bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of CFCs in northern temperate lakes and adjacent groundwater
Authors: Walker John F. , Saad David A. , Hunt Randall J.
Published: April 2007

Three dimictic lakes and one meromictic lake in and near the Trout Lake, Wisconsin, watershed were sampled to determine the variation of chlorofluorocarbon (CFC) concentrations within the lakes. The lakes were sampled during stratified conditions, during fall turnover, and during ice cover. The results demonstrate a considerable variation in CFC concentrations and corresponding atmospheric mixing ratios in the lakes sampled, both with depth and season within a given lake, and across different lakes. CFC profiles and observed degradation were not related to the groundwater inflow rate and hence are likely the result of in‐lake processes influenced by CFC degradation in the (lake) water column, CFC degradation in the lake‐bed sediments, and gas exchange rates and the duration of turnover (turnover efficiency).
Energetic particle precipitation effects on the Southern Hemisphere stratosphere in 1992–2005
Authors: Randall C. E. , Harvey V. L. , Singleton C. S. , Bailey S. M. , Bernath P. F. , Codrescu M. , Nakajima H. , Russell J. M.
Published: April 2007

Measurements from several different satellite instruments are used to estimate effects of energetic particle precipitation (EPP) on NOx (NO + NO2) in the Southern Hemisphere stratosphere from 1992 to 2005. The focus is the EPP Indirect Effect (IE), whereby NOx produced in the mesosphere or thermosphere via EPP (EPP‐NOx) descends to the stratosphere during the polar winter, where it can participate in catalytic ozone destruction. EPP‐NOx entering the stratosphere is found to vary in magnitude from 0.1 to 2.6 gigamoles per year, with maximum values occurring in 1994 and 2003. The interannual variation correlates strongly with several measures of EPP activity, including auroral and medium energy electron hemispheric power, and satellite measurements of thermospheric NO. This represents the first estimation of EPP‐NOx contributions to the stratospheric odd nitrogen budget using observations over an entire solar cycle. The results will be useful for evaluating and constraining global models to investigate coupling of the upper and lower atmosphere by the EPP IE, including any influences this might have on ozone trends and possibly on climate.
Composition of the atmosphere of Venus below the clouds
Authors: Bézard Bruno , de Bergh Catherine
Published: April 2007

The composition of Venus' lower atmosphere, beneath the clouds, has been investigated through both in situ measurements and remote‐sensing observations. In 1978 the mass spectrometers and gas chromatographs aboard the Venera 11–12 landers and Pioneer Venus Large probe returned unique information on the abundances of carbon dioxide, nitrogen, noble gases, and other minor species. Radio occultations from the Pioneer and Magellan spacecraft provided measurements of the vertical profile of sulfuric acid vapor. In the 1980s and 1990s the discovery of near‐infrared emission from the night side of Venus, through narrow spectral windows in the 0.9–2.5 micron region, opened a new opportunity of probing the lower atmosphere and surface. The abundances of water vapor, halides, carbon monoxide, sulfur dioxide, and carbonyl sulfide were determined, as well as the deuterium‐to‐hydrogen ratio. The vertical profile of water vapor in the 0‐ to 45‐km‐altitude range and the CO and OCS mean vertical gradients in the 30‐ to 40‐km region have been determined from various analyses. In addition, evidence for latitudinal variations of these two species was found from Galileo and recent ground‐based nightside observations. Conflicting results have been reported on the SO2 abundance below 35 km and on the H2O profile below 20 km. The whole set of available measurements provides important constraints on the chemistry and dynamics of Venus' lower atmosphere. However, key information is still missing, including the abundances of CO and sulfur compounds near the surface, composition maps at high latitudes, and possible small‐scale and temporal variability of trace compounds.
Numerical studies of ice flow over subglacial geothermal heat sources at Grímsvötn, Iceland, using Full Stokes equations
Authors: Jarosch Alexander H. , Gudmundsson Magnús T.
Published: April 2007

The importance of studying geothermal heat sources under glaciers lies in: (1) the potential for jökulhlaups from such sites; (2) the potential for enhanced sliding of ice masses caused by meltwater lubrication of the ice‐bedrock interface; and (3) the potential to gain a deeper understanding of the interaction between the geothermal system and the overlying ice. We study the temporal evolution of an elongated depression on the eastern side of the geothermally active Grímsvötn caldera through numerical 2‐dimensional forward modeling, solving the full Stokes equation. The 100–150 m deep depression formed gradually between 1998 and 2004. The model results show that heat flux estimates based on depression volume are strongly dependent on the value of the rate factor A in Glen's flow law. If flow of ice into the depression is not taken into account, heat flux underestimates of 15–75% occur, corresponding to rate factors of 10–68 × 10−16 s−1 kPa−3. The estimated heat flux at the study site was 260–390 W m−2, with the best estimate being 280 W m−2, obtained from the best estimate of A = 23 × 10−16s−1 kPa−3. The total power of the modeled site was 250–300 MW, about one tenth of the total heat output of Grímsvötn. This heat flux is of comparable magnitude to that of other powerful subglacial geothermal areas. Finally, as the maximum modeled strain rates (1 × 10−7 s−1) are within the range of the applicability of Glen's flow law, this suggests that the full Stokes approach should be valid for the study of many subglacial geothermal areas.
Bayesian analysis for uncertainty estimation of a canopy transpiration model
Authors: Samanta S. , Mackay D. S. , Clayton M. K. , Kruger E. L. , Ewers B. E.
Published: April 2007

