bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluating and Promoting an In-House Information Team
Authors: Speight Dunstan
Published: March 2012

Much has been written and discussed about the outsourcing of library staff. In the following article, Dunstan Speight, Library Manager at Berwin Leighton Paisner LLP, looks at the role of in-house information teams. Although written from the perspective of the manager of a team of researchers in a City law firm, the author hopes that elements of his experience will have a relevance to other sectors and team structures.
Knowledge Management in Law: a Look at Cultural Resistance
Authors: Zeide Elana , Liebowitz Jay
Published: March 2012

Knowledge management is still a difficult issue within law firms. One of the potential barriers to widespread adoption of knowledge management in law firms has been cited as cultural resistance. In order to better understand this obstacle, a Delphi survey was conducted with key knowledge management experts in US and UK law firms. There were six factors that focused on elements of cultural resistance. This article, written by Elana Zeide and Jay Liebowitz, highlights the findings.
Information Overload: When Information Becomes Hazardous to Your Health
Authors: Woolfson Beverley
Published: March 2012

Beverley Woolfson analyses the concept of information overload: how it has evolved, and its relevance to the information professional in the commercial law firm. Using data gathered during her MSc dissertation research and combining it with current theories on the topic, the writer concludes that while the information intermediary is often vulnerable to the dangers of overload, a number of strategies can be implemented to ensure that its effects are minimised.
Making Molehills Out of Mountains: a Look at Some Emerging Technologies
Authors: Mullan James
Published: March 2012

In this article, James Mullan addresses recent technological developments with particular emphasis on Google+, Cloud Computing, mobile technologies, ebooks and e-readers.
Finding Information on Pending Appeal Cases
Authors: Fathers Nadine
Published: March 2012

In this article Nadine Fathers focuses on the increased accessibility to information relating to pending appeal cases.
Boris and the Pandas: a Blue Print for a Brilliant Intranet
Authors: Fishleigh Jackie
Published: March 2012

Jackie Fishleigh summarises some tried and tested methods that can turn an intranet into an invaluable business tool. This article provides a number of top tips for engaging users and maintaining their interest and attention for the benefit of their working community. The article, which draws heavily on recently published material by Martin White and Interact Intranet, aims to be informative and entertaining!
The Parent Version of the Strengths and Difficulties Questionnaire
Authors: Stone Lisanne L. , Otten Roy , Ringlever Linda , Hiemstra Marieke , Engels Rutger C. M. E. , Vermulst Ad A. , Janssens Jan M. A. M.
Published: March 2012

The Strengths and Difficulties Questionnaire (SDQ) is a widely used screening instrument for child psychopathology. Many studies have consistently reported rather low α values for certain subscales for the SDQ parent version. Further, the factor structure has not been tested frequently by using confirmatory factor analysis (CFA); research into measurement invariance is even scarcer. Therefore, this study evaluates the internal reliability and tests for measurement invariance for the SDQ parent version. In a Dutch sample of 1,484 children we examined reliability by using coefficient ω and tested for invariance across several subgroups. Also, we conducted CFA to examine the five-factor structure of the SDQ. ω yielded higher values than α did, which supports the use of ω in a SEM-based framework. Support for measurement invariance was found on the configural, metric, and scalar level, and as expected, the five-factor structure was confirmed. Scholars are advised to consider ω as an alternative to α, seeing that various problems with α have been discussed. Support for measurement invariance was found for several demographic variables, so that meaningful group comparisons can now be made for the SDQ parent version.
Freak waves under typhoon conditions
Authors: Mori Nobuhito
Published: March 2012

Benjamin‐Feir Index (BFI) and directional spread are measures of nonlinear four‐wave interactions and resultant indices of possible conditions for freak waves. Temporal‐spatial distributions of BFI and directional spread are examined with numerical simulations of a spectral wave model using typhoon conditions. The spatial distributions of wave characteristics such as significant wave height, wave period, BFI and directional spread are different from each other around the eye of the typhoon. BFI is significantly large in the fourth quadrant of the typhoon, while waves are steep and have narrow frequencies and directional spectra. Freak waves resulting from nonlinear four‐wave‐wave interactions have a greater potential of occurring in the fourth quadrant of the typhoon than in the other quadrants. Furthermore, crossing sea states from two‐wind‐wave systems can be observed behind the eye of the typhoon. The crossing, two‐wind systems are also dangerous sea states, although as observed, they are closer to linear wave conditions. Finally, the characteristics of possible freak wave conditions during typhoons are verified with field data.
Examining the effectiveness and robustness of sequential data assimilation methods for quantification of uncertainty in hydrologic forecasting
Authors: DeChant Caleb M. , Moradkhani Hamid
Published: March 2012

In hydrologic modeling, state‐parameter estimation using data assimilation techniques is increasing in popularity. Several studies, using both the ensemble Kalman filter (EnKF) and the particle filter (PF) to estimate both model states and parameters have been published in recent years. Though there is increasing interest and a growing literature in this area, relatively little research has been presented to examine the effectiveness and robustness of these methods to estimate uncertainty. This study suggests that state‐parameter estimation studies need to provide a more rigorous testing of these techniques than has previously been presented. With this in mind, this paper presents a study with multiple calibration replicates and a range of performance measures to test the ability of each technique to calibrate two separate hydrologic models. The results show that the EnKF is consistently overconfident in predicting streamflow, which relates to the assumption of a Gaussian error structure. In addition, the EnKF and PF were found to perform similarly in terms of tracking the observations with an expected value, but the potential for filter divergence in the EnKF is highlighted.
Effective diffusivity and mass flux across the sediment‐water interface in streams
Authors: Grant Stanley B. , Stewardson Michael J. , Marusic Ivan
Published: March 2012

