states at low fields and trap-assisted tunneling at high fields.
A Chebychev propagator with iterative time ordering for explicitly time-dependent Hamiltonians
Authors: Ndong Mamadou , Tal-Ezer Hillel , Kosloff Ronnie , Koch Christiane P.
Published: February 2010

A propagation method for time-dependent Schrödinger equations with an explicitly time-dependent Hamiltonian is developed where time ordering is achieved iteratively. The explicit time dependence of the time-dependent Schrödinger equation is rewritten as an inhomogeneous term. At each step of the iteration, the resulting inhomogeneous Schrödinger equation is solved with the Chebychev propagation scheme presented in the work of M. Ndong et al. [J. Chem. Phys. 130, 124108 (2009)]. The iteratively time-ordering Chebychev propagator is shown to be robust, efficient, and accurate and compares very favorably with all other available propagation schemes.
Disparate product distributions observed in Mo(3−x)WxOy− (x=–3; y=3–9) reactions with D2O and CO2
Authors: Rothgeb David W. , Hossain Ekram , Mann Jennifer E. , Jarrold Caroline Chick
Published: February 2010

Results of gas phase reactivity studies on group six transition metal suboxide clusters, Mo3Oy−, Mo2WOy−, MoW2Oy−, and W3Oy− (Mo(3−x)WxOy−, x=0–3; y=ca. 3–9) with both D2O and CO2 are reported. Sequential oxidation for the more reduced species, Mo(3−x)WxOy−+D2O/CO2→Mo(3−x)WxOy+1−+D2/CO, and dissociative addition for certain species, Mo(3−x)WxOy−+D2O/CO2→Mo(3−x)WxOy+1D2−/Mo(3−x)WxOy+1CO−, is evident in the product distributions observed in mass spectrometric measurements. Reactions with D2O proceed at a rate that is on the order of 102 higher than for CO2. The pattern of reaction products reveals composition-dependent chemical properties of these group six unary and binary clusters. At the core of this variation is the difference in Mo–O and W–O bond energies, the latter of which is significantly higher. This results in a larger thermodynamic drive to higher oxidation states in clusters with more tungsten atoms. However, addition products for more oxidized W-rich clusters are not observed, while they are observed for the more Mo-rich clusters. This is attributed to the following: In the higher oxides (e.g., y=8), addition reactions require distortion of local metal-oxygen bonding, and will necessarily have higher activation barriers for W–O bonds, since the vibrational potentials will be narrower. The binary (x=1,2) clusters generally show sequential oxidation to higher values of y. This again is attributed to higher W–O bond energy, the result being that stable binary structures have W atoms in higher oxidation states, and Mo centers both in more reduced states and sterically unhindered. The reduced Mo center provides a locus of higher reactivity. An unusual result that is not readily explained is the chemically inert behavior of Mo3O6−.
Soliton self-deflection via power-dependent walk-off
Authors: Piccardi Armando , Alberucci Alessandro , Assanto Gaetano
Published: February 2010

We demonstrate, both experimentally and theoretically, excitation-dependent self-bending of spatial solitons in nematic liquid crystals. The observed deflection is explained by nonlinear changes in walk-off, as induced by the rotation of the optic axis via power-driven reorientation.
Interband cascade photovoltaic devices
Authors: Yang Rui Q. , Tian Zhaobing , Klem J. F. , Mishima Tetsuya D. , Santos Michael B. , Johnson Matthew B.
Published: February 2010

A photovoltaic (PV) device based on an interband cascade (IC) structure is proposed for efficiently converting solar and thermal energy to electricity. These IC PV devices employ absorption and transport regions with characteristics that are favorable for achieving high open-circuit voltage and thus possibly improving conversion efficiency over conventional PV devices. Preliminary experiments carried out using IC infrared photodetectors (seven stages) and lasers (11 stages) showed open-circuit voltages that exceed the single-band gap voltage from these devices under infrared illumination. The observed open-circuit voltage demonstrates multiple stages operating in series and provides an initial proof of concept for IC PV devices.
Optical band-gap determination of nanostructured WO3 film
Authors: González-Borrero P. P. , Sato F. , Medina A. N. , Baesso M. L. , Bento A. C. , Baldissera G. , Persson C. , Niklasson G. A. , Granqvist C. G. , Ferreira da Silva A.
Published: February 2010