A Bayesian approach was used to fit a conceptual transpiration model to half‐hourly transpiration rates for a sugar maple (Acer saccharum) stand collected over a 5‐month period and probabilistically estimate its parameter and prediction uncertainties. The model used the Penman‐Monteith equation with the Jarvis model for canopy conductance. This deterministic model was extended by adding a normally distributed error term. This extension enabled using Markov chain Monte Carlo simulations to sample the posterior parameter distributions. The residuals revealed approximate conformance to the assumption of normally distributed errors. However, minor systematic structures in the residuals at fine timescales suggested model changes that would potentially improve the modeling of transpiration. Results also indicated considerable uncertainties in the parameter and transpiration estimates. This simple methodology of uncertainty analysis would facilitate the deductive step during the development cycle of deterministic conceptual models by accounting for these uncertainties while drawing inferences from data.
Formation and spreading of Eurasian source oxygen‐rich halocline water into the Canadian Basin in the Arctic Ocean
Authors: Itoh Motoyo , Carmack Eddy , Shimada Koji , McLaughlin Fiona , Nishino Shigeto , Zimmermann Sarah
Published: April 2007

We identify the source region and spreading pattern of cold, oxygen‐rich water observed in the halocline of the northern Canada Basin using both Joint Western Arctic Climate Studies 2002–2005 and other data. This water originates in the winter mixed‐layer in the Nansen Basin and, because of its convective origin, can be traced by its cold, oxygen‐rich properties together with a signature of low potential vorticity. This water, a component of the cold halocline complex, spreads into the Makarov Basin across the Lomonosov Ridge between 82°N and 86°N, enters the Canada Basin between the Alpha and Mendeleyev ridges, and continues eastward into the Beaufort Gyre north of Chukchi Plateau.
Magnetostriction of ternary Fe–Ga–X (X=C,V,Cr,Mn,Co,Rh) alloys
Authors: Clark A. E. , Restorff J. B. , Wun-Fogle M. , Hathaway K. B. , Lograsso T. A. , Huang M. , Summers E.
Published: April 2007

Binary iron-gallium (Galfenol) alloys have large magnetostrictions over a wide temperature range. Single crystal measurements show that additions of 2at.% or greater of 3d and 4d transition elements with fewer (V, Cr, Mo, Mn) and more (Co, Ni, Rh) valence electrons than Fe, all reduce the saturation magnetostriction. Kawamiya and Adachi [J. Magn. Magn. Mater. 31–34, 145 (1983)] reported that the D03 structure is stabilized by 3d transition elements with electron∕atom ratios both less than iron and greater than iron. If D03 ordering decreases the magnetostriction, the maximum magnetostriction should be largest for the (more disordered) binary Fe–Ga alloys as observed. Notably, addition of small amounts of C (0.07, 0.08, and 0.14at.%) increases the magnetostriction of the slow cooled binary alloy to values comparable to the rapidly quenched alloy. We assume that small atom (C, B, N) additions enter interstitially and inhibit ordering, thus maximizing the magnetostriction without quenching.
Engineering the magnetic properties of Ge1−xMnx nanowires
Authors: Kazakova Olga , Kulkarni Jaideep S. , Arnold Donna C. , Holmes Justin D.
Published: April 2007

Possible origins of room-temperature ferromagnetism in GeMn nanowires (NWs) are investigated. Arrays of Ge1−xMnx NWs and Ge∕Ge1−xMnx nanocables (NCs) (x=1%–5%) have been synthesized within the pores of anodized alumina oxide (AAO) membranes. The influence of annealing on the magnetic properties of Ge1−xMnx NWs is studied. The room-temperature ferromagnetism is preserved after the postfabrication annealing in inert atmosphere (Tann=750°C) demonstrating overall compatibility of Ge1−xMnx NWs with conventional complementary metal-oxide semiconductor technology. The role of oxygen in high-TC ferromagnetic ordering is investigated in double-phased NCs with a Ge sheath. Despite a barrier to oxygen migration from the AAO membrane, samples still display room-temperature ferromagnetism, hence, ruling out any significant role of oxygen in the explanation of the high TC in the system. The magnetic properties of the one-dimensional Ge1−xMnx nanostructures can be understood by considering interface related phenomena.
Density functional self-consistent quantum mechanics/molecular mechanics theory for linear and nonlinear molecular properties: Applications to solvated water and formaldehyde
Authors: Nielsen Christian B. , Christiansen Ove , Mikkelsen Kurt V. , Kongsted Jacob
Published: April 2007

