bluuebunny/crossref_metadata_2025 huggingface dataset:
Biosphere‐atmosphere gross carbon exchange flux and the δ13CO2 and Δ14CO2 disequilibria constrained by the biospheric excess radiocarbon inventory
Authors: Naegler Tobias , Levin Ingeborg
Published: September 2009

Estimates of the global biospheric excess 14C inventory IB14,E from Naegler and Levin (2009) were used to constrain the age distribution a(τ) in heterotrophically respired CO2 with a simple (radio)carbon model of the global biosphere. Subsequently, a(τ) could be used to estimate the global gross carbon exchange FeqC (net primary productivity, NPP, and heterotrophic respiration) between atmosphere and biosphere as well as both the δ13C and Δ14C signatures in heterotrophically respired CO2 (δ13CRH and Δ14CRH, respectively). Our estimates of FeqC range from 41 to 64 petagrams carbon per year (Pg C a−1), with a best estimate of 55 Pg C a−1. The uncertainty of this value is dominated by the uncertainties of IB14,E and of the net biospheric uptake of anthropogenic CO2. Limitations intrinsic to our approach as well as uncertainties in effective global average atmospheric Δ14CO2 add an uncertainty of ±3 Pg C a−1. The δ13CRH of heterotrophically respired CO2 lags the δ13C of assimilated CO2 by ∼10–17 years. This leads to a somewhat smaller estimate of the biospheric 13CO2 disequilibrium flux than previously assumed. Δ14CRH increased from ∼−20‰ in the early 1950s to maximum values of 300–325‰ in the late 1960s/early 1970s. In the 1980s, when the maximum IB14,E occurred, Δ14CRH was in a transient equilibrium with the atmosphere. The Δ14C disequilibrium between atmosphere and biosphere increased to Δ14CDIS = 20–50‰ in the mid‐1990s, before it dropped to 15–40‰ in 2005.
A study of the possibility of sprites in the atmospheres of other planets
Authors: Yair Yoav , Takahashi Yukihiro , Yaniv Roy , Ebert Ute , Goto Yukihiro
Published: September 2009

Sprites are a spectacular type of transient luminous events which occur above thunderstorms immediately after lightning. They have shapes of giant jellyfish, carrots, or columns and last tens of milliseconds. In Earth's atmosphere, sprites mostly emit in red and blue wavelengths from excited N2 and N2+ and span a vertical range between 50 and 90 km above the surface. The emission spectra, morphology, and occurrence heights of sprites reflect the properties of the planetary atmosphere they inhabit and are related to the intensity of the initiating parent lightning. This paper presents results of theoretical calculations of the expected occurrence heights of sprites above lightning discharges in the CO2 atmosphere of Venus, the N2 atmosphere of Titan, and the H2‐He atmosphere of Jupiter. The expected emission features are presented, and the potential of detecting sprites in planetary atmospheres by orbiting spacecraft is discussed.
CO2 flux and seasonal variability in a large subtropical estuarine system, the Pearl River Estuary, China
Authors: Guo Xianghui , Dai Minhan , Zhai Weidong , Cai Wei‐Jun , Chen Baoshan
Published: September 2009

This paper presents the spatial distribution and seasonal changes of the carbonate system and CO2 fluxes in a complex river‐estuary system located in a subtropical region, the Pearl River Estuary, based on five surveys covering primarily a wet and dry seasonal cycle on two major subestuaries of the Pearl River, namely Lingdingyang and Huangmaohai. Significant spatial and seasonal variations of surface water partial pressure of CO2 (pCO2) were observable in these two subestuaries. While both Lingdingyang and Huangmaohai had higher pCO2 in their upper estuaries, which quickly decreased downstream as seen in many estuarine settings elsewhere, significant differences occurred between the two subestuaries in terms of pCO2 level, with much higher pCO2 in the upper Lingdingyang than the upper Huangmaohai. In terms of seasonality, substantially higher pCO2 was observed in warm and wet seasons in both upper estuaries (2100–8350 μatm in the Lingdingyang and 1040–3590 μatm in the Huangmaohai) than in cold and dry seasons (1100–7460 μatm and 560–970 μatm in the Lingdingyang and the Huangmaohai, respectively). As a consequence, CO2 emission from the Pearl River Estuary system in summer was ∼6 times of that in winter. At the same time, we observed a clear drawdown of pCO2 in the lower estuary in both summer and winter, reaching a level of water pCO2 which was below the atmospheric level. This seasonal and spatial contrast can also be seen in the distribution of dissolved inorganic carbon (DIC) and total alkalinity. On the basis of a seasonal and zonal distribution of pCO2, the annual CO2 emission from the Pearl River Estuary was estimated to be ∼3 × 1010 mol C, which is equivalent to ∼6% of the total DIC export flux to the South China Sea from the Pearl River system.
Lightning and anthropogenic NOx sources over the United States and the western North Atlantic Ocean: Impact on OLR and radiative effects
Authors: Choi Yunsoo , Kim Jinwon , Eldering Annmarie , Osterman Gregory , Yung Yuk L. , Gu Yu , Liou K. N.
Published: September 2009