The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green’s function approach using the projector augmented wave method. The theoretical study indicates that the cubic crystal structure shows good agreement with the experimental data.
Indirect land-use changes can overcome carbon savings from biofuels in Brazil
Authors: Lapola David M. , Schaldach Ruediger , Alcamo Joseph , Bondeau Alberte , Koch Jennifer , Koelking Christina , Priess Joerg A.
Published: February 2010

The planned expansion of biofuel plantations in Brazil could potentially cause both direct and indirect land-use changes (e.g., biofuel plantations replace rangelands, which replace forests). In this study, we use a spatially explicit model to project land-use changes caused by that expansion in 2020, assuming that ethanol (biodiesel) production increases by 35 (4) x 109liter in the 2003-2020 period. Our simulations show that direct land-use changes will have a small impact on carbon emissions because most biofuel plantations would replace rangeland areas. However, indirect land-use changes, especially those pushing the rangeland frontier into the Amazonian forests, could offset the carbon savings from biofuels. Sugarcane ethanol and soybean biodiesel each contribute to nearly half of the projected indirect deforestation of 121,970 km2by 2020, creating a carbon debt that would take about 250 years to be repaid using these biofuels instead of fossil fuels. We also tested different crops that could serve as feedstock to fulfill Brazil’s biodiesel demand and found that oil palm would cause the least land-use changes and associated carbon debt. The modeled livestock density increases by 0.09 head per hectare. But a higher increase of 0.13 head per hectare in the average livestock density throughout the country could avoid the indirect land-use changes caused by biofuels (even with soybean as the biodiesel feedstock), while still fulfilling all food and bioenergy demands. We suggest that a closer collaboration or strengthened institutional link between the biofuel and cattle-ranching sectors in the coming years is crucial for effective carbon savings from biofuels in Brazil.
Multilocus tetrasomic linkage analysis using hidden Markov chain model
Authors: Leach Lindsey J. , Wang Lin , Kearsey Michael J. , Luo Zewei
Published: February 2010

The availability of reliable genetic linkage maps is crucial for functional and evolutionary genomic analyses. Established theory and methods of genetic linkage analysis have made map construction a routine exercise in diploids. However, many evolutionarily, ecologically, and/or agronomically important species are autopolyploids, with autotetraploidy being a typical example. These species undergo much more complicated chromosomal segregation and recombination at meiosis than diploids. In addition, there is evidence of polyploidy-induced and highly dynamic changes in the structure of the genome. These polysomic characteristics indicate the inappropriateness of the theory and methods of linkage analysis in diploids for use in these species and a gap in the theory and methodology of tetraploid map construction. This paper presents a theoretical model and statistical framework for multilocus linkage analysis in autotetraploids for use with dominant and/or codominant DNA molecular markers. The theory and methods incorporate the essential features of allele segregation and recombination under tetrasomic inheritance and the major challenges in statistical modeling and marker data analysis. We validated the method and explored its statistical properties by intensive simulation study and demonstrated its utility by analysis of AFLP and SSR marker data from an outbred autotetraploid potato population.
Phylogenetic analyses reveal the shady history of C
4
grasses
Authors: Edwards Erika J. , Smith Stephen A.
Published: February 2010

Grasslands cover more than 20% of the Earth's terrestrial surface, and their rise to dominance is one of the most dramatic events of biome evolution in Earth history. Grasses possess two main photosynthetic pathways: the C
3
pathway that is typical of most plants and a specialized C
4
pathway that minimizes photorespiration and thus increases photosynthetic performance in high-temperature and/or low-CO
2
environments. C
4
grasses dominate tropical and subtropical grasslands and savannas, and C
3
grasses dominate the world's cooler temperate grassland regions. This striking pattern has been attributed to C
4
physiology, with the implication that the evolution of the pathway enabled C
4
grasses to persist in warmer climates than their C
3
relatives. We combined geospatial and molecular sequence data from two public archives to produce a 1,230-taxon phylogeny of the grasses with accompanying climate data for all species, extracted from more than 1.1 million herbarium specimens. Here we show that grasses are ancestrally a warm-adapted clade and that C
4
evolution was not correlated with shifts between temperate and tropical biomes. Instead, 18 of 20 inferred C
4
origins were correlated with marked reductions in mean annual precipitation. These changes are consistent with a shift out of tropical forest environments and into tropical woodland/savanna systems. We conclude that C
4
evolution in grasses coincided largely with migration out of the understory and into open-canopy environments. Furthermore, we argue that the evolution of cold tolerance in certain C
3
lineages is an overlooked innovation that has profoundly influenced the patterning of grassland communities across the globe.
Thalamic deactivation at sleep onset precedes that of the cerebral cortex in humans
Authors: Magnin Michel , Rey Marc , Bastuji Hélène , Guillemant Philippe , Mauguière François , Garcia-Larrea Luis
Published: February 2010

