bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetohydrodynamic waves and gravitational/centrifugal instability in rotating systems
Authors: Ferrière K. M. , Zimmer C. , Blanc M.
Published: August 2003

Interchange motions of magnetic flux tubes are customarily regarded as one of the main contributors to radial plasma transport in planetary magnetospheres, particularly in those magnetospheres, like the Jovian and Saturnian ones, where the centrifugal force is known to play an important role. However, so far, interchange motions have been treated only under a variety of simplifying assumptions which are not always justified. In this paper, we present a rigorous treatment of the interchange instability within the broader context of magnetohydrodynamic waves. After reviewing the existing work on the magnetospheric interchange instability, we derive the full wave equation for magnetohydrodynamic perturbations in the presence of external forces, magnetic field curvature, and overall rotation, and we proceed to a detailed examination of their dispersion relation and stability condition in the one‐dimensional case when the equilibrium parameters vary in a single direction normal to the magnetic field. We then focus on the so‐called “quasi‐interchange” modes, which, by definition, represent all the modes driven by gravitational or magnetic buoyancy (or a combination of both), including, in particular, the interchange mode. We demonstrate that they leave the total pressure virtually unchanged, slightly perturb the plasma density and the magnetic field, and generally give rise to motions both perpendicular and parallel to the background field lines.
Electron velocity distribution functions from the solar wind to the corona
Authors: Pierrard V. , Maksimovic M. , Lemaire J.
Published: August 2003

Typical electron velocity distribution functions observed at 1 AU from the Sun by the 3DP instrument onboard Wind are used as boundary conditions to determine the electron velocity distribution function at 4 solar radii in the corona. The velocity distribution functions (VDFs) at low altitude are obtained by solving the Fokker‐Planck equation, using two different sets of boundary conditions. The first set typically corresponds to a VDF observed in a low‐speed solar wind flow (i.e., characterized by “core” and “halo” electrons); the second one corresponds to high‐speed solar wind (i.e., characterized by “core,” “halo,”, and “strahl” populations). We use the observed electron VDFs as test particles, which are submitted to external forces and Coulomb collisions with a background plasma. Closer to the Sun, the relative density of the core electrons is found to increase compared to the density of the halo population. Nevertheless, we find that in order to match the observed distributions at 1 AU, suprathermal tails have to be present in the VDF of the test electron at low altitudes in the corona.
Mirror‐mode structures at the Galileo‐Io flyby: Instability criterion and dispersion analysis
Authors: Huddleston D. E. , Strangeway R. J. , Blanco‐Cano X. , Russell C. T. , Kivelson M. G. , Khurana K. K.
Published: August 2003

The mirror mode is typically excited in high‐beta plasmas when there is a significant pressure anisotropy, with the greatest plasma pressure perpendicular to the magnetic field, B. Large‐amplitude mirror‐mode structures were identified in the Galileo magnetic field data on the edges of the cold Io wake. Here, despite the high ambient B field and low plasma beta, the enhanced perpendicular pressure due to the ring‐type velocity distributions of heavy Iogenic pickup ions overcomes the instability threshold for the mirror mode and provides the free energy. In the center of the Io wake, the local pickup velocities are very low and hence the perpendicular pressure contribution is small, while farther from Io in the torus, the corotating isotropic plasma dominates and the mirror mode is not unstable but instead ion cyclotron waves grow. Thus the spatial region in which the mirror mode dominates is narrow. A warm plasma dispersion analysis is performed for the multispecies plasma conditions appropriate to the edges of the Io wake. In a multispecies plasma, multiple ion cyclotron modes are possible, each with a growth rate dependent upon the anisotropy and free energy provided by the specific gyroresonant ion species component. However, the mirror mode can dominate, since its growth rate depends on the combined anisotropic pressure of all ions present.
What is solar cycle minimum?
Authors: Harvey Karen L. , White Oran R.
Published: August 2003

Establishing the time of minimum between cycles 22 and 23 is complicated because there are two periods of low solar activity during 1996. To resolve this controversy, we studied the time of minimum in terms of the historical basis for defining this fiducial point in the solar cycle using several measures of solar activity, as well as the cycle membership of active regions observed during the minimum phase between these two cycles. Our conclusion is that cycle minimum is not defined solely on the basis of the occurrence of the minimum in the smoothed sunspot number, but rather by several additional parameters, including the monthly (or rotationally) averaged sunspot number, the number of regions (total, new‐ and old‐cycle), and the number of spotless days. Using these specific measures of solar activity, we recommend that the minimum between cycles 22 and 23 occurred in September 1996 (1996.7) and not in May 1996 (1996.4).
Dawnside magnetopause observed by the Equator‐S Magnetic Field Experiment: Identification and survey of crossings
Authors: Dunlop M. W. , Balogh A. , Baumjohann W. , Haerendel G. , Fornacon K.‐H. , Georgescu E.
Published: August 2003

