bluuebunny/crossref_metadata_2025 huggingface dataset:
Large‐amplitude monochromatic ULF waves detected by Kaguya at the Moon
Authors: Nakagawa Tomoko , Nakayama Akihito , Takahashi Futoshi , Tsunakawa Hideo , Shibuya Hidetoshi , Shimizu Hisayoshi , Matsushima Masaki
Published: February 2012

Large amplitude, monochromatic ultra low frequency (ULF) waves were detected by MAP/LMAG magnetometer onboard Kaguya during the period from 1 January 2008 to 30 November 2008 on its orbit 100 km above the lunar surface. The dominant frequency was 8.3 × 10−3 – 1.0 × 10−2 Hz, corresponding to the periods of 120 s – 100 s. The amplitude was as large as 3 nT. They were observed in 10% of the time when the moon was in the solar wind far upstream of the Earth's bow shock. They were detected only by Kaguya on the orbit around the moon, but not by ACE in the upstream solar wind. The occurrence rate was high above the terminator and on the dayside surface. The direction of the propagation was not exactly parallel to the interplanetary magnetic field, but showed a preference to the direction of the magnetic field and the direction perpendicular to the surface of the moon below the spacecraft. The sense of rotation of the magnetic field was left‐handed with respect to the magnetic field in 53% of the events, while 47% showed right‐handed polarization. The possible generation mechanism is the cyclotron resonance of the magnetohydrodynamic waves with the solar wind protons reflected by the moon. The energy of the reflected protons can account for the energy of the ULF waves. The propagation direction which are not parallel to the incident solar wind flow can explain the observed frequency and the nearly equal percentages of the left‐handed and right‐handed polarizations.
Kinetic instabilities in the lunar wake: ARTEMIS observations
Authors: Tao J. B. , Ergun R. E. , Newman D. L. , Halekas J. S. , Andersson L. , Angelopoulos V. , Bonnell J. W. , McFadden J. P. , Cully C. M. , Auster H.‐U. , Glassmeier K.‐H. , Larson D. E. , Baumjohann W. , Goldman M. V.
Published: February 2012

The Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission is a new two‐probe lunar mission derived from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. On 13 February 2010, one of the two probes, ARTEMIS P1 (formerly THEMIS‐B), made the first lunar wake flyby of the mission. We present detailed analysis of the electrostatic waves observed on the outbound side of the flyby that were associated with electron beams. Halekas et al. (2011) derived a net potential across the lunar wake from observations and suggested that the net potential generated the observed electron beams and the electron beams in turn excited the observed electrostatic waves due to kinetic instabilities. The wavelengths and velocities of the electrostatic waves are estimated, using high‐resolution electric field instrument data with cross‐spectrum analysis and cross‐correlation analysis. In general, the estimated wavelengths vary from a few hundred meters to a couple of thousand meters. The estimated phase velocities are on the order of 1000 km s−1. In addition, we perform 1‐D Vlasov simulations to help identify the mode of the observed electrostatic waves. We conclude that the observed electrostatic waves are likely on the electron beam mode branch.
Characteristics of bubble clouds at various wind speeds
Authors: Anguelova Magdalena D. , Huq Pablo
Published: February 2012

We present the results of a laboratory study on bubble clouds characteristics (length, depth of penetration, width, and void fraction) in fresh water for wind speeds from 9 to 16 m s−1. Temporal and spatial changes of these characteristics and their statistics were extracted from video images from side and top views. Cloud characteristics were scaled with the period T, wavelength L, phase speed c, and significant wave height Hs of the dominant wave. The lifetime of the bubble cloud comprises formation, growth and decay stages. The bubble cloud moves forward horizontally with the wave for the initial 1/3 of the wave period at approximately half the wave phase speed (0.5c). The subsequent dominant motion of the bubble cloud in the wave trough is vertical with a mean speed half that of rising bubbles. The void fraction is as high as 80–99% in the first quarter (0.25T) of the bubble cloud lifetime corresponding to wave phase of up to 90°. The void fraction decreases steadily to about 20–30% at 0.7T (wave phase of ∼270°). Probability density functions of the bubble cloud characteristics show that the bubble cloud length varies from 0.1L to 0.7L; the bubble cloud thickness ranges from 0.5Hs to 2Hs. Scaled bubble cloud characteristics and the cloud void fraction vary weakly with the wind speed for the growth stage. Residual void fractions can persist for long times O(100T).
Global model comparison of heterogeneous ice nucleation parameterizations in mixed phase clouds
Authors: Yun Yuxing , Penner Joyce E.
Published: February 2012

A new aerosol‐dependent mixed phase cloud parameterization for deposition/condensation/immersion (DCI) ice nucleation and one for contact freezing are compared to the original formulations in a coupled general circulation model and aerosol transport model. The present‐day cloud liquid and ice water fields and cloud radiative forcing are analyzed and compared to observations. The new DCI freezing parameterization changes the spatial distribution of the cloud water field. Significant changes are found in the cloud ice water fraction and in the middle cloud fractions. The new DCI freezing parameterization predicts less ice water path (IWP) than the original formulation, especially in the Southern Hemisphere. The smaller IWP leads to a less efficient Bergeron‐Findeisen process resulting in a larger liquid water path, shortwave cloud forcing, and longwave cloud forcing. It is found that contact freezing parameterizations have a greater impact on the cloud water field and radiative forcing than the two DCI freezing parameterizations that we compared. The net solar flux at top of atmosphere and net longwave flux at the top of the atmosphere change by up to 8.73 and 3.52 W m−2, respectively, due to the use of different DCI and contact freezing parameterizations in mixed phase clouds. The total climate forcing from anthropogenic black carbon/organic matter in mixed phase clouds is estimated to be 0.16–0.93 W m−2using the aerosol‐dependent parameterizations. A sensitivity test with contact ice nuclei concentration in the original parameterization fit to that recommended by Young (1974) gives results that are closer to the new contact freezing parameterization.
Satellite remote sensing analysis of the 2010 Eyjafjallajökull volcanic ash cloud over the North Sea during 4–18 May 2010
Authors: Christopher Sundar A. , Feng Nan , Naeger Aaron , Johnson Ben , Marenco Franco
Published: February 2012

