bluuebunny/crossref_metadata_2025 huggingface dataset:
Neural network for AES spectra peak base background removal
Authors: Belič Igor , Poniku Besnik , Jenko Monika
Published: June 2012

One of the constituent elements in Auger electron spectroscopy (AES) spectra that make their automatic analysis next to impossible is the background. To overcome this obstacle and enable further processing, the background removal stage must provide the “clear enough” data for the techniques capable of automatically extracting the requested information from the AES spectra. It is also known that the background in AES spectra contains further information regarding the composition of the sample studied. Thus, although removed, this background should not be disregarded. In our work, the neural networks for data modeling or background function approximation were used. Neural networks were used for the determination of the general shape of the background in AES spectra. Neural networks are model‐less approximators, meaning that they are capable of accomplishing the approximation tasks regardless of any prior knowledge on the nature of the modeled system. According to our analysis, three distinctive parts of the background in the spectra were proposed. One of them is the so‐called peak base. The use of the neural network for the subtraction of the peak base is described further in this article. Copyright © 2012 John Wiley & Sons, Ltd.
Ion‐induced damage evaluation with Ar cluster ion beams
Authors: Yamamoto Yasuyuki , Ichiki Kazuya , Seki Toshio , Aoki Takaaki , Matsuo Jiro
Published: June 2012

Ion‐induced damage on organic materials has been evaluated with secondary ion mass spectrometry. However, conventional sputtering beams such as SF5+ and C60+ cannot etch organic materials without inducing damage, and evaluating the damage depth distribution in these materials is difficult. Large gas cluster ions can etch organic materials without damage, and in this study, the damaged layer thickness was evaluated by molecular depth profiling with Ar cluster ion beam. The characteristic molecular ions were not detected in the spectra after etching with Ar monomer beam, indicating that the chemical structures of phenyl‐C61‐butyric acid methyl ester (PCBM) and polystyrene (PS) were seriously damaged. The intensity of the fullerene molecular ion reached a peak at the depth of about 35 nm. For PS, the peak intensity of m/z 91 increased with sputtering depth and saturated at about 45 nm. These values agreed with the projection range of Ar+ in PCBM and PS, respectively. These results indicate that the ion‐induced damage depth was the same as the projection range of its ion. Copyright © 2012 John Wiley & Sons, Ltd.
Time‐of‐flight SIMS as a novel approach to unlocking the hypoxic properties of cancer
Authors: Armitage Emily G , Kotze Helen L , Fletcher John S , Henderson Alex , Williams Kaye J , Lockyer Nicholas P , Vickerman John C
Published: June 2012

It is known that hypoxia‐inducible factor 1 (HIF‐1) activity results in the coordinated up‐regulation of a large number of proteins that facilitate cell survival in tumours; however, the effect of HIF‐1 on cancer metabolism is less well characterised. With knowledge of the specific effect of HIF‐1 on cancer metabolism, biomarkers could be identified for which new drugs could be targeted. Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) offers the potential to analyse intact cells in situ and has a mass spectral coverage that is applicable to metabolic profiling. It has been used to analyse the effects of HIF‐1 on multicellular tumour models. Multicellular tumour spheroids (MTSs) have been cultured from human colon carcinoma cells with and without the expression of HIF‐1, and the surface of the cross sections of each MTS has been analysed. Because metabolic profiling is an emerging field in ToF‐SIMS, there is a requirement to determine which metabolites can be detected using this technique and which of those can be identified in complex mixtures within biological samples. For this, a selection of metabolites have been analysed, and the ToF‐SIMS standard spectra acquired have been used to localise metabolites in MTS sections. The comparison of metabolic profiles of MTSs with and without the expression of HIF‐1 has elucidated potential biomarkers for tumour survival in hypoxia, some of which may be HIF‐1 regulated. Copyright © 2012 John Wiley & Sons, Ltd.
A Pilot Study Examining the Effects of Kouk Sun Do on University Students with Anxiety Symptoms
Authors: Kim Jong‐Ho , Yang Heewon , Schroeppel Stephen
Published: June 2012

The effects of Kouk Sun Do (KSD), a mind–body exercise on mental health in university students, were investigated in this pilot study. University students (N = 30) with self‐reported anxiety symptoms were randomly assigned to either the treatment group or the waiting list control group. Eighteen participants (N = 18; seven in the treatment group and 11 in the waiting list control group) completed a pre‐test and a post‐test, and 12 participants dropped out before or during the intervention. Ten 70‐min KSD exercise sessions were conducted three times per week over a 4‐week period. Trait anxiety, depressive symptoms and general self‐efficacy in coping with stress were measured with the pre‐test and the post‐test. Qualitative data were collected using open‐ended questions regarding benefits of KSD at the last session. A two (group) by two (time) repeated‐measure analysis of variance was used to analyse the data. Trait anxiety and depressive symptoms decreased whereas general self‐efficacy increased over a 4‐week period. The treatment group had significantly reduced trait anxiety and depressive symptoms compared with the control group across time. Qualitative data provided support that the self‐induced relaxation effects of KSD may lead to reduced anxiety. Copyright © 2012 John Wiley & Sons, Ltd.
Feasibility and Effectiveness of a Chen‐style Tai Chi Programme for Stress Reduction in Junior Secondary School Students
Authors: Lee Linda Y. K. , Chong Yeuk Lan , Li Ngai Yin , Li Man Chung , Lin Lai Na , Wong Lee Yi , Wong Brian Kit , Yip Wing Ping , Hon Cho Hang , Chung Pui Kuen , Man Shuk Yee
Published: June 2012