The German Equator‐S spacecraft provided long‐duration, low‐latitude coverage of the dawnside magnetopause and adjacent magnetosheath. We document 131 magnetopause crossings from 31 orbits, giving coverage from 0600 to 1040 LT and exhibiting a wide range of local magnetic shear. The Tsyganenko model field is used routinely to assist identification and in categorizing the crossings. The apogee of the spacecraft remains close to the magnetopause for mean solar wind pressure. Consequently, magnetosheath intervals often extending several hours are observed, many containing a high number of crossings. For most encounters, a well‐ordered, tangential (draped) magnetosheath field is observed; 30% containing extended intervals of strong mirror signatures. The occurrence of the crossings is summarized, and locations are found to compare well to predicted boundary positions using observed, upstream solar wind IMF and pressure values; some corresponding to unusually high solar wind ram pressure. Other crossing characteristics have also been analyzed, such as boundary normals. Although these are broadly consistent with fitted, model magnetopause orientations, they typically lie sunward of these, suggesting a blunter magnetopause shape in this region than predicated. No strong evidence is found of large deviations in local boundary orientations, possibly consistent with the highly draped magnetosheath field configuration.
Drift‐Alfvén vortices in dusty plasmas
Authors: Pokhotelov O. A. , Onishchenko O. G. , Shukla P. K. , Stenflo L.
Published: August 2003

A set of two‐fluid equations that governs the nonlinear dynamics of drift‐Alfvén waves in a multicomponent dusty plasma is derived. It consists of the electron continuity equation, the electron parallel equation of motion, and the divergence of the total plasma current density. In the linear limit, we obtain a dispersion relation that shows the coupling between drift‐Alfvén and drift convective cells. On the other hand, the stationary solutions of the nonlinear equations can be represented as dipolar vortices. The relevance of our investigation to coherent nonlinear structures in space plasmas is pointed out.
Low‐altitude equatorial ions: A new look with SAMPEX
Authors: Greenspan M. E. , Mason G. M. , Mazur J. E.
Published: August 2003

We have used the Low‐Energy Ion Composition Analyzer (LICA) instrument on the low altitude, polar orbiting SAMPEX spacecraft to survey energetic ions near the magnetic equator from late 1992 through 1998; that is, through the declining phase of Solar Cycle 22, solar minimum, and into the rise of Solar Cycle 23. This survey gives us a unique opportunity to examine both the long‐term variation in the low‐altitude equatorial ion population and short‐term enhancements that occur during magnetic storms. During the survey period, 40 storms with minimum Dst ≤ 100 nT occurred: the majority were accompanied by increases in the equatorial ion flux. Although LICA detects ions with energies far above the bulk of the ring current ion population, the times of the maximum equatorial fluxes clustered around the time of minimum Dst, i.e., the time of maximum ring current energy content. The storm associated flux maxima were unevenly distributed in geographic longitude, with the maximum flux enhancements occurring at longitudes just west of the South Atlantic Anomaly. Except for an increase in 1994, the quiet time monthly average equatorial flux declined steadily from 1992 until early 1998; then it began to rise again. The monthly average equatorial ion fluxes had a very significant correlation with the Ap index during this period (R = 0.54), indicating that geomagnetic activity dominated the long‐term variation. During the survey, we also discovered enhancements in the equatorial ion flux that occurred shortly after the onsets of three recent, large solar energetic particle events. These enhancements began well before the commencements of the associated geomagnetic storms. The major ion species present were H, He, C, and O, therefore ruling out an ionospheric source. These ions could not have penetrated directly from interplanetary space to the magnetic equator, and we do not understand the mechanism that produces the SEP‐associated enhancements.
Solar wind electrons: Parametric constraints
Authors: Gary S. Peter , Neagu Elena , Skoug Ruth M. , Goldstein Bruce E.
Published: August 2003

Solar wind electrons are often observed to consist of two distinguishable components, a thermal, more dense core and a suprathermal, less dense halo. In this core/halo model linear Vlasov theory for the whistler heat flux instability predicts dimensionless heat flux thresholds which decrease as the electron core beta,
, increases. It has been proposed that this theoretical threshold corresponds to an observable upper bound on the electron heat flux. Linear theory also predicts that there is a critical value of
below which the whistler heat flux instability does not have appreciable growth in the solar wind; there is another suggestion that this corresponds to an observable lower bound on
. These two proposals are examined by comparison of linear theory and data from the initial in‐ecliptic phase of the Ulysses mission. The instability threshold does provide a statistical constraint on observed solar wind heat fluxes, and the critical
of theory is not inconsistent with a statistical lower bound on the observations of that parameter.
Perturbations of the Earth's inner radiation belt by two geomagnetic storms: Explorer I revisited
Authors: Van Allen James A.
Published: August 2003

This is a brief report on previously unpublished Explorer I observations of the precipitation of energetic particles from the Earth's inner radiation belt during the great geomagnetic storm of February 11, 1958 (maximum negative value of the Sugiura equatorial index Dst = −409γ) and during the lesser storm of March 11–15, 1958 (Dst = −126γ). These first ever satellite observations within the magnetosphere showed that there was a good linear correlation between a simple quantitative measure of particle precipitation and Dst for the February storm but that such a relationship was less well determined by the sparse data for the more complex March storm. In time coincident with the satellite‐detected effects there were many other geophysical phenomena including exceptional low‐latitude aurorae over the southern United States and Japan during the February storm. Subsequent observations of the precipitation of energetic particles from the inner radiation belt were confined to quiescent or moderately disturbed conditions until about three decades later. Our Explorer I data provide an historical context for contemporary work as solar activity approaches its predicted next maximum in 2000–2001.
Crustal motion in Indonesia from Global Positioning System measurements
Authors: Bock Y. , Prawirodirdjo L. , Genrich J. F. , Stevens C. W. , McCaffrey R. , Subarya C. , Puntodewo S. S. O. , Calais E.
Published: August 2003

