bluuebunny/crossref_metadata_2025 huggingface dataset:
Damage Extension Forces and Piezoelectric Fracture Criteria
Authors: Yang X. H. , Dong L. , Chen C. Y. , Wang C. , Hu Y. T.
Published: May 2011

Due to external loads, damage extension forces will drive mechanical and electrical damages to evolve in piezoelectric materials from the viewpoint of continuum damage mechanics, so it is important for understanding piezoelectric fracture mechanism and estimating the utilizing life and safety of a piezoelectric device to study the damage extension forces. Based on the static piezoelectric damage constitutive model established in our previously published papers, general expressions of the damage extension forces are given. The finite element method and the iterative procedure are utilized to calculate the extension forces at crack-tips in the samples for the experiments of Park and Sun's, and then the linear and nonlinear fracture criteria are presented. It is revealed from the list of the normalized mean square deviations that the nonlinear criterion is better.
A Study on the Safety of Shear design of Reinforced Concrete Beams
Authors: Lu W. Y. , Lin I. J.
Published: May 2011

The shear failure probabilities of reinforced concrete beams have been investigated by Monte Carlo technique. The shear strength provided by the concrete is based on the theoretical model developed by Tureyen and Frosch (2003). The random variables included in this study are the strength of concrete, the strength of reinforcing steel, the dimension of cross-section, the model error of theoretical shear strength provided by the concrete, and the loading. This study shows that based on the new material statistical data (2003) in North America, the shear failure probabilities are acceptable for beams designed using the ACI 318-02 Code. Based on the old material statistical data (1979) in North America the shear failure probabilities of beams designed using the ACI Code are relatively high. For the safety of shear design of reinforced concrete beams, the ACI 318-02 Code is better than the ACI 318-99 Code.
Characteristics of Hydraulic Shock Waves in an Inclined Chute Contraction – Numerical Simulations
Authors: Jan C.-D. , Chang C.-J. , Lai J.-S. , Guo W.-D.
Published: May 2011

This paper presents the results of numerical simulations on the characteristics of hydraulic shockwaves in an inclined chute contraction. A two-dimensional numerical hydraulic simulation model is used to simulate the hydraulic shockwaves, based on the finite-volume multi-stage (FMUSTA) scheme proposed by Guo et al. [1]. This numerical model has been proved having good ability in simulating hydraulic shockwaves through the comparison with the exact solution of idealized shockwaves in a horizontal contraction provided by Ippen and Dawson [2], and the comparison with experimental results provided in the companion paper by Jan et al. [3]. The simulated shockwave parameters such as the shock angle, maximum shockwave height and maximum shockwave position for various conditions are compared with those calculated by the empirical relations obtained in the companion paper. The numerical results validate the applicability of these empirical relations and also extend their applicability to higher approach Froude numbers.
Structural Responses of Surface-Mounted Piezoelectric Beams
Authors: Wang R.-T.
Published: May 2011

The formulation of a beam on which a pair of piezoelectric segments bonded is presented. The method of transfer matrix is adopted to study the structural responses of the surface-mounted actuation beam induced by an external force on the beam and by a voltage on the actuator. Furthermore, the modal frequencies and the corresponding mode shape functions of the beam also are obtained by the method. The orthogonality of any two distinct sets of mode shape functions of the beam is shown. The method of modal analysis is presented to study the forced vibration of the beam due to a concentrated transient force. The effects of length, location and thickness of the piezoelectric pairs on the structural responses and the modal frequencies of the beam are investigated.
Studies of Gas Velocity And Particles Size Effects on Fluidized Bed Hydrodynamics with Cfd Modeling and Experimental Investigation
Authors: Hamzehei Mahdi , Rahimzadeh Hassan , Ahmadi Goodarz
Published: May 2011

With applying Computational Fluid Dynamics (CFD) techniques, hydrodynamics of a twodimensional non-reactive gas-solid fluidized bed reactor was investigated. A multi fluid Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the unsteady state behavior of this reactor and momentum exchange coefficients were calculated by using the Syamlal-O'Brien drag functions. A suitable numerical method that employed finite volume method applied to discritize the equations. Simulation results also indicated that small bubbles were produced at the bottom of the bed. These bubbles collided with each other as they moved upwards forming larger bubbles. Also, solid particles diameter and superficial gas velocity effect on hydrodynamics were studied. Simulation results were compared with the experimental data in order to validate the CFD model. Pressure drops and bed expansion ratio as well as the qualitative Gas-Solid flow patterns predicted by the simulations were in good agreement with experimental measurements at superficial gas velocities higher than the minimum fluidization velocity. Furthermore, this comparison showed that the model can predict hydrodynamicsbehavior of gas solid fluidized bed reasonably well.
Turbulent Film Boiling on A Non-Isothermal Horizontal Elliptical Tube with Steam Heating Surface
Authors: Hu H.-P. , Wang C.-C. , Chen C.-K.
Published: May 2011

