bluuebunny/crossref_metadata_2025 huggingface dataset:
Relation between coronal type II bursts, associated flares and CMEs
Authors: Pothitakis George , Preka-Papadema Panagiota , Moussas Xenophon , Caroubalos Constantine , Alissandrakis Constantine , Tsitsipis Panagiotis , Kontogeorgos Athanasios , Hillaris Alexander
Published: March 2009

We study a sample of complex events; each includes a coronal type II burst, accompanied by a GOES SXR flare and LASCO CME. The radio bursts were recorded by the ARTEMIS-IV radio spectrograph (100-650 MHz range); the GOES SXR flares and SOHO/LASCO CMEs, were obtained from the Solar Geophysical Data (SGD) and the LASCO lists respectively. The radio burst-flare-CME characteristics were compared and two groups of events with similar behavior were isolated. In the first the type II shock exciter appears to be a flare blast wave propagating in the wake of a CME. In the second the type II burst appears CME initiated though it is not always clear if it is driven by the bow or the flanks of the CME or if it is a reconnection shock.
Observations of radio spectra at 1–2.5 GHz associated with CME start time
Authors: Cecatto José R.
Published: March 2009

We know Coronal Mass Ejections (CME) and flares are the most energetic phenomena happening on the Sun. Until now the information about origin and trigger mechanism of CMEs remains scarce. Also, there is unconclusive information about the association between them and flares although progress has been made in recent years. Multi-spectral observations suggested that the flare energy release occurs in regions from where the decimetric radio emission originates. In this case, investigations of the solar emission in this wavelength range can give us valuable information about these questions. During last solar maximum the Brazilian Solar Spectroscope (BSS) observed the solar radio spectrum (1–2.5 GHz) with high time (100–20 ms) and frequency (50–100 channels) resolutions on a daily (11–19 UT) basis. A survey during the period 1999–2002, shows that a significant fraction (20% –57 events) of CMEs recorded by LASCO has an association with the spectra of radio bursts recorded by BSS. Analysis of the radio spectrum associated to CME shows there is a dominance of continuum and/or pulsation and that the association becomes stronger when we consider the CME acceleration since its origin on the Sun. A statistics of this association between CME dynamics and the characteristics of decimetric radio bursts recorded by BSS is presented. Emphasis is given to observations of the association with CME start time.
Explosion of sungrazing comets in the solar atmosphere and solar flares
Authors: Ibadov S. , Ibodov F. S. , Grigorian S. S.
Published: March 2009

Explosive evolution of nuclei of sungrazing comets near the solar surface, which occurs at conditions of intense interaction between the solar atmosphere and falling high-velocity comet nuclei as well as the relation of the phenomenon to the character of solar activity are analytically considered. It is found that, due to aerodynamic fragmentation of the falling body in the solar chromosphere and transversal expansion of the fragmented mass under the action of pressure gradient on the frontal surface, thermalization of the kinetic energy of the body occurs by sharp stopping of the disklike hypervelocity fragmented mass near the solar surface within a relatively very thin subphotospheric layer and has, therefore, an essentially impulsive and strongly explosive character. The specific energy release in the explosion region, erg/g, considerably exceeds the evaporation/sublimation heat of the body so that the process is accompanied by production of a high-temperature plasma. The energetics of such an explosive process corresponds to that of very large solar flares for falling bodies having masses equal to the mass of the nucleus of Comet Halley. Spectral observations of sungrazing comets by SOHO-like telescopes in a wide spectral range, including X rays, with a high time resolution, of the order of 0.1–10 s, are important for revealing solar activity in the form of an impact-generated photospheric flare.
Dynamics of microwave brightness distribution in the giant 24 August 2002 flare loop
Authors: Reznikova Veronika E. , Melnikov Victor F. , Shibasaki Kiyoto , Gorbikov Sergey P. , Pyatakov Nikolai P. , Myagkova Irina N. , Ji Haisheng
Published: March 2009

We have found a similar tendency of the spatial dynamics at 34 GHz for all major temporal sub-peaks of the burst with the re-distribution of the brightness from the footpoints (on the rising phase of each peak) to the upper part of the loop (on the decay phase). Observed dynamics is interpreted by the re-distribution of accelerated electrons number density with their relative enhancement in the loop top. Results of diagnostics show that the ratio of non-thermal electron number density in the loop top and in the footpoint changes 7 times from the peak to decay phase. Model simulations by solving the Fokker-Planck equation allowed to determine an injection type which is able to result in necessary dynamics of energetic electrons.
Magnetic field in active regions of the sun at coronal heights
Authors: Bogod V. M. , Yasnov L. V.
Published: March 2009

A method is developed for estimation of the vertical structure of the magnetic field in active regions using multi-wave spectral-polarization measurements of radio waves which gives not only the dependence of magnetic field strength on height but also determines two-dimensional form of a magnetic flux tube, emitted in the microwave range of wavelengths.
Magnetic helicity content in solar wind flux ropes
Authors: Dasso Sergio
Published: March 2009