We present the crustal motion velocity field for the Indonesian archipelago based on Global Positioning System (GPS) field surveys conducted from 1991 to 1997, and 2001, totaling more than 150 sites, as well as on a reanalysis of global tracking data in the Scripps Orbit and Permanent Array Center archive from 1991 to 2001 in International Terrestrial Reference Frame 2000. We compute poles of rotation for the Australia, Eurasia, and Pacific plates based on our analysis of the global GPS data. We find that regional tectonics is dominated by the interaction of four discrete, rotating blocks spanning significant areas of the Sunda Shelf, the South Banda arc, the Bird's Head region of New Guinea, and East Sulawesi. The largest, the Sunda Shelf block (SSH), is estimated to be moving 6 ± 3 mm/yr SE relative to Eurasia. The South Banda block (SBB) rotates clockwise relative to both the SSH and Australia plate, resulting in 15 ± 8 mm/yr of motion across the Timor trough and 60 ± 3 mm/yr of shortening across the Flores Sea. Southern New Guinea forms part of the Australia plate from which the Bird's Head block (BHB) moves rapidly WSW, subducting beneath the Seram trough. The East Sulawesi block rotates clockwise about a nearby axis with respect to the Sunda Shelf, thereby transferring east‐west shortening between the Pacific and Eurasia plates into north‐south shortening across the North Sulawesi trench. Except for the Sunda Shelf, the crustal blocks are all experiencing significant internal deformation. In this respect, crustal motion in those regions does not fit the microplate tectonics model.
The Mediterranean Ridge: A mass balance across the fastest growing accretionary complex on Earth
Authors: Kopf Achim , Mascle Jean , Klaeschen Dirk
Published: August 2003

Depth migration of seismic reflection profiles across the Mediterranean Ridge accretionary complex between the African and Eurasian blocks illustrates profound variations in the geometry and internal structure along strike. Structural interpretations of four cross sections, together with bathymetric and acoustic surface information and drilling data, are used to volumetrically balance the amount of subduction versus accretion with time. Results suggest the existence of three distinct scenarios, with a jump in décollement in the west, intense backthrusting in the central part between Libya and Crete, and transcurrent tectonism in the east. The onset of accretion coincides with exhumation of thrust sheets (∼19 Ma), followed by rapid sediment accretion with thick, evaporite‐bearing incoming successions facilitating outward growth of the wedge. The minimum rate of accretion (20–25% of the total sediment supply) is observed in the central portion where the ridge suffers maximum deformation. Here the indenting leading edge of the African Plate apparently forces the sediment into subduction, or local underplating. In contrast, an estimated 40–60% of the available sedimentary input was accreted in the western domain where collision is less accentuated. The results support the hypothesis that highly destructive forearc collisional events, like slab break off and exhumation of thrust sheets, can be followed by periods of accretion and continuous growth of accretionary wedges.
Aerosol activation in marine stratocumulus clouds: 1. Measurement validation for a closure study
Authors: Guibert Sarah , Snider Jefferson R. , Brenguier Jean‐Louis
Published: August 2003

This paper is the first of a series dedicated to an observational study of the aerosol indirect effect in marine stratocumulus clouds. The data were collected in 1997, during the second Aerosol Characterization Experiment (ACE‐2) CLOUDYCOLUMN experiment, conducted over the eastern Atlantic Ocean, in the vicinity of the Canary Islands. Here we compare measurements made both on aircraft and at the surface, including condensation nuclei (CN) and accumulation mode aerosol concentrations, and aerosol size spectra. We also compare measured and predicted wet aerosol size spectra and examine statistics of vertical velocity within and below stratocumulus clouds. In general, aircraft and surface measurements of CN concentration, accumulation mode aerosol concentration and size spectra agree within expected uncertainties. However, a substantial disparity is documented in the comparison of predicted and observed wet aerosol spectra. We attribute this to either bias in the wet aerosol measurements, made with an FSSP‐300, or to error in the sizing of dry aerosol particles. The analysis of vertical velocity indicates that the first and third moments of the vertical velocity frequency distribution do not change substantially between below‐cloud and in‐cloud flight segments; however, an increase in the second moment of the distribution across cloud base is documented. Overall, the results lend confidence to the use of surface site aerosol physical and chemical property data, as well as airborne measurements of vertical velocity, for modeling of the aerosol activation process, as described by Snider et al. [2003] (hereinafter referred to as part 2) in the special section. Here, and in the paper by Snider et al. [2003] (hereinafter referred to as part 2), we examine how sensitive the predictions are to the common assumption that the aerosol particles are compact spheres.
Cloud microphysical and radiative properties for parameterization and satellite monitoring of the indirect effect of aerosol on climate
Authors: Brenguier Jean‐Louis , Pawlowska Hanna , Schüller Lothar
Published: August 2003