The migration of enhancements in NO2 concentration, outgoing longwave radiation (OLR), and radiative effects associated with the onset of the North American Monsoon in July 2005 has been investigated using satellite data and the Regional Chemical Transport Model (REAM). The satellite data include the tropospheric NO2 columns, tropospheric O3 profiles, and OLR from OMI, TES and NOAA‐16 satellite, respectively, for June and July 2005. The simulated OLR captures the spatial distribution of the remotely sensed OLR fields with relatively small biases (≤5.7%) and high spatial correlations (R ≥ 0.88). This study reveals that the lightning‐generated NOx exerts a larger, by up to a factor of three, impact on OLR (up to 0.35 Wm−2) and radiative effects (up to 0.55 Wm−2) by enhancing O3 in the upper troposphere than anthropogenic NOx that increases O3 in the lower troposphere, despite the fact that the lightning‐generated NOx and O3 are much smaller than those from the anthropogenic emissions. The radiative effect by lightning‐derived upper tropospheric O3 over the convective outflow regions is affected by the changes in lightning frequency. Thus the changes in convection due to global warming may alter the geographical distribution and magnitude of the radiative effect of lightning‐derived O3, and this paper is a first step in quantifying the current radiative impact.
Hilbert‐Huang Transform of geomagnetic pulsations at auroral expansion onset
Authors: Kataoka Ryuho , Miyoshi Yoshizumi , Morioka Akira
Published: September 2009

The waveform of geomagnetic pulsations at auroral expansion onset looks irregular and is hardly resolved by Fourier transform. Here we perform a novel analysis of the Hilbert‐Huang Transform (HHT) to address this problem, focusing on the event investigated in detail by Morioka et al. (2008), in which the auroral kilometric radiation (AKR) breakup was clearly identified. From the HHT analysis of high‐latitude search coil ground magnetometer data, Pi1, Pc3, and Pi2 pulsations are extracted as the first, second, and third intrinsic mode functions, respectively. Amplification of the Pi1 and Pc3 pulsations is first detected as a clear precursor to the AKR breakup. The Pi1 and Pc3 pulsations show sudden enhancement at the AKR breakup. We suggest that the HHT is capable of automatically extracting the Pi1, Pi2, and Pc3 from the irregular high‐latitude geomagnetic pulsations, providing a new type of diagnostic tools for understanding the onset mechanism of auroral substorms.
Circadian Timing of Food Intake Contributes to Weight Gain
Authors: Arble Deanna M. , Bass Joseph , Laposky Aaron D. , Vitaterna Martha H. , Turek Fred W.
Published: September 2009

Studies of body weight regulation have focused almost entirely on caloric intake and energy expenditure. However, a number of recent studies in animals linking energy regulation and the circadian clock at the molecular, physiological, and behavioral levels raise the possibility that the timing of food intake itself may play a significant role in weight gain. The present study focused on the role of the circadian phase of food consumption in weight gain. We provide evidence that nocturnal mice fed a high‐fat diet only during the 12‐h light phase gain significantly more weight than mice fed only during the 12‐h dark phase. A better understanding of the role of the circadian system for weight gain could have important implications for developing new therapeutic strategies for combating the obesity epidemic facing the human population today.
Regulation of Rnd3 localization and function by protein kinase Cα-mediated phosphorylation
Authors: Madigan James P. , Bodemann Brian O. , Brady Donita C. , Dewar Brian J. , Keller Patricia J. , Leitges Michael , Philips Mark R. , Ridley Anne J. , Der Channing J. , Cox Adrienne D.
Published: September 2009

The Rnd proteins (Rnd1, Rnd2 and Rnd3/RhoE) form a distinct branch of the Rho family of small GTPases. Altered Rnd3 expression causes changes in cytoskeletal organization and cell cycle progression. Rnd3 functions to decrease RhoA activity, but how Rnd3 itself is regulated to cause these changes is still under investigation. Unlike other Rho family proteins, Rnd3 is regulated not by GTP/GDP cycling, but at the level of expression and by post-translational modifications such as prenylation and phosphorylation. We show in the present study that, upon PKC (protein kinase C) agonist stimulation, Rnd3 undergoes an electrophoretic mobility shift and its subcellular localization becomes enriched at internal membranes. These changes are blocked by inhibition of conventional PKC isoforms and do not occur in PKCα-null cells or to a non-phosphorylatable mutant of Rnd3. We further show that PKCα directly phosphorylates Rnd3 in an in vitro kinase assay. Additionally, we provide evidence that the phosphorylation status of Rnd3 has a direct effect on its ability to block signalling from the Rho–ROCK (Rho-kinase) pathway. These results identify an additional mechanism of regulation and provide clarification of how Rnd3 modulates Rho signalling to alter cytoskeletal organization.
Phenylalanine ammonia-lyase (PAL) from tobacco (Nicotiana tabacum): characterization of the four tobaccoPALgenes and active heterotetrameric enzymes
Authors: Reichert Angelika I. , He Xian-Zhi , Dixon Richard A.
Published: September 2009