A combined quantum mechanics/molecular mechanics (QM/MM) method is described, where the polarization between the solvent and solute is accounted for using a self-consistent scheme linear in the solvent polarization. The QM/MM method is implemented for calculation of energies and molecular response properties including the calculation of linear and quadratic response functions using the density-functional theory (DFT) and the Hartree-Fock (HF) theory. Sample calculations presented for ground-state energies, first-order ground-state properties, excitation energies, first-order excited state properties, polarizabilities, first-hyperpolarizabilities, and two-photon absorptions strengths of formaldehyde suggests that DFT may in some cases be a sufficiently reliable alternative to high-level theory, such as coupled-cluster (CC) theory, in modeling solvent shifts, whereas results obtained with the HF wave function deviate significantly from the CC results. Calculations carried out on water gives results that also are comparable with CC calculations in accuracy for ground-state and first-order properties. However, to obtain such accuracy an exchange-correlation functional capable of describing the diffuse Rydberg states must be chosen.
Analytical formula for the tunneling current versus voltage for multilayer barrier structures
Authors: Chapline Michael G. , Wang Shan X.
Published: April 2007

A formula is derived for the quantum mechanical tunneling current as a function of voltage bias for a multilayer barrier structure separated by similar electrodes. In the case of bilayer barriers, this formula has proven useful for confirming that the conduction is due to tunneling and can be used to determine the properties of the individual layers from fits to I-V curves. In contrast with Simmons’ formula [J. Appl. Phys. 34, 1793 (1963)] for the tunneling current in a single layer barrier, it is shown that the expected current versus voltage characteristics is polarity dependent. In the future this formula may prove useful for the analysis of resonant tunnel diodes and magnetic tunnel junctions utilizing multilayer barriers.
On the bimodal dynamics of the turbulent horseshoe vortex system in a wing-body junction
Authors: Paik Joongcheol , Escauriaza Cristian , Sotiropoulos Fotis
Published: April 2007

The turbulent boundary layer approaching a wall-mounted obstacle experiences a strong adverse pressure gradient and undergoes three-dimensional separation leading to the formation of a dynamically rich horseshoe vortex (HSV) system. In a pioneering experimental study, Devenport and Simpson [J. Fluid Mech. 210, 23 (1990)] showed that the HSV system forming at the leading edge region of a wing mounted on a flat plate at Re=1.15×105 exhibits bimodal, low-frequency oscillations, which away from the wall produce turbulent energy and stresses one order of magnitude higher than those produced by the conventional shear mechanism in the approaching turbulent boundary layer. We carry out numerical simulations for the experimental configuration of Devenport and Simpson using the detached-eddy-simulation (DES) approach. The DES length scale is adjusted for this flow to alleviate the well known shortcoming of DES; namely that of premature, laminar-like flow separation. The numerical simulations reproduce with good accuracy most experimental observations, including both the distributions of the mean flow and turbulence quantities and the bimodal dynamics of the velocity field in the HSV region. The only remaining discrepancy between experiments and simulations is the predicted location of the HSV, which is somewhat further upstream from the wing than the measured one. Proper orthogonal decomposition (POD) of the resolved flow field is employed to gain insights into the coherent dynamics of the flow. The POD analysis shows that 85% of the energy in the vortex region is accounted for by the first two POD modes whose dynamics is quasiperiodic. To elucidate the physical mechanisms that lead to the onset of the bimodal dynamics, we employ probability-density-function-based conditional averaging and visualization of the instantaneous three-dimensional structure of the HSV using the q criterion. We show that the bimodal dynamics is due to the continuous and aperiodic interplay of two basic states: an organized state with a coherent necklace-like HSV, and a disorganized state with hairpin vortices wrapping around the HSV. We argue that the emergence of hairpin vortices is the result of centrifugal instability.
On the spatial sampling of wave fields with circular ring apertures
Authors: Simonetti F. , Huang L. , Duric N.
Published: April 2007

This paper investigates the sampling criterion needed to image objects within a circular ring array. The array consists of transducer elements deployed along a circular aperture at regular angular intervals. Each transducer excites waves which propagate towards the center of the array and detects outgoing fields traveling towards it. It is shown that while with conventional linear apertures the sampling criterion is dictated by the wavelength of the probing wave only, in the case of a circular aperture the sampling depends on the size of the object relative to the wavelength and its position with respect to the aperture.
Thermal stability of Co-core-CoO-shell nanoparticles on an ultrathin θ-Al2O3 film support
Authors: Rose V. , Franchy R.
Published: April 2007

The effect of annealing temperature on a system of Co-core-CoO-shell nanoparticles on θ-Al2O3/CoAl(100) has been investigated using a combination of Auger electron spectroscopy, high-resolution electron energy loss spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy. Results show that thermal treatment leads to a decomposition of the CoO-shell above 450 K, and thus it is strongly diminished with respect to the bulk value. Between 550 and 1050 K the Co particles coalescence and diffuse through the oxide into the substrate. Due to defect recovery, the thermal stability of the thin aluminum oxide film remained unchanged compared to as-grown θ-Al2O3.
Modified transmission line model to investigate non-Ohmic contact behavior and its application on GaN
Authors: Wang Yanjie , Chen Weixi , Wei Qiyuan , Chen Weihua , Li Rui , Pan Yaobo , Yang Zhijian , Zhang Guoyi , Hu Xiaodong
Published: April 2007