Using the Moderate Resolution Imaging Spectroradiometer (MODIS), Spinning Enhanced Visible and Infrared Imager (SEVIRI), Clouds and the Earth's Radiant Energy System (CERES) instrument, and BaE146 aircraft data sets, we provide an overview of volcanic ash spatial distribution for six days (4–18 May 2010) and assess their properties and radiative impacts for 17 May primarily over the North Sea. We describe spectral signatures of volcanic ash, compare the MODIS‐retrieved 550 nm aerosol optical thickness (AOT) and effective radii with the aircraft data, and then assess the change in radiative fluxes at the top of atmosphere using CERES. Our results indicate that the MODIS and SEVIRI thermal channels are adept at identifying volcanic ash near the source. However, the volcanic ash far from the volcanic source, especially over land, is contaminated by surface/atmospheric features. We assess the 17 May case in detail and show that MODIS AOTs (0.23–0.86) are higher than the aircraft values (0.07–0.54), probably due to different aerosol models used in the retrieval process. The MODIS effective radii values are between 0.4 and 0.9 μm with fine mode fraction values between 0.4 and 0.7. The aircraft‐derived effective radii values are between 0.82 and 1.2 μm. The TOA shortwave radiative forcing for unit AOT of volcanic ash aerosols at the time of the satellite overpass is −77 ± 4.0 W m−2 and is larger than the longwave forcing per unit optical depth (11 ± 1.2 W m−2) by seven times indicating that ash could significantly impact radiative energy fluxes.
Structure of shock compressed model basaltic glass: Insights from O K‐edge X‐ray Raman scattering and high‐resolution27Al NMR spectroscopy
Authors: Lee Sung Keun , Park Sun Young , Kim Hyo‐Im , Tschauner Oliver , Asimow Paul , Bai Ligang , Xiao Yuming , Chow Paul
Published: February 2012

The detailed atomic structures of shock compressed basaltic glasses are not well understood. Here, we explore the structures of shock compressed silicate glass with a diopside–anorthite eutectic composition (Di64An36), a common Fe‐free model basaltic composition, using oxygen K‐edge X‐ray Raman scattering and high‐ resolution27Al solid‐state NMR spectroscopy and report previously unknown details of shock‐induced changes in the atomic configurations. A topologically driven densification of the Di64An36glass is indicated by the increase in oxygen K‐edge energy for the glass upon shock compression. The first experimental evidence of the increase in the fraction of highly coordinated Al in shock compressed glass is found in the27Al NMR spectra. This unambiguous evidence of shock‐induced changes in Al coordination environments provides atomistic insights into shock compression in basaltic glasses and allows us to microscopically constrain the magnitude of impact events or relevant processes involving natural basalts on Earth and planetary surfaces.
Biogeochemical conditions determine virulence of black band disease in corals
Authors: Glas Martin S , Sato Yui , Ulstrup Karin E , Bourne David G
Published: February 2012

The microenvironmental dynamics of the microbial mat of black band disease (BBD) and its less virulent precursor, cyanobacterial patch (CP), were extensively profiled using microsensors under different light intensities with respect to O2, pH and H2S. BBD mats exhibited vertical stratification into an upper phototrophic and lower anoxic and sulphidic zone. At the progression front of BBD lesions, high sulphide levels up to 4977 μm were measured in darkness along with lower than ambient levels of pH (7.43±0.20). At the base of the coral–BBD microbial mat, conditions were hypoxic or anoxic depending on light intensity exposure. In contrast, CP mats did not exhibit strong microchemical stratification with mostly supersaturated oxygen conditions throughout the mats at all light intensities and with levels of pH generally higher than in BBD. Two of three replicate CP mats were devoid of sulphide, while the third replicate showed only low levels of sulphide (up to 42 μm) present in darkness and at intermediate light levels. The level of oxygenation and sulphide correlated well with lesion migration rates, that is virulence of the mats, which were greater in BBD than in CP. The results suggest that biogeochemical microgradients of BBD shaped by the complex microbial community, rather than a defined pathogen, are the major trigger for high virulence and the associated derived coral mortality of this disease.
Global distribution and diversity of marine Verrucomicrobia
Authors: Freitas Sara , Hatosy Stephen , Fuhrman Jed A , Huse Susan M , Mark Welch David B , Sogin Mitchell L , Martiny Adam C
Published: February 2012