Magnetic helicity (H) is an ideal magnetohydrodynamical (MHD) invariant that quantifies the twist and linkage of magnetic field lines. In magnetofluids with low resistivity, H decays much less than the energy, and it is almost conserved during times shorter than the global diffusion timescale. The extended solar corona (i.e., the heliosphere) is one of the physical scenarios where H is expected to be conserved. The amount of H injected through the photospheric level can be reorganized in the corona, and finally ejected in flux ropes to the interplanetary medium. Thus, coronal mass ejections can appear as magnetic clouds (MCs), which are huge twisted flux tubes that transport large amounts of H through the solar wind. The content of H depends on the global configuration of the structure, then, one of the main difficulties to estimate it from single spacecraft in situ observations (one point - multiple times) is that a single spacecraft can only observe a linear (one dimensional) cut of the MC global structure. Another serious difficulty is the intrinsic mixing between its spatial shape and its time evolution that occurs during the observation period. However, using some simple assumptions supported by observations, the global shape of some MCs can be unveiled, and the associated H and magnetic fluxes (F) can be estimated. Different methods to quantify H and F from the analysis of in situ observations in MCs are presented in this review. Some of these methods consider a MC in expansion and going through possible magnetic reconnections with its environment. We conclude that H seems to be a ‘robust’ MHD quantity in MCs, in the sense that variations of H for a given MC deduced using different methods, are typically lower than changes of H when a different cloud is considered. Quantification of H and F lets us constrain models of coronal formation and ejection of flux ropes to the interplanetary medium, as well as of the dynamical evolution of MCs in the solar wind.
The August 24, 2002 coronal mass ejection: when a western limb event connects to earth
Authors: Lugaz Noé , Roussev Ilia I. , Sokolov Igor V.
Published: March 2009

We discuss how some coronal mass ejections (CMEs) originating from the western limb of the Sun are associated with space weather effects such as solar energetic particles (SEPs), shocks or geo-effective ejecta at Earth. We focus on the August 24, 2002 coronal mass ejection, a fast (~2000 km s−1) eruption originating from W81. Using a three-dimensional magneto-hydrodynamic simulation of this ejection with the Space Weather Modeling Framework (SWMF), we show how a realistic initiation mechanism enables us to study the deflection of the CME in the corona and the heliosphere. Reconnection of the erupting magnetic field with that of neighboring streamers and active regions modify the solar connectivity of the field lines connecting to Earth and can also partly explain the deflection of the eruption during the first tens of minutes. Comparing the results at 1 AU of our simulation with observations by the ACE spacecraft, we find that the simulated shock does not reach Earth, but has a maximum angular span of about 120°, and reaches 35° West of Earth in 58 hours. We find no significant deflection of the CME and its associated shock wave in the heliosphere, and we discuss the consequences for the shock angular span.
Planetary ionospheres – sources and dynamic drivers
Authors: Grebowsky Joseph M. , Aikin Arthur C.
Published: March 2009

External energy inputs into all planetary upper atmospheres (including more than a half dozen moons with atmospheres) are comprised of combinations of solar EUV, soft x-rays, solar energetic particles, solar wind charged particles, magnetospherically accelerated particles, solar wind electric field, interplanetary dust particles as well as propagating lower atmosphere disturbances. Each input has analogous physical interactions with all planetary ionospheres and upper atmospheres, but the integrated consequences of the multiple energy inputs vary from planet to planet. The Earth forms the framework for most fundamental processes because of extensive measurements of the effects of each of the inputs. However the conditions at Earth are far different from those at the carbon dioxide atmosphere of magnetic field-free, slow-rotating Venus, the carbon dioxide atmosphere of Mars with patchy remnant magnetic fields, while the outer planets have hydrogen atmospheres, are fast rotating with intrinsic magnetic fields, and encompass moons that interact with the magnetospheres and have exotic atmospheres. Although the physical processes are known, our understanding of our solar system's ionospheres diminishes with increasing distance from the Sun.
Characteristic signatures of energetic ions upstream from the Kronian magnetosphere as revealed by Cassini/MIMI
Authors: Malandraki Olga E. , Krimigis S. M. , Sarris E. T. , Sergis N. , Dialynas K. , Mitchell D. G. , Hamilton D. C. , Geranios A.
Published: March 2009

We present unique observations obtained by the Magnetospheric Imaging Instrument (MIMI) on the Cassini spacecraft, of the energetic ion population in the environment upstream from the dawn-to-noon sector of the Kronian magnetosphere during the approach phase and subsequent several orbits of the Cassini spacecraft around the planet. High sensitivity observations of energetic ion directional intensities, energy spectra, and ion composition were obtained by the Ion and Neutral Camera (INCA) of the MIMI instrument complement with a geometry factor of ~2.5 cm2sr. Charge state information was provided by the Charge-Energy-Mass-Spectrometer (CHEMS) over the range ~3 to 220 keV per charge. The observations revealed the presence of distinct upstream bursts of energetic hydrogen and oxygen ions up to distances of ~135 RS. The observations are presented and their theoretical implications are addressed.
MHD Kamchatnov-Hopf soliton in the model of primordial solar nebula
Authors: Salmin Vladimir V.
Published: March 2009