The exchange of water between a stream and its hyporheic zone (defined as the sediment beneath and immediately adjacent to a stream) underpins many ecological and hydrological functions in turbulent streams. Hyporheic exchange can be parameterized in terms of an effective diffusion coefficient Deffand considerable effort has gone into developing process‐based models and empirical correlations for predicting the value of this transport parameter. In this paper we demonstrate previous laboratory estimates forDeffcan be biased by as much as a factor of 10, due to errors in the equations and/or ambiguities in the variables used to reduce data from transient tracer experiments in flow‐through and recirculating flumes. After correcting these problems, an analysis of 93 previously published flume experiments revealsDeffdepends on properties of the tracer (molecular diffusivity), flow field (shear velocity, kinematic viscosity), and sediment bed (permeability and depth). The shear velocity depends implicitly on the Darcy‐Weisbach friction factor, which captures the influence of bed roughness and bed forms on hyporheic exchange in both laboratory and field studies. The dependence ofDeffon sediment bed depth is consistent with the hypothesis that coherent turbulence in the water column drives mass transport across the sediment‐water interface. Furthermore, the dependence ofDeff on sediment bed depth raises the possibility that hyporheic exchange rates measured in the laboratory are not representative of hyporheic exchange rates in the field.
Coseismic and postseismic deformation of the 2011 Tohoku‐Oki earthquake constrained by GRACE gravimetry
Authors: Wang Lei , Shum C. K. , Simons Frederik J. , Tapley Byron , Dai Chunli
Published: March 2012

Spaceborne gravimetry data from the Gravity Recovery And Climate Experiment (GRACE) are processed using spatio‐spectral Slepian localization analysis enabling the high‐resolution detection of permanent gravity change associated with both coseismic and postseismic deformation resulting from the great 11 March 2011 Mw 9.0 Tohoku‐Oki earthquake. The GRACE observations are then used in a geophysical inversion to estimate a new slip model containing both coseismic slip and after‐slip. The GRACE estimated moment for the total slip, up to the end of July 2011 is estimated as (4.59 ± 0.49) × 1022 N m, equivalent to a composite Mw of 9.07 ± 0.65. If the moment for the Tohoku‐Oki main shock is assumed to be 3.8 × 1022 N m, the contribution from the after‐slip is estimated to be 3.0 × 1021–12.8 × 1021 N m, in good agreement with a postseismic slip model inverted from GPS data. We conclude that GRACE data provide an independent constraint to quantify co‐ and post‐seismic deformation for the Tohoku‐Oki event.
Evidence for the direct oxidation of organic nitrogen to N2 gas in the Arabian Sea
Authors: Trimmer Mark , Purdy Kevin J
Published: March 2012

We performed a suite of 15N incubations (15NO2−, 15NO3− and 15NH4+) with and without the organic-nitrogen (N) compound allylthiourea (ATU), in the suboxic waters of the Arabian Sea. Production of 29N2 in control (-ATU) incubations with either 15NH4++14NO2−, or their analogues, 15NO2−+14NH4+, though small, confirmed the presence of anammox. In contrast, when we added ATU, along with 15NO2− and 14NH4+, there was a much greater production of 29N2, with 92% of the 15N-label being recovered as 29N2 on average. Such stimulated production of 29N2 could not be due to anammox, as the addition of ATU, along with 15NH4++14NO2−, only produced 29N2 equivalent to that in the controls. The ratios of 29N2 to 30N2 produced also precluded stimulation of denitrification. We present this as evidence for a hitherto uncharacterised metabolism potentially capable of oxidising organic-N (e.g. NH2 groups) directly to N2 gas at the expense of NO2−.
Physical Activity, Sedentary Time, and Pericardial Fat in Healthy Older Adults
Authors: Hamer Mark , Venuraju Shreenidhi M. , Urbanova Livia , Lahiri Avijit , Steptoe Andrew
Published: March 2012

Pericardial fat is emerging as a unique risk factor for coronary disease. We examined the relationship between objectively measured physical activity during free‐living and pericardial fat. Participants were 446 healthy men and women (mean age = 66 ± 6 years), without history or objective signs of cardiovascular disease (CVD), drawn from the Whitehall II epidemiological cohort. Physical activity was objectively measured using accelerometers (Actigraph GT3X) worn around the hip during waking hours for 7 consecutive days (average daily wear time = 889 ± 68 min/day), and was classified as sedentary (<200 counts/min (cpm)), light (200–1,998 cpm), or moderate‐vigorous physical activity (MVPA; ≥1,999 cpm). Pericardial fat volume was measured in each participant using electron beam computed tomography. Average daily cpm in men was 338.0 ± 145.0 and in women 303.8 ± 130.2. There was an inverse association between average cpm and pericardial fat (B = −0.070, 95% confidence interval (CI), −0.101, −0.040, P < 0.001), and this remained significant after adjusting for age, sex, registered wear time, BMI, lipids, glycemic control, blood pressure, smoking, statins, and social status. Both sedentary time (B = 0.081, 95% CI, 0.022, 0.14) and MVPA (B = −0.362, 95% CI, −0.527, −0.197) were also associated with pericardial fat, although associations for sedentary time did not remain significant after adjustment for MVPA. The inverse association between physical activity and pericardial fat was stronger among overweight and obese adults than in normal weight. Objectively assessed daily activity levels are related to pericardial fat in healthy participants, independently of BMI. This might be an important mechanism in explaining the association between physical activity and CVD prevention.
Impaired long-term potentiation and long-term memory deficits in xCT-deficient sut mice
Authors: Li Yan , Tan Zhibing , Li Zhigang , Sun Zhongsheng , Duan Shumin , Li Wei
Published: March 2012