In this article we proposed a modified transmission line model method to analyze non-Ohmic contact. It can differentiate the contact resistance while the current flows into and out of the contact. When the earlier two factors are equal, this method degenerate to traditional method. By this method, we obtained contact parameters for both p-GaN and n-GaN and revealed the validity of this method. To further study the contact characteristics and transportation mechanism between alloyed Ni/Au and p-GaN, we also measured barrier information at different temperature and current. The result indicates the hole passes through the barrier by thermionic emission and the barrier may lowered by image force.
Investigation of the interaction potential and thermodynamic functions of dusty plasma by measured correlation functions
Authors: Fortov V. E. , Gavrikov A. V. , Petrov O. F. , Shakhova I. A. , Vorob’ev V. S.
Published: April 2007

Results of investigation of the compressibility factor, compressibility, and the internal energy of dusty plasma are reported. The integral equations approach is used to calculate charge, screening radius and the interaction potential of dust particles. This approach is based on experimentally obtained pair correlation functions. It is demonstrated that states of dusty plasma structure correspond to supercritical fluid with a greater or lesser density.
Simulation of surface discharge dynamics by means of cellular automata
Authors: Adalev A. S. , Hayakawa M. , Korovkin N. V. , Iudin D. I. , Trakhtengerts V. Yu.
Published: April 2007

A dynamic model of a creeping discharge over a dielectric surface is presented. A discharge area (above a dielectric sheet separating a metal needle from a ground plain electrode) is presented as a system of gas sphere cells covering the dielectric. A discharge tree (conducting cluster) is represented by a nonlinear circuit consisting of capacitances, nonlinear conductances, and controlled sources. The sources simulate the potential caused by the needle electrode and free charge located in the neighboring cells. The coefficients for the controlled sources and cell capacitances are determined from the results of static field calculation. The effects of electron drift, impact ionization, and photoionization are involved into the conductance model. Physical parameters of the latter two processes are deduced from the experimental data available in the literature. The criteria for cell initiation are obtained for different applied voltages such that dynamic characteristics of the model correspond to the experimental ones. The experimental results for the nanosecond discharges are used here considering the streamer phase of discharge development. Further improvement of the conductance model is discussed with respect to plasma heating up to the temperatures enough for the streamer-to-leader transition. In addition to discharge patterns which were created to be similar to experimental Lichtenberg figures, the model allows us to determine such local properties of the discharge as current, voltage drop, loss, field, and charge distribution.
Comparative properties of the interior and blowoff plasmas in a dynamic hohlraum
Authors: Apruzese J. P. , Clark R. W. , Davis J. , Sanford T. W. L. , Nash T. J. , Mock R. C. , Peterson D. L.
Published: April 2007

A Dynamic Hohlraum (DH) is formed when arrays of tungsten wires driven by a high-current pulse implode and compress a cylindrical foam target. The resulting radiation is confined by the wire plasma and forms an intense, ∼200–250eV Planckian x-ray source. The internal radiation can be used for indirect drive inertial confinement fusion. The radiation emitted from the ends can be employed for radiation flow and material interaction studies. This external radiation is accompanied by an expanding blowoff plasma. We have diagnosed this blowoff plasma using K-shell spectra of Mg tracer layers placed at the ends of some of the Dynamic Hohlraum targets. A similar diagnosis of the interior hohlraum has been carried out using Al and Mg tracers placed at 2mm depth from the ends. It is found that the blowoff plasma is about 20–25% as dense as that of the interior hohlraum, and that its presence does not significantly affect the outward flow of the nearly Planckian radiation field generated in the hohlraum interior. However, the electron temperature of the blowoff region, at ∼120eV, is only about half that of the interior hohlraum plasma.
Spin lifetime in high quality InSb epitaxial layers grown on GaAs
Authors: Litvinenko K. L. , Nikzad L. , Allam J. , Murdin B. N. , Pidgeon C. R. , Harris J. J. , Zhang T. , Cohen L. F.
Published: April 2007

The spin relaxation in undoped InSb films grown on GaAs has been investigated in the temperature range from 77to290K. Two distinct lifetime values have been extracted, 1 and 2.5ps, dependent on film thickness. Comparison of this data with a multilayer transport analysis of the films suggests that the longer time (∼2.5ps at 290K) is associated with the central intrinsic region of the film, while the shorter time (∼1ps) is related to the highly dislocated accumulation region at the film-substrate interface. Whereas previous work on InAs films grown on GaAs showed that the native surface defect resulted in an additional charge accumulation layer with high conductivity but very short spin lifetime, in InSb layers the surface states introduce a depletion region. We infer that InSb could be a more attractive candidate for spintronic applications than InAs.
Intrasubband and intersubband transitions in GaAs∕AlxGa1−xAs multiple quantum wells
Authors: Li J. M. , Qian K. Y. , Zhu Q. S. , Wang Z. G.
Published: April 2007

Infrared absorption in GaAs∕AlxGa1−xAs multiple quantum wells is investigated using a polarizer. Two main peaks, with wave numbers 723 and 1092cm−1, are observed. The peak with wave number 1092cm−1 corresponds to the 0→1 intersubband transition, while the other one corresponds to the intrasubband transition. The polarized absorbance is one order of magnitude higher than the unpolarized one. The authors attribute the intrasubband transition to the plasma oscillation in the quantum wells.
Initially π-twisted nematic liquid crystal cell stabilized by a fluorinated polymer wall
Authors: Lee Seong Ryong , Shin Jong-Ha , Baek Jong-In , Oh Min-Cheol , Yoon Tae-Hoon , Kim Jae Chang
Published: April 2007