The spatial variability of the microphysical fields in stratocumulus clouds is documented in this paper with statistics of droplet number concentration, droplet mean volume radius, and liquid water content for eight cases of the second Aerosol Characterization Experiment. Statistics are calculated in five sublayers, from cloud base to cloud top, and they are utilized for deriving estimates of cloud optical thickness and liquid water path, by assuming either random or maximum overlap. The resulting in situ frequency distributions of optical thickness and liquid water path are validated against distributions of these two parameters retrieved from independent remote sensing measurements of cloud radiances. They are also used for testing parameterizations of optical thickness based on liquid water path and either the droplet effective radius or the cloud droplet number concentration. This unique data set of extensive, concomitant, and independent measurements of cloud microphysical and radiative properties is finally used for assessing the detectability of the aerosol indirect effect through examination of the correlation between cloud optical thickness and droplet effective radius. If only cases of comparable values of geometrical thickness are considered, the correlation between optical thickness and effective radius is negative, as anticipated by Twomey [1977]. However, if the most polluted cases are also accounted for, the trend suggests a positive correlation. In fact, the most polluted cloud systems sampled during ACE‐2 were slightly drier, hence thinner, than the marine and intermediate cases, hence producing a positive correlation between optical thickness and droplet effective radius. This study demonstrates that the monitoring of the aerosol indirect effect with satellite observations requires an independent retrieval of the liquid water path together with the cloud optical thickness and droplet effective radius.
A new parameterization for surface and groundwater interactions and its impact on water budgets with the variable infiltration capacity (VIC) land surface model
Authors: Liang Xu , Xie Zhenghui , Huang Maoyi
Published: August 2003

This paper describes a new parameterization to represent surface and groundwater interaction dynamics for land surface models. With the new parameterization, effects of surface and groundwater interactions on soil moisture, evapotranspiration, runoff, and recharge can be dynamically taken into account. The new parameterization is implemented into the three‐layer variable infiltration capacity (VIC‐3L) model, which is a hydrologically based land surface scheme. The new version of VIC (called VIC‐ground) is applied to two watersheds in Pennsylvania over multiple years. Results show that VIC‐ground can properly simulate the movement of the daily groundwater table over multiple years at the study sites. Preliminary comparisons of VIC simulations with and without consideration of the dynamics of surface and groundwater interactions show an important impact of such interactions on the partitioning of water budget components. In particular, soil moisture of the lower layer from the VIC‐ground simulations is generally wetter than that from VIC‐3L. For the top thin soil layer and the upper layer of VIC‐3L, soil moisture is generally drier in VIC‐ground than that in VIC‐3L. Such characteristics of VIC‐ground result in lower surface runoff peaks and higher base flow, as well as generally less evapotranspiration compared to VIC‐3L at the two study sites. Results at both sites show that it takes 3–4 years to have the effects of the initializations of groundwater tables disappear when the groundwater table is initialized to be deeper than the observed level, while it takes much less time (e.g., about 1.5 years) if the groundwater table is initialized to be shallower than the observed level. In addition, the preliminary sensitivity studies at both sites show that there is a more significant persistent signature of the impact of the precipitation when its amount is halved (i.e., 0.5 ppt) than that when its amount is doubled (i.e., 2 ppt).
A new view of lunar ferroan anorthosites: Postmagma ocean petrogenesis
Authors: Longhi John
Published: August 2003

New melting experiments in the range of 0.1 MPa to 4.7 GPa provide the basis for calculations of polybaric crystallization which show that both a >300 km deep magma ocean (MO) enriched in refractory elements and a >600 km deep magma ocean with refractory element concentrations similar to the Earth's upper mantle produce sufficient amounts of differentiated, residual liquid, capable of crystallizing the troctolitic‐noritic mineral assemblages that are prevalent in lunar ferroan anorthosites (LFA). However, the both oceans become saturated with augite after ∼20–30% crystallization of the plagioclase‐saturated residuum and thereafter are no longer capable of producing noritic assemblages. A second set of melting experiments reveals the existence of a previously unrecognized equilibrium (augite + liquid = pigeonite + plagioclase) and a thermal minimum on the pigeonite + plagioclase liquidus surface at 0.6 GPa. These equilibria will produce melts of mafic cumulates with lower Wo content than those from which the cumulates originally formed in a postmagma ocean environment of overturning mafic cumulates. Melt thus formed and entrained in a buoyant segregation of plagioclase would then form diapiric masses that would crystallize troctolitic‐noritic assemblages after intruding upward. Diapiric intrusions could also provide the local deformational environment needed to produce the apparently high (≥95%) plagioclase modes of the LFA. An unstable density profile in the cumulate pile following crystallization of most of the MO should provide the impetus for overturn and the heat for partially remelting mafic cumulates.
Sharp boundary between the inner magnetosphere and active outer plasma sheet
Authors: Sergeev V. A. , Sauvaud J.‐A. , Reme H. , Balogh A. , Daly P. , Zong Q.‐G. , Angelopoulos V. , Andre M. , Vaivads A.
Published: August 2003

