bluuebunny/crossref_metadata_2025 huggingface dataset:
Daily variations of auroral kilometric radiation observed by STEREO
Authors: Panchenko M. , Khodachenko M. L. , Kislyakov A. G. , Rucker H. O. , Hanasz J. , Kaiser M. L. , Bale S. D. , Lamy L. , Cecconi B. , Zarka P. , Goetz K.
Published: March 2009

Daily variations of terrestrial auroral kilometric radiation (AKR) are considered; an effect that is detected in STEREO/WAVES data. It has been found that the intensities of the AKR emitted from Northern and Southern sources are modulated with a period of ∼24 hours. The occurrence frequency of the AKR has been shown to be strongly dependent on the orientation of the rotating oblique magnetic dipole of the Earth relative to the Sun. AKR is found to occur more often and emit in a broader frequency range when the axis of the terrestrial magnetic dipole in the given hemisphere is oriented toward the nightside. We suggest that the observed ∼24 h variations of AKR are connected with diurnal changes of the ambient plasma density in the auroral region.
Assimilated inversion of NOx emissions over east Asia using OMI NO2 column measurements
Authors: Zhao Chun , Wang Yuhang
Published: March 2009

Assimilated inversion on a daily basis using OMI tropospheric NO2 columns is developed and applied in a regional chemical transport model (REAM) to constrain fossil fuel (FF) NOx emissions over east Asia in 2007. The iterative nature of the assimilated inversion improves upon the widely used monthly‐mean inversion by accounting for the chemical feedbacks of changed NOx emissions and reducing the dependence of the a priori emissions. The assimilated a posteriori emissions from FF combustion over east Asia are 9.5 Tg N/yr comparable to 10.9 Tg N/yr of the a priori. Significant changes in the spatial distribution of FF NOx emissions are found in the assimilated inversion from the a priori or monthly‐mean inversion. The assimilated inversion shows that the a priori FF NOx emission inventory tends to overestimate the emissions over the economically developed areas and underestimate over the underdeveloped areas in East China, which may reflect in part FF NOx emission reductions resulting from the urban‐centric air quality controls in China.
Multipoint observations of ions in the 30–160 keV energy range upstream of the Earth's bow shock
Authors: Kronberg E. A. , Kis A. , Klecker B. , Daly P. W. , Lucek E. A.
Published: March 2009

We use multipoint observation data by Cluster during time periods when the interspacecraft separation distance was between 1 and 1.5 Earth radii in order to study the physical processes related to diffuse ions at <200 keV/e. For our analysis we use data from the Research with Adaptive Particle Imaging Detectors (RAPID) experiment onboard Cluster SC1 and SC3. We determine spatial ion density gradients by using proton intensities in the 27.7–159.7 keV energy range and helium intensities in the 137.8–235.1 keV energy range as a function of distance from the bow shock along the magnetic field. Our results show that the diffuse ions are subject to diffusive transport and the ion partial densities decrease exponentially with increasing distance from the bow shock. By complementing RAPID data with Cluster Ion Spectrometry measurements at lower energies (from 10 to 32 keV) from the same upstream ion event we find that the e‐folding distance of energetic ion density increases almost linearly with energy. This effect is also seen in the hardening of the particle spectra with increasing distance from the bow shock. We determine the spatial diffusion mean free path and the diffusion coefficient as a function of ion energy by assuming that upstream diffusion is balanced by downstream convection.
Propagation of unducted whistlers from their source lightning: A case study
Authors: Santolík O. , Parrot M. , Inan U. S. , Burešová D. , Gurnett D. A. , Chum J.
Published: March 2009

We analyze nightside measurements of the DEMETER spacecraft related to lightning activity. At the 707 km altitude of DEMETER, we observe 3‐D electric and magnetic field waveforms of fractional‐hop whistlers. At the same time, the corresponding atmospherics are recorded by a very low frequency (VLF) ground‐based station located in Nançay (France). The source lightning strokes are identified by the METEORAGE lightning detection network. We perform multidimensional analysis of the DEMETER measurements and obtain detailed information on wave polarization characteristics and propagation directions. This allows us for the first time to combine these measurements with ray‐tracing simulation in order to directly characterize how the radiation penetrates upward through the ionosphere. We find that penetration into the ionosphere occurs at nearly vertical wave vector angles (as was expected from coupling conditions) at distances of 100–900 km from the source lightning. The same distance is traveled by the simultaneously observed atmospherics to the VLF ground station. The measured dispersion of fractional‐hop whistlers, combined with the ionosonde measurements at the Ebro observatory in Spain, allows us to derive the density profile in the topside ionosphere.
Thermal effects of fluid circulation in the basement aquifer of subducting ocean crust
Authors: Kummer Troy , Spinelli Glenn A.
Published: March 2009

Most thermal models of subduction zones assume no advection of heat by fluid flow because slow flow through underthrusting sediment, the plate boundary fault zone, and margin wedge likely transports only a minor amount of heat. We model coupled fluid and heat transport in a subduction zone and show that hydrothermal circulation in subducting basaltic basement rocks can greatly influence subduction zone temperatures. Fractured basaltic basement is several orders of magnitude more permeable than a typical plate boundary fault zone or marine sediments, allowing fluid circulation to redistribute and extract heat from a subduction zone. Fluid circulation within the basement aquifer suppresses temperatures along the subducting slab relative to cases with no fluid transport. Heat is extracted from under the margin wedge and transported into the ocean crust near the trench. This circulation has a large effect on subduction zone temperatures when topographic wavelength‐dominated convection occurs (>5 times the critical Rayleigh number). With the exception of very cold subduction zones (i.e., those with very fast convergence or very small taper) topographic wavelength‐dominated convection occurs with aquifer permeability ≥10−11 m2 (in the range typically determined for upper ocean crust), suggesting such fluid circulation may be important in many subduction zones. Because fluid circulation more effectively transports heat in warmer systems, hydrothermal circulation moderates the effects of convergence rate as a control on subduction zone temperatures.
Optimization of a bistatic microwave scattering measurement setup: From high to low scattering targets
Authors: Geffrin Jean‐Michel , Eyraud Christelle , Litman Amélie , Sabouroux Pierre
Published: March 2009

