bluuebunny/crossref_metadata_2025 huggingface dataset:
A stochastic model of range profiles of raindrop size distributions: Application to radar attenuation correction
Authors: Berne A. , Uijlenhoet R.
Published: May 2005

To analyze the influence of the spatial variability of the raindrop size distribution (DSD) on rainfall estimation using weather radar, a stochastic model is proposed in order to simulate range profiles of DSDs and consequently profiles of rainfall intensity, radar reflectivity and specific attenuation. A first application concerning the accuracy of attenuation correction algorithms is presented. Using a Monte Carlo technique, it is shown that an attenuation correction algorithm based on a forward implementation is more sensitive to the inadequacy of power‐law relations than a backward algorithm, the latter being sensitive to the uncertainty of the path integrated attenuation (PIA). The sensitivity to spatial heterogeneity is limited for both algorithms. The corrected profiles remain uncertain because they are based on deterministic power‐law relations which are not fully consistent with the stochastic nature of the DSD.
Comparison of Indonesian Throughflow transport observations, Makassar Strait to eastern Indian Ocean
Authors: Vranes Kevin , Gordon Arnold L.
Published: May 2005

The Pacific to Indian Ocean transport within the passageways of the Indonesian seas (ITF) varies on interannual and longer time scales associated with ENSO, the Asian monsoons and interannual climate variability of the Indian Ocean. Although direct current measurements of the ITF are of limited duration, none long enough to properly describe greater than annual variability of the ITF, observations indicate that the bulk of the ITF passes through Makassar Strait. The repeat expendable bathythermograph (XBT) IX1 section begun in 1983 provides the longest time series of the full ITF introduced into the Indian Ocean between northwest Australia and Java. We find that the surface to 600 dbar Makassar Strait transport, as measured by current meter moorings from December 1996 to July 1998, correlates at r = 0.77 ± 0.14 with the geostrophic transport constructed from IX1 XBT data for that time interval, with a 98 day lag.
Thermohaline circulation at three key sections in the North Atlantic over 1985–2002
Authors: Marsh Robert , de Cuevas Beverly A. , Coward Andrew C. , Bryden Harry L. , Álvarez Marta
Published: May 2005

Efforts are presently underway to monitor the Thermohaline Circulation (THC) in the North Atlantic. A measuring strategy has been designed to monitor both the Meridional Overturning Circulation (MOC) in the subtropics and dense outflows at higher latitudes. To provide a historical context for these new observations, we diagnose an eddy‐permitting ocean model simulation of the period 1985–2002. We present time series of the THC, MOC and heat transport, at key hydrographic sections in the subtropics, the northeast Atlantic and the Labrador Sea. The simulated THC compares well with observations. We find considerable variability in the THC on each section, most strikingly in the Labrador Sea during the early 1990's, consistent with observed changes. Overturning in the northeast Atlantic declines by ∼20% over the 1990's, coincident with an increase in the subtropics. We speculate that MOC weakening may soon be detected in the subtropics, if the decline continues in mid‐latitudes.
Electron precipitation events driven by lightning in hurricanes
Authors: Peter W. B. , Inan U. S.
Published: May 2005

In mid‐September of 2003, Hurricane Isabel passed through the Great Circle Path (GCP) of a subionospherically propagating LF signal between the NAU transmitter in Puerto Rico and a receiver located outside Boston. Cloud‐to‐ground lightning flashes detected by the Long‐Range Lightning Detection Network (LRLDN) and located in the outer rainbands of the hurricane were associated with perturbations in the received LF signal consistent with lightning‐induced electron precipitation (LEP) events. The number of perturbations, detected on the LF signal, exhibiting the known characteristics (rapid onset followed by slow recovery) of LEP events tended to increase with the occurrence of hurricane‐associated lightning near the GCP. The majority (>65%) of causative lightning flashes (those flashes recorded in the LRLDN data that were time‐correlated with spherics associated with LEP events in the VLF/LF data) occurred within 500 km of the GCP; and those flashes associated with Isabel typically occurred in the outer rainbands of the hurricane. While lightning generally occurs more frequently in the outer rainbands of hurricanes than in other tropical oceanic storms, there is no indication that the hurricane‐associated lightning is more likely to induce electron precipitation events than lightning associated with other storm systems. Hurricane Floyd (in September of 1999) and Hurricane Fabian (in August/September of 2003) also passed near the GCP of subionospherically propagating VLF/LF signals, and the received signals exhibited similar perturbation patterns.
A seismological determination of the temperature gradient in D″ beneath the western Pacific
Authors: Kuo Ban‐Yuan , Chen Chin‐Wu
Published: May 2005