The present theoretical study investigates turbulent film boiling on an elliptical tube with steam heating surface inside. The flow direction of the heating steam is opposite to the vapor film of the outer tube. Thus, the surface temperature is expressed by cosine function. The effect of temperature amplitude, eccentricity, nonlinear viscosity, nonlinear thermal conductivity, radiation and eddy diffusivity are all included in the present analysis. And the paper also discusses the vapor thickness, local Nusselt number and mean Nusselt number. The result shows, first, under the free convection turbulent film boiling with temperature variation, the bigger the temperature amplitude value is, the better the heat transfer efficiency is. Next, the increase of the eccentricity values will bring out the increase of the Nusselt number. Finally, a comparison between the results of the present study and those reported in a previous theoretical data is provided.
Large Deformation Analysis for Soft Foams Based on Hyperelasticity
Authors: Silber G. , Alizadeh M. , Salimi M.
Published: May 2011

In Elastomeric foam materials find wide applications for their excellent energy absorption properties. The mechanical property of elastomeric foams is highly nonlinear and it is essential to implement mathematical constitutive models capable of accurate representation of the stress-strain responses of foams. A constitutive modeling method of defining hyperfoam strain energy function by a Simplex Strategy is presented in this work. This study will demonstrate that a strain energy function of finite hyperelasticity for compressible media is applicable to describe the elastic properties of open cell soft foams. This strain energy function is implemented in the FE-tool ABAQUS and proposed for high compressible soft foams. To determine this constitutive equation, experimental data from a uniaxial compression test are used. As the parameters in the constitutive equation are linked in a non-linear way, non-linear optimization routines are adopted. Moreover due to the in homogeneities of the deformation field of the uniaxial compression test, the quality function of the optimization routine has to be determined by an FE-tool. The appropriateness of the strain energy function is tested by a complex loading test.

By using the optimized parameters the FE-simulation of this test is in good accordance with the experimental data.
A Simple Modelling Method for Deflection of Circular Plates Under Impulsive Loading using Dimensionless Analysis and Singular value Decomposition
Authors: Gharababaei H. , Nariman-zadeh N. , Darvizeh A.
Published: May 2011

A novel approach of numerical modelling using input-output experimental data pairs is presented for deflection-thickness ratio of circular plates subjected to impulse loading. In this way, singular value decomposition (SVD) method is used in conjunction with dimensionless parameters incorporated in such complex process. The closed-form obtained model shows very good agreement with some testing experimental data pairs which have been unforeseen during the training process. Moreover, two modifications are consequently suggested for some similar models already proposed in previous works. The approach of this paper can generally be applied to model very complex real-world processes using appropriate experimental data.
Analysis of Earth Pressure for Retaining Wall and Ultimate Bearing Capacity for Shallow Foundation by Variational Method
Authors: Wu Lai-Yun , Tsai Yi-Feng
Published: May 2011

Applying the principle of virtual work, the slice element method, and the variational method proposed in this paper, one can derive the governing equation and transversality conditions for the rupture surface of a sliding mass of retaining wall and shallow foundation under several external conditions. The governing equation, transversality, and boundary conditions can be solved by the finite difference method (FDM) proposed in this paper, so that the rupture surface and its associated earth pressure acting on the retaining wall or the ultimate bearing capacity acting on the foundation can be determined effectively. By comparison of our results with those of some well known earth pressure and bearing capacity estimating methods, it can be concluded that determining the earth pressure on a retaining wall or the ultimate bearing capacity of a shallow foundation by using the variational method and FDM proposed in this paper, a logical and reasonable result can be obtained without the necessity of guessing the rupture surface.
Explicit Solutions For the Magnetoelastic Fields with a Rigid Line Inclusion
Authors: Lin Chun-Bo , Lin Hsien-Mou
Published: May 2011

A general solution to the magnetoelastic problem with a rigid line inclusion is presented. Based upon the complex variable theory, the proposed analysis dealing with sectionally holomorphic functions can be reduced to find the solution of the Hilbert problem. It is indicated that the magnetoelastic stress fields near the inclusion tip possess a square root singularity just like that of the corresponding crack problem. The stress singularity coefficients which are defined in this study to characterize the near tip fields are similar to the stress intensity factors for crack problem. Numerical results of the stress distribution in the vicinity of inclusion tip are also displayed in graphic form to elucidate the effect of various parameters.
The Pairing of Energy Momentum Tensor and Eigentransformation Rate in a Cylindrically Orthotropic Elastic Circular Tube or Bar
Authors: Wu Chien H.
Published: May 2011

The pairing of a chemical potential and its associated concentration rate in the thermodynamic identity is well known. The existence of an experimentally determinable molar volume as a function of molar concentrations is also widely used in chemical engineering. What is perhaps less known and infrequently used is the fact that a spatially nonuniform molar volume leads to a field of geometrically incompatible eigenstrain, or eigentransformation in finite deformation. This incompatibility forces the material environment to deform, and the result is a strain energy trapped inside the material body. The change of this energy with respect to the eigentransformation is a generalized configurational stress, which, in the limit as the eigentransformation tends to the identity transformation, tends to the classical energy momentum tensor of Eshelby [1], or the so-called configurational stress. It is shown that the generalized configurational stress is an integral part of the chemical potentials that are responsible for atomic diffusion. This cycle of cause and effect is demonstrated in an axially symmetric setting where the material configuration is taken to be cylindrically orthotropic.