xCT is the functional subunit of the cystine/glutamate antiporter system xc−, which exchanges intracellular glutamate with extracellular cystine. xCT has been reported to play roles in the maintenance of intracellular redox and ambient extracellular glutamate, which may affect neuronal function. To assess a potential role of xCT in the mouse hippocampus, we performed fear conditioning and passive avoidance for long-term memories and examined hippocampal synaptic plasticity in wild-type mice and xCT-null mutants, sut mice. Long-term memory was impaired in sut mice. Normal basal synaptic transmission and short-term presynaptic plasticity at hippocampal Schaffer collateral–CA1 synapses were observed in sut mice. However, LTP (long-term potentiation) was significantly reduced in sut mice compared with their wild-type counterparts. Supplementation of extracellular glutamate did not reverse the reduction in LTP. Taken together, our results suggest that xCT plays a role in the modulation of hippocampal long-term plasticity.
Effects of lateral straggling of ions on patterned media fabricated by nitrogen ion implantation
Authors: Hinoue Tatsuya , Ito Kenichi , Hirayama Yoshiyuki , Hosoe Yuzuru
Published: March 2012

Patterned media were fabricated by nitrogen ion implantation and how ion lateral straggling affects the pattern size was analyzed to confirm the feasibility for high-density recording. N2+ ions were implanted with ion energies of 6, 10, 14, and 19 keV through an ion-depth-control layer with suitable thicknesses for the ion energies to make the same ion depth profile. The dosage was 1.8 × 1016 ions/cm2. The saturation magnetization in the ion-implanted area was decreased from 0.56 to 0.05 T for all the media. Preamble pattern width was obtained by analyzing the readback signal. It was also estimated using calculated ion lateral straggling width and measured mask width. The reduction ratio of the pattern width against the ion energy was almost the same for the signal analysis and calculation results. This indicates that the pattern width was decreased just by the width of the ion lateral straggling. Therefore, high-density small patterns can be fabricated by reducing ion energy and suppressing ion lateral straggling.
Refrigerant capacity of austenite in as-quenched and annealed Ni51.1Mn31.2In17.7 melt spun ribbons
Authors: Sánchez Llamazares J. L. , Flores-Zuñiga H. , Sánchez-Valdes C. , Ross C. A. , García C.
Published: March 2012

The thermal dependence of the magnetic entropy change (ΔSM(T)) and refrigerant capacity (RC) of austenite in as-quenched ribbons of chemical composition Ni51.1Mn31.2In17.7 produced by melt spinning at a high cooling rate of 48 ms−1 is reported. The effect of annealing at 1073 K on the structure and the magnetic properties was studied. The as-quenched sample is a single-phase austenite that presents a B2 ordered structure. The annealing on the melt spun samples produced a L21-type ordered structure. Austenite is characterized by a broad ΔSM(T) curve that, for a field change of 5.0 T, exhibits a full-width at half-maximum δTFMHW of 107 K, a peak value of the magnetic entropy change ΔSMpeak of −3.1 Jkg−1 K−1, and RC = 345 Jkg−1. Although annealed samples show larger ΔSMpeak values the narrower ΔSM(T) curves leads to a reduction in RC. Thus, the as-quenched sample shows a higher efficiency for a refrigerant cycle.
Electron-phonon scattering dynamics in ferromagnets on ultrafast timescales: Influence of the phonon temperature
Authors: Essert Sven , Christian Schneider Hans
Published: March 2012

The magnetization response of bulk ferromagnets after excitation by an ultrashort optical pulse is calculated using a dynamical model of the Elliott-Yafet type that includes the effects of the spin-orbit interaction in the ab-initio ferromagnetic band structure, the electron-phonon interaction at the level of Boltzmann scattering integrals, and dynamical changes in the temperature of the phonon bath. Using realistic parameters for the ultrashort optical pulse, the computed maximum magnetization quenching achievable with electron-phonon scattering in a fixed band structure is much smaller than the quenching observed in experiments. Heating of the phonon bath is found to not appreciably change the magnetization dynamics on ultrashort timescales.
Recording performance and thermal stability in perpendicular media with enhancement of grain isolation as well as magnetic anisotropy field
Authors: Jung H. S. , Ikeda Y. , Choe G. , Shi Zhupei
Published: March 2012

Magnetic clustering, thermal stability, and recording performance on perpendicular media with multilayered magnetic anisotropy field (Hk)-gradient CoPtCr-oxide/Cap layers with various Ru-oxide layer thicknesses (tRu-oxide) on top of Ru/NiW layers are investigated. With increasing tRu-oxide from 0 to 1.3 nm, Hc and Hs are enhanced but Hn is reduced. Magnetic correlation length (Dn) extracted from a set of major and minor loops significantly decreases but intrinsic switching field distribution remains unaffected. A short-time switching field (Ho) proportional to Hk increases linearly while KuV/kT remains unchanged. Similar KuV/kT is explained by compensation of the reduced Dn with the enhanced Ku induced by a thin Ru-oxide. However, thermal decay rate degrades from 0.06 to 0.32%/decade, which correlates well with Hn. Similar values of initial minor loop slopes indicate no change in magnetic switching behavior. A 1 nm-thick Ru-oxide layer as a well-defined granular template significantly improves recording performance: narrower MCW at 10 T by 8 nm and higher SNR at 2 T by 1.4 dB are observed even at lower OW by 8 dB compared to the media without Ru-oxide. All the recording parameters as a function of Dn correlate well.
Spin-transfer-torque switching in spin valve structures with perpendicular, canted, and in-plane magnetic anisotropies
Authors: Roy U. , Seinige H. , Ferdousi F. , Mantey J. , Tsoi M. , Banerjee S. K.
Published: March 2012