Measurement accuracy is a key point when dealing with microwave scattering measurements of 3‐D targets. This is even more drastic when the targets are small compared to the wavelength. In order to be able to fully exploit a 3‐D spherical multistatic setup and to measure the scattering pattern from 3‐D targets in copolarization and in cross polarization, a detailed analysis of the experimental errors that disturb the scattered field was carried out, and a measurement methodology was derived. Such analysis was performed in the anechoic chamber of Institut Fresnel in Marseille, France. So far, our institute has provided experimental scattered fields in the microwave domain for 2‐D targets. We can now provide 3‐D ones thanks to the analysis presented below. The influence of each error is discussed in this paper, and solutions are proposed to correct for systematic errors, positioning errors, as well as for drift problems. In addition, random errors are characterized, providing confidence intervals for each measurement.
Picosecond accuracy VLBI of the two subsatellites of SELENE (KAGUYA) using multifrequency and same beam methods
Authors: Kikuchi F. , Liu Q. , Hanada H. , Kawano N. , Matsumoto K. , Iwata T. , Goossens S. , Asari K. , Ishihara Y. , Tsuruta S. , Ishikawa T. , Noda H. , Namiki N. , Petrova N. , Harada Y. , Ping J. , Sasaki S.
Published: March 2009

Same beam very long baseline interferometry (VLBI) observations of the two subsatellites of SELENE (KAGUYA) are demonstrated for purpose of the precise gravimetry of the Moon. Same beam VLBI contributes a great deal to cancel out the tropospheric and ionospheric delays and to determine the absolute value of the cycle ambiguity by using the multifrequency VLBI method. As a result, the differential phase delay of the X‐band signal is estimated within an error of below 1 ps. This accuracy is more than 1 order of magnitude smaller than former VLBI results. The preliminary results for the orbit determination of the subsatellites show a decrease of the orbit error from a few hundreds of meters to around 10 m when the differential phase delay data are added to the conventional range and Doppler data. These results reveal the possibility of precise gravimetry.
Variable residence time–based model for solute transport in streams
Authors: Deng Zhi‐Qiang , Jung Hoon‐Shin
Published: March 2009

A variable residence time (VART) model is developed for longitudinal dispersion and transport of solutes in natural streams. The VART model is based on a “double‐layer” conceptual model of transient storage in streams. The upper layer is an advection‐dominated transient storage zone which includes instream and shallow hyporheic storage. The lower layer is an effective diffusion‐dominated storage zone that is deeper in the streambed and farther beneath the banks. The VART model is characterized by the following features. First, a varying residence time is used to simulate the transient storage process. Second, no user‐specified residence time distribution (RTD) functions are required. Third, there are only four parameters to estimate. Fourth, the VART model is also able to accommodate stream water/solute gains or losses in the reach caused by groundwater exchanges. Fifth, the simple VART model is able to produce various compound solute concentration breakthrough curves (BTCs) commonly observed in streams. The early portion of BTCs follows exponential RTDs. The late portion of BTCs can essentially be any distribution. Sixth, performance of the VART model in reproducing various RTDs is comparable to other widely used 1‐D solute transport models that commonly utilize five or more fitting parameters and are limited to the simulation of user‐specified RTDs or underlying RTDs within them. Applications in hydrologically and geomorphically varied streams have indicated that the VART model is a powerful and flexible numerical tool for simulating solute transport in natural streams.
Aerosol radiative forcing under clear, hazy, foggy, and dusty weather conditions over Beijing, China
Authors: Wang Yan , Che Huizheng , Ma Jianzhong , Wang Qiang , Shi Guangyu , Chen Hongbin , Goloub Philippe , Hao Xianjun
Published: March 2009

Direct aerosol radiative forcing (ARF) under four classic weather conditions, i.e., clear, hazy, foggy, and dusty days, over Beijing was investigated using the Santa Barbara Discrete Ordinate Radiative Transfere (SBDART) model, ground‐based sunphotometer measurements, pyranometer measurements, and a back‐trajectory analysis. The ratios of aerosol optical depths (AOD) under hazy, foggy, and dusty weather conditions to the AOD under clear weather condition were much greater than the ratios of surface aerosol concentrations under these conditions. The single scattering albedo and the ratio of ARF at the surface level to ARF at the top of the atmosphere suggested that more absorbing particles existed under hazy and foggy conditions than those under dusty conditions. ARF measured at both the surface level and the top of the atmosphere for dusty days was higher than that for foggy, hazy, and clear days. Therefore, significantly difference exists in ARF over Beijing due to changes in aerosol sources and weather conditions. The altitude of the aerosol transport layer for dusty days was higher than that for foggy days.
Modulation of the hepatic malonyl-CoA–carnitine palmitoyltransferase 1A partnership creates a metabolic switch allowing oxidation of de novo fatty acids
Authors: Akkaoui Marie , Cohen Isabelle , Esnous Catherine , Lenoir Véronique , Sournac Martin , Girard Jean , Prip-Buus Carina
Published: March 2009