Stress is common in junior secondary school students (JSSS). This study aimed to determine the feasibility and effectiveness of a Chen‐style Tai Chi programme for stress reduction in JSSS. A non‐equivalent pre‐test/post‐test control group design was adopted, and a convenience sample of 69 JSSS was recruited. The experimental group (n = 32) joined a Chen‐style Tai Chi programme, which included 10 sessions of 80‐minute Tai Chi training (one session per week). The control group (n = 37) proceeded with self‐study. Participants' stress levels were assessed using the Perceived Stress Scale. Feasibility was determined as the percentage of participants completing and attending the programme. Effectiveness was measured as the significant difference in changes in stress levels before and after the intervention between the two groups. Results preliminarily supported that the programme was feasible for JSSS. Completion rate was 100%, and attendance rate was 90%. However, no significant difference was noted in changes in stress levels before and after the intervention between the two groups. The potential health benefits of Tai Chi could not be detected owing to the restrictions imposed by the research setting and study limitations. The present study represents initial efforts in this direction and serves as reference for future study. Copyright © 2012 John Wiley & Sons, Ltd.
Reoxidation of Al‐Killed Steel by Ca(OH)2 in the High Basicity Slag
Authors: Jiang Fang , Liu Yan , Xie You , Cheng Guoguang
Published: June 2012

In the present work, reoxidation of Al‐killed steel by Ca(OH)2 in high basicity slag was investigated by using laboratory experiments at 1873 K in MgO crucibles with various amount of Ca(OH)2 addition into slag. The CaO–SiO2–Al2O3–MgO–Ca(OH)2 slags were used to study the effect of Ca(OH)2 on total oxygen content, aluminum loss, and FeO content in the slag. It was shown that total oxygen content decreased with the time when no Ca(OH)2 was added into the slag, but it first increased and then decreased with the time when the addition of Ca(OH)2 was made. Moreover, aluminum loss and FeO content in the slag increased with increasing Ca(OH)2 content.
Maternal phenylketonuria: low phenylalaninemia might increase the risk of intra uterine growth retardation
Authors: Teissier Raphaël , Nowak Emmanuel , Assoun Murielle , Mention Karine , Cano Aline , Fouilhoux Alain , Feillet François , Ogier Hélène , Oger Emmanuel , de Parscau Loïc ,   On behalf of the AFDPHE (Association Française pour le Dépistage et la Prévention des Handicaps de l'Enfant)
Published: June 2012

Background

Malformations and mental retardation in the offspring of women with Phenylketonuria (PKU) can be prevented by maintaining maternal blood Phenylalanine (PHE) within a target range (120–300 μmol/L) through a PHE‐restricted diet. In a former French study, a high and unexpected proportion of intra uterine growth retardation (IUGR) has been reported. Guidelines have been proposed to all French centres caring for maternal PKU since 2002.

Objective

To confirm IUGR and investigate its causes. The other goals were to assess the follow‐up of these pregnancies based on the new guidelines and the pertinence of these recommendations.

Design

Clinical, biological and ultrasound data of all pregnancies in PKU women in France, from 2002 to 2007 were retrospectively analyzed.

Results

Data from 115 pregnancies in 86 women with PKU were collected. Ninety percent of women had been informed of the risk of maternal PKU in the absence of a strict diet during pregnancy, 88 % of women had started a diet before conception, and 45 % of infants were born small for gestational age (birth length and/or weight ≤−2 SD). PHE intakes were lower in the group with IUGR from the fifth to the eighth month of pregnancy and duration of time spent at <120 μmol/L during pregnancy was associated with a higher risk of IUGR.

Conclusion

Hyperphenylalaninemia (HPA) is not the only risk factor for IUGR; PHE lower than 120 μmol/L could also be associated with the IUGR occurence. Even if the monitoring of these pregnancies has been improved since the initiation of guidelines, we would like to stress on the importance of the dietary aspect of the disease.
Partially Hydrolyzed Guar Gums Reduce Dietary Fatty Acid and Sterol Absorption in Guinea Pigs Independent of Viscosity
Authors: Santas Jonathan , Espadaler Jordi , Cuñé Jordi , Rafecas Magda
Published: June 2012