PAL (L-phenylalanine ammonia-lyase), the first enzyme of phenylpropanoid biosynthesis, is often encoded by multigene families in plants. A PCR-based approach was used to isolate cDNA clones corresponding to the four PAL genes of tobacco (Nicotiana tabacum). By careful comparison of cDNA and genomic clones, a new PAL gene (PAL4) was defined. PCR amplification of PAL sequences from cDNA led to the generation of chimaeric clones between PAL1 and PAL4, and incorrect annotation of PAL4 ESTs (expressed sequence tags) as PAL1 in the EST database has given rise to a randomly shuffled tentative consensus sequence. The PAL2 previously described in the literature was shown, by domain swapping experiments with PAL1, to possess a single nucleotide substitution leading to an inactive enzyme. The altered amino acid resulting from this substitution maps to the base of the active site pocket in the three-dimensional structure of PAL. The inactive PAL2 allele could not be recovered from 13 different tobacco cultivars examined. PALs 1–4 were co-expressed in multiple plant organs, and were also co-induced following exposure of cell cultures to yeast elicitor or methyl jasmonate. All four tobacco PAL proteins expressed in Escherichia coli displayed normal Michaelis–Menten kinetics, with Km values between 36 and 60 μM. Co-expression of different PAL proteins in E. coli resulted in formation of heterotetramers, which possessed kinetic properties within the same range as those of the individual homotetramers. The potential physiological function of heterotetrameric PAL forms is discussed.
Design of proteolytically stable RI-anchoring disruptor peptidomimetics for in vivo studies of anchored type I protein kinase A-mediated signalling
Authors: Torheim Eirik A. , Jarnæss Elisabeth , Lygren Birgitte , Taskén Kjetil
Published: September 2009

We have reported previously the design of a RIAD (RI-anchoring disruptor) peptide that specifically displaces PKA (protein kinase A) type I from the AKAP (A-kinase-anchoring protein) ezrin, which is present in the immunological synapse of T-cells. This increases immune reactivity by reducing the threshold for activation and may prove a feasible approach for improving immune function in patients with cAMP-mediated T-cell dysfunction. However, the use of RIAD in biological systems is restricted by its susceptibility to enzymatic cleavage and, consequently, its short half-life in presence of the ubiquitous serum peptidases. In the present study, carefully selected non-natural amino acids were employed in the design of RIAD analogues with improved stability. The resulting peptidomimetics demonstrated up to 50-fold increased half-lives in serum compared with RIAD, while maintaining similar or improved specificity and potency with respect to disruption of PKA type I–AKAP interactions.
Escherichia coli glycogen metabolism is controlled by the PhoP-PhoQ regulatory system at submillimolar environmental Mg2+ concentrations, and is highly interconnected with a wide variety of cellular processes
Authors: Montero Manuel , Eydallin Gustavo , Viale Alejandro M. , Almagro Goizeder , Muñoz Francisco J. , Rahimpour Mehdi , Sesma María T. , Baroja-Fernández Edurne , Pozueta-Romero Javier
Published: September 2009

Using the Keio collection of gene-disrupted mutants of Escherichia coli, we have recently carried out a genome-wide screening of the genes affecting glycogen metabolism. Among the mutants identified in the study, ΔmgtA, ΔphoP and ΔphoQ cells, all lacking genes that are induced under low extracellular Mg2+ conditions, displayed glycogen-deficient phenotypes. In this work we show that these mutants accumulated normal glycogen levels when the culture medium was supplemented with submillimolar Mg2+ concentrations. Expression analyses conducted in wild-type, ΔphoP and ΔphoQ cells showed that the glgCAP operon is under PhoP-PhoQ control in the submillimolar Mg2+ concentration range. Subsequent screening of the Keio collection under non-limiting Mg2+ allowed the identification of 183 knock-out mutants with altered glycogen levels. The stringent and general stress responses, end-turnover of tRNA, intracellular AMP levels, and metabolism of amino acids, iron, carbon and sulfur were major determinants of glycogen levels. glgC::lacZY expression analyses using mutants representing different functional categories revealed that the glgCAP operon belongs to the RelA regulon. We propose an integrated metabolic model wherein glycogen metabolism is (a) tightly controlled by the energy and nutritional status of the cell and (b) finely regulated by changes in environmental Mg2+ occurring at the submillimolar concentration range.
Existence of exocytotic hemifusion intermediates with a lifetime of up to seconds in type II pneumocytes
Authors: Miklavc Pika , Albrecht Susanne , Wittekindt Oliver H. , Schullian Peter , Haller Thomas , Dietl Paul
Published: September 2009

Exocytosis proceeds through prefusion stages such as hemifusion, but hemifusion is still an elusive intermediate of unknown duration. Using darkfield and fluorescence microscopy in ATII (alveolar type II) cells containing large secretory vesicles (LBs; lamellar bodies), we show that exocytotic fusion events were accompanied by a mostly biphasic SLID (scattered light intensity decrease) originating from the vesicle border. Correlation with the diffusional behaviour of fluorescence markers for either content or membrane mixing revealed that the onset of the fast second phase of SLID corresponded to fusion pore formation, which was followed by vesicle swelling. In contrast, a slow first phase of SLID preceded pore formation considerably but could still be accompanied by diffusion of farnesylated DsRed, an inner plasma membrane leaflet marker, or Nile Red. We conclude that hemifusion is an exocytotic intermediate that may last for several seconds. SLID is a new, non-invasive approach by which a prefusion phase, including hemifusion, can be continuously recorded and distinguished from fusion pore formation and postfusion vesicle swelling.
How to measure forces with atomic force microscopy without significant influence from nonlinear optical lever sensitivity
Authors: Thormann Esben , Pettersson Torbjön , Claesson Per M.
Published: September 2009