Verrucomicrobia is a bacterial phylum that is commonly detected in soil, but little is known about the distribution and diversity of this phylum in the marine environment. To address this, we analyzed the marine microbial community composition in 506 samples from the International Census of Marine Microbes as well as 11 coastal samples taken from the California Current. These samples from both the water column and sediments covered a wide range of environmental conditions. Verrucomicrobia were present in 98% of the analyzed samples, and thus appeared nearly ubiquitous in the ocean. Based on the occurrence of amplified 16S ribosomal RNA sequences, Verrucomicrobia constituted on average 2% of the water column and 1.4% of the sediment bacterial communities. The diversity of Verrucomicrobia displayed a biogeography at multiple taxonomic levels and thus, specific lineages appeared to have clear habitat preference. We found that subdivision 1 and 4 generally dominated marine bacterial communities, whereas subdivision 2 was more frequent in low salinity waters. Within the subdivisions, Verrucomicrobia community composition were significantly different in the water column compared with sediment as well as within the water column along gradients of salinity, temperature, nitrate, depth and overall water column depth. Although we still know little about the ecophysiology of Verrucomicrobia lineages, the ubiquity of this phylum suggests that it may be important for the biogeochemical cycle of carbon in the ocean.
Fermentable Carbohydrate Alters Hypothalamic Neuronal Activity and Protects Against the Obesogenic Environment
Authors: Anastasovska Jelena , Arora Tulika , Canon Gina J. Sanchez , Parkinson James R.C. , Touhy Kieran , Gibson Glen R. , Nadkarni Nachiket A. , So Po‐Wah , Goldstone Anthony P. , Thomas E. Louise , Hankir Mohammed K. , Van Loo Jan , Modi Neena , Bell Jimmy D. , Frost Gary
Published: February 2012

Obesity has become a major global health problem. Recently, attention has focused on the benefits of fermentable carbohydrates on modulating metabolism. Here, we take a system approach to investigate the physiological effects of supplementation with oligofructose‐enriched inulin (In). We hypothesize that supplementation with this fermentable carbohydrate will not only lead to changes in body weight and composition, but also to modulation in neuronal activation in the hypothalamus. Male C57BL/6 mice were maintained on a normal chow diet (control) or a high fat (HF) diet supplemented with either oligofructose‐enriched In or corn starch (Cs) for 9 weeks. Compared to HF+Cs diet, In supplementation led to significant reduction in average daily weight gain (mean ± s.e.m.: 0.19 ± 0.01 g vs. 0.26 ± 0.02 g, P < 0.01), total body adiposity (24.9 ± 1.2% vs. 30.7 ± 1.4%, P < 0.01), and lowered liver fat content (11.7 ± 1.7% vs. 23.8 ± 3.4%, P < 0.01). Significant changes were also observed in fecal bacterial distribution, with increases in both Bifidobacteria and Lactobacillius and a significant increase in short chain fatty acids (SCFA). Using manganese‐enhanced MRI (MEMRI), we observed a significant increase in neuronal activation within the arcuate nucleus (ARC) of animals that received In supplementation compared to those fed HF+Cs diet. In conclusion, we have demonstrated for the first time, in the same animal, a wide range of beneficial metabolic effects following supplementation of a HF diet with oligofructose‐enriched In, as well as significant changes in hypothalamic neuronal activity.
Light ion source for proton/deuteron production at CEA Saclay for the Spiral2 project
Authors: Tuske O. , Adroit G. , Delferrière O. , Denis J-F. , Gauthier Y. , Girardot P. , Gobin R. , Harrault F. , Graehling P. , Guiho P. , Hosselet J. , Maazouzi C. , Sauce Y. , Uriot D. , Vacher T. , Van Hille C.
Published: February 2012

The production of rare radioactive ion beam (RIB) far from the valley of stability is one of the final purposes of the Spiral2 facility in Caen. The RIB will be produced by impinging a deuteron beam onto a carbon sample to produce a high neutron flux, which will interact with a uranium target. The primary deuteron beam is produced by an ion source based on ECR plasma generation. The deuteron source and the low energy beam transport (LEBT) has been assembled and tested at CEA Saclay. Diagnostics from other laboratories were implemented on the LEBT in order to characterize the deuteron beam produced and compare it to the initial simulations. The ion source has been based on a SILHI-type source, which has demonstrated good performances in pulsed and continuous mode, and also a very good reliability on long term operation. The 5 mA of deuteron beam required at the RFQ entrance is extracted from the plasma source at the energy of 40 kV. After a brief description of the experimental set-up, this article reports on the first beam characterization experiments.
Electrostatic energy analyzer measurements of low energy zirconium beam parameters in a plasma sputter-type negative ion source
Authors: Malapit Giovanni M. , Mahinay Christian Lorenz S. , Poral Matthew D. , Ramos Henry J.
Published: February 2012

A plasma sputter-type negative ion source is utilized to produce and detect negative Zr ions with energies between 150 and 450 eV via a retarding potential-type electrostatic energy analyzer. Traditional and modified semi-cylindrical Faraday cups (FC) inside the analyzer are employed to sample negative Zr ions and measure corresponding ion currents. The traditional FC registered indistinct ion current readings which are attributed to backscattering of ions and secondary electron emissions. The modified Faraday cup with biased repeller guard ring, cut out these signal distortions leaving only ringings as issues which are theoretically compensated by fitting a sigmoidal function into the data. The mean energy and energy spread are calculated using the ion current versus retarding potential data while the beam width values are determined from the data of the transverse measurement of ion current. The most energetic negative Zr ions yield tighter energy spread at 4.11 eV compared to the least energetic negative Zr ions at 4.79 eV. The smallest calculated beam width is 1.04 cm for the negative Zr ions with the highest mean energy indicating a more focused beam in contrast to the less energetic negative Zr ions due to space charge forces.
Initial commissioning results with the NSCL Electron Beam Ion Trap
Authors: Schwarz S. , Bollen G. , López-Urrutia J. R. Crespo , Kester O. , Kittimanapun K. , Lapierre A. , Leitner D. , Ottarson J. , Portillo M.
Published: February 2012

