bluuebunny/crossref_metadata_2025 huggingface dataset:
Atlantic Warm Pool acting as a link between Atlantic Multidecadal Oscillation and Atlantic tropical cyclone activity
Authors: Wang Chunzai , Lee Sang‐Ki , Enfield David B.
Published: May 2008

Multidecadal variability of Atlantic tropical cyclone activity is observed to relate to the Atlantic Multidecadal Oscillation (AMO), a mode manifesting primarily in sea surface temperature (SST) in the high latitudes of the North Atlantic. In the low latitudes of the North Atlantic, a large body of warm water called the Atlantic Warm Pool (AWP) comprises the Gulf of Mexico, the Caribbean Sea, and the western tropical North Atlantic. AWP variability occurs on both interannual and multidecadal timescales as well as with a secular variation. The AWP multidecadal variability coincides with the signal of the AMO; that is, the warm (cool) phases of the AMO are characterized by repeated large (small) AWPs. Since the climate response to the North Atlantic SST anomalies is primarily forced at the low latitudes and the AWP is in the path of or a birthplace for Atlantic tropical cyclones, the influence of the AMO on Atlantic tropical cyclone activity may operate through the mechanism of the AWP‐induced atmospheric changes. The AWP‐induced changes related to tropical cyclones that we emphasize here include a dynamical parameter of tropospheric vertical wind shear and a thermodynamical parameter of convective instability. More specifically, an anomalously large (small) AWP reduces (enhances) the vertical wind shear in the hurricane main development region and increases (decreases) the moist static instability of the troposphere, both of which favor (disfavor) Atlantic tropical cyclone activity. This is the most plausible way in which the AMO relationship with Atlantic tropical cyclones can be understood.
Integrated geophysical‐petrological modeling of the lithosphere and sublithospheric upper mantle: Methodology and applications
Authors: Afonso J. C. , Fernàndez M. , Ranalli G. , Griffin W. L. , Connolly J. A. D.
Published: May 2008

A combined geophysical‐petrological methodology to study the thermal, compositional, density, and seismological structure of lithospheric/sublithospheric domains is presented. A new finite‐element code (LitMod) is used to produce 2‐D forward models from the surface to the 410‐km discontinuity. The code combines data from petrology, mineral physics, and geophysical observables within a self‐consistent framework. The final result is a lithospheric/sublithospheric model that simultaneously fits all geophysical observables and consequently reduces the uncertainties associated with the modeling of these observables alone or in pairs, as is commonly done. The method is illustrated by applying it to both oceanic and continental domains. We show that anelastic attenuation and uncertainties in seismic data make it unfeasible to identify compositional variations in the lithospheric mantle from seismic studies only. In the case of oceanic lithosphere, plates with thermal thicknesses of 105 ± 5 km satisfy geophysical and petrological constraints. We find that Vp are more sensitive to phase transitions than Vs, particularly in the case of the spinel‐garnet transition. A low‐velocity zone with absolute velocities and gradients comparable to those observed below ocean basins is an invariable output of our oceanic models, even when no melt effects are included. In the case of the Archean subcontinental lithospheric mantle, we show that “typical” depleted compositions (and their spatial distribution) previously thought to be representative of these mantle sections are compatible neither with geophysical nor with petrological data. A cratonic keel model consisting of (1) strongly depleted material (i.e., dunitic/harzburgitic) in the first 100–160 km depth and (2) less depleted (approximately isopycnic) lower section extending down to 220–300 km depth is necessary to satisfy elevation, geoid, SHF, seismic velocities, and petrological constraints. This highly depleted (viscous) upper layer, and its chemical isolation, may play a key role in the longevity and stability of cratons.
Absence of propagating upper ocean heat content anomalies in the eastern tropical South Pacific after ENSO events
Authors: Hasegawa Takuya , Hanawa Kimio , Tourre Yves M. , White Warren B.
Published: May 2008

In order to explore why after a mature ENSO warm phase (MEWP), upper ocean heat content (OHC) anomalies disappear in the eastern tropical South Pacific (ETSP: 10°S–20°S, 140°W–100°W), relationships with sea surface temperature (SST), sea level pressure (SLP), wind‐stress curl (WSC) and latent heat flux (LHF), are investigated. After a MEWP, positive SST anomalies in the ETSP are first associated with overlying negative SLP anomalies through enhanced atmospheric convection and atmospheric hydrostatic processes. Then negative SLP anomalies and surface winds, lead to positive WSC and negative LHF anomalies (i.e., oceanic heat loss) which dominate the region. The above mechanisms, combined with a weakened South Equatorial Current, contribute to a rapid decay of positive OHC anomalies. It is exactly the opposite of what has been observed in the western tropical North Pacific, where in contrast OHC anomalies associated with ENSO, do grow with time and propagate.
Broadband ambient noise surface wave tomography across the United States
Authors: Bensen G. D. , Ritzwoller M. H. , Shapiro N. M.
Published: May 2008