Thalamic and cortical activities are assumed to be time-locked throughout all vigilance states. Using simultaneous intracortical and intrathalamic recordings, we demonstrate here that the thalamic deactivation occurring at sleep onset most often precedes that of the cortex by several minutes, whereas reactivation of both structures during awakening is synchronized. Delays between thalamus and cortex deactivations can vary from one subject to another when a similar cortical region is considered. In addition, heterogeneity in activity levels throughout the cortical mantle is larger than previously thought during the descent into sleep. Thus, asynchronous thalamo-cortical deactivation while falling asleep probably explains the production of hypnagogic hallucinations by a still-activated cortex and the common self-overestimation of the time needed to fall asleep.
Mature dendritic cells use endocytic receptors to capture and present antigens
Authors: Platt Craig D. , Ma Jessica K. , Chalouni Cécile , Ebersold Melanie , Bou-Reslan Hani , Carano Richard A. D. , Mellman Ira , Delamarre Lélia
Published: February 2010

In response to inflammatory stimuli, dendritic cells (DCs) trigger the process of maturation, a terminal differentiation program required to initiate T-lymphocyte responses. A hallmark of maturation is down-regulation of endocytosis, which is widely assumed to restrict the ability of mature DCs to capture and present antigens encountered after the initial stimulus. We found that mature DCs continue to accumulate antigens, especially by receptor-mediated endocytosis and phagocytosis. Internalized antigens are transported normally to late endosomes and lysosomes, loaded onto MHC class II molecules (MHCII), and then presented efficiently to T cells. This occurs despite the fact that maturation results in the general depletion of MHCII from late endocytic compartments, with MHCII enrichment being typically thought to be a required feature of antigen processing and peptide loading compartments. Internalized antigens can also be cross-presented on MHC class I molecules, without any reduction in efficiency relative to immature DCs. Thus, although mature DCs markedly down-regulate their capacity for macropinocytosis, they continue to capture, process, and present antigens internalized via endocytic receptors, suggesting that they may continuously initiate responses to newly encountered antigens during the course of an infection.
Stem cell-specific activation of an ancestral
myc
protooncogene with conserved basic functions in the early metazoan
Hydra
Authors: Hartl Markus , Mitterstiller Anna-Maria , Valovka Taras , Breuker Kathrin , Hobmayer Bert , Bister Klaus
Published: February 2010

The c-
myc
protooncogene encodes a transcription factor (Myc) with oncogenic potential. Myc and its dimerization partner Max are bHLH-Zip DNA binding proteins controlling fundamental cellular processes. Deregulation of c-
myc
leads to tumorigenesis and is a hallmark of many human cancers. We have identified and extensively characterized ancestral forms of
myc
and
max
genes from the early diploblastic cnidarian
Hydra
, the most primitive metazoan organism employed so far for the structural, functional, and evolutionary analysis of these genes.
Hydra myc
is specifically activated in all stem cells and nematoblast nests which represent the rapidly proliferating cell types of the interstitial stem cell system and in proliferating gland cells. In terminally differentiated nerve cells, nematocytes, or epithelial cells,
myc
expression is not detectable by in situ hybridization.
Hydra max
exhibits a similar expression pattern in interstitial cell clusters. The ancestral
Hydra
Myc and Max proteins display the principal design of their vertebrate derivatives, with the highest degree of sequence identities confined to the bHLH-Zip domains. Furthermore, the 314-amino acid
Hydra
Myc protein contains basic forms of the essential Myc boxes I through III. A recombinant
Hydra
Myc/Max complex binds to the consensus DNA sequence CACGTG with high affinity. Hybrid proteins composed of segments from the retroviral v-Myc oncoprotein and the
Hydra
Myc protein display oncogenic potential in cell transformation assays. Our results suggest that the principal functions of the Myc master regulator arose very early in metazoan evolution, allowing their dissection in a simple model organism showing regenerative ability but no senescence.