We report observations of a sharp spatial boundary between the outer plasma sheet and the inner magnetosphere. It was successively crossed by the Cluster spacecraft in their pearl‐on‐string configuration near the perigee (∼4 Re) at midnight during a substorm expansion phase. Being mapped presumably to 8–10 Re in the equatorial tail, this boundary was extremely thin, comparable to a gyroradius of plasma sheet proton. Substantial changes on this spatial scale were observed coherently in (1) the fluxes of radiation belt energetic electrons (exceeding a factor 10 at E ≥ 100 keV), (2) the plasma pressure (by a factor of 2), (3) the density and outflow of the cold ionospheric plasma. Strong diverging electric field (azimuthal shear flow) coincides with this boundary and is accompanied by a strong downward field‐aligned current. While this boundary was staying at nearly the same location during the ∼5 min time scale, we also found indications of its dynamical origin. We suppose it could be generated by a sudden braking and azimuthal deflection of localized bursty fast flows produced by the magnetic reconnection which was going on at this time in the near tail.
Lithospheric heterogeneity in the Kyrgyz Tien Shan imaged by magnetotelluric studies
Authors: Bielinski Robert A. , Park Stephen K. , Rybin Anatoly , Batalev Vlad , Jun Shen , Sears Clayton
Published: August 2003

A 450 km long north‐south magnetotelluric profile spanning the Tien Shan from Kazakhstan to western China reveals lateral variations in the resistivity of the mantle lithosphere to depths of 140 km. Minimum changes of one order of magnitude in this depth range result from variations in temperature or composition, or both. Higher resistivities beneath a central portion of the range where the Moho is half as deep as elsewhere in the Tien Shan indicate a strong lithospheric block. We propose that this block protects this region of thin crust from appreciable deformation and instead transmits stresses due to India‐Asia plate convergence from the southern to the northern parts of the range.
POAM measurements of PSCs and water vapor in the 2002 Antarctic vortex
Authors: Nedoluha Gerald E. , Bevilacqua Richard M. , Fromm Michael D. , Hoppel Karl W. , Allen Douglas R.
Published: August 2003

We present Polar Ozone and Aerosol Measurement (POAM) PSC and water vapor measurements obtained in the Antarctic stratosphere in 2002, and compare these with POAM measurements from 1993–1996 and 1998–2002 (PSCs) and 1998–2002 (water vapor). Through mid‐September 2002 POAM observed significantly fewer PSCs than in other years. However, ice PSC observations were only slightly reduced from previous years, and the dehydration was similar to that observed from 1998–2001. After an unprecedented major warming in September 2002, POAM observed only very few PSCs. This sudden decline in PSC activity in 2002 occurred a full month earlier than in any previous POAM measurement years.
Nuclear irradiation-induced superconductivity in the binary semiconductor InAs
Authors: Karpenko A. Ya. , Litovchenko P. G. , Shevtsova O. N. , Sugakov V. I. , Vikhlii G. A.
Published: August 2003

A jumplike increase of the resistance as a function of magnetic field is observed in indium arsenide samples irradiated by α particles with an energy of 80 MeV. The effect is detected at T<5 K. The observed effect is explained by the appearance in the crystal of superconducting areas created by nuclear irradiation. The magnetoresistance is caused by suppression of the superconductivity in the inclusions as the magnetic field is increased. The observed effect is considered in terms of a theory of the magnetoresistance of a medium with superconducting inclusions, proposed earlier. The proposed theory explains qualitatively the experimentally measured dependence of the resistance on magnetic field, namely: the jump of the resistance at a certain value of magnetic field; the shift of the curves towards higher magnetic fields with decrease of temperature; at lower values of the temperature the jump takes place in a wider range of magnetic fields (i.e., the curves became flatter).
Weak ferromagnetism and an intermediate incommensurate antiferromagnetic phase in LiNiPO4
Authors: Kharchenko Yu. N. , Kharcheno N. F. , Baran M. , Szymczak R.
Published: August 2003

The temperature dependence of the magnetization of single-crystal LiNiPO4 is measured for magnetic-field orientations along the a, b, and c crystallographic axes. It is found that the value of the magnetization depends on the magnetic prehistory of the sample. The magnetic behavior of the antiferromagnetic sample is explained by the presence of weak ferromagnetism in LiNiPO4. At a temperature of 5 K the value of the spontaneous magnetic moment along the c axis is around 0.005 G. When the sample is heated to 20.8 K the magnetic moment decreases monotonically to zero. All of the magnetic susceptibility curves M(T)/H exhibit two features: a jump and a kink at temperatures T1 and T2, respectively. At a magnetic field of 10 kOe these temperatures are close to 20.84 and 21.86 K. The observed features indicate that in the establishment of the main antiferromagnetic order in the LiNiPO4 crystal, an intermediate antiferromagnetic phase is spontaneously formed in the temperature interval from TN1=20.8(5) K to TN2=21.8(5). The sequence of continuous and abrupt transitions at the boundary temperatures of its existence region indicate that the intermediate phase is most likely an incommensurate antiferromagnetic state.
Reflection of guided modes in a semiconductor nanowire laser
Authors: Maslov A. V. , Ning C. Z.
Published: August 2003