This study presents surface wave dispersion maps across the contiguous United States determined using seismic ambient noise. Two years of ambient noise data are used from March 2003 through February 2005 observed at 203 broadband seismic stations in the US, southern Canada, and northern Mexico. Cross‐correlations are computed between all station‐pairs to produce empirical Green functions. At most azimuths across the US, coherent Rayleigh wave signals exist in the empirical Green functions implying that ambient noise in the frequency band of this study (5–100 s period) is sufficiently isotropically distributed in azimuth to yield largely unbiased dispersion measurements. Rayleigh and Love wave group and phase velocity curves are measured together with associated uncertainties determined from the temporal variability of the measurements. A sufficient number of measurements (>2000) is obtained between 8 and 25 s period for Love waves and 8 and 70 s period for Rayleigh waves to produce tomographic dispersion maps. Both phase and group velocity maps are presented in these period bands. Resolution is estimated to be better than 100 km across much of the US from 8–40 s period for Rayleigh waves and 8–20 s period for Love waves, which is unprecedented in a study at this spatial scale. At longer and shorter periods, resolution degrades as the number of coherent signals diminishes. The dispersion maps agree well with each other and with known geological and tectonic features and, in addition, provide new information about structures in the crust and uppermost mantle beneath much of the US.
MORB generation beneath the ultraslow spreading Southwest Indian Ridge (9–25°E): Major element chemistry and the importance of process versus source
Authors: Standish Jared J. , Dick Henry J. B. , Michael Peter J. , Melson William G. , O'Hearn Timothy
Published: May 2008

We report highly variable mid‐ocean ridge basalt (MORB) major element and water concentrations from a single 1050‐km first‐order spreading segment on the ultraslow spreading Southwest Indian Ridge, consisting of two supersegments with strikingly different spreading geometry and ridge morphology. To the east, the 630 km long orthogonal supersegment (<10° obliquity) dominantly erupts normal MORB with progressive K/Ti enrichment from east to west. To the west is the 400 km long oblique supersegment (up to 56° obliquity) with two robust volcanic centers erupting enriched MORB and three intervening amagmatic accretionary segments erupting both N‐MORB and E‐MORB. The systematic nature of the orthogonal supersegments' ridge morphology and MORB composition ends at 16°E, where ridge physiography, lithologic abundance, crustal structure, and basalt chemistry all change dramatically. We attribute this discontinuity and the contrasting characteristics of the supersegments to localized differences in the upper mantle thermal structure brought on by variable spreading geometry. The influence of these differences on the erupted composition of MORB appears to be more significant at ultraslow spreading rates where the overall degree of melting is lower. In contrast to the moderate and rather constant degrees of partial melting along the orthogonal supersegment, suppression of mantle melting on the oblique supersegment due to thickened lithosphere means that the bulk source is not uniformly sampled, as is the former. On the oblique supersegment, more abundant mafic lithologies melt deeper thereby dominating the more enriched aggregate melt composition. While much of the local major element heterogeneity can be explained by polybaric fractional crystallization with variable H2O contents, elevated K2O and K/Ti cannot. On the basis of the chemical and tectonic relationship of these enriched and depleted basalts, their occurrence requires a multilithology mantle source. The diversity and distribution of MORB compositions, especially here at ultraslow spreading rates, is controlled not only by the heterogeneity of the underlying mantle, but also more directly by the local thermal structure of the lithosphere (i.e., spreading geometry) and its influence on melting processes. Thus at ultraslow spreading rates, process rather than source may be the principle determiner of MORB composition.
A study of the 2006 and 2007 earthquake sequence of Pisco, Peru, with InSAR and teleseismic data
Authors: Pritchard M. E. , Fielding E. J.
Published: May 2008

We combine interferometric synthetic aperture radar (InSAR) and teleseismic body waves to study the largest earthquake (Mw 8.1) in a sequence of events on the subduction megathrust near Pisco, Peru. Our analysis includes some of the first InSAR data from the ALOS satellite and wide swath data from the Envisat satellite. The teleseismic data indicate the slip maximum occurred 60–90 seconds after the mainshock started. The InSAR data constrain the main slip patch to be about 70 km from the hypocenter, suggesting an extremely low rupture velocity (<1.5 km/s) or long slip rise time. No large earthquake has occurred in the 2007 rupture area since at least 1746 and possibly 1687, suggesting significant aseismic deformation in the area. The slip deficit apparently cannot be filled with rapid after‐slip. In addition, the area where the Nazca Ridge is subducting appears to be either a seismic gap or a persistent area of aseismic slip.
Steady magnetospheric convection selection criteria: Implications of global SuperDARN convection measurements
Authors: McWilliams K. A. , Pfeifer J. B. , McPherron R. L.
Published: May 2008

Quantitative definitions have been developed to detect intervals of steady magnetospheric convection (SMC), but these methods are based only on proxies of convection, such as the Auroral Electrojet (AE) indices. For the first time, observations of ionospheric convection on a global scale are studied during intervals identified as steady magnetospheric convection events. The SMC occurrence and SuperDARN transpolar voltage exhibit a strong seasonal bias, which is believed to be due to the seasonal variation of ionospheric conductivity. Equivalent AE values in winter and summer correspond to similar electrojet current strengths but to different levels of convection. Events selected using a constant AE threshold correspond to enhanced convection but above a variable threshold. This SuperDARN study is the first step in improving the reliability of SMC event selection by using convection observations. We present a new variable AE cutoff function to reduce the seasonal dependence of SMC selection on ionospheric conductivity.
A 2‐year climatology of polar low events over the Nordic Seas from satellite remote sensing
Authors: Blechschmidt A.‐M.
Published: May 2008