The ReA reaccelerator is being added to the National Superconducting Cyclotron Laboratory (NSCL) fragmentation facility in order to provide exotic rare-isotope beams, not available at the Isotope Separation On-Line facilities, in the several-MeV/u energy range. The first stage of the NSCL reaccelerator complex, consisting of an EBIT charge breeder, a room-temperature radiofrequency quadrupole (RFQ) accelerator, and superconducting linear accelerator modules, has been completed and is being put into operation. Commissioning of the EBIT has started by extracting charge-bred residual gas ions, ions created from a Ne gas jet directed across the EBIT’s electron beam and ions captured from an external test ion source. Charge-bred ions from the Ne gas jet have been extracted as a pulse and accelerated through the RFQ and the two cryomodules.
Profiles of ion beams and plasma parameters on a multi-frequencies microwaves large bore electron cyclotron resonance ion source with permanent magnets
Authors: Kato Yushi , Sakamoto Naoki , Kiriyama Ryutaro , Takenaka Tomoya , Kurisu Yosuke , Nozaki Dai , Sato Fuminobu , Iida Toshiyuki
Published: February 2012

In order to contribute to various applications of plasma and beams based on an electron cyclotron resonance, a new concept on magnetic field with all magnets on plasma production and confinement has been proposed with enhanced efficiency for broad and dense ion beam. The magnetic field configuration consists of a pair of comb-shaped magnet surrounding plasma chamber cylindrically. Resonance zones corresponding for 2.45 GHz and 11–13 GHz frequencies are positioned at spatially different positions. We launch simultaneously multiplex frequencies microwaves operated individually, try to control profiles of the plasma parameters and the extracted ion beams, and to measure them in detail.
Test bench to commission a third ion source beam line and a newly designed extraction system
Authors: Winkelmann T. , Cee R. , Haberer T. , Naas B. , Peters A.
Published: February 2012

The HIT (Heidelberg Ion Beam Therapy Center) is the first hospital-based treatment facility in Europe where patients can be irradiated with protons and carbon ions. Since the commissioning starting in 2006 two 14.5 GHz electron cyclotron resonance ion sources are routinely used to produce a variety of ion beams from protons up to oxygen. In the future a helium beam for regular patient treatment is requested, therefore a third ion source (Supernanogan source from PANTECHNIK S.A.) will be integrated. This third ECR source with a newly designed extraction system and a spectrometer line is installed at a test bench at HIT to commission and validate this section. Measurements with different extraction system setups will be presented to show the improvement of beam quality for helium, proton, and carbon beams. An outlook to the possible integration scheme of the new ion source into the production facility will be discussed.
Reliability test of an electron cyclotron resonance ion source for accelerator driven sub-critical system
Authors: Cui B. , Tang B. , Ma R. , Huang Q. , Ma Y. , Chen L. , Jiang W.
Published: February 2012

The reliability test of an electron cyclotron resonance ion source developed for accelerator driven sub-critical system is carried out in China Institute of Atomic Energy. A unique technique to improve the reliability is adopted. The source is operated for more than 200 h at 75 keV, 100 mA extracted hydrogen current, while 2 beam trips are recorded in the period, and uninterrupted operation time is about 150 h. The experimental result is described.
Electron cyclotron resonance plasma production by using pulse mode microwaves and dependences of ion beam current and plasma parameters on the pulse condition
Authors: Kiriyama Ryutaro , Takenaka Tomoya , Kurisu Yousuke , Nozaki Dai , Sato Fuminobu , Kato Yushi , Iida Toshiyuki
Published: February 2012

We measure the ion beam current and the plasma parameters by using the pulse mode microwave operation in the first stage of a tandem type ECRIS. The time averaged extracted ion beam current in the pulse mode operation is larger than that of the cw mode operation with the same averaged microwave power. The electron density ne in the pulse mode is higher and the electron temperature Te is lower than those of the cw mode operation. These plasma parameters are considered to cause in the increase of the ion beam current and are suitable to produce molecular or cluster ions.
The study of loss kinetics of current carriers in copper-indium-gallium selenide by microwave photoconductivity method
Authors: Novikov G. F. , Rabenok E. V. , Jeng M. J. , Chang L. B.
Published: February 2012

This study investigated how stoichiometry affects processes associated with current carriers by undertaking a kinetics investigation of electron loss processes in the copper-indium-gallium selenide (CIGS) samples prepared by PVD and sol-gel methods. Owing to these processes, the current carriers generated by light can be trapped or recombined after a thermalization process and fail to reach electrodes during their lifetime and adversely impact the photovoltaic performance of solar elements. The microwave photoconductivity method provides an effective means of obtaining data on the lifetime and energy distribution of traps for current carriers. Experimental results indicate that the free electron lifetimes in the best samples prepared in both methods are approximately the same, yet decrease with a decline in stoichiometry.
Spin reorientation transition and hard magnetic properties of MnBi intermetallic compound
Authors: Suzuki K. , Wu X. , Ly V. , Shoji T. , Kato A. , Manabe A.
Published: February 2012