The temperature gradient of the thermal boundary layer in the D″ region is one of the basic properties of the mantle that remains difficult to evaluate. We characterize this quantity for a region in the western Pacific using gradient‐sensitive seismological probes. First, both the amplitudes and travel times of the diffracted P and S phases (Pdiff, Sdiff) were analyzed to constrain the regional‐scale vertical gradients of VP and VS. Acceptable models were grid‐searched using synthetic waveforms for trial models that employ only one velocity gradient zone in D″. The VS models were searched over the parameter space of the thickness (H) and the gradient. Solutions show negative deviation from Preliminary Reference Earth Model and a trade‐off between gradient and H from −0.00088 s−1, for190 km to −0.00049 s−1, for 240 km with a typical error of ±0.00015 s−1. Rather than pinning down the best solution, we consider two sets of solutions for VS with H = 190 and 240 km. For these two H values, the gradients of VP were determined solely by amplitude to be −0.00032 s−1 for 190 km and 0.00015 s−1 for 240 km, shrouded in relatively large errors of 0.0002–0.0003 s−1. We derive the temperature gradient from the resolved velocity gradients using the seismological‐thermodynamic equation of Doornbos et al. (1986) and arrive at 9.0 ± 5.8 K/km and 5.7 ± 4.1 K/km over 190 and 240 km, respectively. The difference in gradient between these two models is statistically significant at the 99% confidence level, and the odds that the apparent steeper gradient is caused by squeezing energy of diffracted waves into a thinner zone can also be rejected with high confidence. The combination of the two models is thus consistent with a nonlinear temperature profile that steepens toward the core‐mantle boundary. Both models detect the superadiabatic gradient of temperature in the lowermost mantle.
Seasonally dependent interannual variability of sea ice in the Bering Sea and its relation to atmospheric fluctuations
Authors: Sasaki Yoshi N. , Minobe Shoshiro
Published: May 2005

Interannual variability of sea ice in the Bering Sea and its relationship to atmospheric variability is analyzed using a singular value decomposition (SVD) analysis of sea ice concentrations (SICs) and 1000 hPa wind speeds in winter and spring seasons. The statistically significant first and second SVD modes, explaining 76.3% and 17.6% in winter and 54.6% and 29.6% in spring of the squared covariance between the two fields, are identified for SICs both in the winter and spring seasons with 1 month leading wind speeds. The spatial structures show that the first (second) SVD mode explains the SIC variability in the northeastern (northwestern) Bering Sea, related to the local northwesterly (northerly) wind anomalies for the positive SIC anomalies both in the winter and spring seasons. A comparison of the first SVD modes between the winter and spring seasons suggests that the difference of dominant patterns of wind anomalies results in the difference of SIC anomaly distributions between two seasons. The relationship between sea ice and atmospheric circulation anomalies indicates that one mode of the leading two SVD modes in each season is related to large‐scale atmospheric circulation associated with the Aleutian low and the other mode is related to relatively local atmospheric fluctuations related with pressure anomalies over Alaska. Furthermore, a slight difference of 700 hPa geopotential height anomalies results in the substantially different sea ice anomalies. These results suggest that in order to know the interannual sea ice variability in the Bering Sea, a better understanding of the wind anomalies over the Bering Sea are important.
Tracing tropical and intermediate waters from the South China Sea to the Okinawa Trough and beyond
Authors: Chen Chen‐Tung Arthur
Published: May 2005

Intermediate waters with a salinity minimum from 350 to 1350 m depths have been reported to flow out of the South China Sea (SCS) through the Luzon Strait. This eastward flowing SCS Intermediate Water (SCSIW) is blocked by the northward flowing Black Stream (Kuroshio) southeast of Taiwan and is forced to turn to the north. The SCSIW subsequently enters and occupies the western half of the Okinawa Trough. Because of strong upwelling in the SCS basin, the SCSIW contains more nutrients than does the Kuroshio Intermediate Water in the Philippine Sea. One of the major purposes of this note is to reconfirm that the SCSIW actually does upwell onto the East China Sea (ECS) shelf and to show that the South China Sea Tropical Water (SCSTW), with a salinity maximum of 50–150 m in depth, follows the same pathway as the SCSIW and similarly occupies the western half of the Okinawa Trough. Part of these relatively nutrient‐rich subsurface waters upwell, thereby supplying nutrients to the ECS shelves. The remaining SCSIW and SCSTW flow along with the Kuroshio and can be traced as far east as 140°E, south of Japan. This is just around the region where the Oyashio joins the Kuroshio to form the North Pacific Intermediate Water.
Erosion by flowing Martian lava: New insights for Hecates Tholus from Mars Express and MER data
Authors: Williams David A. , Greeley Ronald , Hauber Ernst , Gwinner Klaus , Neukum Gerhard
Published: May 2005

We have used new compositional information on Martian basaltic rocks from the Mars Exploration Rover Spirit and data from new stereo imaging by the High Resolution Stereo Camera (HRSC) on the Mars Express orbiter to constrain an existing analytical‐numerical computer model to assess the potential of Martian lavas to form lava channels by erosion of substrate. The basaltic rocks studied in Gusev crater by Spirit have compositions consistent with lavas of higher liquidus temperature and lower dynamic viscosity than terrestrial tholeiitic basalts, suggesting that they had a greater potential for turbulent flow and erosion of substrate during flow emplacement than terrestrial basalts, more similar to lunar mare basalts. We modeled a specific case to determine whether these lavas could have formed part of a >66 km long channel on the Martian shield volcano Hecates Tholus. This channel formed on relatively steep slopes (∼2–8°), based on measurements from the HRSC Digital Terrain Model. Our results suggest that erosion rates were of the order of tens to hundreds of centimeters/day, depending on flow rate and ice content of the substrate. Eruption durations required to erode the Hecates channel (∼100–30 m deep over the first ∼20 km, depth decreasing downstream) range from weeks to months, which are consistent with the known eruption durations of terrestrial basaltic lavas and the previous modeling of Wilson and Mouginis‐Mark (2004). Any Hecates lava channels formed from erosion by lava could have served as conduits for later fluvial activity, as recently described by Fassett and Head (2004, 2005).
Forced bars induced by variations of channel width: Implications for incipient bifurcation
Authors: Wu Fu‐Chun , Yeh Tzu‐Hao
Published: May 2005