A new 2‐year data set of polar low events over the Nordic Seas is presented. The detection of polar lows is based on the combined use of thermal infrared AVHRR imagery and SSM/I derived wind speeds from the satellite climatology HOAPS (Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data). A total of 90 polar lows are found in 2004 and 2005 with a maximum of polar low activity during the winter months. The main polar low genesis regions lie between Iceland and Finnmark in the Norwegian Sea, in the Barents Sea and in the lee region of Cape Farewell. Interannual variability in polar low activity results mostly from more frequent cold air outbreaks in 2004. Statistics for several atmospheric parameters (e.g., wind speed, precipitation, cloud top temperatures) which describe the intensity of the cyclones are retrieved from satellite observations. The data set builds a basis for studies about polar low forcing mechanisms and for the validation of mesoscale numerical models.
Combined Therapeutic Strategy Using Erythropoietin and Mesenchymal Stem Cells Potentiates Neurogenesis after Transient Focal Cerebral Ischemia in Rats
Authors: Esneault Elise , Pacary Emilie , Eddi Dauphou , Freret Thomas , Tixier Emmanuelle , Toutain Jérôme , Touzani Omar , Schumann-Bard Pascale , Petit Edwige , Roussel Simon , Bernaudin Myriam
Published: May 2008

Many studies showed beneficial effects of either erythropoietin (EPO) or mesenchymal stem cells (MSCs) treatment in cerebral ischemia. In addition to a neuroprotective role, not only EPO but also MSC favors neurogenesis and functional recovery. In an attempt to further improve postischemic tissue repair, we investigated the effect of a systemic administration of MSC, in the presence or not of EPO, on neurogenesis and functional recovery in a transient focal cerebral ischemia model in the adult rat. Twenty-four hours after ischemia, the rats were divided into four groups, namely vehicle, MSC, EPO, and MSC + EPO, and received a single intravenous injection of MSC (2times106 cells) and/or a repeated intraperitoneal administration of EPO (1,000 UI/kg) for 3 days. The lesion volume, the MSC outcome, neurogenesis, and functional recovery were assessed 51 days after ischemia. The results showed that cellular proliferation and neurogenesis were increased along the lateral ventricle wall in the MSC + EPO group, whereas no significant effect was observed in groups receiving MSC or EPO alone. This effect was accompanied by an improvement of mnesic performances. Mesenchymal stem cells expressing neuronal or glial markers were detected in the ischemic hemisphere. These results suggest that EPO could act in a synergistic way with MSC to potentiate the postischemic neurogenesis.
Non-Faradaic electrochemical activation of catalysis
Authors: Vayenas Costas G. , Koutsodontis Costas G.
Published: May 2008

The use of fuel cells for carrying out oxidation reactions with cogeneration of electrical power and chemicals led, upon cofeeding oxygen and fuel at the anode, to the discovery of the effect of non-Faradaic electrochemical modification of catalytic activity or electrochemical promotion of catalysis. This phenomenon has been studied already for more than 70 catalytic reactions, including oxidations, reductions and isomerizations and using a variety of metal catalysts, and solid electrolytes. In this work we summarize the main features of electrochemical promotion and discuss critically its currently accepted sacrificial promoter mechanism which involves electrochemically controlled migration (spillover-backspillover) of promoting species from the electrolyte to the catalytically active metal-gas interface. It is shown that the spillover ionic species (e.g., Oδ−, Naδ+) form an overall neutral double layer at the catalyst-gas interface which alters the catalyst work function and the binding energies of coadsorbed reactants and intermediates, thus causing very pronounced and reversible alterations in the catalytic activation energy and catalytic rate and selectivity. Recent efforts for the practical utilization of electrochemical promotion are also briefly discussed.
Probing interactions between core-electron transitions by ultrafast two-dimensional x-ray coherent correlation spectroscopy
Authors: Schweigert Igor V. , Mukamel Shaul
Published: May 2008

Two-dimensional x-ray correlation spectra (2DXCS) obtained by varying two delay periods in a time-resolved coherent all-x-ray four-wave-mixing measurement are simulated for the N 1s and O 1s transitions of aminophenol. The necessary valence and core-excited states are calculated using singly and doubly substituted Kohn–Sham determinants within the equivalent-core approximation. Sum-over-states calculations of the 2DXCS signals of aminophenol isomers illustrate how novel information about electronic states can be extracted from the 2D spectra. Specific signatures of valence and core-excited states are identified in the diagonal and off-diagonal peaks arising from core transitions of the same and different types, respectively.
Preface to Special Topic: A Survey of Some New Developments in Heterogeneous Catalysis
Authors: Metiu H.
Published: May 2008

This special topic section on heterogeneous catalysis contains essays on fast-evolving topics by several leading scientists in the field. In this preface, I outline those issues, raised in the special topic articles, that seemed most interesting to me. I selected those aspects that should be of greatest interest to physical chemists who are not experts in catalysis but might be interested in entering this exciting and important field of research.
A method of estimating the noise level in a chaotic time series
Authors: Jayawardena A. W. , Xu Pengcheng , Li W. K.
Published: May 2008

An attempt is made in this study to estimate the noise level present in a chaotic time series. This is achieved by employing a linear least-squares method that is based on the correlation integral form obtained by Diks in 1999. The effectiveness of the method is demonstrated using five artificial chaotic time series, the Hénon map, the Lorenz equation, the Duffing equation, the Rossler equation and the Chua’s circuit whose dynamical characteristics are known a priori. Different levels of noise are added to the artificial chaotic time series and the estimated results indicate good performance of the proposed method. Finally, the proposed method is applied to estimate the noise level present in some real world data sets.
Correlation function of the Schur process with a fixed final partition
Authors: Imamura T. , Sasamoto T.
Published: May 2008