The effects of mechanical grinding (MG) on the crystallite size, the spin reorientation transition temperature (TSR) and the hard magnetic properties in melt-spun low temperature phase (LTP) MnBi have been investigated in order to understand the origin of magnetic hardening induced by MG. The room-temperature coercive field (μ0Hcj) is enhanced dramatically from 0.08 T before MG to 1.5 T after MG for 43.2 ks while TSR is concurrently suppressed from 110 to 38 K. The coercive force exhibits positive temperature dependence approximately 50–60 K above TSR and the lowered TSR after MG could result in magnetic hardening at room temperature. The room-temperature coercive force of LTP-MnBi is highly dependent on the crystallite size (D) and is found to be described phenomenologically by the following relationship: μ0Hcj = μ0Ha(δ/D)n, where μ0Ha is ∼ 4 T, the Bloch wall width δ is 7 nm, and the exponent n is approximately 0.7. Our results suggest that the grain refinement is the primary origin of the hardening effect induced by MG with a possible minor hardening effect due to the suppression of the spin reorientation transition temperature.
Epitaxial Fe(1−x)Gax/GaAs structures via electrochemistry for spintronics applications
Authors: Reddy K. Sai Madhukar , Maqableh Mazin M. , Stadler Bethanie J. H.
Published: February 2012

In this study, thin films of Fe83Ga17 (a giant magnetostrictive alloy) were grown on single-crystalline n-GaAs (001) and polycrystalline brass substrates via electrochemical synthesis from ferrous and gallium sulfate electrolytes. Extensive structural characterization using microdiffraction, high-resolution ω − 2θ, and rocking-curve analysis revealed that the films grown on GaAs(001) are highly textured with ⟨001⟩ orientation along the substrate normal, and the texture improved further upon annealing at 300 °C for 2 h in N2 environment. On the contrary, films grown on brass substrates exhibited ⟨011⟩ preferred orientation. Rocking-curve analysis done on Fe83Ga17/GaAs structures further confirmed that the ⟨001⟩ texture in the Fe83Ga17 thin film is a result of epitaxial nucleation and growth. The non-linear current−voltage plot obtained for the Fe−Ga/GaAs Schottky contacts was characteristic of tunneling injection, and showed improved behavior with annealing. Thus, this study demonstrates the feasibility of fabricating spintronic devices that incorporate highly magnetostrictive Fe(1−x)Gax thin films grown epitaxially via electrochemistry.
The magnetostrictive material effects on magnetic field sensitivity for magnetoelectric sensor
Authors: Chen Lei , Li Ping , Wen Yumei , Qiu Jing
Published: February 2012

The magnetic sensitivity to magnetic field for the magnetoelectric (ME) sensor is studied. Theoretical analysis predicts that the ME voltage sensitivity to Hac (i.e., ∂VME/∂Hac under dc bias field) and the ME voltage sensitivity to Hdc (i.e., ∂VME/∂Hdc under ac bias field) for the ME sensor are significantly dependent on the product of the effective mechanical quality factor of the ME sensor Qm, the saturation magnetostriction λs of the magnetostrictive material, and the square of magnetic permeability μr. The experimental results demonstrate that the greatest value of ∂VME/∂Hac for the FeCuNbSiB/PZT-8/FeCuNbSiB (FePFe) sensor reaches 10 V/Oe due to the largest product of the Qm, λs and the square of μr, relative to FeNi-FACE/PZT-8/FeNi-FACE (FPF) and Terfenol-D/PZT-8/Terfenol-D (MPM) sensors. Meanwhile, the maximum value of ∂VME/∂Hdc for FePFe sensor achieves 242.2 mV/Oe, which is ∼10 times higher than that of the FPF sensor and ∼ 4 times higher than that of the MPM sensor. To obtain the high magnetic sensitivity to dc and ac magnetic field, the mechanical quality factor, the magnetic permeability and the saturation magnetostriction should both be taken into account in selecting the suitable magnetostrictive material.
Spin frustration destruction and ferroelectricity modulation in Ca3CoMnO6: Effects of Mn deficiency
Authors: Lin L. , Guo Y. J. , Xie Y. L. , Dong S. , Yan Z. B. , Liu J.-M.
Published: February 2012

We present careful experiments on the spin order and multiferroicity of Mn-deficient Ca3CoMn1−xO6 with respect to the Co/Mn compensated Ca3Co1+yMn1−yO6. It is revealed that a slight destruction of the Co/Mn ionic order does not damage but significantly enhances the ferroelectricity in terms of the transition point and polarization magnitude, due to the Mn-deficiency enhanced degree of Co/Mn spin ordering in comparison with Ca3Co1+yMn1−yO6. The delicate competition between the ionic (charge) order and spin frustration is the core physics for improving the ferroelectric performance.
Magnetic transitions in erbium at high pressures
Authors: Thomas Sarah A. , Tsoi Georgiy M. , Wenger Lowell E. , Vohra Yogesh K. , Weir Samuel T.
Published: February 2012