Stereographic projection of Hopf field on the 3-sphere into Euclidean 3-space is used as a model of 3D steady flow of ideal compressible fluid in MHD. In such case, flow lines are Villarceau circles lying on tori corresponding to the levels of Bernoulli function. Existence of an optimal torus with minimal relative surface free energy is shown. Beat of oscillations with wave numbers corresponding to structural radii of optimal torus leads to scaling of optimal tori. Spatial intersection of homothetic tori within one torus result in formation of cluster with the size depending on scaling factor. Optimal tori are considered as precursors of planetary orbits.
Energy balance and cascade in MHD turbulence in the solar corona
Authors: Malara Francesco , Nigro Giuseppina , Veltri Pierluigi
Published: March 2009

The dynamics of fluctuations in a closed coronal structure is regulated both by resonance with motions at bases that stores energy in the structure in form of discrete eigenmodes, and by nonlinear couplings that move this energy along the spectrum to smaller scales. The energy balance is evaluated both analytically and, numerically, using an hybrid shell model. The input energy flux is independent of nonlinear effects and is determined by slow (DC) perturbations. Coherent eigenmode couplings determine the nonlinear energy flux and, consequently, the level of fluctuations at large scales. The estimated velocity fluctuation level is in agreement with measures of nonthermal velocity in corona. The resulting turbulence spectrum contains both a pre-inertial range where coherent interactions dominate, and a standard inertial range where the turbulence behaves as in an unbounded system.
Generation and propagation of Alfvén waves in solar atmosphere
Authors: Tsap Yuri T. , Stepanov Alexander V. , Kopylova Yulia. G.
Published: March 2009

The propagation of Alfvén waves from the photosphere into the corona with regard to the fine structure of the magnetic field is considered. The energy flux of Alfvén–type waves generated in the photosphere by convective motions does not depend on the ionization ratio. The reflection coefficient continuously decreases with a decrease of wave period. Influence of the external magnetic field on the Spruit cutoff frequency for transverse (kink) modes excited in the thin magnetic flux tubes is analyzed. Torsional modes can penetrate into the upper atmosphere most effectively since their amplitudes does not increase with height in the photosphere while kink ones can be transformed into shock waves in the lower chromosphere because of a significant increase of amplitudes. In spite of stratification the linearity of Alfvén–type modes in the chromosphere is conserved due to violation of the WKB approximation. The important role of the magnetic canopy is discussed. Alfvén waves generated by convective motions in the photosphere can contribute significantly to the heating of the coronal plasma in quite regions of the Sun.
Alfvén waves in a gravitational field with flows
Authors: Narayanan A. Satya , Kathiravan C. , Ramesh R.
Published: March 2009

The gravitational stratification effect on magnetohydrodynamic waves at a single interface in the solar atmosphere has been studied in the penumbral region of the sunspot recently. The existence of slow and fast magneto acoustic gravity waves and their characteristics has been discussed. The effect of flows on magneto acoustic gravity surface waves leads to modes called flow modes or v-modes. The present geometry is that of a plasma slab moving with uniform velocity surrounded by a plasma of different density. As is applicable to the corona, we assume that the plasma β to be small. The dispersion characteristics change significantly with a change in the value of G (gravity) and uniform flow.
Flows and obstacles in the heliosphere
Authors: Richardson John D.
Published: March 2009

The supersonic solar wind is highly variable on all time scales near the Sun but fluctuations are moderated by self-interaction as this plasma moves outward. The solar wind runs into many obstacles on its way out. The neutrals from the interstellar medium slow it down. Magnetospheres and interplanetary coronal mass ejections (ICMEs) cause shocks to form so that the flow can divert around these obstacles. Finally the solar wind is stopped by the circum-heliospheric interstellar medium (CHISM); it slows at the termination shock and then turns down the heliotail. The shocks and sheaths formed by these interactions cover scales which vary by orders of magnitude; some aspects of these shocks and sheaths look very similar and some very different. We discuss solar wind evolution, interaction with the neutrals from the CHISM, foreshocks, shock structure, shock heating, asymmetries, and sheath variability in different sheath regions.
3D evolution of solar magnetic fields and high-speed solar wind streams near the minimum of solar cycle 23
Authors: Yakovchouk O. S. , Veselovsky I. S. , Mursula K. , Shugai Yu. S.
Published: March 2009

The numerical method developed by Veselovsky & Ivanov (2006), together with magnetograms of the Sun obtained at the photospheric level were used to calculate the coronal magnetic field with open, closed and intermittent topology during March-December 2007. The results of the modelling are compared with stereoscopic images and movies of the corona observed by EUV telescopes onboard STEREO and SOHO spacecraft. The sources of the permanent and transient high speed solar wind streams as well as the sector structure and the heliospheric plasma sheet observed at the Earth's orbit by the ACE and STEREO spacecraft are discussed.
Complexity in earthquake sequences controlled by multiscale heterogeneity in fault fracture energy
Authors: Aochi Hideo , Ide Satoshi
Published: March 2009