We consider a generalization of the Schur process in which a partition evolves from the empty partition into an arbitrary fixed final partition. We obtain a double integral representation of the correlation kernel. For a special final partition with only one row, the edge scaling limit is also discussed by the use of the saddle point analysis. If we appropriately scale the length of the row, the limiting correlation kernel changes from the extended Airy kernel.
Effect of silicon interstitials on Cu precipitation in n-type Czochralski silicon
Authors: Wang Weiyan , Yang Deren , Ma Xiangyang , Que Duanlin
Published: May 2008

The effect of silicon interstitials induced by the prior thermal oxidation at 900°C for 2–50min on copper (Cu) precipitation in n-type silicon has been investigated by means of transmission electron microscopy and optical microscopy. For the sample without the prior thermal oxidation, the Cu precipitates exhibited to be spherelike with induced stress, and they were preferentially delineated as the etching pits. On the other hand, for the samples with the prior thermal oxidation for more than 5min, the Cu precipitate colonies, in which Cu precipitates with sizes of 10–20nm assembled on and around the dislocations, formed with different depth profiles dependent on the oxidation time. Moreover, the Cu precipitate colonies were preferentially delineated as aggregated and individual rods. Phenomenologically, the formation mechanism and depth profile of Cu precipitate colonies were explained in terms of the effect of thermal oxidation induced silicon interstitials.
Carrier relaxation dynamics in InAs∕InP quantum dots
Authors: Miska P. , Even J. , Dehaese O. , Marie X.
Published: May 2008

The electronic properties of InAs∕InP(113)B double-cap quantum dots (QDs) emitting around 1.55μm are investigated. The carrier dynamics in QDs is studied by nonresonant time-resolved photoluminescence experiments. This analysis reveals the electronic structure of the QDs and the transient filling of the confined levels. Under low excitation densities, the spontaneous exciton lifetime is estimated and compared to time-resolved experiments. Under high excitation density, a direct Auger recombination effect is identified. The temperature analysis enables us to distinguish Auger and phonon-assisted relaxation processes.
Mapping exciton quenching in photovoltaic-applicable polymer blends using time-resolved scanning near-field optical microscopy
Authors: Cadby A. , Khalil G. , Fox A. M. , Lidzey D. G.
Published: May 2008

We have used time-resolved scanning near-field microscopy to image the fluorescence decay lifetime across a phase-separated blend of the photovoltaic-applicable polymers poly(9,9′-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly(9,9′-dioctylfluorene-alt-bis- N,N′-(4-butylphenyl)-bis-N,N′-phenyl-1,4-phenylenediamine) (PFB). We show that the efficiency of local fluorescence quenching is composition dependent, with excitons on F8BT molecules being more effectively quenched when F8BT is trapped at a low concentration in a PFB-rich phase. Despite such presumed differences in charge-carrier generation efficiency, our results demonstrate that charge extraction from F8BT:PFB devices is the most dominant mechanism limiting their operational efficiency.
Rheological complexity in simple chain models
Authors: Dotson Taylor C. , Heffernan Julieanne V. , Budzien Joanne , Dotson Keenan T. , Avila Francisco , Limmer David T. , McCoy Daniel T. , McCoy John D. , Adolf Douglas B.
Published: May 2008

Dynamical properties of short freely jointed and freely rotating chains are studied using molecular dynamics simulations. These results are combined with those of previous studies, and the degree of rheological complexity of the two models is assessed. New results are based on an improved analysis procedure of the rotational relaxation of the second Legendre polynomials of the end-to-end vector in terms of the Kohlrausch–Williams–Watts (KWW) function. Increased accuracy permits the variation of the KWW stretching exponent β to be tracked over a wide range of state points. The smoothness of β as a function of packing fraction η is a testimony both to the accuracy of the analytical methods and the appropriateness of (η0−η) as a measure of the distance to the ideal glass transition at η0. Relatively direct comparison is made with experiment by viewing β as a function of the KWW relaxation time τKWW. The simulation results are found to be typical of small molecular glass formers. Several manifestations of rheological complexity are considered. First, the proportionality of α-relaxation times is explored by the comparison of translational to rotational motion (i.e., the Debye–Stokes–Einstein relation), of motion on different length scales (i.e., the Stokes–Einstein relation), and of rotational motion at intermediate times to that at long time. Second, the range of time-temperature superposition master curve behavior is assessed. Third, the variation of β across state points is tracked. Although no particulate model of a liquid is rigorously rheologically simple, we find freely jointed chains closely approximated this idealization, while freely rotating chains display distinctly complex dynamical features.
Theoretical and experimental studies of collision-induced electronic energy transfer from v=–3 of the E(g+) ion-pair state of Br2: Collisions with He and Ar
Authors: Hutchison J. Matthew , O’Hern Robin R. , Stephenson Thomas A. , Suleimanov Yury V. , Buchachenko Alexei A.
Published: May 2008