Symmetry can be used in many occasions to bare the simple meaning of a complex mathematical expression hiding under the disguise of tensors and index notation. We used it to elucidate the “missing” term in surface chemical potential in 1996 [2] and are now applying it to identify the chemical potential in the bulk. Both Professor Thomas C. T. Ting and I are civil engineering graduates of Tai-Da, the world-renowned National Taiwan University, but did not know each other until we joined UIC. It has been a wonderful friendship of many stimulating anisotropic discussions and numerous delicious potluck dinners. Happy birthday, Tom!
Nonuniformly Moving Loads on an Anisotropic Elastic Half-Space
Authors: Wu Kuang-Chong
Published: May 2011

The transient motion in an anisotropic elastic half-space due to a moving surface line load is considered. The load is applied suddenly on the surface and moves off in a fixed direction with nonuniform speed. Integral expressions for the displacements are derived using the reciprocal theorem. The waves generated by the moving load are discussed. Special attention is paid to the singularities in surface displacements generated as the load moves through the Rayleigh wave speed. Explicit expression is obtained for the particle velocity due to a constant load moving with constant speed.
A Half-Infinite Coupled Crack on an Interface of Piezoelectric Bimaterials Without Oscillation
Authors: Yang Xinhua , Chen Chuanyao , Hu Yuantai , Li Guoqing
Published: May 2011

Based on Stroh's formalism, analytic solutions are derived for a half-infinite coupled crack in piezoelectric bimaterials without oscillation by using analytical function technique. Four intensity factors related to the crack tip fields are obtained. It is found that these intensity factors are independent of the bimaterials constants when no oscillation occurs. Some numerical calculations about the stress tensor and the electric field ahead of the crack tip are conducted finally.
Failure Probability of Short High-Strength Concrete Tied Columns
Authors: Lu Wen-Yao , Lin Ing-Juang
Published: May 2011

This paper aims to investigate the failure probability of short high-strength concrete tied columns using the Monte Carlo technique. The random variables considered in this study are the strength of concrete, the strength of steels, the cross-section dimensions, the location of the steel reinforcement, the variability of strength model and the loads. The results show that the failure probabilities of high-strength concrete columns designed according to the ACI Code are relatively high. The current ACI Code may not be conservative for design of short high-strength concrete tied columns.
Continuum Damage Mechanics for Thermo-Piezoelectric Materials
Authors: Yang X.-H. , Zhang Y. , Hu Y.-T. , Chen C.-Y.
Published: May 2011

With rapidly increasing use of piezoelectric materials in high-temperature environment, it is becoming increasingly important for reliable design of piezoelectric devices to study thermo-electroelastic damage and fracture mechanism. As the first step, a thermo-piezoelectric damage constitutive model is presented from continuum damage mechanics and effective properties of a damaged material are connected with both damages and the initial coefficients according to the theorem of energy equivalence in this paper. Then the finite element equations for a thermo-electroelastic damage problem are given by use of the virtual work principle. Finally, as a numerical illustration example, damage fields around a crack-tip in a three-point bending PZT-5H beam subjected to different thermal loads are calculated and analyzed. It is shown from both the damage curves and contours that influence of environmental temperature on the mechanical damage distribution is great but slight on the electrical damage.
Statistical Analysis of Sonar Performance Prediction in Littoral Environments
Authors: Wang C.-W. , Yuan M.-C. , Yang C.-R. , Chang Y.-Y. , Chen C.-F.
Published: May 2011

This paper presents the Statistical Analysis of Passive Sonar Performance Prediction in Littoral Environments. Passive sonar performance and acoustic prediction mainly refer to the detection range. The inputs for estimating the sonar detection range include the Figure of Merit (FOM), Transmission Loss (TL), and Ambient Noise (NL) of the operation region. These inputs are directly related to the ocean environment; hence, the detection range is, too. A littoral environment is highly variable both in time and space. This paper proposes a methodology for analyzing the statistical properties of the detection range from measurements of ocean water column properties. It is found that the detection range of the southwestern region of Taiwan in the summer is 13.8km with 5.9km as the standard deviation and in the winter is 37.8km with 33.6km as the standard deviation.
Particle Migration Rates in a Couette Apparatus
Authors: Hsiao S.-C. , Christensen D. , Ingber M.S. , Mondy L.A. , Altobelli S.A.
Published: May 2011

Bulk migration of particles towards regions of lower shear occurs in suspensions of neutrally buoyant spheres in Newtonian fluids undergoing creeping flow in the annular region between two rotating, coaxial cylinders (a wide-gap Couette). For a monomodal suspension of spheres in a viscous fluid, dimensional analysis indicates that the rate of migration at a given concentration should scale with the square of the sphere radius. However, a previous experimental study [12] showed that the rate of migration of spherical particles at 50% volume concentration actually scaled with the sphere radius to approximately the 2.9 power. In the current study, a series of experiments is performed to extend the previous study to two new concentrations, namely, 35% and 42.5%. The new study indicates that the power scaling decreases with concentration.
What is a Cochrane review?
Authors: Cipriani A. , Furukawa T. A. , Barbui C.
Published: May 2011