A series of dynamic rupture events under constant tectonic loading is simulated on a fault with multiscale heterogeneity and a stochastic rupture initiation process. The fracture energy of the fault plane is assumed to have multiscale heterogeneous distribution using fractal circular patches. The stochastic rupture initiation process as a function of the accumulated stress is introduced in order to take account of unknown smaller‐scale heterogeneity and variability. Five realizations of a statistical spatial distribution of fracture energy (fault heterogeneity maps) are tested for the simulations of earthquake sequences during a few seismic cycles. The diversity of earthquake sequences is principally controlled by the spatial distribution of the patches. The effect of dynamic rupture appears in the residual stress after the characteristic events because of their directivity and this localizes the subsequent sequences. Although the characteristic earthquakes occur rather regularly in time and similarly in different seismic cycles, some irregular behavior is found based on the heterogeneity maps and the randomness of the preceding earthquake sequence, leading to a visible anomaly in the seismicity. Such anomalies are not predicable but understandable through the analysis of the considered earthquakes during the cycle. The similarity and the diversity simulated in this study, governed by the structure of an inherent distribution of multiscale heterogeneity, suggest the importance of the pre‐existing heterogeneity field along the fault for the appearance of earthquake sequences, including those that are characteristic.
Surface circulation in the Gulf of Cadiz: 2. Inflow‐outflow coupling and the Gulf of Cadiz slope current
Authors: Peliz Alvaro , Marchesiello Patrick , Santos A. Miguel P. , Dubert Jesus , Teles‐Machado Ana , Marta‐Almeida Martinho , Le Cann Bernard
Published: March 2009

A study of the upper slope circulation in the Gulf of Cadiz is presented. Observations, both original and revisited, and realistic numerical modeling are used together to describe the structure and variability of the slope current system above the Mediterranean outflow. It is shown that the Mediterranean inflow‐outflow coupling plays a stronger role than that of the atmospheric forcing in driving the upper slope currents. The Mediteranean outflow forces a surface open ocean current toward the Strait of Gibraltar. Part of it is entrained into the outflow and the remaining flows into the Mediterranean. This latter component does not suffice for the observed transport of the Atlantic inflow into the Mediterranean. A secondary contribution to the inflow is therefore needed to complement the transport. This contribution comes from a persistent equatorward current along the upper slope between Cape St. Vincent and the Strait of Gibraltar. The jet is 20–30 km wide and significant in the upper 200 m attaining subinertial maxima as much as 0.3–0.4 m/s and monthly means in the order of 0.1–0.15 m/s. This current shows a strong variability at time scales in the order of 2–8 days, and displays a significant vertical shear. The response of the upper slope current to synoptic and seasonal atmospheric variability is analyzed. Very low correlation was detected at synoptic scales and the response of the system to seasonal forcing is unclear. A cycle of intensification in June–July and a decrease in winter is apparent in the measurements, but is weak in the model results. It is speculated that the cycle in the observed currents is associated with variability in the inflow/outflow coupling system, rather than driven by seasonally changing wind forcing.
Stratospheric variability and tropospheric ozone
Authors: Hsu Juno , Prather Michael J.
Published: March 2009

Changes in the stratosphere‐troposphere exchange (STE) of ozone over the last few decades have altered the tropospheric ozone abundance and are likely to continue doing so in the coming century as climate changes. Combining an updated linearized stratospheric ozone chemistry (Linoz v2) with parameterized polar stratospheric clouds (PSCs) chemistry, a 5‐year (2001–2005) sequence of the European Centre for Medium‐Range Weather Forecasts (ECMWF) meteorology data, and the University of California, Irvine (UCI) chemistry transport model (CTM), we examined variations in STE O3 flux and how it perturbs tropospheric O3. Our estimate for the current STE ozone flux is 290 Tg/a in the Northern Hemisphere (NH) and 225 Tg/a in the Southern Hemisphere (SH). The 2001–2005 interannual root‐mean‐square (RMS) variability is 25 Tg/a for the NH and 30 Tg/a for the SH. STE drives a seasonal peak‐to‐peak NH variability in tropospheric ozone of about 7–8 Dobson unit (DU). Of the interannual STE variance, 20% and 45% can be explained by the quasi‐biennial oscillation (QBO) in the NH and SH, respectively. The CTM matches the observed QBO variations in total column ozone, and the STE O3 flux shows negative anomalies over the midlatitudes during the easterly phases of the QBO. When the observed column ozone depletion from 1979 to 2004 is modeled with Linoz v2, we predicted STE reductions of at most 10% in the NH, corresponding to a mean decrease of 1 ppb in tropospheric O3.
Characterization of oxygen vacancies and their migration in Ba-doped Pb(Zr0.52Ti0.48)O3 ferroelectrics
Authors: Zhang M. F. , Wang Y. , Wang K. F. , Zhu J. S. , Liu J.-M.
Published: March 2009

We investigate in detail the migration kinetics of oxygen vacancies (OVs) in Ba-doped Pb(Zr0.52Ti0.48)O3 (PZT) ferroelectrics by complex impedance spectroscopy. The temperature dependent dc-electrical conductivity σdc suggests that Ba doping into PZT can lower significantly the density of OVs, leading to the distinctly decreased σdc and slightly enhanced activation energy U for the migration of OVs, thus benefiting the polarization fatigue resistance. Furthermore, the polarization fluctuation induced by the relaxation of OVs is reduced by the Ba doping. The Cole–Cole fitting to the dielectric loss manifests strong correlation among OVs, and the migration of OVs appears to be a collective behavior.
Structural and electric properties of SrZrO3 thin films with different annealing conditions
Authors: Tang Chunhong , Lu Xiaomei , Huang Fengzhen , Wu Xiaobo , Cai Wei , Zhu Jinsong
Published: March 2009

