Modelling and assessment of the electric field strength caused by mobile phone to the human head.

PubMed

Buckus, Raimondas; Strukcinskiene, Birute; Raistenskis, Juozas; Stukas, Rimantas

2016-06-01

Electromagnetic field exposure is the one of the most important physical agents that actively affects live organisms and environment. Active use of mobile phones influences the increase of electromagnetic field radiation. The aim of the study was to measure and assess the electric field strength caused by mobile phones to the human head. In this paper the software "COMSOL Multiphysics" was used to establish the electric field strength created by mobile phones around the head. The second generation (2G) Global System for Mobile (GSM) phones that operate in the frequency band of 900 MHz and reach the power of 2 W have a stronger electric field than (2G) GSM mobile phones that operate in the higher frequency band of 1,800 MHz and reach the power up to 1 W during conversation. The third generation of (3G) UMTS smart phones that effectively use high (2,100 MHz) radio frequency band emit the smallest electric field strength values during conversation. The highest electric field strength created by mobile phones is around the ear, i.e. the mobile phone location. The strength of mobile phone electric field on the phantom head decreases exponentially while moving sidewards from the center of the effect zone (the ear), and constitutes 1-12% of the artificial head's surface. The highest electric field strength values of mobile phones are associated with their higher power, bigger specific energy absorption rate (SAR) and lower frequency of mobile phone. The stronger electric field emitted by the more powerful mobile phones takes a higher percentage of the head surface. The highest electric field strength created by mobile phones is distributed over the user's ear.

Non-neutral plasma diode in the presence of a transverse magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pramanik, Sourav; Chakrabarti, Nikhil; Kuznetsov, V. I.

An analytical study of the plasma states in non-neutral plasma diodes in the presence of an external transverse magnetic field is presented for an arbitrary neutralization parameter γ. Considerations are restricted to the regime where no electrons are turned around by the magnetic field. The emitter electric field strength E{sub 0} is used as a characteristic function to investigate the existence of solutions depending on the diode length, the applied voltage, the neutralization parameter, and the magnetic field strength. The potential distribution has a wave form for small magnitudes of the external magnetic field, as well as for the casemore » when magnetic field is absent. A new family of solutions appears along with the Bursian ones. On the other hand, as the Larmor radius becomes comparable with the beam Debye length, oscillations in the potential disappear, and only the Bursian branches remain. Unlike the vacuum diode, there are steady state solutions for the negative values of the emitter field strength. As the neutralization parameter (γ) increases, the emitter field strength relating to the SCL (space charge limit) bifurcation point diminishes, and at γ > 1, the value of the emitter's electric field strength at the space charge limit (E{sub 0,SCL}) turns out to be negative.« less

Pion production via proton synchrotron radiation in strong magnetic fields in relativistic field theory: Scaling relations and angular distributions

DOE PAGES

Maruyama, Tomoyuki; Cheoun, Myung-Ki; Kajino, Toshitaka; ...

2016-03-26

We study pion production by proton synchrotron radiation in the presence of a strong magnetic field when the Landau numbers of the initial and final protons are n(i, f) similar to 10(4)-10(5). We find in our relativistic field theory calculations that the pion decay width depends only on the field strength parameter which previously was only conjectured based upon semi-classical arguments. Moreover, we also find new results that the decay width satisfies a robust scaling relation, and that the polar angular distribution of emitted pion momenta is very narrow and can be easily obtained. This scaling implies that one canmore » infer the decay width in more realistic magnetic fields of 10(15) G, where n(i, f) similar to 10(12)-10(13), from the results for n(i, f) similar to 10(4)-10(5). The resultant pion intensity and angular distributions for realistic magnetic field strengths are presented and their physical implications discussed. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).« less

Monte Carlo study of the impact of a magnetic field on the dose distribution in MRI-guided HDR brachytherapy using Ir-192

NASA Astrophysics Data System (ADS)

Beld, E.; Seevinck, P. R.; Lagendijk, J. J. W.; Viergever, M. A.; Moerland, M. A.

2016-09-01

In the process of developing a robotic MRI-guided high-dose-rate (HDR) prostate brachytherapy treatment, the influence of the MRI scanner’s magnetic field on the dose distribution needs to be investigated. A magnetic field causes a deflection of electrons in the plane perpendicular to the magnetic field, and it leads to less lateral scattering along the direction parallel with the magnetic field. Monte Carlo simulations were carried out to determine the influence of the magnetic field on the electron behavior and on the total dose distribution around an Ir-192 source. Furthermore, the influence of air pockets being present near the source was studied. The Monte Carlo package Geant4 was utilized for the simulations. The simulated geometries consisted of a simplified point source inside a water phantom. Magnetic field strengths of 0 T, 1.5 T, 3 T, and 7 T were considered. The simulation results demonstrated that the dose distribution was nearly unaffected by the magnetic field for all investigated magnetic field strengths. Evidence was found that, from a dose perspective, the HDR prostate brachytherapy treatment using Ir-192 can be performed safely inside the MRI scanner. No need was found to account for the magnetic field during treatment planning. Nevertheless, the presence of air pockets in close vicinity to the source, particularly along the direction parallel with the magnetic field, appeared to be an important point for consideration.

Monte Carlo study of the impact of a magnetic field on the dose distribution in MRI-guided HDR brachytherapy using Ir-192.

PubMed

Beld, E; Seevinck, P R; Lagendijk, J J W; Viergever, M A; Moerland, M A

2016-09-21

In the process of developing a robotic MRI-guided high-dose-rate (HDR) prostate brachytherapy treatment, the influence of the MRI scanner's magnetic field on the dose distribution needs to be investigated. A magnetic field causes a deflection of electrons in the plane perpendicular to the magnetic field, and it leads to less lateral scattering along the direction parallel with the magnetic field. Monte Carlo simulations were carried out to determine the influence of the magnetic field on the electron behavior and on the total dose distribution around an Ir-192 source. Furthermore, the influence of air pockets being present near the source was studied. The Monte Carlo package Geant4 was utilized for the simulations. The simulated geometries consisted of a simplified point source inside a water phantom. Magnetic field strengths of 0 T, 1.5 T, 3 T, and 7 T were considered. The simulation results demonstrated that the dose distribution was nearly unaffected by the magnetic field for all investigated magnetic field strengths. Evidence was found that, from a dose perspective, the HDR prostate brachytherapy treatment using Ir-192 can be performed safely inside the MRI scanner. No need was found to account for the magnetic field during treatment planning. Nevertheless, the presence of air pockets in close vicinity to the source, particularly along the direction parallel with the magnetic field, appeared to be an important point for consideration.

The Relationship between Ultraviolet Line Emission and Magnetic Field Strength in Magnetic Cataclysmic Variables

NASA Astrophysics Data System (ADS)

Howell, Steve B.; Cash, Jennifer; Mason, Keith O.; Herzog, Adrienne E.

1999-02-01

We present the first UV spectral observations of six magnetic cataclysmic variables discovered by the ROSAT Wide Field Camera (WFC). Using the^ International Ultraviolet Explorer (IUE), 1200-3400 Å spectra were obtained of the AM Herculis stars RE 0531-46, RE 1149+28, RE 1844-74, QS Tel (RE 1938-46), and HU Aqr (RE 2107-05) and the DQ Herculis star PQ Gem (RE 0751+14). The high-state UV spectra are dominated by strong emission lines. Continuum flux distributions for these stars (from 100 to 5500 Å) reveal that over this entire range, none of the spectral energy distributions can be fitted by a single-valued blackbody. Our new UV observations and additional archival IUE spectra were used to discover a correlation between the strength of the high-state UV emission lines and the strength of the white dwarf magnetic field. Model spectral results are used to confirm the production of the UV emission lines by photoionization from X-ray and EUV photons.

Field evaporation of ZnO: A first-principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, Yu, E-mail: yuxia@dal.ca; Karahka, Markus; Kreuzer, H. J.

2015-07-14

With recent advances in atom probe tomography of insulators and semiconductors, there is a need to understand high electrostatic field effects in these materials as well as the details of field evaporation. We use density functional theory to study field effects in ZnO clusters calculating the potential energy curves, the local field distribution, the polarizability, and the dielectric constant as a function of field strength. We confirm that, as in MgO, the HOMO-LUMO gap of a ZnO cluster closes at the evaporation field strength signaling field-induced metallization of the insulator. Following the structural changes in the cluster at the evaporationmore » field strength, we can identify the field evaporated species, in particular, we show that the most abundant ion, Zn{sup 2+}, is NOT post-ionized but leaves the surface as 2+ largely confirming the experimental observations. Our results also help to explain problems related to stoichiometry in the mass spectra measured in atom probe tomography.« less

Comparison of electric field strength and spatial distribution of electroconvulsive therapy and magnetic seizure therapy in a realistic human head model

PubMed Central

Lee, Won Hee; Lisanby, Sarah H.; Laine, Andrew F.; Peterchev, Angel V.

2017-01-01

Background This study examines the strength and spatial distribution of the electric field induced in the brain by electroconvulsive therapy (ECT) and magnetic seizure therapy (MST). Methods The electric field induced by standard (bilateral, right unilateral, and bifrontal) and experimental (focal electrically administered seizure therapy and frontomedial) ECT electrode configurations as well as a circular MST coil configuration was simulated in an anatomically realistic finite element model of the human head. Maps of the electric field strength relative to an estimated neural activation threshold were used to evaluate the stimulation strength and focality in specific brain regions of interest for these ECT and MST paradigms and various stimulus current amplitudes. Results The standard ECT configurations and current amplitude of 800–900 mA produced the strongest overall stimulation with median of 1.8–2.9 times neural activation threshold and more than 94% of the brain volume stimulated at suprathreshold level. All standard ECT electrode placements exposed the hippocampi to suprathreshold electric field, although there were differences across modalities with bilateral and right unilateral producing respectively the strongest and weakest hippocampal stimulation. MST stimulation is up to 9 times weaker compared to conventional ECT, resulting in direct activation of only 21% of the brain. Reducing the stimulus current amplitude can make ECT as focal as MST. Conclusions The relative differences in electric field strength may be a contributing factor for the cognitive sparing observed with right unilateral compared to bilateral ECT, and MST compared to right unilateral ECT. These simulations could help understand the mechanisms of seizure therapies and develop interventions with superior risk/benefit ratio. PMID:27318858

Utilization of the Boltzmann tail of TED for the calculation of the ``absolute'' work function and local field strength in FEM

NASA Astrophysics Data System (ADS)

Wysocki, J. K.

1984-02-01

The idea of Young and Clark of independent evaluation of the work function φ and electric field strength F in FEM [R.D. Young and H.E. Clark, Phys. Rev. Letters 17 (1966) 351] has been extended to the energy region above the Fermi level. The estimation of slowly varying elliptic functions, necessary to compute φ and F, using only experimental data is presented. Calculations for the W(111) plane using the field electron energy distribution and the integral field-emission current dependence on retarding voltage have been performed.

Vapor cell geometry effect on Rydberg atom-based microwave electric field measurement

NASA Astrophysics Data System (ADS)

Zhang, Linjie; Liu, Jiasheng; Jia, Yue; Zhang, Hao; Song, Zhenfei; Jia, Suotang

2018-03-01

The geometry effect of a vapor cell on the metrology of a microwave electric field is investigated. Based on the splitting of the electromagnetically induced transparency spectra of cesium Rydberg atoms in a vapor cell, high-resolution spatial distribution of the microwave electric field strength is achieved for both a cubic cell and a cylinder cell. The spatial distribution of the microwave field strength in two dimensions is measured with sub-wavelength resolution. The experimental results show that the shape of a vapor cell has a significant influence on the abnormal spatial distribution because of the Fabry–Pérot effect inside a vapor cell. A theoretical simulation is obtained for different vapor cell wall thicknesses and shows that a restricted wall thickness results in a measurement fluctuation smaller than 3% at the center of the vapor cell. Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA03044200 and 2016YFF0200104), the National Natural Science Foundation of China (Grant Nos. 91536110, 61505099, and 61378013), and the Fund for Shanxi “331 Project” Key Subjects Construction, China.

Detailing magnetic field strength dependence and segmental artifact distribution of myocardial effective transverse relaxation rate at 1.5, 3.0, and 7.0 T.

PubMed

Meloni, Antonella; Hezel, Fabian; Positano, Vincenzo; Keilberg, Petra; Pepe, Alessia; Lombardi, Massimo; Niendorf, Thoralf

2014-06-01

Realizing the challenges and opportunities of effective transverse relaxation rate (R2 *) mapping at high and ultrahigh fields, this work examines magnetic field strength (B0 ) dependence and segmental artifact distribution of myocardial R2 * at 1.5, 3.0, and 7.0 T. Healthy subjects were considered. Three short-axis views of the left ventricle were examined. R2 * was calculated for 16 standard myocardial segments. Global and mid-septum R2 * were determined. For each segment, an artifactual factor was estimated as the deviation of segmental from global R2 * value. The global artifactual factor was significantly enlarged at 7.0 T versus 1.5 T (P = 0.010) but not versus 3.0 T. At 7.0 T, the most severe susceptibility artifacts were detected in the inferior lateral wall. The mid-septum showed minor artifactual factors at 7.0 T, similar to those at 1.5 and 3.0 T. Mean R2 * increased linearly with the field strength, with larger changes for global heart R2 * values. At 7.0 T, segmental heart R2 * analysis is challenging due to macroscopic susceptibility artifacts induced by the heart-lung interface and the posterior vein. Myocardial R2 * depends linearly on the magnetic field strength. The increased R2 * sensitivity at 7.0 T might offer means for susceptibility-weighted and oxygenation level-dependent MR imaging of the myocardium. Copyright © 2013 Wiley Periodicals, Inc.

The structure and statistics of interstellar turbulence

NASA Astrophysics Data System (ADS)

Kritsuk, A. G.; Ustyugov, S. D.; Norman, M. L.

2017-06-01

We explore the structure and statistics of multiphase, magnetized ISM turbulence in the local Milky Way by means of driven periodic box numerical MHD simulations. Using the higher order-accurate piecewise-parabolic method on a local stencil (PPML), we carry out a small parameter survey varying the mean magnetic field strength and density while fixing the rms velocity to observed values. We quantify numerous characteristics of the transient and steady-state turbulence, including its thermodynamics and phase structure, kinetic and magnetic energy power spectra, structure functions, and distribution functions of density, column density, pressure, and magnetic field strength. The simulations reproduce many observables of the local ISM, including molecular clouds, such as the ratio of turbulent to mean magnetic field at 100 pc scale, the mass and volume fractions of thermally stable Hi, the lognormal distribution of column densities, the mass-weighted distribution of thermal pressure, and the linewidth-size relationship for molecular clouds. Our models predict the shape of magnetic field probability density functions (PDFs), which are strongly non-Gaussian, and the relative alignment of magnetic field and density structures. Finally, our models show how the observed low rates of star formation per free-fall time are controlled by the multiphase thermodynamics and large-scale turbulence.

Radial distributions of magnetic field strength in the solar corona as derived from data on fast halo CMEs

NASA Astrophysics Data System (ADS)

Fainshtein, Victor; Egorov, Yaroslav

2018-03-01

In recent years, information about the distance between the body of rapid coronal mass ejection (CME) and the associated shock wave has been used to measure the magnetic field in the solar corona. In all cases, this technique allows us to find coronal magnetic field radial profiles B(R) applied to the directions almost perpendicular to the line of sight. We have determined radial distributions of magnetic field strength along the directions close to the Sun-Earth axis. For this purpose, using the "ice-cream cone" model and SOHO/LASCO data, we found 3D characteristics for fast halo coronal mass ejections (HCMEs) and for HCME-related shocks. With these data, we managed to obtain the B(R) distributions as far as ≈43 solar radii from the Sun's center, which is approximately twice as far as those in other studies based on LASCO data. We have concluded that to improve the accuracy of this method for finding the coronal magnetic field we should develop a technique for detecting CME sites moving in the slow and fast solar wind. We propose a technique for selecting CMEs whose central (paraxial) part actually moves in the slow wind.

Measuring and Modeling Root Distribution and Root Reinforcement in Forested Slopes for Slope Stability Calculations

NASA Astrophysics Data System (ADS)

Cohen, D.; Giadrossich, F.; Schwarz, M.; Vergani, C.

2016-12-01

Roots provide mechanical anchorage and reinforcement of soils on slopes. Roots also modify soil hydrological properties (soil moisture content, pore-water pressure, preferential flow paths) via subsurface flow path associated with root architecture, root density, and root-size distribution. Interactions of root-soil mechanical and hydrological processes are an important control of shallow landslide initiation during rainfall events and slope stability. Knowledge of root-distribution and root strength are key components to estimate slope stability in vegetated slopes and for the management of protection forest in steep mountainous area. We present data that show the importance of measuring root strength directly in the field and present methods for these measurements. These data indicate that the tensile force mobilized in roots depends on root elongation (a function of soil displacement), root size, and on whether roots break in tension of slip out of the soil. Measurements indicate that large lateral roots that cross tension cracks at the scarp are important for slope stability calculations owing to their large tensional resistance. These roots are often overlooked and when included, their strength is overestimated because extrapolated from measurements on small roots. We present planned field experiments that will measure directly the force held by roots of different sizes during the triggering of a shallow landslide by rainfall. These field data are then used in a model of root reinforcement based on fiber-bundle concepts that span different spacial scales, from a single root to the stand scale, and different time scales, from timber harvest to root decay. This model computes the strength of root bundles in tension and in compression and their effect on soil strength. Up-scaled to the stand the model yields the distribution of root reinforcement as a function of tree density, distance from tree, tree species and age with the objective of providing quantitative estimates of tree root reinforcement for best management practice of protection forests.

On intracluster Faraday rotation. II - Statistical analysis

NASA Technical Reports Server (NTRS)

Lawler, J. M.; Dennison, B.

1982-01-01

The comparison of a reliable sample of radio source Faraday rotation measurements seen through rich clusters of galaxies, with sources seen through the outer parts of clusters and therefore having little intracluster Faraday rotation, indicates that the distribution of rotation in the former population is broadened, but only at the 80% level of statistical confidence. Employing a physical model for the intracluster medium in which the square root of magnetic field strength/turbulent cell per gas core radius number ratio equals approximately 0.07 microgauss, a Monte Carlo simulation is able to reproduce the observed broadening. An upper-limit analysis figure of less than 0.20 microgauss for the field strength/turbulent cell ratio, combined with lower limits on field strength imposed by limitations on the Compton-scattered flux, shows that intracluster magnetic fields must be tangled on scales greater than about 20 kpc.

Magnetic Field Strengths and Grain Alignment Variations in the Local Bubble Wall

NASA Astrophysics Data System (ADS)

Medan, Ilija; Andersson, B.-G.

2018-01-01

Optical and infrared continuum polarization is known to be due to irregular dust grains aligned with the magnetic field. This provides an important tool to probe the geometry and strength of those fields, particularly if the variations in the grain alignment efficiencies can be understood. Here, we examine polarization variations observed throughout the Local Bubble for b>30○, using a large polarization survey of the North Galactic cap from Berdyugin et al. (2014). These data are supported by archival photometric and spectroscopic data along with the mapping of the Local Bubble by Lallement et al. (2003). We can accurately model the observational data assuming that the grain alignment variations are due to the radiation from the OB associations within 1 kpc of the sun. This strongly supports radiatively driven grain alignment. We also probe the relative strength of the magnetic field in the wall of the Local Bubble using the Davis-Chandrasekhar-Fermi method. We find evidence for a bimodal field strength distribution, where the variations in the field are correlated with the variations in grain alignment efficiency, indicating that the higher strength regions might represent a compression of the wall by the interaction of the outflow in the Local Bubble and the opposing flows by the surrounding OB associations.

Electric Field Strength Of Coherent Radio Emission In Rock Salt Concerning Ultra High-Energy Neutrino Detection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, Y.; Chiba, M.; Yasuda, O.

2006-07-12

Detection possibility of ultra high-energy (UHE) neutrino (E >1015 eV) in natural huge rock salt formation has been studied. Collision between the UHE neutrino and the rock salt produces electromagnetic (EM) shower. Charge difference (excess electrons) between electrons and positrons in EM shower radiates radio wave coherently (Askar'yan effect). Angular distribution and frequency spectrum of electric field strength of radio wave radiated from 3-dimensional EM shower in rock salt are presented.

Electron beam therapy with coil-generated magnetic fields.

PubMed

Nardi, Eran; Barnea, Gideon; Ma, Chang-Ming

2004-06-01

This paper presents an initial study on the issues involved in the practical implementation of the use of transverse magnetic fields in electron beam therapy. By using such magnetic fields the dose delivered to the tumor region can increase significantly relative to that deposited to the healthy tissue. Initially we calculated the magnetic fields produced by the Helmholtz coil and modified Helmholtz coil configurations. These configurations, which can readily be used to generate high intensity magnetic fields, approximate the idealized magnetic fields studied in our previous publications. It was therefore of interest to perform a detailed study of the fields produced by these configurations. Electron beam dose distributions for 15 MeV electrons were calculated using the ACCEPTM code for a 3T transverse magnetic field produced by the modified Helmholtz configuration. The dose distribution was compared to those obtained with no magnetic field. The results were similar to those obtained in our previous work, where an idealized step function magnetic field was used and a 3T field was shown to be the optimal field strength. A simpler configuration was also studied in which a single external coil was used to generate the field. Electron dose distributions are also presented for a given geometry and given magnetic field strength using this configuration. The results indicate that this method is more difficult to apply to radiotherapy due to its lack of symmetry and its irregularity. For the various configurations dealt with here, a major problem is the need to shield the magnetic field in the beam propagation volume, a topic that must be studied in detail.

Electron energy distribution function in the positive column of a neon glow discharge using the black wall approximation

NASA Astrophysics Data System (ADS)

Al-Hawat, Sh; Naddaf, M.

2005-04-01

The electron energy distribution function (EEDF) was determined from the second derivative of the I-V Langmuir probe characteristics and, thereafter, theoretically calculated by solving the plasma kinetic equation, using the black wall (BW) approximation, in the positive column of a neon glow discharge. The pressure has been varied from 0.5 to 4 Torr and the current from 10 to 30 mA. The measured electron temperature, density and electric field strength were used as input data for solving the kinetic equation. Comparisons were made between the EEDFs obtained from experiment, the BW approach, the Maxwellian distribution and the Rutcher solution of the kinetic equation in the elastic energy range. The best conditions for the BW approach are found to be under the discharge conditions: current density jd = 4.45 mA cm-2 and normalized electric field strength E/p = 1.88 V cm-1 Torr-1.

[Objectivized evaluation of surgeons exposure to radiofrequency electromagnetic fields -- in the context of exposure duration and Polish and new international requirements regarding workers protection].

PubMed

Karpowicz, Jolanta; Gryz, Krzysztof; Leszko, Wieslaw; Zradziński, Patryk

2013-01-01

Use of electro surgery units (ESU) in surgeries is linked with electromagnetic field emission, which is assessed according to the requirements of occupational health and safety legislation. Surgeons' exposure characteristics was monitored during 11 surgeries (proctectomy, patency of artery, hepatectomy, cystectomy, tonsilectomy, laparoscopy) by real time of monopolar ESU activity recorder. Investigations of root-mean-square value of electric and magnetic field strength was also performed at various modes of ESU operations during cutting (output power, 55-150 W; frequency, 330-445 kHz) and coagulating (40-240 W, 335-770 kHz). Statistical parameters of distribution of ESU operation over any 6-min periods (according to international requirements regarding protection against adverse thermal effects of electromagnetic field) were assessed. Electric field strength, measured 10 cm from the cable supplying an active electrode was 147-675 V/m during cutting and 297-558 V/m during coagulating; magnetic field strength was less than 0.2 A/m in both modes. Monitoring of ESUs showed the following ranges of their operation during surgeries 5-66% of time over starting 3 min of surgery, 3-40% over starting 6 min, and the distribution of their use over any 6-min periods 0-12% (median) / 7-43% (maximum value). The real operation time of ESUs ing surgeries was significantly shorter than that declared by workers. The distance of at least 15 cm between cables, connecting electrodes with generator and workers meets the requirements of the Polish legislation on permissible exposure limits. The assessment of localized exposure of the hand needs a detailed analysis of the SAR ratio distribution and further studies are required.

Design of novel dual-port tapered waveguide plasma apparatus by numerical analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, D.; Zhou, R.; Yang, X. Q., E-mail: yyxxqq-mail@163.com

Microwave plasma apparatus is often of particular interest due to their superiority of low cost, electrode contamination free, and suitability for industrial production. However, there exist problems of unstable plasma and low electron density in conventional waveguide apparatus based on single port, due to low strength and non-uniformity of microwave field. This study proposes a novel dual-port tapered waveguide plasma apparatus based on power-combining technique, to improve the strength and uniformity of microwave field for the applications of plasma. A 3D model of microwave-induced plasma (field frequency 2.45 GHz) in argon at atmospheric pressure is presented. On the condition thatmore » the total input power is 500 W, simulations indicate that coherent power-combining will maximize the electric-field strength to 3.32 × 10{sup 5 }V/m and improve the uniformity of distributed microwave field, which raised 36.7% and 47.2%, respectively, compared to conventional waveguide apparatus of single port. To study the optimum conditions for industrial application, a 2D argon fluid model based on above structure is presented. It demonstrates that relatively uniform and high-density plasma is obtained at an argon flow rate of 200 ml/min. The contrastive result of electric-field distribution, electron density, and gas temperature is also valid and clearly proves the superiority of coherent power-combining to conventional technique in flow field.« less

Universal energy distribution for interfaces in a random-field environment

NASA Astrophysics Data System (ADS)

Fedorenko, Andrei A.; Stepanow, Semjon

2003-11-01

We study the energy distribution function ρ(E) for interfaces in a random-field environment at zero temperature by summing the leading terms in the perturbation expansion of ρ(E) in powers of the disorder strength, and by taking into account the nonperturbational effects of the disorder using the functional renormalization group. We have found that the average and the variance of the energy for one-dimensional interface of length L behave as, R∝L ln L, ΔER∝L, while the distribution function of the energy tends for large L to the Gumbel distribution of the extreme value statistics.

Wireless Concrete Strength Monitoring of Wind Turbine Foundations.

PubMed

Perry, Marcus; Fusiek, Grzegorz; Niewczas, Pawel; Rubert, Tim; McAlorum, Jack

2017-12-16

Wind turbine foundations are typically cast in place, leaving the concrete to mature under environmental conditions that vary in time and space. As a result, there is uncertainty around the concrete's initial performance, and this can encourage both costly over-design and inaccurate prognoses of structural health. Here, we demonstrate the field application of a dense, wireless thermocouple network to monitor the strength development of an onshore, reinforced-concrete wind turbine foundation. Up-to-date methods in fly ash concrete strength and maturity modelling are used to estimate the distribution and evolution of foundation strength over 29 days of curing. Strength estimates are verified by core samples, extracted from the foundation base. In addition, an artificial neural network, trained using temperature data, is exploited to demonstrate that distributed concrete strengths can be estimated for foundations using only sparse thermocouple data. Our techniques provide a practical alternative to computational models, and could assist site operators in making more informed decisions about foundation design, construction, operation and maintenance.

Wireless Concrete Strength Monitoring of Wind Turbine Foundations

PubMed Central

Niewczas, Pawel; Rubert, Tim

2017-01-01

Wind turbine foundations are typically cast in place, leaving the concrete to mature under environmental conditions that vary in time and space. As a result, there is uncertainty around the concrete’s initial performance, and this can encourage both costly over-design and inaccurate prognoses of structural health. Here, we demonstrate the field application of a dense, wireless thermocouple network to monitor the strength development of an onshore, reinforced-concrete wind turbine foundation. Up-to-date methods in fly ash concrete strength and maturity modelling are used to estimate the distribution and evolution of foundation strength over 29 days of curing. Strength estimates are verified by core samples, extracted from the foundation base. In addition, an artificial neural network, trained using temperature data, is exploited to demonstrate that distributed concrete strengths can be estimated for foundations using only sparse thermocouple data. Our techniques provide a practical alternative to computational models, and could assist site operators in making more informed decisions about foundation design, construction, operation and maintenance. PMID:29258176

Robustness of radiomic breast features of benign lesions and luminal A cancers across MR magnet strengths

NASA Astrophysics Data System (ADS)

Whitney, Heather M.; Drukker, Karen; Edwards, Alexandra; Papaioannou, John; Giger, Maryellen L.

2018-02-01

Radiomics features extracted from breast lesion images have shown potential in diagnosis and prognosis of breast cancer. As clinical institutions transition from 1.5 T to 3.0 T magnetic resonance imaging (MRI), it is helpful to identify robust features across these field strengths. In this study, dynamic contrast-enhanced MR images were acquired retrospectively under IRB/HIPAA compliance, yielding 738 cases: 241 and 124 benign lesions imaged at 1.5 T and 3.0 T and 231 and 142 luminal A cancers imaged at 1.5 T and 3.0 T, respectively. Lesions were segmented using a fuzzy C-means method. Extracted radiomic values for each group of lesions by cancer status and field strength of acquisition were compared using a Kolmogorov-Smirnov test for the null hypothesis that two groups being compared came from the same distribution, with p-values being corrected for multiple comparisons by the Holm-Bonferroni method. Two shape features, one texture feature, and three enhancement variance kinetics features were found to be potentially robust. All potentially robust features had areas under the receiver operating characteristic curve (AUC) statistically greater than 0.5 in the task of distinguishing between lesion types (range of means 0.57-0.78). The significant difference in voxel size between field strength of acquisition limits the ability to affirm more features as robust or not robust according to field strength alone, and inhomogeneities in static field strength and radiofrequency field could also have affected the assessment of kinetic curve features as robust or not. Vendor-specific image scaling could have also been a factor. These findings will contribute to the development of radiomic signatures that use features identified as robust across field strength.

Driven acoustic oscillations within a vertical magnetic field

NASA Technical Reports Server (NTRS)

Hindman, Bradley W.; Zweibel, Ellen G.; Cally, P. S.

1995-01-01

The effects of a vertical magnetic field on p-mode frequencies, line widths, and eigenfunctions, are examined. A solar model, consisting of a neutrally stable polytropic interior matched to an isothermal chromosphere, is applied. The p-modes are produced by a spatially distributed driver. The atmosphere is threaded by a constant vertical magnetic field. The frequency shifts due to the vertical magnetic field are found to be much smaller than the shifts caused by horizontal fields of similar strength. A large vertical field of 2000 G produces shifts of several nHz. It is found that the frequency shifts decrease with increasing frequency and increase with field strength. The coupling of the acoustic fast mode to the escaping slow modes is inefficient. Constant vertical magnetic field models are therefore incapable of explaining the high level of absorption observed in sunspots and plage.

Analysis of temporal decay of diffuse broadband sound fields in enclosures by decomposition in powers of an absorption parameter

NASA Astrophysics Data System (ADS)

Bliss, Donald; Franzoni, Linda; Rouse, Jerry; Manning, Ben

2005-09-01

An analysis method for time-dependent broadband diffuse sound fields in enclosures is described. Beginning with a formulation utilizing time-dependent broadband intensity boundary sources, the strength of these wall sources is expanded in a series in powers of an absorption parameter, thereby giving a separate boundary integral problem for each power. The temporal behavior is characterized by a Taylor expansion in the delay time for a source to influence an evaluation point. The lowest-order problem has a uniform interior field proportional to the reciprocal of the absorption parameter, as expected, and exhibits relatively slow exponential decay. The next-order problem gives a mean-square pressure distribution that is independent of the absorption parameter and is primarily responsible for the spatial variation of the reverberant field. This problem, which is driven by input sources and the lowest-order reverberant field, depends on source location and the spatial distribution of absorption. Additional problems proceed at integer powers of the absorption parameter, but are essentially higher-order corrections to the spatial variation. Temporal behavior is expressed in terms of an eigenvalue problem, with boundary source strength distributions expressed as eigenmodes. Solutions exhibit rapid short-time spatial redistribution followed by long-time decay of a predominant spatial mode.

New Limits on Extragalactic Magnetic Fields from Rotation Measures

NASA Astrophysics Data System (ADS)

Pshirkov, M. S.; Tinyakov, P. G.; Urban, F. R.

2016-05-01

We take advantage of the wealth of rotation measures data contained in the NRAO VLA Sky Survey catalog to derive new, statistically robust, upper limits on the strength of extragalactic magnetic fields. We simulate the extragalactic magnetic field contribution to the rotation measures for a given field strength and correlation length, by assuming that the electron density follows the distribution of Lyman-α clouds. Based on the observation that rotation measures from distant radio sources do not exhibit any trend with redshift, while the extragalactic contribution instead grows with distance, we constrain fields with Jeans' length coherence length to be below 1.7 nG at the 2 σ level, and fields coherent across the entire observable Universe below 0.65 nG. These limits do not depend on the particular origin of these cosmological fields.

Reversal of radial glow distribution in helicon plasma induced by reversed magnetic field

NASA Astrophysics Data System (ADS)

Wang, Y.; Zhao, G.; Niu, C.; Liu, Z. W.; Ouyang, J. T.; Chen, Q.

2017-02-01

In this work, the reversal of radial glow distribution induced by reversed magnetic field is reported. Based on the Boswell antenna which is symmetric and insensitive to the magnetic field direction, it seems such a phenomenon in theory appears impossible. However, according to the diagnostic of the helicon waves by magnetic probe, it is found that the direction of magnetic field significantly affects the propagation characteristic of helicon waves, i.e., the interchange of the helicon waves at the upper and the lower half of tube was caused by reversing the direction of magnetic field. It is suggested that the variation of helicon wave against the direction of magnetic field causes the reversed radial glow distribution. The appearance of the traveling wave does not only improve the discharge strength, but also determines the transition of the discharge mode.

Determinants of the electric field during transcranial direct current stimulation.

PubMed

Opitz, Alexander; Paulus, Walter; Will, Susanne; Antunes, Andre; Thielscher, Axel

2015-04-01

Transcranial direct current stimulation (tDCS) causes a complex spatial distribution of the electric current flow in the head which hampers the accurate localization of the stimulated brain areas. In this study we show how various anatomical features systematically shape the electric field distribution in the brain during tDCS. We constructed anatomically realistic finite element (FEM) models of two individual heads including conductivity anisotropy and different skull layers. We simulated a widely employed electrode montage to induce motor cortex plasticity and moved the stimulating electrode over the motor cortex in small steps to examine the resulting changes of the electric field distribution in the underlying cortex. We examined the effect of skull thickness and composition on the passing currents showing that thinner skull regions lead to higher electric field strengths. This effect is counteracted by a larger proportion of higher conducting spongy bone in thicker regions leading to a more homogenous current over the skull. Using a multiple regression model we could identify key factors that determine the field distribution to a significant extent, namely the thicknesses of the cerebrospinal fluid and the skull, the gyral depth and the distance to the anode and cathode. These factors account for up to 50% of the spatial variation of the electric field strength. Further, we demonstrate that individual anatomical factors can lead to stimulation "hotspots" which are partly resistant to electrode positioning. Our results give valuable novel insights in the biophysical foundation of tDCS and highlight the importance to account for individual anatomical factors when choosing an electrode montage. Copyright © 2015 Elsevier Inc. All rights reserved.

RF Exposure Analysis for Multiple Wi-Fi Devices In Enclosed Environment

NASA Technical Reports Server (NTRS)

Hwu, Shian U.; Rhodes, Bryan A.; deSilva, B. Kanishka; Sham, Catherine C.; Keiser, James R.

2013-01-01

Wi-Fi devices operated inside a metallic enclosure have been investigation in the recent years. A motivation for this study is to investigate wave propagation inside an enclosed environment such as elevator, car, aircraft, and spacecraft. There are performances and safety concerned that when the RF transmitters are used in the metallic enclosed environments. In this paper, the field distributions inside a confined room were investigated with multiple portable Wi-Fi devices. Computer simulations were performed using the rigorous computational electromagnetics (CEM). The method of moments (MoM) was used to model the mutual coupling among antennas. The geometrical theory of diffraction (GTD) was applied for the multiple reflections off the ground and walls. The prediction of the field distribution inside such environment is useful for the planning and deployment of a wireless radio and sensor system. Factors that affect the field strengths and distributions of radio waves in confined space were analyzed. The results could be used to evaluate the RF exposure safety in confined environment. By comparing the field distributions for various scenarios, it was observed that the Wi-Fi device counts, spacing and relative locations in the room are important factors in such environments. The RF Keep Out Zone (KOZ), where the electric field strengths exceed the permissible RF exposure limit, could be used to assess the RF human exposure compliance. As shown in this study, it s possible to maximize or minimize field intensity in specific area by arranging the Wi-Fi devices as a function of the relative location and spacing in a calculated manner.

Fourier transform ion cyclotron resonance mass resolution and dynamic range limits calculated by computer modeling of ion cloud motion.

PubMed

Vladimirov, Gleb; Hendrickson, Christopher L; Blakney, Greg T; Marshall, Alan G; Heeren, Ron M A; Nikolaev, Eugene N

2012-02-01

Particle-in-Cell (PIC) ion trajectory calculations provide the most realistic simulation of Fourier transform ion cyclotron resonance (FT-ICR) experiments by efficient and accurate calculation of the forces acting on each ion in an ensemble (cloud), including Coulomb interactions (space charge), the electric field of the ICR trap electrodes, image charges on the trap electrodes, the magnetic field, and collisions with neutral gas molecules. It has been shown recently that ion cloud collective behavior is required to generate an FT-ICR signal and that two main phenomena influence mass resolution and dynamic range. The first is formation of an ellipsoidal ion cloud (termed "condensation") at a critical ion number (density), which facilitates signal generation in an FT-ICR cell of arbitrary geometry because the condensed cloud behaves as a quasi-ion. The second phenomenon is peak coalescence. Ion resonances that are closely spaced in m/z coalesce into one resonance if the ion number (density) exceeds a threshold that depends on magnetic field strength, ion cyclotron radius, ion masses and mass difference, and ion initial spatial distribution. These two phenomena decrease dynamic range by rapid cloud dephasing at small ion density and by cloud coalescence at high ion density. Here, we use PIC simulations to quantitate the dependence of coalescence on each critical parameter. Transitions between independent and coalesced motion were observed in a series of the experiments that systematically varied ion number, magnetic field strength, ion radius, ion m/z, ion m/z difference, and ion initial spatial distribution (the present simulations begin from elliptically-shaped ion clouds with constant ion density distribution). Our simulations show that mass resolution is constant at a given magnetic field strength with increasing ion number until a critical value (N) is reached. N dependence on magnetic field strength, cyclotron radius, ion mass, and difference between ion masses was determined for two ion ensembles of different m/z, equal abundance, and equal cyclotron radius. We find that N and dynamic range depend quadratically on magnetic field strength in the range 1-21 Tesla. Dependences on cyclotron radius and Δm/z are linear. N depends on m/z as (m/z)(-2). Empirical expressions for mass resolution as a function of each of the experimental parameters are presented. Here, we provide the first exposition of the origin and extent of trade-off between FT-ICR MS dynamic range and mass resolution (defined not as line width, but as the separation between the most closely resolved masses). © American Society for Mass Spectrometry, 2011

Magnetic field geometry and chemical abundance distribution of the He-strong star CPD -57°3509

NASA Astrophysics Data System (ADS)

Hubrig, S.; Przybilla, N.; Korhonen, H.; Ilyin, I.; Schöller, M.; Järvinen, S. P.; Nieva, M.-F.; Scholz, R.-D.; Kimeswenger, S.; Ramolla, M.; Kholtygin, A. F.; Briquet, M.

2017-10-01

The magnetic field of CPD -57°3509 was recently detected in the framework of the BOB (B fields in OB stars) collaboration. We acquired low-resolution spectropolarimetric observations of CPD -57°3509 with the FOcal Reducer low-dispersion Spectrograph 2 and high-resolution UV-Visual Echelle Spectrograph observations randomly distributed over a few months to search for periodicity, to study the magnetic field geometry and to determine the surface distribution of silicon and helium. We also obtained supplementary photometric observations at a timeline similar to the spectroscopic and spectropolarimetric observations. A period of 6.36 d was detected in the measurements of the mean longitudinal magnetic field. A sinusoidal fit to our measurements allowed us to constrain the magnetic field geometry and estimate the dipole strength in the range of 3.9-4.5 kG. Our application of the Doppler imaging technique revealed the presence of He I spots located around the magnetic poles, with a strong concentration at the positive pole and a weaker one around the negative pole. In contrast, high-concentration Si III spots are located close to the magnetic equator. Furthermore, our analysis of the spectral variability of CPD -57°3509 on short time-scales indicates distinct changes in shape and position of line profiles possibly caused by the presence of β Cep like pulsations. A small periodic variability in line with the changes of the magnetic field strength is clearly seen in the photometric data.

The Effects of Ion heating in Martian Magnetic Crustal Fields: Particle Tracing and Ion Distributions

NASA Astrophysics Data System (ADS)

Fowler, C. M.; Andersson, L.

2014-12-01

Ion heating is a process that may allow low energy ions within the Martian ionosphere to be accelerated and escape. Ion heating can be especially efficient if the ions stay in the heating region for long time durations. With this in mind, the magnetic crustal field regions on Mars are particularly interesting. We focus on ions present within these regions, where changes in magnetic field strength and direction can heat these ions. Since crustal magnetic fields can maintain a trapped particle population it is unclear how efficiently plasma can be built up that can later escape to space. We investigate here two drivers: rotation of the planet and the solar wind pressure. As crustal fields rotate from the wake of the planet to the sub solar point and back, they experience compression and expansion over time scales of ~24 hours. The solar wind pressure on the other hand can cause variations over much shorter time scales (minutes). The effect of these two drivers using a particle tracing simulation that solves the Lorentz force is presented. O+ ions are seeded within the simulation box. The magnetic environment is a linear sum of a dipole field and a solar wind magnetic field. The dipole field represents the magnetic crustal field and the dipole strength is chosen to be consistent with MGS magnetometer observations of Martian crustal field regions. By increasing the solar wind strength the magnetic dipole is compressed. Decreasing solar wind strength allows the dipole to expand. Small magnitude, short time scale variations can be imposed over the top of this larger variation to represent short time scale solar wind variations. Since the purpose of this analysis is to understand the changes of the ion distribution inside the crustal field, simplistic assumptions of the field outside the crustal field can be made. Initial results are presented, with the focus on two main questions: (a) can low energy ions be heated and escape the closed dipole field lines as a result of varying magnetic fields; (b) is the compression and relaxation of the crustal field due to rotation important for the oxygen escape rates when compared to the particle evolution due to high frequency changes in magnetic field and the lifetimes of these ions.

Electric field control in DC cable test termination by nano silicone rubber composite

NASA Astrophysics Data System (ADS)

Song, Shu-Wei; Li, Zhongyuan; Zhao, Hong; Zhang, Peihong; Han, Baozhong; Fu, Mingli; Hou, Shuai

2017-07-01

The electric field distributions in high voltage direct current cable termination are investigated with silicone rubber nanocomposite being the electric stress control insulator. The nanocomposite is composed of silicone rubber, nanoscale carbon black and graphitic carbon. The experimental results show that the physical parameters of the nanocomposite, such as thermal activation energy and nonlinearity-relevant coefficient, can be manipulated by varying the proportion of the nanoscale fillers. The numerical simulation shows that safe electric field distribution calls for certain parametric region of the thermal activation energy and nonlinearity-relevant coefficient. Outside the safe parametric region, local maximum of electric field strength around the stress cone appears in the termination insulator, enhancing the breakdown of the cable termination. In the presence of the temperature gradient, thermal activation energy and nonlinearity-relevant coefficient work as complementary factors to produce a reasonable electric field distribution. The field maximum in the termination insulator show complicate variation in the transient processes. The stationary field distribution favors the increase of the nonlinearity-relevant coefficient; for the transient field distribution in the process of negative lighting impulse, however, an optimized value of the nonlinearity-relevant coefficient is necessary to equalize the electric field in the termination.

The effect of electric field geometry on the performance of electromembrane extraction systems: footprints of a third driving force along with migration and diffusion.

PubMed

Moazami, Hamid Reza; Hosseiny Davarani, Saied Saeed; Mohammadi, Jamil; Nojavan, Saeed; Abrari, Masoud

2015-09-03

The distribution of electric field vectors was first calculated for electromembrane extraction (EME) systems in classical and cylindrical electrode geometries. The results showed that supported liquid membrane (SLM) has a general field amplifying effect due to its lower dielectric constant in comparison with aqueous donor/acceptor solutions. The calculated norms of the electric field vector showed that a DC voltage of 50 V can create huge electric field strengths up to 64 kV m(-1) and 111 kV m(-1) in classical and cylindrical geometries respectively. In both cases, the electric field strength reached its peak value on the inner wall of the SLM. In the case of classical geometry, the field strength was a function of the polar position of the SLM whereas the field strength in cylindrical geometry was angularly uniform. In order to investigate the effect of the electrode geometry on the performance of real EME systems, the analysis was carried out in three different geometries including classical, helical and cylindrical arrangements using naproxen and sodium diclofenac as the model analytes. Despite higher field strength and extended cross sectional area, the helical and cylindrical geometries gave lower recoveries with respect to the classical EME. The observed decline of the signal was proved to be against the relations governing migration and diffusion processes, which means that a third driving force is involved in EME. The third driving force is the interaction between the radially inhomogeneous electric field and the analyte in its neutral form. Copyright © 2015 Elsevier B.V. All rights reserved.

Effects of primordial magnetic field on the formation rate of dark matter halos

NASA Astrophysics Data System (ADS)

Cheera, Varalakshmi; Nigam, Rahul

2018-05-01

We construct and demonstrate a method for computing the formation rate of the dark matter halo in the hierarchical model set up. This method uses the Press-Schecter distribution for the halos and hence applies only to the spherical halos. But this can be generalized to ellipsoidal structures also if one uses the Sheth-Torman distribution. After obtaining the formation rate, we study the effect of primordial magnetic field on the dynamics of these halos. We investigate the effect for different field strengths and conclude that a magnetic field stronger than 10 nG would impact the halos larger than 108 solar masses while a weaker field affects the formation rate of smaller halos.

Impact of Particle Size of Ceramic Granule Blends on Mechanical Strength and Porosity of 3D Printed Scaffolds

PubMed Central

Spath, Sebastian; Drescher, Philipp; Seitz, Hermann

2015-01-01

3D printing is a promising method for the fabrication of scaffolds in the field of bone tissue engineering. To date, the mechanical strength of 3D printed ceramic scaffolds is not sufficient for a variety of applications in the reconstructive surgery. Mechanical strength is directly in relation with the porosity of the 3D printed scaffolds. The porosity is directly influenced by particle size and particle-size distribution of the raw material. To investigate this impact, a hydroxyapatite granule blend with a wide particle size distribution was fractioned by sieving. The specific fractions and bimodal mixtures of the sieved granule blend were used to 3D print specimens. It has been shown that an optimized arrangement of fractions with large and small particles can provide 3D printed specimens with good mechanical strength due to a higher packing density. An increase of mechanical strength can possibly expand the application area of 3D printed hydroxyapatite scaffolds. PMID:28793467

Impact Cratering Calculations

NASA Technical Reports Server (NTRS)

Ahrens, Thomas J.

2001-01-01

We examined the von Mises and Mohr-Coulomb strength models with and without damage effects and developed a model for dilatancy. The models and results are given in O'Keefe et al. We found that by incorporating damage into the models that we could in a single integrated impact calculation, starting with the bolide in the atmosphere produce final crater profiles having the major features found in the field measurements. These features included a central uplift, an inner ring, circular terracing and faulting. This was accomplished with undamaged surface strengths of approximately 0.1 GPa and at depth strengths of approximately 1.0 GPa. We modeled the damage in geologic materials using a phenomenological approach, which coupled the Johnson-Cook damage model with the CTH code geologic strength model. The objective here was not to determine the distribution of fragment sizes, but rather to determine the effect of brecciated and comminuted material on the crater evolution, fault production, ejecta distribution, and final crater morphology.

Computational modeling of magnetic nanoparticle targeting to stent surface under high gradient field

PubMed Central

Wang, Shunqiang; Zhou, Yihua; Tan, Jifu; Xu, Jiang; Yang, Jie; Liu, Yaling

2014-01-01

A multi-physics model was developed to study the delivery of magnetic nanoparticles (MNPs) to the stent-implanted region under an external magnetic field. The model is firstly validated by experimental work in literature. Then, effects of external magnetic field strength, magnetic particle size, and flow velocity on MNPs’ targeting and binding have been analyzed through a parametric study. Two new dimensionless numbers were introduced to characterize relative effects of Brownian motion (BM), magnetic force induced particle motion, and convective blood flow on MNPs motion. It was found that larger magnetic field strength, bigger MNP size, and slower flow velocity increase the capture efficiency of MNPs. The distribution of captured MNPs on the vessel along axial and azimuthal directions was also discussed. Results showed that the MNPs density decreased exponentially along axial direction after one-dose injection while it was uniform along azimuthal direction in the whole stented region (averaged over all sections). For the beginning section of the stented region, the density ratio distribution of captured MNPs along azimuthal direction is center-symmetrical, corresponding to the center-symmetrical distribution of magnetic force in that section. Two different generation mechanisms are revealed to form four main attraction regions. These results could serve as guidelines to design a better magnetic drug delivery system. PMID:24653546

Two-dimensional simulation research of secondary electron emission avalanche discharge on vacuum insulator surface

NASA Astrophysics Data System (ADS)

Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui

2015-01-01

Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.

Effect of interphase permittivity on the electric field distribution of epoxy nanocomposites

NASA Astrophysics Data System (ADS)

Pradeep, Lavanya; Nelson, Avinash; Preetha, P.

2018-05-01

Epoxy plays a vital role in high voltage insulation system due to its superior electrical and thermal properties. Literature reports the enhancement in these properties by the addition of nanofillers to epoxy and this enhancement is attributed to the effect of interphase. Characterization of polymer nanocomposites proves the importance of interphase formed between the polymer and nanoparticle in the composite. It was observed that the permittivity of the interphase is having a significant effect on the properties of these materials. In this work, a three dimensional Epoxy nanocomposite with 0.5 vol%, 1 vol% of alumina particles are modeled using unit cell approach in COMSOL Multiphysics. Simulation is done using several existing interphase permittivity models and field distribution is observed. Results shows the noticeable influence of interphase permittivity on the electric field distribution. A good correlation of electric field distribution with the AC breakdown strength is observed.

Research on the novel FBG detection system for temperature and strain field distribution

NASA Astrophysics Data System (ADS)

Liu, Zhi-chao; Yang, Jin-hua

2017-10-01

In order to collect the information of temperature and strain field distribution information, the novel FBG detection system was designed. The system applied linear chirped FBG structure for large bandwidth. The structure of novel FBG cover was designed as a linear change in thickness, in order to have a different response at different locations. It can obtain the temperature and strain field distribution information by reflection spectrum simultaneously. The structure of novel FBG cover was designed, and its theoretical function is calculated. Its solution is derived for strain field distribution. By simulation analysis the change trend of temperature and strain field distribution were analyzed in the conditions of different strain strength and action position, the strain field distribution can be resolved. The FOB100 series equipment was used to test the temperature in experiment, and The JSM-A10 series equipment was used to test the strain field distribution in experiment. The average error of experimental results was better than 1.1% for temperature, and the average error of experimental results was better than 1.3% for strain. There were individual errors when the strain was small in test data. It is feasibility by theoretical analysis, simulation calculation and experiment, and it is very suitable for application practice.

Particle acceleration magnetic field generation, and emission in Relativistic pair jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C.; Kouveliotou, C.; Fishman, G. J.

2005-01-01

Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) are responsible for particle acceleration in relativistic pair jets. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic pair jet propagating through a pair plasma. Simulations show that the Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. Simulation results show that this instability generates and amplifies highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The "jitter' I radiation from deflected electrons can have different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. The growth rate of the Weibel instability and the resulting particle acceleration depend on the magnetic field strength and orientation, and on the initial particle distribution function. In this presentation we explore some of the dependencies of the Weibel instability and resulting particle acceleration on the magnetic field strength and orientation, and the particle distribution function.

The modeling of attraction characteristics regarding passenger flow in urban rail transit network based on field theory

PubMed Central

Jia, Limin

2017-01-01

Aimed at the complicated problems of attraction characteristics regarding passenger flow in urban rail transit network, the concept of the gravity field of passenger flow is proposed in this paper. We establish the computation methods of field strength and potential energy to reveal the potential attraction relationship among stations from the perspective of the collection and distribution of passenger flow and the topology of network. As for the computation methods of field strength, an optimum path concept is proposed to define betweenness centrality parameter. Regarding the computation of potential energy, Compound Simpson’s Rule Formula is applied to get a solution to the function. Taking No. 10 Beijing Subway as a practical example, an analysis of simulation and verification is conducted, and the results shows in the following ways. Firstly, the bigger field strength value between two stations is, the stronger passenger flow attraction is, and the greater probability of the formation of the largest passenger flow of section is. Secondly, there is the greatest passenger flow volume and circulation capacity between two zones of high potential energy. PMID:28863175

The magnetic field in the disk of our Galaxy

NASA Astrophysics Data System (ADS)

Han, J. L.; Qiao, G. J.

1994-08-01

The magnetic field in the disk of our Galaxy is investigated by using the Rotation Measures (RMs) of pulsars and Extragalactic Radio Sources (ERSes). Through analyses of the RMs of carefully selected pulsar samples, it is found that the Galaxy has a global field of BiSymmetric Spiral (BSS) configuration, rather than a concentric ring or an AxiSymmetric Spiral (ASS) configuration. The Galactic magnetic field of BSS structure is supposed to be of primordial origin. The pitch angle of the BSS structure is -8.2deg+/-0.5deg. The field geometry shows that the field goes along the Carina-Sagittarius arm, which is delineated by Giant Molecular Clouds (GMCs). The amplitude of the BSS field is 1.8+/-0.3μG. The first field strength maximum is at r_0_=11.9+/-0.15 kpc in the direction of l=180deg. The field is strong in the interarm regions and it reverses in the arm regions. In the vicinity of the Sun, it has a strength of ~1.4μG and reverses at 0.2-0.3kpc in the direction of l=0deg. Because of the unknown electron distribution of the Galaxy and other difficulties, it is impossible to derive the galactic field from the RMs of ERSes very quantitatively. Nevertheless, the RMs of ERSes located in the region of the two galactic poles are used to estimate the vertical component of the local galactic field, which is found to have a strength of 0.2-0.3μG and is directed from the south galactic pole to the north galactic pole. The scale height of the magnetic disk of the Galaxy is estimated from the RMs of all-sky distributed ERSes, being about 1.2+/-0.4pc. The regular magnetic field of our Galaxy, which is probably similar to that of M81, extends far from the optical disk.

Electroosmotic Flow Driven by DC and AC Electric Fields in Curved Microchannels

NASA Astrophysics Data System (ADS)

Chen, Jia-Kun; Luo, Win-Jet; Yang, Ruey-Jen

2006-10-01

The purpose of this study is to investigate electroosmotic flows driven by externally applied DC and AC electric fields in curved microchannels. For the DC electric driving field, the velocity distribution and secondary flow patterns are investigated in microchannels with various curvature ratios. We use the Dean number to describe the curvature effect of the flow field in DC electric field. The result implies that the effect of curvatures and the strength of the secondary flows become get stronger when the curvature ratio of C/A (where C is the radius of curvature of the microchannel and A is the half-height of rectangular curved tube.) is smaller. For the AC electric field, the velocity distribution and secondary flow patterns are investigated for driving frequencies in the range of 2.0 kHz (\\mathit{Wo}=0.71) to 11 kHz (\\mathit{Wo}=1.66). The numerical results reveal that the velocity at the center of the microchannel becomes lower at higher frequencies of the AC electric field and the strength of the secondary flow decreases. When the applied frequency exceeds 3.0 kHz (\\mathit{Wo}=0.87), vortices are no longer observed at the corners of the microchannel. Therefore, it can be concluded that the secondary flow induced at higher AC electric field frequencies has virtually no effect on the axial flow field in the microchannel.

A method for establishing constraints on galactic magnetic field models using ultra high energy cosmic rays and results from the data of the Pierre Auger Observatory

NASA Astrophysics Data System (ADS)

Sutherland, Michael Stephen

2010-12-01

The Galactic magnetic field is poorly understood. Essentially the only reliable measurements of its properties are the local orientation and field strength. Its behavior at galactic scales is unknown. Historically, magnetic field measurements have been performed using radio astronomy techniques which are sensitive to certain regions of the Galaxy and rely upon models of the distribution of gas and dust within the disk. However, the deflection of trajectories of ultra high energy cosmic rays arriving from extragalactic sources depends only on the properties of the magnetic field. In this work, a method is developed for determining acceptable global models of the Galactic magnetic field by backtracking cosmic rays through the field model. This method constrains the parameter space of magnetic field models by comparing a test statistic between backtracked cosmic rays and isotropic expectations for assumed cosmic ray source and composition hypotheses. Constraints on Galactic magnetic field models are established using data from the southern site of the Pierre Auger Observatory under various source distribution and cosmic ray composition hypotheses. Field models possessing structure similar to the stellar spiral arms are found to be inconsistent with hypotheses of an iron cosmic ray composition and sources selected from catalogs tracing the local matter distribution in the universe. These field models are consistent with hypothesis combinations of proton composition and sources tracing the local matter distribution. In particular, strong constraints are found on the parameter space of bisymmetric magnetic field models scanned under hypotheses of proton composition and sources selected from the 2MRS-VS, Swift 39-month, and VCV catalogs. Assuming that the Galactic magnetic field is well-described by a bisymmetric model under these hypotheses, the magnetic field strength near the Sun is less than 3-4 muG and magnetic pitch angle is less than -8°. These results comprise the first measurements of the Galactic magnetic field using ultra-high energy cosmic rays and supplement existing radio astronomical measurements of the Galactic magnetic field.

Controlling stray electric fields on an atom chip for experiments on Rydberg atoms

NASA Astrophysics Data System (ADS)

Davtyan, D.; Machluf, S.; Soudijn, M. L.; Naber, J. B.; van Druten, N. J.; van Linden van den Heuvell, H. B.; Spreeuw, R. J. C.

2018-02-01

Experiments handling Rydberg atoms near surfaces must necessarily deal with the high sensitivity of Rydberg atoms to (stray) electric fields that typically emanate from adsorbates on the surface. We demonstrate a method to modify and reduce the stray electric field by changing the adsorbate distribution. We use one of the Rydberg excitation lasers to locally affect the adsorbed dipole distribution. By adjusting the averaged exposure time we change the strength (with the minimal value less than 0.2 V /cm at 78 μ m from the chip) and even the sign of the perpendicular field component. This technique is a useful tool for experiments handling Rydberg atoms near surfaces, including atom chips.

On the velocity distribution of ion jets during substorm recovery

NASA Technical Reports Server (NTRS)

Birn, J.; Forbes, T. G.; Hones, E. W., Jr.; Bame, S. J.; Paschmann, G.

1981-01-01

The velocity distribution of earthward jetting ions that are observed principally during substorm recovery by satellites at approximately 15-35 earth radii in the magnetotail is quantitatively compared with two different theoretical models - the 'adiabatic deformation' of an initially flowing Maxwellian moving into higher magnetic field strength (model A) and the field-aligned electrostatic acceleration of an initially nonflowing isotropic Maxwellian including adiabatic deformation effects (model B). The assumption is made that the ions are protons or, more generally, that they consist of only one species. It is found that both models can explain the often observed concave-convex shape of isodensity contours of the distribution function.

Relative distribution of cosmic rays and magnetic fields

NASA Astrophysics Data System (ADS)

Seta, Amit; Shukurov, Anvar; Wood, Toby S.; Bushby, Paul J.; Snodin, Andrew P.

2018-02-01

Synchrotron radiation from cosmic rays is a key observational probe of the galactic magnetic field. Interpreting synchrotron emission data requires knowledge of the cosmic ray number density, which is often assumed to be in energy equipartition (or otherwise tightly correlated) with the magnetic field energy. However, there is no compelling observational or theoretical reason to expect such a tight correlation to hold across all scales. We use test particle simulations, tracing the propagation of charged particles (protons) through a random magnetic field, to study the cosmic ray distribution at scales comparable to the correlation scale of the turbulent flow in the interstellar medium (≃100 pc in spiral galaxies). In these simulations, we find that there is no spatial correlation between the cosmic ray number density and the magnetic field energy density. In fact, their distributions are approximately statistically independent. We find that low-energy cosmic rays can become trapped between magnetic mirrors, whose location depends more on the structure of the field lines than on the field strength.

Tensile properties to 650 C and deformation structures in a precipitation strengthened titanium-aluminum alloy

NASA Technical Reports Server (NTRS)

Mendiratta, M. G.

1973-01-01

Appreciable strength levels were retained to 650 C in a Ti-10Al-1Si alloy aged in the (alpha + alpha sub 2) phase field to yield optimum room temperature strength and ductility. The aging treatment precipitated a uniform distribution of alpha sub 2-particles such that, at room temperature, dislocations bypassed instead of shearing the particles at low strains. Specimens fractured at room temperature exhibited fine uniform dimples even for those aging conditions that imparted no macroscopic ductility. The main crack appeared to propagate through the planar slip bands that had cut through the alpha sub 2-particles. A two-step aging process produced a higher volume fraction of bimodally distributed alpha sub 2-particles that led to higher strength levels at elevated temperatures. Both for the single size and the bimodal alpha sub 2-particle distributions, elevated-temperature deformation structures consisted mainly of planar slip bands that sheared through the alpha sub 2-particles.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Terai, Tsuyoshi; Takahashi, Jun; Itoh, Yoichi, E-mail: tsuyoshi.terai@nao.ac.jp

Main-belt asteroids have been continuously colliding with one another since they were formed. Their size distribution is primarily determined by the size dependence of asteroid strength against catastrophic impacts. The strength scaling law as a function of body size could depend on collision velocity, but the relationship remains unknown, especially under hypervelocity collisions comparable to 10 km s{sup –1}. We present a wide-field imaging survey at an ecliptic latitude of about 25° for investigating the size distribution of small main-belt asteroids that have highly inclined orbits. The analysis technique allowing for efficient asteroid detections and high-accuracy photometric measurements provides sufficientmore » sample data to estimate the size distribution of sub-kilometer asteroids with inclinations larger than 14°. The best-fit power-law slopes of the cumulative size distribution are 1.25 ± 0.03 in the diameter range of 0.6-1.0 km and 1.84 ± 0.27 in 1.0-3.0 km. We provide a simple size distribution model that takes into consideration the oscillations of the power-law slope due to the transition from the gravity-scaled regime to the strength-scaled regime. We find that the high-inclination population has a shallow slope of the primary components of the size distribution compared to the low-inclination populations. The asteroid population exposed to hypervelocity impacts undergoes collisional processes where large bodies have a higher disruptive strength and longer lifespan relative to tiny bodies than the ecliptic asteroids.« less

The Theory of Distributed Practice as Related to Acquisition of Psychomotor Skills by Adolescents in a Selected Curricular Field.

ERIC Educational Resources Information Center

Drake, James Bob

1981-01-01

From results on the tensile strength and nick-break average jury evaluations test, it was concluded that with the same total practice time, different distributions of welding practice time intervals (15, 30, and 45 minutes) influence the quality of butt welds made by ninth-grade vocational agriculture students. (Author/SJL)

The electric field distribution in the brain during TTFields therapy and its dependence on tissue dielectric properties and anatomy: a computational study

NASA Astrophysics Data System (ADS)

Wenger, Cornelia; Salvador, Ricardo; Basser, Peter J.; Miranda, Pedro C.

2015-09-01

Tumor treating fields (TTFields) are a non-invasive, anti-mitotic and approved treatment for recurrent glioblastoma multiforme (GBM) patients. In vitro studies have shown that inhibition of cell division in glioma is achieved when the applied alternating electric field has a frequency in the range of 200 kHz and an amplitude of 1-3 V cm-1. Our aim is to calculate the electric field distribution in the brain during TTFields therapy and to investigate the dependence of these predictions on the heterogeneous, anisotropic dielectric properties used in the computational model. A realistic head model was developed by segmenting MR images and by incorporating anisotropic conductivity values for the brain tissues. The finite element method (FEM) was used to solve for the electric potential within a volume mesh that consisted of the head tissues, a virtual lesion with an active tumour shell surrounding a necrotic core, and the transducer arrays. The induced electric field distribution is highly non-uniform. Average field strength values are slightly higher in the tumour when incorporating anisotropy, by about 10% or less. A sensitivity analysis with respect to the conductivity and permittivity of head tissues shows a variation in field strength of less than 42% in brain parenchyma and in the tumour, for values within the ranges reported in the literature. Comparing results to a previously developed head model suggests significant inter-subject variability. This modelling study predicts that during treatment with TTFields the electric field in the tumour exceeds 1 V cm-1, independent of modelling assumptions. In the future, computational models may be useful to optimize delivery of TTFields.

The electric field distribution in the brain during TTFields therapy and its dependence on tissue dielectric properties and anatomy: a computational study.

PubMed

Wenger, Cornelia; Salvador, Ricardo; Basser, Peter J; Miranda, Pedro C

2015-09-21

Tumor treating fields (TTFields) are a non-invasive, anti-mitotic and approved treatment for recurrent glioblastoma multiforme (GBM) patients. In vitro studies have shown that inhibition of cell division in glioma is achieved when the applied alternating electric field has a frequency in the range of 200 kHz and an amplitude of 1-3 V cm(-1). Our aim is to calculate the electric field distribution in the brain during TTFields therapy and to investigate the dependence of these predictions on the heterogeneous, anisotropic dielectric properties used in the computational model. A realistic head model was developed by segmenting MR images and by incorporating anisotropic conductivity values for the brain tissues. The finite element method (FEM) was used to solve for the electric potential within a volume mesh that consisted of the head tissues, a virtual lesion with an active tumour shell surrounding a necrotic core, and the transducer arrays. The induced electric field distribution is highly non-uniform. Average field strength values are slightly higher in the tumour when incorporating anisotropy, by about 10% or less. A sensitivity analysis with respect to the conductivity and permittivity of head tissues shows a variation in field strength of less than 42% in brain parenchyma and in the tumour, for values within the ranges reported in the literature. Comparing results to a previously developed head model suggests significant inter-subject variability. This modelling study predicts that during treatment with TTFields the electric field in the tumour exceeds 1 V cm(-1), independent of modelling assumptions. In the future, computational models may be useful to optimize delivery of TTFields.

The electric field distribution in the brain during TTFields therapy and its dependence on tissue dielectric properties and anatomy: a computational study

PubMed Central

Wenger, Cornelia; Salvador, Ricardo; Basser, Peter J; Miranda, Pedro C

2015-01-01

Tumor Treating Fields (TTFields) are a non-invasive, anti-mitotic and approved treatment for recurrent glioblastoma multiforme (GBM) patients. In vitro studies have shown that inhibition of cell division in glioma is achieved when the applied alternating electric field has a frequency in the range of 200 kHz and an amplitude of 1 - 3 V/cm. Our aim is to calculate the electric field distribution in the brain during TTFields therapy and to investigate the dependence of these predictions on the heterogeneous, anisotropic dielectric properties used in the computational model. A realistic head model was developed by segmenting MR images and by incorporating anisotropic conductivity values for the brain tissues. The finite element method (FEM) was used to solve for the electric potential within a volume mesh that consisted of the head tissues, a virtual lesion with an active tumour shell surrounding a necrotic core, and the transducer arrays. The induced electric field distribution is highly non-uniform. Average field strength values are slightly higher in the tumour when incorporating anisotropy, by about 10% or less. A sensitivity analysis with respect to the conductivity and permittivity of head tissues shows a variation in field strength of less than 42% in brain parenchyma and in the tumour, for values within the ranges reported in the literature. Comparing results to a previously developed head model suggests significant inter-subject variability. This modelling study predicts that during treatment with TTFields the electric field in the tumour exceeds 1 V/cm, independent of modelling assumptions. In the future, computational models may be useful to optimize delivery of TTFields. PMID:26350296

Distribution of voids in field concrete.

DOT National Transportation Integrated Search

1978-01-01

This study was intended to evaluate the air void characteristics of concrete in an attempt to identify, quantitatively or semi-quantitatively, different types of voids and to predict their influence on strength and durability. At the outset, it was a...

Changes in measured vector magnetic fields when transformed into heliographic coordinates

NASA Technical Reports Server (NTRS)

Hagyard, M. J.

1987-01-01

The changes that occur in measured magnetic fields when they are transformed into a heliographic coordinate system are investigated. To carry out this investigation, measurements of the vector magnetic field of an active region that was observed at 1/3 the solar radius from disk center are taken, and the observed field is transformed into heliographic coordinates. Differences in the calculated potential field that occur when the heliographic normal component of the field is used as the boundary condition rather than the observed line-of-sight component are also examined. The results of this analysis show: (1) that the observed fields of sunspots more closely resemble the generally accepted picture of the distribution of umbral fields if they are displayed in heliographic coordinates; (2) that the differences in the potential calculations are less than 200 G in field strength and 20 deg in field azimuth outside sunspots; and (3) that differences in the two potential calculations in the sunspot areas are no more than 400 G in field strength but range from 60 to 80 deg in field azimuth in localized umbral areas.