In this study we investigate forced bars that form in a channel with periodic width variations. A depth‐averaged two‐dimensional (2‐D) model incorporating a simplified correction for the helical flows induced by streamline curvature is used to obtain analytical solution of bed deformation. Flume experiments are conducted to verify the model results. With the correction included, the 2‐D model will be comparable to the 3‐D model. Because the no‐slip condition is relaxed at the sidewalls, the model gives distorted results in the near‐bank region, particularly at narrow sections, but the bed topography is satisfactory for the major part of the channel. The forced bars are classified into four types according to the locations of peak deformations. Transition from one type to another is controlled mainly by the aspect ratio β. Increasing the value of β exhibits sequentially the purely central bars (mode 1), transverse bars (central mode 1), side bars, and transverse bars (central mode 2). The analytical solution is used to derive a criterion for central bar formation, which implies a condition required for incipient bifurcation. Given the bank profile, flow, and sediment conditions, the central bars of mode 1 would develop for β < βc1 (a lower critical value), the central bars of mode 2 would develop for β > βc2 (an upper critical value), whereas side bars would form for βc1 < β < βc2. Such criteria for formation of different bar patterns are necessary but not sufficient conditions for establishing stable regimes.
Solitary fracture waves in metastable snow stratifications
Authors: Heierli Joachim
Published: May 2005

Fracture processes in layered snow have many implications on avalanche hazard and mountain safety. This paper is a contribution for a better understanding of fracture dynamics in a stratified medium with a collapsible layer in terms of a simple analytical model involving only field measurable parameters. For this purpose a simple three‐layer snow stratification is considered to consist of a compact basal layer, a collapsible weak layer, and a homogenous top layer. It is shown analytically that the fracture of the weak layer can occur in the form of a localized disturbance zone propagating a collapse with constant velocity and wavelength. Simple analytical expressions describing the disturbance are obtained. The results are in good agreement with observations in the terrain. The presented fracture process is relevant to the release of dry snow slab avalanches and to the propagation of firn quakes and whumpfs but may also apply to other stratified media with appropriate properties.
Radio frequency interference mitigation with phase‐only adaptive beam forming
Authors: Fridman P. A.
Published: May 2005

Connected radio interferometers are sometimes used in the tied array mode: signals from antenna elements are coherently added and the sum signal applied to a very long baseline interferometry (VLBI) back‐end or pulsar‐processing machine. Usually, there is no computer‐controlled amplitude weighting in the existing radio interferometer facilities. Radio frequency interference (RFI) mitigation with phase‐only adaptive beam forming is proposed for this mode of observation. Small phase perturbations are introduced in each of the antenna's signals. The values of these perturbations are optimized in such a way that the signal from a radio source of interest is preserved and RFI signals are suppressed. An evolutionary programming algorithm is used for this task. Computer simulations, made for both one‐dimensional and two‐dimensional array setups, show considerable suppression of RFI and acceptable changes to the main array beam in the radio source direction.
Risk‐cost‐benefit analysis of atrazine in drinking water from agricultural activities and policy implications
Authors: Tesfamichael Aklilu A. , Caplan Arthur J. , Kaluarachchi Jagath J.
Published: May 2005

This study provides an improved methodology for investigating the trade‐offs between the health risks and economic benefits of using atrazine in the agricultural sector by incorporating public attitude to pesticide management in the analysis. Regression models are developed to predict finished water atrazine concentration in high‐risk community water supplies in the United States. The predicted finished water atrazine concentrations are then used in a health risk assessment. The computed health risks are compared with the total economic surplus in the U.S. corn market for different atrazine application rates using estimated demand and supply functions developed in this work. Analysis of different scenarios with consumer price premiums for chemical‐free and reduced‐chemical corn indicate that if the society is willing to pay a price premium, risks can be reduced without a large reduction in the total economic surplus and net benefits may be higher. The results also show that this methodology provides an improved scientific framework for future decision making and policy evaluation in pesticide management.
A novel tracer method for estimating sewer exfiltration
Authors: Rieckermann J. , Borsuk M. , Reichert P. , Gujer W.
Published: May 2005

A novel method is presented to estimate exfiltration from sewer systems using artificial tracers. The method relies upon use of an upstream indicator signal and a downstream reference signal to eliminate the dependence of exfiltration estimates on the accuracy of discharge measurement. An experimental design, a data analysis procedure, and an uncertainty assessment process are described and illustrated by a case study. In a 2‐km reach of unknown condition, exfiltration was estimated at 9.9 ± 2.7%. Uncertainty in this estimate was primarily due to the use of sodium chloride (NaCl) as the tracer substance. NaCl is measured using conductivity, which is present at nonnegligible levels in wastewater, thus confounding accurate identification of tracer peaks. As estimates of exfiltration should have as low a measurement error as possible, future development of the method will concentrate on improved experimental design and tracer selection. Although the method is not intended to replace traditional CCTV inspections, it can provide additional information to urban water managers for rational rehabilitation planning.
The impact of surface albedo on the retrievals of low‐level stratus cloud properties: An updated parameterization
Authors: Dong Xiquan
Published: May 2005