This study investigated the effect of two partially hydrolyzed guar gums (PHGG) on fatty acid and sterol excretion. PHGG were obtained by chemical hydrolysis of guar gum (GG) with H2O:EtOH (1:1) at 100 °C for 1 h (PHGG1) or 2 h (PHGG2). The viscosity of the PHGG in a 1 % (w/v) aqueous solution corresponded to that of a pseudoplastic fluid and was higher for PHGG1 than PHGG2. Guinea pigs (n = 8 per group) were fed high fat diets (17/100 g) that contained 12/100 g of cellulose, PHGG1, or PHGG2 for 4 weeks. Despite the differences in viscosity, the two PHGG exerted similar physiological effects. Compared to the control cellulose group, the body weight gain was lower in animals fed PHGG, although no effect on food consumption was observed. PHGG increased the excretion of fatty acids and neutral sterols, but not bile acids. Consumption of PHGG did not alter the fecal fatty acid profile, while intestinal bioconversion of sterols tended to increase in response to PHGG2. A reduction in the viscosity within the range tested did not correlate with losses in the hypocholesterolemic capacity of PHGG as both were effective in reducing plasma cholesterol. Thus, we conclude that the chemical hydrolysis of guar gum renders the gum suitable for inclusion in food products without significantly altering its beneficial health effects.
The effect of variable thermal diffusivity on kinematic models of subduction
Authors: Maierová P. , Chust T. , Steinle‐Neumann G. , Čadek O. , Čížková H.
Published: June 2012

We examine the influence of variable thermal properties on the thermal state of a subducting slab in the upper mantle and the transition zone by combining a kinematic slab model with models of thermal conductivity. Thermal diffusivity and conductivity models for major mantle minerals in the MgO‐SiO2 system are developed based on experimental measurements on these minerals at high pressure and temperature. The models show significantly higher thermal conductivity for stishovite and clinopyroxene compared to the Mg2SiO4 polymorphs and majorite garnet. In our subduction model we consider scenarios with a differentiated slab (basalt–harzburgite–pyrolite) in a pyrolite mantle and uniform composition for both the slab and the mantle (pyrolite or a pure Mg2SiO4‐based system). The role of highly conductive pyroxene is examined by taking it into account in some models and replacing it in others with majorite garnet. This choice has a strong influence on the thermal state of the slab, shifting the depth of the −1000 K temperature anomaly by as much as 100 km. This is caused by faster cooling of the plate at the surface and thermal insulating effects once subducted. Temperature differences between models with variable thermal diffusivity and those with constant parameters can reach ∼125 K, i.e. 10% of total thermal anomalies of the slab relative to an average geotherm. Taking into account the stable mineral phases we evaluate density variations between different models and find that variable thermal diffusivity results in a modest increase of negative buoyancy of the slab.
Group calls for space policies to transcend politics
Authors: Showstack Randy
Published: June 2012

At a 22 May briefing, the American Institute of Aeronautics and Astronautics (AIAA) called on Congress to “establish space exploration policy goals which transcend partisan political differences.” AIAA president and former NASA administrator Michael Griffin said the “goal of establishing human capability to b e a space‐faring species is not a short‐term goal,” nor is it a goal that belongs to only one political party. “We will not reach long‐term goals without a stable, coherent, sensible plan that transcends elections and leaders,” said Griffin, who has provided advice to Republican U.S. presidential candidate Mitt Romney. Griffin pointed to NASA's 2008 authorization as providing the kind of vision needed for NASA. The act called for human return to the Moon and preparation for the capability for permanent bases on the Moon, among other things, he said. “That's the kind of thing that we need. All of the goals espoused by the 2008 act were long‐term, generational, strategic in scope,” Griffin said, adding that the act, which had bipartisan support, demonstrated “the kind of societal support, rather than political support, that I believe our space program deserves.”
Characterizing atmospheric waves on Venus, Earth, and Mars
Authors: Wilson Colin F. , Piccialli Arianna
Published: June 2012

Atmospheric Waves Workshop; Noordwijk, Netherlands, 9–10 November 2011 Experts in observations and modeling of atmospheric waves from the Earth and planetary atmospheric science communities came together at a November 2011 workshop held at the European Space Agency's (ESA) European Space Research and Technology Centre ( ESTEC) site in the Netherlands to discuss the nature of waves observed in Venus's atmosphere and their comparison to those on Earth and Mars. ESA's Venus Express (VEx) satellite and ground‐based observers find atmospheric waves at many scales. Migrating solar tides and other planetary‐ scale waves are observed in cloud‐ tracking wind vectors and temperature fields. Mesoscale gravity waves (GWs) can also be seen at a variety of levels from the cloud base up to the thermosphere, evident in imagery and in vertical profiles of temperature, density, and aerosol abundance. This workshop focused particularly on GWs, as their role in the atmospheric circulation is still poorly understood.
Changing pressure drives lake methane emissions
Authors: Schultz Colin
Published: June 2012

Within the fine‐grained sediments of a lake bed, microbes feeding on carbon‐rich organic matter can pump out substantial quantities of methane. Recent research has shown that this flow of methane, when combined with other forms of carbon emissions, is enough to turn some lakes into net sources of atmospheric carbon. Investigations over the past decade have shown that ebullition—the propagation of bubbles up to the surface—is an important methane transport mechanism in lakes. Uncertainty remains, however, around figuring out the drivers behind, or the magnitude and frequency of, bubble‐mediated methane emissions.
Charged nanograins in the Enceladus plume
Authors: Balcerak Ernie
Published: June 2012