In an atomic force microscope (AFM), the force is normally sensed by measuring the deflection of a cantilever by an optical lever technique. Experimental results show a nonlinear relationship between the detected signal and the actual deflection of the cantilever, which is widely ignored in literature. In this study we have designed experiments to investigate different possible reasons for this nonlinearity and compared the experimental findings with calculations. It is commonly assumed that this nonlinearity only causes problems for extremely large cantilever deflections. However, our results show that the nonlinear detector response might influence many AFM studies where soft or short cantilevers are used. Based on our analysis we draw conclusions of the main reason for the nonlinearity and suggest a rule of thumb for which cantilevers one should use under different experimental conditions.
Ballistic current in metal-oxide-semiconductor field-effect transistors: The role of device topology
Authors: Pourghaderi M. Ali , Magnus Wim , Sorée Bart , Meuris Marc , De Meyer Kristin , Heyns Marc
Published: September 2009

In this study we investigate the effect of device topology on the ballistic current in n-channel metal-oxide-semiconductor field-effect transistors. Comparison of the nanoscale planar and double-gate devices reveals that, down to a certain thickness of the double gate film, the ballistic current flowing in the double gate device is twice as large compared to its planar counterpart. On the other hand, further thinning of the film beyond this threshold is found to change noticeably the confinement and transport characteristics, which are strongly depending on the film material and the surface orientation. For double gate Ge and Si devices there exists a critical film thickness below which the transverse gate field is no longer effectively screened by the inversion layer electron gas and mutual inversion of the two gates is turned on. In the case of GaAs and other similar III–V compounds, a decrease in the film thickness may drastically change the occupation of the L-valleys and therefore amend the transport properties. The simulation results show that, in both cases, the ballistic current and the transconductance are considerably enhanced.
Influence of Si–N complexes on the electronic properties of GaAsN alloys
Authors: Jin Y. , He Y. , Cheng H. , Jock R. M. , Dannecker T. , Reason M. , Mintairov A. M. , Kurdak C. , Merz J. L. , Goldman R. S.
Published: September 2009

We have investigated the influence of Si–N complexes on the electronic properties of GaAsN alloys. The presence of Si–N complexes is suggested by a decrease in carrier concentration, n, with increasing N-composition, observed in GaAsN:Si films but not in modulation-doped heterostructures. In addition, for GaAsN:Te (GaAsN:Si), n increases substantially (minimally) with annealing-T, suggesting a competition between annealing-induced Si–N complex formation and a reduced concentration of N-related traps. Since Si–N complex formation is enhanced for GaAsN:Si growth with the (2×4) reconstruction, which has limited group V sites for As–N exchange, the (Si–N)As interstitial pair is identified as the dominant Si–N complex.
Vibrations and reorientations of H2O molecules and NO3− anions in [Ca(H2O)4](NO3)2 studied by incoherent inelastic neutron scattering, Raman light scattering, and infrared absorption spectroscopy
Authors: Hetmańczyk Joanna , Hetmańczyk Łukasz , Migdał-Mikuli Anna , Mikuli Edward , Drużbicki Kacper , Wesełucha-Birczyńska Aleksandra , Proniewicz Leonard M.
Published: September 2009

The vibrational and reorientational motions of H2O ligands and NO3− anions were investigated by Fourier transform middle-infrared Raman scattering (RS) spectroscopy and phonon density of states, calculated from incoherent inelastic neutron scattering, in the high- and low-temperature phases of [Ca(H2O)4](NO3)2. The theoretical IR and RS spectra were also calculated by means of the quantum chemistry method using density functional theory with PBE1PBE functional at 6-311++G(2d,2p) basis set level. The temperature dependences of the full width at half maximum values of νs(H2O) bands in both the infrared absorption and the RS spectroscopy suggest that the observed phase transitions (at TC1 and TC2) are not connected with a drastic change in the speed of H2O reorientational motions. However, similar Raman ν4(NO3−) band shape measurements as a function of temperature revealed the existence of a fast NO3− reorientation in phase I, which is abruptly slowed at the phase transition at TC1. Activation energy values for the reorientational motions of H2O ligands and NO3− anions were calculated.
Cyanide complexes of Ti(IV): A computational study
Authors: Rayón Víctor M. , Redondo Pilar , Barrientos Carmen , Largo Antonio
Published: September 2009

Density functional theory (B3LYP) and coupled-cluster techniques [CCSD(T)] including solvent effects have been used to study the homoleptic and mixed cyanide/isocyanide complexes of Ti(IV), [Ti(CN)n]4−n (n=1–6). The most stable isomer is found to be the isocyanide form except for n=6 where the cyanide isomer is preferred. Calculations accounting for solvent effects show that, irrespective of the solvent employed, the hexacyanocomplex should be formed. We have additionally analyzed the bonding situation in these complexes in order to shed some light on the reasons for the predicted cyano-/isocyano preference. We have found that the more advantageous σ-bonding capabilities of the cyanide form become increasingly important for larger n eventually favoring the cyanoisomer for n=6. We finally compare the bonding situation in hexacyanotitanate(IV) with that of hexacyanoferrate(II).
Turbulence-interface interactions in a two-fluid homogeneous flow
Authors: Li Zhaorui , Jaberi Farhad A.
Published: September 2009