An updated version of Dong et al. (1998, hereinafter referred to as D98) parameterization is developed from a total of 40 hours of data with a broad range of surface albedos (0.1–0.8) during the 2000–2002 winter seasons at the DOE ARM SGP site. The updated parameterization includes the impact of surface albedo on the retrievals of stratus cloud microphysical and radiative properties, and has a significant improvement over D98 when surface albedo is high. Comparing the retrievals, the cloud‐droplet effective radii (re) calculated from the updated parameterization have a higher correlation coefficient (0.733) and lower Root‐Mean‐Square (RMS) error (1.74 μm or 17.4%) than those (0.602, 4.0 μm or 40%) from the D98. The cloud albedos also have a much higher correlation coefficient (0.983) and lower RMS (3%) than those (0.465, 26%) from the D98. The upper limit of surface albedo is 0.3 in applying the D98.
Implications of droplet nucleation to mineral dust aerosol deposition and transport
Authors: Fan Song‐Miao , Moxim Walter J. , Levy Hiram
Published: May 2005

Calculations from a microphysics model are shown which indicate the factors that control droplet nucleation scavenging of hydrophilic mineral dust particles over a large range of conditions including the size, chemical composition, and number density of particles in both cumulus and stratus clouds. We focus specifically on the activation threshold radius (ATR) for droplet nucleation which determines the particles that are activated and those available for further transport and subsequent iron deposition to the remote ocean. Results suggest: the ATR is typically found in the range of clay‐sized particles (radius = .1 to 1. μm), a spectrum over which the amount of dust removed declines ∼60% both in surface area and particle number; nucleation of silt‐sized particles (1.–10. μm) occurs under most conditions; larger fractions of mineral aerosols are removed in cumulus clouds than in stratus; and while acid coating of dust particles in polluted environments acts to decrease the ATR, the effect is reduced by competition with soluble aerosols. Regional mineral dust environments exhibit potentially diverse aerosol wet removal impacts. The ATR representative of the tropical Atlantic ocean basin (<.2 μm) indicates ∼80% removal of the total dust surface area, while in the pristine southern hemisphere mid latitudes an ATR ∼.5 μm implies ∼60%. In contrast, varying conditions in the polluted region of East Asia suggest a large ATR spectrum (.2 to 3. μm) with dust surface area removal ranging from >80% to <10%.
Too Important to Fail
Authors: Kappenman John G. , Radasky William A.
Published: May 2005

The looming collision of historically large geomagnetic storms with modern‐day electric power grids may produce significant damage to critical infrastructure. The vulnerability to space weather disturbances has been growing largely unchecked as the power grids have grown in size and complexity as our society and nearly all critical services are increasingly dependent on reliable electricity.
Metabolism is Normal in Astrocytes in Chronically Epileptic Rats: A 13C NMR Study of Neuronal—Glial Interactions in a Model of Temporal Lobe Epilepsy
Authors: Melø Torun M , Nehlig Astrid , Sonnewald Ursula
Published: May 2005

The aim of the present work was to study potential disturbances in metabolism and interactions between neurons and glia in the lithium-pilocarpine model of temporal lobe epilepsy. Rats chronically epileptic for 1 month received [1-13C]glucose, a substrate for neurons and astrocytes, and [1,2-13C]acetate, a substrate for astrocytes only. Analyses of extracts from cerebral cortex, cerebellum, and hippocampal formation (hippocampus, amygdala, entorhinal, and piriform cortices) were performed using 13C and 1H nuclear magnetic resonance spectroscopy and HPLC. In the hippocampal formation of epileptic rats, levels of glutamate, aspartate, N-acetyl aspartate, adenosine triphosphate plus adenosine diphosphate and glutathione were decreased. In all regions studied, labeling from [1,2-13C]acetate was similar in control and epileptic rats, indicating normal astrocytic metabolism. However, labeling of glutamate, GABA, aspartate, and alanine from [1-13C]glucose was decreased in all areas possibly reflecting neuronal loss. The labeling of glutamine from [1-13C]glucose was decreased in cerebral cortex and cerebellum and unchanged in hippocampal formation. In conclusion, no changes were detected in glial—neuronal interactions in the hippocampal formation while in cortex and cerebellum the flow of glutamate to astrocytes was decreased, indicating a disturbed glutamate—glutamine cycle. This is, to our knowledge, the first study showing that metabolic disturbances are confined to neurons inside the epileptic circuit.
Novel Surrogate Markers for Acute Brain Damage: Cerebrospinal Fluid Levels Corrrelate with Severity of Ischemic Neurodegeneration in the Rat
Authors: Siman Robert , Zhang Chen , Roberts Victoria L , Pitts-Kiefer Alex , Neumar Robert W
Published: May 2005