Collisions of Br2, prepared in the E(0g+) ion-pair (IP) electronic state, with He or Ar result in electronic energy transfer to the D, D′, and β IP states. These events have been examined in experimental and theoretical investigations. Experimentally, analysis of the wavelength resolved emission spectra reveals the distribution of population in the vibrational levels of the final electronic states and the relative efficiencies of He and Ar collisions in promoting a specific electronic energy transfer channel. Theoretically, semiempirical rare gas-Br2 potential energy surfaces and diabatic couplings are used in quantum scattering calculations of the state-to-state rate constants for electronic energy transfer and distributions of population in the final electronic state vibrational levels. Agreement between theory and experiment is excellent. Comparison of the results with those obtained for similar processes in the IP excited I2 molecule points to the general importance of Franck–Condon effects in determining vibrational populations, although this effect is more important for He collisions than for Ar collisions.
Formation of dysprosium silicide nanowires on Si(557) with two-dimensional electronic structure
Authors: Wanke M. , Löser K. , Pruskil G. , Dähne M.
Published: May 2008

The self-organized growth of dysprosium silicide nanowires on Si(557) has been studied using scanning tunneling microcopy and angle-resolved photoelectron spectroscopy. The nanowires grow on the (111) facets of the Si(557) surface with lengths exceeding 1000 nm and widths of 3–5 nm. Their metallic electronic structure shows a two-dimensional behavior with a strong dispersion, which is both parallel and perpendicular to the nanowires. For Dy coverages of around 2 Å, it is demonstrated that the nanowires consist of hexagonal DySi2 monolayers, while at higher coverages they are predominantly formed from Dy3Si5 multilayers.
Size and frequency dependence of effective thermal conductivity in nanosystems
Authors: Alvarez F. X. , Jou D.
Published: May 2008

A single phenomenological expression is proposed to describe thermal transport in a wide variety of nanoscale devices. Size and frequency dependence is studied for some nanosystems from the diffusive to the ballistic regimes. In a single expression we obtain the effective thermal conductivity of cross-plane thin layer experiments where the device has a size limitation in the direction of the flux, and nanowire and in-plane experiments where the size limitation is in a transversal direction from the flux in terms of the effective size of the device. For nonzero frequencies, the size dependence has a maximum which becomes narrower at higher frequencies. For a given size, the effective thermal conductivity decreases for increasing frequency. These features may be limited in the design of nanoscale devices, because of the accumulation of dissipated heat.
Dependence of temperature and self-heating on electron mobility in ultrathin body silicon-on-insulator n-metal-oxide-semiconductor field-effect transistors
Authors: Shim Tae-Hun , Kim Seong-Je , Lee Gon-Sub , Kim Kwan-Su , Cho Won-Ju , Park Jea-Gun
Published: May 2008

We investigated the dependence of temperature and self-heating on electron mobility in ultrathin body fully depleted silicon-on-insulator n-metal-oxide-semiconductor field-effect transistors as a function of silicon thickness by analyzing their electron states and electrical characteristics. We found that as the temperature increases, electron mobility decreases regardless of the silicon thickness. We also found that there is a less decrease when the silicon thickness is less than 3 nm than when it is greater than 3 nm. This is because there is a greater electron occupancy in a twofold valley. We demonstrated that the quantum size-effect, i.e., the higher electron mobility in silicon with a thickness less than 3 nm caused by the size-effect, can be eliminated by self-heating.
Si interstitial contribution of F+ implants in crystalline Si
Authors: López Pedro , Pelaz Lourdes , Duffy R. , Meunier-Beillard P. , Roozeboom F. , van der Tak K. , Breimer P. , van Berkum J. G. M. , Verheijen M. A. , Kaiser M.
Published: May 2008

The F effect in crystalline Si is quantified by monitoring defects and B diffusion in samples implanted with 25 keV F+ and/or 40 keV Si+. We estimate that about +0.4 Si interstitials are generated per implanted F+ ion, in agreement with the value resulting from the net separation of Frenkel pairs. For short annealings, B diffusion is lower when F+ is coimplanted with Si+ than when only Si+ is implanted, while for longer annealings, B diffusion is higher. This is consistent with a lower but longer-lasting Si interstitial supersaturation set by the additional defects generated by the F+ implant.
Field emission of bismuth sulfide upright-standing platelets
Authors: Ganesh T. , Lee Jungwoo , Mane Rajaram S. , Yi Whi Kun , Pawar B. N. , Won Cho Byung , Han Sung-Hwan
Published: May 2008

Indium-tin-oxide substrate-supported chemically synthesized bismuth sulfide upright-standing platelets of micron-size height and nanometer-size width are explored for the field emission. Bismuth sulfide upright-standing platelets electrode shows a turn-on field of 2.83 V/μm at a current density of 10 μA/cm2, a maximum emissive current of 49 μA/cm2 (3.5V/μm), and 9396 beta-factor comparable to the field emission studies of carbon nanotubes, when used as a cathode for emitting current under applied voltage.
A cubic boron nitride gasket for diamond-anvil experiments
Authors: Funamori Nobumasa , Sato Tomoko
Published: May 2008

To maximize the thickness of the sample chamber in high-pressure experiments, we have conducted tests and have developed techniques relevant to the cubic boron nitride (c-BN) gasket for diamond-anvil cells. The c-BN gasket provides a sample chamber several times thicker than conventional metal gaskets. We have developed methods to prepare the gasket and to fill the chamber with the sample. By using the c-BN gasket, we have successfully measured x-ray diffraction patterns of SiO2 glass, a low-Z noncrystalline sample, up to 100GPa.
GaMnAs-based hybrid multiferroic memory device
Authors: Overby M. , Chernyshov A. , Rokhinson L. P. , Liu X. , Furdyna J. K.
Published: May 2008