Liver mitochondrial β-oxidation of LCFAs (long-chain fatty acids) is tightly regulated through inhibition of CPT1A (carnitine palmitoyltransferase 1A) by malonyl-CoA, an intermediate of lipogenesis stimulated by glucose and insulin. Moreover, CPT1A sensitivity to malonyl-CoA inhibition varies markedly depending on the physiopathological state of the animal. In the present study, we asked whether an increase in CPT1A activity solely or in association with a decreased malonyl-CoA sensitivity could, even in the presence of high glucose and insulin concentrations, maintain a sustained LCFA β-oxidation and/or protect from triacylglycerol (triglyceride) accumulation in hepatocytes. We have shown that adenovirus-mediated expression of rat CPT1wt (wild-type CPT1A) and malonyl-CoA-insensitive CPT1mt (CPT1AM593S mutant) in cultured fed rat hepatocytes counteracted the inhibition of oleate β-oxidation induced by 20 mM glucose/10 nM insulin. Interestingly, the glucose/insulin-induced cellular triacylglycerol accumulation was prevented, both in the presence and absence of exogenous oleate. This resulted from the generation of a metabolic switch allowing β-oxidation of de novo synthesized LCFAs, which occurred without alteration in glucose oxidation and glycogen synthesis. Moreover, CPT1mt expression was more effective than CPT1wt overexpression to counteract glucose/insulin effects, demonstrating that control of CPT1A activity by malonyl-CoA is an essential driving force for hepatic LCFA metabolic fate. In conclusion, the present study highlights that CPT1A is a prime target to increase hepatic LCFA β-oxidation and that acting directly on the degree of its malonyl-CoA sensitivity may be a relevant strategy to prevent and/or correct hepatic steatosis.
N-terminal domains of CCN family 2/connective tissue growth factor bind to aggrecan
Authors: Aoyama Eriko , Hattori Takako , Hoshijima Mitsuhiro , Araki Daisuke , Nishida Takashi , Kubota Satoshi , Takigawa Masaharu
Published: March 2009

CCN2/CTGF (CCN family 2/connective tissue growth factor) is a multi-cellular protein with a broad range of activities. It modulates many cellular functions, including proliferation, migration, adhesion and extracellular matrix production, and it is thus involved in many biological and pathological processes. In particular, CCN2/CTGF is essential for normal skeletal development. To identify CCN2/CTGF-interactive proteins capable of modulating its action in cartilage, we carried out a yeast two-hybrid screening using CCN2/CTGF peptide as a bait and a cDNA library from a chondrocytic cell line, HCS-2/8. In the present paper, we report the identification of aggrecan, which is a major proteoglycan of the extracellular matrix in cartilage, as a CCN2/CTGF-binding protein. Among the four domains of CCN2/CTGF, the IGFBP [IGF (insulin-like growth factor)-binding protein-like] and/or VWC (von Willebrand factor type C) domains had a direct interaction with aggrecan in a yeast two-hybrid assay. The results of a solid-phase-binding assay using aggrecan-coated plates also showed binding to recombinant CCN2/CTGF in a dose-dependent manner. rIGFBP (recombinant IGFBP) and rVWC (recombinant VWC) module peptides had stronger binding to aggrecan compared with rTSP1 (recombinant thrombospondin type 1 repeat) and rCT (recombinant C-terminal cystine knot) module peptides. SPR (surface plasmon resonance) analysis showed the direct interaction between the CCN2/CTGF and aggrecan, and ectopically overexpressed CCN2/CTGF and AgG3 (G3 domain of aggrecan) confirmed their binding In vivo. Indirect immunofluorescence analysis indicated that CCN2/CTGF was extracellularly co-localized with aggrecan on HCS-2/8 cells. The rIGFBP–rVWC peptide effectively enhanced the production and release of aggrecan compared with the rTSP–rCT peptide in chondrocytes. These results indicate that CCN2/CTGF binds to aggrecan through its N-terminal IGFBP and VWC modules, and this binding may be related to the CCN2/CTGF-enhanced production and secretion of aggrecan by chondrocytes.
Different pressure behavior of GaN/AlGaN quantum structures grown along polar and nonpolar crystallographic directions
Authors: Teisseyre H. , Kamińska A. , Franssen G. , Dussaigne A. , Grandjean N. , Grzegory I. , Łucznik B. , Suski T.
Published: March 2009

High quality GaN/AlGaN multiquantum well (QW) structures were grown by ammonia molecular beam epitaxy along the (0001) polar and (112¯0) nonpolar directions. Each sample contains three QWs with thicknesses of 2, 3, and 4 nm as well as 10 nm Al0.30Ga0.70N barriers. The measured photoluminescence (PL) spectrum consists of three peaks originating from the radiative recombination of excitons in individual QWs. In the nonpolar sample, the energy positions (EPL) of the observed peaks are separated because of the quantum confinement effect, whereas in the polar sample an additional redshift is induced by the quantum confined Stark effect. The dependence of EPL on QW width was used to estimate the built-in electric field magnitude in the latter sample to be about 2 MV/cm. Hydrostatic pressure studies of the PL in both samples gave qualitatively different results. In the polar sample, the pressure shift of EPL, dEPL/dp decreases significantly with QW width. The important finding is derived from the observation of a QW width independent dEPL/dp in the nonpolar sample. It shows that for GaN/Al0.30Ga0.70N, the quantum confinement remains practically independent of the applied hydrostatic pressure. This result reveals that in the polar sample, the variation in dEPL/dp with the QW width is due to the pressure-induced increase in the built-in electric field Fint. Thus, a more quantitative analysis of the latter effect becomes justified. We found that the Fint increases with pressure with a rate of about 80 kV(cm GPa)−1.
An in situ neutron diffraction study of magnetic hardening in Fe3B/Nd2Fe14B nanocomposite magnets induced by rapid thermal annealing
Authors: Suzuki K. , Garitaonandia J. S. , Shih J. C. , Cuello G. J. , Shoji T. , Kato A. , Tajima S.
Published: March 2009