Lateral distribution of the radio signal in extensive air showers measured with LOPES

NASA Astrophysics Data System (ADS)

Apel, W. D.; Arteaga, J. C.; Asch, T.; Badea, A. F.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Brüggemann, M.; Buchholz, P.; Buitink, S.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Finger, M.; Fuhrmann, D.; Gemmeke, H.; Ghia, P. L.; Glasstetter, R.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Kickelbick, D.; Krömer, O.; Kuijpers, J.; Lafebre, S.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Mayer, H. J.; Melissas, M.; Mitrica, B.; Morello, C.; Navarra, G.; Nehls, S.; Nigl, A.; Oehlschläger, J.; Over, S.; Palmieri, N.; Petcu, M.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F.; Sima, O.; Singh, K.; Toma, G.; Trinchero, G. C.; Ulrich, H.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.; Zensus, J. A.; LOPES Collaboration

2010-01-01

The antenna array LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from extensive air showers. The coincident measurements allow us to reconstruct the electric field strength at observation level in dependence of general EAS parameters. In the present work, the lateral distribution of the radio signal in air showers is studied in detail. It is found that the lateral distributions of the electric field strengths in individual EAS can be described by an exponential function. For about 20% of the events a flattening towards the shower axis is observed, preferentially for showers with large inclination angle. The estimated scale parameters R0, describing the slope of the lateral profiles range between 100 and 200 m. No evidence for a direct correlation of R0 with shower parameters like azimuth angle, geomagnetic angle, or primary energy can be found. This indicates that the lateral profile is an intrinsic property of the radio emission during the shower development which makes the radio detection technique suitable for large scale applications.

Measuring Plasma Formation Field Strength and Current Loss in Pulsed Power Diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnston, Mark D.; Patel, Sonal G.; Falcon, Ross Edward

This LDRD investigated plasma formation, field strength, and current loss in pulsed power diodes. In particular the Self-Magnetic Pinch (SMP) e-beam diode was studied on the RITS-6 accelerator. Magnetic fields of a few Tesla and electric fields of several MV/cm were measured using visible spectroscopy techniques. The magnetic field measurements were then used to determine the current distribution in the diode. This distribution showed that significant beam current extends radially beyond the few millimeter x-ray focal spot diameter. Additionally, shielding of the magnetic field due to dense electrode surface plasmas was observed, quantified, and found to be consistent with themore » calculated Spitzer resistivity. In addition to the work on RITS, measurements were also made on the Z-machine looking to quantify plasmas within the power flow regions. Measurements were taken in the post-hole convolute and final feed gap regions on Z. Dopants were applied to power flow surfaces and measured spectroscopically. These measurements gave species and density/temperature estimates. Preliminary B-field measurements in the load region were attempted as well. Finally, simulation work using the EMPHASIS, electromagnetic particle in cell code, was conducted using the Z MITL conditions. The purpose of these simulations was to investigate several surface plasma generations models under Z conditions for comparison with experimental data.« less

Electron and ion distribution functions in magnetopause reconnection

NASA Astrophysics Data System (ADS)

Wang, S.; Chen, L. J.; Bessho, N.; Hesse, M.; Kistler, L. M.; Torbert, R. B.; Mouikis, C.; Pollock, C. J.

2015-12-01

We investigate electron and ion velocity distribution functions in dayside magnetopause reconnection events observed by the Cluster and MMS spacecraft. The goal is to build a spatial map of electron and ion distribution features to enable the indication of the spacecraft location in the reconnection structure, and to understand plasma energization processes. Distribution functions, together with electromagnetic field structures, plasma densities, and bulk velocities, are organized and compared with particle-in-cell simulation results to indicate the proximities to the reconnection X-line. Anisotropic features in the distributions of magnetospheric- and magnetosheath- origin electrons at different locations in the reconnection inflow and exhaust are identified. In particular, parallel electron heating is observed in both the magnetosheath and magnetosphere inflow regions. Possible effects of the guide field strength, waves, and upstream density and temperature asymmetries on the distribution features will be discussed.

Investigating Whistler Mode Wave Diffusion Coefficients at Mars

NASA Astrophysics Data System (ADS)

Shane, A. D.; Liemohn, M. W.; Xu, S.; Florie, C.

2017-12-01

Observations of electron pitch angle distributions have suggested collisions are not the only pitch angle scattering process occurring in the Martian ionosphere. This unknown scattering process is causing high energy electrons (>100 eV) to become isotropized. Whistler mode waves are one pitch angle scattering mechanism known to preferentially scatter high energy electrons in certain plasma regimes. The distribution of whistler mode wave diffusion coefficients are dependent on the background magnetic field strength and thermal electron density, as well as the frequency and wave normal angle of the wave. We have solved for the whistler mode wave diffusion coefficients using the quasi-linear diffusion equations and have integrated them into a superthermal electron transport (STET) model. Preliminary runs have produced results that qualitatively match the observed electron pitch angle distributions at Mars. We performed parametric sweeps over magnetic field, thermal electron density, wave frequency, and wave normal angle to understand the relationship between the plasma parameters and the diffusion coefficient distributions, but also to investigate what regimes whistler mode waves scatter only high energy electrons. Increasing the magnetic field strength and lowering the thermal electron density shifts the distribution of diffusion coefficients toward higher energies and lower pitch angles. We have created an algorithm to identify Mars Atmosphere Volatile and EvolutioN (MAVEN) observations of high energy isotropic pitch angle distributions in the Martian ionosphere. We are able to map these distributions at Mars, and compare the conditions under which these are observed at Mars with the results of our parametric sweeps. Lastly, we will also look at each term in the kinetic diffusion equation to determine if the energy and mixed diffusion coefficients are important enough to incorporate into STET as well.

A family of metric gravities

NASA Astrophysics Data System (ADS)

Shuler, Robert

2018-04-01

The goal of this paper is to take a completely fresh approach to metric gravity, in which the metric principle is strictly adhered to but its properties in local space-time are derived from conservation principles, not inferred from a global field equation. The global field strength variation then gains some flexibility, but only in the regime of very strong fields (2nd-order terms) whose measurement is now being contemplated. So doing provides a family of similar gravities, differing only in strong fields, which could be developed into meaningful verification targets for strong fields after the manner in which far-field variations were used in the 20th century. General Relativity (GR) is shown to be a member of the family and this is demonstrated by deriving the Schwarzschild metric exactly from a suitable field strength assumption. The method of doing so is interesting in itself because it involves only one differential equation rather than the usual four. Exact static symmetric field solutions are also given for one pedagogical alternative based on potential, and one theoretical alternative based on inertia, and the prospects of experimentally differentiating these are analyzed. Whether the method overturns the conventional wisdom that GR is the only metric theory of gravity and that alternatives must introduce additional interactions and fields is somewhat semantical, depending on whether one views the field strength assumption as a field and whether the assumption that produces GR is considered unique in some way. It is of course possible to have other fields, and the local space-time principle can be applied to field gravities which usually are weak-field approximations having only time dilation, giving them the spatial factor and promoting them to full metric theories. Though usually pedagogical, some of them are interesting from a quantum gravity perspective. Cases are noted where mass measurement errors, or distributions of dark matter, can cause one theory to mimic another implying that such estimates or distributions should be first obtained from weakfield measurements before being used to discriminate verification candidates. By this method theorists gain insight into the local constraints on space-time, and GR verification gains strong-field comparative objectives.

Stable solitary waves in super dense plasmas at external magnetic fields

NASA Astrophysics Data System (ADS)

Ghaani, Azam; Javidan, Kurosh; Sarbishaei, Mohsen

2015-07-01

Propagation of localized waves in a Fermi-Dirac distributed super dense matter at the presence of strong external magnetic fields is studied using the reductive perturbation method. We have shown that stable solitons can be created in such non-relativistic fluids in the presence of an external magnetic field. Such solitary waves are governed by the Zakharov-Kuznetsov (ZK) equation. Properties of solitonic solutions are studied in media with different values of background mass density and strength of magnetic field.

In situ rock strength and far field stress in the Nankai accretionary complex: Integration of downhole data from multiple wells

NASA Astrophysics Data System (ADS)

Huffman, K. A.; Saffer, D. M.

2014-12-01

Knowing the magnitude of tectonic stress and rock strength at seismically active margins is important towards understanding fault strength and failure mechanics, yet both are difficult to measure in situ. Recent work at subduction margins, including Integrated Ocean Drilling Program (IODP) Nankai Trough Subduction Zone Experiment (NanTroSEIZE) drillsites, uses the width of compressional wellbore breakouts (BO), which depends on far field stress conditions, rock strength, and borehole annular pressure (APRS), to estimate the magnitude of horizontal principal stresses (SHmax and Shmin); estimates are problematic due to uncertainty in rock strength (unconfined compressive strength/UCS- for which direct measurements are scarce) and rheology that govern stress distribution at the wellbore. We conduct a novel case study at IODP Site C0002, where a hole was drilled twice with different boundary conditions, providing an opportunity to define in situ stress and strength from field data. Site C0002 is the main deep riser borehole for NanTroSEIZE, located near the seaward edge of the Kumano Basin above the seismogenic plate boundary, ~30 km from the trench. Several boreholes were drilled at the site. During IODP Expedition 314 in 2007, Hole C0002A was drilled with a suite of logging while drilling (LWD) tools to 1401 mbsf in a riserless mode. Hole C0002F, ~70 m away, was drilled to 862 mbsf in riserless mode during Exp. 326 in 2010 and deepened to 2005 mbsf in a riser mode during Expedition 338 in 2012-2013. Increased APRS achieved by riser drilling stabilizes the borehole and suppresses BO, consistent with resistivity imaging data from Exp. 314 that document well-developed, continuous BO throughout the borehole, and data from Expedition 338 indicating few BO. We use a semi-Newtonian approach to solve for stress and UCS consistent with the observed BO width and measured APRS in the two holes over the interval from 862-2005 mbsf. Effective SHmax ranges from ~10-30 MPa and indicate a strike-slip or thrust regime. Our results indicate UCS is higher than predicted by empirical relations and a small suite of laboratory tests by as much as 20 MPa. This apparent discrepancy may indicate that the failure criterion, or assumed distribution of stresses around the wellbore in analyses of far field stress, may not be appropriate in this setting.

Modeling knee joint endoprosthesis mode of deformation

NASA Astrophysics Data System (ADS)

Skeeba, V. Yu; Ivancivsky, V. V.

2018-03-01

The purpose of the work was to define the efficient design of the endoprosthesis, working in a multiple-cycle loading environment. Methodology and methods: triangulated surfaces of the base contact surfaces of endoprosthesis butt elements have been created using the PowerShape and SolidWorks software functional environment, and the assemblies of the possible combinations of the knee joint prosthetic designs have been prepared. The mode of deformation modeling took place in the multipurpose program complex ANSYS. Results and discussion: as a result of the numerical modeling, the following data were obtained for each of the developed knee joint versions: the distribution fields of absolute (total) and relative deformations; equivalent stress distribution fields; fatigue strength coefficient distribution fields. In the course of the studies, the following efficient design assembly has been established: 1) Ti-Al-V alloy composite femoral component with polymer inserts; 2) ceramic liners of the compound separator; 3) a Ti-Al-V alloy composite tibial component. The fatigue strength coefficient for the femoral component is 4.2; for the femoral component polymer inserts is 1.2; for the ceramic liners of the compound separator is 3.1; for the tibial component is 2.7. This promising endoprosthesis structure is recommended for further design and technological development.

Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks

DOE PAGES

Paz-Soldan, Carlos; Cooper, Christopher M.; Aleynikov, Pavel; ...

2017-06-22

Novel spatial, temporal, and energetically resolved measurements of bremsstrahlung hard-x-ray (HXR) emission from runaway electron (RE) populations in tokamaks reveal nonmonotonic RE distribution functions whose properties depend on the interplay of electric field acceleration with collisional and synchrotron damping. Measurements are consistent with theoretical predictions of momentum-space attractors that accumulate runaway electrons. RE distribution functions are measured to shift to a higher energy when the synchrotron force is reduced by decreasing the toroidal magnetic field strength. Increasing the collisional damping by increasing the electron density (at a fixed magnetic and electric field) reduces the energy of the nonmonotonic feature andmore » reduces the HXR growth rate at all energies. Higher-energy HXR growth rates extrapolate to zero at the expected threshold electric field for RE sustainment, while low-energy REs are anomalously lost. The compilation ofHXR emission from different sight lines into the plasma yields energy and pitch-angle-resolved RE distributions and demonstrates increasing pitch-angle and radial gradients with energy.« less

Collapse and revival of entanglement between qubits coupled to a spin coherent state

NASA Astrophysics Data System (ADS)

Bahari, Iskandar; Spiller, Timothy P.; Dooley, Shane; Hayes, Anthony; McCrossan, Francis

We extend the study of the Jayne-Cummings (JC) model involving a pair of identical two-level atoms (or qubits) interacting with a single mode quantized field. We investigate the effects of replacing the radiation field mode with a composite spin, comprising N qubits, or spin-1/2 particles. This model is relevant for physical implementations in superconducting circuit QED, ion trap and molecular systems. For the case of the composite spin prepared in a spin coherent state, we demonstrate the similarities of this set-up to the qubits-field model in terms of the time evolution, attractor states and in particular the collapse and revival of the entanglement between the two qubits. We extend our analysis by taking into account an effect due to qubit imperfections. We consider a difference (or “mismatch”) in the dipole interaction strengths of the two qubits, for both the field mode and composite spin cases. To address decoherence due to this mismatch, we then average over this coupling strength difference with distributions of varying width. We demonstrate in both the field mode and the composite spin scenarios that increasing the width of the “error” distribution increases suppression of the coherent dynamics of the coupled system, including the collapse and revival of the entanglement between the qubits.

CSEM-Steel hybrid wiggler/undulator magnetic field studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halbach, K.; Hoyer, E.; Marks, S.

1985-06-01

Current design of permanent magnet wiggler/undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing transverse configuration influence on performance, from a combination of models using CSEMs, REC (H/sub c/ = 9.2 KOe) and NdFe (H/sub c/ = 10.7 kOe), different pole widths and end configurations. Results show peak field improvement using NdFe in placemore » of REC in identical models, gap peak field decrease with pole width decrease (all results less than computed 2-D fields), transverse gap field distributions, and importance of CSEM material overhanging the poles in the transverse direction for highest gap fields. 3 refs., 6 figs.« less

The magnetic field and abundance distribution geometry of the peculiar A star 53 Camelopardalis

NASA Astrophysics Data System (ADS)

Landstreet, J. D.

1988-03-01

New spectra have been obtained of the magnetic Ap star 53 Cam, well spaced through its 8.03 day rotation period, covering the spectral regions λλ3900 - 3960 and 4250 - 4315. These data, and previously obtained Hβ Zeeman analyzer observations of the longitudinal field strength, have been used to derive models of the magnetic field geometry and the abundance distributions of Ca, Cr, Fe, Sr, and Ti. The models have been obtained by use of a new line synthesis program that incorporates the effects of an assumed magnetic field and abundance distribution into the calculation of line profiles. Calculated profiles are compared with observations. The model is used to derive a radius of R/R_sun; = 2.3±0.4, a luminosity of log L/L_sun; = 1.4±0.17, and a mass of M/M_sun; = 2.0±0.3 for 53 Cam.

Life prediction and mechanical reliability of NT551 silicon nitride

NASA Astrophysics Data System (ADS)

Andrews, Mark Jay

The inert strength and fatigue performance of a diesel engine exhaust valve made from silicon nitride (Si3N4) ceramic were assessed. The Si3N4 characterized in this study was manufactured by Saint Gobain/Norton Industrial Ceramics and was designated as NT551. The evaluation was made utilizing a probabilistic life prediction algorithm that combined censored test specimen strength data with a Weibull distribution function and the stress field of the ceramic valve obtained from finite element analysis. The major assumptions of the life prediction algorithm are that the bulk ceramic material is isotropic and homogeneous and that the strength-limiting flaws are uniformly distributed. The results from mechanical testing indicated that NT551 was not a homogeneous ceramic and that its strength were functions of temperature, loading rate, and machining orientation. Fractographic analysis identified four different failure modes; 2 were identified as inhomogeneities that were located throughout the bulk of NT551 and were due to processing operations. The fractographic analysis concluded that the strength degradation of NT551 observed from the temperature and loading rate test parameters was due to a change of state that occurred in its secondary phase. Pristine and engine-tested valves made from NT551 were loaded to failure and the inert strengths were obtained. Fractographic analysis of the valves identified the same four failure mechanisms as found with the test specimens. The fatigue performance and the inert strength of the Si3N 4 valves were assessed from censored and uncensored test specimen strength data, respectively. The inert strength failure probability predictions were compared to the inert strength of the Si3N4 valves. The inert strength failure probability predictions were more conservative than the strength of the valves. The lack of correlation between predicted and actual valve strength was due to the nonuniform distribution of inhomogeneities present in NT551. For the same reasons, the predicted and actual fatigue performance did not correlate well. The results of this study should not be considered a limitation of the life prediction algorithm but emphasize the requirement that ceramics be homogeneous and strength-limiting flaws uniformly distributed as a perquisite for accurate life prediction and reliability analyses.

Magnetic drug targeting through a realistic model of human tracheobronchial airways using computational fluid and particle dynamics.

PubMed

Pourmehran, Oveis; Gorji, Tahereh B; Gorji-Bandpy, Mofid

2016-10-01

Magnetic drug targeting (MDT) is a local drug delivery system which aims to concentrate a pharmacological agent at its site of action in order to minimize undesired side effects due to systemic distribution in the organism. Using magnetic drug particles under the influence of an external magnetic field, the drug particles are navigated toward the target region. Herein, computational fluid dynamics was used to simulate the air flow and magnetic particle deposition in a realistic human airway geometry obtained by CT scan images. Using discrete phase modeling and one-way coupling of particle-fluid phases, a Lagrangian approach for particle tracking in the presence of an external non-uniform magnetic field was applied. Polystyrene (PMS40) particles were utilized as the magnetic drug carrier. A parametric study was conducted, and the influence of particle diameter, magnetic source position, magnetic field strength and inhalation condition on the particle transport pattern and deposition efficiency (DE) was reported. Overall, the results show considerable promise of MDT in deposition enhancement at the target region (i.e., left lung). However, the positive effect of increasing particle size on DE enhancement was evident at smaller magnetic field strengths (Mn [Formula: see text] 1.5 T), whereas, at higher applied magnetic field strengths, increasing particle size has a inverse effect on DE. This implies that for efficient MTD in the human respiratory system, an optimal combination of magnetic drug career characteristics and magnetic field strength has to be achieved.

High-frequency spectral falloff of earthquakes, fractal dimension of complex rupture, b value, and the scaling of strength on faults

USGS Publications Warehouse

Frankel, A.

1991-01-01

The high-frequency falloff ??-y of earthquake displacement spectra and the b value of aftershock sequences are attributed to the character of spatially varying strength along fault zones. I assume that the high frequency energy of a main shock is produced by a self-similar distribution of subevents, where the number of subevents with radii greater than R is proportional to R-D, D being the fractal dimension. In the model, an earthquake is composed of a hierarchical set of smaller earthquakes. The static stress drop is parameterized to be proportional to R??, and strength is assumed to be proportional to static stress drop. I find that a distribution of subevents with D = 2 and stress drop independent of seismic moment (?? = 0) produces a main shock with an ??-2 falloff, if the subevent areas fill the rupture area of the main shock. By equating subevents to "islands' of high stress of a random, self-similar stress field on a fault, I relate D to the scaling of strength on a fault, such that D = 2 - ??. Thus D = 2 corresponds to constant stress drop scaling (?? = 0) and scale-invariant fault strength. A self-similar model of aftershock rupture zones on a fault is used to determine the relationship between the b value, the size distribution of aftershock rupture zones, and the scaling of strength on a fault. -from Author

Random-field-induced disordering mechanism in a disordered ferromagnet: Between the Imry-Ma and the standard disordering mechanism

NASA Astrophysics Data System (ADS)

Andresen, Juan Carlos; Katzgraber, Helmut G.; Schechter, Moshe

2017-12-01

Random fields disorder Ising ferromagnets by aligning single spins in the direction of the random field in three space dimensions, or by flipping large ferromagnetic domains at dimensions two and below. While the former requires random fields of typical magnitude similar to the interaction strength, the latter Imry-Ma mechanism only requires infinitesimal random fields. Recently, it has been shown that for dilute anisotropic dipolar systems a third mechanism exists, where the ferromagnetic phase is disordered by finite-size glassy domains at a random field of finite magnitude that is considerably smaller than the typical interaction strength. Using large-scale Monte Carlo simulations and zero-temperature numerical approaches, we show that this mechanism applies to disordered ferromagnets with competing short-range ferromagnetic and antiferromagnetic interactions, suggesting its generality in ferromagnetic systems with competing interactions and an underlying spin-glass phase. A finite-size-scaling analysis of the magnetization distribution suggests that the transition might be first order.

General-relativistic pulsar magnetospheric emission

NASA Astrophysics Data System (ADS)

Pétri, J.

2018-06-01

Most current pulsar emission models assume photon production and emission within the magnetosphere. Low-frequency radiation is preferentially produced in the vicinity of the polar caps, whereas the high-energy tail is shifted to regions closer but still inside the light cylinder. We conducted a systematic study of the merit of several popular radiation sites like the polar cap, the outer gap, and the slot gap. We computed sky maps emanating from each emission site according to a prescribed distribution function for the emitting particles made of an electron/positron mixture. Calculations are performed using a three-dimensional integration of the plasma emissivity in the vacuum electromagnetic field of a rotating and centred general-relativistic dipole. We compare Newtonian electromagnetic fields to their general-relativistic counterpart. In the latter case, light bending is also taken into account. As a typical example, light curves and sky maps are plotted for several power-law indices of the particle distribution function. The detailed pulse profiles strongly depend on the underlying assumption about the fluid motion subject to strong electromagnetic fields. This electromagnetic topology enforces the photon propagation direction directly, or indirectly, from aberration effects. We also discuss the implication of a net stellar electric charge on to sky maps. Taking into account, the electric field strongly affects the light curves originating close to the light cylinder, where the electric field strength becomes comparable to the magnetic field strength.

Snow Roads at McMurdo Station, Antarctica

DTIC Science & Technology

2010-05-01

is minimized distribution of low strength areas (also called “ holidays ”). Holidays are actually areas of pulverized snow that are missed or inade...quately processed. Though holidays usually occur sporadically, any single flaw may extend through the entire thickness of an unelevated road. The...Pegasus Road and the LDB pad. A few additional sites were chosen for comparison (Williams Field, virgin snow, etc.). Williams Field Road densities

A search for cataclysmic binaries containing strongly magnetic white dwarfs

NASA Technical Reports Server (NTRS)

Bond, H. E.; Chanmugam, G.

1982-01-01

The AM Herculis type binaries which contain accreting white dwarfs with surface magnetic fields of a few times 10 to the seventh power gauss were studied. If white dwarfs in cataclysmic binaries have a range of field strengths similar to that among single white dwarfs. AM Her like systems should exist with fields as high as 3 x 10 to the eighth power gauss. It is suggested that such objects will not have the strong optical polarization of the AM Her variables; however, they exhibit high harmonic cyclotron emission, making them spectacular UV sources. We made IUE observations of seven candidate cataclysmic variables selected for optical similarity to AM Her binaries. Although all seven objects were detected in the UV, none display unusually strong UV continua. It is suggested that the distribution of magnetic field strengths among single white dwarfs may be different from that among binaries.

DC breakdown characteristics of silicone polymer composites for HVDC insulator applications

NASA Astrophysics Data System (ADS)

Han, Byung-Jo; Seo, In-Jin; Seong, Jae-Kyu; Hwang, Young-Ho; Yang, Hai-Won

2015-11-01

Critical components for HVDC transmission systems are polymer insulators, which have stricter requirements that are more difficult to achieve compared to those of HVAC insulators. In this study, we investigated the optimal design of HVDC polymer insulators by using a DC electric field analysis and experiments. The physical properties of the polymer specimens were analyzed to develop an optimal HVDC polymer material, and four polymer specimens were prepared for DC breakdown experiments. Single and reverse polarity breakdown tests were conducted to analyze the effect of temperature on the breakdown strength of the polymer. In addition, electric fields were analyzed via simulations, in which a small-scale polymer insulator model was applied to prevent dielectric breakdown due to electric field concentration, with four DC operating conditions taken into consideration. The experimental results show that the electrical breakdown strength and the electric field distribution exhibit significant differences in relation to different DC polarity transition procedures.

Nanometer scale composition study of MBE grown BGaN performed by atom probe tomography

NASA Astrophysics Data System (ADS)

Bonef, Bastien; Cramer, Richard; Speck, James S.

2017-06-01

Laser assisted atom probe tomography is used to characterize the alloy distribution in BGaN. The effect of the evaporation conditions applied on the atom probe specimens on the mass spectrum and the quantification of the III site atoms is first evaluated. The evolution of the Ga++/Ga+ charge state ratio is used to monitor the strength of the applied field. Experiments revealed that applying high electric fields on the specimen results in the loss of gallium atoms, leading to the over-estimation of boron concentration. Moreover, spatial analysis of the surface field revealed a significant loss of atoms at the center of the specimen where high fields are applied. A good agreement between X-ray diffraction and atom probe tomography concentration measurements is obtained when low fields are applied on the tip. A random distribution of boron in the BGaN layer grown by molecular beam epitaxy is obtained by performing accurate and site specific statistical distribution analysis.

Modelling element distributions in the atmospheres of magnetic Ap stars

NASA Astrophysics Data System (ADS)

Alecian, G.; Stift, M. J.

2007-11-01

Context: In recent papers convincing evidence has been presented for chemical stratification in Ap star atmospheres, and surface abundance maps have been shown to correlate with the magnetic field direction. Radiatively driven diffusion, which is known to be sensitive to the magnetic field strength and direction, is among the processes responsible for these inhomogeneities. Aims: Here we explore the hypothesis that equilibrium stratifications - such that the diffusive particle flux is close to zero throughout the atmosphere - can, in a number of cases, explain the observed abundance maps and vertical distributions of the various elements. Methods: An iterative scheme adjusts the abundances in such a way as to achieve either zero particle flux or zero effective acceleration throughout the atmosphere, taking strength and direction of the magnetic field into account. Results: The investigation of equilibrium stratifications in stellar atmospheres with temperatures from 8500 to 12 000 K and fields up to 10 kG reveals considerable variations in the vertical distribution of the 5 elements studied (Mg, Si, Ca, Ti, Fe), often with zones of large over- or under-abundances and with indications of other competing processes (such as mass loss). Horizontal magnetic fields can be very efficient in helping the accumulation of elements in higher layers. Conclusions: A comparison between our calculations and the vertical abundance profiles and surface maps derived by magnetic Doppler imaging reveals that equilibrium stratifications are in a number of cases consistent with the main trends inferred from observed spectra. However, it is not clear whether such equilibrium solutions will ever be reached during the evolution of an Ap star.

Block rotations, fault domains and crustal deformation in the western US

NASA Technical Reports Server (NTRS)

Nur, Amos

1990-01-01

The aim of the project was to develop a 3D model of crustal deformation by distributed fault sets and to test the model results in the field. In the first part of the project, Nur's 2D model (1986) was generalized to 3D. In Nur's model the frictional strength of rocks and faults of a domain provides a tight constraint on the amount of rotation that a fault set can undergo during block rotation. Domains of fault sets are commonly found in regions where the deformation is distributed across a region. The interaction of each fault set causes the fault bounded blocks to rotate. The work that has been done towards quantifying the rotation of fault sets in a 3D stress field is briefly summarized. In the second part of the project, field studies were carried out in Israel, Nevada and China. These studies combined both paleomagnetic and structural information necessary to test the block rotation model results. In accordance with the model, field studies demonstrate that faults and attending fault bounded blocks slip and rotate away from the direction of maximum compression when deformation is distributed across fault sets. Slip and rotation of fault sets may continue as long as the earth's crustal strength is not exceeded. More optimally oriented faults must form, for subsequent deformation to occur. Eventually the block rotation mechanism may create a complex pattern of intersecting generations of faults.

Magnetic field effects on the energy deposition spectra of MV photon radiation.

PubMed

Kirkby, C; Stanescu, T; Fallone, B G

2009-01-21

Several groups worldwide have proposed various concepts for improving megavoltage (MV) radiotherapy that involve irradiating patients in the presence of a magnetic field-either for image guidance in the case of hybrid radiotherapy-MRI machines or for purposes of introducing tighter control over dose distributions. The presence of a magnetic field alters the trajectory of charged particles between interactions with the medium and thus has the potential to alter energy deposition patterns within a sub-cellular target volume. In this work, we use the MC radiation transport code PENELOPE with appropriate algorithms invoked to incorporate magnetic field deflections to investigate electron energy fluence in the presence of a uniform magnetic field and the energy deposition spectra within a 10 microm water sphere as a function of magnetic field strength. The simulations suggest only very minor changes to the electron fluence even for extremely strong magnetic fields. Further, calculations of the dose-averaged lineal energy indicate that a magnetic field strength of at least 70 T is required before beam quality will change by more than 2%.

Geotechnical sensing using electromagnetic attenuation between radio transceivers

NASA Astrophysics Data System (ADS)

Ghazanfari, Ehsan; Pamukcu, Sibel; Yoon, Suk-Un; Suleiman, Muhannad T.; Cheng, Liang

2012-12-01

Monitoring the onset of a geo-event such as the intrusion of a chemical plume or a slow progressive mass slide that results in marked changes in the physical properties of the host soil could be potentially accomplished using a distributed network of embedded radio transceivers. This paper introduces a new concept of subsurface geo-event monitoring, which takes advantage of the spatial and temporal variations in signal strength of electromagnetic (EM) waves transmitted within the net of distributed radios within a sensing area. Results of experiments in the laboratory and the field demonstrated that variations in EM signal strength could be used to detect physical changes in the subsurface. Changes in selected physical properties of host soil including water content, density, and formation of discontinuities could be discerned from the changes in the signal strength of the transmitted wave between embedded radio transceivers. Good agreement was observed between a theoretical model and the experimental results for inter-transceiver distances less than 55 cm. These results demonstrated a viable new approach for distributed sensing and monitoring of subsurface hazards for civil infrastructure within a networked domain of radio transceivers.

THE DEPENDENCE OF STELLAR MASS AND ANGULAR MOMENTUM LOSSES ON LATITUDE AND THE INTERACTION OF ACTIVE REGION AND DIPOLAR MAGNETIC FIELDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garraffo, Cecilia; Drake, Jeremy J.; Cohen, Ofer

Rotation evolution of late-type stars is dominated by magnetic braking and the underlying factors that control this angular momentum loss are important for the study of stellar spin-down. In this work, we study angular momentum loss as a function of two different aspects of magnetic activity using a calibrated Alfvén wave-driven magnetohydrodynamic wind model: the strengths of magnetic spots and their distribution in latitude. By driving the model using solar and modified solar surface magnetograms, we show that the topology of the field arising from the net interaction of both small-scale and large-scale field is important for spin-down rates andmore » that angular momentum loss is not a simple function of large scale magnetic field strength. We find that changing the latitude of magnetic spots can modify mass and angular momentum loss rates by a factor of two. The general effect that causes these differences is the closing down of large-scale open field at mid- and high-latitudes by the addition of the small-scale field. These effects might give rise to modulation of mass and angular momentum loss through stellar cycles, and present a problem for ab initio attempts to predict stellar spin-down based on wind models. For all the magnetogram cases considered here, from dipoles to various spotted distributions, we find that angular momentum loss is dominated by the mass loss at mid-latitudes. The spin-down torque applied by magnetized winds therefore acts at specific latitudes and is not evenly distributed over the stellar surface, though this aspect is unlikely to be important for understanding spin-down and surface flows on stars.« less

Imaging shear strength along subduction faults

USGS Publications Warehouse

Bletery, Quentin; Thomas, Amanda M.; Rempel, Alan W.; Hardebeck, Jeanne L.

2017-01-01

Subduction faults accumulate stress during long periods of time and release this stress suddenly, during earthquakes, when it reaches a threshold. This threshold, the shear strength, controls the occurrence and magnitude of earthquakes. We consider a 3-D model to derive an analytical expression for how the shear strength depends on the fault geometry, the convergence obliquity, frictional properties, and the stress field orientation. We then use estimates of these different parameters in Japan to infer the distribution of shear strength along a subduction fault. We show that the 2011 Mw9.0 Tohoku earthquake ruptured a fault portion characterized by unusually small variations in static shear strength. This observation is consistent with the hypothesis that large earthquakes preferentially rupture regions with relatively homogeneous shear strength. With increasing constraints on the different parameters at play, our approach could, in the future, help identify favorable locations for large earthquakes.

The exponential rise of induced seismicity with increasing stress levels in the Groningen gas field and its implications for controlling seismic risk

NASA Astrophysics Data System (ADS)

Bourne, S. J.; Oates, S. J.; van Elk, J.

2018-06-01

Induced seismicity typically arises from the progressive activation of recently inactive geological faults by anthropogenic activity. Faults are mechanically and geometrically heterogeneous, so their extremes of stress and strength govern the initial evolution of induced seismicity. We derive a statistical model of Coulomb stress failures and associated aftershocks within the tail of the distribution of fault stress and strength variations to show initial induced seismicity rates will increase as an exponential function of induced stress. Our model provides operational forecasts consistent with the observed space-time-magnitude distribution of earthquakes induced by gas production from the Groningen field in the Netherlands. These probabilistic forecasts also match the observed changes in seismicity following a significant and sustained decrease in gas production rates designed to reduce seismic hazard and risk. This forecast capability allows reliable assessment of alternative control options to better inform future induced seismic risk management decisions.

High-ionic-strength electroosmotic flows in uncharged hydrophobic nanochannels.

PubMed

Kim, Daejoong; Darve, Eric

2009-02-01

We report molecular dynamics simulation results of high-ionic-strength electroosmotic flows inside uncharged nanochannels. The possibility of this unusual electrokinetic phenomenon has been discussed by Dukhin et al. [A. Dukhin, S. Dukhin, P. Goetz, Langmuir 21 (2005) 9990]. Our computed velocity profiles clearly indicate the presence of a net flow with a maximum velocity around 2 m/s. We found the apparent zeta potential to be -29.7+/-6.8 mV, using the Helmholtz-Smoluchowski relation and the measured mean velocity. This value is comparable to experimentally measured values in Dukhin et al. and references therein. We also investigate the orientations of water molecules in response to an electric field by computing polarization density. Water molecules in the bulk region are oriented along the direction of the external electric field, while their near-wall orientation shows oscillations. The computation of three-dimensional density distributions of sodium and chloride ions around each individual water molecule show that chloride ions tend to concentrate near a water molecule, whereas sodium ions are diffusely distributed.

Outdoor characterization of radio frequency electromagnetic fields in a Spanish birth cohort

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calvente, I.; Department of Radiology and Physical Medicine, School of Medicine, University of Granada, Av. Madreid s/n, Granada 18071; Fernández, M.F.

There is considerable public concern in many countries about the possible adverse effects of exposure to non-ionizing radiation electromagnetic fields, especially in vulnerable populations such as children. The aim of this study was to characterize environmental exposure profiles within the frequency range 100 kHz–6 GHz in the immediate surrounds of the dwellings of 123 families from the INMA-Granada birth cohort in Southern Spain, using spot measurements. The arithmetic mean root mean-square electric field (E{sub RMS}) and power density (S{sub RMS}) values were, respectively, 195.79 mV/m (42.3% of data were above this mean) and 799.01 µW/m{sup 2} (30% of values weremore » above this mean); median values were 148.80 mV/m and 285.94 µW/m{sup 2}, respectively. Exposure levels below the quantification limit were assigned a value of 0.01 V/m. Incident field strength levels varied widely among different areas or towns/villages, demonstrating spatial variability in the distribution of exposure values related to the surface area population size and also among seasons. Although recorded values were well below International Commission for Non-Ionizing Radiation Protection reference levels, there is a particular need to characterize incident field strength levels in vulnerable populations (e.g., children) because of their chronic and ever-increasing exposure. The effects of incident field strength have not been fully elucidated; however, it may be appropriate to apply the precautionary principle in order to reduce exposure in susceptible groups. - Highlights: • Spot measurements were performed in the immediate surrounds of children's dwellings. • Mean root mean-square electric field and power density values were calculated. • Most recorded values were far below international standard guideline limits. • Data demonstrate spatial variability in the distribution of exposure levels. • While adverse effects are proven, application of the precautionary principle may be appropriate.« less

A model for predicting field-directed particle transport in the magnetofection process.

PubMed

Furlani, Edward P; Xue, Xiaozheng

2012-05-01

To analyze the magnetofection process in which magnetic carrier particles with surface-bound gene vectors are attracted to target cells for transfection using an external magnetic field and to obtain a fundamental understanding of the impact of key factors such as particle size and field strength on the gene delivery process. A numerical model is used to study the field-directed transport of the carrier particle-gene vector complex to target cells in a conventional multiwell culture plate system. The model predicts the transport dynamics and the distribution of particle accumulation at the target cells. The impact of several factors that strongly influence gene vector delivery is assessed including the properties of the carrier particles, the strength of the field source, and its extent and proximity relative to the target cells. The study demonstrates that modeling can be used to predict and optimize gene vector delivery in the magnetofection process for novel and conventional in vitro systems.

CONSTRAINING THE SOLAR CORONAL MAGNETIC FIELD STRENGTH USING SPLIT-BAND TYPE II RADIO BURST OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kishore, P.; Ramesh, R.; Hariharan, K.

2016-11-20

We report on low-frequency radio (85–35 MHz) spectral observations of four different type II radio bursts, which exhibited fundamental-harmonic emission and split-band structure. Each of the bursts was found to be closely associated with a whitelight coronal mass ejection (CME) close to the Sun. We estimated the coronal magnetic field strength from the split-band characteristics of the bursts, by assuming a model for the coronal electron density distribution. The choice of the model was constrained, based on the following criteria: (1) when the radio burst is observed simultaneously in the upper and lower bands of the fundamental component, the locationmore » of the plasma level corresponding to the frequency of the burst in the lower band should be consistent with the deprojected location of the leading edge (LE) of the associated CME; (2) the drift speed of the type II bursts derived from such a model should agree closely with the deprojected speed of the LE of the corresponding CMEs. With the above conditions, we find that: (1) the estimated field strengths are unique to each type II burst, and (2) the radial variation of the field strength in the different events indicate a pattern. It is steepest for the case where the heliocentric distance range over which the associated burst is observed is closest to the Sun, and vice versa.« less

Photospheric magnetic fields

NASA Technical Reports Server (NTRS)

Howard, R.

1972-01-01

Knowledge on the nature of magnetic fields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magnetic fields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.

Dynamic weight evolution network with preferential attachment

NASA Astrophysics Data System (ADS)

Dai, Meifeng; Xie, Qi; Li, Lei

2014-12-01

A dynamic weight evolution network with preferential attachment is introduced. The network includes two significant characteristics. (i) Topological growth: triggered by newly added node with M links at each time step, each new edge carries an initial weight growing nonlinearly with time. (ii) Weight dynamics: the weight between two existing nodes experiences increasing or decreasing in a nonlinear way. By using continuum theory and mean-field method, we study the strength, the degree, the weight and their distributions. We find that the distributions exhibit a power-law feature. In particular, the relationship between the degree and the strength is nonlinear, and the power-law exponents of the three are the same. All the theoretical predictions are successfully contrasted with numerical simulations.

Study of light-absorbing crystal birefringence and electrical modulation mechanisms for coupled thermal-optical effects.

PubMed

Zhou, Ji; He, Zhihong; Ma, Yu; Dong, Shikui

2014-09-20

This paper discusses Gaussian laser transmission in double-refraction crystal whose incident light wavelength is within its absorption wave band. Two scenarios for coupled radiation and heat conduction are considered: one is provided with an applied external electric field, the other is not. A circular heat source with a Gaussian energy distribution is introduced to present the crystal's light-absorption process. The electromagnetic field frequency domain analysis equation and energy equation are solved to simulate the phenomenon by using the finite element method. It focuses on the influence of different values such as wavelength, incident light intensity, heat transfer coefficient, ambient temperature, crystal thickness, and applied electric field strength. The results show that the refraction index of polarized light increases with the increase of crystal temperature. It decreases as the strength of the applied electric field increases if it is positive. The mechanism of electrical modulation for the thermo-optical effect is used to keep the polarized light's index of refraction constant in our simulation. The quantitative relation between thermal boundary condition and strength of applied electric field during electrical modulation is determined. Numerical results indicate a possible approach to removing adverse thermal effects such as depolarization and wavefront distortion, which are caused by thermal deposition during linear laser absorption.

Research on Orbital Plasma-Electrodynamics (ROPE)

NASA Technical Reports Server (NTRS)

Wu, S. T.; Wright, K.

1994-01-01

Since the development of probe theory by Langmuir and Blodgett, the problem of current collection by a charged spherically or cylindrically symmetric body has been investigated by a number of authors. This paper overviews the development of a fully three-dimensional particle simulation code which can be used to understand the physics of current collection in three dimensions and can be used to analyze data resulting from the future tethered satellite system (TSS). According to the TSS configurations, two types of particle simulation models were constructed: a simple particle simulation (SIPS) and a super particle simulation (SUPS). The models study the electron transient response and its asymptotic behavior around a three dimensional, highly biased satellite. The potential distribution surrounding the satellite is determined by solving Laplace's equation in the SIPS model and by solving Poisson's equation in the SUPS model. Thus, the potential distribution in space is independent of the density distribution of the particles in the SUPS model but it does depend on the density distribution of the particles in the SUPS model. The evolution of the potential distribution in the SUPS model is described. When the spherical satellite is charged to a highly positive potential and immersed in a plasma with a uniform magnetic field, the formation of an electron torus in the equatorial plane (the plane in perpendicular to the magnetic field) and elongation of the torus along the magnetic field are found in both the SIPS and the SUPS models but the shape of the torus is different. The areas of high potential that exist in the polar regions in the SUPS model exaggerate the elongation of the electron torus along the magnetic field. The current collected by the satellite for different magentic field strengths is investigated in both models. Due to the nonlinear effects present in SUPS, the oscillating phenomenon of the current collection curve during the first 10 plasma periods can be seen (this does not appear in SIPS). From the parametric studies, it appears that the oscillating phenomenon of the current collection curve occurs only when the magnetic field strength is less than 0.2 gauss for the present model.

Small amplitude two dimensional electrostatic excitations in a magnetized dusty plasma with q-distributed electrons

NASA Astrophysics Data System (ADS)

Khan, Shahab Ullah; Adnan, Muhammad; Qamar, Anisa; Mahmood, Shahzad

2016-07-01

The propagation of linear and nonlinear electrostatic waves is investigated in magnetized dusty plasma with stationary negatively or positively charged dust, cold mobile ions and non-extensive electrons. Two normal modes are predicted in the linear regime, whose characteristics are investigated parametrically, focusing on the effect of electrons non-extensivity, dust charge polarity, concentration of dust and magnetic field strength. Using the reductive perturbation technique, a Zakharov-Kuznetsov (ZK) type equation is derived which governs the dynamics of small-amplitude solitary waves in magnetized dusty plasma. The properties of the solitary wave structures are analyzed numerically with the system parameters i.e. electrons non-extensivity, concentration of dust, polarity of dust and magnetic field strength. Following Allen and Rowlands (J. Plasma Phys. 53:63, 1995), we have shown that the pulse soliton solution of the ZK equation is unstable, and have analytically traced the dependence of the instability growth rate on the nonextensive parameter q for electrons, dust charge polarity and magnetic field strength. The results should be useful for understanding the nonlinear propagation of DIA solitary waves in laboratory and space plasmas.

Star-disk interaction in Herbig Ae/Be stars

NASA Astrophysics Data System (ADS)

Speights, Christa Marie

2012-09-01

The question of the mechanism of certain types of stars is important. Classical T Tauri (CTTS) stars accrete magnetospherically, and Herbig Ae/Be stars (higher-mass analogs to CTTS) are thought to also accrete magnetospherically, but the source of a kG magnetic field is unknown, since these stars have radiative interiors. For magnetospheric accretion, an equation has been derived (Hartmann, 2001) which relates the truncation radius, stellar radius, stellar mass, mass accretion rate and magnetic field strength. Currently the magnetic field of Herbig stars is known to be somewhere between 0.1 kG and 10 kG. One goal of this research is to further constrain the magnetic field. In order to do that, I use the magnetospheric accretion equation. For CTTS, all of the variables used in the equation can be measured, so I gather this data from the literature and test the equation and find that it is consistent. Then I apply the equation to Herbig Ae stars and find that the error introduced from using random inclinations is too large to lower the current upper limit of the magnetic field range. If Herbig Ae stars are higher-mass analogs to CTTS, then they should have a similar magnetic field distribution. I compare the calculated Herbig Ae magnetic field distribution to several typical magnetic field distributions using the Kolmogorov-Smirnov test, and find that the data distribution does not match any of the distributions used. This means that Herbig Ae stars do not have well ordered kG fields like CTTS.

A new estimate of average dipole field strength for the last five million years

NASA Astrophysics Data System (ADS)

Cromwell, G.; Tauxe, L.; Halldorsson, S. A.

2013-12-01

The Earth's ancient magnetic field can be approximated by a geocentric axial dipole (GAD) where the average field intensity is twice as strong at the poles than at the equator. The present day geomagnetic field, and some global paleointensity datasets, support the GAD hypothesis with a virtual axial dipole moment (VADM) of about 80 ZAm2. Significant departures from GAD for 0-5 Ma are found in Antarctica and Iceland where paleointensity experiments on massive flows (Antarctica) (1) and volcanic glasses (Iceland) produce average VADM estimates of 41.4 ZAm2 and 59.5 ZAm2, respectively. These combined intensities are much closer to a lower estimate for long-term dipole field strength, 50 ZAm2 (2), and some other estimates of average VADM based on paleointensities strictly from volcanic glasses. Proposed explanations for the observed non-GAD behavior, from otherwise high-quality paleointensity results, include incomplete temporal sampling, effects from the tangent cylinder, and hemispheric asymmetry. Differences in estimates of average magnetic field strength likely arise from inconsistent selection protocols and experiment methodologies. We address these possible biases and estimate the average dipole field strength for the last five million years by compiling measurement level data of IZZI-modified paleointensity experiments from lava flows around the globe (including new results from Iceland and the HSDP-2 Hawaii drill core). We use the Thellier Gui paleointensity interpreter (3) in order to apply objective criteria to all specimens, ensuring consistency between sites. Specimen level selection criteria are determined from a recent paleointensity investigation of modern Hawaiian lava flows where the expected magnetic field strength was accurately recovered when following certain selection parameters. Our new estimate of average dipole field strength for the last five million years incorporates multiple paleointensity studies on lava flows with diverse global and temporal distributions, and objectively constrains site level estimates by applying uniform selection requirements on measurement level data. (1) Lawrence, K.P., L. Tauxe, H. Staudigel, C.G. Constable, A. Koppers, W. McIntosh, C.L. Johnson, Paleomagnetic field properties at high southern latitude, Geochemistry Geophysics Geosystems, 10, 2009. (2) Selkin, P.A., L. Tauxe, Long-term variations in palaeointensity, Phil. Trans. R. Soc. Lond., 358, 1065-1088, 2000. (3) Shaar, R., L. Tauxe, Thellier GUI: An integrated tool for analyzing paleointensity data from Thellier-type experiments, Geochemistry Geophysics Geosystems, 14, 2013

Benchmark calculations of nonconservative charged-particle swarms in dc electric and magnetic fields crossed at arbitrary angles.

PubMed

Dujko, S; White, R D; Petrović, Z Lj; Robson, R E

2010-04-01

A multiterm solution of the Boltzmann equation has been developed and used to calculate transport coefficients of charged-particle swarms in gases under the influence of electric and magnetic fields crossed at arbitrary angles when nonconservative collisions are present. The hierarchy resulting from a spherical-harmonic decomposition of the Boltzmann equation in the hydrodynamic regime is solved numerically by representing the speed dependence of the phase-space distribution function in terms of an expansion in Sonine polynomials about a Maxwellian velocity distribution at an internally determined temperature. Results are given for electron swarms in certain collisional models for ionization and attachment over a range of angles between the fields and field strengths. The implicit and explicit effects of ionization and attachment on the electron-transport coefficients are considered using physical arguments. It is found that the difference between the two sets of transport coefficients, bulk and flux, resulting from the explicit effects of nonconservative collisions, can be controlled either by the variation in the magnetic field strengths or by the angles between the fields. In addition, it is shown that the phenomena of ionization cooling and/or attachment cooling/heating previously reported for dc electric fields carry over directly to the crossed electric and magnetic fields. The results of the Boltzmann equation analysis are compared with those obtained by a Monte Carlo simulation technique. The comparison confirms the theoretical basis and numerical integrity of the moment method for solving the Boltzmann equation and gives a set of well-established data that can be used to test future codes and plasma models.

Genesis of magnetic fields in isolated white dwarfs

NASA Astrophysics Data System (ADS)

Briggs, Gordon P.; Ferrario, Lilia; Tout, Christopher A.; Wickramasinghe, Dayal T.

2018-05-01

A dynamo mechanism driven by differential rotation when stars merge has been proposed to explain the presence of strong fields in certain classes of magnetic stars. In the case of the high field magnetic white dwarfs (HFMWDs), the site of the differential rotation has been variously thought to be the common envelope, the hot outer regions of a merged degenerate core or an accretion disc formed by a tidally disrupted companion that is subsequently accreted by a degenerate core. We have shown previously that the observed incidence of magnetism and the mass distribution in HFMWDs are consistent with the hypothesis that they are the result of merging binaries during common envelope evolution. Here we calculate the magnetic field strengths generated by common envelope interactions for synthetic populations using a simple prescription for the generation of fields and find that the observed magnetic field distribution is also consistent with the stellar merging hypothesis. We use the Kolmogorov-Smirnov test to study the correlation between the calculated and the observed field strengths and find that it is consistent for low envelope ejection efficiency. We also suggest that field generation by the plunging of a giant gaseous planet on to a white dwarf may explain why magnetism among cool white dwarfs (including DZ white dwarfs) is higher than among hot white dwarfs. In this picture a super-Jupiter residing in the outer regions of the white dwarf's planetary system is perturbed into a highly eccentric orbit by a close stellar encounter and is later accreted by the white dwarf.

Genesis of magnetic fields in isolated white dwarfs

NASA Astrophysics Data System (ADS)

Briggs, Gordon P.; Ferrario, Lilia; Tout, Christopher A.; Wickramasinghe, Dayal T.

2018-07-01

A dynamo mechanism driven by differential rotation when stars merge has been proposed to explain the presence of strong fields in certain classes of magnetic stars. In the case of the high-field magnetic white dwarfs (HFMWDs), the site of the differential rotation has been variously thought to be the common envelope, the hot outer regions of a merged degenerate core or an accretion disc are formed by a tidally disrupted companion that is subsequently accreted by a degenerate core. We have shown previously that the observed incidence of magnetism and the mass distribution in HFMWDs are consistent with the hypothesis that they are the result of merging binaries during common envelope evolution. Here, we calculate the magnetic field strengths generated by common envelope interactions for synthetic populations using a simple prescription for the generation of fields and find that the observed magnetic field distribution is also consistent with the stellar merging hypothesis. We use the Kolmogorov-Smirnov test to study the correlation between the calculated and the observed field strengths and find that it is consistent for low envelope ejection efficiency. We also suggest that the field generation by the plunging of a giant gaseous planet on to a white dwarf may explain why magnetism among cool white dwarfs (including DZ white dwarfs) is higher than among hot white dwarfs. In this picture, a super-Jupiter residing in the outer regions of the white dwarf's planetary system is perturbed into a highly eccentric orbit by a close stellar encounter and is later accreted by the white dwarf.

Global enhancement and structure formation of the magnetic field in spiral galaxies

NASA Astrophysics Data System (ADS)

Khoperskov, Sergey A.; Khrapov, Sergey S.

2018-01-01

In this paper we study numerically large-scale magnetic field evolution and its enhancement in gaseous disks of spiral galaxies. We consider a set of models with the various spiral pattern parameters and the initial magnetic field strength with taking into account gas self-gravity and cooling and heating processes. In agreement with previous studies we find out that galactic magnetic field is mostly aligned with gaseous structures, however small-scale gaseous structures (spurs and clumps) are more chaotic than the magnetic field structure. In spiral arms magnetic field often coexists with the gas distribution, in the inter-arm region we see filamentary magnetic field structure. These filaments connect several isolated gaseous clumps. Simulations reveal the presence of the small-scale irregularities of the magnetic field as well as the reversal of magnetic field at the outer edge of the large-scale spurs. We provide evidences that the magnetic field in the spiral arms has a stronger mean-field component, and there is a clear inverse correlation between gas density and plasma-beta parameter, compared to the rest of the disk with a more turbulent component of the field and an absence of correlation between gas density and plasma-beta. We show the mean field growth up to >3-10 μG in the cold gas during several rotation periods (>500-800 Myr), whereas ratio between azimuthal and radial field is equal to >4/1. We find an enhancement of random and ordered components of the magnetic field. Mean field strength increases by a factor of >1.5-2.5 for models with various spiral pattern parameters. Random magnetic field component can reach up to 25% from the total strength. By making an analysis of the time-dependent evolution of the radial Poynting flux, we point out that the magnetic field strength is enhanced more strongly at the galactic outskirts which is due to the radial transfer of magnetic energy by the spiral arms pushing the magnetic field outward. Our results also support the presence of sufficient conditions for the development of magnetorotational instability at distances >11 kpc after >300 Myr of evolution.

Estimation of a coronal mass ejection magnetic field strength using radio observations of gyrosynchrotron radiation

NASA Astrophysics Data System (ADS)

Carley, Eoin P.; Vilmer, Nicole; Simões, Paulo J. A.; Ó Fearraigh, Brían

2017-12-01

Coronal mass ejections (CMEs) are large eruptions of plasma and magnetic field from the low solar corona into interplanetary space. These eruptions are often associated with the acceleration of energetic electrons which produce various sources of high intensity plasma emission. In relatively rare cases, the energetic electrons may also produce gyrosynchrotron emission from within the CME itself, allowing for a diagnostic of the CME magnetic field strength. Such a magnetic field diagnostic is important for evaluating the total magnetic energy content of the CME, which is ultimately what drives the eruption. Here, we report on an unusually large source of gyrosynchrotron radiation in the form of a type IV radio burst associated with a CME occurring on 2014-September-01, observed using instrumentation from the Nançay Radio Astronomy Facility. A combination of spectral flux density measurements from the Nançay instruments and the Radio Solar Telescope Network (RSTN) from 300 MHz to 5 GHz reveals a gyrosynchrotron spectrum with a peak flux density at 1 GHz. Using this radio analysis, a model for gyrosynchrotron radiation, a non-thermal electron density diagnostic using the Fermi Gamma Ray Burst Monitor (GBM) and images of the eruption from the GOES Soft X-ray Imager (SXI), we were able to calculate both the magnetic field strength and the properties of the X-ray and radio emitting energetic electrons within the CME. We find the radio emission is produced by non-thermal electrons of energies >1 MeV with a spectral index of δ 3 in a CME magnetic field of 4.4 G at a height of 1.3 R⊙, while the X-ray emission is produced from a similar distribution of electrons but with much lower energies on the order of 10 keV. We conclude by comparing the electron distribution characteristics derived from both X-ray and radio and show how such an analysis can be used to define the plasma and bulk properties of a CME.

Simulation and Analysis of Electric Field for the Disconnector Switch Incomplete Opening Position Based on 220kV GIS

NASA Astrophysics Data System (ADS)

Wang, Feifeng; Huang, Huimin; Su, Yi; Yan, Dandan; Lu, Yufeng; Xia, Xiaofei; Yang, Jian

2018-05-01

It has accounted for a large proportion of GIS equipment defects, which cause the disconnector switches to incomplete open-close position. Once opening operation is not in place, it will arouse continuous arcing between contacts to reduce insulation strength. Otherwise, the intense heat give rise to burn the contact, which has a severe effect on the safe operation of power grid. This paper analyzes some typical defection cases about the opening operation incomplete for disconnector switches of GIS. The COMSOL Multiphysics is applied to verify the influence on electric field distribution. The results show that moving contact out shield is 20 mm, the electric field distribution of the moving contact surface is uneven, and the maximum electric field value can reach 9.74 kV/mm.

47 CFR 73.683 - Field strength contours and presumptive determination of field strength at individual locations.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 4 2011-10-01 2011-10-01 false Field strength contours and presumptive determination of field strength at individual locations. 73.683 Section 73.683 Telecommunication FEDERAL... Stations § 73.683 Field strength contours and presumptive determination of field strength at individual...

LONG-TERM ELECTROMAGNETIC FIELD MEASUREMENT AND ASSESSMENT FOR A SHOPPING MALL.

PubMed

Engiz, Begum Korunur; Kurnaz, Cetin

2017-07-01

As a result of the dense deployment of wireless devices and base stations, measuring and evaluating the electromagnetic (EM) exposure levels they emit have become important to human health especially if they exceed the limits defined in the standards. Base stations, Wi-Fi equipment and other electronic devices are used heavily, especially in densely crowded places like shopping centers. In this study, electric field strength (E) measurements were conducted at one of the largest shopping malls in Turkey. Broadband E measurements were performed using PMM 8053 EM field strength meter for 24 h a day for the duration of one week while frequency selective measurements were carried out with SRM-3006 EM field strength meter. It is concluded from the measurements that the mean measured total E in the band between 100 kHz and 3 GHz is 0.59 V/m while the maximum E is 7.88 V/m, which are both below the limit determined by International Commission on Non-Ionizing Radiation Protection. Evolutions show that E can increase by up to 55% during the daytime. Analyses demonstrate that 71.3% of total E is caused by UMTS2100, 16.3% is produced by GSM900, 6.2% by LTE, 3.5% by Wi-Fi, and 2.7% is generated by devices that use the remaining frequency bands. Based on the detailed statistical analysis of long-term E measurement results, it can be concluded that the measured E levels are not in normal distribution and that they are statistically different with respect to days. Furthermore, distribution of E can be best modeled with the non-parametric approach. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

The pattern of the electromagnetic field emitted by mobile phones in motor vehicle driving simulators.

PubMed

Politański, Piotr; Bortkiewicz, Alicja; Zmyślony, Marek

2013-06-01

The paper reports the results of the determinations of UMTS EMF distributions in the driver’s cab of motor vehicle simulators. The results will serve as the basis for future research on the influence of EMF emitted by mobile phones on driver physiology. Two motor vehicle driving simulators were monitored, while an EMF source was placed at the driver's head or on the dashboard of the motor vehicle driving simulator. For every applied configuration, the maximal electric field strength was measured, as were the values at 16 points corresponding to chosen locations on a driver's or passenger's body. When the power was set for the maximum (49 mW), a value of 27 V/m was measured in the vicinity of the driver's head when the phone was close to the head. With the same power, when the phone was placed on the dashboard, the measured maximum was 15.2 V/m in the vicinity of the driver's foot. Similar results were obtained for the passenger. Significant perturbations in EMF distribution and an increase in electric field strength values in the mo-tor vehicle driving simulator were also observed in comparison to free space measurements, and the electric field strength was up to 3 times higher inside the simulator. This study can act as the basis of future studies concerning the influence of the EMF emitted by mobile phones on the physiology of the driver. Additionally, the authors postulate that it is advisable to keep mobile phones at a distance from the head, i.e. use, whenever possible, hands-free kits to reduce EMF exposure, both for drivers and passengers.

Rotatable Small Permanent Magnet Array for Ultra-Low Field Nuclear Magnetic Resonance Instrumentation: A Concept Study.

PubMed

Vogel, Michael W; Giorni, Andrea; Vegh, Viktor; Pellicer-Guridi, Ruben; Reutens, David C

2016-01-01

We studied the feasibility of generating the variable magnetic fields required for ultra-low field nuclear magnetic resonance relaxometry with dynamically adjustable permanent magnets. Our motivation was to substitute traditional electromagnets by distributed permanent magnets, increasing system portability. The finite element method (COMSOL®) was employed for the numerical study of a small permanent magnet array to calculate achievable magnetic field strength, homogeneity, switching time and magnetic forces. A manually operated prototype was simulated and constructed to validate the numerical approach and to verify the generated magnetic field. A concentric small permanent magnet array can be used to generate strong sample pre-polarisation and variable measurement fields for ultra-low field relaxometry via simple prescribed magnet rotations. Using the array, it is possible to achieve a pre-polarisation field strength above 100 mT and variable measurement fields ranging from 20-50 μT with 200 ppm absolute field homogeneity within a field-of-view of 5 x 5 x 5 cubic centimetres. A dynamic small permanent magnet array can generate multiple highly homogeneous magnetic fields required in ultra-low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) instruments. This design can significantly reduce the volume and energy requirements of traditional systems based on electromagnets, improving portability considerably.

Gravitational Thermodynamics for Interstellar Gas and Weakly Degenerate Quantum Gas

NASA Astrophysics Data System (ADS)

Zhu, Ding Yu; Shen, Jian Qi

2016-03-01

The temperature distribution of an ideal gas in gravitational fields has been identified as a longstanding problem in thermodynamics and statistical physics. According to the principle of entropy increase (i.e., the principle of maximum entropy), we apply a variational principle to the thermodynamical entropy functional of an ideal gas and establish a relationship between temperature gradient and gravitational field strength. As an illustrative example, the temperature and density distributions of an ideal gas in two simple but typical gravitational fields (i.e., a uniform gravitational field and an inverse-square gravitational field) are considered on the basis of entropic and hydrostatic equilibrium conditions. The effect of temperature inhomogeneity in gravitational fields is also addressed for a weakly degenerate quantum gas (e.g., Fermi and Bose gas). The present gravitational thermodynamics of a gas would have potential applications in quantum fluids, e.g., Bose-Einstein condensates in Earth’s gravitational field and the temperature fluctuation spectrum in cosmic microwave background radiation.

High-order above-threshold ionization beyond the electric dipole approximation

NASA Astrophysics Data System (ADS)

Brennecke, Simon; Lein, Manfred

2018-05-01

Photoelectron momentum distributions from strong-field ionization are calculated by numerical solution of the one-electron time-dependent Schrödinger equation for a model atom including effects beyond the electric dipole approximation. We focus on the high-energy electrons from rescattering and analyze their momentum component along the field propagation direction. We show that the boundary of the calculated momentum distribution is deformed in accordance with the classical three-step model including the beyond-dipole Lorentz force. In addition, the momentum distribution exhibits an asymmetry in the signal strengths of electrons emitted in the forward/backward directions. Taken together, the two non-dipole effects give rise to a considerable average forward momentum component of the order of 0.1 a.u. for realistic laser parameters.

A mathematical method for the turbulent behavior of crowds using agent particles

NASA Astrophysics Data System (ADS)

Ohnishi, Teruaki

2016-08-01

Among the people moving as a group there appear social and psychological forces together with physical forces such as friction and resistance. With the definition that the field of the crowd is the region of those forces continuously extending with varying strength, and with the pre-requisite that the spatial distribution of the crowd, i.e., the distribution of the field, varies according to the hydrodynamic rule by the Navier-Stokes equation, a methodology was proposed to describe the behavior of the crowd composed of many agent particles as the movement of a compressible, turbulent fluid. A numerical calculation was exemplified for the dynamic behavior and spatial distribution of crowds during movements when there appears a conflict between groups with different characters, imaging for instance the medieval battle of Breitenfeld.

47 CFR 24.236 - Field strength limits.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 2 2011-10-01 2011-10-01 false Field strength limits. 24.236 Section 24.236... SERVICES Broadband PCS § 24.236 Field strength limits. The predicted or measured median field strength at... to a higher field strength. ...

47 CFR 24.236 - Field strength limits.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 2 2010-10-01 2010-10-01 false Field strength limits. 24.236 Section 24.236... SERVICES Broadband PCS § 24.236 Field strength limits. The predicted or measured median field strength at... to a higher field strength. ...

Electromagnetic-field dependence of the internal excited state of the polaron and the qubit in quantum dot with thickness

NASA Astrophysics Data System (ADS)

Bai, Xu-Fang; Xin, Wei; Yin, Hong-Wu; Eerdunchaolu

2017-06-01

The electromagnetic-field dependence of the ground and the first excited-state (GFES) energy eigenvalues and eigenfunctions of the strong-coupling polaron in a quantum dot (QD) was studied for various QD thicknesses by using the variational method of the Pekar type (VMPT). On this basis, we construct a qubit in the quantum dot (QQD) by taking a two-level structure of the polaron as the carrier. The results of numerical calculations indicate that the oscillation period of the qubit, {itT}{in0}, increases with increasing the thickness of the quantum dot (TQD) {itL}, but decreases with increasing the cyclotron frequency of the magnetic field (CFMF) ω{in{itc}}, electric-field strength {itF}, and electron-phonon coupling strength (EPCS) α. The probability density of the qubit |Ψ({itρ}, {itz}, {itt})|{su2} presents a normal distribution of the electronic transverse coordinate ρ, significantly influenced by the TQD and effective radius of the quantum dot (ERQD) {itR}{in0}, and shows a periodic oscillation with variations in the electronic longitudinal coordinate {itz}, polar angle φ and time {itt}. The decoherence time τ and the quality factor {itQ} of the free rotation increase with increasing the CFMF ω{in{itc}}, dispersion coefficient η, and EPCS α, but decrease with increasing the electric-field strength {itF}, TQD {itL}, and ERQD {itR}{in0}. The TQD is an important parameter of the qubit. Theoretically, the target, which is to regulate the oscillation period, decoherence time and quality factor of the free rotation of the qubit, can be achieved by designing different TQDs and regulating the strength of the electromagnetic field.

Distilling two-center-interference information during tunneling of aligned molecules with orthogonally polarized two-color laser fields

NASA Astrophysics Data System (ADS)

Gao, F.; Chen, Y. J.; Xin, G. G.; Liu, J.; Fu, L. B.

2017-12-01

When electrons tunnel through a barrier formed by the strong laser field and the two-center potential of a diatomic molecule, a double-slit-like interference can occur. However, this interference effect can not be probed directly right now, as it is strongly coupled with other dynamical processes during tunneling. Here, we show numerically and analytically that orthogonally polarized two-color (OTC) laser fields are capable of resolving the interference effect in tunneling, while leaving clear footprints of this effect in photoelectron momentum distributions. Moreover, this effect can be manipulated by changing the relative field strength of OTC fields.

Extreme value statistics analysis of fracture strengths of a sintered silicon nitride failing from pores

NASA Technical Reports Server (NTRS)

Chao, Luen-Yuan; Shetty, Dinesh K.

1992-01-01

Statistical analysis and correlation between pore-size distribution and fracture strength distribution using the theory of extreme-value statistics is presented for a sintered silicon nitride. The pore-size distribution on a polished surface of this material was characterized, using an automatic optical image analyzer. The distribution measured on the two-dimensional plane surface was transformed to a population (volume) distribution, using the Schwartz-Saltykov diameter method. The population pore-size distribution and the distribution of the pore size at the fracture origin were correllated by extreme-value statistics. Fracture strength distribution was then predicted from the extreme-value pore-size distribution, usin a linear elastic fracture mechanics model of annular crack around pore and the fracture toughness of the ceramic. The predicted strength distribution was in good agreement with strength measurements in bending. In particular, the extreme-value statistics analysis explained the nonlinear trend in the linearized Weibull plot of measured strengths without postulating a lower-bound strength.

Effect of magnetic field inhomogeneity on ion cyclotron motion coherence at high magnetic field.

PubMed

Vladimirov, Gleb; Kostyukevich, Yury; Hendrickson, Christopher L; Blakney, Greg T; Nikolaev, Eugene

2015-01-01

A three-dimensional code based on the particle-in-cell algorithm modified to account for the inhomogeneity of the magnetic field was applied to determine the effect of Z(1), Z(2), Z(3), Z(4), X, Y, ZX, ZY, XZ(2) YZ(2), XY and X(2)-Y(2) components of an orthogonal magnetic field expansion on ion motion during detection in an FT-ICR cell. Simulations were performed for magnetic field strengths of 4.7, 7, 14.5 and 21 Tesla, including experimentally determined magnetic field spatial distributions for existing 4.7 T and 14.5 T magnets. The effect of magnetic field inhomogeneity on ion cloud stabilization ("ion condensation") at high numbers of ions was investigated by direct simulations of individual ion trajectories. Z(1), Z(2), Z(3) and Z(4) components have the largest effect (especially Z(1)) on ion cloud stability. Higher magnetic field strength and lower m/z demand higher relative magnetic field homogeneity to maintain cloud coherence for a fixed time period. The dependence of mass resolving power upper limit on Z(1) inhomogeneity is evaluated for different magnetic fields and m/z. The results serve to set the homogeneity requirements for various orthogonal magnetic field components (shims) for future FT-ICR magnet design.

Magnetic field topology and chemical abundance distributions of the young, rapidly rotating, chemically peculiar star HR 5624

NASA Astrophysics Data System (ADS)

Kochukhov, O.; Silvester, J.; Bailey, J. D.; Landstreet, J. D.; Wade, G. A.