Electrical resistance measurements have been carried out on polycrystalline erbium (Er) at temperatures down to 10 K and pressures up to 20 GPa. An abrupt change in the slope of the resistance is observed with decreasing temperature below 84 K which is associated with the c-axis modulated antiferromagnetic (AFM) ordering of the Er moments. With increasing pressure, the temperature of this resistance slope change and the corresponding AFM ordering temperature decrease until vanishing above 10.6 GPa. At higher pressures, a more gradual change in the slope of the resistance is found to occur around 45 K which disappears at pressures near 17 GPa. The transformation from the hexagonal-close-packed structural phase to a nine-layer α-Sm structural phase at a similar pressure of 11 GPa indicates (i) that the disappearance in the c-axis modulated antiferromagnetic ordering of Er moments above 10.6 GPa is correlated to the structural phase change and (ii) that the smaller resistance changes around 45 K result from a different magnetic structure associated with the α-Sm structural phase.
Co/Pt multilayer-based magnetic tunnel junctions with perpendicular magnetic anisotropy
Authors: Kugler Zoë , Grote Jan-Philipp , Drewello Volker , Schebaum Oliver , Reiss Günter , Thomas Andy
Published: February 2012

Temperature-dependent transport measurements of magnetic tunnel junctions with perpendicularly magnetized Co/Pt electrodes are presented. Magnetization measurements of the Co/Pt multilayers are performed to characterize the electrodes. The interface magnetization of the Co layers at the Pt interface is estimated in dependence of the annealing temperature. The effect of the annealing temperature on the tunneling magnetoresistance effect of the magnetic tunnel junctions (MTJs) is investigated. Tunneling magnetoresistance ratios of about 19% at room temperature are attained and two well-defined switching fields are observed. The tunneling magnetoresistance of Co/Pt based tunnel junctions changes by a factor of 1.9 if cooled to 13 K. The results are compared to measurements of MTJs with Co-Fe-B electrodes and in-plane anisotropy.
Structure and properties of metal-exchanged zeolites studied using gradient-corrected and hybrid functionals. II. Electronic structure and photoluminescence spectra
Authors: Göltl Florian , Hafner Jürgen
Published: February 2012

The influence of the choice of the exchange-correlation functional (semilocal gradient corrected or hybrid functionals) on the electronic properties of metal-exchanged zeolites has been investigated for Cu- and Co-exchanged chabazite. The admixture of exact exchange in hybrid functionals increases the fundamental gap of purely siliceous chabazite, leading to better agreement with experiment and many-body perturbation theory for close-packed SiO2 polymorphs where detailed experimental information is available. For the metal-exchanged chabazite the increased exchange splitting strongly influences the position of the cation states relative to the framework bands—in general, gradient-corrected functionals locate the occupied cation states close to the valence-band maximum of the framework, while hybrid functionals shift the occupied cation states to larger binding energies and the empty states to higher energies within the fundamental gap. The photoluminescence spectra have been analyzed using fixed-moment total-energy calculations for excited spin states in structurally relaxed and frozen geometries. The geometrical relaxation of the excited states leads to large differences in excitation and emission energies which are more pronounced in calculations using hybrid functionals. Due to the stronger relaxation effects calculated with hybrid functionals, the large differences in the electronic spectra calculated with both types of functionals are not fully reflected in the photoluminescence spectra.
Elucidation of spin echo small angle neutron scattering correlation functions through model studies
Authors: Shew Chwen-Yang , Chen Wei-Ren
Published: February 2012

Several single-modal Debye correlation functions to approximate part of the overall Debey correlation function of liquids are closely examined for elucidating their behavior in the corresponding spin echo small angle neutron scattering (SESANS) correlation functions. We find that the maximum length scale of a Debye correlation function is identical to that of its SESANS correlation function. For discrete Debye correlation functions, the peak of SESANS correlation function emerges at their first discrete point, whereas for continuous Debye correlation functions with greater width, the peak position shifts to a greater value. In both cases, the intensity and shape of the peak of the SESANS correlation function are determined by the width of the Debye correlation functions. Furthermore, we mimic the intramolecular and intermolecular Debye correlation functions of liquids composed of interacting particles based on a simple model to elucidate their competition in the SESANS correlation function. Our calculations show that the first local minimum of a SESANS correlation function can be negative and positive. By adjusting the spatial distribution of the intermolecular Debye function in the model, the calculated SESANS spectra exhibit the profile consistent with that of hard-sphere and sticky-hard-sphere liquids predicted by more sophisticated liquid state theory and computer simulation.
Quantum confinement in Si and Ge nanostructures
Authors: Barbagiovanni E. G. , Lockwood D. J. , Simpson P. J. , Goncharova L. V.
Published: February 2012

We apply perturbative effective mass theory as a broadly applicable theoretical model for quantum confinement (QC) in all Si and Ge nanostructures including quantum wells (QWs), wires (Q-wires), and dots (QDs). Within the limits of strong, medium, and weak QC, valence and conduction band edge energy levels (VBM and CBM) were calculated as a function of QD diameters, QW thicknesses, and Q-wire diameters. Crystalline and amorphous quantum systems were considered separately. Calculated band edge levels with strong, medium, and weak QC models were compared with experimental VBM and CBM reported from X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS), or photoluminescence (PL). Experimentally, the dimensions of the nanostructures were determined directly, by transmission electron microscopy (TEM), or indirectly, by x-ray diffraction (XRD) or by XPS. We found that crystalline materials are best described by a medium confinement model, while amorphous materials exhibit strong confinement regardless of the dimensionality of the system. Our results indicate that spatial delocalization of the hole in amorphous versus crystalline nanostructures is the important parameter determining the magnitude of the band gap expansion, or the strength of the quantum confinement. In addition, the effective masses of the electron and hole are discussed as a function of crystallinity and spatial confinement.
Ultra-sensitive thermal conductance measurement of one-dimensional nanostructures enhanced by differential bridge
Authors: Wingert Matthew C. , Chen Zack C. Y. , Kwon Shooshin , Xiang Jie , Chen Renkun
Published: February 2012