We exploit canted anisotropies as possible means to enhance spin-transfer-torque (STT) and reduce switching currents. The STTs in spin-valve structures with perpendicular, canted, and, as a reference, in-plane magnetic anisotropies were studied. For perpendicular magnetic anisotropy and canted spin valves the thicknesses and number of Co and Pt layers were varied to obtain different angles of the magnetic anisotropy with respect to the sample plane. Point contact measurements were used to measure the change in the switching-field of the magnetization with the change in the bias current applied to the point contact. A larger STT effect, as evidenced by a larger change in the switching magnetic field for the unit change in the dc bias current, was observed for the sample with 45∘ tilt in magnetization compared to a sample with 12∘ tilt. Tilted magnetization of the reference layer causes precessional switching, decreasing the switching energy and time. Micromagnetic simulations were performed to explain the experimental observations.
The mixing of Fe/Co and its effect on the exchange interaction in SmCo5/α-Fe nanocomposites: A first-principles study
Authors: Liu X. B. , Altounian Z.
Published: March 2012

SmCo 5 / α - Fe is an ideal model for an exchange-coupled magnet. Depending on preparation conditions, some Fe/Co mixing occurs at the interface between the SmCo5 and the α-Fe phases. The mixing behavior of Fe/Co and its effect on the magnetic properties have been studied by a first-principles density functional calculation. For a model system of SmCo5+4Fe (SmCo5Fe4), the calculated substitution energy of Fe in SmCo5 is positive and increases from 40 meV/atom to 61 meV/atom with increasing x from 1 to 3 in SmCo5-xFex, indicating that Fe destabilizes the 1:5 structure. However, the substitution energy of Co in α-Fe changes from negative to positive as x is above 0.68 in Fe1-xCox. The corresponding mixing energy of Fe/Co changes from negative to positive as x is above 2.3 in the virtual alloy of SmCo5-xFex+Fe4-xCox, implying the existence of a concentration limit for the mixing of Fe/Co. The exchange interaction calculations indicate that the inter-atomic exchange interaction of Fe-Co nearest neighbor pairs is stronger than that of Fe-Fe and Co-Co pairs in Sm(Co,Fe)5 and α-(Fe,Co), respectively. The results imply that the Fe/Co mixing enhances the interface exchange-coupling between SmCo5 and α-Fe, which improves the coercivity in the exchange-coupled nano-composite magnets.
Dependence of magnetoelectric properties on sintering temperature for nano-SiC-doped MgB2/Fe wires made by combined in situ/ex situ process
Authors: Li W. X. , Zeng R. , Wang J. L. , Li Y. , Dou S. X.
Published: March 2012

Very fine nano-SiC particles (<15 nm) were doped into a MgB2 superconductor. The influence of self-field supercurrent on the high-field performance of the nano-SiC-doped MgB2/Fe wires is discussed based on comparison of the critical current densities of the in situ processed nano-SiC-doped MgB2 wires and those of the nano-SiC-doped MgB2/Fe wires processed by the combination of in situ/ex situ methods.
Calculation of the spin-wave spectra in planar magnonic crystals with metallic overlayers
Authors: Sokolovskyy M. L. , Klos J. W. , Mamica S. , Krawczyk M.
Published: March 2012

Planar one-dimensional magnonic crystals of nanoscale lattice constant having different types of overlayers, dielectric and metallic, are studied. The dynamics of magnetization is described by the Landau-Lifshitz equation, which is solved using the plane-wave method. The calculations are performed with the nonuniform dynamic dipolar field. At the same time, the finite thickness of the studied structures is taken into account. New possibilities for shaping dispersion relations of spin waves and magnonic bandgaps in planar magnonic crystals by adding metallic/dielectric overlayers on the top of it are found.
Structural properties and magnetic phase transition in HoNi2Mn (57Fe)
Authors: Wang J. L. , Campbell S. J. , Hofmann M. , Hoelzel M. , Zeng R. , Dou S. X. , Kennedy S. J.
Published: March 2012

The structural and magnetic properties of HoNi2Mn(57Fe) have been investigated. The 57Fe-doped HoNi2Mn compound crystallizes in the MgCu2-type structure with Fd-3m space group similar to HoNi2 and HoMn2. HoNi2Mn(57Fe) exhibits ferrimagnetic ordering below a Curie temperature of TC ∼ 60 K—significantly higher than the corresponding values for HoNi2 (TC = 15 K) and HoMn2 (TC = 24 K)—with analyses of dc magnetization and ac susceptibility results confirming that the magnetic transition at TC is second order. The Mössbauer spectra above TC are described well by two sub-spectra representing the 8a and 16d sites while below TC the spectra have been fitted using a site model comprising three sub-spectra. The Debye temperature, θD = 190(20) K, has been determined.
Graphene oxide added carbonyl iron microsphere system and its magnetorheology under applied magnetic fields
Authors: Zhang W. L. , Choi H. J.
Published: March 2012