The authors propose an initially π-twisted nematic liquid crystal (NLC) cell which can be made by phase separation of LC molecules and fluorinated polymer material without using a chiral material. Excellent phase separation is achieved due to strong immiscibility of the fluorinated acrylates with LC molecules. The π-twist state of the LCs surrounded with the fluorinated polymer wall is almost permanently stabilized. The initially π-twisted NLC cell can be operated at a lower driving voltage compared to those of a conventional pi cell and chiral-doped cell. The switching time of the cell is as fast as the conventional pi cell.
Stacking patterns in self-assembly opal photonic crystals
Authors: Checoury X. , Enoch S. , López C. , Blanco A.
Published: April 2007

In this letter the authors present both experimental and numerical studies of the optical properties of four-layer artificial opals. The stacking of four layers of spheres may arise according to three different arrangements: face-centered cubic, hexagonal close packed, or double hexagonal close packed. The study shows that the transmission spectra features are characteristic of the type of stacking, and thus, each color region observed under the optical microscope can be unambiguously associated with one of the stacking types.
Influence of surface states on the extraction of transport parameters from InAs nanowire field effect transistors
Authors: Dayeh Shadi A. , Soci Cesare , Yu Paul K. L. , Yu Edward T. , Wang Deli
Published: April 2007

The capacitive effects of interface trap states in top-gated InAs nanowire field effect transistors and their influence on the experimental extraction of transport parameters are discussed. Time resolved transfer characteristics exhibit transient behavior indicating surface state trapping and detrapping with long characteristic time constants of 45s. Varying gate voltage sweep rate results in a time-dependent extrinsic transconductance; a reduced gate voltage sweep rate leads to a charge neutral interface, reduced interface state capacitance, higher measured transconductance, and minimal hysteresis. These results demonstrate that measurements with a charge neutralized or passivated surface are key to extract intrinsic nanowire transport parameters.
Neodymium doped sol-gel tapered waveguide amplifier
Authors: Peled Asher , Nathan Menachem , Tsukernik Alexander , Ruschin Shlomo
Published: April 2007

The authors report the design, fabrication, and study of a fully monolithic solid-state amplifier based on a neodymium doped sol-gel tapered rib waveguide with a thin guiding layer of 360nm. Signal (1064nm) and pump (803nm) light were coupled into and out of the amplifier by grating couplers. A gain of 4.8dB (3.75dB net internal gain) was obtained from a 1cm long device.
Prevention of In droplets formation by HCl addition during metal organic vapor phase epitaxy of InN
Authors: Kang Sang Won , Park Hyun Jong , Won Yong Sun , Kryliouk Olga , Anderson Tim , Khokhlov Dmitry , Burbaev Timur
Published: April 2007

The low decomposition temperature of InN and relatively high thermal stability of NH3 necessitate the use of a high NH3∕TMIn ratio to prevent In droplet formation on the surface. This work shows that the addition of Cl in the form of HCl (Cl∕In molar ratio range of 0.3–1.4) to the growth chamber allows the growth of high quality InN films without the formation of a second In phase at a very low value of the N∕In molar inlet ratio (2500). Photoluminescence spectra in the temperature range of 144to4.5K showed a broad spectral band with a cutoff energy close to the reported minimum of the InN band gap energy (0.65eV).
Localized strain reduction in strain-compensated InAs∕GaAs stacked quantum dot structures
Authors: Nuntawong N. , Tatebayashi J. , Wong P. S. , Huffaker D. L.
Published: April 2007

The authors report the effect of localized strain in stacked quantum dots (QDs) with strain-compensation (SC) layers by evaluating the vertical coupling probability of QD formation between stacks measured as a function of spacer thickness. The localized strain field induced at each QD can be partially suppressed by SC layers, resulting in reduced coupling probability with moderate spacer thickness along with the improved QD uniformity and optical properties. The authors have simulated the local strain field along with subsequent QD formation and coupling probability based on a distributed surface chemical potential. By fitting the experimentally derived coupling probability to the modeled values, a 19% reduction of the localized strain field is obtained for the SC structures compared to the uncompensated structures.
Time dependent plasticity at real nanoscale deformation
Authors: Wang F. , Huang P. , Xu K. W.
Published: April 2007

Nanoindentation creep test has been carried out in displacement of 4–100nm regime at single grained (SG) Cu and ultrafine grained (UFG) Cu. The strain rate sensitivity m has been determined and exhibits strong indentation size effect. The magnitudes of m in UFG and SG Cu are comparable and can be simulated by the same curve below a critical depth. The authors experimental findings and analysis support that the tip-sample diffusion is the dominant mechanism below a critical indentation depth and the effect of grain boundary media mechanisms will emerge as the indenter penetrates deeper.
Separating dipolar broadening from the intrinsic switching field distribution in perpendicular patterned media
Authors: Hellwig O. , Berger A. , Thomson T. , Dobisz E. , Bandic Z. Z , Yang H. , Kercher D. S. , Fullerton E. E.
Published: April 2007