Thermal conductivity of one-dimensional nanostructures, such as nanowires, nanotubes, and polymer chains, is of significant interest for understanding nanoscale thermal transport phenomena as well as for practical applications in nanoelectronics, energy conversion, and thermal management. Various techniques have been developed during the past decade for measuring this fundamental quantity at the individual nanostructure level. However, the sensitivity of these techniques is generally limited to 1 × 10−9 W/K, which is inadequate for small diameter nanostructures that potentially possess thermal conductance ranging between 10−11 and 10−10 W/K. In this paper, we demonstrate an experimental technique which is capable of measuring thermal conductance of ∼10−11 W/K. The improved sensitivity is achieved by using an on-chip Wheatstone bridge circuit that overcomes several instrumentation issues. It provides a more effective method of characterizing the thermal properties of smaller and less conductive one-dimensional nanostructures. The best sensitivity experimentally achieved experienced a noise equivalent temperature below 0.5 mK and a minimum conductance measurement of 1 × 10−11 W/K. Measuring the temperature fluctuation of both the four-point and bridge measurements over a 4 h time period shows a reduction in measured temperature fluctuation from 100 mK to 0.6 mK. Measurement of a 15 nm Ge nanowire and background conductance signal with no wire present demonstrates the increased sensitivity of the bridge method over the traditional four-point I-V measurement. This ultra-sensitive measurement platform allows for thermal measurements of materials at new size scales and will improve our understanding of thermal transport in nanoscale structures.
Semiconductor core-shell quantum dot: A low temperature nano-sensor material
Authors: Chattopadhyay Saikat , Sen Pratima , Thomas Andrews Joseph , Kumar Sen Pranay
Published: February 2012

This paper presents an analytical study of temperature dependent photoluminescence (PL) in core-shell quantum dots (CSQDs) made of most frequently used II-VI semiconducting materials. The analysis incorporates the temperature dependent radiative recombination processes in the calculation of the integrated PL intensity. The PL intensity has been derived using semiclassical density matrix formalism for the CSQDs exhibiting excitonic and biexcitonic features. The numerical estimates show that the PL intensity response and PL peak shifts are non-trivial at low temperature in such CSQDs and can be useful in the design of a temperature sensor.
Formation of twins in sapphire under shock wave loading: Atomistic simulations
Authors: Kuksin A. Yu. , Yanilkin A. V.
Published: February 2012

This work is devoted to molecular dynamics (MD) simulation of shock-wave loading of sapphire (α-Al2O3). Defect free sapphire and sapphire with the microcrack are considered. Homogeneous nucleation and growth of rhombohedral twins are observed in single crystal alumina. A fast mechanism of plastic deformation is revealed under shock-wave loading of sapphire with microcrack. Rhombohedral twins nucleate and grow as a result of a two stage process. At the first stage the formation of a new type of linear defect takes place in the shock wave front, which is initiated at the surface of the microcrack. At the second stage the rhombohedral twins grow from the primary linear defects and combine with each other. The results are confirmed by first principles calculations.
Experimental study on the field emission properties of metal oxide nanoparticle–decorated graphene
Authors: Theres Baby Tessy , Ramaprabhu Sundara
Published: February 2012

In the present study, electron field emission efficiency of metal oxide nanoparticle–decorated graphene has been investigated. Tin oxide and zinc oxide nanoparticle–decorated hydrogen exfoliated graphene (SnO2/HEG and ZnO/HEG) have been synthesized by chemical reduction and sol-gel techniques, respectively. The samples have been characterized by x ray diffraction, thermo-gravimetric analysis, Raman spectroscopy, and electron microscopy techniques. SnO2/HEG and ZnO/HEG-based field emitters have been fabricated by dispersing them in a suitable solvent, followed by spin coating onto a carbon cloth. The field emission measurement of these vacuum-dried thin films has been carried out under a vacuum of 10–6 mbar, as has their long-term stability. The obtained turn-on voltage for ZnO/HEG and SnO2/HEG is around 0.88 and 0.93 V/μm with field enhancement factors of 6535 and 6367, respectively.
Impact of scaling of dielectric thickness on mobility in top-contact pentacene organic thin film transistors
Authors: Kumar Singh Vinay , Mazhari Baquer
Published: February 2012

The effect of scaling of poly(methylmethacrylate) (PMMA) and cross-linkable poly(4-vinylphenol) (PVP) polymer dielectric thickness on field effect mobility in top contact pentance organic thin film transistors was investigated. Mobility at a constant gate voltage improved significantly with reduction in thickness of both dielectrics. Analysis at a constant gate electric field or identical induced accumulation charge revealed that only a part of the improvement occurs due to simple scaling of dielectric thickness, and the remaining is due to improvement in interface quality. Atomic force microscopic analysis of the dielectric surface revealed that dielectric roughness reduced with reduction in dielectric thickness. A comparison of the two dielectrics also indicates that band mobility is significantly higher in pentacene/PMMA as compared to pentacene/PVP dielectric.
Structural properties and spatial ordering in multilayered ZnMgTe/ZnSe type-II quantum dot structures
Authors: Manna U. , Noyan I. C. , Zhang Q. , Salakhutdinov I. F. , Dunn K. A. , Novak S. W. , Moug R. , Tamargo M. C. , Neumark G. F. , Kuskovsky I. L.
Published: February 2012