Neutron diffraction patterns were acquired in situ from a melt-spun amorphous Fe74Nd5B18Cr3 alloy upon heating at constant rates of 1.7×10−2 and 1.3 K/s. The diffraction patterns revealed the following decomposition reaction with two different intermediate routes: amorphous→Fe3B/Nd2Fe23B3 (at 1.7×10−2 K/s) or Fe3B/Nd2Fe14B (at 1.3 K/s)→Fe/Fe2B/Nd1.1Fe4B4. This confirms that the changeover between the two ternary compounds in the metastable intermediate state is the direct cause of magnetic hardening induced by rapid heating. The effect of group IVA-VIA metals on the magnetic hardness of Fe77Nd5B18 was investigated and only the 3d transition-metal additives appeared to be effective in enhancing the coercivity. The heterogeneous nucleation of Nd2Fe14B on tetragonal-Fe3B precipitates promoted by the 3d transition-metal additives is proposed as a possible mechanism of magnetic hardening.
Seed layer effect on texture and magnetic properties of SmCo5 thin films
Authors: Zhang L. N. , Hu J. F. , Chen J. S. , Ding J.
Published: March 2009

In this work, we have studied the influence of seed layer on the microstructure of the Cu underlayer and its effect on the structure and magnetic properties of subsequently deposited SmCo5 films. Our investigation concentrated on the thickness effect of Ta seed layer. Our study has shown that a smooth Ta seed layer can lead in a highly textured and well crystallized (111) Cu underlayer. At 4 nm (Ta thickness), the full width at half maximum of the rocking curve (Δθ50) of Cu (111) diffraction peak is only 3.3° and the surface root-mean-square roughness (Rq) of Cu surface is only 0.53 nm. With the smooth and highly (111) textured Cu underlayer, the superstructure SmCo5 (000l) peaks are clearly observed. Also, the good texture of SmCo5 results in a high perpendicular coercivity around 20 kOe with a large perpendicular anisotropy.
Characterization of magnetic property depth profiles of surface-modified materials using a model-assisted swept frequency modulation field technique
Authors: Lo C. C. H.
Published: March 2009

This paper reports on a model-assisted approach to characterizing surface-modified materials whose magnetic properties vary continuously with depth. The technique involves measuring ac permeability profiles under a quasistatic biasing field superimposed with an ac modulation field of adjustable frequency and amplitude to control field penetration depth. A frequency dependent magnetic hysteresis model was used to model ac permeability profiles at different modulation field frequencies for direct comparison with measurement results. The approach was applied to characterize a series of surface hardened Fe–C samples. The depth dependence of the magnetic properties was determined by obtaining the best fits of the modeled ac permeability profiles to experimental data at multiple modulation frequencies. The midpoints of the inverted magnetic property profiles and the measured hardness profiles were found to be in agreement.
Exchange interaction in rapidly solidified nanocrystalline RE–(Fe/Co)–B hard magnetic alloys
Authors: Liu Z. W. , Zeng D. C. , Ramanujan R. V. , Zhong X. C. , Davies H. A.
Published: March 2009

The exchange interactions for rapidly solidified (Nd/Pr)(Fe/Co)B hard magnetic alloys with remanence enhancement were studied by analyzing characteristic magnetic curves and Henkel plots. The exchange coupling can be improved by increasing soft phase content within hard matrix. With increasing temperature, the exchange interaction is enhanced due to the increased exchange length. An increased recoil susceptibility was found for the alloys with improved exchange coupling. Analysis of the microstructure parameters indicated that Co substituting Fe and introducing soft α-(Fe,Co) phase not only reduce the stray field effects but also enhance the exchange interaction.
Spray pyrolysis deposited multiferroic BiFeO3 films
Authors: Siwach P. K. , Singh Jai , Singh H. K. , Varma G. D. , Srivastava O. N.
Published: March 2009

BiFeO 3 (BFO) films were prepared by nebulized spray pyrolysis technique on a single crystal LaAlO3 (001) substrate at ∼300 °C and annealing in oxygen at ∼550 °C for 1 h. In all films BFO is the majority phase having a rhombohedrally distorted structure with R3m symmetry and lattice parameters are a=3.96 Å and α=89.7°. Atomic force microscopy reveals smooth and dense surface morphology. Despite the G-type antiferromagnetic spin structure of BFO the present BFO show well-defined M-H loops and unexpected ferromagnetism as evidenced by large saturation magnetization, ∼125 emu/cc. The origin of anomalous ferromagnetism in the present films has been traced to the presence of nanometric Fe2O3 embedded in the BFO matrix.
Defect mediated tuning of exchange bias in IrMn/CoFe nanostructure
Authors: Shams Nazmun N. , Rahman M. Tofizur , Lai Chih-Huang
Published: March 2009