Previously, we identified proteins released from degenerating cultured cortical neurons as novel cerebrospinal fluid (CSF) markers for acute brain injury in the rat. Here, we investigate relationships between CSF changes in these novel markers and the severity of acute ischemic brain injury. Rats underwent sham surgery or 3,6,8, or 10mins of transient global forebrain ischemia. At 48 h after insult, CSF levels of 14-3-3β, 14-3-3ξ, and calpain cleavage products of α-spectrin and tau were quantified. Regional acute neurodegeneration was assessed by Fluoro-Jade and silver impregnation staining, and confirmed by immunohistochemical detection of the activation of calpain and caspase, cysteine proteases involved in neurodegenerative signaling. Ischemic neurodegeneration and activation of at least one cysteine protease were observed in the hippocampal CA1 sector, dentate hilus, caudate nucleus, parietal cortex, thalamus, and inferior colliculus. As expected, the total number of degenerating cells increased as a function of ischemia duration. Cerebrospinal fluid levels of the four marker proteins increased markedly after ischemia, and rose in proportion with its duration. Irrespective of the length of ischemia, CSF levels of the neuron-enriched proteins 14-3-3β and calpain-cleaved tau correlated significantly with the magnitude of acute ischemic neurodegeneration. Additionally, CSF levels of the two proteins correlated with one another. These results show that certain proteins released from degenerating neurons are CSF markers for brain injury in the rat whose levels reflect the severity of acute ischemic neurodegeneration. Measurement of 14-3-3β and calpain-cleaved tau may be useful for the minimally invasive diagnosis, prognosis, and therapeutic evaluation of acute brain damage.
The transient self-excitation of a switched reluctance generator
Authors: Schofield N. , Long S. A.
Published: May 2005

Switched reluctance (SR) drive systems are a candidate technology for electric vehicle applications, particularly where a high degree of component integration is required within a thermally demanding environment—typical of engine-mounted power assist solutions. While various operation and fault scenarios have been presented for such drive systems, this paper discusses the self-excitation of a SR generator via the drive-train dc link capacitance and compounded by the stored inertial energy of the connected mechanics. Test observations are also discussed that suggest the potential for transient self-excitation of the SR generator via residual magnetization of the machine rotor, a fault scenario that has not previously been reported. The SR generator system steady-state control is discussed and results presented from a faulted system.
Self-assembly of magnetic biofunctional nanoparticles
Authors: Sun Xiangcheng , Thode C. J. , Mabry J. K. , Harrell J. W. , Nikles D. E. , Sun K. , Wang L. M.
Published: May 2005

Spherical, ferromagnetic FePt nanoparticles with a particle size of 3 nm were prepared by the simultaneous polyol reduction of Fe(acac)3 and Pt(acac)2 in phenyl ether in the presence of oleic acid and oleylamine. The oleic acid ligands can be replaced with 11-mercaptoundecanoic acid, giving particles that can be dispersed in water. Both x-ray diffraction and transmission electron microscopy indicated that FePt particles were not affected by ligands replacement. Dispersions of the FePt particles with 11-mercaptoundecanoic acid ligands and ammonium counter ions gave self-assembled films consisting of highly ordered hexagonal arrays of particles.
Dielectric resonance in magnetic resonance imaging: Signal inhomogeneities in samples of high permittivity
Authors: Sekino Masaki , Mihara Hiroaki , Iriguchi Norio , Ueno Shoogo
Published: May 2005

A distinctive signal inhomogeneity arises in magnetic resonance (MR) images of samples whose dimension is comparable to the wavelength of electromagnetic fields at the resonant frequency. In this study, spatial distributions of magnitude and phase of MR signals in cylindrical phantoms were obtained by theoretical calculations and experiments. As the diameter of the phantom approaches the wavelength of electromagnetic fields in the phantom, the center of the phantom exhibited high magnitude of MR signals. An increase in conductivity resulted in a suppression of the signal inhomogeneity due to skin effect. In addition, the increase in conductivity caused a phase delay at the center of the phantom.
Magnetic force-induced damping effect for magnetic bearing motor
Authors: Wang Chien-Chang , Yao Y. D. , Chang Yu-Hsiu , Tung Pi-Cheng , Xiao Ren-Bin
Published: May 2005

An innovative damping induced by magnetic force was designed successfully for a totally passive magnetic bearing motor. A magnetic ring of high permeability and an annular-shaped rubber pad were mounted on the stator 0.55 mm below the permanent magnet of the rotor. Computer simulations were compared with experimental measurements to decide on the material and configuration of the critical components. The natural frequencies for lateral and rotational modes of the rotor are around 22 Hz measured by impulse method. Both the magnetic bearing motor with and without magnetic damping are rotated at a rated speed of 3840 rpm, which is far above the first critical speed of 1305 rpm. Without magnetic damping, the natural damping ratio in the radial direction of the rotor is 0.0655. After damping, it increases to 0.1401. We have demonstrated by both experimental measurement and theoretical calculation that the antishock performance is significantly improved by the innovative damping technology in a passive magnetic bearing motor.
Effective magnetoviscosity of planar-Couette magnetic fluid flow
Authors: He Xiaowei , Elborai Shihab , Kim Dokyung , Lee Se-Hee , Zahn Markus
Published: May 2005

Magnetic fluid spin velocity, shear stress, and magnetoviscosity were calculated for a planar-Couette magnetic fluid flow, with applied uniform dc magnetic field transverse to the duct axis and by using Shliomis’ first magnetization relaxation equation, generally valid for low magnetic fields. For simplicity, the magnetic fluid was assumed to be linearly magnetizable with constant magnetic susceptibility. Using the assumption of incompressible flow and the symmetry of the geometry, the solution for the axial flow is a linear function of position within the channel while the spin velocity is spatially constant, where both the spin velocity and the change in viscosity, obey a third order algebraic torque equation due to an imposed magnetic field H or a fifth order algebraic torque equation due to the imposed magnetic flux density B. This analysis describes the conditions for multivalued effective magnetoviscosity and spin velocity.
Magnetic studies of iron oxide nanoparticles coated with oleic acid and Pluronic® block copolymer
Authors: Morales M. A. , Jain Tapan Kumar , Labhasetwar V. , Leslie-Pelecky D. L.
Published: May 2005