SrZrO 3 (SZO) thin films were deposited on (111) Pt/Ti/SiO2/Si substrates via metal organic decomposition method at different temperatures in flowing oxygen or nitrogen atmospheres. The microstructures of the films were characterized by x-ray diffraction. The dielectric properties and the leakage characteristics were investigated as well. The results showed that nitrogen ambient was helpful for the SZO films to crystallize into perovskite phase with polycrystalline structure. Meanwhile, the electric properties varying with annealing conditions were discussed in detail.
Effect of BaTiO3 buffer layer on multiferroic properties of BiFeO3 thin films
Authors: Yang Pan , Kim Kyung Man , Joh Young-Gull , Kim Dong Ho , Lee Jai-Yeoul , Zhu Jinsong , Lee Hee Young
Published: March 2009

BiFeO 3 (BFO) films were processed on BaTiO3 (BTO) buffered (111) Pt/Ti/SiO2/Si substrate by pulsed laser deposition. Improved ferroelectric properties, as well as induced ferromagnetism, were observed by the insertion of a BTO layer for rather thick BFO films (450 nm) deposited at an oxygen pressure of 40 mTorr. Reduced leakage current, coercive field, and increased ferroelectric saturation of BFO/BTO bilayer films were obtained and compared with those of BFO films. In order to better understand the buffer layer effect on the magnetic properties, two thinner (140 and 220 nm) BFO films were also deposited and investigated. Both films showed ferromagnetic hysteresis loops and larger in-plane magnetization than out-of-plane magnetization. By introducing the BTO barrier layer, the remnant and saturated magnetizations were also increased. These results demonstrated not only the interface constraint effect but also a coupling between ferroelectric BTO and magnetic BFO, which deserve further investigation.
Growth mode of sol-gel derived PLT seeding layers on glass substrates and its effect on templating the oriented growth of PLZT thin films
Authors: Du Z. H. , Zhang T. S. , Zhu M. M. , Ma J.
Published: March 2009

Highly (100) oriented PLT (La/Zr/Ti: 14/0/100) seeding layers have been developed on glass substrates by the optimized sol-gel process. The early growth stages of the seeding layers have been studied by continuously decreasing film thickness to tens of atomic layers (∼8 nm thick) from ∼50 nm and Volmer–Weber growth mode has been observed. The seeding layers consist of islandlike clusters inside which the grains were radially assembled. The mechanisms for the oriented growth of the seeding layers were then explained. The seeding layers with different island densities could induce distinct orientation degree and perovskite formation for the subsequently deposited PLZT (9/65/35) films. The PLZT films grown on continuous seeding islands exhibited the highest orientation degree and desirable optical and electro-optic properties.
Graded permanent magnets
Authors: Skomski R. , Hadjipanayis G. C. , Sellmyer D. J.
Published: March 2009

The effect of semihard magnetic phases and interfaces on the performance of nanostructured two-phase permanent magnets is investigated by model calculations. In addition to the trivial coercivity increase due to the replacement of soft regions by semihard regions, there is a coercivity enhancement even if the volume-averaged anisotropy is kept constant during the introduction of the semihard phase. A variational approach is used to derive analytical results for representative anisotropy profiles. The improvement is operative on length scales slightly larger than that of the soft phase in hard-soft composites, but the main challenge is to find semihard light or heavy transition metal phases with a high magnetization. There are several Fe- and Co-based phases, but most are thin-film systems and difficult to use in bulk magnets. Very hard nanostructured magnets may also be created from soft phases with negative but large anisotropy constants (hard-magnetic soft-soft magnets).
Pharmacokinetics of intravenously injected Tc-99m labeled ferrite nanobeads
Authors: Fu Chao-Ming , Wang Yuh-Feng , Guo Yu-Feng , Wang Li-Shin , Chuang May-Haw , Cham Thau-Ming
Published: March 2009

We study the time varying biodistribution of ferrite (Fe3O4) nanoparticles upon in vivo injection. For this purpose, a novel process of directly labeling radioactive Tc-99m with ferrite nanoparticles was developed. The radiobeads serve as a tracer to provide information on the uptake of injected particles by organs. In the course of our study, Tc-99m labeled ferrite beads were intravenously injected into the tail vein of rats. The time course of changes in the radio-intensity of heart, lung, and liver could be achieved by real-time scintigraphic images. It was observed that the particle uptake by organs is very fast and completed within the first few minutes after intravenous injection. The pharmacokinetic behavior of the radiobead uptake was quantitatively described by a two-compartment model.
A study on the integration of contactless energy transfer in the end teeth of a PM synchronous linear motor
Authors: Krop D. C. J. , Lomonova E. A. , Jansen J. W. , Paulides J. J. H.
Published: March 2009

Linear motors find their utilization in an increasing number of industrial applications. Permanent magnet linear synchronous motors (PMLSMs) are favorable in many applications due to their servo characteristics, robustness, and high force density. The major disadvantage of moving coil type PMLSMs is the cable slab that energizes the coils from the fixed world to the moving parts of the machine. These cable slabs introduce extra wear and dynamical distortions. Moreover, in precision application the cable slab is supported by additional linear drives. These disadvantages can be eliminated if the coils could be powered wirelessly. In this paper two topologies are proposed that are capable of transferring 1 kW of power at most. The transformer part of the CET is characterized by means of two dimensional finite element analysis, and the influence of using additional capacitors to boost the output power is examined. Furthermore, an analysis of the core losses is conducted. Conclusions are drawn from the results.
Magnetic fluid micromixer with tapered magnets
Authors: Wei Zung-Hang , Lee Chiun-Peng
Published: March 2009