2017-09-01

Context. The young, rapidly rotating Bp star HR 5624 (HD 133880) shows an unusually strong non-sinusoidal variability of its longitudinal magnetic field. This behaviour was previously interpreted as the signature of an exceptionally strong, quadrupole-dominated surface magnetic field geometry. Aims: We studied the magnetic field structure and chemical abundance distributions of HR 5624 with the aim to verify the unusual quadrupolar nature of its magnetic field and to investigate correlations between the field topology and chemical spots. Methods: We analysed high-resolution, time series Stokes parameter spectra of HR 5624 with the help of a magnetic Doppler imaging inversion code based on detailed polarised radiative transfer modelling of the line profiles. Results: We refined the stellar parameters, revised the rotational period, and obtained new longitudinal magnetic field measurements. Our magnetic Doppler inversions reveal that the field structure of HR 5624 is considerably simpler and the field strength is much lower than proposed by previous studies. We find a maximum local field strength of 12 kG and a mean field strength of 4 kG, which is about a factor of three weaker than predicted by quadrupolar field models. Our model implies that overall large-scale field topology of HR 5624 is better described as a distorted, asymmetric dipole rather than an axisymmetric quadrupole. The chemical abundance maps of Mg, Si, Ti, Cr, Fe, and Nd obtained in our study are characterised by large-scale, high-contrast abundance patterns. These structures correlate weakly with the magnetic field geometry and, in particular, show no distinct element concentrations in the horizontal field regions predicted by theoretical atomic diffusion calculations. Conclusions: We conclude that the surface magnetic field topology of HR 5624 is not as unusual as previously proposed. Considering these results together with other recent magnetic mapping analyses of early-type stars suggests that predominantly quadrupolar magnetic field topologies, invoked to be present in a significant number of stars, probably do not exist in real stars. This finding agrees with an outcome of the MHD simulations of fossil field evolution in stably stratified stellar interiors. Based on observations collected at the European Southern Observatory, Chile (ESO programs 085.D-0296, 089.D-0383, 095.D-0194) and on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Alignments of Dark Matter Halos with Large-scale Tidal Fields: Mass and Redshift Dependence

NASA Astrophysics Data System (ADS)

Chen, Sijie; Wang, Huiyuan; Mo, H. J.; Shi, Jingjing

2016-07-01

Large-scale tidal fields estimated directly from the distribution of dark matter halos are used to investigate how halo shapes and spin vectors are aligned with the cosmic web. The major, intermediate, and minor axes of halos are aligned with the corresponding tidal axes, and halo spin axes tend to be parallel with the intermediate axes and perpendicular to the major axes of the tidal field. The strengths of these alignments generally increase with halo mass and redshift, but the dependence is only on the peak height, ν \\equiv {δ }{{c}}/σ ({M}{{h}},z). The scaling relations of the alignment strengths with the value of ν indicate that the alignment strengths remain roughly constant when the structures within which the halos reside are still in a quasi-linear regime, but decreases as nonlinear evolution becomes more important. We also calculate the alignments in projection so that our results can be compared directly with observations. Finally, we investigate the alignments of tidal tensors on large scales, and use the results to understand alignments of halo pairs separated at various distances. Our results suggest that the coherent structure of the tidal field is the underlying reason for the alignments of halos and galaxies seen in numerical simulations and in observations.

STATISTICAL COMPARISON BETWEEN PORES AND SUNSPOTS BY USING SDO/HMI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, I.-H.; Cho, K.-S.; Bong, S.-C.

2015-09-20

We carried out an extensive statistical study of the properties of pores and sunspots, and investigated the relationship among their physical parameters such as size, intensity, magnetic field, and the line-of-sight (LOS) velocity in the umbrae. For this, we classified 9881 samples into three groups of pores, transitional sunspots, and mature sunspots. As a result, (1) we find that the total magnetic flux inside the umbra of pores, transitional sunspots, and mature sunspots increases proportionally to the powers of the area and the power indices in the three groups significantly differ from each other. (2) The umbral area distribution ofmore » each group shows a Gaussian distribution and they are clearly separated, displaying three distinct peak values. All of the quantities significantly overlap among the three groups. (3) The umbral intensity shows a rapid decrease with increasing area, and their magnetic field strength shows a rapid increase with decreasing intensity. (4) The LOS velocity in pores is predominantly redshifted and its magnitude decreases with increasing magnetic field strength. The decreasing trend becomes nearly constant with marginal blueshift in the case of mature sunspots. The dispersion of LOS velocities in mature sunspots is significantly suppressed compared to pores. From our results, we conclude that the three groups have different characteristics in their area, intensity, magnetic field, and LOS velocity as well in their relationships.« less

Eco-geomorphic controls on slope stability

NASA Astrophysics Data System (ADS)

Hales, T.; Ford, C.; Hwang, T.; Vose, J.; Band, L.

2009-04-01

Vegetation controls soil-mantled landscape evolution primarily through growth of roots into soil and rock. Root-soil interactions affect the spatial distribution and rate of shallow landsliding and other hillslope processes. Yet the distribution and tensile strength of roots depends on a number of geomorphically-influenced parameters, including soil moisture. Our field-based study investigated the effects of topography on root distributions, tensile strengths, and cohesion. Systematic differences in plant species distribution and soil properties are found in the hollow-nose topography of soil-mantled landscapes; with hollows containing thick colluvial soils and mesic tree species and noses containing thinner, more differentiated soils and more xeric species. We investigated whether these topographic variations in geomorphic and ecologic properties affected the spatial distribution of root cohesion by measuring the distribution and tensile strength of roots from soil pits dug downslope of fifteen individual trees in the Coweeta Hydrologic Laboratory, North Carolina. Our soil pits were located to capture variance in plant species (10 species total), topographic positions (nose, hollow), and sizes (a range of DBH between 5 cm and 60 cm). Root tensile strengths showed little variance with different species, but showed strong differences as a function of topography, with nose roots stronger than hollow roots. Similarly, within species, root cellulose content was systematically greater in trees on nose positions compared to those in hollows. For all species, roots were concentrated close to the soil surface (at least 70% of biomass occurred within 50 cm of the surface) and variations in this pattern were primarily a function of topographic position. Hollow roots were more evenly distributed in the soil column than those on noses, yet trees located on noses had higher mean root cohesion than those in hollows because of a higher root tensile force. These data provide an empirical basis for the development of simple geomorphic transport laws that explicitly include vegetation.

Translocation of a Polymer Chain across a Nanopore: A Brownian Dynamics Simulation Study

NASA Technical Reports Server (NTRS)

Tian, Pu; Smith, Grant D.

2003-01-01

We carried out Brownian dynamics simulation studies of the translocation of single polymer chains across a nanosized pore under the driving of an applied field (chemical potential gradient). The translocation process can be either dominated by the entropic barrier resulted from restricted motion of flexible polymer chains or by applied forces (or chemical gradient across the wall), we focused on the latter case in our studies. Calculation of radius of gyrations at the two opposite sides of the wall shows that the polymer chains are not in equilibrium during the translocation process. Despite this fact, our results show that the one-dimensional diffusion and the nucleation model provide an excellent description of the dependence of average translocation time on the chemical potential gradients, the polymer chain length and the solvent viscosity. In good agreement with experimental results and theoretical predictions, the translocation time distribution of our simple model shows strong non-Gaussian characteristics. It is observed that even for this simple tubelike pore geometry, more than one peak of translocation time distribution can be generated for proper pore diameter and applied field strengths. Both repulsive Weeks-Chandler-Anderson and attractive Lennard-Jones polymer-nanopore interaction were studied, attraction facilitates the translocation process by shortening the total translocation time and dramatically improve the capturing of polymer chain. The width of the translocation time distribution was found to decrease with increasing temperature, increasing field strength, and decreasing pore diameter.

Magnetic fields of young solar twins

NASA Astrophysics Data System (ADS)

Rosén, L.; Kochukhov, O.; Hackman, T.; Lehtinen, J.

2016-09-01

Aims: The goal of this work is to study the magnetic fields of six young solar-analogue stars both individually, and collectively, to search for possible magnetic field trends with age. If such trends are found, they can be used to understand magnetism in the context of stellar evolution of solar-like stars and to understand the past of the Sun and the solar system. This is also important for the atmospheric evolution of the inner planets, Earth in particular. Methods: We used Stokes IV data from two different spectropolarimeters, NARVAL and HARPSpol. The least-squares deconvolution multi-line technique was used to increase the signal-to-noise ratio of the data. We then applied a modern Zeeman-Doppler imaging code in order to reconstruct the magnetic topology of all stars and the brightness distribution of one of our studied stars. Results: Our results show a significant decrease in the magnetic field strength and energy as the stellar age increases from 100 Myr to 250 Myr, while there is no significant age dependence of the mean magnetic field strength for stars with ages 250-650 Myr. The spread in the mean field strength between different stars is comparable to the scatter between different observations of individual stars. The meridional field component is weaker than the radial and azimuthal field components in 15 of the 16 magnetic maps. It turns out that 89-97% of the magnetic field energy is contained in l = 1 - 3. There is also no clear trend with age and distribution of field energy into poloidal/toroidal and axisymmetric/non-axisymmetric components within the sample. The two oldest stars in this study show an octupole component that is twice as strong as the quadrupole component. This is only seen in 1 of the 13 maps of the younger stars. One star, χ1 Ori, displays two field polarity switches during almost 5 yr of observations suggesting a magnetic cycle length of 2, 6, or 8 yr. Based on observations made with the HARPSpol instrument on the ESO 3.6 m telescope at La Silla (Chile), under the program ID 091.D-0836. Also based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France.

Dynamical features and electric field strengths of double layers driven by currents. [in auroras

NASA Technical Reports Server (NTRS)

Singh, N.; Thiemann, H.; Schunk, R. W.

1985-01-01

In recent years, a number of papers have been concerned with 'ion-acoustic' double layers. In the present investigation, results from numerical simulations are presented to show that the shapes and forms of current-driven double layers evolve dynamically with the fluctuations in the current through the plasma. It is shown that double layers with a potential dip can form even without the excitation of ion-acoustic modes. Double layers in two-and one-half-dimensional simulations are discussed, taking into account the simulation technique, the spatial and temporal features of plasma, and the dynamical behavior of the parallel potential distribution. Attention is also given to double layers in one-dimensional simulations, and electrical field strengths predicted by two-and one-half-dimensional simulations.

Diffusion with Varying Drag; the Runaway Problem.

NASA Astrophysics Data System (ADS)

Rollins, David Kenneth

We study the motion of electrons in an ionized plasma of electrons and ions in an external electric field. A probability distribution function describes the electron motion and is a solution of a Fokker-Planck equation. In zero field, the solution approaches an equilibrium Maxwellian. For arbitrarily small field, electrons overcome the diffusive effects and are freely accelerated by the field. This is the electron runaway phenomenon. We treat the electric field as a small perturbation. We consider various diffusion coefficients for the one dimensional problem and determine the runaway current as a function of the field strength. Diffusion coefficients, non-zero on a finite interval are examined. Some non-trivial cases of these can be solved exactly in terms of known special functions. The more realistic case where the diffusion coefficient decays with velocity are then considered. To determine the runaway current, the equivalent Schrodinger eigenvalue problem is analysed. The smallest eigenvalue is shown to be equal to the runaway current. Using asymptotic matching a solution can be constructed which is then used to evaluate the runaway current. The runaway current is exponentially small as a function of field strength. This method is used to extract results from the three dimensional problem.

Stellar feedback strongly alters the amplification and morphology of galactic magnetic fields

NASA Astrophysics Data System (ADS)

Su, Kung-Yi; Hayward, Christopher C.; Hopkins, Philip F.; Quataert, Eliot; Faucher-Giguère, Claude-André; Kereš, Dušan

2018-01-01

Using high-resolution magnetohydrodynamic simulations of idealized, non-cosmological galaxies, we investigate how cooling, star formation and stellar feedback affect galactic magnetic fields. We find that the amplification histories, saturation values and morphologies of the magnetic fields vary considerably depending on the baryonic physics employed, primarily because of differences in the gas density distribution. In particular, adiabatic runs and runs with a subgrid (effective equation of state) stellar feedback model yield lower saturation values and morphologies that exhibit greater large-scale order compared with runs that adopt explicit stellar feedback and runs with cooling and star formation but no feedback. The discrepancies mostly lie in gas denser than the galactic average, which requires cooling and explicit fragmentation to capture. Independent of the baryonic physics included, the magnetic field strength scales with gas density as B ∝ n2/3, suggesting isotropic flux freezing or equipartition between the magnetic and gravitational energies during the field amplification. We conclude that accurate treatments of cooling, star formation and stellar feedback are crucial for obtaining the correct magnetic field strength and morphology in dense gas, which, in turn, is essential for properly modelling other physical processes that depend on the magnetic field, such as cosmic ray feedback.

Comparison of transient horizontal magnetic fields in a plage region and in the quiet Sun

NASA Astrophysics Data System (ADS)

Ishikawa, R.; Tsuneta, S.

2009-02-01

Aims: The properties of transient horizontal magnetic fields (THMFs) in both plage and quiet Sun regions are obtained and compared. Methods: Spectro-polarimetric observations with the Solar Optical Telescope (SOT) on the Hinode satellite were carried out with a cadence of about 30 s for both plage and quiet regions located near the disk center. We selected THMFs that have net linear polarization (LP) higher than 0.22%, and an area larger than or equal to 3 pixels, and compared their occurrence rates and distribution of magnetic field azimuth. We obtained probability density functions (PDFs) of magnetic field strength and inclination for both regions. Results: The occurrence rate in the plage region is the same as for the quiet Sun. The vertical magnetic flux in the plage region is ~8 times more than in the quiet Sun. There is essentially no preferred orientation for the THMFs in either region; however, THMFs in the plage region with higher LP have a preferred direction consistent with that of the plage-region's large-scale vertical field pattern. PDFs show that there is no difference in the distribution of field strength of horizontal fields between the quiet Sun and the plage regions when we avoid the persistent vertical flux concentrations for the plage region. Conclusions: The similarity between the PDFs and the occurrence rates in plage and quiet regions suggests that a local dynamo process due to the granular motion may generate THMFs all over the Sun. The preferred orientation for higher LP in the plage indicates that the THMFs may be somewhat influenced by the larger-scale magnetic field pattern of the plage. A movie is only available in electronic form at http://www.aanda.org

Carbon and Nitrogen Abundance Variations Among Red Giant Branch Stars in M10

NASA Astrophysics Data System (ADS)

Gerber, Jeffrey M.; Friel, Eileen D.; Vesperini, Enrico

2016-06-01

We present analysis of the CN and CH molecular band strengths derived for red giants in M10 as part of a first pilot study in the WIYN Indiana Northern Globular Survey (WINGS). This survey plans to use a combination of low-resolution spectroscopy taken with Hydra and wide-field SDSS filter photometry taken with the newly upgraded ODI to study the multiple populations and dynamics of a sample of Milky Way globular clusters. Our sample comes from the first in a series of observation runs conducted in Aug. 2014 using Hydra on the WIYN 3.5m telescope. CN and CH bands are measured for ~100 red giant branch stars and used to characterize the distribution in band strength and to derive carbon and nitrogen abundances by comparing observed band strengths to synthetic spectra produced by the Synthetic Spectrum Generator (SSG), which makes use of MARCS model atmospheres. Band strengths and CN abundances are used to investigate the distribution of stars in nitrogen normal and enhanced populations and to compare these to other ways of characterizing multiple stellar populations with other light elements (such as Na and O).

Near-infrared scattering as a dust diagnostic

NASA Astrophysics Data System (ADS)

Saajasto, Mika; Juvela, Mika; Malinen, Johanna

2018-06-01

Context. Regarding the evolution of dust grains from diffuse regions of space to dense molecular cloud cores, many questions remain open. Scattering at near-infrared wavelengths, or "cloudshine", can provide information on cloud structure, dust properties, and the radiation field that is complementary to mid-infrared "coreshine" and observations of dust emission at longer wavelengths. Aims: We examine the possibility of using near-infrared scattering to constrain the local radiation field and the dust properties, the scattering and absorption efficiency, the size distribution of the grains, and the maximum grain size. Methods: We use radiative transfer modelling to examine the constraints provided by the J, H, and K bands in combination with mid-infrared surface brightness at 3.6 μm. We use spherical one-dimensional and elliptical three-dimensional cloud models to study the observable effects of different grain size distributions with varying absorption and scattering properties. As an example, we analyse observations of a molecular cloud in Taurus, TMC-1N. Results: The observed surface brightness ratios of the bands change when the dust properties are changed. However, even a change of ±10% in the surface brightness of one band changes the estimated power-law exponent of the size distribution γ by up to 30% and the estimated strength of the radiation field KISRF by up to 60%. The maximum grain size Amax and γ are always strongly anti-correlated. For example, overestimating the surface brightness by 10% changes the estimated radiation field strength by 20% and the exponent of the size distribution by 15%. The analysis of our synthetic observations indicates that the relative uncertainty of the parameter distributions are on average Amax, γ 25%, and the deviation between the estimated and correct values ΔQ < 15%. For the TMC-1N observations, a maximum grain size Amax > 1.5μm and a size distribution with γ > 4.0 have high probability. The mass weighted average grain size is ⟨am⟩ = 0.113μm. Conclusions: We show that scattered infrared light can be used to derive meaningful limits for the dust parameters. However, errors in the surface brightness data can result in considerable uncertainties on the derived parameters.

Microelectrode-assisted low-voltage atmospheric pressure glow discharge in air

NASA Astrophysics Data System (ADS)

Liu, Wenzheng; Zhao, Shuai; Niu, Jiangqi; Chai, Maolin

2017-09-01

During the process of discharge, appropriately changing the paths corresponding to electric field lines and the field strength distribution along these paths, as well as increasing the number of initial electrons, can effectively enhance the uniformity of discharge and inhibit the formation of filamentary discharge. A method is proposed that uses a microelectrode to initiate the macroscopic discharge phenomenon. An asymmetric structure was designed comprising a single electrode of carbon fiber; this electrode structure is of helical-contact type. Benefitting from the special electric field distribution and the microdischarge process, a three-dimensional atmospheric pressure glow discharge was achieved in air, characterized by low discharge voltage, low energy consumption, good diffusion performance, and less ozone generation. The plasma studied is uniform and stable with good diffusion characteristics and low levels of contaminants and hence has potential applications in the field of air purification.

AC-electric field dependent electroformation of giant lipid vesicles.

PubMed

Politano, Timothy J; Froude, Victoria E; Jing, Benxin; Zhu, Yingxi

2010-08-01

Giant vesicles of larger than 5 microm, which have been of intense interest for their potential as drug delivery vehicles and as a model system for cell membranes, can be rapidly formed from a spin-coated lipid thin film under an electric field. In this work, we explore the AC-field dependent electroformation of giant lipid vesicles in aqueous media over a wide range of AC-frequency from 1 Hz to 1 MHz and peak-to-peak field strength from 0.212 V/mm to 40 V/mm between two parallel conducting electrode surfaces. By using fluorescence microscopy, we perform in-situ microscopic observations of the structural evolution of giant vesicles formed from spin-coated lipid films under varied uniform AC-electric fields. The real-time observation of bilayer bulging from the lipid film, vesicle growth and fusing further examine the critical role of AC-induced electroosmotic flow of surrounding fluids for giant vesicle formation. A rich AC-frequency and field strength phase diagram is obtained experimentally to predict the AC-electroformation of giant unilamellar vesicles (GUVs) of l-alpha-phosphatidylcholine, where a weak dependence of vesicle size on AC-frequency is observed at low AC-field voltages, showing decreased vesicle size with a narrowed size distribution with increased AC-frequency. Formation of vesicles was shown to be constrained by an upper field strength of 10 V/mm and an upper AC-frequency of 10 kHz. Within these parameters, giant lipid vesicles were formed predominantly unilamellar and prevalent across the entire electrode surfaces. Copyright 2010 Elsevier B.V. All rights reserved.

The effects of lithology and landsliding on hillslope sediment supply: case study from southern Italy

NASA Astrophysics Data System (ADS)

Roda-Boluda, Duna; D'Arcy, Mitch; Whittaker, Alex; McDonald, Jordan

2017-04-01

Sediment supply from hillslopes -including volumes, rates and grain size distributions- controls the sediment fluxes from upland areas and modulates how landscapes respond to tectonics. Here, we present new field data from tectonically-active areas in southern Italy that quantifies how lithology and rock-mass strength control the delivery processes and grain size distributions of sediment supplied from hillslopes. We evaluate the influence of landslides on sediment supply along 8 normal faults with excellent tectonic constraints. Frequency-area analysis of the landslide inventory, and a new field-calibrated area-volume scaling relationship, reveal that landsliding in the area is not dominated by large landslides (β ˜2), with 83% of landslides being < 0.1 km2 and shallower than 3 m. Based on volumetric estimates and published erosion rates, we infer that our inventory likely represents the integrated record of landsliding over 1-3 kyrs, implying minimum sediment fluxes between 6.90 x 102 and 2.07 x 103 m3/yr. We demonstrate that outcrop-scale rock-mass strength controls both landslide occurrence and the grain sizes supplied by bedrock weathering, for different lithologies. Comparisons of particle size distributions from bedrock weathering with those measured on landslide deposits demonstrates that landslides supply systematically coarser material, with lithology influencing the degree of coarsening. Finally, we evaluate the effect of landslide supply on fluvial sediment export, and show that D84 grain size increases by ˜ 6 mm for each 100-m increment in incision depth, due to the combination of enhanced landsliding and transport capacity in more incised catchments. Our results reveal a dual control of lithology and rock-mass strength on both the sediment volumes and grain sizes supplied to the fluvial system, which we demonstrate has a significant impact on sediment export from upland areas. This study provides a uniquely detailed field data set for studying how tectonics and lithology control hillslope erosion and sediment characteristics.

The Global and Small-scale Magnetic Fields of Fully Convective, Rapidly Spinning M Dwarf Pair GJ65 A and B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kochukhov, Oleg; Lavail, Alexis

2017-01-20

The nearby M dwarf binary GJ65 AB, also known as BL Cet and UV Cet, is a unique benchmark for investigation of dynamo-driven activity of low-mass stars. Magnetic activity of GJ65 was repeatedly assessed by indirect means, such as studies of flares, photometric variability, X-ray, and radio emission. Here, we present a direct analysis of large-scale and local surface magnetic fields in both components. Interpreting high-resolution circular polarization spectra (sensitive to a large-scale field geometry) we uncovered a remarkable difference of the global stellar field topologies. Despite nearly identical masses and rotation rates, the secondary exhibits an axisymmetric, dipolar-like globalmore » field with an average strength of 1.3 kG while the primary has a much weaker, more complex, and non-axisymmetric 0.3 kG field. On the other hand, an analysis of the differential Zeeman intensification (sensitive to the total magnetic flux) shows the two stars having similar magnetic fluxes of 5.2 and 6.7 kG for GJ65 A and B, respectively, although there is evidence that the field strength distribution in GJ65 B is shifted toward a higher field strength compared to GJ65 A. Based on these complementary magnetic field diagnostic results, we suggest that the dissimilar radio and X-ray variability of GJ65 A and B is linked to their different global magnetic field topologies. However, this difference appears to be restricted to the upper atmospheric layers but does not encompass the bulk of the stars and has no influence on the fundamental stellar properties.« less

Effects of Power-Law Plasticity on Deformation Fields underneath Vickers Indenter

NASA Astrophysics Data System (ADS)

Chollacoop, Nuwong; Srikant, Gollapudi; Ramamurty, Upadrasta

The effects of power-law plasticity (yield strength σy and strain hardening exponent n) on the plastic strain distribution underneath a Vickers indenter was explicitly investigated by recourse to macro- and micro-indentation experiments on heat-treated Al-Zn-Mg alloy. With carefully designed aging profile, Al alloy can achieve similar σy with different n, and vice versa. Using the Vickers tip, the samples were macro-indented, sectioned and micro-indented to construct the sub-surface strain distribution. Thus, the effects of σy and n on stain distribution underneath Vickers indenter were revealed.

Distributed synaptic weights in a LIF neural network and learning rules

NASA Astrophysics Data System (ADS)

Perthame, Benoît; Salort, Delphine; Wainrib, Gilles

2017-09-01

Leaky integrate-and-fire (LIF) models are mean-field limits, with a large number of neurons, used to describe neural networks. We consider inhomogeneous networks structured by a connectivity parameter (strengths of the synaptic weights) with the effect of processing the input current with different intensities. We first study the properties of the network activity depending on the distribution of synaptic weights and in particular its discrimination capacity. Then, we consider simple learning rules and determine the synaptic weight distribution it generates. We outline the role of noise as a selection principle and the capacity to memorize a learned signal.

Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars

NASA Astrophysics Data System (ADS)

Orlando, S.; Bonito, R.; Argiroffi, C.; Reale, F.; Peres, G.; Miceli, M.; Matsakos, T.; Stehlé, C.; Ibgui, L.; de Sa, L.; Chièze, J. P.; Lanz, T.

2013-11-01

Context. According to the magnetospheric accretion model, hot spots form on the surface of classical T Tauri stars (CTTSs) in regions where accreting disk material impacts the stellar surface at supersonic velocity, generating a shock. Aims: We investigate the dynamics and stability of postshock plasma that streams along nonuniform stellar magnetic fields at the impact region of accretion columns. We study how the magnetic field configuration and strength determine the structure, geometry, and location of the shock-heated plasma. Methods: We model the impact of an accretion stream onto the chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our model considers the gravity, the radiative cooling, and the magnetic-field-oriented thermal conduction (including the effects of heat flux saturation). We explore different configurations and strengths of the magnetic field. Results: The structure, stability, and location of the shocked plasma strongly depend on the configuration and strength of the magnetic field. In the case of weak magnetic fields (plasma β ≳ 1 in the postshock region), a large component of B may develop perpendicular to the stream at the base of the accretion column, which limits the sinking of the shocked plasma into the chromosphere and perturbs the overstable shock oscillations induced by radiative cooling. An envelope of dense and cold chromospheric material may also develop around the shocked column. For strong magnetic fields (β < 1 in the postshock region close to the chromosphere), the field configuration determines the position of the shock and its stand-off height. If the field is strongly tapered close to the chromosphere, an oblique shock may form well above the stellar surface at the height where the plasma β ≈ 1. In general, we find that a nonuniform magnetic field makes the distribution of emission measure vs. temperature of the postshock plasma at T > 106 K lower than when there is uniform magnetic field. Conclusions: The initial magnetic field strength and configuration in the region of impact of the stream are expected to influence the chromospheric absorption and, therefore, the observability of the shock-heated plasma in the X-ray band. In addition, the field strength and configuration also influence the energy balance of the shocked plasma with its emission measure at T > 106 K, which is lower than expected for a uniform field. The above effects contribute to underestimating the mass accretion rates derived in the X-ray band. Movies are available in electronic form at http://www.aanda.org

The Effect of General Statistical Fiber Misalignment on Predicted Damage Initiation in Composites

NASA Technical Reports Server (NTRS)

Bednarcyk, Brett A.; Aboudi, Jacob; Arnold, Steven M.

2014-01-01

A micromechanical method is employed for the prediction of unidirectional composites in which the fiber orientation can possess various statistical misalignment distributions. The method relies on the probability-weighted averaging of the appropriate concentration tensor, which is established by the micromechanical procedure. This approach provides access to the local field quantities throughout the constituents, from which initiation of damage in the composite can be predicted. In contrast, a typical macromechanical procedure can determine the effective composite elastic properties in the presence of statistical fiber misalignment, but cannot provide the local fields. Fully random fiber distribution is presented as a special case using the proposed micromechanical method. Results are given that illustrate the effects of various amounts of fiber misalignment in terms of the standard deviations of in-plane and out-of-plane misalignment angles, where normal distributions have been employed. Damage initiation envelopes, local fields, effective moduli, and strengths are predicted for polymer and ceramic matrix composites with given normal distributions of misalignment angles, as well as fully random fiber orientation.

47 CFR 90.671 - Field strength limits.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Field strength limits. 90.671 Section 90.671... 896-901/935-940 Mhz Band § 90.671 Field strength limits. The predicted or measured field strength at... all bordering MTA licensees agree to a higher field strength. MTA licensees are also required to...

47 CFR 90.671 - Field strength limits.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 5 2011-10-01 2011-10-01 false Field strength limits. 90.671 Section 90.671... 896-901/935-940 Mhz Band § 90.671 Field strength limits. The predicted or measured field strength at... all bordering MTA licensees agree to a higher field strength. MTA licensees are also required to...

Perturbed angular distributions with LaBr3 detectors: The g factor of the first 10+ state in 110Cd reexamined

NASA Astrophysics Data System (ADS)

Gray, T. J.; Stuchbery, A. E.; Reed, M. W.; Akber, A.; Coombes, B. J.; Dowie, J. T. H.; Eriksen, T. K.; Gerathy, M. S. M.; Kibédi, T.; Lane, G. J.; Mitchell, A. J.; Palazzo, T.; Tornyi, T.

2017-11-01

The time differential perturbed angular distribution technique with LaBr3 detectors has been applied to the Iπ=11/2- isomeric state (Ex=846 keV, τ =107 ns) in 107Cd, which was populated and recoil-implanted into a gadolinium host following the 98Mo(12C, 3 n )107Cd reaction. The static hyperfine field strength of Cd recoil implanted into gadolinium was thus measured, together with the fraction of nuclei implanted into field-free sites, under similar conditions as pertained for a previous implantation perturbed angular distribution g -factor measurement on the Iπ=10+ state in 110Cd. The 110Cdg (10+) value was thereby reevaluated, bringing it into agreement with the value expected for a seniority-two ν h11/2 configuration.

The effect of the geomagnetic field on negative voltage spheres in the ionospheric plasma: Fluid simulation

NASA Astrophysics Data System (ADS)

Ma, T.-Z.; Schunk, R. W.

1994-07-01

Experiments involving the interaction of spherical conducting objects biases with hight voltages in the Low-Earth-Orbit (LEO) environment have been conducted and designed. In these experiments, both positive and negative voltages have been applied to the spheres. Previously, there have been theoretical and numerical studies of positive voltage spheres in plasmas with and without magnetic fields. There also have been studies of negative voltage objects in unmagnetized plasmas. Here, we used a fluid model to study the plasma response to a negative voltage sphere immersed in a magnetized plasma. Our main purpose was to investigate the role of the magnetic field during the early-time interaction between the negative voltage sphere and the ambient plasma in the LEO environment. In this study, different applied voltages, magnetic field strengths, and rise-times of the applied voltages were considered. It was found that with the strength of the geomagnetic field the ions are basically not affected by the magnetic field on the time scale of hundreds of plasma periods considered in this study. The ion density distribution around the sphere and the collected ion flux by the sphere are basically the same as in the case without the magnetic field. The electron motion is strongly affected by the magnetic field. One effect is to change the nature of the electron over-shoot oscillation from regular to somewhat turbulent. Although the electrons move along the magnetic field much more easily than across the magnetic field, some redirection effect causes the electron density to distribute as if the magnetic field effect is minimal. The sheath struture and the electric field around the sphere tend to be spherical. A finite rise-time of the applied voltage reduces the oscillatory activities and delays the ion acceleration. However, the effect of the rise-time depends on both the duration of the rise-time and the ion plasma period.

Rotatable Small Permanent Magnet Array for Ultra-Low Field Nuclear Magnetic Resonance Instrumentation: A Concept Study

PubMed Central

Vegh, Viktor; Reutens, David C.

2016-01-01

Object We studied the feasibility of generating the variable magnetic fields required for ultra-low field nuclear magnetic resonance relaxometry with dynamically adjustable permanent magnets. Our motivation was to substitute traditional electromagnets by distributed permanent magnets, increasing system portability. Materials and Methods The finite element method (COMSOL®) was employed for the numerical study of a small permanent magnet array to calculate achievable magnetic field strength, homogeneity, switching time and magnetic forces. A manually operated prototype was simulated and constructed to validate the numerical approach and to verify the generated magnetic field. Results A concentric small permanent magnet array can be used to generate strong sample pre-polarisation and variable measurement fields for ultra-low field relaxometry via simple prescribed magnet rotations. Using the array, it is possible to achieve a pre-polarisation field strength above 100 mT and variable measurement fields ranging from 20–50 μT with 200 ppm absolute field homogeneity within a field-of-view of 5 x 5 x 5 cubic centimetres. Conclusions A dynamic small permanent magnet array can generate multiple highly homogeneous magnetic fields required in ultra-low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) instruments. This design can significantly reduce the volume and energy requirements of traditional systems based on electromagnets, improving portability considerably. PMID:27271886

Electron distributions upstream of the Comet Halley bow shock - Evidence for adiabatic heating

NASA Technical Reports Server (NTRS)

Larson, D. E.; Anderson, K. A.; Lin, R. P.; Carlson, C. W.; Reme, H.; Glassmeier, K. H.; Neubauer, F. M.

1992-01-01

Three-dimensional plasma electron (22 eV to 30 keV) observations upstream of Comet Halley bow shock, obtained by the RPA-1 COPERNIC (Reme Plasma Analyzer - Complete Positive Ion, Electron and Ram Negative Ion Measurements near Comet Halley) experiment on the Giotto spacecraft are reported. Besides electron distributions typical of the undisturbed solar wind and backstreaming electrons observed when the magnetic field line intersects the cometary bow shock, a new type of distribution, characterized by enhanced low energy (less than 100 eV) flux which peaks at 90-deg pitch angles is found. These are most prominent when the spacecraft is on field lines which pass close to but are not connected to the bow shock. The 90-deg pitch angle electrons appear to have been adiabatically heated by the increase in the magnetic field strength resulting from the compression of the upstream solar wind plasma by the cometary mass loading. A model calculation of this effect which agrees qualitatively with the observed 90-deg flux enhancements is presented.

Residual stress characterization of steel TIG welds by neutron diffraction and by residual magnetic stray field mappings

NASA Astrophysics Data System (ADS)

Stegemann, Robert; Cabeza, Sandra; Lyamkin, Viktor; Bruno, Giovanni; Pittner, Andreas; Wimpory, Robert; Boin, Mirko; Kreutzbruck, Marc

2017-03-01

The residual stress distribution of tungsten inert gas welded S235JRC+C plates was determined by means of neutron diffraction (ND). Large longitudinal residual stresses with maxima around 600 MPa were found. With these results as reference, the evaluation of residual stress with high spatial resolution GMR (giant magneto resistance) sensors was discussed. The experiments performed indicate a correlation between changes in residual stresses (ND) and the normal component of local residual magnetic stray fields (GMR). Spatial variations in the magnetic field strength perpendicular to the welds are in the order of the magnetic field of the earth.

Control of the Intrinsic Sensor Response to Volatile Organic Compounds with Fringing Electric Fields.

PubMed

Henning, Alex; Swaminathan, Nandhini; Vaknin, Yonathan; Jurca, Titel; Shimanovich, Klimentiy; Shalev, Gil; Rosenwaks, Yossi

2018-01-26

The ability to control surface-analyte interaction allows tailoring chemical sensor sensitivity to specific target molecules. By adjusting the bias of the shallow p-n junctions in the electrostatically formed nanowire (EFN) chemical sensor, a multiple gate transistor with an exposed top dielectric layer allows tuning of the fringing electric field strength (from 0.5 × 10 7 to 2.5 × 10 7 V/m) above the EFN surface. Herein, we report that the magnitude and distribution of this fringing electric field correlate with the intrinsic sensor response to volatile organic compounds. The local variations of the surface electric field influence the analyte-surface interaction affecting the work function of the sensor surface, assessed by Kelvin probe force microscopy on the nanometer scale. We show that the sensitivity to fixed vapor analyte concentrations can be nullified and even reversed by varying the fringing field strength, and demonstrate selectivity between ethanol and n-butylamine at room temperature using a single transistor without any extrinsic chemical modification of the exposed SiO 2 surface. The results imply an electric-field-controlled analyte reaction with a dielectric surface extremely compelling for sensitivity and selectivity enhancement in chemical sensors.

Constraining the String Gauge Field by Galaxy Rotation Curves and Perihelion Precession of Planets

NASA Astrophysics Data System (ADS)

Cheung, Yeuk-Kwan E.; Xu, Feng

2013-09-01

We discuss a cosmological model in which the string gauge field coupled universally to matter gives rise to an extra centripetal force and will have observable signatures on cosmological and astronomical observations. Several tests are performed using data including galaxy rotation curves of 22 spiral galaxies of varied luminosities and sizes and perihelion precessions of planets in the solar system. The rotation curves of the same group of galaxies are independently fit using a dark matter model with the generalized Navarro-Frenk-White (NFW) profile and the string model. A remarkable fit of galaxy rotation curves is achieved using the one-parameter string model as compared to the three-parameter dark matter model with the NFW profile. The average χ2 value of the NFW fit is 9% better than that of the string model at a price of two more free parameters. Furthermore, from the string model, we can give a dynamical explanation for the phenomenological Tully-Fisher relation. We are able to derive a relation between field strength, galaxy size, and luminosity, which can be verified with data from the 22 galaxies. To further test the hypothesis of the universal existence of the string gauge field, we apply our string model to the solar system. Constraint on the magnitude of the string field in the solar system is deduced from the current ranges for any anomalous perihelion precession of planets allowed by the latest observations. The field distribution resembles a dipole field originating from the Sun. The string field strength deduced from the solar system observations is of a similar magnitude as the field strength needed to sustain the rotational speed of the Sun inside the Milky Way. This hypothesis can be tested further by future observations with higher precision.

Nd2-xCexCuO4-y/Nd2-xCexOy boundary and resistive switchings in mesoscopic structures on base of epitaxial Nd1.86Ce0.14CuO4-у films

NASA Astrophysics Data System (ADS)

Tulina, N. A.; Rossolenko, A. N.; Ivanov, A. A.; Sirotkin, V. V.; Shmytko, I. M.; Borisenko, I. Yu.; Ionov, A. M.

2016-08-01

Reverse and stable bipolar resistive switching effect (BRSE) was observed in planar Nd2-xCex CuO4-y/Nd2-xCexOx/Ag heterostructure. It was shown that the СVС of the BRSE observed has a diode character. Simulations were used to consider the influence of the nonuniform distribution of an electric field at the interface of a heterojunction on the effect of bipolar resistive switching in investigated structures. The inhomogeneous distribution of the electric field near the contact edge creates regions of higher electric field strength which, in turn, stimulates motion and redistribution of defects, changes of the resistive properties of the whole structure and formation of a percolation channel.

Electric dipole-quadrupole hybridization induced enhancement of second-harmonic generation in T-shaped plasmonic heterodimers.

PubMed

Guo, Kai; Zhang, Yong-Liang; Qian, Cheng; Fung, Kin-Hung

2018-04-30

In this work, we demonstrate computationally that electric dipole-quadrupole hybridization (EDQH) could be utilized to enhance plasmonic SHG efficiency. To this end, we construct T-shaped plasmonic heterodimers consisting of a short and a long gold nanorod with finite element method simulation. By controlling the strength of capacitive coupling between two gold nanorods, we explore the effect of EDQH evolution on the SHG process, including the SHG efficiency enhancement, corresponding near-field distribution, and far-field radiation pattern. Simulation results demonstrate that EDQH could enhance the SHG efficiency by a factor >100 in comparison with that achieved by an isolated gold nanorod. Additionally, the far-field pattern of the SHG could be adjusted beyond the well-known quadrupolar distribution and confirms that EDQH plays an important role in the SHG process.

A study of temporal dynamics and spatial variability of power frequency electromagnetic fields in Saint-Petersburg

NASA Astrophysics Data System (ADS)

Sturman, V. I.

2018-01-01

This paper studies spatial distribution and temporal dynamics of power frequency electric and magnetic fields in Saint-Petersburg. It was determined that sanitary-protection and exclusion zones of the standard size high-voltage transmission lines (HVTL) do not always ensure maximum allowable limits of the electrical field depression. A dependence of the electric field strength on meteorological factors was defined. A series of sources create a city-wide background for magnetic fields. That said, the heavier the man-caused load is, the higher the mean values of magnetic induction are. Abnormally high values of magnetic induction are explained by the influence of underground electric cables.

Electromagnetic-field amplification in finite one-dimensional photonic crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gorelik, V. S.; Kapaev, V. V., E-mail: kapaev@sci.lebedev.ru

2016-09-15

The electromagnetic-field distribution in a finite one-dimensional photonic crystal is studied using the numerical solution of Maxwell’s equations by the transfer-matrix method. The dependence of the transmission coefficient T on the period d (or the wavelength λ) has the characteristic form with M–1 (M is the number of periods in the structure) maxima with T = 1 in the allowed band of an infinite crystal and zero values in the forbidden band. The field-modulus distribution E(x) in the structure for parameters that correspond to the transmission maxima closest to the boundaries of forbidden bands has maxima at the center ofmore » the structure; the value at the maximum considerably exceeds the incident-field strength. For the number of periods M ~ 50, more than an order of magnitude increase in the field amplification is observed. The numerical results are interpreted with an analytic theory constructed by representing the solution in the form of a linear combination of counterpropagating Floquet modes in a periodic structure.« less

Modelling of three long-periodic magnetic CP-stars: HD 2453, HD 12288, and HD 200311

NASA Astrophysics Data System (ADS)

Glagolevskij, Yurij V.; Gerth, Ewald

2004-12-01

Using observational data published as phase curves of the effective magnetic field strength Be(P) and the surface field Bs(P), magnetic models of three stars with long rotational periods are calculated by the Magnetic Charge Distribution method. For two of these stars (HD 2453 and HD 12288), the structure of the magnetic field can be described well by a central dipole model. The third star (HD 200311) is better fitted by a model of a displaced dipole, being decentered by triangle r = 0.08 R along the dipole axis.

Coupled-cluster treatment of molecular strong-field ionization

NASA Astrophysics Data System (ADS)

Jagau, Thomas-C.

2018-05-01

Ionization rates and Stark shifts of H2, CO, O2, H2O, and CH4 in static electric fields have been computed with coupled-cluster methods in a basis set of atom-centered Gaussian functions with a complex-scaled exponent. Consideration of electron correlation is found to be of great importance even for a qualitatively correct description of the dependence of ionization rates and Stark shifts on the strength and orientation of the external field. The analysis of the second moments of the molecular charge distribution suggests a simple criterion for distinguishing tunnel and barrier suppression ionization in polyatomic molecules.

Clustering, randomness, and regularity in cloud fields. 4. Stratocumulus cloud fields

NASA Astrophysics Data System (ADS)

Lee, J.; Chou, J.; Weger, R. C.; Welch, R. M.

1994-07-01

To complete the analysis of the spatial distribution of boundary layer cloudiness, the present study focuses on nine stratocumulus Landsat scenes. The results indicate many similarities between stratocumulus and cumulus spatial distributions. Most notably, at full spatial resolution all scenes exhibit a decidedly clustered distribution. The strength of the clustering signal decreases with increasing cloud size; the clusters themselves consist of a few clouds (less than 10), occupy a small percentage of the cloud field area (less than 5%), contain between 20% and 60% of the cloud field population, and are randomly located within the scene. In contrast, stratocumulus in almost every respect are more strongly clustered than are cumulus cloud fields. For instance, stratocumulus clusters contain more clouds per cluster, occupy a larger percentage of the total area, and have a larger percentage of clouds participating in clusters than the corresponding cumulus examples. To investigate clustering at intermediate spatial scales, the local dimensionality statistic is introduced. Results obtained from this statistic provide the first direct evidence for regularity among large (>900 m in diameter) clouds in stratocumulus and cumulus cloud fields, in support of the inhibition hypothesis of Ramirez and Bras (1990). Also, the size compensated point-to-cloud cumulative distribution function statistic is found to be necessary to obtain a consistent description of stratocumulus cloud distributions. A hypothesis regarding the underlying physical mechanisms responsible for cloud clustering is presented. It is suggested that cloud clusters often arise from 4 to 10 triggering events localized within regions less than 2 km in diameter and randomly distributed within the cloud field. As the size of the cloud surpasses the scale of the triggering region, the clustering signal weakens and the larger cloud locations become more random.

Clustering, randomness, and regularity in cloud fields. 4: Stratocumulus cloud fields

NASA Technical Reports Server (NTRS)

Lee, J.; Chou, J.; Weger, R. C.; Welch, R. M.

1994-01-01

To complete the analysis of the spatial distribution of boundary layer cloudiness, the present study focuses on nine stratocumulus Landsat scenes. The results indicate many similarities between stratocumulus and cumulus spatial distributions. Most notably, at full spatial resolution all scenes exhibit a decidedly clustered distribution. The strength of the clustering signal decreases with increasing cloud size; the clusters themselves consist of a few clouds (less than 10), occupy a small percentage of the cloud field area (less than 5%), contain between 20% and 60% of the cloud field population, and are randomly located within the scene. In contrast, stratocumulus in almost every respect are more strongly clustered than are cumulus cloud fields. For instance, stratocumulus clusters contain more clouds per cluster, occupy a larger percentage of the total area, and have a larger percentage of clouds participating in clusters than the corresponding cumulus examples. To investigate clustering at intermediate spatial scales, the local dimensionality statistic is introduced. Results obtained from this statistic provide the first direct evidence for regularity among large (more than 900 m in diameter) clouds in stratocumulus and cumulus cloud fields, in support of the inhibition hypothesis of Ramirez and Bras (1990). Also, the size compensated point-to-cloud cumulative distribution function statistic is found to be necessary to obtain a consistent description of stratocumulus cloud distributions. A hypothesis regarding the underlying physical mechanisms responsible for cloud clustering is presented. It is suggested that cloud clusters often arise from 4 to 10 triggering events localized within regions less than 2 km in diameter and randomly distributed within the cloud field. As the size of the cloud surpasses the scale of the triggering region, the clustering signal weakens and the larger cloud locations become more random.

FIRST MAGNETIC FIELD MODELS FOR RECENTLY DISCOVERED MAGNETIC {beta} CEPHEI AND SLOWLY PULSATING B STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hubrig, S.; Ilyin, I.; Schoeller, M.

2011-01-01

In spite of recent detections of magnetic fields in a number of {beta} Cephei and slowly pulsating B (SPB) stars, their impact on stellar rotation, pulsations, and element diffusion has not yet been sufficiently studied. The reason for this is the lack of knowledge of rotation periods, the magnetic field strength distribution and temporal variability, and the field geometry. New longitudinal field measurements of four {beta} Cephei and candidate {beta} Cephei stars, and two SPB stars were acquired with FORS 2 at the Very Large Telescope. These measurements allowed us to carry out a search for rotation periods and tomore » constrain the magnetic field geometry for four stars in our sample.« less

Galactic X-ray emission from pulsars

NASA Technical Reports Server (NTRS)

Harding, A. K.

1981-01-01

The contribution of pulsars to the gamma-ray flux from the galactic plane is examined using data from the most recent pulsar surveys. It is assumed that pulsar gamma-rays are produced by curvature radiation from relativistic particles above the polar cap and attenuated by pair production in the strong magnetic and electric fields. Assuming that all pulsars produce gamma-rays in this way, their luminosities can be predicted as a function of period and magnetic field strength. Using the distribution of pulsars in the galaxy as determined from data on 328 pulsars detected in three surveys, the local gamma-ray production spectrum, the longitude profile, and the latitude profile of pulsar gamma-ray flux are calculated. The largest sources of uncertainty in the size of the pulsar contribution are the value of the mean interstellar electron density, the turnover in the pulsar radio luminosity function, and the average pulsar magnetic field strength. A present estimate is that pulsars contribute from 15 to 20 % of the total flux of gamma-rays from the galactic plane.

Stark effect of Ar I lines for electric field strength diagnostics in the cathode sheath of glow discharge

NASA Astrophysics Data System (ADS)

Vasiljević, Milica M.; Spasojević, Djordje; Šišović, Nikola M.; Konjević, Nikola

2017-09-01

We present a study of argon glow discharge which shows that measured wavenumber DC Stark shifts Δ ν of two neutral argon lines, Ar I 518.75 nm and Ar I 522.127 nm, can be used for reliable determination of the electric field strength F distribution in the cathode sheath region of the discharge. In order to experimentally determine the coefficient c in quadratic correlation Δ ν =cF2 , manifested in a low field range (up to 15 kV/cm), the discharge is seeded with a small admixture of hydrogen, and the values of F are measured via Stark polarization spectroscopy of the hydrogen Balmer beta line. Once known, this can be used for the determination of F by a simple and inexpensive spectroscopic Stark shift measurement in discharges with other argon admixtures or pure argon. Reported shift results are in good agreement with data extrapolated from measurements performed at high electric fields (over 100 kV/cm) by Windholz (Phys. Scr., 21 (1980) 67).

Indentation of a free-falling lance penetrometer into a poroelastic seabed

NASA Astrophysics Data System (ADS)

Elsworth, Derek; Lee, Dae Sung

2005-02-01

A solution is developed for the build-up, steady and post-arrest dissipative pore fluid pressure fields that develop around a blunt penetrometer that self-embeds from freefall into the seabed. Arrest from freefall considers deceleration under undrained conditions in a purely cohesive soil, with constant shear strength with depth. The resulting decelerating velocity field is controlled by soil strength, geometric bearing capacity factors, and inertial components. At low impact velocities the embedment process is controlled by soil strength, and at high velocities by inertia. With the deceleration defined, a solution is evaluated for a point normal dislocation penetrating in a poroelastic medium with a prescribed decelerating velocity. Dynamic steady pressures, PD, develop relative to the penetrating tip geometry with their distribution conditioned by the non-dimensional penetration rate, UD, incorporating impacting penetration rate, consolidation coefficient and penetrometer radius, and the non-dimensional strength, ND, additionally incorporating undrained shear strength of the sediment. Pore pressures develop to a steady peak magnitude at the penetrometer tip, and drop as PD=1/xD with distance xD behind the tip and along the shaft. Peak induced pressure magnitudes may be correlated with sediment permeabilities, post-arrest dissipation rates may be correlated with consolidation coefficients, and depths of penetration may be correlated with shear strengths. Together, these records enable strength and transport parameters to be recovered from lance penetrometer data. Penetrometer data recorded off La Palma in the Canary Islands (J. Volcanol. Geotherm. Res. 2000; 101:253) are used to recover permeabilities and consolidation coefficients from peak pressure and dissipation response, respectively. Copyright

Feeling Gravity's Pull: Gravity Modeling. The Gravity Field of Mars

NASA Technical Reports Server (NTRS)

Lemoine, Frank; Smith, David; Rowlands, David; Zuber, Maria; Neumann, G.; Chinn, Douglas; Pavlis, D.

2000-01-01

Most people take the constant presence of gravitys pull for granted. However, the Earth's gravitational strength actually varies from location to location. This variation occurs because mass, which influences an object's gravitational pull, is not evenly distributed within the planet. Changes in topography, such as glacial movement, an earthquake, or a rise in the ocean level, can subtly affect the gravity field. An accurate measurement of the Earth's gravity field helps us understand the distribution of mass beneath the surface. This insight can assist us in locating petroleum, mineral deposits, ground water, and other valuable substances. Gravity mapping can also help notice or verify changes in sea surface height and other ocean characteristics. Such changes may indicate climate change from polar ice melting and other phenomena. In addition, gravity mapping can indicate how land moves under the surface after earthquakes and other plate tectonic processes. Finally, changes in the Earth's gravity field might indicate a shift in water distribution that could affect agriculture, water supplies for population centers, and long-term weather prediction. Scientists can map out the Earth's gravity field by watching satellite orbits. When a satellite shifts in vertical position, it might be passing over an area where gravity changes in strength. Gravity is only one factor that may shape a satellite's orbital path. To derive a gravity measurement from satellite movement, scientists must remove other factors that might affect a satellite's position: 1. Drag from atmospheric friction. 2. Pressure from solar radiation as it heads toward Earth and. as it is reflected off the surface of the Earth 3. Gravitational pull from the Sun, the Moon, and other planets in the Solar System. 4. The effect of tides. 5. Relativistic effects. Scientists must also correct for the satellite tracking process. For example, the tracking signal must be corrected for refraction through the atmosphere of the Earth. Supercomputers can calculate the effect of gravity for specific locations in space following a mathematical process known as spherical harmonics, which quantifies the gravity field of a planetary body. The process is based on Laplace's fundamental differential equation of gravity. The accuracy of a spherical harmonic solution is rated by its degree and order. Minute variations in gravity are measured against the geoid, a surface of constant gravity acceleration at mean sea level. The geoid reference gravity model strength includes the central body gravitational attraction (9.8 m/sq s) and a geopotential variation in latitude partially caused by the rotation of the Earth. The rotational effect modifies the shape of the geoid to be more like an ellipsoid, rather than a perfect, circle. Variations of gravity strength from the ellipsoidal reference model are measured in units called milli-Galileos (mGals). One mGal equals 10(exp -5) m/sq s. Research projects have also measured the gravity fields of other planetary bodies, as noted in the user profile that follows. From this information, we may make inferences about our own planet's internal structure and evolution. Moreover, mapping the gravity fields of other planets can help scientists plot the most fuel-efficient course for spacecraft expeditions to those planets.

Recyclable plastics as substrata for settlement and growth of bryozoans Bugula neritina and barnacles Amphibalanus amphitrite.

PubMed

Li, Heng-Xiang; Orihuela, Beatriz; Zhu, Mei; Rittschof, Daniel

2016-11-01

Plastics are common and pervasive anthropogenic debris in marine environments. Floating plastics provide opportunities to alter the abundance, distribution and invasion potential of sessile organisms that colonize them. We selected plastics from seven recycle categories and quantified settlement of (i) bryozoans Bugula neritina (Linnaeus, 1758) in the lab and in the field, and of (ii) barnacles Amphibalanus (= Balanus) amphitrite (Darwin, 1854) in the field. In the laboratory we cultured barnacles on the plastics for 8 weeks and quantified growth, mortality, and breaking strength of the side plates. In the field all recyclable plastics were settlement substrata for bryozoans and barnacles. Settlement depended on the type of plastic. Fewer barnacles settled on plastic surfaces compared to glass. In the lab and in the field, bryozoan settlement was higher on plastics than on glass. In static laboratory rearing, barnacles growing on plastics were initially significantly smaller than on glass. This suggested juvenile barnacles were adversely impacted by materials leaching from the plastics. Barnacle mortality was not significantly different between plastic and glass surfaces, but breaking strength of side plates of barnacles on polyvinyl chloride (PVC) and polycarbonate (PC) were significantly lower than breakage strength on glass. Plastics impact marine ecosystems directly by providing new surfaces for colonization with fouling organisms and by contaminants shown previously to leach out of plastics and impact biological processes. Published by Elsevier Ltd.

Computational methods for analyzing the transmission characteristics of a beta particle magnetic analysis system

NASA Technical Reports Server (NTRS)

Singh, J. J.

1979-01-01

Computational methods were developed to study the trajectories of beta particles (positrons) through a magnetic analysis system as a function of the spatial distribution of the radionuclides in the beta source, size and shape of the source collimator, and the strength of the analyzer magnetic field. On the basis of these methods, the particle flux, their energy spectrum, and source-to-target transit times have been calculated for Na-22 positrons as a function of the analyzer magnetic field and the size and location of the target. These data are in studies requiring parallel beams of positrons of uniform energy such as measurement of the moisture distribution in composite materials. Computer programs for obtaining various trajectories are included.

A total and polarized infrared flux view of the AGN clumpy torus

NASA Astrophysics Data System (ADS)

Lopez Rodriguez, Enrique

2013-12-01

Magnetohydrodynamical theories consider the torus of Active Galactic Nuclei (AGN) to be part of an outflow wind moving away from the central engine. In this framework, the torus is a particular region of the wind, where dusty and optically thick clouds are formed. The outflows are strongly related to the accretion rate and magnetic field strength, which play an important role in the creation, morphology and evolution of the torus. Through infrared (IR) imaging and polarimetry observations, this dissertation (1) searches for signatures of dusty tori in low-luminosity AGN (LLAGN); (2) explores the role and strength of magnetic field in the torus; and (3) investigates the nucleus of radio-loud AGN. Recent theoretical models predicted that LLAGN do not host a Seyfert-like torus, since low-luminosities (<1042 erg s-1 ) cannot sustain the required outflow rate. High-spatial resolution mid-IR (MIR) imaging and nuclear spectral energy distribution of 22 LLAGN reveals different IR characteristics by dividing the sample in terms of the Eddington ratio. These galaxies show a diversity of nuclear morphologies and have a high MIR/X-ray luminosity ratio compared to higher-luminosity AGN. Star formation, jets and/or truncated accretion disk can explain the MIR excess. Although several models have been made to account for the outflowing dusty winds from the central engine, the magnetic field strength at the position of the torus remains poorly characterized. Through a novel study using near-IR polarimetry, the magnetic field strength in the clumpy torus was estimated. Specifically, if paramagnetic alignment is assumed in the dusty clouds of the torus, the magnetic field strength of the torus of IC5063 is estimated to be in the range of 12--128 mG. Alternatively, Chandrasekhar-Fermi method suggests a lower-limit magnetic field strength of 13 mG. For the archetypical radio-loud AGN, Cygnus A, MIR polarimetry using CanariCam on the 10.4-m Gran Telescopio de Canarias revealed a high polarized, 11+/-3% and 12+/-3% (at Si2 and Si5 respectively) unresolved nucleus. Polarimetric modeling suggests that the MIR polarization arises from a synchrotron component. This result represents the most compelling MIR polarization detection of synchrotron radiation in Cygnus A.

Magnetic Field Fluctuations Observed in the Heliosheath and Interstellar Magnetic Field by Voyager 1 at 115.7-124.9 AU during 2011-2013

NASA Astrophysics Data System (ADS)

Burlaga, L. F.; Ness, N. F.; Florinski, V.; Heerikhuisen, J.

2014-09-01

We discuss microscale fluctuations of the hour averages of the magnetic field B observed on a scale of one day by Voyager 1 (V1) from 2011.0 to 2012.3143 (when it was within the distant heliosheath, where the average magnetic field strength langBrang = 0.17 nT) and during the interval from 2012.6503 to 2013.5855 (when it was within the interstellar plasma with langBrang = 0.47 nT). In both regions, the fluctuations were primarily compressive fluctuations, varying along the average B (≈T direction in RTN coordinates). In the heliosheath, the average of the daily standard deviations (SDs) of the compressive and transverse components of B were langSDcrang = 0.010 nT and langSDtrang <= 0.005 nT (which is the limit of the measurement). In the distant heliosheath langSDcrang/langBrang = 0.06, and the distributions of SD were skewed and highly kurtotic. The interstellar magnetic field (ISMF) strength was B = 0.48 nT, but the fluctuations were below the limit of measurement: langSDcrang = 0.004 nT and langabs(SDt)rang = 0.004 nT. The distributions of these interstellar SDs have skewness and kurtosis consistent with a Gaussian noise distribution. We also discuss the fluctuations of 48 s averages of B on a scale of 1 day during a 30 day interval when V1 was observing the ISMF. For the fluctuations in all three components of B, SD = 0.010 nT, which gives an upper limit on the fluctuations of the ISMF on the scales observed by V1. This SD rules out the possibility that there is significant power in electromagnetic fluctuations generated by pickup ion ring instabilities at these scales, which strongly constrains models of the IBEX ribbon.

Outdoor characterization of radio frequency electromagnetic fields in a Spanish birth cohort.

PubMed

Calvente, I; Fernández, M F; Pérez-Lobato, R; Dávila-Arias, C; Ocón, O; Ramos, R; Ríos-Arrabal, S; Villalba-Moreno, J; Olea, N; Núñez, M I

2015-04-01

There is considerable public concern in many countries about the possible adverse effects of exposure to non-ionizing radiation electromagnetic fields, especially in vulnerable populations such as children. The aim of this study was to characterize environmental exposure profiles within the frequency range 100kHz-6GHz in the immediate surrounds of the dwellings of 123 families from the INMA-Granada birth cohort in Southern Spain, using spot measurements. The arithmetic mean root mean-square electric field (ERMS) and power density (SRMS) values were, respectively, 195.79mV/m (42.3% of data were above this mean) and 799.01µW/m(2) (30% of values were above this mean); median values were 148.80mV/m and 285.94µW/m(2), respectively. Exposure levels below the quantification limit were assigned a value of 0.01V/m. Incident field strength levels varied widely among different areas or towns/villages, demonstrating spatial variability in the distribution of exposure values related to the surface area population size and also among seasons. Although recorded values were well below International Commission for Non-Ionizing Radiation Protection reference levels, there is a particular need to characterize incident field strength levels in vulnerable populations (e.g., children) because of their chronic and ever-increasing exposure. The effects of incident field strength have not been fully elucidated; however, it may be appropriate to apply the precautionary principle in order to reduce exposure in susceptible groups. Copyright © 2014 Elsevier Inc. All rights reserved.

Electric wind in a Differential Mobility Analyzer

DOE PAGES

Palo, Marus; Meelis Eller; Uin, Janek; ...

2015-10-25

Electric wind -- the movement of gas, induced by ions moving in an electric field -- can be a distorting factor in size distribution measurements using Differential Mobility Analyzers (DMAs). The aim of this study was to determine the conditions under which electric wind occurs in the locally-built VLDMA (Very Long Differential Mobility Analyzer) and TSI Long-DMA (3081) and to describe the associated distortion of the measured spectra. Electric wind proved to be promoted by the increase of electric field strength, aerosol layer thickness, particle number concentration and particle size. The measured size spectra revealed three types of distortion: wideningmore » of the size distribution, shift of the mode of the distribution to smaller diameters and smoothing out the peaks of the multiply charged particles. Electric wind may therefore be a source of severe distortion of the spectrum when measuring large particles at high concentrations.« less

Asymptotic expansion of pair production probability in a time-dependent electric field

NASA Astrophysics Data System (ADS)

Arai, Takashi

2015-12-01

We study particle creation in a single pulse of an electric field in scalar quantum electrodynamics. We investigate the parameter condition for the case where the dynamical pair creation and Schwinger mechanism respectively dominate. Then, an asymptotic expansion for the particle distribution in terms of the time interval of the applied electric field is derived. We compare our result with particle creation in a constant electric field with a finite-time interval. These results coincide in an extremely strong field, however they differ in general field strength. We interpret the reason of this difference as a nonperturbative effect of high-frequency photons in external electric fields. Moreover, we find that the next-to-leading-order term in our asymptotic expansion coincides with the derivative expansion of the effective action.

Separation of non-stationary multi-source sound field based on the interpolated time-domain equivalent source method

NASA Astrophysics Data System (ADS)

Bi, Chuan-Xing; Geng, Lin; Zhang, Xiao-Zheng

2016-05-01

In the sound field with multiple non-stationary sources, the measured pressure is the sum of the pressures generated by all sources, and thus cannot be used directly for studying the vibration and sound radiation characteristics of every source alone. This paper proposes a separation model based on the interpolated time-domain equivalent source method (ITDESM) to separate the pressure field belonging to every source from the non-stationary multi-source sound field. In the proposed method, ITDESM is first extended to establish the relationship between the mixed time-dependent pressure and all the equivalent sources distributed on every source with known location and geometry information, and all the equivalent source strengths at each time step are solved by an iterative solving process; then, the corresponding equivalent source strengths of one interested source are used to calculate the pressure field generated by that source alone. Numerical simulation of two baffled circular pistons demonstrates that the proposed method can be effective in separating the non-stationary pressure generated by every source alone in both time and space domains. An experiment with two speakers in a semi-anechoic chamber further evidences the effectiveness of the proposed method.

21cm Absorption Line Zeeman Observations And Modeling Of Physical Conditions In M16

NASA Astrophysics Data System (ADS)

Kiuchi, Furea; Brogan, C.; Troland, T.

2011-01-01

We present detailed 21 cm HI absorption line observations of M16 using the Very Large Array. The M16 "pillars of creation" are classic examples of the interaction of ISM with radiation from young, hot stars. Magnetic fields can affect these interactions, the 21 cm Zeeman effect reveals magnetic field strengths in the Photodissociation regions associated with the pillars. The present results yield a 3-sigma upper limit upon the line-of-sight magnetic field of about 300 microgauss. This limit is consistent with a total field strength of 500 microgauss, required in the molecular gas if magnetic energies and turbulent energies in the pillars are in equipartition. Most likely, magnetic fields do not play a dominant role in the dynamics of the M16 pillars. Another goal of this study is to determine the distribution of cold HI in the M16 region and to model the physical conditions in the neutral gas in the pillars. We used the spectral synthesis code Cloudy 08.00 for this purpose. We adopted the results of a published Cloudy HII region model and extended this model into the neutral gas to derive physical conditions therein.

Determination of Anisotropic Ion Velocity Distribution Function in Intrinsic Gas Plasma. Theory.

NASA Astrophysics Data System (ADS)

Mustafaev, A.; Grabovskiy, A.; Murillo, O.; Soukhomlinov, V.

2018-02-01

The first seven coefficients of the expansion of the energy and angular distribution functions in Legendre polynomials for Hg+ ions in Hg vapor plasma with the parameter E/P ≈ 400 V/(cm Torr) are measured for the first time using a planar one-sided probe. The analytic solution to the Boltzmann kinetic equation for ions in the plasma of their parent gas is obtained in the conditions when the resonant charge exchange is the predominant process, and ions acquire on their mean free path a velocity much higher than the characteristic velocity of thermal motion of atoms. The presence of an ambipolar field of an arbitrary strength is taken into account. It is shown that the ion velocity distribution function is determined by two parameters and differs substantially from the Maxwellian distribution. Comparison of the results of calculation of the drift velocity of He+ ions in He, Ar+ in Ar, and Hg+ in Hg with the available experimental data shows their conformity. The results of the calculation of the ion distribution function correctly describe the experimental data obtained from its measurement. Analysis of the result shows that in spite of the presence of the strong field, the ion velocity distribution functions are isotropic for ion velocities lower than the average thermal velocity of atoms. With increasing ion velocity, the distribution becomes more and more extended in the direction of the electric field.

Bivariate- distribution for transition matrix elements in Breit-Wigner to Gaussian domains of interacting particle systems.

PubMed

Kota, V K B; Chavda, N D; Sahu, R

2006-04-01

Interacting many-particle systems with a mean-field one-body part plus a chaos generating random two-body interaction having strength lambda exhibit Poisson to Gaussian orthogonal ensemble and Breit-Wigner (BW) to Gaussian transitions in level fluctuations and strength functions with transition points marked by lambda = lambda c and lambda = lambda F, respectively; lambda F > lambda c. For these systems a theory for the matrix elements of one-body transition operators is available, as valid in the Gaussian domain, with lambda > lambda F, in terms of orbital occupation numbers, level densities, and an integral involving a bivariate Gaussian in the initial and final energies. Here we show that, using a bivariate-t distribution, the theory extends below from the Gaussian regime to the BW regime up to lambda = lambda c. This is well tested in numerical calculations for 6 spinless fermions in 12 single-particle states.

Significantly improved dielectric performances of nanocomposites via loading two-dimensional core-shell structure Bi2Te3@SiO2 nanosheets

NASA Astrophysics Data System (ADS)

Chen, Jianwen; Wang, Xiucai; Yu, Xinmei; Fan, Yun; Duan, Zhikui; Jiang, Yewen; Yang, Faquan; Zhou, Yuexia

2018-07-01

Polymer/semiconductor-insulator nanocomposites can display high dielectric constants with a relatively low dissipation factor under low electric fields, and thus seem to promising for high energy density capacitors. Here, a novel nanocomposite films is developed by loading two-dimensional (2D) core-shell structure Bi2Te3@SiO2 nanosheets in the poly (vinylidene fluoride-hexafluoro propylene) (P(VDF-HFP)) polymer matrix. The 2D Bi2Te3 nanosheets were prepared through simple microwave-assisted method. The experimental results suggesting that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the dielectric constant, dielectric loss, AC conductivity, and breakdown strength of composites films. The composite films load with 10 vol.% 2D Bi2Te3@SiO2 nanosheets exhibits a high dielectric constant of 70.3 at 1 kHz and relatively low dielectric loss of 0.058 at 1 kHz. The finite element simulation of electric field and electric current density distribution revealed that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the energy loss, local electric field strength, and breakdown strength of composite films. Therefore, this work will provide a promising route to achieve high-performance capacitors.

Modulating protein behaviors on responsive surface by external electric fields: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Xie, Yun; Pan, Yufang; Zhang, Rong; Liang, Ying; Li, Zhanchao

2015-01-01

Molecular dynamics simulations were employed to investigate the modulation of protein behaviors on the electrically responsive zwitterionic phosphorylcholine self-assembled monolayers (PC-SAMs). Results show that PC-SAMs could sensitively respond to the applied electric fields and exhibit three states with different charge distributions, namely both the negatively charged phosphate groups and the positively charged choline groups are exposed to the solution in the absence of electric fields (state 1), phosphate groups exposed in the presence of positive electric fields (state 2), and choline groups exposed in the presence of negative electric fields (state 3). Under state 1, the adsorption of Cyt c on the PC-SAM is reversible and the orientations of Cyt c are randomly distributed. Under state 2, the adsorption of Cyt c is enhanced due to the electrostatic attractions between the exposed phosphate groups and the positively charged protein; when adsorbed on the PC-SAMs, Cyt c tends to adopt the orientation with the heme plane perpendicular to the surface plane, and the percentage of this orientation increases as the field strength rises up. Under state 3, the adsorption of Cyt c is retarded because of the electrostatic repulsions between the exposed choline groups and the protein; however, if the gaps between PC chains are large enough, Cyt c could insert into the PC-SAM and access the phosphate groups after overcoming a slight energy barrier. Under three states, the basic backbone structures of Cyt c are well kept within the simulation time since the conformation of Cyt c is mainly affected by the surface-generated electric fields, whose strengths are modulated by the external electric fields and are not strong enough to deform protein. The results indicate the possibility of regulating protein behaviors, including promoting or retarding protein adsorption and regulating protein orientations, on responsive surfaces by applying electric fields on the surfaces without worrying protein deformation, which may be helpful in the applications of protein separation and controlled drug delivery.

Constraints on the Location of γ-Ray Sample of Blazars with Radio Core-shift Measurements

NASA Astrophysics Data System (ADS)

Wu, Linhui; Wu, Qingwen; Yan, Dahai; Chen, Liang; Fan, Xuliang

2018-01-01

We model simultaneous or quasi-simultaneous multi-band spectral energy distributions (SEDs) for a sample of 25 blazars that have radio core-shift measurements, where a one-zone leptonic model and Markov chain Monte Carlo technique are adopted. In the SED fitting for 23 low-synchrotron-peaked (LSP) blazars, the seed photons from the broad-line (BLR) and molecular torus are considered respectively in the external Compton process. We find that the SED fitting with the seed photons from the torus are better than those utilizing BLR photons, which suggest that the γ-ray emitting region may be located outside the BLR. Assuming the magnetic field strength in the γ-ray emitting region as constrained from the SED fitting follows the magnetic field distribution as derived from the radio core-shift measurements (i.e., B{(R)≃ {B}1{pc}(R/1{pc})}-1, where R is the distance from the central engine and {B}1{pc} is the magnetic field strength at 1 pc), we further calculate the location of the γ-ray emitting region, {R}γ , for these blazars. We find that {R}γ ∼ 2× {10}4{R}{{S}}≃ 10 {R}{BLR} ({R}{{S}} is the Schwarzschild radius and {R}{BLR} is the BLR size), where {R}{BLR} is estimated from the broad-line luminosities using the empirical correlations obtained using the reverberation mapping methods.