Systematic reviews carried out by Cochrane Collaboration (an international network of researchers belonging to this independent, not-for-profit organization) are recognized worldwide as the highest standard in evidence-based healthcare. The main reason is that Cochrane reviews follow a common and specific methodology to limit bias and random error. In this issue, we highlight the most important methodological features of Cochrane reviews, also reporting details on the editorial process to publish the review in the Cochrane Library.
Status and Cooperation Shape Lesbian Stereotypes
Authors: Brambilla Marco , Carnaghi Andrea , Ravenna Marcella
Published: May 2011

Research on perceptions of homosexuals implicitly assumes that individuals think about lesbians as an undifferentiated group. By contrast, this paper investigated the stereotypes of the overall category as well as of different subgroups of lesbians within the frame of the stereotype content model (SCM). Participants (N = 70) rated the overall category and four subgroups on perceived warmth, competence, status, and interdependence (cooperative vs. competitive). Results showed that the overall category landed in the middle of the competence-warmth space, while the subgroups spread across the SCM dimensions. Moreover, perceived status and cooperation predicted competence and warmth stereotypes, respectively. Perceived competition failed to predict warmth stereotypes. The importance of these findings for lesbian stereotyping and for the SCM is discussed.
Testing space‐scale methodologies for automatic geomorphic feature extraction from lidar in a complex mountainous landscape
Authors: Passalacqua Paola , Tarolli Paolo , Foufoula‐Georgiou Efi
Published: May 2011

The next generation of digital elevation data (≤3 m resolution) calls for the development of new algorithms for the objective extraction of geomorphic features, such as channel networks, channel heads, bank geometry, landslide scars, and service roads. In this work, we test the performance of two newly developed algorithms for the extraction of geomorphic features: the wavelet‐based extraction methodology developed by Lashermes et al. (2007) and the GeoNet nonlinear diffusion and geodesic paths methodology proposed by Passalacqua et al. (2010). The study area is part of the Rio Cordon basin, a headwater alpine catchment located in the Dolomites, a mountainous region in the eastern Italian Alps. The aim of this work is to compare the capability of the two new algorithms in extracting the channel network and capturing channel heads, relevant channel disruptions corresponding to landslides, and representative channel cross sections. The extracted channel networks are also compared to the ones obtained using classical methodologies on the basis of an area threshold and an area‐slope threshold. A high‐resolution digital terrain model of 1 m served as the basis for such analysis. The results suggest that, although the wavelet‐based methodology performs well in the channel network extraction and is able to detect channel heads and channel disruptions, the local nonlinear filter together with the global geodesic optimization used in GeoNet is more robust and computationally efficient while achieving better localization and extraction of features, especially in areas where gentle slopes prevail. We conclude that these new methodologies should be considered as valid alternatives to classical methodologies for channel network extraction from lidar, in addition to offering the potential for calibration‐free channel source identification and also extraction of additional features of interest.
Sound produced by the rapidly inflating Santiaguito lava dome, Guatemala
Authors: Johnson Jeffrey B. , Lees Jonathan M.
Published: May 2011

Vertical inflation of the Caliente lava dome at Santiaguito (Guatemala) occurs coincidentally with the onset of explosive eruptions and produces infrasound that is generally peaked between 0.5 and 2 Hz with amplitude of up to 5 Pa (at ∼1 km from vent). Inflation of up to ∼1 m progresses rapidly (within ∼2 s) and can encompass the entire surface of the ∼200‐m‐diameter dome. We use particle image velocimetry to quantify the time history of dome uplift and demonstrate that deflection of a volcano's solid surface can generate infrasound waves with amplitudes of a few Pa. The volumetric displacement history is used to model linear volumetric acoustic sources, both compact and of finite extent. Synthetic waveforms match recorded infrasound in terms of timing and frequency content. Amplitude fit is very good for a station located 3.3 km from the vent and less good for stations shielded by near vent topography.
Discovery of the FeO orange bands in the terrestrial night airglow spectrum obtained with OSIRIS on the Odin spacecraft
Authors: Evans W. F. J. , Gattinger R. L. , Slanger T. G. , Saran D. V. , Degenstein D. A. , Llewellyn E. J.
Published: May 2011

An unidentified pseudo‐continuum in the 600 nm region is observed in the upper mesosphere with the limb‐scanning OSIRIS imaging spectrograph on‐board the Odin spacecraft. Averages of low latitude spectra at a series of tangent limb altitudes from 75 to 105 km are assembled and matched with synthetic spectra of the known night airglow emission band systems to isolate the underlying airglow continuum. The upper limit of the NO + O → NO2* air afterglow continuum component in the observed 600 nm pseudo‐continuum is estimated to be 5% at low latitudes. The spectral profile of the unidentified 600 nm residual airglow continuum is very similar to published laboratory measurements of the ‘orange bands’ of FeO. The volume emission rate altitude profile of this 600 nm airglow continuum, derived from averaged limb radiance profiles, is very similar in shape and in altitude to the concurrently observed Na vertical profile suggesting related source mechanisms.
Global ionospheric response observed by COSMIC satellites during the January 2009 stratospheric sudden warming event
Authors: Yue Xinan , Schreiner William S. , Lei Jiuhou , Rocken Christian , Hunt Douglas C. , Kuo Ying‐Hwa , Wan Weixing
Published: May 2011