A magnetic fluid micromixer with high mixing efficiency using nonuniform magnetic field produced by tapered magnets is proposed. From the numerical results, the mixing efficiency increases with the saturation magnetization of the magnets. The larger the saturation magnetization is, the stronger the magnetic force acted on the magnetic fluid will be. On the other hand, asymmetric magnetic stray field that induces circulation between two fluids leads to higher mixing efficiency than a symmetric one.
A novel crystalline soft magnetic intermediate layer for perpendicular recording media
Authors: Park Soyoung , Zhu Jian-Gang , Laughlin David E.
Published: March 2009

In order to improve the recording efficiency in current perpendicular recording media, it is important to reduce the distance from the head to soft underlayer. In this paper, a soft magnetic intermediate layer is proposed to partially replace the presently used Ru intermediate layer. The new soft magnetic intermediate layer serves two purposes, which are as follows: (1) to decrease the thickness of the nonmagnetic Ru intermediate layer by providing a proper crystalline texture and surface morphology for the optimal crystalline grain growth of the magnetic storage layer on top and (2) to act as an additional soft magnetic underlayer that is closer to the head air bearing surface to enhance the recording performance. The prototypes of the soft magnetic intermediate layer consists of CoIr:SiO2/CoPt:SiO2/NiW multilayer structure. CoIr and CoPt were chosen because both have the hcp structure but the opposite sign for K1. A zero effective magnetoanisotropy of a composite grain is accomplished by varying the thickness ratio of each layer of CoIr and CoPt. The developed multilayer film shows the hcp (00.2) orientation with a dome morphology for facilitating the growth of the top magnetic storage layer as well as soft magnetic properties (K1=6.8×105 erg/cc).
Ferroelectric and leakage current behaviors of BiFeO3-Bi(Zn1/2Ti1/2)O3 ceramics
Authors: Cho J. H. , Song T. K. , Wang L. , Yeo H.-G. , Sung Y.-S. , Kim M.-H. , Park D.-S.
Published: March 2009

BiFeO 3 -Bi ( Zn 1 / 2 Ti 1 / 2 ) O 3 (BF-BZT) ceramics were made by a solid state reaction method. Crystal structure and microstructure were observed. Leakage currents were much reduced with BZT doping in BF. Dielectric constants of BF-BZT increased as frequency is decreased. Two distinctive relaxations were observed at about 500 kHz and 3 Hz. Ferroelectriclike hysteresis loops were observed in BF with low electric field and 2.5 and 5 mol % BZT doped ceramics.
Effects of extrapolation length δ on switching time and coercive field
Authors: Musleh Ahmad M. , Ong Lye-Hock , Tilley D. R.
Published: March 2009

The Landau free energy expression for a ferroelectric thin film studied by Tilley and Zeks [Solid State Commun. 49, 823 (1984)] (Tilley–Zeks model) and the Landau–Khalatnikov dynamic equation are used to study the surface effects (represented by the extrapolation length ±δ) on properties of polarization reversal, namely, switching time τS and coercive field eC. Positive δ models a decrease in the local polarization at surfaces, and negative δ an increase, with a smaller absolute value of δ giving a stronger surface effect. For positive δ, τS and eC decrease with decreasing ∣δ∣ while for negative δ, τS and eC increase with decreasing ∣δ∣. Strong surface effects, represented by smaller ∣δ∣, are more profound in thin FE films.
Hydrogen multicenter bonds and reversible hydrogen storage
Authors: Tarakeshwar P. , Kumar T. J. Dhilip , Balakrishnan N.
Published: March 2009

A new strategy for reversible hydrogen storage based on the properties of hydrogen multicenter bonds is proposed. This is demonstrated by carrying out ab initio calculations of hydrogen saturation of titanium and bimetallic titanium-aluminum nanoclusters. Hydrogen saturation leads to the formation of exceptionally and energetically stable hydrogen multicenter bonds. The stabilization results from sharing of the hydrogen atom electron density with the frontier orbitals of the metal cluster. The strength of the hydrogen multicenter bonds can be modulated either by varying the degree of hydrogen loading or by suitable alloying. Mode-specific infrared excitation of the vibrational modes associated with the multicenter hydrogen bonds can release the adsorbed hydrogen, thereby enabling efficient reversible hydrogen storage. The possible formation of hydrogen multicenter bonds involving titanium atoms and its implication to hydrogen adsorption/desorption kinetics in hydrogen cycled Ti-doped NaAlH4 is also discussed.
Evaluation of the irising effect of a slow-gating intensified charge-coupled device on laser-induced incandescence measurements of soot
Authors: Shaddix Christopher R. , Williams Timothy C.
Published: March 2009