Enceladus, which orbits Saturn in the planet's E ring, is one of the few geologically active moons in the outer solar system. It emits a large plume that contains water‐ice dust grains. Hill et al. used instruments on the Cassini spacecraft to observe charged nanometer sized grains of water ice emanating from Enceladus. The authors measured the charge‐to‐mass ratio of each grain and found that the most likely charge per grain is 1 electron charge. In addition, negatively charged grains outnumber positively charged ones by a factor of more than 2000. On the basis of their analysis, the researchers argue that the nanograins are not charged when they leave Enceladus but become charged as they encounter electrons in the plasma around Enceladus. (Journal of Geophysical Research‐Space Physics, doi:10.1029/2011JA017218, 2012)
Energetic neutral atom observations of magnetic anomalies on the lunar surface
Authors: Vorburger A. , Wurz P. , Barabash S. , Wieser M. , Futaana Y. , Holmström M. , Bhardwaj A. , Asamura K.
Published: June 2012

SARA, the Sub‐KeV Atom Analyzer, on board Chandrayaan‐1 recorded the first image of a minimagnetosphere above a lunar magnetic anomaly using energetic neutral atoms (ENAs). It was shown that this magnetosphere, which is located near the Gerasimovich crater, is able to reduce the solar wind ion flux impinging onto the lunar surface by more than 50%. Following this first observation, we investigated all magnetic anomalies that are in the SARA data set. We searched for a possible correlation between the solar wind plasma parameters (dynamic pressure, magnetic field), the local magnetic field, and the reduction in the reflected hydrogen ENA flux (henceforth called shielding efficiency). Having analyzed all observations by SARA, we discovered that the Gerasimovich magnetic anomaly is topologically a very simple, large‐scale magnetic structure, which is favorable for this kind of investigation. Most other magnetic anomalies on the lunar surface have more small‐scale features in their magnetic field structure, which complicates the interpretation of the observed data. We find a clear correlation between the plasma parameters and the shielding efficiency for the Gerasimovich case. For the other observed anomalies only about half of the cases showed such a correlation. We therefore conclude that the solar wind ions‐magnetic anomaly interaction is in general more complex than in the Gerasimovich case.
Bounce‐averaged diffusion coefficients due to resonant interaction of the outer radiation belt electrons with oblique chorus waves computed in a realistic magnetic field model
Authors: Orlova Ksenia G. , Shprits Yuri Y. , Ni Binbin
Published: June 2012

We present the results of calculations of the bounce‐averaged pitch angle, mixed, and momentum diffusion coefficients in a dipole and two realistic field models (the T01s model for quiet and storm conditions). We consider resonant interactions of the outer radiation belt electrons with oblique chorus waves. We demonstrate that on the dayside, the use of a realistic magnetic field versus a dipole field only makes a significant difference for small equatorial pitch angles at energies larger than E = 1 MeV. On the nightside, the differences between the scattering rates calculated in the Tsyganenko and dipole models can reach several orders of magnitude at various equatorial pitch angles for electrons with E ≥ 0.5 MeV. The most significant changes in the scattering rates computed in the realistic and dipole magnetic fields occur during the geomagnetically active conditions. On the nightside, for E ≥ 0.5 MeV, the diffusion coefficients calculated in the Tsyganenko field show significant scattering near the edge of the loss cone that can produce loss of electrons to the atmosphere, while in the dipole model there is no scattering at small equatorial pitch angles. Our computations in the realistic field show that resonant interactions between electrons with E ≤ 1 MeV and chorus waves can be an effective net loss mechanism on both the dayside and the nightside. To explain the differences in the scattering rates associated with a change in the magnetic field model, we present the contribution of various resonant harmonics to the diffusion and examine the changes in the resonance condition.
Solar forcing of Florida Straits surface salinity during the early Holocene
Authors: Schmidt Matthew W. , Weinlein William A. , Marcantonio Franco , Lynch‐Stieglitz Jean
Published: June 2012

Previous studies showed that sea surface salinity (SSS) in the Florida Straits as well as Florida Current transport covaried with changes in North Atlantic climate over the past two millennia. However, little is known about earlier Holocene hydrographic variability in the Florida Straits. Here, we combine Mg/Ca‐paleothermometry and stable oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber (white variety) from Florida Straits sediment core KNR166–2 JPC 51 (24° 24.70′ N, 83° 13.14′ W, 198 m deep) to reconstruct a high‐resolution (∼25 yr/sample) early to mid Holocene record of sea surface temperature and δ18OSW (a proxy for SSS) variability. After removing the influence of global δ18OSW change due to continental ice volume variability, we find that early Holocene SSS enrichments are associated with increased evaporation/precipitation ratios in the Florida Straits during periods of reduced solar forcing, increased ice rafted debris in the North Atlantic and the development of more permanent El Niño–like conditions in the eastern equatorial Pacific. When considered with previous high‐resolution reconstructions of Holocene tropical atmospheric circulation changes, our results provide evidence that variations in solar forcing over the early Holocene had a significant impact on the global tropical hydrologic cycle.
Multicultural Psychology in Iceland: Meeting the Needs of a Changing Society
Authors: Hermannsdóttir Björg S. , Ægisdóttir Stefanía , Gerstein Lawrence H.
Published: June 2012