This paper investigates the global ionospheric response during the January 2009 stratospheric sudden warming (SSW) event by using electron density profiles derived from GPS radio occultation measurements of the COSMIC satellites. The peak density (NmF2), peak height (hmF2), and ionospheric total electron content (ITEC) increase in the morning hours and decrease in the afternoon globally for 75% of the cases, in which electron density profiles during SSW and non‐SSW days are available around the same location and local time bins. NmF2, hmF2, and ITEC during SSW days, on average, increase 19%, 12 km, and 17% in the morning and decrease 23%, 19 km, and 25% in the afternoon, respectively, in comparison with those during non‐SSW days from global COSMIC observations. These results agree well with previous results from total electron content observations in low‐latitude and equatorial regions. Interestingly, the unique COSMIC observations also revealed that during this SSW event the ionosphere responds globally, not only in the equatorial regions but also at the high and middle latitudes. The high‐latitude ionosphere shows increased NmF2 and ITEC and decreased hmF2 in either the morning or afternoon sector. Thus, these results indicate that the ionospheric response in low‐middle latitude and equatorial regions during SSW can be explained by either the modulated vertical drift resulting from the interaction between the planetary waves and tides through E region dynamo or the possible direct propagation of tides from the lower atmosphere, whereas the ionospheric variations at the middle and high latitude during the SSW might be attributed to the neutral background changes due to the direct propagation of tides from the lower atmosphere to the ionospheric F2 region. The competitive effects of different physical processes, such as the electric field, neutral wind, and composition, might cause the complex features of ionospheric variations during this SSW event.
Three‐dimensional numerical simulation of equatorial F region plasma irregularities with bottomside shear flow
Authors: Aveiro H. C. , Hysell D. L.
Published: May 2011

A three‐dimensional numerical simulation of plasma density irregularities in the postsunset equatorial F region ionosphere leading to equatorial spread F (ESF) is described. The simulation advances the plasma number density and electrostatic potential forward in time by enforcing the constraints of quasi‐neutrality and momentum conservation. The magnetic field lines are not modeled as equipotentials. Simulations are performed for cases with no background winds, with no background electric field or gravity, and with winds, a background electric field, and gravity all working in concert. The first run produced generalized Rayleigh Taylor (GRT) instability, and the second produced collisional shear instability (CSI). The combined run produced an instability which developed into an intense ESF event more quickly and with more realistic characteristics than the other two. Simulation results are compared with incoherent and coherent scatter radar data from the magnetic equator. A number of signature ESF characteristics are shown to be reproduced by the simulation.
Properties and distribution of paired candidate stony meteorites at Meridiani Planum, Mars
Authors: Schröder Christian , Herkenhoff Kenneth E. , Farrand William H. , Chappelow John E. , Wang Wei , Nittler Larry R. , Ashley James W. , Fleischer Iris , Gellert Ralf , Golombek Matthew P. , Johnson Jeffrey R. , Klingelhöfer Göstar , Li Ron , Morris Richard V. , Squyres Steven W.
Published: May 2011

The Mars Exploration Rover Opportunity investigated four rocks, informally dubbed Barberton, Santa Catarina, Santorini, and Kasos, that are possible stony meteorites. Their chemical and mineralogical composition is similar to the howardite, eucrite, and diogenite group but with additional metal, similar to mesosiderite silicate clasts. Because of their virtually identical composition and because they appear to represent a relatively rare group of meteorites, they are probably paired. The four rocks were investigated serendipitously several kilometers apart, suggesting that Opportunity is driving across a larger population of similar rock fragments, maybe a meteorite strewn field. Small amounts of ferric Fe are a result of weathering. We did not observe evidence for fusion crusts. Four iron meteorites were found across the same area. Although mesosiderites are stony irons, a genetic link to these irons is unlikely. The stony meteorites probably fell later than the irons. The current atmosphere is sufficiently dense to land such meteorites at shallow entry angles, and it would disperse fragments over several kilometers upon atmospheric breakup. Alternatively, dispersion by spallation from an impacting meteoroid may have occurred. Santa Catarina and a large accumulation of similar rocks were found at the rim of Victoria crater. It is possible that they are associated with the impactor that created Victoria crater, but our limited knowledge about their distribution cannot exclude mere coincidence.
Observational evidence of alpha‐particle capture at Mars
Authors: Stenberg G. , Nilsson H. , Futaana Y. , Barabash S. , Fedorov A. , Brain D.
Published: May 2011