Novel graphene oxide (GO) particle was introduced as an additive to soft magnetic carbonyl iron (CI) micron-sized particle based magnetorheological (MR) fluid to improve its sedimentation and agglomeration problems in which the MR fluid is a colloidal suspension of magnetizable particles dispersed in a nonmagnetic carrier. The added plate-like GO gap-fillers filled the interspaces of CI particles and improved the resistance to sedimentation. The MR properties of two systems with and without additives were evaluated and compared under different magnetic field strengths using a rotational rheometer. Morphology of pure CI and GO/CI mixture were examined via scanning electron microscopy (SEM) images, and X-ray diffraction (XRD) patterns confirm the differences between pure CI and GO/CI mixture further, the sedimentation problem was observed to be improved.
High speed magnetisation reversal in heat-assisted magnetic recording
Authors: John Greaves Simon , Muraoka Hiroaki , Kanai Yasushi
Published: March 2012

Calculations of switching times as a function of temperature and damping constant are discussed. Near to the Curie temperature, the switching time can be much shorter than at room temperature and independent of Ku. Simulations of heat-assisted magnetic recording were used to study the effect of heat and magnetic field pulse durations on the size and sharpness of bits written on various media. In media with small damping constants, the transition width was hardly influenced by the heat pulse duration, whereas, in media with higher damping constants, the transition width increased with the heat pulse duration.
Nano-structure formation of an oxide ceramics with unprecedented magnetization by supercooling
Authors: Yoda Shinichi , Yu Jianding , Kumar Malahalli Vijaya
Published: March 2012

We report a unique microstructure and a specific magnetization behavior resulting from containerless solidification of a deeply super-cooled BiFeO3 sample under microgravity conditions. The microstructure of the solidified material revealed a mixed structure consisting of 10 nm-size crystalline particles and amorphous matrix. More importantly, the nano-structural material exhibited a magnetization phenomenon which has never observed so far: a reversal in the magnetization jump direction occurred at 50 K when the sample temperature was increased from 5 K to 100 K.
Experimental and theoretical evaluation of surface coated exploding wires
Authors: Stephens J. , Neuber A. , Kristiansen M.
Published: March 2012

This paper discusses the effect of surface coatings on exploding wire behavior. Three different surface coatings of different thicknesses and materials have been studied, each with a 99.99% pure silver conducting core. Experimentally, the wires are subjected to peak current densities in excess of 107 A/cm2 on a microsecond time scale. High Speed intensified Charge-Coupled Device (iCCD) images. A theoretical one-dimensional finite difference model has been developed to predict wire behavior and determine the mechanism(s) responsible for the deviations in behavior induced by the presence of a surface coating.
Lévy walk description of suprathermal ion transport
Authors: Gustafson K. , Ricci P.
Published: March 2012

Transport of suprathermal ions is examined from the Lévy walk perspective in a simple magnetized toroidal plasma. Depending on their energy, these suprathermal ions exhibit superdiffusive, diffusive, or subdiffusive dispersion as a result of the complex interplay between ion drifts related to the magnetic field configuration and interaction of the ions with the plasma turbulence. By implementing a diagnostic that translates the ion trajectories into sequences of steps, we successfully describe their microscale dynamics as a Lévy walk process. Previous analytical predictions that link the microscale Lévy walk parameters to the macroscale suprathermal ion transport are confirmed for all observed regimes of ion dispersion. Additionally, we employ a statistical Lévy walk generator for a direct comparison between transport of Lévy walkers and of suprathermal ions, further validating the Lévy walk description.
A statistical model of hydrogen bond networks in liquid alcohols
Authors: Sillrén Per , Bielecki Johan , Mattsson Johan , Börjesson Lars , Matic Aleksandar
Published: March 2012

We here present a statistical model of hydrogen bond induced network structures in liquid alcohols. The model generalises the Andersson-Schulz-Flory chain model to allow also for branched structures. Two bonding probabilities are assigned to each hydroxyl group oxygen, where the first is the probability of a lone pair accepting an H-bond and the second is the probability that given this bond also the second lone pair is bonded. The average hydroxyl group cluster size, cluster size distribution, and the number of branches and leaves in the tree-like network clusters are directly determined from these probabilities. The applicability of the model is tested by comparison to cluster size distributions and bonding probabilities obtained from Monte Carlo simulations of the monoalcohols methanol, propanol, butanol, and propylene glycol monomethyl ether, the di-alcohol propylene glycol, and the tri-alcohol glycerol. We find that the tree model can reproduce the cluster size distributions and the bonding probabilities for both mono- and poly-alcohols, showing the branched nature of the OH-clusters in these liquids. Thus, this statistical model is a useful tool to better understand the structure of network forming hydrogen bonded liquids. The model can be applied to experimental data, allowing the topology of the clusters to be determined from such studies.
A theoretical study on Tan+ cluster cations: Structural assignments, stability, and electronic properties
Authors: Du Jiguang , Sun Xiyuan , Jiang Gang
Published: March 2012