A simple nanofabrication process is introduced to tune the exchange bias in the magnetic nanostructures with a feature size below 15 nm. The IrMn/CoFe films are deposited on the porous alumina oxide (AAO) with different pore diameters from 10 to 48 nm, keeping the center-to-center distance almost the same at 60 nm, which is fabricated on Si wafers. A large enhancement in the exchange field Hex (2.3 times) and the coercivity Hc (8 times) is observed in the nanostructure compared to the continuous film. The exchange field is decreased with increasing pore diameter; on the other hand Hc increases continuously with increase in pore diameter. However, the values of Hex and Hc for all the exchange bias nanostructures are larger than those of the continuous film. These effects are mainly ascribed to the creation of domain walls or domains due to the pinning effect and the physical limitations that the pore size and edge-to-edge distance impose on both ferromagnetic and antiferromagnetic layers. Our results strongly support that exchange bias can be tuned by the AAO pores.
Magnetic domain formation within patterned NiFe/Cu/Co ellipses
Authors: Krycka K. L. , Maranville B. B. , Borchers J. A. , Castaño F. J. , Ng B. G. , Perkinson J. C. , Ross C. A.
Published: March 2009

Neutron reflectometry was used to study the formation and evolution of magnetic domains within a patterned array of NiFe/Cu/Co ellipses. The measurements directly show that domains form upon relaxation away from hard axis magnetic saturation, and their size and shape distributions are invariant throughout the process. Modeling of the data demonstrates that uniform magnetic domains are commensurate with the ellipse structure, but are approximately 75 nm smaller in radius. Together these findings suggest that there is one magnetic domain per nanoparticle whose constituent moments rotate collectively as the field is varied.
Effect of hydrogen doping in UTX compounds
Authors: Mašková Silvie , Havela Ladislav , Šantavá Eva , Miliyanchuk Khrystyna
Published: March 2009

Magnetic measurements on the hydrogenated systems U(Co,Fe)Sn and (U,Th)CoSn were performed as part of our investigation of UTX compounds (T—transitional metal and X—p-metal). Both series studied crystallize in the hexagonal structure of ZrNiAl type, space group P6¯2m symmetry. The crystal-structure type is not changed upon the hydrogenation. In all the cases it leads to a unit-cell expansion (ranging between 3.0% and 3.6%). The Curie temperature TC increases in the hydrides. This increment is reduced with increasing Fe concentration. In the compounds with the Th substitution, the Th concentration at which the ferromagnetism vanishes (∼60%) remains practically unchanged in the hydrides.
Translocation of magnetic beads using patterned magnetic pathways for biosensing applications
Authors: Anandakumar S. , Sudha Rani V. , Jeong J-R. , Kim CheolGi , Kim K. W. , Rao B. Parvatheeswara
Published: March 2009

We have designed, fabricated, and demonstrated a novel system for translocation of magnetic beads at specific sites of the sensor surface on a single chip for biosensor applications. The soft NiFe elliptical (9×4×0.1 μm3) elements are arranged as magnetic pathways connected to the model sensor surface. The patterned NiFe elements can generate different stray magnetic fields when they are subjected to the external rotating magnetic field. The inhomogeneity in stray magnetic fields can govern the magnetic bead motion on the pathways. We demonstrated the motion of Dynabead® M-280 magnetic bead on patterned pathways by controlling the external rotating magnetic field in clockwise and counterclockwise directions. The magnetic beads that were placed on the magnetic elliptical pathways are shown to be transported to the sensor surface, as well as be pulled out away from the surface. This technique enables microtranslocation of the magnetic beads coated with biomolecules to the specific binding sites of the sensor surface and as well as drive off the nonspecific binding biomolecules from the surface in performing number of sequential bead detection experiments for future integrated lab-on-a-chip systems.
Spectral micromagnetic analysis of switching processes
Authors: d’Aquino M. , Serpico C. , Bertotti G. , Schrefl T. , Mayergoyz I. D.
Published: March 2009

The switching process of a submicron-scale ferromagnetic thin-film is numerically computed and analyzed by using spectral representation in terms of the eigenfunctions of the self-adjoint operator which relates the magnetization vector field with the micromagnetic effective field. It is shown that only few spectral modes are involved in the dynamics. The analysis suggests that such basis functions could be used to develop spectral methods using only a considerable low number of modes. The general procedure to determine the nonlinear equation governing the evolution of the mode amplitudes is outlined.
Fabrication and properties of FePt thick films for alternative local field micromagnet
Authors: Jang Pyungwoo , Lee Bonghan , Seomoon Kyu , Rhie Kungwon , Choi Sungwon
Published: March 2009

Growth of FePt films thicker than several tens of a micrometer was attempted on Fe substrates for the use of micromagnets. Several underlayer or intermediate layers were found to be totally ineffective to success. However, 20 μm thick FePt films on the Fe substrates were successfully grown by sputtering after HF surface treatment. (BH)max of the non-annealed film was about 10.7 MG Oe under a maximum applied field of 10 kOe. An excellent adhesion between the Fe substrate and the FePt thick films seems to be due to both improvement of surface cleanliness and roughening which enhanced the chemical and physical bonding strengths.
Sensorless optimal sinusoidal brushless direct current for hard disk drives
Authors: Soh C. S. , Bi C.
Published: March 2009