The two-way interactions between the turbulent velocity field and the interface in an incompressible two-fluid homogeneous turbulent flow are studied with a recently developed Lagrangian–Eulerian interfacial particle level-set method. The numerical results confirm that the rate of change of the interface area is directly related to the work done by the surface tension force. While the surface tension damps the surrounding turbulence in the “interface stretching period” to oppose the increase in interface area, it is shown to actually increase the turbulent kinetic energy when the interface experiences compression. Additionally, the surface tension force is found to generate strong vortical motions close to the interface through the baroclinic torque effects. There is also an increase in strain rate and the viscous dissipation rate of turbulent kinetic energy in the interface region. The effect of interface on the surrounding turbulence appears primarily in the direction perpendicular to the interface. Analysis of the vorticity and kinetic energy equations indicates that the turbulence-interface interactions are strongly dependent on the fluids’ density ratio and the Weber number.
Properties of subsonic open cavity flow fields
Authors: Murray Nathan , Sällström Erik , Ukeiley Lawrence
Published: September 2009

Flow over an open cavity was studied for several different subsonic free stream Mach numbers ranging from 0.19 to nearly 0.73. Velocity field information was acquired through an application of particle image velocimetry, while the fluctuating surface pressure was acquired through a linear array of surface pressure sensors. These data were acquired on the centerline of the cavity which had a length to depth ratio of 6 and a turbulent boundary layer upstream of its leading edge. Over the range of free stream Mach numbers the fluctuating surface pressure spectra in the cavity exhibited different behavior ranging from no apparent resonance to resonance being dominated by the second or third Rossiter modes. The broadband levels of surface pressure spectra with strong resonant tones collapse with scaling by the flow dynamic pressure. Velocity measurements reveal that the center of circulation of the flow within the cavity moves from the aft wall towards the center of the cavity with increasing Mach number. The trend in the mean flow was also apparent in the mean square fluctuating velocities although to a lesser extent. Application of the proper orthogonal decomposition was performed independently on the velocity fields from each of the different free stream cases yielding a spatially dependent basis set. Using a similarity parameter between these spatial orthogonal basis functions it was shown that the first two modes for all of the cases were quantitatively similar. Furthermore this analysis showed some higher less energetic modes that were similar between the cases.
Localized versus delocalized states: Photoluminescence from electrochemically synthesized ZnO nanowires
Authors: Voss T. , Bekeny C. , Gutowski J. , Tena-Zaera R. , Elias J. , Lévy-Clément C. , Mora-Seró I. , Bisquert J.
Published: September 2009

We analyze the near-band-edge photoluminescence of electrochemically deposited ZnO nanowires and directly correlate the photoluminescence properties with the carrier concentration in the nanowires as determined from electrochemical impedance spectroscopy. We find a donor density of 8×1019 cm−3 in the as-deposited nanowires and show that the near-band-edge emission results from band-to-band recombination processes (delocalized states). A photoluminescence band centered at 3.328 eV scales with the diameter of the nanowires and is assigned to recombination processes involving surface states. We show that annealing at 500 °C in air reduces the donor density in the nanowires by more than one order of magnitude, leading to sharp excitonic transitions in the electrochemically deposited nanowires.
Modal characteristics of terahertz surface-emitting distributed-feedback lasers with a second-order concentric-circular metal grating
Authors: Li X. F. , Yu S. F.
Published: September 2009

A theoretical model is developed to study the modal characteristics of a second-order concentric-circular metal grating surface-emitting distributed-feedback (DFB) laser operating at terahertz regime. A series of high-order diffracted fields, which can be expressed as a Floquet–Bloch expansion of Hankel functions, is assumed to be generated from the concentric-circular metal grating. The resonant frequencies and transverse profiles of all the diffracted fields can be deduced from the related eigenequations established through the boundary conditions of the interfaces of the metal-dielectric-metal waveguide. The results show that the interference of the diffracted cylindrical waves can form two types of resonant modes, namely, quasisymmetric and quasiantisymmetric modes. Surface radiation is excited mainly by the influence of quasisymmetric modes, which exhibit constructive interference with the grating geometry. Furthermore, the resultant intensities of the diffracted waves decay exponentially from the center of the circular grating, indicating that the proposed grating geometry has the potential to realize surface terahertz radiation with excellent beam quality. The influence of grating duty cycle on the resonant conditions and transverse distributions of the diffracted fields are also investigated.
Surface sp half-metallicity of zinc-blende calcium monocarbide
Authors: Gao G. Y. , Yao Kai-Lun
Published: September 2009

Recent studies by Gao et al. [Phys. Rev. B 75, 174442 (2007)] indicate zinc-blende CaC, SrC, and BaC exhibit robust sp half-metallic ferromagnetism with Curie temperatures higher than room temperature. Here we further investigate the surface electronic and magnetic properties of CaC by using the first-principles full-potential linearized augmented plane-wave method. The (001) surfaces terminated with Ca and C, respectively, and the (110) surface terminated with both Ca and C are considered. We discuss the surface stabilities from the calculated relaxed surface energies. Electronic structure calculations indicate that the half-metallicity is destroyed for both the Ca- and C-terminated (001) surfaces; however, the (110) surface preserves the half-metallic characteristic of the bulk CaC. We further reveal that the atomic magnetic moments of the (001) surfaces are greatly different from the bulk values, but the difference of atomic magnetic moments between the (110) surface and the bulk CaC is very small.
Manifestation of the electrode-contact effect on the dielectric response and impedance spectra of CaSiO3-doped CaCu3Ti4O12
Authors: Fang Tsang-Tse , Chung Han-Yang , Liou Sz-Chian
Published: September 2009