Intensified charge-coupled devices (ICCDs) are used extensively in many scientific and engineering environments to image weak or temporally short optical events. To optimize the quantum efficiency of light collection, many of these devices are chosen to have characteristic intensifier gate times that are relatively slow, on the order of tens of nanoseconds. For many measurements associated with nanosecond laser sources, such as scattering-based diagnostics and most laser-induced fluorescence applications, the signals rise and decay sufficiently fast during and after the laser pulse that the intensifier gate may be set to close after the cessation of the signal and still effectively reject interferences associated with longer time scales. However, the relatively long time scale and complex temporal response of laser-induced incandescence (LII) of nanometer-sized particles (such as soot) offer a difficult challenge to the use of slow-gating ICCDs for quantitative measurements. In this paper, ultraviolet Rayleigh scattering imaging is used to quantify the irising effect of a slow-gating scientific ICCD camera, and an analysis is conducted of LII image data collected with this camera as a function of intensifier gate width. The results demonstrate that relatively prompt LII detection, generally desirable to minimize the influences of particle size and local gas pressure and temperature on measurements of the soot volume fraction, is strongly influenced by the irising effect of slow-gating ICCDs.
Molecular mechanisms for disilane chemisorption on Si(100)-(2×1)
Authors: Ng Rachel Qiao-Ming , Tok E. S. , Kang H. Chuan
Published: March 2009

The dissociative chemisorption of disilane is an important elementary process in the growth of silicon films. Although factors governing the rate of film growth such as surface temperature and disilane flux have been extensively studied experimentally by a large number of groups, the molecular mechanism for disilane adsorption is not well established. In particular, although it is generally held that chemisorption occurs via silicon-silicon bond dissociation, there have been a number of suggestions that silicon-hydrogen bond dissociation also occurs. We consider this issue in detail hereby examining a number of different paths that disilane can take to chemisorb. In addition to silicon-silicon bond dissociation paths, we examine three different mechanisms for silicon-hydrogen bond dissociation, for each path considering both adsorption at interdimer and intradimer sites. The calculated barriers are critically compared to experimental data. We conclude that silicon-hydrogen bond dissociation is likely, finding two zero barrier paths for chemisorption at interdimer sites, and a precursor-mediated path with a low barrier. We also find two precursor states, and show that each can lead to chemisorption via either silicon-silicon or silicon-hydrogen bond dissociation. Finally, we calculated the barriers for reaction of coadsorbed disilyl and hydrogen to form gas phase silane. Our calculations are performed using density-functional theory within a planewave ultrasoft pseudopotential methodology. We traced the reaction paths with the nudged-elastic band technique.
Magnetoelectric effect of (100−x)BaTiO3–(x)NiFe1.98O4 (x=20–80 wt %) particulate nanocomposites
Authors: Sreenivasulu G. , Babu V. Hari , Markandeyulu G. , Murty B. S.
Published: March 2009

The magnetoelectric (100−x)BaTiO3–(x)NiFe1.98O4 (x=20, 40, 60, and 80 wt %) particulate composites have been prepared and the effects of size and interface are studied through microscopy measurements. Large magnetoelectric voltage coefficient (αE) values accompanied by large piezoelastic coefficient, large magnetostrictive strain coefficient, and an adequate interface contact between the magnetic and electric phases were observed in these nanocomposites. The nanocomposite with x=40 has an αE value of 252 mV cm−1 Oe−1, which is the largest value for any particulate magnetoelectric composite, based on the available open literature.
High sensitivity microwave characterization of organic molecule solutions of nanoliter volume
Authors: Shaforost E. N. , Klein N. , Vitusevich S. A. , Barannik A. A. , Cherpak N. T.
Published: March 2009

A microwave resonator composed of a sapphire cylinder and a quartz plate with a 400 nl cavity was developed for the determination of the complex permittivity of liquids at 10 GHz. This sensor was calibrated over a wide range of values for real and imaginary parts of permittivity. The measured resonator losses induced by the liquid were found to be proportional to the dipole relaxation time of the liquid molecules, as predicted by perturbation theory. Our analysis of weight concentration and temperature dependence of the measured inverse quality factor revealed a sensitivity of about 0.1% for aqueous solutions of glucose.
Light driven microflow in ice
Authors: Weinert Franz M. , Wühr Max , Braun Dieter
Published: March 2009

We optically pump water through micrometer thin ice sheets. The ice is locally moved with speeds exceeding 5 cm/s by repetitive melting and freezing, which occurs around a moving infrared laser spot. The minimal channel width is 10 μm. The diffusion limitation of ice allows for fast spatial biomolecule control without predefined channels, valves, or external pumps. Dye molecules are pumped across an ice-ice interface, showing the possibility of microfluidic applications. Pumping in ice is three orders of magnitude faster than the previously shown for thermoviscous pumping in water.
The fast recovery dynamics of a quantum dot semiconductor optical amplifier
Authors: Erneux Thomas , Viktorov Evgeny A. , Mandel Paul , Piwonski Tomasz , Huyet Guillaume , Houlihan John
Published: March 2009

We consider a rate equation model of a quantum dot semiconductor optical amplifier that takes into account carrier capture, escape, and Pauli blocking processes. We evaluate possible differences between phonon-assisted or Auger processes being dominant for recovery. An analytical solution which corresponds to phonon-assisted interaction is then used to accurately fit experimental recovery curves and allows an estimation of both the carrier capture and escape rates.
Optical diagnosis of an argon/oxygen needle plasma generated at atmospheric pressure
Authors: Li Shou-Zhe , Huang Wen-Tong , Zhang Jialiang , Wang Dezhen
Published: March 2009