Initiated by the availability of digital signal processors and emergence of new applications, market demands for permanent magnet synchronous motors have been surging. As its back-emf is sinusoidal, the drive current should also be sinusoidal for reducing the torque ripple. However, in applications like hard disk drives, brushless direct current (BLDC) drive is adopted instead of sinusoidal drive for simplification. The adoption, however, comes at the expense of increased harmonics, losses, torque pulsations, and acoustics. In this paper, we propose a sensorless optimal sinusoidal BLDC drive. First and foremost, the derivation for an optimal sinusoidal drive is presented, and a power angle control scheme is proposed to achieve an optimal sinusoidal BLDC. The scheme maintains linear relationship between the motor speed and drive voltage. In an attempt to execute the sensorless drive, an innovative power angle measurement scheme is devised, which takes advantage of the freewheeling diodes and measures the power angle through the detection of diode voltage drops. The objectives as laid out will be presented and discussed in this paper, supported by derivations, simulations, and experimental results. The proposed scheme is straightforward, brings about the benefits of sensorless sinusoidal drive, negates the need for current sensors by utilizing the freewheeling diodes, and does not incur additional cost.
Zonal flow in a tokamak pedestal
Authors: Kagan Grigory , Catto Peter J.
Published: March 2009

Neoclassical shielding is the dominant mechanism reducing the collisionless zonal flow in a tokamak. Previously, this phenomenon was analyzed in the case of an essentially homogeneous equilibrium since the wavelength of the zonal flow perturbation was assumed to be much less than the scale length of background plasma parameters. This assumption is not appropriate in a tokamak pedestal. Therefore the pedestal neoclassical polarization and the zonal flow residual differ from the conventional results. This change is due to the strong electric field intrinsic to a subsonic pedestal that modifies neoclassical ion orbits so that their response to a zonal flow perturbation is qualitatively different from that in the core. In addition to orbit squeezing, we find a spatial phase shift between the initial and final zonal flow potentials—an effect absent in previous works. Moreover, we demonstrate that because of orbit modification neoclassical phenomena disappear in the large electric field limit making the residual close to one.
Influence of microstructure on the thermal conductivity of magnetoresistive La0.7Ca0.3MnO3/Mn3O4 manganite/insulating oxide polycrystalline bulk composites
Authors: Mucha J. , Vertruyen B. , Misiorek H. , Ausloos M. , Durczewski K. , Vanderbemden Ph.
Published: March 2009

We report the temperature dependence of the thermal conductivity κ(T) of bulk polycrystalline composite samples containing a magnetoresistive manganite (La0.7Ca0.3MnO3) and an electrically insulating phase (Mn3O4). The sample porosity is shown to be a significant parameter affecting the experimental data: after porosity correction the curves display the characteristics of an ideal composite. A fit of the κ(T) curves at low temperature using the Debye model enables the mean free path of phonons scattered on “boundaries” to be determined. The values are on the order of the grain size but are influenced by the grain arrangement and the presence of twins.
Improvements of electronic and optical characteristics of n-GaN-based structures by photoelectrochemical oxidation in glycol solution
Authors: Shiozaki Nanako , Hashizume Tamotsu
Published: March 2009

Surface control of n-GaN was performed by applying a photoelectrochemical oxidation method in a glycol solution to improve the optical and electronic characteristics. The fundamental properties of the oxidation were investigated. The oxidation, chemical composition, and bonding states were analyzed by x-ray photoelectron spectroscopy and micro-Auger electron spectroscopy, in which confirmed the formation of gallium oxide on the surface. The oxide formation rate was about 8 nm/min under UV illumination of 4 mW/cm2. After establishing the basic properties for control of n-GaN oxidation, the surface control technique was applied to achieve low-damage etching, enhancement of the photoluminescence intensity, and selective passivation of the air-exposed sidewalls in an AlGaN/GaN high electron mobility transistor wire structure. The capacitance-voltage measurement revealed the minimum interface-state density between GaN and anodic oxide to be about 5×1011 cm−2 eV−1, which is rather low value for compound semiconductors.
An efficient algorithm for the density-functional theory treatment of dispersion interactions
Authors: Gräfenstein Jürgen , Cremer Dieter
Published: March 2009

The quasi-self-consistent-field dispersion-corrected density-functional theory formalism (QSCF-DC-DFT) is developed and presented as an efficient and reliable scheme for the DFT treatment of van der Waals dispersion complexes, including full geometry optimizations and frequency calculations with analytical energy derivatives in a routine way. For this purpose, the long-range-corrected Perdew–Burke–Ernzerhof exchange functional and the one-parameter progressive correlation functional of Hirao and co-workers are combined with the Andersson–Langreth–Lundqvist (ALL) long-range correlation functional. The time-consuming self-consistent incorporation of the ALL term in the DFT iterations needed for the calculation of forces and force constants is avoided by an a posteriori evaluation of the ALL term and its gradient based on an effective partitioning of the coordinate space into global and intramonomer coordinates. QSCF-DC-DFT is substantially faster than SCF-DC-DFT would be. QSCF-DC-DFT is used to explore the potential energy surface (PES) of the benzene dimer. The results for the binding energies and intermolecular distances agree well with coupled-cluster calculations at the complete basis-set limit. We identify 16 stationary points on the PES, which underlines the usefulness of analytical energy gradients for the investigation of the PES. Furthermore, the inclusion of analytically calculated zero point energies reveals that large-amplitude vibrations connect the eight most stable benzene dimer forms and make it difficult to identify a dominating complex form. The tilted T structure and the parallel-displaced sandwich form have the same D0 value of 2.40 kcal/mol, which agrees perfectly with the experimental value of 2.40±0.40 kcal/mol.
Observation of the isotopic evolution of pressurized water reactor fuel using an antineutrino detector
Authors: Bowden N. S. , Bernstein A. , Dazeley S. , Svoboda R. , Misner A. , Palmer T.
Published: March 2009