We have prepared and studied iron-oxide nanoparticles coated with oleic acid (OA) and Pluronic® polymer. The mean diameter of the iron-oxide nanoparticles was 9.3(±)0.8nm. Saturation magnetization values measured at 10K varied from 66.1(±0.7)emu∕gto98.7(±0.5)emu∕g. At 300K the loops showed negligible coercive field. The peaks in zero-field-cooled susceptibility decreased from 280to168K with increasing OA concentration up to 10.6wt%, and remained nearly constant for higher concentrations. This suggests that incomplete coverage of the OA allows small, interacting agglomerates to form.
Characteristic analysis of permanent magnet-assisted synchronous reluctance motor for high power application
Authors: Lee Jung-Ho , Jang Young-Jin , Hong Jung-Pyo
Published: May 2005

In this paper, finite element analysis for a permanent magnet-assisted synchronous reluctance motor (PMASynRM) is presented and the inductance, torque characteristics analysis is performed under the effect of saturation. Comparisons are given with inductance and torque characteristics of normal synchronous reluctance motor (SynRM) and those according to quantity of residual flux density (0.1–0.4T) in PMASynRM, respectively. Comparisons are given with output characteristics of normal SynRM and those of PMASynRM, according to load, respectively. It is confirmed that the proposed model results in high output power performance.
Fabrication of magnetic hollow silica nanospheres for bioapplications
Authors: Shao L. , Caruntu D. , Chen J. F. , O’Connor C. J. , Zhou W. L.
Published: May 2005

Different kinds of nanospheres are used in magnetic nanosphere fabrication for bioapplications. In this paper, we report a successful synthesis of magnetic hollow silica nanospheres (MHSNS). The MHSNS were fabricated with a one step coating of Fe3O4 magnetic nanoparticles (NPs)(∼10nm) and silica on nanosized (20–100nm) spherical calcium carbonate (CaCO3) surface under alkaline conditions, in which the nanosized CaCO3 were used as nanotemplates and tetraethoxysilane and magnetic NPs were used as precursors. The as-synthesized nanoshperes were immersed in an acidic solution to remove nanosized CaCO3, forming MHSNS. The MHSNS were characterized by SEM, TEM, and SQUID. SEM and TEM results showed that a smooth surface of MHSNS and a thin layer of silica (∼10nm) embedded with the magnetic NPs was successfully formed. No nanosized CaCO3 nanotemplates were observed. SQUID measurement demonstrated that magnetization of MHSNS was dependent on temperature, exhibiting superparamagnetism. The MHSNS have potential applications in biomedicine and bioseparation.
Improved calculation of winding losses in gapped inductors
Authors: Van den Bossche Alex , Valchev Vencislav Cekov
Published: May 2005

Field patterns in gapped inductors are more complicated than the fields in transformers, thus the winding losses in inductors are given with higher complexity. An improved presentation of winding losses in inductors is reported, using a correction loss factor. The full expression of that correction loss factor, called kF, is tuned using FEM calculations. An approximation of kF as a function of a parameter κ is provided. The parameter is depending on the sum of the distance coil–air gap and 1∕3 winding thickness, divided by the window width. The features of the approach are the fast and straight winding loss calculation combined with sufficient accuracy and wide application for gapped inductors with different frequencies, wire diameters, conductor fittings, and core and air gap constructions.
Easy synthesis and characterization of γ-Fe2O3 nanoparticles for biomedical applications
Authors: An Sung Yong , Shim In-Bo , Kim Chul Sung
Published: May 2005

Easy syntheses of γ-Fe2O3 nanoparticles have been fabricated by the sol–gel method. The powders present average particle size of 7, 10, and 13nm with narrow size distribution for samples as-obtained and annealed at 150, 175, and 200°C, respectively. At a room temperature, 10nm particles were partially superparamagnetic. The Mössbauer spectrum for the 7nm samples at room temperature displays superparamagnetic behavior as demonstrated by the single quadrupole doublet with zero hyperfine fields. Superparamagnetic particles display no sextet in Mössbauer spectra at temperatures above blocking temperature (TB=165K for the 7nm sample).
Optical emission spectroscopy as a tool for the biodistribution investigation of cobalt-ferrite nanoparticles in mice
Authors: Kückelhaus S. , Tedesco A. C. , Oliveira D. M. , Morais P. C. , Boaventura G. R. , Lacava Z. G. M.
Published: May 2005

This study reports on the biodistribution investigation of two magnetic samples both based on cobalt-ferrite nanoparticles, a magnetic fluid sample (CoMF) and a stealth magnetoliposome polyethylene glycol-monolaurate (PEG-ML). Morphology observations and iron and cobalt concentrations were evaluated after treatment of mice upon intravenous injection. Both magnetic samples had an extended distribution throughout all investigated organs. CoMF was quickly eliminated mainly by the fecal via whereas PEG-ML was retained longer in the circulation and slowly eliminated. These differences are probably due to the presence of polyethylene glycol on the PEG-ML surface, recognized to be responsible for the internalization delay of nanoparticles.
Quantitative measurement of magnetic moments with a torsional resonator: Proposal for an ultralow moment reference material
Authors: Min D. H. , Moreland John
Published: May 2005