Effect of External Economic-Field Cycle and Market Temperature on Stock-Price Hysteresis: Monte Carlo Simulation on the Ising Spin Model

NASA Astrophysics Data System (ADS)

Punya Jaroenjittichai, Atchara; Laosiritaworn, Yongyut

2017-09-01

In this work, the stock-price versus economic-field hysteresis was investigated. The Ising spin Hamiltonian was utilized as the level of ‘disagreement’ in describing investors’ behaviour. The Ising spin directions were referred to an investor’s intention to perform his action on trading his stock. The periodic economic variation was also considered via the external economic-field in the Ising model. The stochastic Monte Carlo simulation was performed on Ising spins, where the steady-state excess demand and supply as well as the stock-price were extracted via the magnetization. From the results, the economic-field parameters and market temperature were found to have significant effect on the dynamic magnetization and stock-price behaviour. Specifically, the hysteresis changes from asymmetric to symmetric loops with increasing market temperature and economic-field strength. However, the hysteresis changes from symmetric to asymmetric loops with increasing the economic-field frequency, when either temperature or economic-field strength is large enough, and returns to symmetric shape at very high frequencies. This suggests competitive effects among field and temperature factors on the hysteresis characteristic, implying multi-dimensional complicated non-trivial relationship among inputs-outputs. As is seen, the results reported (over extensive range) can be used as basis/guideline for further analysis/quantifying how economic-field and market-temperature affect the stock-price distribution on the course of economic cycle.

Electrically tunable negative refraction in core/shell-structured nanorod fluids.

PubMed

Su, Zhaoxian; Yin, Jianbo; Guan, Yanqing; Zhao, Xiaopeng

2014-10-21

We theoretically investigate optical refraction behavior in a fluid system which contains silica-coated gold nanorods dispersed in silicone oil under an external electric field. Because of the formation of a chain-like or lattice-like structure of dispersed nanorods along the electric field, the fluid shows a hyperbolic equifrequency contour characteristic and, as a result, all-angle broadband optical negative refraction for transverse magnetic wave propagation can be realized. We calculate the effective permittivity tensor of the fluid and verify the analysis using finite element simulations. We also find that the negative refractive index can vary with the electric field strength and external field distribution. Under a non-uniform external field, the gradient refraction behavior can be realized.

Effects on Subtalar Joint Stress Distribution After Cannulated Screw Insertion at Different Positions and Directions.

PubMed

Yuan, Cheng-song; Chen, Wan; Chen, Chen; Yang, Guang-hua; Hu, Chao; Tang, Kang-lai

2015-01-01

We investigated the effects on subtalar joint stress distribution after cannulated screw insertion at different positions and directions. After establishing a 3-dimensional geometric model of a normal subtalar joint, we analyzed the most ideal cannulated screw insertion position and approach for subtalar joint stress distribution and compared the differences in loading stress, antirotary strength, and anti-inversion/eversion strength among lateral-medial antiparallel screw insertion, traditional screw insertion, and ideal cannulated screw insertion. The screw insertion approach allowing the most uniform subtalar joint loading stress distribution was lateral screw insertion near the border of the talar neck plus medial screw insertion close to the ankle joint. For stress distribution uniformity, antirotary strength, and anti-inversion/eversion strength, lateral-medial antiparallel screw insertion was superior to traditional double-screw insertion. Compared with ideal cannulated screw insertion, slightly poorer stress distribution uniformity and better antirotary strength and anti-inversion/eversion strength were observed for lateral-medial antiparallel screw insertion. Traditional single-screw insertion was better than double-screw insertion for stress distribution uniformity but worse for anti-rotary strength and anti-inversion/eversion strength. Lateral-medial antiparallel screw insertion was slightly worse for stress distribution uniformity than was ideal cannulated screw insertion but superior to traditional screw insertion. It was better than both ideal cannulated screw insertion and traditional screw insertion for anti-rotary strength and anti-inversion/eversion strength. Lateral-medial antiparallel screw insertion is an approach with simple localization, convenient operation, and good safety. Copyright © 2015 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Flow behind an exponential shock wave in a rotational axisymmetric perfect gas with magnetic field and variable density.

PubMed

Nath, G; Sahu, P K

2016-01-01

A self-similar model for one-dimensional unsteady isothermal and adiabatic flows behind a strong exponential shock wave driven out by a cylindrical piston moving with time according to an exponential law in an ideal gas in the presence of azimuthal magnetic field and variable density is discussed in a rotating atmosphere. The ambient medium is assumed to possess radial, axial and azimuthal component of fluid velocities. The initial density, the fluid velocities and magnetic field of the ambient medium are assumed to be varying with time according to an exponential law. The gas is taken to be non-viscous having infinite electrical conductivity. Solutions are obtained, in both the cases, when the flow between the shock and the piston is isothermal or adiabatic by taking into account the components of vorticity vector. The effects of the variation of the initial density index, adiabatic exponent of the gas and the Alfven-Mach number on the flow-field behind the shock wave are investigated. It is found that the presence of the magnetic field have decaying effects on the shock wave. Also, it is observed that the effect of an increase in the magnetic field strength is more impressive in the case of adiabatic flow than in the case of isothermal flow. The assumption of zero temperature gradient brings a profound change in the density, non-dimensional azimuthal and axial components of vorticity vector distributions in comparison to those in the case of adiabatic flow. A comparison is made between isothermal and adiabatic flows. It is obtained that an increase in the initial density variation index, adiabatic exponent and strength of the magnetic field decrease the shock strength.

Enhancement in ion adsorption rate and desalination efficiency in a capacitive deionization cell through improved electric field distribution using electrodes composed of activated carbon cloth coated with zinc oxide nanorods.

PubMed

Laxman, Karthik; Myint, Myo Tay Zar; Bourdoucen, Hadj; Dutta, Joydeep

2014-07-09

Electrodes composed of activated carbon cloth (ACC) coated with zinc oxide (ZnO) nanorods are compared with plain ACC electrodes, with respect to their desalination efficiency of a 17 mM NaCl solution at different applied potentials. Polarization of the ZnO nanorods increased the penetration depth and strength of the electric field between the electrodes, leading to an increase in the capacitance and charge efficiency at reduced input charge ratios. Uniform distribution of the electric field lines between two electrodes coated with ZnO nanorods led to faster ion adsorption rates, reduced the electrode saturation time, and increased the average desalination efficiency by ∼45% for all applied potentials. The electrodes were characterized for active surface area, capacitance from cyclic voltammetry, theoretical assessment of surface area utilization, and the magnitude of electric field force acting on an ion of unit charge for each potential.

MECHANICAL STRENGTH RESPONSES OF POLED LEAD ZIRCONATE TITANATE UNDER EXTREME ELECTRIC FIELD AND VARIOUS TEMPERATURE CONDITIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hong; Matsunaga, Tadashi; Zhang, Kewei

PZT (lead zirconate titanate), particularly PZT-5A, is used in a variety of critical actuation and sensing systems because of its high Curie temperature and large piezoelectric coefficients. However, PZT is susceptible to mechanical failure. The evaluation of the mechanical strength of the material under the target working conditions is very important. This study presents part of the recent experimental developments in mechanical testing and evaluation of PZT materials at Oak Ridge National Laboratory. Ball-on-ring and four-point bending testing setups were used, with modifications made to account for testing requirements from high-level electric field and elevated temperature. The poled PZT-5A ormore » equivalent material was tested under various specimen and testing conditions. The parameters of the distribution of strengths (characteristic strength and Weibull modulus) are discussed in relation to the testing conditions. Fractographic results based on scanning electron microscopy are also presented and discussed. The related data can serve as input for the design of piezoceramic devices, not only those used in energy systems like fuel injectors in heavy-duty diesel engines, but also those used in structural health monitoring, energy harvesting, and other critical systems in aerospace and civil engineering.« less

Transition from the Sector Zone to the Unipolar Zone in the Heliosheath: Voyager 2 Magnetic Field Observations

NASA Technical Reports Server (NTRS)

Burlaga, L. F.; Ness, N. F.

2011-01-01

The magnetic polarity pattern observed by Voyager 2 (V2) evolved with time from a nearly equal mixture of positive and negative polarity sectors in the sector zone from 2007.00 to 2007.67 to nearly uniform positive polarity (magnetic fields directed away from the Sun) in the unipolar zone from 2009.6 to 2010.3. This change was caused by the decreasing latitudinal extent of the sector zone, when the minimum extent of the heliospheric current sheet moved northward toward the solar equator as the solar activity associated with solar cycle 23 decreased a minimum in 2010. In the heliosheath, the distribution of daily averages of the magnetic field strength B was lognormal in the sector zone from 2008.83 to 2009.57 and Gaussian in the unipolar zone from 2009.57 to 2010.27. The distribution of daily increments of B was a Tsallis distribution (q-Gaussian distribution) with q = 1.66 +/- 0.010 in the sector zone and . Gaussian (q = 1.01+/-0.29) in the unipolar zone. The unipolar region appears to be in a relatively undisturbed equilibrium state.

47 CFR 73.153 - Field strength measurements in support of applications or evidence at hearings.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 4 2011-10-01 2011-10-01 false Field strength measurements in support of... (CONTINUED) BROADCAST RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.153 Field strength..., groundwave field strength measurements will take precedence over theoretical values, provided such...

47 CFR 73.311 - Field strength contours.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 4 2010-10-01 2010-10-01 false Field strength contours. 73.311 Section 73.311... Broadcast Stations § 73.311 Field strength contours. (a) Applications for FM broadcast authorizations must show the field strength contours required by FCC Form 301 or FCC Form 340, as appropriate. (b) The...

47 CFR 73.153 - Field strength measurements in support of applications or evidence at hearings.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 4 2010-10-01 2010-10-01 false Field strength measurements in support of... (CONTINUED) BROADCAST RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.153 Field strength..., groundwave field strength measurements will take precedence over theoretical values, provided such...

47 CFR 73.311 - Field strength contours.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 4 2011-10-01 2011-10-01 false Field strength contours. 73.311 Section 73.311... Broadcast Stations § 73.311 Field strength contours. (a) Applications for FM broadcast authorizations must show the field strength contours required by FCC Form 301 or FCC Form 340, as appropriate. (b) The...

Apparatus and method for magnetically processing a specimen

DOEpatents

Ludtka, Gerard M; Ludtka, Gail M; Wilgen, John B; Kisner, Roger A; Jaramillo, Roger A

2013-09-03

An apparatus for magnetically processing a specimen that couples high field strength magnetic fields with the magnetocaloric effect includes a high field strength magnet capable of generating a magnetic field of at least 1 Tesla and a magnetocaloric insert disposed within a bore of the high field strength magnet. A method for magnetically processing a specimen includes positioning a specimen adjacent to a magnetocaloric insert within a bore of a magnet and applying a high field strength magnetic field of at least 1 Tesla to the specimen and to the magnetocaloric insert. The temperature of the specimen changes during the application of the high field strength magnetic field due to the magnetocaloric effect.

Synthesis of kenaf cellulose carbamate and its smart electric stimuli-response.

PubMed

Gan, Sinyee; Piao, Shang Hao; Choi, Hyoung Jin; Zakaria, Sarani; Chia, Chin Hua

2016-02-10

Cellulose carbamate (CC) was produced from kenaf core pulp (KCP) via a microwave reactor-assisted method. The formation of CC was confirmed by Fourier transform infrared spectroscopy and nitrogen content analysis. The degree of substitution, zeta potential and size distribution of CC were also determined. The CC was characterized with scanning electron microscopy, X-ray diffraction and thermogravimetry analysis. The CC particles were then dispersed in silicone oil to prepare CC-based anhydrous electric stimuli-responsive electrorheological (ER) fluids. Rhelogical measurement was carried out using rotational rheometer with a high voltage generator in both steady and oscillatory shear modes to examine the effect of electric field strength on the ER characteristics. The results showed that the increase in electric field strength has enhanced the ER properties of CC-based ER fluid due to the chain formation induced by electric polarization among the particles. Copyright © 2015 Elsevier Ltd. All rights reserved.

Relation of Field-Aligned Currents Measured by the Network of Iridium® Spacecraft to Solar Wind and Substorms

NASA Astrophysics Data System (ADS)

McPherron, R. L.; Anderson, B. J.; Chu, Xiangning

2018-03-01

The strength of field-aligned currents coupling the magnetosphere to the ionosphere was obtained by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) using the network of Iridium® spacecraft. The distribution of current was integrated giving total current in and out of the ionosphere on the dayside and nightside of the Earth in both hemispheres. The onset of auroral zone negative bays and midlatitude positive bays corresponds to an increase in nightside upward current. The total outward current tends toward saturation with increasing solar wind driver strength. The optimum solar wind coupling function for AL index predicts 73% of the variance in nightside upward current. The dayside and nightside predictors of upward current rise to a peak at 30-45 min and decay slowly over 2.5 hr. Nightside response is delayed relative to dayside.

Parameterization of hyperpolarized (13)C-bicarbonate-dissolution dynamic nuclear polarization.

PubMed

Scholz, David Johannes; Otto, Angela M; Hintermair, Josef; Schilling, Franz; Frank, Annette; Köllisch, Ulrich; Janich, Martin A; Schulte, Rolf F; Schwaiger, Markus; Haase, Axel; Menzel, Marion I

2015-12-01

(13)C metabolic MRI using hyperpolarized (13)C-bicarbonate enables preclinical detection of pH. To improve signal-to-noise ratio, experimental procedures were refined, and the influence of pH, buffer capacity, temperature, and field strength were investigated. Bicarbonate preparation was investigated. Bicarbonate was prepared and applied in spectroscopy at 1, 3, 14 T using pure dissolution, culture medium, and MCF-7 cell spheroids. Healthy rats were imaged by spectral-spatial spiral acquisition for spatial and temporal bicarbonate distribution, pH mapping, and signal decay analysis. An optimized preparation technique for maximum solubility of 6 mol/L and polarization levels of 19-21% is presented; T1 and SNR dependency on field strength, buffer capacity, and pH was investigated. pH mapping in vivo is demonstrated. An optimized bicarbonate preparation and experimental procedure provided improved T1 and SNR values, allowing in vitro and in vivo applications.

Fiber Bundle Model Under Heterogeneous Loading

NASA Astrophysics Data System (ADS)

Roy, Subhadeep; Goswami, Sanchari

2018-03-01

The present work deals with the behavior of fiber bundle model under heterogeneous loading condition. The model is explored both in the mean-field limit as well as with local stress concentration. In the mean field limit, the failure abruptness decreases with increasing order k of heterogeneous loading. In this limit, a brittle to quasi-brittle transition is observed at a particular strength of disorder which changes with k. On the other hand, the model is hardly affected by such heterogeneity in the limit where local stress concentration plays a crucial role. The continuous limit of the heterogeneous loading is also studied and discussed in this paper. Some of the important results related to fiber bundle model are reviewed and their responses to our new scheme of heterogeneous loading are studied in details. Our findings are universal with respect to the nature of the threshold distribution adopted to assign strength to an individual fiber.

Influence of catalyst packing configuration on the discharge characteristics of dielectric barrier discharge reactors: A numerical investigation

NASA Astrophysics Data System (ADS)

Gadkari, Siddharth; Gu, Sai

2018-06-01

A two-dimensional numerical fluid model is developed for studying the influence of packing configurations on dielectric barrier discharge (DBD) characteristics. Discharge current profiles and time averaged electric field strength, electron number density, and electron temperature distributions are compared for the three DBD configurations, plain DBD with no packing, partially packed DBD, and fully packed DBD. The results show that a strong change in discharge behaviour occurs when a DBD is fully packed as compared to partial packing or no packing. While the average electric field strength and electron temperature of a fully packed DBD are higher relative to the other DBD configurations, the average electron density is substantially lower and may impede the DBD reactor performance under certain operating conditions. Possible scenarios of the synergistic effect of the combination of plasma with catalysis are also discussed.

Test of quantum thermalization in the two-dimensional transverse-field Ising model

PubMed Central

Blaß, Benjamin; Rieger, Heiko

2016-01-01

We study the quantum relaxation of the two-dimensional transverse-field Ising model after global quenches with a real-time variational Monte Carlo method and address the question whether this non-integrable, two-dimensional system thermalizes or not. We consider both interaction quenches in the paramagnetic phase and field quenches in the ferromagnetic phase and compare the time-averaged probability distributions of non-conserved quantities like magnetization and correlation functions to the thermal distributions according to the canonical Gibbs ensemble obtained with quantum Monte Carlo simulations at temperatures defined by the excess energy in the system. We find that the occurrence of thermalization crucially depends on the quench parameters: While after the interaction quenches in the paramagnetic phase thermalization can be observed, our results for the field quenches in the ferromagnetic phase show clear deviations from the thermal system. These deviations increase with the quench strength and become especially clear comparing the shape of the thermal and the time-averaged distributions, the latter ones indicating that the system does not completely lose the memory of its initial state even for strong quenches. We discuss our results with respect to a recently formulated theorem on generalized thermalization in quantum systems. PMID:27905523

Magnetic field effect on spoke behaviour

NASA Astrophysics Data System (ADS)

Hnilica, Jaroslav; Slapanska, Marta; Klein, Peter; Vasina, Petr

2016-09-01

The investigations of the non-reactive high power impulse magnetron sputtering (HiPIMS) discharge using high-speed camera imaging, optical emission spectroscopy and electrical probes showed that plasma is not homogeneously distributed over the target surface, but it is concentrated in regions of higher local plasma density called spokes rotating above the erosion racetrack. Magnetic field effect on spoke behaviour was studied by high-speed camera imaging in HiPIMS discharge using 3 inch titanium target. An employed camera enabled us to record two successive images in the same pulse with time delay of 3 μs between them, which allowed us to determine the number of spokes, spoke rotation velocity and spoke rotation frequency. The experimental conditions covered pressure range from 0.15 to 5 Pa, discharge current up to 350 A and magnetic fields of 37, 72 and 91 mT. Increase of the magnetic field influenced the number of spokes observed at the same pressure and at the same discharge current. Moreover, the investigation revealed different characteristic spoke shapes depending on the magnetic field strength - both diffusive and triangular shapes were observed for the same target material. The spoke rotation velocity was independent on the magnetic field strength. This research has been financially supported by the Czech Science Foundation in frame of the project 15-00863S.

An Ionosphere/Magnetosphere Coupling Current System Located in the Gap Between Saturn and its Rings

NASA Astrophysics Data System (ADS)

Khurana, K. K.; Dougherty, M. K.; Cao, H.; Hunt, G. J.; Provan, G.

2017-12-01

The Grand Finale Orbits of the Cassini spacecraft traversed through Saturn's D ring and brought the spacecraft to within 3000 km of Saturn's cloud tops. The closest approaches (CA) were near the equatorial plane of Saturn and were distributed narrowly around the local noon. The difference field (observations - internal field - magnetospheric ring current field) obtained from the Grand Finale orbits show persistent residual fields centered around the CA which diminish at higher latitudes on field lines that connect to the ring. Modeling of this perturbation in terms of internal harmonics shows that the perturbation is not of internal origin but is produced by external currents that couple the ionosphere to the magnetosphere. The sense of the current system suggests that the southern feet of the field lines in the ionosphere lead their northern footprints. We show that the observed field perturbations are consistent with a meridional Pedersen current whose strength is 1 MA/radian, i.e. comparable in strength to the Planetary-period-oscillation related current systems observed in the auroral zone. We show that the implied Lorentz force in the ionosphere extracts momentum from the faster moving southern ionosphere and passes it on to the northern ionosphere. We discuss several ideas for generating this current system. In particular, we highlight a mechanism that involves shears in the neutral winds in the thermospheric region to generate the observed magnetic field.

47 CFR 90.689 - Field strength limits.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 5 2011-10-01 2011-10-01 false Field strength limits. 90.689 Section 90.689...-824/851-869 Mhz Band § 90.689 Field strength limits. (a) For purposes of implementing §§ 90.689... or measured field strength at any location on the border of the EA-based service area for EA...

47 CFR 90.689 - Field strength limits.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Field strength limits. 90.689 Section 90.689...-824/851-869 Mhz Band § 90.689 Field strength limits. (a) For purposes of implementing §§ 90.689... or measured field strength at any location on the border of the EA-based service area for EA...

Sound field reproduction as an equivalent acoustical scattering problem.

PubMed

Fazi, Filippo Maria; Nelson, Philip A

2013-11-01

Given a continuous distribution of acoustic sources, the determination of the source strength that ensures the synthesis of a desired sound field is shown to be identical to the solution of an equivalent acoustic scattering problem. The paper begins with the presentation of the general theory that underpins sound field reproduction with secondary sources continuously arranged on the boundary of the reproduction region. The process of reproduction by a continuous source distribution is modeled by means of an integral operator (the single layer potential). It is then shown how the solution of the sound reproduction problem corresponds to that of an equivalent scattering problem. Analytical solutions are computed for two specific instances of this problem, involving, respectively, the use of a secondary source distribution in spherical and planar geometries. The results are shown to be the same as those obtained with analyses based on High Order Ambisonics and Wave Field Synthesis, respectively, thus bringing to light a fundamental analogy between these two methods of sound reproduction. Finally, it is shown how the physical optics (Kirchhoff) approximation enables the derivation of a high-frequency simplification for the problem under consideration, this in turn being related to the secondary source selection criterion reported in the literature on Wave Field Synthesis.

Radio polarization and magnetic field structure in M 101

NASA Astrophysics Data System (ADS)

Berkhuijsen, E. M.; Urbanik, M.; Beck, R.; Han, J. L.

2016-04-01

We observed total and polarized radio continuum emission from the spiral galaxy M 101 at λλ 6.2 cm and 11.1 cm with the Effelsberg telescope. The angular resolutions are 2.´ 5 (=5.4 kpc) and 4.´ 4 (=9.5 kpc), respectively. We use these data to study various emission components in M 101 and properties of the magnetic field. Separation of thermal and non-thermal emission shows that the thermal emission is closely correlated with the spiral arms, while the non-thermal emission is more smoothly distributed indicating diffusion of cosmic ray electrons away from their places of origin. The radial distribution of both emissions has a break near R = 16 kpc (=7.´ 4), where it steepens to an exponential scale length of L ≃ 5 kpc, which is about 2.5 times smaller than at R< 16 kpc. The distribution of the polarized emission has a broad maximum near R = 12 kpc and beyond R = 16 kpc also decreases with L ≃ 5 kpc. It seems that near R = 16 kpc a major change in the structure of M 101 takes place, which also affects the distributions of the strength of the random and ordered magnetic field. Beyond R = 16 kpc the radial scale length of both fields is about 20 kpc, which implies that they decrease to about 0.3 μG at R = 70 kpc, which is the largest optical extent. The equipartition strength of the total field ranges from nearly 10 μG at R< 2 kpc to 4 μG at R = 22-24 kpc. As the random field dominates in M 101 (Bran/Bord ≃ 2.4), wavelength-independent polarization is the main polarization mechanism. We show that energetic events causing H I shells of mean diameter < 625 pc could partly be responsible for this. At radii < 24 kpc, the random magnetic field depends on the star formation rate/area, ΣSFR, with a power-law exponent of b = 0.28 ± 0.02. The ordered magnetic field is generally aligned with the spiral arms with pitch angles that are about 8° larger than those of H I filaments. Based on observations with the 100 m telescope of the MPIfR at Effelsberg.FITS files of the images are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A114

Matrix Dissolution Techniques Applied to Extract and Quantify Precipitates from a Microalloyed Steel

NASA Astrophysics Data System (ADS)

Lu, Junfang; Wiskel, J. Barry; Omotoso, Oladipo; Henein, Hani; Ivey, Douglas G.

2011-07-01

Microalloyed steels possess good strength and toughness, as well as excellent weldability; these attributes are necessary for oil and gas pipelines in northern climates. These properties are attributed in part to the presence of nanosized carbide and carbonitride precipitates. To understand the strengthening mechanisms and to optimize the strengthening effects, it is necessary to quantify the size distribution, volume fraction, and chemical speciation of these precipitates. However, characterization techniques suitable for quantifying fine precipitates are limited because of their fine sizes, wide particle size distributions, and low volume fractions. In this article, two matrix dissolution techniques have been developed to extract precipitates from a Grade100 (yield strength of 690 MPa) microalloyed steel. Relatively large volumes of material can be analyzed, and statistically significant quantities of precipitates of different sizes are collected. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) are combined to analyze the chemical speciation of these precipitates. Rietveld refinement of XRD patterns is used to quantify fully the relative amounts of the precipitates. The size distribution of the nanosized precipitates is quantified using dark-field imaging in the TEM.

Numerical simulation of temperature field, microstructure evolution and mechanical properties of HSS during hot stamping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Dongyong; Liu, Wenquan; Ying, Liang, E-mail: pinghu@dlut.edu.cn

The hot stamping of boron steels is widely used to produce ultra high strength automobile components without any spring back. The ultra high strength of final products is attributed to the fully martensitic microstructure that is obtained through the simultaneous forming and quenching of the hot blanks after austenization. In the present study, a mathematical model incorporating both heat transfer and the transformation of austenite is presented. A FORTRAN program based on finite element technique has been developed which permits the temperature distribution and microstructure evolution of high strength steel during hot stamping process. Two empirical diffusion-dependent transformation models undermore » isothermal conditions were employed respectively, and the prediction capability on mechanical properties of the models were compared with the hot stamping experiment of an automobile B-pillar part.« less

Plasma currents and anisotropy in the tail-dipole transition region

NASA Astrophysics Data System (ADS)

Artemyev, A.; Zhang, X. J.; Angelopoulos, V.; Runov, A.

2017-12-01

Using conjugated THEMIS and Van Allen Probes observations in the nightside magnetosphere, we examine statistically plasma and magnetic field characteristics at multiple locations simultaneously across the 3-10 RE region (i.e., across the tail-dipole transition region, whose location depends on tail flux loading and the strength of global convection). We find that the spatial distributions of ion and electron anisotropies vary significantly but systematically with radial distance and geomagnetic activity. For low Kp (<2), ions are transversely anisotropic near Earth but isotropic in the tail, whereas electrons are isotropic closer to Earth but field-aligned in tail. For large Kp (>4), the anisotropy profiles for ions and electrons reverse: ions are isotropic closer to the Earth and field-aligned in the tail, whereas electrons are transversely anisotropic closer to Earth but isotropic in the tail. Using the measured plasma anisotropy radial profiles we estimate the currents from curvature drifts and compare them with diamagnetic currents. We also discuss the implications of the observed plasma anisotropies for the presence and spatial distribution of field-aligned electric fields.

Electric-field distribution in Au-semi-insulating GaAs contact investigated by positron-lifetime technique

NASA Astrophysics Data System (ADS)

Ling, C. C.; Shek, Y. F.; Huang, A. P.; Fung, S.; Beling, C. D.

1999-02-01

Positron-lifetime spectroscopy has been used to investigate the electric-field distribution occurring at the Au-semi-insulating GaAs interface. Positrons implanted from a 22Na source and drifted back to the interface are detected through their characteristic lifetime at interface traps. The relative intensity of this fraction of interface-trapped positrons reveals that the field strength in the depletion region saturates at applied biases above 50 V, an observation that cannot be reconciled with a simple depletion approximation model. The data, are, however, shown to be fully consistent with recent direct electric-field measurements and the theoretical model proposed by McGregor et al. [J. Appl. Phys. 75, 7910 (1994)] of an enhanced EL2+ electron-capture cross section above a critical electric field that causes a dramatic reduction of the depletion region's net charge density. Two theoretically derived electric field profiles, together with an experimentally based profile, are used to estimate a positron mobility of ~95+/-35 cm2 V-1 s-1 under the saturation field. This value is higher than previous experiments would suggest, and reasons for this effect are discussed.

47 CFR 90.359 - Field strength limits for EA-licensed LMS systems.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 5 2011-10-01 2011-10-01 false Field strength limits for EA-licensed LMS... § 90.359 Field strength limits for EA-licensed LMS systems. EA-licensed multilateration systems shall limit the field strength of signals transmitted from their base stations to 47 dBuV/m at their EA...

Signal-to-noise ratio and MR tissue parameters in human brain imaging at 3, 7, and 9.4 tesla using current receive coil arrays.

PubMed

Pohmann, Rolf; Speck, Oliver; Scheffler, Klaus

2016-02-01

Relaxation times, transmit homogeneity, signal-to-noise ratio (SNR) and parallel imaging g-factor were determined in the human brain at 3T, 7T, and 9.4T, using standard, tight-fitting coil arrays. The same human subjects were scanned at all three field strengths, using identical sequence parameters and similar 31- or 32-channel receive coil arrays. The SNR of three-dimensional (3D) gradient echo images was determined using a multiple replica approach and corrected with measured flip angle and T2 (*) distributions and the T1 of white matter to obtain the intrinsic SNR. The g-factor maps were derived from 3D gradient echo images with several GRAPPA accelerations. As expected, T1 values increased, T2 (*) decreased and the B1 -homogeneity deteriorated with increasing field. The SNR showed a distinctly supralinear increase with field strength by a factor of 3.10 ± 0.20 from 3T to 7T, and 1.76 ± 0.13 from 7T to 9.4T over the entire cerebrum. The g-factors did not show the expected decrease, indicating a dominating role of coil design. In standard experimental conditions, SNR increased supralinearly with field strength (SNR ∼ B0 (1.65) ). To take full advantage of this gain, the deteriorating B1 -homogeneity and the decreasing T2 (*) have to be overcome. © 2015 Wiley Periodicals, Inc.

High and ultra-high resolution metabolite mapping of the human brain using 1H FID MRSI at 9.4T.

PubMed

Nassirpour, Sahar; Chang, Paul; Henning, Anke

2018-03-01

Magnetic resonance spectroscopic imaging (MRSI) is a promising technique for mapping the spatial distribution of multiple metabolites in the human brain. These metabolite maps can be used as a diagnostic tool to gain insight into several biochemical processes and diseases in the brain. In comparison to lower field strengths, MRSI at ultra-high field strengths benefits from a higher signal to noise ratio (SNR) as well as higher chemical shift dispersion, and hence spectral resolution. This study combines the benefits of an ultra-high field magnet with the advantages of an ultra-short TE and TR single-slice FID-MRSI sequence (such as negligible J-evolution and loss of SNR due to T 2 relaxation effects) and presents the first metabolite maps acquired at 9.4T in the healthy human brain at both high (voxel size of 97.6µL) and ultra-high (voxel size of 24.4µL) spatial resolutions in a scan time of 11 and 46min respectively. In comparison to lower field strengths, more anatomically-detailed maps with higher SNR from a larger number of metabolites are shown. A total of 12 metabolites including glutamate (Glu), glutamine (Gln), N-acetyl-aspartyl-glutamate (NAAG), Gamma-aminobutyric acid (GABA) and glutathione (GSH) are reliably mapped. Comprehensive description of the methodology behind these maps is provided. Copyright © 2016 Elsevier Inc. All rights reserved.

Principles and Design of a Zeeman–Sisyphus Decelerator for Molecular Beams

PubMed Central

Tarbutt, M. R.

2016-01-01

Abstract We explore a technique for decelerating molecules using a static magnetic field and optical pumping. Molecules travel through a spatially varying magnetic field and are repeatedly pumped into a weak‐field seeking state as they move towards each strong field region, and into a strong‐field seeking state as they move towards weak field. The method is time‐independent and so is suitable for decelerating both pulsed and continuous molecular beams. By using guiding magnets at each weak field region, the beam can be simultaneously guided and decelerated. By tapering the magnetic field strength in the strong field regions, and exploiting the Doppler shift, the velocity distribution can be compressed during deceleration. We develop the principles of this deceleration technique, provide a realistic design, use numerical simulations to evaluate its performance for a beam of CaF, and compare this performance to other deceleration methods. PMID:27629547

Effects of High-pH and High-Ionic-Strength Groundwater on Iodide, Pertechnetate, and Selenate Sorption to Hanford Sediments: Final Report for Subtask 3a

DOE Office of Scientific and Technical Information (OSTI.GOV)

DI Kaplan; KE Parker; RD Orr

1998-10-14

As part of the Immobilized Low-Activity Waste-Performance Assessment three experiments were conducted to evaluate the effect of the expected near-field chemistry on the sorption of iodide, selenate, and pertechnetate onto a sediment obtained from the Hanford Site. These experiments were performed in fiscal year 1998 at the Pacific Northwest National Laboratory.' During these experiments, attention was directed at the identification of the chemical mechanisms controlling the sorption processes to provide technical defensibility for the selection of the distribution coefficients (IQ to be used in the remainder of the performance assessment. It was found, during the conduct of the experiments, thatmore » selenium and technetium I&s increased as ionic strength increased. The cause for this is most likely to be that the higher ionic strength caused the double layer around the particles to decrease, thereby permitting greater interaction with the mineral surfaces. Further, the pH level had an effect on the sorption of these anions. These are the first-ever experiments conducted with Hanford Site sediment in which the IQ were measured as a function of ionic strength and pH. Overall, the observed trends were consistent with more generalized geochemical principles. One of the most important contributions of these experiments was that they quantified the & changes induced by variations in ionic strength and pH that are expected to exist in the near field.« less

A fast integrated mobility spectrometer for rapid measurement of sub-micrometer aerosol size distribution, Part I: Design and model evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jian; Pikridas, Michael; Spielman, Steven R.

This study discusses, a fast integrated mobility spectrometer (FIMS) was previously developed to characterize submicron aerosol size distributions at a frequency of 1 Hz and with high size resolution and counting statistics. However, the dynamic size range of the FIMS was limited to one decade in particle electrical mobility. It was proposed that the FIMS dynamic size range can be greatly increased by using a spatially varying electric field. This electric field creates regions with drastically different field strengths in the separator, such that particles of a wide diameter range can be simultaneously classified and subsequently measured. A FIMS incorporatingmore » this spatially varying electric field is developed. This paper describes the theoretical frame work and numerical simulations of the FIMS with extended dynamic size range, including the spatially varying electric field, particle trajectories, activation of separated particles in the condenser, and the transfer function, transmission efficiency, and mobility resolution. The influences of the particle Brownian motion on FIMS transfer function and mobility resolution are examined. The simulation results indicate that the FIMS incorporating the spatially varying electric field is capable of measuring aerosol size distribution from 8 to 600 nm with high time resolution. As a result, the experimental characterization of the FIMS is presented in an accompanying paper.« less

A fast integrated mobility spectrometer for rapid measurement of sub-micrometer aerosol size distribution, Part I: Design and model evaluation

DOE PAGES

Wang, Jian; Pikridas, Michael; Spielman, Steven R.; ...

2017-06-01

This study discusses, a fast integrated mobility spectrometer (FIMS) was previously developed to characterize submicron aerosol size distributions at a frequency of 1 Hz and with high size resolution and counting statistics. However, the dynamic size range of the FIMS was limited to one decade in particle electrical mobility. It was proposed that the FIMS dynamic size range can be greatly increased by using a spatially varying electric field. This electric field creates regions with drastically different field strengths in the separator, such that particles of a wide diameter range can be simultaneously classified and subsequently measured. A FIMS incorporatingmore » this spatially varying electric field is developed. This paper describes the theoretical frame work and numerical simulations of the FIMS with extended dynamic size range, including the spatially varying electric field, particle trajectories, activation of separated particles in the condenser, and the transfer function, transmission efficiency, and mobility resolution. The influences of the particle Brownian motion on FIMS transfer function and mobility resolution are examined. The simulation results indicate that the FIMS incorporating the spatially varying electric field is capable of measuring aerosol size distribution from 8 to 600 nm with high time resolution. As a result, the experimental characterization of the FIMS is presented in an accompanying paper.« less

CONSTRAINING THE STRING GAUGE FIELD BY GALAXY ROTATION CURVES AND PERIHELION PRECESSION OF PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheung, Yeuk-Kwan E.; Xu Feng, E-mail: cheung@nju.edu.cn

2013-09-01

We discuss a cosmological model in which the string gauge field coupled universally to matter gives rise to an extra centripetal force and will have observable signatures on cosmological and astronomical observations. Several tests are performed using data including galaxy rotation curves of 22 spiral galaxies of varied luminosities and sizes and perihelion precessions of planets in the solar system. The rotation curves of the same group of galaxies are independently fit using a dark matter model with the generalized Navarro-Frenk-White (NFW) profile and the string model. A remarkable fit of galaxy rotation curves is achieved using the one-parameter stringmore » model as compared to the three-parameter dark matter model with the NFW profile. The average {chi}{sup 2} value of the NFW fit is 9% better than that of the string model at a price of two more free parameters. Furthermore, from the string model, we can give a dynamical explanation for the phenomenological Tully-Fisher relation. We are able to derive a relation between field strength, galaxy size, and luminosity, which can be verified with data from the 22 galaxies. To further test the hypothesis of the universal existence of the string gauge field, we apply our string model to the solar system. Constraint on the magnitude of the string field in the solar system is deduced from the current ranges for any anomalous perihelion precession of planets allowed by the latest observations. The field distribution resembles a dipole field originating from the Sun. The string field strength deduced from the solar system observations is of a similar magnitude as the field strength needed to sustain the rotational speed of the Sun inside the Milky Way. This hypothesis can be tested further by future observations with higher precision.« less

Active Piezoelectric Diaphragms

NASA Technical Reports Server (NTRS)

Bryant, Robert G.; Effinger, Robert T., IV; Aranda, Isaiah, Jr.; Copeland, Ben M.; Covington, Ed W., III

2002-01-01

Several active piezoelectric diaphragms were fabricated by placing unelectroded piezoelectric disks between copper clad films patterned with Inter-Circulating Electrodes "ICE". When a voltage potential is applied to the electrodes, the result is radially distributed electric field that mechanically strains the piezo-ceramic along the Z-axis (perpendicular to the applied electric field), rather than the expected in-plane (XY-axis) direction. Unlike other out of plane piezoelectric actuators, which are benders, these Radial Field Diaphragms (RFDs) strain concentrically yet afford high displacements while maintaining a constant circumference. This paper covers the fabrication and characterization of these diaphragms as a function of poling field strength, ceramic diameter and line spacing, as well as the surface topography, the resulting strain field and displacement as a function of applied voltage ranging from DC to 10 Hz.

Numerical Study of Frictional Properties and the Role of Cohesive End-Zones in Large Strike- Slip Earthquakes

NASA Astrophysics Data System (ADS)

Lovely, P. J.; Mutlu, O.; Pollard, D. D.

2007-12-01

Cohesive end-zones (CEZs) are regions of increased frictional strength and/or cohesion near the peripheries of faults that cause slip distributions to taper toward the fault-tip. Laboratory results, field observations, and theoretical models suggest an important role for CEZs in small-scale fractures and faults; however, their role in crustal-scale faulting and associated large earthquakes is less thoroughly understood. We present a numerical study of the potential role of CEZs on slip distributions in large, multi-segmented, strike-slip earthquake ruptures including the 1992 Landers Earthquake (Mw 7.2) and 1999 Hector Mine Earthquake (Mw 7.1). Displacement discontinuity is calculated using a quasi-static, 2D plane-strain boundary element (BEM) code for a homogeneous, isotropic, linear-elastic material. Friction is implemented by enforcing principles of complementarity. Model results with and without CEZs are compared with slip distributions measured by combined inversion of geodetic, strong ground motion, and teleseismic data. Stepwise and linear distributions of increasing frictional strength within CEZs are considered. The incorporation of CEZs in our model enables an improved match to slip distributions measured by inversion, suggesting that CEZs play a role in governing slip in large, strike-slip earthquakes. Additionally, we present a parametric study highlighting the very great sensitivity of modeled slip magnitude to small variations of the coefficient of friction. This result suggests that, provided a sufficiently well-constrained stress tensor and elastic moduli for the surrounding rock, relatively simple models could provide precise estimates of the magnitude of frictional strength. These results are verified by comparison with geometrically comparable finite element (FEM) models using the commercial code ABAQUS. In FEM models, friction is implemented by use of both Lagrange multipliers and penalty methods.

Colloidal Mechanisms of Gold Nanoparticle Loss in Asymmetric Flow Field-Flow Fractionation.

PubMed

Jochem, Aljosha-Rakim; Ankah, Genesis Ngwa; Meyer, Lars-Arne; Elsenberg, Stephan; Johann, Christoph; Kraus, Tobias

2016-10-07

Flow field-flow fractionation is a powerful method for the analysis of nanoparticle size distributions, but its widespread use has been hampered by large analyte losses, especially of metal nanoparticles. Here, we report on the colloidal mechanisms underlying the losses. We systematically studied gold nanoparticles (AuNPs) during asymmetrical flow field-flow fractionation (AF4) by systematic variation of the particle properties and the eluent composition. Recoveries of AuNPs (core diameter 12 nm) stabilized by citrate or polyethylene glycol (PEG) at different ionic strengths were determined. We used online UV-vis detection and off-line elementary analysis to follow particle losses during full analysis runs, runs without cross-flow, and runs with parts of the instrument bypassed. The combination allowed us to calculate relative and absolute analyte losses at different stages of the analytic protocol. We found different loss mechanisms depending on the ligand. Citrate-stabilized particles degraded during analysis and suffered large losses (up to 74%). PEG-stabilized particles had smaller relative losses at moderate ionic strengths (1-20%) that depended on PEG length. Long PEGs at higher ionic strengths (≥5 mM) caused particle loss due to bridging adsorption at the membrane. Bulk agglomeration was not a relevant loss mechanism at low ionic strengths ≤5 mM for any of the studied particles. An unexpectedly large fraction of particles was lost at tubing and other internal surfaces. We propose that the colloidal mechanisms observed here are relevant loss mechanisms in many particle analysis protocols and discuss strategies to avoid them.

Resolved magnetic dynamo action in the simulated intracluster medium

NASA Astrophysics Data System (ADS)

Vazza, F.; Brunetti, G.; Brüggen, M.; Bonafede, A.

2018-02-01

Faraday rotation and synchrotron emission from extragalactic radio sources give evidence for the presence of magnetic fields extending over ˜ Mpc scales. However, the origin of these fields remains elusive. With new high-resolution grid simulations, we studied the growth of magnetic fields in a massive galaxy cluster that in several aspects is similar to the Coma cluster. We investigated models in which magnetic fields originate from primordial seed fields with comoving strengths of 0.1 nG at redshift z = 30. The simulations show evidence of significant magnetic field amplification. At the best spatial resolution (3.95 kpc), we are able to resolve the scale where magnetic tension balances the bending of magnetic lines by turbulence. This allows us to observe the final growth stage of the small-scale dynamo. To our knowledge, this is the first time that this is seen in cosmological simulations of the intracluster medium. Our mock observations of Faraday rotation provide a good match to observations of the Coma cluster. However, the distribution of magnetic fields shows strong departures from a simple Maxwellian distribution, suggesting that the three-dimensional structure of magnetic fields in real clusters may be significantly different than what is usually assumed when inferring magnetic field values from rotation measure observations.

Magnetic dipole strength in 128Xe and 134Xe in the spin-flip resonance region

NASA Astrophysics Data System (ADS)

Massarczyk, R.; Rusev, G.; Schwengner, R.; Dönau, F.; Bhatia, C.; Gooden, M. Â. E.; Kelley, J. Â. H.; Tonchev, A. Â. P.; Tornow, W.

2014-11-01

The magnetic dipole strength in the energy region of the spin-flip resonance is investigated in 128Xe and 134Xe using quasimonoenergetic and linearly polarized γ -ray beams at the High-Intensity γ -Ray Source facility in Durham, North Carolina, USA. Absorption cross sections were deduced for the magnetic and electric and dipole strength distributions separately for various intervals of excitation energy, including the strength of states in the unresolved quasicontinuum. The magnetic dipole strength distributions show structures resembling a resonance in the spin-flip region around an excitation energy of 8 MeV. The electric dipole strength distributions obtained from the present experiments are in agreement with the ones deduced from an earlier experiment using broad-band bremsstrahlung instead of a quasimonoenergetic beam. The experimental magnetic and electric dipole strength distributions are compared with phenomenological approximations and with predictions of a quasiparticle random phase approximation in a deformed basis.

Infrared fluorescence efficiencies for the nu1 and nu5 bands of formaldehyde in the solar radiation field

NASA Technical Reports Server (NTRS)

Reuter, D. C.; Mumma, M. J.; Nadler, S.

1989-01-01

Formaldehyde scattering strengths have been determined for equilibrium distributions of 100 K, 50 K, 20 K, and for the the non-LTE case of an essentially fully relaxed distribution. Integrated band g factors of 2.89 x 10 to the -4th photons/s per molecule for nu1 and 3.83 x 10 to the -4th for nu 5 are obtained. The results indicate that the most promising regions to search for cometary H2CO are at about 2782/cm, at 2794.5/cm, and at about 2835/cm.

[Using Molecular Simulations to Understand Complex Nanoscale Dynamic Phenomena in Polymer Solutions

NASA Technical Reports Server (NTRS)

Smith, Grant

2004-01-01

The first half of the project concentrated on molecular simulation studies of the translocation of model molecules for single-stranded DNA through a nanosized pore. This has resulted in the publication, Translocation of a polymer chain across a nanopore: A Brownian dynamics simulation study, by Pu Tian and Grant D. Smith, JOURNAL OF CHEMICAL PHYSICS VOLUME 119, NUMBER 21 1 DECEMBER 2003, which is attached to this report. In this work we carried out Brownian dynamics simulation studies of the translocation of single polymer chains across a nanosized pore under the driving of an applied field (chemical potential gradient) designed to mimic an electrostatic field. The translocation process can be either dominated by the entropic barrier resulted from restricted motion of flexible polymer chains or by applied forces (or chemical gradient). We focused on the latter case in our studies. Calculation of radius of gyration of the translocating chain at the two opposite sides of the wall shows that the polymer chains are not in equilibrium during the translocation process. Despite this fact, our results show that the one-dimensional diffusion and the nucleation model provide an excellent description of the dependence of average translocation time on the chemical potential gradients, the polymer chain length and the solvent viscosity. In good agreement with experimental results and theoretical predictions, the translocation time distribution of our simple model shows strong non-Gaussian characteristics. It is observed that even for this simple tube-like pore geometry, more than one peak of translocation time distribution can be generated for proper pore diameter and applied field strengths. Both repulsive Weeks-Chandler-Anderson and attractive Lennard-Jones polymer-nanopore interaction were studied. Attraction facilitates the translocation process by shortening the total translocation time and dramatically improve the capturing of polymer chain. The width of the translocation time distribution was found to decrease with increasing temperature, increasing field strength, and decreasing pore diameter.

Detection of the Velocity Shear Effect on the Spatial Distributions of the Galactic Satellites in Isolated Systems

NASA Astrophysics Data System (ADS)

Lee, Jounghun; Choi, Yun-Young

2015-02-01

We report a detection of the effect of the large-scale velocity shear on the spatial distributions of the galactic satellites around the isolated hosts. Identifying the isolated galactic systems, each of which consists of a single host galaxy and its satellites, from the Seventh Data Release of the Sloan Digital Sky Survey and reconstructing linearly the velocity shear field in the local universe, we measure the alignments between the relative positions of the satellites from their isolated hosts and the principal axes of the local velocity shear tensors projected onto the plane of sky. We find a clear signal that the galactic satellites in isolated systems are located preferentially along the directions of the minor principal axes of the large-scale velocity shear field. Those galactic satellites that are spirals, are brighter, are located at distances larger than the projected virial radii of the hosts, and belong to the spiral hosts yield stronger alignment signals, which implies that the alignment strength depends on the formation and accretion epochs of the galactic satellites. It is also shown that the alignment strength is quite insensitive to the cosmic web environment, as well as the size and luminosity of the isolated hosts. Although this result is consistent with the numerical finding of Libeskind et al. based on an N-body experiment, owing to the very low significance of the observed signals, it remains inconclusive whether or not the velocity shear effect on the satellite distribution is truly universal.

Collapsing spherical star in Scalar-Einstein-Gauss-Bonnet gravity with a quadratic coupling

NASA Astrophysics Data System (ADS)

Chakrabarti, Soumya

2018-04-01

We study the evolution of a self interacting scalar field in Einstein-Gauss-Bonnet theory in four dimension where the scalar field couples non minimally with the Gauss-Bonnet term. Considering a polynomial coupling of the scalar field with the Gauss-Bonnet term, a self-interaction potential and an additional perfect fluid distribution alongwith the scalar field, we investigate different possibilities regarding the outcome of the collapsing scalar field. The strength of the coupling and choice of the self-interaction potential serves as the pivotal initial conditions of the models presented. The high degree of non-linearity in the equation system is taken care off by using a method of invertibe point transformation of anharmonic oscillator equation, which has proven itself very useful in recent past while investigating dynamics of minimally coupled scalar fields.

Glyph-based analysis of multimodal directional distributions in vector field ensembles

NASA Astrophysics Data System (ADS)

Jarema, Mihaela; Demir, Ismail; Kehrer, Johannes; Westermann, Rüdiger

2015-04-01

Ensemble simulations are increasingly often performed in the geosciences in order to study the uncertainty and variability of model predictions. Describing ensemble data by mean and standard deviation can be misleading in case of multimodal distributions. We present first results of a glyph-based visualization of multimodal directional distributions in 2D and 3D vector ensemble data. Directional information on the circle/sphere is modeled using mixtures of probability density functions (pdfs), which enables us to characterize the distributions with relatively few parameters. The resulting mixture models are represented by 2D and 3D lobular glyphs showing direction, spread and strength of each principal mode of the distributions. A 3D extension of our approach is realized by means of an efficient GPU rendering technique. We demonstrate our method in the context of ensemble weather simulations.

Pore geometry as a control on rock strength

NASA Astrophysics Data System (ADS)

Bubeck, A.; Walker, R. J.; Healy, D.; Dobbs, M.; Holwell, D. A.

2017-01-01

The strength of rocks in the subsurface is critically important across the geosciences, with implications for fluid flow, mineralisation, seismicity, and the deep biosphere. Most studies of porous rock strength consider the scalar quantity of porosity, in which strength shows a broadly inverse relationship with total porosity, but pore shape is not explicitly defined. Here we use a combination of uniaxial compressive strength measurements of isotropic and anisotropic porous lava samples, and numerical modelling to consider the influence of pore shape on rock strength. Micro computed tomography (CT) shows that pores range from sub-spherical to elongate and flat ellipsoids. Samples that contain flat pores are weaker if compression is applied parallel to the short axis (i.e. across the minimum curvature), compared to compression applied parallel to the long axis (i.e. across the maximum curvature). Numerical models for elliptical pores show that compression applied across the minimum curvature results in relatively broad amplification of stress, compared to compression applied across the maximum curvature. Certain pore shapes may be relatively stable and remain open in the upper crust under a given remote stress field, while others are inherently weak. Quantifying the shape, orientations, and statistical distributions of pores is therefore a critical step in strength testing of rocks.

Measurement of non-Maxwellian electron velocity distributions in a reflex discharge

NASA Technical Reports Server (NTRS)

Phipps, C. R., Jr.; Bershader, D.

1978-01-01

The results of a ruby laser Thomson scattering study of the space and time-resolved electron velocity distributions in a pulsed Penning discharge in hydrogen are presented. Electron densities were to the order of 10 to the 13th/cu cm and temperatures were roughly 3 eV. This point is just prior to the cessation of the discharge ohmic heating pulse. For magnetic strengths less than 200 G, Maxwellian distributions were found over an energy range six times thermal energy. Temperatures agreed with Langmuir probe data. For fields of 450 G, chaotic plasma potentials were observed to be unstable and the Thomson scattering showed that the electron velocity distributions had central temperatures of 2 eV and wing temperatures of 15-12 eV.

Mechanical characterization of composite materials by optical techniques: A review

NASA Astrophysics Data System (ADS)

Bruno, Luigi

2018-05-01

The present review provides an overview of work published in recent years dealing with the mechanical characterization of composite materials performed by optical techniques. The paper emphasizes the strengths derived from the employment of full-field methods when the strain field of an anisotropic material must be evaluated. This is framed in contrast to the use of conventional measurement techniques, which provide single values of the measured quantities unable to offer thorough descriptions of deformation distribution. The review outlines the intensity and articulation of work in this research field to date and its ongoing importance not only in the academy, but also in industrial sectors where composite materials represent a strategic resource for development.

Field-Aligned Electrostatic Potentials Above the Martian Exobase From MGS Electron Reflectometry: Structure and Variability

NASA Astrophysics Data System (ADS)

Lillis, Robert J.; Halekas, J. S.; Fillingim, M. O.; Poppe, A. R.; Collinson, G.; Brain, David A.; Mitchell, D. L.

2018-01-01

Field-aligned electrostatic potentials in the Martian ionosphere play potentially important roles in maintaining current systems, driving atmospheric escape and producing aurora. The strength and polarity of the potential difference between the observation altitude and the exobase ( 180 km) determine the energy dependence of electron pitch angle distributions (PADs) measured on open magnetic field lines (i.e. those connected both to the collisional atmosphere and to the interplanetary magnetic field). Here we derive and examine a data set of 3.6 million measurements of the potential between 185 km and 400 km altitude from PADs measured by the Mars Global Surveyor Magnetometer/Electron Reflectometer experiment at 2 A.M./2 P.M. local time from May 1999 to November 2006. Potentials display significant variability, consistent with expected variable positive and negative divergences of the convection electric field in the highly variable and dynamic Martian plasma environment. However, superimposed on this variability are persistent patterns whereby potential magnitudes depend positively on crustal magnetic field strength, being close to zero where crustal fields are weak or nonexistent. Average potentials are typically positive near the center of topologically open crustal field regions where field lines are steeper, and negative near the edges of such regions where fields are shallower, near the boundaries with closed fields. This structure is less pronounced for higher solar wind pressures and (on the dayside) higher solar EUV irradiance. Its causes are uncertain at present but may be due to differential motion of electrons and ions in Mars's substantial but (compared to Earth) weak magnetic fields.

A vacuum-sealed miniature X-ray tube based on carbon nanotube field emitters

NASA Astrophysics Data System (ADS)

Heo, Sung Hwan; Kim, Hyun Jin; Ha, Jun Mok; Cho, Sung Oh

2012-05-01

A vacuum-sealed miniature X-ray tube based on a carbon nanotube field-emission electron source has been demonstrated. The diameter of the X-ray tube is 10 mm; the total length of the tube is 50 mm, and no external vacuum pump is required for the operation. The maximum tube voltage reaches up to 70 kV, and the X-ray tube generates intense X-rays with the air kerma strength of 108 Gy·cm2 min-1. In addition, X-rays produced from the miniature X-ray tube have a comparatively uniform spatial dose distribution.

Monodomain dynamics for rigid rod and platelet suspensions in strongly coupled coplanar linear flow and magnetic fields. II. Kinetic theory

NASA Astrophysics Data System (ADS)

Forest, M. Gregory; Sircar, Sarthok; Wang, Qi; Zhou, Ruhai

2006-10-01

We establish reciprocity relations of the Doi-Hess kinetic theory for rigid rod macromolecular suspensions governed by the strong coupling among an excluded volume potential, linear flow, and a magnetic field. The relation provides a reduction of the flow and field driven Smoluchowski equation: from five parameters for coplanar linear flows and magnetic field, to two field parameters. The reduced model distinguishes flows with a rotational component, which map to simple shear (with rate parameter) subject to a transverse magnetic field (with strength parameter), and irrotational flows, for which the reduced model consists of a triaxial extensional flow (with two extensional rate parameters). We solve the Smoluchowski equation of the reduced model to explore: (i) the effect of introducing a coplanar magnetic field on each sheared monodomain attractor of the Doi-Hess kinetic theory and (ii) the coupling of coplanar extensional flow and magnetic fields. For (i), we show each sheared attractor (steady and unsteady, with peak axis in and out of the shearing plane, periodic and chaotic orbits) undergoes its own transition sequence versus magnetic field strength. Nonetheless, robust predictions emerge: out-of-plane degrees of freedom are arrested with increasing field strength, and a unique flow-aligning or tumbling/wagging limit cycle emerges above a threshold magnetic field strength or modified geometry parameter value. For (ii), irrotational flows coupled with a coplanar magnetic field yield only steady states. We characterize all (generically biaxial) equilibria in terms of an explicit Boltzmann distribution, providing a natural generalization of analytical results on pure nematic equilibria [P. Constantin, I. Kevrekidis, and E. S. Titi, Arch. Rat. Mech. Anal. 174, 365 (2004); P. Constantin, I. Kevrekidis, and E. S. Titi, Discrete and Continuous Dynamical Systems 11, 101 (2004); P. Constantin and J. Vukadinovic, Nonlinearity 18, 441 (2005); H. Liu, H. Zhang, and P. Zhang, Comm. Math. Sci. 3, 201 (2005); C. Luo, H. Zhang, and P. Zhang, Nonlinearity 18, 379 (2005); I. Fatkullin and V. Slastikov, Nonlinearity 18, 2565 (2005); H. Zhou, H. Wang, Q. Wang, and M. G. Forest, Nonlinearity 18, 2815 (2005)] and extensional flow-induced equilibria [Q. Wang, S. Sircar, and H. Zhou, Comm. Math. Sci. 4, 605 (2005)]. We predict large parameter regions of bi-stable equilibria; the lowest energy state always has principal axis aligned in the flow plane, while another minimum energy state often exists, with primary alignment transverse to the coplanar field.

Technical Note: A Monte Carlo study of magnetic-field-induced radiation dose effects in mice

PubMed Central

Liao, Zhongxing; Melancon, Adam D.; Guindani, Michele; Followill, David S.; Tailor, Ramesh C.; Hazle, John D.; Court, Laurence E.

2015-01-01

Purpose: Magnetic fields are known to alter radiation dose deposition. Before patients receive treatment using an MRI-linear accelerator (MRI-Linac), preclinical studies are needed to understand the biological consequences of magnetic-field-induced dose effects. In the present study, the authors sought to identify a beam energy and magnetic field strength combination suitable for preclinical murine experiments. Methods: Magnetic field dose effects were simulated in a mouse lung phantom using various beam energies (225 kVp, 350 kVp, 662 keV [Cs-137], 2 MV, and 1.25 MeV [Co-60]) and magnetic field strengths (0.75, 1.5, and 3 T). The resulting dose distributions were compared with those in a simulated human lung phantom irradiated with a 6 or 8 MV beam and orthogonal 1.5 T magnetic field. Results: In the human lung phantom, the authors observed a dose increase of 45% and 54% at the soft-tissue-to-lung interface and a dose decrease of 41% and 48% at the lung-to-soft-tissue interface for the 6 and 8 MV beams, respectively. In the mouse simulations, the magnetic fields had no measurable effect on the 225 or 350 kVp dose distribution. The dose increases with the Cs-137 beam for the 0.75, 1.5, and 3 T magnetic fields were 9%, 29%, and 42%, respectively. The dose decreases were 9%, 21%, and 37%. For the 2 MV beam, the dose increases were 16%, 33%, and 31% and the dose decreases were 9%, 19%, and 30%. For the Co-60 beam, the dose increases were 19%, 54%, and 44%, and the dose decreases were 19%, 42%, and 40%. Conclusions: The magnetic field dose effects in the mouse phantom using a Cs-137, 3 T combination or a Co-60, 1.5 or 3 T combination most closely resemble those in simulated human treatments with a 6 MV, 1.5 T MRI-Linac. The effects with a Co-60, 1.5 T combination most closely resemble those in simulated human treatments with an 8 MV, 1.5 T MRI-Linac. PMID:26328998

Formation of cycloidal features on Europa.

PubMed

Hoppa, G V; Tufts, B R; Greenberg, R; Geissler, P E

1999-09-17

Cycloidal patterns are widely distributed on the surface of Jupiter's moon Europa. Tensile cracks may have developed such a pattern in response to diurnal variations in tidal stress in Europa's outer ice shell. When the tensile strength of the ice is reached, a crack may occur. Propagating cracks would move across an ever-changing stress field, following a curving path to a place and time where the tensile stress was insufficient to continue the propagation. A few hours later, when the stress at the end of the crack again exceeded the strength, propagation would continue in a new direction. Thus, one arcuate segment of the cycloidal chain would be produced during each day on Europa. For this model to work, the tensile strength of Europa's ice crust must be less than 40 kilopascals, and there must be a thick fluid layer below the ice to allow sufficient tidal amplitude.

Magnetic Flux Distribution of Linear Machines with Novel Three-Dimensional Hybrid Magnet Arrays

PubMed Central

Yao, Nan; Yan, Liang; Wang, Tianyi; Wang, Shaoping

2017-01-01

The objective of this paper is to propose a novel tubular linear machine with hybrid permanent magnet arrays and multiple movers, which could be employed for either actuation or sensing technology. The hybrid magnet array produces flux distribution on both sides of windings, and thus helps to increase the signal strength in the windings. The multiple movers are important for airspace technology, because they can improve the system’s redundancy and reliability. The proposed design concept is presented, and the governing equations are obtained based on source free property and Maxwell equations. The magnetic field distribution in the linear machine is thus analytically formulated by using Bessel functions and harmonic expansion of magnetization vector. Numerical simulation is then conducted to validate the analytical solutions of the magnetic flux field. It is proved that the analytical model agrees with the numerical results well. Therefore, it can be utilized for the formulation of signal or force output subsequently, depending on its particular implementation. PMID:29156577

Magnetic Flux Distribution of Linear Machines with Novel Three-Dimensional Hybrid Magnet Arrays.

PubMed

Yao, Nan; Yan, Liang; Wang, Tianyi; Wang, Shaoping

2017-11-18

The objective of this paper is to propose a novel tubular linear machine with hybrid permanent magnet arrays and multiple movers, which could be employed for either actuation or sensing technology. The hybrid magnet array produces flux distribution on both sides of windings, and thus helps to increase the signal strength in the windings. The multiple movers are important for airspace technology, because they can improve the system's redundancy and reliability. The proposed design concept is presented, and the governing equations are obtained based on source free property and Maxwell equations. The magnetic field distribution in the linear machine is thus analytically formulated by using Bessel functions and harmonic expansion of magnetization vector. Numerical simulation is then conducted to validate the analytical solutions of the magnetic flux field. It is proved that the analytical model agrees with the numerical results well. Therefore, it can be utilized for the formulation of signal or force output subsequently, depending on its particular implementation.

Parallels among the ``music scores'' of solar cycles, space weather and Earth's climate

NASA Astrophysics Data System (ADS)

Kolláth, Zoltán; Oláh, Katalin; van Driel-Gesztelyi, Lidia

2012-07-01

Solar variability and its effects on the physical variability of our (space) environment produces complex signals. In the indicators of solar activity at least four independent cyclic components can be identified, all of them with temporal variations in their timescales. Time-frequency distributions (see Kolláth & Oláh 2009) are perfect tools to disclose the ``music scores'' in these complex time series. Special features in the time-frequency distributions, like frequency splitting, or modulations on different timescales provide clues, which can reveal similar trends among different indices like sunspot numbers, interplanetary magnetic field strength in the Earth's neighborhood and climate data. On the pseudo-Wigner Distribution (PWD) the frequency splitting of all the three main components (the Gleissberg and Schwabe cycles, and an ~5.5 year signal originating from cycle asymmetry, i.e. the Waldmeier effect) can be identified as a ``bubble'' shaped structure after 1950. The same frequency splitting feature can also be found in the heliospheric magnetic field data and the microwave radio flux.

Simplified realistic human head model for simulating Tumor Treating Fields (TTFields).

PubMed

Wenger, Cornelia; Bomzon, Ze'ev; Salvador, Ricardo; Basser, Peter J; Miranda, Pedro C

2016-08-01

Tumor Treating Fields (TTFields) are alternating electric fields in the intermediate frequency range (100-300 kHz) of low-intensity (1-3 V/cm). TTFields are an anti-mitotic treatment against solid tumors, which are approved for Glioblastoma Multiforme (GBM) patients. These electric fields are induced non-invasively by transducer arrays placed directly on the patient's scalp. Cell culture experiments showed that treatment efficacy is dependent on the induced field intensity. In clinical practice, a software called NovoTalTM uses head measurements to estimate the optimal array placement to maximize the electric field delivery to the tumor. Computational studies predict an increase in the tumor's electric field strength when adapting transducer arrays to its location. Ideally, a personalized head model could be created for each patient, to calculate the electric field distribution for the specific situation. Thus, the optimal transducer layout could be inferred from field calculation rather than distance measurements. Nonetheless, creating realistic head models of patients is time-consuming and often needs user interaction, because automated image segmentation is prone to failure. This study presents a first approach to creating simplified head models consisting of convex hulls of the tissue layers. The model is able to account for anisotropic conductivity in the cortical tissues by using a tensor representation estimated from Diffusion Tensor Imaging. The induced electric field distribution is compared in the simplified and realistic head models. The average field intensities in the brain and tumor are generally slightly higher in the realistic head model, with a maximal ratio of 114% for a simplified model with reasonable layer thicknesses. Thus, the present pipeline is a fast and efficient means towards personalized head models with less complexity involved in characterizing tissue interfaces, while enabling accurate predictions of electric field distribution.

Single-ion microwave near-field quantum sensor

NASA Astrophysics Data System (ADS)

Wahnschaffe, M.; Hahn, H.; Zarantonello, G.; Dubielzig, T.; Grondkowski, S.; Bautista-Salvador, A.; Kohnen, M.; Ospelkaus, C.

2017-01-01

We develop an intuitive model of 2D microwave near-fields in the unusual regime of centimeter waves localized to tens of microns. Close to an intensity minimum, a simple effective description emerges with five parameters that characterize the strength and spatial orientation of the zero and first order terms of the near-field, as well as the field polarization. Such a field configuration is realized in a microfabricated planar structure with an integrated microwave conductor operating near 1 GHz. We use a single 9 Be+ ion as a high-resolution quantum sensor to measure the field distribution through energy shifts in its hyperfine structure. We find agreement with simulations at the sub-micron and few-degree level. Our findings give a clear and general picture of the basic properties of oscillatory 2D near-fields with applications in quantum information processing, neutral atom trapping and manipulation, chip-scale atomic clocks, and integrated microwave circuits.

47 CFR 18.305 - Field strength limits.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 1 2011-10-01 2011-10-01 false Field strength limits. 18.305 Section 18.305... Standards § 18.305 Field strength limits. (a) ISM equipment operating on a frequency specified in § 18.301... strength levels of emissions which lie outside the bands specified in § 18.301, unless otherwise indicated...

Micro-mechanics of hydro-mechanical coupled processes during hydraulic fracturing in sandstone

NASA Astrophysics Data System (ADS)

Caulk, R.; Tomac, I.

2017-12-01

This contribution presents micro-mechanical study of hydraulic fracture initiation and propagation in sandstone. The Discrete Element Method (DEM) Yade software is used as a tool to model fully coupled hydro-mechanical behavior of the saturated sandstone under pressures typical for deep geo-reservoirs. Heterogeneity of sandstone strength tensile and shear parameters are introduced using statistical representation of cathodoluminiscence (CL) sandstone rock images. Weibull distribution of statistical parameter values was determined as a best match of the CL scans of sandstone grains and cement between grains. Results of hydraulic fracturing stimulation from the well bore indicate significant difference between models with the bond strengths informed from CL scans and uniform homogeneous representation of sandstone parameters. Micro-mechanical insight reveals formed hydraulic fracture typical for mode I or tensile cracking in both cases. However, the shear micro-cracks are abundant in the CL informed model while they are absent in the standard model with uniform strength distribution. Most of the mode II cracks, or shear micro-cracks, are not part of the main hydraulic fracture and occur in the near-tip and near-fracture areas. The position and occurrence of the shear micro-cracks is characterized as secondary effect which dissipates the hydraulic fracturing energy. Additionally, the shear micro-crack locations qualitatively resemble acoustic emission cloud of shear cracks frequently observed in hydraulic fracturing, and sometimes interpreted as re-activation of existing fractures. Clearly, our model does not contain pre-existing cracks and has continuous nature prior to fracturing. This observation is novel and interesting and is quantified in the paper. The shear particle contact forces field reveals significant relaxation compared to the model with uniform strength distribution.

Variation in the strength of reproductive interference from an alien congener to a native species in Taraxacum.

PubMed

Nishida, Sachiko; Hashimoto, Keisuke; Kanaoka, Masahiro M; Takakura, Ko-Ichi; Nishida, Takayoshi

2017-01-01

Reproductive interference (RI) may be a contributing factor to the displacement of native species by an alien congener, and RI strength has been shown theoretically to affect distributional relationships between species. Thus, variations in RI strength from alien to native species result in different consequences of invasions and efforts to conserve native species, but the variations have seldom been examined empirically. We therefore investigated RI strength variations from the alien species Taraxacum officinale and its hybrids to eight populations of native dandelions, four T. japonicum populations and two populations each of two subspecies of T. platycarpum. We examined the association between alien relative abundance and native seed set in field surveys, and we also performed hand-pollination experiments to investigate directly the sensitivity of native flowers to alien pollen. We found that the effect of alien relative abundance on native seed set of even the same native species could differ greatly in different regions, and that the sensitivity of native flowers to alien pollen was also dependent on region. Our results, together with those of previous studies, show that RI from the alien to the native species is strong in regions where the alien species outnumbers the native species and marginal where it does not; this result suggests that alien RI can critically affect distributional relationships between native and alien species. Our study highlights the importance of performing additional empirical investigations of RI strength variation and of giving due attention to alien RI in efforts to conserve regional native biodiversity.

Probabilistic thermal-shock strength testing using infrared imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wereszczak, A.A.; Scheidt, R.A.; Ferber, M.K.

1999-12-01

A thermal-shock strength-testing technique has been developed that uses a high-resolution, high-temperature infrared camera to capture a specimen's surface temperature distribution at fracture. Aluminum nitride (AlN) substrates are thermally shocked to fracture to demonstrate the technique. The surface temperature distribution for each test and AlN's thermal expansion are used as input in a finite-element model to determine the thermal-shock strength for each specimen. An uncensored thermal-shock strength Weibull distribution is then determined. The test and analysis algorithm show promise as a means to characterize thermal shock strength of ceramic materials.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abliz, M.; Grimmer, J.; Dejus, R.