Undoped and CaSiO3-doped CaCu3Ti4O12 (CCTO) ceramics were prepared by solid-state reaction. The structures and compositions were characterized by a field-emission transmission electron microscope, equipped with Gatan image filter and high angle annular dark filed detector. We observed the low-frequency plateaus of frequency dependence of permittivity in CaSiO3-doped CCTO with Au electrode revealing an opposite temperature dependence in contrast to In–Ga electrode, which is evidenced to be related to the grain-boundary capacitance and contact resistance. Impedance spectra of CaSiO3-doped CCTO with In–Ga and Au electrodes can be modeled by an equivalent circuit with series combination of four parallel RC elements including domains, domain boundaries, grain boundaries, and the electrode contacts. We also confirm that the Si ions segregate to either grain boundaries or pore surface and develop an amorphous phase; most of the excess Cu ions are prevented by the segregated Si ions from being along the grain boundaries and form CuO particles in triple-junction pores.
Achieving multifrequency transparency with cylindrical plasmonic Cloak
Authors: Wang Hailei , Zhang Xiangdong
Published: September 2009

In this work, we have theoretically investigated the possibility to achieve multifrequency transparency and cloaking for a cylindrical object by employing a multilayered plasmonic shell. The frequency dispersion of plasmonic material and the size effect of the cylindrical object have been considered. The analytical transparency condition in the quasistatic case has not only been given, an exact numerical calculation based on the Mie scattering theory has also been performed. Our results show that the multifrequency transparency and cloaking for any dielectric or metal cylinder can always be realized by a suitable adjustment of the structure parameter, permittivity, and permeability of the multilayered shell. Such a transparency is not only for a certain polarized wave, it can also be realized for both polarizations of electromagnetic wave at the same time.
Radiation damage resistance of AlGaN detectors for applications in the extreme-ultraviolet spectral range
Authors: Barkusky Frank , Peth Christian , Bayer Armin , Mann Klaus , John Joachim , Malinowski Pawel E.
Published: September 2009

We report on the fabrication of aluminum gallium nitride (AlGaN) Schottky-photodiode-based detectors. AlGaN layers were grown using metal-organic chemical vapor deposition (MOCVD) on Si(111) wafers. The diodes were characterized at a wavelength of 13.5 nm using a table-top extreme-ultraviolet (EUV) radiation source, consisting of a laser-produced xenon plasma and a Schwarzschild objective. The responsivity of the diodes was tested between EUV energies ranging from 320 nJ down to several picojoules. For low fluences, a linear responsivity of 7.14 mAs/J could be determined. Saturation starts at approximately 1 nJ, merging into a linear response of 0.113 mAs/J, which could be attributed to the photoeffect on the Au electrodes on top of the diode. Furthermore, degradation tests were performed up to an absolute dose of 3.3×1019 photons/cm2. AlGaN photodiodes were compared to commercially available silicon-based photodetectors. For AlGaN diodes, responsivity does not change even for the highest EUV dose, whereas the response of the Si diode decreases linearly to ∼93% after 2×1019 photons/cm2.
Comment on “Mathematical and physical aspects of Kappa velocity distribution” [Phys. Plasmas 14, 110702 (2007)]
Authors: Hellberg M. A. , Mace R. L. , Baluku T. K. , Kourakis I. , Saini N. S.
Published: September 2009

A recent paper [L.-N. Hau and W.-Z. Fu, Phys. Plasmas 14, 110702 (2007)] deals with certain mathematical and physical properties of the kappa distribution. We comment on the authors’ use of a form of distribution function that is different from the “standard” form of the kappa distribution, and hence their results, inter alia for an expansion of the distribution function and for the associated number density in an electrostatic potential, do not fully reflect the dependence on κ that would be associated with the conventional kappa distribution. We note that their definition of the kappa distribution function is also different from a modified distribution based on the notion of nonextensive entropy.
A fast method for solving both the time-dependent Schrödinger equation in angular coordinates and its associated “m-mixing” problem
Authors: Reuter Matthew G. , Ratner Mark A. , Seideman Tamar
Published: September 2009

An efficient split-operator technique for solving the time-dependent Schrödinger equation in an angular coordinate system is presented, where a fast spherical harmonics transform accelerates the conversions between angle and angular momentum representations. Unlike previous techniques, this method features facile inclusion of azimuthal asymmetries (solving the “m-mixing” problem), adaptive time stepping, and favorable scaling, while simultaneously avoiding the need for both kinetic and potential energy matrix elements. Several examples are presented.
Interdiffusion of molecular acceptors through organic layers to metal substrates mimics doping-related energy level shifts
Authors: Duhm Steffen , Salzmann Ingo , Bröker Benjamin , Glowatzki Hendrik , Johnson Robert L. , Koch Norbert
Published: September 2009

Photoemission measurements reveal energy level shifts toward the Fermi level when a strong electron acceptor (tetrafluoro-tetracyanoquinodimethane, F4-TCNQ) is deposited on pristine layers of 4,4′,4″-tris(N,N-diphenyl-amino)triphenylamine (TDATA) or 4,4′-bis(N-carbazolyl)biphenyl (CBP). The shifts of the TDATA and CBP energy levels toward the Fermi level of the Au substrate could, in principle, arise from p-type doping of the intrinsic organic layers. While this indeed takes place in TDATA, doping of CBP by F4-TCNQ, i.e., charge transfer complex formation, does not occur. The shifts observed in CBP arise from the diffusion of F4-TCNQ toward the Au substrate, which modifies the buried metal surface potential, leading to a realignment of the energy levels of the organic overlayer.
Two-stream stability properties of the return-current layer for intense ion beam propagation through background plasma
Authors: Startsev Edward A. , Davidson Ronald C. , Dorf Mikhail
Published: September 2009