We present a method for defining the magnetic moment of a reference material based on a torsional resonator with a patterned magnetic film on its surface. Given accurate measurements of the magnitude of the applied field, the moment of inertia of the resonator, and the magnetic stiffening effect of the film on the resonance frequency of the resonator, we can obtain an absolute measurement of the anisotropy energy and magnetic moment of the film independently. With this approach, the anisotropy energy and the magnetic moment of the film are measured directly, eliminating the need for a detailed knowledge of the film’s saturation magnetization or sample volume. In principle, all of the measurements needed for the reference material are traceable to an atomic clock frequency reference. We have performed preliminary measurements on Ni0.8Fe0.2 films patterned in circle of 4.17 mm diameter. Representative samples had measured magnetic moments of 5.04±0.12μAm2 for nominal film thicknesses of 500 nm.
Biological sensing with magnetic nanoparticles using Brownian relaxation (invited)
Authors: Chung S.-H. , Hoffmann A. , Guslienko K. , Bader S. D. , Liu C. , Kay B. , Makowski L. , Chen L.
Published: May 2005

Magnetic nanoparticles coated with biochemical ligands are enabling many biological and medical applications. In particular biomagnetic sensors have potential advantages of simplicity and rapidity. We demonstrate a substrate-free biomagnetic sensing approach using the magnetic ac susceptibility of ferromagnetic particles suspended in a liquid. The magnetic relaxation of these particles is mainly due to Brownian rotational diffusion, which can be modified by binding the particles to the intended target. This scheme has several advantages: (i) it requires only one binding event; (ii) there is an inherent check of integrity; and (iii) the signal contains additional information about the target size.
Design and analysis of a novel stator–doubly-fed doubly salient motor for electric vehicles
Authors: Cheng Ming , Fan Ying , Chau K. T.
Published: May 2005

The design of a stator-doubly-fed doubly salient (SDFDS) machine is presented. The corresponding output power equation is analytically derived. The initial calculation of motor dimensions and parameters are also discussed. Moreover, finite element analysis of this motor is carried out, in which the interaction between the field flux and armature current flux as well as the magnetic saturation are taken into account. Hence, the characteristics of the proposed motor are deduced. A 12∕8-pole SDFDS motor is designed and built for exemplification. Experimental results of the prototype are given to verify the theoretical analysis.
Magnetically tunable micro-strip band-stop filter: Design optimization and characterization
Authors: Kuanr Bijoy K. , Harward I. R. , Deiotte R. T. , Camley R. E. , Celinski Z.
Published: May 2005

We investigate ultra-small band-stop filters made with continuous Fe films and with multilayered Fe∕Cu films. In ferromagnetic resonance measurements, the continuous Fe(100nm) film had a larger linewidth, on the order of 200Oe at 10GHz, resulting in a device linewidth, which typically was close to 2GHz in the operational device. In contrast a [Fe(5nm)∕Cu(0.8nm)]20 multilayer structure showed a ferromagnetic resonance linewidth of 50Oe at 10GHz and had a device linewdith of about 0.5GHz. We expect that the breaking of the Fe films by Cu reduces the typical size of crystallites in Fe, thus reducing the linewidth. The filter demonstrates wide tuning range of 10–30GHz with bias fields up to 4kOe. This work demonstrates a single notch-filter, which can operate from X- to K-band with a linewidth of 1.8GHz at 0.07kOe and 0.33GHz at 4.0kOe. The measured minimum insertion loss in each case is ∼2.5dB, with greater than 15dB return loss in the entire pass-band frequency.
Intracellular translocation of superparamagnetic iron oxide nanoparticles encapsulated with peptide-conjugated poly(D,L lactide-co-glycolide)
Authors: Lee Seung-Jun , Jeong Jong-Ryul , Shin Sung-Chul , Huh Yong-Min , Song Ho-Taek , Suh Jin-Suck , Chang Young-Hwan , Jeon Bong-Sik , Kim Jong-Duk
Published: May 2005

In this study, we propose the use of iron oxide nanoparticle encapsulated with peptide-conjugated poly(D,L lactide-co-glycolide) (PLGA) as a potent intracellular carrier for diagnosis agent. The iron oxide (γ-Fe2O3) nanoparticles were prepared by a chemical coprecipitation method of ferric and ferrous ions in an alkali solution. Arg peptide (RRRRRRRRCK-FITC) were conjugated to the PLGA via a simple coupling reaction between maleimide-derivatized PLGA and thiol-terminated Arg peptide. The γ-Fe2O3-PLGA-Arg-FITC nanoparticle was then prepared by an emulsification-diffusion technique. A confocal laser scanning microscopy revealed that the γ-Fe2O3-PLGA-Arg-FITC nanoparticle was effectively adsorbed onto the membrane of stem cells and delivered into the nuclei without cytotoxicity. Magnetic properties of the γ-Fe2O3-PLGA-Arg-FITC nanoparticle were observed by measuring the zero-field-cooled∕field-cooled magnetization and magnetic hysteresis loop using a superconducting quantum interference device magnetometer from 5K to 300K.
Optimum shell separation for closed axial cylindrical magnetic shields
Authors: Paperno Eugene , Peliwal Saee , Romalis Michael V. , Plotkin Anton
Published: May 2005