The current design of the Advanced Photon Source Upgrade (APS-U) project is a multi-bend achromat (MBA) lattice, which incorporates three-pole wigglers as radiation sources for the bending magnet beamlines. They are located in the short section between the M4 dipole and Q8 quadrupole magnets. Due to space constraints, a hybrid permanent magnet design is necessary to provide the required magnetic field strength. A three-pole wiggler with a flat peak field profile along the beam axis was designed to enhance the photon flux and flatten the transverse flux density distributions. The magnetic peak field at the center pole reached 1.08 Teslamore » for a magnetic gap of 26 mm. The maximum power density, integrated over all vertical angles, is 3.1 W/mm 2, which is substantially higher than that of the existing bending magnets at the APS (0.86 W/mm 2). Detailed designs of the three-pole wiggler is presented, including calculated spectral-angular flux distributions.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abliz, M., E-mail: mabliz@aps.anl.gov; Grimmer, J., E-mail: grimmer@aps.anl.gov; Dejus, R.

The current design of the Advanced Photon Source Upgrade (APS-U) project is a multi-bend achromat (MBA) lattice, which incorporates three-pole wigglers as radiation sources for the bending magnet beamlines. They are located in the short section between the M4 dipole and Q8 quadrupole magnets. Due to space constraints, a hybrid permanent magnet design is necessary to provide the required magnetic field strength. A three-pole wiggler with a flat peak field profile along the beam axis was designed to enhance the photon flux and flatten the transverse flux density distributions. The magnetic peak field at the center pole reached 1.08 Teslamore » for a magnetic gap of 26 mm. The maximum power density, integrated over all vertical angles, is 3.1 W/mm{sup 2}, which is substantially higher than that of the existing bending magnets at the APS (0.86 W/mm{sup 2}). Detailed designs of the three-pole wiggler is presented, including calculated spectral-angular flux distributions.« less

Computed versus measured ion velocity distribution functions in a Hall effect thruster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garrigues, L.; CNRS, LAPLACE, F-31062 Toulouse; Mazouffre, S.

2012-06-01

We compare time-averaged and time-varying measured and computed ion velocity distribution functions in a Hall effect thruster for typical operating conditions. The ion properties are measured by means of laser induced fluorescence spectroscopy. Simulations of the plasma properties are performed with a two-dimensional hybrid model. In the electron fluid description of the hybrid model, the anomalous transport responsible for the electron diffusion across the magnetic field barrier is deduced from the experimental profile of the time-averaged electric field. The use of a steady state anomalous mobility profile allows the hybrid model to capture some properties like the time-averaged ion meanmore » velocity. Yet, the model fails at reproducing the time evolution of the ion velocity. This fact reveals a complex underlying physics that necessitates to account for the electron dynamics over a short time-scale. This study also shows the necessity for electron temperature measurements. Moreover, the strength of the self-magnetic field due to the rotating Hall current is found negligible.« less

The ultimate intrinsic signal-to-noise ratio of loop- and dipole-like current patterns in a realistic human head model.

PubMed

Pfrommer, Andreas; Henning, Anke

2018-03-13

The ultimate intrinsic signal-to-noise ratio (UISNR) represents an upper bound for the achievable SNR of any receive coil. To reach this threshold a complete basis set of equivalent surface currents is required. This study systematically investigated to what extent either loop- or dipole-like current patterns are able to reach the UISNR threshold in a realistic human head model between 1.5 T and 11.7 T. Based on this analysis, we derived guidelines for coil designers to choose the best array element at a given field strength. Moreover, we present ideal current patterns yielding the UISNR in a realistic body model. We distributed generic current patterns on a cylindrical and helmet-shaped surface around a realistic human head model. We excited electromagnetic fields in the human head by using eigenfunctions of the spherical and cylindrical Helmholtz operator. The electromagnetic field problem was solved by a fast volume integral equation solver. At 7 T and above, adding curl-free current patterns to divergence-free current patterns substantially increased the SNR in the human head (locally >20%). This was true for the helmet-shaped and the cylindrical surface. On the cylindrical surface, dipole-like current patterns had high SNR performance in central regions at ultra-high field strength. The UISNR increased superlinearly with B0 in most parts of the cerebrum but only sublinearly in the periphery of the human head. The combination of loop and dipole elements could enhance the SNR performance in the human head at ultra-high field strength. © 2018 International Society for Magnetic Resonance in Medicine.

Residential exposure to radiofrequency fields from mobile phone base stations, and broadcast transmitters: a population-based survey with personal meter.

PubMed

Viel, J F; Clerc, S; Barrera, C; Rymzhanova, R; Moissonnier, M; Hours, M; Cardis, E

2009-08-01

Both the public perceptions, and most published epidemiologic studies, rely on the assumption that the distance of a particular residence from a base station or a broadcast transmitter is an appropriate surrogate for exposure to radiofrequency fields, although complex propagation characteristics affect the beams from antennas. The main goal of this study was to characterise the distribution of residential exposure from antennas using personal exposure meters. A total of 200 randomly selected people were enrolled. Each participant was supplied with a personal exposure meter for 24 h measurements, and kept a time-location-activity diary. Two exposure metrics for each radiofrequency were then calculated: the proportion of measurements above the detection limit (0.05 V/m), and the maximum electric field strength. Residential address was geocoded, and distance from each antenna was calculated. Much of the time, the recorded field strength was below the detection level (0.05 V/m), the FM band standing apart with a proportion above the detection threshold of 12.3%. The maximum electric field strength was always lower than 1.5 V/m. Exposure to GSM and DCS waves peaked around 280 m and 1000 m from the antennas. A downward trend was found within a 10 km range for FM. Conversely, UMTS, TV 3, and TV 4&5 signals did not vary with distance. Despite numerous limiting factors entailing a high variability in radiofrequency exposure assessment, but owing to a sound statistical technique, we found that exposures from GSM and DCS base stations increase with distance in the near source zone, to a maximum where the main beam intersects the ground. We believe these results will contribute to the ongoing public debate over the location of base stations and their associated emissions.

ISIS and META projects

NASA Technical Reports Server (NTRS)

Birman, Kenneth; Cooper, Robert; Marzullo, Keith

1990-01-01

ISIS and META are two distributed systems projects at Cornell University. The ISIS project, has developed a new methodology, virtual synchrony, for writing robust distributed software. This approach is directly supported by the ISIS Toolkit, a programming system that is distributed to over 300 academic and industrial sites. Several interesting applications that exploit the strengths of ISIS, including an NFS-compatible replicated file system, are being developed. The META project, is about distributed control in a soft real time environment incorporating feedback. This domain encompasses examples as diverse as monitoring inventory and consumption on a factory floor and performing load-balancing on a distributed computing system. One of the first uses of META is for distributed application management: the tasks of configuring a distributed program, dynamically adapting to failures, and monitoring its performance. Recent progress and current plans are presented. This approach to distributed computing, a philosophy that is believed to significantly distinguish the work from that of others in the field, is explained.

C-Sphere Strength-Size Scaling in a Bearing-Grade Silicon Nitride

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wereszczak, Andrew A; Jadaan, Osama M.; Kirkland, Timothy Philip

2008-01-01

A C-sphere specimen geometry was used to determine the failure strength distributions of a commercially available bearing-grade silicon nitride (Si3N4) having ball diameters of 12.7 and 25.4 mm. Strengths for both diameters were determined using the combination of failure load, C sphere geometry, and finite element analysis and fitted using two-parameter Weibull distributions. Effective areas of both diameters were estimated as a function of Weibull modulus and used to explore whether the strength distributions predictably strength-scaled between each size. They did not. That statistical observation suggested that the same flaw type did not limit the strength of both ball diametersmore » indicating a lack of material homogeneity between the two sizes. Optical fractography confirmed that. It showed there were two distinct strength-limiting flaw types in both ball diameters, that one flaw type was always associated with lower strength specimens, and that significantly higher fraction of the 24.5-mm-diameter c-sphere specimens failed from it. Predictable strength-size-scaling would therefore not result as a consequence of this because these flaw types were not homogenously distributed and sampled in both c-sphere geometries.« less

Characteristics of Low-latitude Coronal Holes near the Maximum of Solar Cycle 24

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hofmeister, Stefan J.; Veronig, Astrid; Reiss, Martin A.

We investigate the statistics of 288 low-latitude coronal holes extracted from SDO /AIA-193 filtergrams over the time range of 2011 January 01–2013 December 31. We analyze the distribution of characteristic coronal hole properties, such as the areas, mean AIA-193 intensities, and mean magnetic field densities, the local distribution of the SDO /AIA-193 intensity and the magnetic field within the coronal holes, and the distribution of magnetic flux tubes in coronal holes. We find that the mean magnetic field density of all coronal holes under study is 3.0 ± 1.6 G, and the percentaged unbalanced magnetic flux is 49 ± 16%.more » The mean magnetic field density, the mean unsigned magnetic field density, and the percentaged unbalanced magnetic flux of coronal holes depend strongly pairwise on each other, with correlation coefficients cc > 0.92. Furthermore, we find that the unbalanced magnetic flux of the coronal holes is predominantly concentrated in magnetic flux tubes: 38% (81%) of the unbalanced magnetic flux of coronal holes arises from only 1% (10%) of the coronal hole area, clustered in magnetic flux tubes with field strengths >50 G (10 G). The average magnetic field density and the unbalanced magnetic flux derived from the magnetic flux tubes correlate with the mean magnetic field density and the unbalanced magnetic flux of the overall coronal hole (cc>0.93). These findings give evidence that the overall magnetic characteristics of coronal holes are governed by the characteristics of the magnetic flux tubes.« less

Strong transverse fields in delta-spots

NASA Technical Reports Server (NTRS)

Zirin, Harold; Wang, Haimin

1993-01-01

Spectroscopic measurements of the strength and direction of transverse magnetic fields in six delta-spots are presented. The field direction is determined by the relative strength of the pi- and sigma-components at different polarizer orientations, and is, with one exception, parallel to the neutral line and as strong as the umbral field. Field strengths determined by line splitting are as high as 3980 G.

Spectral characterization of plastic scintillation detector response as a function of magnetic field strength

NASA Astrophysics Data System (ADS)

Simiele, E.; Kapsch, R.-P.; Ankerhold, U.; Culberson, W.; DeWerd, L.

2018-04-01

The purpose of this work was to characterize intensity and spectral response changes in a plastic scintillation detector (PSD) as a function of magnetic field strength. Spectra measurements as a function of magnetic field strength were performed using an optical spectrometer. The response of both a PSD and PMMA fiber were investigated to isolate the changes in response from the scintillator and the noise signal as a function of magnetic field strength. All irradiations were performed in water at a photon beam energy of 6 MV. Magnetic field strengths of (0, ±0.35, ±0.70, ±1.05, and  ±1.40) T were investigated. Four noise subtraction techniques were investigated to evaluate the impact on the resulting noise-subtracted scintillator response with magnetic field strength. The noise subtraction methods included direct spectral subtraction, the spectral method, and variants thereof. The PMMA fiber exhibited changes in response of up to 50% with magnetic field strength due to the directional light emission from \\breve{C} erenkov radiation. The PSD showed increases in response of up to 10% when not corrected for the noise signal, which agrees with previous investigations of scintillator response in magnetic fields. Decreases in the \\breve{C} erenkov light ratio with negative field strength were observed with a maximum change at  ‑1.40 T of 3.2% compared to 0 T. The change in the noise-subtracted PSD response as a function of magnetic field strength varied with the noise subtraction technique used. Even after noise subtraction, the PSD exhibited changes in response of up to 5.5% over the four noise subtraction methods investigated.

Unveiling the magnetic structure of VHE SNRs/PWNe with XIPE, the x-ray imaging-polarimetry explorer

NASA Astrophysics Data System (ADS)

de Ona Wilhelmi, E.; Vink, J.; Bykov, A.; Zanin, R.; Bucciantini, N.; Amato, E.; Bandiera, R.; Olmi, B.; Uvarov, Yu.; XIPE Science Working Group

2017-01-01

The dynamics, energetics and evolution of pulsar wind nebulae (PWNe) and supernova remnants (SNRs), are strongly affected by their magnetic field strength and distribution. They are usually strong, extended, sources of non-thermal X-ray radiation, producing intrinsically polarised radiation. The energetic wind around pulsars produces a highly-magnetised, structured flow, often displaying a jet and a torus and different features (i.e. wisps, knots). This magnetic-dominant wind evolves as it moves away from the pulsar magnetosphere to the surrounding large-scale nebula, becoming kinetic-dominant. Basic aspects such how this conversion is produced, or how the jets and torus are formed, as well as the level of turbulence in the nebula are still unknown. Likewise, the processes ruling the acceleration of particles in shell-like SNRs up to 1015 eV, including the amplification of the magnetic field, are not clear yet. Imaging polarimetry in this regard is crucial to localise the regions of shock acceleration and to measure the strength and the orientation of the magnetic field at these emission sites. X-ray polarimetry with the X-ray Imaging Polarimetry Explorer (XIPE) will allow the understanding of the magnetic field structure and intensity on different regions in SNRs and PWNe, helping to unveil long-standing questions such as i.e. acceleration of cosmic rays in SNRs or magnetic-to-kinetic energy transfer. SNRs and PWNe also represent the largest population of Galactic very-high energy gamma-ray sources, therefore the study of their magnetic distribution with XIPE will provide fundamental ingredients on the investigation of those sources at very high energies. We will discuss the physics case related to SNRs and PWNe and the expectations of the XIPE observations of some of the most prominent SNRs and PWNe.

A model for wave control on coral breakage and species distribution in the Hawaiian Islands

USGS Publications Warehouse

Storlazzi, C.D.; Brown, E.K.; Field, M.E.; Rodgers, K.; Jokiel, P.L.

2005-01-01

The fringing reef off southern Molokai, Hawaii, is currently being studied as part of a multi-disciplinary project led by the US Geological Survey. As part of this study, modeling and field observations were utilized to help understand the physical controls on reef morphology and the distribution of different coral species. A model was developed that calculates wave-induced hydrodynamic forces on corals of a specific form and mechanical strength. From these calculations, the wave conditions under which specific species of corals would either be stable or would break due to the imposed wave-induced forces were determined. By combining this hydrodynamic force-balance model with various wave model output for different oceanographic conditions experienced in the study area, we were able to map the locations where specific coral species should be stable (not subject to frequent breakage) in the study area. The combined model output was then compared with data on coral species distribution and coral cover at 12 sites along Molokai's south shore. Observations and modeling suggest that the transition from one coral species to another may occur when the ratio of the coral colony's mechanical strengths to the applied (wave-induced) forces may be as great as 5:1, and not less than 1:1 when corals would break. This implies that coral colony's mechanical strength and wave-induced forces may be important in defining gross coral community structure over large (orders of 10's of meters) spatial scales. ?? Springer-Verlag 2004.

Clustering, randomness, and regularity in cloud fields: 2. Cumulus cloud fields

NASA Astrophysics Data System (ADS)

Zhu, T.; Lee, J.; Weger, R. C.; Welch, R. M.

1992-12-01

During the last decade a major controversy has been brewing concerning the proper characterization of cumulus convection. The prevailing view has been that cumulus clouds form in clusters, in which cloud spacing is closer than that found for the overall cloud field and which maintains its identity over many cloud lifetimes. This "mutual protection hypothesis" of Randall and Huffman (1980) has been challenged by the "inhibition hypothesis" of Ramirez et al. (1990) which strongly suggests that the spatial distribution of cumuli must tend toward a regular distribution. A dilemma has resulted because observations have been reported to support both hypotheses. The present work reports a detailed analysis of cumulus cloud field spatial distributions based upon Landsat, Advanced Very High Resolution Radiometer, and Skylab data. Both nearest-neighbor and point-to-cloud cumulative distribution function statistics are investigated. The results show unequivocally that when both large and small clouds are included in the cloud field distribution, the cloud field always has a strong clustering signal. The strength of clustering is largest at cloud diameters of about 200-300 m, diminishing with increasing cloud diameter. In many cases, clusters of small clouds are found which are not closely associated with large clouds. As the small clouds are eliminated from consideration, the cloud field typically tends towards regularity. Thus it would appear that the "inhibition hypothesis" of Ramirez and Bras (1990) has been verified for the large clouds. However, these results are based upon the analysis of point processes. A more exact analysis also is made which takes into account the cloud size distributions. Since distinct clouds are by definition nonoverlapping, cloud size effects place a restriction upon the possible locations of clouds in the cloud field. The net effect of this analysis is that the large clouds appear to be randomly distributed, with only weak tendencies towards regularity. For clouds less than 1 km in diameter, the average nearest-neighbor distance is equal to 3-7 cloud diameters. For larger clouds, the ratio of cloud nearest-neighbor distance to cloud diameter increases sharply with increasing cloud diameter. This demonstrates that large clouds inhibit the growth of other large clouds in their vicinity. Nevertheless, this leads to random distributions of large clouds, not regularity.

Spectrophotometry of peculiar B and A stars. XIV - 56 Arietis, 41 Tauri, 25 Sextantis, HD 170973, HD 205087, and HD 215441

NASA Astrophysics Data System (ADS)

Adelman, S. J.

1983-03-01

Optical region spectrophotometry of six relatively hot Ap stars is presented. Additional scans of 56 Ari extend the results of an earlier paper in this series. The data for 41 Tau, 25 Sex, HD 170973, and HD 215441 are studied as a function of phase. The observations of HD 205087 are inconclusive about its variability although they show spectrophotometrically that it is a definite Ap star. The observations of HD 215441 show a prominent λ5200 broad, continuum feature with an unusual shape. However, when the data are corrected for interstellar reddening, the energy distribution resembles those of other silicon stars. The λ5200 feature is found to be variable in phase with the U-B and B-V colors and with the magnetic field strength. This feature is strongest when the Balmer jump is smallest, the Paschen continuum the bluest according to B-V, and the surface magnetic field strength the largest.

Reconciling Models of Luminous Blazars with Magnetic Fluxes Determined by Radio Core-shift Measurements

NASA Astrophysics Data System (ADS)

Nalewajko, Krzysztof; Sikora, Marek; Begelman, Mitchell C.

2014-11-01

Estimates of magnetic field strength in relativistic jets of active galactic nuclei, obtained by measuring the frequency-dependent radio core location, imply that the total magnetic fluxes in those jets are consistent with the predictions of the magnetically arrested disk (MAD) scenario of jet formation. On the other hand, the magnetic field strength determines the luminosity of the synchrotron radiation, which forms the low-energy bump of the observed blazar spectral energy distribution (SED). The SEDs of the most powerful blazars are strongly dominated by the high-energy bump, which is most likely due to the external radiation Compton mechanism. This high Compton dominance may be difficult to reconcile with the MAD scenario, unless (1) the geometry of external radiation sources (broad-line region, hot-dust torus) is quasi-spherical rather than flat, or (2) most gamma-ray radiation is produced in jet regions of low magnetization, e.g., in magnetic reconnection layers or in fast jet spines.

RECONCILING MODELS OF LUMINOUS BLAZARS WITH MAGNETIC FLUXES DETERMINED BY RADIO CORE-SHIFT MEASUREMENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nalewajko, Krzysztof; Begelman, Mitchell C.; Sikora, Marek, E-mail: knalew@stanford.edu

2014-11-20

Estimates of magnetic field strength in relativistic jets of active galactic nuclei, obtained by measuring the frequency-dependent radio core location, imply that the total magnetic fluxes in those jets are consistent with the predictions of the magnetically arrested disk (MAD) scenario of jet formation. On the other hand, the magnetic field strength determines the luminosity of the synchrotron radiation, which forms the low-energy bump of the observed blazar spectral energy distribution (SED). The SEDs of the most powerful blazars are strongly dominated by the high-energy bump, which is most likely due to the external radiation Compton mechanism. This high Comptonmore » dominance may be difficult to reconcile with the MAD scenario, unless (1) the geometry of external radiation sources (broad-line region, hot-dust torus) is quasi-spherical rather than flat, or (2) most gamma-ray radiation is produced in jet regions of low magnetization, e.g., in magnetic reconnection layers or in fast jet spines.« less

Two-dimensional nanosecond electric field mapping based on cell electropermeabilization.

PubMed

Chen, Meng-Tse; Jiang, Chunqi; Vernier, P Thomas; Wu, Yu-Hsuan; Gundersen, Martin A

2009-11-11

Nanosecond, megavolt-per-meter electric pulses cause permeabilization of cells to small molecules, programmed cell death (apoptosis) in tumor cells, and are under evaluation as a treatment for skin cancer. We use nanoelectroporation and fluorescence imaging to construct two-dimensional maps of the electric field associated with delivery of 15 ns, 10 kV pulses to monolayers of the human prostate cancer cell line PC3 from three different electrode configurations: single-needle, five-needle, and flat-cut coaxial cable. Influx of the normally impermeant fluorescent dye YO-PRO-1 serves as a sensitive indicator of membrane permeabilization. The level of fluorescence emission after pulse exposure is proportional to the applied electric field strength. Spatial electric field distributions were compared in a plane normal to the center axis and 15-20 mum from the tip of the center electrode. Measurement results agree well with models for the three electrode arrangements evaluated in this study. This live-cell method for measuring a nanosecond pulsed electric field distribution provides an operationally meaningful calibration of electrode designs for biological applications and permits visualization of the relative sensitivities of different cell types to nanoelectropulse stimulation. PACS Codes: 87.85.M-

Atomistic simulation on charge mobility of amorphous tris(8-hydroxyquinoline) aluminum (Alq3): origin of Poole-Frenkel-type behavior.

PubMed

Nagata, Yuki; Lennartz, Christian

2008-07-21

The atomistic simulation of charge transfer process for an amorphous Alq(3) system is reported. By employing electrostatic potential charges, we calculate site energies and find that the standard deviation of site energy distribution is about twice as large as predicted in previous research. The charge mobility is calculated via the Miller-Abrahams formalism and the master equation approach. We find that the wide site energy distribution governs Poole-Frenkel-type behavior of charge mobility against electric field, while the spatially correlated site energy is not a dominant mechanism of Poole-Frenkel behavior in the range from 2x10(5) to 1.4x10(6) V/cm. Also we reveal that randomly meshed connectivities are, in principle, required to account for the Poole-Frenkel mechanism. Charge carriers find a zigzag pathway at low electric field, while they find a straight pathway along electric field when a high electric field is applied. In the space-charge-limited current scheme, the charge-carrier density increases with electric field strength so that the nonlinear behavior of charge mobility is enhanced through the strong charge-carrier density dependence of charge mobility.

The influence of sulcus width on simulated electric fields induced by transcranial magnetic stimulation

PubMed Central

Janssen, A M; Rampersad, S M; Lucka, F; Lanfer, B; Lew, S; Aydin, Ü; Wolters, C H; Stegeman, D F; Oostendorp, T F

2013-01-01

Volume conduction models can help in acquiring knowledge about the distribution of the electric field induced by transcranial magnetic stimulation (TMS). One aspect of a detailed model is an accurate description of the cortical surface geometry. Since its estimation is difficult, it is important to know how accurate the geometry has to be represented. Previous studies only looked at the differences caused by neglecting the complete boundary between the CSF and GM (Thielscher et al. 2011; Bijsterbosch et al. 2012), or by resizing the whole brain (Wagner et al. 2008). However, due to the high conductive properties of the CSF, it can be expected that alterations in sulcus width can already have a significant effect on the distribution of the electric field. To answer this question, the sulcus width of a highly realistic head model, based on T1-, T2- and diffusion-weighted magnetic resonance images (MRI), was altered systematically. This study shows that alterations in the sulcus width do not cause large differences in the majority of the electric field values. However, considerable overestimation of sulcus width produces an overestimation of the calculated field strength, also at locations distant from the target location. PMID:23787706

47 CFR 27.55 - Power strength limits.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 2 2011-10-01 2011-10-01 false Power strength limits. 27.55 Section 27.55... COMMUNICATIONS SERVICES Technical Standards § 27.55 Power strength limits. (a) Field strength limits. For the following bands, the predicted or measured median field strength at any location on the geographical border...

Investigating Global Ion and Neutral Atom Populations with IBEX and Voyager

NASA Technical Reports Server (NTRS)

Florinski, Vladimir

2016-01-01

The main objective of this project was to investigate pickup ion (PUI) production in the solar wind and heliosheath (the region between the termination shock and the heliopause) and compute the distributed energetic neutral atom fluxes throughout the helioshpere. The simulations were constrained by comparing the model output against observations from Ulysses, New Horizons, Voyager 1 and 2, and IBEX space probes. As evidenced by the number of peer reviewed journal publications resulting from the project (13 plus three submitted) and their citation rate (156 citations over three years), the project has made a lasting contribution to the field. The outcome is a significant improvement of our understanding of the pickup ion production and distribution in the distant heliosphere. The team has accomplished the entire set of tasks A-H set forth in the proposal. Namely, the transport modeling framework has been augmented with two populations of pickup ions (PUIs), the boundary conditions for the plasma and interstellar neutral hydrogen were verified against Ulysses and New Horizons PUI and an optimal set of velocity diffusion parameters established. The multi-component fluxes of PUIs were computed and isotropic velocity distributions generated for each cell in the computer simulation that covered the heliosphere from 1.5 AU to the heliopause. The distributions were carefully compared with in situ measurements at 3 AU (Ulysses), 12 AU (New Horizons), and 80-90 AU (Voyager 1 and 2) as well as those inferred from ENA fluxes measured by Cassini and IBEX (Wu et al., 2016). Some examples of modeldata comparison are shown in Figure 1. We have used coupled MHD-plasma and kinetic-neutral code to investigate the likely range of plasma and magnetic field parameters in the local interstellar medium (LISM), based on the assumption that the shape of the IBEX ribbon could be used to determine the orientation of the interstellar magnetic field. While the magnetic field is believed to be oriented toward the center of the ribbon, constraining its strength requires comparing the model-predicted angular diameter and circularity of the ribbon with the observations. The study, published in Heerikhuisen et al. (2014), found that the most likely range for the LISM magnetic field strength is between 0.2 and 0.3 nT, which is less than previously thought. Figure 2 shows the IBEX data (left) and compares it to the simulation with a 0.2 nT interstellar magnetic field (center) and a 0.4 nT (right).

MRI Estimates of Brain Iron Concentration in Normal Aging Using Quantitative Susceptibility Mapping

PubMed Central

Bilgic, Berkin; Pfefferbaum, Adolf; Rohlfing, Torsten; Sullivan, Edith V.; Adalsteinsson, Elfar

2011-01-01

Quantifying tissue iron concentration in vivo is instrumental for understanding the role of iron in physiology and in neurological diseases associated with abnormal iron distribution. Herein, we use recently-developed Quantitative Susceptibility Mapping (QSM) methodology to estimate the tissue magnetic susceptibility based on MRI signal phase. To investigate the effect of different regularization choices, we implement and compare ℓ1 and ℓ2 norm regularized QSM algorithms. These regularized approaches solve for the underlying magnetic susceptibility distribution, a sensitive measure of the tissue iron concentration, that gives rise to the observed signal phase. Regularized QSM methodology also involves a pre-processing step that removes, by dipole fitting, unwanted background phase effects due to bulk susceptibility variations between air and tissue and requires data acquisition only at a single field strength. For validation, performances of the two QSM methods were measured against published estimates of regional brain iron from postmortem and in vivo data. The in vivo comparison was based on data previously acquired using Field-Dependent Relaxation Rate Increase (FDRI), an estimate of MRI relaxivity enhancement due to increased main magnetic field strength, requiring data acquired at two different field strengths. The QSM analysis was based on susceptibility-weighted images acquired at 1.5T, whereas FDRI analysis used Multi-Shot Echo-Planar Spin Echo images collected at 1.5T and 3.0T. Both datasets were collected in the same healthy young and elderly adults. The in vivo estimates of regional iron concentration comported well with published postmortem measurements; both QSM approaches yielded the same rank ordering of iron concentration by brain structure, with the lowest in white matter and the highest in globus pallidus. Further validation was provided by comparison of the in vivo measurements, ℓ1-regularized QSM versus FDRI and ℓ2-regularized QSM versus FDRI, which again yielded perfect rank ordering of iron by brain structure. The final means of validation was to assess how well each in vivo method detected known age-related differences in regional iron concentrations measured in the same young and elderly healthy adults. Both QSM methods and FDRI were consistent in identifying higher iron concentrations in striatal and brain stem ROIs (i.e., caudate nucleus, putamen, globus pallidus, red nucleus, and substantia nigra) in the older than in the young group. The two QSM methods appeared more sensitive in detecting age differences in brain stem structures as they revealed differences of much higher statistical significance between the young and elderly groups than did FDRI. However, QSM values are influenced by factors such as the myelin content, whereas FDRI is a more specific indicator of iron content. Hence, FDRI demonstrated higher specificity to iron yet yielded noisier data despite longer scan times and lower spatial resolution than QSM. The robustness, practicality, and demonstrated ability of predicting the change in iron deposition in adult aging suggest that regularized QSM algorithms using single-field-strength data are possible alternatives to tissue iron estimation requiring two field strengths. PMID:21925274

47 CFR 73.686 - Field strength measurements.

Code of Federal Regulations, 2014 CFR

2014-10-01

... earth radius, of the largest available scale. (c) Collection of field strength data to determine... through the measurement area. (iii) Antenna elevation. When field strength is being measured for a one....686 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO...

47 CFR 73.686 - Field strength measurements.

Code of Federal Regulations, 2013 CFR

2013-10-01

... earth radius, of the largest available scale. (c) Collection of field strength data to determine... through the measurement area. (iii) Antenna elevation. When field strength is being measured for a one....686 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO...

47 CFR 73.686 - Field strength measurements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... earth radius, of the largest available scale. (c) Collection of field strength data to determine... through the measurement area. (iii) Antenna elevation. When field strength is being measured for a one....686 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO...

47 CFR 73.686 - Field strength measurements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... earth radius, of the largest available scale. (c) Collection of field strength data to determine... through the measurement area. (iii) Antenna elevation. When field strength is being measured for a one....686 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES RADIO...

Redesigning existing transcranial magnetic stimulation coils to reduce energy: application to low field magnetic stimulation

NASA Astrophysics Data System (ADS)

Wang, Boshuo; Shen, Michael R.; Deng, Zhi-De; Smith, J. Evan; Tharayil, Joseph J.; Gurrey, Clement J.; Gomez, Luis J.; Peterchev, Angel V.

2018-06-01

Objective. To present a systematic framework and exemplar for the development of a compact and energy-efficient coil that replicates the electric field (E-field) distribution induced by an existing transcranial magnetic stimulation coil. Approach. The E-field generated by a conventional low field magnetic stimulation (LFMS) coil was measured for a spherical head model and simulated in both spherical and realistic head models. Then, using a spherical head model and spatial harmonic decomposition, a spherical-shaped cap coil was synthesized such that its windings conformed to a spherical surface and replicated the E-field on the cortical surface while requiring less energy. A prototype coil was built and electrically characterized. The effect of constraining the windings to the upper half of the head was also explored via an alternative coil design. Main results. The LFMS E-field distribution resembled that of a large double-cone coil, with a peak field strength around 350 mV m‑1 in the cortex. The E-field distributions of the cap coil designs were validated against the original coil, with mean errors of 1%–3%. The cap coil required as little as 2% of the original coil energy and was significantly smaller in size. Significance. The redesigned LFMS coil is substantially smaller and more energy-efficient than the original, improving cost, power consumption, and portability. These improvements could facilitate deployment of LFMS in the clinic and potentially at home. This coil redesign approach can also be applied to other magnetic stimulation paradigms. Finally, the anatomically-accurate E-field simulation of LFMS can be used to interpret clinical LFMS data.

Quantitative analysis of visible surface defect risk in tablets during film coating using terahertz pulsed imaging.

PubMed

Niwa, Masahiro; Hiraishi, Yasuhiro

2014-01-30

Tablets are the most common form of solid oral dosage produced by pharmaceutical industries. There are several challenges to successful and consistent tablet manufacturing. One well-known quality issue is visible surface defects, which generally occur due to insufficient physical strength, causing breakage or abrasion during processing, packaging, or shipping. Techniques that allow quantitative evaluation of surface strength and the risk of surface defect would greatly aid in quality control. Here terahertz pulsed imaging (TPI) was employed to evaluate the surface properties of core tablets with visible surface defects of varying severity after film coating. Other analytical methods, such as tensile strength measurements, friability testing, and scanning electron microscopy (SEM), were used to validate TPI results. Tensile strength and friability provided no information on visible surface defect risk, whereas the TPI-derived unique parameter terahertz electric field peak strength (TEFPS) provided spatial distribution of surface density/roughness information on core tablets, which helped in estimating tablet abrasion risk prior to film coating and predicting the location of the defects. TPI also revealed the relationship between surface strength and blending condition and is a nondestructive, quantitative approach to aid formulation development and quality control that can reduce visible surface defect risk in tablets. Copyright © 2013 Elsevier B.V. All rights reserved.

Continuously distributed magnetization profile for millimeter-scale elastomeric undulatory swimming

NASA Astrophysics Data System (ADS)

Diller, Eric; Zhuang, Jiang; Zhan Lum, Guo; Edwards, Matthew R.; Sitti, Metin

2014-04-01

We have developed a millimeter-scale magnetically driven swimming robot for untethered motion at mid to low Reynolds numbers. The robot is propelled by continuous undulatory deformation, which is enabled by the distributed magnetization profile of a flexible sheet. We demonstrate control of a prototype device and measure deformation and speed as a function of magnetic field strength and frequency. Experimental results are compared with simple magnetoelastic and fluid propulsion models. The presented mechanism provides an efficient remote actuation method at the millimeter scale that may be suitable for further scaling down in size for micro-robotics applications in biotechnology and healthcare.

Effects of magnetic field strength in the discharge channel on the performance of a multi-cusped field thruster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Peng; Liu, Hui; Gao, Yuanyuan

The performance characteristics of a Multi-cusped Field Thruster depending on the magnetic field strength in the discharge channel were investigated. Four thrusters with different outer diameters of the magnet rings were designed to change the magnetic field strength in the discharge channel. It is found that increasing the magnetic field strength could restrain the radial cross-field electron current and decrease the radial width of main ionization region, which gives rise to the reduction of propellant utilization and thruster performance. The test results in different anode voltage conditions indicate that both the thrust and anode efficiency are higher for the weakermore » magnetic field in the discharge channel.« less

Electric dipole polarizability from first principles calculations

DOE PAGES

Miorelli, M.; Bacca, S.; Barnea, N.; ...

2016-09-19

The electric dipole polarizability quantifies the low-energy behavior of the dipole strength and is related to critical observables such as the radii of the proton and neutron distributions. Its computation is challenging because most of the dipole strength lies in the scattering continuum. In our paper we combine integral transforms with the coupled-cluster method and compute the dipole polarizability using bound-state techniques. Furthermore, employing different interactions from chiral effective field theory, we confirm the strong correlation between the dipole polarizability and the charge radius, and study its dependence on three-nucleon forces. Finally, we find good agreement with data for themore » 4He, 40Ca, and 16O nuclei, and predict the dipole polarizability for the rare nucleus 22O.« less

47 CFR 2.1053 - Measurements required: Field strength of spurious radiation.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 1 2011-10-01 2011-10-01 false Measurements required: Field strength of spurious radiation. 2.1053 Section 2.1053 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL... Procedures Certification § 2.1053 Measurements required: Field strength of spurious radiation. (a...

47 CFR 2.1053 - Measurements required: Field strength of spurious radiation.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 47 Telecommunication 1 2014-10-01 2014-10-01 false Measurements required: Field strength of spurious radiation. 2.1053 Section 2.1053 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL... Procedures Certification § 2.1053 Measurements required: Field strength of spurious radiation. (a...

47 CFR 2.1053 - Measurements required: Field strength of spurious radiation.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 47 Telecommunication 1 2013-10-01 2013-10-01 false Measurements required: Field strength of spurious radiation. 2.1053 Section 2.1053 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL... Procedures Certification § 2.1053 Measurements required: Field strength of spurious radiation. (a...

Relationship between magnetic field strength and magnetic-resonance-related acoustic noise levels.

PubMed

Moelker, Adriaan; Wielopolski, Piotr A; Pattynama, Peter M T

2003-02-01

The need for better signal-to-noise ratios and resolution has pushed magnetic resonance imaging (MRI) towards high-field MR-scanners for which only little data on MR-related acoustic noise production have been published. The purpose of this study was to validate the theoretical relationship of sound pressure level (SPL) and static magnetic field strength. This is relevant for allowing adequate comparisons of acoustic data of MR systems at various magnetic field strengths. Acoustic data were acquired during various pulse sequences at field strengths of 0.5, 1.0, 1.5 and 2.0 Tesla using the same MRI unit by means of a Helicon rampable magnet. Continuous-equivalent, i.e. time-averaged, linear SPLs and 1/3-octave band frequencies were recorded. Ramping from 0.5 to 1.0 Tesla and from 1.0 to 2.0 Tesla resulted in an SPL increase of 5.7 and 5.2 dB(L), respectively, when averaged over the various pulse sequences. Most of the acoustic energy was in the 1-kHz frequency band, irrespective of magnetic field strength. The relation between field strength and SPL was slightly non-linear, i.e. a slightly less increase at higher field strengths, presumably caused by the elastic properties of the gradient coil encasings.

Bats Respond to Very Weak Magnetic Fields

PubMed Central

Tian, Lan-Xiang; Pan, Yong-Xin; Metzner, Walter; Zhang, Jin-Shuo; Zhang, Bing-Fang

2015-01-01

How animals, including mammals, can respond to and utilize the direction and intensity of the Earth’s magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth’s magnetic field strength varied and the polarity reversed tens of times over the past fifty million years. PMID:25922944

Bats respond to very weak magnetic fields.

PubMed

Tian, Lan-Xiang; Pan, Yong-Xin; Metzner, Walter; Zhang, Jin-Shuo; Zhang, Bing-Fang

2015-01-01

How animals, including mammals, can respond to and utilize the direction and intensity of the Earth's magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth's magnetic field strength varied and the polarity reversed tens of times over the past fifty million years.

A theoretical study of molecular structure, optical properties and bond activation of energetic compound FOX-7 under intense electric fields

NASA Astrophysics Data System (ADS)

Tao, Zhiqiang; Wang, Xin; Wei, Yuan; Lv, Li; Wu, Deyin; Yang, Mingli

2017-02-01

Molecular structure, vibrational and electronic absorption spectra, chemical reactivity of energetic compound FOX-7, one of the most widely used explosives, were studied computationally in presence of an electrostatic field of 0.01-0.05 a.u. The Csbnd N bond, which usually triggers the decomposition of FOX-7, is shortened/elongated under a parallel/antiparallel field. The Csbnd N bond activation energy varies with the external electric field, decreasing remarkably with the field strength in regardless of the field direction. This is attributed to two aspects: the bond weakening by the field parallel to the Csbnd N bond and the stabilization effect on the transition-state structure by the field antiparallel to the bond. The variations in the structure and property of FOX-7 under the electric fields were further analyzed with its distributional polarizability, which is dependent on the charge transfer characteristics through the Csbnd N bond.

A structural insight into mechanical strength of graphene-like carbon and carbon nitride networks

NASA Astrophysics Data System (ADS)

Rahaman, Obaidur; Mortazavi, Bohayra; Dianat, Arezoo; Cuniberti, Gianaurelio; Rabczuk, Timon

2017-02-01

Graphene, one of the strongest materials ever discovered, triggered the exploration of many 2D materials in the last decade. However, the successful synthesis of a stable nanomaterial requires a rudimentary understanding of the relationship between its structure and strength. In the present study, we investigate the mechanical properties of eight different carbon-based 2D nanomaterials by performing extensive density functional theory calculations. The considered structures were just recently either experimentally synthesized or theoretically predicted. The corresponding stress-strain curves and elastic moduli are reported. They can be useful in training force field parameters for large scale simulations. A comparative analysis of these results revealed a direct relationship between atomic density per area and elastic modulus. Furthermore, for the networks that have an armchair and a zigzag orientation, we observed that they were more stretchable in the zigzag direction than the armchair direction. A critical analysis of the angular distributions and radial distribution functions suggested that it could be due to the higher ability of the networks to suppress the elongations of the bonds in the zigzag direction by deforming the bond angles. The structural interpretations provided in this work not only improve the general understanding of a 2D material’s strength but also enables us to rationally design them for higher qualities.

47 CFR 27.804 - Field strength limits at WMTS facility.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 2 2010-10-01 2010-10-01 false Field strength limits at WMTS facility. 27.804... MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES 1.4 GHz Band § 27.804 Field strength limits at WMTS facility. For any operation in the 1392-1395 MHz band, the predicted or measured field strength—into the WMTS band...

47 CFR 27.804 - Field strength limits at WMTS facility.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 2 2011-10-01 2011-10-01 false Field strength limits at WMTS facility. 27.804... MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES 1.4 GHz Band § 27.804 Field strength limits at WMTS facility. For any operation in the 1392-1395 MHz band, the predicted or measured field strength—into the WMTS band...

Bound and continuum energy distributions of nuclear fragments resulting from tunneling ionization of molecules

NASA Astrophysics Data System (ADS)

Svensmark, Jens; Tolstikhin, Oleg I.; Madsen, Lars Bojer

2018-03-01

We present the theory of tunneling ionization of molecules with both electronic and nuclear motion treated quantum mechanically. The theory provides partial rates for ionization into the different final states of the molecular ion, including both bound vibrational and dissociative channels. The exact results obtained for a one-dimensional model of H2 and D2 are compared with two approximate approaches, the weak-field asymptotic theory and the Born-Oppenheimer approximation. The validity ranges and compatibility of the approaches are identified formally and illustrated by the calculations. The results quantify that at typical field strengths considered in strong-field physics, it is several orders of magnitude more likely to ionize into bound vibrational ionic channels than into the dissociative channel.

A DOUBLE-RING ALGORITHM FOR MODELING SOLAR ACTIVE REGIONS: UNIFYING KINEMATIC DYNAMO MODELS AND SURFACE FLUX-TRANSPORT SIMULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Munoz-Jaramillo, Andres; Martens, Petrus C. H.; Nandy, Dibyendu

The emergence of tilted bipolar active regions (ARs) and the dispersal of their flux, mediated via processes such as diffusion, differential rotation, and meridional circulation, is believed to be responsible for the reversal of the Sun's polar field. This process (commonly known as the Babcock-Leighton mechanism) is usually modeled as a near-surface, spatially distributed {alpha}-effect in kinematic mean-field dynamo models. However, this formulation leads to a relationship between polar field strength and meridional flow speed which is opposite to that suggested by physical insight and predicted by surface flux-transport simulations. With this in mind, we present an improved double-ring algorithmmore » for modeling the Babcock-Leighton mechanism based on AR eruption, within the framework of an axisymmetric dynamo model. Using surface flux-transport simulations, we first show that an axisymmetric formulation-which is usually invoked in kinematic dynamo models-can reasonably approximate the surface flux dynamics. Finally, we demonstrate that our treatment of the Babcock-Leighton mechanism through double-ring eruption leads to an inverse relationship between polar field strength and meridional flow speed as expected, reconciling the discrepancy between surface flux-transport simulations and kinematic dynamo models.« less

Evaluation of pulsed electric fields technology for liquid whole egg pasteurization.

PubMed

Monfort, S; Gayán, E; Raso, J; Condón, S; Alvarez, I

2010-10-01

This investigation evaluated the lethal efficiency of pulsed electric fields (PEFs) to pasteurize liquid whole egg (LWE). To achieve this aim, we describe the inactivation of Salmonella Enteritidis and the heat resistant Salmonella Senftenberg 775 W in terms of treatment time and specific energy at electric field strengths ranging from 20 to 45 kV/cm. Based on our results, the target microorganism for this technology in LWE varied with intensity of the PEF treatment. For electric field strengths greater than 25 kV/cm, Salmonella Enteritidis was the most PEF-resistant strain. For this Salmonella serovar the level of inactivation depended only on the specific energy applied: i.e., 106, 272, and 472 kJ/kg for 1, 2, and 3 Log(10) reductions, respectively. The developed mathematical equations based on the Weibull distribution permit estimations of maximum inactivation level of 1.9 Log(10) cycles of the target Salmonella serovar in the best-case scenario: 250 kJ/kg and 25 kV/cm. This level of inactivation indicates that PEF technology by itself cannot guarantee the security of LWE based on USDA and European regulations. The occurrence of cell damage due to PEF in the Salmonella population opens the possibility of designing combined processes enabling increased microbial lethality in LWE. 2010 Elsevier Ltd. All rights reserved.

Ridging and strength in modeling the thickness distribution of Arctic sea ice

NASA Astrophysics Data System (ADS)

Flato, Gregory M.; Hibler, William D.

1995-09-01

A theory describing evolution of the ice thickness distribution (the probability density of ice thickness) was proposed by Thorndike et al. (1975) and has been used in several sea ice models. The advantage of this theory over the widely used two-level formulation is that it treats ridging explicitly as a redistribution of ice thickness, and ice strength as a function of energy losses incurred by ridge formation. However, the parameterization of these processes remains rather speculative and largely untested, and so our purpose here is to explore these parameterizations using a numerical model based on this theory. The model uses a 160-km resolution grid of the Arctic and 7 years of observed atmospheric forcing data (1979-1985). Monthly oceanic heat flux and current fields are obtained from a 40-km resolution coupled ice-ocean model run separately with the same forcing. By requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift, we estimate the primary strength parameter: the ratio of total to potential energy change during ridging. This ratio depends on the value of other parameters; however, the standard case has a ratio of 17 which is within the range estimated by Hopkins (1994) in simulations of individual ridging events. The effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics. In addition, these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented: first, the process of first-year to multiyear ridge consolidation is ignored; and second, the observed preferential melt of thick ridged ice is not reproduced.

Statistical analysis of suprathermal electron drivers at 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Broiles, Thomas W.; Burch, J. L.; Chae, K.; Clark, G.; Cravens, T. E.; Eriksson, A.; Fuselier, S. A.; Frahm, R. A.; Gasc, S.; Goldstein, R.; Henri, P.; Koenders, C.; Livadiotis, G.; Mandt, K. E.; Mokashi, P.; Nemeth, Z.; Odelstad, E.; Rubin, M.; Samara, M.

2016-11-01

We use observations from the Ion and Electron Sensor (IES) on board the Rosetta spacecraft to study the relationship between the cometary suprathermal electrons and the drivers that affect their density and temperature. We fit the IES electron observations with the summation of two kappa distributions, which we characterize as a dense and warm population (˜10 cm-3 and ˜16 eV) and a rarefied and hot population (˜0.01 cm-3 and ˜43 eV). The parameters of our fitting technique determine the populations' density, temperature, and invariant kappa index. We focus our analysis on the warm population to determine its origin by comparing the density and temperature with the neutral density and magnetic field strength. We find that the warm electron population is actually two separate sub-populations: electron distributions with temperatures above 8.6 eV and electron distributions with temperatures below 8.6 eV. The two sub-populations have different relationships between their density and temperature. Moreover, the two sub-populations are affected by different drivers. The hotter sub-population temperature is strongly correlated with neutral density, while the cooler sub-population is unaffected by neutral density and is only weakly correlated with magnetic field strength. We suggest that the population with temperatures above 8.6 eV is being heated by lower hybrid waves driven by counterstreaming solar wind protons and newly formed, cometary ions created in localized, dense neutral streams. To the best of our knowledge, this represents the first observations of cometary electrons heated through wave-particle interactions.

MAGNETIC FIELD STRENGTH FLUCTUATIONS IN THE HELIOSHEATH: VOYAGER 1 OBSERVATIONS DURING 2009

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burlaga, L. F.; Ness, N. F., E-mail: lburlagahsp@verizon.net, E-mail: nfnudel@yahoo.com

2012-01-01

We analyze the ''microscale fluctuations'' of the magnetic field strength B on a scale of several hours observed by Voyager1 (V1) in the heliosheath during 2009. The microscale fluctuations of B range from coherent to stochastic structures. The amplitude of microscale fluctuations of B during 1 day is measured by the standard deviation (SD) of 48 s averages of B. The distribution of the daily values of SD is lognormal. SD(t) from day of year (DOY) 1 to 331, 2009, is very intermittent. SD(t) has a 1/f or 'pink noise' spectrum on scales from 1 to 100 days, and itmore » has a broad multifractal spectrum f({alpha}) with 0.57 {<=} {alpha} {<=} 1.39. The time series of increments SD(t + {tau}) - SD(t) has a pink noise spectrum with {alpha}' = 0.88 {+-} 0.14 on scales from 1 to 100 days. The increments have a Tsallis (q-Gaussian) distribution on scales from 1 to 165 days, with an average q = 1.75 {+-} 0.12. The skewness S and kurtosis K have Gaussian and lognormal distributions, respectively. The largest spikes in K(t) and S(t) are often associated with a change in B across a data gap and with identifiable physical structures. The 'turbulence' observed by V1 during 2009 was weakly compressible on average but still very intermittent, highly variable, and highly compressible at times. The turbulence observed just behind the termination shock by Voyager 2 was twice as strong. These observations place strong constraints on any model of 'turbulence' in the heliosheath.« less

A New Stochastic Approach to Predict Peak and Residual Shear Strength of Natural Rock Discontinuities

NASA Astrophysics Data System (ADS)

Casagrande, D.; Buzzi, O.; Giacomini, A.; Lambert, C.; Fenton, G.

2018-01-01

Natural discontinuities are known to play a key role in the stability of rock masses. However, it is a non-trivial task to estimate the shear strength of large discontinuities. Because of the inherent complexity to access to the full surface of the large in situ discontinuities, researchers or engineers tend to work on small-scale specimens. As a consequence, the results are often plagued by the well-known scale effect. A new approach is here proposed to predict shear strength of discontinuities. This approach has the potential to avoid the scale effect. The rationale of the approach is as follows: a major parameter that governs the shear strength of a discontinuity within a rock mass is roughness, which can be accounted for by surveying the discontinuity surface. However, this is typically not possible for discontinuities contained within the rock mass where only traces are visible. For natural surfaces, it can be assumed that traces are, to some extent, representative of the surface. It is here proposed to use the available 2D information (from a visible trace, referred to as a seed trace) and a random field model to create a large number of synthetic surfaces (3D data sets). The shear strength of each synthetic surface can then be estimated using a semi-analytical model. By using a large number of synthetic surfaces and a Monte Carlo strategy, a meaningful shear strength distribution can be obtained. This paper presents the validation of the semi-analytical mechanistic model required to support the new approach for prediction of discontinuity shear strength. The model can predict both peak and residual shear strength. The second part of the paper lays the foundation of a random field model to support the creation of synthetic surfaces having statistical properties in line with those of the data of the seed trace. The paper concludes that it is possible to obtain a reasonable estimate of peak and residual shear strength of the discontinuities tested from the information from a single trace, without having access to the whole surface.

THE RECENT REJUVENATION OF THE SUN’S LARGE-SCALE MAGNETIC FIELD: A CLUE FOR UNDERSTANDING PAST AND FUTURE SUNSPOT CYCLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheeley, N. R. Jr.; Wang, Y.-M.

The quiet nature of sunspot cycle 24 was disrupted during the second half of 2014 when the Sun’s large-scale field underwent a sudden rejuvenation: the solar mean field reached its highest value since 1991, the interplanetary field strength doubled, and galactic cosmic rays showed their strongest 27-day modulation since neutron-monitor observations began in 1957; in the outer corona, the large increase of field strength was reflected by unprecedentedly large numbers of coronal loops collapsing inward along the heliospheric current sheet. Here, we show that this rejuvenation was not caused by a significant increase in the level of solar activity asmore » measured by the smoothed sunspot number and CME rate, but instead was caused by the systematic emergence of flux in active regions whose longitudinal distribution greatly increased the Sun’s dipole moment. A similar post-maximum increase in the dipole moment occurred during each of the previous three sunspot cycles, and marked the start of the declining phase of each cycle. We note that the north–south component of this peak dipole moment provides an early indicator of the amplitude of the next cycle, and conclude that the amplitude of cycle 25 may be comparable to that of cycle 24, and well above the amplitudes obtained during the Maunder Minimum.« less

Conduction quantization in monolayer MoS2

NASA Astrophysics Data System (ADS)

Li, T. S.

2016-10-01

We study the ballistic conduction of a monolayer MoS2 subject to a spatially modulated magnetic field by using the Landauer-Buttiker formalism. The band structure depends sensitively on the field strength, and its change has profound influence on the electron conduction. The conductance is found to demonstrate multi-step behavior due to the discrete number of conduction channels. The sharp peak and rectangular structures of the conductance are stretched out as temperature increases, due to the thermal broadening of the derivative of the Fermi-Dirac distribution function. Finally, quantum behavior in the conductance of MoS2 can be observed at temperatures below 10 K.

Cathode fall measurement in a dielectric barrier discharge in helium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hao, Yanpeng; Zheng, Bin; Liu, Yaoge

2013-11-15

A method based on the “zero-length voltage” extrapolation is proposed to measure cathode fall in a dielectric barrier discharge. Starting, stable, and discharge-maintaining voltages were measured to obtain the extrapolation zero-length voltage. Under our experimental conditions, the “zero-length voltage” gave a cathode fall of about 185 V. Based on the known thickness of the cathode fall region, the spatial distribution of the electric field strength in dielectric barrier discharge in atmospheric helium is determined. The strong cathode fall with a maximum field value of approximately 9.25 kV/cm was typical for the glow mode of the discharge.

Parallel plate radiofrequency ion thruster

NASA Technical Reports Server (NTRS)

Nakanishi, S.

1982-01-01

An 8-cm-diam. argon ion thruster is described. It is operated by applying 100 to 160 Mhz rf power across a thin plasma volume in a strongly divergent static magnetic field. No cathode or electron emitter is required to sustain a continuous wave plasma discharge over a broad range of propellant gas flow. Preliminary results indicate that a large fraction of the incident power is being reflected by impedance mismatching in the coupling structure. Resonance effects due to plasma thickness, magnetic field strength, and distribution are presented. Typical discharge losses obtained to date are 500 to 600 W per beam ampere at extracted beam currents up to 60 mA.

On the Contribution of Curl-Free Current Patterns to the Ultimate Intrinsic Signal-to-Noise Ratio at Ultra-High Field Strength.

PubMed

Pfrommer, Andreas; Henning, Anke

2017-05-01

The ultimate intrinsic signal-to-noise ratio (SNR) is a coil independent performance measure to compare different receive coil designs. To evaluate this benchmark in a sample, a complete electromagnetic basis set is required. The basis set can be obtained by curl-free and divergence-free surface current distributions, which excite linearly independent solutions to Maxwell's equations. In this work, we quantitatively investigate the contribution of curl-free current patterns to the ultimate intrinsic SNR in a spherical head-sized model at 9.4 T. Therefore, we compare the ultimate intrinsic SNR obtained with having only curl-free or divergence-free current patterns, with the ultimate intrinsic SNR obtained from a combination of curl-free and divergence-free current patterns. The influence of parallel imaging is studied for various acceleration factors. Moreover results for different field strengths (1.5 T up to 11.7 T) are presented at specific voxel positions and acceleration factors. The full-wave electromagnetic problem is analytically solved using dyadic Green's functions. We show, that at ultra-high field strength (B 0 ⩾7T) a combination of curl-free and divergence-free current patterns is required to achieve the best possible SNR at any position in a spherical head-sized model. On 1.5- and 3T platforms, divergence-free current patterns are sufficient to cover more than 90% of the ultimate intrinsic SNR. Copyright © 2017 John Wiley & Sons, Ltd.

Energy flux determines magnetic field strength of planets and stars.

PubMed

Christensen, Ulrich R; Holzwarth, Volkmar; Reiners, Ansgar

2009-01-08

The magnetic fields of Earth and Jupiter, along with those of rapidly rotating, low-mass stars, are generated by convection-driven dynamos that may operate similarly (the slowly rotating Sun generates its field through a different dynamo mechanism). The field strengths of planets and stars vary over three orders of magnitude, but the critical factor causing that variation has hitherto been unclear. Here we report an extension of a scaling law derived from geodynamo models to rapidly rotating stars that have strong density stratification. The unifying principle in the scaling law is that the energy flux available for generating the magnetic field sets the field strength. Our scaling law fits the observed field strengths of Earth, Jupiter, young contracting stars and rapidly rotating low-mass stars, despite vast differences in the physical conditions of the objects. We predict that the field strengths of rapidly rotating brown dwarfs and massive extrasolar planets are high enough to make them observable.

47 CFR 73.61 - AM directional antenna field strength measurements.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 47 Telecommunication 4 2014-10-01 2014-10-01 false AM directional antenna field strength... RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.61 AM directional antenna field strength measurements. (a) Each AM station using a directional antenna with monitoring point locations...

47 CFR 73.61 - AM directional antenna field strength measurements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 4 2011-10-01 2011-10-01 false AM directional antenna field strength... RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.61 AM directional antenna field strength measurements. (a) Each AM station using a directional antenna with monitoring point locations...

47 CFR 73.61 - AM directional antenna field strength measurements.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 47 Telecommunication 4 2013-10-01 2013-10-01 false AM directional antenna field strength... RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.61 AM directional antenna field strength measurements. (a) Each AM station using a directional antenna with monitoring point locations...

47 CFR 73.61 - AM directional antenna field strength measurements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 47 Telecommunication 4 2012-10-01 2012-10-01 false AM directional antenna field strength... RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.61 AM directional antenna field strength measurements. (a) Each AM station using a directional antenna with monitoring point locations...

47 CFR 73.61 - AM directional antenna field strength measurements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 4 2010-10-01 2010-10-01 false AM directional antenna field strength... RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.61 AM directional antenna field strength measurements. (a) Each AM station using a directional antenna with monitoring point locations...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kilpua, E. K. J.; Olspert, N.; Grigorievskiy, A.

We study the relation between strong and extreme geomagnetic storms and solar cycle characteristics. The analysis uses an extensive geomagnetic index AA data set spanning over 150 yr complemented by the Kakioka magnetometer recordings. We apply Pearson correlation statistics and estimate the significance of the correlation with a bootstrapping technique. We show that the correlation between the storm occurrence and the strength of the solar cycle decreases from a clear positive correlation with increasing storm magnitude toward a negligible relationship. Hence, the quieter Sun can also launch superstorms that may lead to significant societal and economic impact. Our results show thatmore » while weaker storms occur most frequently in the declining phase, the stronger storms have the tendency to occur near solar maximum. Our analysis suggests that the most extreme solar eruptions do not have a direct connection between the solar large-scale dynamo-generated magnetic field, but are rather associated with smaller-scale dynamo and resulting turbulent magnetic fields. The phase distributions of sunspots and storms becoming increasingly in phase with increasing storm strength, on the other hand, may indicate that the extreme storms are related to the toroidal component of the solar large-scale field.« less

Latent mnemonic strengths are latent: a comment on Mickes, Wixted, and Wais (2007).

PubMed

Rouder, Jeffrey N; Pratte, Michael S; Morey, Richard D

2010-06-01

Mickes, Wixted, and Wais (2007) proposed a simple test of latent strength variability in recognition memory. They asked participants to rate their confidence using either a 20-point or a 99-point strength scale and plotted distributions of the resulting ratings. They found 25% more variability in ratings for studied than for new items, which they interpreted as providing evidence that latent mnemonic strength distributions are 25% more variable for studied than for new items. We show here that this conclusion is critically dependent on assumptions--so much so that these assumptions determine the conclusions. In fact, opposite conclusions, such that study does not affect the variability of latent strength, may be reached by making different but equally plausible assumptions. Because all measurements of mnemonic strength variability are critically dependent on untestable assumptions, all are arbitrary. Hence, there is no principled method for assessing the relative variability of latent mnemonic strength distributions.

Character Strengths and Intellectual and Developmental Disability: A Strengths-Based Approach from Positive Psychology

ERIC Educational Resources Information Center

Niemiec, Ryan M.; Shogren, Karrie A.; Wehmeyer, Michael L.

2017-01-01

There has been limited focus in the disability field on assessing and intervening to promote strengths of character. However, character strengths have received significant attention in the broader field of positive psychology. This paper provides an overview of the growing science of character strengths and explores why and how character strengths…

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yadav, Rakesh K.; Poppenhaeger, Katja; Wolk, Scott J.

Despite the lack of a shear-rich tachocline region, low-mass fully convective (FC) stars are capable of generating strong magnetic fields, indicating that a dynamo mechanism fundamentally different from the solar dynamo is at work in these objects. We present a self-consistent three-dimensional model of magnetic field generation in low-mass FC stars. The model utilizes the anelastic magnetohydrodynamic equations to simulate compressible convection in a rotating sphere. A distributed dynamo working in the model spontaneously produces a dipole-dominated surface magnetic field of the observed strength. The interaction of this field with the turbulent convection in outer layers shreds it, producing small-scalemore » fields that carry most of the magnetic flux. The Zeeman–Doppler-Imaging technique applied to synthetic spectropolarimetric data based on our model recovers most of the large-scale field. Our model simultaneously reproduces the morphology and magnitude of the large-scale field as well as the magnitude of the small-scale field observed on low-mass FC stars.« less

Electrostatically Induced Carbon Nanotube Alignment for Polymer Composite Applications

NASA Astrophysics Data System (ADS)

Chapkin, Wesley Aaron

We have developed a non-invasive technique utilizing polarized Raman spectroscopy to measure changes in carbon nanotube (CNT) alignment in situ and in real time in a polymer matrix. With this technique, we have confirmed the prediction of faster alignment for CNTs in higher electric fields. Real-time polarized Raman spectroscopy also allows us to demonstrate the loss of CNT alignment that occurs after the electric field is removed, which reveals the need for fast polymerization steps or the continued application of the aligning force during polymerization to lock in CNT alignment. Through a study on the effect of polymer viscosity on the rate of CNT alignment, we have determined that shear viscosity serves as the controlling mechanism for CNT rotation. This finding matches literature modeling of rigid rod mobility in a polymer melt and demonstrates that the rotational mobility of CNTs can be explained by a continuum model even though the diameters of single-walled CNTs are 1-2 nm. The viscosity dependence indicates that the manipulation of temperature (and indirectly viscosity) will have a direct effect on the rate of CNT alignment, which could prove useful in expediting the manufacturing of CNT-reinforced composites cured at elevated temperatures. Using real-time polarized Raman spectroscopy, we also demonstrate that electric fields of various strengths lead not only to different speeds of CNT rotation but also to different degrees of alignment. We hypothesize that this difference in achievable alignment results from discrete populations of nanotubes based on their length. The results are then explained by balancing the alignment energy for a given electric field strength with the randomizing thermal energy of the system. By studying the alignment dynamics of different CNT length distributions, we show that different degrees of alignment achieved as a function of the applied electric field strength are directly related to the square of the nanotube length. This finding matches an electrostatic potential energy model for CNT rotation. Lastly, we investigate the effects of conductive carbon fibers on electrostatically induced alignment of CNTs within carbon fiber composites. The relative electric field strength throughout the composite is modeled using COMSOL Multiphysics. We show the ability to generate enhanced electric field gradients within the gaps between carbon fibers for various fiber orientations. Using polarized Raman spectroscopy, increased levels of CNT alignment are observed between carbon fiber tows, which is consistent with the modeled higher electric field strengths in these regions. These findings could potentially lead to the development of carbon fiber composites with CNT additions that selectively enhance the composite properties outside the carbon fiber interphase in the neat epoxy.

Communication: Control of chemical reactions using electric field gradients.

PubMed

Deshmukh, Shivaraj D; Tsori, Yoav

2016-05-21

We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition, thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied, the solvents separate and the reactants are concentrated in the same phase or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts.

Coherent perfect absorption in a quantum nonlinear regime of cavity quantum electrodynamics

NASA Astrophysics Data System (ADS)

Wei, Yang-hua; Gu, Wen-ju; Yang, Guoqing; Zhu, Yifu; Li, Gao-xiang

2018-05-01

Coherent perfect absorption (CPA) is investigated in the quantum nonlinear regime of cavity quantum electrodynamics (CQED), in which a single two-level atom couples to a single-mode cavity weakly driven by two identical laser fields. In the strong-coupling regime and due to the photon blockade effect, the weakly driven CQED system can be described as a quantum system with three polariton states. CPA is achieved at a critical input field strength when the frequency of the input fields matches the polariton transition frequency. In the quantum nonlinear regime, the incoherent dissipation processes such as atomic and photon decays place a lower bound for the purity of the intracavity quantum field. Our results show that under the CPA condition, the intracavity field always exhibits the quadrature squeezing property manifested by the quantum nonlinearity, and the outgoing photon flux displays the super-Poissonian distribution.

HEOS-A2: Press kit

NASA Technical Reports Server (NTRS)

Allaway, H. G.; Kukowski, J.

1972-01-01

The characteristics of the HEOS-A2 satellite and its assigned mission are discussed. The spacecraft carries seven experiments to investigate the strength and direction of the magnetic fields encountered, the energy distribution of protons and electrons, the nature of the solar winds, detection of micrometeorites, and low frequency solar observations. The highly elliptical polar orbit required for this mission will have an apogee of 38 earth radii. The lifetime of the satellite is expected to be one year minimum.

47 CFR 1.544 - Application for broadcast station to conduct field strength measurements and for experimental...

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 1 2010-10-01 2010-10-01 false Application for broadcast station to conduct field strength measurements and for experimental operation. 1.544 Section 1.544 Telecommunication... General Filing Requirements § 1.544 Application for broadcast station to conduct field strength...

OH masers towards IRAS 19092+0841

NASA Astrophysics Data System (ADS)

Edris, K. A.; Fuller, G. A.; Etoka, S.; Cohen, R. J.

2017-12-01

Context. Maser emission is a strong tool for studying high-mass star-forming regions and their evolutionary stages. OH masers in particular can trace the circumstellar material around protostars and determine their magnetic field strengths at milliarcsecond resolution. Aims: We seek to image OH maser emission towards high-mass protostellar objects to determine their evolutionary stages and to locate the detected maser emission in the process of high-mass star formation. Methods: In 2007, we surveyed OH maser emission towards 217 high-mass protostellar objects to study its presence. In this paper, we present follow-up MERLIN observations of a ground-state OH maser emission towards one of these objects, IRAS 19092+0841. Results: We detect emissions from the two OH main spectral lines, 1665 and 1667 MHz, close to the central object. We determine the positions and velocities of the OH maser features. The masers are distributed over a region of 5'' corresponding to 22 400 AU (or 0.1 pc) at a distance of 4.48 kpc. The polarization properties of the OH maser features are determined as well. We identify three Zeeman pairs from which we inferred a magnetic field strength of 4.4 mG pointing towards the observer. Conclusions: The relatively small velocity spread and relatively wide spacial distribution of the OH maser features support the suggestion that this object could be in an early evolutionary state before the presence of disk, jets or outflows.

Effects of grain size distribution on the packing fraction and shear strength of frictionless disk packings.

PubMed

Estrada, Nicolas

2016-12-01

Using discrete element methods, the effects of the grain size distribution on the density and the shear strength of frictionless disk packings are analyzed. Specifically, two recent findings on the relationship between the system's grain size distribution and its rheology are revisited, and their validity is tested across a broader range of distributions than what has been used in previous studies. First, the effects of the distribution on the solid fraction are explored. It is found that the distribution that produces the densest packing is not the uniform distribution by volume fractions as suggested in a recent publication. In fact, the maximal packing fraction is obtained when the grading curve follows a power law with an exponent close to 0.5 as suggested by Fuller and Thompson in 1907 and 1919 [Trans Am. Soc. Civ. Eng. 59, 1 (1907) and A Treatise on Concrete, Plain and Reinforced (1919), respectively] while studying mixtures of cement and stone aggregates. Second, the effects of the distribution on the shear strength are analyzed. It is confirmed that these systems exhibit a small shear strength, even if composed of frictionless particles as has been shown recently in several works. It is also found that this shear strength is independent of the grain size distribution. This counterintuitive result has previously been shown for the uniform distribution by volume fractions. In this paper, it is shown that this observation keeps true for different shapes of the grain size distribution.

Radial dependence of HF wave field strength in the BPD column. [Beam Plasma Discharge

NASA Technical Reports Server (NTRS)

Jost, R. J.; Anderson, H. R.; Bernstein, W.; Kellogg, P. J.

1982-01-01

The results of a recent set of RF frequency measurements of the beam plasma discharge (BPD) performed in order to determine a quantitative value for the field strength in the plasma frequency region of the spectrum are presented. The parallel and perpendicular components of the plasma wave electric fields inside the BPD column have comparable field strengths, on the order of 10 volts/m. The radial dependence of the field strength is very strong, decreasing by as much as 40 dB within one meter from the beam center, with the illumination or discharge column approximately one meter in diameter. The field strength inside the column increases as a function of distance along the beam at least for several meters from the gun aperture. The frequency and amplitude of the plasma wave increases with beam current. A particularly rapid increase in these parameters occurs as the beam current approaches the critical current.

Investigation of Influence of Surface Nanoparticle on Emission Properties of Scandia-Doped Dispenser Cathodes

NASA Astrophysics Data System (ADS)

Zhang, Xizhu; Wang, Jinshu; Wang, Yiman; Liu, Wei; Zhou, Meiling; Gao, Zhiyuan

2013-06-01

The microstructure of a fully activated scandia doped dispenser (SDD) cathode has been studied by scanning electron microscope (SEM). The observation results display that nanoparticles appear at the growth steps and the surface of tungsten grains of the fully activated SDD cathode. To study the influence of the nanoparticles on the emission, the local electric field strengths around the nanoparticles have been calculated by Maxwell 2D code and Comsol. The calculation results show that the local electric field strengths are enhanced by 1.1 to 3.8 times to average value based on different model conditions. The highest field strength is about 1.54 × 105 V/cm at an average field strength of 40 KV/cm, which is related to a space-charge limited (SCL) current density of 100 A/cm2 in the experimental configuration. This implies the field strength is not high enough to cause field emission.