Solar wind alpha‐particles are suggested to be the most important source of helium in the Martian atmosphere. Recent hybrid simulations show that as much as 30% of the alpha‐particles passing through the planetary cross section can be lost from the solar wind due to charge‐exchange processes associated with the Mars/solar wind interaction. We use ion data from the ASPERA‐3 instrument on Mars Express to investigate the penetration of alpha‐particles into the Martian atmosphere. We conclude that solar wind alpha‐particles contribute to the helium observed in the atmosphere. In accordance with simulations we see an asymmetry in the capture efficiency related to the solar wind convection electric field.
Did the northeastern Gulf of Mexico become greener after the Deepwater Horizon oil spill?
Authors: Hu Chuanmin , Weisberg Robert H. , Liu Yonggang , Zheng Lianyuan , Daly Kendra L. , English David C. , Zhao Jun , Vargo Gabriel A.
Published: May 2011

Assessment of direct and indirect impacts of oil and dispersants on the marine ecosystem in the northeastern Gulf of Mexico (NEGOM) from the Deepwater Horizon oil spill (April – July 2010) requires sustained observations over multiple years. Here, using satellite measurements, numerical circulation models, and other environmental data, we present some initial results on observed biological changes at the base of the food web. MODIS fluorescence line height (FLH, a proxy for phytoplankton biomass) shows two interesting anomalies. The first is statistically significant (>1 mg m−3 of chlorophyll‐a anomaly), in an area exceeding 11,000 km2 in the NEGOM during August 2010, about 3 weeks after the oil well was capped. FLH values in this area are higher (i.e., water is greener) than in any August since 2002, and higher than ever since 2002 in an area of ∼3,000 km2. Analyses of ocean circulation and other environmental data suggest that this anomaly may be attributed to the oil spill. The second is a spatially coherent FLH anomaly during December 2010 and January 2011, extending from Mobile Bay to the Florida Keys (mainly between 30 and 100‐m isobaths). This anomaly appears to have resulted from unusually strong upwelling and mixing events during late fall. Available data are insufficient to support or reject a hypothesis that the subsurface oil may have contributed to the enhanced biomass during December 2010 and January 2011.
The geomagnetic secular‐variation timescale in observations and numerical dynamo models
Authors: Lhuillier Florian , Fournier Alexandre , Hulot Gauthier , Aubert Julien
Published: May 2011

The knowledge of the spatial power spectra of the main geomagnetic field and of its secular variation makes it possible to define typical timescales τn for each spherical harmonic degree n. Investigating both observations and numerical dynamos, we show that a one‐parameter law of the form τn = τSV/n is satisfied for the non‐dipole field, given the statistical way the observed τn are expected to fluctuate. Consequently, we determine the corresponding secular‐variation timescale τSV from either instantaneous or time‐averaged spectra, leading to a value of 415 ±4555 yr for recent satellite field models. In the broader context of geomagnetic data assimilation, τSV could provide a sensible and convenient means to rescale the time axis of dynamo simulations.
A fault‐zone conductor beneath a compressional inversion zone, northeastern Honshu, Japan
Authors: Ichihara Hiroshi , Uyeshima Makoto , Sakanaka Shinya , Ogawa Tsutomu , Mishina Masaaki , Ogawa Yasuo , Nishitani Tadashi , Yamaya Yusuke , Watanabe Atsushi , Morita Yuichi , Yoshimura Ryokei , Usui Yoshiya
Published: May 2011

A resistivity section based on magnetotelluric data was obtained for the Shonai Plain fault in northeastern Honshu, Japan. Faults in this area were created as normal faults during the opening of the Japan Sea in the Miocene but are now reactivated as high‐angle reverse faults under compressional tectonics. Geological interpretations of the resistivity section support the proposed fault reactivation. An estimated east‐dipping conductor along a deep part of the Shonai Plain fault system probably represents a fluid‐rich zone around the fault zone. The high 3He/4He ratio near the fault indicates transportation of mantle fluid through this fluid‐rich zone. These evidences may reflect the development of pronounced fracture permeability after fault rupturing, as in the fault‐valve hypothesis.
In vivo Magnetization Transfer MRI Shows Dysmyelination in an Ischemic Mouse Model of Periventricular Leukomalacia
Authors: Fatemi Ali , Wilson Mary Ann , Phillips Andre W , McMahon Michael T , Zhang Jiangyang , Smith Seth A , Arauz Edwin J , Falahati Sina , Gummadavelli Abhijeet , Bodagala Hima , Mori Susumu , Johnston Michael V
Published: May 2011

Periventricular leukomalacia, PVL, is the leading cause of cerebral palsy in prematurely born infants, and therefore more effective interventions are required. The objective of this study was to develop an ischemic injury model of PVL in mice and to determine the feasibility of in vivo magnetization transfer (MT) magnetic resonance imaging (MRI) as a potential monitoring tool for the evaluation of disease severity and experimental therapeutics. Neonatal CD-1 mice underwent unilateral carotid artery ligation on postnatal day 5 (P5); at P60, in vivo T2-weighted (T2w) and MT-MRI were performed and correlated with postmortem histopathology. In vivo T2w MRI showed thinning of the right corpus callosum, but no significant changes in hippocampal and hemispheric volumes. Magnetization transfer MRI revealed significant white matter abnormalities in the bilateral corpus callosum and internal capsule. These quantitative MT-MRI changes correlated highly with postmortem findings of reduced myelin basic protein in bilateral white matter tracts. Ventriculomegaly and persistent astrogliosis were observed on the ligated side, along with evidence of axonopathy and fewer oligodendrocytes in the corpus callosum. We present an ischemia-induced mouse model of PVL, which has pathologic abnormalities resembling autopsy reports in infants with PVL. We further validate in vivo MRI techniques as quantitative monitoring tools that highly correlate with postmortem histopathology.
Body Fat and Racial Genetic Admixture Are Associated With Aerobic Fitness Levels in a Multiethnic Pediatric Population
Authors: Willig Amanda L. , Hunter Gary R. , Casazza Krista , Heimburger Douglas C. , Beasley T. Mark , Fernandez Jose R.
Published: May 2011