We report a nonvolatile hybrid multiferroic memory cell with electrostatic control of magnetization based on strain-coupled GaMnAs ferromagnetic semiconductor and a piezoelectric material. We use the crystalline anisotropy of GaMnAs to store information in the orientation of the magnetization along one of the two easy axes, which is monitored via transverse anisotropic magnetoresistance. The magnetization orientation is switched by applying voltage to the piezoelectric material and tuning magnetic anisotropy of GaMnAs via the resulting stress field.
Entropy of polydisperse chains: Solution on the Bethe lattice
Authors: Neto Minos A. , Stilck Jürgen F.
Published: May 2008

We consider the entropy of polydisperse chains placed on a lattice. In particular, we study a model for equilibrium polymerization, where the polydispersivity is determined by two activities, for internal and endpoint monomers of a chain. We solve the problem exactly on a Bethe lattice with arbitrary coordination number, obtaining an expression for the entropy as a function of the density of monomers and mean molecular weight of the chains. We compare this entropy with the one for the monodisperse case and find that the excess of entropy due to polydispersivity is identical to the one obtained for the one-dimensional case. Finally, we obtain an exponential distribution of molecular weights.
Laser oscillation in a highly anisotropic organic crystal with a refractive index of 4.0
Authors: Yamao Takeshi , Yamamoto Kazunori , Taniguchi Yuki , Miki Tomoharu , Hotta Shu
Published: May 2008

We have determined a refractive index of an organic single crystal of a thiophene/phenylene co-oligomer in its laser oscillation wavenumbers. We estimated the refractive index to be 4.0 on the basis of the mode intervals of the well-resolved longitudinal multimodes that are highly polarized along the normal to the (001) plane of the single crystal. This large number is in good agreement with that obtained by the quantum chemical calculations at semiempirical levels. This is also consistent with the high Q factor (∼24 500) obtained from the line shape analysis.
Intensity analysis and crystal-field modeling of Ho3+ in KPb2Cl5 host
Authors: Sardar Dhiraj K. , Chandrasekharan Sree R. , Nash Kelly L. , Gruber John B. , Burger Arnold , Roy Utpal N.
Published: May 2008

Optical absorption and emission intensities are investigated for Ho3+ doped into single-crystal KPb2Cl5. Room temperature absorption spectra of Ho3+(4f10), representing transitions from I58 to excited multiplet manifolds observed between 400 and 2100 nm, have been analyzed using the Judd–Ofelt (JO) model to obtain the phenomenological intensity parameters Ω2, Ω4, and Ω6. The JO intensity parameters are used to calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios of the Ho3+ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds L2S+1J of Ho3+. The room temperature fluorescence spectrum in the near infrared region is reported between 850 and 1550 nm. The emission cross section for the intermanifold transition, F55→I57 (0.98 μm) has been determined. The 8 K absorption spectrum was examined as well. The detailed structure observed in the absorption bands I57, S52, F54, and F53, was analyzed in terms of the crystal-field splitting of each manifold using a charge-compensation model first developed for Er3+ doped into KPb2Cl5. The optical and spectroscopic characteristics of Ho3+:KPb2Cl5 demonstrate that this material has potential as a laser host system at various wavelengths.
Thermal growth and structural and optical characterization of indium tin oxide nanopyramids, nanoislands, and tubes
Authors: Maestre D. , Cremades A. , Piqueras J. , Gregoratti L.
Published: May 2008

In-doped SnO2 microtubes as well as Sn-doped In2O3 (ITO) nano- and microislands have been grown by thermal treatment of compacted SnO2–In2O3 powders under argon flow at 1350 °C in a catalyst-free process. The SnO2 tubes contain about 1 at. % of In, even when the In content in the starting mixture was as high as 52 at. %. However, the ITO nanoislands and nanopyramids, grown preferentially on the faces and edges of the tubes, present an In content up to six times higher than the tubes. Spatially resolved cathodoluminescence shows a higher emission from the Sn-rich structures, so that the In-rich ITO nanoislands show dark contrast in the CL images. CL spectra show that the main emission bands in both, Sn-rich and In-rich, structures, are related to oxygen deficiency. X-ray photoelectron spectroscopy shows differences between the tubes and the nanoislands in the O (1s) spectral region. In particular, a component at 531.9 eV of the O  (1s) signal appears enhanced in the In-rich islands.
Self-assembled organic donor/acceptor nanojunction arrays
Authors: Chen Wei , Zhang Hong Liang , Huang Han , Chen Lan , Wee Andrew Thye Shen
Published: May 2008

We have fabricated well-ordered organic donor/acceptor nanojunction arrays comprising p-sexiphenyl (6P) and C60 via self-assembly of C60 on the molecular nanotemplate of 6P nanostripes on Ag(111). Our scanning tunneling microscopy measurements show that the preferential trapping of C60 triplets atop 6P single molecule leads to the formation of the C60∕6P vertical nanojunctions with well-defined two-dimensional arrangement. Annealing this binary molecular superstructure at 380K results in the insertion of C60 linear chains between the neighboring 6P nanostripes and thereby the appearance of the periodic C60∕6P lateral nanojunction arrays.
Enhanced mechanical strength and ductility of metal-repaired defective carbon nanotubes: A density functional study
Authors: Zheng G. P. , Zhuang H. L.
Published: May 2008