Research on breakdown characteristics of oil-paper insulation in compound field at different temperatures

NASA Astrophysics Data System (ADS)

Li, L.; Chen, M. Y.; Zhu, X. C.; Gao, Z. W.; Zhang, H. D.; Li, G. X.; Zhang, J.; Yu, C. L.; Feng, Y. M.

2018-01-01

The breakdown characteristics of oil-paper insulation in AC, DC and compound field at different temperatures were studied. The breakdown mechanism of oil-paper insulation at different temperatures and in AC and DC electric fields was analyzed. The breakdown characteristic mechanisms of the oil-paper insulation in the compound field at different temperatures were obtained: the dielectric strength of oil-paper compound insulation is changed gradually from dependence on oil dielectric strength to dependence on paperboard dielectric strength at low temperature. The dielectric strength of oil-paper compound insulation is always related to the oil dielectric strength closely at high temperature with decrease of AC content.

A highly optimized code for calculating atomic data at neutron star magnetic field strengths using a doubly self-consistent Hartree-Fock-Roothaan method

NASA Astrophysics Data System (ADS)

Schimeczek, C.; Engel, D.; Wunner, G.

2012-07-01

Our previously published code for calculating energies and bound-bound transitions of medium-Z elements at neutron star magnetic field strengths [D. Engel, M. Klews, G. Wunner, Comput. Phys. Comm. 180 (2009) 302-311] was based on the adiabatic approximation. It assumes a complete decoupling of the (fast) gyration of the electrons under the action of the magnetic field and the (slow) bound motion along the field under the action of the Coulomb forces. For the single-particle orbitals this implied that each is a product of a Landau state and an (unknown) longitudinal wave function whose B-spline coefficients were determined self-consistently by solving the Hartree-Fock equations for the many-electron problem on a finite-element grid. In the present code we go beyond the adiabatic approximation, by allowing the transverse part of each orbital to be a superposition of Landau states, while assuming that the longitudinal part can be approximated by the same wave function in each Landau level. Inserting this ansatz into the energy variational principle leads to a system of coupled equations in which the B-spline coefficients depend on the weights of the individual Landau states, and vice versa, and which therefore has to be solved in a doubly self-consistent manner. The extended ansatz takes into account the back-reaction of the Coulomb motion of the electrons along the field direction on their motion in the plane perpendicular to the field, an effect which cannot be captured by the adiabatic approximation. The new code allows for the inclusion of up to 8 Landau levels. This reduces the relative error of energy values as compared to the adiabatic approximation results by typically a factor of three (1/3 of the original error), and yields accurate results also in regions of lower neutron star magnetic field strengths where the adiabatic approximation fails. Further improvements in the code are a more sophisticated choice of the initial wave functions, which takes into account the shielding of the core potential for outer electrons by inner electrons, and an optimal finite-element decomposition of each individual longitudinal wave function. These measures largely enhance the convergence properties compared to the previous code, and lead to speed-ups by factors up to two orders of magnitude compared with the implementation of the Hartree-Fock-Roothaan method used by Engel and Wunner in [D. Engel, G. Wunner, Phys. Rev. A 78 (2008) 032515]. New version program summaryProgram title: HFFER II Catalogue identifier: AECC_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECC_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: v 55 130 No. of bytes in distributed program, including test data, etc.: 293 700 Distribution format: tar.gz Programming language: Fortran 95 Computer: Cluster of 1-13 HP Compaq dc5750 Operating system: Linux Has the code been vectorized or parallelized?: Yes, parallelized using MPI directives. RAM: 1 GByte per node Classification: 2.1 External routines: MPI/GFortran, LAPACK, BLAS, FMlib (included in the package) Catalogue identifier of previous version: AECC_v1_0 Journal reference of previous version: Comput. Phys. Comm. 180 (2009) 302 Does the new version supersede the previous version?: Yes Nature of problem: Quantitative modellings of features observed in the X-ray spectra of isolated magnetic neutron stars are hampered by the lack of sufficiently large and accurate databases for atoms and ions up to the last fusion product, iron, at strong magnetic field strengths. Our code is intended to provide a powerful tool for calculating energies and oscillator strengths of medium-Z atoms and ions at neutron star magnetic field strengths with sufficient accuracy in a routine way to create such databases. Solution method: The Slater determinants of the atomic wave functions are constructed from single-particle orbitals ψi which are products of a wave function in the z direction (the direction of the magnetic field) and an expansion of the wave function perpendicular to the direction of the magnetic field in terms of Landau states, ψi(ρ,φ,z)=Pi(z)∑n=0NLtinϕni(ρ,φ). The tin are expansion coefficients, and the expansion is cut off at some maximum Landau level quantum number n=NL. In the previous version of the code only the lowest Landau level was included (NL=0), in the new version NL can take values of up to 7. As in the previous version of the code, the longitudinal wave functions are expanded in terms of sixth-order B-splines on finite elements on the z axis, with a combination of equidistant and quadratically widening element borders. Both the B-spline expansion coefficients and the Landau weights tin of all orbitals have to be determined in a doubly self-consistent way: For a given set of Landau weights tin, the system of linear equations for the B-spline expansion coefficients, which is equivalent to the Hartree-Fock equations for the longitudinal wave functions, is solved numerically. In the second step, for frozen B-spline coefficients new Landau weights are determined by minimizing the total energy with respect to the Landau expansion coefficients. Both steps require solving non-linear eigenvalue problems of Roothaan type. The procedure is repeated until convergence of both the B-spline coefficients and the Landau weights is achieved. Reasons for new version: The former version of the code was restricted to the adiabatic approximation, which assumes the quantum dynamics of the electrons in the plane perpendicular to the magnetic field to be fixed in the lowest Landau level, n=0. This approximation is valid only if the magnetic field strengths are large compared to the reference magnetic field BZ, for a nuclear charge Z,BZ=Z24.70108×105 T. Summary of revisions: In the new version, the transverse parts of the orbitals are expanded in terms of Landau states up to n=7, and the expansion coefficients are determined, together with the longitudinal wave functions, in a doubly self-consistent way. Thus the back-reaction of the quantum dynamics along the magnetic field direction on the quantum dynamics in the plane perpendicular to it is taken into account. The new ansatz not only increases the accuracy of the results for energy values and transition strengths obtained so far, but also allows their calculation for magnetic field strengths down to B≳BZ, where the adiabatic approximation fails. Restrictions: Intense magnetic field strengths are required, since the expansion of the transverse single-particle wave functions using 8 Landau levels will no longer produce accurate results if the scaled magnetic field strength parameter βZ=B/BZ becomes much smaller than unity. Unusual features: A huge program speed-up is achieved by making use of pre-calculated binary files. These can be calculated with additional programs provided with this package. Running time: 1-30 min.

Hydrologic Controls on Shallow Landslide Location, Size, and Shape

NASA Astrophysics Data System (ADS)

Bellugi, D.; Milledge, D.; Perron, T.; McKean, J. A.; Dietrich, W.; Rulli, M.

2012-12-01

Shallow landslides, typically involving just the soil mantle, are principally controlled by topography, soil and root strengths, and soil thickness, and are typically triggered by storm-induced increases in pore water pressure. The response of a landscape to landslide-triggering storms will thus depend on factors such as rainfall totals, storm intensity and duration, and antecedent moisture conditions. The two dominant mechanisms that generate high pore water pressures at a point are topographically-steered lateral subsurface flow (over timescales of days to weeks), and rapid vertical infiltration (over timescales of minutes to hours). We aim to understand the impact of different storm characteristics and hydrologic regimes on shallow landslide location, size, and shape. We have developed a regional-scale model, which applies a low-parameter grid-based multi-dimensional slope stability model within a novel search algorithm, to generate discrete landslide predictions. This model shows that the spatial organization of parameters such as root strength and pore water pressure has a strong control on shallow landslide location, size, and shape. We apply this model to a field site near Coos Bay, OR, where a ten-year landslide inventory has been mapped onto high-resolution topographic data. Our model predicts landslide size generally increases with increasing rainfall intensity, except when root strength is extremely high and pore pressures are topographically steered. The distribution of topographic index values (the ratios of contributing area to slope) of predicted landslides is a clear signature of the pore water pressure generation mechanism: as laterally dominated flow increases, landslides develop in locations with lower slopes and higher contributing areas; in contrast, in the case of vertically-dominated pore pressure rise, landslides are consistently found in locations with higher slopes and lower contributing areas. While in both cases landslides are found in the hollows, where the soils are sufficiently deep to overcome the effects of root strength, in the laterally-dominated case they are predicted to occur further down the hollows (which matches field observations). The size distribution of landslides is better predicted in our model when vertical infiltration dominates, but the observed distribution of topographic index values follows that predicted when lateral flow dominates. This suggests that both mechanisms must be taken into account in order to capture both location and size of shallow landslides (consistent with field observations). These results suggest that this modeling approach could allow us to use observed landslide locations and geometries to infer the dominant hydrologic triggering mechanisms. Furthermore, as the spatial and temporal resolution of precipitation forecasting improves, this model will enable us to more accurately predict both location and size of shallow landslides.

Bandstructure modulation for Si-h and Si-g nanotubes in a transverse electric field: Tight binding approach

NASA Astrophysics Data System (ADS)

Chegel, Raad; Behzad, Somayeh

2013-11-01

We have investigated the electronic properties of SiNTs, under the external electric field, using Tight Binding (TB) approximation. It was found that the energy levels, energy gaps, and density of states (DOS) strongly depend on the electric field strength. The large electric strength leads to coupling the neighbor subbands and induce destruction of subband degeneracy, increase of low-energy states, and strong modulation of energy gap which these effects reflect in the DOS spectrum. It has been shown that, the band gap reduction of Si g-NTs is linearly proportional to the electric field strength. The band gap variation for Si h-NTs increases first and later decreases (Metallic) or first remains constant and then decreases (semiconductor). Also we show that the larger diameter tubes are more sensitive to the field strength than smaller ones. The semiconducting metallic transition or vice versa can be achieved through an increasing of applied fields. Number and position of peaks in DOS spectrum are dependent on electric field strength.

Some bivariate distributions for modeling the strength properties of lumber

Treesearch

Richard A. Johnson; James W. Evans; David W. Green

Accurate modeling of the joint stochastic nature of the strength properties of dimension lumber is essential to the determination of reliability-based design safety factors. This report reviews the major techniques for obtaining bivariate distributions and then discusses bivariate distributions whose marginal distributions suggest they might be useful for modeling the...

47 CFR 90.359 - Field strength limits for EA-licensed LMS systems.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Field strength limits for EA-licensed LMS systems. 90.359 Section 90.359 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Intelligent Transportation Systems Radio Service § 90.359 Field strength limits for...

47 CFR 5.87 - Frequencies for field strength surveys or equipment demonstrations.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 47 Telecommunication 1 2012-10-01 2012-10-01 false Frequencies for field strength surveys or... EXPERIMENTAL RADIO SERVICE (OTHER THAN BROADCAST) Applications and Licenses § 5.87 Frequencies for field strength surveys or equipment demonstrations. (a) Authorizations issued under §§ 5.3 (e) and (f) of this...

47 CFR 5.87 - Frequencies for field strength surveys or equipment demonstrations.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 1 2010-10-01 2010-10-01 false Frequencies for field strength surveys or... EXPERIMENTAL RADIO SERVICE (OTHER THAN BROADCAST) Applications and Licenses § 5.87 Frequencies for field strength surveys or equipment demonstrations. (a) Authorizations issued under §§ 5.3 (e) and (f) of this...

47 CFR 5.87 - Frequencies for field strength surveys or equipment demonstrations.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 1 2011-10-01 2011-10-01 false Frequencies for field strength surveys or... EXPERIMENTAL RADIO SERVICE (OTHER THAN BROADCAST) Applications and Licenses § 5.87 Frequencies for field strength surveys or equipment demonstrations. (a) Authorizations issued under §§ 5.3 (e) and (f) of this...

Activation Time of Cardiac Tissue In Response to a Linear Array of Spatial Alternating Bipolar Electrodes

NASA Astrophysics Data System (ADS)

Mashburn, David; Wikswo, John

2007-11-01

Prevailing theories about the response of the heart to high field shocks predict that local regions of high resistivity distributed throughout the heart create multiple small virtual electrodes that hyperpolarize or depolarize tissue and lead to widespread activation. This resetting of bulk tissue is responsible for the successful functioning of cardiac defibrillators. By activating cardiac tissue with regular linear arrays of spatially alternating bipolar currents, we can simulate these potentials locally. We have studied the activation time due to distributed currents in both a 1D Beeler-Reuter model and on the surface of the whole heart, varying the strength of each source and the separation between them. By comparison with activation time data from actual field shock of a whole heart in a bath, we hope to better understand these transient virtual electrodes. Our work was done on rabbit RV using florescent optical imaging and our Phased Array Stimulator for driving the 16 current sources. Our model shows that for a total absolute current delivered to a region of tissue, the entire region activates faster if above-threshold sources are more distributed.

The effect of wall thickness distribution on mechanical reliability and strength in unidirectional porous ceramics.

PubMed

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J

2016-01-01

Macroporous ceramics exhibit an intrinsic strength variability caused by the random distribution of defects in their structure. However, the precise role of microstructural features, other than pore volume, on reliability is still unknown. Here, we analyze the applicability of the Weibull analysis to unidirectional macroporous yttria-stabilized-zirconia (YSZ) prepared by ice-templating. First, we performed crush tests on samples with controlled microstructural features with the loading direction parallel to the porosity. The compressive strength data were fitted using two different fitting techniques, ordinary least squares and Bayesian Markov Chain Monte Carlo, to evaluate whether Weibull statistics are an adequate descriptor of the strength distribution. The statistical descriptors indicated that the strength data are well described by the Weibull statistical approach, for both fitting methods used. Furthermore, we assess the effect of different microstructural features (volume, size, densification of the walls, and morphology) on Weibull modulus and strength. We found that the key microstructural parameter controlling reliability is wall thickness. In contrast, pore volume is the main parameter controlling the strength. The highest Weibull modulus ([Formula: see text]) and mean strength (198.2 MPa) were obtained for the samples with the smallest and narrowest wall thickness distribution (3.1 [Formula: see text]m) and lower pore volume (54.5%).

The effect of wall thickness distribution on mechanical reliability and strength in unidirectional porous ceramics

NASA Astrophysics Data System (ADS)

Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J.

2016-01-01

Macroporous ceramics exhibit an intrinsic strength variability caused by the random distribution of defects in their structure. However, the precise role of microstructural features, other than pore volume, on reliability is still unknown. Here, we analyze the applicability of the Weibull analysis to unidirectional macroporous yttria-stabilized-zirconia (YSZ) prepared by ice-templating. First, we performed crush tests on samples with controlled microstructural features with the loading direction parallel to the porosity. The compressive strength data were fitted using two different fitting techniques, ordinary least squares and Bayesian Markov Chain Monte Carlo, to evaluate whether Weibull statistics are an adequate descriptor of the strength distribution. The statistical descriptors indicated that the strength data are well described by the Weibull statistical approach, for both fitting methods used. Furthermore, we assess the effect of different microstructural features (volume, size, densification of the walls, and morphology) on Weibull modulus and strength. We found that the key microstructural parameter controlling reliability is wall thickness. In contrast, pore volume is the main parameter controlling the strength. The highest Weibull modulus (?) and mean strength (198.2 MPa) were obtained for the samples with the smallest and narrowest wall thickness distribution (3.1 ?m) and lower pore volume (54.5%).

Improving Keyhole Stability by External Magnetic Field in Full Penetration Laser Welding

NASA Astrophysics Data System (ADS)

Li, Min; Xu, Jiajun; Huang, Yu; Rong, Youmin

2018-05-01

An external magnetic field was used to improve the keyhole stability in full penetration laser welding 316L steel. The increase of magnetic field strength gave rise to a shorter flying time of the spatter, a weaker size and brightness of the spatter, and a larger spreading area of vapor plume. This suggested that the dynamic behavior of the keyhole was stabilized by the external magnetic field. In addition, a stronger magnetic field could result in a more homogeneous distribution of laser energy, which increased the width of the weld zone, and the height of the bottom weld zone from 381 μm (0 mT) to 605 μm (50 mT). Dendrite and cellular crystal near the weld center disappeared, and grain size was refined. The external magnetic field was beneficial to the keyhole stability and improved the joint quality, because the weld pool was stirred by a Lorentz force resulting from the coupling effect of the magnetic field and inner thermocurrent.

A probabilistic mechanical model for prediction of aggregates’ size distribution effect on concrete compressive strength

NASA Astrophysics Data System (ADS)

Miled, Karim; Limam, Oualid; Sab, Karam

2012-06-01

To predict aggregates' size distribution effect on the concrete compressive strength, a probabilistic mechanical model is proposed. Within this model, a Voronoi tessellation of a set of non-overlapping and rigid spherical aggregates is used to describe the concrete microstructure. Moreover, aggregates' diameters are defined as statistical variables and their size distribution function is identified to the experimental sieve curve. Then, an inter-aggregate failure criterion is proposed to describe the compressive-shear crushing of the hardened cement paste when concrete is subjected to uniaxial compression. Using a homogenization approach based on statistical homogenization and on geometrical simplifications, an analytical formula predicting the concrete compressive strength is obtained. This formula highlights the effects of cement paste strength and aggregates' size distribution and volume fraction on the concrete compressive strength. According to the proposed model, increasing the concrete strength for the same cement paste and the same aggregates' volume fraction is obtained by decreasing both aggregates' maximum size and the percentage of coarse aggregates. Finally, the validity of the model has been discussed through a comparison with experimental results (15 concrete compressive strengths ranging between 46 and 106 MPa) taken from literature and showing a good agreement with the model predictions.

Global Three-Dimensional Simulation of Earth's Dayside Reconnection Using a Two-Way Coupled Magnetohydrodynamics With Embedded Particle-in-Cell Model: Initial Results

NASA Astrophysics Data System (ADS)

Chen, Yuxi; Tóth, Gábor; Cassak, Paul; Jia, Xianzhe; Gombosi, Tamas I.; Slavin, James A.; Markidis, Stefano; Peng, Ivy Bo; Jordanova, Vania K.; Henderson, Michael G.

2017-10-01

We perform a three-dimensional (3-D) global simulation of Earth's magnetosphere with kinetic reconnection physics to study the flux transfer events (FTEs) and dayside magnetic reconnection with the recently developed magnetohydrodynamics with embedded particle-in-cell model. During the 1 h long simulation, the FTEs are generated quasi-periodically near the subsolar point and move toward the poles. We find that the magnetic field signature of FTEs at their early formation stage is similar to a "crater FTE," which is characterized by a magnetic field strength dip at the FTE center. After the FTE core field grows to a significant value, it becomes an FTE with typical flux rope structure. When an FTE moves across the cusp, reconnection between the FTE field lines and the cusp field lines can dissipate the FTE. The kinetic features are also captured by our model. A crescent electron phase space distribution is found near the reconnection site. A similar distribution is found for ions at the location where the Larmor electric field appears. The lower hybrid drift instability (LHDI) along the current sheet direction also arises at the interface of magnetosheath and magnetosphere plasma. The LHDI electric field is about 8 mV/m, and its dominant wavelength relative to the electron gyroradius agrees reasonably with Magnetospheric Multiscale (MMS) observations.

Effect of a magnetic field on the track structure of low-energy electrons: a Monte Carlo study

NASA Astrophysics Data System (ADS)

Bug, M. U.; Gargioni, E.; Guatelli, S.; Incerti, S.; Rabus, H.; Schulte, R.; Rosenfeld, A. B.

2010-10-01

The increasing use of MRI-guided radiation therapy evokes the necessity to investigate the potential impact of a magnetic field on the biological effectiveness of therapeutic radiation beams. While it is known that a magnetic field, applied during irradiation, can improve the macroscopic absorbed dose distribution of electrons in the tumor region, effects on the microscopic distribution of energy depositions and ionizations have not yet been investigated. An effect on the number of ionizations in a DNA segment, which is related to initial DNA damage in form of complex strand breaks, could be beneficial in radiation therapy. In this work we studied the effects of a magnetic field on the pattern of ionizations at nanometric level by means of Monte Carlo simulations using the Geant4-DNA toolkit. The track structure of low-energy electrons in the presence of a uniform static magnetic field of strength up to 14 T was calculated for a simplified DNA segment model in form of a water cylinder. In the case that no magnetic field is applied, nanodosimetric results obtained with Geant4-DNA were compared with those from the PTB track structure code. The obtained results suggest that any potential enhancement of complexity of DNA strand breaks induced by irradiation in a magnetic field is not related to modifications of the low-energy secondary electrons track structure.

Single functional group interactions with individual carbon nanotubes

NASA Astrophysics Data System (ADS)

Friddle, Raymond W.; Lemieux, Melburne C.; Cicero, Giancarlo; Artyukhin, Alexander B.; Tsukruk, Vladimir V.; Grossman, Jeffrey C.; Galli, Giulia; Noy, Aleksandr

2007-11-01

Carbon nanotubes display a consummate blend of materials properties that affect applications ranging from nanoelectronic circuits and biosensors to field emitters and membranes. These applications use the non-covalent interactions between the nanotubes and chemical functionalities, often involving a few molecules at a time. Despite their wide use, we still lack a fundamental understanding and molecular-level control of these interactions. We have used chemical force microscopy to measure the strength of the interactions of single chemical functional groups with the sidewalls of vapour-grown individual single-walled carbon nanotubes. Surprisingly, the interaction strength does not follow conventional trends of increasing polarity or hydrophobicity, and instead reflects the complex electronic interactions between the nanotube and the functional group. Ab initio calculations confirm the observed trends and predict binding force distributions for a single molecular contact that match the experimental results. Our analysis also reveals the important role of molecular linkage dynamics in determining interaction strength at the single functional group level.

[Methodological aspects of functional neuroimaging at high field strength: a critical review].

PubMed

Scheef, L; Landsberg, M W; Boecker, H

2007-09-01

The last few years have proven that high field magnetic resonance imaging (MRI) is superior in nearly every way to conventional equipment up to 1.5 tesla (T). Following the global success of 3T-scanners in research institutes and medical practices, a new generation of MRI devices with field strengths of 7T and higher is now on the horizon. The introduction of ultra high fields has brought MRI technology closer to the physical limitations and increasingly greater costs are required to achieve this goal. This article provides a critical overview of the advantages and problems of functional neuroimaging using ultra high field strengths. This review is principally limited to T2*-based functional imaging techniques not dependent on contrast agents. The main issues include the significance of high field technology with respect to SNR, CNR, resolution, and sequences, as well as artifacts, noise exposure, and SAR. Of great relevance is the discussion of parallel imaging, which will presumably determine the further development of high and ultra high field strengths. Finally, the importance of high field strengths for functional neuroimaging is explained by selected publications.

Above-threshold ionization of noble gases in elliptically polarized fields: Effects of atomic polarization on photoelectron angular distributions

NASA Astrophysics Data System (ADS)

Wang, YanLan; Yu, ShaoGang; Lai, XuanYang; Liu, XiaoJun; Chen, Jing

2017-06-01

We theoretically investigate the atomic polarization effect on photoelectron angular distributions (PADs) in above-threshold ionization of noble gases with elliptically polarized laser fields at wavelength of 800 nm, ellipticity of 0.25, and intensity of 1.5 ×1014W/cm2 . Simulations based on a semiclassical model that includes both the ionic Coulomb potential and the atomic polarization effect show surprisingly little difference between PADs for Ar, Kr, and Xe, which is in good agreement with recent experimental observations. Our calculations reveal that the atomic polarization effect increases the distance of the tunnel exit point of the photoelectron to the parent ion and weakens the strength of the interaction between the parent ion and the photoelectron on its subsequent classical propagation. As a result, the forward-scattering electrons which contribute to the main lobes in PADs are substantially suppressed. Our results indicate that the insensitivity of PADs for Ar, Kr, and Xe may be closely related to the influence of the atomic polarization effect on the photoelectron dynamics in the strong laser field.

A computer program for geochemical analysis of acid-rain and other low-ionic-strength, acidic waters

USGS Publications Warehouse

Johnsson, P.A.; Lord, D.G.

1987-01-01

ARCHEM, a computer program written in FORTRAN 77, is designed primarily for use in the routine geochemical interpretation of low-ionic-strength, acidic waters. On the basis of chemical analyses of the water, and either laboratory or field determinations of pH, temperature, and dissolved oxygen, the program calculates the equilibrium distribution of major inorganic aqueous species and of inorganic aluminum complexes. The concentration of the organic anion is estimated from the dissolved organic concentration. Ionic ferrous iron is calculated from the dissolved oxygen concentration. Ionic balances and comparisons of computed with measured specific conductances are performed as checks on the analytical accuracy of chemical analyses. ARCHEM may be tailored easily to fit different sampling protocols, and may be run on multiple sample analyses. (Author 's abstract)

Io's Sodium Corona and Spatially Extended Cloud: A Consistent Flux Speed Distribution

NASA Technical Reports Server (NTRS)

Smyth, William H.; Combi, Michael R.

1997-01-01

For Io neutral cloud calculations, an SO2 source strength of approximately 4x10(exp 27) molecules/sec was determined by successfully matching the SO2(+) density profile near the satellite deduced from magnetometer data acquired by the Galileo spacecraft during its close flyby on December 7, 1995. The incomplete collision source velocity distribution for SO2 is the same as recently determined for the trace species atomic sodium by Smyth and Combi (1997). Estimates for the total energy loss rate (i.e. power) of O and S atoms escaping Io were also determined and imply a significant pickup current and a significant reduction in the local planetary magnetic field near Io.

Dust ion-acoustic shock waves in magnetized pair-ion plasma with kappa distributed electrons

NASA Astrophysics Data System (ADS)

Kaur, B.; Singh, M.; Saini, N. S.

2018-01-01

We have performed a theoretical and numerical analysis of the three dimensional dynamics of nonlinear dust ion-acoustic shock waves (DIASWs) in a magnetized plasma, consisting of positive and negative ion fluids, kappa distributed electrons, immobile dust particulates along with positive and negative ion kinematic viscosity. By employing the reductive perturbation technique, we have derived the nonlinear Zakharov-Kuznetsov-Burgers (ZKB) equation, in which the nonlinear forces are balanced by dissipative forces (associated with kinematic viscosity). It is observed that the characteristics of DIASWs are significantly affected by superthermality of electrons, magnetic field strength, direction cosines, dust concentration, positive to negative ions mass ratio and viscosity of positive and negative ions.

Fast Spectroscopic Imaging and Field Compensation Using Frequency Modulation at Ultra-High-Field

NASA Astrophysics Data System (ADS)

Jang, Albert Woo Ju

The high energy phosphates (HEP) in the myocardium, which are critical to understanding the cardiac function in both normal and pathophysiologic states, can be assessed non-invasively in vivo using phosphorus-31 (31P) spectroscopy. Compared to proton, for the same volume and magnetic field strength, the available signal-to-noise (SNR) ratio of the HEP metabolites is orders of magnitude lower mainly due to its intrinsically low concentration. Hence, cardiac spectroscopy greatly benefits when performed at ultra-high-fields (UHF, ≥ 7 T), both in terms of increased SNR and increased spectroscopic resolution. However, at ultra-high-field strengths, complications arise from the RF transmit wavelength becoming comparable or smaller than the field-of-view (FOV), thus exhibiting wave-like behavior. Furthermore, even with the spectroscopic resolution afforded at UHF, measuring myocardial inorganic phosphate (Pi) is still a challenge and has been a major barrier in extracting the ATP turnover rate. Recently, an indirect way of extracting the ATP hydrolysis rate forgoing direct measurement of Pi was established. In this work, we combine this method with the T1 nom method to monitor the transmural distribution of forward creatine kinase reaction (kf,CK) and ATP hydrolysis rate (kr,ATPase) of the myocardium, effectively reducing data acquisition time by up to an order of magnitude. In addition, a new class of 2D FM pulses and multidimensional adiabatic pulses are presented, which can compensate for B1 inhomogeneity through its spatiotemporal properties. These pulses should be valuable for spectroscopic applications at ultra-high-fields.

Structural optimization of 3D-printed synthetic spider webs for high strength

NASA Astrophysics Data System (ADS)

Qin, Zhao; Compton, Brett G.; Lewis, Jennifer A.; Buehler, Markus J.

2015-05-01

Spiders spin intricate webs that serve as sophisticated prey-trapping architectures that simultaneously exhibit high strength, elasticity and graceful failure. To determine how web mechanics are controlled by their topological design and material distribution, here we create spider-web mimics composed of elastomeric filaments. Specifically, computational modelling and microscale 3D printing are combined to investigate the mechanical response of elastomeric webs under multiple loading conditions. We find the existence of an asymptotic prey size that leads to a saturated web strength. We identify pathways to design elastomeric material structures with maximum strength, low density and adaptability. We show that the loading type dictates the optimal material distribution, that is, a homogeneous distribution is better for localized loading, while stronger radial threads with weaker spiral threads is better for distributed loading. Our observations reveal that the material distribution within spider webs is dictated by the loading condition, shedding light on their observed architectural variations.

Structural optimization of 3D-printed synthetic spider webs for high strength.

PubMed

Qin, Zhao; Compton, Brett G; Lewis, Jennifer A; Buehler, Markus J

2015-05-15

Spiders spin intricate webs that serve as sophisticated prey-trapping architectures that simultaneously exhibit high strength, elasticity and graceful failure. To determine how web mechanics are controlled by their topological design and material distribution, here we create spider-web mimics composed of elastomeric filaments. Specifically, computational modelling and microscale 3D printing are combined to investigate the mechanical response of elastomeric webs under multiple loading conditions. We find the existence of an asymptotic prey size that leads to a saturated web strength. We identify pathways to design elastomeric material structures with maximum strength, low density and adaptability. We show that the loading type dictates the optimal material distribution, that is, a homogeneous distribution is better for localized loading, while stronger radial threads with weaker spiral threads is better for distributed loading. Our observations reveal that the material distribution within spider webs is dictated by the loading condition, shedding light on their observed architectural variations.

Measurements by the plasma diagnostics package on STS-3

NASA Technical Reports Server (NTRS)

Shawhan, S. D.; Murphy, G. B.

1982-01-01

A comprehensive set of measurements about the orbiter environment are provided by the plasma diagnostics package (PDP). Ion and electron particle densities, energies, and spatial distribution functions; ion mass for identification of particular molecular ion species; and magnetic fields, electric fields and electromagnetic waves over a broad frequency range are studied. Shuttle environmental measurements will be made both on the pallet and, by use of the remote manipulator system (RMS), the PDP will be maneuvered in and external to the bay area to continue environmental measurements and to carry on a joint plasma experiment with the Utah State University fast-pulsed electron generator. Results of orbiter environment EMI measurements and S-band field strengths as well as preliminary results from wake search operations indicating wake boundary identifiers are reported.

Search for nonthermal effects of 434 MHz microwave radiation on whole human blood

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dunscombe, P.B.; Gammampila, K.; Ramsey, N.W.

1983-11-01

Whole human blood was subjected to a microwave environment at 434 MHz for 6 h with external electric fields corresponding to free space power densities up to 598 mW cm/sup -2/ and the levels of hemoglobin, sodium, and potassium in the plasma were monitored. Under geometrical conditions in which the field strength within the samples was unknown, measurements indicated increased red cell membrane fragility following irradiation. It was possible to exclude localized heating as an explanation of this effect. However, with a known and reasonably uniform electric field distribution within spherical specimens, increased membrane fragility was not observed. We aremore » therefore unable to confirm previously reported results which indicate a nonthermal deleterious effect of microwave radiation on erythrocytes.« less

A parametric study of transonic blade-vortex interaction noise

NASA Technical Reports Server (NTRS)

Lyrintzis, A. S.

1991-01-01

Several parameters of transonic blade-vortex interactions (BVI) are being studied and some ideas for noise reduction are introduced and tested using numerical simulation. The model used is the two-dimensional high frequency transonic small disturbance equation with regions of distributed vorticity (VTRAN2 code). The far-field noise signals are obtained by using the Kirchhoff method with extends the numerical 2-D near-field aerodynamic results to the linear acoustic 3-D far-field. The BVI noise mechanisms are explained and the effects of vortex type and strength, and angle of attack are studied. Particularly, airfoil shape modifications which lead to noise reduction are investigated. The results presented are expected to be helpful for better understanding of the nature of the BVI noise and better blade design.

Characterizing the performance of eddy current probes using photoinductive field-mapping

NASA Astrophysics Data System (ADS)

Moulder, John C.; Nakagawa, Norio

1992-12-01

We present a new method for characterizing the performance of eddy current probes by mapping their electromagnetic fields. The technique is based on the photoinductive effect, the change in the impedance of an eddy current probe induced by laser heating of the material under the probe. The instrument we developed maps a probe's electric field distribution by scanning an infrared laser beam over a thin film of gold lying underneath the probe. Measurements of both photoinductive signals and flaw signals for a series of similar probes demonstrates that the impedance change caused by an electrical-discharge-machined notch or a fatigue crack is proportional to the strength of the photoinductive signal. Thus, photoinductive measurements can supplant the use of artifact standards to calibrate eddy current probes.

Lift distribution and velocity field measurements for a three-dimensional, steady blade/vortex interaction

NASA Technical Reports Server (NTRS)

Dunagan, Stephen E.; Norman, Thomas R.

1987-01-01

A wind tunnel experiment simulating a steady three-dimensional helicopter rotor blade/vortex interaction is reported. The experimental configuration consisted of a vertical semispan vortex-generating wing, mounted upstream of a horizontal semispan rotor blade airfoil. A three-dimensional laser velocimeter was used to measure the velocity field in the region of the blade. Sectional lift coefficients were calculated by integrating the velocity field to obtain the bound vorticity. Total lift values, obtained by using an internal strain-gauge balance, verified the laser velocimeter data. Parametric variations of vortex strength, rotor blade angle of attack, and vortex position relative to the rotor blade were explored. These data are reported (with attention to experimental limitations) to provide a dataset for the validation of analytical work.

Nanometric Scale Investigation of Phase Transformations in Advanced Steels for Automotive Application

NASA Astrophysics Data System (ADS)

Drillet, Josée; Valle, Nathalie; Iung, Thierry

2012-12-01

The current trend toward producing lighter vehicles in the automotive industry is driven by the need to conform to the new exhaust emission control regulations. This objective presents a challenge to steel manufacturers. The difficulty lies in designing new alloys with an optimum strength/formability/cost balance for the various components. Here, the key to success lies in controlling the steel microstructure and especially the phase transformations at the smallest possible scale. Among the different alloying elements, light elements such as carbon and boron are of prime importance due to their major effects on the kinetics of phase transformations. Characterization tools combining high spatial and analytical resolution such as secondary ion mass spectrometry (SIMS) and field emission gun-transmission electron microscopy (TEM) were used. In this article, the examples presented are as follows. (1) Boron segregation and precipitation effects to control hardenability in martensitic steels. (2) Local carbon distribution in advanced high-strength steels, with a specific emphasis on martensite tempering. Links have been established between the boron and carbon distribution and the formability.

Two-mode mazer injected with V-type three-level atoms

NASA Astrophysics Data System (ADS)

Liang, Wen-Qing; Zhang, Zhi-Ming; Xie, Sheng-Wu

2003-12-01

The properties of the two-mode mazer operating on V-type three-level atoms are studied. The effect of the one-atom pumping on the two modes of the cavity field in number-state is asymmetric, that is, the atom emits a photon into one mode with some probability and absorbs a photon from the other mode with some other probability. This effect makes the steady-state photon distribution and the steady-state photon statistics asymmetric for the two modes. The diagram of the probability currents for the photon distribution, given by the analysis of the master equation, reveals that there is no detailed balance solution for the master equation. The computations show that the photon statistics of one mode or both modes can be sub-Poissonian, that the two modes can have anticorrelation or correlation, that the photon statistics increases with the increase of thermal photons and that the resonant position and strength of the photon statistics are influenced by the ratio of the two coupling strengths of the two modes. These properties are also discussed physically.

General planar transverse domain walls realized by optimized transverse magnetic field pulses in magnetic biaxial nanowires

NASA Astrophysics Data System (ADS)

Li, Mei; Wang, Jianbo; Lu, Jie

2017-02-01

The statics and field-driven dynamics of transverse domain walls (TDWs) in magnetic nanowires (NWs) have attracted continuous interests because of their theoretical significance and application potential in future magnetic logic and memory devices. Recent results demonstrate that uniform transverse magnetic fields (TMFs) can greatly enhance the wall velocity, meantime leave a twisting in the TDW azimuthal distribution. For application in high-density NW devices, it is preferable to erase the twisting so as to minimize magnetization frustrations. Here we report the realization of a completely planar TDW with arbitrary tilting attitude in a magnetic biaxial NW under a TMF pulse with fixed strength and well-designed orientation profile. We smooth any twisting in the TDW azimuthal plane thus completely decouple the polar and azimuthal degrees of freedom. The analytical differential equation describing the polar angle distribution is derived and the resulting solution is not the Walker-ansatz form. With this TMF pulse comoving, the field-driven dynamics of the planar TDW is investigated with the help of the asymptotic expansion method. It turns out the comoving TMF pulse increases the wall velocity under the same axial driving field. These results will help to design a series of modern magnetic devices based on planar TDWs.

Gaps between avalanches in one-dimensional random-field Ising models

NASA Astrophysics Data System (ADS)

Nampoothiri, Jishnu N.; Ramola, Kabir; Sabhapandit, Sanjib; Chakraborty, Bulbul

2017-09-01

We analyze the statistics of gaps (Δ H ) between successive avalanches in one-dimensional random-field Ising models (RFIMs) in an external field H at zero temperature. In the first part of the paper we study the nearest-neighbor ferromagnetic RFIM. We map the sequence of avalanches in this system to a nonhomogeneous Poisson process with an H -dependent rate ρ (H ) . We use this to analytically compute the distribution of gaps P (Δ H ) between avalanches as the field is increased monotonically from -∞ to +∞ . We show that P (Δ H ) tends to a constant C (R ) as Δ H →0+ , which displays a nontrivial behavior with the strength of disorder R . We verify our predictions with numerical simulations. In the second part of the paper, motivated by avalanche gap distributions in driven disordered amorphous solids, we study a long-range antiferromagnetic RFIM. This model displays a gapped behavior P (Δ H )=0 up to a system size dependent offset value Δ Hoff , and P (Δ H ) ˜(ΔH -Δ Hoff) θ as Δ H →Hoff+ . We perform numerical simulations on this model and determine θ ≈0.95 (5 ) . We also discuss mechanisms which would lead to a nonzero exponent θ for general spin models with quenched random fields.

The influence of sulcus width on simulated electric fields induced by transcranial magnetic stimulation

NASA Astrophysics Data System (ADS)

Janssen, A. M.; Rampersad, S. M.; Lucka, F.; Lanfer, B.; Lew, S.; Aydin, Ü.; Wolters, C. H.; Stegeman, D. F.; Oostendorp, T. F.

2013-07-01

Volume conduction models can help in acquiring knowledge about the distribution of the electric field induced by transcranial magnetic stimulation. One aspect of a detailed model is an accurate description of the cortical surface geometry. Since its estimation is difficult, it is important to know how accurate the geometry has to be represented. Previous studies only looked at the differences caused by neglecting the complete boundary between cerebrospinal fluid (CSF) and grey matter (Thielscher et al 2011 NeuroImage 54 234-43, Bijsterbosch et al 2012 Med. Biol. Eng. Comput. 50 671-81), or by resizing the whole brain (Wagner et al 2008 Exp. Brain Res. 186 539-50). However, due to the high conductive properties of the CSF, it can be expected that alterations in sulcus width can already have a significant effect on the distribution of the electric field. To answer this question, the sulcus width of a highly realistic head model, based on T1-, T2- and diffusion-weighted magnetic resonance images, was altered systematically. This study shows that alterations in the sulcus width do not cause large differences in the majority of the electric field values. However, considerable overestimation of sulcus width produces an overestimation of the calculated field strength, also at locations distant from the target location.

VLBI2010: Networks and Observing Strategies

NASA Technical Reports Server (NTRS)

Petrachenko, Bill; Corey, Brian; Himwich, Ed; Ma, Chopo; Malkin, Zinovy; Niell, Arthur; Shaffer, David; Vandenberg, Nancy

2004-01-01

The Observing Strategies Sub-group of IVS's Working Group 3 has been tasked with producing a vision for the following aspects of geodetic VLBI: antenna-network structure and observing strategies; source strength/structure/distribution; frequency bands, RFI; and field system and scheduling. These are high level considerations that have far reaching impact since they significantly influence performance potential and also constrain requirements for a number of other \\VG3 sub-groups. The paper will present the status of the sub-group's work on these topics.

Development of a Robust and Cost-Effective Friction Stir Welding Process for Use in Advanced Military Vehicles

DTIC Science & Technology

2011-01-01

aluminum alloys, as well 81 as aluminum matrix composites can be readily FSWed; 82 (j) due to lower attendant temperatures, the residual stres - 83 ses... role of the precipitation hardening mechanism in heat- 372treatable alloys is concerned, the following main observations 373can be made. Typically in...stirring/mixing 470(which plays a critical role in weld quality/joint-strength) is 471increased. 472Nodal Velocity Field. The distribution of nodal

Effect of osteogenesis imperfecta mutations in tropocollagen molecule on strength of biomimetic tropocollagen-hydroxyapatite nanocomposites

NASA Astrophysics Data System (ADS)

Dubey, Devendra K.; Tomar, Vikas

2010-01-01

Osteogenesis Imperfecta (OI) is a genetic disorder that affects cellular synthesis of Type-I collagen fibrils and causes extreme bone fragility. This study reports the effects of OI mutations in Tropocollagen (TC) molecules on strength of model Tropocollagen-Hydroxyapatite biomaterials with two different mineral [hydroxyapatite (HAP)] distributions using three dimensional atomistic simulations. Results show that the effect of TC mutations on the strength of TC-HAP biomaterials is insignificant. Instead, change in mineral distribution showed significant impact on the overall strength of TC-HAP biomaterials. Study suggests that TC mutations manifest themselves by changing the mineral distribution during hydroxyapatite growth and nucleation period.

Constrained dipole oscillator strength distributions, sum rules, and dispersion coefficients for Br2 and BrCN

NASA Astrophysics Data System (ADS)

Kumar, Ashok; Thakkar, Ajit J.

2017-03-01

Dipole oscillator strength distributions for Br2 and BrCN are constructed from photoabsorption cross-sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule, the high-energy behavior of the dipole-oscillator-strength density and molar refractivity data when available. The distributions are used to predict dipole sum rules S (k) , mean excitation energies I (k) , and van der Waals C6 coefficients. Coupled-cluster calculations of the static dipole polarizabilities of Br2 and BrCN are reported for comparison with the values of S (- 2) extracted from the distributions.

Reliability Analysis of Uniaxially Ground Brittle Materials

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.; Nemeth, Noel N.; Powers, Lynn M.; Choi, Sung R.

1995-01-01

The fast fracture strength distribution of uniaxially ground, alpha silicon carbide was investigated as a function of grinding angle relative to the principal stress direction in flexure. Both as-ground and ground/annealed surfaces were investigated. The resulting flexural strength distributions were used to verify reliability models and predict the strength distribution of larger plate specimens tested in biaxial flexure. Complete fractography was done on the specimens. Failures occurred from agglomerates, machining cracks, or hybrid flaws that consisted of a machining crack located at a processing agglomerate. Annealing eliminated failures due to machining damage. Reliability analyses were performed using two and three parameter Weibull and Batdorf methodologies. The Weibull size effect was demonstrated for machining flaws. Mixed mode reliability models reasonably predicted the strength distributions of uniaxial flexure and biaxial plate specimens.

Influence of scale-dependent fracture intensity on block size distribution and rock slope failure mechanisms in a DFN framework

NASA Astrophysics Data System (ADS)

Agliardi, Federico; Galletti, Laura; Riva, Federico; Zanchi, Andrea; Crosta, Giovanni B.

2017-04-01

An accurate characterization of the geometry and intensity of discontinuities in a rock mass is key to assess block size distribution and degree of freedom. These are the main controls on the magnitude and mechanisms of rock slope instabilities (structurally-controlled, step-path or mass failures) and rock mass strength and deformability. Nevertheless, the use of over-simplified discontinuity characterization approaches, unable to capture the stochastic nature of discontinuity features, often hampers a correct identification of dominant rock mass behaviour. Discrete Fracture Network (DFN) modelling tools have provided new opportunities to overcome these caveats. Nevertheless, their ability to provide a representative picture of reality strongly depends on the quality and scale of field data collection. Here we used DFN modelling with FracmanTM to investigate the influence of fracture intensity, characterized on different scales and with different techniques, on the geometry and size distribution of generated blocks, in a rock slope stability perspective. We focused on a test site near Lecco (Southern Alps, Italy), where 600 m high cliffs in thickly-bedded limestones folded at the slope scale impend on the Lake Como. We characterized the 3D slope geometry by Structure-from-Motion photogrammetry (range: 150-1500m; point cloud density > 50 pts/m2). Since the nature and attributes of discontinuities are controlled by brittle failure processes associated to large-scale folding, we performed a field characterization of meso-structural features (faults and related kinematics, vein and joint associations) in different fold domains. We characterized the discontinuity populations identified by structural geology on different spatial scales ranging from outcrops (field surveys and photo-mapping) to large slope sectors (point cloud and photo-mapping). For each sampling domain, we characterized discontinuity orientation statistics and performed fracture mapping and circular window analyses in order to measure fracture intensity (P21) and persistence (trace length distributions). Then, we calibrated DFN models for different combinations of P21/P32 and trace length distributions, characteristic of data collected on different scale. Comparing fracture patterns and block size distributions obtained from different models, we outline the strong influence of field data quality and scale on the rock mass behaviours predicted by DFN. We show that accounting for small scale features (close but short fractures) results in smaller but more interconnected blocks, eventually characterized by low removability and partly supported by intact rock strength. On the other hand, DFN based on data surveyed on slope scale enhance the structural control of persistent fracture on the kinematic degree-of freedom of medium-sized blocks, with significant impacts on the selection and parametrization of rock slope stability modelling approaches.

Bio-engineering traits of Pinus radiata D.Don

NASA Astrophysics Data System (ADS)

Giadrossich, Filippo; Marden, Michael; Marrosu, Roberto; Schwarz, Massimiliano; Phillips, Chris John; Cohen, Denis; Niedda, Marcello

2017-04-01

Pinus radiata is widely cultivated in New Zealand. Due to steep slopes and intense rainfall, the silviculture of Pinus radiata forests is important to control erosion and slope stability. Bio-engineering traits such as root distribution and root tensile strength are fundamental to understand the effectiveness of Pinus radiata. This information is needed to use the state of the art root reinforcement model (the Root Bundle Model) and the physically-based slope stability model SOSlope. Yet, little is known about root distribution and tensile strength for this specie. We measured soil moisture and carried out 30 field tensile tests on roots of Pinus radiata. We also measured root distribution data from 5 plants, digging arc of circles 0.6 radian around the trees in four opposite directions. We fully excavated the root system of two trees. Using the Root Bundle Model, results of our measurements allow estimation of root reinforcement. With the slope stability model SOSlope, information on the intensity and frequency of harvesting and on the development of weak zones that can be supported by a stand of Pinus radiata in relation to slope stability can be calculated. An added value is that the collected data allow us to make inferences between number and sizes of roots, and growth direction.

Quantum phases of dipolar rotors on two-dimensional lattices

NASA Astrophysics Data System (ADS)

Abolins, B. P.; Zillich, R. E.; Whaley, K. B.

2018-03-01

The quantum phase transitions of dipoles confined to the vertices of two-dimensional lattices of square and triangular geometry is studied using path integral ground state quantum Monte Carlo. We analyze the phase diagram as a function of the strength of both the dipolar interaction and a transverse electric field. The study reveals the existence of a class of orientational phases of quantum dipolar rotors whose properties are determined by the ratios between the strength of the anisotropic dipole-dipole interaction, the strength of the applied transverse field, and the rotational constant. For the triangular lattice, the generic orientationally disordered phase found at zero and weak values of both dipolar interaction strength and applied field is found to show a transition to a phase characterized by net polarization in the lattice plane as the strength of the dipole-dipole interaction is increased, independent of the strength of the applied transverse field, in addition to the expected transition to a transverse polarized phase as the electric field strength increases. The square lattice is also found to exhibit a transition from a disordered phase to an ordered phase as the dipole-dipole interaction strength is increased, as well as the expected transition to a transverse polarized phase as the electric field strength increases. In contrast to the situation with a triangular lattice, on square lattices, the ordered phase at high dipole-dipole interaction strength possesses a striped ordering. The properties of these quantum dipolar rotor phases are dominated by the anisotropy of the interaction and provide useful models for developing quantum phases beyond the well-known paradigms of spin Hamiltonian models, implementing in particular a novel physical realization of a quantum rotor-like Hamiltonian that possesses an anisotropic long range interaction.

Microchip Electrophoresis at Elevated Temperatures and High Separation Field Strengths

PubMed Central

Mitra, Indranil; Marczak, Steven P.; Jacobson, Stephen C.

2014-01-01

We report free-solution microchip electrophoresis performed at elevated temperatures and high separation field strengths. We used microfluidic devices with 11-cm long separation channels to conduct separations at temperatures between 22 (ambient) and 45 °C and field strengths from 100 to 1000 V/cm. To evaluate separation performance, N-glycans were used as a model system and labeled with 8-aminopyrene-1,3,6-trisulfonic acid to impart charge for electrophoresis and render them fluorescent. Typically, increased diffusivity at higher temperatures leads to increased axial dispersion and poor separation performance; however, we demonstrate that sufficiently high separation field strengths can be used to offset the impact of increased diffusivity in order to maintain separation efficiency. Efficiencies for these free-solution separations are the same at temperatures of 25, 35, and 45 °C with separation field strengths ≥500 V/cm. PMID:24114979

On the Distribution of Earthquake Interevent Times and the Impact of Spatial Scale

NASA Astrophysics Data System (ADS)

Hristopulos, Dionissios

2013-04-01

The distribution of earthquake interevent times is a subject that has attracted much attention in the statistical physics literature [1-3]. A recent paper proposes that the distribution of earthquake interevent times follows from the the interplay of the crustal strength distribution and the loading function (stress versus time) of the Earth's crust locally [4]. It was also shown that the Weibull distribution describes earthquake interevent times provided that the crustal strength also follows the Weibull distribution and that the loading function follows a power-law during the loading cycle. I will discuss the implications of this work and will present supporting evidence based on the analysis of data from seismic catalogs. I will also discuss the theoretical evidence in support of the Weibull distribution based on models of statistical physics [5]. Since other-than-Weibull interevent times distributions are not excluded in [4], I will illustrate the use of the Kolmogorov-Smirnov test in order to determine which probability distributions are not rejected by the data. Finally, we propose a modification of the Weibull distribution if the size of the system under investigation (i.e., the area over which the earthquake activity occurs) is finite with respect to a critical link size. keywords: hypothesis testing, modified Weibull, hazard rate, finite size References [1] Corral, A., 2004. Long-term clustering, scaling, and universality in the temporal occurrence of earthquakes, Phys. Rev. Lett., 9210) art. no. 108501. [2] Saichev, A., Sornette, D. 2007. Theory of earthquake recurrence times, J. Geophys. Res., Ser. B 112, B04313/1-26. [3] Touati, S., Naylor, M., Main, I.G., 2009. Origin and nonuniversality of the earthquake interevent time distribution Phys. Rev. Lett., 102 (16), art. no. 168501. [4] Hristopulos, D.T., 2003. Spartan Gibbs random field models for geostatistical applications, SIAM Jour. Sci. Comput., 24, 2125-2162. [5] I. Eliazar and J. Klafter, 2006. Growth-collapse and decay-surge evolutions, and geometric Langevin equations, Physica A, 367, 106 - 128.

Magnetic-field-induced dose effects in MR-guided radiotherapy systems: dependence on the magnetic field strength.

PubMed

Raaijmakers, A J E; Raaymakers, B W; Lagendijk, J J W

2008-02-21

Several institutes are currently working on the development of a radiotherapy treatment system with online MR imaging (MRI) modality. The main difference between their designs is the magnetic field strength of the MRI system. While we have chosen a 1.5 Tesla (T) magnetic field strength, the Cross Cancer Institute in Edmonton will be using a 0.2 T MRI scanner and the company Viewray aims to use 0.3 T. The magnetic field strength will affect the severity of magnetic field dose effects, such as the electron return effect (ERE): considerable dose increase at tissue air boundaries due to returning electrons. This paper has investigated how the ERE dose increase depends on the magnetic field strength. Therefore, four situations where the ERE occurs have been simulated: ERE at the distal side of the beam, the lateral ERE, ERE in cylindrical air cavities and ERE in the lungs. The magnetic field comparison values were 0.2, 0.75, 1.5 and 3 T. Results show that, in general, magnetic field dose effects are reduced at lower magnetic field strengths. At the distal side, the ERE dose increase is largest for B = 0.75 T and depends on the irradiation field size for B = 0.2 T. The lateral ERE is strongest for B = 3 T but shows no effect for B = 0.2 T. Around cylindrical air cavities, dose inhomogeneities disappear if the radius of the cavity becomes small relative to the in-air radius of the secondary electron trajectories. At larger cavities (r > 1 cm), dose inhomogeneities exist for all magnetic field strengths. In water-lung-water phantoms, the ERE dose increase takes place at the water-lung transition and the dose decreases at the lung-water transition, but these effects are minimal for B = 0.2 T. These results will contribute to evaluating the trade-off between magnetic field dose effects and image quality of MR-guided radiotherapy systems.

Effect of electrode materials on the space charge distribution of an Al2O3 nano-modified transformer oil under impulse voltage conditions

NASA Astrophysics Data System (ADS)

Yang, Qing; Liu, Mengna; Sima, Wenxia; Jin, Yang

2017-11-01

The combined effect mechanism of electrode materials and Al2O3 nanoparticles on the insulating characteristics of transformer oil was investigated. Impulse breakdown tests of pure transformer oil and Al2O3 nano-modified transformer oil of varying concentrations with different electrode materials (brass, aluminum and stainless steel) showed that the breakdown voltage of Al2O3 nano-modified transformer oil is higher than that of pure transformer oil and there is a there is an optimum concentration for Al2O3 nanoparticles when the breakdown voltage reaches the maximum. In addition, the breakdown voltage was highest with the brass electrode, followed by that with stainless steel and then aluminum, irrespective of the concentration of nanoparticles in the transformer oil. This is explained by the charge injection patterns from different electrode materials according to the results of space charge measurements in pure and nano-modified transformer oil using the Kerr electro-optic system. The test results indicate that there are electrode-dependent differences in the charge injection patterns and quantities and then the electric field distortion, which leads to the difference breakdown strength in result. As for the nano-modified transformer oil, due to the Al2O3 nanoparticle’s ability of shielding space charges of different polarities and the charge injection patterns of different electrodes, these two factors have different effects on the electric field distribution and breakdown process of transformer oil between different electrode materials. This paper provides a feasible approach to exploring the mechanism of the effect of the electrode material and nanoparticles on the breakdown strength of liquid dielectrics and analyzing the breakdown process using the space charge distribution.

Runaway tails in magnetized plasmas

NASA Technical Reports Server (NTRS)

Moghaddam-Taaheri, E.; Vlahos, L.; Rowland, H. L.; Papadopoulos, K.

1985-01-01

The evolution of a runaway tail driven by a dc electric field in a magnetized plasma is analyzed. Depending on the strength of the electric field and the ratio of plasma to gyrofrequency, there are three different regimes in the evolution of the tail. The tail can be (1) stable with electrons accelerated to large parallel velocities, (2) unstable to Cerenkov resonance because of the depletion of the bulk and the formation of a positive slope, (3) unstable to the anomalous Doppler resonance instability driven by the large velocity anisotropy in the tail. Once an instability is triggered (Cerenkov or anomalous Doppler resonance) the tail relaxes into an isotropic distribution. The role of a convection type loss term is also discussed.

Nano-sized Adsorbate Structure Formation in Anisotropic Multilayer System

NASA Astrophysics Data System (ADS)

Kharchenko, Vasyl O.; Kharchenko, Dmitrii O.; Yanovsky, Vladimir V.

2017-05-01

In this article, we study dynamics of adsorbate island formation in a model plasma-condensate system numerically. We derive the generalized reaction-diffusion model for adsorptive multilayer system by taking into account anisotropy in transfer of adatoms between neighbor layers induced by electric field. It will be found that with an increase in the electric field strength, a structural transformation from nano-holes inside adsorbate matrix toward separated nano-sized adsorbate islands on a substrate is realized. Dynamics of adsorbate island sizes and corresponding distributions are analyzed in detail. This study provides an insight into details of self-organization of adatoms into nano-sized adsorbate islands in anisotropic multilayer plasma-condensate systems.

On the Fluctuating Component of the Sun's Large-Scale Magnetic Field

NASA Astrophysics Data System (ADS)

Wang, Y.-M.; Sheeley, N. R., Jr.

2003-06-01

The Sun's large-scale magnetic field and its proxies are known to undergo substantial variations on timescales much less than a solar cycle but longer than a rotation period. Examples of such variations include the double activity maximum inferred by Gnevyshev, the large peaks in the interplanetary field strength observed in 1982 and 1991, and the 1.3-1.4 yr periodicities detected over limited time intervals in solar wind speed and geomagnetic activity. We consider the question of the extent to which these variations are stochastic in nature. For this purpose, we simulate the evolution of the Sun's equatorial dipole strength and total open flux under the assumption that the active region sources (BMRs) are distributed randomly in longitude. The results are then interpreted with the help of a simple random walk model including dissipation. We find that the equatorial dipole and open flux generally exhibit multiple peaks during each 11 yr cycle, with the highest peak as likely to occur during the declining phase as at sunspot maximum. The widths of the peaks are determined by the timescale τ~1 yr for the equatorial dipole to decay through the combined action of meridional flow, differential rotation, and supergranular diffusion. The amplitudes of the fluctuations depend on the strengths and longitudinal phase relations of the BMRs, as well as on the relative rates of flux emergence and decay. We conclude that stochastic processes provide a viable explanation for the ``Gnevyshev gaps'' and for the existence of quasi periodicities in the range ~1-3 yr.

Kinetic Interactions Between the Solar Wind and Lunar Magnetic Fields

NASA Astrophysics Data System (ADS)

Halekas, J. S.; Poppe, A. R.; Fatemi, S.; Turner, D. L.; Holmstrom, M.

2016-12-01

Despite their relatively weak strength, small scale, and incoherence, lunar magnetic anomalies can affect the incoming solar wind flow. The plasma interaction with lunar magnetic fields drives significant compressions of the solar wind plasma and magnetic field, deflections of the incoming flow, and a host of plasma waves ranging from the ULF to the electrostatic range. Recent work suggests that the large-scale features of the solar wind-magnetic anomaly interactions may be driven by ion-ion instabilities excited by reflected ions, raising the possibility that they are analogous to ion foreshock phenomena. Indeed, despite their small scale, many of the phenomena observed near lunar magnetic anomalies appear to have analogues in the foreshock regions of terrestrial planets. We discuss the charged particle distributions, fields, and waves observed near lunar magnetic anomalies, and place them in a context with the foreshocks of the Earth, Mars, and other solar system objects.

Self-induced polar order of active Brownian particles in a harmonic trap.

PubMed

Hennes, Marc; Wolff, Katrin; Stark, Holger

2014-06-13

Hydrodynamically interacting active particles in an external harmonic potential form a self-assembled fluid pump at large enough Péclet numbers. Here, we give a quantitative criterion for the formation of the pump and show that particle orientations align in the self-induced flow field in surprising analogy to ferromagnetic order where the active Péclet number plays the role of inverse temperature. The particle orientations follow a Boltzmann distribution Φ(p) ∼ exp(Ap(z)) where the ordering mean field A scales with the active Péclet number and polar order parameter. The mean flow field in which the particles' swimming directions align corresponds to a regularized Stokeslet with strength proportional to swimming speed. Analytic mean-field results are compared with results from Brownian dynamics simulations with hydrodynamic interactions included and are found to capture the self-induced alignment very well.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deshmukh, Shivaraj D.; Tsori, Yoav, E-mail: tsori@bgu.ac.il

We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition, thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied, the solvents separate and the reactants are concentrated in the same phasemore » or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts.« less

Polarization analysis for magnetic field imaging at RADEN in J-PARC/MLF

NASA Astrophysics Data System (ADS)

Shinohara, Takenao; Hiroi, Kosuke; Su, Yuhua; Kai, Tetsuya; Nakatani, Takeshi; Oikawa, Kenichi; Segawa, Mariko; Hayashida, Hirotoshi; Parker, Joseph D.; Matsumoto, Yoshihiro; Zhang, Shuoyuan; Kiyanagi, Yoshiaki

2017-06-01

Polarized neutron imaging is an attractive method for visualizing magnetic fields in a bulk object or in free space. In this technique polarization of neutrons transmitted through a sample is analyzed position by position to produce an image of the polarization distribution. In particular, the combination of three-dimensional spin analysis and the use of a pulsed neutron beam is very effective for the quantitative evaluation of both field strength and direction by means of the analysis of the wavelength dependent polarization vector. Recently a new imaging instrument “RADEN” has been constructed at the beam line of BL22 of the Materials and Life Science Experimental Facility (MLF) at J-PARC, which is dedicated to energy-resolved neutron imaging experiments. We have designed a polarization analysis apparatus for magnetic field imaging at the RADEN instrument and have evaluated its performance.

The Substructure of a Flux Transfer Event Observed by the MMS Spacecraft

NASA Technical Reports Server (NTRS)

Hwang, K.-J.; Sibeck, D. G.; Giles, B. L.; Pollock, C. J.; Gershman, D.; Avanov, L.; Paterson, W. R.; Dorelli, J. C.; Ergun, R. E.; Russel, C. T.;

Resonant coupling through a slot to a loaded cylindrical cavity: Experimental results

NASA Astrophysics Data System (ADS)

Norgard, John D.; Sega, Ronald M.

1990-03-01

The effect of cavity geometry on the energy coupled through a slot aperture is investigated through the use of planar mappings of the internal cavity field. A copper cylinder, closed at both ends, is constructed with copper mesh sections incorporated at the ends of the cylinder and in the cylinder wall opposite a thin slot aperture placed in the wall. The frequencies used for testing are 2 to 4 GHz. Internal field mapping is accomplished by placing thin carbon-loaded sheets in the plane of interest and recording the digitized temperature distribution using an infrared scanning system. The sheets are calibrated such that the temperature data is transformed to current densities or electric field strengths. Using several positions for the detection material, a three-dimensional field profile is obtained. The onset of the internal cavity resonance is studied as it is related to the energy coupled through small apertures.

THE COSMIC-RAY INTENSITY NEAR THE ARCHEAN EARTH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cohen, O.; Drake, J. J.; Kota, J.

2012-11-20

We employ three-dimensional state-of-the-art magnetohydrodynamic models of the early solar wind and heliosphere and a two-dimensional model for cosmic-ray transport to investigate the cosmic-ray spectrum and flux near the Archean Earth. We assess how sensitive the cosmic-ray spectrum is to changes in the sunspot placement and magnetic field strength, the large-scale dipole magnetic field strength, the wind ram pressure, and the Sun's rotation period. Overall, our results confirm earlier work that suggested the Archean Earth would have experienced a greatly reduced cosmic-ray flux than is the case today. The cosmic-ray reduction for the early Sun is mainly due to themore » shorter solar rotation period and tighter winding of the Parker spiral, and to the different surface distribution of the more active solar magnetic field. These effects lead to a global reduction of the cosmic-ray flux at 1 AU by up to two orders of magnitude or more. Variations in the sunspot magnetic field have more effect on the flux than variations in the dipole field component. The wind ram pressure affects the cosmic-ray flux through its influence on the size of the heliosphere via the pressure balance with the ambient interstellar medium. Variations in the interstellar medium pressure experienced by the solar system in orbit through the Galaxy could lead to order of magnitude changes in the cosmic-ray flux at Earth on timescales of a few million years.« less

All-dielectric fiber-optic passive millimeter-wave antenna

NASA Astrophysics Data System (ADS)

Wang, Wen C.; Lin, Weiping; Marshall, Hank; Schaafsma, David T.; Chaung, Richard

2003-07-01

An integrated Mach-Zehnder interferometer made of electro-optic polymer, which has excellent broadband (>100 GHz) response, was fabricated as a mm-wave receive antenna. When an electric field is applied to the interferometer arm(s) made of EO material, a phase delay is generated which results in a net imbalance in the interferometer and thus a change in the output intensity. This output intensity change, which contains electric field strength and temporal profile information, is then read by a photodetector and processed. To test this antenna in free space, a micro-strip travelling electromagnetic cell, which has uniform electric field distribution in the 1 GHz range, was constructed. The test results show the antenna had good linear response over a 40 dB power range, at 1 GHz center frequency. The measured minimum detectable E-field strength was about 0.22 V/m (or 6.7 nW/cm2) at 1 kHz bandwidth with a laser power of 7.9 μWatt (-21dBm) measured after the sensor, which agrees with our theoretical calculations. The measured E-field signal increases with increasing laser power, which indicates that significant sensitivity improvement, can be easily obtained by lowering passive losses. The antenna was found to be thermally stable over a temperature range from -30 to 50 C. The antenna sensitivity can be further improved by lowering the device insertion loss, optimizing the photodetector and detection circuitry, and using EO polymers with higher electro-optic coefficients.

Individual eigenvalue distributions of crossover chiral random matrices and low-energy constants of SU(2) × U(1) lattice gauge theory

NASA Astrophysics Data System (ADS)

Yamamoto, Takuya; Nishigaki, Shinsuke M.

2018-02-01

We compute individual distributions of low-lying eigenvalues of a chiral random matrix ensemble interpolating symplectic and unitary symmetry classes by the Nyström-type method of evaluating the Fredholm Pfaffian and resolvents of the quaternion kernel. The one-parameter family of these distributions is shown to fit excellently the Dirac spectra of SU(2) lattice gauge theory with a constant U(1) background or dynamically fluctuating U(1) gauge field, which weakly breaks the pseudoreality of the unperturbed SU(2) Dirac operator. The observed linear dependence of the crossover parameter with the strength of the U(1) perturbations leads to precise determination of the pseudo-scalar decay constant, as well as the chiral condensate in the effective chiral Lagrangian of the AI class.

Environmental impact of the use of radiofrequency electromagnetic fields in physiotherapeutic treatment.

PubMed

Gryz, Krzysztof; Karpowicz, Jolanta

2014-01-01

Electromagnetic fields used in physiotherapeutic treatment affect not only patients, but also physiotherapists, patients not undergoing treatment and electronic medical equipment. The aim of the work was to study the parameters of the electromagnetic fields of physiotherapeutic devices with respect to requirements regarding the protection of electronic devices, including medical implants, against electromagnetic intererence, and the protection of the general public (patients not undergoing treatment and bystanders), as well as medical personnel, against the health hazards caused by electromagnetic exposure. The spatial distribution of electric and magnetic field strength was investigated near 3 capacitive short-wave and 3 long-wave diathermies and 3 ultrasound therapy units, as along with the capacitive electric currents caused by electromagnetic field interaction in the upper limbs of the physiotherapists operating these devices. The physiotherapists' exposure to electromagnetic fields depends on the spatial organisation of the workspace and their location during treatment. Electric fields able to interfere with the function of electronic medical implants and in whic anyone not undergoing treatment should not be present were measured up to 150-200 cm away from active applicators of short-wave diathermy, and up to 40-45 cm away from long-wave diathermy ones. Electric fields in which workers should not be present were measured up to 30-40 cm away from the applicators and cables of active short-wave diathermy devices. A capacitive electric current with a strength exceeding many times the international recommendations regarding workers protection was measured in the wrist while touching applicators and cables of active short-wave diathermy devices. The strongest environmental electromagnetic hazards occur near short-wave diathermy devices, and to a lesser degree near long-wave diathermy devices, but were not found near ultrasound therapy units.

Influence of geometry and material of insulating posts on particle trapping using positive dielectrophoresis.

PubMed

Pesch, Georg R; Du, Fei; Baune, Michael; Thöming, Jorg

2017-02-03

Insulator-based dielectrophoresis (iDEP) is a powerful particle analysis technique based on electric field scattering at material boundaries which can be used, for example, for particle filtration or to achieve chromatographic separation. Typical devices consist of microchannels containing an array of posts but large scale application was also successfully tested. Distribution and magnitude of the generated field gradients and thus the possibility to trap particles depends apart from the applied field strength on the material combination between post and surrounding medium and on the boundary shape. In this study we simulate trajectories of singe particles under the influence of positive DEP that are flowing past one single post due to an external fluid flow. We analyze the influence of key parameters (excitatory field strength, fluid flow velocity, particle size, distance from the post, post size, and cross-sectional geometry) on two benchmark criteria, i.e., a critical initial distance from the post so that trapping still occurs (at fixed particle size) and a critical minimum particle size necessary for trapping (at fixed initial distance). Our approach is fundamental and not based on finding an optimal geometry of insulating structures but rather aims to understand the underlying phenomena of particle trapping. A sensitivity analysis reveals that electric field strength and particle size have the same impact, as have fluid flow velocity and post dimension. Compared to these parameters the geometry of the post's cross-section (i.e. rhomboidal or elliptical with varying width-to-height or aspect ratio) has a rather small influence but can be used to optimize the trapping efficiency at a specific distance. We hence found an ideal aspect ratio for trapping for each base geometry and initial distance to the tip which is independent of the other parameters. As a result we present design criteria which we believe to be a valuable addition to the existing literature. Copyright © 2016 Elsevier B.V. All rights reserved.