When an ion beam with sharp edge propagates through a background plasma, its current is neutralized by the plasma return current everywhere except at the beam edge over a characteristic transverse distance Δx⊥∼δpe, where δpe=c/ωpe is the collisionless skin depth and ωpe is the electron plasma frequency. Because the background plasma electrons neutralizing the ion beam current inside the beam are streaming relative to the background plasma electrons outside the beam, the background plasma can support a two-stream surface-mode excitation. Such surface modes have been studied previously assuming complete charge and current neutralization, and have been shown to be strongly unstable. In this paper we study the detailed stability properties of this two-stream surface mode for an electron flow velocity profile self-consistently driven by the ion beam. In particular, it is shown that the self-magnetic field generated inside the unneutralized current layer, which has not been taken into account previously, completely eliminates the instability.
Superconducting quantum interference device amplifiers with over 27 GHz of gain-bandwidth product operated in the 4–8 GHz frequency range
Authors: Spietz Lafe , Irwin Kent , Aumentado José
Published: September 2009

We describe the performance of amplifiers in the 4–8 GHz range using direct current (dc) superconducting quantum interference devices (SQUIDs) in a lumped element configuration. We have used external impedance transformers to couple power into and out of the dc SQUIDs. By choosing appropriate values for coupling capacitors, resonator lengths and output component values, we have demonstrated useful gains in several frequency ranges with different bandwidths, showing over 27 GHz of power gain-bandwidth product. In this work, we describe our design for the 4–8 GHz range and present data demonstrating gain, bandwidth, dynamic range, and drift characteristics.
The effect of molybdenum oxide interlayer on organic photovoltaic cells
Authors: Kim Do Young , Subbiah Jegadesan , Sarasqueta Galileo , So Franky , Ding Huanjun , Irfan  , Gao Yongli
Published: September 2009

Both small molecule and polymer photovoltaic cells were fabricated with molybdenum oxide interlayer at the indium tin oxide electrode. Enhancement in power efficiencies was observed in both small molecule and polymer cells. Specifically, the power conversion efficiencies of small molecule cells with the molybdenum oxide interlayer were enhanced by a maximum of 38% due to a significant enhancement in the fill factor. The improved fill factor is attributed to the reduction in series resistance. Our ultraviolet photoemission spectroscopy data indicate that the formation of band bending and the built-in field at the interface due to the interlayer leads to enhancement in hole extraction from the photoactive layer toward the anode.
Observation of the focusing of liquid surface waves
Authors: Yang J. , Tang Y. F. , Ouyang C. F. , Liu X. H. , Hu X. H. , Zi J.
Published: September 2009

The transmission properties of liquid surface waves through a biconvex array of rigid cylinders, arranged in a two-dimensional periodic lattice, are studied experimentally and numerically. Both experimental and numerical results show that this biconvex array of rigid cylinders can act as a lens, which can focus plane liquid surface waves in a wide range of frequencies.
Practical fast gate rate InGaAs/InP single-photon avalanche photodiodes
Authors: Zhang Jun , Thew Rob , Barreiro Claudio , Zbinden Hugo
Published: September 2009

We present a practical and easy-to-implement method for high-speed near infrared single-photon detection based on InGaAs/InP single-photon avalanche photodiodes (SPADs), combining aspects of both sine gating and self-differencing techniques. At a gating frequency of 921 MHz and temperature of −30 °C we achieve a detection efficiency of 9.3%, a dark count probability of 2.8×10−6 ns−1, while the afterpulse probability is 1.6×10−4 ns−1, with a 10 ns “count-off time” setting. In principle, the maximum count rate of the SPAD can approach 100 MHz, which can significantly improve the performance for diverse applications.
Acceleration of electrons generated during ionization of a gas by a nearly flat profile laser pulse
Authors: Singh Kunwar Pal
Published: September 2009

A scheme of acceleration of electrons generated during ionization of krypton by nearly flat radial and nearly flat temporal laser pulse profiles has been suggested. The energy spectrum of the electrons suggests that energy of the electrons is higher for a nearly flat temporal profile than that for a nearly flat radial profile. The suppression of scattering of the electrons is better for a nearly flat radial profile than that for a nearly flat temporal profile. The energy of the electrons increases, scattering decreases, and beam quality improves with an increase in flatness of radial and temporal profiles.
Peculiar phenomenon of micro-free-jet flow
Authors: Gau Chie , Shen C. H. , Wang Z. B.
Published: September 2009

This is the first time that free microjet flow dynamics is explored experimentally in the open literature. The microjet is issued from a microslot nozzle made by microelectromechanical system techniques. Three different sizes of slot nozzles that have the widths of 50, 100, and 200 μm are fabricated. Careful flow visualization and instantaneous velocity measurements at different locations for these jet flows are made at different Reynolds numbers. The results indicate that the vortex formation and merging processes that occurred in the large-scale macrojet are completely absent in the microjet, and the microjet flow phenomenon is drastically different from that of the macrojet. A microjet can penetrate much deeper than a macrojet. A critical Reynolds number for the breakdown of the microjet is determined. Detailed discussion on the microjet dynamics will be presented in this paper.
SiN-passivated Γ-gate Al0.27Ga0.73N/GaN high electron mobility transistors by using a shifted exposure method
Authors: Lee Ching-Sung , Kao An-Yung
Published: September 2009