Cultural diversity in Iceland has increased substantially in recent years, but research on multicultural topics within Icelandic psychology is still very limited. Icelandic psychologists' self-reported multicultural competence and motivation to engage in multicultural learning and work were examined in relation to their perceived threat of international immigrants in Iceland, their contact with immigrants, and their attitudes toward them. One hundred thirty-one Icelandic psychologists (87 women, 44 men) participated in the study. A canonical correlation analysis (CCA) revealed that lesser perceived threat of immigrants to Icelandic customs, culture, economy, and security, and more positive attitudes toward and contact with people of international origin were associated with greater knowledge of and greater motivation to work with that population. It was also found that more positive attitudes and greater perceived threats to economy and security were associated with increased multicultural awareness. These findings have relevance for the development of multicultural training for current and future psychologists in Iceland.
A Human Being Is Free: The Phenomenological Experience of Liberation in Namibia
Authors: Bartholomew Theodore T.
Published: June 2012

Many oppressed groups throughout Africa have successfully engaged in struggles for liberation to oust colonial rule. To study the psychological experiences of liberation in a specific context, the U.S. researcher traveled to Namibia and, using a phenomenological approach, explored the meanings people ascribed to their independence from South Africa. Six individual interviews were conducted with Ovambo Namibians. Seven themes emerged from 280 invariant structures and their 280 corresponding meaning units: Continuous and Inescapable Oppression, the Tipping Point, Family Ecology and the Choice, Participation in the Struggle, Reconciliation, Dreams of Freedom Realized, and Left Wanting: Disenchantment and Lost Democracy. Findings revealed that liberation was an arduous and traumatic experience and that resilience was required to endure the liberation struggle. Although the experience of liberation among Namibians may share features such as posttraumatic stress and the role of resilience with other struggles, the particular context and history led to unique elements, including rifts that developed within families during the struggle and dissatisfaction with unfulfilled promises.
c(4 × 2) and related structural units on the SrTiO3(001) surface: Scanning tunneling microscopy, density functional theory, and atomic structure
Authors: Becerra-Toledo A. E. , Marshall M. S. J. , Castell M. R. , Marks L. D.
Published: June 2012

Density functional theory is used to simulate high-bias, constant-current scanning tunneling micrographs for direct comparison with experimental images. Coupled to previous spectroscopic data, these simulations are used to determine the atomic structure of Ti-rich nanostructures on strontium titanate (001) surfaces. These nanostructures have three consecutive TiOx surface layers and exploit the distinctive structural motif of the c(4 × 2) reconstruction as their main building block. A structural model of a characteristic triline defect is also proposed.
A divide and conquer real-space approach for all-electron molecular electrostatic potentials and interaction energies
Authors: Losilla S. A. , Sundholm D.
Published: June 2012

A computational scheme to perform accurate numerical calculations of electrostatic potentials and interaction energies for molecular systems has been developed and implemented. Molecular electron and energy densities are divided into overlapping atom-centered atomic contributions and a three-dimensional molecular remainder. The steep nuclear cusps are included in the atom-centered functions making the three-dimensional remainder smooth enough to be accurately represented with a tractable amount of grid points. The one-dimensional radial functions of the atom-centered contributions as well as the three-dimensional remainder are expanded using finite element functions. The electrostatic potential is calculated by integrating the Coulomb potential for each separate density contribution, using our tensorial finite element method for the three-dimensional remainder. We also provide algorithms to compute accurate electron-electron and electron-nuclear interactions numerically using the proposed partitioning. The methods have been tested on all-electron densities of 18 reasonable large molecules containing elements up to Zn. The accuracy of the calculated Coulomb interaction energies is in the range of 10−3 to 10−6 Eh when using an equidistant grid with a step length of 0.05 a0.
Absolute x-ray energy calibration over a wide energy range using a diffraction-based iterative method
Authors: Hong Xinguo , Chen Zhiqiang , Duffy Thomas S.
Published: June 2012

In this paper, we report a method of precise and fast absolute x-ray energy calibration over a wide energy range using an iterative x-ray diffraction based method. Although accurate x-ray energy calibration is indispensable for x-ray energy-sensitive scattering and diffraction experiments, there is still a lack of effective methods to precisely calibrate energy over a wide range, especially when normal transmission monitoring is not an option and complicated micro-focusing optics are fixed in place. It is found that by using an iterative algorithm the x-ray energy is only tied to the relative offset of sample-to-detector distance, which can be readily varied with high precision of the order of 10−5 –10−6 spatial resolution using gauge blocks. Even starting with arbitrary initial values of 0.1 Å, 0.3 Å, and 0.4 Å, the iteration process converges to a value within 3.5 eV for 31.122 keV x-rays after three iterations. Different common diffraction standards CeO2, Au, and Si show an energy deviation of 14 eV. As an application, the proposed method has been applied to determine the energy-sensitive first sharp diffraction peak of network forming GeO2 glass at high pressure, exhibiting a distinct behavior in the pressure range of 2–4 GPa. Another application presented is pair distribution function measurement using calibrated high-energy x-rays at 82.273 keV. Unlike the traditional x-ray absorption-based calibration method, the proposed approach does not rely on any edges of specific elements, and is applicable to the hard x-ray region where no appropriate absorption edge is available.
Magnetoresistance and transistor-like behavior of a double quantum-dot via crossed Andreev reflections
Authors: Siqueira E. C. , Cabrera G. G.
Published: June 2012