A critical requirement for bit patterned media applications is the control and minimization of the switching field distribution (SFD). Here, we use the ΔH(M,ΔM) method to separate dipolar interactions due to neighbor islands from the intrinsic SFD by measuring a series of partial reversal curves of perpendicular anisotropy Co∕Pd based multilayer films deposited onto prepatterned Si substrates. For a 100-nm-period island array the dipolar broadening contributes 22% to the observed SFD. For a 45-nm-period array this value increases to 31%. These results highlight the importance of quantifying long-range dipolar interactions for determining the intrinsic SFD of patterned media.
High performance polythiophene/fullerene bulk-heterojunction solar cell with a TiOx hole blocking layer
Authors: Hayakawa Akinobu , Yoshikawa Osamu , Fujieda Takuya , Uehara Kaku , Yoshikawa Susumu
Published: April 2007

Insertion of a TiOx layer between the Al electrode and the active layer of an organic photovoltaic cell resulted in a high performance with 94% durability under irradiation (100mW∕cm2) for 100h and had improved fill factor and open circuit voltage. An efficiency of 4.05% was achieved by using the cell containing a TiOx layer fabricated and measured in ambient atmosphere. The TiOx layer works as an effective barrier to physical damage and chemical degradation, resulting in high durability under aerobic conditions, and also serves as a hole blocking layer, resulting in improved parallel resistance and rectification.
Atomistic simulation of the size and orientation dependences of thermal conductivity in GaN nanowires
Authors: Wang Zhiguo , Zu Xiaotao , Gao Fei , Weber William J. , Crocombette Jean-Paul
Published: April 2007

The thermal conductivity of GaN nanowires has been determined computationally by applying nonequilibrium atomistic simulation methods using the Stillinger-Weber [Phys. Rev. B 31, 5262 (1985)] potentials. The simulation results show that the thermal conductivity of the GaN nanowires is smaller than that of a bulk crystal and increases with increasing diameter. Surface scattering of phonons and the high surface to volume ratios of the nanowires are primarily responsible for the reduced thermal conductivity and its size dependence behavior. The thermal conductivity is also found to decrease with increasing temperature and exhibits a dependence on axial orientation of the nanowires.
Subpicosecond oxygen trapping in the heme pocket of the oxygen sensor FixL observed by time-resolved resonance Raman spectroscopy
Authors: Kruglik Sergei G. , Jasaitis Audrius , Hola Klara , Yamashita Taku , Liebl Ursula , Martin Jean-Louis , Vos Marten H.
Published: April 2007

Dissociation of oxygen from the heme domain of the bacterial oxygen sensor protein FixL constitutes the first step in hypoxia-induced signaling. In the present study, the photodissociation of the heme-O
2
bond was used to synchronize this event, and time-resolved resonance Raman (TR
3
) spectroscopy with subpicosecond time resolution was implemented to characterize the heme configuration of the primary photoproduct. TR
3
measurements on heme-oxycomplexes are highly challenging and have not yet been reported. Whereas in all other known six-coordinated heme protein complexes with diatomic ligands, including the oxymyoglobin reported here, heme iron out-of-plane motion (doming) occurs faster than 1 ps after iron–ligand bond breaking; surprisingly, no sizeable doming is observed in the oxycomplex of the
Bradyrhizobium japonicum
FixL sensor domain (FixLH). This assessment is deduced from the absence of the iron–histidine band around 217 cm
−1
as early as 0.5 ps. We suggest that efficient ultrafast oxygen rebinding to the heme occurs on the femtosecond time scale, thus hindering heme doming. Comparing WT oxy-FixLH, mutant proteins FixLH-R220H and FixLH-R220Q, the respective carbonmonoxy-complexes, and oxymyoglobin, we show that a hydrogen bond of the terminal oxygen atom with the residue in position 220 is responsible for the observed behavior; in WT FixL this residue is arginine, crucially implicated in signal transmission. We propose that the rigid O
2
configuration imposed by this residue, in combination with the hydrophobic and constrained properties of the distal cavity, keep dissociated oxygen in place. These results uncover the origin of the “oxygen cage” properties of this oxygen sensor protein.
Protection against
Escherichia coli
infection by antibody to the
Staphylococcus aureus
poly-
N
-acetylglucosamine surface polysaccharide
Authors: Cerca Nuno , Maira-Litrán Tomás , Jefferson Kimberly K. , Grout Martha , Goldmann Donald A. , Pier Gerald B.
Published: April 2007