The effect of shell separation on the axial shielding with closed double-shell cylindrical shields is investigated numerically. It is found that the optimum shell separation for practical, equal-thickness shields of the above type is considerably smaller than that for transverse spherical and infinitely long cylindrical shields: in most cases, air gaps equal 5%–10% of the inner shell diameter are wide enough to bring the shielding to 90% of its maximum. This indicates that closely spaced axial shields can be used without much sacrifice in performance. Taking into account the computed optimum shell separation for double-shell shields, one can easily optimize and design a compact and effective multishell shield. Based on the numerical study, an analytical approximation is suggested for the axial shielding with narrowly spaced double-shell cylindrical shields.
Interleukin-1 and interleukin-6 production in mice’s lungs induced by 2, 3 meso-dimercaptosuccinic-coated magnetic nanoparticles
Authors: Chaves S. B. , Silva L. P. , Lacava Z. G. M. , Morais P. C. , Azevedo R. B.
Published: May 2005

In the present study, we evaluated the effects of a water-based (physiological medium) magnetic fluid sample containing magnetite nanoparticles surface coated with a layer of 2, 3 meso-dimercaptosuccinic acid in mice. The animals were killed after times varying from 5minto24h. Tissue analysis was made by light microscopy using hematoxilin and eosin (HE) staining and interleukin 1 and 6 immunohistochemistry. The results showed accumulation of nanoparticles in lungs after 30min of sample administration, with inflammatory process associated to it. It also showed an increase in both interleukins expression, which confirms inflammatory response associated with magnetic nanoparticles.
Water formation reaction on Pt(111): Role of the proton transfer
Authors: Nagasaka Masanari , Kondoh Hiroshi , Ohta Toshiaki
Published: May 2005

The catalytic water formation reaction on Pt(111) was investigated by kinetic Monte Carlo simulations, where the interaction energy between reaction species and the high mobility of H2O molecule was considered. Results obtained clearly reproduce the scanning tunneling microscopy images which show that the reaction proceeds via traveling the reaction fronts on the O-covered Pt(111) surface by creating H2O islands backwards. The reaction front is a mixed layer of OH and H2O with a (3×3)R30° structure. Coverage change during the reaction is also reproduced in which the reaction consists of three characteristic processes, as observed by the previous experiments. The simulation also revealed that the proton transfer from H2O to OH plays an important role to propagate the water formation.
Preparation and investigation of potentiality of different soft ferrites for hyperthermia applications
Authors: Giri Jyotsnendu , Pradhan Pallab , Sriharsha T. , Bahadur D.
Published: May 2005

Water-based ferrofluids of substituted ferrites Fe1−xMnxFe2O4 (0⩽x⩽1) have been prepared by the co-precipitation method and characterized. Particles are superparamagnetic with an average particle size of about 10–12nm. The specific absorption rate (SAR) was measured by calorimetric measurement at a frequency of 300kHz and a field of 10–45kA∕m. The variation of SAR and magnetization of Fe1−xMnxFe2O4 with Mn concentration shows similar dependence. Innocuousness studies of MnFe2O4 ferrofluids to the living cells have been carried out with BHK-21 cells. In vitro studies showed that threshold biocompatible concentration is dependent on the nature of ferrites and coating.
Effects of surfactant friction on Brownian magnetic relaxation in nanoparticle ferrofluids
Authors: Pakhomov Alexandre B. , Bao Yuping , Krishnan Kannan M.
Published: May 2005

Measurement of the variation of relaxation frequency of Brownian rotation of magnetic nanoparticles in a ferrofluid due to binding of organic molecules is a possible tool for detection of biomolecules in solution. We investigate frequency- and temperature-dependent magnetic behavior of model ferro-fluids of surfactant-coated Co nanoparticles, 20nm in diameter, in dichlorobenzene in a wide concentration range. At room temperature the most diluted ferrofluids have a single relaxation frequency determined by the fluid viscosity and effective particle volume. Increasing concentration leads to an appearance of the second, low-frequency relaxation peak, attributed to the effective viscosity associated with interparticle friction.
Effect of design variables on irreversible magnet demagnetization in brushless dc motor
Authors: Kim Tae Heoung , Lee Ju
Published: May 2005

The large demagnetizing currents in brushless dc (BLdc) motor are generated by the short-circuited stator windings and the fault of a drive circuit. So, irreversible magnet demagnetization occurs due to the external demagnetizing field by these currents. In this paper, we deal with the effect of design variables on irreversible magnet demagnetization in BLdc motor through the modeling approach using a two-dimensional finite-element method (2D FEM). The nonlinear analysis of a permanent magnet is added to 2D FEM to consider irreversible demagnetization. As a result, it is shown that magnet thickness, teeth surface width, and rotor back yoke thickness are the most important geometrical dimensions of BLdc motor in terms of irreversible magnet demagnetization.
Effects of an in-plane axisymmetric magnetic field on the vibration of a thin conductive spinning disk
Authors: Michalek Arthur J. , Marzocca Piergiovanni , Moosbrugger John , Hasanyan Davresh
Published: May 2005

This paper details the derivation and solution of the governing equation for linear transverse vibrations of a thin perfectly conducting rotating disk subjected to an axisymmetric in-plane magnetic field having a circumferential flux pattern. Previous works on plates and shells have hypothesized that the application of a magnetic field is capable of increasing the natural frequency of a thin conductive plate. Analytical results show a significant increase in maximum stable operating speed of a thin disk in the presence of a magnetic field. The effect is dependent on both thickness and magnetic field strength.