The electric current and the magnetoresistance effect are studied in a double quantum-dot system, where one of the dots QDa is coupled to two ferromagnetic electrodes (F1,F2), while the second QDb is connected to a superconductor S. For energy scales within the superconductor gap, electric conduction is allowed by Andreev reflection processes. Due to the presence of two ferromagnetic leads, non-local crossed Andreev reflections are possible. We found that the magnetoresistance sign can be changed by tuning the external potential applied to the ferromagnets. In addition, it is possible to control the current of the first ferromagnet (F1) through the potential applied to the second one (F2). We have also included intradot interaction and gate voltages at each quantum dot and analyzed their influence through a mean field approximation. The interaction reduces the current amplitudes with respect to the non-interacting case, but the switching effect still remains as a manifestation of quantum coherence, in scales of the order of the superconductor coherence length.
Origin of self-heating effect induced asymmetrical degradation behavior in InGaZnO thin-film transistors
Authors: Hsieh Tien-Yu , Chang Ting-Chang , Chen Te-Chih , Tsai Ming-Yen , Chen Yu-Te , Chung Yi-Chen , Ting Hung-Che , Chen Chia-Yu
Published: June 2012

This letter investigates asymmetrical degradation behavior induced by the self-heating effect in InGaZnO thin-film transistors. Both the surrounding oxide and other thermal insulating material, as well as the low thermal conductivity of the InGaZnO layer itself, cause the self-heating effect in InGaZnO thin-film transistors. The heated channel layer enhances threshold voltage shift, and the evolution of threshold voltage shift is found to be dominated by charge-trapping effect. Moreover, a non-uniform distribution of channel carrier concentration leads to an uneven temperature distribution through the InGaZnO active layer and results in the asymmetrical degradation behavior after self-heating operation.
A molecular dynamics examination of the relationship between self-diffusion and viscosity in liquid metals
Authors: Lü Yongjun , Cheng Hao , Chen Min
Published: June 2012

The self-diffusion coefficients D and the viscosities η of elemental Ni, Cu, and Ni-Si alloys have been calculated over a wide temperature range by molecular dynamics simulations. For elemental Ni and Cu, Arrhenius-law variations of D and η with temperature dominate. The temperature dependence of Dη can be approximated by a linear relation, whereas the Stokes-Einstein relation is violated. The calculations of D and η are extended to the regions close to the crystallization of Ni95Si5, Ni90Si10, and the glass transitions of Ni80Si20 and Ni75Si25. The results show that both D and η strongly deviate from the Arrhenius law in the vicinity of phase transitions, exhibiting a power-law divergence. We find a decoupling of diffusion and viscous flow just above the crystallization of Ni95Si5 and Ni90Si10. For the two glass-forming alloys, Ni80Si20 and Ni75Si25, the relation Dη = const is obeyed as the glass transition is approached, indicating a dynamic coupling as predicted by the mode-coupling theory. This coupling is enhanced with increasing Si composition and at 25%, Si spans a wide temperature range through the melting point. The decoupling is found to be related to the distribution of local ordered structure in the melts. The power-law governing the growth of solid-like clusters prior to crystallization creates a dynamic heterogeneity responsible for decoupling.
Application of the Z-scan technique to determine the optical Kerr coefficient and two-photon absorption coefficient of magnetite nanoparticles colloidal suspension
Authors: Vivacqua Marco , Espinosa Daniel , Martins Figueiredo Neto Antônio
Published: June 2012

We investigate the occurrence of the optical Kerr effect and two-photon absorption when an oil-based magnetic Fe3O4 nanoparticles colloidal suspension is illuminated with high intensity femtosecond laser pulses. The frequency of the pulses is controlled and the Z-scan technique is employed in our measurements of the nonlinear optical Kerr coefficient (n2) and two-photon absorption coefficient (β). From these values it was possible to calculate the real and imaginary parts of the third-order susceptibility. We observed that increasing the pulse frequency, additional physical processes take place, increasing artificially the absolute values of n2 and β. The experimental conditions are discussed to assure the obtention of reliable values of these nonlinear optical parameters, which may be useful in all-optical switching and optical power limiting applications.
Crowding effect on helix-coil transition: Beyond entropic stabilization
Authors: Koutsioubas A. , Lairez D. , Combet S. , Fadda G. C. , Longeville S. , Zalczer G.
Published: June 2012

We report circular dichroism measurements on the helix-coil transition of poly(L-glutamic acid) in solution with polyethylene glycol (PEG) as a crowding agent. The PEG solutions have been characterized by small angle neutron scattering and are well described by the picture of a network of mesh size ξ, usual for semi-dilute chains in good solvent. We show that the increase of PEG concentration stabilizes the helices and increases the transition temperature. But more unexpectedly, we also notice that the increase of concentration of crowding agent reduces the mean helix extent at the transition, or in other words reduces its cooperativity. This result cannot be taken into account for by an entropic stabilization mechanism. Comparing the mean length of helices at the transition and the mesh size of the PEG network, our results strongly suggest two regimes: helices shorter or longer than the mesh size.
Reproducible domain wall pinning by linear non-topographic features in a ferromagnetic nanowire
Authors: Basith M. A. , McVitie S. , McGrouther D. , Chapman J. N.
Published: June 2012