Aerobic fitness and adiposity are each independently associated with health outcomes among children, although the relationship between these two variables is unclear. Our objectives were to evaluate (i) the association of adiposity with aerobic fitness using objectively measured levels of percent body fat, compared to BMI as a percentile proxy for adiposity while controlling for genetic admixture, and (ii) the congruence of BMI categories with high and low body fat categories of objectively measured percent body fat. Participants were 232 African‐American (AA), European‐American (EA), and Hispanic‐American (HA) children aged 7–12 years (Tanner stage <3). Aerobic fitness was measured via a submaximal indirect calorimetry treadmill test (VO2–170), and physical activity levels with accelerometry. Genetic admixture estimates were obtained using 140 genetic ancestry informative markers to estimate European, African, and Amerindian admixture. Fat mass was determined using dual‐energy x‐ray absorptiometry (DXA). Children were classified into a low body fat group (<25% in males, <30% in females) or a high body fat group based on their percent body fat; children were also categorized according to BMI percentile. Children in the low body fat group had significantly higher aerobic fitness (P < 0.05) regardless of BMI percentile classification. Higher African genetic admixture was associated with lower aerobic fitness (P < 0.05), while physical activity was positively associated with fitness (P < 0.01). In conclusion, aerobic fitness levels differ by percent body fat and genetic admixture irrespective of BMI classification, and such differences should be taken into account when evaluating outcomes of health interventions.
Cardiovascular Regulation Profile Predicts Developmental Trajectory of BMI and Pediatric Obesity
Authors: Graziano Paulo A. , Calkins Susan D. , Keane Susan P. , O'Brien Marion
Published: May 2011

The present study examined the role of cardiovascular regulation in predicting pediatric obesity. Participants for this study included 268 children (141 girls) obtained from a larger ongoing longitudinal study. To assess cardiac vagal regulation, resting measures of respiratory sinus arrhythmia (RSA) and RSA change (vagal withdrawal) to three cognitively challenging tasks were derived when children were 5.5 years of age. Heart period (HP) and HP change (heart rate (HR) acceleration) were also examined. Height and weight measures were collected when children were 5.5, 7.5, and 10.5 years of age. Results indicated that physiological regulation at age 5.5 was predictive of both normal variations in BMI development and pediatric obesity at age 10.5. Specifically, children with a cardiovascular regulation profile characterized by lower levels of RSA suppression and HP change experienced significantly greater levels of BMI growth and were more likely to be classified as overweight/at‐risk for overweight at age 10.5 compared to children with a cardiovascular regulation profile characterized by high levels of RSA suppression and HP change. However, a significant interaction with racial status was found suggesting that the association between cardiovascular regulation profile and BMI growth and pediatric obesity was only significant for African‐American children. An autonomic cardiovascular regulation profile consisting of low parasympathetic activity represents a significant individual risk factor for the development of pediatric obesity, but only for African‐American children. Mechanisms by which early physiological regulation difficulties may contribute to the development of pediatric obesity are discussed.
Controlled optical and magnetic properties of ZnO nanorods by Ar ion irradiation
Authors: Panigrahy Bharati , Aslam M. , Bahadur D.
Published: May 2011

Herein we report a controlled defect-related emission and magnetization properties of zinc oxide nanorods using low energy (2–5 keV) Ar ion irradiation. The ratio of the defect related emission to the excitonic emission decreases by an order magnitude due to the ion bombardment. The hysteresis loops of pristine and irradiated nanorods show ferromagnetic behavior at room temperature. A sharp decrease in the value of magnetization is due to an enhancement of irradiation time and energy. Combining with x-ray photoelectron spectroscopy results, a direct link between the magnetization and defect-emission of ZnO nanorods is established.
Generalized Courant–Snyder theory and Kapchinskij–Vladimirskij distribution for high-intensity beams in a coupled transverse focusing lattice
Authors: Qin Hong , Davidson Ronald C.
Published: May 2011