Metal atoms are filled into the defective sites of single-walled carbon nanotube (SWCN) containing vacancy defects, resulting in a stable repaired SWCN. The tensile deformation of the repaired SWCN is investigated by spin-polarized density functional theory. Compared to the defective SWCN, the repaired CN shows significant enhancements in mechanical strength and ductility that are close to those of pristine CN. The underlying physics of these behaviors are analyzed by the structural transformation, electronic structures, and spin and charge distributions during the tensile tests. A strong magnetomechanical coupling effect is found to be responsible for the enhanced mechanical behaviors of metal-CN hybrid structures.
{110}-facets formation by hydrogen thermal etching on sidewalls of Si and strained-Si fin structures
Authors: Tezuka Tsutomu , Hirashita Norio , Moriyama Yoshihiko , Sugiyama Naoharu , Usuda Koji , Toyoda Eiji , Murayama Ken , Takagi Shin-ichi
Published: May 2008

Si-fin structures for multigate metal-oxide-semiconductor field effect transistors (MOSFETs) with smooth and vertical sidewalls composed of {110} facets were obtained by an anisotropic gas etching in atmospheric hydrogen ambient at 925–1000°C on strained and unstrained (001) Si-on-insulator (SOI) substrates. {110} facets emerged due to higher etching rate for higher-order crystalline plane adjacent to {110} planes. The facet formation effectively eliminated the fin-width variation originating from the lithography process. The uniaxial stress along the fins on the strained SOI substrate was found to be preserved during the process, indicating the availability of this technique for fabrication of multigate MOSFETs with strained-fin channels.
Hole recapture limited single photon generation from a single n-type charge-tunable quantum dot
Authors: Dalgarno P. A. , McFarlane J. , Brunner D. , Lambert R. W. , Gerardot B. D. , Warburton R. J. , Karrai K. , Badolato A. , Petroff P. M.
Published: May 2008

The complete control of the electron occupation of a single InGaAs dot is shown to produce highly antibunched single photon emission with nonresonant optical excitation. Intensity correlation measurements show g(2)(0) values of 3% (50%) at low (high) excitation power. A distinct double peak structure is shown at time zero, demonstrating that although two photons may be emitted per excitation pulse, they are not simultaneously emitted. We interpret this feature as a hole recapture process from the wetting layer into the dot after initial recombination. The recapture dynamics is shown to be adjustable through engineering the valence potential.
c-erbB-2 sensing using AlGaN∕GaN high electron mobility transistors for breast cancer detection
Authors: Chen K. H. , Kang B. S. , Wang H. T. , Lele T. P. , Ren F. , Wang Y. L. , Chang C. Y. , Pearton S. J. , Dennis D. M. , Johnson J. W. , Rajagopal P. , Roberts J. C. , Piner E. L. , Linthicum K. J.
Published: May 2008

Antibody-functionalized, Au-gated AlGaN∕GaN high electron mobility transistors (HEMTs) were used to detect c-erbB-2, which is a breast cancer marker. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN∕GaN HEMT drain-source current showed a rapid response of less than 5s when target c-erbB-2 antigen in a buffer at clinically relevant concentrations was added to the antibody-immobilized surface. We could detect a range of concentrations from 16.7to0.25μg∕ml. These results clearly demonstrate the promise of portable electronic biological sensors based on AlGaN∕GaN HEMTs for breast cancer screening.
Magnetic control of negative permeability metamaterials based on liquid crystals
Authors: Zhang Fuli , Zhao Qian , Kang Lei , Gaillot Davy P. , Zhao Xiaopeng , Zhou Ji , Lippens Didier
Published: May 2008

We report on the tunability, by a magnetic field, of a negative permeability metamaterial consisting of stacked arrays of broadside-coupled split ring resonators infiltrated with liquid crystals (LCs). The resonant frequency shift was numerically assessed by a rigorous anisotropic analysis of the reorientation of LC molecules. Experiments were carried out with a prototype designed and fabricated for X-band operation and infiltrated with a nematic compound with optical birefringence Δn=0.18. Scattering parameters vectorial analysis shows a good agreement between the resonant frequency shifts predicted under anisotropic conditions and those measured under static magnetic control.
Spectroscopic measurement of electric field in dielectric barrier discharge in helium
Authors: Obradović B. M. , Ivković S. S. , Kuraica M. M.
Published: May 2008

Spatial distribution of electric field strength in dielectric barrier discharge in helium is determined from the Stark splitting and shifting of two visible helium lines and their forbidden components. Electric field is calculated by using spectral distance between forbidden and allowed components and results are compared to those obtained by using forbidden/allowed intensity ratio. Distributions of electric field, obtained for 200 and 800mbar pressures, are typical for the glow mode of the discharge.
Construction of an optical wire imprinted in potassium lithium tantalate niobate by He+ implantation
Authors: Ilan Har’el , Gumennik Alexander , Perepelitsa Galina , Israel Abraham , Agranat Aharon J.
Published: May 2008