Effective gate-length reduction, surface passivation, and a field-plate structure upon the gate-drain region of a Γ-gate Al0.27Ga0.73N/GaN high electron mobility transistor (HEMT) have been achieved at the same time. The present SiN-passivated device with a 0.6 μm gate length and a 0.6 μm long field plate has demonstrated superior dc and rf characteristics as compared to a conventional-gated structure. Physical insights of device performance with respect to different SiN layer thicknesses are also investigated.
Enhancement in leaf photosynthesis and upregulation of Rubisco in the C4 sorghum plant at elevated growth carbon dioxide and temperature occur at early stages of leaf ontogeny
Authors: Prasad P. V. Vara , Vu Joseph C. V. , Boote Kenneth J. , Allen L. Hartwell
Published: September 2009

Rising atmospheric carbon dioxide (CO2) concentration and temperature will influence photosynthesis, growth and yield of agronomic crops. To investigate effects of elevated CO2 and high temperature on leaf gas exchanges, activities of Rubisco and phosphoenolpyruvate carboxylase (PEPC) and growth of grain sorghum (Sorghum bicolor L. Moench), plants were grown in controlled environments at day-time maximum/night-time minimum temperatures of 30/20°C or 36/26°C at ambient (350 µmol mol–1) or elevated (700 µmol mol–1) CO2. Gas-exchange rates, activities of Rubisco and PEPC and growth parameters (leaf, stem and total dry weights) were determined at different stages of leaf development. Between 6 and 25 days after leaf tip emergence, leaf carbon exchange rate (CER) of elevated CO2 plants was greater at 30/20°C and 36/26°C than that of ambient CO2 plants at the same temperatures. The positive response of CER to elevated CO2 was greater in young leaves than in old leaves. In young leaves, elevated CO2 enhanced Rubisco activity at 30/20°C and 36/26°C, whereas PEPC activity was not affected by elevated CO2 at 30/20°C but was marginally enhanced at 36/26°C. At 30/20°C, growth parameters were not affected by elevated CO2 until 50 days after sowing (DAS); at 36/26°C, they were progressively enhanced by elevated CO2 to as high as 49 to 62% by 50 DAS. Leaf CER and Rubisco activity were enhanced by elevated CO2 at early stages of leaf ontogeny for the C4 grain sorghum. Such enhancement should have a significant role in dry matter production under elevated CO2.
A realistic molecular model of cement hydrates
Authors: Pellenq Roland J.-M. , Kushima Akihiro , Shahsavari Rouzbeh , Van Vliet Krystyn J. , Buehler Markus J. , Yip Sidney , Ulm Franz-Josef
Published: September 2009

Despite decades of studies of calcium-silicate-hydrate (C-S-H), the structurally complex binder phase of concrete, the interplay between chemical composition and density remains essentially unexplored. Together these characteristics of C-S-H define and modulate the physical and mechanical properties of this “liquid stone” gel phase. With the recent determination of the calcium/silicon (C/S = 1.7) ratio and the density of the C-S-H particle (2.6 g/cm3) by neutron scattering measurements, there is new urgency to the challenge of explaining these essential properties. Here we propose a molecular model of C-S-H based on a bottom-up atomistic simulation approach that considers only the chemical specificity of the system as the overriding constraint. By allowing for short silica chains distributed as monomers, dimers, and pentamers, this C-S-H archetype of a molecular description of interacting CaO, SiO2, and H2O units provides not only realistic values of the C/S ratio and the density computed by grand canonical Monte Carlo simulation of water adsorption at 300 K. The model, with a chemical composition of (CaO)1.65(SiO2)(H2O)1.75, also predicts other essential structural features and fundamental physical properties amenable to experimental validation, which suggest that the C-S-H gel structure includes both glass-like short-range order and crystalline features of the mineral tobermorite. Additionally, we probe the mechanical stiffness, strength, and hydrolytic shear response of our molecular model, as compared to experimentally measured properties of C-S-H. The latter results illustrate the prospect of treating cement on equal footing with metals and ceramics in the current application of mechanism-based models and multiscale simulations to study inelastic deformation and cracking.
“Real-time” obstacle avoidance in the absence of primary visual cortex
Authors: Striemer Christopher L. , Chapman Craig S. , Goodale Melvyn A.
Published: September 2009

When we reach toward objects, we easily avoid potential obstacles located in the workspace. Previous studies suggest that obstacle avoidance relies on mechanisms in the dorsal visual stream in the posterior parietal cortex. One fundamental question that remains unanswered is where the visual inputs to these dorsal-stream mechanisms are coming from. Here, we provide compelling evidence that these mechanisms can operate in “real-time” without direct input from primary visual cortex (V1). In our first experiment, we used a reaching task to demonstrate that an individual with a dense left visual field hemianopia after damage to V1 remained strikingly sensitive to the position of unseen static obstacles placed in his blind field. Importantly, in a second experiment, we showed that his sensitivity to the same obstacles in his blind field was abolished when a short 2-s delay (without vision) was introduced before reach onset. These findings have far-reaching implications, not only for our understanding of the time constraints under which different visual pathways operate, but also in relation to how these seemingly “primitive” subcortical visual pathways can control complex everyday behavior without recourse to conscious vision.