We analyze the waveguiding properties of semiconductor (GaN, ZnO, CdS) single nanowire lasers which were recently demonstrated experimentally. In particular, we compute the reflectivity for a few lowest-order guided modes (HE11, TE01, and TM01) from the nanowire facets. The reflectivity is shown to depend strongly on the mode type, lasing frequency and radius of the nanowire. By using the computed reflectivities, we make realisic estimates of the threshold gain and quality factor for the nanowire lasers. Our results shed light on the lasing mechanism of the nanowire lasers.
Scaling laws of voxels in two-photon photopolymerization nanofabrication
Authors: Sun Hong-Bo , Takada Kenji , Kim Moon-Soo , Lee Kwang-Sup , Kawata Satoshi
Published: August 2003

Understanding the performance of individual voxels is critical to establish two-photon photopolymerization as a nanoprocessing tool. In this letter, we report that at near-threshold exposure condition voxel shape scaling follows different laws in the courses of varying laser power and changing exposure duration. The voxel aspect ratio, when exposure enhanced, monotonically increases and reaches a saturation status for the two processes that are conventionally regarded as equivalent for voxel volume tuning. A growth model that deals with fine photopolymerization process occurring at the submicron-focal volume is proposed and applied to interpret the unexpected phenomenon.
Is there a thermodynamic size limit of nanowires grown by the vapor-liquid-solid process?
Authors: Tan Teh Y. , Li Na , Gösele Ulrich
Published: August 2003

For nanowires grown by the vapor-liquid-solid (VLS) process, expressions of the thermodynamically allowed minimum sizes of the wire and the liquid droplet are derived using Si nanowires (SiNW) grown from metal–silicon (M–Si) liquid as the model case. The liquid droplet minimum size is determined by a unique set of external M and Si vapor phase pressure values. The SiNW minimum size expression contains two contributions, one depending on composition of the liquid and one depending on the droplet size. These expressions do not predict a limit on the attainable VLS SiNW minimum size, implying ever smaller SiNW can be grown until reaching some growth kinetic limit which is presently unknown.
Highly strained 1.24-μm InGaAs/GaAs quantum-well lasers
Authors: Sung L. W. , Lin H. H.
Published: August 2003

Highly strained InGaAs/GaAs quantum wells grown at very low temperature (380 °C) have been studied. The critical thickness of the In0.38Ga0.62As quantum well is 8.8 nm and the photoluminescence peak is at 1.24 μm. An edge-emitting In0.388Ga0.612As/GaAs quantum-well laser demonstrates an emission wavelength of 1.244 μm at 18 °C. The threshold current density is 405 A/cm2 for an as-cleaved diode laser with 873-μm cavity length. The internal quantum efficiency and laser cavity loss are 93% and 6.4 cm−1, respectively.
Microstructure and high critical current density of in situ processed MgB2 tapes made by WSi2 and ZrSi2 doping
Authors: Ma Yanwei , Kumakura H. , Matsumoto A. , Togano K.
Published: August 2003

WSi 2 - and ZrSi2-doped Fe-sheathed MgB2 tapes were prepared through the in situ powder-in-tube method. Both WSi2- and ZrSi2-doped tapes were found to have significantly increased critical current density Jc at 4.2 K in magnetic fields up to 12 T than their undoped counterpart. Scanning electron microscopy investigation revealed that the WSi2 and ZrSi2, doping enhanced intergranular connectivity, thus raising Jc by more than a factor of 2.2 and 3.4, respectively. Moreover, the critical temperature for the doped tapes decreased slightly (less than 0.7 K). It was also found that the improved field dependence of the WSi2 tapes was due to the pinning by possible segregates or defects caused by the WSi2 addition. This role of WSi2 and ZrSi2 may be very beneficial in the fabrication of MgB2 tapes for a large range of applications.
Epitaxial growth and large band-gap bowing of ZnSeO alloy
Authors: Nabetani Y. , Mukawa T. , Ito Y. , Kato T. , Matsumoto T.
Published: August 2003

ZnSeO alloy was grown by molecular-beam epitaxy up to 1.3% O composition on GaAs substrate using rf plasma. The crystal structure of epitaxial ZnSeO alloy was zinc-blende. O composition was estimated by a strain-free lattice constant. No phase separation was observed by in situ reflection high-energy electron diffraction and x-ray diffraction. Photoluminescence intensity was larger than that of ZnSe. The peak energy shifted toward lower energies with increasing O composition. The band-gap energy determined by photoluminescence excitation spectra decreased with increasing O composition. A bowing parameter as high as 8 eV was obtained. This large band-gap bowing widens the controllable energy-gap range of II-VI semiconductor.
Carbon nanotube tips for thermomechanical data storage
Authors: Lantz Mark A. , Gotsmann Bernd , Dürig Urs T. , Vettiger Peter , Nakayama Yoshikazu , Shimizu Tetsuo , Tokumoto Hiroshi
Published: August 2003

We report the demonstration of thermomechanical data storage in a poly(methylmethacrylate) film using a multiwalled carbon nanotube (MWCNT) tip. Indentation densities of >250 Gbits/in2 are achieved. The power efficiency of indent writing with MWCNT tips is found to be higher than that of conventional silicon tips owing to better heat transfer at the tip–polymer interface.
Enhanced quantum efficiency of solar cells with self-assembled Ge dots stacked in multilayer structure
Authors: Alguno Arnold , Usami Noritaka , Ujihara Toru , Fujiwara Kozo , Sazaki Gen , Nakajima Kazuo , Shiraki Yasuhiro
Published: August 2003