A channel waveguide constructed in potassium lithium tantalate niobate (KLTN) substrate by the implantation of He+ ions at 1.65MeV is presented. The waveguide has a trapezoidal profile with a crystalline KLTN core surrounded by amorphized KLTN created by the implantation. The implantation was done through a 2μm thick gold stopping mask with a trapezoidal groove. During the implantation, the contour of the groove was replicated beneath the surface of the substrate forming the trapezoidal cladding of the channel waveguide. The channel waveguide is designed as the interconnecting element in electro-optical integrated circuits.
In-field magnetic force microscope study of dipolar interaction in an ideally ordered Co nanorod array fabricated using nanoimprint lithography
Authors: Wang T. , Wang Y. , Fu Y. , Hasegawa T. , Washiya T. , Saito H. , Ishio S. , Li F. S. , Oshima H. , Itoh K. , Nishio K. , Masuda H.
Published: May 2008

We have performed experimental studies and numerical calculations on the dipolar interaction in an ideally ordered hexagonal nanorod array. The dipolar field in an ordered Co nanorod array was measured using an in-field magnetic force microscope (MFM) with a controlled applied field. The average dipolar fields of neighboring nanorods acting on a center nanorod were calculated by approximating the monopole with a magnetic charge m=MSS on the end of each nanorod. The largest dipolar field obtained from numerical calculation is agreement with that from in-field MFM measurements.
Prepassivation surface treatment effects on pulsed and dc I-V performance of AlGaN∕GaN high-electron-mobility transistors
Authors: Meyer David J. , Flemish Joseph R. , Redwing Joan M.
Published: May 2008

This study has examined the effects that various prepassivation plasma surface treatments had on pulsed and dc I-V characteristics of AlGaN∕GaN high-electron-mobility transistors. Pulsed I-V current recovery data indicates that C2F6, NH3, O2, and Cl2 plasma treatments can be used in conjunction with plasma-enhanced chemical vapor deposited silicon nitride to significantly reduce rf dispersion. The different prepassivation surface treatments, however, produced little variation in dc I-V parameters such as gate leakage current, interdevice isolation current, and off-state breakdown voltage as compared to untreated passivated samples.
Cerebellar-dependent motor learning is based on pruning a Purkinje cell population response
Authors: Catz Nicolas , Dicke Peter W. , Thier Peter
Published: May 2008

The improvement of motor behavior, based on experience, is a form of learning that is critically dependent on the cerebellum. A well studied example of cerebellar motor learning is short-term saccadic adaptation (STSA). In STSA, information on saccadic errors is used to improve future saccades. The information optimizing saccade metrics is conveyed by Purkinje cells simple spikes (PC-SS) because they are the critical input to the premotor circuits for saccades. We recorded PC-SS of monkeys undergoing STSA to reveal the code used for improving behavior. We found that the discharge of individual PC-SS was unable to account for the behavioral changes. The PC-SS population burst (PB), however, exhibited changes that closely paralleled the qualitatively different changes of saccade kinematics associated with gain-increase and gain-decrease STSA, respectively. Gain-increase STSA, characterized by an increase in saccade duration, replicates the relationship between saccade duration and the end of the PB valid for unadapted saccades. In contrast, gain-decrease STSA, which sports normal saccade duration but reduced saccadic velocity, is characterized by a PB that ends well before the adapted saccade. This suggests that the duration of normal as well as gain-increased saccades is determined by appropriately setting the end of PB end. However, the duration of gain-decreased saccades is apparently not modified by the cerebellum because the PB signals ends too early to determine saccade end. In summary, STSA, and most probably cerebellar-dependent learning in general, is based on optimizing the shape of a PC-SS population response.
Prediction of membrane-protein topology from first principles
Authors: Bernsel Andreas , Viklund Håkan , Falk Jenny , Lindahl Erik , von Heijne Gunnar , Elofsson Arne
Published: May 2008

The current best membrane-protein topology-prediction methods are typically based on sequence statistics and contain hundreds of parameters that are optimized on known topologies of membrane proteins. However, because the insertion of transmembrane helices into the membrane is the outcome of molecular interactions among protein, lipids and water, it should be possible to predict topology by methods based directly on physical data, as proposed >20 years ago by Kyte and Doolittle. Here, we present two simple topology-prediction methods using a recently published experimental scale of position-specific amino acid contributions to the free energy of membrane insertion that perform on a par with the current best statistics-based topology predictors. This result suggests that prediction of membrane-protein topology and structure directly from first principles is an attainable goal, given the recently improved understanding of peptide recognition by the translocon.
Hypoxia and the HIF-1 transcriptional pathway reorganize a neuronal circuit for oxygen-dependent behavior in
Caenorhabditis elegans
Authors: Chang Andy J. , Bargmann Cornelia I.
Published: May 2008

Rapid behavioral responses to oxygen are generated by specialized sensory neurons that sense hypoxia and hyperoxia. On a slower time scale, many cells respond to oxygen through the activity of the hypoxia-inducible transcription factor HIF-1. Here, we show that in the nematode
Caenorhabditis elegans
, prolonged growth in hypoxia alters the neuronal circuit for oxygen preference by activating the
hif-1
pathway. Activation of
hif-1
by hypoxia or by mutations in its negative regulator
egl-9
/prolyl hydroxylase shifts behavioral oxygen preferences to lower concentrations and eliminates a regulatory input from food. At a neuronal level,
hif-1
activation transforms a distributed, regulated neuronal network for oxygen preference into a smaller, fixed network that is constitutively active. The
hif-1
pathway acts both in neurons and in gonadal endocrine cells to regulate oxygen preference. These results suggest that physiological detection of hypoxia by multiple tissues provides adaptive information to neuronal circuits to modify behavior.