We demonstrate that for multilayered magnetic nanowires, where the thickness and composition of the individual layers have been carefully chosen, domain walls can be pinned at non-topographic sites created purely by ion irradiation in a focused ion beam system. The pinning results from irradiation induced alloying leading to magnetic property modification only in the affected regions. Using Lorentz transmission electron microscopy, we have studied the pinning behavior of domain walls at the irradiation sites. Depending on the irradiation dose, a single line feature not only pinned the domain walls but also acted to control their structure and the strength of their pinning.
Improved and color tunable electroluminescence from n-ZnO/HfO2/p-GaN heterojunction light emitting diodes
Authors: Huang Huihui , Fang Guojia , Li Yuan , Li Songzhan , Mo Xiaoming , Long Hao , Wang Haoning , Carroll David L. , Zhao Xingzhong
Published: June 2012

n-ZnO/HfO2/p-GaN based heterojunction light emitting diodes were fabricated using a radio frequency magnetron sputtering system. The electroluminescence measurements revealed that dominant violet emissions centered at around 415 nm were emitted and improved performances were observed for the devices with the HfO2 intermediate layer; the color of the devices could be tuned from violet (0.18, 0.10) to cold white (0.22, 0.20) by varying the Ar/O2 flow ratio during the deposition of HfO2, which are probably ascribed to the deep level emission bands in ZnO. The results were studied by peak-deconvolution with Gaussian functions and were discussed in terms of band diagram of the heterojunctions.
Graphene-diamond hybrid structure as spin-polarized conducting wire with thermally efficient heat sinks
Authors: Shiga Takuma , Konabe Satoru , Shiomi Junichiro , Yamamoto Takahiro , Maruyama Shigeo , Okada Susumu
Published: June 2012

We have theoretically investigated electronic, magnetic, and thermal properties of a graphene-diamond hybrid structure consisting of a graphene nanoribbon with zigzag edges connected to diamond surfaces. From the first-principles calculation, we found that the hybrid structure is stable and that the ferro-magnetically ordered edge state appears around the graphene-diamond. On the other hand, from the non-equilibrium molecular dynamics simulations, we found that the thermal conductance at the interface between the graphene and diamond is 7.01±0.05GWm-2K-1 at the room temperature, which is much larger than that for covalently bonded interface between carbon nanotube and silicon. Thus, we propose that the hybrid structure is a potential candidate for spin-polarized conducting wires with thermally efficient heat sinks.
Micro-Brillouin spectroscopy mapping of the residual density field induced by Vickers indentation in a soda-lime silicate glass
Authors: Tran H. , Clément S. , Vialla R. , Vandembroucq D. , Rufflé B.
Published: June 2012

High-resolution Brillouin scattering is used to achieve 3-dimensional maps of the longitudinal acoustic mode frequency shift in soda-lime silicate glasses subject to Vickers indentations. Assuming that residual stress-induced effects are simply proportional to density changes, residual densification fields are obtained. The density gradient is nearly isotropic, confirming earlier optical observations made on a similar glass. The results show that Brillouin micro-spectroscopy opens the way to a fully quantitative comparison of experimental data with predictions of mechanical models for the identification of a constitutive law.
Effect of nonlinear absorption on self focusing of short laser pulse in a plasma
Authors: Kumar Ashok
Published: June 2012

Paraxial theory of self focusing of short pulse laser in a plasma under transient and saturating effects of nonlinearity and nonlinear absorption is developed. The absorption is averaged over the cross-section of the beam and is different for different time segments of the pulse. The electron temperature includes cumulative effect of previous history of temporal profile of pulse intensity, however, the ambipolar diffusion is taken to be faster than the heating time. The relaxation effect causes self-distortion of the pulse temporal profile where as the nonlinear absorption weakens self focusing. For the pulses of duration comparable to the electron ion collision time, the front part of the pulse gets defocused where as the latter part undergoes periodic self focusing.
Shear instability of nanocrystalline silicon carbide during nanometric cutting
Authors: Goel Saurav , Luo Xichun , Reuben Robert L.
Published: June 2012

The shear instability of the nanoscrystalline 3C-SiC during nanometric cutting at a cutting speed of 100 m/s has been investigated using molecular dynamics simulation. The deviatoric stress in the cutting zone was found to cause sp3-sp2 disorder resulting in the local formation of SiC-graphene and Herzfeld-Mott transitions of 3C-SiC at much lower transition pressures than that required under pure compression. Besides explaining the ductility of SiC at 1500 K, this is a promising phenomenon in general nanoscale engineering of SiC. It shows that modifying the tetrahedral bonding of 3C-SiC, which would otherwise require sophisticated pressure cells, can be achieved more easily by introducing non-hydrostatic stress conditions.
Ultra low bending loss equiangular spiral photonic crystal fibers in the terahertz regime
Authors: Agrawal Arti , Kejalakshmy N. , Uthman M. , Rahman B. M. A. , Kumar A. , Grattan K. T. V.
Published: June 2012