We report on the performance of solar cells with stacked self-assembled Ge dots in the intrinsic region of Si-based p-i-n diode. These dots were epitaxially grown on p-type Si(100) substrate via the Stranski–Krastanov growth mode by gas-source molecular beam epitaxy. Enhanced external quantum efficiency (EQE) in the infrared region up to 1.45 μm was observed for the solar cells with stacked self-assembled Ge dots compared with that without Ge dots. Furthermore, the EQE was found to increase with increasing number of stacking. These results show that electron-hole pairs generated in Ge dots can be efficiently separated by the internal electric field, and can contribute to the photocurrent without considerable recombination in Ge dots or at Ge/Si interfaces.
Magnetron-type radio-frequency plasma control yielding vertically well-aligned carbon nanotube growth
Authors: Hirata T. , Satake N. , Jeong G.-H. , Kato T. , Hatakeyama R. , Motomiya K. , Tohji K.
Published: August 2003

In order to understand the effects of plasma parameters on the nanotube formation and further controlled growth, we have investigated the optimal growth condition using a rf plasma-enhanced chemical vapor deposition method. The magnetic field introduced for a magnetron discharge enhances the nanotube growth as a result of the plasma-density increment and the self-bias reduction of a rf electrode. It is also found that the optimum ion flux and ion bombardment energy is a key parameter for the uniform, well-aligned, and density-controlled nanotube growth.
Category 𝒪: Quivers and endomorphism rings of projectives
Authors: Stroppel Catharina
Published: August 2003

We describe an algorithm for computing quivers of category

O

\mathcal O

of a finite dimensional semisimple Lie algebra. The main tool for this is Soergel’s description of the endomorphism ring of the antidominant indecomposable projective module of a regular block as an algebra of coinvariants. We give explicit calculations for root systems of rank 1 and 2 for regular and singular blocks and also quivers for regular blocks for type

A
3

A_3

. The main result in this paper is a necessary and sufficient condition for an endomorphism ring of an indecomposable projective object of

O

\mathcal O

to be commutative. We give also an explicit formula for the socle of a projective object with a short proof using Soergel’s functor

V

\mathbb V

and finish with a generalization of this functor to Harish-Chandra bimodules and parabolic versions of category

O

\mathcal O

.
EDMing turbopump blisks
Authors: Zhan H. , Zhao W.
Published: August 2003

Turbine blisks designed for advanced liquid rocket engine turbopumps are usually of a timed structure with twisted blades, and they can be machined effectively with the electrical discharge machining (EDM) process. After the machining specifications have been designated, the EDM process of a turbopump turbine blisk is discussed, in which the kernel problems are the design of the electrode and the searching of an interference free path to feed the electrode to machine the blisk.
Hygrothermal analysis of composite wing T‐joints
Authors: Kumari Shyama , Sinha P.K.
Published: August 2003

Effects of moisture and temperature on the behaviour of composite T‐joints made of carbon fibre composite (CFC) materials are investigated. T‐joints may be exposed to moisture and temperature during their service life. Under such circumstances moisture and temperature diffuse into T‐joints. As a consequence, the stiffness and strength properties of the laminates are degraded. Moreover, since the laminae in the laminate cannot deform freely, residual stresses are introduced. The analysis is carried out by the finite element method using a modified thick shell element that takes into account the hygrothermal effects. The analysis also accounts for the lamina material properties at elevated moisture concentration and temperature. Deflections are presented in the form of contours, and maximum stresses developed in the Redux layer are presented in tabular forms. Two stacking sequences with clamped boundary conditions are considered for each variation in moisture and temperature
CrVI free primer: from corrosion findings to profile
Authors: Michelin P.
Published: August 2003

Up to now, protection of aircraft structures is achieved by a multilayer system that includes, in general, a porous oxide or a conversion coating, a chromated primer and a top coat. Each layer plays a role in the protection scheme and key factor is addressed by specifications. As environmental concern is a strong driving force, the replacement of hexavalent chromium in paint is considered by all aerospace manufacturers as a risky target to achieve in the next future. The two key paint film properties, adhesion with respect to interfacial failure and transient stress state, and leachability of inhibitors, are discussed in order to propose a profile for the new generation of CF primer capable to meet the requirements of aeronautic technical specifications.
New configurations for the windshield and the canopy for a two‐seater trainer military aircraft
Authors: Lanciotti Agostino , Mantelli Roberto
Published: August 2003

This paper describes the results of a study on new configurations for the windshield and the canopy of the M346, a new military trainer aircraft with two staggered seats, currently in phase of construction at Aermacchi (Venegono Superiore, Italy). The study carried out demonstrated that forward rotation allows a reduction of the weight of the structure, improves the visual field of the pilots and moreover, allows a greater accessibility to the panel instrumentation. Obviously, all the related aspects have been considered in the development of the study, such as the opening/closure, latching/unlatching and locking systems of the canopy, the tightness for pressurisation, tightness for water and dust also when the aircraft is parked, the resistance to bird impact, the forces due to wind when the canopy is opened on the ground and, in the case of emergency, the systems to break the transparent material and to eject the pilots.
Crack‐resistant and anticorrosive coatings based on vulcanized water dispersion of chlorine‐sulpho‐polyethylene
Authors: Figovsky Oleg L. , Karchevsky Valeria M. , Beilin Dmitriy A.
Published: August 2003