Poly-
N
-acetylglucosamine (PNAG) is a surface polysaccharide produced by
Staphylococcus aureus
and
Staphyloccus epidermidis
and is an effective target for opsonic and protective Ab for these two organisms. Recently, it has been found that
Escherichia coli
produces an exo-polysaccharide, designated polyglucosamine, that is biochemically indistinguishable from PNAG. We analyzed 30
E. coli
strains isolated from urinary tract and neonatal bloodstream infections for the
pga locus
, PNAG antigen production, and susceptibility to opsonic killing and protection from lethal infection by Ab to PNAG. Twenty-six of 30 strains carried the
pga
locus, 25 of 30 expressed immunologically detectable PNAG, and 21 of 30 could be killed by rabbit IgG specific for the deacetylated form of the staphylococcal PNAG. Ab to staphylococcal PNAG protected mice against lethality from five different
E. coli
strains expressing PNAG. PNAG expression by both Gram-negative and Gram-positive organisms could make this antigen a conserved vaccine target for multiple pathogenic species of bacteria.
Changes in nitrogen cycling during the past century in a northern hardwood forest
Authors: McLauchlan Kendra K. , Craine Joseph M. , Oswald W. Wyatt , Leavitt Peter R. , Likens Gene E.
Published: April 2007

Nitrogen (N) availability, defined here as the supply of N to terrestrial plants and soil microorganisms relative to their N demands, limits the productivity of many temperate zone forests and in part determines ecosystem carbon (C) content. Despite multidecadal monitoring of N in streams, the long-term record of N availability in forests of the northeastern United States is largely unknown. Therefore, although these forests have been receiving anthropogenic N deposition for the past few decades, it is still uncertain whether terrestrial N availability has changed during this time and, subsequently, whether forest ecosystems have responded to increased N deposition. Here, we used stable N isotopes in tree rings and lake sediments to demonstrate that N availability in a northeastern forest has declined over the past 75 years, likely because of ecosystem recovery from Euro-American land use. Forest N availability has only recently returned to levels forecast from presettlement trajectories, rendering the trajectory of future forest N cycling uncertain. Our results suggest that chronic disturbances caused by humans, especially logging and agriculture, are major drivers of terrestrial N cycling in forest ecosystems today, even a century after cessation.
Sex‐specific Responses to Zinc Supplementation in Nouna, Burkina Faso
Authors: Garenne Michel , Becher Heiko , Ye Yasome , Kouyate Bokar , Müller Olaf
Published: April 2007

Objectives:

To study the different responses by sex to zinc supplementation among young children.

Study Children and Methods:

Double‐blind randomized controlled trial of zinc supplementation in 686 children aged 6–30 months, conducted in Nouna, a rural area of Burkina Faso. Children received either a 12.5‐mg zinc sulfate tablet or a placebo every day for about 6 months. Outcomes were morbidity, nutritional status, and mortality.

Results:

Results revealed significant differences between boys and girls in their responses to zinc supplementation. Boys who received the zinc preparation had fewer days with diarrhea than did control boys (RR = 0.88, P = 0.05), especially less nonfebrile diarrhea (RR = 0.72, P < 0.001) and less dysentery (RR = 0.65, P = 0.05), but more ear infections (RR = 4.00, P < 0.001). By contrast, girls who received the zinc supplement had the same prevalence of diarrhea as did control girls, but more dysentery (RR = 3.70, P < 0.001), fewer ear infections (RR = 0.39, P < 0.001), and fewer eye infections (RR = 0.41, P < 0.001). The effect of supplementation on nutritional status was not detectable in boys, but girls who received supplementation experienced a faster growth velocity in height than did control girls (P = 0.004) and a faster growth velocity for weight and height if they were wasted and not stunted at baseline (P = 0.003).

Conclusions:

Zinc supplementation had positive, nil, or negative effects depending on pathological condition, and the effects were different for boys than for girls.
Quality of Life in Paediatric Gastrointestinal and Liver Disease: A Systematic Review
Authors: Maity Santanu , Thomas Adrian G
Published: April 2007

Objectives:

To identify and appraise all studies relating to and instruments developed to measure quality of life (QOL) in children with gastrointestinal or liver diseases.

Methods:

A literature search was undertaken using MEDLINE, EMBASE, CINAHL, and PsycINFO to identify relevant articles published up to the end of 2005. These were reviewed by both authors and data were extracted using a standardised form. Articles were excluded if no attempt was made to measure QOL, they did not relate to children ages <17 years, they did not relate to gastrointestinal or liver diseases, or they were review articles. Quality of life instruments identified were rated according to proposed criteria.

Results:

From a total of 2379 articles identified in the initial search, a total of 2309 were excluded, leaving 70 included studies. These were assigned to the following categories: inflammatory bowel disease, n = 17; cystic fibrosis, n = 20; liver disease, n = 11; surgery, n = 15; and miscellaneous, n = 7. These studies describe the impact that these diseases have on the QOL of affected children. A total of 11 disease‐specific QOL instruments and 1 generic instrument with a chronic disease module were identified, but only 5 of these fulfilled the proposed quality criteria and can be recommended for future use.