An Equiangular Spiral Photonic Crystal Fiber (ES-PCF) design in Topas® for use in the Terahertz regime is presented. The design shows ultra low bending loss and very low confinement loss compared to conventional Hexagonal PCF (H-PCF). The ES-PCF has excellent modal confinement properties, together with several parameters to allow the optimization of the performance over a range of important characteristics. A full vector Finite Element simulation has been used to characterize the design which can be fabricated by a range of techniques including extrusion and drilling.
High thermoelectric performance of solid solutions CuGa1−xInxTe2 (x = 0–1.0)
Authors: Li Yapeng , Meng Qingsen , Deng Yuan , Zhou Hong , Gao Yulan , Li Yiyun , Yang Jiangfeng , Cui Jiaolin
Published: June 2012

We synthesized the solid solutions CuGa1−xInxTe2 (x = 0–1.0) by isoelectronic substitution of element In (Ga) for Ga(In) in the CuMTe2 (M = Ga, In) lattices and examined their thermoelectric properties. The structure upon substitution provides much high Seebeck coefficient (α), relatively low thermal (κ), and electrical conductivity (σ). AT 701 K, the α, σ, and κ are 283.15 µV K−1, 1.15 × 104 Ω−1 m−1, and 0.71 W m−1 K−1, respectively, for CuGa0.36In0.64Te2, which give the figure of merit (ZT) of 0.91, about two times those of the mother compounds CuGaTe2 and CuInTe2. This material holds great application perspectives at intermediate temperatures.
Communication: The structures of small cationic gas-phase platinum clusters
Authors: Harding Dan J. , Kerpal Christian , Rayner David M. , Fielicke André
Published: June 2012

The structures of small platinum clusters \documentclass[12pt]{minimal}\begin{document}${\rm Pt}_{3-5}^+$\end{document} Pt 3−5+ are determined using far-infrared multiple photon dissociation spectroscopy of their argon complexes combined with density functional theory calculations. The clusters are found to have compact structures, and \documentclass[12pt]{minimal}\begin{document}${\rm Pt}_{4}^+$\end{document} Pt 4+ and \documentclass[12pt]{minimal}\begin{document}${\rm Pt}_{5}^+$\end{document} Pt 5+ already favor three-dimensional geometries, in contrast to a number of earlier predictions. Challenges in applying density functional theory to 3rd row transition metal clusters are addressed. Preliminary calculations suggest that the effects of spin-orbit coupling do not change the favoured lowest-energy isomers.
Communication: Phase incremented echo train acquisition in NMR spectroscopy
Authors: Baltisberger Jay H. , Walder Brennan J. , Keeler Eric G. , Kaseman Derrick C. , Sanders Kevin J. , Grandinetti Philip J.
Published: June 2012

We present an improved and general approach for implementing echo train acquisition (ETA) in magnetic resonance spectroscopy, particularly where the conventional approach of Carr-Purcell-Meiboom-Gill (CPMG) acquisition would produce numerous artifacts. Generally, adding ETA to any N-dimensional experiment creates an N + 1 dimensional experiment, with an additional dimension associated with the echo count, n, or an evolution time that is an integer multiple of the spacing between echo maxima. Here we present a modified approach, called phase incremented echo train acquisition (PIETA), where the phase of the mixing pulse and every other refocusing pulse, ϕP, is incremented as a single variable, creating an additional phase dimension in what becomes an N + 2 dimensional experiment. A Fourier transform with respect to the PIETA phase, ϕP, converts the ϕP dimension into a Δp dimension where desired signals can be easily separated from undesired coherence transfer pathway signals, thereby avoiding cumbersome or intractable phase cycling schemes where the receiver phase must follow a master equation. This simple modification eliminates numerous artifacts present in NMR experiments employing CPMG acquisition and allows “single-scan” measurements of transverse relaxation and J-couplings. Additionally, unlike CPMG, we show how PIETA can be appended to experiments with phase modulated signals after the mixing pulse.
Native plant diversity in tropical savannas decreases when exotic pasture grass cover increases
Authors: Kutt A. S. , Kemp J. E.
Published: June 2012

The invasion of exotic plants into savanna ecosystems can disrupt the natural pattern of vegetation. Indian couch Bothriochloa pertusa was introduced into Australia as a species for rehabilitation of degraded grazing land. In this study the effect of increasing B. pertusa cover on native plant diversity and possible mechanisms of its spread were examined. Forty sites were sampled in uncleared Queensland rangelands with a range of B. pertusa and Bothriochloa ewartiana (a native species) cover. The mean number of native species per quadrat declined with increasing B. pertusa cover but remained stable over sites with increasing B. ewartiana cover. Mean species richness accumulated at a significantly lower rate for sites with B. pertusa present. Canonical analysis of principle coordinates suggested that three groups of sites, ranging from low to high species richness and cover of native plants, were correlated along gradients of B. pertusa cover, grazing intensity and basal area of dead trees. Generalised linear modelling indicated significant negative relationships between B. pertusa cover and total ground cover, forbs and perennial grass richness and cover, and cover of nine native perennial tussock grasses (Aristida leptopoda, B. decipiens, B. ewartiana, Chrysopogon fallax, Dichanthium fecundum, D. sericeum, Heteropogon contortus, H. triticeus and Themeda triandra). This study suggests that an increase in B. pertusa is associated with a substantial change in the cover and species richness of native plant communities. This was considered to occur via competitive effects as well as a result of cattle grazing, rainfall deficit and tree death. Regardless of the mechanism, continued spread of exotic pasture species has the potential to cause significant changes to rangeland biodiversity.