The low-lying structures of tantalum cluster cations up to n = 16 are investigated using hybrid HF/density functional theory (DFT) functionals (B3P86) in conjunction with relativistic effective core potential and corresponding basis set. The vibrational spectra of tantalum cluster cations are simulated with one empirical scaling factor of 0.943, and compared to the experimental ones [P. Gruene, A. Fielicke, G. Meijer, J. Chem. Phys. 127, 234307 (2007)10.1063/1.2806177]. By assigning the vibrational peaks of experimental spectra, the favored geometries actually existing in the molecular beam are obtained for several studied clusters. Based on the favored geometries, the relative stabilities, spin magnetic moments, and electronic dipole moments are determined. Furthermore, spin-related indices ($\omega _s^ \pm$ωs±) are computed and found to be good linear correlation with vertical lower-upper energy gap.
Fractional Schrödinger operator with delta potential localized on circle
Authors: Kondej Sylwia , Vaz Jayme
Published: March 2012

We consider a system governed by the fractional Schödinger operator with a delta potential supported by a circle in \documentclass[12pt]{minimal}\begin{document}$\mathbb {R}^2$\end{document}R2. We find out the function counting the number of bound states, in particular, we give the necessary and sufficient conditions for the absence of bound state in our system. Furthermore, we reproduce the form of eigenfunctions and analyze the asymptotic behavior of eigenvalues for the strong coupling constant case.
Magnetic anisotropy in nanostructured gadolinium
Authors: Hsu Chin-Jui , Prikhodko Sergey V. , Wang Chiu-Yen , Chen Lih-Juann , Carman Gregory P.
Published: March 2012

This experimental work evaluates the magnetic response of 25-nm-thick Gd thin film and 1400 × 70 × 50 nm3 Gd nanobar structures. Neither the thin film nor the nanobars exhibited single domain behavior at temperatures down to 53 K. The Gd thin film exhibited a magnetocrystalline anisotropy induced spin-reorientation due to a hexagonal close-packed (002) texture, something different from that previously reported on epitaxial Gd thin film. The discrepancy is due to grain boundary induced spin-disorder in the nanosacle. The Gd nanobars had a saturation magnetization 75% smaller than the thin film or bulk and is attributed to oxidation as well as the crystallinity changes from hexagonal close-packed to face-centered cubic caused by stress induced stacking faults. These experimental results for both thin film and nanobar show that the crystallinity has a substantial impact to the magnetic anisotropy of Gd nanostructures as well as the formation of single domain structures.
The effect of sample edge recombination on the averaged injection-dependent carrier lifetime in silicon
Authors: Kessler Michael , Ohrdes Tobias , Altermatt Pietro P. , Brendel Rolf
Published: March 2012

In semiconductors, the effective excess carrier lifetime, τeff, measured in dependence on the injection density, Δn, is an important parameter. It is frequently observed that τeff decreases with decreasing Δn at low-level injection conditions (where Δn is smaller than the dopant density Ndop), which has been difficult to explain. We compare measurements with numerical device simulations to demonstrate that this observed reduction of τeff is caused by a combination of (i) Shockley-Read-Hall (SRH) recombination at the edges of the sample and (ii) transport effects of the carriers toward the edges. We measure τeff(Δn) of boron-diffused and surface-passivated p+np+ and p+pp+ silicon wafers with the commonly applied photo-conductance decay technique, and we vary the sample size. The photo-conductance is probed by inductive coupling within a sample region of about 3 × 3 cm2; hence, the measurements yield an average value of both τeff,av and Δnav within that region. For a detailed analysis, we determine τeff with a high spatial resolution using the dynamic infrared lifetime mapping technique, which shows a strong decrease of τeff toward the edges of the p+np+ samples at low-level injection. We analyze the measurements by numerical device modeling and circuit simulation. We conclude that the sample size should be at least 6 × 6 cm2 for reliable τeff(Δn) measurements at low injection conditions. However, at high-injection conditions, the recombination usually dominates at the dopant-diffused surfaces. Therefore, the saturation current-density, J0, can be extracted from the τeff(Δn) measurements in samples as small as 3 × 3 cm2, with a measurement error due to edge recombination below 10%.
Effects of oxidization and deoxidization on charge-propagation dynamics in rare-earth-doped titanium dioxide with room-temperature luminescence
Authors: Ishii Masashi , Towlson Brian , Poolton Nigel , Harako Susumu , Zhao Xinwei , Komuro Shuji , Hamilton Bruce
Published: March 2012

Anatase titanium dioxide (A-TiO2) with a wide band-gap energy of 3.2 eV can be used as a host semiconductor of rare-earth dopants for optical devices. However, the chemical activity of A-TiO2 strongly affects the luminescence properties of the devices. In this study, we analyzed oxidized and deoxidized samarium (Sm)-doped A-TiO2 (TiO2:Sm) by impedance spectroscopy and microscopic photoluminescence. Charge propagation analyses using dielectric relaxation (DR) revealed that different kinds of charge-trapping centers were formed by the oxidization and deoxidization. For oxidization, Sm-oxygen complexes incorporated in the A-TiO2 formed a trapping level that contributed to Sm excitation, while defective complexes at the A-TiO2 boundary formed other levels that dissipated the charges. For deoxidization using thermal treatment in a hydrogen (H) atmosphere, the number of profitable trapping centers in A-TiO2 was reduced but the remainder maintained the property of Sm excitation. It was also found that H adsorption on the A-TiO2 boundary delocalized the electrons. Photoexcited dielectric relaxation (PEDR) studies confirmed the charge recombination at the profitable traps, and the peak height of the spectra corresponded to the luminescence intensity. Microscopic photoluminescence studies provided results consistent with DR and PEDR measurements and also revealed another quenching factor, i.e., Ti2O3 microcrystal formation on the TiO2:Sm surface.
Two-dimensional-Raman-terahertz spectroscopy of water: Theory
Authors: Hamm Peter , Savolainen Janne
Published: March 2012