Disappearance of Anisotropic Intermittency in Large-amplitude MHD Turbulence and Its Comparison with Small-amplitude MHD Turbulence

NASA Astrophysics Data System (ADS)

Yang, Liping; Zhang, Lei; He, Jiansen; Tu, Chuanyi; Li, Shengtai; Wang, Xin; Wang, Linghua

2018-03-01

Multi-order structure functions in the solar wind are reported to display a monofractal scaling when sampled parallel to the local magnetic field and a multifractal scaling when measured perpendicularly. Whether and to what extent will the scaling anisotropy be weakened by the enhancement of turbulence amplitude relative to the background magnetic strength? In this study, based on two runs of the magnetohydrodynamic (MHD) turbulence simulation with different relative levels of turbulence amplitude, we investigate and compare the scaling of multi-order magnetic structure functions and magnetic probability distribution functions (PDFs) as well as their dependence on the direction of the local field. The numerical results show that for the case of large-amplitude MHD turbulence, the multi-order structure functions display a multifractal scaling at all angles to the local magnetic field, with PDFs deviating significantly from the Gaussian distribution and a flatness larger than 3 at all angles. In contrast, for the case of small-amplitude MHD turbulence, the multi-order structure functions and PDFs have different features in the quasi-parallel and quasi-perpendicular directions: a monofractal scaling and Gaussian-like distribution in the former, and a conversion of a monofractal scaling and Gaussian-like distribution into a multifractal scaling and non-Gaussian tail distribution in the latter. These results hint that when intermittencies are abundant and intense, the multifractal scaling in the structure functions can appear even if it is in the quasi-parallel direction; otherwise, the monofractal scaling in the structure functions remains even if it is in the quasi-perpendicular direction.

The Analysis of the Strength, Distribution and Direction for the EEG Phase Synchronization by Musical Stimulus

NASA Astrophysics Data System (ADS)

Ogawa, Yutaro; Ikeda, Akira; Kotani, Kiyoshi; Jimbo, Yasuhiko

In this study, we propose the EEG phase synchronization analysis including not only the average strength of the synchronization but also the distribution and directions under the conditions that evoked emotion by musical stimuli. The experiment is performed with the two different musical stimuli that evoke happiness or sadness for 150 seconds. It is found that the average strength of synchronization indicates no difference between the right side and the left side of the frontal lobe during the happy stimulus, the distribution and directions indicate significant differences. Therefore, proposed analysis is useful for detecting emotional condition because it provides information that cannot be obtained only by the average strength of synchronization.

Electromagnetic exposure compliance estimation using narrowband directional measurements.

PubMed

Stratakis, D; Miaoudakis, A; Xenos, T; Zacharopoulos, V

2008-01-01

The increased number of everyday applications that rely on wireless communication has drawn an attention to several concerns on the adverse health effects that prolonged or even short time exposure might have on humans. International organisations and countries have adopted guides and legislation for the public safety. They include reference levels (RLs) regarding field strength electromagnetic quantities. To check for RLs compliance in an environment with multiple transmitters of various types, analytical simulation models may be implemented provided that all the necessary information are available. Since this is not generally the case in the most practical situations, on-site measurements have to be performed. The necessary equipment for measurements of this type usually includes broadband field metres suitable to measure the field strength over the whole bandwidth of the field sensor used. These types of measurements have several drawbacks; to begin with, given that RLs are frequency depended, compliance evaluation can be misleading since no information is available regarding the measured spectrum distribution. Furthermore, in a multi-transmitter environment there is no way of distinguishing the contribution of a specific source to the overall field measured. Of course, this problem can be resolved using narrowband directional receiver antennas, yet there is always the need for a priori knowledge of the polarisation of the incident electromagnetic wave. In this work, the use of measurement schemes of this type is addressed. A method independent to the polarisation of the incident wave is proposed and a way to evaluate a single source contribution to the total field in a multi-transmitter environment and the polarisation of the measured incident wave is presented.

Measuring the vertical electrical field above an oceanic convection system using a meteorological sounding balloon

NASA Astrophysics Data System (ADS)

Chen, A. B.; Chiu, C.; Lai, S.; Chen, C.; Kuo, C.; Su, H.; Hsu, R.

2012-12-01

The vertical electric field above thundercloud plays an important role in the generation and modeling of transient luminous events. For example, Pasko [1995] proposed that the high quasi-static E-field following the positive cloud-to-ground lightning could accelerate and input energy to ambient electrons; as they collide and excite nitrogen and oxygen molecules in upper atmosphere, sprites may be induced. A series of balloon experiments led by Holzworth have investigated the temporal and spatial fluctuations of the electric field and conductivity in the upper atmosphere at different sites [Holzworth 2005, and references in]. But the strength and variation of the vertical electric field above thundercloud, especially oceanic ones, are not well documented so far. A lightweight, low-cost measurement system including an electric field meter and the associated aviation electronics are developed to carry out the in-situ measurement of the vertical electric field and the inter-cloud charge distribution. Our measuring system was first deployed using a meteorological sounding balloon from Taitung, Taiwan in May 2012. The measured electric field below 3km height shows an exponential decay and it is consistent with the expected potential gradient variation between ionosphere and the Earth surface. But the background strength of the measured E-field grows up exponentially and a violent fluctuations is also observed when the balloon flew over a developing oceanic convection cell. The preliminary results from this flight will be reported and discussed. This low-cost electric field meter is developed within one year. In the coming months, more flights will be performed with the aim to measure the rapid variation of the electric field above thundercloud as well as the E-field that may induce transient luminous events. Our ground campaigns show that the occurrence rates of blue and gigantic jet are relatively high in the vicinity of Taiwan. Our experiment can be used to diagnose the dynamics of the E-field associated with blue and gigantic jets.

Semiconductor Crystal Growth in Static and Rotating Magnetic fields

NASA Technical Reports Server (NTRS)

Volz, Martin

2004-01-01

Magnetic fields have been applied during the growth of bulk semiconductor crystals to control the convective flow behavior of the melt. A static magnetic field established Lorentz forces which tend to reduce the convective intensity in the melt. At sufficiently high magnetic field strengths, a boundary layer is established ahead of the solid-liquid interface where mass transport is dominated by diffusion. This can have a significant effect on segregation behavior and can eliminate striations in grown crystals resulting from convective instabilities. Experiments on dilute (Ge:Ga) and solid solution (Ge-Si) semiconductor systems show a transition from a completely mixed convective state to a diffusion-controlled state between 0 and 5 Tesla. In HgCdTe, radial segregation approached the diffusion limited regime and the curvature of the solid-liquid interface was reduced by a factor of 3 during growth in magnetic fields in excess of 0.5 Tesla. Convection can also be controlled during growth at reduced gravitational levels. However, the direction of the residual steady-state acceleration vector can compromise this effect if it cannot be controlled. A magnetic field in reduced gravity can suppress disturbances caused by residual transverse accelerations and by random non-steady accelerations. Indeed, a joint program between NASA and the NHMFL resulted in the construction of a prototype spaceflight magnet for crystal growth applications. An alternative to the suppression of convection by static magnetic fields and reduced gravity is the imposition of controlled steady flow generated by rotating magnetic fields (RMF)'s. The potential benefits of an RMF include homogenization of the melt temperature and concentration distribution, and control of the solid-liquid interface shape. Adjusting the strength and frequency of the applied magnetic field allows tailoring of the resultant flow field. A limitation of RMF's is that they introduce deleterious instabilities above a critical magnetic field value. Growth conditions in which static magnetic fields rotational magnetic fields, and reduced gravitational levels can have a beneficial role will be described.

Study on aggregation behavior of Cytochrome C-conjugated silver nanoparticles using asymmetrical flow field-flow fractionation.

PubMed

Kim, Sun Tae; Lee, Yong-Ju; Hwang, Yu-Sik; Lee, Seungho

2015-01-01

In this study, 40 nm silver nanoparticles (AgNPs) were synthesized using the citrate reduction method and then the surface of AgNPs was modified by conjugating Cytochrome C (Cyto C) to improve stability and to enhance bioactivity and biocompatibility of AgNPs. It is known that Cyto C may undergo conformational changes under various conditions of pH, temperature, ionic strength, etc., resulting in aggregation of the particles. These parameters also affect the size and size distribution of Cyto C-conjugated AgNPs (Cyto C-AgNP). ζ-potential measurement revealed that the adsorption of Cyto C on the surface of AgNPs is saturated at the molar ratio [Cyto C]/[AgNPs] above about 300. Asymmetrical flow field-flow fractionation (AsFlFFF) analysis showed that hydrodynamic diameter of AgNPs increases by about 4 nm when the particle is saturated by Cyto C. The aggregation behavior of Cyto C-AgNP at various conditions of pH, temperature and ionic strength were investigated using AsFlFFF and UV-vis spectroscopy. It was found that the aggregation of Cyto C-AgNP increases with decreasing pH, increasing temperature and ionic strength due to denaturation of Cyto C on AgNPs and reduction in the thickness of electrostatic double layer on the surface of Cyto C-AgNP. Copyright © 2014 Elsevier B.V. All rights reserved.

Octanol-water distribution of engineered nanomaterials.

PubMed

Hristovski, Kiril D; Westerhoff, Paul K; Posner, Jonathan D

2011-01-01

The goal of this study was to examine the effects of pH and ionic strength on octanol-water distribution of five model engineered nanomaterials. Distribution experiments resulted in a spectrum of three broadly classified scenarios: distribution in the aqueous phase, distribution in the octanol, and distribution into the octanol-water interface. Two distribution coefficients were derived to describe the distribution of nanoparticles among octanol, water and their interface. The results show that particle surface charge, surface functionalization, and composition, as well as the solvent ionic strength and presence of natural organic matter, dramatically impact this distribution. Distributions of nanoparticles into the interface were significant for nanomaterials that exhibit low surface charge in natural pH ranges. Increased ionic strengths also contributed to increased distributions of nanoparticle into the interface. Similarly to the octanol-water distribution coefficients, which represent a starting point in predicting the environmental fate, bioavailability and transport of organic pollutants, distribution coefficients such as the ones described in this study could help to easily predict the fate, bioavailability, and transport of engineered nanomaterials in the environment.

47 CFR 18.305 - Field strength limits.

Code of Federal Regulations, 2010 CFR

2010-10-01

...) Field strength limit (uV/m) Distance (meters) Any type unless otherwise specified (miscellaneous) Any...Any 2515 300300 Ultrasonic Below 490 kHz Below 500500 or more 2,400/F(kHz)2,400/F(kHz)× SQRT(power/500... kHzOn or above 90 kHz AnyAny 1,500300 430 430 1 Field strength may not exceed 10 μV/m at 1600 meters...

Confidence intervals for predicting lumber strength properties based on ratios of percentiles from two Weibull populations.

Treesearch

Richard A. Johnson; James W. Evans; David W. Green

2003-01-01

Ratios of strength properties of lumber are commonly used to calculate property values for standards. Although originally proposed in terms of means, ratios are being applied without regard to position in the distribution. It is now known that lumber strength properties are generally not normally distributed. Therefore, nonparametric methods are often used to derive...

Axion excursions of the landscape during inflation

NASA Astrophysics Data System (ADS)

Palma, Gonzalo A.; Riquelme, Walter

2017-07-01

Because of their quantum fluctuations, axion fields had a chance to experience field excursions traversing many minima of their potentials during inflation. We study this situation by analyzing the dynamics of an axion field ψ , present during inflation, with a periodic potential given by v (ψ )=Λ4[1 -cos (ψ /f )]. By assuming that the vacuum expectation value of the field is stabilized at one of its minima, say, ψ =0 , we compute every n -point correlation function of ψ up to first order in Λ4 using the in-in formalism. This computation allows us to identify the distribution function describing the probability of measuring ψ at a particular amplitude during inflation. Because ψ is able to tunnel between the barriers of the potential, we find that the probability distribution function consists of a non-Gaussian multimodal distribution such that the probability of measuring ψ at a minimum of v (ψ ) different from ψ =0 increases with time. As a result, at the end of inflation, different patches of the Universe are characterized by different values of the axion field amplitude, leading to important cosmological phenomenology: (a) Isocurvature fluctuations induced by the axion at the end of inflation could be highly non-Gaussian. (b) If the axion defines the strength of standard model couplings, then one is led to a concrete realization of the multiverse. (c) If the axion corresponds to dark matter, one is led to the possibility that, within our observable Universe, dark matter started with a nontrivial initial condition, implying novel signatures for future surveys.

Statistical Models of Fracture Relevant to Nuclear-Grade Graphite: Review and Recommendations

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.; Bratton, Robert L.

2011-01-01

The nuclear-grade (low-impurity) graphite needed for the fuel element and moderator material for next-generation (Gen IV) reactors displays large scatter in strength and a nonlinear stress-strain response from damage accumulation. This response can be characterized as quasi-brittle. In this expanded review, relevant statistical failure models for various brittle and quasi-brittle material systems are discussed with regard to strength distribution, size effect, multiaxial strength, and damage accumulation. This includes descriptions of the Weibull, Batdorf, and Burchell models as well as models that describe the strength response of composite materials, which involves distributed damage. Results from lattice simulations are included for a physics-based description of material breakdown. Consideration is given to the predicted transition between brittle and quasi-brittle damage behavior versus the density of damage (level of disorder) within the material system. The literature indicates that weakest-link-based failure modeling approaches appear to be reasonably robust in that they can be applied to materials that display distributed damage, provided that the level of disorder in the material is not too large. The Weibull distribution is argued to be the most appropriate statistical distribution to model the stochastic-strength response of graphite.

Laser-assisted coplanar symmetric (e, 2e) triple differential cross sections

NASA Astrophysics Data System (ADS)

Khalil, D.; Tlidi, M.; Makhoute, A.; Ajana, I.

2017-04-01

The modification due to an external linearly polarized monochromatic laser field on the dynamics of the ionization process of an atomic hydrogen by electron-impact is studied theoretically for a coplanar symmetric geometry. The interaction of the laser field with the unbound electrons is treated in a non-perturbative way. The wave functions of the ingoing and outgoing electrons in the laser field are treated as non-relativistic Volkov waves, while the interaction of the bound electron with the laser field is treated by using first-order perturbation theory, assuming that the electric field strength associated with the external laser field is much less than the atomic unit e/{a}2=5× {10}9 {{V}} {{{cm}}}-1. The influence of the laser parameters on the angular distribution is analyzed and several illustrative examples are discussed. Significant changes are noted both in the shape and magnitude of the triple differential cross sections (TDCS) by the application of the laser field. Numerical results show that the TDCS are strongly dependent on the dressing of the projectile by the laser field at low frequency in (e, 2e) spectroscopy region.

Structural optimization of 3D-printed synthetic spider webs for high strength

PubMed Central

Qin, Zhao; Compton, Brett G.; Lewis, Jennifer A.; Buehler, Markus J.

2015-01-01

Spiders spin intricate webs that serve as sophisticated prey-trapping architectures that simultaneously exhibit high strength, elasticity and graceful failure. To determine how web mechanics are controlled by their topological design and material distribution, here we create spider-web mimics composed of elastomeric filaments. Specifically, computational modelling and microscale 3D printing are combined to investigate the mechanical response of elastomeric webs under multiple loading conditions. We find the existence of an asymptotic prey size that leads to a saturated web strength. We identify pathways to design elastomeric material structures with maximum strength, low density and adaptability. We show that the loading type dictates the optimal material distribution, that is, a homogeneous distribution is better for localized loading, while stronger radial threads with weaker spiral threads is better for distributed loading. Our observations reveal that the material distribution within spider webs is dictated by the loading condition, shedding light on their observed architectural variations. PMID:25975372

Quantitative susceptibility mapping across two clinical field strengths: Contrast-to-noise ratio enhancement at 1.5T.

PubMed

Ippoliti, Matteo; Adams, Lisa C; Winfried, Brenner; Hamm, Bernd; Spincemaille, Pascal; Wang, Yi; Makowski, Marcus R

2018-04-16

Quantitative susceptibility mapping (QSM) is an MRI postprocessing technique that allows quantification of the spatial distribution of tissue magnetic susceptibility in vivo. Contributing sources include iron, blood products, calcium, myelin, and lipid content. To evaluate the reproducibility and consistency of QSM across clinical field strengths of 1.5T and 3T and to optimize the contrast-to-noise ratio (CNR) at 1.5T through bandwidth tuning. Prospective. Sixteen healthy volunteers (10 men, 6 women; age range 24-37; mean age 27.8 ± 3.2 years). 1.5T and 3T systems from the same vendor. Four spoiled gradient echo (SPGR) sequences were designed with different acquisition bandwidths. QSM reconstruction was achieved through a nonlinear morphology-enabled dipole inversion (MEDI) algorithm employing L1 regularization. CNR was calculated in seven regions of interest (ROIs), while reproducibility and consistency of QSM measurements were evaluated through voxel-based and region-specific linear correlation analyses and Bland-Altman plots. Interclass correlation, Wilcoxon rank sum test, linear regression analysis, Bland-Altman analysis, Welch's t-test. CNR analysis showed a statistically significant (P < 0.05) increase in four out of seven ROIs for the lowest bandwidth employed with respect to the highest (25.18% increase in CNR of caudate nucleus). All sequences reported an excellent correlation across field strength and bandwidth variation (R ≥ 0.96, widest limits of agreement from -18.7 to 25.8 ppb) in the ROI-based analysis, while the correlation was found to be good for the voxel-based analysis of averaged maps (R ≥ 0.90, widest limits of agreement from -9.3 to 9.1 ppb). CNR of QSM images reconstructed from 1.5T acquisitions can be enhanced through bandwidth tuning. MEDI-based QSM reconstruction demonstrated to be reproducible and consistent both across field strengths (1.5T and 3T) and bandwidth variation. 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018. © 2018 International Society for Magnetic Resonance in Medicine.

Quantitative Relationships Linking Rock Strength to Channel Morphology: A Case Study in Central Arizona

NASA Astrophysics Data System (ADS)

Larimer, J. E.; Yanites, B.

2016-12-01

River morphology is a consequence of the erosive forces acting on the channel boundary and the resisting forces that limit erosion. For bedrock rivers, the erosive forces are generated by the stresses exerted by impacting sediment and flowing water, while the resisting forces are controlled by the internal strength regime of the local rock. We investigate the susceptibility of different rock types to different erosional processes (i.e. abrasion and plucking) and how changes in channel morphology reflect rock strength properties across lithologic boundaries. The bedrock rivers in the Prescott National Forest, AZ flow over a number of rock types with variable strength including sedimentary, igneous, and metamorphic lithologies providing a natural experiment to quantify the influence of rock strength on channel morphology. We collected bedrock samples and channel surveys from 12 different rock types. Rock-strength and rock-mass properties include compressive strength, tensile strength, fatigue strength, decimeter scale P-wave velocity (varies by 8-fold), Schmidt rebound value, fracture spacing, fracture aperture, and slake durability (as a proxy for weathering susceptibility. Morphological measurements include channel width, channel steepness (varies by 10-fold), and grain size distribution. To distinguish between the major mechanisms of erosion we measure bedrock surface roughness factor at the centimeter scale. Preliminary results show that channel steepness (ksn) increases with P-wave velocity while normalized channel width (kwn) decreases with P-wave velocity. We use these data to quantify scaling relationships of channel geometry with rock strength properties. We consider the results in the context of the driving mechanistic process to develop new quantitative understandings of how rock strength properties influence the efficiency of erosion processes and how rock strength is reflected in river morphology. By comparing the results among different rock types in a landscape subject to spatially consistent tectonic and climatic influence, our work seeks to advance process-based river erosion models through field and laboratory measurements.

Electromagnetic ion cyclotron waves stimulated by modest magnetospheric compressions

NASA Technical Reports Server (NTRS)

Anderson, B. J.; Hamilton, D. C.

1993-01-01

AMPTE/CCE magnetic field and particle data are used to test the suggestion that increased hot proton temperature anisotropy resulting from convection during magnetospheric compression is responsible for the enhancement in Pc 1 emission via generation of electromagnetic ion cyclotron (EMIC) waves in the dayside outer equatorial magnetosphere. The relative increase in magnetic field is used to gauge the strength of the compression, and an image dipole model is used to estimate the motion of the plasma during compression. Proton data are used to analyze the evolution of the proton distribution and the corresponding changes in EMIC wave activity expected during the compression. It is suggested that enhancements in dynamic pressure pump the energetic proton distributions in the outer magnetosphere, driving EMIC waves. Waves are expected to be generated most readily close to the magnetopause, and transient pressure pulses may be associated with bursts of EMIC waves, which would be observed on the ground in association with ionospheric transient signatures.

A phase-field approach to model multi-axial and microstructure dependent fracture in nuclear grade graphite

DOE PAGES

Chakraborty, Pritam; Sabharwall, Piyush; Carroll, Mark C.

2016-04-07

The fracture behavior of nuclear grade graphites is strongly influenced by underlying microstructural features such as the character of filler particles, and the distribution of pores and voids. These microstructural features influence the crack nucleation and propagation behavior, resulting in quasi-brittle fracture with a tortuous crack path and significant scatter in measured bulk strength. This paper uses a phase-field method to model the microstructural and multi-axial fracture in H-451, a historic variant of nuclear graphite that provides the basis for an idealized study on a legacy grade. The representative volume elements are constructed from randomly located pores with random sizemore » obtained from experimentally determined log-normal distribution. The representative volume elements are then subjected to simulated multi-axial loading, and a reasonable agreement of the resulting fracture stress with experiments is obtained. Finally, quasi-brittle stress-strain evolution with a tortuous crack path is also observed from the simulations and is consistent with experimental results.« less

In Situ Generation of Plasmonic Nanoparticles for Manipulating Photon-Plasmon Coupling in Microtube Cavities.

PubMed

Yin, Yin; Wang, Jiawei; Lu, Xueyi; Hao, Qi; Saei Ghareh Naz, Ehsan; Cheng, Chuanfu; Ma, Libo; Schmidt, Oliver G

2018-04-24

In situ generation of silver nanoparticles for selective coupling between localized plasmonic resonances and whispering-gallery modes (WGMs) is investigated by spatially resolved laser dewetting on microtube cavities. The size and morphology of the silver nanoparticles are changed by adjusting the laser power and irradiation time, which in turn effectively tune the photon-plasmon coupling strength. Depending on the relative position of the plasmonic nanoparticles spot and resonant field distribution of WGMs, selective coupling between the localized surface plasmon resonances (LSPRs) and WGMs is experimentally demonstrated. Moreover, by creating multiple plasmonic-nanoparticle spots on the microtube cavity, the field distribution of optical axial modes is freely tuned due to multicoupling between LSPRs and WGMs. The multicoupling mechanism is theoretically investigated by a modified quasipotential model based on perturbation theory. This work provides an in situ fabrication of plasmonic nanoparticles on three-dimensional microtube cavities for manipulating photon-plasmon coupling which is of interest for optical tuning abilities and enhanced light-matter interactions.

Dependence of Brownian and Néel relaxation times on magnetic field strength

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deissler, Robert J., E-mail: rjd42@case.edu; Wu, Yong; Martens, Michael A.

2014-01-15

Purpose: In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS) the relaxation time of the magnetization in response to externally applied magnetic fields is determined by the Brownian and Néel relaxation mechanisms. Here the authors investigate the dependence of the relaxation times on the magnetic field strength and the implications for MPI and MPS. Methods: The Fokker–Planck equation with Brownian relaxation and the Fokker–Planck equation with Néel relaxation are solved numerically for a time-varying externally applied magnetic field, including a step-function, a sinusoidally varying, and a linearly ramped magnetic field. For magnetic fields that are applied as a stepmore » function, an eigenvalue approach is used to directly calculate both the Brownian and Néel relaxation times for a range of magnetic field strengths. For Néel relaxation, the eigenvalue calculations are compared to Brown's high-barrier approximation formula. Results: The relaxation times due to the Brownian or Néel mechanisms depend on the magnitude of the applied magnetic field. In particular, the Néel relaxation time is sensitive to the magnetic field strength, and varies by many orders of magnitude for nanoparticle properties and magnetic field strengths relevant for MPI and MPS. Therefore, the well-known zero-field relaxation times underestimate the actual relaxation times and, in particular, can underestimate the Néel relaxation time by many orders of magnitude. When only Néel relaxation is present—if the particles are embedded in a solid for instance—the authors found that there can be a strong magnetization response to a sinusoidal driving field, even if the period is much less than the zero-field relaxation time. For a ferrofluid in which both Brownian and Néel relaxation are present, only one relaxation mechanism may dominate depending on the magnetic field strength, the driving frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field. Conclusions: A simple treatment of Néel relaxation using the common zero-field relaxation time overestimates the relaxation time of the magnetization in situations relevant for MPI and MPS. For sinusoidally driven (or ramped) systems, whether or not a particular relaxation mechanism dominates or is even relevant depends on the magnetic field strength, the frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field.« less

Solar energetic particle anisotropies and insights into particle transport

NASA Astrophysics Data System (ADS)

Leske, R. A.; Cummings, A. C.; Cohen, C. M. S.; Mewaldt, R. A.; Labrador, A. W.; Stone, E. C.; Wiedenbeck, M. E.; Christian, E. R.; Rosenvinge, T. T. von

2016-03-01

As solar energetic particles (SEPs) travel through interplanetary space, their pitch-angle distributions are shaped by the competing effects of magnetic focusing and scattering. Measurements of SEP anisotropies can therefore reveal information about interplanetary conditions such as magnetic field strength, topology, and turbulence levels at remote locations from the observer. Onboard each of the two STEREO spacecraft, the Low Energy Telescope (LET) measures pitch-angle distributions for protons and heavier ions up to iron at energies of about 2-12 MeV/nucleon. Anisotropies observed using LET include bidirectional flows within interplanetary coronal mass ejections, sunward-flowing particles when STEREO was magnetically connected to the back side of a shock, and loss-cone distributions in which particles with large pitch angles underwent magnetic mirroring at an interplanetary field enhancement that was too weak to reflect particles with the smallest pitch angles. Unusual oscillations in the width of a beamed distribution at the onset of the 23 July 2012 SEP event were also observed and remain puzzling. We report LET anisotropy observations at both STEREO spacecraft and discuss their implications for SEP transport, focusing exclusively on the extreme event of 23 July 2012 in which a large variety of anisotropies were present at various times during the event.

Statistical Characterization of the Mechanical Parameters of Intact Rock Under Triaxial Compression: An Experimental Proof of the Jinping Marble

NASA Astrophysics Data System (ADS)

Jiang, Quan; Zhong, Shan; Cui, Jie; Feng, Xia-Ting; Song, Leibo

2016-12-01

We investigated the statistical characteristics and probability distribution of the mechanical parameters of natural rock using triaxial compression tests. Twenty cores of Jinping marble were tested under each different levels of confining stress (i.e., 5, 10, 20, 30, and 40 MPa). From these full stress-strain data, we summarized the numerical characteristics and determined the probability distribution form of several important mechanical parameters, including deformational parameters, characteristic strength, characteristic strains, and failure angle. The statistical proofs relating to the mechanical parameters of rock presented new information about the marble's probabilistic distribution characteristics. The normal and log-normal distributions were appropriate for describing random strengths of rock; the coefficients of variation of the peak strengths had no relationship to the confining stress; the only acceptable random distribution for both Young's elastic modulus and Poisson's ratio was the log-normal function; and the cohesive strength had a different probability distribution pattern than the frictional angle. The triaxial tests and statistical analysis also provided experimental evidence for deciding the minimum reliable number of experimental sample and for picking appropriate parameter distributions to use in reliability calculations for rock engineering.

A parametric study of segregation effects during vertical Bridgman crystal growth with an axial magnetic field

NASA Astrophysics Data System (ADS)

Ma, N.; Walker, J. S.

2000-01-01

This paper presents a model for the unsteady transport of a dopant during the vertical Bridgman crystal growth process with a planar crystal-melt interface and with an axial magnetic field, and investigates the effects of varying different process variables on the crystal composition. The convective mass transport due to the buoyant convection in the melt produces nonuniformities in the concentration in both the melt and the crystal. The convective mass transport plays an important role for all magnetic field strengths considered. Diffusive mass transport begins to dominate for a magnetic flux density of 4 T and a fast growth rate, producing crystals which have an axial variation of the radially averaged crystal composition approaching that of the diffusion-controlled limit. Dopant distributions for several different combinations of process parameters are presented.

47 CFR 73.186 - Establishment of effective field at one kilometer.

Code of Federal Regulations, 2010 CFR

2010-10-01

... coordinate paper, plot field strengths as ordinate and distance as abscissa. (ii) Using semi-log coordinate paper, plot field strength times distance as ordinate on the log scale and distance as abscissa on the...

The Magnetohydrodynamic Kelvin-Helmholtz Instability. III. The Role of Sheared Magnetic Field in Planar Flows

NASA Astrophysics Data System (ADS)

Jeong, Hyunju; Ryu, Dongsu; Jones, T. W.; Frank, Adam

2000-01-01

We have carried out simulations of the nonlinear evolution of the magnetohydrodynamic (MHD) Kelvin-Helmholtz (KH) instability for compressible fluids in 2.5 dimensions, extending our previous work by Frank et al. and Jones et al. In the present work we have simulated flows in the x-y plane in which a ``sheared'' magnetic field of uniform strength smoothly rotates across a thin velocity shear layer from the z-direction to the x-direction, aligned with the flow field. The sonic Mach number of the velocity transition is unity. Such flows containing a uniform field in the x-direction are linearly stable if the magnetic field strength is great enough that the Alfvénic Mach number MA=U0/cA<2. That limit does not apply directly to sheared magnetic fields, however, since the z-field component has almost no influence on the linear stability. Thus, if the magnetic shear layer is contained within the velocity shear layer, the KH instability may still grow, even when the field strength is quite large. So, here we consider a wide range of sheared field strengths covering Alfvénic Mach numbers, MA=142.9 to 2. We focus on dynamical evolution of fluid features, kinetic energy dissipation, and mixing of the fluid between the two layers, considering their dependence on magnetic field strength for this geometry. There are a number of differences from our earlier simulations with uniform magnetic fields in the x-y plane. For the latter, simpler case we found a clear sequence of behaviors with increasing field strength ranging from nearly hydrodynamic flows in which the instability evolves to an almost steady cat's eye vortex with enhanced dissipation, to flows in which the magnetic field disrupts the cat's eye once it forms, to, finally, flows that evolve very little before field-line stretching stabilizes the velocity shear layer. The introduction of magnetic shear can allow a cat's eye-like vortex to form, even when the field is stronger than the nominal linear instability limit given above. For strong fields that vortex is asymmetric with respect to the preliminary shear layer, however, so the subsequent dissipation is enhanced over the uniform field cases of comparable field strength. In fact, so long as the magnetic field achieves some level of dynamical importance during an eddy turnover time, the asymmetries introduced through the magnetic shear will increase flow complexity and, with that, dissipation and mixing. The degree of the fluid mixing between the two layers is strongly influenced by the magnetic field strength. Mixing of the fluid is most effective when the vortex is disrupted by magnetic tension during transient reconnection, through local chaotic behavior that follows.

Signal-to-noise ratio, T2 , and T2* for hyperpolarized helium-3 MRI of the human lung at three magnetic field strengths.

PubMed

Komlosi, Peter; Altes, Talissa A; Qing, Kun; Mooney, Karen E; Miller, G Wilson; Mata, Jaime F; de Lange, Eduard E; Tobias, William A; Cates, Gordon D; Mugler, John P

2017-10-01

To evaluate T 2 , T2*, and signal-to-noise ratio (SNR) for hyperpolarized helium-3 ( 3 He) MRI of the human lung at three magnetic field strengths ranging from 0.43T to 1.5T. Sixteen healthy volunteers were imaged using a commercial whole body scanner at 0.43T, 0.79T, and 1.5T. Whole-lung T 2 values were calculated from a Carr-Purcell-Meiboom-Gill spin-echo-train acquisition. T2* maps and SNR were determined from dual-echo and single-echo gradient-echo images, respectively. Mean whole-lung SNR values were normalized by ventilated lung volume and administered 3 He dose. As expected, T 2 and T2* values demonstrated a significant inverse relationship to field strength. Hyperpolarized 3 He images acquired at all three field strengths had comparable SNR values and thus appeared visually very similar. Nonetheless, the relatively small SNR differences among field strengths were statistically significant. Hyperpolarized 3 He images of the human lung with similar image quality were obtained at three field strengths ranging from 0.43T and 1.5T. The decrease in susceptibility effects at lower fields that are reflected in longer T 2 and T2* values may be advantageous for optimizing pulse sequences inherently sensitive to such effects. The three-fold increase in T2* at lower field strength would allow lower receiver bandwidths, providing a concomitant decrease in noise and relative increase in SNR. Magn Reson Med 78:1458-1463, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Modal energy analysis for mechanical systems excited by spatially correlated loads

NASA Astrophysics Data System (ADS)

Zhang, Peng; Fei, Qingguo; Li, Yanbin; Wu, Shaoqing; Chen, Qiang

2018-10-01

MODal ENergy Analysis (MODENA) is an energy-based method, which is proposed to deal with vibroacoustic problems. The performance of MODENA on the energy analysis of a mechanical system under spatially correlated excitation is investigated. A plate/cavity coupling system excited by a pressure field is studied in a numerical example, in which four kinds of pressure fields are involved, which include the purely random pressure field, the perfectly correlated pressure field, the incident diffuse field, and the turbulent boundary layer pressure fluctuation. The total energies of subsystems differ to reference solution only in the case of purely random pressure field and only for the non-excited subsystem (the cavity). A deeper analysis on the scale of modal energy is further conducted via another numerical example, in which two structural modes excited by correlated forces are coupled with one acoustic mode. A dimensionless correlation strength factor is proposed to determine the correlation strength between modal forces. Results show that the error on modal energy increases with the increment of the correlation strength factor. A criterion is proposed to establish a link between the error and the correlation strength factor. According to the criterion, the error is negligible when the correlation strength is weak, in this situation the correlation strength factor is less than a critical value.

Attosecond pulse carrier-envelope phase effects on ionized electron momentum and energy distributions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, L.-Y.; Starace, Anthony F.

2007-10-15

We analyze carrier-envelope phase (CEP) effects on electron wave-packet momentum and energy spectra produced by one or two few-cycle attosecond xuv pulses. The few-cycle attosecond pulses are assumed to have arbitrary phases. We predict CEP effects on ionized electron wave-packet momentum distributions produced by attosecond pulses having durations comparable to those obtained by Sansone et al. [Science 314, 443 (2006)]. The onset of significant CEP effects is predicted to occur for attosecond pulse field strengths close to those possible with current experimental capabilities. Our results are based on single-active-electron solutions of the three-dimensional, time-dependent Schroedinger equation including atomic potentials appropriatemore » for the H and He atoms.« less

Global three-dimensional simulation of Earth's dayside reconnection using a two-way coupled magnetohydrodynamics with embedded particle-in-cell model: initial results: 3D MHD-EPIC simulation of magnetosphere

DOE PAGES

Chen, Yuxi; Tóth, Gábor; Cassak, Paul; ...

2017-09-18

Here, we perform a three-dimensional (3D) global simulation of Earth's magnetosphere with kinetic reconnection physics to study the flux transfer events (FTEs) and dayside magnetic reconnection with the recently developed magnetohydrodynamics with embedded particle-in-cell model (MHD-EPIC). During the one-hour long simulation, the FTEs are generated quasi-periodically near the subsolar point and move toward the poles. We also find the magnetic field signature of FTEs at their early formation stage is similar to a ‘crater FTE’, which is characterized by a magnetic field strength dip at the FTE center. After the FTE core field grows to a significant value, it becomesmore » an FTE with typical flux rope structure. When an FTE moves across the cusp, reconnection between the FTE field lines and the cusp field lines can dissipate the FTE. The kinetic features are also captured by our model. A crescent electron phase space distribution is found near the reconnection site. A similar distribution is found for ions at the location where the Larmor electric field appears. The lower hybrid drift instability (LHDI) along the current sheet direction also arises at the interface of magnetosheath and magnetosphere plasma. Finally, the LHDI electric field is about 8 mV/m and its dominant wavelength relative to the electron gyroradius agrees reasonably with MMS observations.« less

Global three-dimensional simulation of Earth's dayside reconnection using a two-way coupled magnetohydrodynamics with embedded particle-in-cell model: initial results: 3D MHD-EPIC simulation of magnetosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yuxi; Tóth, Gábor; Cassak, Paul

Here, we perform a three-dimensional (3D) global simulation of Earth's magnetosphere with kinetic reconnection physics to study the flux transfer events (FTEs) and dayside magnetic reconnection with the recently developed magnetohydrodynamics with embedded particle-in-cell model (MHD-EPIC). During the one-hour long simulation, the FTEs are generated quasi-periodically near the subsolar point and move toward the poles. We also find the magnetic field signature of FTEs at their early formation stage is similar to a ‘crater FTE’, which is characterized by a magnetic field strength dip at the FTE center. After the FTE core field grows to a significant value, it becomesmore » an FTE with typical flux rope structure. When an FTE moves across the cusp, reconnection between the FTE field lines and the cusp field lines can dissipate the FTE. The kinetic features are also captured by our model. A crescent electron phase space distribution is found near the reconnection site. A similar distribution is found for ions at the location where the Larmor electric field appears. The lower hybrid drift instability (LHDI) along the current sheet direction also arises at the interface of magnetosheath and magnetosphere plasma. Finally, the LHDI electric field is about 8 mV/m and its dominant wavelength relative to the electron gyroradius agrees reasonably with MMS observations.« less

Bonded-cell model for particle fracture.

PubMed

Nguyen, Duc-Hanh; Azéma, Emilien; Sornay, Philippe; Radjai, Farhang

2015-02-01

Particle degradation and fracture play an important role in natural granular flows and in many applications of granular materials. We analyze the fracture properties of two-dimensional disklike particles modeled as aggregates of rigid cells bonded along their sides by a cohesive Mohr-Coulomb law and simulated by the contact dynamics method. We show that the compressive strength scales with tensile strength between cells but depends also on the friction coefficient and a parameter describing cell shape distribution. The statistical scatter of compressive strength is well described by the Weibull distribution function with a shape parameter varying from 6 to 10 depending on cell shape distribution. We show that this distribution may be understood in terms of percolating critical intercellular contacts. We propose a random-walk model of critical contacts that leads to particle size dependence of the compressive strength in good agreement with our simulation data.

Terahertz radiation generation by beating of two laser beams in a collisional plasma with oblique magnetic field

NASA Astrophysics Data System (ADS)

Hematizadeh, Ayoob; Jazayeri, Seyed Masud; Ghafary, Bijan

2018-02-01

A scheme for excitation of terahertz (THz) radiation is presented by photo mixing of two super-Gaussian laser beams in a rippled density collisional magnetized plasma. Lasers having different frequencies and wave numbers but the same electric fields create a ponderomotive force on the electrons of plasma in the beating frequency. Super-Gaussian laser beam has the exclusive features such as steep gradient in laser intensity distribution, wider cross-section in comparison with Gaussian profiles, which make stronger ponderomotive force and higher THz radiation. The magnetic field is considered oblique to laser beams propagation direction; in this case, depending on the phase matching conditions different mode waves can propagate in plasma. It is found that amplitude and efficiency of the emitted THz radiation not only are sensitive to the beating frequency, collision frequency, and magnetic field strength but to the angle between laser beams and static magnetic field. The efficiency of THz radiation can be optimized in a certain angle.

Construction and Performance of a Superconducting Multipole Wiggler

NASA Astrophysics Data System (ADS)

Hwang, C. S.; Wang, B.; Chen, J. Y.; Chang, C. H.; Chen, H. H.; Fan, T. C.; Lin, F. Y.; Huang, M. H.; Chang, C. C.; Hsu, S. N.; Hsiung, G. Y.; Hsu, K. T.; Chen, J.; Chien, Y. C.; Chen, J. R.; Chen, C. T.

2004-05-01

A 3.2 Tesla superconducting multipole wiggler was designed and fabricated as an X-ray source. The magnet assembly, which consists of 32 pairs of racetrack NbTi superconducting coils with a periodic length of 60 mm, provides 28 effective poles. A 1.4056 m long elliptical cold-bore stainless steel beam duct with taper flanges and a wall thickness of 1 mm, was developed and constructed to fit the ultra-high vacuum condition for electron beam. The magnetic field strength was measured in liquid helium using a cryogenic Hall probe, revealing a field behavior very close to behavior consistent with the designed values. A Hall generator and the stretch wire methods are used to determine the transfer function of the peak field, the first and second integrated field distributions, and the good field region of the magnet. The quench protection of the magnet, the control algorithm for automatic filling of liquid helium, and the boil off rate of liquid helium and liquid nitrogen will also be discussed.

Computer program documentation for a subcritical wing design code using higher order far-field drag minimization

NASA Technical Reports Server (NTRS)

Kuhlman, J. M.; Shu, J. Y.

1981-01-01

A subsonic, linearized aerodynamic theory, wing design program for one or two planforms was developed which uses a vortex lattice near field model and a higher order panel method in the far field. The theoretical development of the wake model and its implementation in the vortex lattice design code are summarized and sample results are given. Detailed program usage instructions, sample input and output data, and a program listing are presented in the Appendixes. The far field wake model assumes a wake vortex sheet whose strength varies piecewise linearly in the spanwise direction. From this model analytical expressions for lift coefficient, induced drag coefficient, pitching moment coefficient, and bending moment coefficient were developed. From these relationships a direct optimization scheme is used to determine the optimum wake vorticity distribution for minimum induced drag, subject to constraints on lift, and pitching or bending moment. Integration spanwise yields the bound circulation, which is interpolated in the near field vortex lattice to obtain the design camber surface(s).

Regional-Scale Surface Magnetic Fields and Proton Fluxes to Mercury's Surface from Proton-Reflection Magnetometry

NASA Astrophysics Data System (ADS)

Winslow, R. M.; Johnson, C. L.; Anderson, B. J.; Gershman, D. J.; Raines, J. M.; Lillis, R. J.; Korth, H.; Slavin, J. A.; Solomon, S. C.; Zurbuchen, T.

2014-12-01

The application of a recently developed proton-reflection magnetometry technique to MESSENGER spacecraft observations at Mercury has yielded two significant findings. First, loss-cone observations directly confirm particle precipitation to Mercury's surface and indicate that solar wind plasma persistently bombards the planet not only in the magnetic cusp regions but over a large fraction of the southern hemisphere. Second, the inferred surface field strengths independently confirm the north-south asymmetry in Mercury's global magnetic field structure first documented from observations of magnetic equator crossings. Here we extend this work with 1.5 additional years of observations (i.e., to 2.5 years in all) to further probe Mercury's surface magnetic field and better resolve proton flux precipitation to the planet's surface. We map regions where proton loss cones are observed; these maps indicate regions where protons precipitate directly onto the surface. The augmentation of our data set over that used in our original study allows us to examine the proton loss cones in cells of dimension 10° latitude by 20° longitude in Mercury body-fixed coordinates. We observe a transition from double-sided to single-sided loss cones in the pitch-angle distributions; this transition marks the boundary between open and closed field lines. At the surface this boundary lies between 60° and 70°N. Our observations allow the estimation of surface magnetic field strengths in the northern cusp region and the calculation of incident proton fluxes to both hemispheres. In the northern cusp, our regional-scale observations are consistent with an offset dipole field and a dipole moment of 190 nT RM3, where RM is Mercury's radius, implying that any regional-scale variations in surface magnetic field strengths are either weak relative to the dipole field or occur at length scales smaller than the resolution of our observations (~300 km). From the global proton flux map (north of 40° S) derived from proton loss-cone measurements, we find an increase in proton flux near 0° and 180° planetary longitudes. This pattern is consistent with that expected from the combined effects of increased incident solar wind density at these longitudes at local noon (given the 3:2 spin-orbit resonance of Mercury) and phasing of MESSENGER's orbit.

Tu(r)ning weakness to strength: Mechanomutable bioinspired materials

DTIC Science & Technology

2017-04-03

into Strength,” Bio-inspired Materials, Potsdam, Germany March 2012 - “Nonlinear behaviour of silk minimizes damage and begets spider web robustness...atoms to structures – how spiders turn weakness into strength,” Society of Engineering Science Meeting, Atlanta, GA Keynote Lecture October 2012...Georgia Tech, October 19, 2015, Atlanta, GA October 2015 DISTRIBUTION A: Distribution approved for public release. 8 - "Multiscale materials by

SU-E-T-590: Optimizing Magnetic Field Strengths with Matlab for An Ion-Optic System in Particle Therapy Consisting of Two Quadrupole Magnets for Subsequent Simulations with the Monte-Carlo Code FLUKA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baumann, K; Weber, U; Simeonov, Y

Purpose: Aim of this study was to optimize the magnetic field strengths of two quadrupole magnets in a particle therapy facility in order to obtain a beam quality suitable for spot beam scanning. Methods: The particle transport through an ion-optic system of a particle therapy facility consisting of the beam tube, two quadrupole magnets and a beam monitor system was calculated with the help of Matlab by using matrices that solve the equation of motion of a charged particle in a magnetic field and field-free region, respectively. The magnetic field strengths were optimized in order to obtain a circular andmore » thin beam spot at the iso-center of the therapy facility. These optimized field strengths were subsequently transferred to the Monte-Carlo code FLUKA and the transport of 80 MeV/u C12-ions through this ion-optic system was calculated by using a user-routine to implement magnetic fields. The fluence along the beam-axis and at the iso-center was evaluated. Results: The magnetic field strengths could be optimized by using Matlab and transferred to the Monte-Carlo code FLUKA. The implementation via a user-routine was successful. Analyzing the fluence-pattern along the beam-axis the characteristic focusing and de-focusing effects of the quadrupole magnets could be reproduced. Furthermore the beam spot at the iso-center was circular and significantly thinner compared to an unfocused beam. Conclusion: In this study a Matlab tool was developed to optimize magnetic field strengths for an ion-optic system consisting of two quadrupole magnets as part of a particle therapy facility. These magnetic field strengths could subsequently be transferred to and implemented in the Monte-Carlo code FLUKA to simulate the particle transport through this optimized ion-optic system.« less

Electromagnetic-field effects on structure and dynamics of amyloidogenic peptides

NASA Astrophysics Data System (ADS)

Todorova, Nevena; Bentvelzen, Alan; English, Niall J.; Yarovsky, Irene

2016-02-01

Electromagnetic fields (EMFs) are ever-present, and so is the need to better understand their influence on human health and biological matter in general. The interaction between a molecular system and external EMF can alter the structure, and dynamical behaviour, and, hence, biological function of proteins with uncertain health consequences. This urges a detailed investigation of EMF-induced effects on basic protein biophysics. Here, we used all-atom non-equilibrium molecular dynamics simulations to understand and quantify the response mechanisms of the amyloidogenic apoC-II(60-70) peptides to non-ionising radiation by modelling their behaviour under external electromagnetic and electric fields of different strengths. Our simulations show high strength fields (>0.04 V/nm) cause structural changes in apoC-II(60-70) due to the peptide dipole alignment along the applied field direction, which disrupts the inherent β-hairpin conformation known to be the intermediate state for fibril formation. The intermediate field-strength range (0.04-0.004 V/nm) causes a significant acceleration in peptide dynamics, which leads to the increased population of structures with fibril-inhibiting characteristics, such as the separated N- and C-termini and colocation of the aromatic residues at the same peptide face. In contrast, lower field strengths (<0.004 V/nm) promote the formation of the amyloid-prone hairpin structures relative to the ambient conditions. These findings suggest that intermediate-strength electromagnetic fields could be considered for designing alternative treatments of amyloid diseases, while the very high and low field strengths could be employed for engineering well-ordered fibrillar aggregates for non-medicinal applications.

A Multiscale Progressive Failure Modeling Methodology for Composites that Includes Fiber Strength Stochastics

NASA Technical Reports Server (NTRS)

Ricks, Trenton M.; Lacy, Thomas E., Jr.; Bednarcyk, Brett A.; Arnold, Steven M.; Hutchins, John W.

2014-01-01

A multiscale modeling methodology was developed for continuous fiber composites that incorporates a statistical distribution of fiber strengths into coupled multiscale micromechanics/finite element (FE) analyses. A modified two-parameter Weibull cumulative distribution function, which accounts for the effect of fiber length on the probability of failure, was used to characterize the statistical distribution of fiber strengths. A parametric study using the NASA Micromechanics Analysis Code with the Generalized Method of Cells (MAC/GMC) was performed to assess the effect of variable fiber strengths on local composite failure within a repeating unit cell (RUC) and subsequent global failure. The NASA code FEAMAC and the ABAQUS finite element solver were used to analyze the progressive failure of a unidirectional SCS-6/TIMETAL 21S metal matrix composite tensile dogbone specimen at 650 degC. Multiscale progressive failure analyses were performed to quantify the effect of spatially varying fiber strengths on the RUC-averaged and global stress-strain responses and failure. The ultimate composite strengths and distribution of failure locations (predominately within the gage section) reasonably matched the experimentally observed failure behavior. The predicted composite failure behavior suggests that use of macroscale models that exploit global geometric symmetries are inappropriate for cases where the actual distribution of local fiber strengths displays no such symmetries. This issue has not received much attention in the literature. Moreover, the model discretization at a specific length scale can have a profound effect on the computational costs associated with multiscale simulations.models that yield accurate yet tractable results.

A dynamics prediction of nitromethane → methyl nitrite isomerization in external electric field.

PubMed

Ren, Fu-de; Cao, Duan-lin; Shi, Wen-jing

2016-04-01

As a follow-up to our investigation into the effect of external electric field on the chemical bond strength, the effects of external electric field on the CH3NO2 → CH3ONO isomerization dynamics were investigated using the MP2/6-311++G(2d,p) and CCSD/6-311++G(2d,p) methods. The rate constants in the absence and presence of various field strengths were calculated. The results show that, when the field strength is larger than +0.0060 a.u. along the C-NO2 bond axis, the barriers of the isomerization are lower than the C-NO2 bond dissociation energies, leading to the preferences of the isomerization over the C-NO2 bond dissociation. In this case, the sensitivities are higher than that in no field. However, in the other fields, the C-NO2 bond scission is favored and the sensitivities are almost equal to that in no field. Several good linear correlations are found between the field strengths and the changes of the bond lengths or corresponding electron densities.

47 CFR 2.1053 - Measurements required: Field strength of spurious radiation.

Code of Federal Regulations, 2010 CFR

2010-10-01

.... For equipment operating on frequencies below 890 MHz, an open field test is normally required, with... either impractical or impossible to make open field measurements (e.g. a broadcast transmitter installed... 47 Telecommunication 1 2010-10-01 2010-10-01 false Measurements required: Field strength of...

Gamow-Teller strength observed in the 48Ti(n, p) 48Sc reaction: Implications for the double beta decay of 48Ca

NASA Astrophysics Data System (ADS)

Alford, W. P.; Helmer, R. L.; Abegg, R.; Celler, A.; Frekers, D.; Green, P.; Häusser, O.; Henderson, R.; Hicks, K.; Jackson, K. P.; Jeppesen, R.; Miller, C. A.; Trudel, A.; Vetterli, M.; Yen, S.; Pourang, R.; Watson, J.; Brown, B. A.; Engel, J.

1990-07-01

Cross sections for the 48Ti(n, p) reaction have been measured at angles of 0°, 6°, and 12° at an energy of 200 MeV. The measurements are compared with results of DWIA calculations to obtain estimates of transition strengths for L = 0, 1, and ⩾2 up to an excitation energy of 25 MeV. Gamow-Teller strength ( L = 0) is peaked between 3 and 4 MeV excitation energy, with a significant distribution extending to about 12 MeV. The L = 1 strength is found mainly between 6 and 20 MeV while the cross section for transitions with L ⩾2 increases from 10 MeV to the upper limit of the measurements. The distribution of Gamow-Teller strength is in poor agreement with theoretical distributions used to calculate the lifetime for double beta decay of 48Ca.

Effects Of Electric Field On Hydrocarbon-Fueled Flames

NASA Technical Reports Server (NTRS)

Yuan, Z.-G.; Hegde, U.

2003-01-01

It has been observed that flames are susceptible to electric fields that are much weaker than the breakdown field strength of the flame gases. When an external electric field is imposed on a flame, the ions generated in the flame reaction zone drift in the direction of the electric forces exerted on them. The moving ions collide with the neutral species and change the velocity distribution in the affected region. This is often referred to as ionic wind effect. In addition, the removal of ions from the flame reaction zone can alter the chemical reaction pathway of the flame. On the other hand, the presence of space charges carried by moving ions affects the electric field distribution. As a result, the flame often changes its shape, location and color once an external electric field is applied. The interplay between the flame movement and the change of electric field makes it difficult to determine the flame location for a given configuration of electrodes and fuel source. In normal gravity, the buoyancy-induced flow often complicates the problem and hinders detailed study of the interaction between the flame and the electric field. In this work, the microgravity environment established at the 2.2 Second Drop Tower at the NASA Glenn Research Center is utilized to effectively remove the buoyant acceleration. The interaction between the flame and the electric field is studied in a one-dimensional domain. A specially designed electrode makes flame current measurements possible; thus, the mobility of ions, ion density, and ionic wind effect can be evaluated.

Attachment strength of the subtidal seaweed Sargassum horneri (Turner) C. Agardh varies among development stages and depths.

PubMed

Xu, Min; Sakamoto, Shingo; Komatsu, Teruhisa

2016-01-01

Sargassum horneri is one of the most important contributors to the rafts of floating seaweed in the waters off the coasts of northeastern Asia. These rafts serve as spawning and nursery grounds for many marine organisms, including Japanese saury and yellowtail. Thus, the details of the attachment/detachment mechanisms of S. horneri are of commercial significance for the aquaculture industry. Here, we describe variations in the attachment strength of S. horneri as it relates to its developmental stage and depth along a bottom gradient. We measured the attachment strength/dislodgement force of S. horneri samples with holdfast detachment in Shidagaura Cove, Shimoda, Japan, from December 2014 to May 2015. After we had determined the dislodgement forces required to detach thalli from the substratum (using a spring scale device) in the field, we transferred released individuals to the laboratory and measured selected morphological traits. Attachment strength was linearly related to the holdfast basal area when thalli were immature (prior to mid-March), but not when they were mature (mid-March to May). Thus, attachment strength was maintained through the reproductive phase and declined thereafter, allowing released thalli to join the drifting raft community. Rafting may be a mechanism by which the species expands its distribution range, as floating thalli continuing to shed germlings that are able to recruit when suitable habitat is encountered. Attachment strengths were greater in the shallows than in deeper water, reflecting the differences in wave forces experienced at different depths.

Computational micromechanics of dynamic compressive loading of a brittle polycrystalline material using a distribution of grain boundary properties

NASA Astrophysics Data System (ADS)

Kraft, R. H.; Molinari, J. F.; Ramesh, K. T.; Warner, D. H.

A two-dimensional finite element model is used to investigate compressive loading of a brittle ceramic. Intergranular cracking in the microstructure is captured explicitly by using a distribution of cohesive interfaces. The addition of confining stress increases the maximum strength and if high enough, can allow the effective material response to reach large strains before failure. Increasing the friction at the grain boundaries also increases the maximum strength until saturation of the strength is approached. Above a transitional strain rate, increasing the rate-of-deformation also increases the strength and as the strain rate increases, fragment sizes of the damaged specimen decrease. The effects of flaws within the specimen were investigated using a random distribution at various initial flaw densities. The model is able to capture an effective modulus change and degradation of strength as the initial flaw density increases. Effects of confinement, friction, and spatial distribution of flaws seem to depend on the crack coalescence and dilatation of the specimen, while strain-rate effects are result of inertial resistance to motion.

Uncertainties in obtaining high reliability from stress-strength models

NASA Technical Reports Server (NTRS)

Neal, Donald M.; Matthews, William T.; Vangel, Mark G.

1992-01-01

There has been a recent interest in determining high statistical reliability in risk assessment of aircraft components. The potential consequences are identified of incorrectly assuming a particular statistical distribution for stress or strength data used in obtaining the high reliability values. The computation of the reliability is defined as the probability of the strength being greater than the stress over the range of stress values. This method is often referred to as the stress-strength model. A sensitivity analysis was performed involving a comparison of reliability results in order to evaluate the effects of assuming specific statistical distributions. Both known population distributions, and those that differed slightly from the known, were considered. Results showed substantial differences in reliability estimates even for almost nondetectable differences in the assumed distributions. These differences represent a potential problem in using the stress-strength model for high reliability computations, since in practice it is impossible to ever know the exact (population) distribution. An alternative reliability computation procedure is examined involving determination of a lower bound on the reliability values using extreme value distributions. This procedure reduces the possibility of obtaining nonconservative reliability estimates. Results indicated the method can provide conservative bounds when computing high reliability. An alternative reliability computation procedure is examined involving determination of a lower bound on the reliability values using extreme value distributions. This procedure reduces the possibility of obtaining nonconservative reliability estimates. Results indicated the method can provide conservative bounds when computing high reliability.

Effect of loading orientations on the microstructure and property of Al−Cu single crystal during stress aging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jiqiang; Chen, Zhiguo, E-mail: zgchen@mail.csu.edu.cn; Hunan University of Humanities, Science and Technology, Loudi 417000

The precipitation behavior and property of Al−Cu alloy during stress aging under various loading orientations were investigated using single crystals. The resulting microstructures and the strength property were examined by transmission electron microscope (TEM) and compression test, respectively, and the effect of the distribution of θ′-plates on strength property were discussed. The results show that the precipitation distribution of θ′ was significantly affected by the loading orientation during stress aging of Al−Cu single crystals. Loading along close to 〈011〉{sub Al} directions provided more uniform precipitation distribution of θ′ as compared to loading along close to 〈001〉{sub Al} directions, and thereforemore » provided higher strengthening stress of the θ′-plates for the stress aging sample. The results suggested that regulating the distribution of θ′ and therefore improving strength property are possible via controlling the loading orientation during stress aging. - Highlights: • We studied the effect of loading directions on stress aging of Al−Cu single crystal. • Precipitation distribution of θ′ was noticeably affected by the loading direction. • Loading along close to 〈011〉{sub Al} directions reduced the stress-orienting effect. • The strength property is closely related to the precipitation distribution of θ′. • It is possible to regulate the distribution of θ′ and improve strength property.« less

Optical sensor of magnetic fields

DOEpatents

Butler, M.A.; Martin, S.J.

1986-03-25

An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.

Exploiting broad-area surface emitting lasers to manifest the path-length distributions of finite-potential quantum billiards.

PubMed

Yu, Y T; Tuan, P H; Chang, K C; Hsieh, Y H; Huang, K F; Chen, Y F

2016-01-11

Broad-area vertical-cavity surface-emitting lasers (VCSELs) with different cavity sizes are experimentally exploited to manifest the influence of the finite confinement strength on the path-length distribution of quantum billiards. The subthreshold emission spectra of VCSELs are measured to obtain the path-length distributions by using the Fourier transform. It is verified that the number of the resonant peaks in the path-length distribution decreases with decreasing the confinement strength. Theoretical analyses for finite-potential quantum billiards are numerically performed to confirm that the mesoscopic phenomena of quantum billiards with finite confinement strength can be analogously revealed by using broad-area VCSELs.

Design of magnetic Circuit Simulation for Curing Device of Anisotropic MRE

NASA Astrophysics Data System (ADS)

Hapipi, N.; Ubaidillah; Mazlan, S. A.; Widodo, P. J.

2018-03-01

The strength of magnetic field during fabrication of magnetorheological elastomer (MRE) plays a crucial role in order to form a pre-structured MRE. So far, gaussmeter were used to determine the magnetic intensity subjected to the MRE during curing. However, the magnetic flux reading through that measurement considered less accurate. Therefore, a simulation should be done to figure out the magnetic flux concentration around the sample. This paper investigates the simulation of magnetic field distribution in a curing device used during curing stage of anisotropic magnetorheological elastomer (MRE). The target in designing the magnetic circuit is to ensure a sufficient and uniform magnetic field to all the MRE surfaces during the curing process. The magnetic circuit design for the curing device was performed using Finite Element Method Magnetic (FEMM) to examine the magnetic flux density distribution in the device. The material selection was first done instantaneously during a magnetic simulation process. Then, the experimental validation of simulation was performed by measuring and comparing the actual flux generated within the specimen type and the one from the FEMM simulation. İt apparent that the data from FEMM simulation shows an agreement with the actual measurement. Furthermore, the FEMM results showed that the magnetic design is able to provide sufficient and uniform magnetic field all over the surfaces of the MRE.

The effect of turbulence strength on meandering field lines and Solar Energetic Particle event extents

NASA Astrophysics Data System (ADS)

Laitinen, Timo; Effenberger, Frederic; Kopp, Andreas; Dalla, Silvia

2018-02-01

Insights into the processes of Solar Energetic Particle (SEP) propagation are essential for understanding how solar eruptions affect the radiation environment of near-Earth space. SEP propagation is influenced by turbulent magnetic fields in the solar wind, resulting in stochastic transport of the particles from their acceleration site to Earth. While the conventional approach for SEP modelling focuses mainly on the transport of particles along the mean Parker spiral magnetic field, multi-spacecraft observations suggest that the cross-field propagation shapes the SEP fluxes at Earth strongly. However, adding cross-field transport of SEPs as spatial diffusion has been shown to be insufficient in modelling the SEP events without use of unrealistically large cross-field diffusion coefficients. Recently, Laitinen et al. [ApJL 773 (2013b); A&A 591 (2016)] demonstrated that the early-time propagation of energetic particles across the mean field direction in turbulent fields is not diffusive, with the particles propagating along meandering field lines. This early-time transport mode results in fast access of the particles across the mean field direction, in agreement with the SEP observations. In this work, we study the propagation of SEPs within the new transport paradigm, and demonstrate the significance of turbulence strength on the evolution of the SEP radiation environment near Earth. We calculate the transport parameters consistently using a turbulence transport model, parametrised by the SEP parallel scattering mean free path at 1 AU, λ∥*, and show that the parallel and cross-field transport are connected, with conditions resulting in slow parallel transport corresponding to wider events. We find a scaling σφ,max∝(1/λ∥*)1/4 for the Gaussian fitting of the longitudinal distribution of maximum intensities. The longitudes with highest intensities are shifted towards the west for strong scattering conditions. Our results emphasise the importance of understanding both the SEP transport and the interplanetary turbulence conditions for modelling and predicting the SEP radiation environment at Earth.

Influence of Welding Strength Matching Coefficient and Cold Stretching on Welding Residual Stress in Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Lu, Yaqing; Hui, Hu; Gong, Jianguo

2018-05-01

Austenitic stainless steel is widely used in pressure vessels for the storage and transportation of liquid gases such as liquid nitrogen, liquid oxygen, and liquid hydrogen. Cryogenic pressure vessel manufacturing uses cold stretching technology, which relies heavily on welding joint performance, to construct lightweight and thin-walled vessels. Residual stress from welding is a primary factor in cases of austenitic stainless steel pressure vessel failure. In this paper, on the basis of Visual Environment 10.0 finite element simulation technology, the residual stress resulting from different welding strength matching coefficients (0.8, 1, 1.2, 1.4) for two S30408 plates welded with three-pass butt welds is calculated according to thermal elastoplastic theory. In addition, the stress field was calculated under a loading as high as 410 MPa and after the load was released. Path 1 was set to analyze stress along the welding line, and path 2 was set to analyze stress normal to the welding line. The welding strength matching coefficient strongly affected both the longitudinal residual stress (center of path 1) and the transverse residual stress (both ends of path 1) after the welding was completed. However, the coefficient had little effect on the longitudinal and transverse residual stress of path 2. Under the loading of 410 MPa, the longitudinal and transverse stress decreased and the stress distribution, with different welding strength matching coefficients, was less diverse. After the load was released, longitudinal and transverse stress distribution for both path 1 and path 2 decreased to a low level. Cold stretching could reduce the effect of residual stress to various degrees. Transverse strain along the stretching direction was also taken into consideration. The experimental results validated the reliability of the partial simulation.

Dynamics of yield-stress droplets: Morphology of impact craters

NASA Astrophysics Data System (ADS)

Neufeld, Jerome; Sohr, David; Ferrari, Leo; Dalziel, Stuart

2017-11-01

Yield strength can play an important role for the dynamics of droplets impacting on surfaces, whether at the industrial or planetary scale, and can capture a zoo of impact crater morphologies, from simple parabolic craters, to more complex forms with forms with, for example, multiple rings, central peaks. Here we show that the morphology of planetary impact craters can be reproduced in the laboratory using carbopol, a transparent yield-stress fluid, as both impactor and bulk fluid. Using high-speed video photography, we characterise the universal, transient initial excavation stage of impact and show the dependence of the subsequent relaxation to final crater morphology on impactor size, impact speed and yield stress. To further interrogate our laboratory impacts, we dye our impactor to map its final distribution and use particle tracking to determine the flow fields during impact and the maximal extent of the yield surface. We characterise the flow-fields induced during impact, and the maximal extent of the yield surface, by tracking particles within the bulk fluid and map the distribution of impactor and bulk by tracing the final distribution of dyed impactor. The results of laboratory impact droplets are used to infer the properties of planetary impactors, and aid in inter.

Predicting the tensile strength of A UD basalt/ epoxy composite used for the confinement of concrete structures

NASA Astrophysics Data System (ADS)

Ciniņa, I.; Zīle, O.; Andersons, J.

2013-01-01

The principal aim of the present research was to predict the strength of UD basalt fiber/epoxy matrix composites in tension along the reinforcement direction. Tension tests on single basalt fibers were performed to determine the functional form of their strength distribution and to evaluate the parameters of the distribution. Also, microbond tests were carried out to assess the interfacial shear strength of the fibers and polymer matrix. UD composite specimens were produced and tested for the longitudinal tensile strength. The predicted strength of the composite was found to exceed the experimental values by ca. 20%, which can be explained by imperfections in the fiber alignment, impregnation, and adhesion in the composite specimens.

Results of duct area ratio changes in the NASA Lewis H2-O2 combustion MHD experiment

NASA Technical Reports Server (NTRS)

Smith, J. M.

1979-01-01

MHD power generation experiments utilizing a cesium-seeded H2-O2 working fluid were carried out using a diverging area Hall duct having an entrance Mach number of 2. The experiments were conducted in a high field strength cryomagnet facility at field strengths up to 5 tesla. The effects of power takeoff location, generator loading B field strength, and electrode breakdown voltage were investigated. The effect of area ratio, multiple loading of the duct, and duct location within the magnetic field are considered.

Discrete disorder models for many-body localization

NASA Astrophysics Data System (ADS)

Janarek, Jakub; Delande, Dominique; Zakrzewski, Jakub

2018-04-01

Using exact diagonalization technique, we investigate the many-body localization phenomenon in the 1D Heisenberg chain comparing several disorder models. In particular we consider a family of discrete distributions of disorder strengths and compare the results with the standard uniform distribution. Both statistical properties of energy levels and the long time nonergodic behavior are discussed. The results for different discrete distributions are essentially identical to those obtained for the continuous distribution, provided the disorder strength is rescaled by the standard deviation of the random distribution. Only for the binary distribution significant deviations are observed.

ELF Field Strength Measurements Made in Connecticut During 1974

DTIC Science & Technology

1975-10-01

Ionospheric Phenomena on Extremely Low Frequency ( ELF ) Propagation," IEEE Transactions on Communications , vol. COM-22, no. 4, 1974, pp. 484-492...34f" ""WW" I I W»*-«P ’^ AD-A016 795 ELF FIELD STRENGTH MEASUREMENTS MADE IN CONNECTICUT DURING 1974 Peter R. Bannister...Report 4927 CD rH O ELF Field Strength Measurements Made In Connecticut During 1974 PETER R. BANNISTER FREDERICK J. WILLIAMS Submarin

Technique for Predicting the RF Field Strength Inside an Enclosure

NASA Technical Reports Server (NTRS)

Hallett, M.; Reddell, J.

1998-01-01

This Memorandum presents a simple analytical technique for predicting the RF electric field strength inside an enclosed volume in which radio frequency radiation occurs. The technique was developed to predict the radio frequency (RF) field strength within a launch vehicle's fairing from payloads launched with their telemetry transmitters radiating and to the impact of the radiation on the vehicle and payload. The RF field strength is shown to be a function of the surface materials and surface areas. The method accounts for RF energy losses within exposed surfaces, through RF windows, and within multiple layers of dielectric materials which may cover the surfaces. This Memorandum includes the rigorous derivation of all equations and presents examples and data to support the validity of the technique.

Combustion behaviors of GO2/GH2 swirl-coaxial injector using non-intrusive optical diagnostics

NASA Astrophysics Data System (ADS)

GuoBiao, Cai; Jian, Dai; Yang, Zhang; NanJia, Yu

2016-06-01

This research evaluates the combustion behaviors of a single-element, swirl-coaxial injector in an atmospheric combustion chamber with gaseous oxygen and gaseous hydrogen (GO2/GH2) as the propellants. A brief simulated flow field schematic comparison between a shear-coaxial injector and the swirl-coaxial injector reveals the distribution characteristics of the temperature field and streamline patterns. Advanced optical diagnostics, i.e., OH planar laser-induced fluorescence and high-speed imaging, are simultaneously employed to determine the OH radical spatial distribution and flame fluctuations, respectively. The present study focuses on the flame structures under varying O/F mixing ratios and center oxygen swirl intensities. The combined use of several image-processing methods aimed at OH instantaneous images, including time-averaged, root-mean-square, and gradient transformation, provides detailed information regarding the distribution of the flow field. The results indicate that the shear layers anchored on the oxygen injector lip are the main zones of chemical heat release and that the O/F mixing ratio significantly affects the flame shape. Furthermore, with high-speed imaging, an intuitionistic ignition process and several consecutive steady-state images reveal that lean conditions make it easy to drive the combustion instabilities and that the center swirl intensity has a moderate influence on the flame oscillation strength. The results of this study provide a visualized analysis for future optimal swirl-coaxial injector designs.