By operating an antineutrino detector of simple design during several fuel cycles, we observed long term changes in antineutrino flux that result from the isotopic evolution of a commercial pressurized water reactor. Measurements made with simple antineutrino detectors of this kind offer an alternative means for verifying fissile inventories at reactors, as part of International Atomic Energy Agency and other reactor safeguards regimes.
Thermal balance of carbon nanoparticles in sputtering discharges
Authors: Arnas C. , Mouberi A. A.
Published: March 2009

The heating and cooling mechanisms of carbon nanoparticles produced by homogeneous nucleation from sputtering discharges are examined. The experiments show that particulates of several nanometers are graphitelike and therefore, are heated in the plasma. Conversely, particulates of several tens of nanometers have an amorphous carbon structure, characteristic of cold material. A classical model of thermal balance shows that nanoparticles are heated by energy transfer from the plasma particles and that big particles are efficiently cooled by thermal conduction with the discharge gas of low temperature. For a given size, the calculated dust temperature is in good agreement with the dust temperature range deduced from carbon structural analyses.
Lifetime and quantum yield studies of Dy3+ doped GdVO4 nanoparticles: Concentration and annealing effect
Authors: Singh N. Shanta , Ningthoujam R. S. , Yaiphaba N. , Singh S. Dorendrajit , Vatsa R. K.
Published: March 2009

GdVO 4 nanoparticles doped with Dy3+ have been prepared using urea hydrolysis method in ethylene glycol medium. Linear decrease in the unit cell volume indicates the quantitative substitution of Gd3+ lattice sites by Dy3+ in GdVO4. The luminescence intensity of electric dipole transition at 573 nm is more than that of magnetic dipole transition at 483 nm. This has been attributed to the asymmetric environment of Dy3+ ion in GdVO4. Luminescence intensity decreases with increasing Dy3+ concentrations due to concentration quenching. This is supported by lifetime decay studies. There is no particle size effect on the peak positions of Dy3+ emission. There is an increase in the decay lifetime for F49/2 level with increase in heat treatment from 500 to 900 °C. This is attributed to the reduction in nonradiative process arose from surface inhomogeneities. The decay lifetime data follow the biexponential to monoexponential nature with increase of Dy3+ concentrations. There is an increase in the quantum yield with the increase in heat treatment temperature.
Enhanced chemical vapor deposition of diamond by wavelength-matched vibrational excitations of ethylene molecules using tunable CO2 laser irradiation
Authors: Ling H. , Xie Z. Q. , Gao Y. , Gebre T. , Shen X. K. , Lu Y. F.
Published: March 2009

Wavelength-matched vibrational excitations of ethylene (C2H4) molecules using a tunable carbon dioxide (CO2) laser were employed to significantly enhance the chemical vapor deposition (CVD) of diamond in open air using a precursor gas mixture of C2H4, acetylene (C2H2), and oxygen (O2). The CH2-wag vibration mode (ν7) of the C2H4 molecules was selected to achieve the resonant excitation in the CVD process. Both laser wavelengths of 10.591 and 10.532 μm were applied to the CVD processes to compare the C2H4 excitations and diamond depositions. Compared with 10.591 μm produced by common CO2 lasers, the laser wavelength of 10.532 μm is much more effective to excite the C2H4 molecules through the CH2-wag mode. Under the laser irradiation with a power of 800 W and a wavelength of 10.532 μm, the grain size in the deposited diamond films was increased by 400% and the film thickness was increased by 300%. The quality of the diamond crystals was also significantly enhanced.
Surface and interface reactions of sputtered TiNi/Si thin films
Authors: Kumar A. K. Nanda , Jayakumar S. , Kannan M. D. , Rajagopalan S. , Balamurugan A. K. , Tyagi A. K. , Kumar Sanjeev , Reddy G. L. N. , Ramana J. V. , Raju V. S.
Published: March 2009

We present the surface and interfacial chemical analysis of sputter deposited TiNi thin films over Si (100) substrates using Rutherford backscattering spectrometry (RBS), secondary ionization mass spectrometry (SIMS), and grazing incidence x-ray diffraction analysis. Upon annealing to high temperatures, significant diffusion of Ni into the Si substrate was observed. The analysis of the RBS and SIMS spectra confirm the net movement of the film species into the substrate. Further, we discuss the formation mechanism and the composition distribution surrounding the TiNi/Si interface that proves conducive for the nucleation and growth of the detected nickel silicide compound.
Experimental investigation of the swirling flow and the helical vortices induced by a twisted tape inside a circular pipe
Authors: Cazan Radu , Aidun Cyrus K.
Published: March 2009