We discuss the hybrid 2D-Raman-THz spectroscopy of liquid water. This two-dimensional spectroscopy is designed to directly work in the low-frequency range of the intermolecular degrees of freedom. The information content of 2D-Raman-THz spectroscopy is similar to 2D-Raman or 2D-THz spectroscopy, but its experimental implementation should be easier. That is, 2D-Raman-THz spectroscopy is a 3rd-order nonlinear spectroscopy and as such completely avoids cascading of consecutive 3rd-order signals, which turned out to be a major difficulty in 5th-order 2D-Raman spectroscopy. On the other hand, it does not require any intense THz pump-pulse, the lack of which limits 2D-THz spectroscopy to the study of semiconductor quantum wells as the currently available pulse energies are too low for molecular systems. In close analogy to 2D-Raman spectroscopy, the 2D-Raman-THz response of liquid water is simulated from an all-atom molecular dynamics simulation, and the expected spectral features are discussed.
Gradual channel approximation models for organic field-effect transistors: The space-charge field effect
Authors: Weis Martin
Published: March 2012

The gradual channel approximation is widely used for organic field-effect transistors with an assumption of linear potential profile across the channel. However, this is in contradiction with reported potential profiles. Here, we discuss linear and nonlinear potential profiles in the meaning of the space-charge field generated by injected carriers. The influence on current-voltage relation used for mobility evaluation in linear and saturated regions is proposed as well as transition between these states. In addition, the effect of the space-charge on the potential drop and field around the drain electrode in the saturation region is discussed.
Photoemission studies of fluorine functionalized porous graphitic carbon
Authors: Ganegoda Hasitha , Jensen David S. , Olive Daniel , Cheng Lidens , Segre Carlo U. , Linford Matthew R. , Terry Jeff
Published: March 2012

Porous graphitic carbon (PGC) has unique properties desirable for liquid chromatography applications when used as a stationary phase. The polar retention effect on graphite (PREG) allows efficient separation of polar and non-polar solutes. Perfluorinated hydrocarbons however lack polarizabilty and display strong lipo- and hydrophobicity, hence common lipophilic and hydrophilic analytes have low partition coefficiency in fluorinated stationary phases. Attractive interaction between fluorinated stationary phase and fluorinated analytes results in strong retention compared to non-fluorinated analytes. In order to change the selectivities of PGC, it is necessary to develop a bonded PGC stationary phase. In this study, we have synthesized perfluorinated, PGC using hepatadecafluoro-1-iodooctane, under different temperature conditions. Surface functionalization of the raw material was studied using photoelectron spectroscopy (PES). Results indicate the existence of fluorine containing functional groups, −CF, −CF2 along with an intercalated electron donor species. Multiple oxygen functional groups were also observed, likely due to the presence of oxygen in the starting material. These oxygen species may be responsible for significant modifications to planer and tetrahedral carbon ratios.
Positron annihilation studies of the AlOx/SiO2/Si interface in solar cell structures
Authors: Edwardson C. J. , Coleman P. G. , Li T.-T. A. , Cuevas A. , Ruffell S.
Published: March 2012

Film and film/substrate interface characteristics of 30 and 60 nm-thick AlOx films grown on Si substrates by thermal atomic layer deposition (ALD), and 30 nm-thick AlOx films by sputtering, have been probed using variable-energy positron annihilation spectroscopy (VEPAS) and Doppler-broadened spectra ratio curves. All samples were found to have an interface which traps positrons, with annealing increasing this trapping response, regardless of growth method. Thermal ALD creates an AlOx/SiOx/Si interface with positron trapping and annihilation occurring in the Si side of the SiOx/Si boundary. An induced positive charge in the Si next to the interface reduces diffusion into the oxides and increases annihilation in the Si. In this region there is a divacancy-type response (20 ± 2%) before annealing which is increased to 47 ± 2% after annealing. Sputtering seems to not produce samples with this same electrostatic shielding; instead, positron trapping occurs directly in the SiOx interface in the as-deposited sample, and the positron response to it increases after annealing as an SiO2 layer is formed. Annealing the film has the effect of lowering the film oxygen response in all film types. Compared to other structural characterization techniques, VEPAS shows larger sensitivity to differences in film preparation method and between as-deposited and annealed samples.
Strong visible and near-infrared electroluminescence and formation process in Si-rich polymorphous silicon carbon
Authors: Wang Junzhuan , Yu Linwei , Abolmasov Sergey , Kim Ka Hyun , i Cabarrocas Pere Roca
Published: March 2012

We report here a strong and stable electroluminescence (EL) from Si-rich hydrogenated polymorphous silicon carbon thin films (pm-Si1-xCx : H) fabricated in a plasma-enhanced chemical vapor deposition system. We investigate an unusual forming process in the pm-Si1-xCx : H thin films, during initial EL stressing, and propose a current-stress-induced phase separation process for the formation of new Si nanoclusters, which give rise to strongly enhanced emissions in both visible and near infrared ranges at 1.8–2.1 eV and 0.8–1.2 eV, respectively. The sub-crystalline-Si-bandgap emission is particularly attractive to realize a Si-based multi-band light source for optical interconnection and telecommunication.
Metal-oxide-semiconductor field effect transistor humidity sensor using surface conductance
Authors: Song Seok-Ho , Yang Hyun-Ho , Han Chang-Hoon , Ko Seung-Deok , Lee Seok-Hee , Yoon Jun-Bo
Published: March 2012