Effect of Mg and Si co-substitution on microstructure and strength of tricalcium phosphate ceramics.

PubMed

García-Páez, Ismael H; Carrodeguas, Raúl García; De Aza, Antonio H; Baudín, Carmen; Pena, Pilar

2014-02-01

Magnesium and silicon co-doped tricalcium phosphate (TCP) ceramics with compositions corresponding to 0, 5 and 10wt% CaMg(SiO3)2 in the system Ca3(PO4)2-CaMg(SiO3)2 were obtained by conventional sintering of compacted mixtures of Ca3(PO4)2, MgO, SiO2 and CaCO3 powders at temperatures between 1100 and 1450°C. Microstructural analyses were performed by X-ray diffraction and field emission scanning electron microscopy with energy dispersive spectroscopy. Major phases in the obtained ceramics were β- or α+β-tricalcium phosphate containing Mg and Si in solid solution. Certain amounts of liquid were formed during sintering depending on composition and temperature. There were found significant differences in distributions of strength determined by the diametral compression of disc tests (DCDT). Failure strengths were controlled by microstructural defects associated with phase development. Mg and Si additions were found to be effective to improve densification and associated strength of TCP bioceramics due to the enhancement of sintering by the low viscosity liquids formed. The highest density and strength were obtained for the TCP ceramic containing 5wt% CaMg(SiO3)2 sintered at 1300°C. Cracking and porosity increased at higher temperatures due to grain growth and swelling. © 2013 Published by Elsevier Ltd.

Characterization of Silk/Poly 3-Hydroxybutyrate-chitosan-multi-walled Carbon Nanotube Micro-nano Scaffold: A New Hybrid Scaffold for Tissue Engineering Applications.

PubMed

Mirmusavi, Mohammad Hossein; Karbasi, Saeed; Semnani, Dariush; Kharazi, Anousheh Zargar

2018-01-01

Long-term healing tissue engineering scaffolds must hold its full mechanical strength at least for 12 weeks. Nano-micro scaffolds consist of electrospinning nanofibers and textile microfibers to support cell behavior and mechanical strength, respectively. The new nano-micro hybrid scaffold was fabricated by electrospinning poly 3-hydroxybutyrate-chitosan-multi-walled carbon nanotube (MWNT functionalized by COOH) solution on knitted silk in a random manner with different amounts of MWNT. The physical, mechanical, and biodegradation properties were assessed through scanning electron microscopy, Fourier-transform infrared (FTIR) spectroscopy, water contact angle test, tensile strength test, and weight loss test. The scaffold without MWNT was chosen as control sample. An increase in the amount of MWNT up to 1 wt% leads to better fiber diameter distribution, more hydrophilicity, biodegradation rate, and higher tensile strength in comparison with other samples. The porosity percentage of all scaffolds is more than 80%. According to FTIR spectra, the nanofibrous coat on knitted silk did not have any effect on silk fibroin crystallinity structures, and according to tensile strength test, the coat had a significant effect on tensile strength in comparison with pure knitted silk ( P ≤ 0.05). The average fiber diameter decreased due to an increase in electrical conductivity of the solution and fiber stretch in electrical field due to MWNTs. The scaffold containing 1 wt% MWNT was more hydrophilic due to the presence of many COOH groups of functionalized MWNT, thus an increase in the hydrolysis and degradation rate of this sample. High intrinsic tensile strength of MWNTs and improvement of nano-micro interface connection lead to an increase in tensile strength in scaffolds containing MWNT.

Characterization of Silk/Poly 3-Hydroxybutyrate-chitosan-multi-walled Carbon Nanotube Micro-nano Scaffold: A New Hybrid Scaffold for Tissue Engineering Applications

PubMed Central

Mirmusavi, Mohammad Hossein; Karbasi, Saeed; Semnani, Dariush; Kharazi, Anousheh Zargar

2018-01-01

Background: Long-term healing tissue engineering scaffolds must hold its full mechanical strength at least for 12 weeks. Nano-micro scaffolds consist of electrospinning nanofibers and textile microfibers to support cell behavior and mechanical strength, respectively. Methods: The new nano-micro hybrid scaffold was fabricated by electrospinning poly 3-hydroxybutyrate-chitosan-multi-walled carbon nanotube (MWNT functionalized by COOH) solution on knitted silk in a random manner with different amounts of MWNT. The physical, mechanical, and biodegradation properties were assessed through scanning electron microscopy, Fourier-transform infrared (FTIR) spectroscopy, water contact angle test, tensile strength test, and weight loss test. The scaffold without MWNT was chosen as control sample. Results: An increase in the amount of MWNT up to 1 wt% leads to better fiber diameter distribution, more hydrophilicity, biodegradation rate, and higher tensile strength in comparison with other samples. The porosity percentage of all scaffolds is more than 80%. According to FTIR spectra, the nanofibrous coat on knitted silk did not have any effect on silk fibroin crystallinity structures, and according to tensile strength test, the coat had a significant effect on tensile strength in comparison with pure knitted silk (P ≤ 0.05). The average fiber diameter decreased due to an increase in electrical conductivity of the solution and fiber stretch in electrical field due to MWNTs. The scaffold containing 1 wt% MWNT was more hydrophilic due to the presence of many COOH groups of functionalized MWNT, thus an increase in the hydrolysis and degradation rate of this sample. Conclusions: High intrinsic tensile strength of MWNTs and improvement of nano-micro interface connection lead to an increase in tensile strength in scaffolds containing MWNT. PMID:29535924

Coupling of Molecular Emitters and Plasmonic Cavities beyond the Point-Dipole Approximation.

PubMed

Neuman, Tomáš; Esteban, Ruben; Casanova, David; García-Vidal, Francisco J; Aizpurua, Javier

2018-04-11

As the size of a molecular emitter becomes comparable to the dimensions of a nearby optical resonator, the standard approach that considers the emitter to be a point-like dipole breaks down. By adoption of a quantum description of the electronic transitions of organic molecular emitters, coupled to a plasmonic electromagnetic field, we are able to accurately calculate the position-dependent coupling strength between a plasmon and an emitter. The spatial distribution of excitonic and photonic quantum states is found to be a key aspect in determining the dynamics of molecular emission in ultrasmall cavities both in the weak and strong coupling regimes. Moreover, we show that the extreme localization of plasmonic fields leads to the selection rule breaking of molecular excitations.

Kinetic Theory and Fast Wind Observations of the Electron Strahl

NASA Astrophysics Data System (ADS)

Horaites, Konstantinos; Boldyrev, Stanislav; Wilson, Lynn B., III; Viñas, Adolfo F.; Merka, Jan

2017-10-01

Measurements of the electron velocity distribution function (eVDF) in the solar wind exhibit a high-energy, field-aligned beam of electrons, known as the ``strahl''. We develop a kinetic model for the strahl population, based on the solution of the electron drift-kinetic equation at heliospheric distances where the plasma density, temperature, and the strength of the magnetic field decline as power-laws of the distance along a magnetic flux tube. We compare our model with the eVDF measured by the Wind satellite's SWE strahl detector. The model is successful at predicting the angular width of the strahl for the Wind data at 1 AU, in particular, the scaling of the width with particle energy and background density.

PT-1 Plasmoid Thruster Capable of Multi-Mode Operation

NASA Technical Reports Server (NTRS)

Miller, Robert; Rose, Frank; Eskridge, Richard; Martin, Adam; Alam, Mohammed

2008-01-01

This slide presentation reviews the concept of a Plasmoid Thruster that is capable of operating in several different modes. A plasmoid is a compact plasma structure with an integral magnetic field, that may be categorized according to the relative strength of the poloidal and toroidal magnetic fields. A plasmoid thruster would operate by repetitively producing plasmoids that are accelerated to high velocity. The process is inductive, and the magnetic structure of the plasmoid suppresses thermal and mass losses, and improves detachment of the exhaust. The Drive and Bias circuits, the gas distribution, the pre-ionization stage, and the operation sequence are detailed. The advantages of the Plasmoid thruster and the research and technology required for development of this form of propulsion is reviewed.

Mitigation of Electromagnetic Pulse (EMP) Effects from Short-Pulse Lasers and Fusion Neutrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eder, D C; Throop, A; Brown, Jr., C G

2009-03-06

Our research focused on obtaining a fundamental understanding of the source and properties of EMP at the Titan PW(petawatt)-class laser facility. The project was motivated by data loss and damage to components due to EMP, which can limit diagnostic techniques that can be used reliably at short-pulse PW-class laser facilities. Our measurements of the electromagnetic fields, using a variety of probes, provide information on the strength, time duration, and frequency dependence of the EMP. We measure electric field strengths in the 100's of kV/m range, durations up to 100 ns, and very broad frequency response extending out to 5 GHzmore » and possibly beyond. This information is being used to design shielding to mitigate the effects of EMP on components at various laser facilities. We showed the need for well-shielded cables and oscilloscopes to obtain high quality data. Significant work was invested in data analysis techniques to process this data. This work is now being transferred to data analysis procedures for the EMP diagnostics being fielded on the National Ignition Facility (NIF). In addition to electromagnetic field measurements, we measured the spatial and energy distribution of electrons escaping from targets. This information is used as input into the 3D electromagnetic code, EMSolve, which calculates time dependent electromagnetic fields. The simulation results compare reasonably well with data for both the strength and broad frequency bandwidth of the EMP. This modeling work required significant improvements in EMSolve to model the fields in the Titan chamber generated by electrons escaping the target. During dedicated Titan shots, we studied the effects of varying laser energy, target size, and pulse duration on EMP properties. We also studied the effect of surrounding the target with a thick conducting sphere and cube as a potential mitigation approach. System generated EMP (SGEMP) in coaxial cables does not appear to be a significant at Titan. Our results are directly relevant to planned short-pulse ARC (advanced radiographic capability) operation on NIF.« less

Effect of bipolar electric fatigue on polarization switching in lead-zirconate-titanate ceramics

NASA Astrophysics Data System (ADS)

Zhukov, Sergey; Fedosov, Sergey; Glaum, Julia; Granzow, Torsten; Genenko, Yuri A.; von Seggern, Heinz

2010-07-01

From comparison of experimental results on polarization switching in fresh and electrically fatigued lead-zirconate-titanate (PZT) over a wide range of applied fields and switching times it is concluded that fatigue alters the local field distribution inside the sample due to the generation of discrete defects, such as voids and cracks. Such defects have a strong influence on the overall electric field distribution by their shape and dielectric permittivity. On this hypothesis, a new phenomenological model of polarization switching in fatigued PZT is proposed. The model assumes that the fatigued sample can be composed of different local regions which exhibit different field strengths but otherwise can be considered as unfatigued. Consequently the temporal response of a fatigued sample is assumed to be the superposition of the field-dependent temporal responses of unfatigued samples weighted by their respective volume fraction. A certain part of the volume is excluded from the overall switching process due to the domain pinning even at earlier stages of fatigue, which can be recovered by annealing. Suitability of the proposed model is demonstrated by a good correlation between experimental and calculated data for differently fatigued samples. Plausible cause of the formation of such regions is the generation of defects such as microcracks and the change in electrical properties at imperfections such as pores or voids.

Non-equilibrium electron energy distributions in HII regions: Implications for abundance determinations

NASA Astrophysics Data System (ADS)

Dopita, Michael; Nicholls, David

2012-07-01

Although the analysis of HII region emission lines provides the main way of probing the chemical evolution of the universe throughout cosmic time, currently significant (factor of 2) discrepancies exist between the different methods (principally the strong line, electron temperature and recombination line methods) used to calibrate the cosmic chemical abundance scale. Although effects such as temperature fluctuations and geometrical effects have been invoked, these fail to explain the observations, particularly in the UV. Here we will show that there exists good grounds for supposing that the electrons in HII regions, as in other space plasmas, are not distributed according to a Boltzmann law. Rather, they follow a κ- distribution with κ ˜ 10. With this novel formulation, we can resolve the abundance discrepancies which have plagued this field for over three decades. Interestingly enough, the size of the correction in emission line strengths increases as we go into the UV.

Bouchaud-Mézard model on a random network

NASA Astrophysics Data System (ADS)

Ichinomiya, Takashi

2012-09-01

We studied the Bouchaud-Mézard (BM) model, which was introduced to explain Pareto's law in a real economy, on a random network. Using “adiabatic and independent” assumptions, we analytically obtained the stationary probability distribution function of wealth. The results show that wealth condensation, indicated by the divergence of the variance of wealth, occurs at a larger J than that obtained by the mean-field theory, where J represents the strength of interaction between agents. We compared our results with numerical simulation results and found that they were in good agreement.

Research on and Application to BH-HTC High Density Cementing Slurry System on Tarim Region

NASA Astrophysics Data System (ADS)

Yuanhong, Song; Fei, Gao; Jianyong, He; Qixiang, Yang; Jiang, Yang; Xia, Liu

2017-08-01

A large section of salt bed is contented in Tarim region Piedmont which constructs complex geological conditions. For high-pressure gas well cementing difficulties from the region, high density cement slurry system has been researched through reasonable level of particle size distribution and second weighting up. The results of laboratory tests and field applications show that the high density cementing slurry system is available to Tarim region cementing because this system has a well performance in slurry stability, gas breakthrough control, fluidity, water loss, and strength.

Molecular Facts on the Structure and Dynamics of Electrolyte Species in Cu-Cl Cycle for Hydrogen Generation: An Insight from Molecular Dynamic Simulations.

PubMed

Sahu, Pooja; Ali, Sk Musharaf; Shenoy, K T; Mohan, S

2018-04-12

The Cu complex, which is the key chemical species in well-known Cu-Cl hybrid thermochemical cycles and also in numerous metal hydrometallurgical and sedimentary deposit processes, displays a wide variety of structural and dynamical characteristics that are further complicated by the presence of multiple oxidation states of Cu ions with different coordination chemistries, therefore they are difficult to explore from experiments alone. In this article, an attempt has been made to understand the coordination behavior of the Cu complex using MD simulations. The study provides compelling evidence of the experimentally observed multiple stoichiometries of Cu ions, i.e., 1:6:0, 1:5:1, and 1:4:2 for Cu + :H 2 O:Cl - and 1:6:0 for Cu 2+ :H 2 O:Cl - . The presence of the anionic Cu complex, [Cu + Cl 2 ] - ·2H 2 O, [Cu + Cl 2 ] - ·3H 2 O, [Cu 2+ Cl 3 ] - ·H 2 O, and [Cu 2+ Cl 3 ] - ·2H 2 O, was captured in the presence of excess chloride ions. Furthermore, the probability distribution profiles have been estimated to determine the most possible complex in the considered systems. The results establish structural and dynamical reformation of the Cu complex with change in the salt concentration or variation in the solvent medium in which they are dissolved. Moreover, the structure and kinetics of the Cu ions in the Cu-Cl electrolyzer have been explored over a large range of the electric field by extending the simulated systems for varied strengths of the electric fields. It has been observed that with an increase in the strength of the electric field, the water molecules lose their coordination strength with central Cu ions, which, on the other hand, results in a significant change in the structure of the captured complex. The diffusion dynamics of the ions is altered while applying the electric field, which is furthermore modified while increasing the strength of electric field beyond a critical limit. In fact, the diffusion mechanism of the ions was seen to be transformed from Brownian-like to linear motion and then to hopping diffusion with the increasing strength of the electric field. To the best of our knowledge, this is the first time when the multiple oxidation states of the Cu ion are explored using MD simulations, and the coexisting pictures of the multiple coordinations and the solvent effects have been clearly revealed. Also to date, the present article is the first one to report the insights of the structure and the dynamics of the ions in the Cu-Cl electrolyzer over a wide range of the electric field. The present studies will be very helpful in understanding the mechanism involved in numerous metal hydrometallurgical and sedimentary deposit processes and to comprehend the analogies involved in the electrode reactions of the Cu-Cl cycle for hydrogen generation.

Nature of convection-stabilized dc arcs in dual-flow nozzle geometry. I - The cold flow field and dc arc characteristics. II - Optical diagnostics and theory

NASA Astrophysics Data System (ADS)

Serbetci, Ilter; Nagamatsu, H. T.

1990-02-01

Steady-state low-current air arcs in a dual-flow nozzle system are studied experimentally. The cold flow field with no arc is investigated using a 12.7-mm diameter dual-flow nozzle in a steady-flow facility. Mach number and mass flux distributions are determined for various nozzle-pressure ratios and nozzle-gap spacing. It is found that the shock waves in the converging-diverging nozzles result in a decrease in overal resistance by about 15 percent. Also, Schlieren and differential interferometry techniques are used to visualize the density gradients within the arc plasma and thermal mantle. Both optical techniques reveal a laminar arc structure for a reservoir pressure of 1 atm at various current levels. Experimentally determined axial static pressure and cold-flow mass flux rate distributions and a channel-flow model with constant arc temperatre are used to solve the energy integral for the arc radius as a function of axial distance. The arc electric field strength, voltage, resistance, and power are determined with Ohm's law and the total heat transfer is related to arc power.

The Role of Marangoni Convection for the FZ-Growth of Silicon

NASA Technical Reports Server (NTRS)

Dold, P.; Corell, A.; Schweizer, M.; Kaiser, Th.; Szofran, F.; Nakamura, S.; Hibiya, T.; Benz, K. W.

1998-01-01

Fluctuations of the electrical resistivity due to inhomogeneous dopant distribution are still a serious problem for the industrial processing yield of doped silicon crystals. In the case of silicon floating-zone growth, the main sources of these inhomogeneities are time- dependent flows in the liquid phase during the growth process. Excluding radio frequency (RF) induced convection, buoyancy and thermocapillary (Marangoni) convection are the two natural reasons for fluid flow. Both originate from temperature/concentration gradients in the melt, buoyancy convection through thermal/concentrational volume expansion, and thermocapillary convection through the temperature/concentration dependence of the surface tension. To improve the properties of grown crystals, knowledge of the strength, the characteristic, and the relation of these two flow mechanisms is essential. By the use of microgravity, the effect and the strength of buoyancy (gravity dependent) and thermocapillary (gravity independent) convection can be separated and clarified. Applying magnetic fields, both convective modes can be influenced: fluid flow can either be damped (static magnetic fields) or overlaid by a regular flow regime (rotating magnetic fields). Two complementary approaches have been pursued: Silicon full zones (experiments on the German sounding rockets TEXUS 7, 12, 22, 29, and 36) with the maximum temperature at half of the zone height and silicon half zones (experiments on the Japanese sounding rockets TR-IA4 and 6) with the maximum temperature at the top of the melt. With the full zone arrangement, the intensity and the frequency of the dopant striations could be determined and the critical Marangoni number could be identified. The half zone configuration is suited to classify the flow pattern and to measure the amplitude and the frequency of temperature fluctuations in the melt by inserting thermocouples or temperature sensors into the melt. All experiments have been carried out in monoellipsoid mirror furnaces. Typical zone geometries are approx. 8 to 14 mm in diameter and height. The crystals grown under microgravity are compared to crystals grown in static axial magnetic fields (B<5 tesla) and in transversal rotating magnetic fields (B<7.5 mT / f=50 Hz). Experimental results are completed by 3D numerical simulations: the obtained temperature and concentration distribution in the melt confirm the damping effect of rotating magnetic fields and explain the change in the radial segregation under static magnetic fields.

Electrostatics of proteins in dielectric solvent continua. I. An accurate and efficient reaction field description

NASA Astrophysics Data System (ADS)

Bauer, Sebastian; Mathias, Gerald; Tavan, Paul

2014-03-01

We present a reaction field (RF) method which accurately solves the Poisson equation for proteins embedded in dielectric solvent continua at a computational effort comparable to that of an electrostatics calculation with polarizable molecular mechanics (MM) force fields. The method combines an approach originally suggested by Egwolf and Tavan [J. Chem. Phys. 118, 2039 (2003)] with concepts generalizing the Born solution [Z. Phys. 1, 45 (1920)] for a solvated ion. First, we derive an exact representation according to which the sources of the RF potential and energy are inducible atomic anti-polarization densities and atomic shielding charge distributions. Modeling these atomic densities by Gaussians leads to an approximate representation. Here, the strengths of the Gaussian shielding charge distributions are directly given in terms of the static partial charges as defined, e.g., by standard MM force fields for the various atom types, whereas the strengths of the Gaussian anti-polarization densities are calculated by a self-consistency iteration. The atomic volumes are also described by Gaussians. To account for covalently overlapping atoms, their effective volumes are calculated by another self-consistency procedure, which guarantees that the dielectric function ɛ(r) is close to one everywhere inside the protein. The Gaussian widths σi of the atoms i are parameters of the RF approximation. The remarkable accuracy of the method is demonstrated by comparison with Kirkwood's analytical solution for a spherical protein [J. Chem. Phys. 2, 351 (1934)] and with computationally expensive grid-based numerical solutions for simple model systems in dielectric continua including a di-peptide (Ac-Ala-NHMe) as modeled by a standard MM force field. The latter example shows how weakly the RF conformational free energy landscape depends on the parameters σi. A summarizing discussion highlights the achievements of the new theory and of its approximate solution particularly by comparison with so-called generalized Born methods. A follow-up paper describes how the method enables Hamiltonian, efficient, and accurate MM molecular dynamics simulations of proteins in dielectric solvent continua.

Electrostatics of proteins in dielectric solvent continua. I. An accurate and efficient reaction field description.

PubMed

Bauer, Sebastian; Mathias, Gerald; Tavan, Paul

2014-03-14

We present a reaction field (RF) method which accurately solves the Poisson equation for proteins embedded in dielectric solvent continua at a computational effort comparable to that of an electrostatics calculation with polarizable molecular mechanics (MM) force fields. The method combines an approach originally suggested by Egwolf and Tavan [J. Chem. Phys. 118, 2039 (2003)] with concepts generalizing the Born solution [Z. Phys. 1, 45 (1920)] for a solvated ion. First, we derive an exact representation according to which the sources of the RF potential and energy are inducible atomic anti-polarization densities and atomic shielding charge distributions. Modeling these atomic densities by Gaussians leads to an approximate representation. Here, the strengths of the Gaussian shielding charge distributions are directly given in terms of the static partial charges as defined, e.g., by standard MM force fields for the various atom types, whereas the strengths of the Gaussian anti-polarization densities are calculated by a self-consistency iteration. The atomic volumes are also described by Gaussians. To account for covalently overlapping atoms, their effective volumes are calculated by another self-consistency procedure, which guarantees that the dielectric function ε(r) is close to one everywhere inside the protein. The Gaussian widths σ(i) of the atoms i are parameters of the RF approximation. The remarkable accuracy of the method is demonstrated by comparison with Kirkwood's analytical solution for a spherical protein [J. Chem. Phys. 2, 351 (1934)] and with computationally expensive grid-based numerical solutions for simple model systems in dielectric continua including a di-peptide (Ac-Ala-NHMe) as modeled by a standard MM force field. The latter example shows how weakly the RF conformational free energy landscape depends on the parameters σ(i). A summarizing discussion highlights the achievements of the new theory and of its approximate solution particularly by comparison with so-called generalized Born methods. A follow-up paper describes how the method enables Hamiltonian, efficient, and accurate MM molecular dynamics simulations of proteins in dielectric solvent continua.

Lower-extremity strength ratios of professional soccer players according to field position.

PubMed

Ruas, Cassio V; Minozzo, Felipe; Pinto, Matheus D; Brown, Lee E; Pinto, Ronei S

2015-05-01

Previous investigators have proposed that knee strength, hamstrings to quadriceps, and side-to-side asymmetries may vary according to soccer field positions. However, different results have been found in these variables, and a generalization of this topic could lead to data misinterpretation by coaches and soccer clubs. Thus, the aim of this study was to measure knee strength and asymmetry in soccer players across different field positions. One hundred and two male professional soccer players performed maximal concentric and eccentric isokinetic knee actions on the preferred and nonpreferred legs at a velocity of 60° · s. Players were divided into their field positions for analysis: goalkeepers, side backs, central backs, central defender midfielders, central attacking midfielders, and forwards. Results demonstrated that only goalkeepers (GK) differed from most other field positions on players' characteristics, and concentric peak torque across muscles. Although all players presented functional ratios of the preferred (0.79 ± 0.14) and nonpreferred (0.75 ± 0.13) legs below accepted normative values, there were no differences between positions for conventional or functional strength ratios or side-to-side asymmetry. The same comparisons were made only between field players, without inclusion of the GK, and no differences were found between positions. Therefore, the hamstrings to quadriceps and side-to-side asymmetries found here may reflect knee strength functional balance required for soccer skills performance and game demands across field positions. These results also suggest that isokinetic strength profiles should be considered differently in GK compared with other field positions due to their specific physiological and training characteristics.

Theoretical modeling of the infrared fluorescence from interstellar polycyclic aromatic hydrocarbons

NASA Technical Reports Server (NTRS)

Schutte, W. A.; Tielens, A. G. G. M.; Allamandola, L. J.

1993-01-01

We have modeled the family of interstellar IR emission bands at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 microns by calculating the fluorescence from a size distribution of interstellar polycyclic aromatic hydrocarbons (PAHs) embedded in the radiation field of a hot star. It is found that the various emission bands are dominated by distinctly different PAHs, from molecules with much less than about 80 C atoms for the 3.3 micron feature, to molecules with 10 exp 2-10 exp 5 C atoms for the emission in the IRAS 12 and 25 micron bands. We quantitatively describe the influence on the emergent spectrum of various PAH properties such as the molecular structure, the amount of dehydrogenation, the intrinsic strength of the IR active modes, and the size distribution. Comparing our model results to the emission spectrum from the Orion Bar region, we conclude that interstellar PAHs are likely fully, or almost fully, hydrogenated. Moreover, it is found that the intrinsic strengths of the 6.2 and 7.7 micron C-C stretching modes, and the 8.6 micron C-H in-plane bending mode are 2-6 times larger than measured for neutral PAHs in the laboratory.

Differentiation and Response Bias in Episodic Memory: Evidence from Reaction Time Distributions

ERIC Educational Resources Information Center

Criss, Amy H.

2010-01-01

In differentiation models, the processes of encoding and retrieval produce an increase in the distribution of memory strength for targets and a decrease in the distribution of memory strength for foils as the amount of encoding increases. This produces an increase in the hit rate and decrease in the false-alarm rate for a strongly encoded compared…

Calculation of temperature distribution and rheological properties of the lithosphere along geotransect in the Red Sea region

NASA Astrophysics Data System (ADS)

Dérerová, Jana; Kohút, Igor; Radwan, Anwar H.; Bielik, Miroslav

2017-12-01

The temperature model of the lithosphere along profile passing through the Red Sea region has been derived using 2D integrated geophysical modelling method. Using the extrapolation of failure criteria, lithology and calculated temperature distribution, we have constructed the rheological model of the lithosphere in the area. We have calculated the strength distribution in the lithosphere and constructed the strength envelopes for both compressional and extensional regimes. The obtained results indicate that the strength steadily decreases from the Western desert through the Eastern desert towards the Red Sea where it reaches its minimum for both compressional and extensional regime. Maximum strength can be observed in the Western desert where the largest strength reaches values of about 250-300 MPa within the upper crust on the boundary between upper and lower crust. In the Eastern desert we observe slightly decreased strength with max values about 200-250 MPa within upper crust within 15 km with compression being dominant. These results suggest mostly rigid deformation in the region or Western and Eastern desert. In the Red Sea, the strength rapidly decreases to its minimum suggesting ductile processes as a result of higher temperatures.

Dipole interaction of the Quincke rotating particles.

PubMed

Dolinsky, Yu; Elperin, T

2012-02-01

We study the behavior of particles having a finite electric permittivity and conductivity in a weakly conducting fluid under the action of the external electric field. We consider the case when the strength of the external electric field is above the threshold, and particles rotate due to the Quincke effect. We determine the magnitude of the dipole interaction of the Quincke rotating particles and the shift of frequency of the Quincke rotation caused by the dipole interaction between the particles. It is demonstrated that depending on the mutual orientation of the vectors of angular velocities of particles, vector-directed along the straight line between the centers of the particles and the external electric field strength vector, particles can attract or repel each other. In contrast to the case of nonrotating particles when the magnitude of the dipole interaction increases with the increase of the strength of the external electric field, the magnitude of the dipole interaction of the Quincke rotating particles either does not change or decreases with the increase of the strength of the external electric field depending on the strength of the external electric field and electrodynamic parameters of the particles.

Dipole interaction of the Quincke rotating particles

NASA Astrophysics Data System (ADS)

Dolinsky, Yu.; Elperin, T.

2012-02-01

We study the behavior of particles having a finite electric permittivity and conductivity in a weakly conducting fluid under the action of the external electric field. We consider the case when the strength of the external electric field is above the threshold, and particles rotate due to the Quincke effect. We determine the magnitude of the dipole interaction of the Quincke rotating particles and the shift of frequency of the Quincke rotation caused by the dipole interaction between the particles. It is demonstrated that depending on the mutual orientation of the vectors of angular velocities of particles, vector-directed along the straight line between the centers of the particles and the external electric field strength vector, particles can attract or repel each other. In contrast to the case of nonrotating particles when the magnitude of the dipole interaction increases with the increase of the strength of the external electric field, the magnitude of the dipole interaction of the Quincke rotating particles either does not change or decreases with the increase of the strength of the external electric field depending on the strength of the external electric field and electrodynamic parameters of the particles.

C. elegans Demonstrates Distinct Behaviors within a Fixed and Uniform Electric Field

PubMed Central

Chrisman, Steven D.; Waite, Christopher B.; Scoville, Alison G.; Carnell, Lucinda

2016-01-01

C. elegans will orient and travel in a straight uninterrupted path directly towards the negative pole of a DC electric field. We have sought to understand the strategy worms use to navigate to the negative pole in a uniform electric field that is fixed in both direction and magnitude. We examined this behavior by quantifying three aspects of electrotaxis behavior in response to different applied field strengths: the mean approach trajectory angles of the animals’ tracks, turning behavior (pirouettes) and average population speeds. We determined that C. elegans align directly to the negative pole of an electric field at sub-preferred field strength and alter approach trajectories at higher field strengths to maintain taxis within a preferred range we have calculated to be ~ 5V/cm. We sought to identify the sensory neurons responsible for the animals’ tracking to a preferred field strength. eat-4 mutant animals defective in glutamatergic signaling of the amphid sensory neurons are severely electrotaxis defective and ceh-36 mutant animals, which are defective in the terminal differentiation of two types of sensory neurons, AWC and ASE, are partially defective in electrotaxis. To further elucidate the role of the AWC neurons, we examined the role of each of the pair of AWC neurons (AWCOFF and AWCON), which are functionally asymmetric and express different genes. nsy-5/inx-19 mutant animals, which express both neurons as AWCOFF, are severely impaired in electrotaxis behavior while nsy-1 mutants, which express both neurons as AWCON, are able to differentiate field strengths required for navigation to a specific field strength within an electric field. We also tested a strain with targeted genetic ablation of AWC neurons and found that these animals showed only slight disruption of directionality and turning behavior. These results suggest a role for AWC neurons in which complete loss of function is less disruptive than loss of functional asymmetry in electrotaxis behavior within a uniform fixed field. PMID:26998749

Inactivation of Escherichia coli, Saccharomyces cerevisiae, and Lactobacillus brevis in Low-fat Milk by Pulsed Electric Field Treatment: A Pilot-scale Study

PubMed Central

Han, Bok Kung; Choi, Hyuk Joon; Kang, Shin Ho; Baick, Seung Chun

2015-01-01

We investigated the effects of a pulsed electric field (PEF) treatment on microbial inactivation and the physical properties of low-fat milk. Milk inoculated with Escherichia coli, Saccharomyces cerevisiae, or Lactobacillus brevis was supplied to a pilot-scale PEF treatment system at a flow rate of 30 L/h. Pulses with an electric field strength of 10 kV/cm and a pulse width of 30 μs were applied to the milk with total pulse energies of 50-250 kJ/L achieved by varying the pulse frequency. The inactivation curves of the test microorganisms were biphasic with an initial lag phase (or shoulder) followed by a phase of rapid inactivation. PEF treatments with a total pulse energy of 200 kJ/L resulted in a 4.5-log reduction in E. coli, a 4.4-log reduction in L. brevis, and a 6.0-log reduction in S. cerevisiae. Total pulse energies of 200 and 250 kJ/L resulted in greater than 5-log reductions in microbial counts in stored PEF-treated milk, and the growth of surviving microorganisms was slow during storage for 15 d at 4℃. PEF treatment did not change milk physical properties such as pH, color, or particle-size distribution (p<0.05). These results indicate that a relatively low electric-field strength of 10 kV/cm can be used to pasteurize low-fat milk. PMID:26877640

Inactivation of Escherichia coli, Saccharomyces cerevisiae, and Lactobacillus brevis in Low-fat Milk by Pulsed Electric Field Treatment: A Pilot-scale Study.

PubMed

Lee, Gun Joon; Han, Bok Kung; Choi, Hyuk Joon; Kang, Shin Ho; Baick, Seung Chun; Lee, Dong-Un

2015-01-01

We investigated the effects of a pulsed electric field (PEF) treatment on microbial inactivation and the physical properties of low-fat milk. Milk inoculated with Escherichia coli, Saccharomyces cerevisiae, or Lactobacillus brevis was supplied to a pilot-scale PEF treatment system at a flow rate of 30 L/h. Pulses with an electric field strength of 10 kV/cm and a pulse width of 30 μs were applied to the milk with total pulse energies of 50-250 kJ/L achieved by varying the pulse frequency. The inactivation curves of the test microorganisms were biphasic with an initial lag phase (or shoulder) followed by a phase of rapid inactivation. PEF treatments with a total pulse energy of 200 kJ/L resulted in a 4.5-log reduction in E. coli, a 4.4-log reduction in L. brevis, and a 6.0-log reduction in S. cerevisiae. Total pulse energies of 200 and 250 kJ/L resulted in greater than 5-log reductions in microbial counts in stored PEF-treated milk, and the growth of surviving microorganisms was slow during storage for 15 d at 4℃. PEF treatment did not change milk physical properties such as pH, color, or particle-size distribution (p<0.05). These results indicate that a relatively low electric-field strength of 10 kV/cm can be used to pasteurize low-fat milk.

Formation of core-shell structured complex microparticles during fabrication of magnetorheological elastomers and their magnetorheological behavior

NASA Astrophysics Data System (ADS)

Wang, Yonghong; Zhang, Xinru; Chung, Kyungho; Liu, Chengcen; Choi, Seung-Bok; Choi, Hyoung Jin

2016-11-01

To improve mechanical and magnetorheological properties of magnetorheological elastomers (MREs), a facile method was used to fabricate high-performance MREs which consisted of the core-shell complex microparticles with an organic-inorganic network structure dispersed in an ethylene propylene diene rubber. In this work, the proposed magnetic complex microparticles were in situ formed during MREs fabrication as a result of strong interaction between matrix and CIPs using carbon black as a connecting point. The morphology of both isotropic (i-MREs) and anisotropic MREs (a-MREs) was observed by scanning electron microscope (SEM). The effects of carbonyl iron particle (CIP) volume content on mechanical properties and hysteresis loss of MREs were investigated. The effects of CIP volume content on the shear storage modulus, MR effect and loss tangent were studied using a modified dynamic mechanical analyzer under applied magnetic field strengths. The results showed that the orientation effect became more pronounced with increasing CIPs in the a-MREs, whereas CIPs distributed uniformly in the i-MREs. The tensile strength, tear strength and elongation at break decreased with increasing CIP content up to 40 vol.%, while the hardness increased. It is worth noting that the tensile strength of i-MREs and a-MREs containing 40 vol.% CIPs still had high mechanical properties as a result of good compatibility between complex microparticles and rubber matrix. The MR performance of shear storage modulus and damping properties of MREs increased remarkably with CIP content due to strong dipole-dipole interaction of complex microparticles. Besides, the hysteresis loss increased with increasing CIP content as a result of magnetic field induced interfacial sliding between complex microparticles.

Linkage between the Biosphere and Geomagnetic field: Knowns and Unknowns

NASA Astrophysics Data System (ADS)

Pan, Y.; Zhu, R.

2017-12-01

The geomagnetic field extends from Earth's interior into space, and protects our planets habitability by shielding the planet from solar winds and cosmic rays. Recently, single zircon paleomagnetic study provides evidence of the field to ages as old as 4.2 Ga. Many great questions remain, including whether the emergence of life on Earth was a consequence of the field's protection, how organisms utilize the field, and if field variations (polarity reversal, excursion and secular variation) impact the evolution of the biosphere. In the past decade, great efforts have been made to probe these very complex and great challenging questions through the inter-disciplinary subject of biogeomagnetism. Numerous birds, fish, sea turtles, bats and many other organisms utilize the geomagnetic field during orientation and long-distance navigation. We recently found that bats, the second most abundant order of mammals, can use the direction of magnetic field with a weak strength comparable to polarity transitions/excursions, which is indicative of advanced magnetoreception developed in bats co-evolving with the geomagnetic field since the Eocene. Magnetotactic bacteria swim along the geomagnetic field lines by synthesizing intracellular nano-sized and chain-arranged magnetic minerals (magnetosomes). Recent field surveys in China, Europe, America and Australia have shown that these microbes are ubiquitous in aqueous habitats. Both their biogeography distribution and magnetotactic swimming speed are field intensity dependent. On the other hand, it is increasingly accepted that the geomagnetic field influences life through several indirect pathways. For example, it has been discovered that solar wind erosion enhanced the atmospheric oxygen escape during periods of weak magnetic field and global mean ionospheric electron density profiles can be affected by geomagnetic field strength variation. In addition, depletion of the ozone layer during a weak magnetic field could result in strong solar irradiation, which is harmful to many organisms. Together, newly accumulated lines of evidence strongly indicate that the geomagnetic field and its variations have important impacts on life and its evolution. In this paper we will provide an overview of recent observations, progresses and perspectives in this subject.

Comparison of flow cytometry, fluorescence microscopy and spectrofluorometry for analysis of gene electrotransfer efficiency.

PubMed

Marjanovič, Igor; Kandušer, Maša; Miklavčič, Damijan; Keber, Mateja Manček; Pavlin, Mojca

2014-12-01

In this study, we compared three different methods used for quantification of gene electrotransfer efficiency: fluorescence microscopy, flow cytometry and spectrofluorometry. We used CHO and B16 cells in a suspension and plasmid coding for GFP. The aim of this study was to compare and analyse the results obtained by fluorescence microscopy, flow cytometry and spectrofluorometry and in addition to analyse the applicability of spectrofluorometry for quantifying gene electrotransfer on cells in a suspension. Our results show that all the three methods detected similar critical electric field strength, around 0.55 kV/cm for both cell lines. Moreover, results obtained on CHO cells showed that the total fluorescence intensity and percentage of transfection exhibit similar increase in response to increase electric field strength for all the three methods. For B16 cells, there was a good correlation at low electric field strengths, but at high field strengths, flow cytometer results deviated from results obtained by fluorescence microscope and spectrofluorometer. Our study showed that all the three methods detected similar critical electric field strengths and high correlations of results were obtained except for B16 cells at high electric field strengths. The results also demonstrated that flow cytometry measures higher values of percentage transfection compared to microscopy. Furthermore, we have demonstrated that spectrofluorometry can be used as a simple and consistent method to determine gene electrotransfer efficiency on cells in a suspension.

Isospin symmetry of Tz =±3/2→±1/2 Gamow-Teller transitions in A=41 nuclei

NASA Astrophysics Data System (ADS)

Fujita, Y.; Shimbara, Y.; Adachi, T.; Berg, G. P.; Brown, B. A.; Fujita, H.; Hatanaka, K.; Kamiya, J.; Nakanishi, K.; Sakemi, Y.; Sasaki, S.; Shimizu, Y.; Tameshige, Y.; Uchida, M.; Wakasa, T.; Yosoi, M.

2004-11-01

Under the assumption that isospin T is a good quantum number, isobaric analog states and various analogous transitions are expected in isobars with mass number A . The strengths of Tz =±3/2→±1/2 analogous Gamow-Teller (GT) transitions and analogous M1 transitions within the A=41 isobar quartet are compared in detail. The Tz =+3/2→+1/2 GT transitions from the Jπ = 3/2+ ground state of 41K leading to excited Jπ = 1/2+ , 3/2+ , and 5/2+ states in 41Ca were measured using the ( 3He ,t) charge-exchange reaction. With a high energy resolution of 35 keV , many fragmented states were observed, and the GT strength distribution was determined up to 10 MeV excitation energy ( Ex ) . The main part of the strength was concentrated in the Ex =4 6 MeV region. A shell-model calculation could reproduce the concentration, but not so well details of the strength distribution. The obtained distribution was further compared with two results of 41Ti β decay studying the analogous Tz =-3/2→-1/2 GT strengths. They reported contradicting distributions. One-to-one correspondences of analogous transitions and analog states were assigned up to Ex =6 MeV in the comparison with one of these 41Ti β -decay results. Combining the spectroscopic information of the analog states in 41Ca and 41Sc , the most probable Jπ values were deduced for each pair of analog states. It was found that 5/2+ states carry the main part of the observed GT strength, while much less GT strength was carried by 1/2+ and 3/2+ states. The gross features of the GT strength distributions for each J were similar for the isospin analogous Tz =±3/2→±1/2 transitions, but the details were somewhat different. From the difference of the distributions, isospin-asymmetry matrix elements of ≈8 keV were deduced. The Coulomb displacement energy, which is sensitive to the configuration of states, showed a sudden increase of about 50 keV at the excitation energy of 3.8 MeV . The strengths of several M1 transitions to the IAS in 41Ca were compared with the strengths of analogous GT transitions. It was found that ratios of the M1 and GT transition strengths were similar, suggesting that the contributions of the ℓτ term in M1 transitions are small.

The effects of magnetic field in plume region on the performance of multi-cusped field thruster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Peng, E-mail: hupengemail@126.com; Liu, Hui, E-mail: thruster@126.com; Yu, Daren

2015-10-15

The performance characteristics of a Multi-cusped Field Thruster depending on the magnetic field in the plume region were investigated. Five magnetic field shielding rings were separately mounted near the exit of discharge channel to decrease the strength of magnetic field in the plume region in different levels, while the magnetic field in the upstream was well maintained. The test results show that the electron current increases with the decrease of magnetic field strength in the plume region, which gives rise to higher propellant utilization and lower current utilization. On the other hand, the stronger magnetic field in the plume regionmore » improves the performance at low voltages (high current mode) while lower magnetic field improves the performance at high voltages (low current mode). This work can provide some optimal design ideas of the magnetic strength in the plume region to improve the performance of thruster.« less

Dust coagulation and magnetic field strength in a planet-induced gap subject to MRI turbulence

NASA Astrophysics Data System (ADS)

Carballido, Augusto; Matthews, Lorin; Hyde, Truell

2017-01-01

We investigate the coagulation of dust particles in and around a gap opened by a Jupiter-mass planet. To this end, we carry out a high-resolution magnetohydrodynamic (MHD) simulation of the gap environment, which is turbulent due to the magneto rotational instability. From the MHD simulation, we obtain values of the gas velocities, densities and turbulent stresses close to the gap edge, in one of the two gas streams that accrete onto the planet, and inside the low-density gap. The MHD values are then supplied to a Monte Carlo dust coagulation algorithm, which models grain sticking, compaction and bouncing. We consider two dust populations for each region: one whose initial size distribution is monodisperse, with monomer radius equal to 1 micron, and another one whose initial size distribution follows the Mathis-Rumpl-Nordsieck distribution for interstellar dust grains, with an initial range of monomer radii between 0.5 and 10 microns. Without bouncing, our Monte Carlo calculations show steady growth of dust aggregates in all regions, and the mass-weighted (MW) average porosity of the initially mono disperse population reaches extremely high final values of 98%. The final MW porosities in all other cases without bouncing range from 30% to 82%. The efficiency of compaction is due to high turbulent relative speeds between dust particles. When bouncing is introduced, growth is slowed down in the planetary wake and inside the gap.We also analyze the strength of the magnetic field threading the gaps opened by planets of different sub-Jovian masses. Preliminary results show that, in a gap opened by a large-mass planet (~ 1 MJ), the time-averaged radial profile of the vertical component of the field (Bz) increases sharply inside the gap, and less sharply in the case of less massive planets. In gaps opened by intermediate-mass planets (~ 0.5 — 0.75 MJ), the radial profile of Bz exhibits local maxima in the vicinity of the planet, but not at the gap center.

Generalized Reliability Methodology Applied to Brittle Anisotropic Single Crystals. Degree awarded by Washington Univ., 1999

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.

2002-01-01

A generalized reliability model was developed for use in the design of structural components made from brittle, homogeneous anisotropic materials such as single crystals. The model is based on the Weibull distribution and incorporates a variable strength distribution and any equivalent stress failure criteria. In addition to the reliability model, an energy based failure criterion for elastically anisotropic materials was formulated. The model is different from typical Weibull-based models in that it accounts for strength anisotropy arising from fracture toughness anisotropy and thereby allows for strength and reliability predictions of brittle, anisotropic single crystals subjected to multiaxial stresses. The model is also applicable to elastically isotropic materials exhibiting strength anisotropy due to an anisotropic distribution of flaws. In order to develop and experimentally verify the model, the uniaxial and biaxial strengths of a single crystal nickel aluminide were measured. The uniaxial strengths of the <100> and <110> crystal directions were measured in three and four-point flexure. The biaxial strength was measured by subjecting <100> plates to a uniform pressure in a test apparatus that was developed and experimentally verified. The biaxial strengths of the single crystal plates were estimated by extending and verifying the displacement solution for a circular, anisotropic plate to the case of a variable radius and thickness. The best correlation between the experimental strength data and the model predictions occurred when an anisotropic stress analysis was combined with the normal stress criterion and the strength parameters associated with the <110> crystal direction.

Enhancement of the thermoelectric figure of merit in a ferromagnet-quantum dot-superconductor device due to intradot spin-flip scattering and ac field

NASA Astrophysics Data System (ADS)

Xu, Wei-Ping; Zhang, Yu-Ying; Li, Zhi-Jian; Nie, Yi-Hang

2017-08-01

We investigate the thermoelectric properties of a ferromagnet-quantum dot-superconductor hybrid system with the intradot spin-flip scattering and the external microwave field. The results indicate that the increase of figure of merit in the gap is very slight when the spin-flip scattering strength increases, but outside the gap it significantly increases with enhancing spin-flip scattering strength. The presence of microwave field results in photon-assisted Andreev reflection and induces the satellite peaks in conductance spectrum. The appropriate match of spin-flip scattering strength, microwave field strength and frequency can significantly enhances the figure of merit of thermoelectric conversion of the device, which can be used as a scheme improving thermoelectric efficiency using microwave frequency.

Strong Magnetic Field Induced Changes of Gene Expression in Arabidopsis

NASA Astrophysics Data System (ADS)

Paul, A.-L.; Ferl, R. J.; Klingenberg, B.; Brooks, J. S.; Morgan, A. N.; Yowtak, J.; Meisel, M. W.

2005-07-01

We review our studies of the biological impact of magnetic field strengths of up to 30 T on transgenic arabidopsis plants engineered with a stress response gene consisting of the alcohol dehydrogenase (Adh) gene promoter driving the β-glucuronidase (GUS) gene reporter. Field strengths in excess of 15 T induce expression of the Adh/GUS transgene in the roots and leaves. Microarray analyses indicate that such field strengths have a far reaching effect on the genome. Wide spread induction of stress-related genes and transcription factors, and a depression of genes associated with cell wall metabolism are prominent examples.

Effects of convection electric field on the distribution of ring current type protons

NASA Technical Reports Server (NTRS)

Grebowsky, J. M.; Chen, A. J.

1975-01-01

The topology of the boundaries of penetration (or, inversely, the boundaries of the forbidden regions) of 90-deg pitch-angle equatorial protons with energies less than 100 keV are explored for an equatorial convection E-field which is directed in general from dawn to dusk. Due to the dependence of drift path on energy (or magnetic moment), complex structural features are expected in the proton energy spectra detected by satellites since the penetration distance of a proton is not a monotonically increasing or decreasing function of energy. During a storm when the convection E is enhanced, model calculations predict elongations of the forbidden regions analogous to tail extensions of the plasmasphere. Following a reduction in the convection field, spiral-structured forbidden regions can occur. Structural features inherent to large-scale convection field changes may be seen in the nose-like proton spectrograms observed near dusk by instrumentation on Explorer 45. These nose events are modelled by using an electric field model developed originally by Volland (1973). The strength of the field is related to the Kp index through night-time equatorial plasmapause measurements.

Visualizing the optical field strengths in Au/dielectric nanostructures and its correlation to SERS enhancements

NASA Astrophysics Data System (ADS)

Rajesh, Y.; Sangani, L. D. Varma; Shaik, Ummar Pasha; Gaur, Anshu; Mohiddon, Md Ahamad; Krishna, M. Ghanashyam

2017-05-01

The role of dielectric surrounding over the Au nanostructure for surface plasmon resonance (SPR) behavior is investigated by scanning near field optical microscopy (SNOM). The observed optical field strengths are correlated with the surface enhanced Raman scattering (SERS) enhancement recorded for R6G molecule. Discontinuous nanostructured Au thin films are deposited by RF magnatron sputtering at very low rate on to three different dielectric substrates, ZnO, TiO2 and SiO2. These three Au/dielectric nanostructures are investigated using SNOM by illuminating it in near field and collecting in transmission far field configuration. The observed optical near field images of the three different nanostructures are discussed by taking their dielectric constant into the account. The SERS enhancements are correlated with the optical field strengths derived from the near field optical imaging.

On the mechanics of stress analysis of fiber-reinforced composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, V.G.

A general mathematical formulation is developed for the three-dimensional inclusion and inhomogeneity problems, which are practically important in many engineering applications such as fiber pullout of reinforced composites, load transfer behavior in the stiffened structural components, and material defects and impurities existing in engineering materials. First, the displacement field (Green's function) for an elastic solid subjected to various distributions of ring loading is derived in closed form using the Papkovich-Neuber displacement potentials and the Hankel transforms. The Green's functions are used to derive the displacement and stress fields due to a finite cylindrical inclusion of prescribed dilatational eigenstrain such asmore » thermal expansion caused by an internal heat source. Unlike an elliptical inclusion, the interior stress field in the cylindrical inclusion is not uniform. Next, the three-dimensional inhomogeneity problem of a cylindrical fiber embedded in an infinite matrix of different material properties is considered to study load transfer of a finite fiber to an elastic medium. By using the equivalent inclusion method, the fiber is modeled as an inclusion with distributed eigenstrains of unknown strength, and the inhomogeneity problem can be treated as an equivalent inclusion problem. The eigenstrains are determined to simulate the disturbance due to the existing fiber. The equivalency of elastic field between inhomogeneity and inclusion problems leads to a set of integral equations. To solve the integral equations, the inclusion domain is discretized into a finite number of sub-inclusions with uniform eigenstrains, and the integral equations are reduced to a set of algebraic equations. The distributions of eigenstrains, interior stress field and axial force along the fiber are presented for various fiber lengths and the ratio of material properties of the fiber relative to the matrix.« less

Phase coherence induced by correlated disorder.

PubMed

Hong, Hyunsuk; O'Keeffe, Kevin P; Strogatz, Steven H

2016-02-01

We consider a mean-field model of coupled phase oscillators with quenched disorder in the coupling strengths and natural frequencies. When these two kinds of disorder are uncorrelated (and when the positive and negative couplings are equal in number and strength), it is known that phase coherence cannot occur and synchronization is absent. Here we explore the effects of correlating the disorder. Specifically, we assume that any given oscillator either attracts or repels all the others, and that the sign of the interaction is deterministically correlated with the given oscillator's natural frequency. For symmetrically correlated disorder with zero mean, we find that the system spontaneously synchronizes, once the width of the frequency distribution falls below a critical value. For asymmetrically correlated disorder, the model displays coherent traveling waves: the complex order parameter becomes nonzero and rotates with constant frequency different from the system's mean natural frequency. Thus, in both cases, correlated disorder can trigger phase coherence.

UHPC for Blast and Ballistic Protection, Explosion Testing and Composition Optimization

NASA Astrophysics Data System (ADS)

Bibora, P.; Drdlová, M.; Prachař, V.; Sviták, O.

2017-10-01

The realization of high performance concrete resistant to detonation is the aim and expected outcome of the presented project, which is oriented to development of construction materials for larger objects as protective walls and bunkers. Use of high-strength concrete (HSC / HPC - “high strength / performance concrete”) and high-fiber reinforced concrete (UHPC / UHPFC -“Ultra High Performance Fiber Reinforced Concrete”) seems to be optimal for this purpose of research. The paper describes the research phase of the project, in which we focused on the selection of specific raw materials and chemical additives, including determining the most suitable type and amount of distributed fiber reinforcement. Composition of UHPC was optimized during laboratory manufacture of test specimens to obtain the best desired physical- mechanical properties of developed high performance concretes. In connection with laboratory testing, explosion field tests of UHPC specimens were performed and explosion resistance of laboratory produced UHPC testing boards was investigated.

Hillslope hydrology and stability

USGS Publications Warehouse

Lu, Ning; Godt, Jonathan

2012-01-01

Landslides are caused by a failure of the mechanical balance within hillslopes. This balance is governed by two coupled physical processes: hydrological or subsurface flow and stress. The stabilizing strength of hillslope materials depends on effective stress, which is diminished by rainfall. This book presents a cutting-edge quantitative approach to understanding hydro-mechanical processes across variably saturated hillslope environments and to the study and prediction of rainfall-induced landslides. Topics covered include historic synthesis of hillslope geomorphology and hydrology, total and effective stress distributions, critical reviews of shear strength of hillslope materials and different bases for stability analysis. Exercises and homework problems are provided for students to engage with the theory in practice. This is an invaluable resource for graduate students and researchers in hydrology, geomorphology, engineering geology, geotechnical engineering and geomechanics and for professionals in the fields of civil and environmental engineering and natural hazard analysis.

Water's Interfacial Hydrogen Bonding Structure Reveals the Effective Strength of Surface-Water Interactions.

PubMed

Shin, Sucheol; Willard, Adam P

2018-06-05

We combine all-atom molecular dynamics simulations with a mean field model of interfacial hydrogen bonding to analyze the effect of surface-water interactions on the structural and energetic properties of the liquid water interface. We show that the molecular structure of water at a weakly interacting ( i.e., hydrophobic) surface is resistant to change unless the strength of surface-water interactions are above a certain threshold. We find that below this threshold water's interfacial structure is homogeneous and insensitive to the details of the disordered surface, however, above this threshold water's interfacial structure is heterogeneous. Despite this heterogeneity, we demonstrate that the equilibrium distribution of molecular orientations can be used to quantify the energetic component of the surface-water interactions that contribute specifically to modifying the interfacial hydrogen bonding network. We identify this specific energetic component as a new measure of hydrophilicity, which we refer to as the intrinsic hydropathy.

Sandblasting induced stress release and enhanced adhesion strength of diamond films deposited on austenite stainless steel

NASA Astrophysics Data System (ADS)

Li, Xiao; Ye, Jiansong; Zhang, Hangcheng; Feng, Tao; Chen, Jianqing; Hu, Xiaojun

2017-08-01

We firstly used sandblasting to treat austenite stainless steel and then deposited a Cr/CrN interlayer by close field unbalanced magnetron sputtering on it. After that, diamond films were prepared on the interlayer. It is found that the sandblasting process induces phase transition from austenite to martensite in the surface region of the stainless steel, which decreases thermal stress in diamond films due to lower thermal expansion coefficient of martensite phase compared with that of austenite phase. The sandblasting also makes stainless steel's surface rough and the Cr/CrN interlayer film inherits the rough surface. This decreases the carburization extent of the interlayer, increases nucleation density and modifies the stress distribution. Due to lower residual stress and small extent of the interlayer's carburization, the diamond film on sandblast treated austenite stainless steel shows enhanced adhesion strength.

Study for prediction of rotor/wake/fuselage interference, part 1

NASA Technical Reports Server (NTRS)

Clark, D. R.; Maskew, B.

1985-01-01

A method was developed which allows the fully coupled calculation of fuselage and rotor airloads for typical helicopter configurations in forward flight. To do this, an iterative solution is carried out based on a conventional panel representation of the fuselage and a blade element representation of the rotor where fuselage and rotor singularity strengths are determined simultaneously at each step and the rotor wake is allowed to relax (deform) in response to changes in rotor wake loading and fuselage presence. On completion of the iteration, rotor loading and inflow, fuselage singularity strength (and, hence, pressure and velocity distributions) and rotor wake are all consistent. The results of a fully coupled calculation of the flow around representative helicopter configurations are presented. The effect of fuselage components on the rotor flow field and the overall wake structure is detailed and the aerodynamic interference between the different parts of the aircraft is discussed.

Visualizing domain wall and reverse domain superconductivity.

PubMed

Iavarone, M; Moore, S A; Fedor, J; Ciocys, S T; Karapetrov, G; Pearson, J; Novosad, V; Bader, S D

2014-08-28

In magnetically coupled, planar ferromagnet-superconductor (F/S) hybrid structures, magnetic domain walls can be used to spatially confine the superconductivity. In contrast to a superconductor in a uniform applied magnetic field, the nucleation of the superconducting order parameter in F/S structures is governed by the inhomogeneous magnetic field distribution. The interplay between the superconductivity localized at the domain walls and far from the walls leads to effects such as re-entrant superconductivity and reverse domain superconductivity with the critical temperature depending upon the location. Here we use scanning tunnelling spectroscopy to directly image the nucleation of superconductivity at the domain wall in F/S structures realized with Co-Pd multilayers and Pb thin films. Our results demonstrate that such F/S structures are attractive model systems that offer the possibility to control the strength and the location of the superconducting nucleus by applying an external magnetic field, potentially useful to guide vortices for computing application.

TRUMP. Transient & S-State Temperature Distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elrod, D.C.; Turner, W.D.

1992-03-03

TRUMP solves a general nonlinear parabolic partial differential equation describing flow in various kinds of potential fields, such as fields of temperature, pressure, or electricity and magnetism; simultaneously, it will solve two additional equations representing, in thermal problems, heat production by decomposition of two reactants having rate constants with a general Arrhenius temperature dependence. Steady-state and transient flow in one, two, or three dimensions are considered in geometrical configurations having simple or complex shapes and structures. Problem parameters may vary with spatial position, time, or primary dependent variables, temperature, pressure, or field strength. Initial conditions may vary with spatial position,more » and among the criteria that may be specified for ending a problem are upper and lower limits on the size of the primary dependent variable, upper limits on the problem time or on the number of time-steps or on the computer time, and attainment of steady state.« less

Visualizing domain wall and reverse domain superconductivity

PubMed Central

Iavarone, M.; Moore, S. A.; Fedor, J.; Ciocys, S. T.; Karapetrov, G.; Pearson, J.; Novosad, V.; Bader, S. D.

2014-01-01

In magnetically coupled, planar ferromagnet-superconductor (F/S) hybrid structures, magnetic domain walls can be used to spatially confine the superconductivity. In contrast to a superconductor in a uniform applied magnetic field, the nucleation of the superconducting order parameter in F/S structures is governed by the inhomogeneous magnetic field distribution. The interplay between the superconductivity localized at the domain walls and far from the walls leads to effects such as re-entrant superconductivity and reverse domain superconductivity with the critical temperature depending upon the location. Here we use scanning tunnelling spectroscopy to directly image the nucleation of superconductivity at the domain wall in F/S structures realized with Co-Pd multilayers and Pb thin films. Our results demonstrate that such F/S structures are attractive model systems that offer the possibility to control the strength and the location of the superconducting nucleus by applying an external magnetic field, potentially useful to guide vortices for computing application. PMID:25164004

Monte Carlo simulations of particle acceleration at oblique shocks: Including cross-field diffusion

NASA Technical Reports Server (NTRS)

Baring, M. G.; Ellison, D. C.; Jones, F. C.

1995-01-01

The Monte Carlo technique of simulating diffusive particle acceleration at shocks has made spectral predictions that compare extremely well with particle distributions observed at the quasi-parallel region of the earth's bow shock. The current extension of this work to compare simulation predictions with particle spectra at oblique interplanetary shocks has required the inclusion of significant cross-field diffusion (strong scattering) in the simulation technique, since oblique shocks are intrinsically inefficient in the limit of weak scattering. In this paper, we present results from the method we have developed for the inclusion of cross-field diffusion in our simulations, namely model predictions of particle spectra downstream of oblique subluminal shocks. While the high-energy spectral index is independent of the shock obliquity and the strength of the scattering, the latter is observed to profoundly influence the efficiency of injection of cosmic rays into the acceleration process.

Non-Gaussian limit fluctuations in active swimmer suspensions

NASA Astrophysics Data System (ADS)

Kurihara, Takashi; Aridome, Msato; Ayade, Heev; Zaid, Irwin; Mizuno, Daisuke

2017-03-01

We investigate the hydrodynamic fluctuations in suspensions of swimming microorganisms (Chlamydomonas) by observing the probe particles dispersed in the media. Short-term fluctuations of probe particles were superdiffusive and displayed heavily tailed non-Gaussian distributions. The analytical theory that explains the observed distribution was derived by summing the power-law-decaying hydrodynamic interactions from spatially distributed field sources (here, swimming microorganisms). The summing procedure, which we refer to as the physical limit operation, is applicable to a variety of physical fluctuations to which the classical central limiting theory does not apply. Extending the analytical formula to compare to experiments in active swimmer suspensions, we show that the non-Gaussian shape of the observed distribution obeys the analytic theory concomitantly with independently determined parameters such as the strength of force generations and the concentration of Chlamydomonas. Time evolution of the distributions collapsed to a single master curve, except for their extreme tails, for which our theory presents a qualitative explanation. Investigations thereof and the complete agreement with theoretical predictions revealed broad applicability of the formula to dispersions of active sources of fluctuations.

Analysis of regional crustal magnetization in Vector Cartesian Harmonics

NASA Astrophysics Data System (ADS)

Gubbins, D.; Ivers, D. J.; Williams, S.

2017-12-01

We introduce a set of basis functions for analysing magnetization in a plane layer, called Vector Cartesian Harmonics, that separate the part of the magnetization responsible for generating the external potential field from the part that generates no observable field. They are counterparts of similar functions defined on a sphere, Vector Spherical Harmonics, which we introduced earlier for magnetization in a spherical shell. We expand four example magnetizations in these functions and determine which parts are responsible for the observed magnetic field above the layer. For a point dipole, the component of magnetization responsible for the external potential field is the sum of a point dipole of half strength and a distributed magnetization that gives the same field. The dipping prism has no magnetic field if magnetized along strike; otherwise it, like the point dipole, has the correct dipping structure but of half the correct intensity accompanied by a distributed magnetization producing the same magnetic field. Interestingly, the distributed magnetization has singularities at the edges of the dipping slab. The buried cube is done numerically and again only a fraction of the true magnetization appears along with distributed magnetizations, strongest at the edges of the cube, making up the rest of the field. The Bishop model, a model of magnetization often used to test analysis methods, behaves similarly. In cases where the magnetization is induced by a known, non-horizontal field it is always possible to recover the vertically averaged susceptibility except for its horizontal average. Simple damped inversion of magnetic data will return only the harmonics responsible for the external field, so the analysis gives a clear indication of how any combination of induced and remanent magnetization would be returned. In practice, most interpretations of magnetic surveys are done in combination with other geological data and insights. We propose using this prior information to construct a quantitative magnetization that can be expanded in Vector Cartesian Harmonics to determine the part that generates the observed magnetic anomalies; this part can be refined to fit the data while the remaining part can only be improved using different information. The separation is simple and fast to implement using standard software because it involves only elementary manipulations of 2-dimensional Fourier transforms.

Fast torsional waves and strong magnetic field within the Earth's core.

PubMed

Gillet, Nicolas; Jault, Dominique; Canet, Elisabeth; Fournier, Alexandre

2010-05-06

The magnetic field inside the Earth's fluid and electrically conducting outer core cannot be directly probed. The root-mean-squared (r.m.s.) intensity for the resolved part of the radial magnetic field at the core-mantle boundary is 0.3 mT, but further assumptions are needed to infer the strength of the field inside the core. Recent diagnostics obtained from numerical geodynamo models indicate that the magnitude of the dipole field at the surface of a fluid dynamo is about ten times weaker than the r.m.s. field strength in its interior, which would yield an intensity of the order of several millitesla within the Earth's core. However, a 60-year signal found in the variation in the length of day has long been associated with magneto-hydrodynamic torsional waves carried by a much weaker internal field. According to these studies, the r.m.s. strength of the field in the cylindrical radial direction (calculated for all length scales) is only 0.2 mT, a figure even smaller than the r.m.s. strength of the large-scale (spherical harmonic degree n

The paleointensity record of Icelandic subglacial volcanic glasses and recent lavas

NASA Astrophysics Data System (ADS)

Cromwell, G.; Tauxe, L.; Halldorsson, S. A.

2013-05-01

The Earth's ancient magnetic field can be approximated by a geocentric axial dipole (GAD) where the average field intensity is twice as strong at the poles than at the equator. The present day geomagnetic field, and some global paleointensity datasets, support the GAD hypothesis with a virtual axial dipole moment (VADM) of about 80 ZAm2 , which corresponds to surface field intensities of ~30 μT and 60 μT at the equator and poles, respectively. An astounding departure from the GAD hypothesis is found in Antarctica where the average field strength for 0-5 Ma (31.5 ± 2.4 μT, 78° S (1)) is equivalent to predictions at the Earth's equator. Proposed explanations for this decidedly non-GAD behavior at high southern latitudes include incomplete temporal sampling, effects from the tangent cylinder, and hemispheric asymmetry (especially at high latitudes). A comparison of Arctic and Antarctic paleointensity data over similar timescales might offer insights into the GAD field, however northern high latitude data comparable to the Antarctic collection are sparse due to the lack of young (0-5 Ma) and accessible lava flows. One exception is Iceland, a volcanic island on the Mid-Atlantic Ridge with continuous volcanism for the last ~15 Ma. Many of the paleointensity studies from Iceland target very young lavas (Holocene age) or transitional geomagnetic field states, both of which offer limited analysis of the long-term geomagnetic field. Additionally, some studies employ experimental methods that do not provide tests for alteration or other irreversible magnetic behaviors that can occur during multiple high temperature heating steps. We present a detailed collection of Icelandic paleointensity records from 85 volcanic units ranging in age from 1783 C.E. to ~4 Ma. We sample volcanic glass from flow tops and subglacially erupted volcanic units in order to collect single-domain magnetic material, which has been shown to accurately record magnetic field strength (2). Preliminary results from 35 successful sites (0-4 Ma) indicate an average paleointensity of 42.6 ± 15.0 μT with a VADM of 59.5 ± 20.9 ZAm2. The Icelandic data have a higher dipole moment than Antarctica (41.4 ZAm2) with a similar temporal distribution, indicating that the difference in field strength may yet be the result of hemispheric asymmetry or influence from the tangent cylinder. Our average Icelandic VADM is less than the present-day field, 80 ZAm2, and much closer to a lower estimate for long-term dipole field strength of 50 ZAm2 (3). (1) Lawrence, K.P., L. Tauxe, H. Staudigel, C.G. Constable, A. Koppers, W. McIntosh, C.L. Johnson, Paleomagnetic field properties at high southern latitude, Geochemistry Geophysics Geosystems, 10, 2009. (2) Pick, T., L. Tauxe, Holocene paleointensities: Thellier experiments on submarine basaltic glass from the East Pacific Rise, Journal of Geophysical Research, 98, B10, 17949-17964, 1993. (3) Selkin, P.A., L. Tauxe, Long-term variations in palaeointensity, Phil. Trans. R. Soc. Lond., 358, 1065-1088, 2000.

Stress-strain behaviour analysis of Middle Polish glacial tills from Warsaw (Poland) based on the interpretation of advanced field and laboratory tests

NASA Astrophysics Data System (ADS)

Bąkowska, Anna; Dobak, Dobak; Gawriuczenkow, Ireneusz; Kiełbasiński, Kamil; Szczepański, Tomasz; Trzciński, Jerzy; Wójcik, Emilia; Zawrzykraj, Piotr

2016-09-01

The selected parameters of the Wartanian and Odranian tills, with relation to their spatial occurrence, grain size distribution, mineralogical composition, matric suction and other physical characteristics, are presented. The assessment of the lithogenesis and stress history on the microstructure is attempted. The comparison of the compression and permeability characteristics from field and laboratory tests has been performed. Laboratory consolidation tests carried out with up to 20MPa vertical stress, revealed two yield stress values, one in the range of a couple hundreds kPa, the other in the range of a couple thousands kPa. Based on those results, the reliability of the soil preconsolidation assessment, with the use of the two different methods is discussed. The aspect of the triaxial strength reduction under the dynamic loading of diverse frequency and amplitude is raised. The research results depict a variety of possible geological-engineering characteristics, under the divergent constraints scenarios, of compression or strength weakening origin. The effects of the specialized research program will widen the possibilities of physio-mechanical and structural characterization of soils for geological-engineering purposes.

Mapping of electrical potential distribution with charged particle beams. [using an X-ray source

NASA Technical Reports Server (NTRS)

Robinson, J. W.

1979-01-01

Potentials were measured using a beam of soft X-rays in air at 2 x 10 to the -5 power Torr. Ions were detected by a continuous-dynode electron multiplier after they passed through a retarding field. Ultimate resolution depends upon the diameter of the X-ray beam which was 3 mm. When the fields in the region of interest were such to disperse the ions, only a small fraction were detected and the method of measurement was not very reliable. Yet reasonable data could be collected if the ions traveled in parallel paths toward the detector. Development should concentrate on increasing the aperture of the detector from the pinhole which was used to something measured in centimeters. Also increasing the strength of the source would provide a stronger signal and more reliable data. Measurements were made at an estimated ion current to 10 to the -15 power A from a 10 cm length of the X-ray beam, this current being several orders of magnitude below what would have a perturbing effect on the region to be measured. Consequently, the source strength can be increased and prospects for this method of measurement are good.