Conclusions:

Chronic gastrointestinal and liver diseases can have an enormous effect on the QOL of affected individuals and their families. A number of disease‐specific paediatric QOL instruments have been developed and validated. Quality of life is an important outcome that should be incorporated into clinical practice and measured when treatments are evaluated. Future research should explore how QOL can best be improved in children in whom it is severely impaired.
Evaluation of 13C‐Urea Breath Test and Fecal Antigen Immunoassay to Detect Helicobacter pylori Infection in Gambian Infants
Authors: Jones Rhys T , Darboe Momodou K , Doherty Conor P , MacKay William G , Weaver Lawrence T , Campbell David I , Thomas Julian E
Published: April 2007

Helicobacter pylori colonization was measured by [13C]‐urea breath test in 198 Gambian infants and by fecal enzyme‐linked immunosorbent assay in 52 of the 198 at ages 2, 5, and 12 months. By 12 months there was good concordance between tests; 33 of 44 (75%) test results were positive by enzyme‐linked immunosorbent assay, and 29 of 44 (66%) test results were positive by urea breath test. H pylori colonization is common among Gambian infants, and noninvasive tests can provide a reliable means of diagnosis.
Vaccinating in disease-free regions: a vaccine model with application to yellow fever
Authors: Codeço Claudia T , Luz Paula M , Coelho Flavio , Galvani Alison P , Struchiner Claudio
Published: April 2007

Concerns regarding natural or induced emergence of infectious diseases have raised a debate on the pros and cons of pre-emptive vaccination of populations under uncertain risk. In the absence of immediate risk, ethical issues arise because even smaller risks associated with the vaccine are greater than the immediate disease risk (which is zero). The model proposed here seeks to formalize the vaccination decision process looking from the perspective of the susceptible individual, and results are shown in the context of the emergence of urban yellow fever in Brazil. The model decomposes the individual's choice about vaccinating or not into uncertain components. The choice is modelled as a function of (i) the risk of a vaccine adverse event, (ii) the risk of an outbreak and (iii) the probability of receiving the vaccine or escaping serious disease given an outbreak. Additionally, we explore how this decision varies as a function of mass vaccination strategies of varying efficiency. If disease is considered possible but unlikely (risk of outbreak less than 0.1), delay vaccination is a good strategy if a reasonably efficient campaign is expected. The advantage of waiting increases as the rate of transmission is reduced (low
R
0
) suggesting that vector control programmes and emergency vaccination preparedness work together to favour this strategy. The opposing strategy, vaccinating pre-emptively, is favoured if the probability of yellow fever urbanization is high or if expected
R
0
is high and emergency action is expected to be slow. In summary, our model highlights the nonlinear dependence of an individual's best strategy on the preparedness of a response to a yellow fever outbreak or other emergent infectious disease.
The West Indies as a laboratory of biogeography and evolution
Authors: Ricklefs Robert , Bermingham Eldredge
Published: April 2007

Islands have long provided material and inspiration for the study of evolution and ecology. The West Indies are complex historically and geographically, providing a rich backdrop for the analysis of colonization, diversification and extinction of species. They are sufficiently isolated to sustain endemic forms and close enough to sources of colonists to develop a dynamic interaction with surrounding continental regions. The Greater Antilles comprise old fragments of continental crust, some very large; the Lesser Antilles are a more recent volcanic island arc, and the low-lying Bahama Islands are scattered on a shallow oceanic platform. Dating of island lineages using molecular methods indicates over-water dispersal of most inhabitants of the West Indies, although direct connections with what is now southern Mexico in the Early Tertiary, and subsequent land bridges or stepping stone islands linking to Central and South America might also have facilitated colonization. Species–area relationships within the West Indies suggest a strong role for endemic radiations and extinction in shaping patterns of diversity. Diversification is promoted by opportunities for allopatric divergence between islands, or within the large islands of the Greater Antilles, with a classic example provided by theAnolislizards. The timing of colonization events using molecular clocks permits analysis of colonization–extinction dynamics by means of species accumulation curves. These indicate low rates of colonization and extinction for reptiles and amphibians in the Greater Antilles, with estimated average persistence times of lineages in the West Indies exceeding 30 Myr. Even though individual island populations of birds might persist an average of 2 Myr on larger islands in the Lesser Antilles, recolonization from within the archipelago appears to maintain avian lineages within the island chain indefinitely. Birds of the Lesser Antilles also provide evidence of a mass extinction event within the past million years, emphasizing the time-heterogeneity of historical processes. Geographical dynamics are matched by ecological changes in the distribution of species within islands over time resulting from adaptive radiation and shifts in habitat, often following repeatable patterns. Although extinction is relatively infrequent under natural conditions, changes in island environments as a result of human activities have exterminated many populations and others—especially old, endemic species—remain vulnerable. Conservation efforts are strengthened by recognition of aesthetic, cultural and scientific values of the unique flora and fauna of the West Indies.
Mergers 101 (part one): training managers for communications and leadership challenges
Authors: Appelbaum Steven H. , Lefrancois Frederic , Tonna Roberto , Shapiro Barbara T.
Published: April 2007

Purpose

To establish what managers need in terms of being acculturated and trained to manage the implications of mergers and acquisitions (M&A) on their organizations considering the variables: change, communications, leadership, culture and stress.

Design/methodology/approach

The article compiles strategies gleaned from academic research literature with particular reference to the most common problems management encounters during M&A implementation and execution.

Findings

The independent variables that are key for successful M&A implementation and execution are identified: communication, leadership and trust, organizational culture, change and stress. The literature review demonstrates the important roles played by each variable throughout the M&A process.

Originality/value

The article provides management with insights on how to prepare for M&A and design a sound behavioral approach in order to achieve the expected post M&A gains and opportunities in a timely manner. This is significant in training managers dealing with the M&A.