Advanced crack‐resistant coatings based on water dispersion of chlorine‐sulpho‐polyethylene (CSPE, Hypalon®) vulcanized by Mannich alkalis (MA) water solution were obtained. Application of MA as a CSPE structure component makes it possible to produce a vulcanized net of saturated polymer, and thus to receive ecologically safe impenetrable crack resistant coatings of any substrata (concrete, metal, plastic, etc.). The coatings can be applied in aircraft, automotive, shipbuilding, paint and varnish industries, civil engineering, etc. as a corrosion‐resistant material. The optimal coating composition and its mechanical properties have been studied.
Corrosion characteristics of copper‐based IUDs
Authors: Benjamín Valdez S. , Navor Rosas G. , Mónica Carrillo B. , Tezozomoc Pérez L. , Ogura Tetsuya , Celia Beltrán G. , Miguel J. , Beltrán G.
Published: August 2003

A corrosion study of the intra‐uterine device, “TCu 380 A”, was made using cyclic voltammetry (CV), scanning electron microscopy (SEM) and optical microscopy (OM). Blood plasma, whole blood and artificial uterine fluid were used as corrosive media in order to establish a comparative scheme of the corrosion behaviour of copper in the device. In summary, the results obtained were not only similar to work reported previously, but also provided complementary data for a better understanding of the corrosion problem.
Dynamic explanations of industry structure and performance
Authors: Cotterill Ronald W.
Published: August 2003

Examines the exercise of market power in vertical channels. Reviews the development of food systems over the past century. Presents neoclassical models arising from the work of Adam Smith, George Stigler, Harold Demsetz and John Spengler that are in juxtaposition to the more commonly advanced agency theoretic explanation of vertical organization and performance. Develops a structural model of price transmission in a channel that has differentiated product oligopolies at two stages. Increasing concentration at successive stages creates a problem of double marginalization. Vertical trading partners reduce it by avoiding vertical Nash (arms length) pricing via the use of trade promotions and other coordination methods such as private label. Finally, the rise in retail‐buyer concentration (six supermarket chains now control 52.6 percent of supermarket sales in the USA) portends a possible shift to the European model in which food retailers develop and promote their own brands.
Documents and the communication of scientific and scholarly information
Authors: Fjordback Søndergaard Trine , Andersen Jack , Hjørland Birger
Published: August 2003

In 1971 UNISIST proposed a model for scientific and technical communication. This model has been widely cited and additional models have been added to the literature. There is a need to bring this model to the focus of information science (IS) research as well as to update and revise it. There are both empirical and theoretical reasons for this need. On the empirical side much has happened in the developments of electronic communication that needs to be considered. From a theoretical point of view the domain‐analytic view has proposed that differences between different disciplines and domains should be emphasised. The original model only considered scientific and technical communication as a whole. There is a need both to compare with the humanities and social sciences and to regard internal differences in the sciences. There are also other reasons to reconsider and modify this model today. Offers not only a descriptive model, but also a theoretical perspective from which information systems may be understood and evaluated. In addition to this provides empirical exemplification and proposals for research initiatives.
Transforming centres of excellence – the National Heritage Board experience
Authors: Kim Lim Siam
Published: August 2003

Looks at the National Heritage Board (NHB) in Singapore and how it deals with the development of national museums and their archives. Examines the early years of the NHB and its attempts to attract new audiences; then looks at how the digital world is used in archives and museums. Concludes that the NHB aims to maintain standards in order to make heritage a part of every Singaporean’s life.
Food safety at shows and fairs
Authors: Worsfold Denise
Published: August 2003

Food events, such as food festivals, agricultural shows and village fetes take place throughout the UK, usually in outdoor locations. Consumers’ overall satisfaction with the food purchased at such events is high and they have few or no concerns about the food safety on sale. A wide variety of foods, including some high‐risk products are offered for sale to the public. The temporary nature of these events and the vagaries of the UK climate can mean that traders/exhibitors have to cope with environmental conditions that are less than optimum. Organisers of such events are expected by traders/exhibitors to be knowledgeable on a range of relevant topics such as temperature control, display of open food, handwashing facilities, free samples etc. Guidance for traders/exhibitors and organisers of such events is available from local authority Environmental Health departments, and can be found in the Industry Guide to Good Hygiene Practice: Markets and Fairs.
Converting tribology principles into measurable maintenance improvements at Sishen Iron Ore Mine
Authors: Hoffman P.L.
Published: August 2003

Sishen Iron Ore Mine in the Northern Cape province of South Africa utilises 72 primary equipment units to move 119Mt of materials per year, of which 32.5Mt of run‐of‐mine material are sent to the processing plant. The maintenance mission, philosophy and strategy of the Mine are outlined as a background to the discussion of the application of tribology principles. The evolution of Sishen’s tribology outlook is described up to the current position, where the vision for the future is: “no wear”. The current maintenance activities are discussed under the headings: contamination control, lubricants, growing awareness, flushing equipment, and breathers. The results achieved are described, together with the calculated return on investment. Finally, the requirements for success are outlined and possible pitfalls listed.