This letter presents a metal-oxide-semiconductor field effect transistor based humidity sensor which does not use any specific materials to sense the relative humidity. We simply make use of the low pressure chemical vapor deposited (LPCVD) silicon dioxide’s surface conductance change. When the gate is biased and then floated, the electrical charge in the gate is dissipated through the LPCVD silicon dioxide’s surface to the surrounding ground with a time constant depending on the surface conductance which, in turn, varies with humidity. With this method, extremely high sensitivity was achieved—the charge dissipation speed increased thousand times as the relative humidity increased.
Simultaneous enhancement of charge transport and exciton diffusion in single-crystal-like organic semiconductors
Authors: Yang Jianbing , Zhu Feng , Yu Bo , Wang Haibo , Yan Donghang
Published: March 2012

The charge transport and exciton diffusion have been simultaneously enhanced in the highly ordered and oriented zinc phthalocyanine (ZnPc) films which are fabricated by weak epitaxy growth method compared to the normal ZnPc films (charge mobility from 4 × 10−5 cm2/Vs to 1.1 × 10−4 cm2/Vs and exciton diffusion length from 9 nm to 16 nm). The temperature dependent current-voltage (I-V) characteristics are utilized to investigate the charge transport mechanism, which reveal the clear mechanism and the role of traps in different films. These results reveal the direct relationship between traps properties and transport behavior of both exciton and charge.
Electron drift-mobility measurements in polycrystalline CuIn1−xGaxSe2 solar cells
Authors: Dinca S. A. , Schiff E. A. , Shafarman W. N. , Egaas B. , Noufi R. , Young D. L.
Published: March 2012

We report photocarrier time-of-flight measurements of electron drift mobilities for the p-type CuIn1−xGaxSe2 films incorporated in solar cells. The electron mobilities range from 0.02 to 0.05 cm2/Vs and are weakly temperature-dependent from 100–300 K. These values are lower than the range of electron Hall mobilities (2-1100 cm2/Vs) reported for n-type polycrystalline thin films and single crystals. We propose that the electron drift mobilities are properties of disorder-induced mobility edges and discuss how this disorder could increase cell efficiencies.
Current versus temperature-induced switching of a single molecule: Open-system density matrix theory for 1,5-cyclooctadiene on Si(100)
Authors: Zenichowski Karl , Dokić Jadranka , Klamroth Tillmann , Saalfrank Peter
Published: March 2012

The switching of single cyclooctadiene molecules chemisorbed on a Si(100) surface between two stable conformations, can be achieved with a scanning tunneling microscope [Nacci et al., Phys. Rev. B 77, 121405(R) (2008)]. Recently, it was shown by quantum chemical and quantum dynamical simulations that major experimental facts can be explained by a single-mode model with switching enforced by inelastic electron tunneling (IET) excitations and perturbed by vibrational relaxation [Nacci et al., Nano Lett. 9, 2997 (2009)]. In the present paper, we extend the previous theoretical work in several respects: (1) The model is generalized to a two-mode description in which two C2H4 units of COD can move independently; (2) contributions of dipole and, in addition, (cation and anion) resonance-IET rates are considered; (3) the harmonic-linear vibrational relaxation model used previously is generalized to anharmonic vibrations. While the present models highlight generic aspects of IET-switching between two potential minima, they also rationalize specific experimental findings for COD/Si(100): (1) A single-electron excitation mechanism with a linear dependence of the switching rate on tunneling current I, (2) the capability to switch both at negative and positive sample biases, and (3) a crossover temperature around ∼60 K from an IET-driven, T-independent atom tunneling regime, to classical over-the-barrier isomerization with exponential T-dependence at higher temperatures for a bias voltage of +1.5 V and an average tunneling current of 0.73 nA.
Holomorphic Lorentzian simplicity constraints
Authors: Dupuis Maïté , Freidel Laurent , Livine Etera R. , Speziale Simone
Published: March 2012

We develop a Hamiltonian representation of the ${\mathfrak {sl}}(2,{\mathbb C})$sl(2,C) algebra on a phase space consisting of N copies of twistors, or bi-spinors. We identify a complete set of global invariants, and show that they generate a closed algebra including ${\mathfrak {gl}}(N,{\mathbb C})$gl(N,C) as a subalgebra. Then, we define the linear and quadratic simplicity constraints which reduce the spinor variables to (framed) 3d space-like polyhedra embedded in Minkowski spacetime. Finally, we introduce a new version of the simplicity constraints which (i) are holomorphic and (ii) Poisson-commute with each other, and show their equivalence to the linear and quadratic constraints.
Interface engineering of epitaxial graphene on SiC(0001¯) via fluorine intercalation: A first principles study
Authors: Si Chen , Zhou Gang , Li Yuanchang , Wu Jian , Duan Wenhui
Published: March 2012

Our first-principles calculations show that a change of carrier type from electron to hole can be achieved in monolayer epitaxial graphene on SiC(0001¯) by fluorine (F) intercalation. The p-doping level in graphene, however, is not monotonously enhanced as the F coverage increases, and an interesting interface magnetism is observed at the partially passivated interface. Because intercalated F atoms prefer to bond to the substrate than to the graphene, F-intercalation provides a promising way of “interface modulation doping” to tailor the electronic properties of epitaxial graphene on SiC(0001¯) without appreciably degrading its intrinsic high mobility.