The present paper describes the experimental investigation of the turbulent swirling flow induced by a twisted tape (or fin) into a 1 in. diameter pipe. The investigation shows the existence of two corotating helical vortices superimposed over the main swirling flow. The close proximity of the two corotating vortices creates a local reversing flow at the pipe centerline. The flow is investigated using LDV measurements and high speed camera visualization with fine air bubble seeding. Three swirlers with 45, 60, and 90 mm pitch are investigated. Through a reconstruction technique, the tangential flow field induced by a twisted tape swirler with 60 mm pitch at Re=7.7×104 is described by superposition of 385 measurements. Images and movies recorded with regular and high speed cameras clearly show that the helical vortices are very stable and that they rotate around their own axis, confirming the measurements. After extracting the characteristic tangential velocity profiles of the main vortex and of the two secondary vortices, it was observed that the maximum tangential velocity of all three vortices is almost the same, approximately half of the bulk velocity. The pitch of the helical vortices was found to be 4/3 of the pitch of the twisted tape for all three swirlers investigated, independent of Reynolds number. We hypothesize that the helical vortices are generated by vortices originating inside the twisted tape swirler. The main rotational flow accelerates the corotating vortices and decelerates the counter-rotating vortices. As a result, the counter-rotating vortices disappear while the corotating vortices reach the same maximum tangential velocity as the main flow. Thus the tangential velocity near the wall is approximately doubled by the presence of the secondary vortices.
Simulation of reduced glass transition temperature of Cu–Zr alloys by molecular dynamics
Authors: Kao Su-Wen , Hwang Chi-Chuan , Chin Tsung-Shune
Published: March 2009

Estimation of glass forming ability (GFA) of alloys by simulation before experimental trial and errors has long been a tempting pursuit in exploration of bulk metallic glasses. Reduced glass transition temperature (Trg) of CuxZr100−x alloys (x=46, 50, 62) were simulated by molecular dynamics using tight-binding potentials. Glass transition temperature (Tg) and melting temperature (Tm) of each alloy were calculated separately to obtain Trg (=Tg/Tm) as an indicator of GFA. It is shown that the calculated Tg and Trg values of CuxZr100−x alloys are in agreement with experimental data within 2%–8%, and 5%–11%, respectively. Simulation as such provides a possibility to preliminarily sort out alloys worthy of experimental trials.
A micromechanics-based model for temperature effect on piezoelectric and dielectric constants of ferroelectric crystals
Authors: Cao Yang , Li Jackie
Published: March 2009

A micromechanics-based thermodynamic model is applied to study the piezoelectric and dielectric constants of BaTiO3 crystals as a function of temperature upon the cooling from the Curie point. The formation of spontaneous polarization at the beginning of cooling provides dramatic change in symmetry of the system. This plays an important role for the sudden change in piezoelectric constant of d31 at the beginning of the cooling. In this article, by considering such a heterogeneous nature of the crystal at the beginning of the cooling due to spontaneous polarization, the micromechanics-based model is able to evaluate the piezoelectric coefficient d31. To verify this modified model, the dielectric constant k33 of a BaTiO3 crystal in terms of temperature is also calculated and compared with the existing micromechanics-based model in the literature [Y. Su and G. J. Weng, J. Mech. Phys. Solids 53, 2071 (2005)]. It shows agreeable and improved result in dielectric constant k33 of BaTiO3. Both dielectric and piezoelectric constants are also found to be consistent with the available experimental data.
Relativistic all-electron molecular dynamics simulations
Authors: Thar Jens , Kirchner Barbara
Published: March 2009

The scalar-relativistic Douglas–Kroll–Hess method is implemented in the Born–Oppenheimer molecular dynamics simulation package CP2K. Using relativistic densities in a nonrelativistic gradient routine is found to be a valid approximation of relativistic gradients. An excellent agreement between optimized structures and geometries obtained from numerical gradients is observed with an error smaller than 0.02 pm. Hydrogen halide dimers [(HX)2, with X=F, Cl, Br, I] serve as small test systems for first-principles molecular dynamics simulations. Relativistic effects are observed. That is, the amplitude of motion is larger, the frequency of motion is smaller, and the distances are larger in the relativistic picture. Several localization schemes are evaluated for different interatomic and intermolecular distances. The errors of these localization schemes are small for geometries which are similar to the equilibrium structure. They become larger for smaller distances, introducing a slight bias toward closed packed configurations.
Characterization of nonlinear absorption of InN epitaxial films with femtosecond pulsed transmission Z-scan measurements
Authors: Tsai Tsong-Ru , Wu Tsung-Han , Liao Jung-Cheng , Wei Tai-Huei , Chiang Hai-Pang , Hwang Jih-Shang , Tsai Din-Ping , Chen Yang-Fang
Published: March 2009

The femtosecond pulsed Z-scan measurements of the resonant nonlinear optical absorption of the InN epitaxial films in the range of 720–790nm were reported. The absorption saturation behavior was found to gradually decrease with increasing photon energy. The nonlinear optical absorption cross sections of the InN films were estimated and the values are found to be in good agreement with the calculations based on the band-filling model. These results are relevant for the future development of nonlinear optical devices based on InN.
Phase contrast imaging measurements of reversed shear Alfvén eigenmodes during sawteeth in Alcator C-Mod
Authors: Edlund E. M. , Porkolab M. , Kramer G. J. , Lin L. , Lin Y. , Wukitch S. J.
Published: March 2009

Reversed shear Alfvén eigenmodes (RSAEs) have been observed with the phase contrast imaging diagnostic and Mirnov coils during the sawtooth cycle in Alcator C-mod [M. Greenwald et al., Nucl. Fusion 45, S109 (2005)] plasmas with minority ion-cyclotron resonance heating. Both down-chirping RSAEs and up-chirping RSAEs have been observed during the sawtooth cycle. Experimental measurements of the spatial structure of the RSAEs are compared to theoretical models based on the code NOVA [C. Z. Cheng and M. S. Chance, J. Comput. Phys. 71, 124 (1987)] and used to derive constraints on the q profile. It is shown that the observed RSAEs can be understood by assuming a reversed shear q profile (up chirping) or a q profile with a local maximum (down chirping) with q≈1.