We report the structural properties and spatial ordering of multilayer ZnMgTe quantum dots (QDs) embedded in ZnSe, where sub-monolayer quantities of Mg were introduced periodically during growth in order to reduce the valence band offset of ZnTe QDs. The periodicity, period dispersion, individual layer thickness, and the composition of the multilayer structures were determined by comparing the experimental high resolution x-ray diffraction (HRXRD) spectra to simulated ones for the allowed (004) and quasi-forbidden (002) reflections in combination with transmission electron microscopy (TEM) results. Secondary ion mass spectroscopy (SIMS) profiles confirmed the incorporation of Mg inside the QD layers, and the HRXRD analysis revealed that there is approximately 32% Mg in the ZnMgTe QDs. The presence of Mg contributes to higher scattering intensity of the HRXRD, leading to the observation of higher order superlattice peaks in both the (004) and (002) reflections. The distribution of scattered intensity in the reciprocal space map (RSM) shows that the diffuse scattered intensity is elongated along the qx axis, indicating a vertical correlation of the dots, which is found to be less defined for the sample with larger periodicity. The diffuse scattered intensity is also found to be weakly correlated along the qz direction indicating a weak lateral correlation of the dots.
Kinetics aspects of initial stage thin γ-Al2O3 film formation on single crystalline β-NiAl (110)
Authors: Zhang Zhongfan , Jung Keeyoung , Li Long , Yang Judith C.
Published: February 2012

The growth kinetics and mechanisms of thermally-grown thin γ-Al2O3 film at 650 °C in air on single-crystalline β-NiAl (110) was characterized via transmission electron microscopy, X-ray diffractometry, and thermo-gravimetric analyses. The oxidation kinetics as a function of thickness was gradually changing from an inverse-logarithmic to parabolic behavior across the “intermediate thickness regime” as the oxide thickness increases. To define the boundaries of the three thickness regimes, the high field approximation (x1) and Debye-Hückel length (LD) were determined using the existing theoretical kinetics models combined with experimentally measured data. All the relevant constants for each rate law at the three thickness regimes were also experimentally determined to quantitatively describe the initial stage growth kinetics.
Grown-in precipitates in heavily phosphorus-doped Czochralski silicon
Authors: Zeng Yuheng , Ma Xiangyang , Chen Jiahe , Song Weijie , Wang Weiyan , Gong Longfei , Tian Daxi , Yang Deren
Published: February 2012

Through comparing the oxygen precipitation in the heavily and lightly phosphorus (P)-doped Czochralski silicon (CZ Si) specimens subjected to the simulated cooling processes of silicon ingot, we researched the influences of heavily P doping on grown-in precipitates by preferential etching and transmission electron microscopy (TEM). It was found that grown-in precipitates were more significant in heavily P-doped CZ Si than in lightly one. Most grown-in precipitates in heavily P-doped CZ Si were generated at (800–600) °C. The significant grown-in oxygen precipitates in the heavily P-doped CZ Si would change the density and morphology of oxygen precipitation. TEM examination revealed that the grown-in precipitates in heavily P-doped CZ Si were amorphous oxygen precipitates composed of tiny precipitates in essential. Although more or less phosphorus may be incorporated in the grown-in precipitates, however, phosphorus cannot be detected so far. We further confirmed that extending annealing at 550 °C produced significant silicon phosphide (SiP) precipitation in heavily P-doped CZ Si. Summarily, enhancement of grown-in oxygen precipitates was attributed to SiP precipitation and high-concentration vacancy, tentatively. Nonetheless, further investigation on the essential of grown-in precipitates in heavily P-doped CZ Si is worthy.
Discretising the Painlevé equations à la Hirota-Mickens
Authors: Grammaticos B. , Ramani A. , Satsuma J. , Willox R.
Published: February 2012

We present a systematic method for discretising the Painlevé equations inspired by the method of Hirota (while extending it) and by that of Mickens (by specifying it to the case at hand). We derive various discrete analogues of Painlevé I and II. We obtain forms that have been previously derived as well as new ones, in particular, equations with a geometry described by the affine Weyl group \documentclass[12pt]{minimal}\begin{document}${\rm E}_8^{(1)}$\end{document}E8(1). As a by-product we obtain also linearisable equations, some of which are new.
High-pressure phases of NaAlH4 from first principles
Authors: Zhou Xiang-Feng , Dong Xiao , Zhao Zhisheng , Oganov Artem R. , Tian Yongjun , Wang Hui-Tian
Published: February 2012

High-pressure phases of NaAlH4 are predicted using the ab initio evolutionary algorithm. our first-principles calculations reveal that the low-pressure I41/a phase containing AlH4 tetrahedra transforms into the monoclinic P21/c phase at 3.8 GPa and then into the orthorhombic Ima2 phase at 20.5 GPa. The predicted two structures contain AlH6 octahedra and AlH7 decahedra, respectively. Coexistence of P21/c and Ima2 phases can explain better the measured x-ray diffraction patterns, transition pressure, and volume contraction. Our results provide a comprehensive understanding for the experimental findings.