The Courant–Snyder (CS) theory and the Kapchinskij–Vladimirskij (KV) distribution for high-intensity beams in an uncoupled focusing lattice are generalized to the case of coupled transverse dynamics. The envelope function is generalized to an envelope matrix, and the envelope equation becomes a matrix envelope equation with matrix operations that are noncommutative. In an uncoupled lattice, the KV distribution function, first analyzed in 1959, is the only known exact solution of the nonlinear Vlasov-Maxwell equations for high-intensity beams including self-fields in a self-consistent manner. The KV solution is generalized to high-intensity beams in a coupled transverse lattice using the generalized CS invariant. This solution projects to a rotating, pulsating elliptical beam in transverse configuration space. The fully self-consistent solution reduces the nonlinear Vlasov-Maxwell equations to a nonlinear matrix ordinary differential equation for the envelope matrix, which determines the geometry of the pulsating and rotating beam ellipse. These results provide us with a new theoretical tool to investigate the dynamics of high-intensity beams in a coupled transverse lattice. A strongly coupled lattice, a so-called N-rolling lattice, is studied as an example. It is found that strong coupling does not deteriorate the beam quality. Instead, the coupling induces beam rotation and reduces beam pulsation.
Comment on “Acoustic solitons in inhomogeneous pair-ion plasmas” [Phys. Plasmas 17, 122302 (2010)]
Authors: Verheest Frank
Published: May 2011

Using a standard reductive perturbation technique, Shah et al. [Phys. Plasmas 17, 122302 (2010)] derived a Korteweg-de Vries like equation, with an additional term due to the assumed equilibrium density and flow inhomogeneities in a pair-ion plasma. Unfortunately, a basic flaw at the beginning of the derivation invalidates the whole analysis: their model only supports homogeneous densities and flows in the undisturbed conditions.
Control of stellarator properties illustrated by a Wendelstein7-X equilibrium
Authors: Boozer Allen H. , Ku L. P.
Published: May 2011

Plasma properties in stellarators can be controlled by changing the externally produced magnetic field normal to the unperturbed-plasma surface. However, a change in the amplitude of only a few spatial distributions of the externally produced normal field has a linear effect on the plasma properties. The number and the form of the external field distributions to which the plasma has a linear sensitivity is important for determining (a) the flexibility that can be obtained in given device, (b) the required features of coils, so simpler coils sets can be designed, and (c) the degree to which plasma properties can be individually optimized. Features of the linear response are illustrated using the bootstrap current and the effective ripple in the magnetic field strength for a particular equilibrium of the Wendelstein7-X stellarator. For the effective ripple, the available control is determined by just a few distributions of the external magnetic field even though the ripple is a function of position. For the total bootstrap current, the available control is given by a single distribution of the external magnetic field.
Electromagnetic properties of polycrystalline diamond from 35 K to room temperature and microwave to terahertz frequencies
Authors: Floch Jean-Michel Le , Bara Romain , Hartnett John G. , Tobar Michael E. , Mouneyrac David , Passerieux Damien , Cros Dominique , Krupka Jerzy , Goy Philippe , Caroopen Sylvain
Published: May 2011

Dielectric resonators are key components for many microwave and millimeter wave applications, including high-Q filters and frequency-determining elements for precision frequency synthesis. These often depend on the quality of the dielectric material. The commonly used material for building the best cryogenic microwave oscillators is sapphire. However, sapphire is becoming a limiting factor for higher frequency designs. It is, then, important to find new candidates that can fulfill the requirements for millimeter wave low noise oscillators at room and cryogenic temperatures. These clocks are used as a reference in many fields, such as modern telecommunication systems, radio astronomy (very-long-baseline interferometry), and precision measurements at the quantum limit. High resolution measurements were taken of the temperature-dependence of the electromagnetic properties of a polycrystalline diamond disk at temperatures between 35 and 330 K at microwave to submillimeter wave frequencies. The cryogenic measurements were made using a TE01δ dielectric mode resonator placed inside a vacuum chamber connected to a single-stage pulse-tube cryocooler. The high frequency characterization was performed at room temperature using a combination of a quasi-optical two-lens transmission setup, a Fabry–Perot cavity, and a whispering gallery mode resonator excited with waveguides. Our CVD diamond sample exhibits a decreasing loss tangent with increasing frequencies. We compare the results with well known crystals. This comparison makes it clear that polycrystalline diamond could be an important material for generating stable frequencies at millimeter waves.
Impact of contact resistance on the transconductance and linearity of graphene transistors
Authors: Parrish Kristen N. , Akinwande Deji
Published: May 2011

Interest in graphene device physics and technology has been growing rapidly, especially for very high frequency transistor applications. However, the predicted intrinsic performance has not been fully realized due to impurity and parasitic issues introduced in device fabrication. Through a self-consistent model, we show that the normalized contact resistance has an exponentially detrimental impact on the peak transconductance, which is a defining transistor parameter. In addition, we reveal that very high current-gate voltage linearity or input invariant transconductance can be achieved in the limit of negligible contact resistances, a desirable feature for linear electronic systems.
Determination of Clausius–Mossotti factors and surface capacitances for colloidal particles
Authors: Honegger T. , Berton K. , Picard E. , Peyrade D.
Published: May 2011

We propose a method to experimentally determine the Clausius–Mossotti factors and surface capacitances of colloidal particles. This two-step method is based on the following: (i) a precise positioning of particles on activated electrodes according to the applied frequency of an electric field and (ii) particles velocities measurements from a pure dielectrophoretic regime to build the Clausius–Mossotti factor. It confirms previous literature methods and measures the surface capacitance values for a wide range of particles such as polystyrene, silica, and gold whose diameters are at least 200 nm.