An atmospheric-pressure argon/oxygen needle plasma discharge is generated in a long dielectric tube and investigated with respect to its electrical characteristics and the production of oxygen atom by means of optical actinometry. The length of discharge column depends on the operating frequency and applied voltage of power supply, which is interpreted qualitatively with an equivalent circuit model. Moreover it is found that there exists an optimal value of oxygen concentration in the production of oxygen radicals. At last, the oxygen/argon plasma is employed to modify the interior surface of a fine quartz tube to demonstrate its potential applications.
Improved Ni/3C-SiC contacts by effective contact area and conductivity increases at the nanoscale
Authors: Eriksson Jens , Roccaforte Fabrizio , Giannazzo Filippo , Lo Nigro Raffaella , Raineri Vito , Lorenzzi Jean , Ferro Gabriel
Published: March 2009

We report on the evolution of the electrical and structural properties of Ni/3C-SiC contacts during annealing in the temperature range of 600–950 °C. A structural analysis showed the formation of different nickel silicide phases upon annealing. A combination of transmission line model and conductive atomic force microscopy measurements demonstrated a correlation between the macroscale specific contact resistance and the nanoscale resistance, measured locally across the sample. These results further revealed that the structural evolution is accompanied by an increased uniformity of the local current distribution, indicating that an increase of the effective contact area contributes to the improvement of the contact properties.
Daily diaries and minority adolescents: Random coefficient regression modeling of attributional style, coping, and affect
Authors: Roesch Scott C. , Vaughn Allison A. , Aldridge Arianna A. , Villodas Feion
Published: March 2009

Many researchers underscore the importance of coping in thedailylives of adolescents, yet very few studies measure this and related constructs at this level. Using a daily diary approach to stress and coping, the current study evaluated a series of mediational coping models in a sample of low‐income minority adolescents (N = 89). Specifically, coping was hypothesized to mediate the relationship between attributional style (and dimensions) and daily affect. Using random coefficient regression modeling, the relationship between (a) the locus of causality dimension and positive affect was completely mediated by the use of acceptance and humor as coping strategies; (b) the stability dimension and positive affect was completely mediated by the use of both problem‐solving and positive thinking; and (c) the stability dimension and negative affect was partially mediated by the use of religious coping. In addition, the locus of causality and stability (but not globality) dimensions were also directly related to affect. However, the relationship between pessimistic explanatory style and affect was not mediated by coping. Consistent with previous research, these findings suggest that attributions are both directly and indirectly related to indices of affect or adjustment. Thus, attributions may not only influence the type of coping strategy employed, but may also serve as coping strategies themselves.
The global village pioneers
Authors: GINSPARG Paul
Published: March 2009

Paul Ginsparg, who founded the arXiv e‐print archive, recounts the early days of the Web and looks at how it has changed scientific communication.
The impact of host aggressiveness on sex allocation by the gregarious parasitoid wasp
Cotesia glomerata
(L.)
Authors: Tanaka Shingo
Published: March 2009

Parasitoid wasps lay female eggs or a high proportion of female eggs in favourable host insects because female wasps require many more resources during their development. Many studies have tested the effects of host physiological status on the sex allocation of parasitoids, but few have attempted to test the effects of host behavioural traits.
Cotesia glomerata
is a gregarious parasitoid wasp that lays eggs in caterpillars of pierid butterflies. The brood sex ratio in
C. glomerata
females that attacked aggressive host caterpillars was compared with that in females that attacked less aggressive hosts. The male ratio was higher when
C. glomerata
attacked aggressive
Pieris brassicae
caterpillars than when it attacked less aggressive
Pieris rapae crucivora
caterpillars. However, when
C. glomerata
females were induced to oviposit in anaesthetized
P. brassicae
caterpillars, the male ratio in their offspring was significantly lower than when they attacked unanaesthetized caterpillars.
C. glomerata
was attacked by aggressive host caterpillars during oviposition bouts. It is likely that this aggressive host behaviour disturbed the fertilization process in ovipositing
C. glomerata
females. These results suggest that a behavioural defence by host caterpillars affects sex allocation in the parasitoid wasp
C. glomerata
.
Relationships between population size and pollen fates in a moth-pollinated orchid
Authors: Johnson Steven D , Torninger Erica , Ågren Jon
Published: March 2009

Management of small plant populations requires an understanding of their reproductive ecology, particularly in terms of sensitivity to Allee effects. To address this issue, we explored how components of pollen transfer and pollination success of individual plants varied among 36 populations of the self-compatible moth-pollinated orchid
Satyrium longicauda
in South Africa. Mean fruit set, seed production, proportion of flowers with pollen deposited or removed and proportion of removed pollen that reached stigmas (approx. 8% in this species) were not significantly related to population size (range: 1–450 flowering individuals), density or isolation. Plants in small populations did, however, have significantly higher levels of pollinator-mediated self-pollination (determined using colour-labelled pollen) than those in larger populations. Our results suggest that small populations of this orchid species are resilient to Allee effects in terms of overall pollination success, although the higher levels of pollinator-mediated self-pollination in small populations may lead to inbreeding depression and long-term erosion of genetic diversity.